Plated steel sheet

Abstract

To further suppress the occurrence of LME and paint film blistering during welding.A plated steel sheet according to the present invention includes on at least a part of a surface of a steel sheet, a plating layer having a chemical composition containing, by mass %, Al: 30.00 to 70.00%, Mg: 7.00 to 20.00%, Fe: 0.01 to 15.00%, and selectively containing one or two or more elements selected from the group consisting of an element group A to an element group G with a balance composed of 5.00 mass % or more of Zn and impurities, wherein: in a surface structure of the plating layer, an average area ratio of an α / τ lamellar structure being a metal structure in which rod-shaped α phases are dispersed in a τ parent phase is 30% or more and 95% or less; and in a measured result obtained by measuring the plating layer by an X-ray diffraction method, an intensity ratio I220 / I111 of an intensity I220 of a peak corresponding to a (220) plane of the α phase to an intensity I111 of a peak corresponding to a (111) plane of the α phase is 0.25 or more.

Description

TECHNICAL FIELD

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

[0002] A galvanized steel sheet is a widely used material in the fields of construction, automobiles, and the like from the viewpoint of improving the corrosion resistance of structural members. In this case, a method of manufacturing various structural members by welding the galvanized steel sheet galvanized in advance, by arc welding, laser welding, or the like is used.

[0003] Here, problems unique to the case of manufacturing the structural member by welding galvanized steel sheets are liquid metal embrittlement (LME) cracking caused by hot-dip plating at heat-affected portions of a weld metal and a base material and degradation in corrosion resistance around a welded portion (welding heat-affected portion) due to blowhole formation caused by Zn evaporation during welding.

[0004] To solve the above problems of the LME and the blowhole formation, various proposals have been conventionally made. For example, Patent Document 1 below proposes a plated steel material which includes a steel sheet and a plating layer located on a surface of the steel sheet and including a Zn—Al—Mg alloy layer, wherein in a cross-section of the Zn—Al—Mg alloy layer, an area fraction of a MnZn2 phase is 45 to 75%, a total area fraction of the MgZn2 phase and an Al phase is 70% or more, and an area fraction of a Zn—Al—MgZn2 ternary eutectic structure is 0 to 5%, the plating layer having a predetermined chemical composition.PRIOR ART DOCUMENTPatent Document

[0005] Patent Document 1: International Publication Pamphlet No. WO 2018 / 139620SUMMARY OF THE INVENTIONProblems to be Solved by the Invention

[0006] Here, the problems of the LME and blowhole formation can be solved by using the plated steel material proposed in Patent Document 1 above. However, as a result of intensive studies by the present inventors, there is still room for improvement in the technique proposed in Patent Document 1 above. The present inventors have found that further improvement can be expected by employing a technical approach different from Patent Document 1 above to the problem related to the LME and the problem related to the paint film blistering during welding.

[0007] Hence, the present invention has been made in view of the above problems, and an object of the present invention is to provide a plated steel sheet that can further suppress the occurrence of the LME and the paint film blistering during welding.Means for Solving the Problems

[0008] As a result of the intensive studies about the paint film blistering during welding to solve the above problems, the present inventors have found that it is possible to suppress the paint film blistering during welding while suppressing the occurrence of the LME during welding by controlling the orientation of a specific metal structure in a surface structure of the plating layer, and have completed the present invention.

[0009] The gist of the present invention completed based on the findings is as follows.

[0010] (1) A plated steel sheet including on at least a part of a surface of the steel sheet, a plating layer having a chemical composition containing, by mass %, Al: 30.00 to 70.00%, Mg: 7.00 to 20.00%, Fe: 0.01 to 15.00%, and selectively containing one or two or more elements selected from the group consisting of following element group A, element group B, element group C, element group D, element group E, element group F, and element group G with a balance composed of 5.00 mass % or more of Zn and impurities, wherein: in a surface structure of the plating layer, an area ratio of an α / τ lamellar structure being a metal structure in which rod-shaped α phases are dispersed in a τ parent phase is 30% or more and 95% or less; and in a measured result obtained by measuring the plating layer by an X-ray diffraction method, an intensity ratio I220 / I111 of an intensity I220 of a peak corresponding to a (220) plane of the α phase to an intensity I111 of a peak corresponding to a (111) plane of the α phase is 0.25 or more.

[0011] [Element group A]: one or two selected from the group consisting of Si: more than 0% and 10.00% or less and Ca: more than 0% and 4.00% or less

[0012] [Element group B]: one or two or more selected from the group consisting of Sb: more than 0% and 0.5000% or less, Pb: more than 0% and 0.5000% or less, and Sr: more than 0% and 0.5000% or less

[0013] [Element group C]: one or two or more selected from the group consisting of Cu: more than 0% and 1.0000% or less, Ti: more than 0% and 1.0000% or less, Cr: more than 0% and 1.0000% or less, Nb: more than 0% and 1.0000% or less, Ni: more than 0% and 1.0000% or less, Mn: more than 0% and 1.0000% or less, Mo: more than 0% and 1.0000% or less, Co: more than 0% and 1.0000% or less, and V: more than 0% and 1.0000% or less

[0014] [Element group D]: one or two or more selected from the group consisting of Sn: more than 0% and 1.0000% or less, In: more than 0% and 1.0000% or less, and Bi: more than 0% and 1.0000% or less

[0015] [Element group E]: one or two or more selected from the group consisting of Zr: more than 0% and 1.0000% or less, Ag: more than 0% and 1.0000% or less, and Li: more than 0% and 1.0000% or less

[0016] [Element group F]: one or two or more selected from the group consisting of La: more than 0% and 0.5000% or less, Ce: more than 0% and 0.5000% or less, and Y: more than 0% and 0.5000% or less

[0017] [Element group G]: B: more than 0% and 0.5000% or less

[0018] (2) The plated steel sheet according to (1) having a chemical composition containing the element group A.

[0019] (3) The plated steel sheet according to (1) having a chemical composition containing the element group B.

[0020] (4) The plated steel sheet according to (1) having a chemical composition containing the element group C.

[0021] (5) The plated steel sheet according to (1) having a chemical composition containing the element group D.

[0022] (6) The plated steel sheet according to (1) having a chemical composition containing the element group E.

[0023] (7) The plated steel sheet according to (1) having a chemical composition containing the element group F.

[0024] (8) The plated steel sheet according to (1) having a chemical composition containing the element group G.

[0025] (9) The plated steel sheet according to any one of (1) to (8), wherein the plating layer contains 9.00 mass % or more of Mg.

[0026] (10) The plated steel sheet according to any one of (1) to (8), wherein the intensity ratio I220 / I111 is 0.50 or more.

[0027] (11) The plated steel sheet according to (9), wherein the intensity ratio I220 / I111 is 0.50 or more.

[0028] (12) The plated steel sheet according to (10), wherein the intensity ratio I220 / I111 is 1.00 or more.

[0029] (13) The plated steel sheet according to (11), wherein the intensity ratio I220 / I111 is 1.00 or more.Effect of the Invention

[0030] As explained above, according to the present invention, it is possible to provide a plated steel sheet that can further suppress the occurrence of the LME and the paint film blistering during welding.BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1A is an explanatory view schematically illustrating a configuration of a plated steel sheet according to an embodiment of the present invention.

[0032] FIG. 1B is an explanatory view schematically illustrating the configuration of the plated steel sheet according to the embodiment.

[0033] FIG. 2 is a schematic view for explaining an α / τ lamellar structure in a plating layer of the plated steel sheet in this embodiment.

[0034] FIG. 3 is a schematic view for explaining the α / τ lamellar structure in the plating layer of the plated steel sheet in this embodiment.

[0035] FIG. 4 is a schematic view for explaining the α / τ lamellar structure in the plating layer of the plated steel sheet in this embodiment.

[0036] FIG. 5 is an explanatory diagram for explaining the intensity of a peak in an XRD measured result.EMBODIMENTS FOR CARRYING OUT THE INVENTION

[0037] Preferred embodiments of the present invention will be explained in detail below with reference to the accompanying drawings. Note that, in the description and drawings, the same reference signs denote components having substantially the same functional configurations to omit redundant explanation thereof.(Regarding a Plated Steel Sheet)

[0038] First, an overall configuration of a plated steel sheet according to an embodiment of the present invention will be explained with reference to FIG. 1A and FIG. 1B. FIG. 1A and FIG. 1B are explanatory views schematically illustrating an example of the plated steel sheet according to this embodiment.

[0039] As schematically illustrated in FIG. 1A, a plated steel sheet 1 according to this embodiment has a steel sheet 10 being a base material, and a plating layer 20 located on at least a part of a surface of the steel sheet 10. Further, the plating layer 20 may be present on both surfaces of the steel sheet 10 as schematically illustrated in FIG. 1B instead of being present only on one surface of the steel sheet 10 as illustrated in FIG. 1A.<Regarding the Steel Sheet 10>

[0040] The dimension, component, structure, and mechanical property of the steel sheet 10 used as the base material of the plated steel sheet 1 according to this embodiment are not particularly limited. For example, various types of steel sheets can be used according to the mechanical strength (for example, tensile strength) or the like required for the plated steel sheet 1. Examples of the steel sheet 10 include various types of Al-killed steel, ultralow carbon steel containing Ti, Nb, and the like, high-strength steel further containing strengthening elements such as P, Si, and Mn in the ultralow carbon steel, various steel sheets containing other various components (Cr, N, Cu, B, Ni, Mg, Ca, V, Co, Zn, As, Y, Zr, Mo, Sn, Sb, Ta, W, Pb, Bi, REM, and the like), and so on.

[0041] Besides, the thickness of the steel sheet 10 is not particularly limited and only needs to be set appropriately according to the mechanical strength and the like required for the plated steel sheet 1.<Regarding the Plating Layer 20>

[0042] The plating layer 20 is provided on the surface of the steel sheet 10 as schematically illustrated in FIG. 1A and FIG. 1B, and is more preferably provided over the entire surface of the steel sheet 10. In the following, a chemical composition of the plating layer 20 will be first explained in detail.Regarding the Chemical Composition of the Plating Layer 20

[0043] The chemical composition of the plating layer 20 according to this embodiment has, in an aspect, a chemical composition containing, by mass %, Al: 30.00 to 70.00%, Mg: 7.00 to 20.00%, and Fe: 0.01 to 15.00, with the balance composed of 5.0000 mass % or more of Zn and impurities. In other words, in the chemical composition of the plating layer 20 according to this embodiment, the contents of Al, Mg, and Fe are within the above ranges and the total of these contents is 95.0000 mass % or less, with the balance composed of 5.0000 mass % or more of Zn and impurities.

