Coated steel sheet

Abstract

The plated steel sheet comprises a steel sheet and a plating layer disposed on a surface of the steel sheet, wherein the chemical composition of the plating layer comprises, in mass %, Al: 10.0 to 25.0%, Mg: 3.0 to 10.0%, Fe: 0.01 to 2.0%, Si: more than 0% and less than 2.0%, with the remainder containing Zn and impurities, and the number density of Mg2Si phases with a long diameter of 2 μm or more exposed on the surface of the plating layer is per 10000 μm 2 The area is 3 to 150.

Description

Technical Field

[0001] The present invention relates to a plated steel sheet.

[0002] This application claims priority based on Japanese Patent Application No. 2022-100351 filed in Japan on June 22, 2022, the contents of which are incorporated herein by reference. Background Art

[0003] Zn-Al-Mg hot-dip coated steel sheets with a hot-dip Zn coating containing Al and Mg have excellent corrosion resistance and are therefore widely used as materials for structural members requiring corrosion resistance, such as building materials.

[0004] For example, Patent Document 1 describes a plated steel material comprising a steel material and a plating layer comprising a Zn-Al-Mg alloy layer disposed on the surface of the steel material, wherein the Zn-Al-Mg alloy layer comprises a Zn phase and contains a Mg-Sn intermetallic compound phase in the Zn phase, and the plating layer has the following chemical composition: in terms of mass %, comprising Zn: greater than 65.0%, Al: greater than 5.0% and less than 25.0%, Mg: greater than 3.0% and less than 12.5%, Sn: 0.1% to 20.0%, and impurities, and satisfies the following Formulas 1 to 5.

[0005] Formula 1: Bi+In <Sn

[0006] Formula 2: Y+La+Ce≤Ca

[0007] Formula 3: Si <Sn

[0008] Formula 4: O≤Cr+Ti+Ni+Co+V+Nb+Cu+Mn<0.25

[0009] Formula 5: O≤Sr+Sb+Pb+B<0.5

[0010] Patent document 2 describes a plated steel material comprising a steel material and a plating layer disposed on the surface of the steel material and comprising a Zn-Al-Mg alloy layer, wherein in a cross section of the Zn-Al-Mg alloy layer, the area fraction of the MgZn2 phase is 45 to 75%, the combined area fraction of the MgZn2 phase and the Al phase is 70% or more, and the area fraction of the Zn-Al-MgZn2 ternary eutectic structure is 0 to 5%, and the plating layer has the following chemical composition: in mass %, Zn: more than 44.90% and less than 79.90%, Al: more than 15% and less than 35%, Mg: more than 5% and less than 20%, Ca: 0.1% or more and less than 3.0%, and impurities , when element group A is set to Y, La and Ce, element group B is set to Cr, Ti, Ni, Co, V, Nb, Cu and Mn, element group C is set to Sr, Sb and Pb, and element group D is set to Sn, Bi and In, the total content of elements selected from element group A is 0% to 0.5%, the total content of Ca and the elements selected from the above-mentioned element group A is 0.1% or more and less than 3.0%, the total content of elements selected from element group B is 0% to 0.25%, the total content of elements selected from element group C is 0% to 0.5%, and the total content of elements selected from element group D is 0% to 20.00%.

[0011] Patent document 3 describes a hot-dip Al-Zn-Mg-Si plated steel sheet having a plated film on the surface of the steel sheet, wherein the plated film comprises an interface alloy layer present at the interface with the base steel sheet and a main layer present on the alloy layer, and contains 25 to 80 mass% of Al, more than 0.6 mass% and less than 15 mass% of Si, and more than 0.1 mass% and less than 25 mass% of Mg, and the area ratio of Mg2Si at the surface of the main layer is more than 10%.

[0012] In recent years, hot-dip galvanized steel materials used in building materials such as roofing and siding materials have been required to have both high corrosion resistance of the coating itself, i.e., flat surface corrosion resistance, and corrosion resistance of the cut end surface, i.e., end surface corrosion resistance. However, a technology that achieves both high levels of flat surface corrosion resistance and end surface corrosion resistance has not been developed.

[0013] Prior art literature

[0014] Patent Literature

[0015] Patent Document 1: International Publication No. 2018 / 139619

[0016] Patent Document 2: International Publication No. 2018 / 139620

[0017] Patent Document 3: Japanese Patent Application Laid-Open No. 2016-166414 Summary of the Invention

[0018] Problems to be solved by the invention

[0019] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a plated steel sheet having excellent both flat surface corrosion resistance and end surface corrosion resistance.

[0020] Means for solving problems

[0021] In order to solve the above-mentioned problems, the present invention adopts the following configuration.

[0022] [1] A plated steel sheet comprising a steel sheet and a plating layer disposed on a surface of the steel sheet.

[0023] The chemical composition of the above-mentioned coating contains, in mass %, the following:

[0024] Al: 10.0-25.0%,

[0025] Mg: 3.0-10.0%,

[0026] Fe: 0.01-2.0%,

[0027] Si: more than 0% and 2.0% or less,

[0028] further containing one or more species selected from the following groups A, B, and C,

[0029] The remainder contains Zn and impurities.

[0030] The number density of the Mg2Si phase with a long diameter of 2 μm or more exposed on the surface of the plating layer is 2 The area is 3 to 150.

[0031] [Group A]Ni: 0~1.0%

[0032] [Group B] Ca: 0-0.05%

[0033] [Group C] Sb: 0-0.5%, Pb: 0-0.5%, Cu: 0-1.0%, Sn: 0-1.0%, Ti: 0-1.0%, Cr: 0-1.0%, Nb: 0-1.0%, Zr: 0-1.0%, Mn: 0-1.0%, Mo: 0-1.0%, Ag: 0-1.0%, Li: 0-1.0%, La: 0-0.5%, Ce: 0-0.5%, B: 0-0.5%, Y: 0-0.5%, P: 0-0.5%, Sr: 0-0.5%, Co: 0-0.5%, Bi: 0-0.5%, In: 0-0.5%, V: 0-0.5%, W: 0-0.5%; one or more of the following: 0-5% in total

[0034] [2] The plated steel sheet according to [1], wherein the chemical composition of Mg and Si in the plating layer is Mg: 4.5-8 mass %, Si: 0.1-2 mass %,

[0035] The number density of the Mg2Si phase with a long diameter of 2 μm or more exposed on the surface of the plating layer is 2 The area is 15 to 150.

[0036] [3] The plated steel sheet according to [1], wherein the chemical composition of Al, Mg and Si in the coating layer is Al: 15-25 mass%, Mg: 4.5-8 mass%, Si: 0.1-2 mass%,

[0037] The number density of the Mg2Si phase with a long diameter of 2 μm or more exposed on the surface of the plating layer is 2 The area is 30 to 150.

