Title of invention: Plated steel material
Technical field
[0001]
　The present disclosure relates to plated steel materials.
Background technology
[0002]
　For example, in the field of building materials, a wide variety of plated steel materials are used. Most of them are Zn-plated steel materials. Due to the need for longer life of building materials, research on high corrosion resistance of Zn-plated steel materials has been conducted for a long time, and various plated steel materials have been developed. The first highly corrosion-resistant plated steel material for building materials is a Zn-5% Al-plated steel material (galvanized steel material) in which Al is added to the Zn-based plating layer to improve corrosion resistance. It is a well-known fact that Al is added to the plating layer to improve the corrosion resistance, and when 5% Al is added, Al crystals are formed in the plating layer (specifically, the Zn phase) to improve the corrosion resistance. The Zn-55% Al-1.6% Si plated steel material (galvanized steel material) is also basically a plated steel material having improved corrosion resistance for the same reason.
　Therefore, when the Al concentration is improved, the corrosion resistance of the flat surface portion is basically improved. However, the improvement of Al concentration causes a decrease in sacrificial anticorrosion ability.
[0003]
　Here, the attractiveness of the Zn-based plated steel material is the sacrificial anticorrosion effect on the base steel material. That is, in the cut end face portion of the plated steel material, the cracked portion of the plating layer during processing, and the exposed portion of the base steel material that appears due to peeling of the plating layer, the surrounding plating layer is eluted before the base steel material is corroded to protect the plating elution component. Form a film. This makes it possible to prevent red rust from the base steel material to some extent.
[0004]
　In general, it is preferable that the Al concentration is low and the Zn concentration is high for this action. Therefore, a highly corrosion-resistant galvanized steel material in which the Al concentration is suppressed to a relatively low concentration of about 5% to 25% has been put into practical use in recent years. In particular, the plated steel material containing low Al concentration and containing about 1 to 3% Mg has more excellent flat surface corrosion resistance and sacrificial corrosion resistance than the galfan plated steel material. Therefore, it has become a market trend as a plated steel material and is now widely known in the market.
[0005]
　As a plated steel material containing a certain amount of Al and Mg, for example, a plated steel material disclosed in Patent Document 1 has also been developed.
[0006]
　Specifically, Patent Document 1 comprises Al: 5 to 18% by mass, Mg: 1 to 10% by mass, Si: 0.01 to 2% by mass, the balance Zn, and unavoidable impurities on the surface of the steel material. A molten Zn-Al-Mg-Si plated steel material in which 200 or more Al phases are present per 1 mm 2 on the surface of the plated steel material having a plating layer is disclosed.
Prior art literature
Patent documents
[0007]
Patent Document 1: Japanese Patent Application Laid-Open No. 2001-35553
Outline of the invention
Problems to be solved by the invention
[0008]
　However, in the plated steel material containing a certain amount of Al concentration, the corrosion of the plating layer (specifically, the Zn—Al—Mg alloy layer) progresses locally, and there is a high tendency to reach the base steel material at an early stage. As a result, the corrosion resistance of the flat surface portion may deteriorate, and the variation in the corrosion resistance of the flat surface portion may increase. Therefore, the current situation is that a plated steel material having stable and high flat surface corrosion resistance is required.
[0009]
　Therefore, an object of one aspect of the present disclosure is to provide a plated steel material having stable and high flat surface corrosion resistance.
Means to solve problems
[0010]
　The above problem is solved by the following means. That is,
[0011]
<1>
　A plated steel material having a base steel material and a plating layer containing a Zn—Al—Mg alloy layer arranged on the surface of the base steel material,
　wherein the plating layer is in mass%,
　Zn: 65. More than 0%,
　Al: more than 5.0% to less than 25.0%,
　Mg: more than 3.0% to less than 12.5%,
　Sn: 0.1% to 20.0%,
　Bi: 0% to 5 .0% or less,
　In: 0% to less than 2.0%,
　Ca: 0% to 3.00%,
　Y: 0% to 0.5%,
　La: 0% to less than 0.5%,
　Ce: 0 % To less than 0.5%,
　Si: 0% to less than 2.5%,
　Cr: 0% to less than 0.25%,
　Ti: 0% to less than 0.25%,
　Ni: 0% to 0.25% Less than,
　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% ~ 0.25%,
　Fe: 0% ~ 5.0%,
　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
　a chemical composition consisting of impurities.
　The reflection of the Zn—Al—Mg alloy layer obtained when the surface of the Zn—Al—Mg alloy layer is polished to 1/2 of the layer thickness and then observed with a scanning electron microscope at a magnification of 100 times. A plated steel material in which Al crystals are present in the electron image and the average value of the cumulative peripheral lengths of the Al crystals is 88 to 195 mm / mm 2 .
<2> The
　plated steel material according to <1>, wherein the plating layer has an Al—Fe alloy layer having a thickness of 0.05 to 5 μm between the base steel material and the Zn—Al—Mg alloy layer.
Effect of the invention
[0012]
　According to one aspect of the present disclosure, it is possible to provide a plated steel material having stable and high flat surface corrosion resistance.
A brief description of the drawing
[0013]
FIG. 1 is an SEM reflected electron image (magnification 100 times) showing an example of the Zn—Al—Mg alloy layer of the plated steel material of the present disclosure.
FIG. 2 is an SEM reflected electron image (magnification: 500 times) showing an example of the Zn—Al—Mg alloy layer of the plated steel material of the present disclosure.
FIG. 3 is an SEM reflected electron image (magnification of 10000 times) showing an example of the Zn—Al—Mg alloy layer of the plated steel material of the present disclosure.
FIG. 4 is a diagram showing an example of an image processed (binarized) so that Al crystals can identify the reflected electron image (reflected electron image of SEM) of the Zn—Al—Mg alloy layer of the plated steel material of the present disclosure. Is.
Mode for carrying out the invention
[0014]
　Hereinafter, an example of the present disclosure will be described.
　In the present disclosure, the "%" indication of the content of each element in the chemical composition means "mass%".
　The numerical range represented by using "-" means a range including the numerical values ​​before and after "-" as the lower limit value and the upper limit value.
　The numerical range when "greater than" or "less than" is added to the numerical values ​​before and after "to" means a range in which these numerical values ​​are not included as the lower limit value or the upper limit value.
　The content of an element in the chemical composition may be expressed as an element concentration (for example, Zn concentration, Mg concentration, etc.).
　The term "process" is included in this term not only as an independent process but also as long as the intended purpose of the process is achieved even if it cannot be clearly distinguished from other processes.
　The “plane portion corrosion resistance” indicates the property that the plating layer (specifically, the Zn—Al—Mg alloy layer) itself is not easily corroded.
　"Sacrificial corrosion resistance" means corrosion of the base steel material at the exposed part of the base steel material (for example, the cut end face part of the plated steel material, the cracked part of the plating layer during processing, and the part where the base steel material is exposed due to the peeling of the plating layer). Shows the property of suppressing.
[0015]
　The plated steel material of the present disclosure is a plated steel material having a base steel material and a plating layer arranged on the surface of the base steel material and containing a Zn—Al—Mg alloy layer.
　Then, in the plated steel material of the present disclosure, the plating layer has a predetermined chemical composition, the surface of the Zn—Al—Mg alloy layer is polished to 1/2 of the layer thickness, and then the magnification is 100 times by a scanning electron microscope. In the backscattered electron image of the Zn—Al—Mg alloy layer obtained when observed, Al crystals are present, and the average value of the cumulative peripheral lengths of the Al crystals is 88 to 195 mm / mm 2 .
[0016]
　The plated steel material of the present disclosure is a plated steel material having stable and high flat surface corrosion resistance due to the above configuration. The plated steel material of the present disclosure was found based on the following findings.
[0017]
　The inventors analyzed the initial corrosion behavior of the plating layer containing the Zn—Al—Mg alloy layer. As a result, it was found that the corrosion of the plating layer (specifically, the Zn—Al—Mg alloy layer) proceeded locally like an ant's nest, and the periphery of the Al crystal was preferentially corroded.
　This is estimated as follows. Potential difference corrosion occurs between the Al crystal with a relatively high potential and the surrounding tissue with a low potential. Therefore, the larger the contact area between the Al crystal and the phase around the Al crystal, the more easily corrosion around the Al crystal occurs, the worse the corrosion resistance of the flat surface portion, and the larger the variation of the corrosion resistance of the flat surface portion.
[0018]
　Therefore, in order to reduce the contact area between the Al crystal and the phase around the Al crystal as much as possible, the inventors control the cooling conditions after immersion in the plating bath during the production of the plating layer to coarsely precipitate the Al crystal. I came up with that.
　As a result, we found the following. As an index of the size of Al crystals, the cumulative peripheral length of Al crystals by image analysis and the corrosion resistance of the flat surface are well correlated. When the average value of the cumulative peripheral lengths of the Al crystals is set within a predetermined range, the contact area between the Al crystals and the surrounding phases of the Al crystals is reduced. As a result, corrosion around the preferential Al crystal is suppressed, and stable flat surface corrosion resistance can be obtained. However, if the average value of the cumulative peripheral lengths of Al crystals is excessively lowered, the workability is lowered.
[0019]
　From the above, it has been found that the plated steel material of the present disclosure is a plated steel material having stable and high flat surface corrosion resistance.
[0020]
　Hereinafter, the details of the plated steel material of the present disclosure will be described.
[0021]
　The base steel material to be plated will be described.
　There are no particular restrictions on the shape of the base steel material. In addition to steel plates, the base steel material includes steel pipes, civil engineering and building materials (fences, corrugated pipes, drainage ditches, sand-prevention plates, bolts, wire mesh, guard rails, and waterproof walls. Etc.), home appliances (such as the housing of the outdoor unit of an air conditioner), automobile parts (such as undercarriage members), and other molded base steel materials. For the molding process, various plastic working methods such as press working, roll forming, and bending can be used.
[0022]
　There are no particular restrictions on the material of the base steel material. Base steel materials include, for example, general steel, preplated steel, Al killed steel, ultra-low carbon steel, high carbon steel, various high tension steels, and some high alloy steels (steel containing reinforced elements such as Ni and Cr). Various base steel materials are applicable.
　The base steel material is not particularly limited in terms of conditions such as a method for manufacturing the base steel material and a method for manufacturing the base steel sheet (hot rolling method, pickling method, cold rolling method, etc.).
　As the base steel material, a hot-rolled steel plate, a hot-rolled steel strip, a cold-rolled steel plate, and a cold-rolled steel strip described in JIS G 3302 (2010) can also be applied.
[0023]
　The base steel material may be a pre-plated pre-plated steel material. The pre-plated steel material is obtained, for example, by an electrolytic treatment method or a substitution plating method. In the electrolytic treatment method, a pre-plated steel material is obtained by immersing the base steel material in a sulfuric acid bath or a chloride bath containing metal ions of various pre-plating components and performing an electrolytic treatment. In the replacement plating method, a pre-plated steel material is obtained by immersing the base steel material in an aqueous solution containing metal ions of various pre-plating components and adjusting the pH with sulfuric acid to replace and precipitate the metal.
　As a typical example of the pre-plated steel material, Ni pre-plated steel material can be mentioned.
[0024]
　Next, the plating layer will be described.
