TWI869659B - Molten Al-Zn-Si-Mg plated steel plate and its manufacturing method, surface treated steel plate and its manufacturing method, and coated steel plate and its manufacturing method - Google Patents

Abstract

The present invention provides a molten Al-Zn-Si-Mg coated steel sheet with stable and excellent corrosion resistance. In order to achieve the above-mentioned purpose, the present invention relates to a molten Al-Zn-Si-Mg coated steel sheet with a coating film, wherein the coating film has a composition containing Al: 45~65 mass%, Si: 1.0~4.0 mass% and Mg: 1.0~10.0 mass%, and the rest is composed of Zn and inevitable impurities, and the Ni content of the inevitable impurities is less than 0.010 mass% relative to the total mass of the coating film.

Description

Molten Al-Zn-Si-Mg plated steel plate and its manufacturing method, surface treated steel plate and its manufacturing method, and coated steel plate and its manufacturing method

The present invention relates to a molten Al-Zn-Si-Mg-based plated steel plate having stable and excellent corrosion resistance and a method for manufacturing the same, a surface treated steel plate and a method for manufacturing the same, and a coated steel plate and a method for manufacturing the same.

Molten Al-Zn coated steel sheets, represented by 55% Al-Zn, are known to have high corrosion resistance among molten galvanized steel sheets because they have both the sacrificial corrosion resistance of Zn and the high corrosion resistance of Al. Therefore, molten Al-Zn coated steel sheets are mainly used in the field of building materials such as roofs or walls that are exposed to the outdoors for a long time, guardrails, wiring and piping, sound insulation walls, etc. due to their excellent corrosion resistance. In recent years, the demand for molten Al-Zn coated steel plates has increased, especially due to the increasing demand for materials with excellent corrosion resistance or maintenance-free materials in harsher operating environments such as acid rain caused by air pollution, de-icing agents for roads in snowy areas, and development in coastal areas.

The characteristics of the coating film of the molten Al-Zn system plated steel plate are that the supersaturated and Zn-containing Al solidifies into a dendrite-like part (α-Al phase) and the Zn-Al eutectic structure existing in the dendrite gap (inter-dendrite), and has a structure in which the α-Al phase is layered multiple times in the thickness direction of the coating film. Due to this characteristic film structure, the corrosion path from the surface becomes complicated, so corrosion becomes difficult to proceed. It is also known that the molten Al-Zn system plated steel plate can achieve better corrosion resistance than the molten zinc plated steel plate with the same coating film thickness.

Attempts have been made to further extend the life of such molten Al-Zn-based plated steel sheets, and molten Al-Zn-Si-Mg-based plated steel sheets to which Mg is added have been put into practical use. As such molten Al-Zn-Si-Mg-based plated steel sheets, for example, Patent Document 1 discloses a molten Al-Zn-Si-Mg-based plated steel sheet, which contains an Al-Zn-Si alloy containing Mg in the plated film. The Al-Zn-Si alloy is an alloy containing 45 to 60% by weight of elemental aluminum, 37 to 46% by weight of elemental zinc, and 1.2 to 2.3% by weight of Si, and the concentration of Mg is 1 to 5% by weight. In addition, Patent Document 2 discloses a molten Al-Zn-Si-Mg coated steel plate, the purpose of which is to improve the corrosion resistance by containing at least one of 2-10% Mg and 0.01-10% Ca in the coating film, and to improve the protective effect after the base steel plate is exposed. Furthermore, Patent Document 3 discloses a molten Al-Zn-Si-Mg coated steel plate, which forms a coating layer containing Mg: 1-15%, Si: 2-15%, Zn: 11-25% by mass, and the remainder is Al and inevitable impurities, and by making the size of the intermetallic compound such as _Mg2Si phase or _MgZn2 phase existing in the coating film less than 10μm, the corrosion resistance of the plate and the end surface is improved.

The above-mentioned molten Al-Zn coated steel sheet has a beautiful appearance with a white metallic luster and a shiny pattern, so it is often used without being coated. In reality, the appearance is still highly required. Therefore, a technology for improving the appearance of molten Al-Zn coated steel sheets has also been developed. For example, Patent Document 4 discloses a molten Al-Zn-Si-Mg coated steel sheet in which wrinkle-shaped concave-convex defects are suppressed by containing 0.01-10% Sr in the coating film. In addition, Patent Document 5 also discloses a molten Al-Zn-Si-Mg coated steel sheet in which spot defects are suppressed by containing 500-3000 ppm Sr in the coating film.

In addition, regarding the above-mentioned molten Al-Zn-based plated steel sheet, when used in a severe corrosive environment, there is a problem of rusting due to corrosion of the plated film. Since the rusting causes the appearance of the steel sheet to deteriorate, the development of plated steel sheets with improved rust resistance is being carried out. For example, in Patent Document 6, based on the purpose of improving the rust resistance of the processed part, a molten Al-Zn-Si-Mg-based plated steel sheet with an appropriate mass ratio of Mg in the Si-Mg phase to the total amount of Mg in the plated layer is disclosed. In addition, Patent Document 7 discloses a technology for improving black discoloration resistance and rust resistance by forming a chemical film containing a urethane resin on the coating film of a molten Al-Zn-Si-Mg system plated steel sheet.

In addition, coated steel sheets formed with chemical films, base coating films, top coating films, etc. on the surface of molten Al-Zn-based plated steel sheets are required to be subjected to various processes such as 90-degree bending or 180-degree bending by press forming, roll forming, or embossing, and thus require long-term coating durability. In order to meet such requirements, molten Al-Zn-based plated steel sheets are known to have coated steel sheets formed with chemical films containing chromate, chromate-based rust-proof pigments in the base coating film, and a top coating film with excellent weather resistance such as a thermosetting polyester resin film or a fluorine resin film formed thereon. However, for these recently coated steel sheets, the use of chromate, which is a substance that causes environmental load, is considered to be a problem, and there is a strong desire to develop a coated steel sheet that can improve corrosion resistance or surface appearance even without chromate. As a technology to meet these requirements, for example, Patent Document 8 discloses a surface treated molten metal-plated steel material, which is a layer (α) of aluminum-zinc alloy containing Al, Zn, Si and Mg and whose contents are adjusted on the surface of the steel material, and then a film (β) is formed as an upper layer thereof, which has at least one compound (A) selected from titanium compounds and zirconium compounds as a film-forming component, and the mass ratio of the Si-Mg phase in the aluminum-zinc alloy layer (α) relative to the total amount of Mg in the layer is adjusted to be 3% or more. [Prior Technical Document] [Patent Document]

Patent document 1: Japanese Patent No. 5020228 Patent document 2: Japanese Patent No. 5000039 Patent document 3: Japanese Patent Publication No. 2002-12959 Patent document 4: Japanese Patent Publication No. 3983932 Patent document 5: Japanese Patent Publication No. 2011-514934 Patent document 6: Japanese Patent No. 5751093 Patent document 7: Japanese Patent Publication No. 2019-155872 Patent document 8: Japanese Patent Publication No. 2005-169765

[Problems to be solved by the invention]

However, as disclosed in Patent Documents 1 to 3, the technology of adding Mg to the coating film may not necessarily significantly improve the corrosion resistance. Although the molten Al-Zn-Si-Mg coated steel sheets disclosed in Patent Documents 1 to 3 achieve improved corrosion resistance only by adding Mg to the coating composition, the effects of components other than the above four elements (Al, Zn, Si, Mg) and the characteristics of the metal phase and intermetallic compound phase constituting the coating film are not considered, and it is impossible to discuss the corrosion resistance in general. Therefore, even when the molten Al-Zn-Si-Mg coated steel sheet is manufactured using the same coating bath composition of the above four elements, there is a difference in corrosion resistance when the corrosion promotion test is performed, and it may not be superior to the Al-Zn coated steel sheet without Mg addition, which is problematic. Similarly, in improving the coating appearance, simply adding Sr to the coating film may not necessarily eliminate the wrinkle-shaped uneven defects. The molten Al-Zn-Si-Mg coated steel sheets disclosed in Patent Documents 4 and 5 may not have both corrosion resistance and appearance. In addition, since Mg is an easily oxidized element, the Mg contained in the plating bath generates oxides (scum) near the bath surface, or during molten plating, FeAl compounds containing iron (bottom scum) exist in the plating bath or locally at the bottom over time. Such slag adheres to the surface of the coating film, causing convex defects and also damaging the appearance of the coating film surface. In addition, when a steel sheet is plated in a bath in which Mg is added to a molten Al-Zn-Si bath, it is known that in addition to the α-Al phase, _Mg2Si phase, _MgZn2 phase, and Si phase are also precipitated in the coating film. However, the effect of the precipitation amount or existence ratio of each phase on corrosion resistance is still unclear.

In addition, no technology can achieve sufficient improvement in rust resistance. Regarding the molten Al-Zn-Si-Mg coated steel sheet of Patent Document 6, although it is described that the rust resistance of the processed part and the heated flat part is improved, the rust resistance of the unheated flat part is not considered, and achieving stable rust resistance is still a problem. Moreover, regarding the molten Al-Zn-Si-Mg coated steel sheet of Patent Document 7, it is expected not only to obtain stable and excellent corrosion resistance and rust resistance, but also to further improve.

Furthermore, as mentioned above, the coated steel plate is required to have long-term coating durability in various processing states such as 90-degree bending or 180-degree bending by press forming, roll forming, embossing, etc., but the technology of Patent Document 8 cannot necessarily and stably obtain corrosion resistance and surface appearance after processing. The corrosion resistance of the coated steel plate will of course affect the corrosion resistance of the plated steel plate that serves as the base. Regarding the surface appearance, since the height difference of the wrinkle defect reaches tens of μm, even if the surface is smoothed by coating, the unevenness cannot be completely eliminated, and it is believed that it is not possible to expect improvement in the appearance of the coated steel plate. In addition, since the coating becomes thinner on the convex part, there is also a concern that the corrosion resistance may be reduced locally. Therefore, in order to obtain a coated steel plate with excellent corrosion resistance and surface appearance, it is important to improve the corrosion resistance and surface appearance of the underlying coated steel plate.

In view of the above situation, the purpose of the present invention is to provide a stable and excellent corrosion-resistant molten Al-Zn-Si-Mg coated steel plate and a method for manufacturing the same. And the purpose of the present invention is to provide a stable and excellent corrosion-resistant and rust-resistant surface-treated steel plate and a method for manufacturing the same. Furthermore, the purpose of the present invention is to provide a stable and excellent corrosion-resistant and processed part corrosion-resistant coated steel plate and a method for manufacturing the same. [Means for solving the problem]

As a result of the active research conducted by the inventors of the present invention to solve the above-mentioned problems, they focused on the composition of the coating film of the molten Al-Zn-Si-Mg system coated steel sheet, and not only controlled the concentrations of Al, Zn, Si and Mg, but more importantly, also controlled the concentrations of elements contained as impurities. It was found that the degradation of corrosion resistance can be effectively suppressed by properly controlling the Ni content. In addition, the degradation of corrosion resistance can be more effectively suppressed by properly controlling the size and distribution state of the Ni-based compounds existing as impurities in the aforementioned coating film. It was also found that the _Mg2Si phase, _MgZn2 phase and Si phase formed in the coating film of the molten Al-Zn-Si-Mg system plated steel sheet increase or decrease the precipitation amount according to the balance of each component in the coating film or the formation conditions of the coating film, so that their existence ratio changes. Depending on the balance of the composition, there is also a situation where a certain phase does not precipitate. The corrosion resistance of the molten Al- _Zn -Si-Mg system plated steel sheet changes with the existence ratio of these phases. In particular, when the MgZn2 _phase is more than the Mg2Si phase or the Si phase, the corrosion resistance is stably improved. However, it is known that it is very difficult to distinguish the difference between the _Mg2Si phase, _MgZn2 phase and Si phase even when observing the coating film from the surface or cross-section using a general method such as a scanning electron microscope, taking secondary electron images or reflected electron images. Although microscopic information can be obtained by observation using a transmission electron microscope, the existence ratio of the MgSi, _MgZn2 and Si phases that affects the macroscopic information of corrosion resistance or appearance cannot be grasped. Therefore, the inventors of the present invention have conducted further active research and found that by focusing on the X-ray diffraction method, the intensity ratio of the specific diffraction peaks of the Mg ₂ Si phase, the MgZn ₂ phase and the Si phase can be used to quantitatively determine the existence ratio of the phases. In addition, if the Mg ₂ Si phase and the MgZn ₂ phase in the coating film meet the specific existence ratio, in addition to achieving stable and excellent corrosion resistance, the generation of slag can be suppressed and a good surface appearance can be ensured. In addition, the inventors of the present invention have also found that by controlling the Ni content or the film structure in the above-mentioned coating film and controlling the Sr concentration in the coating bath, the generation of wrinkle-shaped concave-convex defects can be reliably suppressed, and a coated steel sheet with excellent surface appearance can be obtained.

