WO2021106260A1

WO2021106260A1 - Zn-Al-Mg HOT-DIPPED STEEL SHEET

Info

Publication number: WO2021106260A1
Application number: PCT/JP2020/025968
Authority: WO
Inventors: ゆきの石川; 浩雅莊司; 哲也鳥羽; 泰平金藤; 信之下田
Original assignee: 日本製鉄株式会社
Priority date: 2019-11-29
Filing date: 2020-07-02
Publication date: 2021-06-03
Also published as: TWI815038B; CN114729437A; TW202126834A; KR20220084142A; KR102658299B1

Abstract

This Zn-Al-Mg hot-dipped steel sheet comprises a hot-dip layer that includes, as a metal structure, an [Al phase] and an [Al/Zn/MgZn₂ three-component eutectic structure]. The hot-dip layer includes a first region and a second region that satisfy either (a) or (b), and the first region or the second region is arranged so as to have a prescribed shape. (a) The first region is a region in which the average length of the [Al phase] at the surface of the hot-dip layer is at least 200 μm, and the second region is a region in which the average length of the [Al phase] at the surface of the hot-dip layer is less than 200 μm. (b) The first region is a region in which the length Le over which the [Al/Zn/MgZn₂ three-component eutectic structure] is opposite the steel sheet at the interface between the steel sheet and the hot-dip layer is greater than 0.3 relative to the length L of the interface, and the second region is a region in which the length Le over which the [Al/Zn/MgZn₂ three-component eutectic structure] is opposite the steel sheet at the interface between the steel sheet and the hot-dip layer is no more than 0.3 relative to the length L of the interface.

Description

Zn-Al-Mg-based hot-dip galvanized steel sheet

The present invention relates to a Zn—Al—Mg-based hot-dip galvanized steel sheet.
The present application claims priority based on Japanese Patent Application No. 2019-216685 and Japanese Patent Application No. 2019-216686 filed in Japan on November 29, 2019, the contents of which are incorporated herein by reference.

Zn-Al-Mg-based hot-dip galvanized steel sheets, which have higher corrosion resistance than hot-dip galvanized steel sheets, are widely used in various manufacturing industries such as building materials, home appliances, and automobile fields, and their usage has been increasing in recent years. ..

By the way, for the purpose of displaying characters, patterns, design images, etc. on the surface of the hot-dip galvanized steel sheet, the hot-dip galvanized layer is subjected to processes such as printing and painting to produce characters, patterns, design images, etc. It may appear on the surface of the hot-dip galvanized layer.

However, if processes such as printing and painting are performed on the hot-dip galvanized layer, there is a problem that the cost and time for applying characters and designs increase. Furthermore, when characters, designs, etc. are displayed on the surface of the plating layer by printing or painting, not only the metallic luster appearance, which is highly favored by consumers, is lost, but also the coating film itself deteriorates over time and the coating film adheres. Due to the problem of sexual deterioration over time, the durability is inferior, and there is a risk that characters, designs, etc. will disappear over time. Further, when characters, designs, etc. are displayed on the surface of the plating layer by stamping the ink, although the cost and time can be relatively reduced, there is a concern that the ink may reduce the corrosion resistance of the hot-dip plating layer. Further, when the design or the like is revealed by grinding the hot-dip plating layer, the durability of the design or the like is excellent, but the thickness of the hot-dip galvanizing layer at the ground portion is significantly reduced, so that the corrosion resistance is inevitably lowered and the plating characteristics are lowered. Is a concern.

As shown in the patent documents below, various technological developments have been made for Zn-Al-Mg hot-dip galvanized steel sheets, but technologies for improving the durability of Zn-Al-Mg hot-dip galvanized steel sheets when characters or designs appear on the surface of the plated layer. Is not known.

Regarding the Zn-Al-Mg-based hot-dip galvanized steel sheet, there is a conventional technique for improving the satin-like plating appearance seen in the Zn-Al-Mg-based hot-dip galvanized steel sheet.
For example, Patent Document 1 describes a Zn—Al—Mg-based hot-dip galvanized steel sheet having a satin-like appearance with fine texture and many smooth glossy portions, that is, a large number of white portions per unit area and gloss. A Zn—Al—Mg-based hot-dip galvanized steel sheet having a good satin-like appearance in which the proportion of the area of the portion is large is described. Further, Patent Document 1 describes that an unfavorable satin finish is a state in which an amorphous white portion and a circular glossy portion are mixed to exhibit a surface appearance scattered on the surface. There is.
Further, in Patent Document 2, in the thickness direction cross section of the plating layer, the portion where Al crystals are absent between the interface between the plating layer and the base iron and the plating surface layer is 10 of the width direction length of the cross section. A Zn—Al—Mg-based plated steel sheet having an improved plating appearance by occupying% to 50% is described.
Further, in Patent Document 3, the average roughness Ra of the center line of the surface of the plated steel sheet is 0.5 to 1.5 μm, and the size is 1.27 μm or more contained per PPI (1 inch (2.54 cm)). A hot-dip galvanized steel sheet having excellent formability, in which the number of peaks) is 150 to 300 and the Pc (the number of peaks having a size of 0.5 μm or more contained per 1 cm) is Pc ≧ PPI / 2.54 + 10. Are listed.
Furthermore, Patent Document 4 describes a highly corrosion-resistant hot-dip galvanized steel sheet in which the glossiness of the plating layer is increased as a whole and the appearance uniformity is improved by refining the ternary eutectic structure of _{Al / MgZn 2 / Zn.} Is described.
However, a technique for improving the durability and not lowering the corrosion resistance when characters or the like appear on the surface of the plating layer has not been known conventionally.

Japanese Patent No. 5043234 Japanese Patent No. 5141899 Japanese Patent No. 360804 International Publication No. 2013/002358

The present invention has been made in view of the above circumstances, and provides a hot-dip galvanized steel sheet capable of displaying characters, designs, etc. on the surface of a plating layer, having excellent durability thereof, and also having excellent corrosion resistance. That is the issue.

The gist of the present invention is as follows.
[1] A steel plate and a hot-dip galvanized layer formed on the surface of the steel plate are provided.
The hot-dip plating layer is
In average composition, Al: 4% by mass or more and less than 25% by mass, Mg: 0% by mass or more and less than 10% by mass, and the balance contains Zn and impurities.
The metal structure includes [Al phase] and [ternary eutectic structure of _{Al / Zn / MgZn 2].}
The hot-dip galvanized layer includes a first region and a second region.
The first region and the second region satisfy either one of the following (a) or (b).
A Zn—Al—Mg-based hot-dip galvanized steel sheet in which the first region or the second region is arranged so as to have a predetermined shape.
(A) The first region is a region in which the average length of the [Al phase] on the surface of the hot-dip plating layer is 200 μm or more, and the second region is the [Al phase] on the surface of the hot-dip plating layer. ] Is a region where the average length is less than 200 μm.
(B) In the first region, the length Le at which the _{[ternary eutectic structure of Al / Zn / MgZn 2} ] faces the steel sheet at the boundary between the steel sheet and the hot-dip galvanized layer is the length of the boundary. The region is more than 0.3 with respect to L, and in the second region, the [ _{ternary eutectic structure of Al / Zn / MgZn 2} ] is the same as that of the steel sheet at the boundary between the steel sheet and the hot-dip galvanized layer. The opposite length Le is a region of 0.3 or less with respect to the boundary length L.
[2] When the first region and the second region are the above (b), the X-ray diffraction intensity I (200) of the (200) plane of the [Al phase] on the surface of the hot-dip galvanized layer. The Zn—Al—Mg-based hot-dip galvanized steel sheet according to [1], wherein the ratio I (200) / I (111) of the X-ray diffraction intensity I (111) on the (111) plane is 0.8 or more.
[3] The first region or the second region has a shape obtained by any one of a straight line portion, a curved portion, a figure, a number, a symbol, a pattern or a character, or a combination of two or more of them. The Zn—Al—Mg-based hot-dip galvanized steel sheet according to [1] or [2], which is arranged.
[4] The Zn—Al—Mg-based hot-dip galvanized steel sheet according to any one of [1] to [3], wherein the first region or the second region is intentionally formed.
[5] The Zn—Al—Mg-based melt according to any one of [1] to [4], wherein the hot-dip galvanized layer further contains Si: 0.0001 to 2% by mass in an average composition. Plated steel plate.
[6] The hot-dip galvanized layer further contains 0.0001 to 2% by mass of any one or more of Ni, Ti, Zr, and Sr in total in an average composition [1] to [1] to [ 5] The Zn—Al—Mg-based hot-dip galvanized steel sheet according to any one of the items.
[7] The hot-dip galvanized layer further has an average composition of any one of Sb, Pb, Sn, Ca, Co, Mn, P, B, Bi, Cr, Sc, Y, REM, Hf, and C. The Zn—Al—Mg-based hot-dip galvanized steel sheet according to any one of [1] to [6], which contains two or more types in a total amount of 0.0001 to 2% by mass.
[8] The Zn—Al—Mg-based hot-dip galvanized steel sheet according to any one of [1] to [7], wherein the amount of adhesion of the hot-dip galvanized layer is 30 to 600 g / m ^{2 in total on both sides of the steel sheet.}

According to the present invention, when characters, designs, etc. appear on the surface of a hot-dip galvanized layer, it is possible to provide a hot-dip galvanized steel sheet having excellent durability and corrosion resistance.

