galvanized steel sheet

Abstract

[Problem] To suppress LME and blowhole formation more reliably while maintaining excellent corrosion resistance. [Solution] The plated steel sheet according to the present invention has a steel sheet that serves as a base material, a plating layer located on at least a portion of the surface of the steel sheet, and an oxide layer located on the surface of the plating layer, wherein the chemical composition of the plating layer consists of a predetermined component and Zn and impurities as the remainder, and when the 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 intensity of the peaks attributed to Al-O bonds, Mg-O bonds, and Zn-O bonds, respectively, is 5.0 or higher.

Description

Technology Field

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

[0002] Galvanized steel sheets are widely used in fields such as construction and automobiles for the purpose of improving the corrosion resistance of structural members. In this context, a method is used to manufacture various structural members by welding pre-galvanized galvanized steel sheets using arc welding or laser welding.

[0003] Here, when manufacturing structural members by welding galvanized steel sheets, a unique problem is the decrease in corrosion resistance around the weld (weld heat-affected zone) accompanied by liquid metal embrittlement (LME) caused by molten plating in the heat-affected zone of the weld metal and base material, or the formation of blowholes caused by Zn evaporation during welding.

[0004] In order to solve the problem of LME or blowhole formation as described above, various proposals have been made in the past. For example, in Patent Document 1 below, a plated steel material is proposed having a steel plate and a plating layer disposed on the surface of the steel plate and comprising a Zn-Al-Mg alloy layer, wherein in the cross-section of the Zn-Al-Mg alloy layer, the area fraction of the MnZn2 phase is 45 to 75%, the area fraction of the total of the MgZn2 phase and the Al phase is 70% or more, and the area fraction of the Zn-Al-MgZn2 trieutectic structure is 0 to 5%, and the plating layer has a predetermined chemical composition. Prior art literature

[0005] International Publication No. 2018 / 139620 The problem to be solved

[0006] Here, it is possible to solve the problem of LME or blowhole formation by using the plated steel proposed in the above Patent Document 1. However, as a result of careful examination by the inventors, it was found that there is still room for improvement in the technology proposed in the above Patent Document 1, and further improvement regarding the problem of LME or blowhole formation can be expected.

[0007] Accordingly, the present invention has been made in consideration of the above problems, and the objective of the present invention is to provide a plated steel sheet that can more reliably suppress LME and blowhole formation while maintaining excellent corrosion resistance. means of solving the problem

[0008] In order to solve the above problem, the inventors carefully examined the matter and found that if the state of the oxide layer formed on the surface of the zinc-based plating layer can be made denser, the occurrence of LME and blowhole formation can be suppressed more reliably while maintaining excellent corrosion resistance, and thus the present invention was completed.

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

[0010] (1) A steel plate serving as a base material, a plating layer located on at least a portion of the surface of the steel plate, and an oxide layer located on the surface of the plating layer, wherein the plating layer contains, in mass%, Al: 1.00 to 80.00%, Mg: 1.00 to 20.00%, Fe: 0.01 to 15.00%, Si: 0 to 10.00%, Ca: 0 to 4.00%, and optionally, 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 It contains 1.000%, Zr: 0 to 1.000%, Ni: 0 to 1.000%, Mn: 0 to 1.000%, V: 0 to 1.000%, Mo: 0 to 1.000%, Ag: 0 to 1.000%, Li: 0 to 1.000%, La: 0 to 0.500%, Ce: 0 to 0.500%, B: 0 to 0.500%, Y: 0 to 0.500%, and Sr: 0 to 0.500% in a total of 0 to 5.000%, and the remainder consists of 5.00 mass% or more of Zn and impurities, and when the position at a depth of 5 nm from the outermost surface of the oxide layer is observed by X-ray photoelectron spectroscopy (XPS), Al-O bonds, Mg-O bonds, and A plated steel sheet in which the value of the intensity ratio ([Al-O]+[Mg-O]) / [Zn-O] calculated from the intensity of the peaks attributed to the Zn-O bonds is 5.0 or higher.

[0011] (2) A plated steel sheet as described in (1), wherein the value of the strength ratio ([Al-O]+[Mg-O]) / [Zn-O] is 10.0 or higher.

[0012] (3) The plating layer is a plated steel sheet described in (1) or (2) containing at least Al: 18.00 to 60.00 mass% and Mg: 5.00 to 15.00 mass%.

[0013] (4) The plating layer contains at least 35.00 to 60.00 mass% Al and 7.00 to 15.00 mass% Mg, and furthermore, in the plating layer, Mg 32 (Al, Zn) 49 A phase exists, and the above Mg 32 (Al, Zn) 49 A plated steel sheet described in any one of (1) to (3), wherein the Mg content [Mg], Zn content [Zn], and Al content [Al] (each unit: atomic %) in the plate satisfy the relationship 0.50 ≤ [Mg] / ([Zn] + [Al]) ≤ 0.83. Effects of the invention

[0014] As explained above, according to the present invention, in a plated steel sheet, it is possible to suppress LME and blowhole formation more reliably while maintaining excellent corrosion resistance. Brief explanation of the drawing

[0015] FIG. 1a is an explanatory diagram schematically illustrating an example of a plated steel sheet according to an embodiment of the present invention. FIG. 1b is an explanatory diagram schematically illustrating an example of a plated steel sheet according to the same embodiment. FIG. 2 is an explanatory diagram for describing a plated steel sheet according to the same embodiment. Figure 3 is an explanatory diagram for explaining the peak intensity in XPS measurement results. Specific details for implementing the invention

[0016] Suitable embodiments of the present invention will be described in detail below with reference to the attached drawings. Furthermore, in this specification and drawings, components having substantially the same functional configuration are given the same reference numerals to avoid redundant descriptions.

[0017] (Regarding plated steel sheets)

[0018] First, with reference to FIGS. 1a and 1b, the overall configuration of a plated steel sheet according to an embodiment of the present invention will be described. FIGS. 1a and 1b are schematic diagrams illustrating an example of a plated steel sheet according to the present embodiment.

[0019] As schematically illustrated in FIG. 1a, the plated steel sheet (1) according to the present embodiment has a base steel sheet (10), 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) are not only present on one surface of the steel sheet (10) as illustrated in FIG. 1a, but may also be present on both surfaces of the steel sheet (10) as schematically illustrated in FIG. 1b.

[0020] <Regarding the steel plate (10)>

[0021] The steel plate (10) used as the base material for the plated steel plate (1) according to the present embodiment is not particularly limited, and various steel plates may be used depending on the mechanical strength (e.g., tensile strength) required for the plated steel plate (1). Examples of such steel plates include various types of Al-killed steel, ultra-low carbon steel containing Ti, Nb, etc., and high-strength steel containing reinforcing elements such as P, Si, Mn in addition to ultra-low carbon steel.

