Hot-dip Al-Zn-Si-Mg plated steel sheet, surface-treated steel sheet, and coated steel sheet

Abstract

The purpose of the present invention is to provide a hot-dip Al-Zn-Si-Mg-based steel sheet which has excellent surface appearance and in which the occurrence of wrinkle-like defects is suppressed without any defects such as scum defects. In order to achieve the purpose, the present invention is a hot-dip Al-Zn-Si-Mg-based steel sheet provided with a plating film, the plating film having a composition containing 45-65% by mass of Al, 1.0-3.0% by mass of Si, 1.0-10.0% by mass of Mg, and 0.01-0.5% by mass of Mn, with the remainder comprising Zn and unavoidable impurities, and the thickness of the plating film being within the range of 50 mm removed from both ends of the steel sheet, the thickness of the plating film being within the range of 50 mm removed from both ends of the steel sheet, the thickness of the plating film being within the range of 50 mm removed from both ends of the steel sheet, and the thickness of the plating film being within the range of 50 mm removed from both ends of the steel sheet. The height difference per 1 mm length of the surface of the steel sheet is 10 [mu] m or less.

Description

Technical Field

[0001] This invention relates to a hot-dip galvanized Al-Zn-Si-Mg series steel sheet, a surface-treated steel sheet, and a coated steel sheet, all of which have excellent surface appearance. Background Technology

[0002] Hot-dip galvanized Al-Zn steel sheets, such as those represented by 55% Al-Zn series steel sheets (as shown in Patent Document 1), are known to combine the sacrificial corrosion resistance of Zn with the high corrosion resistance of Al, thus exhibiting high corrosion resistance among various galvanized steel sheets. Therefore, due to their excellent corrosion resistance, hot-dip galvanized Al-Zn steel sheets are mainly used in building materials such as roofs and walls, as well as in civil engineering fields such as railings, wiring and piping, and soundproof walls, where materials are exposed to the outdoors for extended periods.

[0003] In particular, the demand for corrosion-resistant and maintenance-free materials is constantly increasing in more demanding operating environments such as acid rain caused by air pollution, de-icing agents used to prevent road icing in snowy areas, and development in coastal areas. As a result, the demand for hot-dip Al-Zn series steel plates has been increasing in recent years.

[0004] The coating of hot-dip Al-Zn steel sheets is characterized by a structure consisting of a dendritic portion of supersaturated Zn-containing Al (α-Al phase) solidified into dendrites and a Zn-Al eutectic structure existing in the inter-dendrites, with the α-Al phase stacked in multiple layers along the film thickness direction. It is also known that due to this characteristic coating structure, the corrosion path from the surface becomes complex, making corrosion difficult to occur. Therefore, hot-dip Al-Zn steel sheets achieve superior corrosion resistance compared to hot-dip galvanized steel sheets with the same coating thickness.

[0005] Furthermore, attempts have been made to further extend the service life of hot-dip Al-Zn series steel sheets, and hot-dip Al-Zn-Si-Mg series steel sheets with added Mg are known.

[0006] As an example of such hot-dip Al-Zn-Si-Mg steel sheet, Patent Document 1 discloses a hot-dip Al-Zn-Si-Mg steel sheet, in which the coating film contains an Al-Zn-Si alloy containing Mg. The Al-Zn-Si alloy is an alloy containing 45 to 60 wt% aluminum, 37 to 46 wt% zinc and 1.2 to 2.3 wt% Si, and the concentration of Mg is 1 to 5 wt%.

[0007] In addition, Patent Document 2 discloses a hot-dip Al-Zn-Si-Mg series steel sheet, the purpose of which is to improve corrosion resistance and enhance the protective effect after the base steel sheet is exposed by containing 2 to 10% by mass of Mg and 0.01 to 10% by mass of Ca in the coating film.

[0008] Furthermore, Patent Document 3 discloses a hot-dip Al-Zn-Si-Mg series steel sheet, which forms a coating layer containing Mg: 1-15% by mass, Si: 2-15% by mass, Zn: 11-25% by mass, and the remainder consisting of Al and unavoidable impurities. This reduces the size of intermetallic compounds such as Mg2Si phase and MgZn2 phase present in the coating film to less than 10 μm, thereby improving the corrosion resistance of the flat plate and end face.

[0009] However, hot-dip galvanized Al-Zn-Si-Mg steel sheets suffer from a significantly degraded surface appearance due to the formation of wrinkled, uneven defects described later. If Mg is added to the molten Al-Zn-Si bath and the steel sheet is coated, Mg, being more easily oxidized than other coating elements, reacts with oxygen in the outermost layer exposed to the atmosphere during the cooling and solidification of the coating, forming Mg oxides. Consequently, the Mg concentration near the outermost layer decreases. To compensate for this, Mg diffuses sequentially from the interior of the coating to the outermost layer. As a result, before the coating completely solidifies, Mg oxides form a thick layer on the outermost surface. This difference in flow between the easily flowing interior of the coating and the Mg oxide layer prevents the Mg oxide layer from following the flow within the coating, resulting in wrinkled, uneven defects on the surface of the manufactured hot-dip galvanized Al-Zn-Si-Mg steel sheet.

[0010] Therefore, there is a growing expectation for the development of technologies to improve the wrinkle-like defects in hot-dip galvanized Al-Zn-Si-Mg steel sheets.

[0011] It should be noted that Patent Documents 4 and 5 disclose a technique that suppresses the oxidation of Mg in the coated surface and inhibits the formation of wrinkle-like defects by including Sr in the coated film. These techniques utilize the phenomenon that Sr is preferentially oxidized than Mg in the unsolidified coated surface layer after exiting the plating bath.

[0012] Furthermore, for the aforementioned hot-dip Al-Zn-Si-Mg series steel sheets, white rust can form as the coating corrodes under harsh corrosive environments. This white rust reduces the appearance of the steel sheet, therefore, the development of coated steel sheets with improved white rust resistance is underway.

[0013] Therefore, Patent Documents 6 and 7 disclose a surface-treated steel sheet that improves white rust resistance by forming a chemical conversion coating containing urethane resin on the coating film of a hot-dip Al-Zn-Si-Mg steel sheet.

[0014] However, the surface-treated steel sheets such as those in Patent Documents 6 and 7 are also affected by the hot-dip galvanized Al-Zn-Si-Mg steel sheets that form the base, so it is still necessary to improve the reduced surface appearance caused by the aforementioned wrinkle-like defects.

[0015] Furthermore, the aforementioned hot-dip Al-Zn-Si-Mg series steel sheets are sometimes used as coated steel sheets with a chemical conversion treatment film or primer film formed on the surface and various coatings formed thereon.

[0016] Such coated steel sheets undergo various processing methods, including 90-degree or 180-degree bending, through pressing, roll forming, or embossing. Long-term coating durability is required after use. To meet these requirements, hot-dip Al-Zn steel sheets are typically subjected to a chemical conversion treatment containing chromates. This results in a primer film containing chromate-based anti-rust pigments, upon which a thermosetting polyester resin coating is formed. For even higher weather resistance requirements, a fluorine-based resin coating is used as the top coat for coated galvanized steel sheets.

[0017] However, recently, the use of chromates, which are environmentally burdensome substances, has been considered a problem for such coated steel sheets, and there is a strong desire for chromate-free coated steel sheets that do not contain chromates, for example, chromate-free coated steel sheets such as those disclosed in Patent Document 8 have been proposed.

[0018] Existing technical documents

[0019] Patent documents

[0020] Patent Document 1: Japanese Patent No. 5020228

[0021] Patent Document 2: Japanese Patent No. 5000039

[0022] Patent Document 3: Japanese Patent Application Publication No. 2002-12959

[0023] Patent Document 4: Japanese Patent Application Publication No. 2000-328214

[0024] Patent Document 5: International Publication No. 2020 / 179147

[0025] Patent Document 6: Japanese Patent Application Publication No. 2019-155872

[0026] Patent Document 7: Japanese Patent Application Publication No. 2021-181214

[0027] Patent Document 8: Japanese Patent Application Publication No. 2005-169765 Summary of the Invention

[0028] However, for any of the techniques disclosed in the literature, it is difficult to suppress the formation of the aforementioned wrinkled defects without reducing other physical properties.