It is a figure explaining the method of measuring the magnitude of the Al phase of the Zn—Al—Mg-based hot-dip galvanized steel sheet which is an example of this embodiment. No. It is a photograph which shows the observation result by the scanning electron microscope of the first region of 1-4. No. It is a photograph which shows the observation result by the scanning electron microscope of the 2nd region of 1-4. It is a photograph which shows an example of the Zn—Al—Mg-based hot-dip galvanized steel sheet of Example 1. No. It is a cross-sectional photograph by a scanning electron microscope in the first region of 2-1. No. It is a cross-sectional photograph by a scanning electron microscope in the second region of 2-1. It is a photograph which shows an example of the surface of the hot-dip galvanized layer of the Zn—Al—Mg-based hot-dip galvanized steel sheet of Example 2, and is the photograph which shows the state which showed the predetermined pattern by the 2nd region.

Hereinafter, embodiments of the present invention will be described.
In the present specification, the numerical range represented by using "-" means a range including the numerical values before and after "-" as the lower limit value and the upper limit value.

The Zn—Al—Mg-based hot-dip galvanized steel sheet of the present embodiment includes a steel sheet and a hot-dip galvanized layer formed on the surface of the steel sheet, and the hot-dip galvanized layer has an average composition of Al: 4% by mass or more and 25% by mass. Less than, Mg: 0% by mass or more and less than 10% by mass, the balance contains Zn and impurities, and the metal structure is [Al phase] and [Al / Zn / MgZn ₂ ternary eutectic structure]. Including. The hot-dip galvanized layer includes a first region and a second region, the first region and the second region satisfy either one of the following (a) or (b), and the first region or the second region It is arranged so as to have a predetermined shape.
(A) The first region is a region in which the average length of the [Al phase] on the surface of the hot-dip plating layer is 200 μm or more, and the second region is a region in which the average length of the [Al phase] on the surface of the hot-dip plating layer is 200 μm or more. It is a region of less than 200 μm.
_{(B) In the first region, the length Le at which the [ternary eutectic structure of Al / Zn / MgZn 2} ] faces the steel sheet at the boundary between the steel sheet and the hot-dip galvanized layer is 0 with respect to the boundary length L. The region exceeds .3, and the second region is the length Le at which the _{[ternary eutectic structure of Al / Zn / MgZn 2} ] faces the steel sheet at the boundary between the steel sheet and the hot-dip galvanized layer, and the length of the boundary. It is a region of 0.3 or less with respect to L.

In the Zn—Al—Mg hot-dip galvanized steel sheet of the present embodiment, preferably, the first region or the second region is a straight portion, a curved portion, a figure, a number, a symbol, a pattern or a character, or any one of these. It is arranged so as to form a combination of two or more of them. The first region or the second region is intentionally formed.

Here, the [Al phase] is a _{phase that looks like an island with a clear boundary in the base material of [Al / Zn / MgZn 2} ternary eutectic structure], and this is, for example, the three of Al-Zn-Mg. It corresponds to the "Al" phase at high temperature in the original equilibrium diagram (an Al solid solution that dissolves Zn and contains a small amount of Mg), and is distinguished from Al in the ternary eutectic structure. Hereinafter, in this embodiment, it is referred to as [Al phase].

<Steel plate>
The material of the steel sheet used as the base of the hot-dip plating layer is not particularly limited. Although details will be described later, as the steel sheet, general steel or the like can be used, and Al killed steel or some high alloy steel can also be used. Further, the shape of the steel plate is not particularly limited. By applying the hot-dip galvanizing method described later to the steel sheet, the hot-dip galvanizing layer according to the present embodiment is formed.

<Hot-dip galvanized layer>
(Chemical composition)
Next, the chemical composition of the hot-dip galvanized layer will be described.
The hot-dip galvanized layer contains Al: 4% by mass or more and less than 25% by mass, Mg: 0% by mass or more and less than 10% by mass, and Zn and impurities as a balance in the average composition. The hot-dip galvanized layer preferably contains 4 to 22% by mass of Al and 1 to 10% by mass of Mg in an average composition, and is composed of Zn and impurities as the balance.
The hot-dip galvanized layer may contain Si: 0.0001 to 2% by mass in average composition. The hot-dip galvanized layer may contain 0.0001 to 2% by mass in total of any one or more of Ni, Ti, Zr, and Sr in an average composition. The hot-dip galvanized layer has an average composition of any one or more of Sb, Pb, Sn, Ca, Co, Mn, P, B, Bi, Cr, Sc, Y, REM, and Hf, and is 0 in total. It may contain .0001 to 2% by mass.

[Al: 4% by mass or more and less than 25% by mass]
The content of Al in the hot-dip galvanized layer is 4% by mass or more and less than 25% by mass, preferably 4.0% by mass or more and less than 25.0% by mass in the average composition. Al is an element necessary for ensuring corrosion resistance. If the Al content in the hot-dip galvanized layer is less than 4% by mass, the effect of improving the corrosion resistance is insufficient, and the [Al phase] is not sufficiently formed, which is not preferable for ensuring the design. If it is 25% by mass or more, [Al phase] is excessively formed, which is not preferable for ensuring the design. The Al content in the hot-dip galvanized layer may be 5 to 22% by mass, 5.0 to 22.0% by mass, or 5 to 18% by mass from the viewpoint of corrosion resistance. It may be 5.0 to 18.0% by mass, and may be 6 to 16% by mass. It may be 6.0 to 16.0% by mass.

[Mg: 0% by mass or more and less than 10% by mass]
The content of Mg in the hot-dip galvanized layer may be 0% by mass or more and less than 10% by mass in the average composition, and may be 0% by mass or more and less than 10.0% by mass in the average composition. It is preferably 1% by mass or more and less than 10% by mass, and preferably 1% by mass or more and less than 10.0% by mass. Mg may be added to improve corrosion resistance. When the Mg content in the hot-dip galvanized layer is 1% by mass or more, the effect of improving the corrosion resistance becomes more sufficient, which is preferable. Further, when Mg is 10% by mass or more, the Mg compound crystallizes, which is not preferable for ensuring the design, and dross is significantly generated in the plating bath, making it difficult to stably produce a hot-dip galvanized steel sheet. Therefore, it is not preferable. From the viewpoint of the balance between corrosion resistance and suppression of dross generation, the Mg content in the hot-dip galvanized layer may be 1.5 to 6% by mass, 1.5 to 6.0% by mass, or 2 to 5%. It may be mass%, or may be 2.0 to 5.0 mass%.

The hot-dip galvanized layer may contain Si in the range of 0.0001 to 2% by mass, preferably 0.0001 to 2.000% by mass. Si is an element effective for improving the adhesion of the hot-dip galvanized layer.
Since the effect of improving the adhesion is exhibited by containing 0.0001% by mass or more of Si in the hot-dip plating layer, it is preferable to contain 0.0001% by mass or more of Si.
On the other hand, even if the content exceeds 2% by mass, the effect of improving the plating adhesion is saturated. Therefore, even when the hot-dip galvanizing layer contains Si, the Si content is set to 2% by mass or less.
From the viewpoint of plating adhesion, the Si content in the hot-dip plating layer may be 0.0010 to 1% by mass, 0.0010 to 1.000% by mass, or 0.0100 to 0.8% by mass. It may be 0.0100 to 0.800 mass%.

The hot-dip galvanized layer may contain one or more of Ni, Ti, Zr, and Sr in total in an average composition of 0.0001 to 2% by mass, preferably 0.0001 to 0.0001. It may contain 2.00% by mass. The intermetallic compound containing these elements acts as a crystallizing nucleus of the [Al phase] to make the [Al / MgZn ₂ / Zn ternary eutectic structure] finer and more uniform, and to improve the appearance of the hot-dip plating layer. Improves smoothness. If the content of these elements in the hot-dip galvanized layer is less than 0.0001% by mass, the effect of making the solidified structure finely uniform becomes insufficient, which is not preferable. Further, when the content of these elements in the hot-dip galvanized layer exceeds 2% by mass, _{the effect of refining the [ternary eutectic structure of Al / MgZn 2} / Zn] is saturated, and the surface of the hot-dip galvanized layer is saturated. It is not preferable because the roughness becomes large and the appearance becomes poor.
In particular, when the above-mentioned elements are added for the purpose of improving the appearance of the hot-dip galvanized layer, the content of the above-mentioned elements is preferably 0.001 to 0.5% by mass, preferably 0.001 to 0.50% by mass, and 0. It is more preferably 0.001 to 0.05% by mass, and even more preferably 0.002 to 0.01% by mass.

In the hot-dip galvanized layer, one or more of Sb, Pb, Sn, Ca, Co, Mn, P, B, Bi, Cr, Sc, Y, REM, and Hf are contained in a total of 0. It may contain 0001 to 2% by mass, preferably 0.0001 to 2.00% by mass. When the hot-dip galvanized layer contains these elements, the corrosion resistance can be further improved.
REM refers to one or more rare earth elements having atomic numbers 57 to 71 in the periodic table.

The rest of the chemical composition of the hot-dip galvanized layer is zinc and impurities. Impurities include those that are inevitably contained in zinc and other bullions, and those that are contained by melting steel in a plating bath. In addition, Fe derived from the alloy layer generated at the interface between the plating layer and the steel when the plating is melted may be measured.