　The plating layer includes a Zn—Al—Mg alloy layer. The plating layer may include an Al—Fe alloy layer in addition to the Zn—Al—Mg alloy layer. The Al—Fe alloy layer is provided between the base steel material and the Zn—Al—Mg alloy layer.
[0025]
　That is, the plating layer may have a single-layer structure of a Zn—Al—Mg alloy layer, or may have 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 may be a layer constituting the surface of the plating layer.
　However, although the oxide film of the plating layer constituent element is formed on the surface of the plating layer at about 50 nm, it is considered that the thickness is thin with respect to the thickness of the entire plating layer and does not constitute the main body of the plating layer.
[0026]
　Here, the thickness of the Zn—Al—Mg alloy layer is, for example, 2 μm or more and 95 μm or less (preferably 5 μm or more and 75 μm or less).
[0027]
　On the other hand, the thickness of the entire plating layer is, for example, about 100 μm or less. Since the thickness of the entire plating layer depends on the plating conditions, the upper and lower limits of the thickness of the entire plating layer are not particularly limited. For example, the thickness of the entire plating layer is related to the viscosity and specific gravity of the plating bath in the usual hot-dip galvanizing method. Furthermore, the plating amount is adjusted by the drawing speed of the base steel material and the strength of wiping. Therefore, it can be considered that the lower limit of the thickness of the entire plating layer is about 2 μm.
　On the other hand, due to the weight and uniformity of the plated metal, the upper limit of the thickness of the plating layer that can be produced by the hot-dip galvanizing method is about 95 μm.
　Since the thickness of the plating layer can be freely changed depending on the drawing speed from the plating bath and the wiping conditions, the formation of a plating layer having a thickness of 2 to 95 μm is not particularly difficult to manufacture.
[0028]
　Next, the Al—Fe alloy layer will be described.
[0029]
　The Al—Fe alloy layer is formed on the surface of the base steel material (specifically, between the base steel material and the Zn—Al—Mg alloy layer), and the Al 5 Fe phase is the main phase layer as a structure. The Al—Fe alloy layer is formed by mutual atomic diffusion between the base steel material and the plating bath. When the hot-dip galvanizing method is used as the manufacturing method, the Al—Fe alloy layer is likely to be formed in the plating layer containing the Al element. Since Al is contained in the plating bath at a certain concentration or higher, the Al 5 Fe phase is formed in the largest amount. However, atomic diffusion takes time, and there is a portion where the Fe concentration becomes high in a portion close to the base steel material. Therefore, the Al—Fe alloy layer may partially contain a small amount of AlFe phase, Al 3 Fe phase, Al 5 Fe 2 phase, and the like. Further, since Zn is also contained in the plating bath at a constant concentration, a small amount of Zn is also contained in the Al—Fe alloy layer.
[0030]
　In terms of corrosion resistance, there is no significant difference in any of the Al 5 Fe phase, Al 3 Fe phase, Al Fe phase, and Al 5 Fe 2 phase. The corrosion resistance referred to here is the corrosion resistance in a portion that is not affected by welding.
[0031]
　Here, when Si is contained in the plating layer, Si is particularly easily incorporated into the Al—Fe alloy layer and may become an Al—Fe—Si intermetallic compound phase. The intermetallic compound phase to be identified includes the AlFeSi phase, and the isomers include α, β, q1, q2-AlFeSi phase and the like. Therefore, these AlFeSi phases and the like may be detected in the Al—Fe alloy layer. The Al—Fe alloy layer containing these AlFeSi phases and the like is also referred to as an Al—Fe—Si alloy layer.
　Since the thickness of the Al—Fe—Si alloy layer is smaller than that of the Zn—Al—Mg alloy layer, the effect on the corrosion resistance of the entire plating layer is small.
[0032]
　Further, when various pre-plated steel materials are used as the base steel material (base steel plate or the like), the structure of the Al—Fe alloy layer may change depending on the amount of pre-plating adhered. Specifically, when the pure metal layer used for pre-plating remains around the Al—Fe alloy layer, an intermetal compound phase in which the constituent components of the Zn—Al—Mg alloy layer and the pre-plating component are bonded (for example, When Al 3 Ni phase, etc.) forms an alloy layer, when an Al—Fe alloy layer in which a part of Al atom and Fe atom is substituted is formed, or when a part of Al atom, Fe atom and Si atom is substituted. In some cases, an Al—Fe—Si alloy layer may be formed. In any case, since these alloy layers are also smaller in thickness than the Zn—Al—Mg alloy layer, they have a small effect on the corrosion resistance of the entire plating layer.
[0033]
　That is, the Al—Fe alloy layer is a layer that includes the alloy layers of the various aspects described above in addition to the alloy layer mainly composed of the Al 5 Fe phase.
[0034]
　Of the various pre-plated steel materials, when the plating layer is formed on the Ni pre-plated steel material, the Al—Ni—Fe alloy layer is formed as the Al—Fe alloy layer. Since the thickness of the Al—Ni—Fe alloy layer is smaller than that of the Zn—Al—Mg alloy layer, the effect on the corrosion resistance of the entire plating layer is small.
[0035]
　The thickness of the Al—Fe alloy layer is, for example, 0 μm or more and 5 μm or less.
　That is, the Al—Fe alloy layer does not have to be formed. The thickness of the Al—Fe alloy layer is preferably 0.05 μm or more and 5 μm or less from the viewpoint of enhancing the adhesion of the plating layer (specifically, the Zn—Al—Mg alloy layer) and ensuring workability.
[0036]
　However, usually, when a plating layer having a chemical composition specified in the present disclosure is formed by a hot-dip galvanizing method, an Al—Fe alloy layer having a diameter of 100 nm or more may be formed between the base steel material and the Zn—Al—Mg alloy layer. There are many. The lower limit of the thickness of the Al—Fe alloy layer is not particularly limited, and it has been found that the Al—Fe alloy layer is inevitably formed when the hot-dip galvanized layer containing Al is formed. .. From experience, it is empirically determined that around 100 nm is the thickness when the formation of the Al—Fe alloy layer is suppressed most, and is the thickness that sufficiently secures the adhesion between the plating layer and the base steel material. Since the Al concentration is high unless special measures are taken, it is difficult to form an Al—Fe alloy layer thinner than 100 nm by the hot-dip galvanizing method. However, even if the thickness of the Al—Fe alloy layer is less than 100 nm, and even if the Al—Fe alloy layer is not formed, it is presumed that the plating performance is not significantly affected.
[0037]
　On the other hand, when the thickness of the Al—Fe alloy layer exceeds 5 μm, the Al component of the Zn—Al—Mg alloy layer formed on the Al—Fe alloy layer is insufficient, and further, the adhesion and workability of the plating layer are insufficient. Tends to be extremely worse. Therefore, the thickness of the Al—Fe alloy layer is preferably limited to 5 μm or less.
　The Al—Fe alloy layer is also closely related to the Al concentration and the Sn concentration, and generally, the higher the Al concentration and the Sn concentration, the faster the growth rate tends to be.
[0038]
　Since the Al—Fe alloy layer often contains an Al 5 Fe phase, the chemical composition of the Al—Fe alloy layer is Fe: 25 to 35%, Al: 65 to 75%, Zn: 5% or less. And the balance: a composition containing impurities can be exemplified.
[0039]
　Since the thickness of the Zn—Al—Mg alloy layer is usually thicker than that of the Al—Fe alloy layer, the contribution of the Al—Fe alloy layer to the corrosion resistance of the flat surface portion of the plated steel material is Zn—. It is smaller than the Al—Mg alloy layer. However, the Al—Fe alloy layer contains Al and Zn, which are corrosion resistant elements, at a certain concentration or more, as can be inferred from the component analysis results. Therefore, the Al—Fe alloy layer has a sacrificial anticorrosion ability and a corrosion barrier effect on the base steel material to some extent.
[0040]
　Here, it is difficult to confirm the single corrosion resistance contribution of the thin Al—Fe alloy layer by quantitative measurement. However, for example, when the Al—Fe alloy layer has a sufficient thickness, the Zn—Al—Mg alloy layer on the Al—Fe alloy layer is precisely removed by cutting from the surface of the plating layer by end milling or the like to perform a corrosion test. By applying, the corrosion resistance of the Al—Fe alloy layer alone can be evaluated. Since the Al—Fe alloy layer contains an Al component and a small amount of Zn component, when the Al—Fe alloy layer is provided, red rust is generated in dots, the Al—Fe alloy layer is not provided, and the base steel material is exposed. As in the case, the entire surface does not become red rust.
[0041]
　In addition, during the corrosion test, when the cross-sectional observation of the plating layer up to just before the occurrence of red rust on the base steel material was carried out, only the Al—Fe alloy layer remained even if the upper Zn—Al—Mg alloy layer was eluted and rusted. , It can be confirmed that the base steel is corroded. This is because the Al—Fe alloy layer is electrochemically more noble than the Zn—Al—Mg layer, but is located lower than the base steel material. From these facts, it can be determined that the Al—Fe alloy layer also has a certain degree of corrosion resistance.
[0042]
　From the viewpoint of corrosion, the thicker the Al—Fe alloy layer, the more preferably it has the effect of delaying the red rust generation time. However, since a thick Al—Fe alloy layer causes a significant deterioration in plating processability, the thickness is preferably a certain thickness or less. From the viewpoint of workability, the thickness of the Al—Fe alloy layer is preferably 5 μm or less. When the thickness of the Al—Fe alloy layer is 5 μm or less, the amount of cracks and powdering generated starting from the plated Al—Fe alloy layer is reduced by a V-bending test or the like. The thickness of the Al—Fe alloy layer is more preferably 2 μm or less.
[0043]
　Next, the chemical composition of the plating layer will be described.
　The component composition of the Zn—Al—Mg alloy layer contained in the plating layer is substantially maintained even in the Zn—Al—Mg alloy layer in which the component composition ratio of the plating bath is maintained. Since the reaction of forming the Al—Fe alloy layer in the hot-dip plating method is completed in the plating bath, the Al component and Zn component of the Zn—Al—Mg alloy layer are usually reduced by forming the Al—Fe alloy layer. It is a little.
[0044]
　The chemical composition of the plating layer is as follows in order to realize stable corrosion resistance of the flat surface portion.
[0045]
　That is, the chemical composition of the plating layer is
　Zn: more than 65.0%,
　Al: more than 5.0% to less than 25.0%,
　Mg: more than 3.0% to less than 12.5%,
　Sn in mass%. : 0.1% to 20.0%,
　Bi: 0% to less than 5.0%,
　In: 0% to less than 2.0%,
　Ca: 0% to 3.00%,
　Y: 0% to 0. 5%,
　La: 0% to less than 0.5%,
　Ce: 0% to less than 0.5%,
　Si: 0% to less than 2.5%,
　Cr: 0% to less than 0.25%,
　Ti: 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% Less than,
　Cu: 0% to less than 0.25%,
　Mn: 0% to less than 0.25%,
　Fe: 0% to 5.0%,
　Sr: 0% to less than 0.5%,
　Sb: 0% to Less than 0.5%,
　Pb: 0% to less than 0.5%,
　B: A
　chemical composition consisting of 0% to less than 0.5% and impurities.
[0046]
　In the chemical composition of the plating layer, Bi, In, Ca, Y, La, Ce, Si, Cr, Ti, Ni, Co, V, Nb, Cu, Mn, Fe, Sr, Sb, Pb, and B are arbitrary. It is an ingredient. That is, 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 in the range described later.
[0047]
　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 a Zn—Al—Mg alloy layer, the average chemical composition of the Zn—Al—Mg alloy layer, the plating layer. Is the total average chemical composition of the Al—Fe alloy layer and the Zn—Al—Mg alloy layer in the case of the laminated structure of the Al—Fe alloy layer and the Zn—Al—Mg alloy layer).
[0048]
　Usually, in the hot-dip galvanizing method, the chemical composition of the Zn—Al—Mg alloy layer is almost the same as the chemical composition of the plating bath because the formation reaction of the plating layer is almost completed in the plating bath. Further, in the hot-dip galvanizing method, the Al—Fe alloy layer is instantly formed and grown immediately after being immersed in the plating bath. The formation reaction of the Al—Fe alloy layer is completed in the plating bath, and the thickness thereof is often sufficiently smaller than that of the Zn—Al—Mg alloy layer.
　Therefore, unless special heat treatment such as heat alloying treatment is performed after plating, the average chemical composition of the entire plating layer is substantially equal to the chemical composition of the Zn—Al—Mg alloy layer, and the Al—Fe alloy layer Ingredients can be ignored.
[0049]
　Hereinafter, each element of the plating layer will be described.
[0050]