[0022] In addition, the thickness of the steel plate (10) is not specifically limited and can be appropriately set according to the mechanical strength required of the plated steel plate (1).

[0023] <Regarding the plating layer (20)>

[0024] The plating layer (20) is provided on at least a portion of the surface of the steel plate (10), as schematically illustrated in FIGS. 1a and 1b, and is more preferably provided over the entire surface of the steel plate (10). Below, the chemical composition of the plating layer (20) will first be described in detail.

[0025] Regarding the chemical composition of the plating layer (20)

[0026] The chemical composition of the plating layer (20) according to the present embodiment contains, in mass%, Al: 1.00 to 80.00%, Mg: 1.00 to 20.00%, Fe: 0.01 to 15.00%, Si: 0 to 10.00%, and Ca: 0 to 4.00%, and the remainder consists of Zn of 5.00 mass% or more and impurities. That is, in the chemical composition of the plating layer (20) according to the present embodiment, the content of Al, Mg, Fe, Si, and Ca is within the above range, and the sum of these contents is less than 100 mass%, and the remainder consists of Zn of 5.00 mass% or more and impurities.

[0027] The following describes these components and their contents in detail.

[0028] [Al: 1.00 to 80.00 mass%]

[0029] Al is an element necessary to form the main phase (Zn-Al-Mg alloy phase) of the plating layer (20) according to the present embodiment. Al is contained in a predetermined amount or more to ensure corrosion resistance in the weld heat-affected zone and corrosion resistance in the non-welded zone as a plated steel sheet. If the Al content in the plating layer (20) is less than 1.00 mass%, the corrosion resistance of the weld heat-affected zone and the non-welded zone as described above cannot be guaranteed. Therefore, in the plating layer (20) according to the present 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. By having the Al content within the above range, it becomes possible to ensure the corrosion resistance of the plated steel sheet (1).

[0030] Meanwhile, 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, making it easier for the corrosion of the base iron to proceed, and thus the corrosion resistance of the plated steel sheet (1) cannot be guaranteed. Therefore, in the plating layer (20) according to the present 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.

[0031] [Mg: 1.00 to 20.00 mass%]

[0032] Mg is an element necessary to form the main phase (Zn-Al-Mg alloy phase) of the plating layer (20) according to the present embodiment. Mg is contained in an amount greater than a predetermined amount to ensure corrosion resistance in the weld heat-affected zone and corrosion resistance in the non-welded zone of the plated steel sheet. Therefore, in the plating layer (20) according to the present embodiment, the Mg content 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 having the Mg content within the above range, it becomes possible to ensure the corrosion resistance of the plated steel sheet (1).

[0033] Meanwhile, if the Mg content in the plating layer (20) exceeds 20.00 mass%, the anode dissolution of the plating layer becomes more likely to proceed when placed in a corrosive environment, so the corrosion resistance of the plated steel sheet (1) cannot be guaranteed. Therefore, in the plating layer (20) according to the present 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 having the Mg content within the above range, it becomes possible to guarantee the corrosion resistance of the plated steel sheet (1).

[0034] [Fe: 0.01 to 15.00 mass%]

[0035] In the plating layer (20), elements constituting the steel plate may be incorporated from the base material, the steel plate (10). In particular, in the molten plating method, elements constituting the steel plate (10) are easily incorporated into the plating layer (20) due to mutual diffusion of elements caused by the solid-liquid reaction between the steel plate (10) and the plating layer (20). Due to such incorporation of elements, a predetermined amount of Fe is contained in the plating layer (20), and the content is generally 0.01 mass% or more. When the above mutual diffusion is promoted, the adhesion between the steel plate (10) and the plating layer (20) is improved. From the perspective of improving the adhesion between the steel plate (10) and the plating layer (20), it is preferable that the Fe content in the plating layer (20) be 0.20 mass% or more.

[0036] In addition, Fe may be intentionally added to the plating bath used when manufacturing the plating layer (20) within a range that does not impair the effects of the present invention. However, if the Fe content in the plating layer (20) is 15.00 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, so this is undesirable. In this regard, 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. More preferably, the Fe content in the plating layer (20) is 10.00 mass% or less.

[0037] [Si: 0 to 10.00 mass%]

[0038] Si is an element capable of improving the adhesion between the plating layer and the steel sheet by suppressing the excessive growth of Fe-Al intermetallic compounds formed at the interface between the plating 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, and more preferably 0.20 mass% or more. On the other hand, if the Si content exceeds 10.00 mass%, it forms an excessive amount of Mg and high-melting-point intermetallic compounds, which inhibits the formation of an Al-Mg oxide film that has a Zn evaporation suppression effect, making it difficult to suppress Zn evaporation when such a plated steel sheet is welded.

[0039] Meanwhile, 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 the plating workability may decrease. Therefore, the Si content in the plating bath is adjusted from the perspective of plating workability, 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.

[0040] [Ca: 0 to 4.00 mass%]

[0041] When Ca is contained in the plating layer (20), it forms intermetallic compounds with Al and Zn. Additionally, when Si is contained along with Ca in the plating layer (20), Ca forms an intermetallic compound phase with Si. Since these intermetallic compounds have a high melting point and a stable structure, it becomes possible to suppress the formation of blowholes caused by Zn evaporation during welding of the plated steel sheet and LME. This effect of suppressing blowhole formation and LME during welding is achieved by making the Ca content 0.01 mass% or more. More preferably, the Ca content in the plating layer (20) is 0.10 mass% or more.

[0042] Meanwhile, if the Ca content in the plating layer (20) exceeds 4.00 mass%, the corrosion resistance of the plated steel sheet is reduced. In this regard, 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.

[0043] In the plating layer (20), the remainder of the above Al, Mg, Fe, Si, and Ca is 5.00 mass% or more of Zn and impurities.

[0044] Zn is an element necessary to form the main phase (Zn-Al-Mg alloy phase) of the plating layer (20) according to the present embodiment, and is an important element for improving the corrosion resistance of the plated steel sheet. In addition, by the plating layer (20) containing Al, Mg, Fe, Si, and Ca within the above ranges and also containing Zn of 5.00 mass% or more, it becomes possible to suppress LME and blowhole formation during welding.

[0045] Additionally, the plating layer (20) according to the present embodiment comprises, instead of a portion of the remainder of Zn, also optionally, 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 1.000%, Ni: 0 to 1.000%, Mn: 0 to 1.000%, V: 0 to 1.000%, Mo: 0 to 1.000%, Ag: 0 to 1.000%, Li: 0 to 1.000%, La: 0 to It may contain 0.500%, Ce: 0 to 0.500%, B: 0 to 0.500%, Y: 0 to 0.500%, and Sr: 0 to 0.500%, in a total of 0 to 5.000%. That is, the plating layer (20) according to the present embodiment may contain at least one 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 range, and the total content may be 5.000 mass% or less. In addition, since it is conceivable that the plating layer (20) according to the present embodiment may not contain such optional additive elements, the lower limit of the content of each optional additive element is 0 mass%.

