Hot-dip al -zn-si-mg coated steel sheet, surface-treated steel sheet, and pre-painted steel sheet

Abstract

To provide a hot-dip Al-Zn-Si-Mg coated steel sheet that stably exhibits excellent corrosion resistance. Disclosed is a hot-dip Al-Zn-Si-Mg coated steel sheet including a coating layer, in which the coating layer has a composition containing Al: 45 mass% to 65 mass%, Si: 1.0 mass % to 4.0 mass%, and Mg: 1.0 mass% to 10.0 mass%, with the balance being Zn and inevitable impurities, and diffraction intensities of Mg2Si and MgZn2 in the coating layer as measured by an X-ray diffraction method satisfy the following relation (1): Mg2Si(111) / MgZn2(100)≤ 2.0 (1).

Description

Hot-dip Al-Zn-Si-Mg plated steel sheets, surface-treated steel sheets, and painted steel sheets

[0001] The present invention relates to a hot-dip Al-Zn-Si-Mg plated steel sheet, a surface-treated steel sheet, and a coated steel sheet, all of which have stable and excellent corrosion resistance.

[0002] Hot-dip Al-Zn coated steel sheets, such as 55% Al-Zn, are known to offer high corrosion resistance among hot-dip galvanized steel sheets because they combine the sacrificial corrosion protection of zinc with the high corrosion resistance of aluminum. Therefore, due to their excellent corrosion resistance, hot-dip Al-Zn coated steel sheets are primarily used in building materials such as roofs and walls that are exposed to outdoor conditions for long periods of time, as well as in civil engineering and construction applications such as guardrails, wiring and piping, and soundproof walls. Demand for hot-dip Al-Zn coated steel sheets has been increasing in recent years due to the growing demand for corrosion-resistant and maintenance-free materials, particularly in more severe environments such as acid rain caused by air pollution, the use of deicing agents to prevent road ice in snowy areas, and coastal development.

[0003] The coating of hot-dip Al-Zn coated steel sheets is composed of areas where Al containing supersaturated Zn has solidified in the form of dendrites (α-Al phase) and a Zn-Al eutectic structure that exists in the spaces between the dendrites (interdendrites), and is characterized by a structure in which multiple α-Al phases are layered in the thickness direction of the coating. This unique coating structure creates a complex corrosion progression path from the surface, making it difficult for corrosion to progress easily, and it is known that hot-dip Al-Zn coated steel sheets can achieve superior corrosion resistance compared to hot-dip galvanized steel sheets with the same coating thickness.

[0004] Attempts have been made to further extend the service life of such hot-dip Al-Zn-coated steel sheets, and hot-dip Al-Zn-Si-Mg-coated steel sheets containing magnesium have been put into practical use. Patent Document 1, for example, discloses a hot-dip Al-Zn-Si-Mg-coated steel sheet having a coating containing an Al-Zn-Si alloy containing magnesium, the Al-Zn-Si alloy containing 45 to 60 wt. % aluminum, 37 to 46 wt. % zinc, and 1.2 to 2.3 wt. % silicon, with the magnesium concentration being 1 to 5 wt. Patent Document 2 also discloses a hot-dip Al-Zn-Si-Mg-coated steel sheet containing 2 to 10% magnesium and / or 0.01 to 10% calcium in the coating to improve corrosion resistance and enhance protection after the steel substrate is exposed. Furthermore, Patent Document 3 discloses a hot-dip Al-Zn-Si-Mg-plated steel sheet which forms a coating layer containing, by mass%, 1 to 15% Mg, 2 to 15% Si, 11 to 25% Zn, and the balance being Al and unavoidable impurities, and which aims to improve the corrosion resistance of the flat sheet and edge faces by controlling the size of intermetallic compounds such as Mg2Si phase and MgZn2 phase present in the plating film to 10 μm or less.

[0005] Because the above-mentioned hot-dip Al-Zn-plated steel sheet has a beautiful appearance with a white metallic luster and a spangle pattern, it is often used without painting, and there are strong demands for its appearance. Therefore, technologies to improve the appearance of hot-dip Al-Zn-plated steel sheets have been developed. For example, Patent Document 4 discloses a hot-dip Al-Zn-Si-Mg-plated steel sheet in which the plating film contains 0.01 to 10% Sr, thereby suppressing wrinkle-like irregularity defects. Furthermore, Patent Document 5 also discloses a hot-dip Al-Zn-Si-Mg-plated steel sheet in which the plating film contains 500 to 3000 ppm Sr, thereby suppressing mottling defects. Furthermore, Patent Document 6 discloses a hot-dip Al-Zn-Si-Mg-plated steel sheet in which the plating film contains 0.001 to 1.0% Sr, thereby achieving both excellent surface appearance and corrosion resistance. Furthermore, Patent Document 7 also discloses a hot-dip Al-Zn-Si-Mg-plated steel sheet that achieves both good surface appearance and corrosion resistance in both flat and processed portions by including 0.001 to 1.0% Sr in the plating film. Furthermore, Patent Document 8 also discloses a hot-dip Al-Zn-Si-Mg-plated steel sheet that achieves both good surface appearance and corrosion resistance by including 0.01 to 0.2% Sr in the plating film. Furthermore, Patent Document 9 discloses a hot-dip Al-Zn-Si-Mg-plated steel sheet that improves corrosion resistance by controlling the Si and Mg concentrations in the plating film at a specific ratio.

[0006] The above-mentioned hot-dip Al-Zn-plated steel sheets have a problem of white rust due to corrosion of the plating film when used in a severely corrosive environment. Because this white rust reduces the appearance of the steel sheet, development of plated steel sheets with improved white rust resistance has been underway. For example, Patent Document 10 discloses a hot-dip Al-Zn-Si-Mg-plated steel sheet in which the mass ratio of Mg in the Si-Mg phase to the total amount of Mg in the plating layer is optimized to improve the white rust resistance of processed parts. Patent Document 11 also discloses a technology for improving blackening resistance and white rust resistance by forming a chemical conversion coating containing a urethane resin on the plating film of a hot-dip Al-Zn-Si-Mg-plated steel sheet.

[0007] Furthermore, coated steel sheets with a chemical conversion coating, a primer coating, a topcoat coating, etc. formed on the surface of hot-dip Al-Zn-plated steel sheets are subjected to various processes, such as 90-degree and 180-degree bending, by press forming, roll forming, or embossing, and are also required to have long-term coating durability. To meet these requirements, coated steel sheets are known in which a hot-dip Al-Zn-plated steel sheet is coated with a chromate-containing chemical conversion coating, a primer coating containing a chromate-based rust inhibitor, and a topcoat coating with excellent weather resistance, such as a thermosetting polyester resin coating or a fluororesin coating, is formed on top of the coated steel sheet. However, the use of chromate, an environmentally hazardous substance, in such coated steel sheets has recently been recognized as problematic, and there is a strong demand for the development of coated steel sheets that can improve corrosion resistance and surface appearance without using chromate. As a technique that meets these demands, for example, Patent Document 12 discloses a surface-treated hot-dip plated steel material in which an aluminum-zinc alloy plating layer (α) containing Al, Zn, Si, and Mg and in which the contents of these elements are adjusted is plated on the surface of a steel material, and a coating (β) containing at least one compound (A) selected from titanium compounds and zirconium compounds as a film-forming component is further formed as an upper layer thereon, and the mass ratio of the Si—Mg phase in the aluminum-zinc alloy plating layer (α) to the total amount of Mg in the plating layer is adjusted to 3% or more.

[0008] Japanese Patent No. 5020228 Japanese Patent No. 5000039 Japanese Patent Publication No. 2002-12959 Japanese Patent No. 3983932 Japanese Patent Publication No. 2011-514934 International Publication No. 2020 / 179147 International Publication No. 2020 / 179148 Japanese Patent Publication No. 2020-143370 International Publication No. 2016 / 140370 Japanese Patent No. 5751093 Japanese Patent Publication No. 2019-155872 Japanese Patent Publication No. 2005-169765

[0009] However, the techniques disclosed in Patent Documents 1 to 3, which incorporate magnesium into the coating film, do not necessarily result in improved corrosion resistance. The hot-dip Al-Zn-Si-Mg-plated steel sheets disclosed in Patent Documents 1 to 3 attempt to improve corrosion resistance solely by incorporating magnesium into the coating composition, but they do not take into account the characteristics of the metallic and intermetallic compound phases that make up the coating film, making it impossible to uniformly assess the superiority or inferiority of corrosion resistance. Therefore, even when hot-dip Al-Zn-Si-Mg-plated steel sheets are manufactured using the same coating bath composition, accelerated corrosion tests reveal variations in corrosion resistance, making them less superior to Al-Zn-plated steel sheets without magnesium. Similarly, when it comes to improving coating appearance, simply adding strontium to the coating film does not necessarily eliminate wrinkle-like irregularity defects. The hot-dip Al-Zn-Si-Mg-plated steel sheets disclosed in Patent Documents 4 to 8 sometimes failed to achieve both corrosion resistance and appearance. In addition, because magnesium is an element that easily oxidizes, the magnesium contained in the coating bath can generate oxides (top dross) near the bath surface, and in the case of hot-dip coating, FeAl-based compounds (bottom dross) containing iron can be generated that are unevenly distributed in the coating bath or at the bottom over time. These dross can adhere to the surface of the coating film, causing convex defects and potentially damaging the appearance of the coating film surface.

[0010] Furthermore, it is known that when steel sheets are plated using a molten Al-Zn-Si bath containing Mg, Mg2Si, MgZn2, and Si phases precipitate in addition to the α-Al phase in the plated film. However, the effects of the precipitation amount and abundance ratio of each phase on corrosion resistance have been largely unknown. In the hot-dip Al-Zn-Si-Mg-plated steel sheet disclosed in Patent Document 9, the concentrations of Si and Mg are controlled at a specific ratio to eliminate the precipitation of the Si phase in the plated film, thereby improving corrosion resistance. However, this does not necessarily suppress the formation of the Si phase. Even when the formation of the Si phase in the plated film is suppressed, excellent corrosion resistance may not be obtained, making this technically incomplete.

[0011] Furthermore, none of the techniques have been able to achieve sufficient improvement in white rust resistance. Regarding the hot-dip Al-Zn-Si-Mg-plated steel sheet of Patent Document 10, although it describes improvement in white rust resistance in processed portions and flat portions after heating, it does not consider white rust resistance in unheated flat portions, and achieving stable white rust resistance remains a challenge. Furthermore, with the hot-dip Al-Zn-Si-Mg-plated steel sheet of Patent Document 11, it is not necessarily possible to obtain consistently excellent corrosion resistance and white rust resistance, and further improvement is desired.

[0012] Furthermore, as mentioned above, coated steel sheets are required to have long-term coating film durability even when subjected to various processes, such as 90-degree and 180-degree bending, by press forming, roll forming, embossing, etc. However, the technology of Patent Document 12 does not necessarily provide stable corrosion resistance and surface appearance after processing. The corrosion resistance of coated steel sheets is naturally affected by the corrosion resistance of the underlying plated steel sheet. Regarding surface appearance, the unevenness of wrinkle-like defects can range up to several tens of micrometers. Therefore, even if the surface is smoothed by a coating film, the unevenness cannot be completely eliminated, and it is considered that an improvement in the appearance of the coated steel sheet cannot be expected. Furthermore, since the coating film is thinner at the convex portions, there is a concern that corrosion resistance may be locally reduced. Therefore, to obtain coated steel sheets with excellent corrosion resistance and surface appearance, it is important to improve the corrosion resistance and surface appearance of the underlying plated steel sheet.

[0013] In view of the above circumstances, an object of the present invention is to provide a hot-dip Al-Zn-Si-Mg-plated steel sheet having consistently excellent corrosion resistance. Another object of the present invention is to provide a surface-treated steel sheet having consistently excellent corrosion resistance and white rust resistance. A further object of the present invention is to provide a coated steel sheet having consistently excellent corrosion resistance and corrosion resistance in processed areas.

[0014] The present inventors conducted research aimed at solving the above-mentioned problems and found that the amounts of the Mg2Si, MgZn2, and Si phases formed in the coating of hot-dip Al-Zn-Si-Mg-coated steel sheets increase or decrease, and their abundance ratios change depending on the balance of the components in the coating and the coating formation conditions. Furthermore, they found that some phases may not precipitate depending on the compositional balance. They also found that the corrosion resistance of hot-dip Al-Zn-Si-Mg-coated steel sheets varies depending on the abundance ratios of these phases, and that corrosion resistance is consistently improved when the MgZn2 phase is more abundant than the Mg2Si and Si phases. However, it is known that it is extremely difficult to distinguish between the Mg2Si, MgZn2, and Si phases even when observing the surface or cross-section of the coating using common techniques, such as secondary electron images or backscattered electron images, using a scanning electron microscope. While observation using a transmission electron microscope (TEM) is a more detailed analytical technique that can obtain microscopic information, it has not been possible to ascertain the abundance ratios of the Mg2Si, MgZn2, and Si phases, which affect macroscopic information such as corrosion resistance and appearance. Therefore, the present inventors conducted further intensive research and found that by utilizing the intensity ratios of specific diffraction peaks of the Mg2Si, MgZn2, and Si phases, it is possible to quantitatively determine the abundance ratios of the phases. Furthermore, the present inventors discovered that when the Mg2Si and MgZn2 phases satisfy a specific abundance ratio in a coating, not only can excellent corrosion resistance be stably achieved, but also dross generation can be suppressed and good surface appearance can be ensured. Furthermore, the present inventors discovered that by controlling the abundance ratios of the Mg2Si, MgZn2, and Si phases in a hot-dip Al-Zn-Si-Mg-coated steel sheet, and then controlling the Sr concentration in the bath, the occurrence of wrinkle-like irregularity defects can be reliably suppressed, resulting in a coated steel sheet with excellent surface appearance.

