Specification
Title of invention: Zn-Al-Mg based plated steel sheet
Technical field
[0001]
　TECHNICAL FIELD The present invention relates to a Zn—Al—Mg-based plated steel sheet, and particularly to a Zn—Al—Mg-based plated steel sheet having excellent corrosion resistance and workability.
Background technology
[0002]
　Conventionally, it has been widely known that Zn plating is applied to the surface of a steel material to improve the corrosion resistance of the steel material, and even now, the steel material plated with Zn is mass-produced. However, for many applications, Zn plating alone may be insufficient in corrosion resistance. Therefore, in recent years, a hot-dip Zn—Al alloy-plated steel sheet (Galbarium steel sheet (registered trademark)), which has further improved corrosion resistance of steel material than Zn, has been used.
[0003]
　For example, Patent Document 1 discloses a hot-dip Zn-Al plating in which an alloy plating containing 25 to 75 mass% of Al and 0.5% or more of the Al content of Si and the balance being substantially Zn was applied. A steel plate is disclosed. Patent Document 1 discloses that a hot-dip Zn—Al alloy plating layer having excellent corrosion resistance, good adhesion to steel, and a beautiful appearance can be obtained. However, in the plated steel sheet of Patent Document 1, since the plated layer does not contain Mg, it cannot be said that the corrosion resistance is sufficient.
[0004]
　Patent Document 2 discloses that the corrosion resistance is improved by adding Mg to the plating layer.
　However, in recent years, the demand for corrosion resistance is higher than ever before. As in Patent Document 2, only by including Mg in the plating layer, it cannot be said that the corrosion resistance is sufficient in a more severe environment (an environment where high corrosion resistance is required).
[0005]
　Patent Document 3 discloses an Al—Zn—Si—Mg alloy coated strip in which fine spherical spherical Mg 2 Si phase particles are dispersed in a coating by forced cooling of the coated strip. Patent Document 3 describes that by changing the Mg 2 Si phase into fine spherical particles, cracking of the coating is potentially reduced and the corrosion resistance of the coating is improved.
　Patent Document 4 discloses a molten Al-Zn-Mg system in which the major axis of the precipitation phase in the plating layer is 0.5 μm or less by setting the average cooling rate until the plating layer solidifies to a predetermined range or more. A plated steel sheet is disclosed.
　However, as a result of the study by the present inventors, it was found that sufficient corrosion resistance cannot be obtained in a severe corrosive environment simply by refining the Mg 2 Si phase as in Patent Document 3 and Patent Document 4 .
[0006]
　Patent Document 5 discloses a molten Al-Zn-Mg-Si plated steel sheet containing Mg 2 Si. In Patent Document 5, by cooling the steel sheet at a cooling rate of less than 10° C./sec in a temperature range where Mg 2 Si is likely to be formed, Mg 2 Si is finely and uniformly dispersed in the entire plating main layer, and the processed portion is processed. It is disclosed that the corrosion resistance is improved.
　In Patent Document 6, Mg 2 in Si is generated easily temperature range, Mg by a steel plate at a cooling rate of less than 10 ° C. / sec 2 was entire plated main layer with Si is finely and uniformly dispersed Further, by setting the oxygen concentration of the wiping gas to 10 vol% or more, the area ratio of Mg 2 Si on the surface of the plating main layer is increased to 10% or more, and the corrosion resistance of the flat plate portion and the end portion is improved. It is disclosed.
　However, as a result of the study conducted by the present inventors, it was found that the Mg 2 Si produced by gradually cooling the production temperature range was not sufficiently miniaturized. Insufficient refinement of Mg 2 Si contributes little to corrosion resistance, and the molten Al—Zn—Mg—Si plated steel sheets of Patent Document 5 and Patent Document 6 cannot provide sufficient corrosion resistance in a severe corrosive environment. I also understood that.
Prior art documents
Patent literature
[0007]
Patent Document 1: U.S. Pat. No. 3,343,930 Specification
Patent Document 2: Japanese Unexamined
Patent Publication No. 59-056570 Patent Document 3: Japanese Patent Publication No. 2012-528244
Patent Document 4: Japanese Unexamined Patent Publication No. 2005-133151 Japanese
Patent Document 5: Japanese Patent No. 6059408 discloses
Patent Document 6: Japanese Patent 2016-166414 JP
Summary of the invention
Problems to be Solved by the Invention
[0008]
　The present invention has been made in view of the above circumstances. An object of the present invention is to provide a Zn—Al—Mg-based plated steel sheet having sufficient workability and excellent corrosion resistance.
Means for solving the problem
[0009]
　As a result of intensive studies, the inventors of the present invention have found that the Mg—Si phase (Mg 2 Si) formed in the plating layer is an extremely effective structure for improving the corrosion resistance, and the Mg—Si phase is focused on the surface side. It has been found that it is important to make the Mg—Si phase equivalent diameter equivalent to the average circle equivalent diameter within a predetermined range to improve corrosion resistance without lowering workability.
