Plated steel sheet

Abstract

[Problem] To more reliably suppress LME and blow hole formation, while maintaining superior corrosion resistance. [Solution] A plated steel sheet according to the present invention has a steel sheet that serves as a base material, a plating layer that is located on at least one section of the surface of the steel sheet, and an oxide layer that is located on the surface of the plating layer, wherein the chemical composition of the plating layer comprises a prescribed component or components, the remainder consisting of Zn and unavoidable impurities, and when a location that is at a depth of 5 nm from the most superficial surface of the oxide layer is observed by X-ray photoelectron spectroscopy (XPS), the intensity ratio ([Al–O]+[Mg–O]) / [Zn–O] which is calculated from the intensities of the peaks respectively attributed to Al–O bonds, Mg–O bonds, and Zn–O bonds has a value of 5.0 or greater.

Description

[Technical Field]

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

[0002] Galvanized steel sheets are widely used in the fields of construction, automobiles, etc., from the viewpoint of improving the corrosion resistance of structural members. In this case, a method is used to manufacture various structural members by welding pre-galvanized galvanized steel sheets by arc welding, laser welding, or the like.

[0003] Here, problems specific to the welding of galvanized steel sheets to manufacture structural components include liquid metal embrittlement (LME) caused by hot-dip plating in the heat-affected zone of the weld metal and base material, and reduced corrosion resistance around the weld (weld heat-affected zone) due to the formation of blowholes caused by Zn evaporation during welding.

[0004] Various proposals have been made to solve the problems of LME and blowhole formation described above. For example, Patent Document 1 below proposes a plated steel material that includes a steel sheet and a coating layer that is disposed on the surface of the steel sheet and includes a Zn-Al-Mg alloy layer, in which, in a cross section of the Zn-Al-Mg alloy layer, the area fraction of the MnZn2 phase is 45 to 75%, the total area fraction of the MgZn2 phase and the Al phase is 70% or more, and the area fraction of the Zn-Al-MgZn2 ternary eutectic structure is 0 to 5%, and the coating layer has a predetermined chemical composition. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2018 / 139620 Summary of the Invention [Problem to be solved by the invention]

[0006] Here, it is possible to solve the problems of LME and blowhole formation by using the plated steel material proposed in Patent Document 1. However, as a result of intensive studies by the present inventors, it has been found that there is still room for improvement in the technology proposed in Patent Document 1, and that further improvements can be expected to be made to the problems of LME and blowhole formation.

[0007] Therefore, the present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a plated steel sheet that can more reliably suppress the formation of LME and blowholes while maintaining excellent corrosion resistance. [Means for solving the problem]

[0008] As a result of extensive research conducted by the present inventors to solve the above-mentioned problems, they discovered that if the state of the oxide layer formed on the surface of a zinc-based coating layer could be made denser, it would be possible to more reliably suppress the occurrence of LME and blowhole formation while maintaining excellent corrosion resistance, and thus completed the present invention. The gist of the present invention, which was completed based on these findings, is as follows.

[0009] (1) A steel sheet as a base material, a coating layer located on at least a part of the surface of the steel sheet, and an oxide layer located on the surface of the coating layer, wherein the coating layer contains, in mass%, 1.00 to 80.00% Al, 1.00 to 20.00% Mg, and 0.01 to 15.00% Fe. and optionally containingContains Si:0~10.00%, Ca:0~4.00%, and further selectively contains Sb:0~0.500%, Pb:0~0.500%, Cu:0~1.000%, Sn:0~1.000%, In:0~1.000%, Bi:0~1.000%, Ti:0~1.0 00%, Cr:0~1.000%, Nb:0~1.000%, Zr:0~1.000%, Ni:0~1.000%, Mn:0~1.000%, V:0~1.000%, Mo:0~1.000%, Ag:0~1.000%, Li:0~1.000%, La:0 and a balance consisting of 5.00 mass% or more of Zn and impurities, wherein when a position at a depth of 5 nm from the outermost surface of the oxide layer is observed by X-ray photoelectron spectroscopy (XPS), the value of the intensity ratio ([Al-O] + [Mg-O]) / [Zn-O] calculated from the intensities of peaks respectively assigned to Al-O bonds, Mg-O bonds, and Zn-O bonds is 5.0 or more. (2) The plated steel sheet according to (1), wherein the strength ratio ([Al-O]+[Mg-O]) / [Zn-O] is 10.0 or more. (3) The plated steel sheet according to (1) or (2), wherein the plated layer contains at least 18.00 to 60.00 mass % of Al and 5.00 to 15.00 mass % of Mg. (4) The plating layer contains at least 35.00 to 60.00 mass% of Al and 7.00 to 15.00 mass% of Mg, and the plating layer contains Mg 32 (Al, Zn) 49 phase is present, and the Mg 32 (Al, Zn) 49 The Mg content [Mg], Zn content [Zn], and Al content [Al] (each unit: atomic %) in the phase satisfy the relationship 0.50≦[Mg] / ([Zn]+[Al])≦0.83. (1) or (2) The plated steel sheet according to claim 1. (5) The plating layer contains at least 35.00 to 60.00 mass% of Al and 7.00 to 15.00 mass% of Mg, and the plating layer contains Mg 32 (Al, Zn) 49 phase is present, and the Mg 32 (Al, Zn)49 (4) The plated steel sheet according to (3), wherein the Mg content [Mg], Zn content [Zn], and Al content [Al] (each unit: atomic %) in the phase satisfy the relationship 0.50≦[Mg] / ([Zn]+[Al])≦0.83. [Effects of the Invention]

[0010] As described above, according to the present invention, it is possible to more reliably suppress the formation of LME and blowholes in a plated steel sheet while maintaining excellent corrosion resistance. [Brief explanation of the drawings]

[0011] [Figure 1A] 1 is an explanatory view schematically illustrating an example of a plated steel sheet according to an embodiment of the present invention. FIG. [Figure 1B] FIG. 2 is an explanatory view schematically illustrating an example of a plated steel sheet according to the embodiment. [Figure 2] FIG. 2 is an explanatory diagram for explaining the plated steel sheet according to the embodiment. [Figure 3] FIG. 2 is an explanatory diagram for explaining peak intensities in the results of XPS measurement. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant explanations will be omitted.

[0013] (Regarding plated steel sheets) First, the overall configuration of a plated steel sheet according to an embodiment of the present invention will be described with reference to Figures 1A and 1B. Figures 1A and 1B are explanatory views that schematically show an example of a plated steel sheet according to this embodiment.

[0014] As shown schematically in Fig. 1A, the plated steel sheet 1 according to this embodiment has a steel sheet 10 as a base material, a plating layer 20 located on at least a portion of the surface of the steel sheet 10, and an oxide layer 30 located on the surface of the plating layer 20. Furthermore, the plating layer 20 and the oxide layer 30 may be present on both surfaces of the steel sheet 10, rather than being present on only one surface of the steel sheet 10 as shown in Fig. 1A, as shown schematically in Fig. 1B.