[0015] The present inventors also conducted research into the chemical conversion coating formed on the plating coating, and discovered that by forming the chemical conversion coating from a specific resin and a specific metal compound, the affinity of the chemical conversion coating with the plating coating and its rust prevention effect can be improved, resulting in a stable improvement in white rust resistance.

[0016] Furthermore, the present inventors also investigated the chemical conversion coating and primer coating formed on the plating film, and found that by forming the chemical conversion coating from a specific resin and a specific inorganic compound, and forming the primer coating from a specific polyester resin and an inorganic compound, the barrier properties and adhesion of the coating can be improved, and excellent post-processing corrosion resistance can be achieved even if the coating is chromate-free.

[0017] The present invention was made based on the above findings, and its gist is as follows: 1. A hot-dip Al-Zn-Si-Mg-plated steel sheet having a plating film, wherein the plating film has a composition containing 45 to 65 mass% Al, 1.0 to 4.0 mass% Si, and 1.0 to 10.0 mass% Mg, with the balance consisting of Zn and unavoidable impurities, and wherein the diffraction intensities of Mg2Si and MgZn2 in the plating film, as measured by an X-ray diffraction method, satisfy the following relationship (1): Mg2Si (111) / MgZn2(100)≦2.0 (1) Mg2Si (111): Diffraction intensity of the (111) plane of Mg2Si (plane spacing d = 0.3668 nm), MgZn2 (100): Diffraction intensity of the (100) plane of MgZn2 (plane spacing d = 0.4510 nm)

[0018] 2. The hot-dip Al-Zn-Si-Mg coated steel sheet according to item 1, characterized in that the diffraction intensity of Si in the coating by X-ray diffraction satisfies the following relationship (2): Si (111) = 0 (2) Si (111): Diffraction intensity of the Si (111) plane (planar spacing d = 0.3135 nm)

[0019] 3. The hot-dip Al-Zn-Si-Mg plated steel sheet according to 1 or 2 above, wherein the plated coating further contains 0.01 to 1.0 mass % of Sr.

[0020] 4. The hot-dip Al-Zn-Si-Mg plated steel sheet according to any one of items 1 to 3 above, characterized in that the Al content in the plated coating is 50 to 60 mass %.

[0021] 5. The hot-dip Al-Zn-Si-Mg plated steel sheet according to any one of items 1 to 4 above, characterized in that the Si content in the plated film is 1.0 to 3.0 mass %.

[0022] 6. The hot-dip Al-Zn-Si-Mg plated steel sheet according to any one of items 1 to 5 above, characterized in that the Mg content in the plated film is 1.0 to 5.0 mass%.

[0023] 7. A surface-treated steel sheet comprising the plating film according to any one of items 1 to 6 above and a chemical conversion film formed on the plating film, characterized in that the chemical conversion film contains at least one resin selected from epoxy resins, urethane resins, acrylic resins, acrylic silicone resins, alkyd resins, polyester resins, polyalkylene resins, amino resins, and fluororesins, and at least one metal compound selected from P compounds, Si compounds, Co compounds, Ni compounds, Zn compounds, Al compounds, Mg compounds, V compounds, Mo compounds, Zr compounds, Ti compounds, and Ca compounds.

[0024] 8. A coated steel sheet having a coating film formed on the plating film according to any one of items 1 to 6 above, either directly or via a chemical conversion coating film, wherein the chemical conversion coating film contains a resin component containing 30 to 50 mass% in total of (a): an anionic polyurethane resin having an ester bond and (b): an epoxy resin having a bisphenol skeleton, the content ratio of (a):(b) being within the range of 3:97 to 60:40 by mass, and an inorganic compound containing 2 to 10 mass% of a vanadium compound, 40 to 60 mass% of a zirconium compound, and 0.5 to 5 mass% of a fluorine compound, and the coating film has at least a primer coating film containing a polyester resin having a urethane bond and an inorganic compound containing a vanadium compound, a phosphate compound, and magnesium oxide.

[0025] According to the present invention, it is possible to provide a hot-dip Al-Zn-Si-Mg-plated steel sheet having stably excellent corrosion resistance. Also, according to the present invention, it is possible to provide a surface-treated steel sheet having stably excellent corrosion resistance and white rust resistance. Furthermore, according to the present invention, it is possible to provide a coated steel sheet having stably excellent corrosion resistance and corrosion resistance in processed portions.

[0026] This is a diagram to explain the flow of the Japanese Automobile Standards Combined Cycle Test (JASO-CCT).

[0027] (Hot-dip Al-Zn-Si-Mg-plated steel sheet) The hot-dip Al-Zn-Si-Mg-plated steel sheet of the present invention has a plating film on the surface of the steel sheet. The plating film has a composition containing 45 to 65 mass% Al, 1.0 to 4.0 mass% Si, and 1.0 to 10.0 mass% Mg, with the balance being Zn and unavoidable impurities.

[0028] The Al content in the plating film is 45 to 65 mass%, preferably 50 to 60 mass%, to balance corrosion resistance and operational efficiency. This is because an Al content of at least 45 mass% in the plating film causes dendritic solidification of Al, resulting in a plating film structure primarily composed of an α-Al phase dendritic solidification structure. The dendritic solidification structure is layered in the thickness direction of the plating film, which complicates the corrosion progression path and improves the corrosion resistance of the plating film itself. Furthermore, the more α-Al phase dendritic portions are layered, the more complex the corrosion progression path becomes, making it more difficult for corrosion to reach the substrate steel sheet, thereby improving corrosion resistance. Therefore, it is preferable to set the Al content to 50 mass% or more. On the other hand, if the Al content in the plating film exceeds 65 mass%, most of the Zn changes to a structure in solid solution in the α-Al, making it impossible to suppress the dissolution reaction of the α-Al phase, and the corrosion resistance of the Al-Zn-Si-Mg-based plating deteriorates. For this reason, the Al content in the plating film must be 65 mass % or less, and preferably 60 mass % or less.

[0029] The Si content in the plating film is primarily intended to suppress the growth of Fe-Al and / or Fe-Al-Si interfacial alloy layers at the interface with the substrate steel sheet, thereby preventing deterioration of the adhesion between the plating film and the steel sheet. When a steel sheet is immersed in an Al-Zn plating bath containing Si, Fe on the steel sheet surface reacts with Al and Si in the bath to form an Fe-Al and / or Fe-Al-Si intermetallic compound layer at the interface between the substrate steel sheet and the plating film. Since the growth rate of the Fe-Al-Si alloy is slower than that of the Fe-Al alloy, a higher proportion of the Fe-Al-Si alloy suppresses the growth of the entire interfacial alloy layer. Therefore, the Si content in the plating film must be 1.0% by mass or more. However, if the Si content in the plating film exceeds 4.0% by mass, not only does the effect of suppressing the growth of the interfacial alloy layer saturate, but the presence of excess Si in the plating film also promotes corrosion. Therefore, the Si content is limited to 4.0% or less. Furthermore, the Si content in the plating film is preferably 3.0% or less from the viewpoint of suppressing the presence of an excessive Si phase. Note that, in relation to the Mg content described below, the Si content is preferably 1.0 to 3.0% by mass from the viewpoint of easily satisfying the relational expression (1) described below.

[0030] The plating film contains 1.0 to 10.0% Mg. The inclusion of Mg in the plating film allows the aforementioned Si to exist in the form of an intermetallic compound, the Mg2Si phase, thereby suppressing the acceleration of corrosion. Furthermore, the inclusion of Mg in the plating film also forms an intermetallic compound, the MgZn2 phase, in the plating film, further improving corrosion resistance. If the Mg content in the plating film is less than 1.0% by mass, sufficient corrosion resistance cannot be ensured because Mg is used to dissolve in the α-Al phase, the primary phase, rather than to form the intermetallic compounds (Mg2Si, MgZn2). On the other hand, if the Mg content in the plating film is too high, the corrosion resistance improvement effect saturates and the α-Al phase becomes brittle, resulting in reduced workability. Therefore, the Mg content is set to 10.0% or less. Furthermore, the Mg content in the plating film is preferably 5.0% by mass or less to suppress dross generation during plating formation and facilitate plating bath management. In relation to the Si content, from the viewpoint of easily satisfying the relational expression (1) described below, the Mg content is preferably 3.0 mass%, and in consideration of compatibility with dross suppression, the Mg content is more preferably 3.0 to 5.0 mass%.

[0031] In the hot-dip Al-Zn-Si-Mg-plated steel sheet of the present invention, the diffraction intensities of Mg2Si and MgZn2 in the plating film, as determined by X-ray diffraction, must satisfy the following relationship (1): Mg2Si (111) / MgZn2(100)≦2.0 (1) Mg2Si (111): Diffraction intensity of the Mg2Si (111) plane (planar spacing d=0.3668 nm), MgZn2 (100): Diffraction intensity of the MgZn2 (100) plane (planar spacing d=0.4510 nm).

[0032] As mentioned above, in the present invention, it is important to control the abundance ratio of intermetallic compounds such as Mg2Si and MgZn2 that are generated in the plating film due to the inclusion of Mg to a specific ratio. Investigation into the effects of these on corrosion resistance is currently ongoing, and many points remain unknown, but the following mechanism is presumed.

[0033] When hot-dip Al-Zn-Si-Mg-plated steel sheets are exposed to a corrosive environment, the intermetallic compounds dissolve preferentially over the α-Al phase, resulting in a Mg-rich environment near the formed corrosion products. It is presumed that in such a Mg-rich environment, the formed corrosion products are less likely to decompose, thereby enhancing the protective effect of the plating film. Furthermore, because the protective effect of the plating film is enhanced more effectively with MgZn2 than with Mg2Si, it is believed that increasing the proportion of MgZn2 in the intermetallic compounds present in the plating film is effective.

[0034] The abundance ratio of Mg2Si to MgZn2 in the plating film is required to satisfy the relationship (1): Mg2Si (111) / MgZn2 (100)≦2.0, as determined using diffraction peak intensities obtained by X-ray diffraction. However, if the abundance ratio of Mg2Si to MgZn2 in the plating film does not satisfy the relationship (1), that is, if Mg2Si (111) / MgZn2 (100)>2.0, a large amount of Mg2Si is present in the intermetallic compounds present in the plating film. As a result, the aforementioned Mg-rich environment cannot be obtained in the vicinity of the corrosion products, and it becomes difficult to obtain the improved protective effect of the plating film. With regard to the abundance ratio of Mg2Si and MgZn2 in the plating film, even if the composition of the plating film satisfies the range of the present invention (containing 45 to 65 mass% Al, 1.0 to 4.0 mass% Si, and 1.0 to 10.0 mass% Mg, with the remainder consisting of Zn and unavoidable impurities), if the abundance ratio of Mg2Si and MgZn2 does not satisfy the relationship (1), the effect of improving the protective action of the plating film according to the present invention cannot be sufficiently obtained.

[0035] In the relationship (1), MgSi(111) is the diffraction intensity of the (111) plane of MgSi (planar spacing d = 0.3668 nm), and MgZn(100) is the diffraction intensity of the (100) plane of MgZn (planar spacing d = 0.4510 nm). The MgSi(111) and MgZn(100) can be measured by X-ray diffraction by mechanically scraping a portion of the plating film, powdering it, and then subjecting it to X-ray diffraction (powder X-ray diffraction measurement). The diffraction intensity is measured by measuring the diffraction peak intensity of MgSi corresponding to planar spacing d = 0.3668 nm and the diffraction peak intensity of MgZn corresponding to planar spacing d = 0.4510 nm, and then calculating the ratio of these to obtain MgSi(111) / MgZn(100). The amount of the plating film required for powder X-ray diffraction measurement (the amount of plating film scraped off) is 0.1 g or more, preferably 0.3 g or more, from the viewpoint of accurately measuring MgSi(111) and MgZn(100). Furthermore, when the plating film is scraped off, steel sheet components other than the plating film may be contained in the powder. However, these intermetallic compound phases are contained only in the plating film and do not affect the peak intensity described above. Furthermore, the reason for powdering the plating film and performing X-ray diffraction is that when X-ray diffraction is performed on a plating film formed on a plated steel sheet, it is affected by the plane orientation of the plating film solidification structure, making it difficult to accurately calculate the phase ratio.

[0036] Furthermore, in the hot-dip Al-Zn-Si-Mg-plated steel sheet of the present invention, in order to more stably improve corrosion resistance, it is preferable that the diffraction intensity of Si in the plating film by X-ray diffraction satisfy the following relationship (2): Si(111)=0 (2) Si(111): Diffraction intensity of the Si(111) plane (planar spacing d=0.3135 nm). It is generally known that the presence of Si phase as a cathode site promotes the dissolution of the surrounding α-Al phase during the dissolution reaction of an Al alloy in an aqueous solution. Therefore, reducing the Si phase is also effective in suppressing the dissolution of the α-Al phase. Among these, achieving a film free of Si phase, as shown in relationship (2) (i.e., zero diffraction peak intensity of the Si(111) plane), is the most effective for stabilizing corrosion resistance. The diffraction peak intensity of the Si(111) plane by X-ray diffraction can be measured using the same method as that for measuring Mg2Si(111) and MgZn2(100) described above.

