JP6983153B2 - Zinc alloy plated steel sheet with excellent bendability and its manufacturing method - Google Patents

Description

The present invention relates to a galvanized steel sheet having excellent bending workability and a method for manufacturing the same.

The zinc plating method, which suppresses the corrosion of iron by using cathode anticorrosion, is widely used for producing steel materials having high corrosion resistance because of its excellent anticorrosion performance and economy. In particular, hot-dip galvanized steel sheets that form a plating layer by immersing steel in molten zinc have a simpler manufacturing process and lower product prices than electrogalvanized steel sheets, so automobiles and home appliances. , And its demand is increasing throughout the industry such as building materials.

When exposed to a corrosive environment, the galvanized hot-dip galvanized steel sheet is a sacrificial corrosion protection in which zinc, which has a lower oxidation-reduction potential than iron, corrodes first and the corrosion of the steel sheet is suppressed. Has characteristics. Further, the zinc in the plating layer is oxidized to form a dense corrosion product on the surface of the steel sheet, and the steel material is shielded from the oxidizing atmosphere to improve the corrosion resistance of the steel sheet.

However, with the advancement of industry, air pollution is increasing and the corrosive environment is deteriorating, and due to strict regulations on resource and energy conservation, it is necessary to develop steel materials with even better corrosion resistance than conventional galvanized steel sheets. The need is increasing.

As part of this, various studies have been conducted on the manufacturing technology of zinc alloy-based plated steel sheets that improve the corrosion resistance of steel materials by adding elements such as aluminum (Al) and magnesium (Mg) to the zinc plating bath. Research on the manufacturing technology of Zn-Al-Mg-based galvanized steel sheets by adding Mg to the Zn-Al plating composition system as a typical zinc alloy-based plating material is being actively conducted.

By the way, such a Zn-Al-Mg-based galvanized steel sheet has a drawback that the bending workability is weak. That is, the zinc alloy plated steel plate contains a large amount of Zn-Al-Mg-based intermetallic compounds formed by the thermodynamic interaction of Zn, Al and Mg in the plating layer, and the intermetallic compounds have hardness. Therefore, cracks are induced in the plating layer during bending, and as a result, bending workability is deteriorated.

One of some objects of the present invention is to provide a zinc alloy plated steel sheet having excellent bending workability and a method for manufacturing the same.

The subject of the present invention is not limited to the above-mentioned contents. The content of the additional subject of the present invention is described throughout the specification, and if the person has ordinary knowledge in the technical field to which the present invention belongs, an additional subject of the present invention is described from the specification of the present invention. It is a clear understanding of the challenges.

One aspect of the present invention is a zinc alloy plated steel plate including a base steel plate and a zinc alloy plated layer, and the zinc alloy plated layer has a Zn single-phase structure and a Zn—Al—Mg system as fine structures. The Zn single-phase structure containing an intermetallic compound provides a zinc alloy plated steel plate having a (0001) preferential orientation degree (f) of 50% or more represented by the following relational expression 1.
[Relational expression 1]
f (%) = (I _basic / I _total ) × 100
(Here, I _total means a value obtained by integrating the diffraction peaks of all Zn single phases when the X-ray diffraction pattern is measured from 2θ 10 ° to 100 ° using a Cu—Kα source, and I _basic. Means the value obtained by integrating the diffraction peak of the Zn single phase with respect to the basal plane.)

Another aspect of the present invention is a step of providing a zinc alloy plating bath containing Mg and Al, a step of immersing a base steel plate in the zinc alloy plating bath and performing plating to obtain a zinc alloy plated steel plate, and the above zinc. The stage of gas-wiping the alloy-plated steel plate to adjust the plating adhesion amount, and the stage of injecting droplets of water or an aqueous solution onto the zinc alloy-plated steel plate to which the plating adhesion amount has been adjusted to cool and then air-cooling. 2.