Furthermore, the inventors of the present invention have also examined the chemical film formed on the aforementioned coating film, and have also found that by making the chemical film composed of a specific resin and a specific metal compound, the affinity between the chemical film and the coating film and the rust-proof effect can be improved, and the rust resistance can be stably improved. Furthermore, the inventors of the present invention have also examined the chemical film and the primer film formed on the aforementioned coating film, and have also found that by making the chemical film composed of a specific resin and a specific inorganic compound, and the primer film composed of a specific polyester resin and an inorganic compound, the barrier property and adhesion of the coating can be improved, and excellent post-processing corrosion resistance can be achieved even without chromate.

The present invention is completed based on the above findings, and its gist is as follows. 1. A molten Al-Zn-Si-Mg coated steel plate, which is a molten Al-Zn-Si-Mg coated steel plate having a coating film, characterized in that the coating film has a composition containing Al: 45~65 mass%, Si: 1.0~4.0 mass% and Mg: 1.0~10.0 mass%, and the remainder is composed of Zn and inevitable impurities, the Ni content in the inevitable impurities is less than 0.010 mass% relative to the total mass of the coating film.

2. The molten Al-Zn-Si-Mg coated steel plate as described in 1 above, wherein the coating film contains a Ni compound, and the length of the Ni compound is 4.0 μm or less. 3. The molten Al-Zn-Si-Mg coated steel plate as described in 1 or 2 above, wherein the coating film contains a Ni compound, and the number of the Ni compound present in the direction parallel to the surface of the base steel plate is 5/mm or less. 4. The molten Al-Zn-Si-Mg coated steel plate as described in 1 above, wherein the coating film does not contain a Ni compound.

5. A molten Al-Zn-Si-Mg coated steel sheet as described in any one of 1 to 4 above, wherein the diffraction intensities of _Mg2Si and _MgZn2 in the coating film as measured by X-ray diffraction satisfy the following relationship (1): _Mg2Si (111)/ _MgZn2 (100)≦2.0…(1) _Mg2Si (111): diffraction intensity of (111) plane of _Mg2Si (plane spacing d=0.3668nm) _MgZn2 (100): diffraction intensity of (100) _plane of MgZn2 (plane spacing d=0.4510nm).

6. A molten Al-Zn-Si-Mg coated steel plate as described in any one of 1 to 5 above, wherein the diffraction intensity of Si in the coating film by X-ray diffraction method satisfies the following relationship (2): Si(111)=0…(2) Si(111): diffraction intensity of Si (111) plane (plane spacing d=0.3135nm).

7. The molten Al-Zn-Si-Mg coated steel plate as described in any one of 1 to 6 above, wherein the coating further contains Sr: 0.01~1.0 mass %.

8. The molten Al-Zn-Si-Mg coated steel plate as described in any one of 1 to 7 above, wherein the Al content in the coating is 50-60 mass %.

9. The molten Al-Zn-Si-Mg coated steel plate as described in any one of 1 to 8 above, wherein the Si content in the coating is 1.0-3.0 mass %.

10. The molten Al-Zn-Si-Mg coated steel plate as described in any one of 1 to 9 above, wherein the Mg content in the coating is 1.0-5.0 mass %.

11. A method for manufacturing a molten Al-Zn-Si-Mg coated steel plate, which is a method for manufacturing a molten Al-Zn-Si-Mg coated steel plate having a coating film, wherein the coating film is formed by a molten coating treatment step of immersing a base steel plate in a coating bath containing Al: 45-65 mass%, Si: 1.0-4.0 mass%, and Mg: 1.0-10.0 mass%, with the remainder being Zn and inevitable impurities, and the Ni content in the inevitable impurities of the coating bath is controlled to be less than 0.010 mass% relative to the total mass of the coating bath.

12. A method for producing a molten Al-Zn-Si-Mg based plated steel plate as described in 11 above, wherein the plating bath further contains Sr: 0.01~1.0 mass %.

13. A surface treated steel plate having a coating film as described in any one of 1 to 10 above and a chemical coating formed on the coating film, wherein the chemical coating contains at least one resin selected from epoxy resin, urethane resin, acrylic resin, acrylic silicone resin, alkyd resin, polyester resin, polyurethane 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.

14. A method for manufacturing a surface-treated steel plate, which comprises a coating film formed by the method for manufacturing a molten Al-Zn-Si-Mg-based coating steel plate as described in 11 or 12 above and a chemical film formed on the coating film, wherein the chemical film contains at least one resin selected from epoxy resins, urethane resins, acrylic resins, acrylic silicone resins, alkyd resins, polyester resins, polyurethane 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.

15. A coated steel plate, which is a coated steel plate formed directly or via a chemical coating on a coating film as described in any one of 1 to 10 above, wherein the chemical coating contains: a resin component and an inorganic compound, the resin component 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, the content ratio of (a) to (b) ((a): (b)) is in the range of 3:97 to 60:40 in terms of mass ratio, the inorganic compound contains 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, The aforementioned coating film has at least a base coating film, and the base 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.

16. A method for manufacturing a coated steel plate, wherein a coating film is formed directly or via a chemical film on a coating film formed by the method for manufacturing a molten Al-Zn-Si-Mg-based coated steel plate as described in 11 or 12 above, and the method is characterized in that The chemical film contains: a resin component and an inorganic compound, the resin component contains 30-50% by weight of (a): an anionic polyurethane resin having an ester bond and (b): an epoxy resin having a bisphenol skeleton, the content ratio of (a) to (b) ((a): (b)) is in the range of 3:97-60:40 by weight, the inorganic compound contains 2-10% by weight of a vanadium compound, 40-60% by weight of a zirconium compound and 0.5-5% by weight of a fluorine compound, The coating film at least has a base coating film, the base 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. [Effect of the invention]

According to the present invention, a molten Al-Zn-Si-Mg-based plated steel sheet with stable corrosion resistance and excellent corrosion resistance can be provided. According to the present invention, a surface-treated steel sheet with stable corrosion resistance and excellent rust resistance and a method for manufacturing the same can be provided. Furthermore, according to the present invention, a coated steel sheet with stable corrosion resistance and excellent corrosion resistance of the processed portion and a method for manufacturing the same can be provided.

(Molten Al-Zn-Si-Mg plated steel plate)

The molten Al-Zn-Si-Mg plated steel plate of the present invention has a coating film on the surface of the steel plate. The coating film has the following composition: Al: 45-65 mass%, Si: 1.0-4.0 mass%, and Mg: 1.0-10.0 mass%, and the rest is composed of Zn and inevitable impurities.

The Al content in the aforementioned coating film is 45-65% by mass, preferably 50-60% by mass, based on the balance between corrosion resistance and working surface. The reason is that if the Al content in the aforementioned coating film is at least 45% by mass, Al dendritic solidification occurs, and a coating film structure with a dendritic solidification structure of the α-Al phase as the main body can be obtained. By adopting a structure in which the dendritic solidification structure is layered in the thickness direction of the coating film, the corrosion path becomes complex, thereby improving the corrosion resistance of the coating film itself. The more the dendrites of the α-Al phase are layered, the more complicated the corrosion path is, and the less likely it is for corrosion to reach the base steel plate. Therefore, in order to improve corrosion resistance, the Al content is preferably set to 50% by mass or more. On the other hand, when the Al content in the aforementioned coating exceeds 65% by mass, Zn almost changes to a structure that is solid-dissolved in α-Al, and the dissolution reaction of the α-Al phase cannot be suppressed, so that the corrosion resistance of the Al-Zn-Si-Mg coating is deteriorated. Therefore, the Al content in the aforementioned coating must be 65% by mass or less, preferably 60% by mass or less.

The main purpose of adding Si to the aforementioned coating is to suppress the growth of the Fe-Al and/or Fe-Al-Si interface alloy layer generated at the interface with the base steel plate, so as not to deteriorate the adhesion between the coating and the steel plate. In fact, if the steel plate is immersed in an Al-Zn coating bath containing Si, the Fe on the surface of the steel plate reacts with the Al or Si in the bath to form an Fe-Al and/or Fe-Al-Si intermetallic compound layer at the interface between the base steel plate and the coating. At this time, the growth rate of the Fe-Al-Si alloy is slower than that of the Fe-Al alloy. Therefore, the higher the ratio of the Fe-Al-Si alloy, the more the growth of the interface alloy layer can be suppressed. Therefore, the Si content in the aforementioned coating needs to be 1.0 mass% or more. On the other hand, when the Si content in the aforementioned coating film exceeds 4.0% by mass, not only the growth inhibition effect of the aforementioned interface alloy layer is saturated, but also corrosion is promoted due to the presence of an excessive Si phase in the coating film, so the Si content is set to 4.0% or less. In addition, the Si content in the aforementioned coating film is preferably set to 3.0% or less from the viewpoint of inhibiting the presence of an excessive Si phase. In addition, in terms of the relationship with the Mg content described later, the Si content is preferably set to 1.0 to 3.0% by mass from the viewpoint of easily satisfying the relational expression (1) described later.

The above-mentioned coating film contains 1.0-10.0% Mg. Since the above-mentioned coating film contains Mg, the above-mentioned Si can exist in the form of an intermetallic compound of Mg ₂ Si phase, which can inhibit the promotion of corrosion. In addition, when the above-mentioned coating film contains Mg, an intermetallic compound of MgZn ₂ phase is also formed in the coating film, which can obtain an effect of further improving corrosion resistance. When the Mg content in the above-mentioned coating film is less than 1.0 mass%, due to the formation of the above-mentioned intermetallic compound (Mg ₂ Si, MgZn ₂ ), Mg is used for the solid solution of the main phase α-Al phase, and sufficient corrosion resistance cannot be ensured. On the other hand, when the Mg content in the aforementioned coating film increases, in addition to the saturation of the effect of improving the corrosion resistance, the fragility of the α-Al phase also reduces the workability, so the content is set to 10.0% or less. In addition, the Mg content in the aforementioned coating film is preferably set to 5.0% by mass or less from the viewpoint of suppressing the generation of slag during coating formation and facilitating the management of the coating bath. In addition, in terms of the relationship with the aforementioned Si content, the aforementioned Mg content is preferably set to 3.0% by mass from the viewpoint of easily satisfying the relationship (1) described later. Considering the compatibility with slag suppression, the aforementioned Mg content is more preferably 3.0-5.0% by mass.

Furthermore, the aforementioned coating film contains Zn and inevitable impurities. Among them, the aforementioned inevitable impurities contain Fe. The Fe is inevitably contained in the coating bath due to the dissolution of the steel plate or the equipment in the bath, and is inevitably contained in the aforementioned coating film as a result of diffusion and supply from the base steel plate when the interface alloy layer is formed. The Fe content in the aforementioned coating film is usually about 0.3~2.0 mass%. Other examples of inevitable impurities are Cr, Ni, Cu, etc. These components are dissolved into the plating bath by the base steel plate or stainless steel bath equipment, and are contained as impurities in the metal blocks that become the raw materials of the plating bath. In addition, they are inevitably contained in the aforementioned plating film due to the tank or bath equipment used in the manufacture of the plated steel plate to which these components are intentionally added.

Furthermore, the molten Al-Zn-Si-Mg coated steel sheet of the present invention is characterized in that the Ni content in the aforementioned inevitable impurities is 0.010 mass % or less relative to the total mass of the aforementioned coating film. Since the Ni contained in the aforementioned coating film may deteriorate the corrosion resistance of the molten Al-Zn-Si-Mg coated steel sheet, in addition to properly controlling the Al, Zn, Si and Mg contents in the aforementioned coating film, the Ni content as an inevitable impurity is further suppressed to suppress the deterioration of the corrosion resistance. Based on the same viewpoint, the Ni content of the aforementioned inevitable impurities is preferably 0.005 mass % or less relative to the total weight of the aforementioned coating film.

When Ni is contained in the aforementioned unavoidable impurities, the coating film of the molten Al-Zn-Si-Mg coated steel sheet sometimes contains Ni compounds as impurities. Here, the aforementioned Ni compounds are mainly Ni compounds such as binary intermetallic compounds such as Ni-Al compounds, or ternary intermetallic compounds such as Ni-Al-Fe compounds. As Ni-Al compounds, intermetallic compounds such as NiAl ₃ can be exemplified, and as Ni-Al-Fe compounds, intermetallic compounds such as (Ni,Fe)Al ₃ in which a part of Ni in NiAl ₃ is replaced by Fe can be exemplified, but are not limited to these compounds. Here, the presence of Ni compounds in the aforementioned coating film can be confirmed by, for example, using a scanning electron microscope to observe the coating film from the surface or cross-section with a secondary electron image or a reflected electron image, and analyzing it with energy dispersive X-ray spectroscopy (EDS). For example, 5 to 10 100μm plating sections are randomly selected, and observation and element mapping analysis are performed at an accelerating voltage of less than 5kV. Then, point analysis is performed on the part where Ni is detected to confirm the composition of Ni-containing substances. This method is only an example after all, and any method can be used as long as it can confirm the presence of Ni compounds, without special restrictions.

