Plated steel sheets and automotive components

Abstract

The present invention uses a plated steel sheet equipped with a plating layer disposed on at least part of the surface of a steel sheet, wherein: the plating layer comprises Al in the amount of 10.00-30.00%, Mg in the amount of 1.00-15.00%, and Fe in the amount of 0.01-15.00%, with the remainder being Zn and impurities; the surface of the plating layer is an uneven surface; a cross-section of the plating layer reveals that the relationship between the length Lo of the plating layer in the longitudinal direction of the cross-section in an observed region and the total length Lr of a contour line on the surface of the plating layer in the observed region satisfies the following formula (1); the plating layer includes a plurality of mass-like binary eutectic structures and / or a plurality of mass-like ternary eutectic structures; and at least some of the plurality of mass-like binary eutectic structures or the plurality of mass-like ternary eutectic structures are continuously present from the surface of the plating layer to a location equal to 1 / 2 of the average thickness of the plating layer. Formula (1): (Lr-Lo) / Lo×100≥2.0 (%)

Description

Technical Field

[0001] The present invention relates to a plated steel sheet and an automotive member. This application claims priority based on Japanese Patent Application No. 2023-087179 filed in Japan on May 26, 2023, and incorporates its content herein.

Background Art

[0002] A Zn-Al-Mg-based hot-dip plated steel sheet having a hot-dip Zn plating layer containing Al and Mg has excellent corrosion resistance. Therefore, Zn-Al-Mg-based hot-dip plated steel sheets are widely used as materials for structural members that require corrosion resistance, such as building materials. Recently, due to the high corrosion resistance of Zn-Al-Mg-based hot-dip plating, it has been studied to apply Zn-Al-Mg-based hot-dip plated steel sheets obtained by applying Zn-Al-Mg-based hot-dip plating to high-strength steel sheets such as high-tensile steel to automotive members.

[0003] Patent Document 1 describes a plated steel material having a steel material and a plating layer including a Zn-Al-Mg alloy layer disposed on the surface of the steel material, wherein the Zn-Al-Mg alloy layer has a Zn phase and contains a Mg-Sn intermetallic compound phase in the Zn phase, and the plating layer has a chemical composition consisting of, in mass%, more than 65.0% Zn, more than 5.0% and less than 25.0% Al, more than 3.0% and less than 12.5% Mg, 0.1% to 20.0% Sn, and impurities, and satisfying the following Formulas 1 to 5. Formula 1: Bi + In < Sn Formula 2: Y + La + Ce ≦ Ca Formula 3: Si < Sn Formula 4: O ≦ Cr + Ti + Ni + Co + V + Nb + Cu + Mn < 0.25 Formula 5: O ≦ Sr + Sb + Pb + B < 0.5

[0004] Patent Document 2 describes a plated steel material having a steel material and a plating layer disposed on the surface of the steel material and containing a Zn-Al-Mg alloy layer, wherein in the cross-section of the Zn-Al-Mg alloy layer, the area fraction of the MgZn2 phase is 45-75%, the total area fraction of the MgZn2 phase and Al phase is 70% or more, and the area fraction of the Zn-Al-MgZn2 ternary eutectic structure is 0-5%, and the plating layer consists of, by mass%, Zn: greater than 44.90% to less than 79.90%, Al: greater than 15% to less than 35%, Mg: greater than 5% to less than 20%, Ca: 0.1% to less than 3.0%, and impurities, and element group A is Y, La and Ce, and element When element group B is defined as Cr, Ti, Ni, Co, V, Nb, Cu, and Mn, element group C is defined as Sr, Sb, and Pb, and element group D is defined as Sn, Bi, and In, a plated steel material having a chemical composition in which 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 element group A is 0.1% to 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% is described.

[0005] Automotive plated steel sheets require not only edge corrosion resistance (corrosion resistance at the cut edges) but also good paint adhesion when painted on the plated surface. However, no technology had been considered to improve the paint adhesion of plated layers containing a Zn-Al-Mg alloy layer. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2018 / 139619 [Patent Document 2] International Publication No. 2018 / 139620 [Overview of the project] [Problems that the invention aims to solve]

[0007] This disclosure is made in view of the above circumstances, and aims to provide plated steel sheets and automotive components that have excellent paint adhesion and end-face corrosion resistance. [Means for solving the problem]

[0008] To address the above issues, this disclosure adopts the following configuration. [1] comprising a steel plate and a plating layer disposed on at least a portion of the surface of the steel plate, The average chemical composition of the aforementioned plating layer is, in mass%, Al: 10.00-30.00%, Mg: 1.00~15.00%, Sn: 0.00~1.00%, Si: 0.00~2.00%, Ca: 0.00~2.00%, Ni: 0.00~1.00%, Fe: 0.01~15.00%, Sb: 0.00~0.50%, Pb: 0.00~0.50%, Cu: 0.00~1.00%, Ti: 0.00~1.00%, Cr: 0.00~1.00%, Nb: 0.00~1.00%, Zr: 0.00~1.00%, Mn: 0.00~1.00%, Mo: 0.00~1.00%, Ag: 0.00~1.00%, Li: 0.00~1.00%, Bi: 0.00~1.00%, V: 0.00~1.00%, Co: 0.00~1.00%, In: 0.00~1.00%, W: 0.00~1.00%, P: 0.00~1.00%, La: 0.00~0.50%, Ce: 0.00~0.50%, B: 0.00~0.50%, Y: 0.00 to 0.50%, Sr: 0.00 to 0.50%, Total of Sb, Pb, Cu, Ti, Cr, Nb, Zr, Mn, Mo, Ag, Li, Bi, V, Co, P, In, W, La, Ce, B, Y, Sr: 0.00 to 5.00%, The balance consists of Zn and impurities, The surface of the plating layer is made into an uneven surface, In the cross-section of the plating layer, the relationship between the length Lo in the longitudinal direction of the plating layer within the observation region of the cross-section and the total length Lr of the contour line of the surface of the plating layer within the observation region satisfies the following formula (1), The plating layer contains one or both of a plurality of massive binary eutectic structures or a plurality of massive ternary eutectic structures, A plated steel sheet in which at least a part of the plurality of massive binary eutectic structures or the plurality of massive ternary eutectic structures continuously exists from the surface of the plating layer to a position of 1 / 2 of the average thickness of the plating layer. (Lr - Lo) / Lo × 100 ≥ 2.0 (%) …(1) [2] The plating layer contains an Fe - Al - based interfacial alloy layer in contact with the steel sheet, A plated steel sheet according to [1], in which at least a part of the plurality of massive binary eutectic structures or the plurality of massive ternary eutectic structures continuously exists from the surface of the plating layer to the Fe - Al - based interfacial alloy layer. [3] The number of locations where at least a part of the plurality of massive binary eutectic structures or the plurality of massive ternary eutectic structures continuously exists from the surface of the plating layer to a position of 1 / 2 of the average thickness of the plating layer is 1 to 15 locations per region of a rectangle with a long side of 500 μm and a short side of 150 μm on the surface of the plating layer. The plated steel sheet according to [1]. [4] Instead of the formula (1), the following formula (2) is satisfied, The number of locations where at least a part of the plurality of massive eutectic structures or the plurality of massive ternary eutectic structures is continuously present from the surface of the plating layer to the position of 1 / 2 of the average thickness of the plating layer is 3 to 15 per rectangular region on the surface of the plating layer having a long side of 500 μm and a short side of 150 μm. The plated steel sheet according to [1]. (Lr - Lo) / Lo×100≧6.0(%) …(2) [5] Instead of the formula (1), the following formula (3) is satisfied. The number of locations where at least a part of the plurality of massive eutectic structures or the plurality of massive ternary eutectic structures is continuously present from the surface of the plating layer to the position of 1 / 2 of the average thickness of the plating layer is 5 to 15 per rectangular region on the surface of the plating layer having a long side of 500 μm and a short side of 150 μm. The plated steel sheet according to [1]. (Lr - Lo) / Lo×100≧8.0(%) …(3) [6] At least a part of the plurality of massive eutectic structures or the plurality of massive ternary eutectic structures is continuously present from the surface of the plating layer to the position of 1 / 2 of the average thickness of the plating layer in the concave portion of the uneven surface of the plating layer. The plated steel sheet according to any one of [1], [3], [4], [5]. [7] At least a part of the plurality of massive eutectic structures or the plurality of massive ternary eutectic structures is continuously present from the surface of the plating layer to the Fe - Al - based interfacial alloy layer in the concave portion of the uneven surface of the plating layer. The plated steel sheet according to [2]. [8] In the average chemical composition of the plating layer, Al and Mg are Al: 10.00 to 25.00%, Mg: 4.50 to 15.00%. The plated steel sheet according to [1]. [9] In the average chemical composition of the plating layer, Al and Mg are Al: 15.00 to 22.00%, Mg: 5.00 to 15.00%. The plated steel sheet according to [1]. [[ID=1​​The plated steel sheet according to [1], [8] or [9], wherein the plating layer contains a Mg2Sn phase detected by X-ray diffraction measurement.