[0037] Here, the method for satisfying the above-described relationship (1) or (2) is not particularly limited. For example, to satisfy relationship (1) or (2), the abundance ratios of MgSi, MgZn, and Si (diffraction intensities of MgSi (111), MgZn (100), and Si (111)) can be controlled by adjusting the balance of the Si content, Mg content, and Al content in the plating film. The balance of the Si content, Mg content, and Al content in the plating film does not necessarily satisfy relationship (1) or (2) by setting them to a constant content ratio; for example, it is necessary to change the content ratios of Mg and Al depending on the Si content (mass %). In addition to adjusting the balance of the Si content, Mg content, and Al content in the plating film, the diffraction intensities of MgSi (111), MgZn (100), and Si (111) can be controlled so as to satisfy the relationship (1) or (2) by adjusting the conditions during plating film formation (e.g., cooling conditions after plating).

[0038] The hot-dip Al-Zn-Si-Mg-plated steel sheet of the present invention contains Zn and unavoidable impurities. Among these, the unavoidable impurities include Fe. This Fe is inevitably contained in the plating film due to dissolution of the steel sheet or bath-immersed equipment into the plating bath, and is also supplied by diffusion from the base steel sheet during the formation of the interfacial alloy layer. The Fe content in the plating film is typically approximately 0.3 to 2.0 mass%. Other unavoidable impurities include Cr, Ni, and Cu. The total content of the unavoidable impurities is not particularly limited, but because excessive content may affect various properties of the plated steel sheet, a total content of 5.0 mass% or less is preferred.

[0039] Furthermore, in the hot-dip Al-Zn-Si-Mg steel sheet of the present invention, the plating film preferably contains 0.01 to 1.0 mass% Sr. The inclusion of Sr in the plating film more reliably suppresses the occurrence of surface defects such as wrinkle-like irregularities, thereby achieving good surface appearance. The wrinkle-like defects are wrinkle-like irregularities formed on the surface of the plating film and are observed as whitish streaks on the surface of the plating film. Such wrinkle-like defects are more likely to occur when a large amount of Mg is added to the plating film. Therefore, in the hot-dip galvanized steel sheet, the inclusion of Sr in the plating film causes Sr to be oxidized preferentially over Mg in the surface layer of the plating film, thereby suppressing the oxidation reaction of Mg and thereby suppressing the occurrence of the wrinkle-like defects.

[0040] In the hot-dip Al-Zn-Si-Mg steel sheet of the present invention, it is preferable that the abundance ratios of Mg2Si and MgZn2 in the above-described plating film satisfy relationship (1), and that the plating film contains 0.01 to 1.0 mass% Sr. This allows for greater utilization of the above-described effect of Sr in improving surface appearance. Although the reason for this is unclear, it is presumed that an increase in the Mg2Si content in the plating film makes it difficult to suppress oxidation of the plating surface, thereby affecting the appearance improvement effect of adding Sr. Note that if the Sr content in the plating film is less than 0.01 mass%, it is difficult to achieve the effect of suppressing the occurrence of wrinkle defects described above. If the Sr content in the plating film exceeds 1.0 mass%, Sr is excessively incorporated into the interfacial alloy layer, which may have a greater impact on plating adhesion than on the appearance improvement effect. Therefore, it is preferable that the Sr content in the plating film be 0.01 to 1.0 mass%.

[0041] Furthermore, since the plating film can improve the stability of corrosion products and delay the progression of corrosion in the same way as Mg, it is preferable that the plating film further contains 0.01 to 10 mass% in total of one or more elements selected from Cr, Mn, V, Mo, Ti, Ca, Ni, Co, Sb, and B. The reason why the total content of the above-mentioned elements is set to 0.01 to 10 mass% is that a sufficient corrosion-retarding effect can be obtained and the effect does not saturate.

[0042] The coating weight of the plating film is set to 45 to 120 g / m per side in order to satisfy various characteristics. 2 It is preferable that the coating weight of the plating film is 45 g / m 2 In the above cases, sufficient corrosion resistance can be obtained for applications requiring long-term corrosion resistance, such as building materials, and the coating weight of the plating film is 120 g / m 2 This is because, in the following cases, it is possible to achieve excellent corrosion resistance while suppressing the occurrence of plating cracks during processing. From the same viewpoint, the coating weight of the plating film is 45 to 100 g / m 2 It is more preferable that:

[0043] The coating weight of the plating film can be determined, for example, by a method in which a specific area of ​​the plating film is dissolved and stripped in a mixed solution of hydrochloric acid and hexamethylenetetramine, and the coating weight is calculated from the difference in weight of the steel sheet before and after stripping, as specified in JIS H 0401: 2013. To determine the coating weight per side using this method, the non-target side can be sealed with tape so that the plated surface is not exposed, and then the dissolution described above is carried out.

[0044] The component composition of the plating film can be confirmed, for example, by immersing the plating film in hydrochloric acid or the like to dissolve it, and then subjecting the resulting solution to ICP emission spectroscopy, atomic absorption spectroscopy, etc. This method is merely one example, and any method that can accurately quantify the component composition of the plating film may be used, and is not particularly limited.

[0045] The coating film on the hot-dip Al-Zn-Si-Mg coated steel sheet obtained by the present invention has a composition generally equivalent to that of the coating bath, and therefore the composition of the coating film can be controlled with high precision by controlling the composition of the coating bath.

[0046] Furthermore, the base steel sheet constituting the hot-dip Al-Zn-Si-Mg-plated steel sheet of the present invention is not particularly limited, and a cold-rolled steel sheet, a hot-rolled steel sheet, or the like can be used as appropriate depending on the required performance and specifications.

[0047] Furthermore, the method for obtaining the base steel sheet is not particularly limited. For example, in the case of the hot-rolled steel sheet, a steel sheet that has been subjected to a hot-rolling process and a pickling process can be used, and in the case of the cold-rolled steel sheet, a cold-rolling process can be added to the production. Furthermore, in order to obtain the properties of the steel sheet, a recrystallization annealing process or the like can also be performed before the hot-dip galvanizing process.

[0048] The method for producing the hot-dip Al-Zn-Si-Mg-plated steel sheet of the present invention is not particularly limited. For example, the steel sheet can be produced by cleaning, heating, and immersing the base steel sheet in a coating bath using continuous hot-dip galvanizing equipment. In the steel sheet heating process, recrystallization annealing or the like is performed to control the structure of the base steel sheet itself, and heating in a reducing atmosphere such as a nitrogen-hydrogen atmosphere is effective in preventing oxidation of the steel sheet and reducing the small amount of oxide film present on the surface.

[0049] Furthermore, as for the coating bath used in producing the hot-dip Al-Zn-Si-Mg coated steel sheet of the present invention, as described above, the coating film has a composition that is substantially the same as the coating bath composition as a whole. Therefore, the coating bath may contain 45 to 65 mass% Al, 1.0 to 4.0 mass% Si, and 1.0 to 10.0 mass% Mg, with the balance being Zn, Fe, and unavoidable impurities.

[0050] Furthermore, the bath temperature of the coating bath is not particularly limited, but is preferably in the range of (melting point + 20°C) to 650°C. The reason why the lower limit of the bath temperature is set to melting point + 20°C is that the bath temperature needs to be at or above the solidification point in order to perform hot-dip coating, and setting the bath temperature to melting point + 20°C prevents solidification due to a local drop in the bath temperature of the coating bath. On the other hand, the reason why the upper limit of the bath temperature is set to 650°C is that if the bath temperature exceeds 650°C, it becomes difficult to rapidly cool the coating film, and there is a risk that the interfacial alloy layer formed between the coating film and the steel sheet will become thick.

[0051] Furthermore, the temperature of the base steel sheet immersed in the coating bath (immersion sheet temperature) is not particularly limited, but from the viewpoint of ensuring coating characteristics in continuous hot dip coating operations and preventing changes in bath temperature, it is preferable to control it to within ±20°C of the coating bath temperature.

[0052] Furthermore, the immersion time of the steel sheet in the coating bath is 0.5 seconds or more. This is because if it is less than 0.5 seconds, there is a risk that a sufficient coating film will not be formed on the surface of the base steel sheet. There is no particular upper limit to the immersion time, but a longer immersion time may result in a thicker interfacial alloy layer formed between the coating film and the steel sheet, so it is preferably 8 seconds or less.

[0053] In addition, in the case of hot-dip Al-Zn-Si-Mg-plated steel sheets, a coating film can be formed directly or via an intermediate layer on the plating film, depending on the required performance.

[0054] The method for forming the coating film is not particularly limited and can be appropriately selected depending on the required performance. Examples include roll coater coating, curtain flow coating, and spray coating. After applying a coating material containing an organic resin, the coating film can be formed by heating and drying the coating material using means such as hot air drying, infrared heating, and induction heating.

[0055] The intermediate layer is not particularly limited as long as it is a layer formed between the plating film of the hot-dip plated steel sheet and the coating film.

[0056] (Surface-treated steel sheet) The surface-treated steel sheet of the present invention comprises a plating film on the surface of the steel sheet and a chemical conversion film formed on the plating film, wherein the configuration of the plating film is the same as that of the plating film of the above-mentioned hot-dip Al-Zn-Si-Mg-plated steel sheet of the present invention.

[0057] The surface-treated steel sheet of the present invention has a chemical conversion coating formed on the coating. The chemical conversion coating may be formed on at least one surface of the surface-treated steel sheet, and may also be formed on both surfaces of the surface-treated steel sheet depending on the application and required performance.

[0058] The surface-treated steel sheet of the present invention is characterized in that the chemical conversion coating contains at least one resin selected from the group consisting of epoxy resins, urethane resins, acrylic resins, acrylic silicone resins, alkyd resins, polyester resins, polyalkylene resins, amino resins, and fluororesins, and at least one metal compound selected from the group consisting of P compounds, Si compounds, Co compounds, Ni compounds, Zn compounds, Al compounds, Mg compounds, V compounds, Mo compounds, Zr compounds, Ti compounds, and Ca compounds. Forming the above-described chemical conversion coating on a plated coating improves affinity with the plated coating, enabling the chemical conversion coating to be formed uniformly on the plated coating, and also enhancing the rust prevention and barrier effects of the chemical conversion coating. As a result, the surface-treated steel sheet of the present invention can achieve stable corrosion resistance and white rust resistance.

[0059] Here, the resin constituting the chemical conversion coating is at least one selected from epoxy resin, urethane resin, acrylic resin, acrylic silicone resin, alkyd resin, polyester resin, polyalkylene resin, amino resin, and fluororesin from the viewpoint of improving corrosion resistance. From the same viewpoint, the resin preferably contains at least one of urethane resin and acrylic resin. The resin constituting the chemical conversion coating also includes addition polymers of the above-mentioned resins.

[0060] Examples of the epoxy resin that can be used include glycidyl etherified epoxy resins such as bisphenol A type, bisphenol F type, and novolac type epoxy resins; glycidyl etherified bisphenol A type epoxy resins to which propylene oxide, ethylene oxide, or polyalkylene glycol has been added; aliphatic epoxy resins; alicyclic epoxy resins; and polyether-based epoxy resins.

[0061] As the urethane resin, for example, an oil-modified polyurethane resin, an alkyd-based polyurethane resin, a polyester-based polyurethane resin, a polyether-based polyurethane resin, a polycarbonate-based polyurethane resin, or the like can be used.

[0062] Examples of the acrylic resin include polyacrylic acid and copolymers thereof, polyacrylic acid esters and copolymers thereof, polymethacrylic acid and copolymers thereof, polymethacrylic acid esters and copolymers thereof, urethane-acrylic acid copolymers (or urethane-modified acrylic resins), and styrene-acrylic acid copolymers. Furthermore, these resins may be modified with other alkyd resins, epoxy resins, phenolic resins, or the like.

[0063] The acrylic silicone resin may be, for example, a resin containing a hydrolyzable alkoxysilyl group at the side chain or end of an acrylic copolymer as a main component, to which a curing agent is added. In addition, when an acrylic silicone resin is used, excellent weather resistance can be expected in addition to corrosion resistance.

[0064] Examples of the alkyd resin include oil-modified alkyd resins, rosin-modified alkyd resins, phenol-modified alkyd resins, styrenated alkyd resins, silicon-modified alkyd resins, acrylic-modified alkyd resins, oil-free alkyd resins, and high-molecular-weight oil-free alkyd resins.

[0065] The polyester resin is a polycondensate synthesized by dehydration condensation of a polycarboxylic acid and a polyalcohol to form an ester bond. Examples of the polycarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the polyalcohol include ethylene glycol, 1,3-propanediol, 1,4-butanediol, and 1,4-cyclohexanedimethanol. Specific examples of the polyester include polyethylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, and polybutylene naphthalate. Acrylic-modified versions of these polyester resins can also be used.

