JP7502607B2 - Plated Steel Sheet - Google Patents

Description

This disclosure relates to plated steel sheets, and more specifically to plated steel sheets having a textured surface.

Electrical equipment and building materials are often required to have attractive exterior designs. As a means of enhancing the aesthetic appeal of such products, a technology has been proposed for forming a texture on the surface of a plated steel sheet.

For example, in JP 2010-509495 A (Patent Document 1) and JP 2006-124824 A (Patent Document 2), a plated steel sheet having a single layer of hot-dip galvanized coating is provided with a hairline, which is a type of texture, formed on the surface of the hot-dip galvanized layer to enhance the design of the plated steel sheet.

In addition, in JP 2017-136645 A (Patent Document 3) and JP 2013-536901 A (Patent Document 4), a hairline is formed on the surface of an electrolytic zinc-plated layer of a plated steel sheet on which a single layer of electrolytic zinc-plated coating has been formed, thereby improving the design of the plated steel sheet.

JP 2010-509495 A JP 2006-124824 A JP 2017-136645 A JP 2013-536901 A

Incidentally, among steel sheets that require design, not only design but also corrosion resistance is required, particularly for steel sheets used as building materials. Therefore, plated steel sheets are required to have not only design but also excellent corrosion resistance. In particular, for steel sheets used as building materials, it is preferable that the design does not deteriorate over time. Therefore, plated steel sheets that maintain excellent design over time while also having excellent corrosion resistance are required.

Patent Documents 1 to 4 disclose plated steel sheets with excellent design and corrosion resistance. However, these documents do not fully consider the maintenance of design over time.

The objective of this disclosure is to provide a plated steel sheet that maintains excellent design over time and has excellent corrosion resistance.

The plated steel sheet according to the present disclosure has:
A base steel plate;
A hot-dip galvanized layer formed on a surface of the base steel sheet and containing 0.1% or more of Al by mass%,
and an electrolytic galvanized layer formed on the hot-dip galvanized layer,
When viewed from above the electrolytic zinc plating layer, a texture is formed on the surface of the plated steel sheet.

The plated steel sheet of the present invention maintains excellent design even over time and has excellent corrosion resistance.

FIG. 1 is a cross-sectional view of a plated steel sheet according to the present embodiment. FIG. 2 is a plan view of the plated steel sheet shown in FIG. 1, viewed from above the electrolytic zinc plating layer. FIG. 3 is a diagram showing an example of a cross section perpendicular to the rolling direction of the plated steel sheet shown in FIGS. 1 and 2. As shown in FIG. FIG. 4 is a diagram showing an example of a cross section perpendicular to the rolling direction of the plated steel sheet shown in FIGS. 1 and 2, which is different from FIG. 3. FIG. 5 is a cross-sectional view showing another configuration of the plated steel sheet of the present embodiment, which is different from that of FIG. FIG. 6 is a diagram showing an example of a cross section perpendicular to the rolling direction of a plated steel sheet, which is different from FIGS. 3 and 4 . FIG. 7 is a flow diagram showing an example of a manufacturing process of the plated steel sheet of this embodiment.

The inventors have investigated a plated steel sheet that can maintain excellent design even over time and has excellent corrosion resistance.

As described above, in general, in order to achieve both design and corrosion resistance, hot-dip galvanized single-layer plated steel sheets or electroplated single-layer plated steel sheets have been proposed. Therefore, the present inventors first re-examined hot-dip galvanized layers and electroplated galvanized layers from the two standpoints of design over time and corrosion resistance. As a result, the present inventors have come to the following findings regarding hot-dip galvanized layers and electroplated galvanized layers.

The hot-dip galvanized layer formed on the hot-dip galvanized steel sheet as typified by Patent Documents 1 and 2 contains Al and Zn, and further contains Mg as necessary. The manufacturing method of hot-dip galvanization makes it easy to increase the thickness of the plating layer and improve corrosion resistance. Furthermore, by containing Al and Mg, a dense Zn protective film is formed on the surface of the hot-dip galvanized layer. This improves the corrosion resistance of the hot-dip galvanized steel sheet. However, the hot-dip galvanized layer suffers from a blackening phenomenon in which the surface turns black over time due to the Al contained in the layer. Even if the blackening phenomenon occurs, the corrosion resistance does not decrease. However, the blackening phenomenon that occurs over time reduces the design of the hot-dip galvanized steel sheet. Therefore, the blackening phenomenon is a factor that reduces the design over time.

In addition, spangles and primary Al phases are prone to form in hot-dip galvanized layers. Spangles and primary Al phases impair the texture pattern. In other words, spangles and primary Al phases are factors that reduce the design quality of plated steel sheets.

Furthermore, the hot-dip galvanized layer may contain dross. Dross is an intermetallic compound that is generated in the hot-dip galvanized bath when hot-dip galvanizing is performed. Specifically, in the hot-dip galvanizing process, Fe is dissolved into the hot-dip galvanized bath from the steel sheet immersed in the hot-dip galvanized bath. When the Fe dissolved from the steel sheet into the hot-dip galvanized bath reacts with Al and Zn present in the hot-dip galvanized bath, an intermetallic compound called dross is generated. In the hot-dip galvanizing process, dross may be caught in the hot-dip galvanized layer. Dross is harder than the hot-dip galvanized layer. Therefore, the part of the hot-dip galvanized layer where dross exists is prone to defects. In the following explanation, defects caused by dross are also called "dross defects". Even when a texture is formed on the plated steel sheet, dross defects are visible. Therefore, dross defects are also a factor that reduces the design of the plated steel sheet.

On the other hand, the electrogalvanized layer formed on the electrogalvanized steel sheet as typified by Patent Documents 3 and 4 does not substantially contain Al. Therefore, the blackening phenomenon does not occur. The electrogalvanized layer is further composed of fine crystal grains and is less likely to generate spangles. Furthermore, since it does not substantially contain Al, primary Al phase is not generated. In other words, the electrogalvanized layer does not suffer from a decrease in design due to spangles or primary Al phase. Furthermore, the electrogalvanized process does not produce dross. Therefore, the electrogalvanized layer does not suffer from a decrease in design due to dross defects.

However, compared to a hot-dip galvanized layer, it is difficult to form an electrolytic galvanized layer thick. Specifically, when forming a thick electrolytic galvanized layer, the electrolytic galvanizing process time becomes very long, and the manufacturing costs become high. Therefore, when considering normal industrial production, it is difficult to form an electrolytic galvanized layer with a thickness similar to that of a hot-dip galvanized layer.

As a result of the above studies, in order to achieve both excellent design over time and excellent corrosion resistance, the inventors have come up with the idea of utilizing a hot-dip galvanized layer as a corrosion resistance function and an electrogalvanized layer as a design over time maintenance function in a textured plated steel sheet. Specifically, the inventors have come up with the idea of forming a hot-dip galvanized layer on the surface of a base steel sheet, forming an electrogalvanized layer on the hot-dip galvanized layer, and forming a texture on the surface of the plated steel sheet when viewed from above the electrogalvanized layer. In the case of a plated steel sheet having this configuration, the electrogalvanized layer is formed on the hot-dip galvanized layer. Therefore, the blackening phenomenon, spangles, primary crystal Al phase, and dross defects that cause a decrease in design in the hot-dip galvanized layer are covered by the electrogalvanized layer. Therefore, it is possible to realize excellent design, and it is possible to suppress the deterioration of design over time due to the blackening phenomenon. Furthermore, it is possible to maintain excellent corrosion resistance by the hot-dip galvanized layer formed as a lower layer of the electrogalvanized layer on which the texture is formed.

As typified by Patent Documents 1 to 4, conventional textured plated steel sheets have been constructed with a single layer of hot-dip galvanized or electrolytic galvanized. However, when considering both further improvements in design, including maintaining the design over time, and corrosion resistance, the inventors have discovered that by using the unconventional idea of combining two types of plating layers, that is, a two-layer plating layer with a hot-dip galvanized layer as the lower layer and an electrolytic galvanized layer as the upper layer, it is possible to maintain both excellent design and corrosion resistance over time in textured plated steel sheets.

As described above, the plated steel sheet of the present embodiment, which has been completed based on a technical concept completely different from that of the prior art, has the following configuration.
[1]
A plated steel sheet,
A base steel plate;
A hot-dip galvanized layer formed on a surface of the base steel sheet and containing 0.1% or more of Al by mass%,
and an electrolytic galvanized layer formed on the hot-dip galvanized layer,
When viewed from above the electrogalvanized layer, a texture is formed on the surface of the plated steel sheet.
Galvanized steel sheet.

[2]
The plated steel sheet according to [1],
The texture is a hairline.
Plated Steel Sheet

[3]
The plated steel sheet according to [1] or [2], further comprising:
A coating film is provided on the electrogalvanized layer.
Galvanized steel sheet.

Here, the coating film may be an inorganic coating film or an organic coating film. The coating film may further be a multi-layered film in which an inorganic coating film and an organic coating film are laminated, or may be an organic-inorganic composite film in which organic and inorganic are mixed. Examples of inorganic coating films include chromate films, zirconium oxide chemical conversion films, silicate films, and silane coupling agent films. Examples of organic coating films include films made of organic resins. Both inorganic coating films and organic coating films have translucency. Here, translucency in this specification means that the texture of the plated steel sheet can be visually recognized when the plated steel sheet having the coating film is placed in an environment equivalent to sunlight on a clear morning (illuminance of about 65,000 lux).

If the product has a coating film, it is possible to further suppress the occurrence of white rust, which may occur due to Zn in the electrolytic zinc plating layer. As a result, the design can be further improved.

[4]
The plated steel sheet according to any one of [1] to [3],
The texture is
A plurality of recesses whose bottoms reach the hot-dip galvanized layer are included.
Galvanized steel sheet.

In this case, the bottoms of the multiple recesses that make up the texture reach the hot-dip galvanized layer, so over time the bottoms of the recesses turn black. The rest of the surface of the plated steel sheet, other than the bottoms of the recesses, remains metallic in color and does not change color. This increases the contrast between the bottoms of the recesses and the rest of the surface of the plated steel sheet, further emphasizing the texture in the appearance of the steel sheet. As a result, the design is further improved.

[5]
The plated steel sheet according to [4],
When viewed from above the electrolytic galvanized layer, the exposure rate of the hot-dip galvanized layer is 5.0% to 30.0%.
Galvanized steel sheet.