[11] The plated steel sheet according to [1], [8] or [9], wherein the average chemical composition of the plating layer contains either or both La and Ce, and the total amount of La and Ce is 0.05 to 0.50%.

[12] The plated steel sheet according to

[10] , wherein the average chemical composition of the plating layer contains either or both La and Ce, and the total amount of La and Ce is 0.05 to 0.50%.

[13] A steel material, a plating layer disposed on at least a portion of the surface of the steel material, and a paint film disposed on the surface of the plating layer, The average chemical composition of the aforementioned plating layer is, in mass%, Al: 10.00-30.00%, Mg: 1.00~15.00%, Sn: 0.00~1.00%, Si: 0.00~2.00%, Ca: 0.00~2.00%, Ni: 0.00~1.00%, Fe: 0.01~15.00%, Sb: 0.00~0.50%, Pb: 0.00~0.50%, Cu: 0.00~1.00%, Ti: 0.00~1.00%, Cr: 0.00~1.00%, Nb: 0.00~1.00%, Zr: 0.00~1.00%, Mn: 0.00~1.00%, Mo: 0.00~1.00%, Ag: 0.00~1.00%, Li: 0.00~1.00%, Bi: 0.00~1.00%, V: 0.00~1.00%, Co: 0.00~1.00%, In: 0.00~1.00%, W: 0.00~1.00%, P: 0.00~1.00%, La: 0.00~0.50%, Ce: 0.00~0.50%, B: 0.00~0.50%, Y: 0.00~0.50%, Sr: 0.00~0.50%, Total of Sb, Pb, Cu, Ti, Cr, Nb, Zr, Mn, Mo, Ag, Li, Bi, V, Co, P, In, W, La, Ce, B, Y, Sr: 0.00~5.00%, The remainder consists of Zn and impurities. The surface of the aforementioned plating layer is an uneven surface, In the cross-section of the plating layer, the relationship between the longitudinal length Lo of the plating layer within the observation area of ​​the cross-section and the total length Lr of the contour line of the surface of the plating layer within the observation area satisfies the following equation (4): The plating layer includes one or both of a plurality of bulky binary eutectic structures or a plurality of bulky ternary eutectic structures. An automotive component in which at least a portion of the multiple lumpy binary eutectic structures or the multiple lumpy ternary eutectic structures are continuously present from the surface of the plating layer to a position half the average thickness of the plating layer. (Lr-Lo) / Lo×100≧2.0(%) …(4) [Effects of the Invention]

[0009] According to this disclosure, it is possible to provide plated steel sheets and automotive components that are excellent in both end-face corrosion resistance and paint adhesion. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic cross-sectional view of a plated steel sheet according to one embodiment of the present disclosure. [Figure 2] Figure 2 is a schematic diagram showing an example of the field of view when observing a cross-section of a plating layer with a scanning electron microscope. [Figure 3] Figure 3 is a schematic diagram showing an example of the field of view when observing a cross-section of a plating layer with a scanning electron microscope. [Figure 4]Figure 4 is a schematic diagram showing an example of the field of view when observing a cross-section of the plating layer of conventional plated steel material with a scanning electron microscope. [Figure 5] Figure 5 is a flowchart of an example of a method for manufacturing a plated steel sheet according to one aspect of the present disclosure. [Modes for carrying out the invention]

[0011] The inventors investigated means to improve the adhesion of paint to the plated layer. The metallic structure of a Zn-Al-Mg hot-dip plated layer containing Al, Mg, and Zn includes various phases or structures. For example, it is known that the Al phase and MgZn2 phase crystallize in the early stages of solidification, and a binary eutectic or ternary eutectic structure crystallizes in the later stages of solidification. The inventors investigated and found that the binary eutectic or ternary eutectic structure has superior adhesion to the paint film compared to the Al phase and MgZn2 phase.

[0012] Incidentally, in conventional Zn-Al-Mg hot-dip galvanized layers, binary or ternary eutectic structures may be exposed on the surface of the galvanized layer. These binary or ternary eutectic structures are often distributed on the surface of the galvanized layer, specifically from the surface to a depth of 1 / 4 to 1 / 3 of the average thickness of the galvanized layer. Conventionally, it was thought that these eutectic structures exposed on the surface of the galvanized layer improved paint adhesion. However, when manufacturing automotive components from plated steel sheets, it is necessary to obtain automotive components of the desired shape by performing various processing on the plated steel sheets. When the galvanized layer is processed, microscopic cracks may occur on its surface due to the strain during processing. It has been found that when such cracks occur around the eutectic structures exposed on the surface of the galvanized layer, the eutectic structures surrounded by the cracks may detach from the galvanized layer, resulting in so-called powdering or flaking, which may not contribute to improved paint adhesion.

[0013] In particular, because the Zn-Al-Mg hot-dip plating layer is harder than the conventional Zn-based plating layer, there is a possibility of a relatively large number of cracks occurring, which increases the frequency of eutectic structure detachment from the plating layer and raises concerns about a decrease in paint adhesion.

[0014] Furthermore, it was expected that having an uneven surface rather than a flat surface on the plated layer could improve paint adhesion.

[0015] Therefore, the inventors investigated and found that by controlling the atmosphere from the time the molten plating bath is removed from the steel plate after the molten plating bath is applied by the molten plating method until the start of cooling, adjusting the cooling rate during cooling, and further selecting a suitable cooling gas, the binary eutectic structure or ternary eutectic structure can be made to exist continuously to a depth deeper than the surface of the plating layer, specifically, at least to a depth of half the average thickness of the plating layer from the surface of the plating layer. Even if cracks occur, the eutectic structure will not detach from the plating layer, thereby preventing a decrease in paint adhesion. Furthermore, they found that by controlling the atmosphere, adjusting the cooling rate, and selecting a suitable cooling gas, the surface of the plating layer can become uneven, further improving paint adhesion.

[0016] The following describes the plated steel sheet and automotive exterior material, which are embodiments of the present disclosure. The plated steel sheet of this embodiment comprises a steel sheet and a plating layer disposed on at least a portion of the surface of the steel sheet, wherein the average chemical composition of the plating layer is, in mass%, Al: 10.00~30.00%, Mg: 1.00~15.00%, Sn: 0.00~1.00%, Si: 0.00~2.00%, Ca: 0.00~2.00%, Ni: 0.00~1.00%, Fe: 0.01~15.00%, Sb: 0.00~0.50%, Pb: 0.00~0.50%, Cu :0.00~1.00%, Ti:0.00~1.00%, Cr:0.00~1.00%, Nb:0.00~1.00%, Zr:0.00~1.00%, Mn:0.00~1.00%, Mo:0.00~1.00%, Ag :0.00~1.00%, Li:0.00~1.00%, Bi:0.00~1.00%, V:0.00~1.00%, Co:0.00~1.00%, In:0.00~1.00%, W:0.00~1.00%, P:0. The composition is as follows: 0.00~1.00%, La:0.00~0.50%, Ce:0.00~0.50%, B:0.00~0.50%, Y:0.00~0.50%, Sr:0.00~0.50%, total of Sb, Pb, Cu, Ti, Cr, Nb, Zr, Mn, Mo, Ag, Li, Bi, V, Co, P, In, W, La, Ce, B, Y, Sr:0.00~5.00%, remainder: Zn and impurities, the surface of the plating layer is uneven, and in the cross-section of the plating layer, cross-section The relationship between the longitudinal length Lo of the plating layer within the observation area and the total length Lr of the contour line on the surface of the plating layer within the observation area satisfies the following equation (1), and the plating layer contains one or both of a plurality of bulky binary eutectic structures or a plurality of bulky ternary eutectic structures, and at least a portion of the plurality of bulky binary eutectic structures or a plurality of bulky ternary eutectic structures exists continuously from the surface of the plating layer to a position half the average thickness of the plating layer, in the case of a plated steel sheet. (Lr-Lo) / Lo×100≧2.0(%) …(1)

[0017] Furthermore, in the plated steel sheet of this embodiment, it is preferable that the plating layer includes an Fe-Al interface alloy layer in contact with the steel sheet, and that at least a portion of a plurality of massive binary eutectic structures or a plurality of massive ternary eutectic structures are continuously present from the surface of the plating layer to the Fe-Al interface alloy layer.

[0018] Furthermore, in the plated steel sheet of this embodiment, it is preferable that at least a portion of the multiple bulky binary eutectic structures or multiple bulky ternary eutectic structures exist continuously from the surface of the plating layer to a position half the average thickness of the plating layer, in the recesses of the uneven surface of the plating layer. Furthermore, in the plated steel sheet of this embodiment, it is preferable that at least a portion of a plurality of massive binary eutectic structures or a plurality of massive ternary eutectic structures exist continuously from the surface of the plating layer to the Fe-Al interface alloy layer, in the recesses of the uneven surface of the plating layer.