As one of some effects of the present invention, the galvanized steel sheet according to the embodiment of the present invention has an advantage that it is excellent in corrosion resistance and bending workability.

Further, as one of some effects of the present invention, the galvanized steel sheet according to the embodiment of the present invention has an advantage that the surface appearance is excellent.

As one of some effects of the present invention, the galvanized steel sheet according to the embodiment of the present invention has an advantage of excellent scratch resistance.

1A and 1B are the results of observing the fine structure of the surface portion of the present invention, in which FIG. 1A shows Invention Example 1 and FIG. 1B shows Comparative Example 5. 2A and 2B are the results of observing the fine structure of the cross section of the present invention, in which FIG. 2A shows Invention Example 1 and FIG. 2B shows Comparative Example 5. FIG. 3 shows the results of XRD (x-ray diffraction) analysis of Invention Example 1 of the present invention.

Hereinafter, a zinc alloy plated steel sheet having excellent bending workability according to one aspect of the present invention will be described in detail.

The zinc alloy plated steel sheet according to one aspect of the present invention includes a base steel sheet and a zinc alloy plated layer. In the present invention, the type of the base steel sheet is not particularly limited, but the base steel sheet may be, for example, a hot-rolled steel sheet or a cold-rolled steel sheet used as a base of a normal galvanized steel sheet. However, in the case of a hot-rolled steel sheet, there is a large amount of oxide scale on the surface, and the oxide scale has a problem of lowering the plating adhesion and lowering the plating quality. It is more preferable to use the removed hot-rolled steel sheet as a base material. On the other hand, the zinc alloy plating layer can be formed on one side or both sides of the base steel sheet.

The zinc alloy plating layer can contain Al: 0.5 to 3%, Mg: 0.5 to 3%, the balance Zn and unavoidable impurities in% by weight.

Mg is an element that plays a very important role in improving the corrosion resistance of the plated steel plate by reacting with Zn and Al in the zinc alloy plating layer to form a Zn-Al-Mg-based intermetallic compound. If the content is excessively low, a sufficient amount of Zn-Al-Mg-based intermetallic compound cannot be obtained in the fine structure of the plating layer, so that the effect of improving corrosion resistance may not be sufficient. be. Therefore, the Mg in the zinc alloy plating layer may be 0.5% by weight or more, preferably 1.0% by weight or more. However, if the content is too large, not only the effect of improving the corrosion resistance is saturated, but also Mg oxide dross in the plating bath is formed, which may deteriorate the plating property. In addition, an excessively large amount of Zn-Al-Mg-based intermetallic compounds having high hardness may be formed in the fine structure of the plating layer, which may reduce bendability. Therefore, the Mg in the zinc alloy plating layer may be 3% by weight or less, preferably 2.9% by weight or less.

The Al suppresses the formation of Mg oxide dross and reacts with Zn and Mg in the plating layer to form a Zn-Al-Mg-based metal-to-metal compound, which is very important for improving the corrosion resistance of the plated steel plate. It is an element that plays a role. If the content is too low, the ability to suppress Mg dross formation is insufficient, and a sufficient amount of Zn-Al-Mg-based intermetallic compound cannot be obtained in the fine structure of the plating layer, resulting in corrosion resistance. There is a possibility that the improvement effect of is not sufficient. Therefore, the Al in the zinc alloy plating layer may be 0.5% by weight or more, preferably 0.6% by weight or more. However, if the content is too large, not only the effect of improving the corrosion resistance is saturated, but also the temperature of the plating bath may rise, which may adversely affect the durability of the plating apparatus. In addition, an excessively large amount of Zn-Al-Mg-based intermetallic compounds having high hardness may be formed in the fine structure of the plating layer, which may reduce bendability. Therefore, the Al in the zinc alloy plating layer may be 3% by weight or less, preferably 2.6% by weight or less.