　The present invention was made based on the above findings, and the summary thereof is as follows.
[0010]
　(1) A Zn—Al—Mg-based plated steel sheet according to one aspect of the present invention is a steel sheet, an alloy layer formed on the surface of the steel sheet, containing Fe and Si, and the opposite side of the alloy layer from the steel sheet. And a plating layer formed on the surface of the alloy layer, and the average composition of the plating layer and the alloy layer is, by mass%, Al: 45.0 to 65.0%, Si: 0.50 to 5.00%. , Mg: 1.00 to 10.00%, the balance consisting of Zn, Fe and impurities, and the plating layer contains a Mg—Si phase with a volume fraction of 0.1 to 20.0%, When a range of 1 μm in the thickness direction of the plating layer from the surface of the plating layer is defined as the surface layer portion of the plating layer, the average circle of the Mg—Si phase in the direction in which the plating layer of the surface layer portion is viewed in plan view. The equivalent diameter is 0.1 to 15.0 μm, and the position of 1/2 of the thickness of the plating layer from the surface of the plating layer toward the interface between the plating layer and the alloy layer is the plating layer thickness center. Defined, when the Si content is measured over the entire thickness of the plating layer, the integrated value of the Si content from the surface of the plating layer to the center of the thickness of the plating layer is the plating layer. It is 0.55 times or more the integrated value of the Si content from the surface to the interface.
[0011]
　(2) In the Zn—Al—Mg-based plated steel sheet according to (1), the integrated value of the Si content from the surface of the plating layer to the center of thickness of the plating layer is the surface of the plating layer. It may be 0.60 times or more of the integrated value of the Si content from to the interface.
[0012]
　(3) In the Zn-Al-Mg-based plated steel sheet according to (1) above, the average composition of the plating layer and the alloy layer is one or more of Cr, Ca, Sr, and Ni in total of 0. It may further contain 01 to 1.00%.
Effect of the invention
[0013]
　According to the present invention, it is possible to provide a Zn-Al-Mg-based plated steel sheet having sufficient workability and excellent corrosion resistance. Further, the Zn-Al-Mg-based plated steel sheet of the present invention is suitable for building materials, automobiles, and home appliances.
Brief description of the drawings
[0014]
[FIG. 1] Manufacturing No. in the example using GDS 3 (invention example) and manufacturing No. 3 It is a figure which shows the result of having measured Si content and Fe content in the thickness direction of the plating layer from the surface of the plating layer about 23 (comparative example).
2A] Manufacturing No. in the example. It is the EPMA analysis result of the plating layer surface layer part measured from the plating layer surface side of No. 3 (Example of the present invention).
[FIG. 2B] Manufacturing No. in the example. It is the EPMA analysis result of the plating layer surface layer part measured from the plating layer surface side of No. 23 (Comparative Example).
[FIG. 3A] Manufacturing No. in the example. 3 is an EPMA analysis result of a cross section of a plating layer of Example 3 (Example of the present invention).
[FIG. 3B] Manufacturing No. in the example. It is the EPMA analysis result of the plating layer cross section of No. 23 (Comparative Example).
MODE FOR CARRYING OUT THE INVENTION
[0015]
　By immersing the steel plate which is the original plating plate in a hot dip plating bath containing Al, Si, Mg and Zn, a plating layer containing these elements is formed on the surface of the steel plate. The present inventors have confirmed that by adjusting the composition of the plating bath, Mg 2 Si that is a compound of Mg and Si is formed as a Mg—Si phase in the plating layer . The presence of Mg 2 Si in the plating layer improves the corrosion resistance of the plating layer.
[0016]
　As a result of further studies, the inventors of the present invention distributed a large amount of Mg 2 Si on the side close to the surface of the plating layer (the surface opposite to the surface in contact with the alloy layer) to improve the corrosion resistance of the plating layer. We have found that it can be improved. However, it has also been found that simply increasing the amount of the Mg—Si phase is not preferable, because if the volume fraction of the Mg—Si phase in the plating layer becomes too high, the workability decreases.
　Therefore, the inventors of the present invention controlled the Mg—Si phase to be distributed more on the surface side of the plating layer, and the size of Mg 2 Si existing at a position closer to the surface of the plating layer (average circle equivalent diameter). It has been found that the corrosion resistance can be further improved while ensuring sufficient workability by reducing the value to a predetermined range.
　Hereinafter, a Zn—Al—Mg-based plated steel sheet according to an embodiment of the present invention (hereinafter sometimes referred to as a plated steel sheet according to the present embodiment) will be described.