[0038] [4] The plated steel sheet according to any one of [1] to [3], wherein the chemical composition of Al, Mg, and Si in the coating layer is Al: 15-25 mass%, Mg: 4.5-8 mass%, Si: 0.1-2 mass%,

[0039] The number density of the Mg-Si-Zn-Al phase with a long diameter of 2 μm or more exposed on the surface of the plating layer is 2 The area is 5 to 150.

[0040] [5] The plated steel sheet according to any one of [1] to [3], wherein the chemical composition of the coating layer contains Sn: 0.05 to 0.5 mass %, and in an X-ray diffraction measurement of the coating layer, a Mg2Sn phase is detected in the coating layer.

[0041] [6] The plated steel sheet according to [4], wherein the chemical composition of the coating layer contains Sn: 0.05 to 0.5 mass %, and in an X-ray diffraction measurement of the coating layer, a Mg2Sn phase is detected in the coating layer.

[0042] [7] The plated steel sheet according to [1], wherein the plating layer has a chemical composition containing the above-mentioned group A in mass %.

[0043] [8] The plated steel sheet according to [1], wherein the plating layer has a chemical composition containing the group B in mass %.

[0044] [9] The plated steel sheet according to [1], wherein the plating layer has a chemical composition containing the above-mentioned Group C in mass %.

[0045] Effects of the Invention

[0046] According to the above-described aspects of the present invention, a plated steel sheet excellent in both flat surface corrosion resistance and end surface corrosion resistance can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a schematic cross-sectional view of a hot-dip plated steel material as an embodiment of the present invention. DETAILED DESCRIPTION

[0048] The plated steel sheet is cut, thereby exposing the end face of the steel sheet at the cut end face of the plated steel sheet. The corrosion resistance of the end face of the steel sheet (hereinafter referred to as end face corrosion resistance) is generally achieved by the following operation. That is, it is achieved by forming a coating containing an element with a higher ionization tendency than the base metal (such as Zn, Mg, etc.) on the surface of the steel sheet as a coating, causing the coating to corrode preferentially with respect to the base metal to generate corrosion products, and utilizing these corrosion products to protect the end face of the steel sheet from corrosion. Therefore, the improvement of the end face corrosion resistance brought about by the coating is incompatible with the improvement of the corrosion resistance of the coating itself, that is, the improvement of the flat corrosion resistance.

[0049] Therefore, the inventors of the present invention conducted extensive research to improve both the flat and end surface corrosion resistance of coatings containing Al and Mg. Coatings containing Al, Mg, Si, and Zn may contain a Mg2Si phase. This Mg2Si phase contains a relatively high amount of Mg, which can contribute to the corrosion resistance of the steel sheet's end surfaces. However, in conventional plated steel sheets, the Mg2Si phase is often found within the coating, particularly near the interface with the steel sheet, and is generally massive in shape. Therefore, in the initial stages of corrosion of the coating, the Mg2Si phase is not affected by the corrosion.

[0050] However, the inventors of the present invention conducted extensive research and, by adjusting the coating production conditions, successfully crystallized a relatively large number of needle-shaped Mg2Si phases on the coating surface. The presence of a large number of Mg2Si phases on the coating surface corrodes the Mg2Si phases from the early stages of corrosion. As the Mg2Si phases corrode, Mg ions are generated as corrosion products, which protect the end faces of the steel sheet from corrosion. This process successfully improved the corrosion resistance of the end faces.

[0051] In addition, since there are a large number of Mg2Si phases on the surface of the coating, the end face corrosion resistance can be improved by the corrosion products of the Mg2Si phase from the initial stage of corrosion. Therefore, the end face corrosion resistance can be improved without sacrificing the planar corrosion resistance of the coating, thereby achieving a balance between the planar corrosion resistance and the end face corrosion resistance of the coating.

[0052] Hereinafter, a plated steel sheet as an embodiment of the present invention will be described.

[0053] The plated steel sheet of the present embodiment includes a steel sheet and a plating layer disposed on the surface of the steel sheet, wherein the chemical composition of the plating layer comprises, in mass %, Al: 10.0-25.0%, Mg: 3.0-10.0%, Fe: 0.01-2.0%, Si: more than 0% and less than 2.0%, and further contains one or more selected from the following Group A, Group B, and Group C, with the remainder containing Zn and impurities, and the number density of the Mg2Si phase with a long diameter of 2 μm or more exposed on the surface of the plating layer is per 10000 μm 2 3 to 150.

[0054] [Group A]Ni: 0~1.0%

[0055] [Group B] Ca: 0-0.05%

[0056] [Group C] Sb: 0-0.5%, Pb: 0-0.5%, Cu: 0-1.0%, Sn: 0-1.0%, Ti: 0-1.0%, Cr: 0-1.0%, Nb: 0-1.0%, Zr: 0-1.0%, Mn: 0-1.0%, Mo: 0-1.0%, Ag: 0-1.0%, Li: 0-1.0%, La: 0-0.5%, Ce: 0-0.5%, B: 0-0.5%, Y: 0-0.5%, P: 0-0.5%, Sr: 0-0.5%, Co: 0-0.5%, Bi: 0-0.5%, In: 0-0.5%, V: 0-0.5%, W: 0-0.5%; one or more of the following: 0-5% in total

[0057] In the following description, the "%" expression of the content of each element in the chemical composition means "mass %". The content of the elements in the chemical composition is sometimes recorded as element concentration (for example, Zn concentration, Mg concentration, etc.). "Plastic corrosion resistance" refers to the property of the coating (specifically, the Zn-Al-Mg alloy layer) itself that is not easily corroded. "End surface corrosion resistance" refers to the property of suppressing corrosion of the steel sheet at the exposed part of the steel sheet (for example, the cut end surface of the plated steel sheet). "Coating" refers to a plating film produced by a so-called hot-dip plating process.

[0058] like Figure 1 As shown in FIG, the plated steel sheet 1 of this embodiment includes a steel sheet 11. The shape of the steel sheet 11 is not particularly limited. Furthermore, the steel sheet 11 may be a base steel sheet that is formed into, for example, steel pipes, civil engineering materials (gates, corrugated pipes, gutter covers, sand shields, bolts, metal mesh, guardrails, waterproof walls, etc.), home appliance components (such as air conditioner outdoor unit frames), and automotive components (such as running components). Forming processes include various plastic working methods such as pressing, roll forming, and bending.