[0044] Further, the chemical composition of the plating layer 20 according to this embodiment has, in another aspect, a chemical composition containing, by mass %, Al: 30.00 to 70.00%, Mg: 7.00 to 20.00%, Fe: 0.01 to 15.00%, and one or two or more selected from the group consisting of the following element group A, element group B, element group C, element group D, element group E, element group F, and element group G, with the balance composed of 5.0000 mass % or more of Zn and impurities. In other words, in the chemical composition of the plating layer 20 according to this embodiment, the contents of Al, Mg, and Fe are within the above ranges and the total of the contents of these Al, Mg, Fe, and element group A to element group G is 95.0000 mass % or less, with the balance composed of 5.0000 mass % or more of Zn and impurities.

[0045] [Element group A]: one or two selected from the group consisting of Si: more than 0% and 10.00% or less and Ca: more than 0% and 4.00% or less

[0046] [Element group B]: one or two or more selected from the group consisting of Sb: more than 0% and 0.5000% or less, Pb: more than 0% and 0.5000% or less, and Sr: more than 0% and 0.5000% or less

[0047] [Element group C]: one or two or more selected from the group consisting of Cu: more than 0% and 1.0000% or less, Ti: more than 0% and 1.0000% or less, Cr: more than 0% and 1.0000% or less, Nb: more than 0% and 1.0000% or less, Ni: more than 0% and 1.0000% or less, Mn: more than 0% and 1.0000% or less, Mo: more than 0% and 1.0000% or less, Co: more than 0% and 1.0000% or less, and V: more than 0% and 1.0000% or less

[0048] [Element group D]: one or two or more selected from the group consisting of Sn: more than 0% and 1.0000% or less, In: more than 0% and 1.0000% or less, and Bi: more than 0% and 1.0000% or less

[0049] [Element group E]: one or two or more selected from the group consisting of Zr: more than 0% and 1.0000% or less, Ag: more than 0% and 1.0000% or less, and Li: more than 0% and 1.0000% or less

[0050] [Element group F]: one or two or more selected from the group consisting of La: more than 0% and 0.5000% or less, Ce: more than 0% and 0.5000% or less, and Y: more than 0% and 0.5000% or less

[0051] [Element group G]: B: more than 0% and 0.5000% or less

[0052] As explained above, the plating layer 20 according to this embodiment is a plating layer having a chemical composition containing, by mass %, Al: 30.00 to 70.00%, Mg: 7.00 to 20.00%, Fe: 0.01 to 15.00%, and selectively containing one or two or more elements selected from the group consisting of the element group A, element group B, element group C, element group D, element group E, element group F, and element group G, with the balance composed of 5.0000 mass % or more of Zn and impurities.

[0053] [Al: 30.00 to 70.00 mass %]

[0054] Al is an element necessary to constitute a main metal structure (Zn—Al—Mg-based metal structure) of the plating layer 20 according to this embodiment, and is contained in a predetermined content or more to ensure corrosion resistance of a region to be a welding heat-affected portion and corrosion resistance of a region to be a non-welded portion, as a plated steel sheet. If an Al content in the plating layer 20 is less than 30.00 mass %, the above corrosion resistance of the regions to be the welding heat-affected portion and the non-welded portion cannot be ensured. Therefore, in the plating layer 20 according to this embodiment, the Al content is 30.00 mass % or more. The Al content is preferably 34.00 mass % or more, and more preferably 38.00 mass % or more. The Al content falling within the above range can ensure the corrosion resistance of the plated steel sheet 1.

[0055] On the other hand, if the Al content in the plating layer 20 exceeds 70.00 mass %, an Al phase which functions as a cathode when placed in a corrosive environment excessively increases and the corrosion of base iron is likely to proceed, so that the corrosion resistance of the plated steel sheet 1 cannot be ensured. Therefore, in the plating layer 20 according to this embodiment, the Al content is 70.00 mass % or less. The Al content is preferably 60.00 mass % or less, and more preferably 50.00 mass % or less.

[0056] [Mg: 7.00 to 20.00 mass %]

[0057] Mg is an element necessary to constitute the main metal structure (Zn—Al—Mg-based metal structure) of the plating layer 20 according to this embodiment, and is contained in a predetermined content or more to ensure the corrosion resistance of the region to be the welding heat-affected portion and the corrosion resistance of the region to be the non-welded portion, as the plated steel sheet. Therefore, in the plating layer 20 according to this embodiment, an Mg content is 7.00 mass % or more. The Mg content is preferably 9.00 mass % or more, and more preferably 10.00 mass % or more. The Mg content falling within the above range can ensure the corrosion resistance of the plated steel sheet 1.

[0058] On the other hand, if the Mg content in the plating layer 20 exceeds 20.00 mass %, anodic dissolution of the plating layer when placed in the corrosive environment is likely to proceed, so that the corrosion resistance of the plated steel sheet 1 cannot be ensured. Therefore, in the plating layer 20 according to this embodiment, the Mg content is 20.00 mass % or less. The Mg content is preferably 15.00 mass % or less, and more preferably 13.00 mass % or less. The Mg content falling within the above range can ensure the corrosion resistance of the plated steel sheet 1.

[0059] [Fe: 0.01 to 15.00 mass %]

[0060] Elements constituting the steel sheet 10, which is the base material, may be sometimes mixed into the plating layer 20. Especially in a hot-dip plating method, the elements constituting the steel sheet 10 are easily mixed into the plating layer 20 due to interdiffusion of the elements by a solid-liquid reaction between the steel sheet 10 and the plating layer 20. Due to the mixing of the elements, a certain amount of Fe is contained in the plating layer 20, and its content is generally 0.01 mass % or more. When the above interdiffusion is promoted, adhesiveness between the steel sheet 10 and the plating layer 20 is improved. From the viewpoint of improving the adhesiveness between the steel sheet 10 and the plating layer 20, an Fe content in the plating layer 20 is preferably 0.20 mass % or more.

[0061] Further, Fe may be intentionally added to a plating bath to be used when manufacturing the plating layer 20 within a range that does not impair the effect of the present invention. However, when the Fe content in the plating bath is increased, a high-melting point intermetallic compound of Fe and Al is formed in the plating bath, and the high-melting point intermetallic compound adheres, as dross, to the plating layer 20 to significantly degrade an appearance quality, which is undesirable. From this viewpoint, the Fe content in the plating bath is adjusted so that the Fe content in the plating layer 20 is 15.00 mass % or less. The Fe content in the plating layer 20 is more preferably 10.00 mass % or less.

[0062] In the plating layer 20, the balance of Al, Mg, and Fe is composed of 5.0000 mass % or more of Zn and impurities.

[0063] Zn is an element necessary to constitute the main metal structure (Zn—Al—Mg-based metal structure) of the plating layer 20 according to this embodiment, and is an important element to improve the corrosion resistance of the plated steel sheet. Further, the plating layer 20 containing the above Al, Mg, and Fe in the above ranges and further containing 5.00 mass % or more of Zn makes it possible to ensure the corrosion resistance required for the plated steel sheet.

[0064] Next, the element group A to the element group E which the chemical composition of the plating layer 20 according to another aspect of this embodiment can selectively have will be explained in detail.

[0065] Note that in the case where at least any of the following elements belonging to the element group B to element group E is contained in the plating layer 20 according to this embodiment, it is preferable that at least any of the following elements belonging to the element group B to element group E is contained in the following content range and a total content is 5.0000 mass % or less.

[0066] Setting the total content of the elements belonging to the element group B to the element group E to 5.0000 mass % or less makes it possible to enjoy the effects exhibited by the addition of the elements as explained in detail below without impairing effects each other. The total content of the elements belonging to the element group B to the element group E is preferably 1.0000 mass % or less, and more preferably 0.2000 mass % or less.The Element Group A

[0067] The element group A which the plating layer 20 can contain in another aspect of the plating layer 20 according to this embodiment will be explained. At least any of the following elements in the element group A is an element which can be contained in the plating layer 20 in place of a part of the balance Zn.

[0068] [Element group A]: one or two selected from the group consisting of Si: more than 0% and 10.00% or less and Ca: more than 0% and 4.00% or less

[0069] [Si: 0 to 10.00 mass %]

[0070] A case where the plating layer 20 according to this embodiment does not contain Si is conceivable, and therefore the lower limit of its content is 0 mass %. On the other hand, Si is an element capable of suppressing excessive growth of a Fe—Al-based intermetallic compound phase that is formed at an interface between the plating layer and the steel sheet and further improving the adhesiveness between the plating layer and the steel sheet. In the case where Si is contained in the plating layer 20, a Si content is preferably 0.05 mass % or more and more preferably 0.20 mass % or more to suppress the excessive growth of the Fe—Al-based metal structure. On the other hand, if the Si content exceeds 10.00 mass %, an intermetallic compound for a high melting point with Mg may be excessively formed to inhibit the formation of an Al—Mg oxide having Zn evaporation suppression effect, so that it becomes difficult to suppress Zn evaporation when the plated steel sheet is welded.

[0071] On the other hand, if the Si content in the plating bath for manufacturing the plating layer 20 is too high, the viscosity of the plating bath may increase more than necessary, and operability during the manufacture of the plated steel sheet (hereinafter, called “plating operability”) may decrease. Therefore, the Si content in the plating bath is adjusted from the viewpoint of the plating operability, so that the Si content in the plating layer 20 is preferably 5.00 mass % or less, more preferably 4.00 mass % or less, and furthermore preferably 2.00 mass % or less.

[0072] [Ca: 0 to 4.00 mass %]

[0073] A case where the plating layer 20 according to this embodiment does not contain Ca is conceivable, and therefore the lower limit of its content is 0 mass %. On the other hand, when Ca is contained in the plating layer 20, it forms intermetallic compounds with Al and Zn. Furthermore, when Si is contained together with Ca in the plating layer 20, Ca forms an intermetallic compound with Si. These intermetallic compounds have high melting points and stable structures, and therefore can further suppress liquid metal embrittlement (LME) during welding of the plated steel sheet. In the case where Ca is contained in the plating layer 20, the effect of suppressing the LME during welding can be exhibited by setting the Ca content to 0.01 mass % or more. The Ca content in the plating layer 20 is more preferably 0.10 mass % or more.

[0074] On the other hand, if the Ca content in the plating layer 20 exceeds 4.00 mass %, the corrosion resistance of the plated steel sheet may decrease. From this viewpoint, the Ca content in the plating layer 20 is 4.00 mass % or less. The Ca content in the plating layer 20 is preferably 2.50 mass % or less, and more preferably 1.50 mass % or less.The Element Group B

[0075] Next, the element group B which the plating layer 20 can contain in another aspect of the plating layer 20 according to this embodiment will be explained. At least any of the following elements in the element group B is an element which can be contained in the plating layer 20 in place of a part of the balance Zn.