Furthermore, when the aforementioned coating film contains a Ni compound, the length of the Ni compound is preferably less than 4.0 μm. The Ni compound present in the aforementioned coating film functions as a cathode in a corrosive environment, and forms a local battery with the surrounding solidified structure, thereby causing corrosion resistance to deteriorate. In particular, when coarse Ni compounds are present in the aforementioned coating film, there is a risk that the corrosion resistance of the molten Al-Zn-Si-Mg coated steel sheet will be significantly reduced. Therefore, in order to obtain a molten Al-Zn-Si-Mg coated steel sheet with better corrosion resistance, it is effective to control the size of the Ni-based compound contained as an impurity in the coating film to be smaller. Specifically, it is better to control the length of the Ni-based compound to be less than 4.0μm, more preferably less than 3.0μm, and more preferably less than 2.0μm. The length of the aforementioned Ni-based compound can be measured by, for example, observing the coating film from a cross section with a reflected electron image using a scanning electron microscope, confirming that it is a Ni-based compound with EDS, and observing the magnified reflected electron image of the observation field containing the Ni compound. The length of the aforementioned Ni-based compound is the maximum length of the Ni-based compound confirmed in the observation field of the aforementioned coating film.

In addition, when the aforementioned coating film contains Ni-based compounds, it is also effective to reduce the amount of the aforementioned Ni-based compounds that serve as corrosion starting points from the perspective of obtaining more stable high corrosion resistance. Specifically, the number of particles of the Ni-based compounds in the aforementioned coating film is preferably 5 or less/mm in the direction parallel to the surface of the base steel plate, more preferably 2 or less/mm, and the best is 0/mm (non-existent). Therefore, by suppressing the amount of Ni-containing compounds in the aforementioned coating film, the corrosion resistance degradation of the molten Al-Zn-Si-Mg coating steel plate can be more reliably suppressed. In order to obtain such a coating structure (a coating structure that does not contain Ni-based compounds), it is important to reduce the Ni content in the aforementioned unavoidable impurities, specifically, to make the Ni content less than 0.005 mass% relative to the total mass of the aforementioned coating film. In addition, regarding the number of particles of the aforementioned Ni-based compounds, for example, a scanning electron microscope can be used to continuously observe the cross-section of the coated film parallel to the surface of the base steel plate with a length of more than 1 mm using a reflected electron image. The number of Ni-based compounds confirmed by EDS is divided by the measured length (mm), and the number of Ni-based compounds present within a length range of 1 mm can be calculated.

In addition, although there is no particular restriction on the total content of inevitable impurities in the aforementioned coating film, excessive content may affect various properties of the coated steel sheet, so it is preferably set to 5.0 mass % or less.

In addition to controlling the concentrations of Al, Zn, Si, Mg and Ni as an inevitable impurity, the molten Al- _Zn -Si-Mg coated steel sheet of the present invention preferably satisfies the following relationship (1) in terms of diffraction intensity of Mg2Si and _MgZn2 in the coating film by X-ray diffraction method in order to more stably improve corrosion resistance. _Mg2Si (111)/ _MgZn2 (100)≦2.0…(1) _Mg2Si (111): diffraction intensity of (111) plane of _Mg2Si (plane spacing d=0.3668nm) _MgZn2 (100): diffraction intensity of (100) plane of _MgZn2 (plane spacing d=0.4510nm).

As mentioned above, the molten Al-Zn-Si-Mg coated steel sheet of the present invention is important in that the presence ratio of intermetallic compounds such as _Mg2Si and _MgZn2 generated in the coating film is controlled to a specific ratio by containing the aforementioned Mg. The influence of these on corrosion resistance is still under investigation and there are still many unknowns, but the following mechanism is speculated.

When the molten Al-Zn-Si-Mg plated steel sheet is exposed to a corrosive environment, the above-mentioned intermetallic compound dissolves preferentially over the α-Al phase, and the area around the formed corrosion products becomes a Mg-rich environment. It is presumed that the formed corrosion products are not easily decomposed in such a Mg-rich environment, and as a result, the protective effect of the coating film is improved. Moreover, the protective effect of the coating film is improved because _MgZn2 is greater than _Mg2Si , so it is believed that increasing the abundance ratio of _MgZn2 in the intermetallic compound present in the above-mentioned coating film is effective.

Furthermore, it is important that the abundance ratio of _Mg2Si and _MgZn2 in the above-mentioned coating film satisfies the relationship (1): _Mg2Si (111)/ _MgZn2 (100)≦2.0 using the diffraction peak intensity obtained by the X-ray diffraction method. When the abundance ratio of _Mg2Si and _MgZn2 in the above-mentioned coating film does not satisfy the relationship (1), that is, _Mg2Si (111)/ _MgZn2 (100)＞2.0, since _Mg2Si is present in a larger amount in the intermetallic compound present in the above-mentioned coating film, the above-mentioned Mg-rich environment cannot be obtained near the corrosion product, and there is a possibility that the protective effect of the above-mentioned coating film cannot be easily obtained.

Here, in the above relationship (1), _Mg2Si (111) is the diffraction intensity of the (111) plane of _Mg2Si (plane spacing d=0.3668nm), and _MgZn2 (100) is the diffraction intensity of the (100) plane of _MgZn2 (plane spacing d=0.4510nm). As a method for measuring _Mg2Si (111) and _MgZn2 (100) by X-ray diffraction, a part of the above-mentioned coating film can be mechanically cut off and X-ray diffraction can be performed in a powder state (powder X-ray diffraction measurement method) to calculate. Regarding the diffraction intensity measurement, the diffraction peak intensity of Mg ₂ Si corresponding to the plane spacing d = 0.3668nm and the diffraction peak intensity of MgZn ₂ corresponding to the plane spacing d = 0.4510nm are measured, and by calculating these ratios, Mg ₂ Si (111) / MgZn ₂ (100) can be obtained. In addition, the amount of coating film required for the powder X-ray diffraction measurement (the amount of coating film cut out) is sufficient to be 0.1g or more, preferably 0.3g or more, from the viewpoint of accurately measuring Mg ₂ Si (111) and MgZn ₂ (100). Furthermore, when the coating is cut out, steel plate components other than the coating may be included in the powder, but the intermetallic compound phase is contained only in the coating and does not affect the peak intensity. In addition, the reason for X-ray diffraction of the coating in the form of powder is that when X-ray diffraction is performed on the coating formed on the coated steel plate, it is affected by the plane orientation of the solidified structure of the coating, making it difficult to calculate the correct phase ratio.

In addition, in the molten Al-Zn-Si-Mg coated steel sheet of the present invention, in addition to controlling the concentrations of the aforementioned Al, Zn, Si, Mg and Ni as an inevitable impurity, based on the viewpoint of more stably improving the corrosion resistance, the diffraction intensity of Si in the aforementioned coating film by X-ray diffraction method preferably satisfies the following relationship (2). Si(111)=0…(2) Si(111): diffraction intensity of the (111) plane of Si (plane spacing d=0.3135mm). In the dissolution reaction of general Al alloys in aqueous solution, it is known that Si phase exists as a cathode site and promotes the dissolution of the surrounding α-Al phase. Therefore, the viewpoint that reducing Si phase inhibits the dissolution of α-Al phase is also effective. Among them, as in relation (2), it is best to have no Si phase film (the aforementioned diffraction peak intensity of Si (111) is zero) in order to stabilize the corrosion resistance. In addition, the method for measuring the diffraction peak intensity of Si (111) plane by X-ray diffraction can be the same method as the above-mentioned method for measuring Mg ₂ Si (111) and MgZn ₂ (100).

Here, there is no particular limitation on the method for satisfying the above-mentioned relationship (1) and relationship (2). For example, in order to satisfy the relationship (1) and relationship (2), by adjusting the balance of the Si content, the Mg content and the Al content in the aforementioned coating film, the existence ratio of _Mg2Si , _MgZn2 and Si (the diffraction intensity of _Mg2Si (111), _MgZn2 (100) and Si(111)) can be controlled. In addition, if the balance of the Si content, the Mg content and the Al content in the aforementioned coating film is necessarily set to a certain content ratio, it is not interpreted as satisfying the relationship (1) and relationship (2). For example, it is necessary to change the content ratio of Mg and Al according to the Si content (mass %). In addition to adjusting the balance of Si content, Mg content and Al content in the coating film, the diffraction intensity of _Mg2Si (111), _MgZn2 (100) and Si(111) can also be controlled by adjusting the conditions during coating film formation (e.g. cooling conditions after coating) to satisfy relations (1) and (2).

In addition, in the molten Al-Zn-Si-Mg steel plate of the present invention, it is preferred that the aforementioned coating film contains 0.01 to 1.0 mass % Sr. By containing Sr in the aforementioned coating film, the occurrence of surface defects such as wrinkle-shaped concave-convex defects can be more reliably suppressed, and good surface appearance can be achieved. In addition, the aforementioned wrinkle defects are wrinkle-shaped concave-convex defects formed on the surface of the aforementioned coating film, and white stripes are observed on the surface of the aforementioned coating film. Such wrinkle defects are easy to occur when more Mg is added to the coating film. Therefore, the aforementioned molten coated steel plate, by containing Sr in the aforementioned coating film, makes the Sr in the surface layer of the aforementioned coating film oxidized more preferentially than Mg, and by suppressing the oxidation reaction of Mg, the occurrence of the aforementioned wrinkle defects can be suppressed.

Furthermore, in the molten Al-Zn-Si-Mg steel sheet of the present invention, it is preferred that the ratio of _Mg2Si to _MgZn2 in the coating film satisfies the relation (1), and the coating film contains 0.01 to 1.0 mass % Sr. Thus, the surface appearance improvement effect of Sr can be more enjoyed. Although the reason is not clear, it is speculated that if the coating film contains more _Mg2Si , the oxidation of the coating surface layer is not easily suppressed, which affects the appearance improvement effect when Sr is added. Furthermore, when the Sr content in the aforementioned coating film is less than 0.01 mass %, it is difficult to obtain the effect of suppressing the occurrence of the above-mentioned wrinkle defects. If the Sr content in the aforementioned coating film exceeds 1.0 mass %, Sr is excessively incorporated into the interface alloy layer, and there is a risk that the impact on the coating adhesion, etc. will be greater than the appearance improvement effect, etc. Therefore, the Sr content in the aforementioned coating film is preferably 0.01~1.0 mass %.

In addition, the aforementioned coating film preferably contains 0.01 to 10% by mass of one or more selected from Cr, Mn, V, Mo, Ti, Ca, Ni, Co, Sb and B in total from the viewpoint of improving the stability of corrosion products and exerting the effect of delaying the progress of corrosion, as in the case of Mg. The reason why the total content of the above components is set to 0.01 to 10% by mass is that a sufficient corrosion delay effect can be obtained and the effect will not be saturated.

In addition, the coating weight of the above-mentioned coating is preferably 45-120 g/m ² per side from the viewpoint of satisfying various characteristics. When the coating weight of the above-mentioned coating is 45 g/m ² or more, sufficient corrosion resistance can be obtained for applications requiring long-term corrosion resistance such as building materials, and when the coating weight of the above-mentioned coating is 120 g/m ² or less, the coating cracking during processing can be suppressed, and excellent corrosion resistance can be achieved. Based on the same viewpoint, the coating weight of the above-mentioned coating is more preferably 45-100 g/m ² .

The amount of the coating film can be derived by, for example, dissolving and peeling off a specific area of the coating film with a mixture of hydrochloric acid and hexamethylenetetramine as shown in JIS H 0401: 2013, and calculating from the weight difference of the steel plate before and after peeling. The amount of coating film per single side can be obtained by sealing with tape so that the coating surface of the non-target side is not exposed and then performing the dissolution.

The composition of the coating film is the same as the Ni content, and can be dissolved by immersing the coating film in hydrochloric acid, etc., and the solution can be confirmed by ICP emission spectrometry or atomic absorption analysis. This method is only an example, and any method can be used without particular limitation as long as the composition of the coating film can be accurately quantified.

Furthermore, the coating film of the molten Al-Zn-Si-Mg coated steel sheet obtained by the present invention has substantially the same composition as the coating bath. Therefore, by controlling the coating bath composition, the coating film composition can be controlled with high precision.

Furthermore, there is no particular limitation on the base steel plate constituting the molten Al-Zn-Si-Mg based coated steel plate of the present invention, and a cold rolled steel plate or a hot rolled steel plate can be appropriately used according to the required performance and specifications.

In addition, there is no particular limitation on the method for obtaining the aforementioned base steel sheet. For example, in the case of the aforementioned hot-rolled steel sheet, a steel sheet that has been subjected to a hot-rolling step and a pickling step may be used, and in the case of the aforementioned cold-rolled steel sheet, a steel sheet that has been subjected to a further cold-rolling step may be used. Furthermore, in order to obtain the characteristics of the steel sheet, a recrystallization annealing step may be performed before the melt-plating step.

