Plated steel material and method for manufacturing plated steel material

Abstract

Provided are: a plated steel material in which a plating layer thereof has a prescribed chemical composition, Zn / Al / MgZn2 ternary eutectics are present in a backscattered electron image of a Zn-Al-Mg alloy layer obtained when a surface of the plating layer is observed at a magnification of x100 by using a scanning electron microscope after polishing the surface of the plating layer until reaching 1 / 2 the layer thickness, and the average total perimeter of the Zn / Al / MgZn2 ternary eutectics is 100-300 mm / mm2; and a method for manufacturing said plated steel material.

Description

Plated steel product and method for manufacturing the same

[0001] The present disclosure relates to plated steel products and methods for manufacturing plated steel products.

[0002] For example, in the field of building materials, a wide variety of plated steels are used. Most of these are zinc-plated steels. Due to the need for longer life spans for building materials, research into improving the corrosion resistance of zinc-plated steels has been conducted for a long time, and various plated steels have been developed. The first highly corrosion-resistant plated steel for building materials was Zn-5% Al-plated steel (galvanized steel), which had improved corrosion resistance due to the addition of Al to the zinc-based plating layer. It is well known that adding Al to a plating layer improves corrosion resistance, and the addition of 5% Al forms Al crystals in the plating layer (specifically, the Zn phase), improving corrosion resistance. Zn-55% Al-1.6% Si-plated steel (galvalume steel) is also a plated steel with improved corrosion resistance for essentially the same reason.

[0003] The appeal of zinc-based plated steel is its sacrificial corrosion protection effect on the base steel. That is, at the cut end of plated steel, at areas where the plating layer breaks during processing, and at areas where the base steel is exposed due to peeling of the plating layer, the surrounding plating layer dissolves before the base steel corrodes, and the eluted components form a protective film. This makes it possible to prevent red rust from forming on the base steel to some extent.

[0004] Generally, a low Al concentration and a high Zn concentration are preferable because this effect is more likely to be exhibited. Therefore, highly corrosion-resistant plated steel materials with a relatively low Al concentration of about 5% to 25% have been put into practical use in recent years. In particular, plated steel materials with a low Al concentration and containing about 1 to 3% Mg have superior corrosion resistance to Galvanic Acid Plated Steel. For this reason, they have become a market trend for plated steel materials and are now widely known on the market.

[0005] As a plated steel material containing a certain amount of Al and Mg, for example, the plated steel material disclosed in Patent Document 1 has been developed.

[0006] Specifically, Patent Document 1 describes a method for producing a plated steel material having a plating layer on the surface of the steel material, the plating layer comprising Al: 5 to 18 mass %, Mg: 1 to 10 mass %, Si: 0.01 to 2 mass %, the balance being Zn and unavoidable impurities, in which an Al phase is formed to a thickness of 1 mm. ２ The publication discloses a hot-dip Zn-Al-Mg-Si plated steel material in which 200 or more particles exist per one particle.

[0007] Furthermore, Patent Document 2 describes a plated steel material having a steel material and a plating layer including a Zn—Al—Mg alloy layer disposed on the surface of the steel material, wherein the plating layer has a chemical composition containing more than 65.0% Zn, more than 5.0% to less than 25.0% Al, more than 3.0% to less than 12.5% ​​Mg, and 0.1% to 20.0% Sn, and wherein the surface of the Zn—Al—Mg alloy layer is polished to half its thickness, and then observed with a scanning electron microscope at a magnification of 100 times. In a backscattered electron image of the Zn—Al—Mg alloy layer, Al crystals are present, and the average cumulative perimeter of the Al crystals is 88 to 195 mm / mm. ２ "Plated steel material which is

[0008] Patent Document 1: JP 2001-355053 A Patent Document 2: WO2019 / 221193

[0009] However, when plated steel sheets with a high Mg concentration in the plating layer are processed, the plating layer peels off, resulting in poor workability.Furthermore, in environments where water is likely to accumulate, such as when the plated steel sheet is used in an orientation parallel to the ground, the corrosion resistance of the plated steel sheets is poor.

[0010] Therefore, an object of the present disclosure is to provide a plated steel material that has excellent workability and corrosion resistance even when used in an environment where water is likely to accumulate, and a method for manufacturing the same.

[0011] The above problems can be solved by the following means. <1> A plated steel material having a base steel material and a plating layer including a Zn-Al-Mg alloy layer disposed on a surface of the base steel material, wherein the plating layer contains, in mass %, Zn: more than 65.00%, Al: more than 5.00% and less than 25.00%, Mg: more than 3.00% and less than 12.50%, Sn: 0% to 3.00%, Bi: 0% to less than 5.00%, In: 0% to less than 2.00%, Ca: 0% to 3.00%, Y: 0% to 0.50%, La: 0% to less than 0.50%, Ce: 0% to less than 0.50%, Si: 0% to less than 2.50%, Cr: 0% to less than 0.25%, Ti: 0% to less than 0.25%, Zr: 0% to less than 0.25%, Mo: 0% to less than 0.25%, W: 0% to less than 0.25%, Ag: 0% to less than 0.25%, P: 0% to less than 0.25%, Ni: 0% to less than 0.25%, Co: 0% to less than 0.25%, V: 0% to less than 0.25%, Nb: 0% to less than 0.25%, Cu: 0% to less than 0.25%, Mn: 0% to less than 0.25%, Li: 0% to less than 0.25%, Na: 0% to less than 0.25%, K: 0% to less than 0.25%, Fe: 0% to 5.00%, Sr: 0% to less than 0.5%, Sb: 0% to less than 0.5%, Pb: 0% to less than 0.5%, B : 0% to less than 0.5%, and impurities, and a backscattered electron image of the Zn-Al-Mg alloy layer obtained by polishing the surface of the plating layer to 1 / 2 of the layer thickness and then observing it with a scanning electron microscope at a magnification of 100 times shows Zn / Al / MgZn ２ There is a ternary eutectic, and the Zn / Al / MgZn ２ The average cumulative circumference of the ternary eutectic is 100 to 300 mm / mm ２<2> The plated steel material according to <1>, wherein the plating layer includes an Al-Fe alloy layer between the base steel material and the Zn-Al-Mg alloy layer. <3> The plated steel material according to <1> or <2>, wherein the interface roughness Ra between the base steel material and the plating layer is 0.3 to 2.0 μm. <4> The method for producing a plated steel material according to any one of <1> to <3>, comprising immersing a base steel material having a surface roughness Ra of 0.3 to 2.0 μm on the surface to be plated in a plating bath and removing it from the plating bath, followed by cooling the base steel material at an average cooling rate of 5 to 20°C / s in a temperature range of 450 to 395°C, cooling the base steel material at an average cooling rate of 3°C / s or less in a temperature range of 395 to 340°C, and cooling the base steel material at an average cooling rate of 10 to 20°C / s in a temperature range of 340 to 280°C.