[0029] In the technologies disclosed in Patent Documents 4 and 5, when manufacturing hot-dip Al-Zn-Si-Mg steel sheets in which Sr is added to the coating film, there is a problem that the surface of the coating bath with added Sr is easily oxidized, and the newly generated oxide slag adheres to the slag defect of the coating film, resulting in the deterioration of the surface appearance.

[0030] Furthermore, while the technologies in Patent Documents 6 and 7 can improve resistance to white rust, even in the case of surface-treated steel sheets, they are still affected by the hot-dip galvanized Al-Zn-Si-Mg steel sheets that form the base, and it is still desirable to improve the reduced surface appearance caused by the formation of wrinkled defects.

[0031] Furthermore, regarding the technology in Patent Document 8, needless to say, the surface appearance, especially the clarity, of the coated steel sheet is affected by the surface shape of the plated steel sheet that serves as the substrate. With the aforementioned wrinkle-like defects and scum defects, the unevenness can reach tens of μm. Therefore, even if the surface is smoothed by the coating, the unevenness cannot be completely eliminated, and improving the surface appearance of the coated steel sheet remains a challenge. In addition, regarding the coating formed on the protrusions of the plated film, its thickness is reduced, which may locally decrease its corrosion resistance. Therefore, it is desirable to improve the surface appearance, especially the surface shape, of the plated steel sheet that serves as the substrate.

[0032] In view of the above, the present invention aims to provide a hot-dip galvanized Al-Zn-Si-Mg steel sheet that is free from other defects such as scum defects, has suppressed the generation of wrinkle defects, and has an excellent surface appearance.

[0033] In addition, the present invention aims to provide a surface-treated steel sheet with excellent surface appearance and resistance to white rust, as well as a coated steel sheet with excellent surface appearance and excellent corrosion resistance.

[0034] In order to solve the above-mentioned problems, the inventors conducted research and found that by adding Mn to the coating film of hot-dip Al-Zn-Si-Mg steel sheet, dross defects and wrinkle defects can be suppressed. By adjusting the amount of Mn added, the height difference on the surface of the steel sheet (the surface of the coating film) can be suppressed to a small extent, thereby suppressing the generation of wrinkle defects.

[0035] This invention was made based on the above insights, and its main points are as follows.

[0036] 1. A hot-dip galvanized Al-Zn-Si-Mg steel sheet, characterized in that it is a hot-dip galvanized Al-Zn-Si-Mg steel sheet with a coating film.

[0037] The aforementioned coating has the following composition: containing Al: 45-65% by mass, Si: 1.0-3.0% by mass, Mg: 1.0-10.0% by mass, and Mn: 0.01-0.5% by mass, with the remainder consisting of Zn and unavoidable impurities.

[0038] Within a range after removing 50mm from both ends of the steel plate, the height difference on the surface of the steel plate is less than 10μm for every 1mm length.

[0039] 2. The hot-dip Al-Zn-Si-Mg series steel sheet according to 1 above, characterized in that the Mn content in the above-mentioned coating film is 0.1 to 0.3 by mass.

[0040] 3. The hot-dip Al-Zn-Si-Mg series steel sheet according to 1 or 2 above, characterized in that an alloy layer containing Mn is provided at the interface between the coating film and the base steel sheet.

[0041] 4. The hot-dip Al-Zn-Si-Mg series steel sheet according to any one of 1 to 3 above, characterized in that the coating further contains a total of 0.01 to 3.0% by mass of one or more of B, Ca, Ti, V, Cr, Sr, Mo, In, Sn, Sb, Ce and Bi.

[0042] 5. A surface-treated steel sheet, characterized in that it is a surface-treated steel sheet having a coating film as described in any one of 1 to 4 above and a chemical conversion coating film formed on the coating film,

[0043] The aforementioned chemical conversion coating contains at least one resin selected from epoxy resin, urethane resin, acrylic resin, silicone acrylic resin, alkyd resin, polyester resin, polyalkylene resin, amino resin and fluororesin, and at least one metal compound selected from P compound, Si compound, Co compound, Ni compound, Zn compound, Al compound, Mg compound, V compound, Mo compound, Zr compound, Ti compound and Ca compound.

[0044] 6. A coated steel sheet, characterized in that it is a coated steel sheet on which a coating is formed directly or indirectly through a chemical conversion coating on the plated coating described in any one of the above 1 to 4.

[0045] The aforementioned chemical conversion coating contains resin components and inorganic compounds. The resin components comprise a total of 30-50% by mass of (a): an anionic polyurethane resin with ester bonds and (b): an epoxy resin with a bisphenol backbone. The content ratio of (a): (b) is in the range of 3:97 to 60:40 by mass. The inorganic compounds comprise 2-10% by mass of vanadium compounds, 40-60% by mass of zirconium compounds, and 0.5-5% by mass of fluorine compounds.

[0046] The aforementioned coating film has at least a primer film containing a polyester resin having urethane bonds and an inorganic compound comprising a vanadium compound, a phosphoric acid compound, and magnesium oxide.

[0047] According to the present invention, it is possible to provide hot-dip galvanized Al-Zn-Si-Mg steel sheets that are free from other defects such as scum defects, suppress the generation of wrinkle-like defects, and have an excellent surface appearance.

[0048] Furthermore, according to the present invention, it is possible to provide surface-treated steel sheets with excellent surface appearance and resistance to white rust, as well as coated steel sheets with excellent surface appearance and excellent corrosion resistance. Detailed Implementation

[0049] <Hot-dip Al-Zn-Si-Mg series steel sheet>

[0050] The hot-dip Al-Zn-Si-Mg series steel sheet of the present invention has a coating film on the surface of the steel sheet.

[0051] The above-mentioned coating has the following composition: containing Al: 45-65% by mass, Si: 1.0-3.0% by mass, Mg: 1.0-10.0% by mass and Mn: 0.01-0.5% by mass, with the remainder consisting of Zn and unavoidable impurities.

[0052] From the perspective of balancing corrosion resistance and operation, the Al content in the above-mentioned coating film is 45-65% by mass, preferably 50-60% by mass.

[0053] This is because if the Al content in the aforementioned coating is at least 45% by mass, Al dendrite solidification occurs, resulting in a coating structure dominated by α-Al phase dendrite solidification. This dendrite solidification structure has a layered structure along the thickness direction of the coating, thereby complicating the corrosion path and improving the corrosion resistance of the coating itself. Furthermore, the more layers of α-Al phase dendrites are stacked, the more complex the corrosion path becomes, making it difficult for corrosion to easily reach the base steel plate, thus improving corrosion resistance. Therefore, it is preferable to set the Al content to 50% by mass or more. On the other hand, if the Al content in the aforementioned coating exceeds 65% by mass, most of the Zn becomes a solid solution in α-Al, which cannot suppress the dissolution reaction of the α-Al phase, potentially deteriorating the corrosion resistance of the hot-dip Al-Zn-Si-Mg steel sheet. Therefore, the Al content in the aforementioned coating needs to be 65% by mass or less, preferably 60% by mass or less.

[0054] The Si in the aforementioned coating is mainly added to suppress the growth of Fe-Al and / or Fe-Al-Si interfacial alloy layers at the interface with the base steel plate, preventing deterioration of the adhesion between the coating and the steel plate. In practice, if the steel plate is immersed in an Al-Zn coating bath containing Si, the Fe on the steel plate surface undergoes an alloying reaction with the Al and Si in the bath, resulting in the formation of Fe-Al and / or Fe-Al-Si intermetallic compound layers at the interface between the base steel plate and the coating. However, the growth rate of the Fe-Al-Si alloy is slower than that of the Fe-Al alloy. Therefore, a higher proportion of Fe-Al-Si alloy further suppresses the overall growth of the interfacial alloy layer.

