JP7421082B2 - Hot-dip plating method - Google Patents

Description

The present invention relates to a hot-dip plating method for metal materials, and particularly to a hot-dip plating method for steel materials.

Methods (hot-dip plating methods) currently used for manufacturing hot-dip plated products are broadly classified into continuous hot-dip plating methods and immersion plating methods. In the following, a hot-dip plating method for steel will be explained using steel as a representative metal material.

The continuous hot-dip plating method is a method of plating a coiled steel material (metal strip) by continuously passing (immersing and passing through) a hot-dip plating bath. In addition, the immersion plating method is a method called "dip plating," which is a method in which flux is attached to a preformed steel material, and then the steel material is immersed in a hot-dip plating bath for plating. .

The equipment used to carry out the continuous hot-dip plating method (continuous hot-dip plating equipment) usually includes pre-treatment equipment, a reduction heating furnace, a hot-dip plating bath (molten metal pot), and post-treatment equipment. The pretreatment equipment performs a process to remove rolling oil and dirt adhering to the steel material. In the reduction heating furnace, the Fe oxide present on the surface of the steel material is reduced by heating the steel material in an atmosphere containing _H2 . In the hot-dip plating bath section, the steel material treated in the reduction heating furnace is immersed and passed through the hot-dip plating bath while being maintained in a reducing atmosphere or in an atmosphere that prevents re-oxidation of the surface of the steel material. Hot-dip plating is applied to. In the above-mentioned post-treatment equipment, various treatments are performed on the hot-dipped steel material depending on the purpose.

On the other hand, the equipment used to carry out dobuzuke plating (dobuzuke plating equipment) is degreasing equipment that removes oil and dirt from preformed steel materials, and removes Fe oxide layers (referred to as rust or black scale). The method includes a pickling facility for applying flux to the pickled steel, a fluxing facility for applying flux to the pickled steel, and a hot-dip plating bath for hot-dipping the steel after the flux has dried. If necessary, post-processing equipment may be attached to the dip plating equipment, similar to the above-mentioned continuous hot-dip plating equipment. The above flux is used to improve the reactivity between the steel material and the hot-dip plating bath.

Conventionally, in hot-dip plating methods, a problem may arise in which plating defects (referred to as unplated spots or pinholes) occur on the surface of a plated product (semi-finished product) after hot-dip plating. A plating defect is a portion where molten metal does not adhere to the steel material and no plating metal exists on the surface of the steel material. Various factors are thought to be responsible for the occurrence of plating defects, and countermeasures have been taken for many years. For example, as one of the countermeasures, a technique has been proposed in which hot-dip plating is applied while applying ultrasonic vibration to the metal strip after heat treatment (reduction treatment) in a continuous hot-dip plating method (Patent Documents 1 and 2). ). In dobu-dip plating as well, to address the issue of unplated spots caused by burns (exposure of the alloy layer), a technology has been proposed that uses ultrasonic waves to perform dobu-dip plating (Patent Document 3). ).

Generally, in the continuous hot-dip plating method, before the metal strip is immersed in the molten metal pot, the material of the metal strip itself is annealed and the oxide film present on the surface of the metal strip is reduced in the reduction heating furnace. . In the reduction heating furnace, the metal strip is heated in a mixed atmosphere of nitrogen and hydrogen, for example, in order to reduce the oxide film. In this heat treatment, the heating temperature of the metal strip is set according to the purpose of use of the plated product, and in order to improve the reactivity between the metal strip and the hot-dip plating bath, the metal strip is heated to at least the temperature of the hot-dip plating bath. heated.

Since the oxide film on the surface of the metal strip is removed by the treatment in the reduction heating furnace, the reactivity between the metal strip and the hot-dip plating bath is improved. Therefore, hot-dip plated metal strips can be stably produced.

Japanese Patent Application Publication No. 2-125850 Japanese Unexamined Patent Publication No. 2-282456 Japanese Patent Application Publication No. 2000-064020

However, plating defects may occur on the surface of plated products depending on various factors such as the composition of the metal material or manufacturing conditions. The same applies when manufacturing plated products.

Furthermore, in recent years, there has been an increasing demand for (i) energy saving in hot-dip plating methods, and (ii) for workers to be able to engage in hot-dip plating work in a clean working environment.

The reduction heating furnace in the continuous hot-dip plating equipment requires a very large amount of heat and consumes a large amount of nitrogen and hydrogen used as atmospheric gas. This also applies to the techniques described in Patent Documents 1 and 2. In conventional continuous hot-dip plating methods, it is not easy to reduce energy consumption while satisfying the requirements for hot-dip-plated products (fewer plating defects, etc.).

In addition, dip plating equipment is usually equipped with flux equipment to ensure good plating properties. In this case, the following problems arise from the viewpoint of the working environment. That is, (i) it is necessary to handle chlorides (including ZnCl ₂ , NH ₄ Cl, etc.), which are the main components of flux, and (ii) when the metal material is immersed in a hot-dip plating bath after the flux has dried, There are problems such as a large amount of white smoke and odor being generated. In dip plating equipment, it is difficult to improve the working environment while meeting the demands for hot-dip plated products.

One aspect of the present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to improve plating properties on the surface of a metal material after hot-dip plating, and to consume less energy than the conventional method. An object of the present invention is to provide a hot-dip plating method that can reduce the amount of plating and improve the working environment.

In order to solve the above problems, a hot-dip plating method in one aspect of the present invention involves introducing a metal material into a molten Al-based plating bath containing aluminum as a main component, and coating the metal material with molten Al-based molten metal. A hot-dip plating method for coating the metal material with the molten metal while applying vibration to the molten Al-based plating bath while the metal material is in contact with the molten metal. In the plating process, the acoustic spectrum measured in the molten Al plating bath satisfies the relationship of the following formula (1), with the frequency of the vibration applied to the molten Al plating bath being the fundamental frequency. It is characterized in that the above-mentioned vibration is applied to the vibration.

(IB-NB)/(IA-NA)>0.2...(1)
(here,
IA: Average value of sound pressure in the entire measurement frequency band IB: (i) Between the sound pressure peak at the fundamental frequency and the sound pressure peak at the second harmonic frequency, and (ii) Sound pressure at multiple harmonic frequencies Average value of the sound pressure in a specific frequency band between adjacent peaks of . NA: Average value of the sound pressure in the entire measurement frequency band when the vibration is not applied. NB: Specified with respect to IB above. (This is the average value of the sound pressure in the specific frequency band when the vibration is not applied.)

In this specification, the intensity ratio determined by (IB-NB)/(IA-NA) as described above may be referred to as a characteristic intensity ratio. The present inventors have discovered that plating wettability and plating adhesion of a metal material can be improved by performing hot-dip Al-based plating under conditions where the characteristic strength ratio is greater than 0.2.

According to one aspect of the present invention, a hot-dip plating method can provide good plating properties on the surface of a metal material after hot-dip plating, and can reduce energy consumption and improve the working environment compared to conventional methods. can be provided.

1 is a schematic diagram showing an example of a hot-dip plating apparatus that implements a hot-dip plating method in Embodiment 1 of the present invention. It is a graph which shows an example of the acoustic spectrum measured by the spectrum analyzer with which the said hot-dip plating apparatus is equipped. It is a graph showing an example of an acoustic spectrum measured by the above-mentioned spectrum analyzer when changing ultrasonic output. (a) is a graph showing the influence of ultrasonic output on the average intensity of the entire measurement frequency band in the acoustic spectrum and the average intensity between harmonics, and (b) is a graph showing the influence of the ultrasonic output on the average intensity of the entire measurement frequency band in the acoustic spectrum. , a graph showing the influence of ultrasonic output on the ratio of average intensities between overtones. 1 is a schematic diagram showing an example of a hot-dip plating apparatus that implements a hot-dip plating method in Example 1 of the present invention. FIG. 3 is a side view showing the state of the sample material after plating. It is a graph showing the acoustic spectrum measured by changing the output of the ultrasonic transducer at each distance when the distance between the tip of the waveguide rod and the steel plate is changed, and (a) is a graph when the distance is 1 mm. , (b) shows the case where the distance is 5 mm, (c) shows the case where the distance is 10 mm, (d) shows the case where the distance is 30 mm, and (e) shows the case where the distance is 80 mm. It is a graph which shows the relationship between the said distance and characteristic intensity ratio. It is a schematic diagram showing an example of the hot-dip plating apparatus which carries out the hot-dip plating method in Embodiment 3 of this invention. It is a schematic diagram showing an example of the hot-dip plating apparatus which carries out the hot-dip plating method in Embodiment 5 of this invention. It is a schematic diagram showing an example of the hot-dip plating equipment which implements the hot-dip plating method in Embodiment 6 of the present invention. It is a schematic diagram showing a modification of the above-mentioned hot-dip plating equipment. (a) is a schematic diagram showing how a steel plate is introduced into a hot-dipping bath in an atmospheric atmosphere, and (b) is an enlarged schematic diagram of the area (A1) in the diagram shown in (a). It is a partially enlarged view. This is an acoustic spectrum observed when vibration is applied to a hot-dip plating bath using an ultrasonic vibrator with an output of 380W. (a) is a schematic diagram showing how hot-dip plating is applied to a steel plate having a relatively thick oxide film in a comparative example, and (b) is a schematic diagram showing a pretreatment to reduce the thickness of the oxide film in an example of the present invention. FIG. 2 is a schematic diagram showing how hot-dip plating is applied to a steel plate. FIG. 2 is a schematic diagram for explaining a plating adhesion test.

Embodiments of the present invention will be described below with reference to the drawings. It should be noted that the following description is provided for better understanding of the gist of the invention, and is not intended to limit the invention unless otherwise specified. Furthermore, in this application, "A to B" indicates that the number is greater than or equal to A and less than or equal to B. The shapes and dimensions of the structures shown in the drawings in this application do not necessarily reflect the actual shapes and dimensions, but have been appropriately changed for clarity and simplification of the drawings.

