JP7436840B2 - Hot-dip Zn-Al-Mg plated steel - Google Patents

Description

The present invention relates to hot-dip Zn-Al-Mg plated steel materials.

In the fields of home appliances, automobiles, building materials, and civil engineering, hot-dip Zn-Al-Mg-based plated steel materials with excellent corrosion resistance are often used. Patent Documents 1 to 6 describe various hot-dip Zn-Al-Mg-based plated steel materials. In the field mentioned above, the cross section of the steel material may be exposed by cutting the hot-dip Zn-Al-Mg coated steel material into a predetermined part shape. The plating layer may be deformed due to plastic working such as.

Patent Document 1 discloses that the surface of the steel plate contains Mg: 1 to 10% by weight, Al: 2 to 19% by weight, and Si: 0.01 to 2% by weight, and Mg and Al are expressed by the following formula, Mg (%)+Al(%)≦20%, the remainder is Zn and unavoidable impurities, and the Zn alloy plating layer has a [ternary eutectic structure of Al/Zn/MgZn ₂ ]. A plated steel sheet having excellent corrosion resistance and having a metal structure in which [Mg ₂ Si phase], [MgZn _two phases], and [Zn phase] are mixed in the base material is described.

Patent Document 2 discloses that a hot-dip Zn-Al-Mg plating layer consisting of Al: 4.0 to 10% by weight, Mg: 1.0 to 4.0% by weight, and the balance being Zn and unavoidable impurities is formed on the surface of a steel sheet. A hot-dip Zn-based plated steel sheet, in which the plating layer has a metal structure in which [Al phase] is mixed in the base [ternary eutectic structure of Al/Zn/MgZn ₂ ], and has good corrosion resistance and surface appearance. A hot-dip Zn-Al-Mg coated steel sheet is described.

Patent Document 3 discloses that zinc contains 4 to 10% by mass of Al, 1 to 5% by mass of Mg, and 0.01% by mass or less of Ti, with the balance consisting of zinc and inevitable impurities, on one or both sides of a steel plate. A highly corrosion-resistant coated steel sheet with excellent image clarity is described, which has a chemical conversion coating such as a chromate coating or a phosphate coating as an intermediate layer, and an organic coating layer with a thickness of 0.2 to 100 μm as an upper layer. has been done.

Patent Document 4 discloses a Zn alloy plating layer containing 2.8% or more of Mg, 10.5% or more of Al, 0.01 to 0.5% of Si, and the remainder consisting of Zn and inevitable impurities. However, a hot-dip Zn--Al--Mg--Si-plated steel sheet having a uniform appearance in which the X-ray intensity ratio of Mg ₂ Zn ₁₁ /MgZn ₂ in the Zn alloy plating layer is 0.5 or less is described.

Patent Document 5 describes a steel plate, a hot-dipped layer containing 4% by mass or more and 22% by mass or less Al, 1% by mass or more and 5% by mass or less Mg, and the balance containing Zn and inevitable impurities; and the X-ray diffraction intensity I(200) of the (200) plane of the Al phase and the X-ray diffraction intensity I( A Zn-Al-Mg hot-dip plated steel sheet is described in which the diffraction intensity ratio I(200)/1(111), which is the ratio of

Patent Document 6 discloses that the surface of the steel material has a plating layer consisting of Al: 5 to 18% by mass, Mg: 1 to 10% by mass, Si: 0.01 to 2% by mass, the balance being Zn and inevitable impurities. A hot-dip Zn--Al--Mg--Si-plated steel material with excellent surface properties in which 200 or more [Al phases] exist per 1 mm ² on the surface of the plated steel material is described.

As described above, when a hot-dip Zn-Al-Mg-based plated steel material is cut into a predetermined part shape, a cross section of the steel material and the plating layer appears at the end including the cut surface. Since there is no plating layer on the cross section of the steel plate, corrosion resistance may be inferior. Furthermore, when plastic working such as bending is applied to hot-dip Zn-Al-Mg plated steel, the plating layer may be deformed at the bent portion, and corrosion may progress from this deformed portion.
For this reason, hot-dip Zn--Al--Mg based plated steel materials are required to have improved corrosion resistance at the edges and at processed parts.

Japanese Patent Application Publication No. 2000-104154 Japanese Patent Application Publication No. 10-226865 Japanese Patent Application Publication No. 2004-225157 Japanese Patent Application Publication No. 2006-193791 International Publication No. 2011/001662 Japanese Patent Application Publication No. 2001-355053

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a hot-dip Zn-Al-Mg-based plated steel material that has excellent corrosion resistance at edges and processed parts.

In order to solve the above problems, the present invention employs the following configuration.
[1] Comprising a steel material and a plating layer formed on the surface of the steel material,
The plating layer has an average composition of Mg: 1 to 10% by mass, Al: 4 to 22% by mass, and the remainder consists of Zn and impurities,
The plating layer contains [Al/Zn mixed structure] in the base of [ternary eutectic structure of Al/Zn/MgZn _2] ,
The [Al/Zn mixed structure] includes a first region where the Zn concentration is in the range of 75% by mass or more and less than 85% by mass, and a region inside the first region where the Zn concentration is in the range of 67% by mass or more and 75% by mass. and a second region in a range of less than %,
In the second region, an Al phase and a Zn phase are mixed, and the average particle size of the Al phase and the Zn phase in a cross section of the plating layer perpendicular to the surface of the plating layer is 50 nm or less. A hot-dip Zn-Al-Mg based plated steel material.
[2] The hot-dip Zn-Al-Mg-based plated steel material according to [1], wherein the Al phase in the second region contains an intermetallic compound phase containing Mg.
[3] The intermetallic compound phase containing Mg is one or more of MgZn ₂ , Mg ₂ Zn ₁₁ , Mg ₂ Si, Mg ₃₂ (Al, Zn) ₄₉ The hot-dip Zn-Al-Mg-based plated steel material according to [2].
[4] The molten Zn-Al-Mg system according to [2] or [3], wherein the number of the Mg-containing intermetallic compound phases contained in the Al phase is 3 or more. Plated steel.
[5] The area ratio of the [Al/Zn mixed structure] in a cross section of the plating layer perpendicular to the surface of the plating layer is in the range of 10 to 70% [1] to [4]. The hot-dip Zn-Al-Mg-based plated steel material according to any one of the items.
[6] The average composition of the plating layer contains Mg: 1 to 10% by mass, Al: 8 to 22% by mass, and the remainder is Zn and impurities,
The [Al/Zn mixed structure] includes the first region, the second region, and a third region located inside the second region and having a Zn concentration in a range of 55% by mass or more and less than 67% by mass. The hot-dip Zn-Al-Mg-based plated steel material according to any one of [1] to [5], characterized by comprising a region.
[7] When the plating layer is divided into two equal parts at 1/2 position in the plating thickness direction into the steel material side and the plating layer surface side, among the nucleation points of the [Al/Zn mixed structure] Molten Zn-Al-Mg according to any one of [1] to [6], wherein 60% or more of the nucleation points are present in the region on the steel material side of the plating layer. Series plated steel.
[8] The molten Zn-Al- according to any one of [1] to [7], wherein the plating layer further contains Si in an average composition of 0.0001 to 2% by mass. Mg-based plated steel.
[9] The plating layer further contains one or more of Ni, Ti, Zr, and Sr in an average composition of 0.0001 to 2% by mass in total [ 1] to [8], the hot-dip Zn-Al-Mg-based plated steel material.
[10] The plating layer further contains one or more of Sb, Pb, Sn, Ca, Co, Mn, P, B, Bi, Cr, Sc, Y, REM, and Hf in an average composition. The hot-dip Zn-Al-Mg-based plated steel material according to any one of [1] to [9], characterized in that the total content is in the range of 0.0001 to 2% by mass.