[0012] According to the present disclosure, it is possible to provide a plated steel material that has excellent workability and excellent corrosion resistance even when used in an environment where water is likely to accumulate, and a method for manufacturing the same.

[0013] Fig. 1(A) is a backscattered electron image of the Zn—Al—Mg alloy layer of a Zn—Al—Mg-plated steel material according to the present disclosure, obtained by polishing the surface of the plating layer to half its thickness and then observing it with a scanning electron microscope at a magnification of 100 times. Fig. 1(B) is a binarized image of the backscattered electron image of the Zn—Al—Mg alloy layer.

[0014] An example of the present disclosure will be described below. In this disclosure, the "%" representation of the content of each element in a chemical composition means "mass %." A numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. When "greater than" or "less than" is added to the numerical values ​​written before and after "to", the numerical range does not include these numerical values ​​as the lower or upper limit. The content of an element in a chemical composition may be expressed as an element concentration (e.g., Zn concentration, Mg concentration, etc.).

[0015] The plated steel material of the present disclosure has a base steel material and a plating layer including a Zn-Al-Mg alloy layer disposed on the surface of the base steel material. The plated steel material of the present disclosure has a plating layer having a predetermined chemical composition, and the surface of the plating layer is polished to half its thickness, and then observed with a scanning electron microscope at a magnification of 100 times. In a backscattered electron image of the Zn-Al-Mg alloy layer, Zn / Al / MgZn is observed. ２ There is a ternary eutectic, and the Zn / Al / MgZn ２ The average cumulative circumference of the ternary eutectic is 100 to 300 mm / mm ２ is.

[0016] The plated steel material of the present disclosure, due to the above-described configuration, is a plated steel material that has excellent workability and excellent corrosion resistance even when used in an environment where water is likely to accumulate. The plated steel material of the present disclosure was discovered based on the following findings.

[0017] In plated steel products with a high Mg concentration in the plating layer, a hard intermetallic compound phase is formed in the plating layer. Therefore, when the plated steel product is processed, the intermetallic compound phase cracks, making the plating layer prone to peeling. In addition, when used in an environment where water is likely to accumulate, the Zn / Al / MgZn in the plating layer ２ The ternary eutectic corrodes locally, and corrosion quickly reaches the base steel.

[0018] Therefore, the Zn / Al / MgZn in the plating layer, which causes localized corrosion, ２ The ternary eutectic is uniformly dispersed. That is, Zn / Al / MgZn ２ The average value of the cumulative perimeter of the ternary eutectic is set within a predetermined range. ２ It can reduce localized corrosion of ternary eutectic. In addition, soft Zn / Al / MgZn ２ The ternary eutectic acts as a buffer during processing, reducing cracking of the surrounding intermetallic compound phase.

[0019] From the above findings, it has been discovered that the plated steel material of the present disclosure, due to the above configuration, is a plated steel material that has excellent workability and excellent corrosion resistance even when used in an environment where water is likely to accumulate.

[0020] Hereinafter, the plated steel material of the present disclosure will be described in detail.

[0021] (Base Steel Material) There are no particular limitations on the shape of the base steel material. Examples of the base steel material include steel plates, as well as formed base steel materials such as steel pipes, civil engineering and construction materials (fences, corrugated pipes, drainage ditch covers, sand-blocking plates, bolts, wire mesh, guardrails, water-blocking walls, etc.), home appliance components (casings for outdoor units of air conditioners, etc.), and automobile parts (suspension components, etc.). For the forming, various plastic processing techniques such as press working, roll forming, and bending can be used.

[0022] The material of the base steel is not particularly limited. Various types of base steel can be used, such as general steel, pre-plated steel, Al-killed steel, extra-low carbon steel, high carbon steel, various high-tensile steels, and some high-alloy steels (steels containing strengthening elements such as Ni and Cr). The manufacturing conditions for the base steel, such as the manufacturing method for the base steel and the manufacturing method for the base steel sheet (hot rolling, pickling, cold rolling, etc.), are also not particularly limited. Hot-rolled steel sheets, hot-rolled steel strips, cold-rolled steel sheets, and cold-rolled steel strips specified in JIS G 3302 (2010) can also be used as the base steel.

[0023] The interface roughness Ra between the base steel material and the plating layer is preferably 0.3 to 2.0 μm. By making the surface roughness Ra of the base steel material 0.3 μm or more, the Zn / Al / MgZn ２ The average value of the cumulative perimeter of the ternary eutectic can be controlled within the above range. By setting the surface roughness Ra of the base steel material to 2.0 μm or less, bare plating is suppressed. The method for measuring the interface roughness Ra between the base steel material and the plating layer is described below.

[0024] The base steel may be a pre-plated steel material that has been pre-plated. Pre-plated steel materials can be obtained, for example, by an electrolytic treatment method or a displacement plating method. In the electrolytic treatment method, the base steel material is immersed in a sulfate bath or chloride bath containing metal ions of various pre-plating components for electrolytic treatment to obtain the pre-plated steel material. In the displacement plating method, the base steel material is immersed in an aqueous solution containing metal ions of various pre-plating components and the pH of which is adjusted with sulfuric acid to cause displacement precipitation of the metal to obtain the pre-plated steel material. A typical example of a pre-plated steel material is pre-Ni-plated steel material.

[0025] (Plated layer) The plated layer includes a Zn—Al—Mg alloy layer. The plated layer may include an Al—Fe alloy layer in addition to the Zn—Al—Mg alloy layer. The Al—Fe alloy layer is disposed between the base steel and the Zn—Al—Mg alloy layer.

[0026] That is, the plating layer may have a single-layer structure of a Zn—Al—Mg alloy layer, or a laminated structure including a Zn—Al—Mg alloy layer and an Al—Fe alloy layer. In the case of a laminated structure, the Zn—Al—Mg alloy layer is preferably the layer that constitutes the surface of the plating layer. However, although an oxide film of the plating layer constituent elements having a thickness of about 50 nm may be formed on the surface of the plating layer, this is considered to be thin relative to the overall thickness of the plating layer (about 8 to 60 μm) and does not constitute the main part of the plating layer.