　Zn is an element necessary for obtaining sacrificial corrosion resistance in addition to corrosion resistance on a flat surface. Considering the atomic composition ratio, the Zn concentration is a plating layer composed of elements having a low specific gravity such as Al and Mg, so that the atomic composition ratio also needs to be mainly Zn.
　Therefore, the Zn concentration is set to more than 65.0%. The Zn concentration is preferably 70% or more. The upper limit of the Zn concentration is the concentration of elements other than Zn and the balance other than impurities.
[0051]

　Al is an essential element for forming Al crystals and ensuring both corrosion resistance on a flat surface and sacrificial corrosion resistance. Al is an essential element for enhancing the adhesion of the plating layer and ensuring processability. Therefore, the lower limit of the Al concentration is set to exceed 5.0% (preferably 10.0% or more).
　On the other hand, when the Al concentration increases, the sacrificial anticorrosion property tends to deteriorate. Therefore, the upper limit of the Al concentration is set to less than 25.0% (preferably 23.0% or less).
[0052]

　Mg is an essential element for ensuring both corrosion resistance and sacrificial corrosion resistance of flat surfaces. Therefore, the lower limit of the Mg concentration is set to exceed 3.0% (preferably over 5.0%).
　On the other hand, as the Mg concentration increases, the workability tends to deteriorate. Therefore, it is set to less than 12.5% ​​(preferably 10.0% or less).
[0053]

　Sn is an essential element that imparts high sacrificial anticorrosion properties. Therefore, the lower limit of the Sn concentration is 0.1% or more (preferably 0.2% or more).
　On the other hand, as the Sn concentration increases, the corrosion resistance of the flat surface portion tends to deteriorate. Therefore, the upper limit of the Sn concentration is set to 20.0% or less (preferably 5.0% or less).
[0054]

　Bi is an element that contributes to sacrificial anticorrosion. Therefore, the lower limit of the Bi concentration is preferably more than 0% (preferably 0.1% or more, more preferably 3.0% or more).
　On the other hand, as the Bi concentration increases, the corrosion resistance of the flat surface portion tends to deteriorate. Therefore, the upper limit of the Bi concentration is set to less than 5.0% (preferably 4.8% or less).
[0055]

　In is an element that contributes to sacrificial anticorrosion. Therefore, the lower limit of the In concentration is preferably more than 0% (preferably 0.1% or more, more preferably 1.0% or more).
　On the other hand, as the In concentration increases, the corrosion resistance of the flat surface portion tends to deteriorate. Therefore, the upper limit of the In concentration is set to less than 2.0% (preferably 1.8% or less).
[0056]

　Ca is an element capable of adjusting the optimum amount of Mg elution to impart corrosion resistance and sacrificial corrosion resistance to flat surfaces. Therefore, the lower limit of the Ca concentration is preferably more than 0% (preferably 0.05% or more).
　On the other hand, as the Ca concentration increases, the corrosion resistance and workability of the flat surface tend to deteriorate. Therefore, the upper limit of the Ca concentration is 3.00% or less (preferably 1.00% or less).
[0057]

　Y is an element that contributes to sacrificial anticorrosion. Therefore, the lower limit of the Y concentration is preferably more than 0% (preferably 0.1% or more).
　On the other hand, as the Y concentration increases, the corrosion resistance of the flat surface portion tends to deteriorate. Therefore, the upper limit of the Y concentration is 0.5% or less (preferably 0.3% or less).
[0058]

　La and Ce are elements that contribute to sacrificial anticorrosion. Therefore, the lower limit values ​​of the La concentration and the Ce concentration are preferably more than 0% (preferably 0.1% or more), respectively.
　On the other hand, as the La concentration and the Ce concentration increase, the corrosion resistance of the flat surface portion tends to deteriorate. Therefore, the upper limits of the La concentration and the Ce concentration are set to less than 0.5% (preferably 0.4% or less), respectively.
[0059]

　Si is an element that suppresses the growth of the Al—Fe alloy layer and contributes to the improvement of corrosion resistance. Therefore, the Si concentration is preferably over 0% (preferably 0.05% or more, more preferably 0.1% or more).
　On the other hand, as the Si concentration increases, the corrosion resistance, sacrificial corrosion resistance, and processability of the flat surface tend to deteriorate. Therefore, the upper limit of the Si concentration is set to less than 2.5%. In particular, from the viewpoint of flat surface corrosion resistance and sacrificial corrosion resistance, the Si concentration is preferably 2.4% or less, more preferably 1.8% or less, still more preferably 1.2% or less.
[0060]