In this case, an appropriate contrast is obtained between the bottom parts of the recesses and the other parts of the surface of the plated steel sheet, and the texture is beautifully emphasized in the appearance of the steel sheet. As a result, the design is further improved.

The plated steel sheet of this embodiment is described in detail below.

[Regarding plated steel sheet 1]
Fig. 1 is a cross-sectional view of a plated steel sheet 1 according to the present embodiment. In Fig. 1, a direction perpendicular to the paper surface is defined as a rolling direction RD of the plated steel sheet 1. A thickness direction of the plated steel sheet 1 is defined as a sheet thickness direction TD. A direction perpendicular to the rolling direction RD and the sheet thickness direction TD of the plated steel sheet 1 is defined as a width direction WD.

Referring to FIG. 1, the plated steel sheet 1 of this embodiment includes a base steel sheet 100, a hot-dip galvanized layer 10, and an electrogalvanized layer 11. The hot-dip galvanized layer 10 is formed on the surface of the base steel sheet 100. The electrogalvanized layer 11 is formed on the surface 10S of the hot-dip galvanized layer 10. In other words, the hot-dip galvanized layer 10 is disposed between the base steel sheet 100 and the electrogalvanized layer 11.

Figure 2 is a plan view of the plated steel sheet 1 shown in Figure 1, viewed from above the electrolytic zinc plating layer 11. Referring to Figure 2, a texture T1 is formed on the surface of the plated steel sheet 1. In Figure 2, the texture T1 is a hairline. Here, the hairline is a linear uneven pattern formed by a plurality of grooves T11 (see Figure 3) extending in one direction (the rolling direction RD in Figure 2). The hairline is a well-known texture, and is formed by polishing the surface in one direction with an abrasive belt or the like.

The base steel sheet 100, the hot-dip galvanized layer 10, the electrogalvanized layer 11, and the texture T1 are described below.

[Regarding base steel sheet 100]
As the base steel sheet 100, a known steel sheet applied to plated steel sheets (electrogalvanized steel sheet, electrogalvanized zinc alloy plated steel sheet, hot-dip galvanized steel sheet, alloyed hot-dip galvanized steel sheet, etc.) may be used depending on the mechanical properties (e.g., tensile strength, workability, etc.) required for the plated steel sheet to be manufactured. For example, as the base steel sheet 100, a steel sheet for electrical equipment use may be used, or a steel sheet for building material use may be used. The base steel sheet 100 may be a hot-rolled steel sheet or a cold-rolled steel sheet.

[Regarding hot-dip galvanized layer 10]
The hot-dip galvanized layer 10 is formed on the surface of the base steel sheet 100. More specifically, the hot-dip galvanized layer 10 is disposed between the base steel sheet 100 and an electrogalvanized layer 11. Here, in this specification, the hot-dip galvanized layer 10 means a plated layer produced by a process including a hot-dip galvanizing treatment process. Specifically, the hot-dip galvanized layer 10 in this specification includes a hot-dip galvanized layer and an alloyed hot-dip galvanized layer (so-called alloyed hot-dip galvanized layer).

The hot-dip galvanized layer 10 has a known chemical composition. Specifically, the chemical composition of the hot-dip galvanized layer 10 contains, by mass%, 0.1% or more of Al, with the remainder consisting of Zn and impurities. The chemical composition of the hot-dip galvanized layer 10 may contain Mg as an optional element.

The chemical composition of the hot-dip galvanized layer 10 preferably contains the following elements. Hereinafter, the percentages for the elements refer to mass percentages.

Al: 0.1 to 60.0%
Aluminum (Al) is an easily oxidizable element, and forms an oxide film with excellent corrosion resistance on the plating surface, thereby enhancing the corrosion resistance of the hot-dip galvanized layer. This effect can be sufficiently obtained if the Al content is 0.1% or more. There is no particular upper limit to the Al content. The upper limit of the Al content is, for example, 60.0%. Therefore, the preferred Al content is 0.1 to 60.0%.

Mg: 0 to 12.5%
Magnesium (Mg) is an optional element and may not be contained. In other words, the Mg content may be 0%. When contained, that is, when the Mg content is more than 0%, Mg improves the stability of the oxide film and enhances the corrosion resistance of the hot-dip galvanized layer. Even if even a small amount of Mg is contained, the above effect can be obtained to some extent. There is no particular upper limit to the Mg content. The upper limit of the Mg content is, for example, 12.5%. Therefore, the Mg content is 0 to 12.5%. The preferable lower limit of the Mg content is 0.1%, and more preferably 0.5%.

As described above, the remainder of the chemical composition of the hot-dip galvanized layer 10 according to this embodiment is composed of Zn and impurities. Here, impurities refer to substances that are mixed in from the raw materials when the hot-dip galvanizing process is carried out, and are not intentionally included, but are permissible within a range that does not adversely affect the hot-dip galvanized steel sheet according to this embodiment.

[Regarding other optional elements in the chemical composition of the hot-dip galvanized layer 10]
The chemical composition of the hot-dip galvanized layer according to the present embodiment may further contain, in place of a portion of Zn, one or more elements selected from the following element group:
First group: one or more elements selected from the group consisting of Si: 0-2.5%, Ca: 0-3.0%, Y: 0-3.0%, La: 0-3.0%, Ce: 0-3.0%, Sn: 0-2.0%, Bi: 0-2.0%, and In: 0-2.0%. Second group: one or more elements selected from the group consisting of Cr: 0-0.5%, Ti: 0-0.5%, Ni: 0-0.5%, Co: 0-0.5%, V: 0-0.5%, Nb: 0-0.5%, Cu: 0-0.5%, Mn: 0-0.5%, Sr: 0-0.5%, Sb: 0-0.5%, and Pb: 0-0.5%. Third group: B: 0-0.50%
Fourth group: Fe: 0 to 12.0%

When each element in the first group is contained, it further improves the corrosion resistance of the hot-dip galvanized layer 10. When each element in the second group is contained, it improves the design of the hot-dip galvanized layer 10. When B in the third group is contained, it suppresses melting cracks. When Fe is contained, it increases the hardness of the hot-dip galvanized layer 10 and improves the workability of the plated steel sheet.

As described above, the chemical composition of the hot-dip galvanized layer 10 contains Al as an essential element, Mg as an optional element, and one or more of the elements of groups 1 to 4 as an optional element, with the balance being Zn and impurities. If the Zn content is too low, the mechanical properties required for a hot-dip galvanized steel sheet may not be obtained. Therefore, the Zn content is 35.0% or more. The preferred lower limit of the Zn content is 37.0%, and more preferably 39.0%. The upper limit of the Zn content is not particularly limited, but is substantially 99.9%. The above-mentioned chemical composition of the hot-dip galvanized layer 10 is well known.

[Regarding electrolytic zinc plating layer 11]
The electrogalvanized layer 11 is formed on the surface 10S of the hot-dip galvanized layer 10. It is sufficient that the electrogalvanized layer 11 has a known chemical composition. Specifically, the electrogalvanized layer 11 is mainly composed of Zn, and the Al content is less than 0.1% by mass. Here, "mainly composed of Zn" means that the Zn content in the electrogalvanized layer 11 is at least 64.9% or more. For example, the chemical composition of the electrogalvanized layer 11 contains 64.9% or more Zn by mass, and the Al content as an impurity is less than 0.1%.

An example of the chemical composition of the electrogalvanized layer 11 is, for example, 64.9% or more Zn by mass%, 0 to 30.0% in total of one or more selected from the group consisting of Ni, Fe, Co, and Cr as optional elements, and 0 to 5.0% C as optional elements. Ni, Fe, Co, Cr, and C may not be contained. The preferred lower limit of the Zn content is 80.0%, more preferably 90.0%, more preferably 95.0%, more preferably 99.5%, and even more preferably 99.9%. The Zn content may be 100%. The electrogalvanized layer 11 is a concept that includes an electrogalvanized layer and an electrogalvanized zinc alloy layer. As described above, the chemical composition of the electrogalvanized layer 11 is well known, and is mainly composed of Zn, with an Al content of less than 0.1%.

[Method of measuring chemical composition of hot-dip galvanized layer 10 and electrogalvanized layer 11]
The chemical compositions of the hot-dip galvanized layer 10 and the electrogalvanized layer 11 can be measured by the following method. A sample including a cross section (hereinafter referred to as the observation surface) perpendicular to the rolling direction RD of the plated steel sheet 1 and including the hot-dip galvanized layer 10 and the electrogalvanized layer 11 is taken. On the observation surface of the sample, a line analysis based on the EPMA (Electron Probe Micro Analyzer) analysis method is performed from the surface 11S of the electrogalvanized layer 11 in the sheet thickness direction TD to obtain the content (mass%) of each element on the line to be measured. The line analysis is performed at any 10 points. A continuous region from the surface 11S of the electrogalvanized layer 11 in which the Al content in the line analysis is less than 0.1% is identified as the region of the electrogalvanized layer 11. In addition, a continuous region in which the Al content in the line analysis is 0.1% or more is identified as the region of the hot-dip galvanized layer 10. In the measurements at 10 locations, the arithmetic mean value (mass %) of the Zn content and the arithmetic mean value (mass %) of the Al content are determined in the region identified as the electrogalvanized layer 11. The chemical composition of the electrogalvanized layer 11 is identified based on the determined arithmetic mean values of the contents of each element. Similarly, the arithmetic mean values of the contents of each element, such as the arithmetic mean value (mass %) of the Zn content and the arithmetic mean value (mass %) of the Al content, are determined in the region identified as the hot-dip galvanized layer 10. The chemical composition of the hot-dip galvanized layer 10 is identified based on the determined arithmetic mean values of the contents of each element.

[Thickness of hot-dip galvanized layer 10 and thickness of electrolytic galvanized layer 11]
The thickness of the hot-dip galvanized layer 10 is not particularly limited, and any known thickness will suffice. The thickness of the hot-dip galvanized layer 10 is, for example, 5.0 to 80.0 μm. A preferred lower limit of the thickness of the hot-dip galvanized layer 10 is 25.0 μm. By carrying out a known hot-dip galvanizing process, it is possible to adjust the thickness of the hot-dip galvanized layer 10 to the above range.