According to one example, the content of Mg and Al contained in the zinc alloy plating layer can satisfy the following relational expression 2. When [Mg] / [Al] is 1.0 or less, scratch resistance may deteriorate. On the other hand, if [Mg] / [Al] exceeds 4.0, a large amount of Mg-based dross may be generated in the hot-dip plating bath, and workability may be deteriorated.
[Relational expression 2 ]
1.0 <[Mg] / [Al] ≤ 4.0
(Here, [Mg] and [Al] mean the weight% of the corresponding element, respectively.)

The zinc alloy plating layer can contain a Zn single-phase structure and a Zn—Al—Mg-based intermetallic compound as a fine structure. In the present invention, the type of the Zn-Al-Mg-based metal-to-metal compound is not particularly limited, but the Zn-Al-Mg-based metal-to-metal compound is, for example, a Zn / Al / MgZn ₂ ternary eutectic structure. It can be one or more selected from the group consisting of a binary eutectic structure of Zn / MgZn _2, a binary eutectic structure of Zn / Al, and _{a monophasic structure of MgZn 2.}

As a result of deep research in order to improve the bending workability of the zinc alloy plated steel sheet, the present inventors have found that Zn having a hexagonal close-packed structure (HCP, Hexagonal Close Packing) in the fine structure of the zinc alloy plated layer. It has been found that when the single-phase structure is grown in the (0001) orientation, it becomes easy to slip and the ductility increases, which can significantly reduce the generation of cracks during bending.

In the present invention, in order to obtain such an effect, the Zn single-phase structure preferably controls the (0001) preferential orientation degree (f) represented by the following relational expression 1 to 50% or more, preferably 60% or more. It is more preferable to control.
[Relational expression 1]
f (%) = (I _basic / I _total ) × 100
(Here, I _total means a value obtained by integrating the diffraction peaks of all Zn single phases when the X-ray diffraction pattern is measured from 2θ 10 ° to 100 ° using a Cu—Kα source, and I _basic. Means the value obtained by integrating the diffraction peak of the Zn single phase with respect to the basal plane.)

Further, the present inventors have found that reducing the size of the Zn single-phase structure coarsely formed in the zinc alloy plating layer also helps to reduce the occurrence of cracks during bending.

In order to obtain the desired effect in the present invention, it is preferable to control the average particle size of the Zn single-phase structure to 15 μm or less, more preferably to 12 μm or less, and further preferably to 10 μm or less. .. Here, the average particle size of the Zn single-phase structure means the average circular diameter of the Zn single-phase structure detected by observing the cross section of the plating layer in the plate thickness direction.

The galvanized steel sheet according to the present invention has an advantage that it is not only very excellent in corrosion resistance but also very excellent in bending workability.

According to one example, the galvanized steel sheet according to the present invention is also very excellent in surface appearance. More specifically, the number per unit area of the black spot (black spot) in the surface of the zinc alloy coated steel sheet can be 0.1 / cm ² or less.

In the present invention, in order to obtain such an effect, the area fraction of the Zn single-phase structure observed on the surface of the zinc alloy plating layer is preferably 40% or less (excluding 0%). That is, the appearance of the surface can be improved by maximizing the ratio of the Zn-Al-Mg-based intermetallic compound observed on the surface of the zinc alloy plating layer.

According to one example, the galvanized steel sheet according to the present invention is also very excellent in scratch resistance.

According to the research results of the present inventors, the area fraction _{of the ternary eutectic structure of Zn / MgZn 2 and} the ternary eutectic structure of Zn / Al / MgZn ₂ observed on the surface of the zinc alloy plated layer. When maximizing, it can be confirmed that the scratch resistance is significantly improved.

In order to obtain the desired effect in the present invention, the area fraction _{of the binary eutectic structure of Zn / MgZn 2 and} the ternary eutectic structure of Zn / Al / MgZn _{2 observed on the surface of the zinc alloy plating layer.} It is preferable that the total of the above is 50% or more (excluding 100%), and _{the area fraction of the single-phase structure of MgZn 2} is 10% or less (including 0%). Since _{the single-phase structure of MgZn 2} has a high hardness, it induces cracks during processing. Therefore, it is preferable to reduce the surface integral to the maximum.