[0017]
　The plated steel sheet according to the present embodiment includes a steel sheet, an alloy layer containing Fe and Si formed on the surface of the steel sheet, and a plating layer formed on a surface of the alloy layer opposite to the steel sheet. ..
　The plating layer and the alloy layer have an average composition of mass% of Al: 45.0 to 65.0%, Si: 0.50 to 5.00%, and Mg: 1.00 to 10.00%. Optionally, one or more of Cr, Ca, Sr, and Ni are contained in a total amount of 0.01 to 1.0%, and the balance is Zn, Fe, and impurities.
　Further, this plating layer contains the Mg—Si phase in a volume fraction of 0.1 to 20% by volume, and the average equivalent circle diameter of the Mg—Si phase in the surface layer portion of the plating layer is 0.1 to 15.0 μm. is there.
　Further, in this plating layer, when the Si content is measured over the entire thickness of the plating layer from the surface of the plating layer toward the interface between the plating layer and the alloy layer, the thickness of the plating layer is measured from the surface of the plating layer. The integrated value of Si content up to the center of is 0.55 times or more of the integrated value of Si content of the entire thickness of the plating layer. That is, Si is more present in the plating layer upper layer portion which is the plating layer surface side from the 1/2 thickness position than in the lower region which is the steel plate side from the 1/2 thickness position of the plating layer.
　The plating layer and the alloy layer may be formed on one side or both sides of the steel sheet.
[0018]
The steel plate serving as the
　plating original plate may be any of hot rolled steel plate, cold rolled steel plate and the like, and is not particularly limited. The material is also not particularly limited, and any of general steel, Al-killed steel, high alloy steel and the like can be applied.
　The galvanized steel sheet according to the present embodiment is obtained by applying the hot dip plating method to the steel sheet that serves as the plating original sheet.
[0019]
　The plate thickness of the steel plate is not particularly limited as long as it can be passed through the continuous hot dip plating facility, but from the viewpoint of stable production, a plate having a large plate thickness is preferable. When the plate thickness is large, the amount of heat retained by the steel plate during plating is large, and the temperature decrease behavior of the steel plate becomes gradual. Therefore, it is advantageous to cool the molten metal of the plating bath adhering to the steel sheet so that solidification proceeds from the surface side to the steel sheet side in one direction.
[0020]
　
　(Average Composition of Plating Layer and Alloy Layer) When the
　steel sheet is immersed in a plating bath, the plating layer is formed on the steel sheet and a part of the plating layer is alloyed to form a gap between the plating layer and the steel sheet. An alloy layer is formed on.
　The average composition of the plating layer and the alloy layer formed on this steel sheet is Al: 45.0 to 65.0%, Si: 0.50 to 5.00%, and Mg: 1.00 to 10.00%. The balance is Zn, Fe and impurities. If necessary, Cr, Ca, Sr, and Ni may be contained in a total amount of 0.01 to 1.0%. The unit of average composition is% by mass. In the following description, it is simply expressed as %.
　The average composition of the plating layer and the alloy layer is the composition of the plating layer and the alloy layer, which is obtained by dissolving the plating layer and the alloy layer from the plated steel sheet according to the present embodiment in which the plating layer and the alloy layer are formed using hydrochloric acid or the like. Can be measured by ICP analysis. Specifically, the plating composition can be determined by using the mass of the plating layer and the alloy layer dissolved with hydrochloric acid as the denominator and the mass of the element quantified by ICP as the numerator.
　The reasons for limiting each component will be described below.
[0021]
(Al: 45.0 to 65.0%) When the
　Al content is less than 45.0%, the corrosion resistance of the flat portion of the plating layer becomes insufficient. Therefore, the Al content is set to 45.0% or more. It is preferably at least 50.0%.
　On the other hand, when the Al content exceeds 65.0%, the corrosion resistance of the cut end surface of the plating layer decreases. Further, if the Al content exceeds 65.0%, it is necessary to maintain the temperature of the plating bath high, which causes a problem such as an increase in manufacturing cost. Therefore, the Al content is 65.0% or less. A more preferable range is 60.0% or less.
　Further, regarding corrosion resistance, when the effect of improving the barrier property of the plating layer by Al is the main effect rather than the effect of sacrificial corrosion by Zn, it is preferable that the Al content be greater than the Zn content.
[0022]
(Si: 0.50 to 5.00%)
　Si is an element that forms a compound with Mg and contributes to the improvement of corrosion resistance. Moreover, Si suppresses the alloy layer formed between the steel plate surface and the plating layer from being formed excessively thick when forming the plating layer on the steel plate, and the adhesion between the steel plate and the plating layer is improved. It is also an element that has the effect of increasing
　If the Si content is less than 0.50%, these effects cannot be sufficiently obtained. Therefore, the Si content is set to 0.50% or more. It is preferably 1.00% or more.