[0059] The material of the steel plate 11 is not particularly limited. The steel plate 11 can be, for example, ordinary steel, Al-killed steel, ultra-low carbon steel, high-carbon steel, various high-tensile steels, and some high-alloy steels (steels containing strengthening elements such as Ni and Cr). The steel plate 11 can also be a hot-rolled steel plate, hot-rolled steel strip, cold-rolled steel plate, or cold-rolled steel strip as described in JIS G 3302:2010. The manufacturing method (hot rolling, pickling, cold rolling, etc.) and its specific manufacturing conditions are also not particularly limited.

[0060] As described below, a steel sheet 11 having an adjusted surface roughness is used as the steel sheet to be plated. The surface roughness of the steel sheet can be adjusted, for example, by setting the surface of a roller or a skin-pass rolling roller to a predetermined surface roughness, or by transferring the surface shape of the roller during rolling or skin-pass rolling.

[0061] The plated steel sheet 1 of this embodiment includes a plating layer 12 disposed on the surface of a steel sheet 11. The plating layer 12 of the plated steel sheet 1 of this embodiment is primarily composed of a Zn-Al-Mg alloy layer, based on the chemical composition described below. Furthermore, the plating layer 12 of the plated steel sheet 1 of this embodiment may also include an interface alloy layer primarily composed of Fe and Al between the steel sheet 11 and the Zn-Al-Mg alloy layer. Specifically, the plating layer 12 may have a single-layer structure of the Zn-Al-Mg alloy layer or a laminated structure including a Zn-Al-Mg alloy layer and an interface alloy layer.

[0062] The chemical composition of the coating layer of this embodiment consists of Zn and other alloying elements. The chemical composition of the coating layer is described in detail below. It should be noted that elements whose lower concentration limits are indicated as 0% are optional elements. While they are not essential for resolving the issues of the plated steel sheet of this embodiment, they may be included in the coating layer for purposes such as improving properties.

[0063] <Al:10.0~25.0%>

[0064] Al contributes to improving flat corrosion resistance, end corrosion resistance, and workability. Therefore, the Al concentration is set to 10.0% or higher. Alternatively, the Al concentration can be set to 11.0%, 12.0%, or 15.0%. On the other hand, excessive Al reduces the Mg and Zn concentrations, degrading end corrosion resistance. Therefore, the Al concentration is set to 25.0% or lower. Alternatively, the Al concentration can be set to 24.0%, 22.0%, or 20.0%.

[0065] <Mg:3.0~10.0%>

[0066] Mg is an element necessary to ensure planar corrosion resistance and end-face corrosion resistance. In addition, it is also necessary for the crystallization of the Mg2Si phase. Therefore, the Mg concentration is set to 3.0% or more. The Mg concentration can also be set to 4.0% or more, 5.0% or more, or 6.0% or more. On the other hand, if the Mg concentration is excessive, the workability, especially the pulverization property, may deteriorate, and furthermore, the planar corrosion resistance may deteriorate. Thus, the Mg concentration is set to 10.0% or less. The Mg concentration can also be set to 8.0% or less or 7.0% or less.

[0067] <Fe: 0.01% to 2.0%>

[0068] The concentration of Fe can also be 0%, but Fe can also be contained in the coating at 0.01% or more. It has been confirmed that if the Fe concentration is 2.0% or less, there is no adverse effect on the properties of the coating. The Fe concentration can also be set, for example, to 0.05% or more, 0.1% or more, 0.5% or more, or 1.0% or more. The Fe concentration is set to 2.0% or less. The Fe concentration can also be set to 1.8% or less or 1.5% or less. Since Fe may be mixed in from the base steel plate, the Fe concentration can also be 0.05% or more.

[0069] <Si: more than 0% and 2.0% or less>

[0070] Si helps to improve the planar corrosion resistance. In addition, it is also necessary for the crystallization of the Mg2Si phase. Therefore, the Si concentration can also be set to more than 0%, 0.01% or more, 0.02% or more, or 0.06% or more. On the other hand, if the Si concentration is excessive, the planar corrosion resistance and end-face corrosion resistance deteriorate. Therefore, the Si concentration is set to 2.0% or less. The Si concentration can also be set to 1.8% or less, 1.6% or less, 1.2% or less, or 1.0% or less.

[0071] Furthermore, the coating of the present embodiment may also contain one or more selected from the following Group A, Group B, and Group C.

[0072] [Group A] Ni: 0 to 1.0%

[0073] [Group B] Ca: 0 to 0.05%

[0074] [Group C] Sb: 0-0.5%, Pb: 0-0.5%, Cu: 0-1.0%, Sn: 0-1.0%, Ti: 0-1.0%, Cr: 0-1.0%, Nb: 0-1.0%, Zr: 0-1.0%, Mn: 0-1.0%, Mo: 0-1.0%, Ag: 0-1.0%, Li: 0-1.0%, La: 0-0.5%, Ce: 0-0.5%, B: 0-0.5%, Y: 0-0.5%, P: 0-0.5%, Sr: 0-0.5%, Co: 0-0.5%, Bi: 0-0.5%, In: 0-0.5%, V: 0-0.5%, W: 0-0.5%; one or more of the following: 0-5% in total

[0075] <Ni:0~1.0%>

[0076] The concentration of Ni, which is a member of Group A, may be 0%. On the other hand, Ni contributes to improving end surface corrosion resistance. Therefore, the Ni concentration may be set to 0.05% or more, 0.08% or more, or 0.1% or more. On the other hand, if the Ni concentration is excessive, flat surface corrosion resistance deteriorates. Therefore, the Ni concentration is set to 1.0% or less. The Ni concentration may also be set to 0.8% or less, 0.6% or less, or 0.5% or less.

[0077] <Ca:0%~0.05%>

[0078] The Ca concentration in Group B can also be 0%. On the other hand, Ca is an element that can adjust the optimal Mg dissolution amount for imparting flat corrosion resistance. Therefore, the Ca concentration can be 0.005% or higher, or 0.01% or higher. On the other hand, excessive Ca concentration deteriorates flat corrosion resistance and workability. Therefore, the Ca concentration is set to 0.05% or lower. It can also be set to 0.04% or lower.

[0079] Furthermore, in the plating layer of this embodiment, as group C, one or more elements selected from the group consisting of Sb: 0-0.5%, Pb: 0-0.5%, Cu: 0-1.0%, Sn: 0-1.0%, Ti: 0-1.0%, Cr: 0-1.0%, Nb: 0-1.0%, Zr: 0-1.0%, Mn: 0-1.0%, Mo: 0-1.0%, Ag: 0-1.0%, Li: 0-1.0%, La: 0-0.5%, Ce: 0-0.5%, B: 0-0.5%, Y: 0-0.5%, P: 0-0.5%, Sr: 0-0.5%, Co: 0-0.5%, Bi: 0-0.5%, In: 0-0.5%, V: 0-0.5%, and W: 0-0.5% may be contained. The total content of these elements is set to 0 to 5%. If the total content exceeds 5%, the flat surface corrosion resistance and the end surface corrosion resistance may be reduced.