According to the present invention, it is possible to provide a hot-dip Zn-Al-Mg-based plated steel material that has excellent corrosion resistance at the end portions and corrosion resistance at the processed portions.

FIG. 1A is a backscattered electron image photograph of a cross section of the plating layer of Comparative Example 5 observed in the backscattered electron mode of a scanning electron microscope. FIG. 1B is a backscattered electron image photograph of a cross section of the plating layer of Invention Example 1 observed in the backscattered electron mode of a scanning electron microscope. FIG. 2A is a schematic diagram showing an example of a 3D-AP analysis result of a fine Al phase. FIG. 2B is a schematic diagram showing another example of the 3D-AP analysis results of the fine Al phase.

Hot-dip Zn-Al-Mg-based plated steel has components including Mg, Al, and the balance Zn and impurities, and has a metal structure in the base of [ternary eutectic structure of Al/Zn/MgZn ₂ ]. , [MgZn _two- phase], [Zn phase], and [Al/Zn mixed structure]. Moreover, when Si is contained in the hot-dip plating layer in addition to Zn, Al, and Mg, [Mg ₂ Si phase] may be contained in addition to the above-mentioned phases and structures. When forming a plating layer, the steel material is immersed in a plating bath containing Mg, Al, and Zn and then pulled up, thereby solidifying the molten metal attached to the surface of the steel material. When the plating layer solidifies, the [Al/Zn mixed structure] crystallizes out, and then the matrix of [ternary eutectic structure of Al/Zn/MgZn ₂ ] crystallizes, thereby forming the plating layer.

In order to improve the surface corrosion resistance of such hot-dip Zn-Al-Mg plated steel materials, the present inventors conducted extensive studies and found that [Al/Zn mixed structure] is the initial starting point of corrosion. [Al/Zn mixed structure] originates from the high-temperature Al'' phase (an Al solid solution containing Zn and often containing a small amount of Mg) in the ternary equilibrium phase diagram of Al-Zn-Mg. According to the phase diagram, it is in a state containing a fine Zn phase and a fine Al phase at room temperature.A detailed study of the internal structure of this [Al/Zn mixed structure] revealed that [Al/Zn The mixed structure] can be divided into a first region with a relatively high Zn concentration and a second region inside the first region with a relatively low Zn concentration, and the cross-sectional area of the second region is 1 μm ² . It was found that the end face corrosion resistance tends to decrease when the average grain size of the Zn phase and Al phase is larger than 50 nm. It was found that the average grain size of the Zn phase and Al phase per area of 1 μm ² was larger than 50 nm. Therefore, the precipitation form of the Zn phase and Al phase in the second region was determined to be 50 nm in average grain size per 1 μm ² of area. It has been found that a hot-dip Zn-Al-Mg-based plated steel material with excellent corrosion resistance at the end face can be obtained by doing the following.Also, the corrosion resistance at the end face of the hot-dip Zn-Al-Mg-based plated steel material is improved. It has been found that the corrosion resistance of the processed parts of hot-dip Zn-Al-Mg plated steel material is also improved.

The hot-dip Zn-Al-Mg-based plated steel material of the present embodiment includes a steel material and a plating layer formed on the surface of the steel material, and the plating layer has an average composition of Mg: 1 to 10% by mass, Al: 4 The plating layer contains [Al/Zn mixed structure] in the [ternary eutectic structure of Al/Zn/MgZn2 _] . [Al/Zn mixed structure] includes a first region where the Zn concentration is in the range of 75% by mass or more and less than 85% by mass, and a region inside the first region where the Zn concentration is in the range of 67% by mass or more and 75% by mass. %, the second region contains an Al phase and a Zn phase, and the Al phase and Zn phase in a cross section of the plating layer perpendicular to the surface of the plating layer. The average particle size is 50 nm or less.
Further, in the hot-dip Zn-Al-Mg-based plated steel material of the present embodiment, it is preferable that an intermetallic compound phase containing Mg is included in the Al phase in the second region.
Further, in the hot-dip Zn-Al-Mg-based plated steel material of the present embodiment, the Mg-containing intermetallic compound phase contained in the Al phase in the second region is MgZn ₂ , Mg ₂ Zn ₁₁ , Mg ₂ Si, Mg ₃₂ (Al, Zn) ₄₉ is preferable.
Further, in the hot-dip Zn--Al--Mg based plated steel material of the present embodiment, it is preferable that the number of Mg-containing intermetallic compound phases contained in the Al phase in the second region is 3 or more.
Further, in the hot-dip Zn-Al-Mg-based plated steel material of the present embodiment, the area ratio of the [Al/Zn mixed structure] in the cross section of the plating layer perpendicular to the surface of the plating layer is in the range of 10 to 70%. preferable.
Further, in the hot-dip Zn-Al-Mg-based plated steel material of the present embodiment, the average composition of the plating layer is Mg: 1 to 10% by mass, Al: 8 to 22% by mass, and the remainder is Zn and impurities. , [Al/Zn mixed structure] includes a first region, a second region, and a third region located inside the second region and having a Zn concentration in a range of 55% by mass or more and less than 67% by mass. It is preferable to include.
Furthermore, in the hot-dip Zn-Al-Mg-based plated steel material of this embodiment, when the plating layer is divided into two parts at 1/2 position in the plating thickness direction into the steel material side and the plating layer surface side, the [Al -Zn mixed structure] It is preferable that 60% or more of the nucleation points in terms of number ratio exist in the region of the plating layer on the steel material side.
The hot-dip Zn--Al--Mg based plated steel material of this embodiment will be explained below.