(Definition of terms)
In this specification, various molten metals (molten metals) constituting a hot-dip plating bath may be referred to as "hot-dip plating bath metals." Further, in this specification, the material and shape of the steel material to be subjected to hot-dip plating using a hot-dip plating bath are not particularly limited unless otherwise specified. Furthermore, "steel plate" may be read as "steel strip" unless there is any inconvenience.

In general, in the hot-dip plating method, "platability" refers to both the plating wettability between the metal material and the hot-dip plating bath, and the plating adhesion between the metal material and the plating layer formed on the surface of the metal material. This is sometimes referred to as plating property. In this specification, "plating properties", "plating wettability", and "plating adhesion" are used in the same meanings as in the past.

<Schematic explanation of the knowledge of the invention>
In general, (i) a steel plate (steel strip) that has not been subjected to reduction treatment is introduced into a hot-dip coating bath, or (ii) a steel plate is introduced into a hot-dip coating bath in an atmosphere (high oxygen concentration) without using a snout. If they enter, the reaction between the steel sheet and the metal in the hot-dip plating bath will be inhibited, making it impossible to obtain good plating properties. The reason for this will be explained in detail using FIG. 13 as follows. FIG. 13(a) is a schematic diagram showing how a steel plate is introduced into a hot-dip plating bath under an atmospheric atmosphere. FIG. 13B is a partially enlarged view schematically showing the area (A1) in FIG. 13A.

As shown in FIG. 13(a), a steel plate 100 that has not been subjected to reduction treatment is introduced into a hot-dip plating bath 110 in an atmospheric atmosphere. An oxide film (oxide film) is formed on the surface of the steel plate 100. Further, bath surface oxide 112 exists at the boundary between the hot-dip plating metal 111 inside the hot-dip plating bath 110 and the atmosphere (atmosphere) outside the hot-dip plating bath 110 (i.e., the surface of the hot-dip plating bath 110). do.

As shown in FIG. 13(b), the steel plate 100 (i) entrains oxides 112 on the bath surface, and (ii) entrains an air entrainment layer 120 formed by atmospheric gas (air) on the surface of the hot-dip plating bath 110. It enters the hot-dip plating bath 110 so as to be rolled up. As a result, a reaction inhibiting portion 130 is formed inside the hot-dip plating bath 110 between the hot-dip plating bath metal 111 and the oxide film 101 of the steel plate 100. This reaction inhibiting portion 130 is formed in a composite manner by the bath surface oxide 112 and the air entrainment layer 120. Since the reaction between the steel sheet 100 and the hot-dip plating bath metal 111 is inhibited by the oxide film 101 and the reaction inhibiting portion 130, plating defects (pinholes or unplated areas) appear on the surface of the plated product after it has been pulled out of the hot-dip plating bath 110. etc.) can easily occur.

Therefore, in the conventional hot-dip plating method, as mentioned above, the steel sheet whose oxide film on the surface of the steel sheet has been reduced using a heating furnace is introduced into the hot-dip plating bath through the snout held in a reducing atmosphere ( For example, see Patent Documents 1 and 2). In this case, when the steel plate enters the hot-dip plating bath, the reaction between the steel plate and the metal in the hot-dip plating bath proceeds rapidly.

The present inventors have conducted intensive studies on a hot-dip plating method that can reduce energy consumption using a new method different from the conventional techniques as described above. As a result, when the steel material enters the hot-dip plating bath, the reactivity between the steel material and the metal in the hot-dip plating bath can be increased due to the vibration activation effect generated by applying vibration under specific conditions to the hot-dip plating bath. We discovered a new finding. According to this knowledge, the plating wettability of the steel material can be improved even when the steel material at room temperature is introduced into a hot-dip plating bath under an atmospheric atmosphere. This is a phenomenon that was completely unexpected in the prior art, as can be seen from the fact that conventional hot-dip plating equipment had a reduction heating furnace placed before the hot-dip plating section.

A more detailed explanation of the differences between the knowledge discovered by the present inventors and the prior art is as follows. That is, conventionally, a technique has been proposed in which a high-sound pressure vibration is applied to a hot-dip plating bath using a high-output (for example, several hundred W class) ultrasonic vibrator, and in this case, for example, as shown in FIG. An acoustic spectrum (a white noise-like spectrum with almost no characteristic peaks) is observed. FIG. 14 shows the acoustic spectrum observed when vibration is applied to the hot-dip plating bath using an ultrasonic vibrator with an output of 380 W. This type of technology uses the cavitation effect caused by high-power ultrasonic irradiation to the hot-dip plating bath to physically remove the oxide film existing on the surface of the steel sheet (or the oxide film remaining on the surface of the steel sheet after reduction treatment). By destroying it, the plating properties of the steel sheet were improved.

In contrast, the present inventors have found that the vibration activation effect of the present invention is observed even when a low-output ultrasonic vibrator is used, and that the plating wettability of steel sheets is effectively improved. I found out. In this case, a characteristic peak is observed in the acoustic spectrum, which will be specifically described later. The present inventors consider the above-mentioned vibration activation effect, which occurs even at low sound pressure, as follows, which is different from the conventional technology.

Specifically, although it is not yet clear, even when applying low sound pressure to a hot-dip plating bath, the hot-dip plating metal in the molten state causes pressure vibrations due to the sound waves, and this pressure vibration causes vibrations in the plating bath. Bubbles are generated. It is thought that when the generated bubble collapses due to pressure vibration, a shock wave is generated toward the periphery of the bubble. It is also believed that pressure vibration causes the bubbles to expand and contract repeatedly, and that this expansion and contraction may cause local flow of the hot-dip plated metal around the bubbles. The effects of the above-mentioned shock waves and the above-mentioned local flows based on acoustic energy promote mass transfer at the interface between the steel material and the plating bath, resulting in effects such as reducing the thickness of the boundary layer or increasing the mass transfer rate. This is thought to be a mechanism in which plating wettability between the steel material and the hot-dip plating bath is ensured.

Note that even in the conventional technology (in which vibrations with high sound pressure are applied to the hot-dip plating bath), the phenomenon of promotion of mass transfer at the interface between the steel material and the hot-dip plating bath is considered to occur. However, according to the findings of the present invention, it is not necessary to apply vibrations with high sound pressure to the hot-dip plating bath, and the vibration energy has a vibration activation effect that can ensure plating wettability between the steel material and the hot-dip plating bath. It was found that it is sufficient as long as it occurs only to the extent that it occurs. Further, the conventional technique of applying high sound pressure vibrations to a plating bath has disadvantages from the following points.

In other words, when high sound pressure vibrations are applied to a hot-dip plating bath, the cavitation effect that occurs simultaneously with shock waves and local flow causes the steel material to quickly dissolve in the hot-dip plating bath, causing a corrosion phenomenon called erosion. An inconvenience arises in that it is more likely to occur. This means that if the steel material is a steel plate, the thickness of the steel plate after hot-dip coating will be smaller than before entering the hot-dip coating bath, making it difficult to guarantee the product thickness of the hot-dip coated steel plate. There are concerns. In addition, the reaction in which steel material dissolves in the hot-dip plating bath increases the concentration of steel components such as iron (Fe) in the hot-dip plating bath, which tends to lead to the generation of dross. There are also concerns. Furthermore, members that are immersed in the hot-dip plating bath (ultrasonic horn) to apply vibrations of high sound pressure to the hot-dip plating bath are likely to undergo erosion, and maintenance of these members becomes complicated.

The hot-dip plating method (hereinafter sometimes simply referred to as the present hot-dip plating method) in one embodiment of the present invention based on the knowledge discovered by the present inventors will be briefly described as follows. That is, by (i) applying ultrasonic vibrations to the steel material, or (ii) applying ultrasonic vibrations to the hot-dip plating bath using, for example, a diaphragm, vibrations of low sound pressure can be applied to the hot-dip plating bath. Give. Then, the acoustic spectrum is measured using an acoustic measuring instrument immersed in the hot-dip plating bath. In this hot-dip plating method, the ultrasonic vibration is applied to the hot-dip plating bath so that the acoustic spectrum satisfies predetermined conditions. Ultrasonic vibrations applied to the steel material or the diaphragm produce a vibration activation effect in the hot-dip plating bath. The above-mentioned predetermined conditions are defined in order to indirectly specify the strength of the vibration activation effect using the acoustic spectrum in the hot-dip plating bath so that a vibration activation effect of a certain level or more is generated.

As a result of further study, the present inventors obtained the following knowledge. That is, hot-dip plating is performed while applying ultrasonic vibrations to a molten Al-based plating bath so as to satisfy the predetermined conditions as described above. It has been found that, as a result, the plating adhesion on the surface of the steel material after hot-dip Al plating is improved.

Although the details of the principle by which plating adhesion can be improved by the hot-dip plating method as described above are not clear, the explanation will be as follows using FIG. 15. FIGS. 15A and 15B are schematic diagrams showing how hot-dip Al-based plating is applied to a steel plate in an example of the present invention.

As shown in FIGS. 15(a) and 15(b), while applying ultrasonic vibration to the steel plate 2 of Example 1 of the present invention on which a relatively thick oxide film 6 is formed, molten Al-based When plating is applied, ultrasonic vibrations produce a vibration activation effect in the molten Al-based plating bath. That is, the hot-dip plating bath metal 21 (in this case, the molten Al-based alloy) in a molten state undergoes pressure vibrations due to the sound waves, and bubbles are generated in the molten Al-based plating bath due to the pressure vibrations. It is thought that when the generated bubble collapses due to pressure vibration, a shock wave is generated toward the periphery of the bubble. It is also considered that the bubbles repeat expansion and contraction due to pressure vibrations, and that this expansion and contraction causes local flow of the hot-dip plating bath metal 21 around the bubbles. Effects such as the shock wave based on acoustic energy and the local flow promote mass transfer at the interface between the steel material and the molten Al plating bath, reducing the thickness of the boundary layer or increasing the mass transfer rate. It is thought that this will bring about Energy is then applied to the oxide film 6 from the vibration activation region 23 generated in the hot-dip plating bath metal 21. A reaction layer 7 is formed on the surface of the steel sheet 2 after hot-dip plating as a result of mutual atomic diffusion between the oxide film 6, the steel sheet 2, and the hot-dip plating bath metal 21. This reaction layer 7 is an alloy layer containing the components of the steel plate 2 and the hot-dip plating bath metal 21. The reaction layer 7 allows the steel plate 2 and the plating layer 8 to be relatively firmly bonded to each other. As a result, it is thought that the plating adhesion on the surface of the steel plate 2 after hot-dip plating is improved.