The average composition of the hot-dip galvanized layer can be measured by the following method. First, the surface coating film is removed with a coating film release agent that does not erode the plating (for example, Neo River SP-751 manufactured by Sansai Kako Co., Ltd.), and then a hot-dip plating layer is used with hydrochloric acid containing an inhibitor (for example, Hiviron manufactured by Sugimura Chemical Industrial Co., Ltd.). Can be determined by dissolving the solution and subjecting the obtained solution to inductively coupled plasma (ICP) emission spectroscopic analysis. The concentration of hydrochloric acid may be, for example, 10% by mass. Further, when the surface layer coating film is not provided, the work of removing the surface layer coating film can be omitted.

(Metal structure)
Next, the metal structure of the hot-dip galvanized layer will be described. The hot-dip galvanized layer according to the present embodiment contains [Al phase] and [ternary eutectic structure of _{Al / Zn / MgZn 2] as a metal structure.}
Specifically, the hot-dip galvanized layer according to the present embodiment has a form in which [Al phase] is included in the base material of _{[Al / Zn / MgZn 2 ternary eutectic structure].}
_{Further, [MgZn 2} phase] and [Zn phase] may be contained in the base material of [Al / Zn / MgZn _{2 ternary eutectic structure].}
Further, when Si is added _{, [Mg 2} Si phase] may be contained in the base material of _{[Al / Zn / MgZn 2 ternary eutectic structure].}

[Tripartite eutectic structure of Al / Zn / MgZn _2]
Here, the [ternary eutectic structure of Al / Zn / MgZn ₂ ] is a ternary eutectic structure of the Al phase, the Zn phase and the metal compound MgZn ₂ phase, and is [Al / Zn / MgZn _2]. The Al phase forming the ternary eutectic structure] is, for example, the "Al" phase at high temperature in the ternary system equilibrium diagram of Al-Zn-Mg (Al solid solution that solid-dissolves Zn, and a small amount. Corresponds to (including Mg).
The Al ″ phase at high temperature usually appears as a fine Al phase and a fine Zn phase at room temperature. The Zn phase in [Al / Zn / MgZn ₂ ternary eutectic structure] is small. It is a Zn solid solution in which Al is solid-dissolved and, in some cases, a smaller amount of Mg is solid-dissolved. _{The MgZn two-} _{phase in [Al / Zn / MgZn 2} ternary eutectic structure] is a Zn—Mg binary system. Zn: An intermetallic compound phase existing in the vicinity of about 84% by mass in the equilibrium state diagram.
As far as the phase diagram is concerned, it is considered that other additive elements are not solid-solved in each phase, or even if they are solid-solved, the amount is extremely small. However, since the amount cannot be clearly distinguished by ordinary analysis, the ternary eutectic structure consisting of these three phases is referred to as [Al / Zn / MgZn ₂ ternary eutectic structure] in the present specification.

_{In the present embodiment, as will be described later, the length Le at which the [ternary eutectic structure of Al / Zn / MgZn 2} ] faces the steel sheet at the boundary between the steel sheet and the hot-dip galvanized layer is the length Le, and the length of the boundary in the first region. The region may be more than 0.3 with respect to the L, and may be 0.3 or less with respect to the boundary length L in the second region.

[Al phase]
The [Al phase] is a phase that looks like an island with a clear boundary in the base solution of [Al / Zn / MgZn ₂ ternary eutectic structure], and this is, for example, a ternary equilibrium of Al—Zn—Mg. It corresponds to the "Al" phase at high temperature in the phase diagram (an Al solid solution that dissolves Zn and contains a small amount of Mg). The amount of Zn and Mg that dissolves in the Al "phase at high temperature differs depending on the concentration of Al and Mg in the plating bath. The Al" phase at high temperature is usually a fine Al phase at room temperature. Although it separates from the fine Zn phase, the island-like shape seen at room temperature is considered to be due to the shape of the Al ″ phase at high temperature.
As far as the phase diagram is concerned, it is considered that other additive elements are not solid-solved in this phase, or even if they are solid-solved, the amount is extremely small. However, since it cannot be clearly distinguished by ordinary analysis, the phase derived from the Al ″ phase at high temperature and morphologically derived from the shape of the Al ″ phase is referred to as [Al phase] in the present specification.
The [Al phase] can be clearly distinguished from the Al phase forming [Al / Zn / MgZn _{2 ternary eutectic structure] by microscopic observation.}
In the present embodiment, as will be described later, when the first region and the second region satisfy the above (a), the average length of the [Al phase] is set to 200 μm or more in the first region and the second region. Then, it may be less than 200 μm.

[Zn phase]
The [Zn phase] is a _{phase that looks like an island with a clear boundary in the substrate of [Al / Zn / MgZn 2} ternary eutectic structure], and actually dissolves a small amount of Al and a small amount of Mg in a solid solution. I have something to do. As far as the phase diagram is concerned, it is considered that other additive elements are not solid-solved in this phase, or even if they are solid-solved, the amount is extremely small.
The [Zn phase] can be clearly distinguished from the Zn phase forming [Al / Zn / MgZn _{2 ternary eutectic structure] by microscopic observation.} The hot-dip galvanized layer according to the present embodiment may contain a [Zn phase] depending on the production conditions, but the effect on the corrosion resistance due to the [Zn phase] was hardly observed. Therefore, even if the hot-dip plating layer contains [Zn phase], there is no particular problem.

[MgZn _2- phase]
[MgZn _2- phase] is a phase that looks like an island with a clear boundary in the base material of [Al / Zn / MgZn ₂ ternary eutectic structure], and is actually a solid solution of a small amount of Al. Sometimes. As far as the phase diagram is concerned, it is considered that other additive elements are not solid-solved in this phase, or even if they are solid-solved, the amount is extremely small.
The [MgZn ₂ phase] and [Al / Zn / MgZn ₂ ternary eutectic structure] is formed by being MgZn ₂ phase, it can be clearly distinguished in microscopic observation. The hot-dip galvanized layer according to the present embodiment may _{not contain [MgZn 2-} phase] depending on the manufacturing conditions, but is contained in the hot-dip galvanized layer under most manufacturing conditions.

[Mg ₂ Si phase]
The [Mg ₂ Si phase] is a phase that looks like an island with a clear boundary in the solidified structure of the Si-added plating layer. As far as the _{phase diagram is concerned, it is considered that Zn, Al and other additive elements are not solid-solved in [Mg 2} Si phase], or even if they are solid-solved, they are in a very small amount. [Mg ₂ Si phase] can be clearly distinguished from other phases in the hot-dip galvanized layer by microscopic observation.

The hot-dip galvanized layer of the present embodiment is formed by immersing the steel sheet in a plating bath and then pulling it up, and then solidifying the molten metal adhering to the surface of the steel sheet. At this time, the [Al phase] is first formed, and then the [ternary eutectic structure of _{Al / Zn / MgZn 2] is formed as the temperature of the molten metal decreases.}
Chemical components of the molten plating layer (i.e., the chemical composition of the plating bath) may be, in the matrix of [Al / Zn / MgZn ₂ ternary eutectic structure], _[Mg 2 Si phase], [MgZn ₂ phase] or [Zn phase] may be formed.

(1st area and 2nd area)
Next, the first region and the second region of the hot-dip plating layer will be described. The hot-dip galvanized layer (surface of the hot-dip galvanized layer) according to the present embodiment has a first region and a second region. As will be described later, the first region and the second region can be distinguished with the naked eye, under a magnifying glass, or under a microscope.

The first region may represent a straight portion, a curved portion, or the like, and the second region may represent a straight portion, a curved portion, or the like. When the first region represents a straight line portion, a curved portion, or the like, the first region can be arranged so as to have a predetermined shape, and the other regions can be designated as the second region. When the second region represents a straight line portion, a curved portion, or the like, the second region can be arranged so as to have a predetermined shape, and the other region can be the first region.
The boundary between the first region and the second region can be grasped with the naked eye, under a magnifying glass or under a microscope.

When the first region is arranged so as to have a predetermined shape, the first region may be formed to a size that allows the existence of the first region to be discriminated with the naked eye, under a magnifying glass, or under a microscope. In this case, the second region is a region other than the first region in the hot-dip plating layer (surface of the hot-dip plating layer), and may occupy most of the hot-dip plating layer. Further, the first region may be arranged in the second region. Specifically, the first region is a shape in which one of a straight line portion, a curved portion, a figure, a number, a symbol, a pattern and a character, or a combination of two or more of them is used in the second region. It may be arranged so as to be. By adjusting the shape of the first region, the surface of the hot-dip galvanized layer is formed by any one of straight lines, curved lines, figures, numbers, symbols, patterns and letters, or a combination of two or more of them. Is revealed. This shape is an artificially formed shape, not a naturally formed one.

On the other hand, when the second region is arranged so as to have a predetermined shape, the second region is formed to a size that allows the existence of the second region to be discriminated with the naked eye, under a magnifying glass, or under a microscope. Good. In this case, the first region is a region other than the second region in the hot-dip plating layer (the surface of the hot-dip plating layer), and may occupy most of the hot-dip plating layer. Further, the second region may be arranged in the first region. Specifically, the second region is a shape in which one of a straight line portion, a curved portion, a figure, a number, a symbol, a pattern and a character, or a combination of two or more of them is used in the first region. It may be arranged so as to be. By adjusting the shape of the second region, the surface of the hot-dip galvanized layer is formed by any one of straight lines, curved lines, figures, numbers, symbols, patterns and letters, or a combination of two or more of them. Is revealed. This shape is an artificially formed shape, not a naturally formed one.