[0019] Figure 1 shows a schematic cross-sectional view of the plated steel sheet 1. Figure 1 is a schematic diagram to explain the positional relationship between the steel sheet 11 and the plating layer 12. Note that the uneven surface of the plating layer 12 is omitted from the description in Figure 1.

[0020] As shown in Figure 1, the plated steel sheet 1 according to this embodiment has a steel sheet 11. There are no particular restrictions on the shape of the steel sheet 11. The steel sheet 11 may also be a raw steel sheet that has been formed into, for example, a steel pipe, civil engineering and construction material (fences, corrugated pipes, drainage ditch covers, sand-drift prevention plates, bolts, wire mesh, guardrails, watertight walls, etc.), home appliance component (air conditioner outdoor unit housing, etc.), or automobile component (undercarriage component, exterior component, interior component, structural component, etc.). Forming processes include various plastic deformation methods such as press forming, roll forming, and bending.

[0021] There are no particular restrictions on the material of the steel sheet 11. The steel sheet 11 can be various types of steel sheets, such as general steel, Al-killed steel, ultra-low carbon steel, high carbon steel, various high-tensile steels, and some high-alloy steels (steel containing reinforcing elements such as Ni and Cr). The steel sheet 11 may also be a hot-rolled steel sheet, hot-rolled steel strip, cold-rolled steel sheet, or cold-rolled steel strip as described in JIS G 3302:2010. There are no particular restrictions on the manufacturing method of the steel sheet (hot rolling method, pickling method, cold rolling method, etc.) and its specific manufacturing conditions.

[0022] Furthermore, the steel sheet 11 constituting the plated steel sheet 1 according to this embodiment may be a high-tensile steel sheet for automotive components.

[0023] The plated steel sheet 1 according to this embodiment has a plating layer 12 disposed on at least a portion of the surface of the steel sheet 11. In Figure 1, the plating layer 12 is formed on one side of the steel sheet 11, but the plating layer 12 may be formed on both sides of the steel sheet 11. Preferably, the plating layer 12 is a plating film produced by a so-called hot-dip plating process.

[0024] The plating layer 12 is mainly composed of a Zn-Al-Mg alloy layer, due to its chemical composition which will be described later. In addition, the plating layer 12 of the plated steel sheet 1 according to this embodiment may include an Fe-Al interface alloy layer mainly composed of Fe and Al between the steel sheet 11 and the Zn-Al-Mg alloy layer. In other words, the plating layer 12 may be a single-layer structure of Zn-Al-Mg alloy layers, or it may be a laminated structure including a Zn-Al-Mg alloy layer and an Fe-Al interface alloy layer.

[0025] The following describes the chemical composition of the plating layer. The "%" notation for the content of each element in the chemical composition refers to "mass percent". The elemental content in the chemical composition may also be expressed as elemental concentration (e.g., Zn concentration, Mg concentration, etc.).

[0026] Furthermore, "paint adhesion" refers to the property of the paint film being resistant to peeling when a paint film is applied to the surface of the plating layer, or when a chemical conversion treatment film and a paint film are applied to the surface of the plating layer. "Planar corrosion resistance" refers to the corrosion-resistant property of the plating layer (specifically, the Zn-Al-Mg alloy layer) itself. "End face corrosion resistance" refers to the property of suppressing corrosion of steel sheets at exposed areas (for example, the cut ends of plated steel sheets).

[0027] The plating layer according to this embodiment contains Zn and other alloying elements. The chemical composition of the plating layer is described in detail below. Elements described as having a lower concentration limit of 0.00% are not essential for solving the problems of the plated steel sheet according to this embodiment, but are optional elements that may be included in the plating layer for purposes such as improving properties.

[0028] <Al:10.00~30.00%> Al contributes to improved surface corrosion resistance and workability. Therefore, the Al concentration should be 10.00% or higher. On the other hand, if Al is in excess, the Mg and Zn concentrations will relatively decrease, and the end face corrosion resistance will deteriorate. Therefore, the Al concentration should be 30.00% or lower. The Al concentration may be 10.00 to 25.00% or 15.00 to 22.00%. The Al concentration may be 11.00% or higher, 13.00% or higher, or 16.00% or higher. The Al concentration may be 28.00% or lower, 24.00% or lower, or 20.00% or lower.

[0029] <Mg:1.00~15.00%> Mg is an essential element for ensuring planar corrosion resistance. It is also necessary for crystallizing binary eutectic structures, ternary eutectic structures, and Mg2Sn phases. Therefore, the Mg concentration should be 1.00% or higher. On the other hand, if the Mg concentration is too high, the workability, especially the powdering properties, will deteriorate, and the planar corrosion resistance may further deteriorate. Therefore, the Mg concentration should be 15.00% or lower. The Mg concentration may also be 4.50-15.00% or 5.00-15.00%. The Mg concentration may also be 2.00% or higher, 3.00% or higher, or 4.00% or higher. The Mg concentration may also be 13.00% or lower, 10.00% or lower, or 8.00% or lower.

[0030] The elements described below, with the exception of Fe and Zn, are all optional additives, so their lower limit is set to 0%.

[0031] <Sn:0.00~1.00%> The Sn concentration may be 0%. On the other hand, Sn is an element that forms intermetallic compounds with Mg and improves the planar corrosion resistance of the plating layer. Therefore, the Sn concentration may be 0.05% or higher, 0.10% or higher, or 0.20% or higher. However, if the Sn concentration is too high, the planar corrosion resistance will deteriorate. Therefore, the Sn concentration should be 1.00% or lower. The Sn concentration may also be 0.80% or lower, 0.60% or lower, 0.50% or lower, 0.20% or lower, or 0.06% or lower.

[0032] <Si:0.00%~2.00%> The Si concentration may be 0.00%. On the other hand, Si contributes to improving planar corrosion resistance. It is also a necessary element for crystallizing the Mg2Si phase. Therefore, the Si concentration may be greater than 0.00%, 0.01% or more, 0.05% or more, or 0.10% or more. On the other hand, if the Si concentration is too high, planar corrosion resistance deteriorates. Therefore, the Si concentration should be 2.00% or less. The Si concentration may also be 1.80% or less, 1.50% or less, 1.20% or less, or 1.00% or less.

[0033] <Ca:0.00~2.00%> The Ca concentration may be 0%. On the other hand, Ca is an element that can adjust the optimal amount of Mg elution to impart planar corrosion resistance. Therefore, the Ca concentration may be 0.01% or higher, or 0.02% or higher. On the other hand, if the Ca concentration is too high, planar corrosion resistance and workability will deteriorate. Therefore, the Ca concentration should be 2.00% or lower. The Ca concentration may also be 1.00% or lower, 0.50% or lower, 0.10% or lower, or 0.05% or lower.

[0034] <Ni:0.00~1.00%> The Ni concentration may be as low as 0.00%. On the other hand, Ni contributes to improving end-face corrosion resistance. Therefore, the Ni concentration may be 0.001% or higher. However, if the Ni concentration is too high, the planar corrosion resistance deteriorates. Therefore, the Ni concentration should be 1.00% or less. The Ni concentration may also be 0.50% or less, 0.10% or less, or 0.01% or less.

[0035] <Fe:0.01~15.00%> The Fe concentration may be 0%, but since Fe may be mixed into the plating layer from the base steel sheet, it may be contained in the plating layer at a concentration of 0.01% or more. It has been confirmed that there is no adverse effect on the performance of the plating layer if the Fe concentration is 15.00% or less. The Fe concentration may be, for example, 0.01% or more, 0.10% or more, or 0.50% or more. The Fe concentration shall be 15.00% or less. The Fe concentration may be 10.00% or less, 5.00% or less, 2.00% or less, or 1.00% or less.

[0036] <Sb、Pb:それぞれ0.00~0.50%> The concentrations of Sb and Pb may be as low as 0.00%. On the other hand, Sb and Pb contribute to improving end face corrosion resistance. Therefore, the concentrations of Sb and Pb, respectively, may be 0.01% or higher, 0.03% or higher, or 0.05% or higher. On the other hand, if the concentrations of Sb and Pb are excessive, the surface corrosion resistance deteriorates. Therefore, the concentrations of Sb and Pb, respectively, should be 0.50% or lower. The concentrations of Sb and Pb, respectively, may be 0.40% or lower, 0.20% or lower, or 0.10% or lower.