(Method for producing molten Al-Zn-Si-Mg coated steel plate) The method for producing molten Al-Zn-Si-Mg coated steel plate of the present invention is a method for producing molten Al-Zn-Si-Mg coated steel plate having a coating film, wherein the coating film is formed by a molten coating treatment step of immersing a base steel plate in a coating bath containing Al: 45~65 mass%, Si: 1.0~4.0 mass% and Mg: 1.0~10.0 mass%, with the remainder being Zn and inevitable impurities. In addition, in the molten coating treatment step, there is no particular restriction except for the coating bath conditions described later. For example, the above-mentioned base steel plate can be manufactured by washing, heating, and immersing in a coating bath using a continuous melt coating device. In the heating step of the steel plate, recrystallization annealing is performed to control the structure of the above-mentioned base steel plate itself, and heating in a reducing environment such as a nitrogen-hydrogen environment is effective to prevent oxidation of the steel plate and reduce the trace oxide film on the surface.

Furthermore, regarding the plating bath used in the aforementioned melt plating treatment step, as described above, since the composition of the aforementioned plating film is generally substantially equal to the composition of the plating bath, a composition containing 45 to 65 mass % of Al, 1.0 to 4.0 mass % of Si, and 1.0 to 10.0 mass % of Mg, with the remainder being Zn and unavoidable impurities, can be used.

Next, the manufacturing method of the molten Al-Zn-Si-Mg coated steel sheet of the present invention is characterized in that the Ni content in the inevitable impurities of the aforementioned coating bath is controlled to be less than 0.010 mass % relative to the total mass of the aforementioned coating bath. As mentioned above, since the Ni contained in the aforementioned coating film has the effect of deteriorating the corrosion resistance of the molten Al-Zn-Si-Mg coated steel sheet, in addition to properly controlling the contents of Al, Zn, Si and Mg in the coating bath, the degradation of corrosion resistance can be suppressed by further suppressing the content of Ni as an inevitable impurity. In addition, the content of Ni as an inevitable impurity in the aforementioned coating bath needs to be controlled to be less than 0.010 mass %, preferably less than 0.005 mass % relative to the total mass of the coating bath. The reason is that if the Ni content in the aforementioned coating bath exceeds 0.005 mass%, the corrosion resistance of the produced molten Al-Zn-Si-Mg coated steel sheet may deteriorate. If it exceeds 0.010%, there is a possibility of significantly causing corrosion resistance deterioration. In addition, there is no lower limit on the Ni content that has an adverse effect on corrosion resistance.

Here, the method of reducing the Ni content in the plating bath is not particularly limited. For example, since it is effective to suppress the dissolution of the bath equipment made of stainless steel into the plating bath, it is better to treat the surface of the bath equipment with a spray film or the like. This is because by forming the spray film or the like, the bath equipment can be given corrosion resistance to the plating bath, and the dissolution of the bath equipment into the plating bath can be suppressed. The type of the spray film is not particularly limited, but a WC-based or MoB-based film with heat resistance and corrosion resistance can be selected. Moreover, it is more effective to use a bath equipment made of a heat-resistant material that does not contain Ni. In this case, even if the bath equipment dissolves, the Ni content can be prevented from increasing.

As another method of reducing the Ni content in the plating bath, it is better to use a metal block with a low Ni content in the impurities as a raw material for the plating bath. In addition, it is also effective not to use a tank or bath equipment used in the production of the molten Al-Zn-Si-Mg plated steel plate to intentionally add Ni. The reason is that the Ni-containing metal block attached to the aforementioned tank or the aforementioned bath equipment can be suppressed from dissolving and mixing into the plating bath.

In addition, the bath temperature of the aforementioned coating bath is not particularly limited, and is preferably within the temperature range of (melting point + 20°C) ~ 650°C. The reason why the lower limit of the aforementioned bath temperature is set to melting point + 20°C is that in order to carry out the melt coating treatment, the aforementioned bath temperature must be above the solidification point, and the reason why it is set to melting point + 20°C is to prevent solidification caused by a local decrease in the bath temperature of the aforementioned coating bath. On the other hand, the reason why the upper limit of the aforementioned bath temperature is set to 650°C is that if it exceeds 650°C, the aforementioned coating film is difficult to cool rapidly, and there is a risk that the interface alloy layer formed between the coating film and the steel plate will become thicker.

Furthermore, the temperature of the base steel plate immersed in the coating bath (immersion plate temperature) is not particularly limited, but is preferably controlled within ±20°C relative to the temperature of the coating bath from the viewpoint of ensuring the coating characteristics in the above-mentioned continuous melt coating operation and preventing the bath temperature from varying.

Furthermore, the immersion time of the base steel plate in the plating bath is preferably 0.5 seconds or longer. The reason is that if it is less than 0.5 seconds, there is a risk that a sufficient plating film may not be formed on the surface of the base steel plate. There is no particular upper limit on the immersion time, but if the immersion time is too long, the interface alloy layer formed between the plating film and the steel plate may become thicker, so it is more preferably within 8 seconds.

In addition, the molten Al-Zn-Si-Mg based plated steel sheet can be coated directly or with an intermediate layer on the aforementioned plated film, depending on the required performance.

Furthermore, the method for forming the aforementioned coating film is not particularly limited and can be appropriately selected according to the required performance. Examples include roller coating, curtain coating, spray coating, etc. After coating the coating material containing the organic resin, the coating film can be formed by heating and drying by means of hot air drying, infrared heating, induction heating, etc.

Furthermore, the intermediate layer is not particularly limited as long as it is a layer formed between the coating film of the molten-coated steel sheet and the coating film.

(Surface treated steel plate) The surface treated steel plate of the present invention has a coating film on the surface of the steel plate and a chemical film formed on the coating film. The composition of the coating film is the same as the coating film of the molten Al-Zn-Si-Mg system coated steel plate of the present invention.

The surface treated steel plate of the present invention forms a chemical film on the aforementioned film. In addition, the aforementioned chemical film only needs to be formed on at least one side of the surface treated steel plate, and can also be formed on both sides of the surface treated steel plate according to the application or required performance.

Moreover, in the surface treated steel sheet of the present invention, the aforementioned chemical film is characterized by containing at least one resin selected from epoxy resin, urethane resin, acrylic resin, acrylic silicone resin, alkyd resin, polyester resin, polyurethane 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. By forming the aforementioned chemical film on the plated film, in addition to improving the affinity with the plated film and uniformly forming the chemical film on the aforementioned plated film, the anti-rust effect and barrier effect of the chemical film can also be improved. As a result, the surface treated steel plate of the present invention can achieve stable corrosion resistance and rust resistance.

Here, for the resin constituting the aforementioned chemical film, based on the viewpoint of improving corrosion resistance, at least one selected from epoxy resin, urethane resin, acrylic resin, acrylic silicone resin, alkyd resin, polyester resin, polyurethane resin, amino resin and fluororesin is used. Based on the same viewpoint, the aforementioned resin preferably contains at least one of urethane resin and acrylic resin. In addition, the resin constituting the aforementioned chemical film also includes addition polymers of the above resins.

As the epoxy resin, for example, bisphenol A type, bisphenol F type, novolac type epoxy resins and the like which are etherified with glycidyl, bisphenol A type epoxy resins which are etherified with glycidyl by adding propylene oxide, ethylene oxide or polyalkylene glycol, aliphatic epoxy resins, alicyclic epoxy resins, polyether epoxy resins and the like can be used.

As the urethane resin, for example, oil-modified polyurethane resin, alkyd polyurethane resin, polyester polyurethane resin, polyether polyurethane resin, polycarbonate polyurethane resin, etc. can be used.

Examples of the acrylic resin include polyacrylic acid and copolymers thereof, polyacrylate and copolymers thereof, polymethacrylic acid and copolymers thereof, polymethacrylate and copolymers thereof, urethane-acrylic acid copolymers (or urethane-modified acrylic resins), styrene-acrylic acid copolymers, and the like. Furthermore, these resins modified by other alkyd resins, epoxy resins, phenolic resins, and the like may be used.

Examples of the acrylic silicone resin include a resin having a hydrolyzable alkoxysilyl group on the side chain or at the end of an acrylic copolymer as a main agent and a hardener added thereto. When the acrylic silicone resin is used, in addition to corrosion resistance, excellent weather resistance can be expected.

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

The aforementioned polyester resin is a polycondensate synthesized by dehydrating and condensing a polycarboxylic acid and a polyol to form an ester bond. As the polycarboxylic acid, for example, terephthalic acid, 2,6-naphthalene dicarboxylic acid, etc. are used, and as the polyol, for example, ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, etc. are used. Specifically, the aforementioned polyester is exemplified by polyethylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, etc. In addition, the polyester resins modified with acrylic acid can also be used.

Examples of the polyalkane resin include ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers, vinyl copolymers of carboxyl-modified polyolefin resins, ethylene-unsaturated carboxylic acid copolymers, and vinyl isomers. Furthermore, these resins modified with other alkyd resins, epoxy resins, phenolic resins, and the like can be used.

The aforementioned amino resin is a thermosetting resin generated by the reaction of an amine or amide compound with an aldehyde, and examples thereof include melamine resin, guanamine resin, thiourea resin, etc. From the viewpoint of corrosion resistance, weather resistance, adhesion, etc., melamine resin is preferably used. The melamine resin is not particularly limited, and examples thereof include butylated melamine resin, methylated melamine resin, water-based melamine resin, etc.

Examples of the fluororesin include fluoroolefin polymers, or copolymers of fluoroolefin and alkyl vinyl ether, cycloalkyl vinyl ether, carboxylic acid-modified vinyl ester, hydroxy alkyl allyl ether, tetrafluoropropyl vinyl ether, etc. When such fluororesins are used, not only corrosion resistance but also excellent weather resistance and excellent hydrophobicity can be expected.

Furthermore, the resin constituting the chemical film preferably uses a hardener in order to improve corrosion resistance and processability. As the hardener, urea resins (butylated urea resins, etc.), melamine resins (butylated melamine resins, butylated melamine resins, etc.), butylated urea-melamine resins, benzoguanamine resins, etc., amino resins, blocked isocyanates, oxazoline compounds, phenol resins, etc. can be appropriately used.

In addition, as for the metal compound constituting the chemical film, at least one 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 can be used. Based on the same viewpoint, the metal compound preferably contains at least one of P compounds, Si compounds and V compounds.

Here, by including the aforementioned P compound in the aforementioned chemical film, corrosion resistance and sweat resistance can be improved. The aforementioned P compound is a compound containing P, and can contain, for example, one or more selected from inorganic phosphoric acid, organic phosphoric acid and salts thereof.

As the aforementioned inorganic phosphoric acid, organic phosphoric acid and salts thereof, any compound can be used without particular limitation. For example, as the aforementioned inorganic phosphoric acid, it is preferred to use one or more selected from phosphoric acid, dihydrogen phosphate, hydrogen phosphate, phosphate, pyrophosphoric acid, pyrophosphate, tripolyphosphoric acid, tripolyphosphate, phosphorous acid, phosphite, hypophosphorous acid, and hypophosphite. And as the aforementioned organic phosphoric acid, it is preferred to use phosphonic acid (phosphonic acid compound). In addition, as the aforementioned phosphonic acid, it is preferred to use one or more selected from nitrogen trimethylenephosphonic acid, phosphonobutane tricarboxylic acid, methyl diphosphonic acid, methylenephosphonic acid and ethylene diphosphonic acid. Furthermore, when the aforementioned P compound is a salt, the salt is preferably a salt of an element from Group 1 to Group 13 in the periodic table, more preferably a metal salt, and preferably at least one selected from an alkali metal salt and an alkaline earth metal salt.

When the chemical treatment liquid containing the above-mentioned P compound is applied to the molten Al-Zn-Si-Mg coated steel plate, the surface of the coating film is etched by the action of the P compound, and a concentrated layer of Al, Zn, Si and Mg, which are the constituent elements of the coating film, is formed on the coating film side in front of the chemical film. By forming the above-mentioned concentrated layer, the bonding between the chemical film and the coating film surface becomes firm, and the adhesion of the chemical film is improved. The concentration of the P compound in the above-mentioned chemical treatment liquid is not particularly limited, and can be set to 0.25 mass%~5 mass%. When the concentration of the aforementioned P compound is less than 0.25 mass%, not only the etching effect is insufficient, the adhesion with the coating interface is reduced, the corrosion resistance of the plane part is reduced, but also the corrosion resistance and sweat resistance of the defective part, the cut end face part, and the damaged part of the coating film caused by processing may be reduced. Based on the same viewpoint, the concentration of the P compound is preferably 0.35 mass% or more, and more preferably 0.50 mass% or more. On the other hand, when the concentration of the aforementioned P compound exceeds 5 mass%, not only the life of the chemical treatment solution is shortened, but also the appearance of the film when formed is easily uneven, and the amount of P eluted from the chemical film increases, and there is also a possibility of reduced blackening resistance. Based on the same viewpoint, the concentration of the P compound is preferably 3.5 mass % or less, more preferably 2.5 mass % or less. Regarding the P compound content in the chemical film, for example, a chemical treatment liquid with a P compound concentration of 0.25 mass % to 5 mass % can be applied and dried to make the P adhesion amount in the chemical film after drying 5 to 100 mg/m ² .

The Si compound is a component that forms the skeleton of the chemical film together with the resin, and can improve the affinity with the coating film and form the chemical film uniformly. The Si compound is a compound containing Si, and is preferably one or more selected from silicon oxide, trialkoxysilane, tetraalkoxysilane and silane coupling agent.