The thickness of the electrogalvanized layer 11 is not particularly limited, and any well-known thickness will suffice. As described above, the electrogalvanized layer 11 is typically thinner than the hot-dip galvanized layer 10. The thickness of the electrogalvanized layer 11 is, for example, 0.5 to 5.0 μm. By carrying out a well-known electrogalvanized process, it is possible to adjust the thickness of the electrogalvanized layer 11 to be within the above range.

[Method for measuring thickness of hot-dip galvanized layer 10 and electrogalvanized layer 11]
The thickness of the hot-dip galvanized layer 10 and the thickness of the electrolytic galvanized layer 11 can be determined by EPMA analysis.

Specifically, the measurement is performed in the following manner. A sample is taken that includes a cross section (hereinafter referred to as the observation surface) perpendicular to the rolling direction RD of the plated steel sheet 1 and that includes the hot-dip galvanized layer 10 and the electrogalvanized layer 11. On the observation surface of the sample, a line analysis based on the EPMA analysis method is performed from the surface 11S of the electrogalvanized layer 11 in the sheet thickness direction TD to determine the content (mass%) of each element on the line to be measured. The line analysis is performed at any 20 locations.

At each measurement point, a continuous region from the surface 11S of the electrogalvanized layer 11 where the Al content in line analysis is less than 0.1% is identified as the region of the electrogalvanized layer 11 (region L11 in FIG. 3). A continuous region where the Al content in line analysis is 0.1% or more (region L10 in FIG. 3) is identified as the region of the hot-dip galvanized layer 10. The lengths of the identified regions L11 and L10 are measured. Of the region L11 measured at 20 points, the thicknesses of 10 points are selected in order from the thickest value. The arithmetic mean value (μm) of the thicknesses of the 10 points is defined as the thickness (μm) of the electrogalvanized layer 11. Similarly, of the region L10 measured at 20 points, the thicknesses of 10 points are selected in order from the thickest value. The arithmetic mean value (μm) of the thicknesses of the 10 points is defined as the thickness (μm) of the hot-dip galvanized layer 10.

[Regarding Texture T1]
With reference to FIG. 2, the surface of the plated steel sheet 1 has a texture T1 when viewed from above the electrogalvanized layer 11. In this specification, the term "texture" refers to an uneven pattern formed on the surface of the plated steel sheet 1 by a physical or chemical method. In FIG. 2, the texture T1 is a hairline. FIG. 3 is a diagram showing an example of a cross section perpendicular to the rolling direction RD of the plated steel sheet 1 shown in FIG. 1 and FIG. 2. With reference to FIG. 2 and FIG. 3, a hairline (hereinafter also referred to as a hairline T1), which is an example of the texture T1, includes a plurality of grooves T11 corresponding to a plurality of recesses T11. The extension directions of the plurality of grooves T11 are the same direction. The term "same direction" as used here means that, when the plated steel sheet 1 is viewed from above the electrogalvanized layer 11 (i.e., in a plan view as in FIG. 2), 90% or more of the angles formed between adjacent grooves T11 arranged in the width direction WD are less than ±5°.

In Figures 1 and 2, a hairline is shown as texture T1. However, texture T1 is not limited to a hairline. In addition to a hairline, texture T1 may be, for example, an embossed pattern, a vibration finish, a matte (blast) finish, a hammered pattern finish, a cloth grain (satin) finish, etc. Preferably, texture T1 is a hairline.

Figure 4 is a diagram showing an example of a cross section perpendicular to the rolling direction RD of the plated steel sheet 1 shown in Figures 1 and 2, which is different from Figure 3. Referring to Figure 4, a recess T10 is formed below the recess T11. The recess T10 is formed on the surface 10S of the hot-dip galvanized layer 10. That is, in Figure 4, texture processing is performed on the surface 10S of the hot-dip galvanized layer 10, and multiple recesses T10 are formed on the surface 10S of the hot-dip galvanized layer 10. Then, an electrogalvanized layer 11 is formed by electrogalvanizing on the surface 10S of the hot-dip galvanized layer 10 having multiple recesses T10. In this case, the electrogalvanized layer 11 is formed along the shape of the recesses T10. As a result, multiple recesses T11 are formed on the surface 11S of the electrogalvanized layer 11, and a texture T1 is formed on the surface 11S of the electrogalvanized layer 11.

[Function of Plated Steel Sheet 1]
As described above, the plated steel sheet 1 has a hot-dip galvanized layer 10 formed on the surface of the base steel sheet 100, and an electrogalvanized layer 11 formed on the surface 10S of the hot-dip galvanized layer 10. When viewed from above the electrogalvanized layer 11, a texture T1 (hairline in Figs. 1 to 4) is formed on the surface of the plated steel sheet 1. As described above, the hot-dip galvanized layer 10 exhibits excellent corrosion resistance by containing not only Zn but also Al. However, since the hot-dip galvanized layer 10 contains Al, a blackening phenomenon occurs over time. Furthermore, since the hot-dip galvanized layer 10 contains Al, spangles and primary Al phases are generated on the surface 10S. Furthermore, the hot-dip galvanized layer 10 contains dross defects. The blackening phenomenon, spangles, primary Al phase, and dross defects all reduce the designability of the plated steel sheet 1.

On the other hand, the electrogalvanized layer 11 does not substantially contain Al. The electrogalvanized layer 11 is also difficult to make as thick as the hot-dip galvanized layer 10, and is thinner than the hot-dip galvanized layer 10. Therefore, the corrosion resistance of the electrogalvanized layer 11 is lower than that of the hot-dip galvanized layer 10. However, since the electrogalvanized layer 11 does not substantially contain Al, the blackening phenomenon does not occur. The electrogalvanized layer 11 is further composed of fine crystal grains, and spangles do not occur. Furthermore, since it does not substantially contain Al, the primary Al phase is not generated in the electrogalvanized layer 11. Furthermore, dross is not generated in the electrogalvanized process. Therefore, the electrogalvanized layer 11 does not cause blackening, spangles, primary Al phase, and dross defects compared to the hot-dip galvanized layer 10. Therefore, the electrogalvanized layer 11 is extremely beautiful and has excellent design compared to the hot-dip galvanized layer 10.

Therefore, in this embodiment, the plating layer formed on the base steel sheet 100 has a two-layer structure. Specifically, a hot-dip galvanized layer 10 is formed on the surface of the base steel sheet 100. The hot-dip galvanized layer 10 mainly serves to enhance the corrosion resistance of the plated steel sheet 1. Then, an electrogalvanized layer 11 is formed on the surface 10S of the hot-dip galvanized layer 10, and a texture T1 is formed on the surface 11S of the electrogalvanized layer 11. The electrogalvanized layer 11 mainly serves to enhance the design. As described above, the plated steel sheet 1 ensures the beauty (design) of the surface including the texture T1 by the upper layer, the electrogalvanized layer 11, and further ensures the corrosion resistance by the lower layer, the hot-dip galvanized layer 10. Therefore, the plated steel sheet 1 of this embodiment has excellent design. And since the blackening phenomenon does not occur in the electrogalvanized layer 11, it is possible to maintain excellent design even over time. Furthermore, it also has excellent corrosion resistance. In other words, plated steel sheet 1 can achieve both excellent design and excellent corrosion resistance.

[Other configuration 1: Coating film 12]
Fig. 5 is a cross-sectional view showing another configuration of the plated steel sheet of the present embodiment, which is different from that of Fig. 1. Referring to Fig. 5, the plated steel sheet 1 is newly provided with a coating film 12, as compared with Fig. 1. The coating film 12 is formed on a surface 11S of an electrogalvanized layer 11.

The coating film 12 is a light-transmitting film. In this specification, light-transmitting means that the texture of the plated steel sheet can be seen when the plated steel sheet is placed in an environment equivalent to sunlight on a clear morning (illuminance of approximately 65,000 lux).

The coating film may be an inorganic coating film or an organic coating film. The coating film may further be a multi-layer film in which an inorganic coating film and an organic coating film are laminated, or may be an organic-inorganic composite film in which organic and inorganic are mixed.

The inorganic coating film is, for example, a chromate film, a zirconium oxide chemical conversion film, a silicate film, a silane coupling agent film, etc. The organic coating film is, for example, an organic resin. The resin is not particularly limited as long as it has the translucency defined above, and well-known natural resins or well-known synthetic resins can be used. The resin is, for example, one or more types selected from the group consisting of epoxy resins, urethane resins, polyester resins, phenol resins, polyethersulfone resins, melamine alkyd resins, acrylic resins, polyamide resins, polyimide resins, silicone resins, polyvinyl acetate resins, polyolefin resins, polystyrene resins, vinyl chloride resins, and vinyl acetate resins.

When the plated steel sheet 1 is provided with the coating film 12, it can provide functions such as fingerprint resistance, workability, and white rust resistance that cannot be provided by the plating layer alone. To further enhance the above-mentioned functions, the coating film may contain additives. Examples of additives include extender pigments (calcium carbonate, talc, etc.), coloring pigments (carbon black, titanium white, etc.), waxes (polyethylene, etc.), and rust inhibitors (phosphate, vanadium, silica, etc.). In order to improve the paint properties, the coating film may further contain thickeners, leveling agents, defoamers, etc., to the extent that they do not inhibit the desired coating functions.

The thickness of the coating film 12 is not particularly limited. The thickness of the coating film 12 is, for example, 0.1 to 30.0 μm. By carrying out a known coating film formation process, it is possible to adjust the thickness of the coating film 12 to the above range. The thickness of the coating film can be determined by the following method. A sample including a cross section (hereinafter referred to as the observation surface) perpendicular to the rolling direction RD of the plated steel sheet 1 and including the coating film 12 is taken. A heavy element such as Au is vapor-deposited on the surface of the coating film 12 to form a vapor-deposition layer on the coating film 12. The sample on which the vapor-deposition layer is formed is embedded in resin and polished to prepare a cross-sectional sample. A reflected electron image is observed with a scanning electron microscope (SEM) using the prepared cross-sectional sample. In the reflected electron image, the upper end of the electrogalvanized layer 11 and the vapor-deposition layer are included, and the field of view that is the largest is observed. The contrast makes it easy to distinguish the coating film 12, the plating layer (electrogalvanized layer 11 and hot-dip galvanized layer 10), and the vapor-deposition layer. The thickness (μm) is measured at 10 random locations on the coating film 12. The arithmetic mean value of the 10 thicknesses obtained is defined as the thickness (μm) of the coating film 12.