[0015] <About Steel Plate 10> The steel sheet 10 used as the base material of the plated steel sheet 1 according to this embodiment is not particularly limited, and various steel sheets can be used depending on the mechanical strength (e.g., tensile strength) required of the plated steel sheet 1. Examples of such steel sheet 10 include various steel sheets such as various types of Al-killed steel, ultra-low carbon steel containing Ti, Nb, etc., and high-strength steel in which extra-low carbon steel further contains strengthening elements such as P, Si, Mn, etc.

[0016] Furthermore, the thickness of the steel sheet 10 is not particularly limited, and may be set appropriately depending on the mechanical strength required of the plated steel sheet 1, etc.

[0017] <Regarding plating layer 20> 1A and 1B, the plating layer 20 is provided on at least a portion of the surface of the steel sheet 10, and more preferably over the entire surface of the steel sheet 10. First, the chemical composition of the plating layer 20 will be described in detail below.

[0018] ◇Chemical composition of plating layer 20 The chemical composition of the plating layer 20 according to this embodiment contains, in mass%, 1.00-80.00% Al, 1.00-20.00% Mg, 0.01-15.00% Fe, 0-10.00% Si, and 0-4.00% Ca, with the balance consisting of 5.00 mass% or more Zn and impurities. That is, in the chemical composition of the plating layer 20 according to this embodiment, the contents of Al, Mg, Fe, Si, and Ca are within the above ranges and the total of these contents is less than 100 mass%, with the balance consisting of 5.00 mass% or more Zn and impurities.

[0019] These components and their contents will be described in detail below.

[0020] [Al:1.00~80.00% by mass] Al is an element necessary for constituting the main phase (Zn-Al-Mg alloy phase) of the plating layer 20 according to this embodiment. Al is contained in a predetermined content or more to ensure corrosion resistance in the portion of the plated steel sheet that will become the weld heat affected zone and the portion of the plated steel sheet that will become the non-welded portion. If the Al content in the plating layer 20 is less than 1.00 mass%, the corrosion resistance of the portions that will become the weld heat affected zone and the non-welded portion cannot be ensured. Therefore, in the plating layer 20 according to this embodiment, the Al content is 1.00 mass% or more. The Al content is preferably 18.00 mass% or more, and more preferably 35.00 mass% or more. When the Al content is within the above range, the corrosion resistance of the plated steel sheet 1 can be ensured.

[0021] On the other hand, if the Al content in the plating layer 20 exceeds 80.00 mass%, the Al phase that functions as a cathode when placed in a corrosive environment increases excessively, facilitating corrosion of the base steel, and therefore 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 80.00 mass% or less. The Al content is preferably 60.00 mass% or less, and more preferably 50.00 mass% or less.

[0022] [Mg:1.00~20.00% by mass] Mg is an element necessary for constituting the main phase (Zn-Al-Mg alloy phase) of the plating layer 20 according to this embodiment. Mg is contained in a predetermined amount or more to ensure corrosion resistance in the portion of the plated steel sheet that will become the weld heat-affected zone and in the portion of the plated steel sheet that will become the non-welded zone. Therefore, the Mg content in the plating layer 20 according to this embodiment is 1.00 mass% or more. The Mg content is preferably 5.00 mass% or more, and more preferably 7.00 mass% or more. By ensuring that the Mg content falls within the above range, the corrosion resistance of the plated steel sheet 1 can be ensured.

[0023] On the other hand, if the Mg content in the plating layer 20 exceeds 20.00 mass%, anodic dissolution of the plating layer is likely to proceed when placed in a corrosive environment, making it impossible to ensure the corrosion resistance of the plated steel sheet 1. 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. By ensuring that the Mg content falls within the above range, it is possible to ensure the corrosion resistance of the plated steel sheet 1.

[0024] [Fe:0.01~15.00% by mass] The plating layer 20 may contain elements constituting the steel sheet 10 from the base material, that is, the steel sheet. In particular, in the hot-dip galvanizing method, interdiffusion of elements due to a solid-liquid reaction between the steel sheet 10 and the plating layer 20 facilitates the incorporation of the elements constituting the steel sheet 10 into the plating layer 20. Due to the incorporation of such elements, a predetermined amount of Fe is contained in the plating layer 20, and the content is generally 0.01 mass% or more. If the interdiffusion is promoted, the adhesion between the steel sheet 10 and the plating layer 20 is improved. From the viewpoint of improving the adhesion between the steel sheet 10 and the plating layer 20, the Fe content in the plating layer 20 is preferably 0.20 mass% or more.

[0025] Furthermore, Fe may be intentionally added to the plating bath used to produce the plating layer 20, provided that the effects of the present invention are not impaired. However, if the Fe content in the plating layer 20 is 15.00% by mass or more, high-melting-point intermetallic compounds of Fe and Al are formed in the plating bath, and these high-melting-point intermetallic compounds adhere to the plating layer as dross, significantly degrading the appearance quality, which is undesirable. From this perspective, the Fe content in the plating bath is adjusted so that the Fe content in the plating layer 20 is 15.00% by mass or less. The Fe content in the plating layer 20 is more preferably 10.00% by mass or less.

[0026] [Si:0~10.00% by mass] Si is an element that can suppress the excessive growth of Fe-Al intermetallic compounds that form at the interface between the coating layer and the steel sheet, thereby improving the adhesion between the coating layer and the steel sheet. To suppress the excessive growth of Fe-Al intermetallic compounds, the Si content is preferably 0.05 mass% or more, more preferably 0.20 mass% or more. On the other hand, if the Si content exceeds 10.00 mass%, high-melting-point intermetallic compounds are formed with Mg in excess, inhibiting the formation of an Al-Mg oxide film that has the effect of suppressing Zn evaporation, making it difficult to suppress Zn evaporation when such coated steel sheets are welded.

[0027] On the other hand, if the Si content in the plating bath for producing the plating layer 20 is too high, the viscosity of the plating bath may increase more than necessary, which may reduce plating operability. Therefore, the Si content in the plating bath is adjusted from the viewpoint of plating operability, so that the Si content in the plating layer 20 is preferably 5.00 mass% or less, and more preferably 2.00 mass% or less.

[0028] [Ca:0~4.00% by mass] When contained in the coating layer 20, Ca forms an intermetallic compound with Al and Zn. Furthermore, when Si is contained together with Ca in the coating layer 20, Ca forms an intermetallic compound phase with Si. These intermetallic compounds have a high melting point and a stable structure, making it possible to suppress the formation of blowholes caused by Zn evaporation during welding of coated steel sheets and LME. The effect of suppressing the formation of blowholes and LME during welding is achieved by setting the Ca content to 0.01% by mass or more. The Ca content in the coating layer 20 is more preferably 0.10% by mass or more.

[0029] 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 will decrease. From this viewpoint, the Ca content in the plating layer 20 is set to 4.00 mass % or more. The Ca content in the plating layer 20 is preferably 2.50 mass % or less, and more preferably 1.50 mass % or less.