[0066] Examples of the polyalkylene resin include ethylene-based copolymers such as ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers, and carboxyl-modified polyolefin resins, ethylene-unsaturated carboxylic acid copolymers, and ethylene-based ionomers. Furthermore, these resins may be modified with other alkyd resins, epoxy resins, phenolic resins, or the like.

[0067] The amino resin is a thermosetting resin produced by the reaction of an amine or amide compound with an aldehyde, and examples thereof include melamine resin, guanamine resin, and thiourea resin. Melamine resin is preferred from the viewpoints of corrosion resistance, weather resistance, adhesion, etc. The melamine resin is not particularly limited, but examples thereof include butylated melamine resin, methylated melamine resin, and aqueous melamine resin.

[0068] Examples of the fluororesin include fluoroolefin polymers and copolymers of fluoroolefins with alkyl vinyl ethers, cycloalkyl vinyl ethers, carboxylic acid-modified vinyl esters, hydroxyalkyl allyl ethers, tetrafluoropropyl vinyl ethers, etc. When these fluororesins are used, not only corrosion resistance but also excellent weather resistance and excellent hydrophobicity can be expected.

[0069] Furthermore, in order to improve corrosion resistance and processability, it is particularly preferable to use a curing agent, such as urea resin (butylated urea resin, etc.), melamine resin (butylated melamine resin, butyl etherified melamine resin, etc.), butylated urea-melamine resin, amino resin such as benzoguanamine resin, blocked isocyanate, oxazoline compound, phenol resin, etc.

[0070] The metal compound constituting the chemical conversion coating is at least one selected from the group consisting of P compounds, Si compounds, Co compounds, Ni compounds, Zn compounds, Al compounds, Mg compounds, V compounds, Mo compounds, Zr compounds, Ti compounds, and Ca compounds. From the same viewpoint, it is preferable that the metal compound contains at least one of P compounds, Si compounds, and V compounds.

[0071] The P compound contained in the chemical conversion coating can improve corrosion resistance and sweat resistance. The P compound is a compound containing P, and may contain, for example, one or more selected from inorganic phosphoric acid, organic phosphoric acid, and salts thereof.

[0072] The inorganic phosphoric acid, organic phosphoric acid, and salts thereof are not particularly limited and any compound can be used. For example, the inorganic phosphoric acid is preferably one or more selected from phosphoric acid, monophosphate, diphosphate, triphosphate, pyrophosphoric acid, pyrophosphate, tripolyphosphoric acid, tripolyphosphate, phosphorous acid, phosphite, hypophosphorous acid, and hypophosphite. The organic phosphoric acid is preferably phosphonic acid (phosphonic acid compound). The phosphonic acid is preferably one or more selected from nitrilotrismethylenephosphonic acid, phosphonobutanetricarboxylic acid, methyldiphosphonic acid, methylenephosphonic acid, and ethylidenediphosphonic acid. When the P compound is a salt, the salt is preferably a salt of an element from Groups 1 to 13 of the periodic table, more preferably a metal salt, and preferably one or more selected from alkali metal salts and alkaline earth metal salts.

[0073] When a chemical conversion treatment solution containing the above-mentioned P compound is applied to a hot-dip Al-Zn-Si-Mg-plated steel sheet, the P compound acts to etch the plating film surface, forming a concentrated layer containing the Al, Zn, Si, and Mg components of the plating film on the plating film side of the chemical conversion treatment solution. The formation of this concentrated layer strengthens the bond between the chemical conversion film and the plating film surface, improving the adhesion of the chemical conversion film. The concentration of the P compound in the chemical conversion treatment solution is not particularly limited, but can be 0.25% to 5% by mass. A concentration of the P compound less than 0.25% by mass results in insufficient etching effect, reducing adhesion to the plating interface and reducing corrosion resistance at flat surfaces. This may also reduce corrosion resistance and sweat resistance at defects, cut edges, and damaged areas of the plating or coating caused by processing. From the same perspective, the concentration of the P compound is preferably 0.35% by mass or more, more preferably 0.50% by mass or more. On the other hand, if the concentration of the P compound exceeds 5 mass %, not only will the life of the chemical conversion treatment solution be shortened, but the appearance of the formed film will likely be uneven, and the amount of P eluted from the chemical conversion film will increase, which may reduce resistance to blackening. From the same perspective, the concentration of the P compound is preferably 3.5 mass % or less, and more preferably 2.5 mass % or less. Regarding the content of the P compound in the chemical conversion film, for example, by applying and drying a chemical conversion treatment solution with a P compound concentration of 0.25 mass % to 5 mass %, the amount of P deposited in the dried chemical conversion film will be 5 to 100 mg / m 2 It can be said that:

[0074] The Si compound is a component that forms the framework of the chemical conversion coating together with the resin, and enhances the affinity with the plating coating, enabling the formation of a uniform chemical conversion coating. The Si compound is a compound containing Si, and preferably contains one or more selected from, for example, silica, trialkoxysilane, tetraalkoxysilane, and a silane coupling agent.

[0075] The silica is not particularly limited and any silica can be used. For example, at least one of wet silica and dry silica can be used. As colloidal silica, which is a type of wet silica, for example, Snowtex O, C, N, S, 20, OS, OXS, NS, etc. manufactured by Nissan Chemical Industries, Ltd. can be suitably used. Furthermore, as the dry silica, for example, AEROSIL 50, 130, 200, 300, 380, etc. manufactured by Nippon Aerosil Co., Ltd. can be suitably used.

[0076] The trialkoxysilane is not particularly limited and any trialkoxysilane can be used. For example, it is preferable to use a trialkoxysilane represented by the general formula: R1Si(OR2)3 (wherein R1 is hydrogen or an alkyl group having 1 to 5 carbon atoms, and R2 is the same or different alkyl group having 1 to 5 carbon atoms). Examples of such trialkoxysilanes include trimethoxysilane, triethoxysilane, and methyltriethoxysilane.

[0077] The tetraalkoxysilane is not particularly limited and any tetraalkoxysilane can be used. For example, it is preferable to use a tetraalkoxysilane represented by the general formula: Si(OR)4 (wherein R is the same or different alkyl group having 1 to 5 carbon atoms). Examples of such tetraalkoxysilane include tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane.

[0078] The silane coupling agent is not particularly limited and any one can be used, for example, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldiethoxysilane, γ-aminopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-mercaptopropylmethyldimethoxysilane, γ-mercaptopropyltrimethoxysilane, vinyltriethoxysilane, γ-isocyanatepropyltriethoxysilane, etc.

[0079] Incorporating the Si compound into a chemical conversion coating causes the Si compound to undergo dehydration condensation, forming an amorphous chemical conversion coating with siloxane bonds that provides a high barrier effect for blocking corrosion factors. Furthermore, bonding with the resin described above results in the formation of a chemical conversion coating with even higher barrier properties. Furthermore, in a corrosive environment, dense and stable corrosion products are formed in defects or damaged areas of the plating or coating caused by processing, and the combined effect of the Si compound and the plating coating also inhibits corrosion of the substrate steel sheet. From the viewpoint of a high effect of forming stable corrosion products, it is preferable to use at least one of colloidal silica and fumed silica as the Si compound.

[0080] The concentration of the Si compound in the chemical conversion treatment solution for forming the chemical conversion coating is 0.2% by mass to 9.5% by mass. If the concentration of the Si compound in the chemical conversion treatment solution is 0.2% by mass or more, a barrier effect due to siloxane bonds can be obtained, resulting in improved corrosion resistance in flat surfaces, as well as improved corrosion resistance in defective areas, cut areas, and areas damaged by processing, etc., and sweat resistance. Furthermore, if the concentration of the Si compound is 9.5% by mass or less, the life of the chemical conversion treatment solution can be extended. By applying and drying a chemical conversion treatment solution with a Si compound concentration of 0.2% by mass to 9.5% by mass, the Si deposition amount in the chemical conversion coating after drying can be 2 to 95 mg / m 2 It can be said that:

[0081] The inclusion of the Co compound and the Ni compound in the chemical conversion coating can improve blackening resistance. This is thought to be because Co and Ni have the effect of delaying the elution of water-soluble components from the coating in a corrosive environment. Furthermore, Co and Ni are elements that are less likely to oxidize than Al, Zn, Si, Mg, etc. Therefore, by concentrating at least one of the Co compound and the Ni compound at the interface between the chemical conversion coating and the plating coating (forming a concentrated layer), the concentrated layer acts as a barrier against corrosion, thereby improving blackening resistance.

[0082] By using a chemical conversion treatment solution containing the Co compound, Co can be contained in the chemical conversion coating and incorporated into the concentrated layer. A cobalt salt is preferably used as the Co compound. It is more preferable to use one or more cobalt salts selected from the group consisting of cobalt sulfate, cobalt carbonate, and cobalt chloride. Furthermore, by using a chemical conversion treatment solution containing the Ni compound, Ni can be contained in the chemical conversion coating and incorporated into the concentrated layer. A nickel salt is preferably used as the Ni compound. It is more preferable to use one or more nickel salts selected from the group consisting of nickel sulfate, nickel carbonate, and nickel chloride.

[0083] The concentration of the Co compound and / or Ni compound in the chemical conversion treatment solution is not particularly limited, but can be 0.25% by mass to 5% by mass in total. If the concentration of the Co compound and / or Ni compound is less than 0.25% by mass, the interfacial enrichment layer will be non-uniform, reducing the corrosion resistance of flat surfaces and potentially reducing the corrosion resistance of defective areas, cut edge surfaces, and areas damaged by plating or coating due to processing. From the same perspective, the concentration is preferably 0.5% by mass or more, more preferably 0.75% by mass or more. On the other hand, if the concentration of the Co compound and / or Ni compound exceeds 5% by mass, the appearance of the formed coating is likely to be non-uniform, potentially reducing corrosion resistance. From the same perspective, the concentration is preferably 4.0% by mass or less, more preferably 3.0% by mass or less. By applying and drying a chemical conversion treatment solution having a total concentration of the Co compound and / or Ni compound of 0.25% by mass to 5% by mass, the total deposition amount of Co and Ni in the dried chemical conversion coating can be 5 to 100 mg / m 2 It can be said that:

[0084] By adding the Al compound, the Zn compound, and the Mg compound to the chemical conversion treatment solution, a concentrated layer containing at least one of Al, Zn, and Mg can be formed on the plating film side of the chemical conversion coating. The formed concentrated layer can improve corrosion resistance. The Al compound, the Zn compound, and the Mg compound are not particularly limited as long as they are compounds containing Al, Zn, and Mg, respectively, but are preferably inorganic compounds, and are preferably salts, chlorides, oxides, or hydroxides.

[0085] Examples of the Al compound include one or more selected from aluminum sulfate, aluminum carbonate, aluminum chloride, aluminum oxide, and aluminum hydroxide. Examples of the Zn compound include one or more selected from zinc sulfate, zinc carbonate, zinc chloride, zinc oxide, and zinc hydroxide. Examples of the Mg compound include one or more selected from magnesium sulfate, magnesium carbonate, magnesium chloride, magnesium oxide, and magnesium hydroxide.

[0086] The total concentration of the Al compound, Zn compound, and / or Mg compound in the chemical conversion treatment solution for forming the chemical conversion coating is preferably 0.25% by mass to 5% by mass. If the total concentration is 0.25% by mass or more, the concentrated layer can be formed more effectively, resulting in further improved corrosion resistance. On the other hand, if the total concentration is 5% by mass or less, the appearance of the chemical conversion coating becomes more uniform, and the corrosion resistance of flat areas, defective areas, and areas damaged by processing or other factors in the plating or coating is further improved.

[0087] The V compound contained in the chemical conversion coating allows the V to dissolve appropriately in a corrosive environment and bond with zinc ions and other plating components that also dissolve in a corrosive environment to form a dense protective coating. The formed protective coating can further improve corrosion resistance not only on the flat surfaces of the steel sheet, but also against defects, damaged areas in the plating coating caused by processing, and corrosion that progresses from cut edges to the flat surfaces.

[0088] The V compound is a compound containing V, and examples thereof include one or more selected from sodium metavanadate, vanadyl sulfate, and vanadium acetylacetonate.

[0089] The V compound in the chemical conversion treatment solution for forming the chemical conversion coating is preferably 0.05% by mass to 4% by mass. If the V compound concentration is 0.05% by mass or more, it will be more likely to dissolve in a corrosive environment and form a protective coating, improving the corrosion resistance of defects, cut edge portions, and damaged portions of the plating coating caused by processing. On the other hand, if the V compound concentration exceeds 4% by mass, the appearance of the formed chemical conversion coating will likely be uneven and blackening resistance will be reduced.

[0090] The Mo compound, when contained in the chemical conversion coating, can enhance the blackening resistance of the surface-treated steel sheet. The Mo compound is a compound containing Mo and can be obtained by adding one or both of molybdic acid and a molybdate to the chemical conversion treatment solution. Examples of the molybdate include one or more selected from sodium molybdate, potassium molybdate, magnesium molybdate, and zinc molybdate.

[0091] The concentration of the Mo compound in the chemical conversion treatment solution for forming the chemical conversion coating is preferably 0.01% by mass to 3% by mass. If the concentration of the Mo compound is 0.01% by mass or more, the generation of oxygen-deficient zinc oxide is further suppressed, and blackening resistance can be further improved. On the other hand, if the concentration of the Mo compound is 3% by mass or less, the life of the chemical conversion treatment solution is further extended and corrosion resistance can be further improved.