The above means that the steel plate 2 of Example 2 of the present invention on which the relatively thin oxide film 6 is formed is subjected to hot-dip Al-based plating while applying ultrasonic vibration, as shown in FIG. The same is considered to apply when applying.

In this hot-dip plating method, the thickness of the oxide film 6 is not particularly limited. At least when the oxide film 6 of a typical thickness is formed on the surface of the steel plate 2, the thickness of the oxide film 6 has little effect on the plating adhesion of the steel plate 2 after plating. Although the detailed mechanism is not clear, when a hot-dip Al plating bath is used, a reaction occurs between the steel sheet 2 and the plating layer 8 due to factors such as the relatively high temperature of the plating bath and the high reactivity of Al. It is considered that layer 7 is relatively easy to generate.

[Embodiment 1]
Embodiments of the present invention will be described in detail below.

In this embodiment, a plate-shaped steel material (steel plate) among metal materials is used, and the hot-dip plating method (so-called Explain about dobu-zuke plating. Moreover, in the hot-dip plating method in this embodiment, the above-mentioned dip plating is performed in an atmospheric atmosphere. Note that the hot-dip plating method in one embodiment of the present invention is not necessarily limited to this. This hot-dip plating method can be applied, for example, to various metal materials that are generally subjected to hot-dip plating. Further, the present hot-dip plating method can be applied to a continuous hot-dip plating method in which a steel strip is used as the steel material and the steel strip is continuously hot-dipped. Moreover, this hot-dip plating method can also be applied when using a steel wire as the steel material and subjecting the steel wire to dip plating or continuous hot-dip plating.

(steel plate)
The steel plate used in the hot-dip plating method of the present embodiment may be appropriately selected from various known steel plates depending on the application, and examples of the steel type constituting the steel plate include carbon steel (ordinary steel, high-strength steel, etc.). Examples include high Si/high Mn steel)), stainless steel, and the like. The thickness of the steel plate is not particularly limited, but may be, for example, 0.2 mm to 6.0 mm. Further, the shape of the steel plate is not particularly limited, but may be rectangular, for example. Steel plates generally used for hot-dip Al-based plating can be used in the hot-dip plating method of this embodiment.

The above-mentioned steel plate does not need to be subjected to reduction heat treatment or the like before hot-dip Al-based plating treatment. Therefore, the steel sheet may have an oxide film on its surface at the time of being thrown into the molten Al-based plating bath. The thickness of the oxide film depends on the type of steel constituting the steel sheet, but for example, in a cold-rolled steel sheet, it is approximately several tens of nanometers to several hundreds of nanometers in an untreated state. In the hot-dip plating method of this embodiment, the thickness of the oxide film on the steel sheet is not particularly limited at the time the steel sheet is put into the hot-dip plating bath.

Furthermore, in the hot-dip plating method of the present embodiment, the temperature of the steel sheet before entering the hot-dip Al-based plating bath may be room temperature. In other words, the temperature of the steel plate may be, for example, room temperature to 700°C.

In the hot-dip plating method of this embodiment, it is not necessary to subject the steel plate to flux treatment or the like before the hot-dip Al-based plating process. However, the above-mentioned steel plate may be subjected to heat treatment, reduction treatment, flux treatment, etc., as necessary, before the hot-dip Al-based plating treatment.

(Hot-dip plating bath)
As the molten Al-based plating bath in this embodiment, various known molten Al-based plating baths can be used. Examples of the molten Al-based plating bath include an Al-based plating bath, an Al-Si-based plating bath, and the like.

The temperature of the molten Al-based plating bath in the present hot-dip plating method may be the same as the temperature of the molten Al-based plating bath used in known hot-dip plating methods.

For example, the molten Al-based plating bath in one embodiment of the present invention contains aluminum as a main component, and has an Al concentration of, for example, 85% by mass or more.
The molten Al-based plating bath may contain Si in a range of 0.1% by mass to 12% by mass, and Fe in a range of 1.0% by mass to 3.0% by mass. The remainder of the molten Al-based plating bath may consist of Al and unavoidable impurities.

(Hot-dip plating equipment)
A hot-dip plating apparatus 1 that implements the hot-dip plating method in this embodiment will be described using FIGS. 1 and 2. Note that the hot-dip plating apparatus 1 is one example, and the apparatus for implementing the present hot-dip plating method is not particularly limited. FIG. 1 is a schematic diagram showing a hot-dip plating apparatus 1 that implements the hot-dip plating method according to the present embodiment.

As shown in FIG. 1, the hot-dip plating apparatus 1 includes an ultrasonic horn (vibration generator) 10, an ultrasonic power supply D1, a molten Al-based plating bath 20, and a measuring device 30. The ultrasonic horn 10 is provided with an ultrasonic vibrator 11. A steel plate 2 is fixed to the tip of the ultrasonic horn 10 with bolts 12.

Ultrasonic power supply device D1 includes an oscillator 13, a power amplifier 14, and a power meter 15. The oscillator 13 generates an AC signal of an arbitrary frequency, and the power amplifier 14 amplifies the AC signal to generate an ultrasonic signal. The ultrasonic horn 10 receives the ultrasonic signal supplied via the wattmeter 15. As a result, the ultrasonic vibrator 11 vibrates ultrasonically. The vibration of the ultrasonic vibrator 11 causes the steel plate 2 connected to the ultrasonic horn 10 to vibrate.

The vibration of the steel plate 2 causes a vibration activation effect in the molten Al-based plating bath 20, and a vibration-activated region 23 is generated near the steel plate 2 inside the molten Al-based plating bath 20. The molten Al-based plating bath 20 is stored in a pot 24 and includes a molten plating bath metal 21 and a bath surface oxide 22 . The vibration activation region 23 occurs in both the hot-dip plating bath metal 21 and the bath surface oxide 22 in the molten Al-based plating bath 20 .

A waveguide rod 31 is inserted into the molten Al-based plating bath 20 . One end of the waveguide rod 31 is placed at an appropriate position inside the molten Al-based plating bath 20 so as to be able to obtain the vibration frequency of the hot-dip plating bath metal 21, and the other end is connected to a vibration sensor 32. There is. The vibration sensor 32 is a device that converts the vibration of the waveguide rod 31 into an electrical signal using a piezoelectric element. The electrical signal transmitted from the vibration sensor 32 is amplified via the amplifier 33 and then transmitted to the spectrum analyzer 34. The spectrum analyzer 34 includes a display section 34a. In this embodiment, a case will be described in which the spectrum analyzer 34 includes a display section 34a, but the display section 34a may be replaced by an external device connected to the spectrum analyzer 34.

For example, the frequency of the ultrasonic vibrator 11 is set to 20 kHz, the output of the ultrasonic vibrator 11 is reduced, and vibrations of low sound pressure are applied to the molten Al plating bath 20, and the steel plate 2 is When pickled plating is performed, an acoustic spectrum as shown in FIG. 2 is typically displayed on the display section 34a. Here, the distance L1 between the waveguide rod 31 and the steel plate 2 was 10 mm, and the depth D1 of the tip of the waveguide rod 31 (distance from the tip to the bath surface of the molten Al-based plating bath 20) was 30 mm. FIG. 2 is a graph showing an example of an acoustic spectrum measured by the spectrum analyzer 34 included in the hot-dip plating apparatus 1. In the graph of FIG. 2, the horizontal axis is the frequency, and the vertical axis is the power value measured by the spectrum analyzer 34. The unit of this power value is dBm (more precisely, dBmW: decibel milliwatt), which represents power in decibels with 1 mW as a reference. Such a power value can be used as an index representing the intensity of the acoustic spectrum. Further, the magnitude of the intensity (vertical axis in FIG. 2) in the acoustic spectrum corresponds to the magnitude of the sound pressure in the molten Al-based plating bath 20. Therefore, the intensity peak in the acoustic spectrum corresponds to the sound pressure peak.

As shown in FIG. 2, the acoustic spectrum includes a peak indicating the fundamental tone (frequency: 20 kHz) corresponding to the vibration applied to the molten Al plating bath 20, and a peak indicating the overtone (frequency of an integral multiple of the fundamental tone). is mainly expressed. Here, the frequency of the fundamental tone is defined as the fundamental frequency f, and the frequency range (width) in which the acoustic spectrum is measured is defined as the measurement frequency band. In addition, a predetermined value is determined from the intermediate frequencies (specifically, 3/2f, 5/2f, 7/2f, 9/2f) of the fundamental frequency f and multiple overtone frequencies (integer overtones: 2f, 3f, 4f, 5f). Let the range of width be the interharmonic band (specific frequency band). In this specification, for convenience of explanation, a range of a predetermined width from the intermediate frequency between the fundamental frequency f and the second harmonic frequency 2f is also referred to as an interharmonic band.

In this embodiment, the predetermined width of the inter-harmonic band is set to a range of 1/3 f centered on the intermediate frequency. However, this predetermined width is not necessarily limited to this, and may be appropriately set to be a frequency band between adjacent peaks among multiple main peaks (a peak at the fundamental frequency and multiple peaks at overtone frequencies) in the acoustic spectrum. do it.

When vibrations with a low sound pressure (for example, an output of 10 W) are applied to the molten Al plating bath 20, as shown in FIG. Here, a peak also appears in a region of 1/3 f around 30 kHz). As the output of the ultrasonic transducer 11 is increased, the intensity of the interharmonic band also increases (see FIG. 3, which will be described later). The reason why such an increase in strength occurs is not clear, but it is thought that it may be caused by, for example, the generation and disappearance of bubbles due to vibrations in the molten Al-based plating bath 20.