[0030] In the plating layer 20, the balance of the above Al, Mg, Fe, Si, and Ca is 5.00 mass % or more of Zn and impurities. Zn is an element necessary for constituting the main phase (Zn-Al-Mg alloy phase) of the plating layer 20 according to this embodiment, and is an important element for improving the corrosion resistance of the plated steel sheet. Furthermore, when the plating layer 20 contains the above-mentioned Al, Mg, Fe, Si, and Ca within the above-mentioned ranges, and further contains 5.00 mass% or more of Zn, it becomes possible to suppress the formation of LME and blowholes during welding.

[0031] Furthermore, the plating layer 20 according to this embodiment further selectively replaces a part of the remaining Zn with Sb: 0 to 0.500%, Pb: 0 to 0.500%, Cu: 0 to 1.000%, Sn: 0 to 1.000%, In: 0 to 1.000%, Bi: 0 to 1.000%, Ti: 0 to 1.000%, Cr: 0 to 1.000%, Nb: 0 to 1.000%, Zr: 0 to 1.0 00%, Ni: 0-1.000%, Mn: 0-1.000%, V: 0-1.000%, Mo: 0-1.000%, Ag: 0-1.000%, Li: 0-1.000%, La: 0-0.500%, Ce: 0-0.500%, B: 0-0.500%, Y: 0-0.500%, and Sr: 0-0.500%, for a total content of 0-5.000%. That is, the plating layer 20 according to this embodiment may contain at least any of Sb, Pb, Cu, Sn, In, Bi, Ti, Cr, Nb, Zr, Ni, Mn, V, Mo, Ag, Li, La, Ce, B, Y, and Sr as optional additive elements within the above content ranges and in a total content of 5.000 mass% or less. It is possible that the plating layer 20 according to this embodiment does not contain any of the optional additional elements described above, and therefore the lower limit of the content of each optional additional element is 0 mass %.

[0032] By setting the total content of the above optional additional elements to 5.000% by mass or less, it becomes possible to enjoy the effects exerted by the addition of each optional additional element as described in detail below without impairing each other. The total content of the above optional additional elements is preferably 1.000% by mass or less, and more preferably 0.200% by mass or less. The content of each optional added element will be described in detail below.

[0033] [Sb:0~0.500% by mass] [Pb:0~0.500% by mass] [Sr:0~0.500% by mass] When at least one 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 improving the design of the plated steel sheet, it is preferable that at least one of Sb, Pb, and Sr is contained in the plating layer 20. Such an effect of improving the design is realized when the content of at least one of Sb, Pb, and Sr is 0.050 mass% or more. Therefore, when at least one of Sb, Pb, and Sr is contained in the plating layer 20, it is preferable that the content of each of these elements is independently 0.050 mass% or more.

[0034] On the other hand, if the coating layer 20 is formed such that the content of any of Sb, Pb, and Sr exceeds 0.500 mass%, the amount of dross generated in the coating bath used to form the coating layer 20 increases, making it impossible to produce a coated steel sheet with good coating properties. Therefore, the contents of Sb, Pb, and Sr in the coating layer 20 are each independently 0.500 mass% or less. The contents of Sb, Pb, and Sr are each independently preferably 0.200 mass% or less.

[0035] [Cu:0~1.000% by mass] [Ti:0~1.000% by mass] [Cr:0~1.000% by mass] [Nb:0~1.000% by mass] [Ni:0~1.000% by mass] [Mn:0~1.000% by mass] [V:0~1.000% by mass] When at least one of Cu, Ti, Cr, Nb, Ni, Mn, and V is contained in the plating layer 20, these elements are incorporated into the Al-Fe alloy phase generated by welding when the plated steel sheet is welded, thereby improving the corrosion resistance of the welded joint. This effect of improving the corrosion resistance of the welded joint is achieved when the content of any of Cu, Ti, Cr, Nb, Ni, Mn, and V in the plating layer 20 is 0.005 mass% or more. Therefore, when at least one of Cu, Ti, Cr, Nb, Ni, Mn, and V is contained in the plating layer 20, it is preferable that the content of each of these elements is independently 0.005 mass% or more.

[0036] On the other hand, if the plating layer 20 is formed such that the content of any of Cu, Ti, Cr, Nb, Ni, Mn, and V exceeds 1.000 mass%, these elements form various intermetallic compounds in the plating bath used to form the plating layer 20, resulting in an increase in the viscosity of the plating bath and making it impossible to produce a plated steel sheet with good plating properties. Therefore, the contents of Cu, Ti, Cr, Nb, Ni, Mn, and V in the plating layer 20 are each independently set to 1.000 mass% or less. The contents of Cu, Ti, Cr, Nb, Ni, Mn, and V are each independently set to preferably 0.200 mass% or less.

[0037] [Sn:0~1.000% by mass] [In:0~1.000% by mass] [Bi:0~1.000% by mass] Sn, In, and Bi are elements that increase the Mg dissolution rate when the plating layer 20 containing Zn, Al, and Mg is placed in a corrosive environment. When the Mg dissolution rate increases, Mg ions are supplied to exposed portions of the steel sheet 10, improving corrosion resistance. From this perspective, when Sn, In, and Bi are contained, the Sn, In, and Bi contents are each independently set to 0.0050 mass% or more. On the other hand, excessive addition of Sn, In, or Bi may excessively accelerate the Mg dissolution rate, potentially reducing the corrosion resistance of the plated steel sheet. Since this increase in the Mg dissolution rate becomes significant when any of the Sn, In, and Bi contents exceeds 1.000 mass%, the Sn, In, and Bi contents are each independently set to 1.000 mass% or less. The Sn, In, and Bi contents are each preferably independently set to 0.200 mass% or less.

[0038] [Zr:0~1.000% by mass] When Zr is contained in the plating layer 20, it is possible to improve plating operability. Such an effect of improving plating operability is realized when the Zr content is 0.010 mass% or more. Therefore, when Zr is contained, the content is preferably 0.010 mass% or more.

[0039] On the other hand, when forming a coating layer 20 having a Zr content exceeding 1.000% by mass, a large amount of dross is likely to be generated in the coating bath used to form the coating layer 20. Therefore, the Zr content is 1.000% by mass or less. The Zr content is preferably 0.100% by mass or less.

[0040] [Mo:0~1.000% by mass] When Mo is contained in the plating layer 20, it is possible to improve corrosion resistance. The effect of improving corrosion resistance is realized when the Mo content is 0.010 mass% or more. Therefore, when Mo is contained, the content is preferably 0.010 mass% or more.

[0041] On the other hand, forming a coating layer 20 with a Mo content exceeding 1.000% by mass is undesirable because it causes a large amount of dross to be generated in the coating bath used. Therefore, the Mo content is 1.000% by mass or less. The Mo content is preferably 0.050% by mass or less.

[0042] [Ag:0~1.000% by mass] When Ag is contained in the plating layer 20, it is possible to improve plating operability. Such an effect of improving plating operability is realized when the Ag content is 0.010 mass% or more. Therefore, when Ag is contained, the content is preferably 0.010 mass% or more.