There are no particular restrictions on the steel material that forms the base of the plating layer. As for the material, it is possible to apply general steel, Al-killed steel, and some high-alloy steels, and there is no particular restriction on the shape, and a steel plate may be used. Further, the steel material may be subjected to Ni pre-plating. The plating layer according to this embodiment is formed by applying the hot-dip plating method described below to the steel material.

Next, the chemical components of the plating layer will be explained.
The plating layer according to this embodiment contains Mg: 1 to 10% by mass, Al: 4 to 22% by mass, and the balance contains Zn and impurities. Further, the hot-dip plating layer may contain Si: 0.0001 to 2% by mass in average composition. Further, the average composition of the hot-dip plated layer may contain a total of 0.0001 to 2% by mass of any one or more of Ni, Ti, Zr, and Sr. Furthermore, the hot-dip plating layer has an average composition of one or more of Fe, Sb, Pb, Sn, Ca, Co, Mn, P, B, Bi, Cr, Sc, Y, REM, and Hf. may contain a total of 0.0001 to 2% by mass.

The Mg content ranges from 1 to 10% by mass in terms of average composition. Mg is an element necessary to improve the corrosion resistance of the plating layer. If the Mg content in the plating layer is less than 1% by mass, the effect of improving corrosion resistance will be insufficient, and if it exceeds 10% by mass, dross generation in the plating bath will become significant, making it difficult to stably produce plated steel materials. becomes difficult. From the viewpoint of the balance between corrosion resistance and dross generation, the content is preferably 1.5 to 6% by mass. More preferably, it is in the range of 2 to 5% by mass.

The average content of Al is in the range of 4 to 22% by mass. Al is an element necessary to ensure corrosion resistance. If the content of Al in the plating layer is less than 4% by mass, the effect of improving corrosion resistance will be insufficient, and if it exceeds 22% by mass, the effect of improving corrosion resistance will be saturated. From the viewpoint of corrosion resistance, the content is preferably 8 to 22% by mass. More preferably, it is 9 to 13% by mass.

Further, the hot-dip plating layer may contain Si in a range of 0.0001 to 2% by mass. Si is an effective element for improving the adhesion of the hot-dip plating layer. It is preferable to contain Si in an amount of 0.0001% by mass or more because the effect of improving adhesion is exhibited by containing 0.0001% by mass or more of Si. On the other hand, the effect of improving plating adhesion is saturated even if the content exceeds 2% by mass, so the content of Si is set to 2% by mass or less. From the viewpoint of plating adhesion, the content may be in the range of 0.02 to 1% by mass, or may be in the range of 0.03 to 0.8% by mass.

Further, the hot-dip plating layer may contain a total of 0.0001 to 2% by mass of any one or more of Ni, Ti, Zr, and Sr in an average composition. Intermetallic compounds containing these elements act as crystallization nuclei of [Al/Zn mixed structure], make [ternary eutectic structure of Al/MgZn ₂ /Zn] finer and more uniform, and improve the plating layer. Improve appearance and smoothness. The reason why one or more of these elements is set to 0.0001 to 2% by mass in total is that if it is less than 0.0001% by mass, the effect of making the solidified structure fine and uniform will be insufficient. If it exceeds 2% by mass, the effect of refining the [ternary eutectic structure of Al/Zn/MgZn2 _] will not only become saturated, but also increase the surface roughness of the plating layer and worsen its appearance. The upper limit is 2% by mass. Particularly when added for the purpose of improving appearance, it is desirable to contain 0.001 to 0.5% by mass. It is more preferably in the range of 0.001 to 0.05% by mass, and still more preferably in the range of 0.002 to 0.01% by mass.

The average composition of the hot-dip plating layer is one or more of Fe, Sb, Pb, Sn, Ca, Co, Mn, P, B, Bi, Cr, Sc, Y, REM, and Hf in total. It may contain 0.0001 to 2% by mass. By containing these elements, corrosion resistance can be further improved. REM is one or more rare earth elements with atomic numbers 57 to 71 in the periodic table.

The remainder of the chemical components of the plating layer are zinc and impurities.

Next, the structure of the plating layer will be explained. The plating layer according to the present embodiment includes [Al/Zn mixed structure] in the base of [ternary eutectic structure of Al/Zn/MgZn _2] . In addition, in the matrix of the [ternary eutectic structure of Al/Zn/MgZn ₂ ], in addition to the [Al/Zn mixed structure], there are also [MgZn ₂ phase], [Zn phase], and [Mg ₂ Si phase]. may be included.

[Al/Zn/MgZn ₂ ternary eutectic structure] is a ternary eutectic structure of an Al phase, a Zn phase, and an intermetallic compound MgZn ₂ phase, and [Al/Zn/MgZn ₂ For example, the Al phase forming the ternary eutectic structure of (often contains Mg). This Al'' phase at high temperature usually appears separated into a fine Al-based phase and a fine Zn-based phase at room temperature.Also, the Zn-based phase in [ternary eutectic structure of Al/Zn/MgZn2 _] It is a Zn solid solution containing a small amount of Al and, in some cases, an even smaller amount of Mg.The MgZn ₂ phase of [ternary eutectic structure of Al/Zn/MgZn ₂ ] is Zn in the system equilibrium phase diagram: This is an intermetallic compound phase that exists in the vicinity of approximately 84% by mass.As seen in the phase diagram, it is thought that each phase contains Si and other elements in solid solution, but only in small amounts. Since the amounts cannot be clearly distinguished by ordinary analysis, the ternary eutectic structure consisting of these three phases is herein referred to as [ternary eutectic structure of Al/Zn/MgZn ₂ ].

Next, [Al/Zn mixed structure] will be explained. In this embodiment, the structure formed by separating the high-temperature Al phase into a fine Zn-based phase and a fine Al-based phase during cooling is referred to as an [Al/Zn mixed structure]. Note that the Zn-based phase may contain Al and Mg in solid solution. The Al-based phase may form a solid solution of Zn and Mg. When the plating layer contains Si, it may contain a small amount of Si.

[Al/Zn mixed structure] is a phase that appears in the form of islands with clear boundaries in the matrix of [ternary eutectic structure of Al/Zn/ _MgZn2 ] in the backscattered electron image of a scanning electron microscope. corresponds to, for example, the "Al''phase" (an Al solid solution containing a Zn phase and containing a small amount of Mg) at a high temperature in the ternary equilibrium phase diagram of Al--Zn--Mg. The amount of Zn and Mg dissolved in this Al'' phase at high temperature varies depending on the Al and Mg concentrations of the plating bath. If the plating layer contains Si, it may also contain a small amount of Si. The Al'' phase at high temperatures normally separates into a fine Al phase and a fine Zn phase at room temperature, but the island-like shape seen at room temperature is thought to be the remains of the Al'' phase at high temperatures. A structure that originates from this Al'' phase at high temperatures and retains the shape of the Al'' phase is referred to herein as an [Al/Zn mixed structure]. This [Al/Zn mixed structure] ] can be clearly distinguished from the Al phase forming [ternary eutectic structure of Al/Zn/MgZn ₂ ] in a backscattered electron image of a scanning electron microscope.