[0076] [Element group B]: one or two or more selected from the group consisting of Sb: more than 0% and 0.5000% or less, Pb: more than 0% and 0.5000% or less, and Sr: more than 0% and 0.5000% or less

[0077] [Sb: 0 to 0.5000 mass %]

[0078] [Pb: 0 to 0.5000 mass %]

[0079] [Sr: 0 to 0.5000 mass %]

[0080] A case where the plating layer 20 according to this embodiment does not contain Sb, Pb, and Sr is conceivable, and therefore the lower limits of the contents of these elements are 0 mass %. On the other hand, when at least any of Sb, Pb, and Sr is contained in the plating layer 20, spangles are formed on the surface of the plating layer 20, making it possible to improve metallic luster. Therefore, from the viewpoint of further improving the design of the plated steel sheet, at least any of Sb, Pb, and Sr is preferably contained in the plating layer 20. The design improvement effect is exhibited when the content of at least any of Sb, Pb, and Sr is 0.0500 mass % or more. Therefore, when at least any of Sb, Pb, and Sr is contained in the plating layer 20, the contents of these elements are each independently preferably 0.0500 mass % or more.

[0081] On the other hand, when forming the plating layer 20 in which any of the contents of Sb, Pb, and Sr exceeds 0.5000 mass %, an amount of dross generated in the plating bath used to form the plating layer 20 increases, so that a plated steel sheet with good plating properties cannot be manufactured. Therefore, the contents of Sb, Pb, and Sr in the plating layer 20 are each independently preferably 0.5000 mass % or less. The contents of Sb, Pb, and Sr are each independently preferably 0.2000 mass % or less.The Element Group C

[0082] Next, the element group C which the plating layer 20 can contain in another aspect of the plating layer 20 according to this embodiment will be explained. At least any of the following elements in the element group C is an element which can be contained in the plating layer 20 in place of a part of the balance Zn.

[0083] [Element group C]: one or two or more selected from the group consisting of Cu: more than 0% and 1.0000% or less, Ti: more than 0% and 1.0000% or less, Cr: more than 0% and 1.0000% or less, Nb: more than 0% and 1.0000% or less, Ni: more than 0% and 1.0000% or less, Mn: more than 0% and 1.0000% or less, Mo: more than 0% and 1.0000% or less, Co: more than 0% and 1.0000% or less, and V: more than 0% and 1.0000% or less

[0084] [Cu: 0 to 1.0000 mass %]

[0085] [Ti: 0 to 1.0000 mass %]

[0086] [Cr: 0 to 1.0000 mass %]

[0087] [Nb: 0 to 1.0000 mass %]

[0088] [Ni: 0 to 1.0000 mass %]

[0089] [Mn: 0 to 1.0000 mass %]

[0090] [Co: 0 to 1.0000 mass %]

[0091] [V: 0 to 1.0000 mass %]

[0092] A case where the plating layer 20 according to this embodiment does not contain Cu, Ti, Cr, Nb, Ni, Mn, Co, and V is conceivable, and therefore the lower limits of the contents of these elements are 0 mass %. On the other hand, when at least any of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V is contained in the plating layer 20, these elements are incorporated into the Fe—Al-based metal structure formed by welding when the plated steel sheet is welded, so that the corrosion resistance of a welded portion to be formed can be further improved. The effect of improving the corrosion resistance of the welded portion is exhibited when the content of at least any of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V in the plating layer 20 is 0.0050 mass % or more. Therefore, when at least any of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V is contained in the plating layer 20, the contents of these elements are each independently preferably 0.0050 mass % or more.

[0093] On the other hand, when forming the plating layer 20 in which any of the contents of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V exceeds 1.0000 mass %, these elements form various intermetallic compounds in the plating bath for forming the plating layer 20, thus causing an increase in viscosity of the plating bath to fail to manufacture a plated steel sheet with good plating properties. Therefore, the contents of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V in the plating layer 20 are each independently 1.0000 mass % or less. The contents of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V are each independently preferably 0.2000 mass % or less.

[0094] [Mo: 0 to 1.0000 mass %]

[0095] A case where the plating layer 20 according to this embodiment does not contain Mo is conceivable, and therefore the lower limit of its content is 0 mass %. On the other hand, when Mo is contained in the plating layer 20, the corrosion resistance can be further improved. The effect of improving the corrosion resistance is exhibited when the Mo content is 0.0100 mass % or more. Therefore, when Mo is contained, its content is preferably 0.0100 mass % or more.

[0096] On the other hand, when forming the plating layer 20 in which the Mo content exceeds 1.0000 mass %, it undesirably causes a large amount of dross generated in the plating bath to be used. Therefore, the Mo content is 1.0000 mass % or less. The Mo content is preferably 0.0500 mass % or less.The Element Group D

[0097] Next, the element group D which the plating layer 20 can contain in another aspect of the plating layer 20 according to this embodiment will be explained. The following elements in the element group D are elements which can be contained in the plating layer 20 in place of a part of the balance Zn.

[0098] [Element group D]: one or two or more selected from the group consisting of Sn: more than 0% and 1.0000% or less, In: more than 0% and 1.0000% or less, and Bi: more than 0% and 1.0000% or less

[0099] [Sn: 0 to 1.0000 mass %]

[0100] [In: 0 to 1.0000 mass %]

[0101] [Bi: 0 to 1.0000 mass %]

[0102] A case where the plating layer 20 according to this embodiment does not contain Sn, In, and Bi is conceivable, and therefore the lower limits of their contents are 0 mass %. Sn, In, and Bi are elements that increase an Mg dissolution rate when the plating layer 20 containing them is placed in the corrosive environment. When the Mg dissolution rate increases, Mg ions are supplied to portions where the steel sheet 10 is exposed, so that the corrosion resistance is further improved. From this viewpoint, when Sn, In, and Bi are contained, the contents of Sn, In, and Bi are each independently preferably 0.0050 mass % or more.

[0103] On the other hand, excessive addition of Sn, In, and Bi may excessively promote the Mg dissolution rate and decrease the corrosion resistance of the plated steel sheet. The increase in the Mg dissolution rate becomes pronounced when any of the contents of Sn, In, and Bi exceeds 1.0000 mass %, so that the contents of Sn, In, and Bi are each independently 1.0000 mass % or less. The contents of Sn, In, and Bi are each independently preferably 0.2000 mass % or less.The Element Group E

[0104] Next, the element group E which the plating layer 20 can contain in another aspect of the plating layer 20 according to this embodiment will be explained. At least any of the following elements in the element group E is an element which can be contained in the plating layer 20 in place of a part of the balance Zn.

[0105] [Element group E]: one or two or more selected from the group consisting of Zr: more than 0% and 1.0000% or less, Ag: more than 0% and 1.0000% or less, and Li: more than 0% and 1.0000% or less

[0106] [Zr: 0 to 1.0000 mass %]

[0107] [Ag: 0 to 1.0000 mass %]

[0108] [Li: 0 to 1.0000 mass %]

[0109] A case where the plating layer 20 according to this embodiment does not contain Zr, Ag, and Li is conceivable, and therefore the lower limits of the contents of these elements are 0 mass %. On the other hand, when at least any of Zr, Ag, and Li is contained in the plating layer 20, the plating operability can be further improved. The effect of improving the plating operability is exhibited when the content of at least any of Zr, Ag, and Li in the plating layer 20 is 0.0100 mass % or more. Therefore, when at least any of Zr, Ag, and Li is contained, the contents of these elements are each independently preferably 0.0100 mass % or more.

[0110] On the other hand, when forming the plating layer 20 in which any of the contents of Zr, Ag, and Li exceeds 1.00000 mass %, a large amount of dross is likely to be generated in the plating bath to be used for forming the plating layer 20. Therefore, each content of at least any of Zr, Ag, and Li is independently 0.10000 mass % or less. Each content of at least any of Zr, Ag, and Li is independently preferably 0.1000 mass % or less.The Element Group F

[0111] Next, the element group F which the plating layer 20 can contain in another aspect of the plating layer 20 according to this embodiment will be explained. At least any of the following elements in the element group F is an element which can be contained in the plating layer 20 in place of a part of the balance Zn.

[0112] [Element group F]: one or two or more selected from the group consisting of La: more than 0% and 0.5000% or less, Ce: more than 0% and 0.5000% or less, and Y: more than 0% and 0.5000% or less

[0113] [La: 0 to 0.5000 mass %]

[0114] [Ce: 0 to 0.5000 mass %]

[0115] [Y: 0 to 0.5000 mass %]

[0116] A case where the plating layer 20 according to this embodiment does not contain La, Ce, and Y is conceivable, and therefore the lower limits of the contents of these elements are 0 mass %. On the other hand, La, Ce, and Y are elements that exhibit almost the same effect as Ca and further suppress the blowhole formation during welding. This is because an atomic radius of each element is close to the atomic radius of Ca. When these elements are contained in the plating layer 20, they replace Ca positions. Therefore, these elements are detected at the same positions as Ca by EDS (Energy Dispersive X-ray Spectroscopy).

[0117] The effect of suppressing the blowhole formation during welding is exhibited when the contents of these elements are each independently 0.0100 mass % or more. Therefore, when at least any of Zr, Ag, and Li is contained, the contents of these elements are each independently preferably 0.0100 mass % or more. The contents of La, Ce, and Y in the plating layer 20 are each independently more preferably 0.0500 mass % or more.

[0118] On the other hand, if the La, Ce, and Y contents in the plating bath for manufacturing the plating layer 20 are too high, the viscosity of the plating bath may increase more than necessary and the plating operability may decrease. Therefore, the La, Ce, and Y contents in the plating bath are adjusted from the viewpoint of the plating operability, so that the contents of La, Ce, and Y are each independently 0.5000 mass % or less. The contents of La, Ce, and Y are each independently preferably 0.1000 mass % or less.The Element Group G

[0119] Next, the element group G which the plating layer 20 can contain in another aspect of the plating layer 20 according to this embodiment will be explained. The following element in the element group G is an element which can be contained in the plating layer 20 in place of a part of the balance Zn.

[0120] [Element group G]: B: more than 0% and 0.5000% or less

[0121] [B: 0 to 0.5000 mass %]

[0122] A case where the plating layer 20 according to this embodiment does not contain B is conceivable, and therefore the lower limit of its content is 0 mass %. On the other hand, when B is contained in the plating layer 20, there is an effect of further suppressing the LME. This is presumably because when B is contained in the plating layer 20, it combines with at least any of Zn, Al, Mg, and Ca to form various intermetallic compounds. Further, the presence of B in the plating layer 20 is considered to produce the effect of further suppressing the LME of the steel sheet 10 because B diffuses from the plating layer 20 into the steel sheet 10 and strengthens the grain boundary. Furthermore, it is presumed that since the various intermetallic compounds formed concerning B have extremely high melting points, they also act in suppressing the Zn evaporation during welding. These improvement effects are exhibited when 0.0500 mass % or more of B is contained. Therefore, when B is contained, the content of B is preferably 0.0500 mass % or more.