The zinc alloy plated steel sheet of the present invention described above can be manufactured by various methods, and the manufacturing method is not particularly limited. However, as a preferable example, when the zinc alloy plating layer in a molten state is solidified, droplets (droplets) are jetted onto the surface thereof to cool the layer, and then air-cooled, the preferred orientation and the average particle size as described above are obtained. be able to.

At this time, the droplet injection may be a charge injection so that the droplet is adhered to the zinc alloy plated steel sheet by electrostatic attraction. Such charged injection not only helps to form the droplets finely and uniformly, but also reduces the amount of droplets that pop out after the ejected droplets collide with the surface of the zinc alloy plated steel plate to form a molten state. It is also advantageous to rapidly cool the zinc alloy plating layer. This is also effective for growth and miniaturization of the Zn single-phase structure in the (0001) orientation.

The droplet may be an aqueous phosphate solution. Such a phosphate aqueous solution is effective in growing a Zn single-phase structure in a (0001) orientation and making it finer by rapidly cooling the molten zinc alloy plating layer by an endothermic reaction. For example, an aqueous solution of ammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ), an aqueous solution of sodium ammonium hydrogen phosphate (NaNH ₄ HPO ₄ ), a first aqueous solution of zinc phosphate (Zn (H ₂ PO ₄ ) ₂ ), and calcium phosphate (N). Ca ₃ (PO ₄ ) ₂ ) Aqueous solution and the like can be mentioned.

Further, the concentration of the aqueous phosphate solution can be 1 to 3% by weight. If the concentration of the aqueous phosphate solution is less than 1% by weight, the effect may not be sufficient. On the other hand, if it exceeds 3% by weight, not only the effect is saturated, but also in the case of continuous production, a nozzle clogging phenomenon may occur and the production may be hindered.

When injecting the droplets, the droplet injection start temperature can be 405 to 425 ° C, more preferably 41 to 420 ° C. At this time, the droplet injection start temperature means the surface temperature of the zinc alloy plated steel sheet at the time when the droplet injection is started. If the droplet injection start temperature is less than 405 ° C., solidification of the Zn single phase has already started, and black spots may be induced on the surface of the zinc alloy plated steel sheet. On the other hand, if the temperature exceeds 425 ° C., the endothermic reaction by droplet injection is not effective, and it may be difficult to secure the target structure.

Further, when the droplet is ejected, the droplet injection end temperature can be 380 to 400 ° C, more preferably 390 to 400 ° C. At this time, the droplet injection end temperature means the surface temperature of the zinc alloy plated steel sheet at the time when the droplet injection is completed. If the droplet injection end temperature exceeds 400 ° C., the endothermic reaction by the droplet injection is not effective, and it may be difficult to secure the target structure. On the other hand, in the case of less than 380 ° C. is, Zn / MgZn when solidification of ₂ binary eutectic phase and ternary eutectic phase of Zn / Al / MgZn ₂ is started, supercooling is caused _Mg 2 Zn _{Since the 11th} phase is induced and a large amount of black spots are generated, the (0001) preferential orientation of the Zn single-phase structure may be lowered.

Further, when injecting the droplet, the difference between the droplet injection start temperature and the droplet injection end temperature can be 15 ° C. or more. If the temperature difference is less than 15 ° C., the endothermic reaction by droplet injection is not effective, and it may be difficult to secure the target structure.

When the droplets are ejected, the droplet ejection amount can be 50 to 100 g / m ² . If the injection amount is ^{less than 50 g / m 2} , the effect may be insufficient. On the other hand, if ^{it exceeds 100 g / m 2} , the effect is saturated, which is not preferable.

Hereinafter, the present invention will be described in more detail through examples. However, it should be noted that the following examples are for exemplifying and embodying the present invention, and not for limiting the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the claims and the matters reasonably inferred from them.