　On the other hand, if the Si content exceeds 5.00%, excessive Si is deposited in the plating layer, which not only lowers the corrosion resistance but also lowers the workability of the plating layer. Therefore, the Si content is set to 5.00% or less. From the viewpoint of workability, it is preferably 3.00% or less. A more preferable range of the Si content is 2.00% or less.
[0023]
(Mg: 1.00 to 10.00%)
　Mg is an element having an effect of enhancing the corrosion resistance of the plating layer. When the Mg content is less than 1.00%, Mg 2 Si is not formed favorably, so the corrosion resistance is not significantly improved. Therefore, the Mg content is set to 1.00% or more. It is preferably 1.50% or more.
　On the other hand, when the Mg content exceeds 10.00%, the effect of improving the corrosion resistance is saturated and the workability of the plated layer is deteriorated. In addition, manufacturing problems such as an increase in the amount of dross generated in the plating bath occur. Therefore, the Mg content is set to 10.00% or less. From the viewpoint of manufacturability, it is more preferably 3.50% or less. It is more preferably 3.00% or less.
[0024]
　The plating layer and the alloy layer of the plated steel sheet according to the present embodiment basically contain the above elements and the balance is Zn, Fe and impurities. However, in order to further improve the corrosion resistance of the plating layer, an alkaline earth metal such as Sr or Ca, or Cr or Ni may be contained if necessary. Since these elements are not necessarily contained, the lower limit is 0%.
　Impurities mean elements such as Pb, Sb, Sn, Cd, Mn, Cu, and Ti that are inevitably mixed in during the plating process. If the total amount of these impurities is 1.0% or less, it does not adversely affect the characteristics and may be included.
[0025]
(Total of Cr, Ca, Sr and Ni: 0 to 1.00%) Since
　these elements do not necessarily have to be contained, the lower limit is 0%. If the total is less than 0.01%, a sufficient effect of improving the corrosion resistance cannot be seen. Therefore, in order to obtain the effect of improving the corrosion resistance, it is preferable to contain one or more of these elements in a total amount of 0.01% or more. More preferably, it is 0.05% or more in total.
　On the other hand, when the total content of Cr, Ca, Sr, and Ni exceeds 1.00%, not only the effect of improving corrosion resistance is saturated, but also the amount of dross generated in the plating bath may exceed the allowable range.
　Therefore, even when Sr, Ca, Cr and/or Ni is contained, the total content is preferably 1.00% or less. A more preferable upper limit is 0.20%, and a still more preferable upper limit is 0.10%.
[0026]
(Volume Ratio
　of Mg-Si Phase in Plating Layer ) By setting the volume fraction of Mg-Si phase in the plating layer to 0.1% or more, the corrosion resistance of the plating layer can be improved. Therefore, the volume fraction of the Mg-Si phase is set to 0.1% or more. It is preferably 1.0% or more, more preferably 2.0% or more, even more preferably 5.0% or more, still more preferably 10.0% or more.
　On the other hand, if the volume fraction of the Mg—Si phase exceeds 20.0%, the workability will decrease. Therefore, the volume fraction of the Mg—Si phase is set to 20.0% or less. It is preferably 18.0% or less, more preferably 15.0% or less, still more preferably 10.0% or less, still more preferably 5.0% or less.
[0027]
　The volume fraction of each phase forming the plating layer is equal to the area percentage of each phase exposed in the cross section of the plating layer. Therefore, the volume fraction can be specified by mapping the element distribution of SEM-EDS to obtain the area ratio (cross-sectional area ratio) of each phase in the cross section of the plating layer.
[0028]
(Average circle-equivalent diameter of the Mg-Si phase in the surface layer portion) When
　the surface layer portion of the plating layer was defined to be 1 μm in the thickness direction of the plating layer from the surface of the plating layer, the plating layer in the surface layer portion was viewed in plan view. The average equivalent circle diameter of the Mg—Si phase in the direction is 0.1 to 15.0 μm.
　If the average equivalent circle diameter is less than 0.1 μm, the corrosion resistance of the plating layer is reduced. Therefore, the average equivalent circle diameter of the Mg—Si phase in the plating layer surface layer portion is set to 0.1 μm or more. On the other hand, when the average equivalent circle diameter of the Mg—Si phase exceeds 15.0 μm, the plating layer itself becomes brittle and the workability deteriorates. Therefore, the average equivalent circle diameter of the Mg—Si phase in the surface layer portion is set to 15.0 μm or less.
[0029]
　The average equivalent circle diameter in this embodiment can be measured using the following method.