[0080] <Sb and Pb: 0 to 0.5% respectively>

[0081] The concentrations of Sb and Pb can also be 0%. On the other hand, Sb and Pb contribute to the improvement of the end face corrosion resistance. Therefore, the concentrations of Sb and Pb can also be set to 0.05% or more, 0.10% or more, or 0.15% or more respectively. On the other hand, if the concentrations of Sb and Pb are excessive, the planar corrosion resistance deteriorates. Therefore, the concentrations of Sb and Pb are set to 0.5% or less. The concentrations of Sb and Pb can also be set to 0.4% or less, 0.3% or less, or 0.25% or less.

[0082] <Cu, Ti, Cr, Nb, Zr, Mn, Mo, Ag and Li: 0 to 1.0% respectively>

[0083] The concentrations of Cu, Ti, Cr, Nb, Zr, Mn, Mo, Ag and Li can also be 0% respectively. On the other hand, they contribute to the improvement of the end face corrosion resistance. Therefore, the concentrations of Cu, Ti, Cr, Nb, Zr, Mn, Mo, Ag and Li can also be set to 0.05% or more, 0.08% or more, or 0.10% or more respectively. On the other hand, if the concentrations of Cu, Ti, Cr, Nb, Zr, Mn, Mo, Ag and Li are excessive, the planar corrosion resistance deteriorates. Therefore, the concentrations of Cu, Ti, Cr, Nb, Zr, Mn, Mo, Ag and Li are set to 1.0% or less. The concentrations of Cu, Ti, Cr, Nb, Zr, Mn, Mo, Ag and Li can also be set to 0.8% or less, 0.7% or less, or 0.6% or less.

[0084] <Sn: 0 to 1.0%>

[0085] The Sn concentration can also be 0%. On the other hand, Sn is an element that forms an intermetallic compound with Mg and improves the end face corrosion resistance of the coating. Therefore, the Sn concentration can also be set to 0.05% or more, 0.1% or more, or 0.2% or more. However, if the Sn concentration is excessive, the planar corrosion resistance deteriorates. Therefore, the Sn concentration is set to 1.0% or less. The Sn concentration can also be set to 0.8% or less, 0.6% or less, or 0.5% or less.

[0086] <La, Ce, B, Y, P and Sr: 0 to 0.5% respectively>

[0087] The concentration of each of La, Ce, B, Y, P, and Sr may also be 0%. On the other hand, La, Ce, B, Y, P, and Sr contribute to the improvement of the end face corrosion resistance. Therefore, the concentration of each of La, Ce, B, Y, P, and Sr may also be set to 0.10% or more, 0.15% or more, or 0.20% or more. On the other hand, if the concentration of La, Ce, B, Y, P, and Sr is excessive, the planar corrosion resistance deteriorates. Therefore, the concentration of each of La, Ce, B, Y, P, and Sr is set to 0.5% or less. The concentration of each of La, Ce, B, Y, P, and Sr may also be set to 0.4% or less, 0.3% or less.

[0088] <Co, Bi, In, V, W: 0 to 0.5% respectively>

[0089] The concentration of each of Co, Bi, In, V, and W may also be 0%. On the other hand, Co, Bi, In, V, and W contribute to the improvement of the end face corrosion resistance. Therefore, the concentration of each of Co, Bi, In, V, and W may also be set to 0.10% or more, 0.15% or more, or 0.20% or more. On the other hand, if the concentration of Co, Bi, In, V, and W is excessive, the planar corrosion resistance deteriorates. Therefore, the concentration of each of Co, Bi, In, V, and W is set to 0.5% or less. The concentration of each of Co, Bi, In, V, and W may also be set to 0.4% or less, 0.3% or less.

[0090] <The remainder: Zn and impurities>

[0091] The remainder of the composition of the plating layer in this embodiment is Zn and impurities. Zn is an element that gives the plating layer planar corrosion resistance and end face corrosion resistance. Impurities refer to the components contained in the raw materials or the components mixed in during the manufacturing process. For example, in the plating layer, it is possible that in addition to Fe, other components are also slightly mixed as impurities through the mutual atomic diffusion between the base steel plate and the plating bath.

[0092] The chemical composition of the plating layer is measured by the following method. First, the plating layer is stripped and dissolved using an acid containing an inhibitor that inhibits the corrosion of the steel plate to obtain an acid solution. Then, the obtained acid solution is subjected to inductively coupled plasma (ICP) analysis. Thereby, the chemical composition of the plating layer can be obtained. The type of acid only needs to be an acid that can dissolve the plating layer, and there is no particular limitation. It should be noted that the chemical composition measured by the above means is the average chemical composition of the entire plating layer.

[0093] Next, the metal structure of the plating layer will be described.

[0094] On the surface of the plating layer of this embodiment, a Mg2Si phase with a long diameter of 2 μm or more is exposed. The number density of the Mg2Si phase on the surface is 2 The number of Mg2Si phases is 3 to 150. When the Mg2Si phase is exposed on the surface of the coating, it corrodes in the early stages of corrosion of the coating, forming corrosion products. These corrosion products improve the corrosion resistance of the end faces of the steel sheet. This improves the corrosion resistance of the end faces without compromising the flat surface corrosion resistance of the coating.

[0095] An electron beam microanalyzer (EPMA) is used to identify the Mg2Si phase on the surface of the coating. The surface of the coating is observed using a scanning electron microscope attached to the EPMA to identify the intermetallic compound being analyzed. Elemental analysis is then performed on the identified intermetallic compound to determine whether it is a Mg2Si phase. Regarding the identification of the Mg2Si phase, an intermetallic compound containing 55 atomic percent or more of Mg and 30 atomic percent or more of Si is considered a Mg2Si phase. In addition to Mg and Si, the Mg2Si phase may also contain Ca, Zn, and Sn, each within a range of 10 atomic percent or less.

[0096] The shape of the Mg2Si phase needs to have a major diameter of 2 μm or greater, more preferably a needle-like shape with a major diameter of 2 μm or greater. Furthermore, the aspect ratio is more preferably greater than 2. By setting the Mg2Si phase to have a major diameter of 2 μm or greater, the Mg2Si phase is easily dissolved in the early stages of corrosion, allowing more corrosion products to be supplied to the end face of the steel plate, thereby improving end face corrosion resistance.