[0055] Therefore, the Si content in the aforementioned coated film needs to be 1.0% by mass or more. On the other hand, if the Si content in the aforementioned coated film exceeds 4.0% by mass, not only will the growth inhibition effect of the aforementioned interface alloy layer be saturated, but corrosion will also be promoted due to the presence of excessive Si phase in the coated film. Therefore, the Si content in the aforementioned coated film should be 4.0% by mass or less. Furthermore, from the viewpoint of suppressing the presence of excessive Si phase, the Si content in the aforementioned coated film is preferably 3.0% by mass or less.

[0056] The aforementioned coating contains 1.0 to 10.0% by mass of Mg. By including Mg in the aforementioned coating, the aforementioned Si can exist in the form of an intermetallic compound of the Mg2Si phase, which can suppress the promotion of corrosion.

[0057] Furthermore, if the aforementioned coating contains Mg, the MgZn2 phase, which is an intermetallic compound, is also formed in the coating, further improving corrosion resistance. When the Mg content in the aforementioned coating is less than 1.0% by mass, Mg is used for solid solution in the α-Al phase, which is the main phase, rather than for the formation of the intermetallic compounds (Mg2Si, MgZn2), thus insufficient corrosion resistance cannot be guaranteed. On the other hand, if the Mg content in the aforementioned coating increases, in addition to the saturation of the corrosion resistance improvement effect, the processability decreases due to the embrittlement of the α-Al phase; therefore, the content is typically 10.0% by mass or less.

[0058] Furthermore, from the viewpoints of suppressing slag formation during coating formation, facilitating plating bath management, and further improving surface appearance, the Mg content in the aforementioned coating film is preferably 5.0% by mass or less.

[0059] Furthermore, in the hot-dip Al-Zn-Si-Mg steel sheet of the present invention, the aforementioned coating contains 0.01 to 0.5% by mass of Mn. By containing 0.01% by mass or more of Mn in the aforementioned coating, a needle-like and / or blocky Mn-Fe interfacial alloy layer is formed between the coating and the base iron. This alloy layer, through its anchoring effect, suppresses the movement of the plating liquid film during the complete solidification of the coating, thereby suppressing the generation of wrinkle-like defects caused by Mg oxides formed on the surface of the coating.

[0060] On the other hand, if the Mn content in the aforementioned coating exceeds 0.5% by mass, the melting point of the coating bath increases, forcing the coating process to be carried out at a high bath temperature. This results in abnormal growth of the interfacial alloy layer between the coating and the base iron, deteriorating processability. Furthermore, the amount of dross generated increases, and the coating appearance, especially the surface shape, deteriorates. It should be noted that if the Mn content in the aforementioned coating is 0.5% by mass or less, the amount of dross generated in the coating bath is the same as in the case without added Mn. Therefore, the generation of dross defects can be suppressed, and a consistently excellent surface appearance can be obtained.

[0061] Therefore, the Mn content in the above-mentioned coated film is 0.01 to 0.5% by mass. From the same point of view, the Mn content in the above-mentioned coated film is preferably 0.1 to 0.3% by mass.

[0062] Regarding the Mg and Mn content in the aforementioned coating, from the viewpoint of balancing the effects of improving corrosion resistance, suppressing wrinkle defects, and suppressing scum defects, the ratio of Mn content to Mg content (Mn / Mg) is preferably 0.02 or more by mass (Mn / Mg ≥ 0.02). From the same viewpoint, the ratio of Mn content to Mg content (Mn / Mg) is more preferably 0.03 or more (Mn / Mg ≥ 0.03).

[0063] In addition to Al, Si, Mg and Mn, the above-mentioned coating film also contains Zn and unavoidable impurities.

[0064] Among the unavoidable impurities mentioned above, Fe is present. This Fe is unavoidably present by dissolving into the plating bath through the steel plate and the equipment in the plating bath, and is also supplied through diffusion from the base steel plate during the formation of the interface alloy layer, resulting in its unavoidable inclusion in the plating film. The Fe content in the plating film is typically around 0.3 to 2.0% by mass. Other unavoidable impurities include Ni and Cu.

[0065] There is no particular limit to the total content of the aforementioned unavoidable impurities, but excessive content may affect various properties of the coated steel sheet. Therefore, the total content is preferably 5.0% by mass or less.

[0066] Furthermore, the aforementioned coating preferably contains, as needed, one or more elements selected from B, Ca, Ti, V, Cr, Sr, Mo, In, Sn, Sb, Ce, and Bi, totaling 0.1 to 3% by mass. These elements can improve the stability of corrosion products and delay corrosion during the corrosion of the coating, stabilize the zinc spangle size on the coating surface, and improve the surface appearance.

[0067] It should be noted that the composition of the aforementioned coating can be confirmed, for example, by immersing the coating in hydrochloric acid or similar substances to dissolve it, and then analyzing the solution using ICP emission spectroscopy, atomic absorption spectroscopy, or similar methods. This method is merely an example; any method capable of accurately quantifying the composition of the coating can be used, and there are no particular limitations.

[0068] Furthermore, the coating film of the hot-dip Al-Zn-Si-Mg steel sheet obtained by this invention has a composition that is generally the same as that of the coating bath. Therefore, the composition of the coating film can be controlled with high precision by controlling the composition of the coating bath.

[0069] Furthermore, the hot-dip Al-Zn-Si-Mg based steel sheet of the present invention is characterized in that, within a range of 50 mm removed from both ends of the steel sheet surface, the height difference of the coated surface per 1 mm length is 10 μm or less. When the height difference of the steel sheet surface, i.e. the coated surface, is 10 μm or less, there are no wrinkle-like defects, and an excellent surface appearance can be obtained.

[0070] As described above, the aforementioned wrinkled defects refer to defects caused by Mg-based oxides that result in a wrinkled, uneven surface on the coated film, appearing as white striped patterns on the surface of the coated film. Therefore, suppressing wrinkled defects means that the striped patterns are not visually perceptible. Thus, by suppressing the height difference over a 1mm length range on the steel plate surface to within 10μm, it is prevented from being visually perceived as a striped pattern, resulting in an excellent surface appearance. From the same viewpoint, the height difference over a 1mm length range on the steel plate surface is preferably within 5μm.

[0071] It should be noted that the above-mentioned steel plate surface refers to the outermost surface of the steel plate, and in the case of hot-dip galvanized Al-Zn-Si-Mg series steel plates, it refers to the surface of the coating.

[0072] Here, the height difference on the surface of the steel plate refers to the difference between the height of the highest point and the lowest point on the steel plate (on the coated film) when the direction perpendicular to the surface of the base steel plate (the direction of the coating thickness) is taken as the height.

[0073] In addition, for the method of obtaining the height difference of the above-mentioned steel plate surface within a 1 mm length range, for example, it can be obtained by using a laser microscope to measure the height difference of a 1 mm range at any 100 locations of the hot-dip Al-Zn-Si-Mg steel plate with the coating film, and calculating the average of the measured values.

[0074] Furthermore, as a reason for controlling the height difference of the steel plate surface within a 50mm range from both ends, it is generally difficult to control the amount of coating in the center of the steel plate at both ends of the molten steel plate, and the cooling rates are also different, which easily leads to wrinkled defects. In addition, since the ends of such steel plates are mostly used after trimming, the surface appearance is hardly a problem.

[0075] For the method of controlling the height difference on the surface of the steel plate per 1 mm length of the above-mentioned coating to be less than 10 μm, there are no particular limitations other than the Mn content (0.01 to 0.5% by mass) in the above-mentioned coating. For example, the height difference on the coating surface can be suppressed by adjusting the content ratio of Mg to Mn in the above-mentioned coating, or by performing other surface treatments to suppress the height difference.

[0076] Furthermore, in the hot-dip Al-Zn-Si-Mg based steel sheet of the present invention, it is preferable to form an alloy layer containing Mn at the interface between the above-mentioned coated film and the base iron. This alloy layer is formed by an alloying reaction between Mn and Al, Fe, and Si in a bath, and is mainly an intermetallic compound of the Fe-Al-Mn or Fe-Al-Si-Mn system. Because it has an uneven shape relative to the direction of the coated surface, the adhesion between the above-mentioned coated film and the base steel sheet can be further improved through an anchoring effect.