　Using EPMA, from the surface side of the plating layer (from the plane view of the surface of the plating layer), in the field of view of 500×500 μm or more, the surface layer part of the plating layer (position at a depth of about 1 μm from the surface of the plating layer) Up to the range). In the plated layer of the plated steel sheet according to the present embodiment, since Si substantially exists as a Mg—Si phase as described later, the measured cross-sectional area of ​​the phase containing Si is calculated as The diameter of a circle having the same area is the equivalent circle diameter of the Mg—Si phase. The average equivalent circle diameter is obtained by averaging the equivalent circle diameters of the Mg—Si phase measured in the visual field.
　An example of measuring the Si distribution by the above method is shown in FIGS. 2A and 2B.
[0030]
(Distribution State of Mg-Si Phase in Plating Layer) In
　the plating layer of the plated steel sheet according to the present embodiment, the Mg-Si phase is located closer to the surface side of the plating layer than the steel sheet side with respect to the center in the thickness direction of the plating layer. It is distributed so that there are many. Thereby, excellent corrosion resistance can be obtained without impairing workability.
　Here, as can be seen from the EPMA analysis result of the cross section of the plating layer shown in FIG. 3A, Si is present at the same position as Mg in the plating layer of the plated steel sheet according to the present embodiment. That is, it is considered that Si exists as a Mg—Si phase (Mg 2 Si).
　Therefore, in the plated layer of the plated steel sheet according to the present embodiment, the position of 1/2 of the thickness of the plated layer from the surface of the plated layer in the thickness direction of the plated layer (hereinafter, sometimes referred to as the center of the plated layer thickness) If the distribution is such that Si is present more on the surface side than the plating layer thickness center than on the steel plate side from the plating layer thickness center, the Mg-Si phase will be based on the plating layer thickness center as a reference. It can be judged that there is more on the surface side than on the steel plate side, based on the center of the plating layer thickness.
　Hereinafter, with respect to the plating layer thickness center, the steel plate side from the plating layer thickness center may be referred to as the plating layer lower layer portion, and the surface side from the plating layer thickness center may be referred to as the plating layer upper layer portion.
[0031]
　In the plated steel sheet according to the present embodiment, regarding the Mg—Si phase in the plated layer, it is determined that “the Mg—Si phase is present more in the plated layer upper layer portion than in the plated layer lower layer portion” in the following cases.
[0032]
　Specifically, using a GDS (Glow Discharge Emission Spectroscopy) with a measurement diameter of 4 mm, the sample is dug by sputtering from the surface of the plating layer toward the interface between the plating layer and the alloy layer in the thickness direction. The Si content is continuously measured by performing elemental analysis. Then, with respect to the obtained measured value, the Si content from the surface of the plating layer to the center of the thickness of the plating layer is integrated to calculate the integrated value (surface-side Si content integrated value). Further, the Si content over the entire thickness of the plating layer (from the surface of the plating layer to the interface between the plating layer and the alloy layer) is integrated to calculate the integrated value (total thickness Si content integrated value).
　When the surface side Si content integrated value is 0.55 times or more of the total thickness Si content integrated value, that is, (surface side Si content integrated value)/(total thickness Si content integrated value)≧0. In the case of 55, it is judged that there is clearly more Si in the plating layer upper layer portion than in the plating layer lower layer portion.
　From the viewpoint of corrosion resistance, it is preferable that (surface-side Si content integrated value)/(total thickness Si content integrated value)≧0.60.
[0033]
　FIG. 1 shows the thickness direction using GDS for the plated steel sheet (Production No. 3 of the example described below) and the comparative plated steel sheet (Production No. 23 of the example described below) according to the present embodiment. It is the figure which made the graph the result of having measured Si content.
　In FIG. 1, the left side of the graph is the surface of the plating layer, and the horizontal axis is the distance from the surface of the plating layer. The vertical axis represents the detection intensity of Si or Fe.
　In the present embodiment, it is determined that the position where the detected strength of Fe is 50% of the maximum detected strength is the interface between the steel plate and the alloy layer, and the position where the detected strength of Fe is 25% of the maximum detected strength is the alloy layer. It is determined that the interface is between the plating layer and the plating layer. Then, the position at a half distance from the surface of the plating layer to the interface between the plating layer and the alloy layer is defined as the thickness center of the plating layer.
　That is, the manufacturing number of FIG. For example, the position in the thickness direction (position A) where the detected intensity of Fe is 50% of the maximum detected intensity is the interface between the steel sheet and the alloy layer, and the detected intensity of Fe is 25% of the maximum detected intensity. The position in the thickness direction (position B) is determined to be the interface between the plating layer and the alloy layer. A position (position C) which is half the distance from the surface of the plating layer to position B is the center of the thickness of the plating layer.
[0034]
　From FIG. 1, it can be seen that the plating layer of the plated steel sheet according to the present embodiment has a large amount of Si on the surface side. On the other hand, in the steel corresponding to the conventional steel, much Si exists on the steel plate side.