[0027] The coating weight of the plating layer is 40 to 300 g / m per side. ２ The coating weight of the plating layer is preferably 40 g / m ２ If the coating weight of the plating layer is 300 g / m or more, corrosion resistance can be more reliably ensured. ２ If the thickness is set to the above range, poor appearance such as sagging of the plating layer can be suppressed.

[0028] Next, the chemical composition of the plating layer will be described. The chemical composition of the plating layer is, in mass%, as follows: Zn: more than 65.00%, Al: more than 5.00% and less than 25.00%, Mg: more than 3.00% and less than 12.50%, Sn: 0% to 3.00%, Bi: 0% to less than 5.00%, In: 0% to less than 2.00%, Ca: 0% to 3.00%, Y: 0% to 0.50%, La: 0% to less than 0.50%, Ce: 0% to less than 0.50%, Si: 0% to less than 2.50%, Cr: 0% to less than 0.25%, Ti: 0% to less than 0.25%, Zr: 0% to less than 0.25%, Mo: 0% to less than 0.25%, W: 0% to less than 0.25%, The chemical composition is Ag: 0% to less than 0.25%, P: 0% to less than 0.25%, Ni: 0% to less than 0.25%, Co: 0% to less than 0.25%, V: 0% to less than 0.25%, Nb: 0% to less than 0.25%, Cu: 0% to less than 0.25%, Mn: 0% to less than 0.25%, Li: 0% to less than 0.25%, Na: 0% to less than 0.25%, K: 0% to less than 0.25%, Fe: 0% to 5.00%, Sr: 0% to less than 0.50%, Sb: 0% to less than 0.50%, Pb: 0% to less than 0.50%, B: 0% to less than 0.50%, and impurities.

[0029] In the chemical composition of the plating layer, Sn, Bi, In, Ca, Y, La, Ce, Si, Cr, Ti, Zr, Mo, W, Ag, P, Ni, Co, V, Nb, Cu, Mn, Li, Na, K, Fe, Sr, Sb, Pb, and B are optional components. In other words, these elements do not have to be contained in the plating layer. When these optional components are contained, the content of each optional element is preferably within the range described below.

[0030] Here, the chemical composition of this plating layer is the average chemical composition of the entire plating layer (when the plating layer has a single-layer structure of Zn—Al—Mg alloy layer, the average chemical composition of the Zn—Al—Mg alloy layer; when the plating layer has a laminated structure of Al—Fe alloy layer and Zn—Al—Mg alloy layer, the average chemical composition of the sum of the Al—Fe alloy layer and the Zn—Al—Mg alloy layer).

[0031] Each element in the plating layer will be described below.

[0032] Zn: More than 65.00% Zn is an element necessary for obtaining corrosion resistance. When considering the Zn concentration in terms of atomic composition ratio, since the plating layer is composed of elements with low specific gravity such as Al and Mg, Zn must be the main component in terms of atomic composition ratio as well. Therefore, the Zn concentration is set to more than 65.00%. The Zn concentration is preferably 70.00% or more. The upper limit of the Zn concentration is the concentration that is the remainder excluding elements other than Zn and impurities.

[0033] Al: More than 5.00% to Less than 25.00% Al is an essential element for forming Al crystals and ensuring corrosion resistance. Furthermore, Al is also an essential element for improving the adhesion of the coating layer and ensuring workability. Therefore, the lower limit of the Al concentration is set to more than 5.00% (preferably 10.00% or more). On the other hand, if the Al concentration increases too much, corrosion resistance tends to deteriorate. Therefore, the upper limit of the Al concentration is set to less than 25.00% (preferably 23.00% or less).

[0034] Mg: more than 3.00% to less than 12.50% Mg is an essential element for ensuring corrosion resistance. Therefore, the lower limit of the Mg concentration is set to more than 3.0% (preferably more than 4.00%). On the other hand, if the Mg concentration increases too much, workability tends to deteriorate. Therefore, the upper limit of the Mg concentration is set to less than 12.50% (preferably 10.00% or less).

[0035] Sn: 0 to 3.00% Sn is an element that contributes to corrosion resistance and initial discoloration resistance. Therefore, the lower limit of the Sn concentration is preferably more than 0.00% (preferably 0.05% or more, more preferably 0.10% or more). On the other hand, if the Sn concentration increases too much, corrosion resistance and initial discoloration resistance tend to deteriorate. Therefore, the upper limit of the Sn concentration is set to 3.00% or less.

[0036] Bi: 0% to less than 5.00% Bi is an element that contributes to corrosion resistance. Therefore, the lower limit of the Bi concentration is preferably more than 0.00% (preferably 0.10% or more, more preferably 3.00% or more). On the other hand, if the Bi concentration increases too much, corrosion resistance tends to deteriorate. Therefore, the upper limit of the Bi concentration is set to less than 5.00% (preferably 4.80% or less).

[0037] In: 0% to less than 2.00% In is an element that contributes to corrosion resistance. Therefore, the lower limit of the In concentration is preferably more than 0.00% (preferably 0.10% or more, more preferably 1.00% or more). On the other hand, if the In concentration increases too much, corrosion resistance tends to deteriorate. Therefore, the upper limit of the In concentration is set to less than 2.00% (preferably 1.80% or less).

[0038] Ca: 0% to 3.00% Ca is an element that can adjust the optimal amount of Mg elution to impart corrosion resistance. Therefore, the lower limit of the Ca concentration is preferably more than 0.00% (preferably 0.05% or more). On the other hand, if the Ca concentration increases too much, corrosion resistance and workability tend to deteriorate. Therefore, the upper limit of the Ca concentration is set to 3.00% or less (preferably 1.00% or less).

[0039] Y: 0% to 0.50% Y is an element that contributes to corrosion resistance. Therefore, the lower limit of the Y concentration is preferably more than 0.00% (preferably 0.10% or more). On the other hand, if the Y concentration increases too much, corrosion resistance tends to deteriorate. Therefore, the upper limit of the Y concentration is set to 0.50% or less (preferably 0.30% or less).

[0040] La and Ce: 0% to less than 0.50% La and Ce are elements that contribute to corrosion resistance. Therefore, the lower limit of each of the La concentration and the Ce concentration is preferably more than 0.00% (preferably 0.10% or more). On the other hand, if the La concentration and the Ce concentration are too high, corrosion resistance tends to deteriorate. Therefore, the upper limit of each of the La concentration and the Ce concentration is set to less than 0.50% (preferably 0.40% or less).