[0097] The major axis of the Mg2Si phase is defined as the maximum length of the Mg2Si phase when observed using a scanning electron microscope. The aspect ratio is the ratio of the major axis to the minor axis (major axis / minor axis). The minor axis is the length perpendicular to the major axis. More specifically, it is defined as the maximum length within a range of ±5° relative to the perpendicular direction of the major axis.

[0098] The number density of the Mg2Si phase at the surface is set to be per 10000 μm 2 3 to 150. The number density is less than 3 (pieces / 10000μm 2 ), the Mg2Si phase is too small and the end surface corrosion resistance becomes insufficient. On the other hand, even if the number density of the Mg2Si phase exceeds 150 (pieces / 10000 μm 2 ), the effect of improving the end surface corrosion resistance is also saturated, so 150 (pieces / 10000μm 2 ) is set as the upper limit. When the unit is set to (pieces / 10000μm 2), the number density of the Mg2Si phase may be greater than 15, or greater than 30. In addition, the number density of the Mg2Si phase may be less than 120, less than 100, less than 70, less than 50, or less than 30.

[0099] The number density of the Mg2Si phase at the surface of the coating may be affected by the average chemical composition of the coating. When the chemical composition of the coating is Mg: 4.5 to 8 mass % and Si: 0.1 to 2 mass %, the number density of the Mg2Si phase with a long diameter of 2 μm or more exposed on the surface of the coating may be 10000 μm. 2 The area is 15 to 150.

[0100] Furthermore, when the chemical composition of Al, Mg, and Si in the plating layer is Al: 15-25 mass %, Mg: 4.5-8 mass %, and Si: 0.1-2 mass %, the number density of the Mg2Si phase with a long diameter of 2 μm or more exposed on the surface of the plating layer may be per 10000 μm 2 The area is 30 to 150.

[0101] Next, on the surface of the plating layer of this embodiment, a Mg-Si-Zn-Al phase with a long diameter of 2 μm or more may be exposed. The number density of the Mg-Si-Zn-Al phase on the surface is preferably 10000 μm. 2 The number of Mg-Si-Zn-Al phases is 5 to 150. If the Mg-Si-Zn-Al phase is exposed on the surface of the plating layer, the Mg-Si-Zn-Al phase is corroded in the early stages of corrosion of the plating layer, forming a dense corrosion product of Mg, Si, Zn, and Al. The formation of this corrosion product further improves the flat corrosion resistance of the plating layer.

[0102] To identify the Mg-Si-Zn-Al phase in the coating, an electron beam microanalyzer (EPMA) is used. The surface of the coating is observed using a scanning electron microscope attached to the EPMA to identify the intermetallic compound to be analyzed. Elemental analysis is then performed on the identified intermetallic compound to determine whether it is a Mg-Si-Zn-Al phase. Regarding the identification of the Mg-Si-Zn-Al phase, an intermetallic compound containing 20 to 45 atomic percent Mg, 15 to 40 atomic percent Si, 15 to 40 atomic percent Zn, and 5 to 20 atomic percent Al is considered a Mg-Si-Zn-Al phase.

[0103] The number density of the Mg-Si-Zn-Al phase at the surface of the coating is affected by the average chemical composition of the coating. 2The number of the plating layers is preferably 5 to 150, and the chemical composition of Al, Mg and Si in the plating layer is preferably Al: 15 to 25 mass %, Mg: 4.5 to 8 mass %, and Si: 0.1 to 2 mass %.

[0104] The shape of the Mg-Si-Zn-Al phase is preferably a needle-shaped phase with a long diameter of 2 μm or more, more preferably a needle-shaped phase with a long diameter of 2 μm or more. Furthermore, the aspect ratio is preferably 2 or more. By setting the shape of the Mg2Si phase to have a long diameter of 2 μm or more, the Mg-Si-Zn-Al phase is easily dissolved in the early stages of corrosion, forming more dense corrosion products and improving the flat corrosion resistance.

[0105] The major axis of the Mg-Si-Zn-Al phase is set to the maximum length of the Mg-Si-Zn-Al phase when observing the Mg-Si-Zn-Al phase with an electron microscope. The aspect ratio is the ratio of the major axis to the minor axis (major axis / minor axis). The minor axis is the length in the direction perpendicular to the major axis. More specifically, it is set to the maximum length within a range of ±5° relative to the perpendicular direction of the major axis.

[0106] The number density of the Mg-Si-Zn-Al phase at the surface is preferably 2 The number density is set to 5 (pieces / 10000 μm 2 ) or more, the flat corrosion resistance can be further improved. On the other hand, even if the number density of the Mg-Si-Zn-Al phase exceeds 150 ( / 10000 μm 2 ), the effect of improving the flat corrosion resistance is also saturated, so 150 (pieces / 10000μm 2 ) is set as the upper limit. When the unit is set to (pieces / 10000μm 2 ), the number density of the Mg-Si-Zn-Al phase may be greater than 10, or greater than 15. Furthermore, the number density of the Mg-Si-Zn-Al phase may be less than 120, less than 100, less than 80, less than 70, less than 50, or less than 30.

[0107] It should be noted that the Mg-Si-Zn-Al phase can also be per 10000 μm 2 An area greater than 0 and a number density less than 5 exist on the surface of the coating.

[0108] The method for measuring the number density of Mg2Si phase and Mg-Si-Zn-Al phase is described. A 50μm square measurement area is set on the surface of the coating. The measurement area is set to 8 locations, and 8 measurement areas are randomly configured on the surface of the coating. The measurement areas are separated in a non-overlapping manner. The intermetallic compound is confirmed by observing the set measurement area with a scanning electron microscope. Then, EPMA is used to analyze the composition of the intermetallic compound to distinguish the Mg2Si phase and the Mg-Si-Zn-Al phase. Furthermore, the number of Mg2Si phase and Mg-Si-Zn-Al phase in each measurement area is measured. The measurement conditions of EPMA are, for example, set to: an acceleration voltage of 15kV, a current of 0.05μA, and an irradiation time of 50ms. As EPMA, for example, JXA-8230 made by JEOL Ltd. is used.

[0109] When the Mg2Si phase and Mg-Si-Zn-Al phase are needle-shaped, it is possible that part of the phase is within the measurement area and the rest of the phase is outside the measurement area, but such phases are also included in the number of measurement objects.

[0110] Furthermore, when the Mg2Si phase and the Mg-Si-Zn-Al phase are needle-shaped, multiple Mg2Si phases or multiple Mg-Si-Zn-Al phases may overlap. In such cases, if the overlapping phases have their major axes oriented in different directions, the number of each overlapping phase is counted. For example, if two Mg2Si phases overlap and their major axes are oriented in different directions, the number is counted as two.