[Other configuration 2: bottom TB11 of texture T1 reaches hot-dip galvanized layer 10]
The cross section perpendicular to the rolling direction RD of the plated steel sheet 1 of the present embodiment is not limited to Fig. 3 and Fig. 4. Fig. 6 is a diagram showing an example of a cross section perpendicular to the rolling direction RD of the plated steel sheet 1, which is different from Fig. 3 and Fig. 4. The enlarged cross-sectional view of the plated steel sheet 1 shown in Fig. 6 corresponds to Fig. 1 or Fig. 5, and the plan view corresponds to Fig. 2.

In the plated steel sheet 1 shown in Figures 3 and 4, the bottoms of the multiple recesses T11 of the texture T1 do not reach the hot-dip galvanized layer 10, but are located within the electrogalvanized layer 11. On the other hand, in the plated steel sheet 1 shown in Figure 6, the recesses T11 penetrate the electrogalvanized layer 11, and the bottoms TB11 of the recesses T11 reach the hot-dip galvanized layer 10. Preferably, the bottoms TB11 of the recesses T11 reach within the hot-dip galvanized layer 10.

In the case of the plated steel sheet 1 having the configuration shown in FIG. 6, the bottoms TB11 of the multiple recesses T11 reach the hot-dip galvanized layer 10. In other words, the hot-dip galvanized layer 10 is exposed at the bottoms TB11. In this case, over time, a blackening phenomenon occurs at the bottoms TB11 of the texture T1 (the bottoms TB11 of the grooves T11 when the texture T1 is a hairline), and the bottoms TB11 turn black. As a result, the contrast between the bottoms TB11 and other parts becomes stronger, and the texture T1 is more emphasized in the appearance of the plated steel sheet 1. On the other hand, since the parts other than the bottoms TB11 are covered with the electrogalvanized layer 11, factors that reduce the design, such as spangles, primary crystal Al phases, and dross defects, are not exposed on the surface of the plated steel sheet 1. As a result, the texture T1 can be more emphasized by the blackening of the bottoms TB11, and the design can be further improved. In addition, even if the blackening phenomenon occurs, the corrosion resistance is not affected in any way, so the plated steel sheet 1 also has excellent corrosion resistance.

In the above description, a hairline is used as an example of texture T1. However, as described above, texture T1 is not limited to a hairline. For example, when texture T1 is an embossed pattern, texture T1 includes multiple recesses T11. The bottoms TB11 of the multiple recesses T11 may reach the hot-dip galvanized layer 10. In this case, as described above, the bottoms TB11 turn black over time. This further accentuates the embossed pattern, further enhancing the design of the plated steel sheet 1. In short, the above effect can be obtained as long as the bottoms TB11 of the multiple recesses T11 reach the hot-dip galvanized layer 10 in texture T1.

[Preferable Exposure Rate of Hot-Dip Galvanized Layer 10 When Viewed in Plane of Galvanized Steel Sheet 1]
In the case of the plated steel sheet 1 having the configuration shown in Fig. 6, when the plated steel sheet 1 is viewed from above the electrogalvanized layer 11 (i.e., when the plated steel sheet 1 is viewed in plan), the hot-dip galvanized layer 10 is exposed at bottoms TB11 of the multiple recesses T11 of the texture T1. The exposure rate is not particularly limited. Preferably, when the plated steel sheet 1 is viewed from above the electrogalvanized layer 11, the exposure rate of the hot-dip galvanized layer 10 is 3.5% to 30.0%.

If the exposure rate of the hot-dip galvanized layer 10 is 3.5% or more, the texture T1 is significantly emphasized by the blackening of the bottom TB11, and the design is significantly improved. The preferred lower limit of the exposure rate of the hot-dip galvanized layer 10 is 4.0%, and more preferably 6.0%. The upper limit of the exposure rate of the hot-dip galvanized layer 10 is not particularly limited. However, if the exposure rate of the hot-dip galvanized layer 10 is too high, the blackened area increases, and the design is actually reduced. Therefore, the upper limit of the exposure rate of the hot-dip galvanized layer 10 is, for example, 30.0%. The upper limit of the exposure rate of the hot-dip galvanized layer 10 may be 25.0%, 20.0%, or 15.0%.

The exposure rate of the hot-dip galvanized layer 10 when the plated steel sheet 1 is viewed from above the electrogalvanized layer 11 is measured by the following method. A plated steel sheet 1 is prepared. When the plated steel sheet 1 has a coating film 12, the coating film 12 is removed with a stripping agent such as a solvent or remover (for example, Neo River S-701, product name, manufactured by Sansai Kako Co., Ltd.) that does not attack the zinc plating layer (electrogalvanized layer 11 and hot-dip galvanized layer 10) to prepare a plated steel sheet 1. When the plated steel sheet 1 is viewed from above the electrogalvanized layer 11 (when the plated steel sheet 1 is viewed in plan), five arbitrary rectangular areas of 1 mm x 1 mm are selected. An EPMA analysis (surface analysis) is performed on the selected rectangular areas. By image analysis, areas that contain Zn and 0.1% or more of Al are identified in each rectangular area. The identified areas are judged to be areas where the hot-dip galvanized layer 10 is exposed. The total area of the hot-dip galvanized layer 10 is calculated for the five rectangular areas. The exposure rate (area %) of the hot-dip galvanized layer 10 is calculated based on the total area of the five rectangular regions and the total area of the hot-dip galvanized layer 10 region.

As described above, in the plated steel sheet 1 of this embodiment, the hot-dip galvanized layer 10 is formed on the surface of the base steel sheet 100, the electrogalvanized layer 11 is formed on the surface of the hot-dip galvanized layer 10, and the electrogalvanized layer 11 is formed on the surface of the plated steel sheet 1 when viewed from above. In this case, the electrogalvanized layer 11 plays a role in enhancing the design of the plated steel sheet 1 having the texture T1, and the hot-dip galvanized layer 10 plays a role in enhancing the corrosion resistance of the plated steel sheet 1. Therefore, the plated steel sheet 1 can achieve both excellent design and excellent corrosion resistance. When the plated steel sheet 1 has a coating film 12, the design is further improved. In addition, when the bottom TB11 of the recess T11 of the texture T1 reaches the hot-dip galvanized layer 10, the contrast of the texture T1 can be strengthened by deliberately utilizing the blackening phenomenon, and the design can be further improved.

[Production method]
An example of a method for manufacturing the plated steel sheet 1 of the present embodiment will be described below. The manufacturing method described below is one example for manufacturing the plated steel sheet 1 of the present embodiment. Therefore, the plated steel sheet 1 having the above-mentioned configuration may be manufactured by a manufacturing method other than the manufacturing method described below. However, the manufacturing method described below is a preferred example of a method for manufacturing the plated steel sheet 1 of the present embodiment.

7 is a flow diagram showing an example of a manufacturing process for the plated steel sheet 1 of the present embodiment. The manufacturing method is classified into the following two cases.
Case 1: When the plated steel sheet 1 has a cross section shown in FIG. 3 or FIG. 6. Case 2: When the plated steel sheet 1 has a cross section shown in FIG. 4. Each case will be described below.

[Manufacturing process of plated steel sheet 1 of case 1]
In the case of Case 1, the manufacturing method of the plated steel sheet 1 includes a step of preparing a base steel sheet 100 (base steel sheet preparation step: S11), a step of performing a hot-dip galvanizing process on the prepared base steel sheet 100 to form a hot-dip galvanized layer 10 on the surface of the base steel sheet 100 (hot-dip galvanizing process step: S12), a step of forming an electrogalvanized layer 11 on the surface 10S of the hot-dip galvanized layer 10 (electrogalvanizing process step: S13), a step of forming a texture T1 (texture processing step: S14), and, if necessary, a step of forming a coating film 12 on the surface of the plated steel sheet 1 on which the texture T1 has been formed (coating film formation step: S15). Each step will be described below.

[Base steel plate preparation step (S11)]
In the base steel plate preparation step (S11), the above-mentioned base steel plate 100 is prepared. When the base steel plate 100 is a steel plate, the base steel plate 100 may be a hot-rolled steel plate or a cold-rolled steel plate.

[Hot-dip galvanizing treatment step (S12)]
In the galvanizing process ( S<b>12 ), a hot-dip galvanizing process is performed on the prepared base steel sheet 100 to form a hot-dip galvanized layer 10 on the surface of the base steel sheet 100 .

The hot-dip galvanizing process may be performed by a known method. Specifically, the hot-dip galvanizing layer 10 is formed by a known hot-dip galvanizing process or an alloyed hot-dip galvanizing process. In this case, a known galvanizing bath is prepared. The galvanizing bath contains, for example, Zn as a main component and Al. The galvanizing bath may further contain other elements such as Mg. When the galvanizing layer is to be the hot-dip galvanizing layer 10, the base steel sheet 100 is immersed in a galvanizing bath whose bath temperature and chemical composition are adjusted to form the hot-dip galvanizing layer 10 on the surface of the base steel sheet 100. When the hot-dip galvanizing layer 10 is to be an alloyed hot-dip galvanizing layer, the base steel sheet 100 on which the hot-dip galvanizing layer is formed is subjected to a known heat treatment in a known alloying furnace to form the hot-dip galvanizing layer 10 into an alloyed hot-dip galvanizing layer. The thickness of the hot-dip galvanizing layer 10 in the hot-dip galvanizing process can be adjusted by adjusting the immersion time in the plating bath and the amount of hot-dip galvanizing removed by gas wiping. Before the hot-dip galvanizing process, the base steel sheet 100 may be subjected to a known degreasing process such as electrolytic degreasing. For example, the steel sheet is electrolytically degreased under known conditions using a Na ₄ SiO ₄ treatment solution, and then rinsed with water. The steel sheet after electrolytic degreasing is immersed in an aqueous H ₂ SO ₄ solution for a predetermined period of time, and then rinsed with water.

[Electrolytic zinc plating process (S13)]
In the electrogalvanizing treatment step (S13), an electrogalvanizing treatment is performed on the base steel sheet 100 on which the hot-dip galvanized layer 10 has been formed, to form an electrogalvanized layer 11 on the surface 10S of the hot-dip galvanized layer 10. Note that the electrogalvanizing treatment may be performed after the above-mentioned degreasing treatment is performed on the base steel sheet 100 on which the hot-dip galvanized layer 10 has been formed.