[0046] By making the total content of the above optional additive elements 5.000 mass% or less, it becomes possible to enjoy the effects expressed by the addition of each optional additive element, as described in detail below, without damaging each other. The total content of the above optional additive elements is preferably 1.000 mass% or less, and more preferably 0.200 mass% or less.

[0047] The content of each optional added element is described in detail below.

[0048] [Sb: 0 to 0.500 mass%]

[0049] [Pb: 0 to 0.500 mass%]

[0050] [Sr: 0 to 0.500 mass%]

[0051] If 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 the metallic luster. Therefore, from the perspective of improving the aesthetic appearance of the plated steel sheet, it is preferable that at least one of Sb, Pb, and Sr be contained in the plating layer (20). This effect of improving aesthetic appearance is manifested 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 these elements be 0.050 mass% or more, independently.

[0052] Meanwhile, if a plating layer (20) is formed in which any of the contents of Sb, Pb, and Sr exceeds 0.500 mass%, the amount of dross generated in the plating bath used to form the plating layer (20) increases, and 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 0.500 mass% or less. The contents of Sb, Pb, and Sr are each independently preferably 0.200 mass% or less.

[0053] [Cu: 0 to 1.000 mass%]

[0054] [Ti: 0 to 1.000 mass%]

[0055] [Cr: 0 to 1.000 mass%]

[0056] [Nb: 0 to 1.000 mass%]

[0057] [Ni: 0 to 1.000 mass%]

[0058] [Mn: 0 to 1.000 mass%]

[0059] [V: 0 to 1.000 mass%]

[0060] If at least one of Cu, Ti, Cr, Nb, Ni, Mn, and V is contained in the plating layer (20), when the plated steel plate is welded, these elements are introduced into the Al-Fe alloy produced by welding, making it possible to improve the corrosion resistance of the formed weldment. This effect of improving the corrosion resistance of the weldment is manifested when the content of any one 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 be 0.005 mass% or more independently.

[0061] Meanwhile, if a plating layer (20) is formed in which any of the contents of Cu, Ti, Cr, Nb, Ni, Mn, and V exceed 1.000 mass%, these elements form various intermetallic compounds in the plating bath for forming the plating layer (20), causing an increase in the viscosity of the plating bath, and thus it is not possible to manufacture 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 1.000 mass% or less. The contents of Cu, Ti, Cr, Nb, Ni, Mn, and V are each independently preferably 0.200 mass% or less.

[0062] [Sn: 0 to 1.000 mass%]

[0063] [In: 0 to 1.000 mass%]

[0064] [Bi: 0 to 1.000 mass%]

[0065] Sn, In, and Bi are elements that increase the Mg leaching rate when a plating layer (20) containing Zn, Al, and Mg is placed in a corrosive environment. When the Mg leaching rate increases, Mg ions are supplied to the exposed parts of the steel plate (10), thereby improving corrosion resistance. In this regard, when Sn, In, and Bi are included, the content of Sn, In, and Bi is each independently 0.0050 mass% or more. On the other hand, excessive addition of Sn, In, and Bi may excessively accelerate the Mg leaching rate, potentially lowering the corrosion resistance of the plated steel plate. Since this increase in the Mg leaching rate becomes significant when any of the contents of Sn, In, and Bi exceeds 1.000 mass%, the content of Sn, In, and Bi is each independently 1.000 mass% or less. The content of Sn, In, and Bi is each independently preferably 0.200 mass% or less.

[0066] [Zr: 0 to 1.000 mass%]

[0067] When Zr is included in the plating layer (20), it becomes possible to improve plating workability. This effect of improving plating workability is manifested when the Zr content is 0.010 mass% or more. Therefore, when including Zr, it is preferable to have the content be 0.010 mass% or more.

[0068] Meanwhile, when forming a plating layer (20) in which the Zr content exceeds 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 Zr content is 1.000 mass% or less. The Zr content is preferably 0.100 mass% or less.

[0069] [Mo: 0 to 1.000 mass%]

[0070] When Mo is included in the plating layer (20), it becomes possible to improve corrosion resistance. This improvement in corrosion resistance is manifested when the Mo content is 0.010 mass% or more. Therefore, when Mo is included, it is preferable to make the content 0.010 mass% or more.

[0071] Meanwhile, forming a plating layer (20) with a Mo content exceeding 1.000 mass% is undesirable because it causes a large amount of dross to be generated in the plating bath used. Therefore, the Mo content is 1.000 mass% or less. The Mo content is preferably 0.050 mass% or less.

[0072] [Ag: 0 to 1.000 mass%]

[0073] When Ag is contained in the plating layer (20), it becomes possible to improve plating workability. This effect of improving plating workability is manifested when the Ag content is 0.010 mass% or more. Therefore, when Ag is included, it is preferable that the content be 0.010 mass% or more.

[0074] Meanwhile, when forming a plating layer (20) in which the Ag content exceeds 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.

[0075] [Li: 0 to 1.000 mass%]

[0076] When Li is included in the plating layer (20), it becomes possible to improve plating workability. This effect of improving plating workability is manifested when the Li content is 0.010 mass% or more. Therefore, when Li is included, it is preferable that the content be 0.010 mass% or more.

[0077] Meanwhile, when forming a plating layer (20) in which the Li content exceeds 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 Li content is 1.000 mass% or less. The Li content is preferably 0.050 mass% or less.

[0078] [La: 0 to 0.500 mass%]

[0079] [Ce: 0 to 0.500 mass%]

[0080] [Y: 0 to 0.500 mass%]

[0081] La, Ce, and Y are elements that exhibit an effect nearly equivalent to Ca and suppress the formation of blowholes during welding. This is due to the fact that the atomic radius of each element is similar to the atomic radius of Ca. When these elements are contained in the plating layer (20), they are substituted for the Ca position. Therefore, these elements are detected at the same position as Ca in EDS. Furthermore, even when these elements become oxides after welding the plated steel sheet, the oxides of these elements are detected at the same position as CaO.

[0082] The effect of suppressing blowhole formation during welding is achieved by making the content of these elements each independently 0.010 mass% or more. Therefore, the content of La, Ce, and Y in the plating layer (20) is more preferably 0.050 mass% or more, each independently.

[0083] Meanwhile, if the content of La, Ce, and Y in the plating bath for manufacturing the plating layer (20) is too high, the viscosity of the plating bath may increase more than necessary, potentially lowering plating operability. Therefore, the content of La, Ce, and Y in the plating bath is adjusted from the perspective of plating operability, so that the content of La, Ce, and Y is each independently 0.500 mass% or less. More preferably, the content of La, Ce, and Y is each independently 0.100 mass% or less.