[0041] Si: 0% to less than 2.50% Si is an element that suppresses the growth of the Al—Fe alloy layer and contributes to improving corrosion resistance. Therefore, the Si concentration is preferably greater than 0.00% (preferably 0.05% or more, more preferably 0.10% or more). In particular, when Sn is not included (i.e., when the Sn concentration is 0%), the Si concentration is preferably 0.10% or more (preferably 0.20% or more) from the viewpoint of ensuring corrosion resistance. On the other hand, if the Si concentration is too high, corrosion resistance and workability tend to deteriorate. Therefore, the upper limit of the Si concentration is set to less than 2.50%. In particular, from the viewpoint of corrosion resistance, the Si concentration is preferably 2.40% or less, more preferably 1.80% or less, and even more preferably 1.20% or less.

[0042] Cr, Ti, Zr, Mo, W, Ag, P, Ni, Co, V, Nb, Cu, Mn, Li, Na, and K: 0% to less than 0.25% Cr, Ti, Zr, Mo, W, Ag, P, Ni, Co, V, Nb, Cu, Mn, Li, Na, and K are elements that contribute to corrosion resistance. Therefore, the lower limit of the concentration of Cr, Ti, Zr, Mo, W, Ag, P, Ni, Co, V, Nb, Cu, Mn, Li, Na, and K is preferably more than 0.00% (preferably 0.05% or more, more preferably 0.10% or more). On the other hand, if the concentrations of Cr, Ti, Zr, Mo, W, Ag, P, Ni, Co, V, Nb, Cu, Mn, Li, Na, and K are too high, corrosion resistance tends to deteriorate. Therefore, the upper limits of the concentrations of Cr, Ti, Zr, Mo, W, Ag, P, Ni, Co, V, Nb, Cu, Mn, Li, Na, and K are each set to less than 0.25%.The upper limits of the concentrations of Cr, Ti, Zr, Mo, W, Ag, P, Ni, Co, V, Nb, Cu, Mn, Li, Na, and K are preferably set to 0.22% or less.

[0043] Fe: 0% to 5.00% When a plating layer is formed by hot-dip plating, a certain concentration of Fe is contained in the Zn—Al—Mg alloy layer and the Al—Fe alloy layer. It has been confirmed that Fe contained in the plating layer (particularly the Zn—Al—Mg alloy layer) with a concentration of up to 5.00% does not adversely affect performance. Since most of the Fe is often contained in the Al—Fe alloy layer, the thicker this layer is, the higher the Fe concentration will generally be.

[0044] Sr, Sb, Pb, and B: 0% to less than 0.50% Sr, Sb, Pb, and B are elements that contribute to corrosion resistance. Therefore, the lower limit of the concentration of Sr, Sb, Pb, and B is preferably more than 0.00% (preferably 0.05% or more, more preferably 0.10% or more). On the other hand, if the concentrations of Sr, Sb, Pb, and B are too high, corrosion resistance tends to deteriorate. Therefore, the upper limit of the concentration of Sr, Sb, Pb, and B is each set to less than 0.50%.

[0045] Impurities are components contained in raw materials or components mixed in during the manufacturing process, but are not intentionally added. For example, trace amounts of components other than Fe may be mixed into the coating layer as impurities due to atomic diffusion between the base steel and the coating bath.

[0046] The chemical composition of the plating layer is measured by the following method. First, the plating layer is stripped and dissolved using an acid containing an inhibitor that suppresses corrosion of the base steel material to obtain an acid solution. Next, the obtained acid solution is measured by ICP analysis to obtain the chemical composition of the plating layer (the chemical composition of the Zn-Al-Mg alloy layer when the plating layer has a single-layer structure of Zn-Al-Mg alloy layer, or the combined chemical composition of the Al-Fe alloy layer and the Zn-Al-Mg alloy layer when the plating layer has a laminate structure of Al-Fe alloy layer and Zn-Al-Mg alloy layer). There are no particular restrictions on the type of acid, as long as it can dissolve the plating layer. The chemical composition is measured as an average chemical composition. In ICP analysis, the Zn concentration is calculated using the formula: Zn concentration = 100% - concentration of other elements (%).

[0047] Here, when a pre-plated steel material is used as the base steel material, the components of the pre-plating are also detected. For example, when a pre-Ni plated steel material is used, ICP analysis detects not only Ni in the plating layer but also Ni in the pre-Ni plating. Specifically, for example, when the Ni deposition amount is 1 g / m ２ ~3g / m ２When pre-plated steel (thickness: approximately 0.1 to 0.3 μm) is used as the base steel, even if the Ni concentration in the plating layer is 0%, the Ni concentration is detected as 0.1 to 15% when measured by ICP analysis. The method for determining whether the base steel is pre-Ni-plated steel is as follows: A sample is taken from the target steel, with the cross section cut along the thickness direction of the plating layer as the measurement surface. An electron probe microanalyzer (FE-EPMA) is used to perform line analysis of the sample's measurement surface near the interface between the plating layer and the base steel to measure the Ni concentration. The measurement conditions are an acceleration voltage of 15 kV, a beam diameter of approximately 100 nm, an irradiation time per point of 1000 ms, and a measurement pitch of 60 nm. The measurement distance may be any distance that allows confirmation of whether or not the Ni concentration is enriched at the interface between the plating layer and the base steel material of the steel material. If the Ni concentration is enriched at the interface between the plating layer and the base steel material of the steel material, the base steel material is determined to be pre-Ni-plated steel material. When pre-Ni-plated steel material is used as the base steel material, the Ni concentration of the plating layer is defined as the value measured as follows. First, the Ni emission intensity is measured for three or more standard samples (Zn alloy standard samples IMN ZH1, ZH2, and ZH4 manufactured by BAS) with different Ni concentrations using a high-frequency glow discharge optical emission surface analyzer (GDS: manufactured by HORIBA, Ltd., model number: GD-Profiler2). A calibration curve is created from the relationship between the obtained Ni emission intensity and the Ni concentration of the standard samples. Next, the Ni emission intensity at the 1 / 2 position of the plating layer of the plated steel material to be measured is measured using a high-frequency glow discharge optical emission surface analyzer (GDS: manufactured by HORIBA, Ltd., model number: GD-Profiler2). The Ni concentration at the 1 / 2 position of the plating layer is determined from the obtained Ni emission intensity and the created calibration curve. The obtained Ni concentration at the 1 / 2 position of the plating layer is defined as the Ni concentration of the plating layer. When pre-Ni plated steel material is used as the base steel material, the Zn concentration of the plating layer is defined as the Zn concentration calculated from the following formula: Formula: Zn concentration = 100 - (concentration of elements other than Zn and Ni determined by ICP analysis + Ni concentration determined by GDS)

[0048] The measurement conditions for the high-frequency glow discharge optical emission surface analyzer are as follows: H.V.: 630 V, anode diameter: φ4 mm, gas: Ar, gas pressure: 600 Pa, output: 35 W.