[0037] <Cu、Ti、Cr、Nb、Zr、Mn、Mo、AgおよびLi:それぞれ0.00~1.00%> The concentrations of Cu, Ti, Cr, Nb, Zr, Mn, Mo, Ag, and Li may each be 0%. On the other hand, these elements contribute to improved end-face corrosion resistance. Therefore, the concentration of each of these elements may be 0.01% or higher. On the other hand, if the concentration of each of these elements is excessive, the planar corrosion resistance deteriorates. Therefore, the concentration of each of these elements should be 1.00% or less. The concentrations of these elements may also be 0.50% or less, 0.10% or less, 0.05% or less, or 0.03% or less, respectively.

[0038] <Bi、V、Co、In、W:それぞれ0.00~1.00%> The concentrations of Bi, V, Co, In, and W may be 0%. On the other hand, each of these elements contributes to improving end face corrosion resistance. Therefore, the concentrations of these elements may be set to 0.001% or higher, or 0.01% or higher, respectively. On the other hand, if the concentrations of these elements are excessive, the planar corrosion resistance deteriorates. Therefore, the concentrations of Bi, V, Co, In, and W should be 1.00% or lower, respectively. The concentrations of these elements may also be 0.50% or lower, 0.10% or lower, 0.02% or lower, or 0.01% or lower, respectively.

[0039] <P:0.00~1.00%> The concentration of P may be 0%. On the other hand, P contributes to improving end face corrosion resistance. Therefore, the concentration of P may be 0.005% or higher, or 0.01% or higher. On the other hand, if the concentration of P is excessive, the surface corrosion resistance deteriorates. Therefore, the concentration of P should be 1.00% or lower. The concentration of P may be 0.05% or lower, 0.03% or lower, or 0.01% or lower.

[0040] <B、YおよびSr:それぞれ0.00~0.50%> The concentrations of B, Y, and Sr may be 0.00%. On the other hand, B, Y, and Sr contribute to improving end face corrosion resistance. Therefore, the concentrations of these elements may be 0.001% or higher, or 0.01% or higher, respectively. On the other hand, if the concentrations of B, Y, and Sr are excessive, the planar corrosion resistance deteriorates. Therefore, the concentrations of these elements should be 0.50% or lower, respectively. The concentrations of these elements may also be 0.10% or lower, 0.02% or lower, or 0.01% or lower, respectively.

[0041] <La、Ce:それぞれ0.00~0.50%> The concentrations of La and Ce may be 0%. On the other hand, La and Ce contribute to improving the corrosion resistance of the end face. Therefore, the concentrations of these elements may each be 0.01% or more. On the other hand, if the concentrations of La and Ce are excessive, the planar corrosion resistance deteriorates. Therefore, the concentrations of these elements are each set to 0.50% or less. The concentrations of these elements may each be 0.10% or less, 0.05% or less, or 0.02% or less. Also, the total amount of La and Ce is preferably set to 0.05 to 0.50%.

[0042] <Total of Sb, Pb, Cu, Ti, Cr, Nb, Zr, Mn, Mo, Ag, Li, Bi, V, Co, In, W, P, La, Ce, B, Y, Sr: 0.00 - 5.00%> The total of these elements is set to 0 to 5%. If the total exceeds 5%, the planar corrosion resistance or the end - face corrosion resistance may decrease.

[0043] <Balance: Zn and impurities> The balance of the components of the plating layer according to this embodiment is Zn and impurities. Zn is an element that provides planar corrosion resistance and end - face corrosion resistance to the plating layer. Impurities refer to components contained in the raw materials or components mixed in the manufacturing process, and are not components intentionally contained. For example, in the plating layer, due to the mutual atomic diffusion between the base steel plate and the plating bath, trace amounts of components other than Fe may be mixed in as impurities.

[0044] Also, for the plating layer according to this embodiment, the total of Al, Mg, and Zn is preferably 74.00% or more, and may be 80.00% or more, 90.00% or more, 95.00% or more, or 98.00% or more.

[0045] The chemical composition of the plating layer is measured by the following method. First, an acid solution containing an inhibitor that suppresses the corrosion of the steel plate is used to strip and dissolve the plating layer to obtain an acid solution. Next, the obtained acid solution is subjected to ICP analysis. Thereby, the chemical composition of the plating layer can be obtained. The type of acid is not particularly limited as long as it can dissolve the plating layer. Note that the chemical composition measured by the above means is the average chemical composition of the entire plating layer.

[0046] <Surface of the plated layer> The surface of the plating layer in this embodiment is an uneven surface. The roughness of the uneven surface is expressed by the relationship between Lo and Lr, as shown in the following formula (1). That is, (Lr-Lo) / Lo×100 must be 2.0(%) or more. If (Lr-Lo) / Lo×100 is less than 2.0(%), the roughness of the uneven surface is small, and the paint adhesion cannot be improved. It is more preferable that (Lr-Lo) / Lo×100 satisfies the following formula (2), and even more preferable that it satisfies the following formula (3). There is no particular upper limit required for (Lr-Lo) / Lo×100, but if it is too large, the surface smoothness of the plating layer will decrease, and consequently the surface flatness of the paint film will also decrease, so it is preferable to have a value of 40(%) or less, 20(%) or less, or 12(%) or less.

[0047] (Lr-Lo) / Lo×100≧2.0(%) …(1) (Lr-Lo) / Lo×100≧6.0(%) …(2) (Lr-Lo) / Lo×100≧8.0(%) …(3)

[0048] In equations (1) to (3), length Lo is the longitudinal length of the plating layer within the observation area of ​​the cross-section, and Lr is the total length of the contour line on the surface of the plating layer within the observation area. The observation area is the field of view when observing the cross-section of the plating layer with a scanning electron microscope. Lo is the longitudinal length of the plating layer that fits within this field of view, and Lr is the total length of the contour line on the surface of the plating layer corresponding to the longitudinal length Lo. When measuring Lo and Lr, it is desirable to set the field of view when observing with a scanning electron microscope so that the longitudinal length Lo of the plating layer is 500 μm. Alternatively, multiple fields of view may be combined to synthesize an observation field in which the longitudinal length Lo of the plating layer is 500 μm. The observation field of view should be positioned at least 5 mm away from the edge of the plated steel sheet. If the plated steel sheet has a welded section, the observation field of view should be positioned at least 1 mm away from the weld bead. Furthermore, if the plated steel sheet has a bent section, the observation field of view should be positioned at least 2 mm away from the bent section. This eliminates the influence of cutting, welding, and bending processes on the surface properties of the plating layer from the measurement results. The field of view is preferably positioned on a flat surface. However, plated steel sheets may not always have flat surfaces. For example, when plated steel sheets are used as exterior parts for automobiles, they may have a generally gently curved shape and may not have flat surfaces. In this case, it is preferable to position the field of view in an area with a radius of curvature of 5 mm or more. The number of observation fields will be 5. First, calculate (Lr-Lo) / Lo × 100 for each of the 5 observation fields, and then find the arithmetic mean of these values. This arithmetic mean will be considered as (Lr-Lo) / Lo × 100 for the plated steel sheet. Figure 2 shows a schematic example of the field of view observed with a scanning electron microscope. Figure 2 also shows the relationship between Lo and Lr. In Figure 2, reference numeral 11 denotes the steel plate, reference numeral 12 denotes the plating layer, and reference numeral 13 denotes the interface alloy layer. The double arrows for Lo and Lr schematically represent the lengths of Lo and Lr, respectively. Figure 2 also schematically represents the surface irregularities of the plating layer.

[0049] <Structure of the plated layer> The plating layer of this embodiment includes one or both of a plurality of bulky binary eutectic structures or a plurality of bulky ternary eutectic structures. The binary eutectic structure is a eutectic structure of η-Zn phase and Al-Zn phase, and the ternary eutectic structure is a eutectic structure of Al phase, Zn phase and MgZn2 phase. These eutectic structures may be formed by the lamellar aggregation of each phase constituting the eutectic structure. That is, the binary eutectic structure may have a lamellar structure in which layered η-Zn phase and layered Al-Zn phase are superimposed. The ternary eutectic structure may have a lamellar structure in which layered Al phase, layered Zn phase and layered MgZn2 phase are superimposed.

[0050] In addition to these eutectic structures, the plating layer also contains massive Al phases, Al-Zn phases, Zn phases, MgZn2 phases, etc. Furthermore, the plating layer may form a eutectoid structure containing layered Zn phases and layered Al phases. This eutectoid structure has a lamellar structure but does not correspond to a binary eutectic or ternary eutectic structure.

[0051] In the plating layer of this embodiment, at least a portion of multiple massive binary eutectic or ternary eutectic structures are continuously present from the surface of the plating layer to a position half the average thickness of the plating layer. At least a portion of these massive binary eutectic or ternary eutectic structures are exposed on the surface of the plating layer. Compared to other phases such as the Al phase and Al-Zn phase, the binary eutectic or ternary eutectic structure has excellent adhesion to the paint film. Therefore, the exposure of the binary eutectic or ternary eutectic structure to the surface of the plating layer improves the adhesion of the paint film to the entire plating layer.