As the aforementioned silicon oxide, any one can be used without particular limitation. As the aforementioned silicon oxide, for example, at least one of wet silicon oxide and dry silicon oxide can be used. As colloidal silicon oxide, which is one of the aforementioned wet silicon oxides, for example, SNOWTEX O, C, N, S, 20, OS, OXS, NS, etc. manufactured by Nissan Chemical Co., Ltd. can be appropriately used. Also, as the aforementioned dry silicon oxide, for example, AEROSIL50, 130, 200, 300, 380, etc. manufactured by Nippon Aerosil Co., Ltd. can be appropriately used.

Any trialkoxysilane may be used without particular limitation. Preferably, a trialkoxysilane represented by the general formula: R ₁ Si(OR ₂ ) ₃ (wherein R ₁ is hydrogen or an alkyl group having 1 to 5 carbon atoms, and R ₂ is the same or different alkyl group having 1 to 5 carbon atoms) is used. Examples of the trialkoxysilane include trimethoxysilane, triethoxysilane, methyltriethoxysilane, and the like.

As the aforementioned tetraalkoxysilane, any one can be used without particular limitation. Preferably, 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) is used. Examples of such tetraalkoxysilane include tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane.

As the silane coupling agent, any one can be used without particular limitation, and examples thereof include γ-glycidyloxypropyl trimethoxysilane, γ-glycidyloxypropyl methyldiethoxysilane, γ-glycidyloxypropyl triethoxysilane, γ-aminopropyl trimethoxysilane, γ-aminopropyl methyldiethoxysilane, γ-aminopropyl triethoxysilane, γ-methacryloxypropyl trimethoxysilane, γ-methacryloxypropyl triethoxysilane, γ-butylylpropyl methyldimethoxysilane, γ-butylylpropyl trimethoxysilane, vinyltriethoxysilane, and γ-isocyanatepropyltriethoxysilane.

Furthermore, by containing the aforementioned Si compound in the chemical film, the Si compound is dehydrated and condensed to form an amorphous chemical film with a siloxane bond having a high barrier effect for shielding corrosion factors. Furthermore, by combining with the aforementioned resin, a chemical film with higher barrier properties is formed. In addition, in a corrosive environment, a dense and stable corrosion product is formed in a defective part or a damaged part of the coating film produced by processing, and the corrosion of the base steel plate is also inhibited by the composite effect with the aforementioned coating film. Based on the viewpoint of a higher effect of forming a stable corrosion product, it is preferred to use at least one of colloidal silicon oxide and dry silicon oxide as the aforementioned Si compound.

The concentration of the aforementioned Si compound in the chemical treatment liquid used to form the aforementioned chemical film is 0.2 mass% to 9.5 mass%. If the concentration of the Si compound in the aforementioned chemical treatment liquid is 0.2 mass% or more, a barrier effect due to siloxane bonds can be obtained, and as a result, in addition to the corrosion resistance of the planar portion, the corrosion resistance of the defective portion, the cut portion, and the damaged portion caused by processing, etc., and the sweat resistance are improved. Moreover, if the concentration of the aforementioned Si compound is 9.5 mass% or less, the life of the chemical treatment liquid can be extended. The chemical treatment liquid with a concentration of Si compound set to 0.2 mass% to 9.5 mass% can be applied and dried, and the Si adhesion amount in the chemical film after drying can be 2 to 95 mg/ ^m2 .

By including the aforementioned Co compound and the aforementioned Ni compound in the aforementioned chemical film, the blackening resistance can be improved. This is considered to be because Co and Ni have the effect of slowing down the dissolution of water-soluble components from the film in a corrosive environment. Moreover, the aforementioned Co and the aforementioned Ni are elements that are more difficult to oxidize than Al, Zn, Si, and Mg. Therefore, by concentrating at least one of the aforementioned Co compound and the aforementioned Ni compound at the interface between the aforementioned chemical film and the aforementioned plated film (forming a concentrated layer), the concentrated layer becomes a barrier to corrosion, and the blackening resistance can be improved.

By using a chemical treatment solution containing the aforementioned Co compound, Co can be contained in the aforementioned chemical film and incorporated into the aforementioned concentrated layer. As the aforementioned Co compound, cobalt salt is preferably used. As the aforementioned cobalt salt, one or more selected from cobalt sulfate, cobalt carbonate and cobalt chloride is more preferably used. In addition, by using a chemical treatment solution containing the aforementioned Ni compound, Ni can be contained in the aforementioned chemical film and incorporated into the aforementioned concentrated layer. As the aforementioned Ni compound, nickel salt is preferably used. As the aforementioned nickel salt, one or more selected from nickel sulfate, nickel carbonate and nickel chloride is more preferably used.

The concentration of the Co compound and/or the Ni compound in the aforementioned chemical treatment solution is not particularly limited, but the total can be 0.25 mass% to 5 mass%. When the concentration of the aforementioned Co compound and/or the Ni compound is less than 0.25 mass%, the interface concentration layer becomes uneven, and not only the corrosion resistance of the plane portion is reduced, but also the corrosion resistance of the defective portion, the cut end portion, and the coating film damaged due to processing, etc. may be reduced. Based on the same viewpoint, it is preferably 0.5 mass% or more, and more preferably 0.75 mass% or more. On the other hand, when the concentration of the aforementioned Co compound and/or the Ni compound exceeds 5 mass%, the appearance of the film when it is formed is prone to be uneven, and there is a risk of reduced corrosion resistance. Based on the same viewpoint, it is preferably 4.0 mass % or less, and more preferably 3.0 mass % or less. The chemical treatment solution having a total concentration of 0.25 mass % to 5 mass % of the Co compound and/or Ni compound can be applied and dried to make the total amount of Co and Ni in the chemical film after drying to be 5 to 100 mg/m ² .

The Al compound, Zn compound and Mg compound mentioned above can be contained in the chemical treatment solution to form a concentration layer containing at least one selected from Al, Zn and Mg on the coating film side of the chemical film. The formed concentration layer can improve the corrosion resistance. In addition, if the Al compound, Zn compound and Mg compound are compounds containing Al, Zn and Mg, they are not particularly limited, and are preferably inorganic compounds, preferably salts, chlorides, oxides or hydroxides.

As the aforementioned Al compound, for example, one or more selected from aluminum sulfate, aluminum carbonate, aluminum chloride, aluminum oxide, and aluminum hydroxide. As the aforementioned Zn compound, for example, one or more selected from zinc sulfate, zinc carbonate, zinc chloride, zinc oxide, and zinc hydroxide. As the aforementioned Mg compound, for example, one or more selected from magnesium sulfate, magnesium carbonate, magnesium chloride, magnesium oxide, and magnesium hydroxide.

The total concentration of the Al compound, Zn compound and/or Mg compound in the chemical treatment solution used to form the chemical film is preferably 0.25 mass% to 5 mass%. If the total concentration is 0.25 mass% or more, the concentration layer can be formed more effectively, and the corrosion resistance can be further improved. On the other hand, if the concentration of the compound is 5 mass% or less, the appearance of the chemical film will be more uniform, and the corrosion resistance of the damaged part of the coating film caused by processing or the like will be further improved.

Since the aforementioned V compound is contained in the aforementioned chemical film, V can be appropriately dissolved in a corrosive environment, and combined with zinc ions of the plating component dissolved in the same corrosive environment to form a dense protective film. The formed protective film can further improve the corrosion resistance of not only the flat part of the steel plate, but also the defective part, the damaged part of the plating film caused by processing, and the corrosion from the cut end surface to the flat part.

The aforementioned V compound is a compound containing V, for example, one or more selected from sodium metavanadate, vanadium sulfate and vanadium acetylacetonate.

The V compound in the chemical treatment solution used to form the chemical film is preferably 0.05 mass% to 4 mass%. If the concentration of the V compound is 0.05 mass% or more, it is easy to dissolve in a corrosive environment to form a protective film, and the corrosion resistance of the defective part, the cut end face part, and the film damage caused by processing is improved. On the other hand, when the concentration of the V compound exceeds 4 mass%, the appearance of the chemical film is prone to be uneven, and the blackening resistance is also reduced.

By including the aforementioned Mo compound in the aforementioned chemical film, the blackening resistance of the surface treated steel plate can be improved. The aforementioned Mo compound is a compound containing Mo, and can be obtained by adding one or both of molybdenum acid and a molybdate salt to a chemical treatment solution. The aforementioned molybdate salt may be, for example, one or more selected from sodium molybdate, potassium molybdate, magnesium molybdate, and zinc molybdate.

The concentration of the Mo compound in the chemical treatment solution used to form the chemical film is preferably 0.01 mass% to 3 mass%. If the concentration of the Mo compound is 0.01 mass% or more, the generation of oxygen-deficient zinc oxide can be further suppressed, and the blackening resistance can be further improved. On the other hand, if the concentration of the Mo compound is 3 mass% or less, in addition to further extending the life of the chemical treatment solution, the corrosion resistance can also be further improved.

By including the Zr compound and the Ti compound in the chemical film, the chemical film can be prevented from becoming porous and the film can be made dense. As a result, corrosion factors are less likely to penetrate the chemical film, and corrosion resistance can be improved.

The Zr compound is a compound containing Zr, and for example, one or more selected from zirconium acetate, zirconium sulfate, zirconium potassium carbonate, sodium zirconium carbonate, and zirconium ammonium carbonate can be used. Among them, organic titanium chelate compounds are preferred because when the chemical treatment liquid is dried to form a film, the film is densified, thereby obtaining better corrosion resistance.

The Ti compound is a compound containing Ti, and for example, at least one selected from titanium sulfate, titanium chloride, titanium hydroxide, titanium acetylacetonate, titanium octanediol, and titanium ethylacetylacetonate can be used.

The concentration of Zr compound and/or Ti compound in the chemical treatment solution for forming the chemical film is preferably 0.2 mass% to 20 mass%. If the total concentration of the Zr compound and/or Ti compound is 0.2 mass% or more, the corrosion factor penetration inhibition effect is improved, not only the corrosion resistance of the plane part is improved, but also the corrosion resistance of the defective part, the cut end face part, and the coating film damaged part caused by processing is further improved. On the other hand, if the total concentration of the Zr compound and/or Ti compound is 20 mass% or less, the life of the chemical treatment solution can be further extended.

By including the aforementioned Ca compound in the aforementioned chemical film, the effect of reducing the corrosion rate can be exhibited.

The aforementioned Ca compound is a compound containing Ca, and examples thereof include Ca oxides, Ca nitrates, Ca sulfates, and intermetallic compounds containing Ca. More specifically, examples of the aforementioned Ca compound include CaO, CaCO ₃ , Ca(OH) ₂ , Ca(NO ₃ ) ₂ ･4H ₂ O, and CaSO ₄ ･2H ₂ O. The content of the aforementioned Ca compound in the aforementioned chemical film is not particularly limited.

Furthermore, the chemical film may contain various ingredients commonly used in the field of coatings, as required, such as various surface conditioners such as leveling agents and defoaming agents, dispersants, anti-settling agents, UV absorbers, light stabilizers, silane coupling agents, titanium salt coupling agents, various additives, coloring pigments, physical pigments, brighteners, etc., curing catalysts, organic solvents, lubricants, etc.

In addition, the surface treated steel sheet of the present invention preferably has the aforementioned chemical coating that does not contain harmful components such as hexavalent chromium, trivalent chromium, fluorine, etc. Since the chemical treatment solution used to form the aforementioned chemical coating does not contain such harmful components, it is highly safe and has a relatively small environmental load.

The amount of the chemical film is not particularly limited. For example, from the viewpoint of ensuring more reliable corrosion resistance and preventing the chemical film from peeling off, the amount of the chemical film is preferably 0.1 to 3.0 g/m ² , and more preferably 0.5 to 2.5 g/m ² . By setting the amount of the chemical film to 0.1 g/m ² , corrosion resistance can be more reliably ensured, and by setting the amount of the chemical film to 3.0 g/m ² or less, cracking and peeling of the chemical film can be prevented. The amount of the chemical film can be obtained by appropriately selecting a method from existing methods such as a method of analyzing the film by fluorescent X-rays to determine the amount of an element whose content is known in advance.

Furthermore, the method for forming the aforementioned chemical film is not particularly limited and can be appropriately selected according to the required performance or manufacturing equipment. For example, the aforementioned coating film can be continuously coated with a chemical treatment liquid by a roller coater, and then dried at a plate temperature of about 60 to 200°C (peak metal temperature (Peak Metal Temperature): PMT) using hot air or induction heating. The aforementioned chemical treatment liquid can be coated by a known method other than a roller coater, such as an airless spray, an electrostatic spray, a curtain coater, etc. In addition, if the aforementioned chemical film contains the aforementioned resin and the aforementioned metal compound, it can be either a single-layer film or a multi-layer film, without particular limitation.

Furthermore, the surface treated steel plate of the present invention can also form a coating on the aforementioned chemical film as needed.