[0077] Furthermore, the anchoring effect caused by the alloy layer containing Mn is manifested when the coating film solidifies. The Mn-based interfacial alloy layer plays a role in minimizing the movement of the coating liquid film, thus also suppressing the formation of wrinkled defects.

[0078] Furthermore, in the hot-dip Al-Zn-Si-Mg steel sheet of the present invention, in order to impart excellent corrosion resistance, the diffraction intensities of Si and Mg2Si in the above-mentioned coating film obtained by X-ray diffraction preferably satisfy the following relationship (1).

[0079] Si(111) / Mg2Si(111)≤0.8・・・(1)

[0080] Si(111): Diffraction intensity of the (111) plane of Si (interface spacing d = 0.3135 nm), Mg2Si(111): Diffraction intensity of the (111) plane of Mg2Si (interface spacing d = 0.3668 nm).

[0081] As described above, in this invention, it is preferable to control the ratio of the Mg2Si phase and the Si phase generated in the coated film to a specific ratio by including Mg and Si. The influence of these phases on corrosion resistance is still under investigation and many aspects remain unclear, but the mechanism is inferred as follows.

[0082] When a hot-dip Al-Zn-Si-Mg coated film is exposed to a corrosive environment, the intermetallic compounds mentioned above dissolve preferentially compared to the α-Al phase, resulting in a Mg-rich environment near the corrosion products. It is inferred that in such a Mg-rich environment, the corrosion products are less prone to decomposition, thus enhancing the protective effect of the coated film. Furthermore, it is believed that this enhanced protective effect is more reliably manifested when Si in the coated film exists as the Mg2Si phase rather than the Si phase; therefore, reducing the ratio of the Si phase to the Mg2Si phase is effective.

[0083] The ratio of Mg2Si to Si in the above-mentioned coating film, using the diffraction peak intensity obtained by X-ray diffraction, preferably satisfies the relationship (1): Si(111) / Mg2Si(111)≤0.8. However, if the ratio of Mg2Si to Si in the above-mentioned coating film does not satisfy relationship (1), that is, Si(111) / Mg2Si(111)>0.8, the Si phase present in the above-mentioned coating film becomes more abundant. Therefore, it is difficult to obtain the Mg-rich environment near the corrosion products, and it is difficult to obtain the improved protective effect of the above-mentioned coating film. From the same point of view, the ratio of Si to Mg2Si (Si(111) / Mg2Si(111)) is more preferably 0.5 or less, more preferably 0.3 or less, and particularly preferably 0.2 or less.

[0084] Here, in the above relationship (1), Si (111) is the diffraction intensity of the (111) plane of Si (interface spacing d = 0.3135 nm), and Mg2Si (111) is the diffraction intensity of the (111) plane of Mg2Si (interface spacing d = 0.3668 nm).

[0085] It should be noted that, as a method for determining Si(111) and Mg2Si(111) by X-ray diffraction as described above, it can be calculated by mechanically scraping off a portion of the above-mentioned coating film to form a powder and then performing X-ray diffraction (powder X-ray diffraction method). For the determination of diffraction intensity, the ratio of Si(111) / Mg2Si(111) can be obtained by measuring the diffraction peak intensity of Si with an interplanar spacing d = 0.3135 nm and the diffraction peak intensity of Mg2Si with an interplanar spacing d = 0.3668 nm.

[0086] From the viewpoint of high-precision determination of Si (111) and Mg2Si (111), the amount of coating film required for powder X-ray diffraction (the amount of coating film removed) is 0.1 g or more, preferably 0.3 g or more. Furthermore, when the coating film is scraped off, steel plate components other than the coating film may be included in the powder, but these intermetallic compound phases are only contained in the coating film and do not affect the peak intensity. Moreover, the coating film is made into powder for X-ray diffraction because if X-ray diffraction is performed on the coating film formed on the coated steel plate, the planar orientation of the solidified structure of the coating film would affect the accuracy of the ratio calculation.

[0087] Furthermore, in the hot-dip Al-Zn-Si-Mg steel sheet of the present invention, from the perspective of being able to more stably improve corrosion resistance, the diffraction intensity of Si in the above-mentioned coating film based on X-ray diffraction preferably satisfies the following relationship (2).

[0088] Si(111)=0・・・(2)

[0089] Si(111): Diffraction intensity of the (111) plane of Si (interface spacing d = 0.3135 nm).

[0090] Generally speaking, it is known that in the dissolution reaction of Al alloys in aqueous solution, the presence of the Si phase as a cathode site promotes the dissolution of the surrounding α-Al phase. Therefore, reducing the Si phase is also effective in suppressing the dissolution of the α-Al phase. Among them, forming a film without the Si phase as in relation (2) (making the diffraction peak intensity of the above Si (111) zero) is the most ideal for stabilizing corrosion resistance.

[0091] It should be noted that the method for determining the intensity of the diffraction peaks of the (111) plane of Si based on X-ray diffraction is as described above.

[0092] Here, there are no particular limitations on the methods for satisfying the above relationships (1) and (2). For example, to satisfy relationships (1) and (2), the ratio of Mg2Si to Si (the diffraction intensity of Mg2Si (111) and Si (111)) can be controlled by adjusting the balance of Si, Mg and Al content in the above-mentioned coated film. It should be noted that the balance of Si, Mg and Al content in the above-mentioned coated film does not necessarily satisfy relationships (1) and (2) simply by setting a certain content ratio. For example, it is necessary to change the content ratio of Mg and Al by adjusting the Si content (mass%).

[0093] In addition to adjusting the balance of Si, Mg and Al content in the above-mentioned coating film, the diffraction intensity of Mg2Si(111) and Si(111) can be controlled by adjusting the conditions during coating film formation (e.g., cooling conditions after coating) in order to satisfy relations (1) and (2).

[0094] From the perspective of satisfying various characteristics, the preferred adhesion amount of the above-mentioned coating is 45-120 g / m² per single side. 2 Because the adhesion amount of the above-mentioned coating is 45g / m². 2 Under the above conditions, corrosion resistance is sufficient for applications requiring long-term corrosion resistance, such as building materials. Furthermore, the adhesion amount of the aforementioned coating is 120 g / m². 2 Under the following conditions, the generation of plating cracks during processing can be suppressed, and excellent corrosion resistance can be achieved. From the same point of view, the adhesion amount of the aforementioned plating film is more preferably 45–100 g / m². 2 .

[0095] It should be noted that the amount of coating adhesion described above can be derived, for example, by dissolving and peeling off a specific area of ​​the coating using a mixture of hydrochloric acid and hexamethylenetetramine as shown in JIS H 0401:2013, and calculating based on the weight difference of the steel sheet before and after peeling. To determine the amount of coating adhesion per single side using this method, the dissolution process can be performed after sealing the non-target coating surface with tape to prevent exposure.

[0096] Furthermore, there are no particular limitations on the base steel plate constituting the hot-dip Al-Zn-Si-Mg series steel plate of the present invention, and cold-rolled steel plate, hot-rolled steel plate, etc. may be used appropriately according to the required performance and specifications.

[0097] There are no particular limitations on the method for obtaining the aforementioned base steel sheet. For example, when using the aforementioned hot-rolled steel sheet, a steel sheet that has undergone hot rolling and pickling processes can be used; when using the aforementioned cold-rolled steel sheet, a further cold rolling process can be added. Furthermore, in order to obtain the properties of the steel sheet, a recrystallization annealing process can be performed before the hot-dip galvanizing process.

[0098] It should be noted that there are no particular limitations on the method for manufacturing the hot-dip galvanized Al-Zn-Si-Mg steel sheet of the present invention. For example, it can be manufactured by cleaning, heating, and immersing the aforementioned base steel sheet in a galvanizing bath using a continuous hot-dip galvanizing apparatus. In the heating process of the steel sheet, recrystallization annealing or similar processes are performed to control the microstructure of the base steel sheet itself. At the same time, heating in a reducing atmosphere such as a nitrogen-hydrogen atmosphere is effective in preventing oxidation of the steel sheet and reducing the trace amounts of oxide film present on the surface.