　Cr, Ti, Ni, Co, V, Nb, Cu and Mn are elements that contribute to sacrificial corrosion protection. Is. Therefore, the lower limit of the concentrations of Cr, Ti, Ni, Co, V, Nb, Cu and Mn is preferably more than 0% (preferably 0.05% or more, more preferably 0.1% or more).
　On the other hand, when the concentrations of Cr, Ti, Ni, Co, V, Nb, Cu and Mn increase, the corrosion resistance of the flat surface portion tends to deteriorate. Therefore, the upper limit of the concentrations of Cr, Ti, Ni, Co, V, Nb, Cu and Mn is set to less than 0.25%, respectively. The upper limit of the concentrations of Cr, Ti, Ni, Co, V, Nb, Cu and Mn is preferably 0.22% or less.
[0061]
When
　the plating layer is formed by the hot-dip galvanizing method, the Zn—Al—Mg alloy layer and the Al—Fe alloy layer contain a constant Fe concentration.
　It has been confirmed that the Fe concentration up to 5.0% does not adversely affect the performance even if it is contained in the plating layer (particularly the Zn—Al—Mg alloy layer). Since most of Fe is often contained in the Al—Fe alloy layer, the larger the thickness of this layer, the higher the Fe concentration in general.
[0062]

　Sr, Sb, Pb and B are elements that contribute to sacrificial anticorrosion. Therefore, the lower limit of the concentrations of Sr, Sb, Pb and B is preferably more than 0% (preferably 0.05% or more, more preferably 0.1% or more).
　On the other hand, when the concentrations of Sr, Sb, Pb and B increase, the corrosion resistance of the flat surface portion tends to deteriorate. Therefore, the upper limit of the concentrations of Sr, Sb, Pb and B is set to less than 0.5%, respectively.
[0063]