[0035]
(Structure of
　Plating Layer ) The plating layer contains at least the above-mentioned Mg—Si phase and a phase containing Al and Zn as its structure.
　The phase containing Al and Zn is mainly composed of a dendrite-like α-Al phase and a ZnAlMg eutectic phase. The phase containing Al and Zn may include a MgZn 2 phase, a Si phase, and/or a FeAl phase, depending on the average composition of the plating layer .
[0036]
　The Mg-Si phase is a phase composed of Mg 2 Si which is an intermetallic compound of Si and Mg . The Mg-Si phase is precipitated between the arms of the α-Al phase.
　In the plated steel sheet according to the present embodiment, after pulling up the steel sheet from the plating bath and solidifying the molten metal under predetermined conditions, the temperature of the molten metal is preferentially lowered from the surface side of the molten metal, at this time. A Mg-Si phase is precipitated as a primary crystal. After the Mg—Si phase is precipitated, the remaining molten metal solidifies to form a phase containing Al and Zn. In particular, when a phase containing Al and Zn is formed, the Mg—Si phase previously formed on the surface layer side of the molten metal is sandwiched between the α-Al phase arms.
[0037]
　A part of the Mg—Si phase formed on the surface side of the plating layer may be exposed on the surface of the plating layer. The exposed Mg—Si phase is observed as islands.
　When part of the Mg—Si phase (for example, 1.0% or more) is exposed on the surface of the plating layer, spangle formation on the surface is suppressed. Therefore, the appearance of the plated steel sheet according to the present embodiment is significantly different from that of Galvalume steel sheet (registered trademark) or the like in which spangles are positively generated on the surface.
[0038]
(Amount of Plating Layer Adhesion) The amount of
　plating layer adhesion is not particularly limited. However, if the adhesion amount is too small, the effect of improving the corrosion resistance by the plating layer becomes small. On the other hand, if the adhesion amount is too large, the bending workability of the plating layer is deteriorated, and problems such as cracks are likely to occur. Therefore, it is preferable that the adhesion amount is 40 to 250 g/m 2 .
[0039]
When the
　steel sheet is hot-dipped, an alloy layer (interfacial alloy layer) is formed between the steel sheet and the plated layer. The alloy layer contains Fe and Si, or Fe, Si and Al. The thickness is 10 μm or less, preferably 5 μm or less, more preferably 3 μm or less.
[0040]
A Mg oxide film
　having a thickness of 5 nm or more and 100 nm or less may be further formed on the surface layer of the plating layer. The presence of the Mg oxide film having a thickness of 5 nm or more can further improve the corrosion resistance. On the other hand, even when the Mg oxide film is formed, if the thickness exceeds 100 nm, the workability is remarkably deteriorated, so the upper limit of the thickness is set to 100 nm.
[0041]
　If the plated steel sheet according to the present embodiment has the above-mentioned configuration regardless of the manufacturing method, the effect can be obtained. However, for example, according to the following manufacturing method, the plating layer according to the present embodiment can be obtained.
[0042]
　First, it is preferable that the steel sheet after being pulled up from the plating bath is rapidly cooled to a temperature range where the Mg—Si phase (Mg 2 Si) is precipitated. Since the quenching increases the precipitation driving force, it is possible to finely precipitate the Mg—Si phase as a primary crystal. When gradually cooled, there is a concern that the Mg-Si phase will not become fine.
[0043]
　After quenching, the steel sheet to which the molten metal has adhered is soaked in a plating bath so that it stays in a temperature range in which the Mg-Si phase precipitates and other phases do not precipitate. This temperature range varies depending on the components of the plating layer, but is 400 to 450° C. in the case of the plated steel sheet according to the present embodiment.
　In the case of rapid cooling, the temperature of the surface side of the molten metal is lower than that of the steel sheet side (inside) of the molten metal. Therefore, the Mg—Si phase preferentially precipitates on the surface side. When the Mg-Si phase precipitates on the surface side of the molten metal, the Mg and Si concentrations on the surface side become lower than those on the steel sheet side, and a concentration gradient occurs, but in the residence temperature range, the parts other than the Mg-Si phase Is in a molten state, Mg and Si move in the plating layer from the steel sheet side to the surface side so as to eliminate the concentration gradient. As a result, more Mg—Si phase is precipitated on the surface side of the plating layer than on the steel sheet side.
　When the residence temperature is low or the residence time is short, the molten metal solidifies before Mg and Si are concentrated on the surface side in the molten metal, and as a result, many Mg—Si phases cannot exist on the surface side.
　In order to obtain the above effects, it is preferable that the residence time is, for example, 5 seconds or more in the residence temperature range. On the other hand, if the residence time exceeds 60 seconds, the effect is saturated and the productivity is lowered, which is not preferable.