[0099] Furthermore, regarding the plating bath used in manufacturing the hot-dip Al-Zn-Si-Mg series steel sheet of the present invention, as described above, the composition of the plating film is almost identical to that of the plating bath. Therefore, a composition containing Al: 45-65% by mass, Si: 1.0-3.0% by mass, Mg: 1.0-10.0% by mass, and Mn: 0.1-0.5% by mass, with the remainder consisting of Zn, Fe, and unavoidable impurities, can be used.

[0100] Furthermore, the temperature of the above-mentioned plating bath is not particularly limited, but it is preferably in the temperature range of (melting point + 20°C) to 650°C.

[0101] The lower limit of the bath temperature is set to the melting point + 20°C because, for hot-dip galvanizing, the bath temperature needs to be above the freezing point. Setting it to the melting point + 20°C prevents solidification caused by localized temperature drops in the galvanizing bath. On the other hand, the upper limit of the bath temperature is set to 650°C because if it exceeds 650°C, the galvanized film will be difficult to cool quickly, and the interfacial alloy layer formed between the galvanized film and the steel plate may become thicker.

[0102] In addition, there is no particular limitation on the temperature of the base steel plate immersed in the plating bath (immersion temperature), but from the viewpoint of ensuring the plating characteristics in the above-mentioned continuous hot-dip plating operation and preventing changes in the bath temperature, it is preferable to control the temperature of the plating bath within ±20°C.

[0103] Furthermore, the immersion time in the plating bath for the aforementioned base steel plate is 0.5 seconds or more. This is because if the immersion time is less than 0.5 seconds, it may be impossible to form a sufficient plating film on the surface of the base steel plate. There is no particular upper limit to the immersion time, but if the immersion time is extended, the interfacial alloy layer formed between the plating film and the steel plate may become thicker; therefore, 8 seconds or less is preferred.

[0104] It should be noted that hot-dip Al-Zn-Si-Mg series steel sheets can form a coating directly or through an intermediate layer on the above-mentioned coating film, depending on the required performance.

[0105] It should be noted that there are no particular limitations on the methods for forming the above-mentioned coating film, and the appropriate method can be selected according to the required performance. For example, roller coating, curtain coating, and spraying are all possible methods. The coating film can also be formed by heating and drying the coating containing organic resin after application, using methods such as hot air drying, infrared heating, or induction heating.

[0106] Furthermore, there are no particular limitations on the intermediate layer, as long as it is a layer formed between the coating film on the molten steel sheet and the coating film.

[0107] <Surface-treated steel sheet>

[0108] The surface-treated steel sheet of the present invention has a coating film and a chemical conversion film formed on the coating film on the surface of the steel sheet.

[0109] The composition of the coating film is the same as that of the coating film of the hot-dip Al-Zn-Si-Mg steel sheet of the present invention.

[0110] Furthermore, the other components of the aforementioned coating are the same as those of the coating of the hot-dip Al-Zn-Si-Mg steel sheet of the present invention.

[0111] The surface-treated steel sheet of the present invention has a chemical conversion coating formed on the above-mentioned coating.

[0112] It should be noted that the above-mentioned chemical conversion coating can be formed on at least one side of the surface-treated steel sheet, or on both sides of the surface-treated steel sheet depending on the application and required performance.

[0113] Furthermore, in the surface-treated steel sheet of the present invention, the aforementioned chemical conversion coating is characterized by containing at least one resin selected from epoxy resin, urethane resin, acrylic resin, silicone acrylic resin, alkyd resin, polyester resin, polyalkylene resin, amino resin, and fluororesin, and at least one metal compound selected from P compound, Si compound, Co compound, Ni compound, Zn compound, Al compound, Mg compound, V compound, Mo compound, Zr compound, Ti compound, and Ca compound.

[0114] By forming the aforementioned chemical conversion coating on the coated film, the affinity with the coated film can be improved, and the chemical conversion coating can be uniformly formed on the coated film. Furthermore, the rust-preventive and barrier effects of the chemical conversion coating can be improved. As a result, the surface-treated steel sheet of the present invention achieves stable corrosion resistance and white rust resistance.

[0115] Here, for the resin constituting the above-mentioned chemical conversion coating, from the viewpoint of improving corrosion resistance, at least one selected from epoxy resin, urethane resin, acrylic resin, silicone acrylic resin, alkyd resin, polyester resin, polyalkylene resin, amino resin, and fluororesin is used. From the same viewpoint, the above-mentioned resin preferably contains at least one selected from urethane resin and acrylic resin. It should be noted that the resin constituting the above-mentioned chemical conversion coating also includes addition polymers of the above-mentioned resins.

[0116] For the aforementioned epoxy resins, for example, resins obtained by glycidyl etherification of bisphenol A type, bisphenol F type, phenolic varnish type, etc., resins obtained by glycidyl etherification of propylene oxide, ethylene oxide, or polyalkylene glycol with bisphenol A type epoxy resin, aliphatic epoxy resins, alicyclic epoxy resins, polyether-based epoxy resins, etc., can be used.

[0117] For the aforementioned urethane resins, oil-modified polyurethane resins, alkyd polyurethane resins, polyester polyurethane resins, polyether polyurethane resins, polycarbonate polyurethane resins, etc., can be used.

[0118] Examples of the aforementioned acrylic resins include polyacrylic acid and its copolymers, polyacrylate and its copolymers, polymethacrylic acid and its copolymers, polymethacrylate and its copolymers, urethane-acrylic acid copolymers (or urethane-modified acrylic resins), styrene-acrylic acid copolymers, etc. Resins obtained by modifying these resins with other alkyd resins, epoxy resins, phenolic resins, etc., can be further used.

[0119] Examples of acrylic silicone resins include resins formed by adding a curing agent to the side chains or terminal hydrolyzable alkoxysilyl groups of an acrylic copolymer that serves as the main agent. Furthermore, in addition to corrosion resistance, excellent weather resistance can be expected when using acrylic silicone resins.

[0120] Examples of alkyd resins mentioned above include oil-modified alkyd resins, rosin-modified alkyd resins, phenolic-modified alkyd resins, styrene-modified alkyd resins, silicone-modified alkyd resins, acrylic-modified alkyd resins, oil-free alkyd resins, and high molecular weight oil-free alkyd resins.

[0121] The aforementioned polyester resin is a condensation polymer synthesized by dehydrating and condensing a polycarboxylic acid with a polyol to form an ester bond. Examples of polycarboxylic acids used include terephthalic acid and 2,6-naphthalenedicarboxylic acid, while examples of polyols include ethylene glycol, 1,3-propanediol, 1,4-butanediol, and 1,4-cyclohexanediol. Specifically, examples of the aforementioned polyesters include polyethylene terephthalate, polyethylene terephthalate, polyethylene naphthalate, and polybutylene naphthalate. Alternatively, resins obtained by modifying these polyester resins with acrylic acid can also be used.

[0122] Examples of the aforementioned polyalkylene resins include ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers, carboxyl-modified polyolefin resins and other ethylene-based copolymers, ethylene-unsaturated carboxylic acid copolymers, and ethylene-based ionomers. In addition, resins modified from these resins by other alkyd resins, epoxy resins, phenolic resins and the like can be used.

[0123] The aforementioned amino resins are thermosetting resins produced by the reaction of amine or amide compounds with aldehydes. Examples include melamine resin, guanidine resin, and thiourea resin. However, from the viewpoints of corrosion resistance, durability, and adhesion, melamine resin is preferred. There are no particular limitations on the type of melamine resin, but examples include butylated melamine resin, methylated melamine resin, and waterborne melamine resin.

[0124] Examples of fluororesins include fluoroolefin polymers and copolymers of fluoroolefins with alkyl vinyl ethers, cycloalkyl vinyl ethers, carboxylic acid-modified vinyl esters, hydroxyalkyl allyl ethers, tetrafluoropropyl vinyl ethers, etc. When using these fluororesins, not only corrosion resistance but also excellent weather resistance and excellent hydrophobicity can be expected.