The area ratio of the [Al/Zn mixed structure] in the cross section of the plating layer perpendicular to the surface of the plating layer is preferably in the range of 10 to 70%. If the area ratio of the [Al/Zn mixed structure] is within this range, the corrosion resistance of the end portions and processed portions can be improved.

The area ratio of the [Al/Zn mixed structure] is measured by observing a cross section of the plating layer perpendicular to the surface of the plating layer using a backscattered electron image using a scanning electron microscope. Photograph five locations at a magnification of 1000x.
Photographs should be taken so that the entire thickness of the plating layer is visible. The photo shooting position is randomly selected. Do not arbitrarily reselect the shooting position based on the calculated area ratio. Then, by measuring the total cross-sectional area of the [Al/Zn mixed structure] appearing in all the cross-sectional photographs and dividing this by the cross-sectional area of the plating layer appearing in all the cross-sectional photographs, Zn mixed structure] is measured.

Next, the [Zn phase] contained in the matrix of [ternary eutectic structure of [Al/Zn/MgZn ₂ ] has a clear boundary in the matrix of [ternary eutectic structure of [Al/Zn/MgZn _2] ]. This phase appears to be island-like, but it may actually contain a small amount of Al or even a small amount of Mg in solid solution. As far as we can see from the phase diagram, it is thought that Si and other additive elements are not dissolved in solid solution in this phase, or even if they are dissolved in solid solution, the amount is extremely small. This [Zn phase] can be clearly distinguished from the Zn phase forming [ternary eutectic structure of Al/Zn/MgZn ₂ ] in a backscattered electron image of a scanning electron microscope. The plating layer of this embodiment may contain a [Zn phase] depending on the manufacturing conditions, but experiments showed that it had almost no effect on improving end face corrosion resistance and processed part corrosion resistance. ] is included, there is no particular problem.

In addition, the [MgZn _two phases] contained in the matrix of [ternary eutectic structure of Al/Zn/MgZn ₂ ] have clear boundaries in the matrix of [ternary eutectic structure of Al/Zn/MgZn ₂ ]. This phase appears to be island-like, but it may actually contain a small amount of Al dispersed or dissolved in solid solution. As far as we can see from the phase diagram, it is thought that Si and other additive elements are not dissolved in solid solution in this phase, or even if they are dissolved in solid solution, the amount is extremely small. This [MgZn _two phase] can be clearly distinguished from the MgZn _two phase forming [ternary eutectic structure of Al/Zn/MgZn _2] in a backscattered electron image of a scanning electron microscope. The plating layer of this embodiment may not contain [MgZn _two- phase] depending on the manufacturing conditions, but it is included in the plating layer under most manufacturing conditions.

In addition, the [Mg ₂ Si phase] contained in the matrix of the [ternary eutectic structure of Al/Zn/MgZn ₂ ] appears as an island-like phase with clear boundaries in the solidified structure of the Si-containing plating layer. It is. As far as we can see from the phase diagram, it is thought that Zn, Al, and other additive elements are not dissolved in solid solution, or even if they are dissolved in solid solution, the amount is extremely small. This [Mg ₂ Si phase] can be clearly distinguished in a backscattered electron image of a scanning electron microscope during plating.

Next, the microstructure of the [Al/Zn mixed structure] will be explained. As mentioned above, the [Al/Zn mixed structure] exhibits an island-like shape that retains the remains of the Al'' phase at high temperatures. Also, the internal structure of the [Al/Zn mixed structure] is as follows according to the phase diagram. , it is presumed that it shows a morphology separated into a fine Al phase and a fine Zn phase.The fine Al phase and the fine Zn phase can be distinguished from the backscattered electron image of a scanning electron microscope. As explained, the [Al/Zn mixed structure] is divided into a first region, a second region, and a third region.

Focusing on the Zn concentration of the [Al/Zn mixed structure], the [Al/Zn mixed structure] has at least a first region and a second region that is inside the first region and has a lower average Zn concentration than the first region. It can be divided into Further, when the average Al concentration of the plating layer is 8 to 22% by mass, a third region having an average Zn concentration lower than that of the second region is included inside the second region. The first region is located at the outermost side of the [Al/Zn-containing structure] when the plating layer is viewed in cross section, and forms the boundary with the [ternary eutectic structure of Al/Zn/MgZn _2] . There is. The second region is inside the first region, and the third region is further inside the second region.

The first region is a region where the Zn concentration is 75% by mass or more and less than 85% by mass, the second region is a region where the Zn concentration is 67% by mass or more and less than 75% by mass, and the third region is a region where the Zn concentration is The content is in the range of 55% by mass or more and less than 67% by mass. The remainder other than Zn is Al and impurities. Additionally, each region may contain a small amount of Mg. Furthermore, when the plating layer contains Si, Si may be contained in any or all of the first region, the second region, and the third region.

The second region contains a mixture of Zn phase and Al phase, and the average amount of Zn phase and Al phase per 1 μm ² of the cross section of the second region (cross section of the plating layer perpendicular to the surface of the plating layer) The particle size must be 50 nm or less. When the average grain size of the Zn phase and Al phase per 1 μm ² of cross-sectional area of the second region is larger than 50 nm, less corrosion products are generated due to corrosion in the second region, and the edges and processed parts of the steel material are corroded. Corrosion protection is no longer possible due to the product. By setting the precipitation form of the Zn phase and Al phase in the second region to an average particle size of 50 nm or less per ¹ μm area, the second region will be corroded preferentially, improving the corrosion resistance of the end face. It is presumed that. Note that the first region and the third region also contain a Zn phase and an Al phase, but the area of the cross section of the first region and the third region (the cross section of the plating layer perpendicular to the surface of the plating layer) is 1 μm ² The average particle diameters of the Zn phase and Al phase do not affect the end face corrosion resistance and the processed part corrosion resistance.

Further, in the Al phase included in the second region, an intermetallic compound phase containing Mg may exist as a precipitated phase. The presence of such a precipitated phase further improves the end face corrosion resistance and processed part corrosion resistance. The precipitated phase is one or more of MgZn ₂ , Mg ₂ Zn ₁₁ , Mg ₂ Si, and Mg ₃₂ (Al, Zn) ₄₉ . When three or more precipitated phases are contained on average per fine Al phase, the end face corrosion resistance and the processed part corrosion resistance are further improved.