[0111] Then, based on the number of Mg2Si phases and Mg-Si-Zn-Al phases with a long diameter of 2 μm or more measured in the 8 measurement areas and the total area of the measurement areas, the total area per 10000 μm was calculated. 2 The number of is taken as the number density.

[0112] In addition, when the coating contains 0.05 to 0.5 mass% Sn, it is preferred that the coating contain a Mg2Sn phase. Since the Mg2Sn phase is a small amount, its presence is detected and confirmed by X-ray diffraction measurement. By containing the Mg2Sn phase in the coating, the corrosion resistance of the end face of the coating is further improved. Whether the coating contains the Mg2Sn phase is determined by whether a diffraction peak unique to Mg2Sn appears. Here, the diffraction peak unique to Mg2Sn refers to a peak that appears at a diffraction angle 2θ of 23.4±0.3 degrees.

[0113] The coating weight per single side of the plating layer is set to, for example, 20 to 150 g / m 2By setting the adhesion amount per single side to 20g / m 2 The above can further improve the flat corrosion resistance and end surface corrosion resistance of the plated steel sheet. On the other hand, by setting the coating weight per single side to 150 g / m 2 The following can further improve the workability of the plated steel sheet.

[0114] Next, a method for producing the plated steel sheet of the present embodiment will be described, but the method for producing the plated steel sheet of the present embodiment is not particularly limited. For example, the plated steel sheet of the present embodiment can be obtained under the production conditions described below.

[0115] The manufacturing method of the plated steel sheet of the present embodiment is to anneal the steel sheet with adjusted surface roughness in a reducing atmosphere, immerse the steel sheet just after annealing in a hot dip coating bath and then pick it up, thereby forming a coating on the surface of the steel sheet. Then, cooling gas is blown while the temperature of the coating decreases from the bath temperature to 300°C or less. Regarding the gas flow when blowing the cooling gas, the gas flow from the bath temperature to the controlled cooling temperature (the gas flow rate in the temperature range above the controlled cooling temperature and below the bath temperature) is set to 100 to 5000 L / min / m 2 The gas flow rate (gas flow rate in the temperature range above the cooling stop temperature and below the controlled cooling temperature) from the controlled cooling temperature to the cooling stop temperature (300°C or less in this embodiment) is set to 10,000 to 80,000 L / min / m 2 range.

[0116] The cooling temperature is controlled and set to a temperature within a range of -10°C to -80°C relative to the crystallization temperature of the Mg2Si phase.

[0117] Regarding the roughness of the steel sheet surface to be plated, the length L of the roughness curve per reference length L0 is p The ratio (L p / L0) is set to 1.0 or more, and the arithmetic mean roughness Ra is set to 0.1μm or more. If it is out of this range, a large amount of Mg2Si phase may be crystallized near the interface between the coating and the steel sheet, and the number density of the Mg2Si phase at the surface of the coating is reduced. (L p The upper limit of the roughness ( / L0) is preferably 3.0 or less, but may also be 2.5 or less, or 2.0 or less. The upper limit of the arithmetic mean roughness Ra is preferably 4.0 μm or less, but may also be 3.5 μm or less. There are no particular restrictions on adjusting the surface roughness of the steel sheet, but for example, adjustment can be made by rolling the plated base sheet using a roll or temper rolling roll whose surface has been adjusted to the desired roughness, thereby transferring the roll's surface shape. Alternatively, adjustment can be made by pickling.

[0118] (L p / L0) and the arithmetic mean roughness are measured, for example, using a shape measurement laser microscope (model: VK-8700) manufactured by KEYENCE Co., Ltd. The measurement conditions are, for example, set to measurement mode: laser confocal, measurement quality: high precision, pitch: 0.75 μm, double scan: open, optical zoom: 1x, objective lens name: plan achromat (Plan), γ coefficient: 0.45, bias: 0%, and the measurement is performed. It should be noted that (L p The measuring device used for measuring the arithmetic mean roughness (L / L0) is not limited to the above examples. The roughness curve is obtained by sequentially applying the profile curve filters with cutoff values λc and λs to the cross-sectional curve obtained by measurement in accordance with JIS B 0601:2013. Specifically, the components with wavelength λc of 0.001 mm or less and the components with wavelength λs of 0.2 mm or more are removed from the obtained measurement results to obtain the roughness curve. Based on the obtained roughness curve, (L p / L0) and arithmetic mean roughness.

[0119] Annealing of the steel sheet to be plated is performed in a reducing atmosphere. The reducing atmosphere and annealing conditions are not particularly limited. This annealing removes as much oxide as possible from the surface of the steel sheet.

[0120] Next, the immediately annealed steel sheet is immersed in a hot-dip coating bath. The chemical composition of the hot-dip coating bath can be appropriately adjusted to achieve the chemical composition of the coating layer described above. The temperature of the hot-dip coating bath is also not particularly limited; a temperature suitable for hot-dip coating can be appropriately selected. For example, the coating bath temperature can be set at a value approximately 20°C or higher than the melting point of the coating bath.

[0121] Next, the steel sheet is removed from the hot-dip coating bath. The amount of coating deposited can be controlled by controlling the speed at which the steel sheet is removed. If necessary, the coated steel sheet can be wiped to control the amount of coating deposited. The amount of coating deposited is not particularly limited and can, for example, be set within the above-mentioned range.

[0122] Next, the coating is cooled. Cooling is performed by blowing cooling gas onto the steel sheet immediately after it is removed from the hot-dip coating bath. Cooling by blowing cooling gas is performed continuously while the steel sheet temperature reaches 300°C from the bath temperature. Cooling conditions below 300°C are not particularly limited; subsequent cooling by blowing cooling gas or natural cooling may be performed.

[0123] In the cooling by blowing cooling gas, it is carried out by arranging a cooling belt along the conveying path of the steel plate. In the cooling belt, there are a plurality of blowing nozzles for cooling gas. The shape of the gas nozzle that sprays the cooling gas is set to a diameter range of 1 to 50 mm, for example. The angle between the front end of the gas nozzle and the steel plate is set to a range of 70 to 110 degrees, more preferably 90 degrees (right angle). The distance between the front end of the gas nozzle and the steel plate is set to a range of 30 to 1000 mm. It should be noted that the shape, angle, and distance of the gas nozzle are simply examples and are not limited to the above ranges.

[0124] The cooling gas to be blown is not particularly limited, and may be a non-oxidizing gas such as nitrogen, an inert gas such as argon, or air, or a mixed gas thereof.