[0125] Furthermore, to improve corrosion resistance and processability, a curing agent is particularly preferred for the resin constituting the aforementioned chemical conversion coating. As a curing agent, urea-formaldehyde resin (butylated urea-formaldehyde resin, etc.), melamine resin (butylated melamine resin, butylated etherified melamine resin, etc.), butylated urea-melamine resin, benzoguanamine resin, and other amino resins, blocked isocyanates, etc., can be appropriately used. Azoline compounds, phenolic resins, etc.

[0126] Furthermore, for the metal compound constituting the aforementioned chemical conversion coating, 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 is used. From the same viewpoint, the aforementioned metal compound preferably contains at least one of P compounds, Si compounds, and V compounds.

[0127] Here, the aforementioned P compound, by being included in the aforementioned chemical conversion coating, can improve corrosion resistance and perspiration resistance. The aforementioned P compound refers to a compound containing P, for example, it may contain one or more selected from inorganic phosphoric acid, organic phosphoric acid, and their salts.

[0128] As the aforementioned inorganic phosphoric acid, organic phosphoric acid, and their salts, any compound may be used without particular limitation. For example, as the aforementioned inorganic phosphoric acid, it is preferable to use one or more selected from phosphoric acid, dihydrogen phosphate, hydrogen phosphate, phosphate, pyrophosphate, pyrophosphate, tripolyphosphoric acid, tripolyphosphate, phosphorous acid, phosphite, hypophosphoric acid, and hypophosphite. Furthermore, as the aforementioned organic phosphoric acid, phosphonic acid (phosphonic acid compound) is preferably used. Moreover, as the aforementioned phosphonic acid, it is preferable to use one or more selected from nitrotrimethylenephosphonic acid, phosphonobutanetricarboxylic acid, methyldiphosphonic acid, methylenephosphonic acid, and ethyldiphosphonic acid.

[0129] It should be noted that when the above-mentioned P compound is a salt, the salt is preferably a salt of an element from Group 1 to Group 13 of the periodic table, more preferably a metal salt, and preferably selected from one or more alkali metal salts and alkaline earth metal salts.

[0130] If a chemical conversion treatment solution containing the aforementioned P compound is applied to a coated steel sheet, the surface of the coated film is etched due to the action of the P compound, forming an enriched layer of Al, Zn, Si, and Mg, which are constituent elements of the coated film, on the coated film side of the chemical conversion film. By forming the aforementioned enriched layer, the bonding between the chemical conversion film and the surface of the coated film becomes stronger, and the adhesion of the chemical conversion film is improved.

[0131] The concentration of the phosphorus compound in the aforementioned chemical conversion treatment solution is not particularly limited and can be from 0.25% to 5% by mass. If the concentration of the phosphorus compound is less than 0.25% by mass, not only will the etching effect be insufficient, but the adhesion to the plating interface will also decrease, and the corrosion resistance of the planar portion will decrease. Furthermore, the corrosion resistance and perspiration resistance of defective portions, cut ends, and damaged portions of the coating caused by processing may also decrease. From the same viewpoint, the concentration of the phosphorus compound is preferably 0.35% by mass or more, and more preferably 0.50% by mass or more. On the other hand, if the concentration of the phosphorus compound exceeds 5% by mass, not only will the lifespan of the chemical conversion treatment solution be shortened, but the appearance of the coating will easily become uneven. In addition, the amount of phosphorus dissolved from the chemically converted coating will increase, and the resistance to blackening may also decrease. From the same viewpoint, the concentration of the phosphorus compound is preferably 3.5% by mass or less, and more preferably 2.5% by mass or less. Regarding the content of phosphorus compound (P) in the aforementioned chemical conversion coating, for example, it can be achieved by coating and drying a chemical conversion treatment solution with a P compound concentration of 0.25% to 5% by mass, thereby resulting in a P adhesion amount of 5 to 100 mg / m² in the dried chemical conversion coating. 2 .

[0132] The aforementioned Si compound forms the framework of the chemical conversion coating together with the aforementioned resin, thereby improving its affinity with the coating and uniformly forming the chemical conversion coating. The aforementioned Si compound is a compound containing Si, and preferably contains one or more selected from silicon dioxide, trialkoxysilane, tetrakoxysilane, and silane coupling agents.

[0133] There are no particular limitations on the silica used; any type of silica can be used. For example, at least one of wet silica and dry silica can be used. As a type of wet silica, colloidal silica such as SNOWTEX O, C, N, S, 2O, OS, OXS, and NS manufactured by Nissan Chemical Co., Ltd. is preferred. Furthermore, as dry silica, AEROSIL50, 130, 200, 300, and 380 manufactured by AEROSIL Co., Ltd. of Japan is preferred.

[0134] As the aforementioned trialkoxysilane, any substance may be used without particular limitation. For example, a trialkoxysilane represented by the general formula: R1Si(OR2)3 (where R1 is hydrogen or an alkyl group having 1 to 5 carbon atoms, and R2 is the same or different alkyl groups having 1 to 5 carbon atoms) is preferred. Examples of such trialkoxysilanes include trimethoxysilane, triethoxysilane, and methyltriethoxysilane.

[0135] As the aforementioned tetraalkoxysilane, any substance may be used without particular limitation. For example, a tetraalkoxysilane represented by the general formula: Si(OR)4 (where R is an alkyl group having the same or different carbon atoms with 1 to 5 carbon atoms) is preferred. Examples of such tetraalkoxysilanes include tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane.

[0136] As the aforementioned silane coupling agent, any substance can be used without particular limitation. Examples include γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldiethoxysilane, γ-aminopropyltriethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, γ-methacryloyloxypropyltriethoxysilane, γ-mercaptopropylmethyldiethoxysilane, γ-mercaptopropyltrimethoxysilane, vinyltriethoxysilane, and γ-isocyanate-propyltriethoxysilane.

[0137] It should be noted that by containing the aforementioned Si compound in the chemical conversion coating, the Si compound undergoes dehydration condensation to form an amorphous chemical conversion coating with siloxane bonds, exhibiting high barrier properties against corrosion. Furthermore, by combining with the aforementioned resin, a chemical conversion coating with even higher barrier properties is formed. Moreover, in corrosive environments, dense and stable corrosion products are formed at defective areas, coatings resulting from processing, and damaged areas of the coating. The combined effect with the aforementioned coating also inhibits corrosion of the substrate steel plate. From the viewpoint of high effectiveness in forming stable corrosion products, at least one of colloidal silica and dry silica is preferably used as the aforementioned Si compound.

[0138] The concentration of the Si compound in the chemical conversion treatment solution used to form the above-mentioned chemical conversion coating is 0.2% to 9.5% by mass. If the concentration of the Si compound in the chemical conversion treatment solution is 0.2% by mass or more, a barrier effect due to siloxane bonds can be obtained. As a result, in addition to improved corrosion resistance of planar portions, the corrosion resistance and perspiration resistance of defective portions, cut portions, and damaged portions caused by processing are also improved. Furthermore, if the concentration of the Si compound is 9.5% by mass or less, the lifespan of the chemical conversion treatment solution can be extended. By coating and drying a chemical conversion treatment solution with a Si compound concentration of 0.2% to 9.5% by mass, the Si adhesion amount of the dried chemical conversion coating can be 2 to 95 mg / m³. 2 .

[0139] The aforementioned Co and Ni compounds can improve resistance to blackening by being included in the aforementioned chemical conversion coating. This is believed to be because Co and Ni have the effect of delaying the dissolution of water-soluble components from the coating under corrosive environments. Furthermore, Co and Ni are elements that are less susceptible to oxidation compared to Al, Zn, Si, and Mg. Therefore, by enriching at least one of the aforementioned Co and Ni compounds at the interface between the aforementioned chemical conversion coating and the aforementioned coated coating (forming an enriched layer), the enriched layer acts as a barrier against corrosion, resulting in improved resistance to blackening.

[0140] By using a chemical conversion treatment solution containing the aforementioned Co compound, Co can be contained in the aforementioned chemical conversion coating and obtained into the aforementioned enrichment layer. As the aforementioned Co compound, a cobalt salt is preferred. As the aforementioned cobalt salt, one or more selected from cobalt sulfate, cobalt carbonate, and cobalt chloride are more preferably used.