[0092] The inclusion of the Zr compound and the Ti compound in the chemical conversion coating prevents the chemical conversion coating from becoming porous and densifies the coating, making it more difficult for corrosion factors to permeate the chemical conversion coating and improving corrosion resistance.

[0093] The Zr compound is a compound containing Zr, and can be, for example, one or more selected from zirconyl acetate, zirconyl sulfate, potassium zirconyl carbonate, sodium zirconyl carbonate, and ammonium zirconyl carbonate. Among these, organic titanium chelate compounds are preferred because they densify the coating when the chemical conversion treatment liquid is dried to form the coating, thereby providing better corrosion resistance.

[0094] The Ti compound is a compound containing Ti, and for example, one or more selected from titanium sulfate, titanium chloride, titanium hydroxide, titanium acetylacetonate, titanium octylene glycolate, and titanium ethylacetoacetate can be used.

[0095] The total concentration of Zr compounds and / or Ti compounds in the chemical conversion treatment solution for forming the chemical conversion coating is preferably 0.2% to 20% by mass. If the total concentration of Zr compounds and / or Ti compounds is 0.2% by mass or more, the effect of inhibiting the permeation of corrosion factors is enhanced, and corrosion resistance can be further improved not only in flat surfaces but also in defects, cut edges, and areas of plating film damage caused by processing. On the other hand, if the total concentration of Zr compounds and / or Ti compounds is 20% by mass or less, the life of the chemical conversion treatment solution can be further extended.

[0096] The Ca compound contained in the chemical conversion coating can exert the effect of reducing the corrosion rate.

[0097] The Ca compound is a compound containing Ca, and examples thereof include Ca oxide, Ca nitrate, Ca sulfate, and Ca-containing intermetallic compounds. More specifically, examples of the Ca compound include CaO, CaCO3, Ca(OH)2, Ca(NO3)2.4H2O, and CaSO4.2H2O. The content of the Ca compound in the chemical conversion coating is not particularly limited.

[0098] The chemical conversion coating may contain various known components commonly used in the coatings field, as needed, such as various surface conditioners such as leveling agents and antifoaming agents, various additives such as dispersants, anti-settling agents, ultraviolet absorbers, light stabilizers, silane coupling agents and titanate coupling agents, various pigments such as color pigments, extender pigments and luster materials, curing catalysts, organic solvents and lubricants.

[0099] In the surface-treated steel sheet of the present invention, the chemical conversion coating preferably does not contain harmful components such as hexavalent chromium, trivalent chromium, fluorine, etc. This is because the chemical conversion treatment solution for forming the chemical conversion coating does not contain these harmful components, resulting in high safety and low environmental impact.

[0100] The coating weight of the chemical conversion coating is not particularly limited. For example, from the viewpoint of more reliably ensuring corrosion resistance while preventing peeling of the chemical conversion coating, the coating weight of the chemical conversion coating is set to 0.1 to 3.0 g / m 2 It is preferable to set the density to 0.5 to 2.5 g / m 2 It is more preferable that the coating weight of the chemical conversion coating is 0.1 g / m. 2 By setting the coating weight at 3.0 g / m or more, corrosion resistance can be more reliably ensured, and the coating weight of the chemical conversion coating can be set at 3.0 g / m or more. 2 The chemical conversion coating weight can be determined by an appropriate method selected from existing techniques, such as a method of measuring the amount of elements present in the coating whose contents are known in advance by performing fluorescent X-ray analysis of the coating.

[0101] The method for forming the chemical conversion coating is not particularly limited and can be selected appropriately depending on the required performance, manufacturing equipment, etc. For example, the chemical conversion coating can be formed by continuously applying a chemical conversion treatment solution to the plating film using a roll coater or the like, followed by drying at a peak metal temperature (PMT) of approximately 60 to 200°C using hot air or induction heating. In addition to roll coaters, known methods such as airless spraying, electrostatic spraying, and curtain flow coaters can also be used to apply the chemical conversion treatment solution. Furthermore, the chemical conversion coating is not particularly limited and may be either a single-layer film or a multi-layer film, as long as it contains the resin and the metal compound.

[0102] Furthermore, in the surface-treated steel sheet of the present invention, a paint film can be formed on the chemical conversion coating, if necessary.

[0103] (Coated Steel Sheet) The coated steel sheet of the present invention is a coated steel sheet having a coating film formed on a plating film directly or via a chemical conversion coating. The configuration of the plating film is the same as that of the plating film of the above-mentioned hot-dip Al-Zn-Si-Mg-plated steel sheet of the present invention.

[0104] The coated steel sheet of the present invention can have a chemical conversion coating formed on the plating film. The chemical conversion coating may be formed on at least one side of the coated steel sheet, or may be formed on both sides of the coated steel sheet depending on the application and required performance.

[0105] The coated steel sheet of the present invention is characterized in that the chemical conversion coating contains a resin component containing a total of 30 to 50 mass% of (a): an anionic polyurethane resin having an ester bond and (b): an epoxy resin having a bisphenol skeleton, with the content ratio of (a):(b) being in the range of 3:97 to 60:40 by mass, and an inorganic compound containing 2 to 10 mass% of a vanadium compound, 40 to 60 mass% of a zirconium compound, and 0.5 to 5 mass% of a fluorine compound. Forming the above-mentioned chemical conversion coating on a plating coating can increase the strength and adhesion of the chemical conversion coating while also improving corrosion resistance.

[0106] The resin components constituting the chemical conversion coating include (a): an anionic polyurethane resin having an ester bond and (b): an epoxy resin having a bisphenol skeleton.

[0107] The anionic polyurethane resin (a) having an ester bond may be a resin obtained by copolymerizing a reaction product of a polyester polyol with a diisocyanate or polyisocyanate having two or more isocyanate groups with a dimethylol alkyl acid. A chemical conversion treatment solution can be obtained by dispersing the resin in a liquid such as water by a known method.

[0108] Examples of the polyester polyol include polyesters obtained by a dehydration condensation reaction between a glycol component and an acid component such as an ester-forming derivative of a hydroxylcarboxylic acid, polyesters obtained by a ring-opening polymerization reaction of a cyclic ester compound such as ε-caprolactone, and copolymer polyesters thereof. Examples of the polyisocyanate include aromatic polyisocyanates, aliphatic polyisocyanates, and alicyclic polyisocyanates. Examples of the aromatic polyisocyanate include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, m-xylene diisocyanate, diphenylmethane diisocyanate, 2,4-diphenylmethane diisocyanate, 2,2-diphenylmethane diisocyanate, triphenylmethane triisocyanate, polymethylene polyphenyl polyisocyanate, naphthalene diisocyanate, and derivatives thereof (e.g., prepolymers obtained by reaction with polyols, modified polyisocyanates such as carbodiimide compounds of diphenylmethane diisocyanate, etc.).

[0109] When synthesizing a urethane by reacting the polyester polyol with the diisocyanate or polyisocyanate, the anionic polyurethane resin having an ester bond (a) can be obtained by copolymerizing a dimethylol alkyl acid, self-emulsifying it, and dissolving it in water (dispersing it in water). In this case, examples of the dimethylol alkyl acid include dimethylol alkyl acids having 2 to 6 carbon atoms, and more specifically, dimethylol ethanoic acid, dimethylol propanoic acid, dimethylol butanoic acid, dimethylol heptanoic acid, and dimethylol hexanoic acid.

[0110] Furthermore, known epoxy resins can be used as the (b) epoxy resin having a bisphenol skeleton. Examples include bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, bisphenol AD-type epoxy resins, and bisphenol S-type epoxy resins. These epoxy resins can be obtained by reacting a bisphenol compound such as bisphenol A, bisphenol F, bisphenol AD, or bisphenol S with epichlorohydrin in the presence of an alkali catalyst. Among these, component [A] preferably contains a bisphenol A-type epoxy resin or a bisphenol F-type epoxy resin, and more preferably contains a bisphenol A-type epoxy resin. A chemical conversion treatment solution can be obtained by dispersing the (b) epoxy resin having a bisphenol skeleton in a liquid such as water using a known method.

[0111] The resin component acts as a binder for the chemical conversion coating. The (a) anionic polyurethane resin with ester bonds, which constitutes the binder, is flexible and therefore less likely to break (peel) during processing. The (b) epoxy resin with a bisphenol skeleton improves adhesion to the underlying zinc-plated steel sheet and the overlying primer coating. The resin component is contained in the chemical conversion coating in a total amount of 30 to 50% by mass. If the resin component content is less than 30% by mass, the binder effect of the chemical conversion coating is reduced. If the resin component content exceeds 50% by mass, the functions of the inorganic components described below, such as their inhibitory action, are reduced. From the same perspective, the resin component content in the chemical conversion coating is preferably 35 to 45% by mass.

[0112] Furthermore, the resin component must have a mass ratio ((a):(b)) of the (a) anionic polyurethane resin having an ester bond to the (b) epoxy resin having a bisphenol skeleton of 3:97 to 60:40. If the (a):(b) ratio is outside this range, the chemical conversion coating will have reduced flexibility and adhesion, resulting in insufficient corrosion resistance. From the same perspective, the (a):(b) ratio is preferably 10:90 to 55:45.

[0113] The resin component may contain other resins (other resin components) besides the above-described (a) anionic polyurethane resin having an ester bond and (b) epoxy resin having a bisphenol skeleton, depending on the required performance. The other resin components are not particularly limited, and may be, for example, at least one or a combination of two or more selected from acrylic resins, acrylic silicone resins, alkyd resins, polyester resins, polyalkylene resins, amino resins, and fluororesins. When the resin component contains other resins, the total content of the (a) anionic polyurethane resin having an ester bond and the (b) epoxy resin having a bisphenol skeleton is preferably 50% by mass or more, and more preferably 75% by mass or more. This is to more reliably achieve reduced flexibility and adhesion as a chemical treatment coating.

[0114] The chemical conversion coating also contains, as inorganic compounds, 2 to 10 mass % of a vanadium compound, 40 to 60 mass % of a zirconium compound, and 0.5 to 5 mass % of a fluorine compound, which can enhance the corrosion resistance of the chemical conversion coating.

[0115] The vanadium compound is added to a chemical conversion treatment solution and acts as a rust inhibitor. The inclusion of the vanadium compound in the chemical conversion coating allows the vanadium compound to dissolve appropriately in a corrosive environment and bond with zinc ions and other plating components that also dissolve in a corrosive environment, forming a dense protective coating. The formed protective coating can further enhance corrosion resistance not only to the flat surface of the steel sheet, but also to defects, damaged areas in the plating coating caused by processing, and corrosion progressing from the cut edge to the flat surface. Examples of the vanadium compound include vanadium pentoxide, metavanadate, ammonium metavanadate, vanadium oxytrichloride, vanadium trioxide, vanadium dioxide, magnesium vanadate, vanadyl acetylacetonate, and vanadium acetylacetonate. Among these, it is particularly desirable to use a tetravalent vanadium compound or a tetravalent vanadium compound obtained by reduction or oxidation.

[0116] The content of the vanadium compound in the chemical conversion coating is 2 to 10 mass %. If the content of the vanadium compound in the chemical conversion coating is less than 2 mass %, the inhibitor effect is insufficient, resulting in a decrease in corrosion resistance, while if the content of the vanadium compound exceeds 10 mass %, the moisture resistance of the chemical conversion coating decreases.

[0117] The zirconium compound contained in the chemical conversion coating is expected to improve the strength and corrosion resistance of the chemical conversion coating by reacting with the plating metal and coexisting with the resin component, and furthermore, the zirconium compound itself contributes to the formation of a dense chemical conversion coating and is expected to provide a barrier effect due to its excellent coating properties. Examples of the zirconium compound include neutral salts of zirconium sulfate, zirconium carbonate, zirconium nitrate, zirconium lactate, zirconium acetate, and zirconium chloride.

[0118] The content of the zirconium compound in the chemical conversion coating is 40 to 60 mass %. If the content of the zirconium compound in the chemical conversion coating is less than 40 mass %, the strength and corrosion resistance of the chemical conversion coating will decrease, and if the content of the zirconium compound exceeds 60 mass %, the chemical conversion coating will become embrittled, causing the chemical conversion coating to break or peel when subjected to severe processing.

[0119] The fluorine compound is contained in the chemical conversion coating and acts as an adhesive agent for the plating coating. As a result, the corrosion resistance of the chemical conversion coating can be improved. Examples of the fluorine compound that can be used include fluoride salts such as ammonium salts, sodium salts, and potassium salts, and fluorine compounds such as ferrous fluoride and ferric fluoride. Among these, it is preferable to use fluoride salts such as ammonium fluoride, sodium fluoride, and potassium fluoride.

[0120] The content of the fluorine compound in the chemical conversion coating is 0.5 to 5% by mass, because if the content of the fluorine compound in the chemical conversion coating is less than 0.5% by mass, sufficient adhesion cannot be obtained at the processed portion, and if the content of the fluorine compound exceeds 5% by mass, the moisture resistance of the chemical conversion coating decreases.