(Example 1)
A low-carbon cold-rolled steel sheet (that is, a base steel sheet) having a thickness of 0.8 mm, a width of 100 mm, and a length of 200 mm is provided as a test piece for plating, and then the base steel sheet is immersed in acetone and ultrasonically cleaned to clean the surface. Foreign substances such as rolling oil present in the steel sheet were removed. Then, in order to secure the mechanical properties of the steel sheet in a general hot-dip plating environment, a reducing atmosphere heat treatment was performed at 750 ° C., and then the plating bath (plating bath temperature: 450 ° C.) having the composition shown in Table 1 below was used. A zinc alloy plated steel sheet was manufactured by dipping. Subsequently, each of the manufactured galvanized steel sheets was gas-wiped to ^{adjust the plating adhesion amount to 70 g / m 2} per side, cooled under the conditions shown in Table 1 below, and then air-cooled. On the other hand, although not shown in Table 1 below, in Comparative Example 5, a zinc alloy plated steel sheet manufactured using the same plating bath as in Invention Example 1 was gas-wiped, and the plating adhesion amount was 70 g / m per side. ^{After adjusting to 2} , the plating layer was cooled to a point where the plating layer was completely solidified (about 300 ° C. or lower) at an average cooling rate of 12 ° C./sec using a normal cooling device.

Next, the fine structure of the zinc alloy plated steel sheet manufactured by FE-SEM (SUPRA-55VP, ZEISS) was observed, the results are shown in FIGS. 1 and 2, and the average particle size of the Zn single-phase structure was measured. The results are shown in Table 2.

Then, the (0001) priority orientation degree (f) of the Zn single-phase structure was measured based on the following relational expression 1, and the results are shown in Table 2 below.
[Relational expression 1]
f (%) = (I _basic / I _total ) × 100
(Here, I _total means a value obtained by integrating the diffraction peaks of all Zn single phases when the X-ray diffraction pattern is measured from 2θ 10 ° to 100 ° using a Cu—Kα source, and I _basic. Means the value obtained by integrating the diffraction peak of the Zn single phase with respect to the basal plane.)

Subsequently, the bending workability of the manufactured galvanized steel sheet was evaluated, and the results are shown in Table 2 below.

Corrosion resistance was evaluated by the following method.
Elapsed time until the red rust generation area becomes 5% on the surface of the plated layer after performing a corrosion acceleration test on each zinc alloy plated steel sheet with a salt spray tester (salt spray standard test based on KS-C-0223). Was measured.

The bending workability was evaluated by the following method.
After 3T bending of each galvanized steel sheet, the length of the bending top was observed by SEM, and then the area ratio of bending cracks was measured using an image analysis system (image analysis).

With reference to Table 2, it can be confirmed that in the cases of Invention Examples 1 and 2 satisfying the conditions provided by the present invention, both are excellent in bending workability.

On the other hand, Comparative Examples 1 to 5 are excellent in corrosion resistance, but since the value of f does not reach 50%, it can be confirmed that the bending workability is weak.

1A and 1B are the results of observing the fine structure of the surface portion of the present invention, in which FIG. 1A shows Invention Example 1 and FIG. 1B shows Comparative Example 5. Further, FIG. 2 shows the results of observing the fine structure of the cross-sectional portion of the present invention, in which (a) shows Invention Example 1 and (b) shows Comparative Example 5.

FIG. 3 shows the results of XRD (x-ray diffraction) analysis of Invention Example 1 of the present invention. The peaks corresponding to "○" and "●" shown in FIG. 3 correspond to the diffraction peaks of all Zn single phases, and the peaks corresponding to "○" correspond to the diffraction peaks of the Zn single phase relating to the basal plane. Equivalent to.