[0043] On the other hand, when forming a plating layer 20 having an Ag content exceeding 1.000 mass%, a large amount of dross is likely to be generated in the plating bath used to form the plating layer 20. Therefore, the Ag content is 1.000 mass% or less. The Ag content is preferably 0.050 mass% or less.

[0044] [Li:0~1.000% by mass] When Li is contained in the plating layer 20, it is possible to improve plating operability. Such an effect of improving plating operability is realized when the Li content is 0.010 mass% or more. Therefore, when Li is contained, the content is preferably 0.010 mass% or more.

[0045] On the other hand, when forming a plating layer 20 having a Li content exceeding 1.000% by mass, a large amount of dross is likely to be generated in the plating bath used to form the plating layer 20. Therefore, the Li content is 1.000% by mass or less. The Li content is preferably 0.050% by mass or less.

[0046] [La:0~0.500% by mass] [Ce:0~0.500% by mass] [Y:0~0.500% by mass] La, Ce, and Y are elements that exhibit almost the same effect as Ca, suppressing the formation of blowholes during welding. This is because the atomic radius of each element is close to that of Ca. When these elements are contained in the coating layer 20, they substitute for Ca. Therefore, these elements are detected at the same position as Ca by EDS. Furthermore, even if these elements become oxides after welding of the coated steel sheet, the oxides of these elements are detected at the same position as CaO.

[0047] The effect of suppressing the formation of blowholes during welding is achieved by making the contents of these elements independently 0.010% by mass or more. Therefore, the contents of La, Ce, and Y in the plating layer 20 are more preferably independently 0.050% by mass or more.

[0048] On the other hand, if the La, Ce, and Y contents in the plating bath for producing the plating layer 20 are too high, the viscosity of the plating bath may increase more than necessary, potentially reducing plating operability. Therefore, from the perspective of plating operability, the La, Ce, and Y contents in the plating bath are adjusted so that the La, Ce, and Y contents are each independently 0.500 mass% or less. More preferably, the La, Ce, and Y contents are each independently 0.100 mass% or less.

[0049] [B:0~0.500% by mass] When B is contained in the coating layer 20, it has the effect of further suppressing LME. This is presumably because, when B is contained in the coating layer 20, it combines with at least one of Zn, Al, Mg, and Ca to form various intermetallic compound phases. Furthermore, the presence of B in the coating layer 20 is thought to have the effect of diffusing from the coating layer 20 to the steel sheet 10, strengthening the grain boundaries and further suppressing LME in the steel sheet 10. Furthermore, because the various intermetallic compounds formed with B have extremely high melting points, it is presumed that they also act to suppress Zn evaporation during welding. These improving effects are achieved by including 0.050% or more of B. Therefore, the B content in the coating layer 20 is more preferably 0.050% or more of B.

[0050] On the other hand, if an excessive amount of B is added to the plating bath in order to incorporate B into the plating layer 20, a rapid rise in the plating melting point occurs, reducing plating operability and making it impossible to produce a plated steel sheet with excellent plating properties. Such a reduction in operability becomes significant when the B content exceeds 0.500% by mass, so the B content is 0.500% by mass or less. The B content is preferably 0.100% by mass or less.

[0051] [Method of measuring chemical components] The chemical composition of the plating layer 20 can be measured using ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) or ICP-MS (Inductively Coupled Plasma Mass Spectrometry). ICP-AES is used to analyze chemical compositions down to 0.1% by mass, while ICP-MS is used to analyze trace amounts of chemical compositions less than 0.1% by mass. The plated steel sheet is immersed in a 10% HCl aqueous solution containing an inhibitor for approximately 1 minute to remove the plating layer, and a solution containing the dissolved plating layer is prepared. The resulting solution is analyzed using ICP-AES or ICP-MS to obtain the overall average chemical composition of the plating layer.

[0052] ◇More preferable chemical composition of plating layer 20 The plating layer 20 according to this embodiment has the above-mentioned chemical composition, but a more preferable chemical composition is as follows. That is, the plating layer 20 according to this embodiment preferably contains, as a chemical composition, at least 18.00 to 60.00 mass% Al and 5.00 to 15.00 mass% Mg, and further contains the above-mentioned optional additional elements as required.

[0053] The plating layer 20 according to this embodiment contains, as a chemical composition, at least 35.00 to 60.00 mass % of Al and 7.00 to 15.00 mass % of Mg, and may further contain the above-mentioned optional additional elements as needed. 32 (Al, Zn) 49 It is even more preferred that a phase is present.

[0054] where Mg 32 (Al, Zn) 49 The phase is Mg 32 (Al, Zn) 49 It is defined as a phase in which the Mg content [Mg], Zn content [Zn], and Al content [Al] contained within the grains of the phase satisfy the following atomic percentages: 0.5≦[Mg] / ([Zn]+[Al])≦0.83. In other words, it is defined as a crystalline or quasicrystalline phase in which the ratio of Mg atoms to the total of Zn atoms and Al atoms, Mg:(Zn+Al), is 3:6 to 5:6. Mg 32 (Al, Zn) 49 The chemical composition of the phase is preferably measured using TEM-EDX (Transmission Electron Microscope-Energy Dispersive X-ray Spectroscopy). 32 (Al, Zn) 49 The phase may be detected as both a crystalline phase and a quasicrystalline phase. In the case of the crystalline phase, the electron diffraction pattern in TEM observation shows that the crystal structure is Mg 32 (Al, Zn) 49 It is possible to identify the Mg phase. 32 (Al, Zn) 49 If the phase is a quasicrystalline phase, it can be confirmed by taking an electron diffraction image using a TEM and checking whether a five-fold symmetric crystal structure is observed in the electron diffraction image. A five-fold symmetric crystal structure can be identified by obtaining an electron diffraction image called a Penrose pattern.

[0055] Mg 32 (Al, Zn) 49The Mg phase exerts sacrificial corrosion protection on plated steel sheets, suppressing corrosion of the base steel from cuts and welds where the base steel is exposed, and improving red rust resistance. 32 (Al, Zn) 49 The phase itself has excellent corrosion resistance, 32 (Al, Zn) 49 Since the corrosion rate of this phase is slow even in a corrosive environment, it suppresses under-film corrosion and also has the effect of improving corrosion resistance after painting in terms of the width of blistering of the paint film.

[0056] ◇About the amount of plating layer 20 The coating weight of the plating layer 20 as described above is not particularly limited, but for example, it is 15 to 250 g / m per one side of the steel sheet. 2 When the coating weight of the plating layer 20 falls within the above range, the plated steel sheet 1 according to this embodiment can exhibit sufficient corrosion resistance.

[0057] The coating weight of the plating layer 20 is measured as follows. First, a sample measuring 30 mm x 30 mm is cut out from the plated steel sheet, and the mass of the sample is measured in advance. A tape seal is attached to one side of the sample to prevent the plating layer on this side from dissolving in the next process. The sample is then immersed in a 10% HCl aqueous solution containing an inhibitor to remove the plating layer by pickling, and the mass of the sample after pickling is measured. The coating weight of the plating layer 20 per side can be determined from the change in mass of the sample before and after pickling.