　Impurities refer to components contained in raw materials or components mixed in the manufacturing process and not intentionally contained. For example, a small amount of components other than Fe may be mixed in the plating layer as impurities due to mutual atomic diffusion between the base steel material and the plating bath.
[0064]
　The chemical composition of the plating layer is measured by the following method.
　First, an acid solution obtained by exfoliating and dissolving the plating layer with an acid containing an inhibitor that suppresses corrosion of the base steel material is obtained. Next, by measuring the obtained acid solution by ICP analysis, the chemical composition of the plating layer (when the plating layer has a single layer structure of a Zn—Al—Mg alloy layer, the chemical composition of the Zn—Al—Mg alloy layer When the plating layer has a laminated structure of an Al—Fe alloy layer and a Zn—Al—Mg alloy layer, the total chemical composition of the Al—Fe alloy layer and the Zn—Al—Mg alloy layer) can be obtained. The acid type is not particularly limited as long as it is an acid capable of dissolving the plating layer. The chemical composition is measured as an average chemical composition.
[0065]
　Next, the metal structure of the Zn—Al—Mg alloy layer will be described.
[0066]
　Al crystals are present in the metal structure of the Zn—Al—Mg alloy layer, and the average value of the cumulative peripheral lengths of the Al crystals is 88 to 195 mm / mm 2 .
[0067]
　If the average value of the cumulative peripheral length of the Al crystals is less than 88 mm / mm 2 , the Al crystals become too coarse and the workability deteriorates.
　On the other hand, when the average value of the cumulative peripheral length of the Al crystal is more than 195 mm / mm 2 , the Al crystal is refined and the contact area between the Al crystal and the peripheral phase of the Al crystal is increased. As a result, the larger the contact area between the Al crystal and the phase around the Al crystal, the more easily corrosion around the Al crystal occurs, the worse the corrosion resistance of the flat surface portion, and the larger the variation of the corrosion resistance of the flat surface portion.
　Therefore, the average value of the cumulative peripheral lengths of Al crystals is set to 88 to 195 mm / mm 2 . The lower limit of the average value of the cumulative peripheral lengths of Al crystals is preferably 95 mm / mm 2 or more, and more preferably 105 mm / mm 2 or more. The upper limit of the average value of the cumulative peripheral lengths of Al crystals is preferably 185 mm / mm 2 or less, and more preferably 170 mm / mm 2 or less.
[0068]
　The metal structure of the Zn—Al—Mg alloy layer has Al crystals. The metal structure of the Zn—Al—Mg alloy layer may have a Zn—Al phase in addition to the Al crystal.
[0069]
　The Al crystal corresponds to the "α phase in which Zn with a concentration of 0 to 3% is solid-solved". On the other hand, the Zn—Al phase corresponds to “a β phase containing 70% to 85% of a Zn phase (η phase) and in which the α phase and the Zn phase (η phase) are finely separated”.
[0070]
　Here, FIGS. 1 to 3 show an example of an SEM reflected electron image of the Zn—Al—Mg alloy layer on the polished surface obtained by polishing the surface of the Zn—Al—Mg alloy layer to 1/2 of the layer thickness. FIG. 1 is an SEM reflected electron image having a magnification of 100 times, FIG. 2 is a magnification of 500 times, and FIG. 3 is a magnification of 10000 times.
　In FIGS. 1 to 3, Al represents an Al crystal, Zn—Al represents a Zn—Al phase, MgZn 2 represents an MgZn 2 phase, and Zn—Eu represents a Zn-based eutectic phase.
[0071]
　In the reflected electron image of the Zn—Al—Mg alloy layer, the area fraction of each structure is not particularly limited, but the area fraction of the Al crystal is preferably 8 to 45% from the viewpoint of improving stable corrosion resistance of the flat surface portion. , 15-35% is more preferred. That is, it is preferable that the Al crystal exists within the range of the surface integral.
[0072]
　Al The remaining structure other than the crystal and Zn-Al phase, MgZn 2 phase (specifically, Zn-Al-MgZn Zn-based eutectic phase 2 -Mg 2 Sn, etc.) and the like.
[0073]
　Here, the average value of the cumulative peripheral lengths of Al crystals and the method of measuring the surface integral of Al crystals will be described.
[0074]
　The average value of the cumulative peripheral length of Al crystals and the area fraction of Al crystals are measured at a magnification of 100 times by a scanning electron microscope after polishing the surface of the Zn—Al—Mg alloy layer to 1/2 of the layer thickness. It is measured using the reflected electron image of the Zn—Al—Mg alloy layer obtained when observed. Specifically, it is as follows.
[0075]
　First, a sample is taken from the plated steel material to be measured. However, the sample shall be collected from a place other than the vicinity of the punched end face of the plated steel material (2 mm from the end face) where there is no defect in the plating layer.
[0076]
　Next, the surface of the plating layer (specifically, Zn—Al—Mg alloy layer) of the sample is polished in the thickness direction of the plating layer (hereinafter, also referred to as “Z-axis direction”).
　In the Z-axis direction polishing of the surface of the plating layer, the surface of the Zn—Al—Mg alloy layer is polished to 1/2 of the layer thickness. In this polishing, the surface of the Zn—Al—Mg alloy layer is dry-polished with a # 1200 number polishing sheet, and then a finishing liquid containing alumina having an average particle size of 3 μm, a finishing liquid containing alumina having an average particle size of 1 μm, and colloidal. Finish polishing is performed using each of the finishing liquids containing silica in this order.
　Before and after polishing, the Zn strength on the surface of the Zn—Al—Mg alloy layer was measured by XRF (fluorescent X-ray analysis), and the Zn strength after polishing became 1/2 of the Zn strength before polishing. , 1/2 of the layer thickness of the Zn—Al—Mg alloy layer.
[0077]
　Next, the polished surface of the Zn—Al—Mg alloy layer of the sample was observed with a scanning electron microscope (SEM) at a magnification of 100 times, and a reflected electron image of the Zn—Al—Mg alloy layer (hereinafter referred to as “SEM reflected electron image”). Also called). The SEM observation conditions are an acceleration voltage of 15 kV, an irradiation current of 10 nA, and a visual field size of 1222.2 μm × 927.8 μm.
[0078]
　In order to identify each phase contained in the Zn-Al-Mg alloy layer, an FE-SEM or a TEM (transmission electron microscope) equipped with an EDS (energy dispersive X-ray analyzer) is used. When TEM is used, the polished surface of the Zn—Al—Mg alloy layer of the same sample to be measured is subjected to FIB (focused ion beam) processing. After the FIB processing, an electron diffraction image of the TEM of the polished surface of the Zn—Al—Mg alloy layer is obtained. Then, the metal contained in the Zn—Al—Mg alloy layer is identified.
[0079]
　Next, the reflected electron image of the SEM is compared with the identification result of the electron diffraction image of the FE-SEM or the TEM, and each phase contained in the Zn—Al—Mg alloy layer is identified in the reflected electron image of the SEM. In the identification of each phase contained in the Zn—Al—Mg alloy layer, it is preferable to perform EDS point analysis and collate the result of EDS point analysis with the identification result of the electron diffraction image of TEM. An EPMA device may be used to identify each phase.
[0080]
　Next, in the reflected electron image of the SEM, the three values ​​of the gray scale brightness, hue and contrast value indicated by each phase of the Zn—Al—Mg alloy layer are determined. Since the three values ​​of brightness, hue, and contrast value indicated by each phase reflect the atomic numbers of the elements contained in each phase, usually, the smaller the atomic number of Al and the larger the Mg content, the blacker the color. The larger the amount of Zn, the more likely it is to exhibit white color.
[0081]
　Based on the EDS collation result, image processing (binarization) that changes the color only in the above three-value range indicated by the Al crystal contained in the Zn—Al—Mg alloy layer so as to match the reflected electron image of the SEM. ) (For example, the area (number of pixels) of each phase in the visual field is calculated by displaying only a specific phase as a white image. See FIG. 4). By carrying out this image processing, the area fraction of Al crystals in the Zn—Al—Mg alloy layer in the reflected electron image of the SEM is obtained.
　Note that FIG. 4 is an example of an image processed (binarized) so that the Al crystal can identify the reflected electron image (reflected electron image of SEM) of the Zn—Al—Mg alloy layer. In FIG. 4, Al represents an Al crystal.
[0082]
　Then, the area fraction of the Al crystal in the Zn—Al—Mg alloy layer is the average value of the area fraction of the Al crystal obtained by the above operation in the three visual fields.
　If it is difficult to distinguish the Al crystal, electron diffraction or EDS point analysis by TEM is performed.
[0083]
　As an example, using the binary processing function of WinROOF2015 (image analysis software) manufactured by Mitani Shoji with two threshold values, an Al crystal in an SEM reflected electron image (grayscale image saved in 8 bits, 256 color display) is displayed. The method of identification is described. In the grayscale image saved in 8 bits, when the luminous intensity is 0, it represents black, and when the maximum value is 255, it represents white. In the case of the backscattered electron image of the SEM described above, it has been found from the identification results by FE-SEM and TEM that Al crystals are accurately identified when the threshold values ​​of luminosity are set to 10 and 95. Therefore, the image is processed so that the range of these luminosities of 10 to 95 changes color, and Al crystals are identified. Image analysis software other than WinROOF2015 may be used for the binarization process.
[0084]
　Next, using the automatic shape feature measurement function of WinROOF2015 (image analysis software) manufactured by Mitani Shoji, the peripheral lengths of the Al crystals identified by the above image processing are accumulated, and the cumulative peripheral lengths of the Al crystals are obtained. Then, the cumulative peripheral length of the Al crystal is divided by the area of ​​the visual field to calculate the cumulative peripheral length of the Al crystal per unit area (mm 2 ).
　This operation is performed in three fields of view, and the arithmetic mean of the cumulative peripheral length of Al crystals per unit area (mm 2 ) is defined as "the average value of the cumulative peripheral lengths of Al crystals".
[0085]
　The surface integral of Al crystals can also be obtained by using the automatic shape feature measurement function of WinROOF2015 (image analysis software) manufactured by Mitani Corporation. Specifically, in the reflected electron image of the Zn—Al—Mg alloy layer, the area fraction (area fraction with respect to the visual field area) of the Al crystal identified by binarization is calculated by using this function. Then, this operation is performed in three fields of view, and the calculated average is used as the surface integral of the Al crystal.
[0086]
　The thickness of the Al—Fe alloy layer is measured as follows.
　After embedding the sample in resin, it is polished and the SEM reflected electron image of the cross section of the plating layer (cut surface along the thickness direction of the plating layer) (however, the magnification is 5000 times, the size of the field of view: length 50 μm × width 200 μm, In the field of view where the Al—Fe alloy layer can be visually recognized.), The thickness is measured at any five points of the identified Al—Fe alloy layer. Then, the arithmetic mean of the five points is taken as the thickness of the interfacial alloy layer.
[0087]
　Next, an example of the method for producing the plated steel material of the present disclosure will be described.
[0088]
　The plated steel material of the present disclosure is obtained by forming a plating layer having the above-mentioned predetermined chemical composition and metal structure on the surface (that is, one side or both sides) of a base steel material (base steel plate or the like) by a hot-dip galvanizing method.
[0089]
　Specifically, as an example, the hot-dip galvanizing treatment is performed under the following conditions.