[0049] Next, the Al-Fe alloy layer will be described. The Al-Fe alloy layer may be formed on the surface of the base steel material (specifically, between the base steel material and the Zn-Al-Mg alloy layer), and has an Al structure. ５ The Fe phase is the main phase layer. The Al-Fe alloy layer is formed by mutual atomic diffusion between the base steel material and the coating bath. Since the steel material of the present disclosure has a coating layer formed by hot-dip coating, an Al-Fe alloy layer is likely to be formed in the coating layer containing Al element. Since the coating bath contains Al at a certain concentration or more, Al ５ The Fe phase is formed most frequently. However, atomic diffusion takes time, and there are also areas where the Fe concentration is high near the base steel material. Therefore, the Al-Fe alloy layer is partially composed of AlFe phase, Al ３ Fe phase, Al ５ Fe ２ In addition, since the plating bath contains a certain concentration of Zn, the Al-Fe alloy layer also contains a small amount of Zn.

[0050] Al ５ Fe phase, Al ３ Fe phase, AlFe phase, and Al ５ Fe ２ The corrosion resistance of each phase is not significantly different. The corrosion resistance here refers to the corrosion resistance in the parts not affected by welding.

[0051] Here, when the plating layer contains Si, Si is particularly likely to be incorporated into the Al—Fe alloy layer, and may form an Al—Fe—Si intermetallic compound phase. Identified intermetallic compound phases include the AlFeSi phase, and isomers such as α, β, q1, and q2-AlFeSi phases exist. Therefore, these AlFeSi phases may be detected in the Al—Fe alloy layer. An Al—Fe alloy layer containing these AlFeSi phases is also referred to as an Al—Fe—Si alloy layer. The Al—Fe—Si alloy layer is also thinner than the Zn—Al—Mg alloy layer, and therefore has little effect on the corrosion resistance of the entire plating layer.

[0052] Furthermore, when various pre-plated steel materials are used as the base steel material, the structure of the Al-Fe alloy layer may change depending on the amount of pre-plating applied. Specifically, when the pure metal layer used for pre-plating remains around the Al-Fe alloy layer, an intermetallic compound phase (e.g., Al ３ Ni phase, etc.) forms an alloy layer, an Al—Fe alloy layer in which some of the Al atoms and Fe atoms are substituted, or an Al—Fe—Si alloy layer in which some of the Al atoms, Fe atoms, and Si atoms are substituted.

[0053] That is, the Al—Fe alloy layer is made of Al ５ In addition to the alloy layer mainly composed of an Fe phase, the layer includes alloy layers of the above-mentioned various modes.

[0054] When a plating layer is formed on a pre-Ni plated steel material among various pre-plated steel materials, an Al-Ni-Fe alloy layer is formed as the Al-Fe alloy layer.

[0055] The thickness of the Al—Fe alloy layer is, for example, 0 μm or more and 7 μm or less, and is preferably 0.05 μm or more and 5 μm or less from the viewpoints of improving the adhesion of the plating layer (specifically, the Zn—Al—Mg alloy layer) and ensuring corrosion resistance and workability.

[0056] Since the Zn-Al-Mg alloy layer is usually thicker than the Al-Fe alloy layer, the contribution of the Al-Fe alloy layer to the corrosion resistance of the plated steel is smaller than that of the Zn-Al-Mg alloy layer. However, as can be inferred from the results of component analysis, the Al-Fe alloy layer contains Al and Zn, which are corrosion-resistant elements, at a certain concentration or higher. Therefore, the Al-Fe alloy layer has a certain degree of corrosion resistance against the base steel.

[0057] Furthermore, when a plating layer having the chemical composition specified in the present disclosure is formed by hot-dip plating, an Al—Fe alloy layer having a thickness of 100 nm or more is often formed between the base steel material and the Zn—Al—Mg alloy layer.

[0058] From the viewpoint of corrosion resistance, the thicker the Al—Fe alloy layer, the better. Therefore, the thickness of the Al—Fe alloy layer is preferably 0.05 μm or more. However, a thick Al—Fe alloy layer significantly deteriorates workability, so the thickness of the Al—Fe alloy layer is preferably 7 μm or less. When the thickness of the Al—Fe alloy layer is 7 μm or less, the amount of cracks and powdering that originate from the Al—Fe alloy layer is reduced, improving workability. The thickness of the Al—Fe alloy layer is more preferably 5 μm or less, and even more preferably 2 μm or less.

[0059] The thickness of the Al—Fe alloy layer is measured as follows. After embedding the sample in resin and polishing it, the thickness of the identified Al—Fe alloy layer is measured at any five points on an SEM backscattered electron image (magnification: 10,000x, field of view: 50 μm long x 200 μm wide, field of view in which the Al—Fe alloy layer is visible) of the cross section of the plating layer (a cross section along the thickness direction of the plating layer). The arithmetic average of the measurements at the five points is then taken as the thickness of the Al—Fe alloy layer. The thickness of the plating layer is also measured at any five points on the cross section SEM backscattered electron image (magnification: 500x, field of view: 198 μm long x 244 μm wide, field of view in which the entire plating layer is visible). The arithmetic average of the measurements at the five points is then taken as the thickness of the plating layer.

[0060] (Characteristics of plated steel) - Zn / Al / MgZn ２Average value of cumulative perimeter of ternary eutectic - The surface of the plating layer is polished to 1 / 2 of the thickness, and then observed with a scanning electron microscope at a magnification of 100 times. In the backscattered electron image of the Zn-Al-Mg alloy layer, Zn / Al / MgZn is ２ There is a ternary eutectic, Zn / Al / MgZn ２ The average cumulative circumference of the ternary eutectic is 100 to 300 mm / mm ２ is.

[0061] Zn / Al / MgZn ２ The average cumulative circumference of the ternary eutectic is 100 mm / mm ２ If it is less than 100%, the Zn / Al / MgZn alloy will cause localized corrosion. ２ The ternary eutectic crystals become coarse and the corrosion resistance deteriorates. In particular, when used in an environment where water is likely to accumulate, the Zn / Al / MgZn in the plating layer ２ The ternary eutectic corrodes locally, and the corrosion quickly reaches the base steel. In addition, when the plated steel is processed, ２ The ternary eutectic does not function as a buffer material, the intermetallic compound phase cracks, the plating layer becomes prone to peeling, and workability becomes poor.