A method for identifying the fine structure of [Al/Zn mixed structure] will be explained. The method for identifying the fine structure of the [Al/Zn mixed structure] utilizes the elemental mapping data of the photograph used to measure the area ratio of the [Al/Zn mixed structure]. First, the distribution of Zn concentration inside [Al/Zn mixed structure] is analyzed. When analyzing, an energy dispersive X-ray elemental analyzer attached to a scanning electron microscope (SEM) is used, and the acceleration voltage of the SEM is set to 15 kV. In this case, due to the escape depth of characteristic X-rays, the Zn concentration is substantially measured for each region of about 1 μm ² . By mapping this, component analysis using a mesh of approximately 1 μm becomes possible. Based on the Zn concentration (mass %) obtained from the component analysis results, the ranges of the first region, second region, and third region are determined.

Specifically, from the component analysis results, a region in which the Zn concentration is in the range of 75% by mass or more and less than 85% by mass is identified as the first region, and a region in which the Zn concentration is in the range of 67% by mass or more and less than 75% by mass is identified as the first region. The second region is defined as the second region, and the third region is defined as the third region where the Zn concentration ranges from 55% by mass to less than 67% by mass. Then, the cross-sectional area of each region is measured. The above measurements are performed on all [Al/Zn mixed structures] appearing in all the photographs.

Further, the average particle size of the Zn phase and Al phase per 1 μm ² of area in the second region is measured as follows. First, in the cross section of the plating layer (the cross section of the plating layer perpendicular to the surface of the plating layer) , an accelerating voltage of 2 kV was applied to the second region of the [Al/Zn mixed structure] identified by the above method using a scanning electron microscope. 50,000 times the backscattered electron images are taken at each of the five locations. Due to the compositional contrast, the Al phase is observed to be dark and the Zn phase to be observed to be bright. The obtained image is binarized using general-purpose image processing software (for example, Adobe Photoshop (registered trademark) manufactured by Adobe), and the areas of the white region and the black region are respectively measured. Also, measure the total number of white areas and black areas. Next, the area of each white area or black area is determined by dividing the total area of the white area and the black area by the total number of white areas and black areas. From this area, the equivalent circle diameter of the white region or the black region is determined, and this is taken as the average particle diameter of the Zn phase and the Al phase.

Moreover, the determination of whether or not an intermetallic compound phase containing Mg exists in the Al phase of the second region is performed by a three-dimensional atom probe method. First, a partially cut out plating layer is processed into a needle-shaped measurement sample with a tip diameter of 100 nm. The tip of the needle-shaped measurement sample is made to include a second region of [Al/Zn mixed structure]. Next, a positive voltage of about 10 kV at maximum is applied to the needle-shaped measurement sample to generate an electric field evaporation phenomenon at the leading edge of the measurement sample. The atomic arrangement is determined by detecting the field-evaporated ions using a two-dimensional detector. Ion species can also be identified from the flight time of atoms until they reach the detector. A three-dimensional atomic distribution is obtained by sequentially detecting the individually detected ions in this way in the depth direction and reconstructing the data by arranging the ions in the order in which they were detected. From the obtained atomic distribution, the presence or absence of any one of the intermetallic compound phases of MgZn ₂ , Mg ₂ Zn ₁₁ , Mg ₂ Si, and Mg ₃₂ (Al, Zn) ₄₉ is confirmed. Further, if an intermetallic compound phase is confirmed, the total number of intermetallic compound phases in one second region is counted. The total number of intermetallic compound phases is counted for the five measurement samples, and the average value is taken as the number of intermetallic compound phases.

Further, the hot-dip Zn-Al-Mg-based plated steel material of the present embodiment is formed by immersing the steel material in a plating bath and then pulling the steel material to solidify the molten metal deposited on the surface of the steel material. As described above, when the plating layer solidifies, the [Al/Zn mixed structure] is first crystallized, and then the matrix of the [ternary eutectic structure of Al/Zn/MgZn _2] is crystallized. The [Al/Zn mixed structure] that crystallizes first originates from the high-temperature Al'' phase in the ternary equilibrium phase diagram of Al-Zn-Mg, and this high-temperature Al'' phase finally It becomes [Al/Zn mixed structure] in the form. In the [Al/Zn mixed structure], first, a nucleation point generated in the molten metal serves as a starting point, a primary arm grows from the nucleation point, and a secondary arm is further generated from the primary arm. Therefore, the [Al/Zn mixed structure] has a dendrite-like structure starting from the nucleation point.

In the hot-dip Zn-Al-Mg-based plated steel material of this embodiment, when the plating layer is divided into two equal parts at the 1/2 position in the plating thickness direction into the steel material side and the plating layer surface side, the [Al -Zn mixed structure] It is preferable that 60% or more of the nucleation points in terms of number ratio exist in the region of the plating layer on the steel material side. As a result, among the constituent structures of the plating layer, [Al/Zn mixed structure], which is the initial starting point of corrosion, is present in large amounts in the region on the steel material side, and [Al/Zn mixed structure] in the region on the surface side of the plating layer becomes more abundant. The proportion of Zn mixed structure] decreases. This further improves the corrosion resistance of the processed portion of the plating layer.

In addition, since a large amount of [Al/Zn mixed structure] exists in the region on the steel side, the sacrificial corrosion protection of the steel material at the cut end surface when hot-dip Zn-Al-Mg coated steel material is cut at an arbitrary position can also be improved. You can expect it. Since the [Al/Zn mixed structure] is located near the steel material, the corrosion products generated by the corrosion of the [Al/Zn mixed structure] can immediately cover the steel material, causing damage over a wide range of the end face of the steel material. Corrosion resistance improves.

The method for measuring the distribution of nucleation points in [Al/Zn mixed structure] is as follows. First, the thickness of the plating layer is measured by observing the cross section of the plating layer. Next, on the surface of the plating layer, a square area of 1 mm on a side is defined as a measurement area. Next, the plating layer in the measurement area is gradually ground from the surface, and the newly appeared ground surface is observed using an electron microscope. Specifically, when the total thickness of the plating layer is t, t/4 position, t/2 position, and 3t/4 position are sequentially exposed in the depth direction from the surface of the plating layer by grinding, and on each ground surface, Each time, the morphology of the [Al/Zn mixed structure] is confirmed using an electron microscope. The depth of grinding is controlled by observing changes in the shape of the indentations made in advance.