[0052] Furthermore, when cracks occur in the plating layer during processing of plated steel sheets, the resulting cracks often propagate along the interface between the binary eutectic or ternary eutectic structure and other phases / structures. In this embodiment, at least a portion of the binary eutectic or ternary eutectic structure is continuously present up to half the average thickness of the plating layer. Therefore, cracks generated during bending propagate from the surface of the plating layer toward the steel sheet, and are less likely to propagate in a direction parallel to the surface of the plating layer. As a result, even if cracks occur, the eutectic structure is less likely to detach from the plating layer, and powdering or flaking is suppressed. Consequently, even if the plating layer is processed, the paint adhesion of the plating layer does not deteriorate.

[0053] In this embodiment, it is preferable that at least a portion of the multiple bulky binary eutectic or ternary eutectic structures are continuously present from the surface of the plating layer to the Fe-Al interface alloy layer. This further suppresses the occurrence of powdering or flaking, and improves the paint adhesion of the plating layer.

[0054] Figure 3 shows an enlarged schematic diagram of an example of the plating layer of this embodiment. It shows the presence of a binary eutectic or ternary eutectic structure. In Figure 3, the uneven surface of the plating layer 12 is schematically represented, and the presence of a binary eutectic or ternary eutectic structure is shown. The shaded area in the figure represents the binary eutectic or ternary eutectic structure. In Figure 3, reference numeral 11 denotes the steel plate, reference numeral 12 denotes the plating layer, reference numeral 13 denotes the interface alloy layer, and reference numeral 14 denotes the binary eutectic or ternary eutectic structure.

[0055] As shown in Figure 3, it can be seen that the binary eutectic or ternary eutectic structure 14 is continuous from the surface of the plating layer 12 toward the steel sheet 11. Furthermore, it can be seen that the binary eutectic or ternary eutectic structure 14 is continuously present up to the Fe-Al interface alloy layer 13 on the steel sheet 11 side of the plating layer 12. In Figure 3, an example is shown where most of the binary eutectic or ternary eutectic structure 14 is continuous up to the Fe-Al interface alloy layer 13 on the steel sheet 11 side of the plating layer 12. However, this embodiment is not limited to this, and may include binary eutectic or ternary eutectic structures 14 that are continuous up to the 1 / 2 position of the plating layer 12.

[0056] For reference, a schematic cross-sectional view of a conventional plating layer is shown in Figure 4. In the conventional plating layer 112, the surface of the plating layer is flat, and the binary eutectic or ternary eutectic structure 114 is distributed near the interface alloy layer 113 of the plating layer 112 or near the surface of the plating layer. No binary eutectic or ternary eutectic structure 114 is found that extends continuously to the 1 / 2 position of the plating layer 112.

[0057] Furthermore, as illustrated in Figures 2 and 3, the surface of the plating layer 12 in this embodiment is an uneven surface. The binary eutectic structure or ternary eutectic structure 14, which exists continuously to a depth of half the average thickness of the plating layer 12, is abundant in the depressions of the uneven surface, as shown in Figure 3. This is because, as will be described later, the binary eutectic structure or ternary eutectic structure 14 crystallizes in the latter half of the solidification process of the plating layer. The concentration of the binary eutectic structure or ternary eutectic structure 14 in the depressions, combined with the morphological effects of the uneven surface, can improve paint adhesion.

[0058] Furthermore, in this embodiment, a binary eutectic or ternary eutectic structure that extends continuously from the surface of the plating layer to the Fe-Al interface alloy layer may be present in large quantities in the recesses of the uneven surface.

[0059] As will be described later in the explanation of the manufacturing method, the binary eutectic or ternary eutectic structure begins to crystallize after the Al phase or Al-Zn phase has crystallized. It is thought that the crystallization of these eutectic structures begins with nucleation in the region of the plating layer on the steel sheet side, more specifically on the surface of the Fe-Al interface alloy layer. It is also thought that the crystallization of the eutectic structure progresses toward the surface of the plating layer. Therefore, it is thought that most of the binary eutectic or ternary eutectic structures in this embodiment exist continuously from the surface of the plating layer to the Fe-Al interface alloy layer.

[0060] However, when observing the internal structure of the plating layer in any cross-section, the entire binary eutectic or ternary eutectic structure is not always observed in a continuous form from the surface of the plating layer to the Fe-Al interface alloy layer. This is because the individual shapes of the massive binary eutectic or ternary eutectic structures are irregular, and therefore, the form of the binary eutectic or ternary eutectic structure appears different depending on the position of the cross-section.

[0061] The inventors have found that if, at least a portion of multiple massive binary eutectic or ternary eutectic structures are observed to be continuously present from the surface of the plating layer to a position half the average thickness of the plating layer, then it is highly probable that a large portion of the binary eutectic or ternary eutectic structures exist in a continuous form from the surface of the plating layer to the Fe-Al interface alloy layer, thereby improving paint adhesion.

[0062] In this embodiment, it is preferable that the number of locations where a binary eutectic or ternary eutectic structure exists continuously from the surface of the plating layer to a position half the average thickness of the plating layer is 1 to 15 locations per rectangular area on the surface of the plating layer with a long side of 500 μm and a short side of 150 μm. It is undesirable if the number of locations is less than 1, as this will result in insufficient paint adhesion. Furthermore, if formula (2) is true, it is preferable that the number of such locations be 3 to 15. Moreover, if formula (3) is true, it is preferable that the number of such locations be 5 to 15.

[0063] The presence of a binary or ternary eutectic structure can be confirmed as follows: A rectangular area with a long side of 500 μm and a short side of 150 μm is defined on the surface of the plating layer. The position of this area is determined by the same means as the observation field used to evaluate the roughness of the uneven surface of the plating layer, as described above. Within the region in question, the number and location of binary eutectic or ternary eutectic structures exposed on the surface of the plating layer are confirmed. Next, the surface of the plating layer including the region in question is sequentially ground down to depths of 1 / 4, 1 / 2, 3 / 4, and 9 / 10 of the average thickness of the plating layer, and then mirror-polished to create an observation surface. Then, at each of the 1 / 4, 1 / 2, 3 / 4, and 9 / 10 depths, the number and location of binary eutectic or ternary eutectic structures on the observation surface at each depth are confirmed. Finally, the number of binary eutectic or ternary eutectic structures appearing at the same location is counted at the surface of the plating layer, and at the 1 / 4 and 1 / 2 depths. Whether a structure appears at the same location can be considered to be the same if the eutectic structure is within a projection range of a radius of 15 μm from the centroid of the eutectic structure on the surface of the plating layer. A binary or ternary eutectic structure appearing in the same location is determined to be continuous from the surface of the plating layer to a point half the average thickness of the plating layer. There are no particular restrictions on the grinding method, but examples include precision machining such as polishing and focused ion beam (FIB) processing.

[0064] Furthermore, the presence of a binary or ternary eutectic structure appearing at the same location is confirmed at all depths: the surface of the plating layer, 1 / 4 position depth, 1 / 2 position depth, 3 / 4 position depth, and 9 / 10 position depth. As a result, the binary or ternary eutectic structure appearing at the same location is identified as being continuous from the surface of the plating layer to the Fe-Al interface alloy layer.

[0065] The average thickness of the plating layer is defined as the average thickness of the plating layer in a rectangular area with a long side of 500 μm and a short side of 150 μm. Then, the position at the interface between the steel plate and the plating layer, at a height corresponding to the average thickness of the plating layer, is estimated as the average surface position of the plating layer. Based on this estimated surface position, the 1 / 4, 1 / 2, 3 / 4, and 9 / 10 position depths of the average thickness of the plating layer are determined.

[0066] Furthermore, when the plating layer contains 0.05 to 0.5% Sn, it is preferable that the plating layer also contains a Mg2Sn phase. Since the amount of Mg2Sn phase is small, its presence can be detected and confirmed by X-ray diffraction measurement using the θ-2θ method. The inclusion of the Mg2Sn phase in the plating layer further improves the edge corrosion resistance of the plating layer. X-ray diffraction measurement to detect the Mg2Sn phase can be performed using the θ-2θ measurement method.

[0067] The amount of plating deposited on one side of the plated layer is, for example, 20-200 g / m². 2 It should be within the range. The amount of adhesive applied per side should be 20g / m². 2 By doing so, the corrosion resistance of the plated steel sheet on both the surface and the edges can be further improved. On the other hand, the amount of coating applied per side is 200 g / m². 2 The processability of plated steel sheets can be further improved by doing the following.

[0068] In this embodiment, a film may be formed on the plated steel sheet. One or more layers of film can be formed. Examples of films that can be formed directly on the plated layer include chromate films, phosphate films, and chromate-free films. These films can be formed by known methods such as chromate treatment, phosphate treatment, and chromate-free treatment, as will be described later.