The electrolytic zinc plating process may be carried out by a known method. The electrolytic zinc plating bath and the electrolytic zinc alloy plating bath may be known baths. Examples of electrolytic plating baths include sulfate baths, chloride baths, zincate baths, cyanide baths, pyrophosphate baths, boric acid baths, citric acid baths, other complex baths, and combinations of these. The electrolytic zinc alloy plating bath contains, in addition to Zn ions, one or more single ions or complex ions selected from Fe, Ni, Co, and Cr. In addition, organic additives may be added to the electrolytic plating bath as appropriate to obtain desired effects such as a leveling effect or increased hardness.

In the electrogalvanizing process, the chemical composition, temperature, flow rate, and plating conditions (current density, current pattern, etc.) of the electrogalvanizing bath and electrogalvanizing zinc alloy plating bath can be adjusted as appropriate. The thickness of the electrogalvanizing layer 11 in the electrogalvanizing process can be adjusted by adjusting the current value and time within the range of the current density in the electrogalvanizing process.

The electrogalvanizing bath is an acidic or alkaline bath. However, during the electrogalvanizing process, an electric potential is applied to the steel sheet. Therefore, the hot-dip galvanized layer 10 is not dissolved by the electrogalvanizing bath, and an electrogalvanized layer 11 is formed on the hot-dip galvanized layer 10. Through the above manufacturing process, a plated steel sheet including the base steel sheet 100, the hot-dip galvanized layer 10, and the electrogalvanized layer 11 is manufactured.

[Texture processing step (S14)]
In the texturing step (S14), a texture T1 is formed on the surface of the plated steel sheet 1 by carrying out a well-known texturing process on the surface of the electrolytic zinc plating layer 11 of the plated steel sheet.

When the texture T1 is a hairline, a known hairline processing is performed. For example, the hairline processing method includes a method of forming a hairline by polishing the surface with a known abrasive belt, a method of forming a hairline by polishing the surface with a known abrasive brush, and a method of forming a hairline by rolling and transferring the hairline with a roll to which a hairline shape has been applied. The length, depth, and frequency of the hairline can be adjusted by adjusting the grain size of the known abrasive belt, the grain size of the known abrasive brush, and the surface shape of the roll. In other words, by adjusting the grain size of the known abrasive brush and the surface shape of the roll, the plated steel sheet 1 with the cross section of FIG. 3 can be formed, and the plated steel sheet 1 with the cross section of FIG. 6 can also be formed. Furthermore, when the plated steel sheet 1 with the cross section of FIG. 6 is used, the exposure rate of the hot-dip galvanized layer 10 can also be adjusted by adjusting the grain size of the known abrasive brush and the surface shape of the roll. In addition, as a method of imparting a hairline, it is preferable to form a hairline by polishing the surface with an abrasive belt or an abrasive brush from the viewpoint of surface quality.

When the texture T1 has an uneven shape such as an embossed shape, a well-known transfer method using a roll may be carried out. Specifically, a roll is prepared on which the texture T1 having an uneven shape such as an embossed shape is formed. The prepared roll is pressed against the surface 11S of the electrogalvanized layer 11 of the plated steel sheet, and the uneven shape formed on the roll is transferred to the surface 11S of the electrogalvanized layer 11. Through the above steps, an uneven shape such as an embossed shape can be formed on the surface of the plated steel sheet 1.

The above manufacturing process allows the plated steel sheet 1 for case 1 to be manufactured.

[Coating film forming step (S15)]
The coating film forming step (S15) does not have to be performed. In other words, the coating film forming step (S15) is an optional step. If performed, in the coating film forming step (S15), a coating film 12 is formed on the surface of the electrogalvanized layer 11 of the plated steel sheet 1 on which the texture T1 is formed.

The method for forming the coating film 12 on the electrogalvanized layer 11 may be a well-known method. When forming an organic coating film as the coating film 12, a paint constituting the organic coating is prepared. The prepared paint is applied to the electrogalvanized layer 11 by a spraying method, a roll coater method, a curtain coater method, a dip and pull method, or the like. The paint on the electrogalvanized layer 11 is then naturally dried or baked to form the coating film 12. The drying temperature, drying time, baking temperature, and baking time can be adjusted as appropriate.

When forming an inorganic coating film as the coating film 12, an agent for the inorganic coating film is applied onto the electrolytic zinc plating layer 11 by a roll coater method, a dip ringer method, a spray ringer method, an electrolytic method, or the like. The agent applied onto the electrolytic zinc plating layer 11 is naturally dried or baked to form the coating film 12. The drying temperature, drying time, baking temperature, and baking time can be adjusted as appropriate.

By using the above manufacturing process, the plated steel sheet 1 with the cross section shown in Figure 3 or Figure 6 can be manufactured.

[Manufacturing process of plated steel sheet 1 of case 2]
In case 2, after the base steel sheet preparation step (S11) and the hot-dip galvanizing treatment step (S12) are performed, a texture processing step (S14) is performed to form a texture (plurality of recesses T10) on the surface 10S of the hot-dip galvanized layer 10. Then, an electrogalvanizing treatment step (S13) is performed. Through the above steps, a plated steel sheet 1 having a cross section shown in FIG. 4 can be manufactured. If necessary, a coating film formation step (S15) can be performed to form a coating film 12 on the electrogalvanized layer 11.

The plated steel sheet 1 of this embodiment can be manufactured by the above manufacturing process. Note that the plated steel sheet 1 of this embodiment is not limited to the above manufacturing method, and the plated steel sheet 1 of this embodiment may be manufactured by a manufacturing method other than the above manufacturing method as long as the plated steel sheet 1 having the above configuration can be manufactured. However, the above manufacturing method is suitable for manufacturing the plated steel sheet 1 of this embodiment.

The effects of one aspect of the present invention will be explained in more detail below using examples. The conditions in the following examples are one example of conditions adopted to confirm the feasibility and effects of the plated steel sheet 1 of this embodiment. Therefore, the present invention is not limited to this one example of conditions. Various conditions may be adopted in the present invention as long as they do not deviate from the gist of the present invention and achieve the object of the present invention.

Plated steel sheets were manufactured with the test numbers shown in Table 1. The steel sheets of each plated steel sheet were SPCC as specified in JIS G 3141 (2017), and had a thickness of 0.6 mm.

Each steel sheet was subjected to a well-known degreasing process under the same conditions. After that, for each test number, a plating layer was formed as shown in Table 1, and a texture processing process was carried out.

Specifically, in test number 1, a hot-dip galvanized layer was formed on a base steel sheet. In the hot-dip galvanizing process, a hot-dip galvanized bath was prepared to form a hot-dip galvanized layer of Zn-0.2%Al. The hot-dip galvanized layer was formed by a well-known hot-dip galvanizing process. The chemical composition of the hot-dip galvanized layer was analyzed by the above-mentioned EPMA analysis method. As a result, the chemical composition of the hot-dip galvanized layer was 0.2% Al, with the remainder being Zn. In Table 1, the chemical composition of the plating layer with an Al content of 0.2% and the remainder being Zn is represented as "Zn-0.2Al". In addition, the thickness of the hot-dip galvanized layer was measured by the above-mentioned method. The measurement results are shown in the "Thickness (μm)" column of the "Lower Layer" column in Table 1.

In test number 1, after the hot-dip galvanized layer was formed, no electrogalvanized layer was formed (indicated by "-" in the "Type", "Chemical composition", and "Thickness" columns in the "Upper layer" column in Table 1). The above-mentioned texturing process was carried out on the surface of the hot-dip galvanized layer to form a hairline. The exposed rate of the hot-dip galvanized layer in a plan view of the plated steel sheet was 100.0%.

An organic coating film was formed on the plated steel sheet of test number 1 on which the texture was formed ("Organic" is written in the "Type" column of the "Coating Film" column in Table 1). A paint in which a urethane resin (manufactured by ADEKA Corporation, product name: HUX-232) was dispersed in water was prepared as the organic resin. The thickness of the organic coating film was measured by the method described above. The measurement results are shown in the "Thickness (μm)" column of the "Coating Film" column in Table 1. The plated steel sheet of test number 1 was manufactured by the above manufacturing process.

In test number 2, a hot-dip galvanized layer was not formed on the base steel sheet (indicated by "-" in the "Type", "Chemical composition" and "Thickness" in the "Lower layer" column in Table 1). Instead, an electrogalvanized layer was formed on the base steel sheet. Specifically, the following electrogalvanized process was performed to form an electrogalvanized layer. A plating bath containing 1.0 mol/l of Zn sulfate heptahydrate and 50 g/L of anhydrous sodium sulfate and adjusted to a pH of 2.0 was prepared. In the electroplating, the bath temperature was set to 50°C and the current density was set to 50 A/ ^dm2 . The plating time was adjusted so that the thickness was about 3.0 μm. Through the above steps, an electrogalvanized layer was formed on the base steel sheet. The chemical composition of the electrogalvanized layer was analyzed by the above-mentioned EPMA analysis method. As a result, the chemical composition of the electrogalvanized layer was a chemical composition consisting of Zn, and the Al content was less than 0.1%. In Table 1, the chemical composition of the electrogalvanized layer, which is composed of Zn and contains less than 0.1% Al, is indicated as "Zn". The thickness of the electrogalvanized layer was measured by the above-mentioned method. The measurement results are shown in the "Thickness (μm)" column of the "Upper layer" column in Table 1.

The above-mentioned texture processing process was carried out on the surface of the electrolytic zinc-plated layer to form a hairline. Note that in test number 2, no hot-dip galvanized layer was formed, so the exposure rate of the hot-dip galvanized layer was 0%.

An organic coating film was formed on the textured plated steel sheet of test number 2 in the same manner as test number 1 (in Table 1, "Organic" is written in the "Type" column of the "Coating film" column). The organic resin was the same as in test number 1. The thickness of the organic coating film was measured by the above-mentioned method. The measurement results are shown in the "Thickness (μm)" column of the "Coating film" column in Table 1. The plated steel sheet of test number 2 was manufactured by the above manufacturing process.