The first region and the second region are not limited to the naked eye, and may be distinguishable under a magnifying glass or a microscope. Specifically, the shape of the straight portion or the like composed of the first region or the second region may be identifiable in a field of view of 50 times or less. If the field of view is 50 times or less, the predetermined shape composed of the first region or the second region can be identified by the difference in the surface state.
The first region or the second region can be identified preferably 20 times or less, more preferably 10 times or less, and more preferably 5 times or less.

The first region and the second region satisfy either (a) or (b) below.
(A) The first region is a region in which the average length of the [Al phase] on the surface of the hot-dip plating layer is 200 μm or more, and the second region is a region in which the average length of the [Al phase] on the surface of the hot-dip plating layer is 200 μm or more. It is a region of less than 200 μm.
_{(B) In the first region, the length Le at which the [ternary eutectic structure of Al / Zn / MgZn 2} ] faces the steel sheet at the boundary between the steel sheet and the hot-dip galvanized layer is 0 with respect to the boundary length L. The region exceeds .3, and the second region is the length Le at which the _{[ternary eutectic structure of Al / Zn / MgZn 2} ] faces the steel sheet at the boundary between the steel sheet and the hot-dip galvanized layer, and the length of the boundary. It is a region of 0.3 or less with respect to L.
Hereinafter, the case (a) and the case (b) will be described in order.

(When the first region and the second region satisfy the above (a))
In the first region when the above (a) is satisfied, metallic luster due to the Al phase having a long average length is observed. Therefore, the gloss can be recognized linearly as compared with the second region. On the other hand, in the second region, the metallic luster is recognized as dots as compared with the first region due to the Al phase having a short average length. This makes the first and second regions distinguishable with the naked eye, under a magnifying glass or under a microscope.

At least [Al phase] and [ _{ternary eutectic structure of Al / Zn / MgZn 2} ] are present in the hot-dip galvanized layer. The hot-dip galvanized layer has a form in which [Al phase] is included in the base material of _{[Al / Zn / MgZn 2 ternary eutectic structure].} The [Al phase] is precipitated relatively early when the hot-dip plating layer is solidified, and the morphology of the [Al phase] at that time is dendritic.

When the above (a) is satisfied, the average length of the [Al phase] existing in the first region is 200 μm or more.
When the average length of the [Al phase] is 200 μm or more, relatively large dendritic crystals of the [Al phase] are exposed on the surface of the hot-dip galvanized layer, and the surrounding [Al / Zn / MgZn ₂ ternary elements] are exposed. The [Al phase], which has a metallic luster, is longer than that of the [eutectic structure], and the unevenness becomes clear, so that it can be visually recognized linearly as a whole.

On the other hand, the average length of the [Al phase] existing in the second region is less than 200 μm. When the average length of the [Al phase] is less than 200 μm, relatively small dendritic crystals of the [Al phase] are exposed on the surface of the hot-dip galvanized layer, and the surrounding [Al / Zn / MgZn ₂ ternary elements] are exposed. Since the [Al phase], which has a metallic luster, is shorter than that of the [eutectic structure] and the unevenness is unclear, it can be visually recognized as dots as a whole. The second region is preferably a region in which the average length of the [Al phase] is 180 μm or less, and more preferably a region in which the average length of the [Al phase] is less than 150 μm. The larger the difference between the average length of the [Al phase] in the first region and the average length of the [Al phase] in the second region, the easier it is to distinguish between the first region and the second region, which is preferable.

It is presumed that the first region is formed by the formation of the [Al phase] at a relatively low number density at the initial stage of solidification of the hot-dip plating layer and the coarsening of the [Al phase] itself. Further, the second region is formed by forming the [Al phase] at a relatively high number density at the initial stage of solidification of the hot-dip plating layer, and the [Al phase] itself does not become coarse and remains fine. It is presumed to be.

In order to control the size of the [Al phase], the cooling rate of the molten metal may be controlled when the hot-dip plating layer is solidified. Specifically, when the [Al phase] is coarsened, the cooling rate during solidification should be slowed down, and when the [Al phase] is miniaturized, the cooling rate during solidification should be increased. When the steel sheet is immersed in the hot-dip galvanizing bath and then pulled up, the cooling rate of the molten metal on the surface of the steel sheet is partially increased or decreased, so that straight parts, curved parts, figures, numbers, symbols, patterns and A shape obtained by combining any one of the characters or two or more of them can be intentionally or artificially expressed by a manufacturing method described later.

The average length of the [Al phase] is measured by the following method. First, on each of the first region and the second region of the surface of the hot-dip galvanized layer, regions of arbitrary three fields of view are photographed with a reflected electron image of a scanning electron microscope. The size of each region is a rectangular region of 500 μm × 360 μm. In the photograph taken, the dendritic Al phase is confirmed. As shown in FIG. 1, the dendritic Al phase generally has a shape having a main shaft portion and a secondary arm portion extending from the main shaft portion. For the Al phase in the photograph, the length A in the longitudinal direction is measured. The lengths A of all Al phases are obtained in the three fields of view, and the average value thereof is taken as the average length of the Al phases in the first region or the second region. The dendritic Al phase often grows radially from the solidified nucleus, but it is not always arranged in the same plane, and when observing from the surface, only a part thereof, for example, the tip of the secondary arm is observed. Or, only the spindle may be observed. Such Al phase is excluded from the measurement target. On the other hand, those that can be observed as if another phase overlaps between the main shaft and the secondary arm and are not connected are targeted.

(When the first region and the second region satisfy the above (b))
When the above (b) is satisfied, the first region has a low metallic luster on the surface thereof and is relatively white or gray as compared with the second region. On the other hand, the second region is a region in which the metallic luster of the surface thereof is relatively higher than that of the first region. This makes the first and second regions distinguishable with the naked eye, under a magnifying glass or under a microscope.

When the above (b) is satisfied, in the first region, the length Le at which the _{[ternary eutectic structure of Al / Zn / MgZn 2} ] faces the steel sheet at the boundary between the steel sheet and the hot-dip galvanized layer is the boundary length. It is a region of more than 0.3, preferably more than 0.30 with respect to L. _{As a result, [Al / Zn / MgZn 2} ternary eutectic structure] is relatively abundant on the steel sheet side in the thickness direction of the hot-dip galvanized layer in the first region, and [Al phase] and other phases or structures are present. Relatively less. As a result, a relatively large amount of dendritic [Al phase] is present on the surface side of the hot-dip galvanized layer in the thickness direction. Therefore, it is presumed that the surface roughness Ra of the surface of the first region becomes relatively large, the light incident on the first region is diffusely reflected, and the surface becomes relatively white to gray as compared with the second region. Will be done.

_{In the first region, the length Le at which the [ternary eutectic structure of Al / Zn / MgZn 2} ] faces the steel sheet at the boundary between the steel sheet and the hot-dip galvanized layer is preferably 0.30 with respect to the boundary length L. It's super. That is, Le / L in the first region is preferably more than 0.30.

On the other hand, in the second region, the length Le at which the _{[ternary eutectic structure of Al / Zn / MgZn 2} ] faces the steel sheet at the boundary between the steel sheet and the hot-dip galvanized layer is 0. It is a region of 3 or less, more preferably 0.30 or less. _{As a result, [Al / Zn / MgZn 2} ternary eutectic structure] is relatively small on the steel sheet side in the thickness direction of the hot-dip galvanized layer in the second region, and [Al phase] and other phases or structures are present. It will be relatively large. As a result, relatively few dendritic [Al phases] are present on the surface side of the hot-dip galvanized layer in the thickness direction. Therefore, it is presumed that the surface roughness Ra of the surface of the second region is relatively small, and that the second region exhibits a metallic luster relatively as compared with the first region.

_{In the second region, the length Le at which the [ternary eutectic structure of Al / Zn / MgZn 2} ] faces the steel sheet at the boundary between the steel sheet and the hot-dip galvanized layer is preferably 0.30 with respect to the boundary length L. The region is as follows, more preferably 0.15 or less, still more preferably 0.1 or less, and particularly preferably 0.10 or less. The larger the difference between Le / L in the first region and Le / L in the second region, the easier it is to distinguish between the first region and the second region, which is preferable.

The [Al phase] generated during solidification of the hot-dip galvanized layer is usually deposited in the entire thickness direction of the hot-dip galvanized layer. However, the surface of the hot-dip galvanized layer is formed by intentionally or artificially controlling the length Le _{of the [Al / Zn / MgZn 2} ternary eutectic structure] facing the steel sheet at the boundary between the steel sheet and the hot-dip galvanized layer. The abundance ratio of [Al phase] in Since the [Al phase] has the form of dendritic crystals, the surface roughness of the hot-dip galvanized layer increases as the abundance ratio of the [Al phase] on the surface of the hot-dip galvanized layer increases, while the surface roughness of the hot-dip galvanized layer increases. When the abundance ratio of [Al phase] on the surface becomes small, the surface roughness of the hot-dip galvanized layer becomes small. _{In this way, by controlling the length Le of [Al / Zn / MgZn 2} ternary eutectic structure] facing the steel sheet at the boundary between the steel sheet and the hot-dip galvanized layer, the first surface of the hot-dip galvanized layer is Regions and second regions can be formed.