[0084] [B: 0 to 0.500 mass%]

[0085] When B is contained in the plating layer (20), it has the effect of further suppressing LME. This is presumed to be because when B is contained in the plating layer (20), it combines with at least one of Zn, Al, Mg, and Ca to form various intermetallic compound phases. In addition, it is thought that the presence of B in the plating layer (20) causes B to diffuse from the plating layer (20) to the steel plate (10), thereby having the effect of further suppressing LME in the steel plate (10) through grain boundary strengthening. Furthermore, it is presumed that the various intermetallic compounds formed with respect to B have very high melting points, and thus also act to suppress Zn evaporation during welding. These improvement effects are manifested by containing B at a level of 0.050 mass% or more. Therefore, the content of B in the plating layer (20) is more preferably 0.050 mass% or more.

[0086] Meanwhile, in order to include B in the plating layer (20), if B is included in excess in the plating bath, it causes a rapid increase in the plating melting point, which lowers plating operability and makes it impossible to manufacture a plated steel sheet with excellent plating properties. Since this lowering of operability becomes significant when the B content exceeds 0.500 mass%, the B content is 0.500 mass% or less. The B content is preferably 0.100 mass% or less.

[0087] [Method for Measuring Chemical Components]

[0088] 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). Additionally, when analyzing chemical composition down to 0.1 mass%, ICP-AES is used, and when analyzing trace amounts of chemical composition less than 0.1 mass%, ICP-MS is used. A plated steel plate is immersed in a 10% HCl aqueous solution containing an inhibitor for about 1 minute to peel off the plating layer portion, and a solution is prepared in which the plating layer is dissolved. The obtained solution is analyzed by ICP-AES or ICP-MS to obtain the chemical composition as the overall average of the plating layer.

[0089] ◇ Regarding a more desirable chemical composition of the plating layer (20)

[0090] The plating layer (20) according to the present embodiment has the chemical composition as described above, but a more preferred chemical composition is as follows.

[0091] That is, the plating layer (20) according to the present embodiment contains at least 18.00 to 60.00 mass% of Al and 5.00 to 15.00 mass% of Mg as a chemical composition, and if necessary, additionally contains optional additive elements such as those above.

[0092] In addition, the plating layer (20) according to the present 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 if necessary, additionally contains optional additive elements as described above, and further, in the plating layer (20), Mg 32 (Al, Zn) 49It is even more desirable that an image exists.

[0093] Here, Mg 32 (Al, Zn) 49 Plaque, 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 particles of the phase satisfy, in atomic %, 0.5 ≤ [Mg] / ([Zn] + [Al]) ≤ 0.83. That is, it is defined as a crystalline or quasicrystalline phase in which the ratio of Mg atoms to the sum of Zn atoms and Al atoms, Mg:(Zn+Al), is 3:6 to 5:6. Mg 32 (Al, Zn) 49 It is preferable to measure the chemical composition of the phase using TEM-EDX (Transmission Electron Microscope-Energy Dispersive X-ray Spectroscopy). Mg 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, its crystal structure is identified as Mg from the electron diffraction pattern during TEM observation. 32 (Al, Zn) 49 It is possible to sympathize with the merchant. Also, Mg 32 (Al, Zn) 49 In the case where the phase is a quasicrystalline phase, it can be confirmed by taking an electron beam diffraction image using TEM and checking whether a crystal structure with five-fold symmetry is observed in the electron beam diffraction image. A crystal structure with five-fold symmetry can be identified by obtaining an electron beam diffraction image called a Penrose pattern.

[0094] Mg 32 (Al, Zn) 49 The phase exhibits sacrificial corrosion resistance to plated steel sheets, thereby suppressing corrosion of the underlying steel from exposed cut or weld sections, and has the effect of improving corrosion resistance. In addition to this, Mg 32(Al, Zn) 49 The corrosion resistance of the phase itself is also excellent, so Mg 32 (Al, Zn) 49 Since the phase exhibits a slow corrosion rate even in corrosive environments, it suppresses corrosion beneath the coating and also has the effect of improving post-coating corrosion resistance in terms of coating expansion.

[0095] ◇Regarding the amount of plating layer (20) attached

[0096] Regarding the amount of plating layer (20) attached as described above, it is not specifically defined, but, for example, it is preferably about 15 to 250 g / m² per side of the steel plate. By ensuring that the amount of plating layer (20) attached is within the above range, the plated steel plate (1) according to the present embodiment can exhibit sufficient corrosion resistance.

[0097] In addition, the amount of the plating layer (20) attached is measured as follows. First, a sample is cut from a plated steel plate to a size of 30 mm × 30 mm, and the mass of the sample is measured in advance. Also, a tape seal is attached to one side of the sample so that the plating layer on that side does not dissolve in the next process. After that, the sample is immersed in a 10% HCl aqueous solution with an inhibitor added to pickle the plating layer, and the mass of the sample after pickling is measured. It is possible to determine the amount of the plating layer (20) attached per side from the change in mass of the sample before and after pickling.

[0098] <Regarding the oxide layer (30)>

[0099] Next, the oxide layer (30) having the plated steel sheet (1) according to the present embodiment will be described in detail.

[0100] As schematically illustrated in FIGS. 1a and 1b, an oxide layer (30) is located on the surface of the plating layer (20) as described above.

[0101] This oxide layer (30) is formed by the reaction of an element that is prone to oxidation among the elements constituting the plating layer (20) with oxygen in the heat treatment atmosphere during the cooling treatment to solidify the plating layer during the manufacture of the plated steel sheet.

[0102] As such, since this oxide layer (30) is composed mainly of oxides of elements constituting the plating layer (20) as described above, its chemical composition varies depending on the elements contained in the plating layer (20). This oxide layer (30) is presumed to contain at least 50 mass% of Zn oxide, Mg oxide, and Al oxide in total, and also to be a layer that may contain impurities, etc., such as the hydroxides of Zn, Mg, and Al, or the oxides or hydroxides of other constituent elements in the plating layer (20).

[0103] Here, the oxide layer (30) according to the present embodiment exists in a specific state as described below by undergoing a specific heat treatment process as described in detail below during the manufacture of the plated steel sheet. Below, this state will be described in detail with reference to FIGS. 2 and FIGS. 3. FIG. 2 is a schematic diagram illustrating a part of a cross-section parallel to the plate thickness direction of the oxide layer. FIG. 3 is an explanatory diagram for explaining the intensity of the peak in the XPS measurement results.