[0141] Furthermore, by using a chemical conversion treatment solution containing the aforementioned Ni compound, Ni can be contained within the aforementioned chemical conversion coating and acquired into the aforementioned enrichment layer. As the aforementioned Ni compound, a nickel salt is preferred. As the aforementioned nickel salt, one or more selected from nickel sulfate, nickel carbonate, and nickel chloride are more preferably used.

[0142] The concentration of Co and / or Ni compounds in the aforementioned chemical conversion treatment solution is not particularly limited and can be a total of 0.25% to 5% by mass. If the concentration of the aforementioned Co and / or Ni compounds is less than 0.25% by mass, the interfacial enrichment layer becomes uneven, which may reduce the corrosion resistance not only of the planar portion but also of the defective portion, the cut end portion, the coating caused by processing, and the damaged portion of the film. From the same viewpoint, it is preferable to be 0.5% by mass or more, and more preferably 0.75% by mass or more. On the other hand, if the concentration of the aforementioned Co and / or Ni compounds exceeds 5% by mass, the appearance of the film formed is prone to become uneven, and the corrosion resistance may decrease. From the same viewpoint, it is preferable to be 4.0% by mass or less, and more preferably 3.0% by mass or less. By coating and drying the chemical conversion treatment solution with a total concentration of 0.25% to 5% by mass of the aforementioned Co and / or Ni compounds, the total amount of Co and Ni adhering in the dried chemical conversion film can be 5 to 100 mg / m³. 2 .

[0143] By including the aforementioned Al, Zn, and Mg compounds in a chemical conversion treatment solution, an enriched layer containing at least one of Al, Zn, and Mg can be formed on the coating side of the chemical conversion coating. The formed enriched layer improves corrosion resistance.

[0144] It should be noted that the above-mentioned Al compound, Zn compound, and Mg compound are not particularly limited as long as they are compounds containing Al, Zn, and Mg respectively, but are preferably inorganic compounds, preferably chlorine, chloride, oxide, or hydroxide.

[0145] Examples of the aforementioned Al compounds include one or more selected from aluminum sulfate, aluminum carbonate, aluminum chloride, aluminum oxide, and aluminum hydroxide.

[0146] Examples of the aforementioned Zn compounds include one or more selected from zinc sulfate, zinc carbonate, zinc chloride, zinc oxide, and zinc hydroxide.

[0147] Examples of the aforementioned Mg compounds include, for instance, one or more selected from magnesium sulfate, magnesium carbonate, magnesium chloride, magnesium oxide, and magnesium hydroxide.

[0148] The total concentration of Al, Zn, and / or Mg compounds in the chemical conversion treatment solution used to form the aforementioned chemical conversion coating is preferably 0.25% to 5% by mass. If the total concentration is 0.25% by mass or higher, the enriched layer can be formed more effectively, resulting in further improved corrosion resistance. On the other hand, if the total concentration is 5% by mass or lower, the appearance of the chemical conversion coating becomes more uniform, and the corrosion resistance in planar areas, defective areas, coatings formed during processing, and damaged areas of the coating is further improved.

[0149] The aforementioned V compound, by being contained in the aforementioned chemical conversion coating, allows V to dissolve to a moderate degree in a corrosive environment, combining with zinc ions and other plating components that also dissolve in a corrosive environment to form a dense protective coating. This protective coating not only improves the corrosion resistance of the flat portion of the steel plate but also further enhances its resistance to defects, damage to the plating coating caused by processing, and corrosion occurring from the cut end towards the flat portion.

[0150] The above-mentioned V compound is a compound containing V, for example, one or more selected from sodium metavanadate, vanadium oxysulfate and vanadium acetylacetonate.

[0151] The V compound in the chemical conversion treatment solution used to form the aforementioned chemical conversion coating is preferably 0.05% to 4% by mass. If the concentration of the V compound is 0.05% by mass or more, it readily dissolves in corrosive environments to form a protective coating, improving the corrosion resistance of defective areas, cut ends, and damaged areas resulting from the coating during processing. On the other hand, if the concentration of the V compound exceeds 4% by mass, the appearance of the chemical conversion coating is prone to unevenness, and its resistance to blackening decreases.

[0152] The aforementioned Mo compound, by being incorporated into the aforementioned chemical conversion coating, can improve the resistance to blackening of the surface-treated steel sheet. The aforementioned Mo compound is a Mo-containing compound, which can be obtained by adding one or both of molybdic acid and molybdate to the chemical conversion treatment solution.

[0153] It should be noted that, for example, one or more of the above molybdates can be selected from sodium molybdate, potassium molybdate, magnesium molybdate, and zinc molybdate.

[0154] The concentration of the Mo compound in the chemical conversion treatment solution used to form the aforementioned chemical conversion coating is preferably 0.01% to 3% by mass. If the concentration of the Mo compound is 0.01% by mass or more, the formation of oxygen-deficient zinc oxide is further suppressed, and the resistance to blackening can be further improved. On the other hand, if the concentration of the Mo compound is 3% by mass or less, in addition to further extending the life of the chemical conversion treatment solution, the corrosion resistance can be further improved.

[0155] The Zr and Ti compounds described above, by being incorporated into the chemical conversion coating, prevent the coating from becoming porous and instead densify it. As a result, corrosive agents are less likely to penetrate the chemical conversion coating, thus improving corrosion resistance.

[0156] The Zr compounds mentioned above are Zr-containing compounds, and for example, one or more selected from zirconium acetate, zirconium sulfate, potassium zirconium carbonate, sodium zirconium carbonate, and ammonium zirconium carbonate can be used. Among these compounds, organotitanium chelate compounds are preferred because they densify the film when the chemical conversion treatment solution is dried to form a film, resulting in better corrosion resistance.

[0157] The above-mentioned Ti compound is a compound containing Ti, for example, one or more selected from titanium sulfate, titanium chloride, titanium hydroxide, titanium acetylacetone, titanium octanediol, and titanium ethyl acetoacetate can be used.

[0158] The total concentration of Zr and / or Ti compounds in the chemical conversion treatment solution used to form the aforementioned chemical conversion coating is preferably 0.2% to 20% by mass. If the total concentration of Zr and / or Ti compounds is 0.2% by mass or more, the effect of inhibiting the transmission of corrosion factors is improved, which not only enhances the corrosion resistance of planar portions but also further improves the corrosion resistance of defective portions, cut ends, and portions damaged by the coating caused by processing. On the other hand, if the total concentration of Zr and / or Ti compounds is 20% by mass or less, the lifespan of the chemical conversion treatment solution can be further extended.

[0159] The aforementioned Ca compounds, by being contained in the aforementioned chemical conversion coating, can thus exhibit the effect of reducing the corrosion rate.

[0160] The aforementioned Ca compounds are compounds containing Ca, such as Ca oxides, Ca nitrates, Ca sulfates, and intermetallic compounds containing Ca. More specifically, examples of the aforementioned Ca compounds include CaO, CaCO3, Ca(OH)2, Ca(NO3)2·4H2O, and CaSO4·2H2O. The content of the aforementioned Ca compounds in the chemical conversion coating is not particularly limited.

[0161] It should be noted that the aforementioned chemical conversion coating may contain various well-known components commonly used in the coatings industry, as needed. Examples include various surface modifiers such as leveling agents and defoamers, dispersants, anti-settling agents, UV absorbers, light stabilizers, silane coupling agents, titanate coupling agents, and other additives, coloring pigments, filler pigments, gloss materials, curing catalysts, organic solvents, lubricants, etc.

[0162] It should be noted that in the surface-treated steel sheet of the present invention, the chemical conversion coating preferably does not contain harmful components such as hexavalent chromium, trivalent chromium, and fluorine. This is because the chemical conversion treatment solution used to form the chemical conversion coating does not contain these harmful components, thus ensuring high safety and reducing environmental impact.

[0163] Furthermore, there is no particular limitation on the amount of the chemical conversion coating applied. For example, from the viewpoint of more reliably ensuring corrosion resistance and preventing the peeling of the chemical conversion coating, it is preferable to set the amount of the chemical conversion coating applied to be 0.1 to 3.0 g / m³. 2 More preferably, it is 0.5–2.5 g / m 2 The adhesion amount of the above chemical conversion film was set to 0.1 g / m. 2 The above measures ensure corrosion resistance more reliably by setting the adhesion amount of the chemical conversion coating to 3.0 g / m. 2 The following measures can prevent the chemical conversion coating from cracking and peeling.