[0123] On the other hand, if B is excessively contained in the plating bath so that B is contained in the plating layer 20, a plating melting point rapidly increases to decrease the plating operability, failing to manufacture a plated steel sheet with excellent plating property. The decrease in plating operability becomes pronounced when the content of B exceeds 0.5000 mass %, so that the content of B is 0.5000 mass % or less. The content of B is preferably 0.1000 mass % or less.[Measurement Method of the Chemical Components]

[0124] The chemical components of the above plating layer 20 can be measured using ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) or ICP-MS (Inductively Coupled Plasma Mass Spectrometry). Note that ICP-AES shall be used in the case of analyzing the chemical component up to 0.1 mass % unit, and ICP-MS shall be used in the case of analyzing the chemical component in a trace amount of less than 0.1 mass %. The plated steel sheet is immersed in a 10% HCl aqueous solution with an inhibitor added for about 1 minute to peel off the plating layer part, thereby preparing the solution dissolving the plating layer. The obtained solution can be analyzed by ICP-AES or ICP-MS to obtain chemical components as an overall average of the plating layer.Regarding the Deposition Amount of the Plating Layer 20

[0125] The deposition amount of the plating layer 20 as explained above is not particularly specified and is preferably, for example, about 15 to 250 g / m2 per one side of the steel sheet. When the deposition amount of the plating layer 20 falls within the above range, the plated steel sheet 1 according to this embodiment can exhibit sufficient corrosion resistance.

[0126] Note that the deposition amount of the plating layer 20 is measured such that a sample having a size of 30 mm×30 mm in plane view is cut out from the plated steel sheet and its mass is measured in advance. Note that when cutting out the sample, it is cut out entirely in the thickness direction. A tape seal is bonded to one side of the sample to prevent the plating layer on the one side from dissolving in the next process. The sample is then immersed in a 10% HCl aqueous solution with an inhibitor added to peel off the plating layer by pickling, and the mass of the sample after pickling is measured. From a change in mass of the sample between before and after pickling, the deposition amount of the plating layer 20 per side can be decided.Regarding the Metal Structure of the Plating Layer 20

[0127] Next, the metal structure of the plating layer 20 having the chemical composition explained above will be explained.

[0128] The plating layer 20 according to this embodiment has the above chemical composition and is formed through a manufacturing method as will be explained in detail below, and thereby contains metal structures such as an ηZn phase, an α phase, a τ phase, a MgZn2 phase, a Mg2Zn3 phase, a MgZn phase, and so on. Further, the plating layer 20 can contain metal structures such as an Al—Si—Ca phase, an Al—Si—Ca—Fe phase, a Mg2Si phase, a Mg2Sn phase, and so on in addition to the above metal structures depending on elements which the plating layer 20 can further contain. The plating layer 20 according to this embodiment has the above metal structures and thereby comes to exhibit the properties that suppress the occurrence of the LME and is excellent also in corrosion resistance.

[0129] Here, which metal structures the plating layer 20 according to this embodiment has can be identified by observing the surface of the plating layer 20 under a scanning electron microscope (SEM). In other words, it is possible to observe solidified structures of the plating layer 20 under the SEM and identify which metal structures the plating layer 20 has from a point analysis result by a SEM-EPMA (Electron Probe Micro Analyzer) and the form of a crystal phase in the reflected electron image in an observation field of view. In this event, for example, a pre-treatment such as polishing does not need to be performed before the SEM observation. However, if a chemical conversion treatment film or the like is applied, polishing or the like may be performed to remove the chemical conversion treatment film. In the case of performing polishing, the polishing is performed such that 80% or more of the thickness of the plating layer remains, and the surface is brought into a mirror finish state, then observed under the SEM, and regarded as a surface structure.

[0130] More specifically, the size of a region to be observed by the observation under the SEM is set to 300 μm×300 μm. This range is observed with an acceleration voltage: 15.0 kV, an irradiation current: 4.999×10−8 A, an irradiation time: 50 milliseconds, and a magnification of 2000 times. The reflected electron image in the range to be focused on is acquired under these conditions, and then the point analysis for each of the metal structures only needs to be performed at three points using the contrast in the reflected electron image.

[0131] The present inventors focused attention on the α phase and the τ phase (Mg32(Al, Zn)49 phase) of the above metal structures when considering paint film blistering at the welded portion occurring during welding.

[0132] The α phase is α phase that is circular or rod-shaped in the reflected electron image and has a minor axis of less than 3 μm, and is a metal structure containing Al and Zn in an analysis result of the EPMA. Here, the above “circular” also includes “elliptical”. More specifically, in the analysis result of the EPMA, the α phase is a metal structure satisfying Al: 20 to 99 atom %, Zn: 0.5 to 80 atom %, Mg: 0 to 5 atom %, and a total of Al and Zn of 70 atom % or more. The circular form in the cross-section observation can be considered as a state of observing a stage at which the α phase has not grown into a rod shape when three-dimensionally capturing the α phase or a state of observing a cross-section obtained by cutting the α phase grown to a rod shape in a direction orthogonal to the major axis direction. In the plating layer 20 according to this embodiment, the α phase can be considered to have a rod-shaped form.

[0133] Besides, the τ phase (Mg32(Al, Zn)49 phase) is defined as a metal structure in which the Mg content [Mg], Zn content [Zn], and Al content [Al] contained in grains of the Mg32(Al, Zn)49 phase satisfy 0.50≤[Mg] / ([Zn]+[Al])≤0.83 by atom %. In other words, it is defined as a crystal phase or a quasi-crystalline phase where Mg: (Zn+Al), which is a ratio between Mg atoms and a total of Zn atoms and Al atoms, is 3:6 to 5:6. The chemical component of the Mg32(Al, Zn)49 phase is preferably measured by using TEM-EDX (Transmission Electron Microscope-Energy Dispersive X-ray Spectroscopy). The Mg32(Al, Zn)49 phase may be detected as both the quasi-crystalline phase as well as the crystal phase. In the case of the crystal phase, it is possible to identify the crystal structure as the Mg32(Al, Zn)49 phase from an electron diffraction image in the TEM observation. Note that whether the Mg32(Al, Zn)49 phase is the quasi-crystalline phase can be confirmed by imaging an electron diffraction image by the TEM and checking whether a five-fold symmetric crystal structure can be observed in the electron diffraction image. When the five-fold symmetric crystal structure is observed in the electron diffraction image, the Mg32(Al, Zn)49 phase can be determined to be the quasi-crystalline phase, whereas when the five-fold symmetric crystal structure is not observed in the electron diffraction image, the Mg32(Al, Zn)49 phase can be determined not to be the quasi-crystalline phase. Note that the five-fold symmetric crystal structure can be determined by obtaining an electron diffraction image called a Penrose pattern, and the person skilled in the art can easily determine it.

[0134] The Mg32(Al, Zn)49 phase exhibits sacrificial corrosion resistance for the plated steel sheet, and thereby has an effect of suppressing corrosion of base iron from a cut portion where the base iron is exposed and the welded portion to improve red rust resistance. In addition to the effect, the Mg32(Al, Zn)49 phase itself has excellent corrosion resistance and a corrosion rate of the Mg32(Al, Zn)49 phase is slow even in a corrosive environment, and therefore also has an effect of suppressing corrosion under paint film to improve corrosion resistance after painting also from a viewpoint of a paint film blistering width.

[0135] FIG. 2 to FIG. 4 are schematic views for explaining an α / τ lamellar structure in the plating layer of the plated steel sheet in this embodiment.

[0136] In the plating layer 20 according to this embodiment, when observing the metal structures of the plating layer 20 under the SEM in plane view of the surface of the plating layer 20, the rod-shaped α phases exist in a state of being dispersed in the τ phase being the parent phase as schematically illustrated in FIG. 2. In other words, in the plating layer 20 according to this embodiment, the rod-shaped α phases and the τ phase are eutectic, and exist as the α / τ lamellar structure as schematically illustrated in FIG. 2. The α / τ lamellar structure here refers to a structure in which a first phase and a second phase constituting the structure are periodically aligned at a predetermined interval λ. The α / τ lamellar structure according to this embodiment is a structure in which the α phases being the second phases are dispersed in the τ phase being the first phase and is a region where the interval between the α phases closest to each other separated by the τ phase satisfies a “grain size (minor axis) of the α phase±80%”. As a result of verification by the present inventors, it has been found that an extending direction (major axis direction of the rod shape) of the crystal phase in the rod-shaped α phase corresponds to the (220) plane of the α phase.

[0137] The (220) plane of the above α phase is a plane parallel to a normal direction to an RD-TD plane in a material coordinate system defined by an RD (Rolling Direction) axis and a TD (Transversal Direction: direction orthogonal to the rolling direction, width direction) axis when performing polar point measurement in an X-ray diffraction (XRD). In other words, the (220) plane of the above α phase can be grasped as a plane expanding parallel to the normal direction to the surface of the plated steel sheet 1.

[0138] The present inventors performed verification about the paint film blistering at the welded portion occurring during welding, and have newly found that corrosion proceeds along the interface between the α phase and the τ phase in the α / τ lamellar structure as illustrated in FIG. 2 in the plating layer having the above metal structure and the paint film blistering occurs due to the proceeding of the corrosion.

[0139] The present inventors have identified the above mechanism about the paint film blistering, and thereby have obtained an idea that if the corrosion proceeds along the interface of the α / τ lamellar structure, the paint film blistering at the welded portion occurring during welding might be suppressed by controlling the orientation of the α / τ lamellar structure.

[0140] As schematically illustrated in FIG. 3, the case where the plated steel sheet 1 according to this embodiment is welded with another steel sheet (may be the plated steel sheet 1 according to this embodiment) is considered. In this event, the substance being a cause of corrosion at the welded portion can be considered to intrude along a direction parallel to the surface of the steel sheet 10. On the other hand, such an idea has been obtained that since the corrosion proceeds along the interface of the α / τ lamellar structure as above, the proceeding of the corrosion can be efficiently suppressed to suppress the paint film blistering if the α / τ lamellar structure is grown from the steel sheet 10 side along the vertical direction (thickness direction of the plating layer 20) in the plating layer 20 as schematically illustrated in FIG. 3.

[0141] Specifically, such an idea has been obtained that the direction of the (220) plane of the α phase in the rod shape in the α / τ lamellar structure (direction in which the (220) plane expands) only needs to exist to be parallel to the normal direction to the surface of the steel sheet 10 in the plating layer 20 according to this embodiment as schematically illustrated in FIG. 4.