By the way, even if vibration is applied to the steel plate 2 using the ultrasonic horn 10, what kind of vibration is generated in the hot-dip plating bath metal 21 due to the vibration, in other words, how much activity is generated in the vicinity of the steel plate 2? It is not easy to evaluate whether the vibration activation region 23 is formed. This is because, for example, the viscosity, vapor pressure, density, vibration propagation velocity, acoustic impedance, etc. of the hot-dip plating bath metal 21 change depending on, for example, the component composition and temperature of the molten Al-based plating bath 20. In other words, since the way the vibration of the steel plate 2 is transmitted to the hot-dip plating bath metal 21 is affected by various conditions, the range, activity level, etc. of the vibration activation region 23 is evaluated based only on the output of the ultrasonic vibrator 11. and difficult to control.

Therefore, the present inventors focused on the ratio of the spectral intensity of the above-mentioned interharmonic band in the acoustic spectrum to the spectral intensity of the entire acoustic spectrum. This will be explained below with reference to FIG. FIG. 3 is a graph showing an example of an acoustic spectrum measured by the spectrum analyzer included in the hot-dip plating apparatus 1 when the ultrasonic output is changed. In FIG. 3, the horizontal axis shows frequency (Hz) and the vertical axis shows intensity (dBm). Also, here, the results are shown when the fundamental frequency is 20 kHz and the ultrasonic output is varied from 0.1 W to 30 W.

As shown in FIG. 3, when the output of the ultrasonic transducer 11 was varied from 0.1 W to 30 W, the higher the output, the more the intensity of the acoustic spectrum increased overall across the frequency range. Furthermore, when vibration is not applied to the molten Al-based plating bath 20 (the output of the ultrasonic vibrator 11 is 0 W), the intensity of the acoustic spectrum measured by the spectrum analyzer can be considered as noise. In this measurement system, the level (noise level) when no ultrasonic vibration was applied was -100 dBm.

In any output, the acoustic spectrum measured by the spectrum analyzer clearly has a peak at the fundamental frequency (20kHz) and a peak at the overtone frequency, and the intensity also varies between these peaks (in the interharmonic band). There is an increase and a decrease in In the interharmonic band, there were several peaks with relatively low intensity, and the peak frequencies of these peaks varied depending on the output. The present inventors have discovered that there is a relationship between the strength (increase and decrease in strength) in this interharmonic band and the plating properties of a steel plate immersed in the molten Al-based plating bath 20. Specifically, it is as follows. In addition, in this specification, the average value of the intensity in the above-mentioned interharmonic band may be referred to as the interharmonic average intensity.

FIG. 4A is a graph showing the influence of the ultrasonic output on the average intensity of the entire measurement frequency band and the average intensity between overtones in the acoustic spectrum. In FIG. 4(a), the horizontal axis shows the ultrasonic output and the vertical axis shows the average intensity. As shown in FIG. 4(a), when the ultrasonic output is 10 W or less, the average intensity between overtones is smaller than the average intensity in the entire measurement frequency band. On the other hand, when the ultrasonic output becomes 20 W or more, the average intensity in the entire measurement frequency band and the average intensity between overtones become equal to each other.

In order to more accurately evaluate the average intensity of the entire measurement frequency band and the average intensity between overtones, the noise level was evaluated as a reference. That is, the average intensity of the entire measurement frequency band and the average intensity between overtones are evaluated as a signal intensity ratio to the noise level. Then, we organized the relationship between the ratio of these average intensities and the output. The results will be explained below using FIG. 4(b).

FIG. 4B is a graph showing the influence of ultrasonic output on the intensity ratio of the average intensity between overtones (noise reference) to the average intensity (noise reference) of the entire measurement frequency band in the acoustic spectrum. In FIG. 4(b), the horizontal axis represents the ultrasonic output, and the vertical axis represents the intensity ratio. In this specification, the above intensity ratio (formula (1) described below) may be referred to as a characteristic intensity ratio.

As shown in FIG. 4(b), as the ultrasonic power increased from 0.1 W to 20 W, the characteristic intensity ratio increased. When the ultrasonic output was increased to 20 W or more, the characteristic intensity ratio became approximately 1 and remained approximately constant.

The present inventors hot-dip-plated a steel plate 2 using a hot-dip plating apparatus 1 while varying the ultrasonic output. As a result, it has been found that the plating wettability of the steel sheet 2 is improved when hot-dip plating is performed under conditions where the characteristic strength ratio is greater than 0.2. That is, by applying vibrations that satisfy the above conditions to the molten Al-based plating bath 20, the reactivity between the surface of the steel plate 2 and the molten plating bath metal 21 can be improved. Specifically, the unplated rate on the surface of the plated product after hot-dip plating can be less than 10%.

Further, the present inventors introduced the steel plate 2 into the molten Al-based plating bath 20, and performed hot-dip plating while applying vibrations to the molten Al-based plating bath 20 so as to satisfy the above equation (1). It has been found that when this is done, the plating adhesion of the steel plate 2 is improved. Specifically, the plating peeling rate can be less than 10% when the plated product after hot-dip plating is bent and subjected to a plating peeling test (see the explanation of Example 1 below). Depending on the conditions, the plating peeling rate can be less than 5%, or the plating peeling rate can be 0%. As the molten Al-based plating bath 20, it is preferable to use a molten Al-based plating bath containing 85% by mass or more of Al.

The above can be summarized as follows.

That is, in the hot-dip plating method in one aspect of the present invention, a steel material (metal material) is introduced into a molten Al-based plating bath containing aluminum as a main component, and the metal material comes into contact with the molten Al-based molten metal. The method includes a plating step in which the steel material is coated with the molten metal while applying vibration to the molten Al-based plating bath. The frequency of the vibration applied to the molten Al-based plating bath is defined as a fundamental frequency. In the plating step, the vibration is applied so that the acoustic spectrum measured in the molten Al-based plating bath satisfies the relationship of formula (1) below:
(IB-NB)/(IA-NA)>0.2...(1)
here,
IA: Average value of the sound pressure in the entire measurement frequency band IB: (i) between the peak of the sound pressure at the fundamental frequency and the peak of the sound pressure at the second harmonic frequency, and (ii) between the sound pressure peak at the above fundamental frequency and (ii) at multiple integer harmonic frequencies (2 or more NA: The average value of the sound pressure in a specific frequency band between adjacent sound pressure peaks at (an integer of (This is the average value of the sound pressure in the specific frequency band defined for the IB when the vibration is not applied).

(Vibration frequency/output)
In the above example, the ultrasonic horn 10 applied vibrations at a frequency of 20 kHz to the steel plate 2 by the ultrasonic vibrator 11 vibrating. However, the present invention is not limited thereto, and the ultrasonic horn 10 may apply vibrations at a frequency of 15 kHz to 150 kHz to the steel plate 2, for example. Further, the intensity of the vibration applied to the steel plate 2 by the ultrasonic horn 10 (output of the ultrasonic vibrator 11) is set so that an acoustic spectrum satisfying the above equation (1) is generated in the molten Al-based plating bath. That's fine. For example, the output of the ultrasonic transducer 11 is determined to produce an acoustic spectrum that satisfies the relationship of formula (1) above in a molten Al plating bath. You can check each condition in advance.

(advantageous effect)
As described above, according to the hot-dip plating method in one aspect of the present invention, while the steel sheet 2 and the hot-dip Al-based plating bath 20 are in contact, the predetermined condition is satisfied (the relationship of formula (1) above is satisfied). ) is applied to the steel plate 2. As a result, the bath surface oxide 22 and the atmosphere caught in the molten Al-based plating bath 20 are dispersed in the bath. That is, the reaction inhibiting portion is dispersed in the bath. In addition, mass transfer is promoted at the interface between the steel plate 2 and the molten Al-based plating bath 20, resulting in effects such as reducing the thickness of the boundary layer or increasing the mass transfer rate. Thereby, plating wettability between the steel plate 2 and the molten Al-based plating bath 20 is ensured. Therefore, the reaction between the hot-dip plating bath metal 21 and the steel plate 2 proceeds smoothly. As a result, even when using the steel plate 2 that has not been subjected to heat treatment (reduction treatment) in advance, the plating wettability of the steel plate 2 can be made good. Therefore, it is possible to provide a hot-dip plating method in which the plating wettability between the hot-dip plating bath metal 21 and the steel plate 2 is good, and the amount of energy consumed can be reduced compared to the conventional method.

Further, according to the hot-dip plating method in one embodiment of the present invention, it is not necessary to perform flux treatment. Therefore, running costs can be reduced and the working environment can be improved.

According to the hot-dip plating method in one aspect of the present invention, when newly introducing hot-dip plating equipment, the cost and materials for installing a heating furnace are not required, and the introduction cost can be reduced. Furthermore, since the heating furnace has a long furnace length, the total length of the hot-dip plating equipment can be shortened by not requiring the installation of a heating furnace.

Furthermore, according to the hot-dip plating method in one aspect of the present invention, the reaction layer 7 can be suitably formed on the surface of the steel sheet 2 after hot-dip plating, and the reaction layer 7 is interposed between the steel sheet 2 and the hot-dip Al-based plating layer. are relatively firmly bonded. As a result, even when using a steel plate 2 that has not been subjected to heat treatment (reduction treatment) in advance, the plating adhesion of the steel plate 2 can be made good. Therefore, it is possible to provide a hot-dip plating method that provides good plating adhesion on the steel plate 2 after hot-dip plating and can reduce energy consumption compared to the conventional method.

(Preprocessing)
In the hot-dip plating method of this embodiment, either the heat treatment or the reduction treatment before the hot-dip plating treatment (plating step) may be omitted, or both of them may be omitted. In addition, in the hot-dip plating method of this embodiment, the steel plate 2 may be subjected to milder heat treatment and reduction treatment than conventional methods before the plating process, and in this case, the energy consumption in both of these treatments is reduced. amount can be reduced.