[0058] <Regarding the oxide layer 30> Next, the oxide layer 30 of the plated steel sheet 1 according to this embodiment will be described in detail. As shown schematically in FIGS. 1A and 1B, an oxide layer 30 is located on the surface of the plating layer 20 as described above.

[0059] Such oxide layer 30 is formed when easily oxidized elements constituting the plating layer 20 react with oxygen in the heat treatment atmosphere during the cooling process for solidifying the plating layer, which is carried out during the production of the plated steel sheet.

[0060] As described above, the oxide layer 30 is mainly composed of oxides of the elements that make up the plating layer 20, and therefore its chemical composition varies depending on the elements contained in the plating layer 20. The oxide layer 30 is presumed to contain 50 mass% or more of Zn oxide, Mg oxide, and Al oxide in total, and may further contain hydroxides of these Zn, Mg, and Al, at least one of oxides or hydroxides of other constituent elements in the plating layer 20, impurities, etc.

[0061] Here, the oxide layer 30 according to this embodiment exists in the following specific state by undergoing a specific heat treatment step, which will be described in detail below, during the production of the plated steel sheet. This state will be described in detail below with reference to Figs. 2 and 3. Fig. 2 is a diagram schematically showing a part of a cross section of the oxide layer parallel to the sheet thickness direction. Fig. 3 is an explanatory diagram for explaining the peak intensities in the XPS measurement results.

[0062] By being manufactured through a specific heat treatment process as described in detail below, the oxide layer 30 according to this embodiment is a dense coating in which the total amount of at least one of Al oxide or hydroxide and at least one of Mg oxide or hydroxide is greater than the amount of at least one of Zn oxide or hydroxide. This will be explained in more detail below.

[0063] 2, attention is now focused on a position 5 nm deep from the outermost surface of the oxide layer 30 ("position A" in FIG. 2). In the oxide layer 30 according to this embodiment, when this position is observed by X-ray photoelectron spectroscopy (XPS), the intensity ratio ([Al-O] + [Mg-O]) / [Zn-O] calculated from the intensities of the peaks respectively attributed to Al-O bonds, Mg-O bonds, and Zn-O bonds is 5.0 or more.

[0064] Here, there is a possibility that dirt such as oil and grease may be attached to the outermost surface of the oxide layer 30. Therefore, it is desirable to carry out the above-mentioned XPS measurement in a state where such dirt and the like are not present. From this viewpoint, the surface of the oxide layer 30 is subjected to a treatment such as ultrasonic cleaning in ethanol to remove the dirt and the like, and the surface obtained by such treatment is used as the "outermost surface of the oxide layer 30" when carrying out the above-mentioned XPS measurement.

[0065] Then, the oxide layer 30 obtained as described above is removed from the outermost surface to a depth of 5 nm by Ar ion etching, and the surface of the obtained oxide layer 30 is measured by XPS. Here, the XPS measurement conditions may be, for example, as follows. X-ray source: mono-Al Kα (1486.6eV) X-ray diameter: 50 to 200 μm Measurement area: 100~700μm×100~700μm Vacuum degree: 1×10 -10 ~1×10 -11 torr (1 torr is 133.32 Pa) Acceleration voltage: 1 to 10 kV

[0066] In this embodiment, we focus on the peaks attributable to Al-O bonds, Mg-O bonds, and Zn-O bonds in the obtained XPS measurement results. These bonds are characteristic of oxides and hydroxides of Al, Mg, and Zn. It can be considered that the intensity of the peaks attributable to these bonds is positively correlated with the amount of at least one of the oxides and hydroxides of Al, Mg, and Zn present.

[0067] Here, the peaks attributed to Al-O bonds are those observed in the range of 72 to 76 eV in the XPS spectrum focusing on Al 2p3 / 2. The peaks attributed to Mg-O bonds are those observed in the range of 48 to 52 eV in the XPS spectrum focusing on Mg 2p3 / 2. The peaks attributed to Zn-O bonds are those observed in the range of 1018 to 1024 eV in the XPS spectrum focusing on Zn 2p3 / 2.

[0068] The intensity of the peaks assigned to each bond can be calculated by taking into account the baseline of the peak in the XPS spectrum shown in Figure 3. p to baseline intensity I b (i.e., "I p -I b ").

[0069] A more detailed method for calculating the intensity ratio is as follows. That is, XPS is measured as described above at any location on the surface corresponding to a position 5 nm deep from the outermost surface (the surface at "Position A" in FIG. 2 ), and the intensity ratio ([Al-O] + [Mg-O]) / [Zn-O] is calculated. This measurement and calculation process is performed at any five locations on the surface corresponding to "Position A," and the average of the five obtained intensity ratios is used as the intensity ratio ([Al-O] + [Mg-O]) / [Zn-O] in the oxide layer 30 according to this embodiment.

[0070] In the oxide layer 30 according to this embodiment, a dense coating is formed such that the intensity ratio is 5.0 or more, thereby suppressing Zn evaporation during welding and preventing the formation of blowholes due to Zn evaporation. If the intensity ratio is less than 5.0, the oxide layer 30 will not have the required density, and it will not be possible to prevent the formation of blowholes during welding. The intensity ratio is preferably 10.0 or more. On the other hand, the upper limit of the intensity ratio ([Al-O] + [Mg-O]) / [Zn-O] is not particularly specified, but a practical upper limit is approximately 100.0.

[0071] The thickness (more specifically, the average thickness) of the oxide layer 30 as described above is not particularly limited, but is preferably, for example, about 0.05 to 2.00 μm per side of the steel sheet. When the thickness of the oxide layer 30 falls within the above range, the plated steel sheet 1 according to this embodiment can sufficiently suppress the formation of blowholes due to Zn evaporation during welding. Furthermore, the oxide layer 30 having the above thickness can be achieved by subjecting the steel sheet to a heat treatment process, as described in detail below, while controlling the steel sheet threading speed within an appropriate range.

[0072] The thickness of the oxide layer 30 can be measured using XPS. XPS measurement is performed in the depth direction from the surface of the plated steel sheet at intervals of 1 to 3 nm, and the depth at which the maximum oxygen intensity reaches 1 / 20 of the maximum intensity at the outermost surface is defined as the thickness of the oxide layer. The XPS measurement conditions may be the same as those described above.

[0073] The plated steel sheet 1 according to this embodiment has been described in detail above with reference to Figures 1A to 3. The plated steel sheet 1 according to this embodiment as described above can be suitably used, for example, as a material for automobile suspension parts.

[0074] The plated steel sheet 1 according to this embodiment may further have one or more of various coating layers on the oxide layer 30. Examples of such coating layers include a chromate coating, a phosphate coating, a chromate-free coating, and an organic resin coating.

[0075] (Regarding the manufacturing method of plated steel sheets) Next, an example of a method for producing the above-described plated steel sheet will be described. The plated steel sheet 1 according to this embodiment is produced by forming the plating layer 20 and the oxide layer 30 on the surface of the steel sheet 10 as a base material.