[0121] The coating weight of the chemical conversion coating is not particularly limited. For example, from the viewpoint of improving the adhesion of the chemical conversion coating while more reliably ensuring corrosion resistance, the coating weight of the chemical conversion coating is set to 0.025 to 0.5 g / m. 2 It is preferable that the coating weight of the chemical conversion coating is 0.025 g / m 2 By setting the coating weight at 0.5 g / m or more, corrosion resistance can be more reliably ensured, and the coating weight of the chemical conversion coating can be set at 0.5 g / m or more. 2 The chemical conversion coating weight can be determined by an appropriate method selected from existing techniques, such as a method of measuring the amount of elements present in the coating whose contents are known in advance by fluorescent X-ray analysis of the coating.

[0122] The method for forming the chemical conversion coating is not particularly limited and can be selected appropriately depending on the required performance, manufacturing equipment, etc. For example, the chemical conversion coating can be formed by continuously applying a chemical conversion treatment solution to the plating film using a roll coater or the like, followed by drying at a peak metal temperature (PMT) of approximately 60 to 200°C using hot air or induction heating. In addition to roll coaters, known methods such as airless spraying, electrostatic spraying, and curtain flow coaters can also be used to apply the chemical conversion treatment solution. Furthermore, the chemical conversion coating is not particularly limited and may be either a single-layer film or a multi-layer film, as long as it contains the resin and the metal compound.

[0123] As described above, the coated steel sheet of the present invention has a coating film formed on a plating film directly or via a chemical conversion coating, and the coating film has at least a primer coating film.

[0124] In the present invention, the primer coating film contains a polyester resin having a urethane bond and an inorganic compound containing a vanadium compound, a phosphate compound, and magnesium oxide. By containing the polyester resin having a urethane bond and the inorganic compound, the primer coating film can improve adhesion of the coating film and corrosion resistance.

[0125] The primer coating contains a polyester resin having a urethane bond as a main component. The polyester resin having a urethane bond is flexible and strong, which provides the effect of preventing cracks from occurring in the primer coating when processed, and has a high affinity with chemical conversion coatings containing a urethane resin, which contributes to improving the corrosion resistance of processed parts in particular. Note that the "main component" here means the component that is contained in the greatest amount among the components in the primer coating.

[0126] The polyester resin having a urethane bond may be a known resin such as a resin obtained by reacting a polyester polyol with a diisocyanate or polyisocyanate having two or more isocyanate groups. Alternatively, a resin obtained by reacting the polyester polyol with the diisocyanate or polyisocyanate in an excess hydroxyl group state (urethane-modified polyester resin) with a blocked polyisocyanate may be cured.

[0127] The polyester polyol can be obtained by a known method utilizing a dehydration condensation reaction between a polyhydric alcohol component and a polybasic acid component. Examples of the polyhydric alcohol include glycols and trihydric or higher polyhydric alcohols. Examples of the glycols include ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, neopentyl glycol, hexylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2-butyl-2-ethyl-1,3-propanediol, methylpropanediol, cyclohexanedimethanol, and 3,3-diethyl-1,5-pentanediol. Examples of the trihydric or higher polyhydric alcohols include glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, and dipentaerythritol. These polyhydric alcohols can be used alone or in combination. As the polybasic acid, a polycarboxylic acid is usually used, but a monobasic fatty acid or the like can be used in combination if necessary. Examples of the polycarboxylic acid include phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, 4-methylhexahydrophthalic acid, bicyclo[2,2,1]heptane-2,3-dicarboxylic acid, trimellitic acid, adipic acid, sebacic acid, succinic acid, azelaic acid, fumaric acid, maleic acid, itaconic acid, pyromellitic acid, dimer acid, and the like, as well as acid anhydrides thereof, as well as 1,4-cyclohexanedicarboxylic acid, isophthalic acid, tetrahydroisophthalic acid, hexahydroisophthalic acid, hexahydroterephthalic acid, and the like. These polybasic acids can be used alone or in combination of two or more.

[0128] Examples of the polyisocyanate include aliphatic diisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and dimer acid diisocyanate; aromatic diisocyanates such as xylylene diisocyanate (XDI), metaxylylene diisocyanate, tolylene diisocyanate (TDI), and 4,4-diphenylmethane diisocyanate (MDI); alicyclic diisocyanates such as isophorone diisocyanate, hydrogenated XDI, hydrogenated TDI, and hydrogenated MDI; and adducts, biurets, and isocyanurates thereof. These polyisocyanates can be used alone or in combination of two or more.

[0129] The hydroxyl value of the polyester resin having a urethane bond is not particularly limited, but is preferably 5 to 120 mgKOH / g, more preferably 7 to 100 mgKOH / g, and even more preferably 10 to 80 mgKOH / g, from the viewpoints of solvent resistance, processability, etc. Furthermore, the number average molecular weight of the polyester resin having a urethane bond is preferably 500 to 15,000, more preferably 700 to 12,000, and even more preferably 800 to 10,000, from the viewpoints of solvent resistance, processability, etc.

[0130] The content of the polyester resin having a urethane bond in the primer coating is preferably 40 to 88% by mass. If the content of the polyester resin having a urethane bond is less than 40% by mass, the binder function of the primer coating may be reduced, whereas if the content of the polyester resin having a urethane bond exceeds 88% by mass, the functions of the inorganic substance described below, such as the inhibitor action, may be reduced.

[0131] Vanadium compounds, which are one of the inorganic compounds, act as inhibitors. Examples of vanadium compounds include vanadium pentoxide, metavanadate, ammonium metavanadate, vanadium oxytrichloride, vanadium trioxide, vanadium dioxide, magnesium vanadate, vanadyl acetylacetonate, and vanadium acetylacetonate. Among these, it is particularly desirable to use tetravalent vanadium compounds or tetravalent vanadium compounds obtained by reduction or oxidation. The vanadium compound added to the primer coating film may be the same or different from the vanadium compound added to the chemical conversion coating film. It is believed that vanadate ions, which gradually dissolve in moisture entering from the outside, react with ions on the surface of the zinc-based plated steel sheet to form a highly adhesive passive film, protecting exposed metal areas and providing rust prevention.

[0132] The content of the vanadium compound in the primer coating film is not particularly limited, but is preferably 4 to 20 mass % from the viewpoint of achieving both corrosion resistance and moisture resistance. If the content of the vanadium compound is less than 4 mass %, the inhibitor effect may be reduced, which may lead to a decrease in corrosion resistance, while if the content of the vanadium compound is more than 20 mass %, the moisture resistance of the primer coating film may be reduced.

[0133] Phosphate compounds, which are one of the inorganic compounds, also act as inhibitors. Examples of the phosphate compounds that can be used include phosphoric acid, ammonium salts of phosphoric acid, alkali metal salts of phosphoric acid, and alkaline earth metal salts of phosphoric acid. In particular, alkali metal salts of phosphoric acid, such as calcium phosphate, are preferably used.

[0134] The content of the phosphate compound in the primer coating film is not particularly limited, but is preferably 4 to 20% by mass from the viewpoint of achieving both corrosion resistance and moisture resistance. If the content of the phosphate compound is less than 4% by mass, the inhibitor effect may be reduced, resulting in a decrease in corrosion resistance, while if the content of the phosphate compound is more than 20% by mass, the moisture resistance of the primer coating film may be reduced.

[0135] Magnesium oxide, one of the inorganic compounds, produces a product containing Mg during initial corrosion, and as a sparingly soluble magnesium salt, it has the effect of stabilizing the material and improving corrosion resistance.

[0136] The content of the magnesium oxide in the primer coating is not particularly limited, but is preferably 4 to 20% by mass from the viewpoint of achieving both corrosion resistance and corrosion resistance of the processed portion. If the content of the magnesium oxide is less than 4% by mass, the above effect may be reduced, resulting in a decrease in corrosion resistance, while if the content of the magnesium oxide exceeds 20% by mass, the flexibility of the primer coating may be reduced, resulting in a decrease in corrosion resistance of the processed portion.

[0137] The primer coating film may also contain components other than the polyester resin having a urethane bond and the inorganic compound described above. Examples include crosslinking agents used in forming the primer coating film. The crosslinking agent reacts with the polyester resin having a urethane bond to form a crosslinked coating film. Examples include oxazoline compounds, epoxy compounds, melamine compounds, isocyanate compounds, carbodiimide compounds, and silane coupling compounds. Two or more crosslinking agents can also be used in combination. Among these, blocked polyisocyanate compounds are preferred from the viewpoint of corrosion resistance of the processed portion of the resulting coated steel sheet. Examples of blocked polyisocyanates include those in which the isocyanate group of a polyisocyanate compound is blocked with, for example, alcohols such as butanol, oximes such as methyl ethyl ketoxime, lactams such as ε-caprolactams, diketones such as acetoacetic acid diesters, imidazoles such as imidazole and 2-ethylimidazole, or phenols such as m-cresol.

[0138] Furthermore, the primer coating film may contain various known components commonly used in the coatings field, as needed, such as various surface conditioners such as leveling agents and antifoaming agents, various additives such as dispersants, anti-settling agents, ultraviolet absorbers, light stabilizers, silane coupling agents and titanate coupling agents, various pigments such as coloring pigments and extender pigments, luster materials, curing catalysts, organic solvents, etc.

[0139] The thickness of the primer coating film is preferably 1.5 μm or more, because by making the thickness of the primer coating film 1.5 μm or more, it is possible to more reliably obtain the effect of improving corrosion resistance and the effect of improving adhesion with the chemical conversion coating film and the top coating film formed on the primer coating film.

[0140] The method for forming the primer coating film is not particularly limited. The coating composition constituting the primer coating film can be preferably applied by a method such as roll coater coating or curtain flow coating. After applying the coating composition, the primer coating film can be obtained by baking the coating composition using a heating method such as hot air heating, infrared heating, or induction heating. The baking treatment is typically carried out at a maximum plate temperature of about 180 to 270°C for about 30 seconds to 3 minutes.

[0141] Furthermore, it is preferable that the coating film constituting the coated steel sheet of the present invention further comprises a topcoat coating film formed on the primer coating film, which not only imparts aesthetic appearance such as color, gloss, and surface condition to the coated steel sheet, but also improves various performance properties such as processability, weather resistance, chemical resistance, stain resistance, water resistance, and corrosion resistance.

[0142] The composition of the topcoat film is not particularly limited, and the material, thickness, etc. can be appropriately selected depending on the required performance. For example, the topcoat film can be formed using a polyester resin paint, a silicone polyester resin paint, a polyurethane resin paint, an acrylic resin paint, a fluororesin paint, etc. Furthermore, the topcoat film can contain appropriate amounts of titanium oxide, red iron oxide, mica, carbon black, or other coloring pigments; metallic pigments such as aluminum powder and mica; extender pigments such as carbonates and sulfates; various fine particles such as silica fine particles, nylon resin beads, and acrylic resin beads; curing catalysts such as p-toluenesulfonic acid and dibutyltin dilaurate; wax; and other additives.

[0143] From the viewpoint of achieving both good appearance and good processability, the thickness of the top coat film is preferably 5 to 30 μm. When the thickness of the top coat film is 5 μm or more, it is possible to more reliably stabilize the color appearance, and when the thickness of the top coat film is 30 μm or less, it is possible to more reliably prevent a decrease in processability (the occurrence of cracks in the top coat film).

[0144] The method for applying the coating composition to form the topcoat film is not particularly limited. For example, the coating composition can be applied by roll coater coating, curtain flow coating, or other methods. After applying the coating composition, the topcoat film can be formed by baking using a heating method such as hot air heating, infrared heating, or induction heating. The baking treatment is typically carried out at a maximum plate temperature of about 180 to 270°C for about 30 seconds to 3 minutes.

[0145] Example 1: Samples 1 to 44 Using a cold-rolled steel sheet having a thickness of 0.8 mm produced by a conventional method as a base steel sheet, Samples 1 to 44 of hot-dip galvanized steel sheets were produced under the conditions shown in Table 1 by annealing and plating using a hot-dip galvanizing simulator manufactured by Rhesca Corporation. The composition of the coating bath used to produce the hot-dip galvanized steel sheets was varied within the ranges of 30 to 75 mass% Al, 0.5 to 4.5 mass% Si, 0 to 10 mass% Mg, and 0.00 to 0.15 mass% Sr so as to obtain the coating composition of each sample shown in Table 1. The temperature of the coating bath was 590°C for 30 to 60 mass% Al and 630°C for more than 60 mass% Al, and was controlled so that the temperature of the substrate steel sheet entering the coating was the same as the temperature of the coating bath. Furthermore, the plating process was carried out under the condition that the sheet temperature was cooled to a temperature range of 520 to 500°C in 3 seconds. In addition, the coating weight of the plating film was 85±5 g / m per side for samples 1 to 41. 2 , Samples 42 to 44: 51 to 125 g / m per side 2 It was controlled so that

[0146] (Evaluation) Each sample of the hot-dip plated steel sheet obtained as described above was evaluated as follows. The evaluation results are shown in Table 1.