　In the present embodiment, the term “dwell” means that the steel sheet temperature is kept in the residence temperature range for a predetermined time, and if the temperature remains in the residence temperature range, the temperature may be changed without being limited to isothermal holding.
[0044]
　Since the Mg-Si phase precipitated on the surface side is fixed after the retention, it is preferable to rapidly cool the steel sheet to below the solidification temperature of the plating layer.
[0045]
　As described above, the plated steel sheet according to the present embodiment can be manufactured.
Example
[0046]
　Hereinafter, examples of the present invention will be described, but the conditions in the examples are one condition example adopted for confirming the feasibility and effects of the present invention, and the present invention is limited to this one condition example. It is not something that will be done. The present invention can employ various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.
[0047]
　A plating bath was prepared by using a predetermined amount of pure metal ingot so that the plating bath composition shown in Table 1 was obtained. The plating original plate was made into a plated steel plate by using a batch type hot dip plating apparatus including the above plating bath. The plating bath temperature was 605°C.
　As a plating original plate, a cold-rolled steel plate defined by JIS G3141 having a plate thickness of 0.8 mm was cut into 100 mm length×200 mm width and used.
[0048]
　In this example, an apparatus having a structure assuming a hot dipping line was used. Specifically, this apparatus has a plating original plate heating part, a snout part, a hot dip bath part, a wiping part, and a heating/cooling device. Further, in this apparatus, all the steps up to plating can be performed in an N 2 -5% H 2 environment.
[0049]
　First, before immersion in a plating bath, the surface of the plating original plate was reduced by holding it for 1 minute in an atmosphere of N 2 -5% H 2 gas having a dew point of −40° C. and a temperature of 800° C. Then, the steel plate (plating original plate) was air-cooled with N 2 gas, and after the steel plate temperature reached 620° C., the steel plate was immersed at a dipping speed of 500 mm/sec and held in the plating bath for about 3 seconds.
　After immersion in the plating bath, the steel plate was pulled up at a pulling rate of 150 mm/sec. At the time of pulling up, the coating adhesion amount was adjusted to 40 to 250 g/m 2 by wiping gas (N 2 ) . The oxygen concentration in the snout in contact with the plating bath was set to 20 ppm or less. 　The cooling conditions after the adjustment of the coating weight are shown in Table 2. N 2 gas was used for cooling . In this way, various plated steel sheets were manufactured. The steel plate temperature during hot dipping is the surface temperature of the central part of the original plate.
[0050]
[table 1]

[0051]
[Table 2]

[0052]
　Regarding the obtained plated steel sheet, the average composition of the plated layer and the alloy layer, the volume fraction (cross-sectional area ratio) of the Mg—Si phase in the plated layer, the average equivalent circle diameter of the Mg—Si phase in the surface layer portion, and (the surface Side Si content integrated value)/(total thickness Si content integrated value) was determined by the following methods.
　In addition, the corrosion resistance and workability were evaluated.
[0053]
(Average composition of
　plating layer and alloy layer ) The average composition of the plating layer and alloy layer is determined by dissolving and separating the plating layer and alloy layer from the plated steel sheet on which the plating layer and alloy layer are formed using hydrochloric acid, The plating composition can be determined by using the mass of the dissolved plating layer and alloy layer as the denominator and the mass of the element determined by ICP for the separated plating layer and alloy layer as the numerator.
[0054]
(Volume Fraction of Mg-Si Phase in Plating Layer)
　By mapping the element distribution of SEM-EDS to obtain the area ratio of each phase (cross-sectional area ratio) in the cross section of the plating layer, the volume fraction of Mg-Si phase is obtained. Calculated the rate.
[0055]
(Equivalent circle equivalent diameter of Mg-Si phase of surface layer) Using
　EPMA, from the surface side of the plating layer to the surface layer part of the plating layer (about 1 μm from the surface of the plating layer) within a range (field of view) of 500×500 μm. The distribution of Si in the range up to the depth position of was measured. The area of ​​the measured phase containing Si was calculated, and the diameter of a circle having an area equivalent to the area was defined as the equivalent circle diameter of the Mg—Si phase. Further, the equivalent circle diameters of the obtained Mg—Si phases were averaged to obtain the average equivalent circle diameter.
[0056]
(Surface-side Si content integrated value)/(Total thickness Si content integrated value) Using a
　Marcus-type high frequency glow discharge emission surface analyzer (GD-Profiler: manufactured by Horiba Ltd.), the measured diameter was 4 mm and the surface of the plating layer From the above, the Si content was continuously measured by performing elemental analysis while digging the sample by Ar sputtering toward the interface between the plating layer and the alloy layer in the thickness direction. Then, with respect to the obtained measured values, the Si contents from the surface of the plating layer to the center of the thickness of the plating layer were integrated to calculate the integrated value (surface-side Si content integrated value). In addition, the Si content over the entire thickness of the plating layer (from the surface of the plating layer to the interface between the plating layer and the alloy layer) was integrated to calculate the integrated value (total thickness Si content integrated value).