[0104] By being manufactured through a specific heat treatment process as described in detail below, the oxide layer (30) according to the present embodiment is formed as a dense film in which the sum of the amount of at least one of the oxide or hydroxide of Al and the amount of at least one of the oxide or hydroxide of Mg is greater than the amount of at least one of the oxide or hydroxide of Zn. This will be explained in more detail below.

[0105] Now, attention is paid to a position at a depth of 5 nm from the outermost surface of the oxide layer (30) as schematically illustrated in FIG. 2 (position A in FIG. 2). In the oxide layer (30) according to the present embodiment, when this position is observed by X-ray photoelectron spectroscopy (XPS), the value of the intensity ratio ([Al-O]+[Mg-O]) / [Zn-O] calculated from the intensity of the peaks attributed to the Al-O bond, Mg-O bond, and Zn-O bond, respectively, is 5.0 or higher.

[0106] Here, there is a possibility that contaminants such as oil may be attached to the outermost surface of the oxide layer (30). Therefore, it is desired that the XPS measurement as described above be performed in a state where such contaminants are not present. In this regard, contaminants are removed by performing a treatment such as ultrasonic cleaning in ethanol on the surface of the oxide layer (30), and the surface obtained by such treatment is designated as the "outermost surface of the oxide layer (30)" when performing the XPS measurement as described above.

[0107] After that, the oxide layer (30) is removed by Ar ion etching to a depth of 5 nm from the outermost surface obtained as described above, and the surface of the obtained oxide layer (30) is measured by XPS. Here, the measurement conditions for XPS can be, for example, as follows.

[0108] X-ray source: mono-Al Kα(1486.6 eV)

[0109] X-ray diameter: 50 to 200 µm

[0110] Measurement area: 100 to 700㎛ × 100 to 700㎛

[0111] Vacuum level: 1×10⁻⁶ -10 Up to 1×10 - 11 torr(1 torr is 133.32 Pa.)

[0112] Acceleration voltage: 1 to 10 kV

[0113] In the present embodiment, attention is paid to the peaks attributed to Al-O bonds, Mg-O bonds, and Zn-O bonds, respectively, in the obtained XPS measurement results. Such bonds are characteristic of the oxides and hydroxides of Al, Mg, and Zn. It can be assumed that the intensity of the peaks attributed to these bonds has a positive correlation with the amount of at least one of the oxides or hydroxides of Al, Mg, and Zn.

[0114] Here, the peak attributed to the Al-O bond is the peak observed within the range of 72 to 76 eV in the XPS spectrum focusing on Al 2p3 / 2. The peak attributed to the Mg-O bond is the peak observed within the range of 48 to 52 eV in the XPS spectrum focusing on Mg 2p3 / 2. The peak attributed to the Zn-O bond is the peak observed within the range of 1018 to 1024 eV in the XPS spectrum focusing on Zn 2p3 / 2.

[0115] In addition, the intensity of the peak attributed to each combination is, in the XPS spectrum schematically illustrated in FIG. 3, the intensity I of the peak of interest after considering the baseline of the peak of interest. p Baseline intensity I from b subtracted (i.e., "I p -I b 」)

[0116] A more detailed method for calculating the strength ratio is as follows.

[0117] That is, at any location on the surface (the surface of "Position A" in FIG. 2) at a depth of 5 nm from the outermost surface obtained as described above, XPS is measured as described above to calculate the value of the intensity ratio ([Al-O]+[Mg-O]) / [Zn-O]. This measurement and calculation process is performed at any 5 locations on the surface corresponding to "Position A", and the average value of the 5 obtained intensity ratios is taken as the value of the intensity ratio ([Al-O]+[Mg-O]) / [Zn-O] in the oxide layer (30) of the present embodiment.

[0118] In the oxide layer (30) according to the present embodiment, a dense film is formed such that the value of the strength ratio is 5.0 or higher, thereby suppressing the evaporation of Zn during welding and suppressing the formation of blowholes caused by Zn evaporation. If the value of the strength ratio is less than 5.0, the density required for the oxide layer (30) becomes insufficient, and thus the formation of blowholes during welding cannot be suppressed. The value of the strength ratio is preferably 10.0 or higher. Meanwhile, the upper limit of the value of the strength ratio ([Al-O]+[Mg-O]) / [Zn-O] is not specifically defined, but approximately 100.0 is the practical upper limit.

[0119] The thickness (more specifically, average thickness) of the oxide layer (30) described above is not specifically defined, but, for example, it is preferably about 0.05 to 2.00 μm per side of the steel plate. By making the thickness of the oxide layer (30) within the above range, the plated steel plate (1) according to the present embodiment can sufficiently suppress the formation of blowholes caused by Zn evaporation during welding. In addition, the oxide layer (30) with the above thickness is realized by undergoing a heat treatment process described in detail below while controlling the passing speed of the steel plate to an appropriate range.

[0120] In addition, the thickness of this oxide layer (30) can be measured using XPS. XPS measurements are performed in the depth direction at a pitch of 1 to 3 nm from the surface of the plated steel sheet, and the depth until the maximum oxygen intensity becomes 1 / 20 of the maximum intensity of the outermost surface is defined as the thickness of the oxide layer. In addition, regarding the XPS measurement conditions, the same conditions as above may be used.

[0121] With reference to FIGS. 1a to 3, the plated steel sheet (1) according to the present embodiment has been described in detail above. The plated steel sheet (1) according to the present embodiment as described above can be suitably used, for example, as a material for suspension parts of an automobile.

[0122] In addition, the plated steel sheet (1) according to the present embodiment may also have one or more layers of various coatings on the oxide layer (30). Examples of such coatings include a chromate coating, a phosphate coating, a chromate-free coating, an organic resin coating, etc.

[0123] (Regarding the manufacturing method of galvanized steel sheets)

[0124] Next, an example of a method for manufacturing a plated steel sheet as described above will be explained.

[0125] The plated steel sheet (1) according to the present embodiment is manufactured by using the steel sheet (10) as a base material and forming a plating layer (20) and an oxide layer (30) on the surface of the steel sheet (10).

[0126] Here, in addition to the molten plating method, thermal spraying, cold spraying, sputtering, deposition, electroplating, etc., can be applied to form the plating layer (20). However, to form a plating layer of a thickness generally used in automobiles, the molten plating method is the most preferable in terms of cost.

[0127] After that, an oxide layer (30) is formed on the surface of the plating layer (20) by performing a specific heat treatment process as described below on the obtained plated steel sheet (steel sheet (10) having a plating layer (20)). By doing so, a plated steel sheet (1) according to the present embodiment can be manufactured.

[0128] Hereinafter, an example of a manufacturing method for obtaining a plated steel sheet (1) according to the present embodiment using a molten plating method will be described in detail.

[0129] In the manufacturing process of such plated steel sheets (1), first, a steel sheet (10) used as a base material is rolled by the Sendzimir method to a desired thickness, then wound into a coil, and installed in a molten plating line.