Note that the steel plate 2 may be subjected to various pretreatments before the hot-dip plating treatment. For example, it does not matter if reduction treatment is performed as a pretreatment for the plating process. Moreover, the steel plate 2 may be subjected to degreasing treatment or pickling treatment, or both thereof may be performed as necessary. In this hot-dip plating method, the steel plate 2 may be subjected to a degreasing treatment and a pickling treatment as a pretreatment for the plating process, and it is particularly preferable to perform at least a degreasing treatment. A pickling treatment may be performed following the degreasing treatment.

Further, the hot-dip plating method in one aspect of the present invention may include a film thickness adjustment step of performing pretreatment to reduce the thickness of the oxide film formed on the surface of the steel plate 2 prior to the plating step. In the film thickness adjustment step, the thickness of the oxide film formed on the surface of the steel plate 2 is reduced, for example, by subjecting the steel plate 2 to pickling treatment.

(Other configurations)
In the hot-dip plating method in one aspect of the present invention, the measurement frequency band may include the fundamental frequency and have a frequency width that is four times or more the fundamental frequency. For example, the measurement frequency band may be 10 kHz or more and 90 kHz or less.

Furthermore, between each peak in the specific frequency band, the fundamental frequency is f, and the frequency width is (1/3) f with the frequency (n + (1/2)) f (n is a natural number) as the center. You can.

In the plating step, the vibration is applied to the plating bath using a vibration generator (ultrasonic horn 10), and the output of the vibration generator may be 0.5 W or more. In this hot-dip plating method, even if the output of the vibration generator is 0.5 W or more and 30 W or less, and the frequency of the vibration applied to the molten Al-based plating bath 20 via the steel plate 2 is 15 kHz or more and 150 kHz or less, good. Further, the vibration generator applies vibration at a frequency of 15 kHz or more and 150 kHz or less to the molten Al plating bath 20, and may have an output of 1 W or more and 30 W or less, or 5 W or more and 30 W or less.

Further, in the plating step, the time for applying the vibration to the molten Al-based plating bath using a vibration generator may be 2 seconds or more and 90 seconds or less. In the above plating step, the temperature (inlet temperature) of the steel plate 2 immediately before being immersed in the molten Al-based plating bath 20 may be room temperature, for example, 100°C or lower, or 50°C or lower. It may be.

In the plating process, the acoustic spectrum in the molten Al-based plating bath is measured using a vibration detection device (eg, vibration sensor 32, amplifier 33, spectrum analyzer 34). The distance between the vibration detection point in the molten Al plating bath and the steel plate 2 may be 1 mm or more and 10 mm or less. The above distance is measured while the steel plate 2 is immersed in the molten Al-based plating bath 20 before the ultrasonic horn 10 starts to vibrate.

[Example 1]
An example of the hot-dip plating method in Embodiment 1 of the present invention will be described below.

In this example, a hot-dip plating apparatus shown in FIG. 5 was used as a device for carrying out the hot-dip plating method in Embodiment 1 of the present invention. FIG. 5 is a schematic diagram showing an example of a hot-dip plating apparatus used when the hot-dip plating method according to one embodiment of the present invention is applied to dip plating in an atmospheric atmosphere.

As shown in FIG. 5, the hot-dip plating apparatus 40 includes a carbon crucible 42 housed inside a crucible furnace 41, and heats the carbon crucible 42 by causing resistance heating in a heating zone 43. A hot-dip plating bath metal 21 is stored in the carbon crucible 42, and a bath surface oxide 22 is generated on the surface of the hot-dip plating bath metal 21. In the hot-dip plating apparatus 40, the surface of the hot-dip plating bath metal 21 is in an atmospheric atmosphere.

Similar to the hot-dip plating device 1 described above (see FIG. 1), the hot-dip plating device 40 includes an ultrasonic horn 10, and the steel plate 2 is fixed to the tip of the ultrasonic horn 10. The ultrasonic transducer 11 of the ultrasonic horn 10 receives an ultrasonic signal supplied from the ultrasonic power supply device D1 (including an oscillator 13, a power amplifier 14, and a power meter 15), and receives an ultrasonic signal from the ultrasonic power supply device D1. Vibration is applied to the steel plate 2 at a set output.

As the ultrasonic transducer 11, a commercially available bolted Langevin type transducer can be used. Moreover, as the ultrasonic horn 10, an ultrasonic horn made of aluminum, titanium, ceramics, etc. can be used.

The hot-dip plating apparatus 40 also includes a waveguide rod 51, an acoustic emission sensor (hereinafter sometimes referred to as an AE sensor) 52, and a measurement device 50 (corresponding to the measurement device 30 in FIG. 1) that measures an acoustic spectrum. A measuring section 53 is provided. The measurement unit 53 includes a spectrum analyzer and an amplifier. One end of the waveguide rod 51 is immersed in the hot-dip plating bath metal 21, and the other end is connected to the AE sensor 52.

The various devices used in the hot-dip plating apparatus 40 in this example are specifically as follows.

(Ultrasonic vibration supply system)
・Ultrasonic transducer 11: Made by Honda Electronics, bolted Langevin type transducer ・Ultrasonic horn 10: Material <Aluminum alloy A2024A>
・Oscillator 13: Manufactured by Agilent Technologies, 33220A
・Power amplifier 14: M-2141 manufactured by Mestech Co., Ltd.
・Watt meter 15: Manufactured by Hioki Electric Co., Ltd., PW-3335
(Ultrasonic vibration measurement system)
・Waveguide rod 51: Material <SUS430>, φ6mm x 300mm
・AE sensor 52: AE-900M manufactured by NF Circuit Design Block Co., Ltd.
・Amplifier: AE9922 manufactured by NF Circuit Design Block Co., Ltd.
- Spectrum analyzer: E4408B manufactured by Agilent Technologies.

Further, in this example, as the steel plate 2 (plating base material), carbon steel (steel type A and steel type B) shown in Table 1 below or stainless steel (steel type C to steel type F) shown in table 2 below was used. Steel types A to F are all annealed materials.

In Table 2, "-" indicates that no component analysis was performed, and "tr." indicates that the content was below the detection limit of the analysis.

(Plating wettability test method)
The plating wettability was evaluated as follows using the sample after dip-dipping plating as the test material. FIG. 6 is a side view showing the condition of the sample material 3 after plating. As shown in FIG. 6, a plated region 3a is formed in the sample material 3 after plating, where molten Al-based plating is applied. Further, in a part of the plating region 3a, there may be an unplated portion 4 to which molten Al-based plating is not applied.

For example, the depth of the portion of the sample material 3 immersed in the molten Al-based plating bath is L11, and the width of the sample material 3 is L12. In this case, on the plate surface (both sides) shown in FIG. 6, L11×L12×2 becomes the ideal area α of the plating region. Furthermore, the area β of the unplated portion 4 is measured using a known area measuring means. The area β of the unplated portion 4 is the area measured for both plated surfaces (both plate surfaces) of the sample material 3. Then, the non-plating rate was calculated by calculating (β/α)×100. The plating properties of the sample material 3 were evaluated based on the following criteria, and those with a rating of △ or above were considered to be passed.

◎: Unplated rate is 0%
○: Unplated rate is more than 0% and less than 1% △: Unplated rate is 1% or more and less than 10% ×: Unplated rate is 10% or more and less than 80% XX: Unplated rate is 80% or more.

(Plating adhesion test method)
FIG. 16 is a schematic diagram for explaining the plating adhesion test. As shown in FIG. 16(a), a steel plate after hot-dip Al-based plating was used as a test material 200, and the test material 200 was first subjected to 0T contact bending (180° bending). Then, cellophane tape 210 was attached to the bent portion 201 so as to be in close contact with it, and then the cellophane tape 210 was peeled off.

Next, as shown in FIG. 16(b), the peeled off cellophane tape 210 was attached to Xerox paper. Then, black and white binarization processing was performed on the captured image of the Xerox paper to which the cellophane tape 210 was attached. From the image after the binarization process, the area A of the portion 211 of the cellophane tape 210 that was in close contact with the bent portion 201 is calculated, and the plating layer 230 that has been peeled off from the bent portion 201 attached to the cellophane tape 210 is calculated. The area B was calculated. Then, the value obtained by calculating (B/A)×100 was calculated as the plating peeling rate. The plating adhesion of the sample material 200 was evaluated according to the following criteria, and a score of △ or above was considered to be a pass.

◎: Plating peeling rate is 0%
○: Plating peeling rate is greater than 0% and less than 5% △: Plating peeling rate is 5% or more and less than 10% ×: Plating peeling rate is 10% or more and less than 80% XX: Plating peeling rate is 80% or more.

(Evaluation of plating wettability and plating adhesion)
The above steel plates A to F shown in Tables 1 and 2 were subjected to alkaline degreasing and pickling using 10% hydrochloric acid as pretreatments, respectively. Each pretreated steel plate is attached to the tip of the ultrasonic horn 10, and placed in the hot-dip Al plating bath at a depth of 60 mm (in other words, the length of the steel plate immersed in the bath in the depth direction of the plating bath). ), and the dipping time was set to 100 seconds, and dobu-dip plating was performed. When applying vibration to the steel plate, the application of vibration was started 10 seconds after the start of immersion of the steel plate attached to the tip of the ultrasonic horn 10 into the molten Al-based plating bath, and the vibration was applied for 90 seconds.

Three types of molten Al-based plating baths were prepared as plating baths. The composition of each molten Al-based plating bath is shown in Table 3 below. The temperature of the molten Al-based plating bath was set at 630° C. to 700° C., and when applying vibration to the molten Al-based plating bath, the fundamental frequency and the output of the ultrasonic vibrator 11 were changed. Further, as a comparative example, dip plating was performed without applying vibration to the molten Al-based plating bath.

The results of the above-mentioned plating wettability test and plating adhesion test are summarized and shown in Table 4. In Table 4, the plating base material is a steel plate, and whether or not the plating base material is heated means whether or not the steel plate is heated in a step before hot-dip Al-based plating. Moreover, the inlet temperature means the temperature of the steel plate at the time of introduction into the molten Al-based plating bath. The sound intensity (noise standard) in the table is determined by IA-NA, and the average intensity between integer harmonics (that is, the average intensity between harmonics based on noise standard) is determined by IB-NB. The ratio (characteristic intensity ratio) is determined by (IB-NB)/(IA-NA) (see the above-mentioned formula (1) for these symbols). The above also applies hereinafter.