[0076] Here, in addition to hot-dip plating, methods such as thermal spraying, cold spraying, sputtering, vapor deposition, and electroplating can be used to form the plating layer 20. However, hot-dip plating is most preferable in terms of cost for forming a plating layer of a thickness generally used in automobiles and the like.

[0077] Thereafter, the obtained plated steel sheet (steel sheet 10 having the plated layer 20) is subjected to a specific heat treatment process as described below, thereby forming an oxide layer 30 on the surface of the plated layer 20. In this way, the plated steel sheet 1 according to this embodiment can be manufactured.

[0078] An example of a manufacturing method for obtaining the plated steel sheet 1 according to this embodiment using a hot dip galvanizing method will be described in detail below. In the manufacturing process of such a plated steel sheet 1, first, the steel sheet 10 used as the base material is rolled by the Sendzimir method to a desired thickness, and then wound into a coil and placed in a hot dip plating line.

[0079] In a hot-dip galvanizing line, steel sheets are continuously fed from a coil and threaded through the line. During this process, the steel sheets are heated and reduced at 800°C in an N2-5% H2 gas atmosphere in an environment where the oxygen concentration is 20 ppm or less, making oxidation unlikely. The steel sheets are then air-cooled with N2 gas to a temperature approximately 20°C above the bath temperature of the subsequent galvanizing bath, and then immersed in the galvanizing bath.

[0080] Here, a molten plating alloy having the above-described chemical components is prepared in the plating bath. The temperature of the plating bath is set to be equal to or higher than the melting point of the plating alloy (for example, approximately 460 to 600°C). When preparing the plating alloy material, it is preferable to use pure metals (purity of 99% or higher) as the alloy material. First, predetermined amounts of alloy metals are mixed to obtain the above-described plating layer composition, and then completely melted to obtain an alloy using a high-frequency induction furnace or an arc furnace under vacuum or inert gas replacement conditions. Next, the alloy mixed with the predetermined components (the above-described plating layer composition) is melted in the atmosphere, and the resulting molten material is used as the plating bath.

[0081] In addition, there is no particular restriction on using pure metals when preparing the plating alloys described above, and existing Zn alloys, Mg alloys, and Al alloys may be melted and used. In this case, there is no problem as long as the alloy has a predetermined composition with few impurities.

[0082] After immersing the steel sheet in the above-described plating bath, it is pulled up at a predetermined speed. During this process, the coating weight is controlled, for example, by using N2 wiping gas, so that the resulting plating layer 20 has a desired thickness. General plating operating conditions may be applied except for the bath temperature, and no special equipment or conditions are required.

[0083] Subsequently, the molten plating alloy located on the steel sheet is subjected to the following first and second cooling steps to convert the molten plating alloy into a plating layer 20 and to form an oxide layer 30 on the surface of the plating layer 20. The first and second cooling steps will be described in detail below.

[0084] The first cooling step is performed when the temperature of the plating alloy is within a range of 250°C or more below the bath temperature, and involves quenching the plated steel sheet within the above temperature range at an average cooling rate of 10°C / second or more in an atmosphere with a dew point of -20°C or less. When a hot-dip plating method is used in the plating step, the first cooling step is performed immediately after the steel sheet leaves the plating bath. This solidifies the plating alloy present on the surface of the steel sheet, forming a plating layer.

[0085] Thereafter, when the temperature of the plated alloy (plated layer) is within the range of less than 250°C and not less than 50°C, a second cooling step is carried out. This second cooling step is a step in which the plated steel sheet, which is within the temperature range of less than 250°C and not less than 50°C, is slowly cooled at an average cooling rate of less than 10°C / second in an atmosphere with a dew point of not less than 0°C. This controls the state of the oxide formed on the surface of the plated layer, and a desired oxide layer is formed.

[0086] As described above, by undergoing a two-stage cooling process in which the plating layer is rapidly cooled in the temperature range of 250°C or higher below the bath temperature and slowly cooled in the temperature range of 50°C or higher but lower than 250°C, a dense oxide layer 30 is formed on the surface of the plating layer 20, which satisfies specific conditions in the XPS measurement results.

[0087] Here, the interval between the end of the first cooling step and the start of the second cooling step is preferably 3 seconds or less, and the second cooling step is preferably started immediately after the end of the first cooling step. If the interval between the end of the first cooling step and the start of the second cooling step exceeds 3 seconds, an unintended cooling process occurs, making it impossible to achieve the desired oxide layer 30.

[0088] Here, in the first cooling step, the lower limit of the dew point is not particularly specified, but for example, about -90°C is a practical lower limit. The average cooling rate is more preferably 40°C / sec or more. The upper limit of the average cooling rate is not particularly specified, but for example, about 90°C / sec is a practical upper limit.

[0089] In the second cooling step, the upper limit of the dew point is not particularly specified, but a practical upper limit is, for example, about 20° C. In addition, the average cooling rate is more preferably 4° C. / second or less.

[0090] Note that if either the first cooling step or the second cooling step is not performed, it is not possible to realize the desired oxide layer 30. By performing both the first cooling step and the second cooling step, the oxide layer 30 according to this embodiment can be realized.

[0091] Furthermore, if an alloying heat treatment step (e.g., a heat treatment step involving heating to a sheet temperature of about 480 to 550°C), which is generally performed in the manufacture of galvannealed steel sheets, is performed after the second cooling step, the oxide formation state controlled by the first cooling step and the second cooling step is disrupted, and the oxides grow excessively, making it impossible to obtain the Zn evaporation suppression effect that is the focus of this embodiment. From this perspective, it is important not to perform a heat treatment step after the second cooling step.

[0092] Here, the cooling process described above can be performed using commonly known methods such as N2 gas cooling, mist cooling, submersion in water, etc. In addition to N2 gas, gases with high heat removal effects, such as He gas and hydrogen gas, may also be used as the cooling gas.

[0093] The temperature of the coating layer can be measured, for example, using a contact thermocouple (K-type). By attaching a contact thermocouple to the base steel sheet, the average temperature of the entire coating layer can be constantly monitored. Furthermore, by mechanically controlling various speeds and thicknesses and standardizing various operating conditions such as the steel sheet preheating temperature and the hot-dip coating bath temperature, it becomes possible to monitor the temperature of the entire coating layer at that time under those manufacturing conditions almost accurately. This makes it possible to precisely control the cooling treatments in the first and second cooling steps. The surface temperature of the coating layer can also be measured using a non-contact radiation thermometer, although this is not as accurate as a contact thermometer.