[0069] The plated steel sheet of this embodiment described above has excellent paint adhesion and edge corrosion resistance.

[0070] Furthermore, the automotive component of this embodiment is obtained by cutting the plated steel sheet of this embodiment into a predetermined planar shape and processing it into a predetermined three-dimensional shape by press forming or the like, and then forming a paint film thereafter. That is, the automotive component of this embodiment comprises a steel material, a plating layer disposed on at least a part of the surface of the steel material, and a paint film disposed on the surface of the plating layer, wherein the average chemical composition of the plating layer is as described above, the surface of the plating layer is an uneven surface, and in the cross-section of the plating layer, the relationship between the longitudinal length Lo of the plating layer in the observation area of ​​the cross-section and the total length Lr of the contour line of the surface of the plating layer in the observation area satisfies the following formula (4), and the plating layer contains one or both of a plurality of bulky binary eutectic structures or a plurality of bulky ternary eutectic structures, and at least a part of the plurality of bulky binary eutectic structures or a plurality of bulky ternary eutectic structures exists continuously from the surface of the plating layer to a position half the thickness of the plating layer.

[0071] (Lr-Lo) / Lo×100≧2.0 …(4)

[0072] The automotive component of this embodiment described above exhibits excellent paint adhesion and end-face corrosion resistance.

[0073] Next, the manufacturing method for the plated steel sheet of this embodiment will be described. While the manufacturing method is not limited to a specific method as long as the plated steel sheet of this embodiment can be manufactured, for example, the plated steel sheet of this embodiment can be easily obtained by the manufacturing conditions described below.

[0074] The manufacturing method for plated steel sheets in this embodiment involves annealing the steel sheet in a reducing atmosphere, immersing the annealed steel sheet in a molten plating bath immediately after annealing, and then removing it to form a plating layer on the surface of the steel sheet. Next, cooling is performed by blowing a cooling gas onto the plated layer until its temperature rises from the bath temperature to 260°C. During this process, the oxygen concentration in the atmosphere on the surface of the plating bath and the oxygen concentration in the atmosphere from the time the steel sheet is removed from the plating bath until cooling is completed are controlled to be within the range of 100 to 5000 ppm. Furthermore, the average cooling rate during which the temperature of the plated layer rises from the bath temperature to 260°C is set to 15°C / second or higher. In addition, cooling is performed by injecting a cooling gas, and the dew point of the cooling gas is set to 0°C or higher.

[0075] That is, the method for manufacturing the plated steel sheet in this embodiment is as shown in the flowchart of Figure 5, (S1) A process of annealing steel plates in a reducing atmosphere, (S2) A step of immersing a steel plate in a molten plating bath, (S3) The process of removing the steel plate from the molten plating bath, (S4) A step of blowing cooling gas onto a steel plate to which a molten plating bath has been applied, It has, (A) In immersion S2 and withdrawal S3, the oxygen concentration in the atmosphere on the surface of the molten plating bath is set to a range of 100 to 5000 ppm. (B) In spraying S4, the dew point of the cooling gas is set to 0°C or higher. (C) In spraying S4, the average cooling rate until the temperature of the plating layer rises from the temperature of the molten plating bath to 260°C shall be 15°C / second or more. (D) In ​​spraying S4, the oxygen concentration in the atmosphere from the time the steel sheet is removed from the plating bath until the cooling is completed is set to a range of 100 to 5000 ppm. By combining all of conditions A, B, C, and D, the plated steel sheet of this embodiment is obtained. The details of the manufacturing method will be described below in order.

[0076] (S1 Annealing) Annealing of the steel sheet to be used as the plating base is carried out 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.

[0077] (S2 immersion) Next, the annealed steel plate is immersed in a molten plating bath. The chemical composition of the plating bath can be adjusted as appropriate to obtain the chemical composition of the plating layer described above. The temperature of the plating bath is also not particularly limited, and any temperature at which molten plating can be performed can be appropriately selected. For example, the plating bath temperature may be set to a value approximately 20°C or more higher than the melting point of the plating bath.

[0078] (S3 upgrade) Next, the steel sheet is removed from the plating bath. The amount of plating layer can be controlled by controlling the removal speed of the steel sheet. If necessary, the amount of plating layer can also be controlled by wiping the steel sheet with the plating layer attached. The amount of plating layer is not particularly limited and can be, for example, within the range described above.

[0079] (S4 spray application) Next, the plating layer is cooled. Cooling is performed by blowing a cooling gas onto the steel plate immediately after it is removed from the molten plating bath. Cooling by blowing the cooling gas is performed continuously until the temperature of the steel plate rises from the bath temperature to 260°C. The cooling conditions below 260°C are not particularly limited, and cooling by blowing the cooling gas may be continued, or natural cooling may be allowed.

[0080] The oxygen concentration in the atmosphere on the surface of the plating bath, and the oxygen concentration in the atmosphere from the time the steel plate is removed from the plating bath until cooling is completed, are controlled to be in the range of 100 to 5000 ppm. Preferably, the oxygen concentration in these atmospheres is in the range of 100 to 1000 ppm. When the molten metal of the plating bath adhering to the steel plate solidifies, an oxide film is formed on the outermost surface of the molten metal in the initial stages of solidification, and the thickness of this oxide film is affected by the oxygen concentration in the atmosphere. When the oxide film reaches an appropriate thickness, in the subsequent solidification process, the oxide film follows the change in shape of the surface of the plating layer, and an uneven surface satisfying the above formula (1) is formed.

[0081] If the oxygen concentration on the surface of the plating bath and in the atmosphere from the time the steel plate is removed from the plating bath until cooling is complete is less than 100 ppm, a sufficiently thick oxide film will not form, making it difficult to create an uneven surface on the plated layer. Furthermore, if the oxygen concentration in the atmosphere exceeds 5000 ppm, a relatively thick oxide film with a flat surface shape will form in the early stages of solidification. The oxide film will not follow the changes in the shape of the plated layer surface during the solidification process, resulting in a flat surface on the plated layer after solidification, and thus failing to satisfy equation (1) above. In addition, if the oxygen concentration in the atmosphere exceeds 5000 ppm, the oxide film becomes prone to cracking, and it may become difficult to maintain the shape of the plated layer during solidification. The means for maintaining the oxygen concentration in the atmosphere above the surface of the plating bath within the range of 100 to 5000 ppm are not particularly limited. For example, a cover can be provided to cover the surface of the plating bath, and a gas with an oxygen concentration of 100 to 5000 ppm can be supplied inside the cover. The type of gas supplied to the surface of the plating bath is not particularly limited as long as the oxygen concentration is within the range of 100 to 5000 ppm, and may be a non-oxidizing gas such as nitrogen, an inert gas such as argon, or a mixture of these gases. To maintain an oxygen concentration in the atmosphere between 100 and 5000 ppm from the time the steel plate is removed from the plating bath until cooling is complete, for example, the oxygen concentration of the cooling gas sprayed onto the steel plate should be within the range of 100 to 5000 ppm. If air is used as the cooling gas, the oxygen concentration of the cooling gas will be excessive, and a suitable plating layer cannot be obtained.

[0082] Furthermore, by raising the dew point of the cooling gas to 0°C or higher, the function of maintaining the shape of the oxide film can be maintained. If the dew point of the cooling gas falls below 0°C, a plating layer whose surface shape satisfies the above formula (1) cannot be obtained. The type of cooling gas is not particularly limited as long as the oxygen concentration is within the range of 100 to 5000 ppm, and may be a non-oxidizing gas such as nitrogen, an inert gas such as argon, or a mixture of these gases.

[0083] Furthermore, the average cooling rate during which the temperature of the plating layer rises from the bath temperature to 260°C shall be 15°C / second or higher. There is no particular upper limit to the average cooling rate, but for example, it may be 200°C / second or lower. By setting the average cooling rate to 15°C / second or higher, sufficient crystallization of Al primary crystals (Al phase) and Al-Zn phase is achieved in the initial stages of the solidification process. The average cooling rate during which the temperature of the plating layer rises from the bath temperature to 260°C is calculated using the following formula. Cooling time is the time from when the steel plate is removed from the plating bath until the temperature of the plating layer drops to 260°C. Average cooling rate = (bath temperature - 260) ÷ cooling time

[0084] As the primary Al phase (Al phase) and Al-Zn phase crystallize sufficiently in the initial stages of solidification, the amount of molten metal on the surface of the steel sheet decreases. Then, as the temperature of the molten metal decreases, the crystallization of binary eutectic and ternary eutectic structures begins, and these eutectic structures form to fill the periphery of the Al phase and Al-Zn phase that have already crystallized. Since the crystallization of eutectic structures begins when the amount of remaining molten metal is small, the binary eutectic and ternary eutectic structures form depressions in the plating layer. Furthermore, the crystallization of eutectic structures mainly begins in the region of the plating layer closer to the steel sheet, and more specifically, crystallization begins from nucleation on the surface of the Fe-Al interface alloy layer and progresses toward the surface of the plating layer. As a result, the binary eutectic and ternary eutectic structures exist continuously from the steel sheet side to the surface side of the plating layer.