First, the evaluation results of plating wettability will be explained. No. of Table 4 As shown in 1 to 13, a steel plate is dip-plated while applying vibration to a molten Al plating bath under conditions such that an acoustic spectrum within the range of the present invention is measured in the molten Al plating bath. When applied, the plating wettability of the steel sheet improved, and the unplated rate of the plated product became less than 10%. In addition, No. 1 with an output of 5W to 20W. In the examples shown in 3 to 13, the unplated rate of the plated products was 0%.

On the other hand, if the vibration applied to the molten Al plating bath is too weak (the sound pressure is too low), the acoustic spectrum within the range of the present invention will not be measured in the molten Al plating bath, and the No. ．． As shown in Figures 14 to 16, the unplated rate of plated products was 10% or more. In addition, when molten Al plating was performed without applying vibration to the molten Al plating bath, No. 4 in Table 4. As shown in Nos. 17 to 24, the unplated rate of the plated products was 80% or more.

Next, the evaluation results of plating adhesion will be explained. No. 1 evaluated for plating wettability. The plating adhesion was evaluated as described above using the samples Nos. 1 to 24 after dip-dipping plating as test materials.

No. of Table 4 As shown in 1 to 13, a steel plate is dip-plated while applying vibration to a molten Al plating bath under conditions such that an acoustic spectrum within the range of the present invention is measured in the molten Al plating bath. When applied, the plating adhesion of the steel plate improved, and the plating peeling rate was 0% as a result of a plating adhesion test on the plated product.

On the other hand, if the vibration applied to the molten Al plating bath is too weak (the sound pressure is too low), the acoustic spectrum within the range of the present invention will not be measured in the molten Al plating bath, and the No. ．． As shown in 14 to 16, the plating peeling rate was 10% or more as a result of the plating adhesion test performed on the plated products. In addition, when hot-dip plating was performed without applying vibration to the hot-dip Al-based plating bath, No. 4 in Table 4. As shown in Nos. 17 to 24, the plating peeling rate was 80% or more as a result of the plating adhesion test.

[Embodiment 2]
Other embodiments of the invention will be described below. For convenience of explanation, members having the same functions as the members described in the above embodiment are given the same reference numerals, and the description thereof will not be repeated.

In the hot-dip plating apparatus 1 (see FIG. 1) in the first embodiment, the distance L1 between the tip of the waveguide rod 31 and the surface of the steel plate 2 in the molten Al-based plating bath 20 is fixed at 10 mm, and the acoustic spectrum is measured. did. Further study by the present inventors revealed that the characteristic intensity ratio in the acoustic spectrum can change as the position at which the acoustic spectrum is measured changes.

Therefore, the acoustic spectrum was measured while changing the distance L1 from 1 mm to 80 mm and changing the output of the ultrasonic transducer 11 from 0.1 W to 20 W. The results are shown in FIGS. 7(a) to (e). (a) to (e) of FIG. 7 are graphs showing acoustic spectra measured by changing the output of the ultrasonic transducer 11 at each distance L1, (a) is a graph when the distance L1 is 1 mm, and (b) is a graph. The distance L1 is 5 mm, (c) is 10 mm, (d) is 30 mm, and (e) is 80 mm.

FIG. 8 is a graph showing the relationship between the distance L1 and the characteristic intensity ratio. As shown in FIG. 8, the characteristic intensity ratio tends to decrease as the distance L1 increases, and this tendency is particularly noticeable when the output is weak (specifically, 0.1W, 0.5W). be. From this, for example, when the output is 0.1 W or 0.5 W, in order to detect the acoustic spectrum, it is preferable to set the distance L1 to 10 mm or less.

Furthermore, as shown in FIGS. 7(a) to (e), if the distance L1 is too large, the signal strength of the acoustic spectrum decreases and falls below the noise level, making it difficult to detect the signal. Therefore, it may be difficult to accurately evaluate the vibration state within the molten Al-based plating bath 20. Therefore, in this hot-dip plating method, it is preferable that the output is 0.5 W or more and the distance L1 is 10 mm or less.

[Embodiment 3]
Other embodiments of the invention will be described below. For convenience of explanation, members having the same functions as the members described in the above embodiment are given the same reference numerals, and the description thereof will not be repeated.

In the first and second embodiments, the ultrasonic horn 10 was used to apply vibration to the steel plate 2 with the steel plate 2 attached to the tip of the ultrasonic horn 10. In contrast, in the present embodiment, with the diaphragm attached to the tip of the ultrasonic horn 10, vibration is applied to the diaphragm using the ultrasonic horn 10, and via the molten Al plating bath 20, The difference is that vibration is indirectly applied to the steel plate 2.

(Hot-dip plating equipment)
A hot-dip plating apparatus 60 that implements the hot-dip plating method in this embodiment will be described using FIG. 9. Note that the hot-dip plating apparatus 60 is one example, and the apparatus that implements the present hot-dip plating method is not particularly limited. FIG. 9 is a schematic diagram showing a hot-dip plating apparatus 60 that implements the hot-dip plating method in this embodiment.

As shown in FIG. 9, the hot-dip plating apparatus 60 includes a gas reduction heating zone 61, a hot-dip plating section 62, an ultrasonic horn 10, and a measuring device 50 for measuring an acoustic spectrum. The gas reduction heating zone 61 includes an atmospheric gas introduction section 61a and a heating section 61b, and is capable of heat-treating the steel plate 2 in a desired atmosphere.

In the hot-dip plating section 62, the space above the crucible furnace 41 is isolated from the atmosphere by a port flange 64 and an O-ring 65. Further, an atmospheric gas introduction section 66 is provided in a part of the port flange 64, so that the atmosphere in the hot-dip plating section 62 can be controlled.

A gate valve 63 is provided between the gas reduction heating zone 61 and the hot-dip plating section 62. The steel plate 2 processed in the gas reduction heating zone 61 is transferred to the hot-dip plating section 62 without being exposed to the atmosphere by opening the gate valve 63. The steel plate 2 is subjected to pretreatment such as atmosphere control and heat treatment in the gas reduction heating zone 61 above the gate valve 63, and then enters the hot-dip plating bath metal 21.

Furthermore, in the hot-dip plating apparatus 60 of this embodiment, a diaphragm 70 is fixed to the tip of the ultrasonic horn 10 instead of the steel plate 2 . The diaphragm 70 is made of ordinary steel (the same type of steel as steel plate A in Table 1) and has a length of 150 mm, a width of 50 mm, and a thickness of 0.8 mm. The vibration of the diaphragm 70 imparts vibration to the hot-dip plating bath metal 21. As a result, vibration is applied to the steel plate 2 via the hot-dip plating bath metal 21. That is, the hot-dip plating apparatus 60 is configured to indirectly apply vibration to the steel plate 2. Note that the material of the diaphragm 70 is not limited to the above materials. The diaphragm 70 is preferably made of a material that has strong corrosion resistance when immersed in a molten Al plating bath and does not have good wettability to the molten Al plating bath. For example, ceramics can be used.

The other configurations of the measuring device 50 and the like are the same as those of the hot-dip plating device 40 described above (see FIG. 5), so detailed explanations will be omitted.

The hot-dip plating apparatus 60 as described above can be applied to a continuous hot-dip plating method. That is, in the continuous hot-dip plating method, it is difficult to directly apply vibration to the steel plate, but it is possible to indirectly apply vibration to the steel plate 2 as in the hot-dip plating apparatus 60. Therefore, the results demonstrated using the hot-dip plating apparatus 60 as described above can be applied to a continuous hot-dip plating method. An example of application to a continuous hot-dip plating method will be specifically described later.

[Embodiment 4]
In the hot-dip Al-plated steel sheet produced by the hot-dip plating method of the present invention, a base chemical conversion film that improves corrosion resistance and film adhesion may be formed on the surface of the Al-based plating layer. As the base chemical conversion coating, an inorganic coating is preferable, and more specifically, one containing a valve metal oxide or hydroxide and a valve metal fluoride is preferable. Here, "valve metal" refers to a metal whose oxide exhibits high insulation resistance. The valve metal element is preferably one or more elements selected from Ti, Zr, Hf, V, Nb, Ta, Mo, and W. Further, the base chemical conversion coating may contain a soluble or hardly soluble metal phosphate or a composite phosphate. Furthermore, the base chemical conversion coating may contain organic waxes such as fluorine-based, polyethylene-based, and styrene-based waxes, or inorganic lubricants such as silica, molybdenum disulfide, and talc. The base chemical conversion coating may be an organic coating based on urethane resin, acrylic resin, epoxy resin, olefin resin, polyester resin, or the like.

In addition, the hot-dip Al-plated steel sheet produced by the hot-dip plating method of the present invention is coated with polyester, acrylic resin, fluororesin, vinyl chloride resin, urethane resin, or epoxy resin on the surface of the Al-based plating layer. It is possible to apply resin-based paints such as the following by methods such as roll coating, spray coating, curtain flow coating, and dip coating. Alternatively, it can also be used as a base material for film laminate when laminating plastic films such as acrylic resin films.

[Embodiment 5]
Other embodiments of the invention will be described below. For convenience of explanation, members having the same functions as the members described in the above embodiment are given the same reference numerals, and the description thereof will not be repeated.

In the hot-dip plating method in this embodiment, a part of the ultrasonic horn is immersed in the molten Al-based plating bath, and vibrations are applied to the molten Al-based plating bath from the tip of the ultrasonic horn. As a result, vibrations are indirectly transmitted from the tip of the ultrasonic horn to the steel plate via the molten Al-based plating bath, and the steel plate is subjected to dowel plating.