[0094] Alternatively, the relationship between the surface temperature of the coating layer and the average temperature of the entire coating layer may be determined by a simulation using heat conduction analysis. Specifically, the surface temperature of the coating layer and the average temperature of the entire coating layer are determined based on various manufacturing conditions, such as the preheating temperature of the steel sheet, the temperature of the hot-dip coating bath, the pulling speed of the steel sheet from the coating bath, the thickness of the steel sheet, the thickness of the coating layer, the amount of heat exchanged between the coating layer and the manufacturing equipment, and the amount of heat dissipated from the coating layer. The relationship between the surface temperature of the coating layer and the average temperature of the entire coating layer can then be determined using the obtained results. This makes it possible to estimate the average temperature of the entire coating layer at that time under those manufacturing conditions by actually measuring the surface temperature of the coating layer during the manufacturing of the coated steel sheet. As a result, it becomes possible to precisely control the cooling treatments in the first and second cooling processes.

[0095] An example of the method for manufacturing a plated steel sheet according to this embodiment has been specifically described above.

[0096] In the method for producing a plated steel sheet according to this embodiment, after the second cooling step, a treatment may be further carried out to form one or more various coating layers, such as a chromate treatment, a phosphate treatment, a chromate-free treatment, or an organic resin coating formation treatment.

[0097] Chromate treatments include electrolytic chromate treatments in which a chromate film is formed by electrolysis, reactive chromate treatments in which a film is formed by utilizing a reaction with the material and then excess treatment liquid is washed away, and application-type chromate treatments in which a treatment liquid is applied and then dried without rinsing with water to form a film, and any of these chromate treatments may be used.

[0098] Examples of electrolytic chromate treatments include those using chromic acid, silica sol, resin (phosphate resin, acrylic resin, vinyl ester resin, vinyl acetate acrylic emulsion, carboxylated styrene butadiene latex, diisopropanolamine-modified epoxy resin, etc.), and hard silica.

[0099] Examples of the phosphate treatment include zinc phosphate treatment, zinc calcium phosphate treatment, and manganese phosphate treatment.

[0100] Chromate-free treatments are particularly suitable because they do not impose a burden on the environment. Examples of such chromate-free treatments include electrolytic chromate-free treatments that form a chromate-free film by electrolysis, reactive chromate-free treatments that form a film by utilizing a reaction with the material and then wash away excess treatment liquid, and application-type chromate-free treatments that apply a treatment liquid and dry it without rinsing with water to form a film. Any of these chromate-free treatments may be used.

[0101] Furthermore, the organic resin used in the organic resin film formation process is not limited to a specific resin, and various resins can be used, such as polyester resin, polyurethane resin, epoxy resin, acrylic resin, polyolefin resin, modified versions of these resins, etc. Here, the modified version refers to a resin obtained by reacting a reactive functional group contained in the structure of these resins with another compound (e.g., a monomer, a crosslinking agent, etc.) containing a functional group in its structure that can react with the functional group.

[0102] As the organic resin, one of the above-mentioned organic resins may be used alone, or two or more organic resins (unmodified) may be used in combination. Alternatively, one 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 in combination. Alternatively, an aqueous organic resin may be used by dissolving or dispersing it in water. Furthermore, various color pigments and rust-preventive pigments may be incorporated into the organic resin film. [Example]

[0103] The plated steel sheet according to the present invention will be specifically described below with reference to examples and comparative examples. Note that the examples shown below are merely 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 shown below.

[0104] In the following examples and comparative examples, a 3.2 mm thick hot-rolled steel sheet (0.05 mass % C-0.007 mass % Si-0.25 mass % Mn, manufactured by Nippon Steel Corporation) was used as the steel sheet serving as the base material. The hot-rolled steel sheet was cut into a size of 100 mm × 200 mm to prepare a test piece.

[0105] The coating baths for achieving the coating layer compositions shown in Table 1 below were prepared and installed in a batch-type hot-dip galvanizing test apparatus manufactured by our company, and the test specimens were coated. The test specimen temperatures were measured using a thermocouple spot-welded to the center of the test specimens. Furthermore, before immersion in the coating baths, the surfaces of the test specimens were subjected to a heat reduction treatment at 800°C in an N2-5% H2 gas atmosphere in a furnace with an oxygen concentration of 20 ppm or less. After the heat reduction treatment, the test specimens were air-cooled with N2 gas. After the test specimens reached a temperature 20°C above the bath temperature, they were immersed in the coating bath of the hot-dip galvanizing test apparatus for approximately 3 seconds.

[0106] After immersion in the plating bath, the test piece was pulled up at a pulling speed of 20 to 200 mm / sec. During pulling, N2 wiping gas was used to control the desired plating adhesion weight. In the following examples and comparative examples, the plating layer adhesion weight per side of the test piece after drying was 15 to 250 g / m 2 The coating weight was controlled so that the coating weight was 0.015g. After the test piece was removed from the coating bath, it was cooled from the coating bath temperature to room temperature under the conditions shown in Table 1 below. In the examples and comparative examples shown below, the second cooling step was started immediately after the first cooling step was completed (i.e., the interval between the completion of the first cooling step and the start of the second cooling step was set to 0.2 seconds or less). For comparison, an example was also prepared in which the test piece was subjected to an alloying treatment after the second cooling step, with the ultimate temperature of 500°C and the holding time being 15 seconds (No. 44 in Table 1).

[0107] Here, a plated steel sheet measuring 30 mm × 30 mm was cut out from the test piece plated as described above, and the plated steel sheet was immersed in a 10% HCl aqueous solution containing an inhibitor to peel off the plating layer by pickling. The elements dissolved in the aqueous solution were then subjected to ICP analysis to measure the composition of the plating layer.

[0108] In addition, the obtained plating layer was photographed using a TEM to take an electron diffraction image. Based on whether or not a five-fold symmetric crystal structure was observed in the electron diffraction image, the Mg 32 (Al, Zn) 49 The presence or absence of phases was confirmed.

[0109] Furthermore, the XPS spectrum of the obtained oxide layer was measured according to the above-mentioned method, and the intensity ratio ([Al-O] + [Mg-O]) / [Zn-O] was calculated. The obtained intensity ratio was evaluated based on the following criteria. <Evaluation Criteria> Grade "A": Intensity ratio value is 10.0 or more "B": Intensity ratio value is 5.0 or more and less than 10.0 "C": Intensity ratio value is less than 5.0

[0110] Furthermore, each of the obtained test pieces was evaluated from the viewpoints of blowhole formation during welding, LME occurrence during welding, and corrosion resistance.

[0111] <Evaluation of blowhole formation during welding> From the obtained test piece, a piece of 150 mm × 50 mm was cut out as the first steel plate, and a piece of 150 mm × 30 mm was cut out as the second steel plate. The long sides of these steel plates were overlapped and welded by arc welding or laser welding (lap fillet welding).