[0062] Zn / Al / MgZn ２ The average cumulative circumference of the ternary eutectic is 300 mm / mm ２ When it exceeds Zn / Al / MgZn ２ Because the ternary eutectic is too fine, when the plated steel is processed, Zn / Al / MgZn ２ The ternary eutectic does not function as a buffer material, the intermetallic compound phase cracks, the plating layer becomes prone to peeling, and workability becomes poor.

[0063] Therefore, Zn / Al / MgZn ２ The average cumulative circumference of the ternary eutectic is 100 to 300 mm / mm ２ Zn / Al / MgZn ２ The average cumulative circumference of the ternary eutectic is 105 to 290 mm / mm ２ is preferable, and 110 to 280 mm / mm ２ is more preferred.

[0064] In the backscattered electron image of the Zn-Al-Mg alloy layer, Zn / Al / MgZn２ The area fraction of the ternary eutectic is not particularly limited, but from the viewpoint of workability and corrosion resistance, it is preferably 10 to 50%, more preferably 13 to 45%.

[0065] Zn / Al / MgZn ２ The remaining structure other than the ternary eutectic is Al crystal, MgZn ２ Phases, etc.

[0066] Here, Zn / Al / MgZn ２ The average cumulative perimeter of the ternary eutectic, and Zn / Al / MgZn ２ The method for measuring the area fraction of the ternary eutectic will be described.

[0067] Zn / Al / MgZn ２ The average cumulative perimeter of the ternary eutectic, and Zn / Al / MgZn ２ The area fraction of the ternary eutectic is measured using a backscattered electron image of the Zn—Al—Mg alloy layer obtained by polishing the surface of the plating layer to half of the layer thickness and then observing it with a scanning electron microscope at a magnification of 100 times. Specifically, it is as follows.

[0068] First, a sample is taken from the plated steel product to be measured. The sample is taken from a location that does not have defects in the plating layer, other than the vicinity of the punched end surface of the plated steel product (2 mm from the end surface).

[0069] Next, the surface of the plating layer (substantially the Zn—Al—Mg alloy layer) of the sample is polished in the thickness direction of the plating layer (hereinafter also referred to as the "Z-axis direction"). Specifically, the surface of the plating layer is dry-polished with a #1200 grit polishing sheet, and then finish-polished using a finishing solution containing alumina with an average particle size of 3 μm, a finishing solution containing alumina with an average particle size of 1 μm, and a finishing solution containing colloidal silica, in that order. The Zn intensity of the plating layer surface before and after polishing is measured by XRF (X-ray fluorescence analysis), and the point at which the Zn intensity after polishing is half of the Zn intensity before polishing is defined as half the thickness of the plating layer. Because the Zn—Al—Mg alloy layer occupies more than half the thickness of the plating layer, the polished surface polished to half the thickness of the plating layer is the polished surface of the Zn—Al—Mg alloy layer. Therefore, analyzing the polished surface allows the metal structure contained in the Zn—Al—Mg alloy layer to be identified.

[0070] Next, the polished surface is observed under a scanning electron microscope (SEM) at a magnification of 100 times to obtain a backscattered electron image (hereinafter also referred to as a "SEM backscattered electron image"). The SEM observation conditions are an acceleration voltage of 15 kV, a probe current of 10 nA, and a field of view of 1000 μm × 800 μm.

[0071] Using the binary processing function with two thresholds in WinROOF2015 (image analysis software) manufactured by Mitani Corporation, the Zn / Al / MgZn backscattered electron image (8-bit grayscale image, 256-color display) was analyzed. ２ It identifies ternary eutectic. In grayscale images saved in 8-bit, luminosity of 0 is black, and maximum value of 255 is white. Usually, phases with smaller atomic numbers and higher Al and Mg contents tend to be blacker, while phases with higher Zn contents tend to be whiter. Among the structures of the plating layer, the whitest structure is Zn / Al / MgZn. ２ In the case of a backscattered electron image of an SEM, when the threshold values ​​of light intensity are set to 160 and 215, Zn / Al / MgZn is obtained. ２It has been found from the results of identification using FE-SEM or TEM that ternary eutectic can be accurately identified. Therefore, the image is processed so that the range of luminosity 160 to 215 changes color, and Zn / Al / MgZn ２ Identify the ternary eutectic (see Figure 1(B)).

[0072] Next, the automatic shape feature measurement function of WinROOF2015 (image analysis software) manufactured by Mitani Shoji was used to analyze the Zn / Al / MgZn identified by the image processing. ２ The perimeter of the ternary eutectic was summed up, and the Zn / Al / MgZn ２ The cumulative perimeter of the ternary eutectic is calculated. ２ The cumulative perimeter of the ternary eutectic is divided by the area of ​​the field of view to obtain the unit area (mm ２ ) Zn / Al / MgZn ２ The cumulative perimeter of the ternary eutectic is calculated. This operation is carried out in three fields of view, and the unit area (mm ２ ) Zn / Al / MgZn ２ The arithmetic mean of the cumulative perimeter of the ternary eutectic is defined as "Zn / Al / MgZn ２ The average value of the cumulative perimeter of the ternary eutectic.

[0073] Also, Zn / Al / MgZn ２ The area fraction of the ternary eutectic can also be determined using the automatic shape feature measurement function of WinROOF2015 (image analysis software) manufactured by Mitani Corporation. Specifically, in the backscattered electron image of the Zn-Al-Mg alloy layer, the binarized and identified Zn / Al / MgZn ２ The area fraction of the ternary eutectic (area fraction relative to the area of ​​the field of view) is calculated using this function. This operation is performed for three fields of view, and the arithmetic average is calculated as "Zn / Al / MgZn ２ The area fraction of the "ternary eutectic" is

[0074] (Method for Producing Plated Steel Product) Hereinafter, an example of a method for producing a plated steel product according to the present disclosure will be described.

[0075] The plated steel material of the present disclosure is obtained by forming a plating layer having the above-mentioned specified chemical composition and metal structure on the surface (i.e., one side or both sides) of a base steel material (such as a base steel sheet) by a hot-dip galvanizing method.