The nucleation point in the [Al/Zn mixed structure] is the connection point between the primary arms of the [Al/Zn mixed structure]. On the ground surface relatively far from the nucleation point of [Al/Zn mixed structure], the primary arms appear to be arranged discretely, but on the ground surface relatively close to the nucleation point, there are four or six primary arms. The two primary arms appear to be close together. Therefore, when observing each ground surface, we can estimate whether the nucleation point is on the steel side of the ground surface being observed or on the surface side of the plating layer from the change in the shape of the primary arm on each ground surface. do. In this way, by checking the morphology of [Al/Zn mixed structure] on the ground surface at t/4 position, t/2 position, and 3t/4 position in the depth direction from the surface of the plating layer each time, the nucleus It can be confirmed whether the generation point is closer to the steel material than the t/2 position or closer to the surface of the plating layer. Then, among the total number of nucleation points of [Al/Zn mixed structure] observed in the measurement region, the ratio of nucleation points located on the steel material side with respect to the t/2 position is determined. The above method is carried out for a total of five measurement regions, and the average of the obtained values is taken as the percentage of nucleation points located on the steel material side from the t/2 position of the plating layer.

The amount of the plating layer deposited is preferably in the range of 10 to 300 g/m ² , and may be in the range of 20 to 250 g/m ² . If the amount of deposited plating layer is small, sufficient corrosion resistance cannot be ensured. Furthermore, if the amount of the plating layer adhered is too thick, there is a risk that the plating layer will crack during processing into a part shape or the like.

Next, a method for manufacturing the hot-dip Zn--Al--Mg based plated steel material of this embodiment will be explained. The hot-dip Zn-Al-Mg-based plated steel material of the present embodiment is formed by a so-called hot-dip plating method in which a plating bath is attached to the surface of the steel material, and then the steel material is pulled up from the plating bath to solidify the molten metal that has adhered to the surface of the steel material. .

The composition of the plating bath is preferably one containing Mg: 1 to 10% by mass, Al: 4 to 22% by mass, and the balance containing Zn and impurities. Further, the plating bath may contain Si: 0.0001 to 2% by mass. Furthermore, the plating bath may contain a total of 0.0001 to 2% by mass of any one or more of Ni, Ti, Zr, and Sr. Furthermore, the plating bath contains one or more of Fe, Sb, Pb, Sn, Ca, Co, Mn, P, B, Bi, Cr, Sc, Y, REM, and Hf in total, It may contain 0.0001 to 2% by mass.

The temperature of the plating bath is preferably in the range of 340 to 600°C, and may be in the range of 400 to 600°C.

It is preferable that the surface of the steel material before being immersed in the plating bath be subjected to reduction treatment by heating in a reducing atmosphere. For example, heat treatment is performed at 600° C. or higher, preferably 750° C. or higher for 30 seconds or longer in a mixed atmosphere of nitrogen and hydrogen. After the reduction treatment has been completed, the steel material is cooled to the temperature of the plating bath, and then immersed in the plating bath. The immersion time may be, for example, 1 second or more. When pulling up the steel material immersed in the plating bath, the amount of plating deposited is adjusted by gas wiping. As mentioned above, the adhesion amount is preferably in the range of 10 to 300 g/m ² , and may be in the range of 20 to 250 g/m ² .

In the method for manufacturing hot-dip Zn-Al-Mg-based plated steel according to this embodiment, the cooling conditions after pulling the steel out of the plating bath are important. After being removed from the plating bath, the plated layer is cooled at an average cooling rate of 3 to 6°C/sec until the surface temperature of the plated layer is in the range of 200°C to 250°C, and then rapidly cooled. The average cooling rate during rapid cooling is controlled to a range of 40° C./second or more. If the quenching start temperature is set higher than 250° C., the desired microstructure cannot be obtained. Furthermore, if the quenching start temperature is lower than 200° C., the structure of the [Al/Zn mixed structure] changes and the mixed form of the Al phase and Zn phase does not become the desired form, which is not preferable. The rapid cooling stop temperature shall be 100°C or less. Note that the average cooling rate during quenching is the value obtained by dividing the temperature difference from the quenching start temperature to the quenching stop temperature by the required quenching time.

By cooling the plating layer until its surface temperature falls within the range of 200°C to 250°C, the plating layer solidifies and the [Al/Zn mixed structure] and [ternary eutectic structure of Al/Zn/ _MgZn2 ] are formed. It is formed. Thereafter, by rapidly cooling at the above average cooling rate, the microstructure of the second region is controlled so that the average grain size of the Zn phase and Al phase per unit area in the second region is 50 μm or less. If the above cooling conditions are not met, it becomes difficult to control the average particle size of the Zn phase and Al phase per 1 μm ² of cross-sectional area of the second region within a preferable range.

Through the above steps, the hot-dip Zn--Al--Mg based plated steel material of this embodiment can be manufactured.
The hot-dip Zn-Al-Mg-based plated steel material of this embodiment can further improve the corrosion resistance at the edges and processed parts.

After degreasing SPCC (JIS G3141) with a plate thickness of 0.8 mm or 2.3 mm, heat reduction treatment was performed at 800°C in an N ₂ - H ₂ atmosphere using a hot-dip plating simulator manufactured by Toeisha, and after cooling to the plating bath temperature. , immersed in plating baths with various compositions corresponding to the average composition of the plating layer listed in Table 1, and then wiping with N ₂ to give a coating weight of 135 g/m ² on one side. The plating bath temperature was 450°C.

[Al/Zn mixed structure] was controlled by cooling control after plating. The plated steel plate is cooled at an average cooling rate of 3 to 6°C/sec until the surface temperature of the plating layer is in the range of 200 to 250°C, and after cooling is finished, the average cooling rate is 40°C/sec or more and 100°C or less. It was rapidly cooled until The means of rapid cooling was water cooling. In this way, plated steel sheets of Invention Examples 1 to 44 and Comparative Examples 1 to 6 were produced.

The average composition of the plating layer was measured by peeling off the plating layer and dissolving it, and then analyzing the content of elements contained in the plating layer using inductively coupled plasma emission spectrometry.

The area ratio of [Al/Zn mixed structure] in the plating layer can be determined using a backscattered electron image of a cross section of the plating layer (a cross section of the plating layer perpendicular to the surface of the plating layer) magnified 1000 times using a scanning electron microscope. Photographed at 5 locations. The photographs were taken so that the entire thickness of the plating layer could be seen. The photographic location was randomly selected. Furthermore, using an energy dispersive X-ray elemental analyzer attached to a scanning electron microscope, elemental mapping data corresponding to the photographed photograph was obtained, and [Al/Zn mixed structure] was identified. Then, by measuring the total cross-sectional area of the [Al/Zn mixed structure] appearing in all the cross-sectional photographs and dividing this by the cross-sectional area of the plating layer appearing in all the cross-sectional photographs, The area ratio of [Zn mixed structure] was measured.