(Method for manufacturing surface-treated steel plate) The method for manufacturing surface-treated steel plate of the present invention is a method for manufacturing a surface-treated steel plate having a coating film and a chemical film formed on the coating film. Moreover, in the manufacturing method of the present invention, the aforementioned chemical film contains at least one resin selected from epoxy resin, urethane resin, acrylic resin, acrylic silicone resin, alkyd resin, polyester resin, polyurethane 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. The aforementioned coating film is formed under the same conditions as the manufacturing method of the molten Al-Zn-Si-Mg system plated steel plate of the present invention.

As mentioned above, Ni contained in the aforementioned coating film may deteriorate the corrosion resistance of the molten Al-Zn-Si-Mg system plated steel sheet. Therefore, in addition to properly controlling the contents of Al, Zn, Si and Mg in the coating bath, the degradation of corrosion resistance can be suppressed by further suppressing the content of Ni as an inevitable impurity.

In addition, the conditions of the aforementioned molten plating treatment step are the same as those described in the molten Al-Zn-Si-Mg system plated steel sheet of the present invention. And, the composition of the aforementioned chemical film is the same as that described in the chemical film of the surface treated steel sheet of the present invention.

(Coated steel plate) The coated steel plate of the present invention is a coated steel plate formed by directly or via a chemical coating on a coating film. The coating film is the same as the coating film of the molten Al-Zn-Si-Mg coated steel plate of the present invention.

The coated steel plate of the present invention can form a chemical film on the aforementioned coating film. In addition, the aforementioned chemical film only needs to be formed on at least one side of the coated steel plate, and can also be formed on both sides of the coated steel plate according to the application or required performance.

Moreover, in the manufacturing method of the present invention, the chemical film contains: a resin component and an inorganic compound, the resin component contains 30-50% by weight of (a): an anionic polyurethane resin having an ester bond and (b): an epoxy resin having a bisphenol skeleton, the content ratio of (a) to (b) ((a): (b)) is in the range of 3:97-60:40 by weight, the inorganic compound contains 2-10% by weight of a vanadium compound, 40-60% by weight of a zirconium compound and 0.5-5% by weight of a fluorine compound, The coating film at least has a base coating film, the base 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, The aforementioned coating film is formed under the same conditions as the manufacturing method of the molten Al-Zn-Si-Mg system coated steel plate of the present invention.

As mentioned above, Ni contained in the aforementioned coating film may deteriorate the corrosion resistance of the molten Al-Zn-Si-Mg system plated steel sheet. Therefore, in addition to properly controlling the contents of Al, Zn, Si and Mg in the coating bath, the degradation of corrosion resistance can be suppressed by further suppressing the content of Ni as an inevitable impurity.

Furthermore, the conditions of the aforementioned molten plating treatment step are the same as those described in the molten Al-Zn-Si-Mg system plated steel sheet of the present invention. Moreover, the composition of the aforementioned chemical film and the aforementioned coating are the same as those described in the chemical film and coating of the coated steel sheet of the present invention. [Example]

<Example 1: Samples 1 to 62> A cold rolled steel plate with a thickness of 0.8 mm manufactured by a conventional method was used as a base steel plate, and annealing treatment and plating treatment were performed using a melt plating simulator manufactured by RHESCA Co., Ltd. to manufacture samples 1 to 62 of melt-plated steel plates under the conditions shown in Table 1. In addition, regarding the composition of the plating bath used for manufacturing the melt-plated steel plates, the composition of the plating bath was variously changed in the range of Al: 5 to 75 mass%, Si: 0.0 to 4.5 mass%, Mg: 0 to 10 mass%, and Sr: 0.000 to 0.025 mass% so as to obtain the composition of the coating film of each sample shown in Table 1. The bath temperature of the plating bath is 450°C when Al: 5 mass%, 480°C when Al: 15 mass%, 590°C when Al: 30-60 mass%, and 630°C when Al: more than 60 mass%. The plate temperature of the base steel plate is controlled to be the same as the plating bath temperature. In addition, the plating treatment is carried out under the condition that the plate temperature is cooled to a temperature range of 520-500°C within 3 seconds when Al: 30-60 mass%. The coating weight of samples 1 to 59 was controlled at 85±5 g/m ² per side, sample 60 was controlled at 50±5 g/m ² per side, sample 61 was controlled at 100±5 g/m ² per side, and sample 62 was controlled at 125±5 g/m ² per side.

(Evaluation) The following evaluation was performed on each sample of the molten-coated steel plate obtained as described above. The evaluation results are shown in Table 1.

(1) Composition of the coating film (adhesion amount, composition, Ni-based compounds, X-ray diffraction intensity) For each sample after coating, a 100 mm φ punch was applied, and the non-measurement surface was sealed with tape. The coating was then stripped off by dissolving it with a mixture of hydrochloric acid and hexamethylenetetramine as specified in JIS H 0401:2013. The adhesion amount of the coating film was calculated from the difference in sample mass before and after stripping. The calculated results and the adhesion amount of the obtained coating film are shown in Table 1. Then, the stripping liquid was filtered, and the filter liquid and solid content were analyzed separately. Specifically, the filter liquid was analyzed by ICP emission spectrometry to quantify the components other than insoluble Si. After the solids were dried and ashed in a heating furnace at 650°C, sodium carbonate and sodium tetraborate were added to dissolve. The dissolve was then dissolved with hydrochloric acid, and the insoluble Si was quantified by ICP emission spectrometry analysis of the solution. The Si concentration in the coating film was the sum of the soluble Si concentration obtained by the filter solution analysis and the insoluble Si concentration obtained by the solid content analysis. The calculated results and the composition of the coating film are shown in Table 1. Furthermore, for each sample, after cutting into a size of 15mm×15mm, the sample was embedded in a conductive resin in a manner that the steel plate cross section could be observed, and after mechanical polishing, a scanning electron microscope (ULTRA55 manufactured by Carl Zeiss) was used to continuously capture reflected electron images with a width of 100μm for a continuous cross section of the coating film with a length of more than 2mm in a direction parallel to the surface of the base steel plate at an accelerating voltage of 3kV. In addition, in the same device, an energy dispersive X-ray spectrometer (Ultim Extreme manufactured by Oxford Instruments) was used to perform element mapping analysis (Al, Zn, Si, Mg, Fe, Sr, and Ni) of each cross section at an accelerating voltage of 3kV. For the part where high Ni intensity is detected in the analysis, the spectrometer is used to perform point analysis at an accelerating voltage of 3 kV, and the substance is identified based on the semi-quantitative value of the obtained components. The length diameters of all Ni-based compounds confirmed in the observation field are measured, and the maximum length diameter is obtained. In addition, the number of all Ni-based compound particles present in the observed continuous section is counted and divided by the observed section length (mm), and the number of Ni-based compound particles per 1 mm in the direction parallel to the surface of the base steel plate (pieces/mm) is calculated. For the part where high Ni intensity is detected in the analysis, the spectrometer is used to perform point analysis at an accelerating voltage of 3 kV, and the substance is identified based on the semi-quantitative value of the obtained components. The analysis results are shown in Table 1. In addition, for each sample, after cutting into a size of 100 mm × 100 mm, the coating film on the evaluation symmetry surface was mechanically cut until the base steel plate was exposed. After the obtained powder was fully mixed, 0.3 g was taken out and the powder was qualitatively analyzed using an X-ray diffraction device ("SmartLab" manufactured by RIGAKU Co., Ltd.) using X-ray: Cu-Kα (wavelength = 1.54178Å), kβ ray removal: Ni filter, tube voltage: 40 kV, tube current: 30 mA, scanning speed: 4°/min, sampling interval: 0.020°, divergent slit: 2/3°, parallel slit (Soller slit): 5°, detector: high-speed one-dimensional detector (D/teX Ultra). The intensity obtained by subtracting the base intensity from each peak intensity was taken as each diffraction intensity (cps), and the diffraction intensity of the (111) plane of _Mg2Si (plane spacing d = 0.3668nm), the diffraction intensity of the (100) plane of _MgZn2 (plane spacing d = 0.4510nm), and the diffraction intensity of the (111) plane of Si (plane spacing d = 0.3135nm) were measured. The measurement results are shown in Table 1.

(2) Corrosion resistance evaluation For each sample of the obtained molten-coated steel plate, cut it into a size of 120 mm × 120 mm, and seal the area 10 mm away from each edge of the evaluation target surface and the end face of the sample with the evaluation non-target surface with tape, and use the sample with the evaluation target surface exposed in a size of 100 mm × 100 mm as the evaluation sample. In addition, three identical evaluation samples were prepared. For the three evaluation samples prepared as above, the corrosion promotion test was carried out in the cycle shown in Figure 1. The corrosion promotion test was carried out from the start of the wet test to 300 cycles. The corrosion loss of each sample was measured according to the method described in JIS Z 2383 and ISO8407, and the evaluation was carried out according to the following criteria. The evaluation results are shown in Table 1. ◎: The corrosion loss of the three samples was less than 45g/ ^m2 ○: The corrosion loss of the three samples was less than 95g/ ^m2 ×: The corrosion loss of more than one sample exceeded 95g/ ^m2

(3) Surface appearance For each sample of the obtained molten-coated steel plate, the coating film surface was visually observed. Then, the observation results were evaluated according to the following criteria. The evaluation results are shown in Table 1. ◎: No wrinkle defects were observed at all ○: Wrinkle defects were observed only within a range of 50 mm from the edge ×: Wrinkle defects were observed outside a range of 50 mm from the edge

(4) Processability For each sample of the obtained melt-coated steel plate, cut it into a size of 70 mm × 150 mm, sandwich 8 plates of the same thickness on the inside and perform 180° bending (8T bending). After bending, SELLOTAPE (registered trademark) glass tape is strongly adhered to the outer surface of the bent part and then peeled off. Visually observe the surface condition of the coating film outside the bent part and whether the coating film is attached (peeled off) on the surface using the tape, and evaluate the processability according to the following criteria. The evaluation results are shown in Table 1. ○: No cracking or peeling was observed on the coated film △: There were cracks on the coated film, but no peeling was observed ×: Both cracking and peeling were observed on the coated film

(5) Bath stability When manufacturing each sample of molten-coated steel sheets, the bath surface state of the coating bath was visually confirmed and compared with the bath surface of the coating bath used when manufacturing molten Al-Zn-based coated steel sheets (bath surface without Mg oxide). The evaluation was based on the following criteria, and the evaluation results are shown in Table 1. ○: The same level as the molten Al-Zn-based coating bath (55 mass% Al-the rest Zn-1.6 mass% bath) △: Compared with the molten Al-Zn-based coating bath (55 mass% Al-the rest Zn-1.6 mass% bath), there are more white oxides ×: Black oxide formation was observed in the coating bath

As shown in Table 1, the samples of the present invention have a good balance in terms of corrosion resistance, surface appearance, processability and bath stability compared with the samples of the comparative examples.

<Example 2: Samples 1 to 148> (1) A cold rolled steel plate with a thickness of 0.8 mm manufactured by a conventional method was used as a base steel plate, and annealing treatment and plating treatment were performed using a melt plating simulator manufactured by RHESCA Co., Ltd. to manufacture melt-plated steel plate samples with the coating film conditions shown in Tables 3 and 4. In addition, regarding the composition of the plating bath used for the manufacture of the melt-plated steel plate, the composition of the plating bath was varied in various ranges such as Al: 5 to 75 mass%, Si: 0.0 to 4.5 mass%, Mg: 0 to 10 mass%, and Sr: 0.000 to 0.025 mass% so as to obtain the coating film compositions of the samples shown in Tables 3 and 4. The bath temperature of the plating bath is 450°C when Al: 5 mass%, 480°C when Al: 15 mass%, 590°C when Al: 30-60 mass%, and 630°C when Al: more than 60 mass%, and the plate temperature of the base steel plate is controlled to be the same as the plating bath temperature. In addition, the plating treatment is carried out under the condition that the plate temperature is cooled to a temperature range of 520-500°C within 3 seconds when Al: 30-60 mass%. In addition, the adhesion amount of the coating film was controlled at 85±5g/m ² per side for samples 1-118 and 131-148, 50±5g/m ² per side for samples 119-120, 100±5g/m ² per side for samples 121-122, 125±5g/m ² per side for samples 123-124, and 70±5g/m ² per side for samples 125-130.

(2) Subsequently, a chemical treatment liquid was applied to the coating film of each sample of the prepared molten-coated steel plate using a rod coater, and dried using a hot air furnace (heating rate: 60°C/s, PMT: 120°C) to form a chemical film, thereby preparing each sample of the surface-treated steel plate shown in Tables 3 and 4. The chemical treatment liquid is prepared by dissolving each component in water as a solvent to prepare surface treatment liquids A to F. The types of components (resin, metal compound) contained in the surface treatment liquid are as follows. (Resin) Urethane resin: SUPER FLEX 130, SUPER FLEX 126 (Daiichi Kogyo Pharmaceutical Co., Ltd.) Acrylic resin: BONCOAT EC-740EF (DIC Co., Ltd.) (Metallic compound) P compound: dihydrogen aluminum tripolyphosphate Si compound: silicon oxide V compound: sodium metavanadate Mo compound: molybdenum acid Zr compound: potassium zirconium carbonate Table 2 shows the composition of the prepared chemical conversion treatment solution A~F and the amount of chemical film formed. In addition, the concentration of each component in Table 2 of this manual is the solid concentration (mass %).