[0076] Specifically, as an example, hot-dip galvanizing is performed under the following conditions. For example, a base steel material having a surface roughness Ra of 0.3 to 2.0 μm on the surface to be plated is immersed in a plating bath, and after being pulled out of the plating bath, is cooled in a temperature range of 450 to 395°C at an average cooling rate of 5 to 20°C / s. Next, it is cooled in a temperature range of 395 to 340°C at an average cooling rate of 3°C / s or less. Next, it is cooled in a temperature range of 340 to 280°C at an average cooling rate of 10 to 20°C / s. Here, the plating is performed using a continuous hot-dip metal plating method such as the Sendzimir method.

[0077] By setting the surface roughness Ra of the surface to be plated of the base steel material to 0.3 μm or more, solidification nuclei of the structure of the plated layer are easily formed, and primary crystals of Al etc. are densely crystallized. ２ The ternary eutectic is finely dispersed, Zn / Al / MgZn ２ The average value of the cumulative perimeter of the ternary eutectic can be controlled within the above range. However, if the surface roughness Ra of the surface to be plated of the base steel exceeds 2.0 μm, the wettability of the plating is poor, and bare spots are likely to occur. The surface roughness Ra of the surface to be plated of the base steel is measured as follows in accordance with JIS B 0633:2001. The average surface roughness of the surface to be plated of the base steel before plating is measured three times in two arbitrary directions forming an angle of 90°, each at a length of 10 mm. The arithmetic mean of the obtained average surface roughness measurements (two directions x three times, a total of six measurements) is calculated. This arithmetic mean value is taken as the surface roughness Ra of the surface to be plated of the base steel.

[0078] When measuring the interfacial roughness Ra between a base steel material and a coating layer, the coating layer is first removed from the plated steel material by dissolving it in hydrochloric acid containing an inhibitor. The surface of the base steel material from which the coating layer was removed is then measured using the same method as above, and the average value is calculated. This is the interfacial roughness Ra between the base steel material and the coating layer. In this disclosure, the interfacial roughness Ra between the base steel material and the coating layer in a plated steel material (i.e., after plating) generally coincides with the surface roughness Ra of the surface to be plated of the base steel material before plating. In other words, by using a base steel material with a surface roughness Ra of the surface to be plated of 0.3 to 2.0 μm, the interfacial roughness Ra between the base steel material and the coating layer in the resulting plated steel material can be made 0.3 to 2.0 μm.

[0079] Here, the plating layer is made of primary Al, Al / MgZn ２ phase, MgZn crystallized around the primary Al crystals ２ Peritectic, Zn / Al / MgZn ２ It solidifies in the order of ternary eutectic.

[0080] Therefore, by cooling in the temperature range of 450 to 395°C at an average cooling rate of 5°C / s or more, primary Al crystals and Al / MgZn ２ Then, by cooling in the temperature range of 395 to 340°C at an average cooling rate of 3°C / s or less, MgZn phases are dispersed around the Al primary crystals. ２ This ensures that the peritectic phase is crystallized. ２ However, if the average cooling rate in the temperature range of 450 to 395°C exceeds 20°C / s, the Al primary crystal and Al / MgZn ２ The phase is too finely crystallized, and the Zn / Al / MgZn ２ The ternary eutectic is also excessively refined. ２ The average cumulative perimeter of the ternary eutectic exceeds the above range.

[0081] Next, the Zn / Al / MgZn alloy is cooled in the temperature range of 340 to 280°C at an average cooling rate of 10 to 20°C / s. ２ The ternary eutectic is refined, resulting in the formation of Zn / Al / MgZn ２The average cumulative perimeter of the ternary eutectic is controlled to be within the above range.

[0082] The post-treatments that can be applied to the plated steel material of the present disclosure will be described below.

[0083] The plated steel material of the present disclosure may have a coating formed on the plating layer. The coating may be one layer or two or more layers. Examples of types of coatings that may be formed directly on the plating layer include chromate coatings, phosphate coatings, and chromate-free coatings. The chromate treatment, phosphate treatment, and chromate-free treatment that form these coatings can be performed by known methods.

[0084] Chromate treatments include electrolytic chromate treatments that form a chromate film by electrolysis, reactive chromate treatments that form a film by utilizing a reaction with the material and then wash away excess treatment solution, and paint-on chromate treatments that apply a treatment solution to the substrate and dry it without rinsing with water to form a film. Any of these treatments may be used.

[0085] Examples of electrolytic chromate treatments include electrolytic chromate treatments using chromic acid, silica sol, resin (acrylic resin, vinyl ester resin, vinyl acetate acrylic emulsion, carboxylated styrene butadiene latex, diisopropanolamine-modified epoxy resin, etc.), and hard silica.

[0086] Examples of the phosphate treatment include zinc phosphate treatment, zinc calcium phosphate treatment, and manganese phosphate treatment.

[0087] Chromate-free treatments are particularly suitable because they place no burden on the environment. 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 paint-on chromate-free treatments that apply a treatment liquid to the substrate and dry it without rinsing with water to form a film. Any of these treatments may be used.

[0088] Furthermore, one or more organic resin coatings may be provided on the coating directly on the plating layer. The organic resin is not limited to a specific type, and examples thereof include polyester resins, polyurethane resins, epoxy resins, acrylic resins, polyolefin resins, and modified versions of these resins. Here, the term "modified version" refers to a resin obtained by reacting a reactive functional group contained in the structure of these resins with another compound (such as a monomer or a crosslinking agent) containing a functional group capable of reacting with the functional group.

[0089] Such organic resins may be a mixture of one or more unmodified organic resins, or a mixture of one or more organic resins obtained by modifying at least one other organic resin in the presence of at least one organic resin. The organic resin film may also contain any coloring pigment or anti-rust pigment. Water-based organic resins obtained by dissolving or dispersing them in water may also be used.

[0090] (Examples) A ​​coating bath was prepared in the atmosphere using a predetermined amount of pure metal ingot so as to obtain a coating layer with the chemical composition shown in Tables 1 and 2. A hot-dip coating simulator was used to prepare the coated steel sheets. A 2.3 mm thick general-purpose hot-rolled steel sheet (C concentration <0.1%) was used as the base steel, which was brush-polished, and degreased and pickled immediately before the coating process. The surface roughness Ra of the surface to be coated of the base steel (referred to as "surface roughness Ra" in the tables) was as shown in Tables 1 and 2. In some examples, pre-Ni-plated steel, which had been further pre-coated with Ni, was used as the base steel. The Ni deposition weight was 1 g / m ２ ~3g / m ２ In addition, examples in which pre-Ni plated steel was used as the base steel are indicated as "Pre-Ni" in the "Base steel" column in the table. A contact-type K thermocouple was attached to the backside of the surface to be plated of the base steel in order to monitor the temperature of the steel during the plated steel sheet production process.