(Example 2)
A low-carbon cold-rolled steel sheet (that is, a base steel sheet) having a thickness of 0.8 mm, a width of 100 mm, and a length of 200 mm is provided as a test piece for plating, and then the base steel sheet is immersed in acetone and ultrasonically cleaned to clean the surface. Foreign substances such as rolling oil present in the steel sheet were removed. Then, in order to secure the mechanical properties of the steel sheet in a general hot-dip plating environment, a reducing atmosphere heat treatment is performed at 750 ° C., and then the steel sheet is immersed in a plating bath having the composition shown in Table 3 below to manufacture a zinc alloy plated steel sheet. did. Subsequently, each of the manufactured galvanized steel sheets was gas-wiped to ^{adjust the plating adhesion amount to 70 g / m 2} per side, and cooling was performed under the same conditions as in Invention Example 1 of Example 1.

Next, the phase fraction of the fine structure observed on the surface of each galvanized steel sheet was measured, the number of black spots was measured, and the results are shown in Tables 3 and 4, respectively.

After that, for the friction property test (liner friction test), a total of 20 times of friction was performed with a constant pressure applied to the surface of each galvanized steel sheet manufactured by a tool head. .. At this time, the target load was 333.3 kgf, the pressure was 3.736 MPa, the moving distance of the tool head (tool head) at the time of one friction was 200 mm, and the moving speed of the tool head (tool head) was 20 mm / s. ..

After rubbing, a peeling test was performed on each galvanized steel sheet. More specifically, a cellophane adhesive tape (Nichiban NB-1) is adhered to the bent portion of each zinc alloy plated steel plate bent by 10R, and then this is momentarily peeled off to form an optical microscope (Nichiban Co., Ltd. NB-1). The number of defects in the plating layer was measured using a magnification of 50). As a result of the measurement, when the number of defects in the plating layer is 5 / m ² or less, it is evaluated as "○", and when the number of defects in the plating layer ^{exceeds 5 / m 2} , it is evaluated as "x", and the results are evaluated in Table 4 below. Both are shown in.

After rubbing, each galvanized steel sheet was charged into a salt spray tester, and the red rust generation time was measured according to an international standard (ASTM B117-11). At this time, 5% salt water (temperature 35 ° C., pH 6.8) was used, and 2 ml / 80 cm ² salt water per hour was sprayed. When the red rust generation time was 500 hours or more, it was evaluated as "○", and when it was less than 500 hours, it was evaluated as "x", and the results are shown in Table 4 below.

With reference to Table 4, it can be confirmed that in the cases of Invention Examples A to E satisfying the conditions provided by the present invention, both the appearance of the surface and the scratch resistance are excellent.

On the other hand, in Comparative Example A, Comparative Example B, Comparative Example D, and Comparative Example E, the surface appearance was inferior because the area fraction of the Zn single-phase structure observed on the surface of the plating layer was too high, and the comparison was made. In Examples A to G, the scratch resistance was inferior because the area fractions _{of the binary eutectic structure of Zn / MgZn 2 and} the ternary eutectic structure of Zn / Al / MgZn _{2 were too low.}

Claims (16)