[0147] (1) Plating Film Structure (Deposition Weight, Composition, and X-ray Diffraction Intensity) After plating, a 100 mm diameter punch was punched out from each sample, and the non-measurement surface was sealed with tape. The plating was dissolved and stripped using a mixture of hydrochloric acid and hexamethylenetetramine as specified in JIS H 0401:2013. The deposition weight of the plating film was calculated from the mass difference between the sample before and after stripping. The resulting deposition weights of the plating film are shown in Table 1. The stripping solution was then filtered, and the filtrate and solids were analyzed separately. Specifically, the filtrate was subjected to ICP atomic emission spectroscopy to quantify components other than insoluble silicon. The solids were dried and incinerated in a heating furnace at 650°C, and then melted by adding sodium carbonate and sodium tetraborate. The melt was then dissolved in hydrochloric acid, and the solution was subjected to ICP atomic emission spectroscopy to quantify the insoluble silicon. The silicon concentration in the plating film was calculated by adding the soluble silicon concentration obtained from the filtrate analysis to the insoluble silicon concentration obtained from the solids analysis. The compositions of the resulting plating films are shown in Table 1. Each sample was sheared to a size of 100 mm x 100 mm, and the plating film on the surface to be evaluated was mechanically scraped off until the steel substrate was exposed. The resulting powder was thoroughly mixed, and 0.3 g of the powder was then subjected to qualitative analysis using an X-ray diffraction apparatus (Rigaku Corporation, "SmartLab") under the following conditions: X-ray: Cu-Kα (wavelength = 1.54178 Å), Kβ ray removal: Ni filter, tube voltage: 40 kV, tube current: 30 mA, scanning speed: 4° / min, sampling interval: 0.020°, divergence slit: 2 / 3°, Soller slit: 5°, and detector: high-speed one-dimensional detector (D / teX Ultra). The diffraction intensity (cps) was calculated by subtracting the base intensity from each peak intensity. The diffraction intensity of the Mg2Si (111) plane (interplanar spacing d = 0.3668 nm), the diffraction intensity of the MgZn2 (100) plane (interplanar spacing d = 0.4510 nm), and the diffraction intensity of the Si (111) plane (interplanar spacing d = 0.3135 nm) were measured. The measurement results are shown in Table 1.

[0148] (2) Corrosion Resistance Evaluation Each sample of the obtained hot-dip galvanized steel sheet was sheared to a size of 120 mm × 120 mm, and a 10 mm area from each edge of the surface to be evaluated, as well as the end faces and the surface not to be evaluated, were sealed with tape to expose a 100 mm × 100 mm area of ​​the surface to be evaluated, which was used as the evaluation sample. Three identical evaluation samples were prepared. Accelerated corrosion tests were conducted on all three evaluation samples prepared as described above, using the cycle shown in Figure 1. The accelerated corrosion test was started from wetting and continued for 300 cycles. After that, the corrosion weight loss of each sample was measured using the methods specified in JIS Z 2383 and ISO 8407, and evaluated according to the following criteria. The evaluation results are shown in Table 1. ◎: The corrosion weight loss of all three samples was 45 g / m 2 ○: The corrosion weight loss of all three samples was 90 g / m 2 Less than ×: Corrosion loss of one or more samples is 90 g / m 2 Overcoming

[0149] (3) Surface Appearance The surface of the plating film of each sample of the obtained hot-dip plated steel sheet was visually observed. The observation results were then evaluated according to the following criteria. The evaluation results are shown in Table 1. ⊚: No wrinkle-like defects were observed. ◯: Wrinkle-like defects were observed only within a range of 50 mm from the edge. ×: Wrinkle-like defects were observed outside a range of 50 mm from the edge.

[0150] (4) Workability Each sample of the obtained hot-dip galvanized steel sheet was sheared to a size of 70 mm x 150 mm, and then eight sheets of the same thickness were sandwiched inside and bent 180° (8T bend). Cellotape (registered trademark) was firmly attached to the outer surface of the bent part after bending and then peeled off. The surface condition of the plating film on the outer surface of the bent part and the presence or absence of adhesion (peeling) of the plating film on the surface of the tape used were visually observed, and the workability was evaluated according to the following criteria. The evaluation results are shown in Table 1. ◯: Neither cracks nor peeling were observed in the plating film. △: Cracks were observed in the plating film, but no peeling was observed. ×: Both cracks and peeling were observed in the plating film.

[0151] (5) Bath stability When producing each sample of hot-dip galvanized steel sheet, the state of the bath surface of the coating bath was visually inspected and compared with the bath surface of the coating bath (bath surface without Mg-containing oxides) used when producing hot-dip Al-Zn coated steel sheet. Evaluation was performed according to the following criteria, and the evaluation results are shown in Table 1. ◯: Similar to the hot-dip Al-Zn coating bath (55% by mass Al, balance Zn-1.6% by mass bath) △: More white oxide than the hot-dip Al-Zn coating bath (55% by mass Al, balance Zn-1.6% by mass bath) ×: Formation of black oxide was observed in the coating bath

[0152]

[0153] The results in Table 1 show that the samples of the invention are well-balanced and superior in corrosion resistance, surface appearance, workability, and bath stability compared to the samples of the comparative examples.

[0154] Example 2: Samples 1 to 112 (1) Using a cold-rolled steel sheet having a thickness of 0.8 mm produced by a conventional method as a base steel sheet, annealing and plating were performed using a hot-dip galvanizing simulator manufactured by Rhesca Corporation to produce hot-dip galvanized steel sheet samples with the coating conditions shown in Tables 3 and 4. The composition of the coating bath used to produce the hot-dip galvanized steel sheets was varied within the ranges of 30 to 75 mass% Al, 0.5 to 4.5 mass% Si, 0 to 10 mass% Mg, and 0.00 to 0.15 mass% Sr, so as to obtain the coating compositions of the samples shown in Table 2. The temperature of the coating bath was 590°C for 30 to 60 mass% Al and 630°C for more than 60 mass% Al, and was controlled so that the temperature of the substrate steel sheet entering the coating was the same as the temperature of the coating bath. Furthermore, the plating process was carried out under the condition that the sheet temperature was cooled to a temperature range of 520 to 500°C in 3 seconds. The coating weight of the plating film was 85±5 g / m per side for samples 1 to 82 and 95 to 112. 2 , Samples 83 to 94: 51 to 125 g / m per side 2(2) Then, a chemical conversion treatment solution was applied to the plating film of each sample of hot-dip galvanized steel sheet prepared using a bar coater, and the resulting solution was dried in a hot air oven (heating rate: 60°C / s, PMT: 120°C) to form a chemical conversion coating, thereby producing the surface-treated steel sheet samples shown in Tables 3 and 4. Surface treatment solutions A to F were prepared by dissolving each component in water as a solvent. The types of components (resin, metal compounds) contained in the surface treatment solutions are as follows: (Resin) Urethane resin: Superflex 130, Superflex 126 (Dai-ichi Kogyo Seiyaku Co., Ltd.) Acrylic resin: Boncoat EC-740EF (DIC Corporation) (Metal compounds) P compound: aluminum dihydrogen tripolyphosphate Si compound: silica V compound: sodium metavanadate Mo compound: molybdic acid Zr compound: potassium zirconyl carbonate The compositions of the prepared chemical conversion treatment solutions A to F and the coating weights of the formed chemical conversion coatings are shown in Table 2. The concentration of each component in Table 2 of this specification is the concentration (mass %) of the solid content.

[0155]

[0156] (Evaluation) The following evaluations were carried out on each sample of the hot-dip plated steel sheet and the surface-treated steel sheet obtained as described above. The evaluation results are shown in Tables 3 and 4.

[0157] (1) Plating Film Structure (Weight, Composition, and X-ray Diffraction Intensity) Each hot-dip galvanized steel sheet sample was punched out to a diameter of 100 mm, and the non-measurement surface was sealed with tape. The plating was then dissolved and stripped using a mixture of hydrochloric acid and hexamethylenetetramine as specified in JIS H 0401:2013. The coating weight of the plating film was calculated from the mass difference between the sample before and after stripping. The calculated coating weights of the plating film are shown in Tables 3 and 4. The stripping solution was then filtered, and the filtrate and solids were analyzed. Specifically, the filtrate was subjected to ICP atomic emission spectroscopy to quantify components other than insoluble silicon. The solids were then dried and incinerated in a heating furnace at 650°C, and then melted by adding sodium carbonate and sodium tetraborate. The melt was then dissolved in hydrochloric acid, and the solution was subjected to ICP atomic emission spectroscopy to quantify insoluble silicon. The silicon concentration in the plating film was calculated by adding the soluble silicon concentration obtained by filtrate analysis to the insoluble silicon concentration obtained by solids analysis. The compositions of the resulting plating films are shown in Tables 3 and 4. Each sample was sheared to a 100 mm x 100 mm size, and the plating film on the evaluation surface was mechanically scraped off until the steel substrate was exposed. The resulting powder was thoroughly mixed and 0.3 g of the powder was extracted. Qualitative analysis of the powder was performed using an X-ray diffraction analyzer (Rigaku Corporation, "SmartLab") under the following conditions: Cu-Kα X-ray (wavelength = 1.54178 Å), Kβ ray removal: Ni filter, tube voltage: 40 kV, tube current: 30 mA, scanning speed: 4° / min, sampling interval: 0.020°, divergence slit: 2 / 3°, solar slit: 5°, and a high-speed one-dimensional detector (D / teX Ultra). The diffraction intensity (cps) was calculated by subtracting the base intensity from each peak intensity. The diffraction intensity of the Mg2Si (111) plane (interplanar spacing d = 0.3668 nm), the diffraction intensity of the MgZn2 (100) plane (interplanar spacing d = 0.4510 nm), and the diffraction intensity of the Si (111) plane (interplanar spacing d = 0.3135 nm) were measured. The measurement results are shown in Tables 3 and 4.

[0158] (2) Corrosion Resistance Evaluation Each sample of hot-dip galvanized steel sheet and surface-treated steel sheet was sheared to a size of 120 mm × 120 mm. A 10 mm area from each edge of the evaluation surface, as well as the sample edge and the non-evaluation surface, were sealed with tape to expose a 100 mm × 100 mm area of ​​the evaluation surface, which was used as the evaluation sample. Three identical evaluation samples were prepared. Accelerated corrosion tests were conducted on all three evaluation samples prepared as described above, using the cycle shown in Figure 1. The accelerated corrosion test was conducted starting from wetting and continuing for 300 cycles. After that, the corrosion weight loss of each sample was measured using the methods specified in JIS Z 2383 and ISO 8407, and evaluated according to the following criteria. The evaluation results are shown in Tables 3 and 4. ◎: The corrosion weight loss of all three samples was 30 g / m or less. 2 ○: The corrosion weight loss of all three samples was 70 g / m 2 Less than ×: Corrosion loss of one or more samples is 70 g / m 2 Overcoming

[0159] (3) White Rust Resistance Each sample of hot-dip galvanized steel sheet and surface-treated steel sheet was sheared to a size of 120 mm x 120 mm, and then a 10 mm area from each edge of the surface to be evaluated, as well as the end faces of the sample and the surface not to be evaluated, were sealed with tape, leaving a 100 mm x 100 mm area of ​​the surface to be evaluated, which was used as the evaluation sample. Using the above evaluation samples, a salt spray test according to JIS Z 2371 was carried out for 90 hours and evaluated according to the following criteria. The evaluation results are shown in Tables 3 and 4. ⊚: No white rust on the flat plate. ◯: White rust occurred on less than 10% of the flat plate area. ×: White rust occurred on 10% or more of the flat plate area.

[0160] (4) Surface Appearance The surface of the plating film of each sample of hot-dip galvanized steel sheet was visually observed. The observation results were then evaluated according to the following criteria. The evaluation results are shown in Tables 3 and 4. ⊚: No wrinkle-like defects were observed. ◯: Wrinkle-like defects were observed only within a range of 50 mm from the edge. ×: Wrinkle-like defects were observed outside a range of 50 mm from the edge.

[0161] (5) Workability Each hot-dip galvanized steel sheet sample was sheared to a size of 70 mm x 150 mm, and then eight sheets of the same thickness were sandwiched inside and bent 180° (8T bend). Cellotape (registered trademark) was firmly attached to the outer surface of the bent portion after bending and then peeled off. The surface condition of the plating film on the outer surface of the bent portion and the presence or absence of adhesion (peeling) of the plating film on the surface of the tape used were visually observed, and the workability was evaluated according to the following criteria. The evaluation results are shown in Tables 3 and 4. ◯: Neither cracks nor peeling were observed in the plating film. △: Cracks were observed in the plating film, but no peeling was observed. ×: Both cracks and peeling were observed in the plating film.

[0162] (5) Bath stability During hot dip coating, the state of the coating bath surface was visually inspected and compared with the bath surface of the coating bath used in producing hot dip Al-Zn coated steel sheets (bath surface free of Mg-containing oxides). Evaluation was performed according to the following criteria, and the evaluation results are shown in Tables 3 and 4. ◯: Similar to the hot dip Al-Zn coating bath (55% by mass Al, balance Zn-1.6% by mass bath) △: More white oxide than the hot dip Al-Zn coating bath (55% by mass Al, balance Zn-1.6% by mass bath) ×: Formation of black oxide was observed in the coating bath

[0163]

[0164]

[0165] The results in Tables 3 and 4 show that the samples of the invention are well-balanced and superior in corrosion resistance, white rust resistance, surface appearance, workability, and bath stability compared to the samples of the comparative examples. Furthermore, the results in Table 4 show that the samples subjected to chemical conversion treatments A to D exhibited particularly excellent white rust resistance.