(Hot-dip plating equipment)
A hot-dip plating apparatus 80 that implements the hot-dip plating method in this embodiment will be described using FIG. 10. Note that the hot-dip plating apparatus 80 is one example, and the apparatus that implements the present hot-dip plating method is not particularly limited. FIG. 10 is a schematic diagram showing a hot-dip plating apparatus 80 that implements the hot-dip plating method in this embodiment.

As shown in FIG. 10, the hot-dip plating apparatus 80 includes an elevating device 81, an ultrasonic horn 10A, a measuring device 50 for measuring an acoustic spectrum, and a carbon crucible 42 in which hot-dip plating bath metal 21 is stored. ing. In the hot-dip plating apparatus 80, the steel plate 2 is immersed in the hot-dip Al-based plating bath 20 in the atmosphere and without heating the steel plate 2.

The lifting device 81 is a device that makes it possible to immerse the steel plate 2 in the molten Al-based plating bath 20 while holding the steel plate 2, and to lift the steel plate 2 from the molten Al-based plating bath 20. . As the elevating device 81, a known device may be used, and detailed description thereof will be omitted.

The ultrasonic horn 10A includes an ultrasonic transducer 11, a tip portion 17, and a connecting portion 16 that connects the ultrasonic vibrator 11 and the tip portion 17. The ultrasonic transducer 11 is fixed by a transducer fixing stage 19. The connecting portion 16 has a length that allows it to easily resonate in accordance with the frequency of vibration generated by the ultrasonic transducer 11. The connecting portion 16 may be a mere adapter, or may be a booster that amplifies the amplitude generated by the ultrasonic transducer 11 and transmits it to the tip portion 17.

With at least a portion of the tip 17 of the ultrasonic horn 10A immersed in the molten Al plating bath 20, the ultrasonic vibrator 11 receives an ultrasonic signal transmitted from the ultrasonic power supply device D1 and generates an ultrasonic wave. Sound waves vibrate. This ultrasonic vibration is transmitted to the tip 17 via the connecting portion 16, and the tip 17 applies vibration to the molten Al-based plating bath 20.

When the steel plate 2 is immersed in the molten Al-based plating bath 20 by the lifting device 81, the steel plate 2 is placed in front of the tip portion 17. A vibrating surface 17A is formed at the end of the tip portion 17 that is far from the connecting portion 16 in the longitudinal direction so that the cross-sectional shape of the end portion is an isosceles triangle. It faces the surface of the steel plate 2 immersed in the Al-based plating bath 20.

It is preferable that the tip portion 17 is made of ceramic. This is to reduce deterioration of the tip 17 that may occur due to ultrasonic vibration of the tip 17 in the molten Al-based plating bath 20.

Note that the hot-dip plating apparatus 80 may use an integrated ultrasonic horn instead of the ultrasonic horn 10A. In this case, the tip of the ultrasonic horn may be made of ceramics.

The distance L2 between the vibration surface 17A of the tip portion 17 and the surface of the steel plate 2 may be 0 mm, or may be greater than 0 mm and less than or equal to 50 mm. The distance L2 of 0 mm means that the vibration surface 17A and the surface of the steel plate 2 are in contact with each other before the ultrasonic horn 10A vibrates ultrasonically (ie, at the time of setting). For example, the lifting device 81 can move the steel plate 2 in the horizontal direction, and the distance L2 can be adjusted by moving the steel plate 2 in the horizontal direction using the lifting device 81. The distance L2 is preferably greater than 0 mm and less than or equal to 5 mm.

In the hot-dip plating apparatus 80, the frequency, output, etc. of vibration applied to the molten Al-based plating bath 20 using the ultrasonic horn 10A are the same as those described in the first embodiment.

[Example 2]
Examples of the hot-dip plating method in Embodiment 5 of the present invention will be described below. In this example, the hot-dip plating apparatus 80 shown in FIG. 10 described above was used.

The various devices used in the hot-dip plating apparatus 80 in this example are specifically as follows.

(Ultrasonic vibration supply system)
- Ultrasonic transducer 11: Manufactured by Hielscher, 20kHz transducer - Connection part 16 (booster): Material <Ti>, amplification factor 2.2 times, 1/2 wavelength type, length 126 mm
・Tip part 17: Material <Ti>, 1/2 wavelength type, length 250mm
・Ultrasonic power supply device D1: Manufactured by Hielscher, 20kHz, 2kW power supply (ultrasonic vibration measurement system)
・Waveguide rod 51: Material <SUS430>, φ6mm x 300mm
・AE sensor 52: AE-900M manufactured by NF Circuit Design Block Co., Ltd.
・Measurement part 53
Amplifier: AE9922 manufactured by NF Circuit Design Block Co., Ltd.
Spectrum analyzer: E4408B manufactured by Agilent Technologies.

Steel plates A to F shown in Tables 1 and 2 in Example 1 were dip-dipped in a variety of conditions using the hot-dip Al plating bath shown in Table 3 in Example 1.

When applying vibration to the molten Al plating bath using the ultrasonic horn 10A, the distance L2 was set to 0 mm to 50 mm, and the fundamental frequency was set to 20 kHz.

When applying vibration to the molten Al-based plating bath using the ultrasonic horn 10A, start applying the vibration 10 seconds after starting to immerse the steel plate 2 in the molten Al-based plating bath, and then apply the vibration for 2 seconds to 60 seconds. Added vibration.

The ultrasonic transducer 11 has a built-in amplitude sensor for monitoring the amplitude of the ultrasonic transducer 11. A display device was used to receive the output from the amplitude sensor and display the output with a full scale of 5V. Since the magnitude of the amplitude of the ultrasonic transducer 11 is reflected in the output displayed by the display device, in the following, the full scale 5V is taken as 100% output, and an index representing the magnitude of the amplitude of the ultrasonic transducer 11 is used. "Output %" was used as the value.

Here, in the method of directly vibrating the steel plate (direct method), the load for the ultrasonic power source is considered to be the steel plate itself. On the other hand, in the case of a method of indirectly vibrating a steel plate via a molten Al-based plating bath (indirect method), the load on the ultrasonic power source is the steel plate and the molten Al-based plating bath. Therefore, instead of the output (W) from the ultrasonic power source itself, "output %", which is an index representing the amplitude of the ultrasonic vibrator when it resonates, is used to represent the vibration application conditions.

Further, as a comparative example, each sample material was dip-dipped using the hot-dip plating apparatus 80 without applying vibration to the molten Al-based plating bath. The test results are summarized and shown in Table 5.

First, the evaluation results of plating wettability will be explained. When dip-dipping plating is applied to a steel plate while applying vibration to a molten Al plating bath under conditions such that an acoustic spectrum within the range of the present invention is measured in the molten Al plating bath, the following results are obtained. was gotten. No. of Table 5 As shown in 25 to 28 and 35 to 41, when the distance L2 between the ultrasonic horn 10A and the steel plate was 2 mm or less, the plating wettability was greatly improved and the uncoated rate of the plated product was 0%. . In addition, No. 1 in which the distance L2 between the ultrasonic horn 10A and the steel plate was 5 mm. In the examples shown in Nos. 29, 33, and 34, the unplated rate of the plated products was less than 1%. The slight variation in plating wettability in the sample after plating may be due to factors such as test errors or the influence of the inter-plate distance L2 being slightly large.

Also, No. of Table 5. As shown in Figures 30 to 32, when the inter-plate distance L2 was 10 mm to 50 mm, the unplated rate of the plated products was less than 10%. It was suggested that the larger the inter-plate distance L2, the lower the plating wettability.

On the other hand, when molten Al plating was performed without applying vibration to the molten Al plating bath, No. As shown in 42 to 49, the unplated rate of the plated products was 80% or more.

Next, the evaluation results of plating adhesion will be explained. No. 1 evaluated for plating wettability. The plating adhesion was evaluated as described above in Example 1 using samples Nos. 25 to 49 after dip-dipping plating as test materials.

No. of Table 5 As shown in 25 to 41, a steel plate is dip-plated while applying vibration to a molten Al plating bath under conditions such that an acoustic spectrum within the range of the present invention is measured in the molten Al plating bath. When applied, the plating adhesion of the steel plate improved, and the plating peeling rate was 0% as a result of a plating adhesion test on the plated product.

On the other hand, when a steel plate is dip-dipped in a hot-dip Al plating bath without applying vibration, No. 5 in Table 5. As shown in Nos. 42 to 49, the plating layer was not sufficiently formed on the plated product, and the plating adhesion could not be tested.

[Embodiment 6]
Other embodiments of the invention will be described below. For convenience of explanation, members having the same functions as the members described in the above embodiment are given the same reference numerals, and the description thereof will not be repeated.

In the hot-dip plating method in this embodiment, continuous hot-dip plating equipment is used in which the steel strip is continuously passed through a molten Al-based plating bath, and a part of the ultrasonic horn is immersed in the molten Al-based plating bath. Place the tip of the ultrasonic horn near the steel strip. While applying vibration to the hot-dip Al-based plating bath or the steel strip from the tip of the ultrasonic horn, the steel strip is continuously subjected to hot-dip Al-based plating.

(Hot-dip plating equipment)
A hot-dip plating equipment 90A that implements the hot-dip plating method in this embodiment will be described using FIG. 11. Note that the hot-dip plating apparatus 90A is one example, and the apparatus that implements the present hot-dip plating method is not particularly limited. FIG. 11 is a schematic diagram showing an example of hot-dip plating equipment 90A that implements the hot-dip plating method according to the present embodiment.

As shown in FIG. 11, the hot-dip plating equipment 90A has a configuration in which an ultrasonic horn 10B and a measuring device 50 are added to a general continuous hot-dip plating equipment. The steel strip 2A is immersed in the molten Al-based plating bath 20 through the snout 91. The steel strip 2A is passed through the molten Al-based plating bath 20 by guide rolls 92 and support rolls 93, and then pulled up and the amount of plating deposited is adjusted by gas spraying or the like.

The iron oxide layer on the surface of the steel strip 2A may be removed by pickling treatment or the like as a pretreatment for the plating process. Further, the hot-dip plating equipment 90A may be configured to heat the steel strip 2A to a temperature suitable for hot-dip plating using a heating device (not shown) provided upstream of the snout 91.