The average Zn concentration in the first region, second region, and third region in [Al/Zn mixed structure] was measured as follows.
A cross section of the plating layer (a cross section of the plating layer parallel to the surface of the plating layer) was magnified 1000 times using a scanning electron microscope, and backscattered electron images were taken at five locations. The photographs were taken so that the entire thickness of the plating layer could be seen. The photographic location was randomly selected. Furthermore, using an energy dispersive X-ray elemental analyzer attached to a scanning electron microscope, elemental mapping data corresponding to the photographed photograph was obtained, and [Al/Zn mixed structure] was identified. The accelerating voltage of the SEM during acquisition of elemental mapping data was set to 15 kV. In this case, the Zn concentration is measured for each area of about 1 μm ² , making it possible to analyze the components with a mesh of about 1 μm. The ranges of the first region, second region, and third region were determined based on the Zn% obtained from the component analysis results of the elemental mapping data.

Specifically, a region in which the Zn concentration is in a range of 75% by mass or more and less than 85% by mass is specified as the first region, and a region in which the Zn concentration is in the range of 67% by mass or more and less than 75% by mass is specified as the second region. , the region in which the Zn concentration ranged from 55% by mass to less than 67% by mass was specified as the third region.

Furthermore, the average particle diameters of the Zn phase and Al phase per 1 μm ² of area in the second region were measured as follows. First, on the cross section of the plating layer, a backscattered electron image was taken at 50,000x magnification at 2kV acceleration voltage at 5 locations for the second region of [Al/Zn mixed structure] identified by the above method using a scanning electron microscope. did. Due to the compositional contrast, the Al phase is observed to be dark and the Zn phase to be observed to be bright. The obtained image was binarized using general-purpose image processing software (Adobe Photoshop (registered trademark) manufactured by Adobe), and the areas of the white region and the black region were measured. In addition, the total number of white areas and black areas was measured. Next, the area of each white area or black area was determined by dividing the total area of the white area and the black area by the total number of white areas and black areas. From this area, the equivalent circle diameter of the white region or the black region was determined, and this was taken as the average particle diameter of the Zn phase and Al phase per 1 μm ² of area in the second region.

Further, the determination as to whether or not an intermetallic compound phase containing Mg was present in the Al phase in the second region was performed using a three-dimensional atom probe method. First, a partially cut out plating layer was processed into a needle-shaped measurement sample with a tip diameter of 100 nm. The tip of the needle-shaped measurement sample included a second region of [Al/Zn mixed structure]. Next, a positive voltage of about 10 kV at maximum was applied to the needle-shaped measurement sample to generate an electric field evaporation phenomenon at the leading edge of the measurement sample. The atomic arrangement was determined by detecting the field-evaporated ions using a two-dimensional detector. In addition, the ion species were identified from the flight time of the atoms until they reached the detector. A three-dimensional atomic distribution was obtained by sequentially detecting the individually detected ions in this way in the depth direction and reconstructing the data by arranging the ions in the order in which they were detected. The presence or absence of an intermetallic compound phase was confirmed from the obtained atomic distribution. In addition, when an intermetallic compound phase was confirmed, the total number of intermetallic compound phases in one second region was counted. The total number of intermetallic compound phases was counted for the five measurement samples, and the average value was taken as the number of intermetallic compound phases. FIGS. 2A and 2B show examples of the results of the three-dimensional atom probe method (3D-AP analysis) of the Al phase. According to this measurement method, it is possible to detect that an intermetallic compound is contained in the measurement sample.

The method for measuring the distribution of nucleation points in [Al/Zn mixed structure] was as follows. First, the thickness of the plating layer was measured by observing the cross section of the plating layer. Subsequently, on the surface of the plating layer, a square area with one side of 1 mm was set as a measurement area. Next, the plating layer in the measurement area was gradually ground from the surface, and the newly appeared ground surface was observed using an electron microscope. Specifically, when the total thickness of the plating layer is t, the ground surfaces are sequentially exposed at t/4 position, t/2 position, and 3t/4 position in the depth direction from the surface of the plating layer, and each ground surface is In each case, the morphology of the [Al/Zn mixed structure] was confirmed using an electron microscope. The depth of grinding was controlled by observing changes in the shape of the indentations made in advance.

The nucleation point in the [Al/Zn mixed structure] is the connection point between the primary arms of the [Al/Zn mixed structure]. On the ground surface relatively far from the nucleation point of [Al/Zn mixed structure], the primary arms appear to be arranged discretely, but on the ground surface relatively close to the nucleation point, there are four or six primary arms. The two primary arms appear to be close together. Therefore, when observing each ground surface, we can estimate whether the nucleation point is on the steel side of the ground surface being observed or on the surface side of the plating layer from the change in the shape of the primary arm on each ground surface. did. In this way, by checking the morphology of [Al/Zn mixed structure] on the ground surface at t/4 position, t/2 position, and 3t/4 position in the depth direction from the surface of the plating layer each time, the nucleus It was confirmed whether the generation point was closer to the steel material than the t/2 position or closer to the surface of the plating layer. Then, among the total number of nucleation points of [Al/Zn mixed structure] observed in the measurement region, the ratio of nucleation points located on the steel material side from the t/2 position was determined. The above method was carried out for a total of five measurement regions, and the average of the obtained values was taken as the percentage of nucleation points located on the steel material side from the t/2 position of the plating layer.

Table 2 has a column for the position of the nucleation point of [Al/Zn mixed structure], and the plating layer is divided into two parts at 1/2 position in the plating thickness direction into the steel material side and the plating layer surface side. In this case, if 60% or more of the nucleation points in the [Al/Zn mixed structure] are present in the area on the steel side of the plating layer, it is marked as ○, otherwise it is marked as × And so.

(Edge corrosion resistance (edge corrosion resistance))
A plated steel plate obtained using a plate with a plate thickness of 2.3 mm was cut into 100 mm x 50 mm and subjected to an end face corrosion resistance test. The end face corrosion resistance was evaluated by an outdoor exposure test (in a place where the chloride ion concentration in the environment is 100 ppm or less), and the end face red rust area ratio was evaluated after 3 days. The evaluation criteria were as follows, and ◎, ○, and △ were regarded as passing.

◎: Red rust area ratio 0% or more and less than 20% ○: Red rust area ratio 20% or more and less than 30% △: Red rust area ratio 30% or more and less than 40% ×: Red rust area ratio 40% or more and less than 100%

(Corrosion resistance of processed parts)
A plated steel plate obtained by using a plate with a thickness of 0.8 mm was cut into 30×60 mm, and after 2T bending, the processed portion was subjected to corrosion resistance. The corrosion resistance of processed parts was evaluated by CCT test (salt spray (0.5% NaCl, 35°C) for 6 hours → drying (50°C, 45% RH) for 3 hours → wet (50°C, 95% RH) for 14 hours → drying. (50° C., 45% RH) for 1 hour) and evaluated by the number of cycles in which red rust appeared on the top of the head. The evaluation criteria were as follows, and ◎, ○, and △ were regarded as passing.