　First, the plating bath temperature is set to the melting point of the plating bath + 20 ° C. or higher, and after the base steel material is pulled up from the plating bath, the temperature range from the plating bath temperature to the plating solidification start temperature is set to -30 ° C from the plating solidification start temperature to the plating solidification start temperature. Cool at an average cooling rate that is greater than the average cooling rate in the temperature range of.
　Next, the temperature range from the plating solidification start temperature to the plating solidification start temperature −30 ° C. is cooled at an average cooling rate of 12 ° C./s or less.
　Next, the temperature range from the plating solidification start temperature −30 ° C. to 300 ° C. is cooled at an average cooling rate larger than the average cooling rate in the temperature range from the plating solidification start temperature to the plating solidification start temperature −30 ° C.
[0090]
　That is, in an example of the method for producing a plated steel material of the present disclosure, the plating bath temperature is set to the melting point of the plating bath + 20 ° C. or higher, the base steel material is pulled up from the plating bath, and then the average cooling in the temperature range from the plating bath temperature to the plating solidification start temperature is performed. When the rate is A, the average cooling rate in the temperature range from the plating solidification start temperature to the plating solidification start temperature -30 ° C is B, and the average cooling rate from the plating solidification start temperature -30 ° C to 300 ° C is C, A> B, B ≦ 12 ° C./s, C> B, the hot-dip galvanizing treatment is performed on the base steel material under the condition of three-step cooling.
[0091]
　Al crystals are generated by setting the plating bath temperature to the melting point of the plating bath + 20 ° C. or higher and pulling the base steel material from the plating bath.
　Then, by cooling the temperature range from the plating solidification start temperature to the plating solidification start temperature −30 ° C. at an average cooling rate of 12 ° C./s or less, Al crystals are present in the Zn—Al—Mg alloy layer, and Al crystals are present. A metal structure is formed in which the average value of the cumulative peripheral lengths of the above ranges. Cooling at this average cooling rate is performed, for example, by air cooling in which the atmosphere is blown with a weak wind.
　However, from the viewpoint of preventing plating wrapping around the top roll or the like, the lower limit of the average cooling rate in the temperature range from the plating solidification start temperature to the plating solidification start temperature −30 ° C. is 0.5 ° C./s or more.
[0092]
　The plating solidification start temperature can be measured by the following method. The temperature at which the peak of the suggested heat first appears when the sample is taken from the plating bath, heated to the melting point of the plating bath + 20 ° C. or higher by DSC, and then cooled at 10 ° C./min is the plating solidification start temperature.
[0093]
　In the method for producing a plated steel material of the present disclosure, the average cooling rate in the temperature range from the temperature at which the base steel material is pulled up from the plating bath (that is, the plating bath temperature) to the plating solidification start temperature is not particularly limited, but the top roll or the like From the viewpoint of preventing plating wrapping around the surface and suppressing appearance defects such as wind patterns, the temperature is preferably 0.5 ° C./s to 20 ° C./s.
　However, the average cooling rate in the temperature range from the plating bath temperature to the plating solidification start temperature is set to be a larger average cooling rate than the average cooling rate in the temperature range from the plating solidification start temperature to the plating solidification start temperature −30 ° C. Thereby, the nucleation sites of Al crystals can be increased, and excessive coarsening of Al crystals can be suppressed.
[0094]
　Further, the average cooling rate in the temperature range from the plating solidification start temperature of -30 ° C to 300 ° C is not particularly limited, but from the viewpoint of preventing plating wrapping around the top roll or the like, 0.5 ° C / s to 20 ° C. It is preferable to set the temperature / s.
　However, the average cooling rate in the temperature range from the plating solidification start temperature of -30 ° C to 300 ° C shall be a higher average cooling rate than the average cooling rate in the temperature range from the plating solidification start temperature to the plating solidification start temperature of -30 ° C. .. As a result, it is possible to suppress excessive coarsening of Al crystals and ensure workability.
[0095]
　The Al—Fe alloy layer formed between the base steel material and the base steel material rapidly forms and grows in less than 1 second immediately after the plating immersion. The growth rate is higher when the plating bath temperature is high, and is even higher when the immersion time in the plating bath is long. However, when the plating bath temperature is less than 500 ° C., the plating bath hardly grows, so it is better to reduce the immersion time or immediately move from solidification to the cooling process.
[0096]
　Further, if the plated steel material is once solidified and then reheated to remelt the plated layer, all the constituent phases disappear and the plated steel material becomes a liquid phase state. Therefore, for example, even if the plated steel material has been rapidly cooled once, it is possible to carry out the structure control specified in the present disclosure in the step of reheating offline and performing an appropriate heat treatment. In this case, the reheating temperature of the plating layer is preferably set to a temperature range immediately above the melting point of the plating bath so that the Al—Fe alloy layer does not grow excessively.
[0097]
　Hereinafter, the post-treatment applicable to the plated steel material of the present disclosure will be described.
[0098]
　In the plated steel material of the present disclosure, a film may be formed on the plated layer. The film can form one layer or two or more layers. Examples of the type of film immediately above the plating layer include chromate film, phosphate film, and chromate-free film. Chromate treatment, phosphate treatment, and chromate-free treatment for forming these films can be performed by known methods.
[0099]
　Chromate treatment includes electrolytic chromate treatment that forms a chromate film by electrolysis, reactive chromate treatment that forms a film using the reaction with the material, and then rinses away excess treatment liquid, and the treatment liquid is applied to the object to be coated. There is a coating type chromate treatment that dries to form a film without washing with water. Any process may be adopted.
[0100]
　As the electrolytic chromate treatment, electrolytic chromate treatment 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 is performed. It can be exemplified.
[0101]
　Examples of the phosphate treatment include zinc phosphate treatment, zinc phosphate calcium treatment, and manganese phosphate treatment.
[0102]
　Chromate-free treatment is particularly suitable because it does not burden the environment. Chromate-free treatment includes electrolytic chromate-free treatment that forms a chromate-free film by electrolysis, reactive chromate-free treatment that forms a film using the reaction with the material, and then rinses away excess treatment liquid. There is a coating type chromate-free treatment that is applied to an object to be coated and dried without washing with water to form a film. Any process may be adopted.
[0103]
　Further, one layer or two or more organic resin films may be provided on the film directly above the plating layer. The organic resin is not limited to a specific type, and examples thereof include polyester resin, polyurethane resin, epoxy resin, acrylic resin, polyolefin resin, and modified products of these resins. Here, the modified product is obtained by reacting a reactive functional group contained in the structure of these resins with another compound (monomer, cross-linking agent, etc.) containing a functional group capable of reacting with the functional group. Refers to resin.
[0104]
　As such an organic resin, one kind or two or more kinds of organic resins (not modified) may be mixed and used, or at least one kind and others in the presence of at least one kind of organic resin. The organic resin obtained by modifying the organic resin of the above may be used alone or in combination of two or more. Further, the organic resin film may contain any coloring pigment or rust preventive pigment. Water-based products can also be used by dissolving or dispersing in water.
Example
[0105]
Examples of the present disclosure will be described, but the conditions in the examples are one condition example adopted for confirming the feasibility and effect of the present disclosure, and the present disclosure is limited to this one condition example. It's not a thing. The present disclosure may adopt various conditions as long as the gist of the present disclosure is not deviated and the object of the present disclosure is achieved.
[0106]
(Example) In
　order to obtain a plating layer having the chemical composition shown in Tables 1 and 2, a predetermined amount of pure metal ingot is used to melt the ingot in a vacuum melting furnace, and then the plating bath is placed in the air. I took a bath. A batch hot-dip galvanizing apparatus was used to produce the plated steel sheet.
　As the base steel material, a 2.3 mm general hot-rolled carbon steel sheet (C concentration <0.1%) was used, and degreasing and pickling were carried out immediately before the plating step.
　Further, in some examples, as the base steel material, a Ni pre-plated steel sheet obtained by subjecting a 2.3 mm general hot-rolled carbon steel sheet to Ni pre-plating was used. The amount of Ni adhered was 2 g / m 2 . An example in which a Ni pre-plated steel sheet was used as the base steel material was described as "Ni pre-plating" in the "base steel material" column in the table.
[0107]
　In all of the sample preparations, the same reduction treatment method was carried out for the base steel material in the steps up to the time of immersion in the plating bath. That is, in an environment where the base steel material is N 2- H 2 (5%) (dew point -40 ° C or less, oxygen concentration less than 25 ppm), the temperature is raised from room temperature to 800 ° C by energization heating, held for 60 seconds, and then N 2 The plating bath temperature was cooled to + 10 ° C. by spraying gas, and the mixture was immediately immersed in the plating bath.
　For all the plated steel sheets, the immersion time in the plating bath was the time shown in the table. The N2 gas wiping pressure was adjusted to prepare a plated steel sheet so that the plating thickness was 30 μm (± 1 μm).
[0108]
　The plating bath temperature was basically a melting point of + 20 ° C., and the temperature was further raised at some levels for plating. The plating bath immersion time was 2 seconds. After pulling the base steel material out of the plating bath, a plating layer was obtained by a cooling process in which the average cooling rates of the following 1st to 3rd stages shown in Tables 1 and 2 were set as the conditions shown in Tables 1 and 2.
・ First stage average cooling rate: Average cooling rate in the temperature range from the plating bath temperature to the plating solidification start temperature
・ Second stage average cooling rate: Average cooling in the temperature range from the plating solidification start temperature to the plating solidification start temperature -30 ° C Speed
・ 3rd stage average cooling rate: Plating solidification start temperature -30 ° C to 300 ° C average cooling rate
[0109]
-Various measurements- A
　sample was cut out from the obtained plated steel sheet. Then, the following items were measured according to the method described above.
-Average value of the cumulative peripheral length of Al crystals (denoted as "peripheral length of Al crystals" in the table)
-Area fraction of Al crystals
-Thickness of Al-Fe alloy layer (However, Ni pre-plated steel plate as the base steel material In the example using, the thickness of the Al—Ni—Fe alloy layer is shown.)
[0110]