(Evaluation) The following evaluation was performed on each sample of the molten-coated steel plate and the surface-treated steel plate obtained as described above. The evaluation results are shown in Tables 3 and 4.

(1) Composition of the coating film (adhesion amount, composition, Ni-based compounds, X-ray diffraction intensity) For each sample of the melt-coated steel plate, a 100 mm φ punch was made, and the non-measurement surface was sealed with tape. The coating was then stripped off by dissolving it with a mixture of hydrochloric acid and hexamethylenetetramine as specified in JIS H 0401:2013. The adhesion amount of the coating film was calculated from the difference in sample mass before and after stripping. The calculated results and the adhesion amount of the obtained coating film are shown in Tables 3 and 4. Then, the stripping liquid was filtered, and the filter liquid and solid content were analyzed separately. Specifically, the filter liquid was analyzed by ICP emission spectrometry to quantify the components other than insoluble Si. After the solids were dried and ashed in a heating furnace at 650°C, sodium carbonate and sodium tetraborate were added to dissolve. The dissolve was then dissolved with hydrochloric acid, and the insoluble Si was quantified by ICP emission spectrometry analysis of the solution. The Si concentration in the coating film was the sum of the soluble Si concentration obtained by the filter solution analysis and the insoluble Si concentration obtained by the solid content analysis. The calculated results and the composition of the obtained coating film are shown in Tables 3 and 4. Furthermore, for each sample, after cutting into a size of 15mm×15mm, the sample was embedded in a conductive resin in a manner that the steel plate section could be observed, and after mechanical polishing, a scanning electron microscope (ULTRA55 manufactured by Carl Zeiss) was used to continuously capture reflected electron images with a width of 100μm for a continuous section of the coating film with a length of more than 2mm in a direction parallel to the surface of the base steel plate at an accelerating voltage of 3kV. In addition, in the same device, an energy dispersive X-ray spectrometer (Ultim Extreme manufactured by Oxford Instruments) was used to perform element mapping analysis (Al, Zn, Si, Mg, Fe, Sr and Ni) of each section at an accelerating voltage of 3kV. For the part where high Ni intensity is detected in the analysis, the spectrometer is used to perform point analysis at an accelerating voltage of 3 kV, and the substance is identified based on the semi-quantitative value of the obtained components. The length diameters of all Ni-based compounds confirmed in the observation field are measured, and the maximum length diameter is obtained. In addition, the number of all Ni-based compound particles present in the observed continuous section is counted and divided by the observed section length (mm), and the number of Ni-based compound particles per 1 mm in the direction parallel to the surface of the base steel plate (pieces/mm) is calculated. For the part where high Ni intensity is detected in the analysis, the spectrometer is used to perform point analysis at an accelerating voltage of 3 kV, and the substance is identified based on the semi-quantitative value of the obtained components. The analysis results are shown in Tables 3 and 4. In addition, for each sample, after cutting into a size of 100 mm × 100 mm, the coating film on the evaluation symmetric surface was mechanically cut until the base steel plate was exposed. After the obtained powder was fully mixed, 0.3 g was taken out and the powder was qualitatively analyzed using an X-ray diffraction device ("SmartLab" manufactured by RIGAKU Co., Ltd.) using X-ray: Cu-Kα (wavelength = 1.54178Å), kβ ray removal: Ni filter, tube voltage: 40 kV, tube current: 30 mA, scanning speed: 4°/min, sampling interval: 0.020°, divergent slit: 2/3°, parallel slit: 5°, detector: high-speed one-dimensional detector (D/teX Ultra). The intensity obtained by subtracting the base intensity from each peak intensity was taken as each diffraction intensity (cps), and the diffraction intensity of the (111) plane of _Mg2Si (plane spacing d = 0.3668nm), the diffraction intensity of the (100) plane of _MgZn2 (plane spacing d = 0.4510nm), and the diffraction intensity of the (111) plane of Si (plane spacing d = 0.3135nm) were measured. The measurement results are shown in Tables 3 and 4.

(2) Corrosion resistance evaluation For each sample of the hot-dip plated steel plate and the surface treated steel plate, cut into a size of 120 mm × 120 mm, and seal the area 10 mm away from each edge of the evaluation target surface and the end face of the sample with the evaluation non-target surface with tape, leaving the evaluation target surface exposed in a size of 100 mm × 100 mm. The evaluation samples were used as evaluation samples. Three identical evaluation samples were prepared. For the three evaluation samples prepared as described above, the corrosion promotion test was carried out in the cycle shown in Figure 1. The corrosion promotion test was carried out from the start of the wet test until 300 cycles. The corrosion loss of each sample was measured according to the method described in JIS Z 2383 and ISO8407, and the evaluation was carried out according to the following criteria. The evaluation results are shown in Tables 3 and 4. ◎: The corrosion loss of the three samples was less than 30g/ ^{m2 ○} : The corrosion loss of the three samples was less than 75g/m2×: The corrosion loss of more than one sample exceeded 75g/ ^m2

(3) Rust resistance For each sample of the hot-dip plated steel plate and the surface treated steel plate, cut into pieces of 120 mm × 120 mm in size, and seal the area 10 mm away from each edge of the evaluation target surface and the end face of the sample with the non-evaluation target surface with tape, leaving the evaluation target surface exposed in a size of 100 mm × 100 mm. Using the above evaluation samples, the salt water spray test described in 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 rust on the flat plate ○: The rust occurrence area of the flat plate is less than 10% ×: The rust occurrence area of the flat plate is more than 10%

(4) Surface appearance For each sample of the molten-coated steel plate, the coating film surface was visually observed. Then, the observation results were evaluated according to the following criteria. The evaluation results are shown in Tables 3 and 4. ◎: No wrinkle defects were observed at all ○: Wrinkle defects were observed only within a range of 50 mm from the edge ×: Wrinkle defects were observed outside a range of 50 mm from the edge

(5) Processability For each sample of the melt-coated steel plate, cut it into a size of 70 mm × 150 mm, sandwich 8 plates of the same thickness on the inside and perform 180° bending (8T bending). After bending, strongly adhere SELLOTAPE (registered trademark) glass tape to the outer surface of the bend and then peel it off. Visually observe the surface condition of the coating film outside the bend and whether the coating film is attached (peeled) on the surface using the tape, and evaluate the processability based on the following criteria. The evaluation results are shown in Tables 3 and 4. ○: No cracking or peeling was observed on the coated film △: There were cracks on the coated film, but no peeling was observed ×: Both cracking and peeling were observed on the coated film

(6) Bath stability During molten plating, the bath surface of the coating bath was visually checked and compared with the bath surface of the coating bath used in the production of molten Al-Zn coated steel sheets (bath surface without Mg oxide). The evaluation was based on the following criteria, and the evaluation results are shown in Tables 3 and 4. ○: The same level as the molten Al-Zn coating bath (55 mass% Al-the rest Zn-1.6 mass% bath) △: Compared with the molten Al-Zn coating bath (55 mass% Al-the rest Zn-1.6 mass% bath), there are more white oxides ×: Black oxide formation was observed in the coating bath

From the results in Tables 3 and 4, it can be seen that the samples of the present invention have better balance in corrosion resistance, rust resistance, surface appearance, processability and bath stability than the samples of the comparative examples. In addition, from the results in Table 4, it can be seen that the rust resistance of the samples subjected to chemical treatments A to D shows particularly excellent results.

<Example 3: Samples 1 to 41> (1) A cold rolled steel plate with a thickness of 0.8 mm manufactured by a conventional method was used as a base steel plate, and annealing treatment and plating treatment were performed using a melt plating simulator manufactured by RHESCA Co., Ltd. to manufacture melt-plated steel plate samples with the coating film conditions shown in Table 6. In addition, regarding the composition of the plating bath used for manufacturing the melt-plated steel plate, the composition of the plating bath was varied in various ways within the range of Al: 30 to 75 mass%, Si: 0.5 to 4.5 mass%, Mg: 0 to 10 mass%, and Sr: 0.001 to 0.025 mass% so as to obtain the coating film compositions of the samples shown in Table 6. The bath temperature of the coating bath was set to 590°C when Al: 30-60 mass %, and to 630°C when Al: exceeded 60 mass %, and the coating immersion plate temperature of the base steel plate was controlled to be the same as the coating bath temperature. In addition, the coating treatment was carried out under the condition that the plate temperature was cooled to a temperature range of 520-500°C within 3 seconds. In addition, the adhesion amount of the coating film was controlled to 85±5g/m ² per single side for samples 1-38, 50±5g/m ² per single side for sample 39, 100±5g/m ² per single side for sample 40, and 125±5g/m ² per single side for sample 41.

(2) Subsequently, the chemical treatment liquid shown in Table 5 was applied to the coating film of each sample of the produced melt-coated steel plate by a rod coater, and dried in a hot air drying furnace (reaching plate temperature: 90°C) to form a chemical treatment film with an adhesion amount of 0.1 g/ ^m2 . The chemical treatment liquid used was a chemical treatment liquid prepared by dissolving each component in water as a solvent and adjusting the pH to 8-10. The types of each component (resin component, inorganic compound) contained in the chemical treatment liquid are as follows. (Resin ingredients) Resin A: (a) anionic polyurethane resin having an ester bond ("SUPER FLEX210" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and (b) epoxy resin having a bisphenol skeleton ("YUKA RESIN 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 Co., Ltd.) (Inorganic compounds) Vanadium compound: organic vanadium compound chelated with acetylacetone Zirconium compound: zirconium carbonate Ammonium fluoride compound: ammonium fluoride

(3) Next, a base coating material was applied on the chemical film formed as described above using a rod coater, and the steel plate was baked at a temperature of 230°C for 35 seconds to form a base coating film having the composition shown in Table 5. Subsequently, a top coating material composition was applied on the base coating film formed as described above using a rod coater, and the steel plate was baked at a temperature of 230°C to 260°C for 40 seconds to form a top coating film having the resin conditions and film thickness shown in Table 5, and coated steel plates of various samples were prepared. In addition, the primer coating material was obtained by mixing the components and stirring them with a ball mill for about 1 hour. The resin components and inorganic compounds constituting the primer coating film 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, resin acid value 3, number average molecular weight 5,600, hydroxyl value 36) was used and cured with blocked isocyanate. In addition, the urethane-modified polyester resin was prepared under the following conditions. 320 parts by mass of isophthalic acid, 200 parts by mass of adipic acid, 60 parts by mass of trihydroxymethylpropane, and 420 parts by mass of cyclohexanedimethanol were added to a flask equipped with a stirrer, a distillation tower, a water separator, a cooling tube, and a thermometer. The mixture was heated and stirred. The generated condensation water was distilled out of the system while the temperature was raised from 160°C to 230°C at a constant speed over 4 hours. After the temperature reached 230°C, 20 parts by mass of xylene were slowly added. The condensation reaction was continued while the temperature was maintained at 230°C. The reaction was terminated when the acid value was below 5. After cooling to 100°C, SOLVESSO 100 (EXXON MOBILE Co., Ltd., trade name, high boiling point aromatic hydrocarbon solvent) 120 parts by mass, butyl solvent 100 parts by mass, and a polyester resin solution was obtained. Resin β: Urethane curing polyester resin ("EVERCLAD 4900" manufactured by Kansai Coating Co., Ltd.) (Inorganic compound) Vanadium compound: Magnesium vanadate Phosphoric acid compound: Calcium phosphate Magnesium oxide compound: Magnesium oxide And the resin used for the top coating film shown in Table 5 is the following coating. Resin I: Melamine-cured polyester coating ("PRECOLOR HD0030HR" manufactured by BASF JAPAN Co., Ltd.) Resin II: Organic sol-bonded fluororesin coating with a mass ratio of 80:20 of polyvinylidene fluoride and acrylic resin ("PRECOLOR No.8800HR" manufactured by BASF JAPAN Co., Ltd.)

(Evaluation) The following evaluation was performed on each sample of the coated steel plate obtained as described above. The evaluation results are shown in Table 6.