[0112] Here, the welding conditions for the arc welding are as follows. Welding current: 220A, welding voltage: 25.2V, welding speed: 100cm / min Welding gas: 20% CO2 + Ar, gas flow rate: 20 L / min Welding wire: YGW16, manufactured by Nippon Steel Welding Industry Co., Ltd., φ1.2 mm (C: 0.1% by mass, Si: 0.80% by mass, Mn: 1.5% by mass, P: 0.015% by mass, S: 0.008% by mass, Cu: 0.36% by mass) Welding torch tilt angle: 45° Overlap: 10mm Steel plate size: Upper plate (first steel plate) 150 x 50 mm, lower plate (second steel plate) 150 x 30 mm Gap: 0mm

[0113] The welding conditions for the laser welding are as follows: Output: 7kW, welding speed: 400cm / min, forward / reverse angle: 0° Steel plate size: Upper plate (first steel plate) 150 x 50 mm, lower plate (second steel plate) 150 x 30 mm Overlap: 50mm Gap: 0mm

[0114] The presence or absence of blowholes, which may be formed during welding, can be easily determined by performing an X-ray examination of the welded test piece from above. In this example, after the above-described welding, an X-ray examination was performed on the region including the weld bead and toe formed by the welding. The areas where blowholes were formed and areas where they were not formed were identified, and the projected area of ​​each area was calculated. Specifically, an YXLON SMART300HP X-ray inspection device was used. After the test piece was fixed to a base, the X-ray inspection device was set so that the focal distance from the tip of the irradiation nozzle was 750 mm, and X-rays were irradiated from an angle inclined at 60° to the evaluation surface. The applied current was 3 mA, the applied voltage was 125 kV, and the application time was 1 minute. The projected area of ​​the area where blowholes were formed was divided by the total projected area to calculate the blowhole occupancy rate (%) = {(projected area of ​​the area where blowholes were formed / total projected area) × 100}, and the evaluation was performed based on the following evaluation criteria. <Evaluation Criteria> Rating "AAA": Blowhole occupancy rate less than 5% "AA": Blowhole occupancy rate 5% to less than 10% "A": Blowhole occupancy rate is 10% or more but less than 20% "B": Blowhole occupancy rate 20% or more

[0115] The "toe" mentioned above is a position defined in JIS Z3001 (2018) and corresponds to the point where the surface of the base material and the surface of the weld bead intersect. In this example, the point where the surface of the oxide layer of the plated steel sheet intersects with the surface of the weld bead corresponds to this "toe."

[0116] <Evaluation of LME resistance> The LME resistance of the obtained test pieces was evaluated by a hot tensile test. More specifically, the obtained test specimen and the unplated steel sheet were both heated to 800°C at a heating rate of 100°C / s, held at 800°C for 1 second, and then subjected to a tensile test at a stroke speed of 50 mm / s. This resulted in the acquisition of stress-stroke curves for both the unplated steel sheet and the test specimen. From the obtained stress-stroke curves, the stress × stroke value (area of ​​the stress-stroke curve) was then calculated, and the evaluation value (%) = {(stress × stroke value of test specimen) / (stress × stroke value of unplated steel sheet) × 100} was evaluated based on the following evaluation criteria. <Evaluation Criteria> Rating "AA": Evaluation value 95% or more "A": Evaluation value is 85% or more but less than 95% "B": Evaluation value less than 85%

[0117] <Corrosion resistance evaluation> The corrosion resistance of the obtained test pieces was evaluated as follows. Specifically, 50 x 100 mm samples were taken from the plated steel sheets and subjected to a zinc phosphate treatment (SD5350 System: Nippon Paint Industrial Coating standard). Subsequently, electrodeposition coating (PN110 Powernics Gray: Nippon Paint Industrial Coating standard) was applied to a thickness of 15 μm and baked at 150°C for 20 minutes. A 70 mm long cut was introduced into the painted plated steel sheets (electrodeposition-coated plated steel sheets) using a cutter, reaching all the way to the steel substrate. The sheets were then subjected to a cyclic corrosion test in accordance with JASO (M609-91). The maximum blister width on one side from the cut was measured to evaluate corrosion resistance after painting. <Evaluation Criteria> Grade "AAA": Less than 1 mm "AA": 1mm or more and less than 2mm "A": 2mm or more and less than 3mm "B": 3mm or more

[0118] The results obtained are summarized in Table 1 below.

[0119] [Table 1]

[0120] As is clear from Table 1 above, the examples corresponding to the examples of the present invention are able to suppress blowhole formation and LME while maintaining excellent corrosion resistance, whereas the examples corresponding to the comparative examples of the present invention are unable to exhibit sufficient performance in at least one of corrosion resistance, blowhole formation, and LME.

[0121] Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications and alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention. [Explanation of symbols]

[0122] 1. Plated steel sheet 10 steel plate 20 plating layer 30 oxide layer

Claims

1. A steel plate as the base material, a plating layer located on at least a part of the surface of the steel sheet; an oxide layer located on the surface of the plating layer; It has The plating layer comprises, in mass %, Al: 1.00-80.00%, Mg: 1.00-20.00%, Fe: 0.01-15.00%, and optionally containing Si: 0 to 10.00%, Ca: 0-4.00%, and optionally further comprising Sb: 0 to 0.500%, Pb: 0 to 0.500%, Cu: 0 to 1.000%, Sn: 0-1.000%, In: 0 to 1.000%, Bi: 0-1.000%, Ti: 0 to 1.000%, Cr: 0-1.000%, Nb: 0 to 1.000%, Zr: 0 to 1.000%, Ni: 0-1.000%, Mn: 0 to 1.000%, V: 0-1.000%, Mo: 0-1.000%, Ag: 0-1.000%, Li: 0 to 1.000%, La: 0 to 0.500%, Ce: 0-0.500%, B: 0-0.500%, Y: 0-0.500%, Sr: 0-0.500%, The balance is 5.00 mass% or more of Zn and impurities, the plated steel sheet, wherein, when a position at a depth of 5 nm from the outermost surface of the oxide layer is observed by X-ray photoelectron spectroscopy (XPS), the value of the intensity ratio ([Al—O]+[Mg—O]) / [Zn—O] calculated from the intensities of peaks respectively assigned to an Al—O bond, an Mg—O bond, and a Zn—O bond is 5.0 or more.

2. 2. The plated steel sheet according to claim 1, wherein the strength ratio ([Al—O]+[Mg—O]) / [Zn—O] has a value of 10.0 or more.

3. The plating layer is Al: 18.00 to 60.00% by mass, Mg: 5.00 to 15.00% by mass, The plated steel sheet according to claim 1 or 2, comprising at least

4. The plating layer is Al: 35.00 to 60.00% by mass, Mg: 7.00 to 15.00% by mass, and The plating layer contains Mg ３２ (Al, Zn) ４９ There are phases, The Mg ３２ (Al, Zn) ４９ 3. The plated steel sheet according to claim 1, wherein the Mg content [Mg], Zn content [Zn], and Al content [Al] (each unit: atomic %) in the phase satisfy the relationship 0.50≦[Mg] / ([Zn]+[Al])≦0.

83.

5. The plating layer is Al: 35.00 to 60.00% by mass, Mg: 7.00 to 15.00% by mass, and The plating layer contains Mg ３２ (Al, Zn) ４９ There are phases, The Mg ３２ (Al, Zn) ４９ 4. The plated steel sheet according to claim 3, wherein the Mg content [Mg], Zn content [Zn], and Al content [Al] (each unit: atomic %) in the phase satisfy the relationship 0.50≦[Mg] / ([Zn]+[Al])≦0.83.

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