[0130] In the hot-dip galvanizing line, steel sheets are continuously passed through while being ejected from the coil. At that time, the steel sheets are subjected to a heat reduction treatment at 800°C in an N2-5% H2 gas atmosphere, for example, under an environment where oxidation is unlikely to occur with an oxygen concentration of 20 ppm or less, by means of an annealing facility provided on the line. Afterward, they are air-cooled with N2 gas to approximately the bath temperature of the subsequent plating bath + 20°C and immersed in the plating bath.

[0131] Here, a plating alloy in a molten state having the chemical composition as described above is prepared in the plating bath. The temperature of the plating bath is set above the melting point of the plating alloy (e.g., about 460 to 600°C). When preparing the material for the plating alloy, it is preferable to use a pure metal (purity of 99% or more) as the alloy material. First, a predetermined amount of alloy metal is mixed to obtain the composition of the plating layer as described above, and then completely melted into an alloy using a high-frequency induction furnace or an arc furnace under vacuum or inert gas exchange conditions. Furthermore, the alloy mixed with the predetermined components (composition of the plating layer above) is melted in the atmosphere, and the resulting molten material is used as the plating bath.

[0132] Furthermore, in the production of the plating alloys described above, there are no specific restrictions on using pure metals; existing Zn, Mg, and Al alloys may be melted and used. In this case, there is no problem as long as only alloys of a specified composition with low impurity levels are used.

[0133] After immersing the steel plate in the plating bath as described above, it is pulled up at a predetermined speed. At this time, the amount of plating applied is controlled, for example, by N2 wiping gas, so that the plating layer (20) formed becomes a desired thickness. Here, regarding conditions other than the bath temperature, general plating operation conditions can be applied, and no special equipment or conditions are required.

[0134] Next, a first cooling process and a second cooling process are performed on a molten plating alloy located on a steel plate, thereby forming the molten plating alloy into a plating layer (20) and forming an oxide layer (30) on the surface of the plating layer (20). The first cooling process and the second cooling process will be described in detail below.

[0135] The first cooling process is a cooling process performed when the temperature of the plating alloy is within a range of 250°C or higher below the bath temperature, and the plated steel sheet within such a temperature range is rapidly cooled at an average cooling rate of 10°C / second or higher under an atmosphere of dew point -20°C or lower. In addition, when a molten plating method is adopted in the plating process, this first cooling process is performed immediately after the steel sheet is removed from the plating bath. As a result, the plating alloy located on the surface of the steel sheet solidifies, and a plating layer is formed.

[0136] After that, when the temperature of the plating alloy (plating layer) is within the range of less than 250°C and greater than 50°C, a second cooling process is performed. This second cooling process is a process of slowly cooling a plated steel sheet within the temperature range of less than 250°C and greater than 50°C at an average cooling rate of less than 10°C / second under an atmosphere with a dew point of 0°C or higher. By doing so, the state of the oxide formed on the surface of the plating layer is controlled to form a desired oxide layer.

[0137] As described above, by undergoing a two-stage cooling process in which rapid cooling is performed in a temperature range of 250°C or higher below the bath temperature, and slow cooling is performed in a temperature range of 50°C or lower below 250°C, a dense oxide layer (30) is formed on the surface of the plating layer (20) that satisfies specific conditions in the XPS measurement results.

[0138] Here, it is preferable that the interval between ending the first cooling process and starting the second cooling process be within 3 seconds, and it is preferable to start the second cooling process immediately after ending the first cooling process. If the interval between ending the first cooling process and starting the second cooling process exceeds 3 seconds, an unintended cooling process occurs, and the desired oxide layer (30) cannot be realized.

[0139] Here, in the first cooling process, the lower limit of the dew point is not specifically defined, but for example, about -90°C is a practical lower limit. Also, the average cooling rate is more preferably 40°C / second or higher. Also, the upper limit of the average cooling rate is not specifically defined, but for example, about 90°C / second is a practical upper limit.

[0140] In addition, in the second cooling process above, the upper limit of the dew point is not specifically defined, but for example, about 20°C serves as a practical upper limit. Also, the average cooling rate is more preferably 4°C / second or less.

[0141] In addition, if either the first cooling process or the second cooling process as described above is not performed, the desired oxide layer (30) cannot be realized. By performing both the first cooling process and the second cooling process as described above, the oxide layer (30) according to the present embodiment can be realized.

[0142] In addition, if an alloying heat treatment process (e.g., a heat treatment process involving heating to a target temperature of about 480 to 550°C), which is commonly performed in the manufacture of alloyed hot-dip galvanized steel sheets, is carried out after the second cooling process, the oxide formation state controlled by the first and second cooling processes is disrupted, and as a result, the oxide grows excessively, the effect of suppressing Zn evaporation as noted in this embodiment cannot be obtained. From this perspective, it is important not to carry out a heat treatment process after the second cooling process.

[0143] Here, for the cooling treatment described above, generally known methods such as N2 gas cooling, mist cooling, and submersion can be applied. In addition, for the cooling gas, gases with high heat dissipation effects, such as He gas or hydrogen gas, may be used in addition to N2 gas.

[0144] Furthermore, as a method for measuring the temperature of the plating layer, a contact-type thermocouple (K-type) can be used, for example. By installing a contact-type thermocouple on the base steel plate, the average temperature of the entire plating layer can be monitored at all times. Additionally, by mechanically controlling various speeds and thicknesses to standardize various operating conditions, such as the steel plate preheating temperature and the molten plating bath temperature, it becomes possible to monitor the temperature of the entire plating layer at that specific point in time under these manufacturing conditions with near accuracy. This enables precise control of the cooling treatment in the first and second cooling processes. Furthermore, although not as accurate as the contact type, the surface temperature of the plating layer may be measured using a non-contact radiation thermometer.

[0145] In addition, the relationship between the surface temperature of the plating layer and the average temperature of the entire plating layer may be determined through a simulation that performs thermal conduction analysis. Specifically, the surface temperature of the plating layer and the average temperature of the entire plating layer are determined based on various manufacturing conditions, such as the preheating temperature of the steel sheet, the temperature of the molten plating bath, the lifting speed of the steel sheet from the plating bath, the thickness of the steel sheet, the thickness of the plating layer, the amount of heat exchanged between the plating layer and the manufacturing equipment, and the amount of heat dissipated by the plating layer. Subsequently, the relationship between the surface temperature of the plating layer and the average temperature of the entire plating layer can be determined using the obtained results. By doing so, it becomes possible to estimate the average temperature of the entire plating layer at that point in time under those manufacturing conditions by actually measuring the surface temperature of the plating layer during the manufacturing of the plated steel sheet. As a result, it becomes possible to precisely control the cooling treatment in the first and second cooling processes.