When an interfacial alloy layer containing Fe and Zn is formed at the boundary between the steel sheet and the hot-dip galvanized layer, [Al / Zn / MgZn ₂ ternary eutectic structure] faces the steel sheet via the interfacial alloy layer. The length Le to be formed may be set within the above range. However, since the interfacial alloy layer is very thin compared to the thickness of the hot-dip galvanized layer, as described below, when measuring the length Le with a microscope, the interface is dependent on the magnification at the time of measurement. In some cases, the alloy layer cannot be confirmed and the interface between the steel sheet and the hot-dip galvanized layer can be confirmed.
_{In this case, in the first region, the length Le at which the [ternary eutectic structure of Al / Zn / MgZn 2} ] faces the steel sheet at the interface between the steel sheet and the hot-dip galvanized layer is 0 with respect to the interface length L. The region may be more than .3. Further, in the second region, the length Le at which the _{[ternary eutectic structure of Al / Zn / MgZn 2} ] faces the steel sheet at the interface between the steel sheet and the hot-dip galvanized layer is 0. The area may be 3 or less.

At the boundary (interface) between the steel sheet and the hot-dip galvanized layer, the ratio of the length Le in which the _{[ternary eutectic structure of Al / Zn / MgZn 2] faces the steel sheet with respect to the length L of the boundary (interface) is as follows.} It can be measured by such a method. First, the cross section of the Zn—Al—Mg-based hot-dip galvanized steel sheet in the plate thickness direction is exposed. There are five cross sections for each of the first region and the second region. Each cross section is photographed with a scanning electron microscope. In each cross section, a region having a length of 150 μm is arbitrarily selected from the boundary (interface) between the steel plate and the hot-dip galvanized layer. This length is defined as the boundary length L (interface length L). _{Then, the [ternary eutectic structure of Al / Zn / MgZn 2} ] is confirmed in the range of the selected boundary (interface) length, and all [Al / Zn / at the boundary (interface) between the steel sheet and the hot-dip galvanized layer). The total length Le of MgZn ₂ ternary eutectic structure] is measured to determine Le / L. Le / L was obtained from each of the five cross sections of the first region and the second region, and the average thereof was [Al / Zn] with respect to the length L of the boundary (interface) at the boundary (interface) between the steel sheet and the hot-dip galvanized layer. / MgZn ₂ ternary eutectic structure] is the ratio of the length Le facing the steel sheet.

The [Al phase] generated during solidification of the hot-dip galvanized layer is usually deposited in the entire thickness direction of the hot-dip galvanized layer. However, if a substance that becomes a solidified nucleus is arranged in advance on the surface of the steel sheet, in the region where the solidified nucleus is arranged, when the molten metal adhering to the surface of the steel sheet solidifies, the solidified nucleus on the surface of the steel sheet becomes a nucleus and a large number of Al phase] precipitates. The generated [Al phase] segregates on the side relatively close to the steel sheet.
Further, in the region where the solidified nuclei are arranged, the [Al phase] is generated at a relatively high density, so that the [Al phase] itself does not become coarse and remains fine. Therefore, in the region where the solidified nuclei are arranged, the [Al phase] does not grow to the surface side of the hot-dip galvanized layer, and a large amount of the [Al phase] is deposited near the boundary (interface) between the steel sheet and the hot-dip galvanized layer. _{As a result, the amount of precipitation of [Al / Zn / MgZn 2} ternary eutectic structure] in the region where the solidified nuclei are arranged is reduced, and [Al / Zn / MgZn 2 of _{[Al / Zn / MgZn 2]} with respect to the length L of the boundary (interface) is reduced. The ratio of the length Le in which the ternary eutectic structure] faces the steel plate becomes small.

In the case of (b) above, the region where the solidified nuclei are present on the surface of the steel sheet is the second region of the hot-dip galvanized layer, and the region where the solidified nuclei are not present is the first region of the hot-dip galvanized layer. Further, since the second region is formed by the mechanism as described above, solidified nuclei may be present at the boundary (interface) between the steel plate and the hot-dip galvanized layer in the second region. More specifically, at the boundary (intersection) between the steel plate in the second region and the hot-dip plating layer, carbon (C), nickel (Ni), calcium (Ca), boron (B), phosphorus (P), titanium ( One or more of the elements selected from the group consisting of Ti), manganese (Mn), iron (Fe), cobalt (Co), zirconium (Zr), molybdenum (Mo), and tungsten (W). Alternatively, there may be a compound containing any one or more of the above-mentioned elements.

To confirm the presence of the above-mentioned elements or compounds at the boundary (interface) between the steel sheet and the hot-dip plating layer, a steel sheet in the second region is used while digging a sample by sputtering using a glow discharge emission spectrophotometer (GDS). It can be confirmed by performing elemental analysis at the boundary between the and the hot-dip plating layer.

As described above, before immersing the steel sheet in the hot-dip galvanizing bath, the shape of the surface of the steel sheet is one of straight parts, curved parts, figures, numbers, symbols and letters, or a combination of two or more of them. By arranging the solidified nuclei in, a second region having these shapes can be formed in the hot-dip galvanized layer.

Further, before immersing the steel sheet in the hot-dip galvanizing bath, the area excluding the shape obtained by combining one of straight lines, curved lines, figures, numbers, symbols and letters or two or more of these on the surface of the steel sheet. By arranging the solidified nuclei in the hot-dip galvanized layer, a first region having these shapes can be formed in the hot-dip galvanized layer.

Further, in the case of (b) above, the ratio of the X-ray diffraction intensity I (200) on the (200) plane and the X-ray diffraction intensity I (111) on the (111) plane of the Al phase on the surface of the hot-dip galvanized layer. I (200) / I (111) is preferably 0.8 or more, and more preferably 0.80 or more. The ratio I (200) / I (111) is preferably 0.8 or more, more preferably 0.80 or more, regardless of the first region and the second region.

As the ratio I (200) / I (111) increases, the number of [Al phase] in which the (200) plane is parallel to the surface of the hot-dip plating layer increases, and the (111) plane becomes hot-dip galvanized. There is less [Al phase] parallel to the surface of the layer. As a result, when viewed from the surface of the hot-dip galvanized layer, there are many dendritic crystals that look like a cross, and few dendritic crystals that look like a hexagon. In the process of solidification of the hot-dip plating layer from the molten state, when the [Al phase] precipitated as primary crystals grows in a cross shape from the crystal nuclei when viewed from the plating surface side, the angle between the branches. Is widened, and a flow path of the melt is easily formed in the direction perpendicular to the plating surface, and the [Al phase] on the plating surface _{is covered with the [Al / Zn / MgZn 2} ternary eutectic structure] that solidifies at the end. It becomes easy to be damaged. As a result, as the ratio I (200) / I (111) increases, the surface becomes metallic luster. This makes it possible to improve the overall appearance of the hot-dip galvanized layer. _{Further, in the first region, there are many [ternary eutectic structures of Al / Zn / MgZn 2} ] near the boundary (interface) in the plate thickness direction, and therefore many [Al phase] are present near the surface. There is a tendency. On the other hand, the second region is the opposite. In a place where a large amount of [Al phase] is present on the surface, the metallic luster is further emphasized for the above reason, so that the first region and the second region can be distinguished more clearly.

The ratio I (200) / I (111) on the surface of the hot-dip galvanized layer can be controlled by adjusting the cooling rate after the plating layer is formed.

<Chemical conversion coating film layer and coating film layer>
The Zn—Al—Mg-based hot-dip galvanized steel sheet according to the present embodiment may have a chemical conversion treatment film layer or a coating film layer on the surface of the hot-dip galvanized layer. Here, the type of the chemical conversion-treated film layer or the coating film layer is not particularly limited, and a known chemical conversion-treated film layer or coating film layer can be used.

[Manufacturing method of Zn-Al-Mg-based hot-dip galvanized steel sheet]
Hereinafter, a method for producing a Zn—Al—Mg-based hot-dip galvanized steel sheet of the present embodiment will be described. In the following description, the case where the first region and the second region satisfy the above (a) or (b) will be sequentially described.

(Manufacturing method when the first region and the second region satisfy the above (a))
In the manufacturing method when the first region and the second region satisfy the above (a), first, a hot-rolled steel sheet is manufactured, and if necessary, hot-rolled sheet is annealed. After pickling, cold rolling is performed to obtain a cold rolled plate. After degreasing and washing the cold-rolled plate with water, it is annealed (annealed by cold-rolled plate), and the cold-rolled plate after annealing is immersed in a hot-dip galvanizing bath to form a hot-dip plating layer. The hot-dip galvanizing method may be a continuous hot-dip galvanizing method in which a steel sheet is continuously passed through a hot-dip galvanizing bath. But it may be.

The hot-dip galvanizing bath preferably contains Al: 4% by mass or more and less than 25% by mass, Mg: 0% by mass or more and less than 10% by mass, and Zn and impurities as the balance. Further, the hot-dip galvanizing bath may contain Al: 4 to 22% by mass and Mg: 1 to 10% by mass, and the balance may contain Zn and impurities. Further, the hot-dip galvanizing bath may contain Si: 0.0001 to 2% by mass. Furthermore, the hot-dip galvanizing bath is any one or 2 of Ni, Ti, Zr, Sr, Sb, Pb, Sn, Ca, Co, Mn, P, B, Bi, Cr, Sc, Y, REM, and Hf. A total of 0.001 to 2% by mass of seeds or more may be contained. The average composition of the hot-dip galvanized layer of the present embodiment is almost the same as the composition of the hot-dip galvanized bath.