(1) Composition of the coating film (adhesion amount, composition, presence of Ni-based compounds, X-ray diffraction intensity) For each sample of the melt-coated steel plate, a 100 mm φ punch was made, and the non-measurement surface was sealed with tape. The coating was then stripped by dissolving it with a mixture of hydrochloric acid and hexamethylenetetramine as specified in JIS H 0401:2013. The adhesion amount of the coating film was calculated from the difference in sample mass before and after stripping. The calculated results and the adhesion amount of the obtained coating film are shown in Table 6. Then, the stripping liquid was filtered, and the filter liquid and solid content were analyzed separately. Specifically, the filter liquid was analyzed by ICP emission spectrometry to quantify the components other than insoluble Si. After the solids were dried and ashed in a heating furnace at 650°C, sodium carbonate and sodium tetraborate were added to dissolve. The dissolve was then dissolved with hydrochloric acid, and the insoluble Si was quantified by ICP emission spectrometry analysis of the solution. The Si concentration in the coating film was the sum of the soluble Si concentration obtained by the filtrate analysis and the insoluble Si concentration obtained by the solid content analysis. The calculated results and the composition of the coating film are shown in Table 6. Furthermore, for each sample, after cutting into a size of 15mm×15mm, the steel plate cross section was embedded in a conductive resin in a manner that allowed observation, and after mechanical polishing, a scanning electron microscope (ULTRA55 manufactured by Carl Zeiss) was used to take reflected electron images of a 100μm-width coating cross section of any choice at an accelerating voltage of 3kV. In addition, in the same device, an energy dispersive X-ray spectrometer (Ultim Extreme manufactured by Oxford Instruments) was used to perform elemental mapping analysis (Al, Zn, Si, Mg, Fe, Sr, and Ni) of each cross section at an accelerating voltage of 3kV. For the part where high Ni intensity was detected in the analysis, the spectrometer was used to perform point analysis under the condition of accelerating voltage 3 kV, and the substance was identified based on the semi-quantitative value of the obtained composition. The analysis results are shown in Table 6. In addition, for each sample, after cutting into a size of 100 mm × 100 mm, the coating film on the evaluation symmetric surface was mechanically cut until the base steel plate was exposed. After the obtained powder was fully mixed, 0.3 g was taken out and the powder was qualitatively analyzed using an X-ray diffraction device ("SmartLab" manufactured by RIGAKU Co., Ltd.) using X-ray: Cu-Kα (wavelength = 1.54178Å), kβ ray removal: Ni filter, tube voltage: 40 kV, tube current: 30 mA, scanning speed: 4°/min, sampling interval: 0.020°, divergent slit: 2/3°, parallel slit: 5°, detector: high-speed one-dimensional detector (D/teX Ultra). The intensity obtained by subtracting the base intensity from each peak intensity was taken as each diffraction intensity (cps), and the diffraction intensity of the (111) plane of _Mg2Si (plane spacing d = 0.368nm), the diffraction intensity of the (100) plane of _MgZn2 (plane spacing d = 0.4510nm), and the diffraction intensity of the (111) plane of Si (plane spacing d = 0.3135nm) were measured. The measurement results are shown in Table 6.

(2) Corrosion resistance evaluation For each sample of the coated steel plate, cut it into a size of 120mm×120mm, seal the area 10mm away from each edge of the evaluation target surface and the end surface of the sample with the non-evaluation target surface with tape, and use the sample with the evaluation target surface exposed in a size of 100mm×100mm as the evaluation sample. In addition, three identical evaluation samples were prepared. For the three evaluation samples prepared as above, the corrosion promotion test was carried out in the cycle shown in Figure 1. The corrosion promotion test started from wetting, and the sample was taken out every 20 cycles. After washing and drying, the red rust on the cut end surface of one side that was not sealed was confirmed by visual observation. Next, the number of cycles when red rust was detected was evaluated according to the following criteria. The evaluation results are shown in Table 6. ◎: The number of cycles when red rust occurred in 3 samples ≥ 600 cycles ○: 600 cycles > 3 samples ≥ 400 cycles ×: The number of cycles when red rust occurred in at least 1 sample < 400 cycles

(3) Appearance after coating For each sample of the coated steel plate, the surface was visually observed. Then, the observation results were evaluated according to the following criteria. The evaluation results are shown in Table 6. ○: No wrinkle defects were observed at all ×: Wrinkle defects were observed in at least a portion

(4) Processability after coating For each sample of coated steel plate, cut into 70mm×150mm size, insert 8 plates of the same thickness on the inside and perform 180° bending (8T bending). After bending, strongly adhere SELLOTAPE (registered trademark) glass tape to the outer surface of the bend and peel off. Visually observe the surface condition of the coating film outside the bend and the presence of coating film adhesion (peeling) on the surface using tape, and evaluate the processability according to the following criteria. The evaluation results are shown in Table 6. ○: No cracks or peeling were observed on the coating film △: There were cracks on the coating film, but no peeling was observed ×: Both cracks and peeling were observed on the coating film

(5) Bath stability During molten plating, the bath surface of the coating bath was visually checked and compared with the bath surface of the coating bath used in the production of molten Al-Zn coated steel sheets (bath surface without Mg oxide). The evaluation was based on the following criteria, and the evaluation results are shown in Table 6. ○: The same level as the molten Al-Zn coating bath (55 mass% Al-the rest Zn-1.6 mass% bath) △: Compared with the molten Al-Zn coating bath (55 mass% Al-the rest Zn-1.6 mass% bath), there are more white oxides ×: Black oxide formation was observed in the coating bath

From the results in Table 6, it can be seen that the samples of the present invention are well-balanced in terms of corrosion resistance, appearance after painting, processability after painting, and bath stability compared to the samples of the comparative examples. [Industrial Applicability]

According to the present invention, a stable molten Al-Zn-Si-Mg based plated steel sheet with excellent corrosion resistance and a method for manufacturing the same can be provided.

[Figure 1] is a diagram used to illustrate the process of the Japanese Automobile Standards Combined Cycle Test (JASO-CCT).

Claims (18)

A molten Al-Zn-Si-Mg coated steel plate, which is a molten Al-Zn-Si-Mg coated steel plate with a coating film, wherein the coating film has a composition containing Al: 45~65 mass%, Si: 1.0~4.0 mass% and Mg: 1.0~10.0 mass%, and the remainder is composed of Zn and inevitable impurities, the Ni content in the inevitable impurities is less than 0.009 mass% relative to the total mass of the coating film, the coating film contains Ni compounds, and the number of the Ni compounds existing in the direction parallel to the surface of the base steel plate is less than 5/mm. A molten Al-Zn-Si-Mg coated steel plate having a coating film, wherein the coating film has a composition of 45-65 mass %, Si: 1.0-4.0 mass % and Mg: 1.0-10.0 mass %, and the remainder is composed of Zn and inevitable impurities, the Ni content of the inevitable impurities is less than 0.009 mass % relative to the total mass of the coating film, and the _Mg2Si and MgZn in the coating film are less than 0.009 mass %. ₂ by X-ray diffraction method satisfies the following relationship (1), and the diffraction intensity of Si in the aforementioned coating film by X-ray diffraction method satisfies the following relationship (2); Mg ₂ Si (111) / MgZn ₂ (100) ≦ 2.0 ... (1) Mg ₂ Si (111): diffraction intensity of the (111) plane of Mg ₂ Si (plane spacing d = 0.3668nm) MgZn ₂ (100): diffraction intensity of the (100) plane of MgZn ₂ (plane spacing d = 0.4510nm); Si (111) = 0 ... (2) Si (111): diffraction intensity of the (111) plane of Si (plane spacing d = 0.3135nm). As in claim 1 or 2, the molten Al-Zn-Si-Mg coated steel plate, wherein the coating film contains a Ni compound, and the length of the Ni compound is less than 4.0 μm. As in claim 2, the molten Al-Zn-Si-Mg coated steel plate, wherein the coating film contains Ni compounds, and the number of the Ni compounds in the direction parallel to the surface of the base steel plate is 5 or less/mm. As in claim 1 or 2, the molten Al-Zn-Si-Mg coated steel plate, wherein the coating film does not contain Ni compounds. The molten Al-Zn-Si-Mg coated steel plate of claim 1, wherein the diffraction intensities of _Mg2Si and _MgZn2 in the coating film as measured by X-ray diffraction method satisfy the following relationship (1): _Mg2Si (111)/ _MgZn2 (100)≦2.0…(1) _Mg2Si (111): diffraction intensity of (111) plane of _Mg2Si (plane spacing d=0.3668nm) _MgZn2 (100): diffraction intensity of (100) plane of _MgZn2 (plane spacing d=0.4510nm). For example, in the molten Al-Zn-Si-Mg coated steel plate of claim 1, the diffraction intensity of Si in the aforementioned coating film by X-ray diffraction method satisfies the following relationship (2): Si(111)=0…(2)Si(111): diffraction intensity of the (111) plane of Si (plane spacing d=0.3135nm). For example, the molten Al-Zn-Si-Mg coated steel plate of claim 1 or 2, wherein the coating film further contains Sr: 0.01~1.0 mass %. For the molten Al-Zn-Si-Mg coated steel plate of claim 1 or 2, the Al content in the aforementioned coating is 50~60 mass %. For the molten Al-Zn-Si-Mg coated steel plate of claim 1 or 2, the Si content in the aforementioned coating is 1.0~3.0 mass %. For the molten Al-Zn-Si-Mg coated steel plate of claim 1 or 2, the Mg content in the aforementioned coating is 1.0~5.0 mass %. A method for manufacturing a molten Al-Zn-Si-Mg coated steel plate, which is a method for manufacturing a molten Al-Zn-Si-Mg coated steel plate having a coating film, wherein the coating film is formed by immersing a base steel plate in a material containing 45-65 mass % Al, 1.0-4.0 mass % Si and 1.0-10.0 mass % Mg, and the rest A molten plating treatment step in a plating bath composed of Zn and inevitable impurities, wherein the Ni content in the inevitable impurities of the aforementioned plating bath is controlled to be less than 0.009 mass % relative to the total mass of the aforementioned plating bath, and the aforementioned plating film is formed to contain Ni-based compounds, and the number of the aforementioned Ni-based compounds existing in a direction parallel to the surface of the base steel plate is less than 5/mm. A method for manufacturing a molten Al-Zn-Si-Mg coated steel plate, which is a method for manufacturing a molten Al-Zn-Si-Mg coated steel plate having a coating film, wherein the coating film is formed by a molten coating treatment step of immersing a base steel plate in a coating bath containing Al: 45-65 mass %, Si: 1.0-4.0 mass % and Mg: 1.0-10.0 mass %, with the remainder being Zn and inevitable impurities, wherein the Ni content in the inevitable impurities of the coating bath is controlled to be less than 0.009 mass % relative to the total mass of the coating bath, and the _Mg2Si and MgZn in the coating film are formed. ₂ by X-ray diffraction method satisfies the following relationship (1), and the diffraction intensity of Si in the aforementioned coating film by X-ray diffraction method satisfies the following relationship (2); Mg ₂ Si (111) / MgZn ₂ (100) ≦ 2.0 ... (1) Mg ₂ Si (111): diffraction intensity of the (111) plane of Mg ₂ Si (plane spacing d = 0.3668nm) MgZn ₂ (100): diffraction intensity of the (100) plane of MgZn ₂ (plane spacing d = 0.4510nm); Si (111) = 0 ... (2) Si (111): diffraction intensity of the (111) plane of Si (plane spacing d = 0.3135nm). The method for manufacturing a molten Al-Zn-Si-Mg coated steel plate as claimed in claim 12 or 13, wherein the coating bath further contains Sr: 0.01~1.0 mass %. A surface treated steel plate having a coating film as in any one of claims 1 to 11 and a chemical coating formed on the coating film, wherein the chemical coating contains at least one resin selected from epoxy resin, urethane resin, acrylic resin, acrylic silicone resin, alkyd resin, polyester resin, polyurethane 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. A method for manufacturing a surface-treated steel plate, which comprises a coating film formed by the method for manufacturing a molten Al-Zn-Si-Mg system coated steel plate as in claim 12 or 13 and a chemical film formed on the coating film, wherein the chemical film contains at least one resin selected from epoxy resin, urethane resin, acrylic resin, acrylic silicone resin, alkyd resin, polyester resin, polyurethane 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. A coated steel plate, wherein a coating is formed on a coating film as in any one of claims 1 to 11 directly or via a chemical coating, wherein the chemical coating comprises: a resin component and an inorganic compound, wherein the resin component comprises 30 to 50% by weight of (a): an anionic polyurethane resin having an ester bond and (b): an epoxy resin having a bisphenol skeleton, wherein the content ratio of (a) to (b) is 30 to 50% by weight. The ratio ((a): (b)) is in the range of 3:97~60:40 by mass ratio, the inorganic compound comprises 2~10 mass% of vanadium compound, 40~60 mass% of zirconium compound and 0.5~5 mass% of fluorine compound, the aforementioned coating film has at least a base coating film, and the base coating film contains: a polyester resin having a urethane bond, and an inorganic compound comprising a vanadium compound, a phosphoric acid compound and magnesium oxide. A method for manufacturing a coated steel plate, wherein a coated film is formed directly or via a chemical film on a coated film formed by a method for manufacturing a molten Al-Zn-Si-Mg coated steel plate as in claim 12 or 13, wherein the chemical film contains: a resin component and an inorganic compound, wherein the resin component contains 30-50% by weight of (a): an anionic polyurethane resin having an ester bond and (b): a bisphenol skeleton The epoxy resin of (a) and (b) has a mass ratio ((a): (b)) of 3:97~60:40, the inorganic compound comprises 2~10 mass% of vanadium compound, 40~60 mass% of zirconium compound and 0.5~5 mass% of fluorine compound, the aforementioned coating film has at least a base coating film, and the base coating film comprises: a polyester resin having a urethane bond, and an inorganic compound comprising a vanadium compound, a phosphoric acid compound and magnesium oxide.

Images