A zinc alloy plated steel sheet containing a base steel sheet and a zinc alloy plated layer.
The zinc alloy plating layer contains a Zn single-phase structure and a Zn—Al—Mg-based intermetallic compound as microstructures.
The Zn single-phase structure is a zinc alloy plated steel sheet having a (0001) priority orientation degree (f) represented by the following relational expression 1 of 50% or more.
[Relational expression 1]
f (%) = (I _basic / I _total ) × 100
(Here, I _total means a value obtained by integrating the diffraction peaks of all Zn single phases when the X-ray diffraction pattern is measured from 2θ 10 ° to 100 ° using a Cu—Kα source, and I _basic. Means the value obtained by integrating the diffraction peak of the Zn single phase with respect to the basal plane.) The zinc alloy-plated steel sheet according to claim 1, wherein the Zn single-phase structure has a (0001) priority orientation degree (f) represented by the relational expression 1 of 60% or more. The Zn-Al-Mg-based intermetallic compound has a Zn / MgZn ₂ binary eutectic structure, a Zn / Al binary eutectic structure, a MgZn ₂ single-phase structure, and a Zn / Al / MgZn ₂ ternary. The zinc alloy plated steel sheet according to claim 1, which is one or more selected from the group consisting of a eutectic structure. The zinc alloy-plated steel sheet according to claim 1, wherein the area fraction of the Zn single-phase structure observed on the surface of the zinc alloy-plated layer is 40% or less (excluding 0%). _{The total area fraction of the Zn / MgZn 2} binary eutectic structure and the Zn / Al / MgZn ₂ ternary eutectic structure observed on the surface of the zinc alloy plating layer is 50% or more (excluding 100%). The zinc alloy plated steel sheet according to claim 1. The zinc alloy-plated steel sheet according to claim 1, wherein the area fraction of the single-phase structure of _{MgZn 2} observed on the surface of the zinc alloy-plated layer is 10% or less (including 0%). The zinc alloy-plated steel sheet according to claim 1, wherein the average particle size of the Zn single-phase structure observed in the cross section of the zinc alloy-plated layer in the plate thickness direction is 15 μm or less (excluding 0 μm). The zinc alloy-plated steel sheet according to claim 1, wherein the zinc alloy-plated layer contains Al: 0.5 to 3%, Mg: 0.5 to 3%, the balance Zn and unavoidable impurities in% by weight. The zinc alloy-plated steel sheet according to claim 1, wherein the zinc alloy-plated layer satisfies the following relational expression 2.
[Relational expression 2]
1.0 <[Mg] / [Al] ≤ 4.0
(Here, [Mg] and [Al] mean the weight% of the corresponding element, respectively) The zinc alloy-plated steel sheet according to claim 1, wherein the number of black spots on the surface of the zinc alloy-plated steel sheet per unit area is 0.1 pieces / cm ^{2 or less.} At the stage of providing a zinc alloy plating bath containing Mg and Al,
At the stage of immersing the base steel sheet in the zinc alloy plating bath and performing plating to obtain a zinc alloy plated steel sheet,
At the stage of gas wiping the zinc alloy plated steel sheet to adjust the amount of plating adhesion,
It includes a step of injecting droplets of a phosphate aqueous solution onto a galvanized steel sheet having an adjusted amount of plating adhesion to cool the galvanized steel sheet, and then air-cooling the steel sheet.
When injecting the liquid droplet, the droplet injection start temperature was 410-420 ° C., the droplet jetting end temperature Ri 390 to 400 ° C. der,
A method for producing a galvanized steel sheet, wherein the concentration of the aqueous phosphate solution is 1 to 3% by weight. The method for manufacturing a galvanized steel sheet according to claim 11, wherein the difference between the droplet injection start temperature and the droplet injection end temperature is 15 ° C. or more when the droplets are ejected. The method for manufacturing a galvanized steel sheet according to claim 11, wherein when the droplets are ejected, the droplets are charged and injected so as to be adhered to the galvanized steel sheet by electrostatic attraction. The method for producing a galvanized steel sheet according to claim 11, wherein the droplet injection amount is 50 to 100 g / m ^{2 when the droplets are ejected.} The aqueous phosphate solution includes an aqueous solution of ammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ), an aqueous solution of sodium ammonium hydrogen phosphate (NaNH ₄ HPO ₄ ), and a first zinc phosphate (Zn (H ₂ PO ₄ ) ₂ ). The method for producing a zinc alloy plated steel sheet according to claim 11 , which is one or more selected from the group consisting of an aqueous solution and a calcium phosphate (Ca ₃ (PO ₄ ) _{2) aqueous solution.} The method for producing a zinc alloy-plated steel sheet according to claim 11, wherein the zinc alloy-plated bath contains Al: 0.5 to 3%, Mg: 0.5 to 3%, the balance Zn and unavoidable impurities in% by weight. ..

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