The temperature of the hot-dip galvanizing bath varies depending on the composition, but is preferably in the range of 400 to 500 ° C., for example. This is because if the temperature of the hot-dip galvanizing bath is within this range, a desired hot-dip galvanizing layer can be formed.
Further, the amount of adhesion of the hot-dip galvanized layer may be adjusted by means such as gas wiping with respect to the steel sheet pulled up from the hot-dip galvanized bath. The amount of adhesion of the hot-dip plating layer is preferably adjusted so that the total amount of adhesion on both sides of the steel sheet is in ^{the range of 30 to 600 g / m 2.} If the adhesion amount is ^{less than 30 g / m 2} , the corrosion resistance of the hot-dip galvanized steel sheet is lowered, which is not preferable. If the amount of adhesion exceeds 600 g / m ^2, the molten metal adhering to the steel sheet will hang down and the surface of the hot-dip plating layer cannot be smoothed, which is not preferable.

In order to form the first region and the second region that satisfy the above (a), after adjusting the amount of adhesion of the hot-dip galvanized layer, the entire steel sheet is cooled and the non-oxidizing gas with respect to the molten metal. Is locally sprayed by a gas nozzle. As the non-oxidizing gas, it is preferable to use a non-oxidizing gas such as nitrogen or argon.

In order to make the first region have a predetermined shape, the average cooling rate between the bath temperature and 345 ° C. is set to 10 ° C./sec for almost the entire hot-dip galvanized layer for the formation of the second region. Cool with the above. Further, for the formation of the first region, the average cooling rate between the bath temperature and 345 ° C. is cooled to a part of the hot-dip galvanized layer at a rate slower than that of the second region, which is less than 8 ° C./sec. ..

More preferably, blast cooling or mist cooling is performed on almost the entire hot-dip galvanized layer for the formation of the second region while keeping the average cooling rate between the bath temperature and 345 ° C. at 15 ° C./sec or higher. A part of the hot-dip galvanized layer is allowed to cool (leave) without cooling for the formation of the first region, or a relatively high temperature non-oxidizing gas is sprayed from the bath temperature to 345 ° C. The average cooling rate during that period shall be 5 ° C./sec or less. The temperature of the non-oxidizing gas in this case may be, for example, in the range of 100 to 300 ° C. However, the temperature of the non-oxidizing gas need not be limited as long as the above average cooling rate can be satisfied.

Further, in order to make the second region have a predetermined shape, in order to form the first region, the average cooling rate between the bath temperature and 345 ° C. is set to 8 ° C. with respect to almost the entire hot-dip galvanized layer. Cool at / sec or less. Further, for the formation of the second region, the average cooling rate between the bath temperature and 345 ° C. is cooled to a part of the hot-dip galvanized layer at 10 ° C./sec or more, which is faster than the first region. ..

More preferably, for the formation of the first region, almost the entire hot-dip galvanized layer is allowed to cool so that the average cooling rate between the bath temperature and 345 ° C. is 5 ° C./sec or less, while the formation of the second region is performed. Therefore, by spraying a relatively low temperature non-oxidizing gas onto a part of the hot-dip galvanized layer, the average cooling rate between the bath temperature and 345 ° C. is set to 15 ° C./sec or more. Cooling of the first region may be performed in an atmosphere of 50 to 150 ° C. in order to reduce the cooling rate. Further, the temperature of the non-oxidizing gas when cooling the second region may be, for example, in the range of 10 to 30 ° C., or may be a mist gas containing water droplets. However, if the above average cooling rate can be satisfied, the ambient temperature and the temperature of the non-oxidizing gas at the time of cooling the first region need not be limited.

(Manufacturing method when the first region and the second region satisfy the above (b))
In the manufacturing method when the first region and the second region satisfy the above (b), solidified nuclei are arranged on the steel sheet in a predetermined pattern, then the steel sheet is immersed in a hot-dip galvanizing bath and then pulled up, and then pulled up. A Zn—Al—Mg-based hot-dip galvanized steel sheet is manufactured by cooling and solidifying the hot-dip galvanized layer.

First, a hot-rolled steel sheet is manufactured, and if necessary, hot-rolled sheet is annealed. After pickling, cold rolling is performed to obtain a cold rolled plate. After degreasing and washing the cold-rolled plate with water, it is annealed (annealed by cold-rolled plate), and the cold-rolled plate after annealing is immersed in a hot-dip galvanizing bath to form a hot-dip plating layer.

Here, between cold rolling and immersion in a hot-dip galvanizing bath, solidified nuclei are attached to the surface of the steel sheet, and any one of straight parts, curved parts, figures, numbers, symbols and letters, or any of these, is attached. A pattern portion having a shape in which two or more of the above are combined is formed. Adhesion of solidified nuclei occurs either between cold rolling and cold-rolled sheet annealing, between cold-rolled sheet annealing and immersion in a hot-dip galvanizing bath, or just prior to the final annealing of cold-rolled sheet annealing. It is good to carry out.

The component that forms solidified nuclei (hereinafter, may be referred to as a solidified nuclei-forming component) is not particularly limited as long as it is a component that forms solidified nuclei in the process of solidifying the plating layer. Examples of the solidification nucleating component include carbon (C), nickel (Ni), calcium (Ca), boron (B), phosphorus (P), titanium (Ti), manganese (Mn), iron (Fe), and cobalt. Any one or more of the elements selected from the group consisting of (Co), zirconium (Zr), molybdenum (Mo), and tungsten (W), or any one or more of the above-mentioned elements. Examples include compounds containing. The above components may be used in combination of 1 or 2 or more. As an example of the method of adhering the solidified nuclei to the surface of the steel sheet, in addition to the solidified nucleation component itself, a method of containing the solidified nucleation component in an alloy foil, resin, surfactant, ink, oil, etc. and adhering to the surface of the steel sheet. Can be mentioned. These solidified nucleation components may be solids themselves, or may be dissolved or dispersed in water or an organic solvent. Alternatively, it may be contained in the ink as a pigment or a dye.

As a method of adhering the solidified nuclei to the surface of the steel sheet, for example, a method of transferring, applying, or spraying a material containing a solidified nucleation component to the surface of the steel sheet can be exemplified. For example, a foil transfer method using hot stamps and cold stamps, a printing method using various plates (gravure printing, flexographic printing, offset printing, silk printing, etc.), an inkjet method, a thermal transfer method using an ink ribbon, etc. , A general printing method can be used.

An example of a transfer method using an alloy foil is a method in which a heated silicon roll is pressed against the alloy foil to transfer it to the surface of the steel sheet while adhering the alloy foil containing the solidified nucleation component to the surface of the steel sheet.

As an example of a printing method using a plate, a rubber roll or a rubber stamp is attached to the surface of a steel plate while adhering an ink or a surfactant containing a component that becomes a solidification nucleus to a rubber roll or a rubber stamp having a printing pattern formed on the peripheral surface. A method of pressing to transfer the ink or the surfactant can be mentioned. With this method, the solidified nucleation-forming component can be efficiently adhered to the surface of the steel sheet that is continuously passed through.

The amount of coagulated nuclei attached is preferably in the range of, for example, 50 mg / m ² or more and 5000 mg / m ^{2 or less.} If the adhesion amount is ^{less than 50 mg / m 2} , the first region may not be formed to the extent that it can be discerned with the naked eye, a magnifying glass, or a microscope, which is not preferable. On the other hand, when the adhesion amount exceeds 5000 mg / m ² , the adhesion of the hot-dip plating layer may decrease, which is not preferable.

Next, the steel plate on which the pattern portion consisting of solidified nuclei is formed is immersed in a hot-dip galvanizing bath. The hot-dip galvanizing method may be a continuous hot-dip galvanizing method in which a steel sheet is continuously passed through a hot-dip galvanizing bath. But it may be.

The composition of the hot-dip galvanizing bath, the temperature of the hot-dip galvanizing bath, the adhering amount of the hot-dip plating layer, and the control method of the adhering amount may be the same as the manufacturing method when the first region and the second region satisfy the above (a).

In the manufacturing method when the first region and the second region satisfy the above (b), it is necessary to adjust the temperature at the time of wiping so that the hot-dip plating layer is still in a molten state after adjusting the adhesion amount. Further, after passing through wiping, rapid cooling is required to generate many Al-phase fine crystals during plating. On the other hand, in order to align the direction of solidification, it is necessary to maintain the solidified state for a certain period of time. Therefore, within 1 second after passing through the wiping, the temperature is cooled to a temperature lower than the temperature at which solidification starts (liquidus line temperature) and higher than the temperature at which the plating completely solidifies (solid phase line temperature). In order to sufficiently precipitate fine crystals, it is desirable to cool the fine crystals to a temperature 20 ° C. or higher lower than the liquidus temperature within 1 second.

Further, since it is also required that Al is preferentially precipitated, the temperature is rapidly higher than the temperature at _{which MgZn 2} phase is precipitated in addition to Al existing on the solid phase line (referred to as MgZn _{2 phase precipitation temperature line).} It is more desirable to stop cooling. By cooling to a temperature of (MgZn _2- phase precipitation temperature +5) ° C. or higher, only fine crystals of Al are generated, and it becomes easy to align the crystal orientation of Al. After that, in order to grow crystals, it is cooled to 300 ° C. or lower by slow cooling at an average cooling rate of less than 10 ° C./sec.

When a chemical conversion treatment layer is formed on the surface of the hot-dip plating layer after the hot-dip plating layer is formed, the hot-dip galvanized steel sheet after the hot-dip plating layer is formed is subjected to the chemical conversion treatment. The type of chemical conversion treatment is not particularly limited, and a known chemical conversion treatment can be used.
When a coating film layer is formed on the surface of the hot-dip plating layer or the surface of the chemical conversion treatment layer, the hot-dip galvanized steel sheet after the hot-dip plating layer is formed or the chemical conversion treatment layer is formed is coated. Perform processing. The type of coating treatment is not particularly limited, and a known coating treatment can be used.