[0142] In the above mechanism of suppressing the paint film blistering obtained by the present inventors, it is needed to allow the α / τ lamellar structure to exist at a predetermined abundance in the plating layer 20 and control the growth direction of the α / τ lamellar structure. As a result of further studies by the present inventors from the viewpoint, it has been enabled to allow the α / τ lamellar structure brought into the orientation state as schematically illustrated in FIG. 3 to exist in the plating layer 20 by undergoing it through a specific manufacturing method.

[0143] In the plating layer 20 according to this embodiment realized according to the above mechanism, when the surface structure of the plating layer 20 is observed under the SEM as above, an average area ratio of the α / τ lamellar structure being the metal structure in which the rod-shaped α phases are dispersed in the τ parent phase is 30% or more and 95% or less.

[0144] Here, the above average area ratio is measured as follows.

[0145] Specifically, the surface of the plating layer 20 to be focused on is observed under the SEM without performing a pre-treatment such as polishing. In this event, an arbitrary position of the surface of the plating layer 20 is observed according to the following measurement conditions, and the α / τ lamellar structure is identified based on the point analysis result by SEM-EPMA and the form of the crystal phase in the reflected electron image. The α / τ lamellar structure is a structure in which the α phases being the second phases are dispersed in the τ phase being the first phase as above, and is a region where the interval between the α phases closest to each other separated by the τ phase satisfies “grain size (minor axis) of the α phase±80%”. Then, the area ratio of the α / τ lamellar structure in a size of the observation field of view is calculated.

[0146] More specifically, for the flat portion separated from the end portion of the plated steel sheet 1 by 50 mm or more, a region (corresponding to a magnification of about 1000 times) of 130 μm×100 μm in plane view at an arbitrary position on the surface of the plating layer 20 is observed under the SEM. In this event, a metal structure, in which black α phases having a granular to plate-like shape (three-dimensional shape is a rod shape) are dispersed in the τ phase (Mg32(Al, Zn)49) being a white parent phase, is found in the reflected electron image. Here, the black α phase having an equivalent circle diameter falling within a range of, for example, 0.1 to 4.0 μm is focused on. For the metal structure in which the black phases are dispersed in the white parent phase, the point analysis is performed on the black phase and the white phase by SEM-EPMA. The black phase satisfying Al: 20 to 99 atom %, Zn: 0.5 to 80 atom %, Mg: 0 to 5 atom %, and a total of Al and Zn of 70 atom % or more is determined as the above α phase. In this event, the black phases existing around a region determined as the α phase are collectively determined as the α phase. Besides, the white parent phase satisfying Mg: 10 to 50 atom %, Zn: 10 to 40 atom %, Al: 10 to 40 atom % and satisfying, by atom %, 0.50≤[Mg] / ([Zn]+[Al])≤0.83 is determined as the above τ phase. In this event, the white phases existing around a region determined as the τ phase are collectively determined as the τ phase.

[0147] By the above method, the α phase and the τ phase are identified, and then the region of the α / τ lamellar structure is identified. Specifically, the α phase located at the outermost position in a “structure in which the α phases are dispersed in the τ phase and a region where the interval between the nearest α phases separated by the τ phase satisfies the grain size (minor axis) of the α phase±80%” is identified, and a contour line representing the boundary between the α phase located at the outermost position and the τ phase is manually drawn on an image analysis application. By performing the above operation, the region corresponding to the α / τ lamellar structure can be identified. In a part of FIG. 2, the region of the α / τ lamellar structure identified by the above operation is illustrated by a broken line. The area ratio of the region identified as above is calculated using various image analysis applications (for example, ImageJ and the like).

[0148] The above measurement and calculation processing is performed at arbitrary five points on the surface of the plating layer 20, and an average value of the five area ratios obtained is regarded as an average area ratio of the α / τ lamellar structure in the plating layer 20 according to this embodiment.

[0149] When the average area ratio of the α / τ lamellar structure is less than 30%, the abundance of the α / τ lamellar structure in the plating layer 20 is too small, failing to suppress the paint film blistering at the welded portion during welding. The α / τ lamellar structure is lower in melting point than the other structures (for example, an α phase that is not lamellar but clumpy, a Mg—Zn phase, the τ phase, and the like), and forms a liquid phase Zn—Mg—Al earlier than the other structures during welding. At this time, it is estimated that Mg is in a concentrated state in the liquid phase, and the highly concentrated Mg suppresses the alloying reaction between Zn in the liquid phase and the steel sheet at the early stage of welding and the alloying between Al in the liquid phase and the steel sheet to thereby suppress the LME cracking. When the average area ratio of the α / τ lamellar structure is 30% or more, it is possible to suppress not only the LME during welding but also the paint film blistering at the welded portion. The average area ratio of the α / τ lamellar structure is preferably 35% or more, and more preferably 40% or more.

[0150] On the other hand, when the average area ratio of the α / τ lamellar structure exceeds 95%, which undesirably causes a decrease in processability of the plating layer 20. When the average area ratio of the α / τ lamellar structure is 95% or less, it is possible to suppress not only the LME during welding but also the paint film blistering at the welded portion. The average area ratio of the α / τ lamellar structure is preferably 80% or less, and more preferably 70% or less.

[0151] Further, in the plating layer 20 according to this embodiment, the orientation state of the α / τ lamellar structure can be determined based on whether the following conditions are satisfied, using XRD.

[0152] Specifically, when the surface of the plating layer 20 according to this embodiment is measured by a commercially available wide-angle X-ray diffraction apparatus, it is possible to determine that the orientation state of the (220) plane as illustrated in FIG. 3 and FIG. 4 is realized when an intensity ratio I220 / I111 of an intensity I220 of a peak corresponding to the (220) plane of the α phase to an intensity I111 of a peak corresponding to the (111) plane of the α phase is 0.25 or more in the obtained measured result.

[0153] The commercially available wide-angle X-ray diffraction apparatus (for example, RINT 1500 manufactured by Rigaku Corporation or the like)

[0154] X-ray source: Cu tube bulb

[0155] Voltage: 40 kV

[0156] Current: 150 mA

[0157] Attachment: sample changer sample stage

[0158] Filter: no

[0159] Monochromator: use

[0160] In more detail, the surface of the plating layer 20 to be focused on is observed by the above XRD without performing a pre-treatment such as polishing. In this event, an arbitrary position on the surface of the plating layer 20 is observed, and the intensity ratio I220 / I11 is calculated. The above measurement and calculation processing is performed at arbitrary five points on the surface of the plating layer 20, and an average value of the five intensity ratios I220 / I111 obtained is regarded as the intensity ratio I220 / I111 in the plating layer 20 according to this embodiment.

[0161] Note that in the XRD spectrum measured according to the above measurement conditions, the peak corresponding to the (220) plane is a peak observed at 2θ=65.05±0.4°, and the peak corresponding to the (111) plane is a peak observed at 2θ=38.57±0.4°. Further, when two or more peaks are observed in the range, the one existing at a position nearer to a reference position shall be employed as a corresponding peak.

[0162] Further, the intensity of the peak belonging to each plane direction shall be the one obtained by subtracting an intensity Ib on the baseline from an intensity Ip of the peak to be focused on (namely, “Ip−Ib”) while taking the baseline of the peak to be focused on into account in the XRD spectrum as schematically illustrated in FIG. 5.

[0163] When the intensity ratio I220 / I111 is less than 0.25, the orientation state of the α / τ lamellar structure is not in the state as illustrated in FIG. 3 and FIG. 4, failing to suppress the paint film blistering of the welded portion during welding. The intensity ratio I220 / I111 is preferably 0.50 or more, and more preferably 1.00 or more.

[0164] On the other hand, the upper limit of the intensity ratio I220 / I111 is not particularly limited, and the upper limit is actually about 5.00 though it is understood that the orientation state is more preferable as the intensity ratio is higher.

[0165] Note that when the orientation control of the α / τ lamellar structure is not performed and the α phases randomly exist in the τ phase, the above intensity ratio I220 / I111 theoretically indicates a value of 0.22. However, in consideration of the measurement error of the XRD spectrum, when the α phases randomly exist in the τ phase, the above intensity ratio I220 / I111 indicates a value in a range of 0.20 to 0.24.

[0166] The plated steel sheet 1 according to this embodiment has been explained above in detail referring to FIG. 1A to FIG. 5. The plated steel sheet 1 according to this embodiment as explained above can be preferably used, for example, as a material for automobile undercarriage parts.

[0167] Note that the plated steel sheet 1 according to this embodiment may further have one or two or more layers of various types of films on the plating layer 20. Examples of the film include a chromate film, a phosphate film, a chromate-free film, an organic resin film, and so on.(Regarding a Manufacturing Method for the Plated Steel Sheet)

[0168] Next, an example of a manufacturing method for the plated steel sheet as explained above will be explained.

[0169] The plated steel sheet 1 according to this embodiment is manufactured by using the steel sheet 10 as explained above as a base material and applying strain to the surface of the steel sheet 10 by heavy duty grinding and then forming the plating layer 20 on the surface to which the strain has been applied.

[0170] By grinding the surface of the steel sheet 10 by a heavy duty grinding brush to apply strain to the surface, a nucleus growth site for growing the α / τ lamellar structure is produced on the surface of the steel sheet 10. Thereafter, a specific thermal treatment is performed on the plating layer 20 formed on the surface of the steel sheet 10, whereby the α / τ lamellar structure grows in a desired orientation.

[0171] For the formation of the plating layer 20, a thermal spraying method, cold spraying method, sputtering method, vapor deposition method, electroplating method, and the like can be applied in addition to a hot-dip plating method. However, the hot-dip plating method is the most preferable in terms of cost in order to form a plating layer with a thickness generally used in automobiles and the like.

[0172] Thereafter, by performing a specific thermal treatment process explained below on the obtained plated steel sheet (steel sheet 10 having the plating layer 20), the plated steel sheet 1 according to this embodiment can be manufactured.

[0173] Hereinafter, an example of the manufacturing method for obtaining the plated steel sheet 1 according to this embodiment using the hot-dip plating method will be explained in detail.

[0174] In the manufacturing process of the plated steel sheet 1, first, the steel sheet 10 to be used as the base material is rolled by a Sendzimir method to a desired thickness, and then coiled and installed on a hot-dip plating line.

[0175] On the hot-dip plating line, the steel sheet is continuously passed while being unrolled from the coil. At the passing of the steel sheet, the heavy duty grinding brush provided at a predetermined position applies strain to the surface of the steel sheet. Thereafter, the steel sheet is subjected to a heat reduction treatment by an annealing facility installed on the line at 700 to 900° C. for more than 0 seconds and 300 seconds or less in an atmosphere of a N2-(1 to 10)% H2 gas at a dew point of −60 to 10° C. under an environment with an oxygen concentration of 20 ppm or less where oxidation is less likely to occur, then air-cooled with a N2 gas down to about a bath temperature of the plating bath at a subsequent stage+20° C., and then immersed in the plating bath. Note that the strain is applied to the steel sheet before the annealing in the above flow, but even if at least part of the applied stain is released by the annealing, the re-crystallization occurring in a steel surface layer is promoted during the annealing, so that Fe becomes finer in grain size and comes to function as a nucleus growth site at the solidification of the plating layer in the plating process at the subsequent stage.