　-Corrosion resistance of flat surface-In order to compare stable corrosion resistance of flat surface , the production sample was subjected to a corrosion acceleration test (JASO M609-91) for 120 cycles and immersed in a 30% chromic acid aqueous solution at room temperature to remove white rust. The corrosion resistance of the flat surface was evaluated from the loss of corrosion. The test was carried out 5 times, and when the average corrosion weight loss was 80 g / m 2 or less and the maximum and minimum values ​​of the corrosion weight loss in n = 5 were within ± 100% of the average value, it was evaluated as "A +" and averaged. When the corrosion weight loss is 100 g / m 2 or less and the maximum and minimum values ​​of the corrosion weight loss in n = 5 are within ± 100% of the average value, the evaluation is "A", and the other cases are evaluated as "NG". ..
[0111]
-Sacrificial corrosion resistance (corrosion resistance at the end face of the cut part
　) -In order to compare the sacrificial corrosion resistance (corrosion resistance at the end face of the cut part), the sample was shear-cut to 50 mm x 100 mm, and the upper and lower end surfaces were sealed to promote corrosion test (JASO M609-91). The average value of the red rust generation area ratio of the exposed end face of the side surface was evaluated by subjecting it to 120 cycles. A red rust generation area ratio of 50% or less was evaluated as "A +", 70% or less was evaluated as "A", and more than 70% was evaluated as "NG".
[0112]
- processability -
　To assess the workability of the plating layer, the plated steel sheet was bent 90 ° V, detached by pressing a cellophane tape V bending width 24mm in valleys, it was evaluated powdering visually. The tape on which the powdering release powder did not adhere was evaluated as "A", the tape on which it adhered slightly was evaluated as "A-", and the tape on which it adhered was evaluated as "NG".
[0113]
- Overall rating -
　plane portion corrosion resistance, sacrificial corrosion resistance and workability Evaluation Evaluation results of all "A", "A +" or "A-" "A] an example is, even one that is" NG "," It was evaluated as "NG".
[0114]
　Examples are listed in Tables 1 and 2.
[0115]
[table 1]