◎: Number of cycles where red rust occurs: 100 cycles or more ○: Number of cycles where red rust occurs: 80 or more but less than 100 cycles △: Number of cycles where red rust occurs: 60 or more but less than 80 cycles ×: Number of cycles where red rust occurs: 60 cycles or less

FIG. 1A shows a backscattered electron image photograph of a cross section of the plating layer of Comparative Example 5 observed in the backscattered electron mode of a scanning electron microscope, and FIG. 1B shows a backscattered electron image photograph of Invention Example 1. All contained [Al/Zn mixed structure] in the matrix of [ternary eutectic structure of Al/Zn/MgZn _2] .
Similarly, invention example No. 2 to 44, Comparative Example No. Plating layers 1 to 4 and 6 included [Al/Zn mixed structure] in the base of [ternary eutectic structure of Al/Zn/MgZn _2] .
As shown in Tables 1 and 2, invention example No. All of the hot-dip Zn-Al-Mg-based plated steel sheets of Nos. 1 to 44 satisfy the scope of the present invention, and have good end face corrosion resistance and processed part corrosion resistance. In addition, as shown in Table 2, hot-dip Zn-Al-Mg coated steel materials for which the position of the nucleation point of [Al/Zn mixed structure] was evaluated as "○" have better end face corrosion resistance and processed part corrosion resistance. ing.

On the other hand, comparative example No. The hot-dip Zn-Al-Mg-based plated steel material No. 1 has a low Al content in the plating layer, a low area ratio of the [Al/Zn mixed structure] in the plating layer, and a large number of particles in the [Al/Zn mixed structure]. Two areas were not included. For this reason, the end face corrosion resistance and processed part corrosion resistance were inferior.
Comparative example no. In the hot-dip Zn-Al-Mg-based plated steel material No. 2, the Al content in the plated layer is excessive, and the area ratio of [Al/Zn mixed structure] in the plated layer becomes high, resulting in inferior end face corrosion resistance and processed part corrosion resistance. became.
Comparative example no. Since the hot-dip Zn-Al-Mg-based plated steel material of No. 3 did not contain Mg in the plating layer, the end face corrosion resistance and processed part corrosion resistance were inferior.
Comparative example no. In the hot-dip Zn-Al-Mg-based plated steel material of No. 4, the end face corrosion resistance and processed part corrosion resistance were inferior because the Mg content in the plating layer was excessive.
Comparative example no. Since the hot-dip Zn-Al-Mg-based plated steel material of No. 5 was rapidly cooled outside the range of 200°C to 250°C, the Zn phase and Al phase per 1 μm ² of the cross-sectional area of the second region in the [Al/Zn mixed structure] The average particle size of the steel was out of the invention range, and the end face corrosion resistance and processed part corrosion resistance were inferior.
Comparative example no. Since the hot-dip Zn-Al-Mg-based plated steel material No. 6 was rapidly cooled at a cooling rate of less than 40°C/s, the Zn phase and Al phase per 1 μm ² of the cross-sectional area of the second region in the [Al/Zn mixed structure] The average particle size of the steel was out of the invention range, and the end face corrosion resistance and processed part corrosion resistance were inferior.

Claims (10)

comprising a steel material and a plating layer formed on the surface of the steel material,
The plating layer has an average composition of Mg: 1 to 10% by mass, Al: 4 to 22% by mass, and the remainder consists of Zn and impurities,
The plating layer contains [Al/Zn mixed structure] in the base of [ternary eutectic structure of Al/Zn/MgZn _2] ,
The [Al/Zn mixed structure] includes a first region where the Zn concentration is in the range of 75% by mass or more and less than 85% by mass, and a region inside the first region where the Zn concentration is in the range of 67% by mass or more and 75% by mass. and a second region in a range of less than %,
In the second region, an Al phase and a Zn phase are mixed, and the average particle size of the Al phase and the Zn phase in a cross section of the plating layer perpendicular to the surface of the plating layer is 50 nm or less. A hot-dip Zn-Al-Mg based plated steel material. The hot-dip Zn--Al--Mg based plated steel material according to claim 1, wherein the Al phase in the second region includes an intermetallic compound phase containing Mg. Claim ₂ , wherein the Mg-containing intermetallic compound phase is one or more of _MgZn2 , _Mg2Zn11 , _Mg2Si , _Mg32 (Al, Zn) ₄₉ . The hot-dip Zn-Al-Mg-based plated steel material described in . The hot-dip Zn-Al-Mg-based plated steel material according to claim 2 or 3, wherein the number of the Mg-containing intermetallic compound phases contained in the Al phase is three or more. Any one of claims 1 to 4, wherein the area ratio of the [Al/Zn mixed structure] in a cross section of the plating layer perpendicular to the surface of the plating layer is in the range of 10 to 70%. The hot-dip Zn-Al-Mg-based plated steel material described in 2. The average composition of the plating layer contains Mg: 1 to 10% by mass, Al: 8 to 22% by mass, and the remainder is Zn and impurities,
The [Al/Zn mixed structure] includes the first region, the second region, and a third region located inside the second region and having a Zn concentration in a range of 55% by mass or more and less than 67% by mass. The hot-dip Zn-Al-Mg based plated steel material according to any one of claims 1 to 5, characterized by comprising a region. When the plating layer is divided into two equal parts at the 1/2 position in the plating thickness direction into the steel material side and the plating layer surface side, the number ratio of the nucleation points of the [Al/Zn mixed structure] The hot-dip Zn-Al-Mg-based plated steel material according to any one of claims 1 to 6, wherein 60% or more of nucleation points are present in a region on the steel material side of the plating layer. . The molten Zn-Al-Mg based plating according to any one of claims 1 to 7, wherein the plating layer further contains Si in an average composition of 0.0001 to 2% by mass. Steel material. The plating layer further contains one or more of Ni, Ti, Zr, and Sr in an average composition in a total amount of 0.0001 to 2% by mass. The hot-dip Zn-Al-Mg-based plated steel material according to claim 8. The plating layer further contains one or more of Sb, Pb, Sn, Ca, Co, Mn, P, B, Bi, Cr, Sc, Y, REM, and Hf in average composition, The hot-dip Zn-Al-Mg-based plated steel material according to any one of claims 1 to 9, characterized in that the content is in the range of 0.0001 to 2% by mass.