[0125] In this embodiment, the gas flow during cooling gas blowing is controlled in two stages. That is, the gas flow from the coating bath temperature to the controlled cooling temperature (a temperature in the range of -10 to -80°C relative to the crystallization temperature of the Mg2Si phase) is set to 100 to 5000 L / min / m 2 The range is preferably set to 500 to 5000 L / min / m 2 The gas flow rate from the controlled cooling temperature to below 300°C is set to 10,000 to 80,000 L / min / m 2 The controlled cooling temperature is a temperature presumed to be the crystallization start temperature of the Mg2Si phase.

[0126] When the gas flow is set to 5000L / min / m 2 When the gas flow is set to 10000 L / min / m 2 In the case of the above range, vibration can be applied to the steel plate during cooling.

[0127] Furthermore, by setting the gas flow from the coating bath temperature to the controlled cooling temperature to 100 to 5000 L / min / m 2 The range is preferably set to 500 to 5000 L / min / m 2 The range of , thereby promoting the nucleation of Si-containing phases other than Mg2Si phase without vibrating the steel plate, so that Mg and Si are concentrated in the unsolidified liquid phase. Next, the gas flow is set to 10000-80000 L / min / m from the controlled cooling temperature to below 300 ° C. 2The range of the gas stream is such that the surface of the unsolidified liquid phase can be vibrated, thereby crystallizing a large amount of Mg2Si phase on the surface of the coating. If the range of the gas stream deviates from the above range, it becomes difficult to crystallize a large amount of Mg2Si phase on the surface of the coating.

[0128] The Mg2Si phase crystallization temperature varies depending on the chemical composition of the coating, so it is calculated using a computational state diagram. Specifically, the thermodynamic data of the intermetallic compound phase and the metal phase that may be contained in the Al-Mg-Zn alloy are collected to construct a computational state diagram database, and the Mg2Si phase crystallization temperature is calculated for each chemical composition of the coating by using the CALPHAD method (phase diagram calculation; CALculation of PHAseDiagram) method. More specifically, the Mg2Si phase crystallization temperature can be estimated by using the thermodynamic equilibrium calculation software "Thermo-Calc" ((Thermo-Calc is a registered trademark) Thermo-Calc Software Co., Ltd.). It should be noted that the thermodynamic equilibrium calculation software used in the calculation is not limited to "Thermo-Calc" (registered trademark), and other software can also be used. The temperature within the range of -10 to -80°C relative to the obtained Mg2Si phase crystallization temperature is used as the controlled cooling temperature.

[0129] In the above-described manufacturing method, by pre-adjusting the surface roughness of the steel sheet, the nucleation of the Mg2Si phase can be suppressed, thereby suppressing the crystallization of the Mg2Si phase near the interface between the coating and the steel sheet. By hot-dip coating such a steel sheet and then controlling the cooling conditions after coating as described above, a large amount of Mg2Si phase is crystallized on the surface of the coating. It is speculated that this can form a large amount of Mg2Si phase with a long diameter of 2 μm or more on the surface of the coating.

[0130] It should be noted that as long as the necessary conditions shown in the present invention are met, the manufacturing method of the plated steel sheet is not limited to the above content. Instead of hot dipping, electroplating, vapor deposition coating, spraying, cold spraying, etc. can also be used.

[0131] Example

[0132] The following describes an embodiment of the present invention. However, the conditions in the embodiment are merely examples of conditions adopted to confirm the feasibility and effectiveness of the present invention. The present invention is not limited to this example of conditions. Various conditions can be adopted in the present invention as long as they do not deviate from the main purpose of the present invention and achieve the purpose of the present invention.

[0133] For the plated base sheet, a cold-rolled steel sheet (0.05C-0.1Si-0.2Mn) with a thickness of 2.3mm is used. A portion of the plated base sheet is subjected to surface roughness control using a skin-pass mill, etc. The steel sheet with adjusted surface roughness is annealed. The annealed steel sheet is immersed in various hot-dip baths and then removed, thereby attaching a coating to the surface of the steel sheet. Subsequently, the steel sheet is cooled using a cooling gas from the time it is removed from the bath until the coating reaches 300°C, thereby producing various plated steel sheets.

[0134] Regarding the surface roughness of the steel sheet surface to be plated, the curve length L of the roughness curve per reference length L0 is p The ratio (L p / L0) is set to 1.1 to 2.7, and the arithmetic mean roughness Ra is set to the range of 0.5 to 3.7 μm.

[0135] (L p The surface roughness (L / L0) and arithmetic mean roughness were measured using a KEYENCE laser microscope (Model: VK-8700). The measurement conditions were: laser confocal mode, high-precision measurement quality, 0.75 μm pitch, dual scan on, 1x optical zoom, plan achromat objective lens, γ coefficient of 0.45, and 0% bias.

[0136] Annealing conditions for steel sheets in a reducing atmosphere include a soaking temperature of 600°C and a soaking time of 10 seconds. The annealing atmosphere is a reducing atmosphere consisting of a mixed gas of 5% hydrogen and the remainder nitrogen. The annealed steel sheets are then air-cooled with nitrogen until the dip plate temperature reaches 20°C above the bath temperature. The sheets are then immersed in the hot-dip coating bath and removed from the bath. The removal speed is set at 20 to 200 mm / second.

[0137] The chemical composition of the plating layer is shown in Table 1. The manufacturing conditions were set as shown in Table 2. The metal structure of the plating layer was evaluated, and the results are shown in Table 3. Furthermore, the flat surface corrosion resistance and end surface corrosion resistance of the plated steel sheet were evaluated, and the results are shown in Table 3.

[0138] The chemical composition and metallographic structure of the coating were evaluated using the aforementioned methods. It should be noted that for Mg2Si phases, measurements were performed on phases with a major diameter of 2 μm or greater. Furthermore, for Mg-Si-Zn-Al phases, measurements were performed on phases with a major diameter of 2 μm or greater. The aspect ratios of the measured Mg2Si and Mg-Si-Zn-Al phases were 2 or greater.

[0139] The evaluation of flat corrosion resistance was performed as follows. The resulting hot-dip coated steel was cut into 100 mm x 50 mm sections and subjected to a flat corrosion resistance evaluation test. Flat corrosion resistance was evaluated using the corrosion acceleration test specified in JASO-CCT-M609, comparing the corrosion loss after 120 cycles. The evaluation criteria were set as follows, with "AAA," "AA," and "A" considered acceptable.

[0140] AAA: Corrosion loss less than 50g / m 2

[0141] AA: Corrosion loss is 50g / m 2 Above and below 90g / m 2

[0142] A: Corrosion loss is 90g / m 2 Above and below 120g / m 2

[0143] B: Corrosion loss is 120g / m 2 above

[0144] For end surface corrosion resistance, the plated steel sheet was cut at an arbitrary location to expose the cut end surface. The cut end surface was then subjected to a neutral salt water spray test specified in JIS Z 2371. Evaluation was based on the occurrence of red rust on the cut end surface. The evaluation criteria for the red rust area ratio are shown below. "AAA," "AA," and "A" were considered acceptable.