[0116]
[Table 2]

[0117]
　From the above results, it can be seen that the examples corresponding to the plated steel materials of the present disclosure have stable flat surface corrosion resistance as compared with the comparative examples.
　In particular, in Comparative Example (Test No. 70) in which the average cooling rate was not changed at 15 ° C./s even if the chemical composition of the plating layer of the present disclosure was satisfied, the average value of the cumulative peripheral lengths of Al crystals became excessively large. It can be seen that stable flat surface corrosion resistance has not been obtained.
　On the other hand, a comparative example in which the average cooling rate of the second stage is excessively low (Comparative Example No. 71), a comparative example in which the average cooling rate is changed in only two stages (Test No. 72), and an average cooling rate of 6 ° C./s. In the comparative example (test No. 73) which does not change, it can be seen that the average value of the cumulative peripheral lengths of Al crystals becomes excessively small and the workability is deteriorated.
[0118]
　Although the preferred embodiments of the present disclosure have been described in detail with reference to the accompanying drawings, the present disclosure is not limited to such examples. It is clear that anyone with ordinary knowledge in the field of technology to which this disclosure belongs can come up with various modifications or modifications within the scope of the technical ideas set forth in the claims. , These are also naturally understood to belong to the technical scope of the present disclosure.
[0119]
　The description of the code is as follows.
Al Al crystal
Zn-Al Zn-Al phase
MgZn 2 MgZn 2- phase
Zn-Eu Zn-based eutectic phase
[0120]
　The entire disclosure of Japanese Patent Application No. 2018-094481 is incorporated herein by reference in its entirety.
　All documents, patent applications, and technical standards described herein are to the same extent as if the individual documents, patent applications, and technical standards were specifically and individually stated to be incorporated by reference. Incorporated herein by reference.
The scope of the claims
[Claim 1]
　A plated steel material having a base steel material and a plating layer containing a Zn—Al—Mg alloy layer arranged on the surface of the base steel material,
　wherein the plating layer is
　Zn: more than 65.0% in mass%. ,
　Al: more than 5.0% to less than 25.0%,
　Mg: more than 3.0% to less than 12.5%,
　Sn: 0.1% to 20.0%,
　Bi: 0% to 5.0% Less than,
　In: 0% to less than 2.0%,
　Ca: 0% to 3.00%,
　Y: 0% to 0.5%,
　La: 0% to less than 0.5%,
　Ce: 0% to 0 .Less than 5.5%,
　Si: 0% to less than 2.5%,
　Cr: 0% to less than 0.25%,
　Ti: 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 0. Less than 25%,
　Fe: 0% to 5.0%,
　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
　a
　Zn—Al—Mg alloy layer having a chemical composition consisting of impurities. Al crystals are present in the reflected electron image of the Zn—Al—Mg alloy layer obtained when the surface of the above is polished to 1/2 of the layer thickness and then observed with a scanning electron microscope at a magnification of 100 times. A plated steel material having an average cumulative peripheral length of Al crystals of 88 to 195 mm / mm 2 .
[Claim 2]
　The plated steel material according to claim 1, wherein the plating layer has an Al—Fe alloy layer having a thickness of 0.05 to 5 μm between the base steel material and the Zn—Al—Mg alloy layer.