[0146] Above, an example of a method for manufacturing a plated steel sheet according to the present embodiment has been described in detail.

[0147] In addition, in the method for manufacturing a plated steel sheet according to the present embodiment, after the second cooling process, a treatment to form one or more layers of various films may also be performed. Examples of such treatments include chromate treatment, phosphate treatment, chromate-free treatment, and organic resin film formation treatment.

[0148] Chromate treatments include electrolytic chromate treatment, which forms a chromate film by electrolysis; reactive chromate treatment, which forms a film by utilizing a reaction with the material and then washes off the excess treatment solution; and coating chromate treatment, which forms a film by applying a treatment solution and drying it without rinsing; any of these chromate treatments may be adopted.

[0149] Examples of electrolytic chromate treatment include electrolytic chromate treatment 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.

[0150] Examples of phosphate treatments include zinc phosphate treatment, zinc calcium phosphate treatment, and manganese phosphate treatment.

[0151] Chromate-free treatment is particularly suitable because it does not impose a burden on the environment. Such chromate-free treatments include electrolytic chromate-free treatment, which forms a chromate-free film by electrolysis; reactive chromate-free treatment, which forms a film by reacting with the material and then washes off the excess treatment solution; and coating chromate-free treatment, which forms a film by applying a treatment solution and drying it without rinsing; any of these chromate-free treatments may be adopted.

[0152] Furthermore, the organic resin used for the organic resin film formation treatment is not limited to a specific resin; various resins such as polyester resin, polyurethane resin, epoxy resin, acrylic resin, polyolefin resin, and modified versions of these resins may be used. Here, a modified version refers to a resin in which a reactive functional group contained in the structure of these resins is reacted with another compound (e.g., a monomer or a crosslinking agent) that contains a functional group capable of reacting with such functional group.

[0153] As for the organic resin, one of the above may be used alone, or two or more types of organic resins (unmodified) may be mixed and used. In addition, one or more types of organic resins obtained by modifying at least one other organic resin in the presence of at least one organic resin may be mixed and used. In addition, an organic resin that has been made water-based by dissolving or dispersing in water may be used. Furthermore, various coloring pigments or anti-corrosion pigments may be contained in such organic resin films.

[0154] Examples

[0155] Hereinafter, the plated steel sheet according to the present invention will be described in detail while presenting examples and comparative examples. Furthermore, 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.

[0156] In the examples and comparative examples shown below, a hot-rolled steel sheet with a thickness of 3.2 mm (0.05 mass% C-0.007 mass% Si-0.25 mass% Mn, manufactured by Nippon Seitetsu Co., Ltd.) was used as the base material. This hot-rolled steel sheet was cut into pieces measuring 100 mm × 200 mm to be used as test specimens.

[0157] A plating bath for realizing a plating layer with the composition shown in Table 1 below was prepared for each, installed in a batch-type molten plating test apparatus of our company, and plating was performed on the test specimen. Here, the temperature of the test specimen was measured using a thermocouple spot-welded to the center of the test specimen. In addition, for the test specimen to be immersed in the plating bath, prior to immersion in the plating bath, the surface of the plating plate was subjected to a heat reduction treatment at 800°C in an N2-5% H2 gas atmosphere inside a furnace with an oxygen concentration of 20 ppm or less. After the heat reduction treatment, the test specimen was air-cooled with N2 gas, and after the temperature of the test specimen reached the bath temperature + 20°C, the test specimen was immersed in the plating bath of the molten plating test apparatus for about 3 seconds.

[0158] After immersion in the plating bath, the test specimen was lifted at a lifting speed of 20 to 200 mm / second. During lifting, the amount of plating deposited was controlled by N2 wiping gas to achieve the desired amount. In the following examples and comparative examples, the amount of plating deposited was controlled so that the amount of the plating layer deposited after drying per side of the test specimen was 15 to 250 g / m². After lifting the test specimen from the plating bath, the test specimen was cooled from the plating bath temperature to room temperature under the conditions shown in Table 1 below. In the examples and comparative examples shown below, the second cooling process was started immediately after the end of the first cooling process (i.e., the interval from the end of the first cooling process to the start of the second cooling process was set to 0.2 seconds or less). In addition, for comparison, an example was prepared in which an alloying treatment was performed on the test specimen after the second cooling process, with a plate temperature of 500°C × a holding time of 15 seconds (No. 44 in Table 1).

[0159] Here, a plated steel sheet was cut to a size of 30 mm × 30 mm from the test specimen plated as described above, and the plated steel sheet was immersed in a 10% HCl aqueous solution with an inhibitor added to pickle the plating layer, and then the composition of the plating layer was measured by analyzing the elements leached into the aqueous solution using ICP.

[0160] In addition, regarding the obtained plating layer, electron diffraction patterns were captured by TEM, and based on whether a crystal structure with 5-fold symmetry was observed in the electron diffraction patterns, Mg 32 (Al, Zn) 49 I checked whether the top was present or not.

[0161] In addition, for the obtained oxide layer, the XPS spectrum was measured based on the above method, and the value of the intensity ratio ([Al-O]+[Mg-O]) / [Zn-O] was calculated. The obtained intensity ratio was evaluated based on the following criteria.

[0162] ≪Evaluation Criteria≫

[0163] Rating "A": Intensity ratio value is 10.0 or higher

[0164] 「B」: Intensity ratio value is 5.0 or higher and less than 10.0

[0165] 「C」: Intensity ratio value less than 5.0

[0166] In addition, each obtained test specimen was evaluated in terms of blowhole formation during welding, occurrence of LME during welding, and corrosion resistance.

[0167] <Evaluation of Blowhole Formation During Welding>

[0168] From the obtained test specimens, a piece cut to a size of 150 mm × 50 mm was designated as the first steel plate, and a piece cut to a size of 150 mm × 30 mm was designated as the second steel plate. The long sides of these steel plates were overlapped and welded by arc welding or laser welding (overlapping fillet welding).

[0169] Here, the welding conditions for arc welding are as follows.

[0170] Welding current: 220A, Welding voltage: 25.2V, Welding speed: 100cm / min

[0171] Welding gas: 20% CO2+Ar, Gas flow rate: 20L / min

[0172] Welding wire: YGW16, manufactured by Nittetsu Yosetsu Kogyo Co., Ltd., φ1.2㎜

[0173] (C: 0.1 mass%, Si: 0.80 mass%, Mn: 1.5 mass%, P: 0.015 mass%, S: 0.008 mass%, Cu: 0.36 mass%)

[0174] Welding torch bevel angle: 45°

[0175] Overlap allowance: 10mm

[0176] Steel plate size: Top side (1st steel plate) 150×50㎜, Bottom side (2nd steel plate) 150×30㎜

[0177] Plate gap: 0 mm

[0178] In addition, the welding conditions for laser welding are as follows.