In test number 3, a hot-dip galvanized layer was formed on the base steel sheet. In the hot-dip galvanizing process, a hot-dip galvanized bath was prepared to form a hot-dip galvanized layer of Zn-0.2%Al-0.5%Mg. The hot-dip galvanized layer was formed by a well-known hot-dip galvanizing process. The chemical composition of the hot-dip galvanized layer was analyzed by the above-mentioned EPMA analysis method. As a result, the chemical composition of the hot-dip galvanized layer was 0.2% Al, 0.5% Mg, and the balance Zn. In Table 1, the chemical composition of the plating layer with 0.2% Al, 0.5% Mg, and the balance Zn is represented as "Zn-0.2Al-0.5Mg". In addition, the thickness of the hot-dip galvanized layer was measured by the above-mentioned method. The measurement results are shown in the "Thickness (μm)" column of the "Lower Layer" column in Table 1.

In test number 3, similar to test number 1, after forming the hot-dip galvanized layer, no electrogalvanized layer was formed. The above-mentioned texture processing process was carried out on the surface of the hot-dip galvanized layer to form a hairline. The exposed rate of the hot-dip galvanized layer in a plan view of the plated steel sheet was 100.0%. An organic coating film was formed on the plated steel sheet of test number 3 on which the texture was formed, using the same method as test number 1. The organic resin was the same as that of test number 1. The thickness of the organic coating film was measured using the above-mentioned method. The plated steel sheet of test number 3 was manufactured using the above manufacturing process.

In test number 4, a hot-dip galvanized layer was formed on the base steel sheet. In the hot-dip galvanizing process, a hot-dip galvanized bath was prepared to form a hot-dip galvanized layer of Zn-55.0%Al-1.6%Si. The hot-dip galvanized layer was formed by a well-known hot-dip galvanizing process. The chemical composition of the hot-dip galvanized layer was analyzed by the above-mentioned EPMA analysis method. As a result, the chemical composition of the hot-dip galvanized layer was 55.0% Al, 1.6% Si, and the balance Zn. In Table 1, the chemical composition of the plating layer with 55.0% Al, 1.6% Si, and the balance Zn is represented as "Zn-55.0Al-1.6Si". In addition, the thickness of the hot-dip galvanized layer was measured by the above-mentioned method. The measurement results are shown in the "Thickness (μm)" column of the "Lower Layer" column in Table 1.

In test number 4, similar to test number 1, after forming the hot-dip galvanized layer, no electrogalvanized layer was formed. The above-mentioned texture processing process was carried out on the surface of the hot-dip galvanized layer to form a hairline. The exposed rate of the hot-dip galvanized layer in a plan view of the plated steel sheet was 100.0%. An organic coating film was formed on the plated steel sheet of test number 4 on which the texture was formed, using the same method as test number 1. The organic resin was the same as that of test number 1. The thickness of the organic coating film was measured using the above-mentioned method. The plated steel sheet of test number 4 was manufactured using the above manufacturing process.

In test numbers 5 to 7, the manufacturing process of case 1 shown in Figure 7 was carried out to produce plated steel sheets. Specifically, a hot-dip galvanized layer was formed on the surface of the base steel sheet by the same method as in test number 1. The chemical composition and thickness of the hot-dip galvanized layer were as shown in the "Chemical composition" and "Thickness (μm)" in the "Lower layer" column in Table 1. In test numbers 5 to 7, the base steel sheet on which the hot-dip galvanized layer was formed was subjected to an electrogalvanizing process under the same conditions as in test number 2 to form an electrogalvanized layer on the hot-dip galvanized layer. The chemical composition and thickness of the electrogalvanized layer were as shown in the "Chemical composition" and "Thickness (μm)" in the "Upper layer" column in Table 1.

A texture processing process was carried out on the plated steel sheets of test numbers 5 to 7 on which an electrolytic zinc plating layer was formed, to form hairlines. As a result, the plated steel sheets of test numbers 5 and 7 had the cross section shown in FIG. 6, and the plated steel sheet of test number 6 had the cross section shown in FIG. 3. The exposure rate of the hot-dip zinc plating layer in a plan view of the plated steel sheet was measured using the method described above. The measurement results are shown in the "Exposure rate (area%)" column. An organic coating film was formed on the plated steel sheets of test numbers 5 to 7 on which a texture was formed, using the same method as test number 1. The organic resin was the same as test number 1. The thickness of the organic coating film was measured using the method described above. The plated steel sheets of test numbers 5 to 7 were manufactured using the above manufacturing process.

In test numbers 8 to 13, the manufacturing process of case 1 shown in Figure 7 was carried out to manufacture plated steel sheets. Specifically, a hot-dip galvanized layer was formed on the surface of the base steel sheet by the same method as in test number 1. The chemical composition and thickness of the hot-dip galvanized layer were as shown in the "Chemical composition" and "Thickness (μm)" in the "Lower layer" column in Table 1. In test numbers 8 to 13, the base steel sheet on which the hot-dip galvanized layer was formed was subjected to an electrogalvanizing process under the same conditions as in test number 2 to form an electrogalvanized layer on the hot-dip galvanized layer. The chemical composition and thickness of the electrogalvanized layer were as shown in the "Chemical composition" and "Thickness (μm)" in the "Upper layer" column in Table 1.

A texture processing process was carried out on the plated steel sheets of test numbers 8 to 12 on which an electrolytic zinc plating layer was formed, to form hairlines. As a result, the plated steel sheets of test numbers 8, 9, and 12 had the cross section shown in FIG. 3. On the other hand, the plated steel sheets of test numbers 10 and 11 had the cross section shown in FIG. 6. Furthermore, an embossed pattern was formed as texture processing on test number 13. The plated steel sheets of test number 13 had the cross section shown in FIG. 3. By the above-mentioned method, the exposure rate of the hot-dip zinc plating layer in the plan view of the plated steel sheets of test numbers 8 to 13 was measured. The measurement results are shown in the "Exposure rate (area%)" column. An organic coating film was formed on the plated steel sheets of test numbers 8, 10, and 13 on which a texture was formed, by the same method as that of test number 1. The organic resin was the same as that of test number 1. On the other hand, in test number 9, an inorganic coating film was formed on the plated steel sheet on which a texture was formed, by a well-known method (indicated as "inorganic" in the "Type" column of the "Coating film" column in Table 1). The inorganic coating film was Li silicate. In test number 11, a primer layer was applied to the textured plated steel sheet, and then an organic coating film was formed in the same manner as in test number 1 (in Table 1, "Type" in the "Coating Film" column is marked "Organic + Inorganic"). The thicknesses of the coating films in test numbers 8 to 11 and 13 were measured using the method described above. In test number 12, no coating film was formed. Plated steel sheets in test numbers 8 to 13 were manufactured using the above manufacturing process.

In test number 14, the manufacturing process of case 1 shown in FIG. 7 was carried out to produce a plated steel sheet. Specifically, a hot-dip galvanized layer was formed on the surface of the base steel sheet by the same method as in test number 1. The chemical composition and thickness of the hot-dip galvanized layer were as shown in the "Chemical composition" and "Thickness (μm)" in the "Lower layer" column in Table 1. In test number 14, an electrolytic zinc alloy plating bath was prepared for the base steel sheet on which the hot-dip galvanized layer was formed, and an electrolytic zinc alloy plating layer of Zn-12.0%Ni was formed. Specifically, the following electrolytic zinc alloy plating process was carried out to form an electrolytic zinc alloy plating layer. A plating bath containing 0.4 mol/l Zn sulfate heptahydrate, 0.6 mol/l Ni sulfate hexahydrate, and 50 g/L anhydrous sodium sulfate, and adjusted to a pH of 2.0, was prepared. In the electroplating, the bath temperature was set to 50°C, and the current density and plating time were adjusted so that the plating composition was Zn-12.0%Ni and the thickness was about 2.0μm. Through the above process, an electrolytic zinc alloy plating layer was formed on the hot-dip galvanized layer. The chemical composition of the electrolytic zinc alloy plating layer was analyzed by the above-mentioned EPMA analysis method. As a result, the chemical composition of the electrolytic zinc alloy plating layer was 12.0% Ni, with the remainder being Zn. The chemical composition of the plating layer with a Ni content of 12.0% and the remainder being Zn is expressed as "Zn-12.0Ni". The chemical composition and thickness of the electrolytic zinc alloy plating layer were as shown in the "Chemical composition" and "Thickness (μm)" in the "Upper layer" column in Table 1.

A texture processing process was carried out on the plated steel sheet of test number 14 on which an electrolytic zinc alloy plating layer of Zn-12.0%Ni was formed, to form hairlines. As a result, test number 14 became a plated steel sheet having the cross section shown in FIG. 3. Using the method described above, the exposure rate of the hot-dip galvanized layer in a plan view of the plated steel sheet of test number 14 was measured. The measurement results are shown in the "Exposure rate (area%)" column. An organic coating film was formed on the plated steel sheet of test number 14 on which the texture was formed, using the same method as test number 1. The organic resin was the same as test number 1. Using the method described above, the thickness of the coating film of test number 14 was measured. Using the above manufacturing process, the plated steel sheet of test number 14 was manufactured.

In test number 15, the manufacturing process of case 1 shown in FIG. 7 was carried out to produce a plated steel sheet. Specifically, a hot-dip galvanized layer was formed on the surface of the base steel sheet by the same method as in test number 1. The chemical composition and thickness of the hot-dip galvanized layer were as shown in the "Chemical composition" and "Thickness (μm)" in the "Lower layer" column in Table 1. In test number 15, an electrolytic zinc alloy plating bath was prepared for the base steel sheet on which the hot-dip galvanized layer was formed, and an electrolytic zinc alloy plating layer of Zn-10.0%Fe was formed. Specifically, the following electrolytic zinc alloy plating process was carried out to form an electrolytic zinc alloy plating layer. A plating bath containing 0.4 mol/l Zn sulfate heptahydrate, 0.6 mol/l Fe sulfate heptahydrate, and 50 g/L anhydrous sodium sulfate, and adjusted to a pH of 1.6, was prepared. In the electroplating, the bath temperature was set to 50°C, and the current density and plating time were adjusted so that the plating composition was Zn-10%Fe and the thickness was about 2.0μm. Through the above process, an electrolytic zinc alloy plating layer was formed on the hot-dip galvanized layer. The chemical composition of the electrolytic zinc alloy plating layer was analyzed by the above-mentioned EPMA analysis method. As a result, the chemical composition of the electrolytic zinc alloy plating layer was 10.0% Fe, with the remainder being Zn. The chemical composition of the plating layer with an Fe content of 10.0% and the remainder being Zn is expressed as "Zn-10.0Fe". The chemical composition and thickness of the electrolytic zinc alloy plating layer were as shown in the "Chemical composition" and "Thickness (μm)" in the "Upper layer" column in Table 1.