[0166] Example 3: Samples 1 to 44 (1) Using a cold-rolled steel sheet having a thickness of 0.8 mm produced by a conventional method as a base steel sheet, annealing and plating were performed using a hot-dip galvanizing simulator manufactured by Rhesca Corporation to produce hot-dip galvanized steel sheet samples with the plating film conditions shown in Table 6. The composition of the plating bath used to produce the hot-dip galvanized steel sheets was varied within the ranges of 30 to 75 mass% Al, 0.5 to 4.5 mass% Si, 0 to 10 mass% Mg, and 0.00 to 0.15 mass% Sr so as to obtain the plating film composition of each sample shown in Table 6. The bath temperature of the plating bath was 590°C for 30 to 60 mass% Al and 630°C for more than 60 mass% Al, and was controlled so that the temperature of the substrate steel sheet entering the plating bath was the same as the temperature of the plating bath. Furthermore, the plating process was carried out under the condition that the sheet temperature was cooled to a temperature range of 520 to 500°C in 3 seconds. In addition, the coating weight of the plating film was 85±5 g / m per side for samples 1 to 41. 2 , and samples 42 to 44 are 42 to 125 g / m per side. 2 It was controlled so that

[0167] (2) Then, the chemical conversion treatment solution shown in Table 5 was applied to the plating film of each sample of the prepared hot-dip galvanized steel sheet using a bar coater, and the coating was dried in a hot-air drying furnace (achieved sheet temperature: 90°C) until the coating weight reached 0.1 g / m. 2 The chemical conversion coating film was formed as follows. The chemical conversion treatment solution used was one with a pH of 8 to 10, prepared by dissolving each component in water as a solvent. The types of components (resin components, inorganic compounds) contained in the chemical conversion treatment solution are as follows. (Resin Components) Resin A: (a) an anionic polyurethane resin having an ester bond (Superflex 210, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) and (b) an epoxy resin having a bisphenol skeleton (Yukarejin RE-1050, manufactured by Yoshimura Oil Chemical Co., Ltd.) mixed at a mass ratio of (a):(b) = 50:50. Resin B: acrylic resin (Boncoat EC-740EF, manufactured by DIC Corporation). (Inorganic Compounds) Vanadium compound: organic vanadium compound chelated with acetylacetone. Zirconium compound: ammonium zirconium carbonate. Fluorine compound: ammonium fluoride.

[0168] (3) A primer coating was then applied to the chemical conversion coating formed as described above using a bar coater and baked at a steel plate temperature of 230°C for a baking time of 35 seconds to form a primer coating film having the component composition shown in Table 5. A topcoat coating composition was then applied to the primer coating formed as described above using a bar coater and baked at a steel plate temperature of 230°C to 260°C for a baking time of 40 seconds to form a topcoat coating film having the resin composition and film thickness shown in Table 5, thereby producing each sample coated steel plate. The primer coating was obtained by mixing the components and then stirring in a ball mill for approximately 1 hour. The resin components and inorganic compounds constituting the primer coating were as follows: (Resin components) Resin α: Urethane-modified polyester resin (obtained by reacting 455 parts by mass of polyester resin and 45 parts by mass of isophorone diisocyanate, with a resin acid value of 3, a number average molecular weight of 5,600, and a hydroxyl value of 36) cured with blocked isocyanate. The polyester resin to be urethane-modified was prepared under the following conditions: A flask equipped with a stirrer, a rectification column, a water separator, a condenser, and a thermometer was charged with 320 parts by mass of isophthalic acid, 200 parts by mass of adipic acid, 60 parts by mass of trimethylolpropane, and 420 parts by mass of cyclohexanedimethanol. The mixture was heated and stirred, and the resulting condensation water was distilled out of the system. The temperature was raised from 160°C to 230°C at a constant rate over 4 hours. After the temperature reached 230°C, 20 parts by mass of xylene was gradually added, and the condensation reaction was continued while maintaining the temperature at 230°C. The reaction was terminated when the acid value reached 5 or less. The mixture was then cooled to 100°C, and 120 parts by mass of Solvesso 100 (a high-boiling aromatic hydrocarbon solvent, manufactured by ExxonMobil Corporation) and 100 parts by mass of butyl cellosolve were added to obtain a polyester resin solution. Resin β: urethane-cured polyester resin (Evaclad 4900 manufactured by Kansai Paint Co., Ltd.) (inorganic compounds) Vanadium compound: magnesium vanadate Phosphate compound: calcium phosphate Magnesium oxide compound: magnesium oxide Furthermore, the following paints were used for the resins used in the topcoat paint film.Resin I: Melamine-cured polyester paint ("Precolor HD0030HR" manufactured by BASF Japan Ltd.) Resin II: Organosol-based bake-type fluororesin paint ("Precolor No. 8800HR" manufactured by BASF Japan Ltd.) containing polyvinylidene fluoride and acrylic resin in a mass ratio of 80:20.

[0169]

[0170] (Evaluation) Each of the coated steel sheet samples obtained as described above was evaluated as follows. The evaluation results are shown in Table 6.

[0171] (1) Plating Film Structure (Adhesion Weight, Composition, and X-ray Diffraction Intensity) Each hot-dip galvanized steel sheet sample was punched out to a diameter of 100 mm, and the non-measurement surface was sealed with tape. The plating was then dissolved and stripped using a mixture of hydrochloric acid and hexamethylenetetramine as specified in JIS H 0401:2013. The plating film adhesion weight was calculated from the mass difference between the sample before and after stripping. The resulting plating film adhesion weights are shown in Table 6. The stripping solution was then filtered, and the filtrate and solids were analyzed separately. Specifically, the filtrate was subjected to ICP atomic emission spectroscopy to quantify components other than insoluble Si. The solids were then dried and incinerated in a heating furnace at 650°C, and then melted by adding sodium carbonate and sodium tetraborate. The melt was then dissolved in hydrochloric acid, and the solution was subjected to ICP atomic emission spectroscopy to quantify insoluble Si. The silicon concentration in the plating film was calculated by adding the soluble silicon concentration obtained by filtrate analysis to the insoluble silicon concentration obtained by solids analysis. The composition of the resulting plating film is shown in Table 6. Each sample was then sheared to a 100 mm x 100 mm size, and the plating film on the evaluation surface was mechanically scraped off until the steel substrate was exposed. The resulting powder was thoroughly mixed and 0.3 g of the powder was extracted. Qualitative analysis of the powder was performed using an X-ray diffraction analyzer (Rigaku Corporation, "SmartLab") under the following conditions: Cu-Kα X-ray (wavelength = 1.54178 Å), Kβ ray removal: Ni filter, tube voltage: 40 kV, tube current: 30 mA, scanning speed: 4° / min, sampling interval: 0.020°, divergence slit: 2 / 3°, solar slit: 5°, and a high-speed one-dimensional detector (D / teX Ultra). The diffraction intensity (cps) was calculated by subtracting the base intensity from each peak intensity. The diffraction intensity of the Mg2Si (111) plane (interplanar spacing d = 0.3668 nm), the diffraction intensity of the MgZn2 (100) plane (interplanar spacing d = 0.4510 nm), and the diffraction intensity of the Si (111) plane (interplanar spacing d = 0.3135 nm) were measured. The measurement results are shown in Table 6.

[0172] (2) Corrosion Resistance Evaluation Each coated steel sheet sample was sheared to a size of 120 mm × 120 mm. Three randomly selected edges of the evaluation surface were sealed with tape within 10 mm of the sample, along with the edges of the three randomly selected edges and the non-evaluation surface, leaving a 100 mm × 100 mm exposed evaluation surface. Three identical evaluation samples were prepared. Each of the three evaluation samples prepared as described above underwent accelerated corrosion testing according to the cycle shown in Figure 1. The accelerated corrosion testing began with wetting, and every 20 cycles, the sample was removed, washed with water, dried, and visually inspected for the presence of red rust on the sheared edge of one side that was not sealed with tape. The number of cycles required for red rust to be observed was evaluated according to the following criteria. The evaluation results are shown in Table 6. ◎: Number of cycles in which red rust appeared on three samples ≥ 600 cycles ○: Number of cycles in which red rust appeared on three samples > 600 cycles ≥ 400 cycles ×: Number of cycles in which red rust appeared on at least one sample < 400 cycles

[0173] (3) Appearance after painting The surface of each painted steel sheet sample was visually inspected. The inspection results were evaluated according to the following criteria. The evaluation results are shown in Table 6. ⊚: No wrinkle defects were observed. ◯: Wrinkle defects were observed only within 50 mm from the edge. ×: Wrinkle defects were observed outside the range of 50 mm from the edge.

[0174] (5) Workability after painting Each coated steel sheet sample was sheared to a size of 70 mm x 150 mm, and then eight sheets of the same thickness were sandwiched inside and bent 180° (8T bending). Cellotape (registered trademark) was firmly attached to the outer surface of the bent part after bending and then peeled off. The surface condition of the coating on the outer surface of the bent part and the presence or absence of adhesion (peeling) of the coating on the surface of the tape used were visually observed, and the workability was evaluated according to the following criteria. The evaluation results are shown in Table 6. ◯: Neither cracks nor peeling were observed in the plating film. △: Cracks were observed in the plating film, but no peeling was observed. ×: Both cracks and peeling were observed in the plating film.

[0175] (5) Bath Stability During hot dip coating, the state of the coating bath surface was visually inspected and compared with the bath surface of the coating bath used in producing hot dip Al-Zn coated steel sheets (bath surface free of Mg-containing oxides). Evaluation was performed according to the following criteria, and the evaluation results are shown in Table 6. ◯: Similar to the hot dip Al-Zn coating bath (55% by mass Al, balance Zn-1.6% by mass bath) △: More white oxide than the hot dip Al-Zn coating bath (55% by mass Al, balance Zn-1.6% by mass bath) ×: Formation of black oxide was observed in the coating bath

[0176]

[0177] The results in Table 6 show that the samples of the invention are well-balanced and excellent in terms of corrosion resistance, appearance after coating, workability after coating, and bath stability compared to the samples of the comparative examples.

[0178] According to the present invention, it is possible to provide a hot-dip Al-Zn-Si-Mg-plated steel sheet having stably excellent corrosion resistance. Also, according to the present invention, it is possible to provide a surface-treated steel sheet having stably excellent corrosion resistance and white rust resistance. Furthermore, according to the present invention, it is possible to provide a coated steel sheet having stably excellent corrosion resistance and corrosion resistance in processed portions.

Claims

1. A hot-dip Al-Zn-Si-Mg alloy coated steel sheet having a plating film, wherein the plating film has a composition containing Al: 45 to 65% by mass, Si: 1.0 to 4.0% by mass, and Mg: 1.0 to 10.0% by mass, with the balance being Zn and inevitable impurities, and Mg in the plating film 2 Si and MgZn 2 The diffraction intensity by X-ray diffraction method of satisfies the following relationship (1). Mg 2 Si (111) / MgZn 2 (100) ≦ 2.0... (1) Mg 2 Si (111): Mg 2 Diffraction intensity of the (111) plane (interplanar spacing d = 0.3668 nm) of Si, MgZn 2 (100): MgZn 2 Diffraction intensity of the (100) plane (interplanar spacing d = 0.4510 nm) 2. The galvanized coating steel sheet according to claim 1, wherein the diffraction intensity of Si in the galvanized coating by X-ray diffraction satisfies the following relationship (2). Si (111) = 0... (2) Si (111): Diffraction intensity of the (111) plane of Si (interplanar spacing d = 0.3135 nm) 3. The galvanized coating steel sheet according to claim 1 or 2, wherein the galvanized coating further contains 0.01 to 1.0% by mass of Sr.

4. The galvanized coating steel sheet according to any one of claims 1 to 3, wherein the content of Al in the galvanized coating is 50 to 60% by mass.

5. The galvanized coating steel sheet according to any one of claims 1 to 4, wherein the content of Si in the galvanized coating is 1.0 to 3.0% by mass.

6. The galvanized coating steel sheet according to any one of claims 1 to 5, wherein the content of Mg in the galvanized coating is 1.0 to 5.0% by mass.

7. A surface-treated steel sheet comprising the galvanized coating according to any one of claims 1 to 6 and a chemical conversion coating formed on the galvanized coating, wherein the chemical conversion coating contains at least one resin selected from epoxy resin, urethane resin, acrylic resin, acrylic silicone resin, alkyd resin, polyester resin, polyalkylene resin, amino resin, and fluororesin, and at least one metal compound selected from P compound, Si compound, Co compound, Ni compound, Zn compound, Al compound, Mg compound, V compound, Mo compound, Zr compound, Ti compound, and Ca compound.

8. A coated steel sheet having a coating film formed directly or via a chemical conversion film on the plating film according to any one of claims 1 to 6, wherein the chemical conversion film contains a total of 30 to 50% by mass of (a) an anionic polyurethane resin having an ester bond and (b) an epoxy resin having a bisphenol skeleton, and the content ratio of (a) to (b) ((a):(b)) is in the range of 3:97 to 60:40 by mass, a resin component, an inorganic compound containing 2 to 10% by mass of a vanadium compound, 40 to 60% by mass of a zirconium compound, and 0.5 to 5% by mass of a fluorine compound, and the coating film has at least a primer coating film, and the primer coating film contains a polyester resin having a urethane bond and an inorganic compound containing a vanadium compound, a phosphoric acid compound, and magnesium oxide. A coated steel sheet characterized by the above.