[0085] After the plating layer is formed, various chemical conversion treatments and painting treatments may be performed.

[0086] In this embodiment, a coating may be formed on the hot-dip galvanized steel material. One or more coatings may be formed. Examples of coatings directly on the galvanized layer include chromate coatings, phosphate coatings, and chromate-free coatings. These coatings can be formed by known methods such as chromate treatment, phosphate treatment, and chromate-free treatment.

[0087] Chromate treatments include electrolytic chromate treatment, which forms a chromate film by electrolysis; reactive chromate treatment, which forms a film by reacting with the material and then washes away excess treatment solution; and coating chromate treatment, which applies the treatment solution to the object to be coated and allows it to dry without washing with water to form a film. Any of these treatments may be used.

[0088] Examples of electrolytic chromate treatments include those using chromic acid, silica sol, resins (such as phosphoric acid, acrylic resin, vinyl ester resin, vinyl acetate acrylic emulsion, carboxylated styrene-butadiene latex, diisopropanolamine-modified epoxy resin, etc.), and hard silica.

[0089] Examples of phosphate treatments include zinc phosphate treatment, zinc calcium phosphate treatment, and manganese phosphate treatment.

[0090] Chromate-free treatment is particularly suitable because it does not burden the environment. Chromate-free treatments include electrolytic chromate-free treatment, which forms a chromate-free film by electrolysis; reactive chromate-free treatment, which forms a film using a reaction with the material and then washes away excess treatment solution; and coating-type chromate-free treatment, which applies the treatment solution to the object to be coated and forms a film by drying without washing. Any of these treatments may be used.

[0091] Furthermore, one or more layers of organic resin film may be present on the film directly above the plating layer. The organic resin is not limited to any particular type and can include, for example, polyester resin, polyurethane resin, epoxy resin, acrylic resin, polyolefin resin, or modified versions of these resins. Here, a modified version refers to a resin obtained by reacting a reactive functional group contained in the structure of these resins with another compound (such as a monomer or crosslinking agent) that contains a functional group in its structure that can react with that functional group.

[0092] Such organic resins may be a mixture of one or more organic resins (unmodified), or a mixture of one or more organic resins obtained by modifying at least one other organic resin in the presence of at least one organic resin. The organic resin film may also contain any coloring pigment or rust-preventive pigment. Water-based solutions can also be used by dissolving or dispersing them in water.

[0093] Furthermore, as long as the requirements shown in this disclosure are met, the method for manufacturing plated steel sheets is not limited to the above, and electroplating, vapor deposition, thermal spraying, cold spraying, etc., may be used instead of the hot-dip galvanizing method. [Examples]

[0094] The following describes embodiments of the present invention. However, the conditions in the embodiments are merely examples of conditions adopted to confirm the feasibility and effectiveness of the present invention. The present invention is not limited to these examples of conditions. The present invention can adopt various conditions as long as it does not depart from the spirit of the invention and achieves the objectives of the present invention.

[0095] Cold-rolled steel sheet (0.05C-0.1Si-0.2Mn) with a thickness of 1.6 mm was used as the base material for plating. First, the steel sheet was annealed. After annealing, the steel sheet was immersed in various molten plating baths and then removed to deposit a plating layer on the surface of the steel sheet. Next, various plated steel sheets were manufactured by cooling with a cooling gas from immediately after removal from the plating bath until the plating layer reached 260°C. The cooling gas consisted mainly of nitrogen gas. The oxygen concentration and dew point of the cooling gas are as shown in Tables 2A and 2B.

[0096] The annealing conditions for steel plates in a reducing atmosphere were as follows: the soaking temperature was set to 800°C and the soaking time to 10 seconds. The annealing atmosphere was a reducing atmosphere consisting of a mixed gas of 5% hydrogen and the remainder nitrogen. The oxygen concentration in the annealing atmosphere was kept below 20 ppm. After annealing, the steel plates were air-cooled with nitrogen gas until the immersion plate temperature reached the bath temperature + 20°C. Then, they were immersed in the molten plating bath for approximately 3 seconds before being removed. The removal speed was set to 20-200 mm / second. During removal, the amount of plating deposited was controlled with N2 wiping gas.

[0097] The chemical composition of the plating layer was as shown in Tables 1A and 1B. The manufacturing conditions were as shown in Tables 2A and 2B. The morphology of the binary eutectic or ternary eutectic structure in the plating layer was evaluated, and the results are shown in Tables 3A and 3B. Furthermore, the paint adhesion and edge corrosion resistance of the plated steel sheet were evaluated, and the results are shown in Tables 3A and 3B.

[0098] The chemical composition, microstructure, and surface topography of the plating layer were evaluated using the methods described above. The surface topography was evaluated by setting an observation field where the longitudinal length Lo of the plating layer was within a range of 500 μm. The presence or absence of the Mg2Sn phase was determined by performing X-ray diffraction measurements on the surface of the plating layer and confirming whether or not a diffraction peak of Mg2Sn was observed.

[0099] End face corrosion resistance (simulated end face corrosion resistance) was evaluated by cutting plated steel sheets at arbitrary points to expose the cut ends, subjecting the cut ends to a neutral salt spray test as defined in JIS Z 2371, and evaluating the degree of red rust formation at the cut ends. The evaluation criteria for the red rust area ratio are shown below. "AAA", "AA", and "A" were considered acceptable. The results are shown in Tables 3A and 3B.

[0100] (evaluation) AAA: Red rust area ratio of 10% or less after 2500 hours AA: Red rust area ratio of 10% or less after 2000 hours A: Red rust area ratio of 20% or less after 1500 hours B: Red rust area ratio exceeds 20% after 1500 hours

[0101] To assess paint adhesion (adhesion strength), a 50 x 100 mm sample was taken from a plated steel sheet, treated with Zn phosphoric acid (SD5350 system: Nippon Paint Industrial Coating Co., Ltd. standard), and then electrodeposited (PN110 Powernix® Gray: Nippon Paint Industrial Coating Co., Ltd. standard) to a thickness of 20 μm. The sample was then baked at 150°C for 20 minutes. Afterward, the steel sheet was subjected to V-bending using a die with a 60° angle and a radius of curvature of 10 mm. After unbending, it was immersed in a 5% NaAl aqueous solution at 50°C for 1000 hours. A tape peel test was then performed by applying adhesive tape only to the V-bent surface and instantly peeling it off. The ratio of the area where the paint peeled off to the area where the adhesive tape was applied was calculated and evaluated as follows. "AAA", "AA", and "A" were considered acceptable. The results are shown in Tables 3A and 3B.

[0102] (evaluation) AAA: Peeling area ratio less than 13% AA: Peeling area ratio of 13% or more and less than 25% A: Peeling area ratio of 25% or more and less than 35% B: Peeling area ratio of 35% or more

[0103] The plated steel sheets No. 1 to 31 had an uneven surface on the plated layer, and contained multiple massive binary eutectic structures or ternary eutectic structures, or both, within the plated layer. A portion of the eutectic structure, which extends continuously from the plated layer surface to half the thickness of the plated layer or to the depth of the Fe-Al interface alloy layer, was located in the recesses of the uneven surface. The chemical composition of the plated layer and the morphology of the eutectic structure were within the scope of this disclosure, and both end-face corrosion resistance and paint adhesion were excellent.

[0104] No. 32 had insufficient Al content in the plating layer. As a result, (Lr-Lo) / Lo × 100 was small for No. 32, leading to insufficient paint adhesion.

[0105] In No. 33, the amount of Al in the plating layer was excessive. As a result, the (Lr-Lo) / Lo × 100 ratio for No. 33 was small, leading to insufficient paint adhesion.

[0106] In No. 34, the amount of Mg in the plating layer was insufficient. As a result, (Lr-Lo) / Lo × 100 was small in No. 34, leading to insufficient paint adhesion. End face corrosion resistance was also reduced.

[0107] In No. 35, the amount of Mg in the plating layer was excessive. As a result, (Lr-Lo) / Lo × 100 was small in No. 35, leading to insufficient paint adhesion.

[0108] In No. 36, the oxygen concentration in the atmosphere from the top of the plating bath to the end of the cooling process exceeded 5000 ppm. As a result, (Lr-Lo) / Lo × 100 was small in No. 36, resulting in insufficient paint adhesion.

[0109] In No. 37, the average cooling rate from the plating bath temperature to 260°C was low. As a result, in No. 37, the primary Al crystal (Al phase or Al-Zn phase) did not crystallize sufficiently, (Lr-Lo) / Lo × 100 became small, and paint adhesion was insufficient.