[0176] Here, a plating alloy in a molten state having the chemical components as above is prepared in the plating bath in advance. The bath temperature of the plating bath is set to the melting point of the plating alloy or higher (for example, approximately 460 to 660° C.). In this event, the bath temperature of the plating bath is preferably decided to a value of a theoretical temperature of higher (for example, about a theoretical temperature+40° C.) while focusing attention on the above melting point of the plating alloy and based on the “theoretical temperature at which an α / τ lamellar structure nucleates” (hereinafter, referred to also as a theoretical temperature) explained below.

[0177] When producing the material of the plating alloy, it is preferable to prepare it using pure metal (purity of 99% or more) as the alloy material. First, a predetermined amount of the alloy metal is mixed so as to obtain the composition of the plating layer as explained above, and completely melted into an alloy using a high-frequency induction furnace, arc furnace, or the like in vacuum or inert gas replacement state. Furthermore, the alloy mixed with the predetermined components (composition of the above plating layer) is melted in air, and the resulting melt is used as the plating bath.

[0178] Note that there is no particular restriction on using the pure metal in the production of the plating alloy as explained above, and existing Zn alloy, Mg alloy, and Al alloy may be melted and used. In this case, there is no problem as long as a predetermined composition alloy with less impurities is used.

[0179] The steel sheet is immersed in the plating bath as explained above, and then pulled up at a predetermined speed. In this event, a plating deposition amount is controlled by, for example, a N2 wiping gas so that the plating layer 20 to be formed has a desired thickness. Here, for the conditions other than the bath temperature, general plating operation conditions may be applied, and no special facilities or conditions are required.

[0180] Next, a first cooling process and a second cooling process as follows are performed on the plating alloy in a molten state located on the steel sheet with the surface to which the strain has been applied by the heavy duty grinding brush, to make the plating alloy in the molten state into the plating layer 20 and to grow the α / τ lamellar structure in a desired orientation. Hereinafter, the first cooling process and the second cooling process will be explained in detail.

[0181] The first cooling process is a cooling process performed when the temperature of the plating alloy is in a range from the bath temperature to the “theoretical temperature at which the α / τ lamellar structure nucleates” (theoretical temperature). In the first cooling process, the plated steel sheet in the above temperature range is rapidly cooled at an average cooling rate of 15° C. / sec or more by spraying a cooling medium at a flow rate of 5000 L / m2 / min or less. Note that when the hot-dip plating method is employed in the plating process, the first cooling process is performed immediately after the steel sheet is pulled up from the plating bath. This causes the α / τ lamellar structure to nucleate at the nucleus growth site provided on the surface of the steel sheet.

[0182] Here, the above “theoretical temperature at which the α / τ lamellar structure nucleates” (theoretical temperature) can be decided from a calculation state diagram according to the CALPHAD method regarding the Mg—Al—Zn ternary system.

[0183] The flow rate of the cooling medium in the first cooling process is preferably 3000 L / m2 / min or less, and more preferably 1500 L / m2 / min or less. Further, the average cooling rate is preferably 25° C. / sec or more. Note that the lower limit value of the flow rate of the cooling medium is not particularly specified and, for example, about 5 L / m2 / min is a substantial lower limit. Further, the upper limit value of the average cooling rate is also not particularly specified and, for example, about 90° C. / sec is a substantial upper limit. If the cooling rate in the first cooling process is excessive and if the flow rate of the cooling medium is excessive, not the interface between the plating layer and the steel sheet but the surface of the plating layer becomes the nucleus growth site, so that even if the cooling in the subsequent second cooling process is performed, the orientation control becomes difficult.

[0184] Thereafter, when the temperature of the plating alloy (plating layer) is within a range of the “theoretical temperature at which the α / τ lamellar structure nucleates” (theoretical temperature) to 300° C., the second cooling process is performed. This second cooling process gradually cools the plated steel sheet within the above temperature range at an average cooling rate of 5° C. / sec or less by spraying the cooling medium at a flow rate of 5000 L / m2 / min or less. This grows the nucleated α / τ lamellar structure such that the (220) direction of the α phase becomes parallel to the direction normal to the surface of the steel plate.

[0185] Here, the flow rate of the cooling medium is preferably 3000 L / m2 / min or less, and more preferably 2000 L / m2 / min or less. Besides, the average cooling rate is preferably 3° C. / sec or less, and more preferably 1° C. / sec or less. Note that the lower limit value of the flow rate of the cooling medium is not particularly specified and, for example, about 500 L / m2 / min is a substantial lower limit.

[0186] As explained above, the plating layer is formed in a state where the strain is applied to the surface of the steel sheet by the heavy duty grinding brush, and the plating layer is subjected to a two-stage cooling process of the rapid cooling in the temperature range of the bath temperature to the theoretical temperature and the gradual cooling in the temperature range of the theoretical temperature to 300° C., whereby the α / τ lamellar structure in the plating layer 20 can be grown into a specific state.

[0187] Note that the cooling state from 300° C. to room temperature is not particularly specified, and the cooling down to room temperature may be performed by various methods.

[0188] Here, an interval between the end of the first cooling process and the start of the second cooling process is preferably within 3 seconds, and the second cooling process is preferably started immediately after the end of the first cooling process. If the interval between the end of the first cooling process and the start of the second cooling process exceeds 3 seconds, an unintended cooling process occurs to fail to realize the desired orientation control.

[0189] Note that when any one of the above first cooling process and second cooling process is not performed even if the strain has been appropriately applied to the surface of the steel sheet, the desired orientation control cannot be realized. The plating layer 20 according to this embodiment in which the orientation direction is controlled as illustrated in FIG. 2 and FIG. 3 can be realized by appropriately applying the strain to the surface of the steel sheet and then performing both the first cooling process and the second cooling process as above.

[0190] Further, when an alloying thermal treatment process (for example, a thermal treatment process involving heating to an ultimate sheet temperature of about 480 to 550° C.) which is often performed generally in the manufacture of an alloyed hot-dip galvanized steel sheet is applied after the above second cooling process, the orientation state of the α / τ lamellar structure controlled by the first cooling process and the second cooling process is disrupted, resulting in a failure to obtain the effect of suppressing the paint film blistering focused on in this embodiment. From this viewpoint, it is important not to perform the thermal treatment process after the second cooling process.

[0191] Here, in the above cooling treatment, generally known methods such as N2 gas cooling, mist cooling, water submergence, and the like can be applied. Further, in addition to the N2 gas, gases high in heat removal effect such as a He gas and a hydrogen gas may be used as the cooling gas.

[0192] Note that as a substantial measurement method of the temperature of the plating layer, a contact-type thermocouple (K-type) only needs to be used. By attaching the contact-type thermocouple to the steel sheet as the base material, the average temperature of the entire plating layer can be always monitored. Besides, by mechanically controlling various speeds and thicknesses and standardizing various operating conditions such as a preheating temperature of the steel sheet and the temperature of the plating bath, the temperature of the entire plating layer at that point in time under the manufacturing conditions can be monitored almost accurately. This makes it possible to precisely control the cooling treatments in the first cooling process and the second cooling process. Note that the surface temperature of the plating layer may also be measured by a non-contact radiation thermometer, although not as accurate as the contact type.

[0193] Further, a relationship between the surface temperature of the plating layer and the average temperature of the entire plating layer may be found by a simulation that performs heat conduction analysis. Specifically, the surface temperature of the plating layer and the average temperature of the entire plating layer are found based on various manufacturing conditions such as the preheating temperature of the steel sheet, the temperature of the plating bath, the pulling-up speed of the steel sheet from the plating bath, the sheet thickness of the steel sheet, the layer thickness of the plating layer, an amount of heat exchange between the plating layer and the manufacturing facility, and a heat release amount of the plating layer. Then, using the obtained results, the relationship between the surface temperature of the plating layer and the average temperature of the entire plating layer may be found. This makes it possible to estimate the average temperature of the entire plating layer at that point in time under the manufacturing conditions by actually measuring the surface temperature of the plating layer during the manufacture of the plated steel sheet. As a result, the cooling treatments in the first cooling process and the second cooling process can be precisely controlled.

[0194] One example of the manufacturing method for the plated steel sheet according to this embodiment has been concretely explained above.

[0195] Note that in the manufacturing method for the plated steel sheet according to this embodiment, a treatment for further forming one layer or two or more layers of various types of films may be performed after the above second cooling process. Examples of the treatment include a chromate treatment, a phosphate treatment, a chromate-free treatment, an organic resin film formation treatment, and so on.

[0196] Examples of the chromate treatment include an electrolytic chromate treatment for forming a chromate film by electrolysis, a reactive chromate treatment for forming a film using a reaction with a material and then washing off excessive treatment solution, and a coating-type chromate treatment for forming a film by applying a treatment solution and drying it without water washing, and so on, and any of the chromate treatments may be employed.

[0197] Examples of the electrolytic chromate treatment include electrolytic chromate treatments using, for example, chromic acid, silica sol, resins (phosphoric acid resin, acrylic resin, vinyl ester resin, vinyl acetate acrylic emulsion, carboxylated styrene butadiene latex, diisopropanolamine-modified epoxy resin, and the like), and hard silica.

[0198] Examples of the phosphate treatment include a zinc phosphate treatment, a calcium zinc phosphate treatment, a manganese phosphate treatment, and so on.

[0199] The chromate-free treatment is particularly suitable because it does not place a burden on the environment. Examples of the chromate-free treatment include an electrolytic chromate-free treatment for forming a chromate-free film by electrolysis, a reactive chromate-free treatment for forming a film using a reaction with a raw material and then washing off excessive treatment solution, a coating-type chromate-free treatment for forming a film by applying a treatment solution and drying it without water washing, and so on, and any of the chromate-free treatments may be employed.

[0200] Further, the organic resin to be used in the organic resin film formation treatment is not limited to a specific resin and, for example, various resins such as polyester resin, polyurethane resin, epoxy resin, acrylic resin, polyolefin resin, and modified versions of these resins can be used. The modified versions here refer to resins in which reactive functional groups contained in structures of these resins are reacted with other compounds (for example, monomers, crosslinking agents, or the like) containing, in the structures, functional groups which can react with the functional groups.