A texture processing process was carried out on the plated steel sheet of test number 15 on which an electrolytic zinc alloy plating layer of Zn-10.0%Fe was formed to form hairlines. As a result, test number 15 became a plated steel sheet having the cross section shown in FIG. 3. Using the method described above, the exposure rate of the hot-dip galvanized layer in a plan view of the plated steel sheet of test number 15 was measured. The measurement results are shown in the "Exposure rate (area%)" column. An organic coating film was formed on the plated steel sheet of test number 15 on which the texture was formed, using the same method as test number 1. The organic resin was the same as test number 1. Using the method described above, the thickness of the coating film of test number 15 was measured. Using the above manufacturing process, the plated steel sheet of test number 15 was manufactured.

In test number 16, the manufacturing process of case 1 shown in FIG. 7 was carried out to produce a plated steel sheet. Specifically, a hot-dip galvanized layer was formed on the surface of the base steel sheet by the same method as in test number 1. The chemical composition and thickness of the hot-dip galvanized layer were as shown in the "Chemical composition" and "Thickness (μm)" in the "Lower layer" column in Table 1. In test number 16, an electrolytic zinc alloy plating bath was prepared for the base steel sheet on which the hot-dip galvanized layer was formed, and an electrolytic zinc alloy plating layer of Zn-1.0%Co was formed. Specifically, the following electrolytic zinc alloy plating process was carried out to form an electrolytic zinc alloy plating layer. A plating bath containing 0.9 mol/l Zn sulfate heptahydrate, 0.1 mol/l Co sulfate heptahydrate, and 50 g/L anhydrous sodium sulfate, and adjusted to a pH of 1.8, was prepared. In the electroplating, the bath temperature was set to 50°C, and the current density and plating time were adjusted so that the plating composition was Zn-1.0%Co and the thickness was about 3.0μm. Through the above process, an electrolytic zinc alloy plating layer was formed on the hot-dip galvanized layer. The chemical composition of the electrolytic zinc alloy plating layer was analyzed by the above-mentioned EPMA analysis method. As a result, the chemical composition of the electrolytic zinc alloy plating layer was 1.0% Co, with the remainder being Zn. The chemical composition of the plating layer with a Co content of 1.0% and the remainder being Zn is expressed as "Zn-1.0Co". The chemical composition and thickness of the electrolytic zinc alloy plating layer were as shown in the "Chemical composition" and "Thickness (μm)" in the "Upper layer" column in Table 1.

A texture processing process was carried out on the plated steel sheet of test number 16 on which an electrolytic zinc alloy plating layer of Zn-1.0%Co was formed, to form hairlines. As a result, test number 16 became a plated steel sheet having the cross section shown in FIG. 6. Using the method described above, the exposure rate of the hot-dip galvanized layer in a plan view of the plated steel sheet of test number 16 was measured. The measurement results are shown in the "Exposure rate (area%)" column. An organic coating film was formed on the plated steel sheet of test number 16 on which the texture was formed, using the same method as test number 1. The organic resin was the same as test number 1. Using the method described above, the thickness of the coating film of test number 16 was measured. Using the above manufacturing process, the plated steel sheet of test number 16 was manufactured.

In test number 17, the manufacturing process of case 1 shown in FIG. 7 was carried out to manufacture a plated steel sheet. Specifically, a hot-dip galvanized layer was formed on the surface of the base steel sheet by the same method as in test number 1. Furthermore, a well-known alloying process was carried out on the formed hot-dip galvanized layer to form an alloyed hot-dip galvanized layer. The chemical composition of the alloyed hot-dip galvanized layer was analyzed by the above-mentioned EPMA analysis method. As a result, the chemical composition of the hot-dip galvanized layer was 0.1% Al, 15.0% Fe, and the balance Zn. In Table 1, the chemical composition of the plating layer with 0.1% Al, 15.0% Fe, and the balance Zn is represented as "Zn-0.1Al-15.0Fe". The thickness of the hot-dip galvanized layer was measured by the above-mentioned method.

In test number 17, the base steel sheet on which the galvannealed layer was formed was subjected to an electrolytic galvanizing process under the same conditions as in test number 2 to form an electrolytic galvanized layer on the galvannealed layer. The chemical composition and thickness of the electrolytic galvanized layer were as shown in the "Chemical composition" and "Thickness (μm)" in the "Upper layer" column in Table 1.

A texture processing process was carried out on the plated steel sheet of test number 17 on which an electrolytic zinc plating layer was formed, to form hairlines. As a result, test number 17 became a plated steel sheet having the cross section shown in FIG. 3. Using the method described above, the exposure rate of the hot-dip zinc plating layer in a plan view of the plated steel sheet of test number 17 was measured. The measurement results are shown in the "Exposure rate (area%)" column. An organic coating film was formed on the plated steel sheet of test number 17 on which a texture was formed, using the same method as test number 1. The organic resin was the same as test number 1. Using the method described above, the thickness of the coating film of test number 17 was measured. Using the above manufacturing process, the plated steel sheet of test number 17 was manufactured.

In test numbers 18 to 20, the manufacturing process of case 1 shown in FIG. 7 was carried out to manufacture plated steel sheets. Specifically, in test number 18, the same hot-dip galvanizing bath as in test number 4 was prepared, in test number 19, a hot-dip galvanizing bath capable of forming a hot-dip galvanizing layer of Zn-11.0%Al-3.0%Mg-0.2%Si was prepared, and in test number 20, a hot-dip galvanizing bath capable of forming a hot-dip galvanizing layer of Zn-6.0%Al-3.0%Mg-0.1%Si was prepared. The hot-dip galvanizing layer was formed by a well-known hot-dip galvanizing process. The chemical composition of the hot-dip galvanizing layer was analyzed by the above-mentioned EPMA analysis method. As a result, the chemical composition of the hot-dip galvanizing layer of test number 19 was 11.0% Al, 3.0% Mg, 0.2% Si, and the balance was Zn. In Table 1, the chemical composition of the coating layer with an Al content of 11.0%, an Mg content of 3.0%, an Si content of 0.2%, and the balance of Zn is expressed as "Zn-11.0Al-3.0Mg-0.2Si". The chemical composition of the hot-dip galvanized layer of test number 20 was an Al content of 6.0%, an Mg content of 3.0%, an Si content of 0.1%, and the balance of Zn. In Table 1, the chemical composition of the coating layer with an Al content of 6.0%, an Mg content of 3.0%, an Si content of 0.1%, and the balance of Zn is expressed as "Zn-6.0Al-3.0Mg-0.1Si". The thickness of the hot-dip galvanized layer was measured by the above-mentioned method. The measurement results are shown in the "Thickness (μm)" column of the "Lower layer" column in Table 1.

In test numbers 18 to 20, the base steel sheet on which the hot-dip galvanized layer was formed was subjected to an electrolytic galvanizing process under the same conditions as test number 2 to form an electrolytic galvanized layer on the hot-dip galvanized layer. The chemical composition and thickness of the electrolytic galvanized layer were as shown in the "Chemical composition" and "Thickness (μm)" in the "Upper layer" column in Table 1. A texture processing process was performed on the plated steel sheets of test numbers 18 to 20 on which the electrolytic galvanized layer was formed to form hairlines. As a result, test number 18 became a plated steel sheet having the cross section shown in Figure 3. On the other hand, test numbers 19 and 20 became plated steel sheets having the cross section shown in Figure 6. The exposure rate of the hot-dip galvanized layer in the plan view of the plated steel sheets of test numbers 18 to 20 was measured by the above-mentioned method. The measurement results are shown in the "Exposure rate (area%)" column. An organic coating film was formed on the plated steel sheets of test numbers 18 to 20 on which the texture was formed by the same method as test number 1. The organic resin was the same as test number 1. Using the method described above, the thickness of the coating film for test numbers 18 to 20 was measured. Using the above manufacturing process, plated steel sheets for test numbers 18 to 20 were manufactured.

In test number 21, the manufacturing process of case 1 shown in FIG. 7 was carried out to manufacture a plated steel sheet. However, after the base steel sheet preparation process, an electric Ni plating layer of 250 mg/m ² was formed. Specifically, for the electric Ni plating layer, a plating solution containing 0.5 mol/l Ni sulfate hexahydrate and 45 g/l boric acid was prepared, and the bath temperature was set to 45° C., and the plating time was adjusted so that the deposition amount was about 250 mg/m ² at a current density of 20 A/dm ^2. A hot-dip galvanized layer was formed on the surface of the base steel sheet on which the electric Ni plating layer was formed by the same method as in test number 1. The chemical composition of the hot-dip galvanized layer was analyzed by the above-mentioned EPMA analysis method. As a result, the chemical composition of the hot-dip galvanized layer was 0.2% Al, 0.1% Ni, and the balance was Zn. In Table 1, the chemical composition of the plating layer having an Al content of 0.2%, a Ni content of 0.1%, and the balance of Zn is expressed as "Zn-0.2Al-0.1Ni". The thickness of the hot-dip galvanized layer was measured by the above-mentioned method. The measurement results are shown in the "Thickness (μm)" column in the "Lower Layer" column in Table 1. In Test No. 21, further, an electrogalvanized treatment was performed under the same conditions as in Test No. 2 on the base steel sheet on which the hot-dip galvanized layer was formed, to form an electrogalvanized layer on the hot-dip galvanized layer. The chemical composition and thickness of the electrogalvanized layer were as shown in the "Chemical Composition" and "Thickness (μm)" columns in the "Upper Layer" column in Table 1.

A texture processing process was carried out on the plated steel sheet of test number 21 on which an electrolytic zinc plating layer was formed, to form hairlines. As a result, the plated steel sheet of test number 21 had the cross section shown in FIG. 6. Using the method described above, the exposure rate of the hot-dip zinc plating layer in a plan view of the plated steel sheet was measured. The measurement results are shown in the "Exposure rate (area%)" column. An organic coating film was formed on the plated steel sheet of test number 21 on which a texture was formed, using the same method as test number 1. The organic resin was the same as test number 1. The thickness of the organic coating film was measured using the method described above. Using the above manufacturing process, the plated steel sheet of test number 21 was manufactured.