Here, the hot-dip plating equipment 90A does not need to be provided with a reduction heating device upstream of the snout 91, unlike a general continuous hot-dip plating equipment. In the hot-dip plating equipment 90A, by applying ultrasonic vibration to the molten Al-based plating bath 20 using the ultrasonic horn 10B, the steel strip 2A can be coated even if the surface of the steel strip 2A is not subjected to reduction treatment. It can improve wettability and plating adhesion.

In this embodiment, the ultrasonic horn 10B is an integrated device that includes the ultrasonic vibrator 11, the tip 17, and the connection part 16 in the ultrasonic horn 10A described in the fifth embodiment. Note that the hot-dip plating equipment 90A may use an ultrasonic horn 10A instead of the ultrasonic horn 10B.

In the hot-dip plating equipment 90A, the ultrasonic horn 10B is arranged such that the tip of the ultrasonic horn 10B is immersed in the molten Al-based plating bath 20 and located near the steel strip 2A near the exit of the snout 91. has been done.

It is preferable that the end of the ultrasonic horn 10B closer to the steel strip 2A in the longitudinal direction is chamfered to form a vibration surface 17A. The vibrating surface 17A faces the surface of the steel strip 2A passing through the molten Al-based plating bath 20. Thereby, vibration can be efficiently transmitted from the ultrasonic horn 10B to the steel strip 2A while keeping the distance between the vibration surface 17A and the surface of the steel strip 2A constant in accordance with the sheet passing direction.

In addition, in the hot-dip plating equipment 90A, in the vicinity of the second surface of the steel strip 2A, which is opposite to the first surface of the steel strip 2A facing the vibration surface 17A, in the hot-dip Al-based plating bath 20, , the tip of the waveguide rod 51 is arranged. It is preferable that the waveguide rod 51 is arranged along the threading direction of the steel strip 2A. Furthermore, the waveguide rod 51 may be provided with a protective tube or the like that covers the portion other than the tip in the molten Al plating bath 20 in order to reduce noise and the like in the acoustic spectrum.

The distance L3 between the vibration surface 17A and the surface of the steel strip 2A may be 0 mm, or may be greater than 0 mm and less than or equal to 50 mm. When the distance L3 is 0 mm, it means that the vibration surface 17A and the surface of the steel strip 2A are in contact with each other before the ultrasonic horn 10B vibrates ultrasonically (ie, at the time of setting).

Even though the ultrasonic horn 10B applies ultrasonic vibration to one side of the steel strip 2A, if the distance L3 is sufficiently short, the steel strip 2A is vibrated at the same fundamental frequency as the ultrasonic horn 10B. It is possible to do so. As a result, plating wettability and plating adhesion can be improved not only on the first surface but also on the second surface of the steel strip 2A.

In the hot-dip plating equipment 90A, the frequency, output, etc. of vibration applied to the molten Al-based plating bath 20 using the ultrasonic horn 10B are the same as those described in the first embodiment.

(Modified example of hot-dip plating equipment)
FIG. 12 is a schematic diagram showing a modified example of hot-dip plating equipment 90B and hot-dip plating equipment 90C.

The hot-dip plating equipment 90B and the hot-dip plating equipment 90C differ from the above-described hot-dip plating equipment 90A in that an ultrasonic horn 10B is disposed near the support roll 93. In the hot-dip plating equipment 90B and the hot-dip plating equipment 90C, an ultrasonic horn 10B is disposed at a position after the steel strip 2A is passed through the molten Al-based plating bath 20 and passes the support roll 93. Even when the ultrasonic horn 10B is arranged in this way, the plating wettability and plating adhesion of the steel strip 2A can be improved by applying ultrasonic vibrations from the ultrasonic horn 10B to the molten Al plating bath 20 or the steel strip 2A. You can increase your sexuality.

In addition, the arrangement of the ultrasonic horns 10B in the hot-dip plating equipment 90A to 90C is combined to apply ultrasonic vibration to the molten Al-based plating bath 20 or the steel strip 2A using a plurality of ultrasonic horns 10B. Good too. A configuration that provides good plating wettability and plating adhesion of the steel strip 2A may be appropriately selected.

In addition, in the hot-dip plating equipment 90A to 90C, instead of specifically specifying the time period for applying ultrasonic vibration to the steel strip 2A, the steel strip is The sheet passing speed of 2A may be adjusted as appropriate.

[Example 3]
An example of the hot-dip plating method in Embodiment 6 of the present invention will be described below. In this example, the hot-dip plating equipment 90A shown in FIG. 11 described above was used.

The various devices used in the hot-dip plating equipment 90A in this example are specifically as follows.

(Ultrasonic vibration supply system)
- Ultrasonic transducer 11: manufactured by Hielscher, 20kHz transducer - Connection part 16 (booster): Material <Ti>, 1/2 wavelength type, length 126 mm
・Tip part 17: Material <Super Sialon>, 2 wavelength type, length 500mm
・Ultrasonic power supply device D1: Manufactured by Hielscher, 20kHz, 2kW power supply (ultrasonic vibration measurement system)
・Waveguide rod 51: Material <SUS430>, φ6mm x 300mm
・AE sensor 52: AE-900M manufactured by NF Circuit Design Block Co., Ltd.
・Measurement part 53
Amplifier: AE9922 manufactured by NF Circuit Design Block Co., Ltd.
Spectrum analyzer: E4408B manufactured by Agilent Technologies.

Steel plates A to F shown in Tables 1 and 2 in Example 1 were subjected to continuous hot-dip plating under various conditions using the hot-dip Al plating baths shown in Table 3 in Example 1. .

The atmosphere in the snout was changed to an air atmosphere, a nitrogen atmosphere, a 3% hydrogen-nitrogen atmosphere, or a 30% hydrogen-nitrogen atmosphere. In addition, when heat treatment is performed before the snout, the steel strip is heat treated in an air atmosphere, a nitrogen atmosphere, a 3% hydrogen-nitrogen atmosphere, or a 30% hydrogen-nitrogen atmosphere. .

When applying vibration to the molten Al-based plating bath using the ultrasonic horn 10B, the distance L3 was set to 0 mm, and the fundamental frequency was set to 20 kHz. The threading speed of the steel strip in the hot-dip Al plating bath was 20 m/min in the example with heat treatment before the snout, and 3 m/min in the example without heat treatment.

Further, as a comparative example, continuous hot-dip plating was applied to the steel strip 2A using the hot-dip plating equipment 90A without applying vibration to the hot-dip Al-based plating bath. The test results are summarized and shown in Tables 6 and 7. Table 6 shows the results without heat treatment at the front stage of the snout, and Table 7 shows the results with heat treatment.

No. of Table 6 Nos. 50 to 81 and Table 7. As shown in 90 to 113, continuous plating equipment was used while applying vibration to the molten Al plating bath under conditions such that an acoustic spectrum within the range of the present invention was measured in the molten Al plating bath. When hot-dip plating was applied to a steel strip, the following results were obtained. In other words, the plating wettability and plating adhesion of the steel strip are improved regardless of whether the steel strip is heated in an air atmosphere or a non-oxidizing atmosphere, and regardless of the atmosphere in the snout (plating bath atmosphere). did. Specifically, the non-plating rate of the plated product was 0%, and the plating peeling rate as a result of conducting a plating adhesion test on the plated product was 0%.

On the other hand, No. in Table 6. 82 to 89 and No. 89 in Table 7. As shown in Nos. 114 to 122, when hot-dip plating was performed on a steel strip using continuous plating equipment without applying vibration to the hot-dip plating bath, the following results were obtained. In other words, regardless of whether the steel strip was heated in an atmospheric atmosphere or a non-oxidizing atmosphere, and regardless of the atmosphere in the snout (plating bath atmosphere), a sufficient coating layer was not formed on the plated product. . Specifically, the unplated rate of the plated product was 80% or more, and the plating adhesion could not be tested.

[Additional notes]
The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. are also included within the technical scope of the present invention.

2 Steel plate (metal material)
2A Steel strip (metal material)
20 Molten Al plating bath

Claims (2)

A hot-dip plating method in which a metal material is introduced into a molten Al-based plating bath containing aluminum as a main component, and the metal material is coated with a molten Al-based molten metal, the method comprising:
A plating step of coating the metal material with the molten metal while applying vibration to the molten Al-based plating bath while the metal material is in contact with the molten metal,
The frequency of the vibration applied to the molten Al plating bath is the fundamental frequency,
In the plating step, the vibration is applied so that the acoustic spectrum measured in the molten Al-based plating bath satisfies the following formula (1) ,
The vibration is applied to the molten Al-based plating bath by (i) vibrating the metal material fixed to the vibration generator in the molten Al-based plating bath, or (ii) the above-mentioned applied to the molten Al plating bath by vibrating a diaphragm attached to the tip of the vibration generator or the tip of the vibration generator in the molten Al plating bath;
When the vibration is applied to the molten Al plating bath by the diaphragm or the tip, the distance between the vibration surface of the diaphragm or the tip and the metal material is 0 mm or more and 50 mm or less. There is a hot-dip plating method.
0.2< (IB-NB)/(IA-NA) ≦0.91 ...(1)
(here,
IA: Average value of sound pressure in the entire measurement frequency band IB: (i) Between the sound pressure peak at the fundamental frequency and the sound pressure peak at the second harmonic frequency, and (ii) Sound pressure at multiple harmonic frequencies Average value of the sound pressure in a specific frequency band between adjacent peaks of . NA: Average value of the sound pressure in the entire measurement frequency band when the vibration is not applied. NB: Specified with respect to IB above. This is the average value of the sound pressure in the specific frequency band above when the above vibration is not applied)
(However, IA, IB, NA, and NB are measured by a waveguide rod immersed in the molten Al plating bath, and the distance between the tip of the waveguide rod and the surface of the metal material is L1. This is the value when L1 is 10 mm) 2. The hot-dip plating method according to claim 1, wherein the hot-dip Al-based plating bath contains 85% by mass or more of Al.

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