[0145] AAA: Red rust area rate is less than 10% after 2500h

[0146] AA: Red rust area rate is less than 10% after 2000h

[0147] A: After 1500h, the red rust area rate is less than 20%

[0148] B: Red rust area rate exceeds 20% at 1500h

[0149] As shown in Tables 1 to 3, Examples 1 to 30 and 39 of the present invention, in which the chemical composition and metal structure of the coating are appropriately controlled, have excellent both flat corrosion resistance and end surface corrosion resistance. 2 range.

[0150] In Comparative Example 31, the amount of Al in the plating layer was insufficient. Therefore, in Comparative Example 31, Si crystallized as a Si phase instead of a Mg2Si phase, resulting in insufficient flat corrosion resistance.

[0151] In Comparative Example 32, the amount of Al in the coating was excessive. Consequently, an Fe-Al-Si interfacial alloy layer formed at the interface between the coating and the steel sheet. However, Si was consumed by the formation of the interfacial alloy layer, preventing the Mg2Si phase from crystallizing on the surface, resulting in reduced end face corrosion resistance.

[0152] In Comparative Example 33, the amount of Mg in the plating layer was insufficient. Therefore, in Comparative Example 33, Si crystallized as a Si phase instead of a Mg2Si phase, and the flat surface corrosion resistance and the end surface corrosion resistance decreased.

[0153] In Comparative Example 34, the amount of Mg in the plating layer was excessive. Therefore, in Comparative Example 34, nucleation of the Mg2Si phase progressed inside the plating layer, and the Mg2Si phase did not crystallize on the surface, resulting in reduced flat corrosion resistance.

[0154] In Comparative Example 35, the Si content of the plating layer was excessive. Therefore, in Comparative Example 35, the nucleation of the Mg2Si phase progressed within the plating layer, and the Mg2Si phase did not crystallize on the surface, resulting in reduced flat and end surface corrosion resistance.

[0155] In Comparative Example 36, the amount of Ca in the plating layer was excessive. Therefore, in Comparative Example 36, a large amount of Ca-containing compounds was generated, and the Mg2Si phase was not crystallized, resulting in reduced flat corrosion resistance and end surface corrosion resistance.

[0156] In Comparative Example 37, the cooling gas flow from the bath temperature to the controlled cooling temperature was excessive. Consequently, in Comparative Example 37, nucleation of the Mg2Si phase progressed within the coating layer, and the Mg2Si phase did not crystallize on the surface, resulting in reduced flat and end surface corrosion resistance.

[0157] In Comparative Example 38, the cooling gas flow was insufficient from the time the cooling temperature was controlled to 300°C. Consequently, in Comparative Example 38, nucleation of the Mg2Si phase progressed within the coating layer, and the Mg2Si phase did not crystallize on the surface, resulting in reduced flat and end surface corrosion resistance.

[0158] [Table 1]

[0159]

[0160] The underlined portion indicates that it is outside the scope of the present invention.

[0161] [Table 2]

[0162]

[0163] The underlined portion indicates conditions outside the range of preferred production conditions.

[0164] [Table 3]

[0165]

[0166] The underlined portion indicates that it is outside the scope of the present invention.

[0167] Industrial applicability

[0168] The plated steel sheet of the present disclosure is excellent in both flat surface corrosion resistance and paint adhesion, and therefore has high industrial applicability.

[0169] Explanation of symbols

[0170] 1 coated steel plate, 11 steel plate, 12 coating.

Claims

1. A plated steel sheet, characterized in that: It comprises a steel plate and a plating layer disposed on the surface of the steel plate. The chemical composition of the coating contains, in mass %,: Al：10.0～25.0％、 Mg: 3.0-10.0%, Fe: 0.01-2.0%, Si: more than 0% and 2.0% or less, further containing one or more species selected from the following groups A, B, and C, The remainder contains Zn and impurities. The number density of the Mg2Si phase with a long diameter of 2 μm or more exposed on the surface of the plating layer is 2 The area is 3 to 150, [Group A]Ni: 0~1.0% [Group B] Ca: 0-0.05% [Group C] One or more of Sb: 0-0.5%, Pb: 0-0.5%, Cu: 0-1.0%, Sn: 0-1.0%, Ti: 0-1.0%, Cr: 0-1.0%, Nb: 0-1.0%, Zr: 0-1.0%, Mn: 0-1.0%, Mo: 0-1.0%, Ag: 0-1.0%, Li: 0-1.0%, La: 0-0.5%, Ce: 0-0.5%, B: 0-0.5%, Y: 0-0.5%, P: 0-0.5%, Sr: 0-0.5%, Co: 0-0.5%, Bi: 0-0.5%, In: 0-0.5%, V: 0-0.5%, W: 0-0.5%: the total is 0-5%.

2. The plated steel sheet according to claim 1, wherein The chemical composition of the plating layer includes Mg: 4.5-8 mass %, Si: 0.1-2 mass %, The number density of the Mg2Si phase with a long diameter of 2 μm or more exposed on the surface of the plating layer is 2 The area is 15 to 150.

3. The plated steel sheet according to claim 1, wherein The chemical composition of Al, Mg and Si in the plating layer is Al: 15-25 mass %, Mg: 4.5-8 mass %, Si: 0.1-2 mass %, The number density of the Mg2Si phase with a long diameter of 2 μm or more exposed on the surface of the plating layer is 2 The area is 30 to 150.

4. The plated steel sheet according to any one of claims 1 to 3, wherein The chemical composition of Al, Mg and Si in the plating layer is Al: 15-25 mass %, Mg: 4.5-8 mass %, Si: 0.1-2 mass %, The number density of the Mg-Si-Zn-Al phase with a long diameter of 2 μm or more exposed on the surface of the plating layer is 2 The area is 5 to 100.

5. The plated steel sheet according to any one of claims 1 to 3, wherein The chemical composition of the plating layer is Sn: 0.05-0.5 mass%, In an X-ray diffraction measurement of the coating, a Mg2Sn phase was detected in the coating. The plated steel sheet according to claim 4 , wherein: The chemical composition of the plating layer is Sn: 0.05-0.5 mass%, In an X-ray diffraction measurement of the coating, a Mg2Sn phase was detected in the coating.

7. The plated steel sheet according to claim 1, wherein The plating layer has a chemical composition containing the group A in mass %.

8. The plated steel sheet according to claim 1, wherein The plating layer has a chemical composition containing the B group in mass %.

9. The plated steel sheet according to claim 1, wherein The plating layer has a chemical composition containing the C group in mass %.

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