[0201] As the organic resin, one of the above-mentioned organic resins may be used alone, or a mixture of two or more organic resins (not modified) may be used. Further, one or two or more organic resins obtained by modifying at least one other organic resin in the presence of at least one organic resin may be used by mixture. In addition, an organic resin that has been made aqueous by dissolving or dispersing it in water may be used. Furthermore, various kinds of coloring pigments and rust preventive pigments may be contained in the organic resin films.EXAMPLES

[0202] Hereinafter, the plated steel sheet according to the present invention will be concretely explained while illustrating examples and comparative examples. Note that the examples illustrated below are only examples of the plated steel sheet according to the present invention, and the plated steel sheet according to the present invention is not limited to the examples illustrated below.

[0203] In the following examples and comparative examples, a hot-rolled steel sheet (0.05 mass % C-0.007 mass % Si-0.25 mass % Mn, manufactured by Nippon Steel Corporation) having a sheet thickness of 3.2 mm was used as the steel sheet being the base material. The hot-rolled steel sheet was used to produce a plurality of test pieces.

[0204] For the prepared test pieces, the strain was applied to the surfaces of the test pieces using the following two kinds of heavy duty grinding brushes. Note that when grinding, 1.0 to 5.0% NaOH aqueous solution was applied in advance to the surfaces of the steel sheets. By appropriately adjusting a brush rotation speed in a range of 100 to 1000 rpm with a brush pressure drop in a range of 0.5 to 10.0 mm, the strain amount to be applied to the surface was controlled. Note that a brush kind A of the two kinds of heavy duty grinding brushes illustrated below is a brush with a stronger grinding force. Note that test pieces on which the heavy duty grinding was not applied were also prepared for comparison.

[0205] Brush kind A: D-100 manufactured by HOTANI Co., Ltd.

[0206] Brush kind B: M-33 manufactured by HOTANI Co., Ltd.

[0207] Plating baths to realize plating layers with compositions as listed in Table 1 below were each prepared, and each plating bath was installed in a batch-type hot-dip plating test apparatus manufactured in-house and performed plating on the above test pieces. Here, the temperature of each test piece was measured using a thermocouple spot-welded to the center of the test piece. Further, for the test piece to be immersed in the plating bath, a heat-reduction treatment was performed on the surface of a plated substrate at 800° C. in a N2-5% H2 gas atmosphere in a furnace with an oxygen concentration of 20 ppm or less before immersion in the plating bath. After the heat-reduction treatment, the test piece was air-cooled with a N2 gas and immersed in the plating bath of the hot-dip plating test apparatus for about 3 seconds after the temperature of the test piece reached the bath temperature+20° C.

[0208] After the immersion in the plating bath, the test piece was pulled up at a pulling-up speed of 20 to 200 mm / sec. At the time of pulling-up, control was performed using a N2 wiping gas so as to obtain a desired plating deposition amount. In the following examples and comparative examples, the plating deposition amount was controlled so that the deposition amount of the plating layer after drying per one side of each test piece was 40 to 120 g / m2. After pulling up the test piece from the plating bath, the test piece was cooled from the plating bath temperature to room temperature under the conditions listed in Table 1 below. In the following examples and comparative examples, the second cooling process was started immediately after the end of the first cooling process (namely, the interval between the end of the first cooling process and the start of the second cooling process was set to 0.2 seconds or less).

[0209] Here, a plated steel sheet having a size of 30 mm×30 mm was cut out from each test piece plated as explained above, the plated steel sheet was immersed in a 10% HCl aqueous solution with an inhibitor added so that the plating layer was pickled and peeled off, and then the composition of the plating layer was measured by ICP analysis of elements dissolved into the aqueous solution.

[0210] Further, for each obtained plating layer, the area ratio of the ahi lamellar structure was identified by the SEM observation according to the above-explained method and the intensity ratio I220 / I111 was calculated by the XRD measurement.<Evaluation of the Paint Film Blistering During Welding>

[0211] From each obtained test piece, a steel sheet cut out into a size of 150 mm×50 mm was regarded as a first steel sheet, and a steel sheet cut out into a size of 150 mm×30 mm was regarded as a second steel sheet. These steel sheets were overlapped at their long sides and welded by arc welding or laser welding (lap fillet welding).

[0212] Here, welding conditions in the arc welding are as follows.

[0213] Welding current: 250 A, welding voltage: 26.4 V, welding speed: 100 cm / min

[0214] Welding gas: 20% CO2+Ar, gas flow rate: 20 L / min

[0215] Welding wire: YGW16 manufactured by Nippon Steel Welding & Engineering Co., Ltd., φ1.2 mm

[0216] (C: 0.1 mass %, Si: 0.80 mass %, Mn: 1.5 mass %, P: 0.015 mass %, S: 0.008 mass %, Cu: 0.36 mass %)

[0217] Inclination angle of welding torch: 45°

[0218] Overlap allowance: 10 mm

[0219] Steel sheet size: upper sheet side (first steel sheet) 150×50 mm, lower sheet side (second steel sheet) 150×30 mm

[0220] Gap between steel sheets: 0 mm

[0221] Further, welding conditions in the laser welding are as follows.

[0222] Output: 7 kW, welding speed: 400 cm / min, forward / backward angle: 0°

[0223] Steel sheet size: upper sheet side (first steel sheet) 150×50 mm, lower sheet side (second steel sheet) 150×30 mm

[0224] Overlap allowance: 50 mm

[0225] Gap between steel sheets: 0 mm

[0226] The welded joint obtained as above was subjected to an automobile phosphoric acid conversion treatment (Zn phosphoric acid treatment, SD5350 system: Nipponpaint Industrial Coatings Co., LTD. standard), and to electrodeposition coating (PN110 Power Nix Gray: Nipponpaint Industrial Coatings Co., LTD. standard). In this event, the electrodeposition film thickness was set to 20 μm. The sample after the electrodeposition coating was subjected to a combined cyclic corrosion test (60 cycles) according to JASO (M609-91), and the paint film blistering width at the bead toe portion was evaluated. The evaluation criteria are as follows.<<Evaluation Criteria>>Grade “AAA”: paint film blistering width of 1.5 mm or less

[0228] “AA”: paint film blistering width of more than 1.5 mm and 2.5 mm or less

[0229] “A”: paint film blistering width of more than 2.5 mm and 3.5 mm or less

[0230] “B”: paint film blistering width of more than 3.5 mm

[0231] Note that the above “toe” is a position specified in JIS Z3001 (2018) and corresponds to a point where the surface of the base material and a surface of a weld bead intersect. In this example, a point where the surface of the plating layer on the plated steel sheet and the surface of the weld bead portion intersect corresponds to this “toe”.

[0232] Further, when the above paint film blistering width is 3.5 mm or less, the test piece to be focused on can be evaluated to have excellent post-painting corrosion resistance.<Evaluation of LME Resistance>

[0233] The LME resistance of each obtained test piece was evaluated by a hot tensile test.

[0234] More precisely, both the obtained test piece and an unplated steel sheet were increased in temperature up to 800° C. at a temperature increasing rate of 100° C. / sec, held at 800° C. for 1 second, and then subjected to the tensile test at a stroke speed of 50 mm / sec. Stress-stroke curves were thus obtained for both the unplated steel sheet and the test piece. A stress×stroke value (area of the stress-stroke curve) was then calculated from each obtained stress-stroke curve, and an evaluation value (%)={(stress×stroke value of test piece) / (stress×stroke value of unplated steel sheet)×100} was evaluated based on the following evaluation criteria.<<Evaluation Criteria>>Grade “AA”: evaluation value of 95% or more

[0236] “A”: evaluation value of 85% or more and less than 95%

[0237] “B”: evaluation value of less than 85%

[0238] The obtained results are collectively listed in Table 1 below.TABLE 1PLATING LAYER COMPOSITION (mass %)BATHOTHERSTEMPER-COMPO-ATURENoCATEGORYZnAlMgSiCaFeSITIONTYPE(° C.) 1EXAMPLE61.5030.00 7.000.000.001.500  —570 2EXAMPLE55.8933.50 7.800.000.502.30  0.0100Co540 3EXAMPLE50.1035.7010.000.000.703.50  0.0020V560 4EXAMPLE49.5035.80 9.200.500.501.500  —560 5EXAMPLE33.8935.8020.000.600.509.20  0.0100Ti620 6EXAMPLE44.2936.7012.200.700.905.20  0.0100Zr570 7EXAMPLE43.3038.9011.200.601.005.00  0.0010Ni570 8EXAMPLE37.1939.4015.000.702.505.20  0.0100Sn580 9EXAMPLE39.6039.9012.100.602.205.60  0.0010Nb58010EXAMPLE41.4040.1011.900.700.905.000  —58011EXAMPLE40.9841.2010.500.701.005.60  0.0200Sb58012EXAMPLE39.0742.5011.001.101.005.30  0.0300Pb58013EXAMPLE37.9943.1012.000.801.005.10  0.0100Mo58014EXAMPLE36.5045.5011.100.800.905.20  0.0020Cu58015EXAMPLE34.2046.1012.500.900.805.50  0.0010Cr58016EXAMPLE31.2049.0012.601.101.105.00  0.0020La58017EXAMPLE27.8051.0012.500.901.106.70  0.0020Ce58018EXAMPLE20.5052.2015.001.104.007.20  0.0010B64019EXAMPLE28.4053.3010.101.200.806.20  0.0003In60020EXAMPLE23.6054.1015.001.100.505.70  0.0030Bl60021EXAMPLE24.0055.7011.202.100.906.10  0.0001Ag60022EXAMPLE18.5958.9013.502.200.806.00  0.0080Mo60023EXAMPLE20.7958.0012.502.500.106.10  0.0060Y62024EXAMPLE19.6960.40 9.703.100.606.50  0.0060Y65025EXAMPLE12.1065.8011.003.200.707.20  0.0050Mn66026EXAMPLE 5.2070.0012.004.000.708.100  —66027COMPARATIVE68.7029.70 1.500.000.000.100  —450EXAMPLE28COMPARATIVE 2.9081.00 7.200.000.108.800  —680EXAMPLE29COMPARATIVE47.3040.00 6.600.001.005.100  —570EXAMPLE30COMPARATIVE42.0030.4021.500.001.005.100  —580EXAMPLE31COMPARATIVE54.8030.50 7.900.000.006.800  —670EXAMPLE32COMPARATIVE55.4030.30 7.500.000.006.800  —670EXAMPLE33COMPARATIVE93.80 3.00 3.000.000.100.100  —500EXAMPLE34COMPARATIVE90.40 2.20 1.300.001.005.100  —570EXAMPLE35COMPARATIVE93.70 4.00 2.100.000.100.100  —500EXAMPLE36COMPARATIVE42.2040.0011.200.501.005.100  —570EXAMPLE37EXAMPLE21.7052.0014.501.003.607.20  0.0010Li64038EXAMPLE23.2051.2014.000.903.607.10  0.0010Sr640MANUFACTURING CONDITIONSTRUCTURE OFBATH TEMPERATURESWITCHINGPLATING LAYERTO CONTROLLEDTEMPERATUREα / τ LAMELLARα PHASEEVALUATIONCOOLING TEMPERATURETO 300° C.STRUCTUREORIENTATIONPAINTHEAVYTHEORETICALCOOLINGFLOWCOOLINGFLOWAVERAGEINTENSITYFILM DUTYTEMPERATURERATERATERATERATEAREARATIOBLIST-NoGRINDING(° C. / s)(° C. / s)(L / m2 / min)(° C. / s)(L / m2 / min)RATIO (%)I220 / I111LMEERING 1A530153000 55000300.25AA 2B500153000 35000350.51AAA 3B520151000 35000371.00AAAAA 4B520151000 35000341.22AAAAA 5B580151000 35000411.12AAAAA 6B530151000 35000441.55AAAAA 7B530151000 35000441.55AAAAA 8B540151000 35000461.52AAAAA 9B540151000 35000461.52AAAAA10B540151000 35000611.56AAAAA11B540151000 35000691.66AAAAA12B540151000 35000781.78AAAAA13B540151000 35000801.81AAAAA14B540151000 35000821.89AAAAA15A540151000 35000800.93AAAA16B540151000 35000831.94AAAAA17B540151000 35000821.91AAAAA18B600151000 35000781.90AAAAA19B560151000 35000652.12AAAAA20B560151000 35000642.22AAAAA21B560151000 35000602.24AAAAA22B580151000 32000602.26AAAAA23B580151000 35000512.26AAAAA24B610151000 35000562.24AAAAA25B620151000 35000332.66AAAAA26B620151000 35000312.99AAAAA27A410151000 55000100.11BB28A640151000 55000120.20BB29A530151000 55000150.20BB30A540151000 55000 90.14AB31A670151000 55000310.11AB32A630 51000 55000330.11AB33A460154000 55000320.13AB34A530151000155000300.19AB35A460151000 56000320.18AB36—530151000 55000350.15AB37B600151000 35000771.90AAAAA38B600151000 35000781.89AAAAA