As described above, in the Zn—Al—Mg-based hot-dip galvanized steel sheet of the present embodiment, the hot-dip galvanized layer includes a first region and a second region, and the first region and the second region are as follows (a). ) Or (b), the first region and the second region can be distinguished. Since the first region and the second region are not formed by printing or painting, the durability is high. Further, since the first region and the second region are not formed by printing or painting, there is no influence on the corrosion resistance of the hot-dip galvanized layer. Further, the first region and the second region are not formed by grinding or the like on the surface of the hot-dip plating layer. Therefore, the hot-dip galvanized steel sheet of the present embodiment has excellent corrosion resistance.

Further, according to the present embodiment, it is possible to provide a Zn—Al—Mg-based hot-dip galvanized steel sheet having high durability in the first region or the second region molded into a predetermined shape and having suitable plating characteristics such as corrosion resistance. In particular, the first area or the second area can be intentionally or artificially shaped, and any one of straight lines, curved lines, dots, figures, numbers, symbols, patterns or letters, or any of these. The first region or the second region can be arranged so as to form a shape in which two or more of the above are combined.

In the Zn—Al—Mg-based hot-dip galvanized steel sheet of the present embodiment, various designs, trademarks, and other identification marks can be displayed on the surface of the hot-dip galvanized layer without printing or painting. It is possible to improve the distinctiveness of the source and the design. Further, depending on the first region or the second region, information necessary for process control, inventory control, etc. and arbitrary information required by the consumer can be added to the Zn—Al—Mg-based hot-dip galvanized steel sheet. This can contribute to the improvement of the productivity of the Zn—Al—Mg-based hot-dip galvanized steel sheet.

Next, an embodiment of the present invention will be described.

(Example 1)
After degreasing and washing the steel sheet with water, reduction annealing, plating bath immersion, adhesion amount control, and cooling were performed to obtain the No. 1 shown in Tables 2A and 2B. The hot-dip galvanized steel sheets 1-1 to 1-21 were manufactured. For cooling after controlling the amount of adhesion, after pulling up the steel sheet from the plating bath and adjusting the amount of adhesion by gas wiping, nitrogen gas is locally sprayed onto the molten metal by a gas nozzle while cooling the entire steel sheet. It was. After that, it was cooled to completely solidify the molten metal. The blowing range of nitrogen gas was controlled so as to form a grid pattern at intervals of 50 mm. Table 1 shows the cooling conditions. The average cooling rates shown in Table 1 are all average cooling rates between the bath temperature and 345 ° C.

Cooling conditions A to C were used to express a grid pattern in the second region, and cooling conditions D were used to express a grid pattern in the first region. Further, the cooling conditions E and F were the patterns of the comparative examples.

Under the cooling condition A, the entire steel sheet was slowly cooled in an atmosphere of 120 ° C., and nitrogen gas at 30 ° C. was sprayed as a non-oxidizing gas.
Under the cooling condition B, nitrogen gas at 20 ° C. was sprayed as a non-oxidizing gas while allowing the entire steel sheet to cool.
Under the cooling condition C, nitrogen gas containing mist was sprayed as a non-oxidizing gas while allowing the entire steel sheet to cool.
Under the cooling condition D, the entire steel sheet was cooled with a nitrogen gas containing mist, and nitrogen gas at 250 ° C. was sprayed as a non-oxidizing gas.
Further, under the cooling condition E, the entire steel sheet was allowed to cool in nitrogen gas at 30 ° C., and nitrogen gas at 30 ° C. was sprayed as a non-oxidizing gas. Under the cooling condition F, the entire steel sheet was allowed to cool.

Further, a Zn-Al-Mg-based hot-dip galvanized steel sheet was manufactured in the same manner as above. Then, a grid pattern at intervals of 50 mm was printed on the surface of the hot-dip plating layer by an inkjet method. This result is referred to as No. It is shown in Table 2A and Table 2B as 1-22.

Further, a Zn-Al-Mg-based hot-dip galvanized steel sheet was manufactured in the same manner as above. Then, the surface of the hot-dip galvanized layer was ground to form a grid pattern at intervals of 50 mm. This result is referred to as No. It is shown in Table 2A and Table 2B as 1-23.

For the obtained galvanized steel sheet, the average length of the Al phase in the first region and the second region was determined. First, the boundary between the first region and the second region was identified by visually observing the surface of the hot-dip galvanized layer. In the case where the boundary is difficult to distinguish, the nitrogen gas spraying range is assumed to be the first region or the second region.

The average length of the [Al phase] was measured by the following method. First, on the surface of the hot-dip galvanized layer, in each of the first region and the second region, regions of arbitrary three fields of view were photographed by a reflected electron image of a scanning electron microscope. The size of each region was a rectangular region of 500 μm × 360 μm. In the photograph taken, a dendritic [Al phase] was confirmed. As shown in FIG. 1, the dendritic [Al phase] has a shape having a main shaft portion and a primary arm portion extending from the main shaft portion. For the [Al phase] in the photograph, the length A in the longitudinal direction was measured. The lengths A of all [Al phase] were determined in three fields of view, and the average value was taken as the average length of [Al phase] in the first region or the second region. The dendritic [Al phase] often grows radially from the solidified nucleus, but it is not always arranged in the same plane, and when observing from the surface, only a part thereof, for example, the tip of the arm is observed. Or, only the spindle may be observed. Such [Al phase] was excluded from the measurement targets. On the other hand, the measurement target was one in which another phase overlapped between the spindle and the arm and could be observed as if they were not connected.

[Identity]
The test plates with a grid pattern in the initial state immediately after production and those in the aged state exposed outdoors for 6 months were visually evaluated based on the following criteria. A to C were accepted in both the initial state and the time-lapse state.

A: The grid pattern can be visually recognized even from 5 m away.
B: The grid pattern cannot be visually recognized from 5 m ahead, but the visibility is high from 3 m ahead.
C: The grid pattern cannot be visually recognized from 3 m ahead, but the visibility is high from 1 m ahead.
D: The grid pattern cannot be visually recognized from 1 m ahead.

[Corrosion resistance]
The test plate was cut to a size of 150 × 70 mm, and a corrosion acceleration test CCT conforming to JASO-M609 was tested for 30 cycles, and then the rust generation state was investigated and evaluated based on the following criteria. A to C were accepted.
A: No rust is generated, and both the grid pattern and other areas maintain a beautiful design appearance.
B: No rust is generated, but a slight change in design appearance is observed in the grid pattern and other areas.
C: The appearance of the design is slightly impaired, but the grid pattern and other areas can be visually distinguished.
D: The appearance quality of the grid pattern and the other areas is significantly deteriorated and cannot be visually distinguished.

As shown in Table 2A and Table 2B, No. 1-1 to No. The Zn—Al—Mg-based hot-dip galvanized steel sheet of the example of the present invention of 1-19 was excellent in both discriminative property and corrosion resistance. In FIG. 2, No. The observation results of the first region of 1-4 with a scanning electron microscope are shown, and FIG. 3 shows No. The observation results by the scanning electron microscope in the second region of 1-4 are shown. The [Al phase] in the first region shown in FIG. 2 has a larger average length of the [Al phase] than the [Al phase] in the second region shown in FIG. 3, and each exhibits a different appearance. It can be seen that the first region and the second region can be identified.

No. 1-20 and No. In 1-21, the grid pattern was not confirmed because the cooling conditions were not appropriate.

In addition, No. 1 in which a grid pattern was printed by an inkjet method. The pattern of 1-22 was thinned by outdoor exposure for 6 months, and the distinctiveness was deteriorated.
In addition, No. 1 in which a grid pattern was formed by grinding. In 1-23, the thickness of the plating layer at the ground portion was reduced, and the corrosion resistance at the ground portion was reduced.

In addition, No. 1-1 to No. The plating layer of 1-23 contained [Al phase] and [ternary eutectic structure of _{Al / Zn / MgZn 2].}

FIG. 4 shows the surface of a hot-dip galvanized steel sheet representing a character string (alphabet) by spraying nitrogen gas onto the Zn—Al—Mg-based hot-dip galvanized layer.
According to the present invention, characters and marks can be intentionally displayed on the surface of a hot-dip galvanized steel sheet.

(Example 2)
The steel sheet after cold rolling was degreased and washed with water. Next, an ink containing a solidified nucleation component (fine particles of C or Ni) shown in Table 3 was attached to a rubber plate having a shape in which a grid pattern at intervals of 50 mm was transferred. By pressing this rubber plate against the steel sheet after washing with water, the ink adhered to the surface of the steel sheet. Then, the steel sheet was annealed by cold rolling. The steel sheet after cold-rolled sheet was immersed in a hot-dip galvanizing bath and then pulled up. Then, the amount of adhesion was adjusted by gas wiping, and further cooling was performed. The cooling after controlling the amount of adhesion was carried out under cooling conditions in which the temperature of the hot-dip galvanized layer 1 second after passing through the gas wiping became the temperature shown in Table 4, and then allowed to cool. In this way, the No. 1 shown in Tables 5A and 5B. 2-1 to No. A 2-20 Zn—Al—Mg-based hot-dip galvanized steel sheet was manufactured. The temperature of the steel plate in Table 4 is lower than the temperature at which solidification starts (liquidus temperature) and higher than the temperature at which the plating completely solidifies (solid phase temperature), and preferably (MgZn ₂ starts to precipitate). The temperature was in the range of +5) ° C. or higher and lower than (liquidus line temperature -20) ° C.