[0110] [Table 1A]

[0111] [Table 1B]

[0112] [Table 2A]

[0113] [Table 2B]

[0114] [Table 3A]

[0115] [Table 3B] [Explanation of symbols]

[0116] 1…Plated steel sheet 11...Steel plate 12, 112… Plating layer 13, 113...Interfacial alloy layer 14, 114...Binary eutectic or ternary eutectic structure

Claims

1. The device comprises a steel plate and a plating layer disposed on at least a portion of the surface of the steel plate, The average chemical composition of the aforementioned plating layer is, in mass%, Al: 10.00-30.00%, Mg: 1.00-15.00%, Sn: 0.00-1.00%, Si: 0.00-2.00%, Ca: 0.00-2.00%, Ni: 0.00 to 1.00%, Fe: 0.01-15.00%, Sb: 0.00 to 0.50%, Pb: 0.00-0.50%, Cu: 0.00-1.00%, Ti: 0.00-1.00%, Cr: 0.00-1.00%, Nb: 0.00-1.00%, Zr: 0.00 to 1.00%, Mn: 0.00-1.00%, Mo: 0.00-1.00%, Ag: 0.00-1.00%, Li: 0.00-1.00%, Bi: 0.00-1.00%, V: 0.00-1.00%, Co: 0.00-1.00%, In: 0.00 to 1.00%, W: 0.00~1.00%, P: 0.00-1.00%, La: 0.00-0.50%, Ce: 0.00-0.50%, B: 0.00-0.50%, Y: 0.00-0.50%, Sr: 0.00-0.50%, Total of Sb, Pb, Cu, Ti, Cr, Nb, Zr, Mn, Mo, Ag, Li, Bi, V, Co, P, In, W, La, Ce, B, Y, Sr: 0.00 to 5.00%, The remainder consists of Zn and impurities. The surface of the aforementioned plating layer is an uneven surface, In the cross-section of the plating layer, the relationship between the longitudinal length Lo of the plating layer within the observation area of ​​the cross-section and the total length Lr of the contour line of the surface of the plating layer within the observation area satisfies the following equation (1): The aforementioned plating layer includes one or both of a plurality of bulky binary eutectic structures or a plurality of bulky ternary eutectic structures. At least a portion of the multiple bulky binary eutectic structures or the multiple bulky ternary eutectic structures are continuously present from the surface of the plating layer to a position half the average thickness of the plating layer. The aforementioned observation area is the field of view when the cross-section of the plating layer is observed with a scanning electron microscope. The length of the plating layer in the longitudinal direction that falls within the observation field is Lo. The total length of the contour line on the surface of the plating layer corresponding to the length Lo in the longitudinal direction of the plating layer is Lr. When measuring Lo and Lr, the observation field when observing with the scanning electron microscope is set such that the length Lo in the longitudinal direction of the plating layer is 500 μm. Plated steel sheet. 40(%)≧(Lr-Lo) / Lo×100≧2.0(%)…(1)

2. The plating layer includes an Fe-Al interface alloy layer in contact with the steel plate. The plated steel sheet according to claim 1, wherein at least a portion of the multiple bulky binary eutectic structures or the multiple bulky ternary eutectic structures are continuously present from the surface of the plating layer to the Fe-Al interface alloy layer.

3. The plated steel sheet according to claim 1, wherein the number of locations where at least a portion of the multiple lumpy binary eutectic structures or multiple lumpy ternary eutectic structures are continuously present from the surface of the plating layer to a position half the average thickness of the plating layer is 1 to 15 locations per rectangular area on the surface of the plating layer with a long side of 500 μm and a short side of 150 μm.

4. Instead of equation (1) above, the following equation (2) must be satisfied: The plated steel sheet according to claim 1, wherein the number of locations where at least a portion of the multiple lumpy binary eutectic structures or multiple lumpy ternary eutectic structures are continuously present from the surface of the plating layer to a position half the average thickness of the plating layer is 3 to 15 locations per rectangular area on the surface of the plating layer with a long side of 500 μm and a short side of 150 μm. 40(%)≧(Lr-Lo) / Lo×100≧6.0(%)…(2)

5. Instead of equation (1) above, the following equation (3) must be satisfied: The plated steel sheet according to claim 1, wherein the number of locations where at least a portion of the multiple lumpy binary eutectic structures or multiple lumpy ternary eutectic structures are continuously present from the surface of the plating layer to a position half the average thickness of the plating layer is 5 to 15 locations per rectangular area on the surface of the plating layer with a long side of 500 μm and a short side of 150 μm. 40(%)≧(Lr-Lo) / Lo×100≧8.0(%)…(3)

6. A plated steel sheet according to any one of claims 1, 3, 4, or 5, wherein at least a portion of the multiple lumpy binary eutectic structures or the multiple lumpy ternary eutectic structures are continuously present in a location extending from the surface of the plating layer to a position half the average thickness of the plating layer, and this location is in a recess of the uneven surface of the plating layer.

7. The plated steel sheet according to claim 2, wherein at least a portion of the multiple bulky binary eutectic structures or the multiple bulky ternary eutectic structures are continuously present from the surface of the plating layer to the Fe-Al interface alloy layer, and the locations where these structures are present are in the recesses of the uneven surface of the plating layer.

8. The plated steel sheet according to claim 1, wherein the average chemical composition of the plating layer is Al: 10.00 to 25.00% and Mg: 4.50 to 15.00%.

9. The plated steel sheet according to claim 1, wherein the average chemical composition of the plating layer is Al: 15.00 to 22.00% and Mg: 5.00 to 15.00%.

10. In the average chemical composition of the aforementioned plating layer, Sn is 0.05 to 0.50%. Mg detected in the aforementioned plating layer by X-ray diffraction measurement ２ A plated steel sheet according to claim 1, claim 8, or claim 9, which has an Sn phase.

11. The plated steel sheet according to claim 1, claim 8, or claim 9, wherein the average chemical composition of the plating layer contains either or both La and Ce, and the total amount of La and Ce is 0.05 to 0.50%.

12. The plated steel sheet according to claim 10, wherein the average chemical composition of the plating layer contains either or both La and Ce, and the total amount of La and Ce is 0.05 to 0.50%.

13. The invention comprises a steel material, a plating layer disposed on at least a portion of the surface of the steel material, and a paint film disposed on the surface of the plating layer, The average chemical composition of the aforementioned plating layer is, in mass%, Al: 10.00-30.00%, Mg: 1.00-15.00%, Sn: 0.00-1.00%, Si: 0.00-2.00%, Ca: 0.00-2.00%, Ni: 0.00 to 1.00%, Fe: 0.01-15.00%, Sb: 0.00 to 0.50%, Pb: 0.00-0.50%, Cu: 0.00-1.00%, Ti: 0.00-1.00%, Cr: 0.00-1.00%, Nb: 0.00-1.00%, Zr: 0.00 to 1.00%, Mn: 0.00-1.00%, Mo: 0.00-1.00%, Ag: 0.00-1.00%, Li: 0.00-1.00%, Bi: 0.00-1.00%, V: 0.00-1.00%, Co: 0.00-1.00%, In: 0.00 to 1.00%, W: 0.00~1.00%, P: 0.00-1.00%, La: 0.00-0.50%, Ce: 0.00-0.50%, B: 0.00-0.50%, Y: 0.00-0.50%, Sr: 0.00-0.50%, Total of Sb, Pb, Cu, Ti, Cr, Nb, Zr, Mn, Mo, Ag, Li, Bi, V, Co, P, In, W, La, Ce, B, Y, Sr: 0.00 to 5.00%, The remainder consists of Zn and impurities. The surface of the aforementioned plating layer is an uneven surface, In the cross-section of the plating layer, the relationship between the longitudinal length Lo of the plating layer within the observation area of ​​the cross-section and the total length Lr of the contour line of the surface of the plating layer within the observation area satisfies the following equation (4): The aforementioned plating layer includes one or both of a plurality of bulky binary eutectic structures or a plurality of bulky ternary eutectic structures. At least a portion of the multiple bulky binary eutectic structures or the multiple bulky ternary eutectic structures are continuously present from the surface of the plating layer to a position half the average thickness of the plating layer. The aforementioned observation area is the field of view when the cross-section of the plating layer is observed with a scanning electron microscope. The length of the plating layer in the longitudinal direction that falls within the observation field is Lo. The total length of the contour line on the surface of the plating layer corresponding to the length Lo in the longitudinal direction of the plating layer is Lr. When measuring Lo and Lr, the observation field when observing with the scanning electron microscope is set such that the length Lo in the longitudinal direction of the plating layer is 500 μm. Automotive components. 40(%)≧(Lr-Lo) / Lo×100≧2.0(%)…(4)

Images