[0179] Output: 7kW, Welding Speed: 400cm / min, Advance / Reverse Angle: 0°

[0180] Steel plate size: Top side (1st steel plate) 150×50㎜, Bottom side (2nd steel plate) 150×30㎜

[0181] Overlap allowance: 50 mm

[0182] Plate gap: 0 mm

[0183] The presence or absence of blowholes that may be formed during welding can be easily determined by performing an X-ray transmission test from above on the test specimen after welding. In this example, after welding as described above, an X-ray transmission test was performed on the area including the weld bead and toe generated by welding, and 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, using an X-Lon manufacturer's SMART300HP model number, the test specimen was fixed to a support, and the X-ray inspection device was set so that the focal distance from the tip of the irradiation hole was 750 mm, and X-rays were irradiated from an angle inclined at 60° with respect to the evaluation surface. At this time, the applied current was 3 mA, the applied voltage was 125 kV, and the application time was 1 min. After that, the projected area of ​​the blowhole formed was divided by the total projected area to calculate the blowhole occupancy rate (%) = {(projected area of ​​the blowhole formed / total projected area) × 100}, and an evaluation was performed based on the following evaluation criteria.

[0184] ≪Evaluation Criteria≫

[0185] Rating "AAA": Blowhole share less than 5%

[0186] "AA": Blowhole share 5% or more and less than 10%

[0187] "A": Blowhole occupancy rate 10% or more and less than 20%

[0188] "B": Blowhole share 20% or more

[0189] In addition, the above "edge" is a location 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 in the plated steel sheet intersects the surface of the weld bead corresponds to this "edge."

[0190] <Assessment of LME Intenseness>

[0191] The LME resistance of the obtained test specimens was evaluated by hot tensile testing.

[0192] More specifically, for both the obtained test specimen and the steel plate without plating, the temperature was raised to 800°C at a heating rate of 100°C / second, maintained at 800°C for 1 second, and then a tensile test was performed at a stroke rate of 50 mm / second. By doing so, stress-stroke curves were obtained for both the steel plate without plating and the test specimen. Subsequently, the stress × stroke value (area of ​​the stress-stroke curve) was calculated from the obtained stress-stroke curves, and an evaluation was performed based on the following evaluation criteria for the evaluation value (%) = {(stress × stroke value of the test specimen) / (stress × stroke value of the steel plate without plating) × 100}.

[0193] ≪Evaluation Criteria≫

[0194] Rating "AA": Ratings of 95% or higher

[0195] "A": Evaluation value 85% or higher and less than 95%

[0196] "B": Evaluation value less than 85%

[0197] Evaluation of Corrosion Resistance

[0198] The corrosion resistance of the obtained test specimens was evaluated as follows.

[0199] Specifically, a 50×100 mm sample was taken from the plated steel sheet and subjected to Zn phosphoric acid treatment (SD5350 system: standard manufactured by Nippon Paint & Industrial Coding). Afterward, an electrodeposition coating (PN110 Powernics Gray: standard manufactured by Nippon Paint & Industrial Coding) was applied to a thickness of 15 μm, and baking was performed at a baking temperature of 150°C for 20 minutes. On this coated plated steel sheet (plated steel sheet subjected to electrodeposition coating), a cut groove 70 mm in length was introduced using a cutter to reach the base steel, and then subjected to a combined cycle corrosion test according to JASO (M609-91). The corrosion resistance after coating was evaluated by measuring the maximum expansion width on one side from the cut section.

[0200] ≪Evaluation Criteria≫

[0201] Rating "AAA": Less than 1 mm

[0202] "AA": 1 mm or more and less than 2 mm

[0203] "A": 2 mm or more and less than 3 mm

[0204] "B": 3 mm or more

[0205] The obtained results were integrated and presented in Table 1 below.

[0206]

[0207] As is evident from Table 1 above, in the example corresponding to the embodiment of the present invention, blowhole formation and LME can be suppressed while maintaining excellent corrosion resistance, whereas in the example corresponding to the comparative example of the present invention, sufficient performance cannot be achieved in at least any of corrosion resistance, blowhole formation, and LME.

[0208] Although suitable 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 evident to those skilled in the art that various modifications or alterations can be made within the scope of the technical concept described in the claims, and these are also naturally understood to fall within the technical scope of the present invention. Explanation of the symbols

[0209] 1: Galvanized steel sheet 10: Steel plate 20: Plating layer 30: Oxide layer

Claims

Claim 1 The present invention comprises a steel plate serving as a base material, a plating layer located on at least a portion of the surface of the steel plate, and an oxide layer located on the surface of the plating layer, wherein the plating layer contains, in mass%, Al: 1.00 to 80.00%, Mg: 1.00 to 20.00%, Fe: 0.01 to 15.00%, Si: 0 to 10.00%, and Ca: 0 to 4.00%, and additionally, 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%, and Nb: 0 to It contains 1.000%, Zr: 0 to 1.000%, Ni: 0 to 1.000%, Mn: 0 to 1.000%, V: 0 to 1.000%, Mo: 0 to 1.000%, Ag: 0 to 1.000%, Li: 0 to 1.000%, La: 0 to 0.500%, Ce: 0 to 0.500%, B: 0 to 0.500%, Y: 0 to 0.500%, and Sr: 0 to 0.500% in a total of 0 to 5.000%, and the remainder consists of 5.00 mass% or more of Zn and impurities, and when the position at a depth of 5 nm from the outermost surface of the oxide layer is observed by X-ray photoelectron spectroscopy (XPS), Al-O bonds, Mg-O A plated steel sheet in which the value of the intensity ratio ([Al-O]+[Mg-O]) / [Zn-O] calculated from the intensity of the peaks attributed to the bond and the Zn-O bond, respectively, is 5.0 or greater and 100.0 or less. Claim 2 A plated steel sheet according to claim 1, wherein the value of the strength ratio ([Al-O]+[Mg-O]) / [Zn-O] is 10.0 or more and 100.0 or less. Claim 3 A plated steel sheet according to claim 1 or 2, wherein the plating layer contains at least Al: 18.00 to 60.00 mass% and Mg: 5.00 to 15.00 mass%. Claim 4 In claim 1 or 2, the plating layer contains at least Al: 35.00 to 60.00 mass% and Mg: 7.00 to 15.00 mass%, and furthermore, in the plating layer, Mg 32 (Al, Zn) 49 A phase exists, and the above Mg 32 (Al, Zn) 49 A plated steel sheet in which the Mg content [Mg], Zn content [Zn], and Al content [Al] (each unit: atomic %) satisfy the relationship 0.50 ≤ [Mg] / ([Zn] + [Al]) ≤ 0.83.

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