Further, a Zn—Al—Mg-based hot-dip galvanized steel sheet was produced in the same manner as above except that the steel sheet to which the solidified nuclei were not adhered was subjected to a hot-dip galvanizing treatment. This is No. 2-21 are shown in Tables 5A and 5B.

Further, a Zn—Al—Mg-based hot-dip galvanized steel sheet was produced in the same manner as above except that the steel sheet to which the solidified nuclei were not adhered was subjected to a hot-dip galvanizing treatment. A grid pattern at intervals of 50 mm was printed on the surface of the hot-dip galvanized layer of this steel sheet by an inkjet method. In this way, No. A 2-22 Zn—Al—Mg-based hot-dip galvanized steel sheet was manufactured.

Further, a Zn—Al—Mg-based hot-dip galvanized steel sheet was produced in the same manner as above except that the steel sheet to which the solidified nuclei were not adhered was subjected to a hot-dip galvanizing treatment. Then, the surface of the hot-dip galvanized layer was ground to form a grid pattern at intervals of 50 mm. In this way, No. A 2-23 Zn—Al—Mg-based hot-dip galvanized steel sheet was manufactured.

For the obtained hot-dip galvanized steel sheet, the ratio of the length Le of the ternary eutectic structure facing the steel sheet to the boundary length L at the boundary between the steel sheet and the hot-dip galvanized layer in the first region and the second region was determined. .. First, the boundary between the first region and the second region was identified by visually observing the surface of the hot-dip galvanized layer. In the case where the boundary is difficult to distinguish, the adhesion range of the solidified nucleus is assumed to be the second region.

At the boundary between the steel sheet and the hot-dip galvanized layer, the ratio of the length Le of the ternary eutectic structure to the length L of the boundary facing the steel sheet was measured by the following method. First, the cross section of the Zn—Al—Mg-based hot-dip galvanized steel sheet in the plate thickness direction was exposed. The cross section was set to 5 points each for the first region and the second region. Each cross section was photographed with a scanning electron microscope. In each cross section, a region having a length of 150 μm was arbitrarily selected from the boundary between the steel plate and the hot-dip galvanized layer. This length was defined as the boundary length L. Then, check the [Al / Zn / MgZn ₂ ternary eutectic structure] in the range of boundary selected length, all at the boundary between the steel sheet and the molten plating layer [Al / Zn / MgZn ₂ ternary co The total length Le of the crystal structure] is measured, and Le / L is determined. Le / L was obtained in each of the five cross sections of the first region and the second region, and the average thereof was calculated as the [Al / Zn / MgZn ₂ ternary] with respect to the boundary length L at the boundary between the steel sheet and the hot-dip galvanized layer. The eutectic structure] was defined as the ratio of the length Le facing the steel sheet.

Further, at an arbitrary position on the surface of the hot-dip galvanized layer, the ratio I (200) / of the X-ray diffraction intensity I (200) of the (200) plane and the X-ray diffraction intensity I (111) of the (111) plane of the Al phase. I (111) was calculated. By the X-ray diffraction method using CuKα1 ray, the X-ray diffraction intensity I (200) on the (200) plane and the X-ray diffraction intensity I (111) on the (111) plane of the Al phase are obtained on the surface of the hot-dip galvanized layer. The measurement was performed, and the ratio I (200) / I (111) was determined. The peak intensity of the (200) plane of the Al phase was defined as the intensity of the (200) plane diffraction peak of Al appearing at 44.74 ° in the 2θ range. The peak intensity of the (111) plane of the Al phase was defined as the intensity of the (111) plane diffraction peak of Al appearing in the range of 38.47 in the 2θ range. For the X-ray diffraction measurement, an X-ray diffractometer for measuring a minute region was used. The step was 0.02 °, the scanning speed was 5 ° / min, and a high-speed semiconductor two-dimensional detector was used as the detector. The X-rays emitted from the X-ray light source were focused by the polycapillaries. The X-ray irradiation range after condensing was a circle with a diameter of 1 mm.

A: The grid pattern can be visually recognized even from 8 m away.
B: The grid pattern cannot be visually recognized from 8 m ahead, but the visibility is high from 4 m ahead.
C: The grid pattern cannot be visually recognized from 4 m ahead, but the visibility is high from 1 m ahead.
D: The grid pattern cannot be visually recognized from 1 m ahead.

As shown in Table 5A and Table 5B, No. 2-1 to No. The Zn—Al—Mg-based hot-dip galvanized steel sheet of the example of the present invention of 2-20 was excellent in both discriminative property and corrosion resistance. In FIG. 5, No. The cross-sectional observation results of the first region of 2-1 with a scanning electron microscope are shown, and FIG. The cross-sectional observation result by the scanning electron microscope of the second region of 2-1 is shown. It can be seen that the first region and the second region have different appearances and can be distinguished.

No. In 2-21, since the solidified nuclei were not attached, the second region was not formed and the grid pattern was not formed.

In addition, No. 1 in which a grid pattern was printed by an inkjet method. In 2-22, the pattern was thinned by outdoor exposure for 6 months, and the design was deteriorated. Moreover, since the solidified nucleus was not attached, the second region was not formed.
Furthermore, No. 1 in which a grid pattern was formed by grinding. In 2-23, the thickness of the plating layer at the ground portion was reduced, and the corrosion resistance at the ground portion was reduced. Moreover, since the solidified nucleus was not attached, the second region was not formed.

In addition, No. 2-1 to No. The hot-dip galvanized layer of 2-23 contained [Al phase] and [ternary eutectic structure of _{Al / Zn / MgZn 2].}

FIG. 7 shows the surface of a hot-dip galvanized steel sheet in which a character string (alphabet) is represented by a second region on a Zn—Al—Mg-based hot-dip galvanized layer.
According to the present invention, characters and marks can be intentionally displayed on the surface of a hot-dip galvanized steel sheet.

According to the present invention, various designs, trademarks, and other identification marks can be displayed on the surface of the Zn—Al—Mg-based hot-dip galvanized layer without printing or painting, and the origin of the steel sheet can be identified. The design can be improved. Further, depending on the first region or the second region, information necessary for process control, inventory control, etc. and arbitrary information required by the consumer can be added to the Zn—Al—Mg-based hot-dip galvanized steel sheet. This can contribute to the improvement of the productivity of the Zn—Al—Mg-based hot-dip galvanized steel sheet. Therefore, it has sufficient industrial applicability.

Claims

A steel plate and a hot-dip galvanized layer formed on the surface of the steel plate are provided.
The hot-dip plating layer is
In average composition, Al: 4% by mass or more and less than 25% by mass, Mg: 0% by mass or more and less than 10% by mass, and the balance contains Zn and impurities.
The metal structure includes [Al phase] and [ternary eutectic structure of Al / Zn / MgZn 2].
The hot-dip galvanized layer includes a first region and a second region.
The first region and the second region satisfy either one of the following (a) or (b).
A Zn—Al—Mg-based hot-dip galvanized steel sheet in which the first region or the second region is arranged so as to have a predetermined shape.
(A) The first region is a region in which the average length of the [Al phase] on the surface of the hot-dip plating layer is 200 μm or more, and the second region is the [Al phase] on the surface of the hot-dip plating layer. ] Is a region where the average length is less than 200 μm.
(B) In the first region, the length Le at which the [ternary eutectic structure of Al / Zn / MgZn 2 ] faces the steel sheet at the boundary between the steel sheet and the hot-dip galvanized layer is the length of the boundary. The region is more than 0.3 with respect to L, and in the second region, the [ ternary eutectic structure of Al / Zn / MgZn 2 ] is the same as that of the steel sheet at the boundary between the steel sheet and the hot-dip galvanized layer. The opposite length Le is a region of 0.3 or less with respect to the boundary length L.
When the first region and the second region are the above (b), the X-ray diffraction intensities I (200) and (111) of the (200) plane of the [Al phase] on the surface of the hot-dip galvanized layer. The Zn—Al—Mg-based hot-dip galvanized steel sheet according to claim 1, wherein the ratio I (200) / I (111) of the X-ray diffraction intensity I (111) of the surface) is 0.8 or more.
The first region or the second region is arranged so as to form a straight line portion, a curved portion, a figure, a number, a symbol, a pattern, or a character, or a combination of two or more of them. The Zn—Al—Mg-based hot-dip galvanized steel sheet according to claim 1 or 2.
The Zn—Al—Mg-based hot-dip galvanized steel sheet according to any one of claims 1 to 3, wherein the first region or the second region is intentionally formed.
The Zn—Al—Mg-based hot-dip galvanized steel sheet according to any one of claims 1 to 4, wherein the hot-dip galvanized layer further contains Si: 0.0001 to 2% by mass in an average composition.
Claims 1 to 5, wherein the hot-dip galvanized layer further contains 0.0001 to 2% by mass of any one or more of Ni, Ti, Zr, and Sr in an average composition. The Zn—Al—Mg-based hot-dip galvanized steel sheet according to any one of the items.
The hot-dip galvanized layer further has one or more of Sb, Pb, Sn, Ca, Co, Mn, P, B, Bi, Cr, Sc, Y, REM, Hf, and C in average composition. The Zn—Al—Mg-based hot-dip galvanized steel sheet according to any one of claims 1 to 6, which contains 0.0001 to 2% by mass in total.
The Zn—Al—Mg-based hot-dip galvanized steel sheet according to any one of claims 1 to 7, wherein the amount of adhesion of the hot-dip galvanized layer is 30 to 600 g / m 2 in total on both sides of the steel sheet.