In test numbers 22 to 24, the manufacturing process of case 2 shown in FIG. 7 was carried out to manufacture plated steel sheets. Specifically, in test number 22, a hot-dip galvanized layer was formed on the surface of the base steel sheet by the same method as in test number 1. In test number 23, a hot-dip galvanized layer was formed on the surface of the base steel sheet by the same method as in test number 3. In test number 24, a hot-dip galvanized layer was formed on the surface of the base steel sheet by the same method as in test number 19. The chemical composition and thickness of the hot-dip galvanized layer were as shown in the "Chemical composition" and "Thickness (μm)" in the "Lower layer" column in Table 1. In test numbers 22 to 24, a texture processing process was carried out on the hot-dip galvanized layer formed with the hairline, and an electrogalvanized layer was formed by carrying out an electrogalvanized process under the same conditions as in test number 2. The chemical composition and thickness of the electrogalvanized layer were as shown in the "Chemical composition" and "Thickness (μm)" in the "Upper layer" column in Table 1.

By the above method, plated steel sheets having the cross section shown in Figure 4 were manufactured. By the above method, the exposure rate of the hot-dip galvanized layer in a plan view of the plated steel sheets of test numbers 22 to 24 was measured. An organic coating film was formed on the plated steel sheets of test numbers 22 to 24 on which texture was formed, by the same method as for test number 1. The organic resin was the same as for test number 1. By the above method, the thickness of the coating film of test numbers 22 to 24 was measured. By the above manufacturing process, the plated steel sheets of test numbers 22 to 24 were manufactured. By the above manufacturing process, the plated steel sheets of test numbers 22 to 24 were manufactured.

In test number 25, first, an electrolytic zinc alloy plating layer of Zn-12.0%Ni was formed on the base steel sheet. Specifically, an electrolytic zinc alloy plating layer of Zn-12.0%Ni was formed on the base steel sheet by the same method as the electrolytic zinc alloy plating layer of test number 14. The chemical composition and thickness of the electrolytic zinc alloy plating layer were as shown in the "chemical composition" and "thickness (μm)" in the "lower layer" column in Table 1. In test number 25, a hot-dip galvanized layer was further formed on the base steel sheet on which the electrolytic zinc alloy plating layer was formed by the same method as test number 1. The chemical composition and thickness of the hot-dip galvanized layer were as shown in the "chemical composition" and "thickness (μm)" in the "upper layer" column in Table 1. A texture processing process was performed on the plated steel sheet of test number 25 on which the hot-dip galvanized layer was formed to form a hairline. The exposure rate of the hot-dip galvanized layer in a plan view of the plated steel sheet of test number 25 was measured. The measurement results are shown in the "Exposure rate (area %)" column. An organic coating film was formed on the textured plated steel sheet of test number 25 in the same manner as in test number 1. The organic resin was the same as in test number 1. The thickness of the coating film of test number 25 was measured using the method described above. The plated steel sheet of test number 25 was manufactured using the above manufacturing process.

[Evaluation test]
[Corrosion resistance evaluation test]
The corrosion resistance (long-term corrosion resistance) of the plated steel sheets of each test number was evaluated by the following method. A test piece of 75 mm x 100 mm was taken from the plated steel sheets of each test number. The end faces and back faces of the test pieces were protected with tape seals. Then, cross-cut scratches reaching the plating layer were formed (the plated steel sheets with cross-cut scratches are referred to as red rust resistance test pieces). Next, a salt spray test of 5% NaCl held at 35°C was performed on the red rust resistance test pieces in accordance with JIS Z 2371 (2015). The test was performed for up to 2000 hours, and the red rust generation time after the test was obtained. Evaluation was performed according to the red rust generation time as follows.
Evaluation A: Red rust generation time is 2000 hours or more Evaluation B: Red rust generation time is 240 hours or more and less than 2000 hours Evaluation X: Red rust generation time is less than 240 hours Evaluations A and B were judged to have excellent corrosion resistance ("A" or "B" in the "Corrosion Resistance" column in Table 1). Evaluation X was judged to have poor corrosion resistance ("X" in the "Corrosion Resistance" column in Table 1).

[Blackening phenomenon evaluation test]
The occurrence of the blackening phenomenon was confirmed for the plated steel sheets of each test number by the following method. Samples were taken from each test number. First, the plated steel sheets were stacked with the evaluation surfaces facing each other and packaged (the plated steel sheets after packaging are referred to as blackening-resistant test pieces). The blackening-resistant test pieces were then held in an environment of 70°C and 85% RH for one week, and the change in lightness (ΔL ^* ) before and after holding was measured. The ΔL ^* values before and after holding were determined by color tone measurement (JIS Z 8781-4 (2013)) based on the CIE color system (L ^* a ^* b ^* color system) using a spectrophotometer (manufactured by Suga Test Instruments Co., Ltd., product name: SC-T45).

Based on the obtained ΔL ^* value, the blackening phenomenon was evaluated as follows.
Evaluation A: 0≦ΔL ^* <1.0
Evaluation B: 1.0≦ΔL ^* <3.0
Evaluation X: 3.0≦ΔL ^*
In the cases of evaluations A and B, the blackening phenomenon was suppressed, and it was determined that excellent design properties could be maintained even over time. On the other hand, in the case of evaluation X, it was determined that the design properties deteriorated over time.

[Texture design evaluation test]
After the blackening phenomenon evaluation test, the plated steel sheets of each test number were subjected to a texture design evaluation test by the following method. The plated steel sheets of each test number were placed in an environment equivalent to sunlight on a clear day in the morning (illuminance of about 65,000 lux). Then, the plated steel sheets were observed at various angles between the light source, the steel sheet, and the line of sight to confirm whether the texture was visible or not. If the texture was visible at all angles from 5° to 80° with respect to the vertical direction of the steel sheet surface, the steel sheet was evaluated as having excellent design and passing ("A" in the "Texture" column in Table 1). If the texture was visible at some angles from 5° to 80° with respect to the vertical direction of the steel sheet surface, the steel sheet was evaluated as having good design and passing ("B" in the "Texture" column in Table 1). On the other hand, if the texture was visible but spangles, primary crystal Al phase, and dross defects were also confirmed, or if the blackening phenomenon progressed and 70% or more of the surface had turned black, the steel sheet was evaluated as having poor design and failing ("X" in the "Texture" column in Table 1).

[Evaluation results]
With reference to Table 1, in test numbers 5 to 24, a hot-dip galvanized layer was formed on the base steel sheet, and an electrogalvanized layer was formed on the hot-dip galvanized layer. Then, a texture was formed on the surface of the plated steel sheet. As a result, in all test numbers, the corrosion resistance was good (evaluation "A" or "B"). Furthermore, in all test numbers, the blackening phenomenon was suppressed (evaluation "A" or "B"). Furthermore, the design of the texture was also high (evaluation "A" to "B"). Therefore, the plated steel sheets of test numbers 5 to 24 were able to achieve both excellent design and excellent corrosion resistance, and were able to maintain their excellent design even over time.

In particular, the thickness of the hot-dip galvanized layer was thick in test numbers 5 to 8, 12, and 21 to 23. Furthermore, test numbers 18 to 20, and 24 contained not only Al but also optional elements such as Mg. As a result, the corrosion resistance was high (evaluation "A"). Furthermore, in test numbers 7, 10, 11, 16, and 19 to 21, the bottom of the recesses in the texture reached the hot-dip galvanized layer. Furthermore, the exposure rate of the hot-dip galvanized layer was within the range of 3.5 to 30.0%. As a result, the texture had excellent design (evaluation "A").

On the other hand, the plated steel sheets of test numbers 1, 3 and 4 had a hot-dip galvanized layer, but no electrogalvanized layer was formed on the hot-dip galvanized layer. As a result, blackening progressed and the design was poor ("X" in the blackening phenomenon evaluation test, and "X" in the texture design evaluation test).

The plated steel sheet of test number 2 had an electrolytic zinc-plated layer, but no hot-dip galvanized layer was formed as an underlayer of the electrolytic zinc-plated layer. As a result, it had poor corrosion resistance (a rating of "X" in the corrosion resistance evaluation test).

In test number 25, an electrolytic zinc-plated layer was formed on the base steel sheet, and a hot-dip zinc-plated layer was formed on the electrolytic zinc-plated layer. As a result, blackening progressed and the design was poor ("X" in the blackening phenomenon evaluation test, and "X" in the texture design evaluation test).

The above describes an embodiment of the present invention. However, the above-described embodiment is merely an example for implementing the present invention. Therefore, the present invention is not limited to the above-described embodiment, and the above-described embodiment can be modified as appropriate within the scope of the spirit of the present invention.

Reference Signs List 1: Plated steel sheet 10: Hot-dip galvanized layer 11: Electrogalvanized layer T1: Texture 12: Coating film

Claims (5)

A plated steel sheet,
A base steel plate;
A hot-dip galvanized layer formed on a surface of the base steel sheet;
and an electrolytic galvanized layer formed on the hot-dip galvanized layer,
The chemical composition of the hot-dip galvanized layer is, in mass%,
Al: 0.1 to 60.0%,
Mg: 0 to 12.5%, and
Zn: 35.0% or more;
The chemical composition of the electrolytic zinc plating layer is, in mass %,
Al: less than 0.1%; and
Zn: 64.9% or more;
When viewed from above the electrogalvanized layer, a texture is formed on the surface of the plated steel sheet.
Galvanized steel sheet. The plated steel sheet according to claim 1,
The texture is a hairline.
Galvanized steel sheet. The plated steel sheet according to claim 1 or 2, further comprising:
A coating film is provided on the electrogalvanized layer.
Galvanized steel sheet. The plated steel sheet according to any one of claims 1 to 3,
The texture is
A plurality of recesses whose bottoms reach the hot-dip galvanized layer are included.
Galvanized steel sheet. The plated steel sheet according to claim 4,
When viewed from above the electrolytic galvanized layer, the exposed rate of the hot-dip galvanized layer is 3.5% to 30.0%.
Galvanized steel sheet.

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