[0091] In the preparation of all samples, the base steel was subjected to the same reduction treatment method before immersion in the plating bath. ２ -H ２(5%) (dew point -40°C or less, oxygen concentration less than 25 ppm), the temperature was raised from room temperature to 800°C by electrical heating, and after holding for 60 seconds, N ２ The steel sheets were cooled to a temperature 10°C above the plating bath temperature by gas spraying and immediately immersed in the plating bath. The plating bath temperature for all of the plated steel sheets was 500°C as the base temperature, with some of the temperatures being higher. The immersion time in the plating bath was the time shown in the table (2 seconds). ２ The gas wiping pressure was adjusted so that the plating thickness was 30 μm (±1 μm).

[0092] Then, after the base steel material was pulled out of the coating bath, a coating layer was obtained by a cooling process in which the average cooling rates for the following first to third stages shown in Tables 1 and 2 were set as shown in Tables 1 and 2. - First stage average cooling rate: Average cooling rate in the temperature range of 450 to 395°C - Second stage average cooling rate: Average cooling rate in the temperature range of 395 to 340°C - Third stage average cooling rate: Average cooling rate in the temperature range of 340 to 280°C In the cooling process, N was added to the coated steel material. ２ The steel material was cooled by blowing gas onto it. At this time, N was blown onto the steel material so as to achieve a predetermined cooling rate within the above temperature range. ２ The cooling was carried out while adjusting the amount of gas blown.

[0093] -Various Measurements- Samples were cut out from the obtained plated steel sheets. Then, the following items were measured according to the methods described above. ２ Average value of cumulative perimeter of ternary eutectic (referred to as "perimeter of ternary eutectic" in the table) Zn / Al / MgZn ２ Ternary eutectic area fraction (indicated as "ternary eutectic area fraction" in the table) Thickness of Al-Fe alloy layer (however, in the case of an example where a pre-Ni plated steel sheet is used as the base steel, the thickness of the Al-Ni-Fe alloy layer is shown.)

[0094] - Workability - Samples were cut out from the obtained plated steel sheets. After bending the samples by 1T, the bent portion was peeled off with tape and the area ratio of the plated layer adhered to the tape was evaluated. An area ratio of the plated layer adhered to the tape of 5% or less was evaluated as "A", and an area ratio of more than 5% was evaluated as "NG".

[0095] - Corrosion resistance - Samples were cut out from the obtained plated steel sheets. Then, the samples were laid flat and subjected to 21 cycles of a combined cyclic corrosion test (CCT) in accordance with the accelerated corrosion test (JASO M609-91). After the corrosion test, the corrosion weight loss was 35 g / m ２ The following cases are evaluated as "A" and 35 g / m ２ Super was rated as "NG".

[0096] Examples are listed in Tables 1 and 2.

[0097]

[0098]

[0099]

[0100]

[0101]

[0102]

[0103]

[0104]

[0105] The above results show that the Examples corresponding to the plated steel materials of the present disclosure are superior in workability and corrosion resistance compared to the Comparative Examples, even when used in an environment where water is likely to accumulate.

[0106] In Test No. 95, there were many unplated areas and the appearance varied widely, so the perimeter and area fraction of the ternary eutectic were not measured.

[0107] Although the preferred embodiments and examples of the present disclosure have been described in detail above with reference to the accompanying drawings, the present disclosure is not limited to such examples. It is clear that a person skilled in the art to which the present disclosure pertains can conceive of various modified or altered examples within the scope of the technical ideas described in the claims, and it is understood that these also naturally fall within the technical scope of the present disclosure.

[0108] The disclosure of Japanese Patent Application No. 2022-044295 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually indicated to be incorporated by reference.

Claims

1. A plated steel product having a base steel material and a plating layer including a Zn-Al-Mg alloy layer disposed on the surface of the base steel material, wherein the plating layer contains, in mass %, Zn: more than 65.00%, Al: more than 5.00% but less than 25.00%, Mg: more than 3.00% but less than 12.50%, Sn: 0% to 3.00%, Bi: 0% to less than 5.00%, In: 0% to less than 2.00%, Ca: 0% to 3.00%, Y: 0% to 0.50%, La: 0% to less than 0.50%, Ce: 0% to less than 0.50%, Si: 0% to less than 2.50%, Cr: 0% to less than 0.25%, Ti: 0% to less than 0.25%, Zr: 0% to less than 0.25%, Mo: 0% to less than 0.25%, W: 0% to less than 0.25%, Ag: 0% to less than 0.25%, P: 0% to less than 0.25%, Ni: 0% to less than 0.25%, Co: 0% to less than 0.25%, V: 0% to less than 0.25%, Nb: 0% to less than 0.25%, Cu: 0% to less than 0.25%, Mn: 0% to less than 0.25%, Li: 0% to less than 0.25%, Na: 0% to less than 0.25%, K: 0% to less than 0.25%, Fe: 0% to 5.00%, Sr: 0% to less than 0.50%, Sb: 0% to less than 0.50%, Pb: 0% to less than 0.50%, B : 0% to less than 0.50%, and a chemical composition consisting of impurities, wherein the surface of the plating layer is polished to 1 / 2 of the layer thickness, and then observed with a scanning electron microscope at a magnification of 100 times, in a backscattered electron image of the Zn-Al-Mg alloy layer, Zn / Al / MgZn ２ There is a ternary eutectic, and the Zn / Al / MgZn ２ The average cumulative circumference of the ternary eutectic is 100 to 300 mm / mm ２ This is plated steel.

2. The plated steel material according to claim 1, wherein the plated layer includes an Al-Fe alloy layer between the base steel material and the Zn-Al-Mg alloy layer.

3. The plated steel material according to claim 1 or 2, wherein the interface roughness Ra between the base steel material and the plated layer is 0.3 to 2.0 μm.

4. A method for producing plated steel according to claim 1 or claim 2, comprising immersing a base steel material having a surface roughness Ra of 0.3 to 2.0 μm on the surface to be plated in a plating bath, and then removing it from the plating bath, cooling it in a temperature range of 450 to 395°C at an average cooling rate of 5 to 20°C / s, cooling it in a temperature range of 395 to 340°C at an average cooling rate of 3°C / s or less, and cooling it in a temperature range of 340 to 280°C at an average cooling rate of 10 to 20°C / s.

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