　Then, (surface-side Si content integrated value) was divided by (total thickness Si content integrated value) to obtain (surface-side Si content integrated value)/(total thickness Si content integrated value).
[0057]
(Corrosion resistance) As
　an evaluation of the corrosion resistance, the corrosion weight loss (the steel plate weight before the test-the steel plate weight after the test) after exposing the plated steel plate to shade in Miyakojima, Okinawa for 1 year was determined. The corrosion weight loss was evaluated according to the following criteria, and it was judged that "G" or more was excellent in corrosion resistance. The results are shown in Table 4.
EX: Corrosion weight loss 5 g/m 2 or less
VG: Corrosion weight loss 5 g/m 2 or more and less than 10 g/m 2
G: Corrosion weight loss 10 g/m 2 or more and less than 20 g/m 2
F: Corrosion weight loss 20 g/m 2 or more and 25 g/m 2 Less than
B: Corrosion weight loss 25 g/m 2 or more
[0058]
　The test site on Miyako Island, Okinawa Prefecture, where the corrosion resistance evaluation test was conducted, is an exposure site with a coast 2 km south of an island of about 160 km 2 located in the East China Sea, just north of the Tropic of Cancer , and its environment. Is an oceanic subtropical climate, and is an environment with many natural deterioration factors such as high temperature and humidity, solar radiation, and sea salt particles.
[0059]
(Workability) As
　an evaluation of workability, a bending test was performed on a plated steel sheet under the condition of a bending radius R=2 mm. The presence or absence of cracking and peeling was visually observed, the results were evaluated as follows, and G or higher was regarded as a pass.
VG: No cracking or peeling
G: Cracking, no peeling
B: Peeling The
　results are shown in Table 4.
[0060]
[Table 3]

[0061]
[Table 4]

[0062]
　As shown in Tables 1 to 4, the average composition of the plating layer and the alloy layer, the volume fraction of the Mg—Si phase in the plating layer, the average equivalent circle diameter of the Mg—Si phase in the surface layer portion of the plating layer, the surface side Si content integrated value)/(total thickness Si content integrated value) is within the range of the present invention. Nos. 1 to 22 have excellent corrosion resistance and workability.
　On the other hand, a manufacturing No. in which any of the conditions is out of the range of the present invention. In Nos. 23 to 32, either the workability or the corrosion resistance was poor.
　As described above, it is presumed that there is a difference in corrosion resistance and workability between the example and the comparative example due to the difference in the composition of the plating layer and the segregation state of the Mg—Si phase.
Industrial availability
[0063]
　According to the above aspect of the present invention, it is possible to provide a Zn-Al-Mg-based plated steel sheet having excellent corrosion resistance and workability. This Zn-Al-Mg-based plated steel sheet is suitable for building materials, automobiles, home appliances, and has high industrial utility value.
The scope of the claims
[Claim 1]
　A steel plate, an
　alloy layer containing Fe and Si formed on the surface of the
　steel plate, and a plating layer formed on a surface of the alloy layer opposite to the steel plate, the
　plating layer and the alloy layer The average composition of
　　Al is 45.0 to 65.0%,
　　Si is 0.50 to 5.00%,
　　Mg is 1.00 to 10.00%,
and the
　　balance is Zn and Fe. And an impurity, and the
　plating layer contains a Mg—Si phase with a volume fraction of 0.1 to 20.0%, and the
　plating layer has a range of 1 μm from the surface of the plating layer in the thickness direction of the plating layer. Defined as the surface layer part, the average equivalent circle diameter of the Mg—Si phase in the direction of the plating layer of the surface layer part in a plan view is 0.1 to 15.0 μm, and
　from the surface of the plating layer When the position of 1/2 of the thickness of the plating layer is defined as the plating layer thickness center toward the interface between the plating layer and the alloy layer, and the Si content is measured over the entire thickness of the plating layer. In addition, the integrated value of the Si content from the surface of the plating layer to the center of the plating layer thickness is 0.55 times or more the integrated value of the Si content from the surface of the plating layer to the interface. There is
　a Zn-Al-Mg based plated steel sheet.
[Claim 2]
　The integrated value of the Si content from the surface of the plating layer to the center of the thickness of the plating layer is 0.60 times or more the integrated value of the Si content from the surface of the plating layer to the interface. The Zn-Al-Mg-based plated steel sheet according to claim 1, wherein
[Claim 3]
　The average composition of the plating layer and the alloy layer further comprises 0.01 to 1.00% of one or more of Cr, Ca, Sr, and Ni in total. The Zn-Al-Mg-based plated steel sheet described.