[0239] As is clear from Table 1 above, the LME and the paint film blistering can be suppressed in examples corresponding to the examples of the present invention, whereas sufficient performance cannot be exhibited in at least any of the LME and the paint film blistering in examples corresponding to the comparative examples of the present invention.

[0240] For example, No. 27 in which the Al content of the plating layer was outside the range of the present invention was insufficient in abundance of the α / τ lamellar structure because the τ phase crystallized before the α phase and they did not solidify as the α / τ lamellar structure, thus failing to suppress the LME and the paint film blistering. No. 28 in which the Al content of the plating layer was outside the range of the present invention was insufficient in abundance of the α / τ lamellar structure because the α phase crystallized before the τ phase and they did not solidify as the α / τ lamellar structure, thus failing to suppress the LME and the paint film blistering.

[0241] No. 29 in which the Mg content of the plating layer was outside the range of the present invention was insufficient in abundance of the α / τ lamellar structure because the α phase crystallized before the τ phase and they did not solidify as the α / τ lamellar structure, thus failing to suppress the LME and the paint film blistering. No. 29 in which the Mg content of the plating layer was outside the range of the present invention was insufficient in abundance of the α / τ lamellar structure because the τ phase crystallized before the α phase and they did not solidify as the α / τ lamellar structure, thus failing to suppress the paint film blistering.

[0242] No. 31 which was not subjected to the cooling control in the first cooling process was insufficient in orientation of the metal structure, thus failing to suppress the paint film blistering. No. 32 in which the average cooling rate in the first cooling process was outside the range of the present invention and No. 33 in which the flow rate of the cooling medium in the first cooling process was outside the range of the present invention were insufficient in orientation of the metal structure, thus failing to suppress the paint film blistering.

[0243] No. 34 in which the average cooling rate in the second cooling process was outside the range of the present invention and No. 35 in which the flow rate of the cooling medium in the second cooling process was outside the range of the present invention were insufficient in orientation of the metal structure, thus failing to suppress the paint film blistering.

[0244] No. 36 in which the application of the strain to the steel sheet was not performed was insufficient in orientation of the metal structure, thus failing to suppress the paint film blistering.

[0245] Preferred embodiments of the present invention have been explained above in detail with reference to the attached drawings, but the present invention is not limited to the embodiments. It should be understood that various changes and modifications are readily apparent to those skilled in the art who have the common general knowledge in the technical field to which the present invention pertains, within the scope of the technical spirit as set forth in claims, and they should also be covered by the technical scope of the present invention.

[0246] The embodiments disclosed herein are examples in all respects and should not be considered to be restrictive. Various omissions, substitutions, and changes may be made in the embodiments without departing from the scope of the attached claims, and the configuration and the spirit belonging to the technical field of the present invention as will be described. For example, configuration requirements of the above embodiments can be arbitrarily combined as long as the effects thereof are not impaired. From an arbitrary combination, the operations and effects about the configuration requirements relating to the combination can be obtained as a matter of course, and other operations and other effects apparent to those skilled in the art are obtained from the description herein.

[0247] Besides, the effects explained herein are merely explanatory or illustrative in all respects and not restrictive. In other words, the technique relating to the present invention can offer other clear effects to those skilled in the art from the description herein in addition to or in place of the above effects.EXPLANATION OF CODES1 plated steel sheet

[0249] 10 steel sheet

[0250] 20 plating layer

Claims

1. A plated steel sheet comprisingon at least a part of a surface of a steel sheet, a plating layer comprising a chemical composition containing, by mass %,Al: 30.00 to 70.00%,Mg: 7.00 to 20.00%,Fe: 0.01 to 15.00%, andselectively containing one or two or more elements selected from the group consisting of following element group A, element group B, element group C, element group D, element group E, element group F, and element group G with a balance composed of 5.00 mass % or more of Zn and impurities, wherein:in a surface structure of the plating layer, an average area ratio of an α / τ lamellar structure being a metal structure in which rod-shaped α phases are dispersed in a τ parent phase is 30% or more and 95% or less; andin a measured result obtained by measuring the plating layer by an X-ray diffraction method, an intensity ratio I220 / I111 of an intensity I220 of a peak corresponding to a (220) plane of the α phase to an intensity I111 of a peak corresponding to a (111) plane of the α phase is 0.25 or more,[Element group A]: one or two selected from the group consisting of Si: more than 0% and 10.00% or less and Ca: more than 0% and 4.00% or less[Element group B]: one or two or more selected from the group consisting of Sb: more than 0% and 0.5000% or less, Pb: more than 0% and 0.5000% or less, and Sr: more than 0% and 0.5000% or less[Element group C]: one or two or more selected from the group consisting of Cu: more than 0% and 1.0000% or less, Ti: more than 0% and 1.0000% or less, Cr: more than 0% and 1.0000% or less, Nb: more than 0% and 1.0000% or less, Ni: more than 0% and 1.0000% or less, Mn: more than 0% and 1.0000% or less, Mo: more than 0% and 1.0000% or less, Co: more than 0% and 1.0000% or less, and V: more than 0% and 1.0000% or less[Element group D]: one or two or more selected from the group consisting of Sn: more than 0% and 1.0000% or less, In: more than 0% and 1.0000% or less, and Bi: more than 0% and 1.0000% or less[Element group E]: one or two or more selected from the group consisting of Zr: more than 0% and 1.0000% or less, Ag: more than 0% and 1.0000% or less, and Li: more than 0% and 1.0000% or less[Element group F]: one or two or more selected from the group consisting of La: more than 0% and 0.5000% or less, Ce: more than 0% and 0.5000% or less, and Y: more than 0% and 0.5000% or less[Element group G]: B: more than 0% and 0.5000% or less.

2. The plated steel sheet according to claim 1 comprising a chemical composition containing the element group A.

3. The plated steel sheet according to claim 1 comprising a chemical composition containing the element group B.

4. The plated steel sheet according to claim 1 comprising a chemical composition containing the element group C.

5. The plated steel sheet according to claim 1 comprising a chemical composition containing the element group D.

6. The plated steel sheet according to claim 1 comprising a chemical composition containing the element group E.

7. The plated steel sheet according to claim 1 comprising a chemical composition containing the element group F.

8. The plated steel sheet according to claim 1 comprising a chemical composition containing the element group G.

9. The plated steel sheet according to claim 1, whereinthe plating layer contains 9.00 mass % or more of Mg.

10. The plated steel sheet according to claim 1, whereinthe intensity ratio I220 / I111 is 0.50 or more.

11. (canceled)12. The plated steel sheet according to claim 10, whereinthe intensity ratio I220 / I111 is 1.00 or more.

13. (canceled)14. A plated steel sheet comprisingon at least a part of a surface of a steel sheet, a plating layer comprising a chemical composition containing, by mass %,Al: 30.00 to 70.00%,Mg: 7.00 to 20.00%,Fe: 0.01 to 15.00%, andselectively containing one or more of following element group A, element group B, element group C, element group D, element group E, element group F, and element group G with a balance comprising 5.00 mass % or more of Zn and impurities, wherein:in a surface structure of the plating layer, an average area ratio of an α / τ lamellar structure comprising a metal structure in which rod-shaped α phases are dispersed in a τ parent phase is 30% or more and 95% or less; andin a measured result obtained by measuring the plating layer by an X-ray diffraction method, an intensity ratio I220 / I111 of an intensity I220 of a peak corresponding to a (220) plane of the α phase to an intensity I111 of a peak corresponding to a (111) plane of the α phase is 0.25 or more,[Element group A]: one or two of Si: more than 0% and 10.00% or less and Ca: more than 0% and 4.00% or less[Element group B]: one or more of Sb: more than 0% and 0.5000% or less, Pb: more than 0% and 0.5000% or less, and Sr: more than 0% and 0.5000% or less[Element group C]: one or more of Cu: more than 0% and 1.0000% or less, Ti: more than 0% and 1.0000% or less, Cr: more than 0% and 1.0000% or less, Nb: more than 0% and 1.0000% or less, Ni: more than 0% and 1.0000% or less, Mn: more than 0% and 1.0000% or less, Mo: more than 0% and 1.0000% or less, Co: more than 0% and 1.0000% or less, and V: more than 0% and 1.0000% or less[Element group D]: one or more of Sn: more than 0% and 1.0000% or less, In: more than 0% and 1.0000% or less, and Bi: more than 0% and 1.0000% or less[Element group E]: one or more of Zr: more than 0% and 1.0000% or less, Ag: more than 0% and 1.0000% or less, and Li: more than 0% and 1.0000% or less[Element group F]: one or more of La: more than 0% and 0.5000% or less, Ce: more than 0% and 0.5000% or less, and Y: more than 0% and 0.5000% or less[Element group G]: B: more than 0% and 0.5000% or less.

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