[0164] The amount of the aforementioned chemical conversion coating can be determined by appropriately selecting a conventional method, such as determining the amount of elements present in the coating by fluorescence X-ray analysis of the coating.

[0165] It should be noted that the method used to form the above-mentioned chemical conversion coating is not particularly limited, and can be appropriately selected according to the required performance, manufacturing equipment, etc. For example, it can be formed by continuously coating the above-mentioned coating film with a chemical conversion treatment solution using a roller coater or the like, and then drying it at a peak metal temperature (PMT) of about 60 to 200°C using hot air, induction heating, etc. In addition to using a roller coater, the coating of the above-mentioned chemical conversion treatment solution can also be carried out by known methods such as airless spraying, electrostatic spraying, and curtain flow coating machines. Furthermore, as long as the above-mentioned chemical conversion coating contains the above-mentioned resin and the above-mentioned metal compound, it can be either a single-layer film or a multi-layer film, without particular limitation.

[0166] Furthermore, the surface-treated steel sheet of the present invention, like the hot-dip Al-Zn-Si-Mg steel sheet of the present invention described above, has a height difference of less than 10 μm per 1 mm length within the range after removing 50 mm from both ends of the steel sheet surface (chemical conversion coating surface).

[0167] When the surface elevation difference of the chemically converted film is less than 10 μm, there are no wrinkled defects, resulting in an excellent surface appearance.

[0168] As described above, the aforementioned wrinkled defects refer to defects where the surface of the chemically converted coating becomes wrinkled and uneven due to Mg-based oxides. These defects appear as white stripe patterns on the surface of the chemically converted coating. Therefore, suppressing wrinkled defects means making the stripe patterns visually undetectable. Thus, by suppressing the height difference within a 1mm range on the surface of the steel plate, i.e., the surface of the chemically converted coating, to within 10μm, the stripe patterns become visually undetectable, resulting in an excellent surface appearance. From the same perspective, the height difference within a 1mm range on the surface of the steel plate is preferably within 5μm.

[0169] It should be noted that the above-mentioned steel plate surface refers to the outermost surface of the steel plate, and in the case of surface-treated steel plates, it refers to the surface of the chemically converted coating.

[0170] Here, the height difference on the steel plate surface refers to the difference between the height of the highest point and the lowest point on the steel plate (on the chemical conversion coating), when the direction perpendicular to the surface of the base steel plate (the film thickness direction of the coating) is set as the height.

[0171] In addition, the method for obtaining the height difference within a 1 mm range on the surface of the aforementioned chemical conversion coating is similar to that for the coated coating surface described above. It can be obtained by using a laser microscope to measure the height difference within a 1 mm range at any 100 locations on the surface-treated steel plate and calculating the average of the measured values.

[0172] Furthermore, within a 50mm area removed from both ends of the aforementioned steel plate surface, as a reason for controlling the height difference of the steel plate surface, it is generally difficult to control the amount of coating at the ends of the hot-dip galvanized steel plate relative to the center of the plate, and the cooling rates are also different, thus wrinkling defects are prone to occur. In addition, since the ends of such steel plates are mostly trimmed before use, surface appearance is hardly an issue.

[0173] For the method of controlling the height difference of the coating surface per 1 mm length of the above-mentioned steel plate surface to be less than 10 μm, it is important to suppress the height difference of the coating surface. This can be achieved by adjusting the content ratio of Mg and Mn in the coating or by performing other surface treatments to suppress the height difference.

[0174] In addition, the surface-treated steel sheet of the present invention may also have a coating formed on the above-mentioned chemical conversion film as needed.

[0175] It should be noted that the method for manufacturing the surface-treated steel sheet of the present invention is a method for manufacturing a surface-treated steel sheet having a coating film and a chemical conversion film formed on the coating film.

[0176] Furthermore, in the manufacturing method of the present invention, the above-mentioned chemical conversion coating contains at least one resin selected from epoxy resin, urethane resin, acrylic resin, silicone acrylic resin, alkyd resin, polyester resin, polyalkylene resin, amino resin, and fluororesin, and at least one metal compound selected from P compound, Si compound, Co compound, Ni compound, Zn compound, Al compound, Mg compound, V compound, Mo compound, Zr compound, Ti compound, and Ca compound.

[0177] The formation of the above-mentioned coating film includes a hot-dip coating process, in which the base steel plate is immersed in a coating bath containing Al: 45-65% by mass, Si: 1.0-4.0% by mass and Mg: 1.0-10.0% by mass, with the remainder consisting of Zn and unavoidable impurities.

[0178] It should be noted that the conditions for the above-mentioned hot-dip galvanizing process are the same as those described in the hot-dip galvanized Al-Zn-Si-Mg steel sheet of the present invention.

[0179] <Painted Steel Sheet>

[0180] The coated steel sheet of the present invention is a coated steel sheet on which a coating is formed directly or through chemical conversion of a coated film.

[0181] The composition of the coating film is the same as that of the coating film of the hot-dip Al-Zn-Si-Mg steel sheet of the present invention.

[0182] Furthermore, the other components of the aforementioned coating are the same as those of the coating of the hot-dip Al-Zn-Si-Mg steel sheet of the present invention.

[0183] The coated steel sheet of the present invention can form a chemical conversion coating on the above-mentioned coating film.

[0184] It should be noted that the above-mentioned chemical conversion coating can be formed on at least one side of the coated steel sheet, or on both sides of the coated steel sheet depending on the application and required performance.

[0185] • Chemical conversion coating

[0186] Furthermore, in the coated steel sheet of the present invention, the chemical conversion coating is characterized in that the above-mentioned chemical conversion coating contains a resin component and an inorganic compound, wherein the resin component contains a total of 30 to 50% by mass of (a): anionic polyurethane resin having ester bonds and (b): epoxy resin having a bisphenol backbone, the content ratio of (a) to (b) ((a):(b)) is in the range of 3:97 to 60:40 by mass, and the inorganic compound contains 2 to 10% by mass of vanadium compound, 40 to 60% by mass of zirconium compound and 0.5 to 5% by mass of fluorine compound.

[0187] By forming the aforementioned chemical conversion coating on the coated film, the strength and adhesion of the chemical conversion coating can be improved, as well as its corrosion resistance.

[0188] Here, the resin components constituting the above-mentioned chemical conversion coating include (a): an anionic polyurethane resin having ester bonds and (b): an epoxy resin having a bisphenol backbone.

[0189] For the anionic polyurethane resin with ester bonds mentioned above (a), examples include resins obtained by copolymerizing a polyester polyol with a diisocyanate or polyisocyanate having two or more isocyanate groups and a dimethylolalkyl acid. Alternatively, a chemical conversion treatment solution can be obtained by dispersing it in a liquid such as water using known methods.

[0190] Examples of the aforementioned polyester polyols include polyesters obtained by dehydration condensation reaction of an acid component such as a diol component and an ester derivative of a hydroxycarboxylic acid, polyesters obtained by ring-opening polymerization of cyclic ester compounds such as ε-caprolactone, and their copolyesters.

[0191] Examples of the aforementioned polyisocyanates include aromatic polyisocyanates, aliphatic polyisocyanates, and alicyclic polyisocyanates. Examples of aromatic polyisocyanates include, for instance, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, isophenyl diisocyanate, diphenylmethane diisocyanate, 2,4-diphenylmethane diisocyanate, 2,2-diphenylmethane diisocyanate, triphenylmethane triisocyanate, polymethylene polyphenyl polyisocyanate, naphthalene diisocyanate, and their derivatives (e.g., prepolymers obtained by reaction with polyols, modified polyisocyanates such as carbodiimide compounds of diphenylmethane diisocyanate, etc.).

[0192] It should be noted that when the above-mentioned polyester polyol is reacted with the above-mentioned diisocyanate or polyisocyanate to synthesize urethane, for example, a dimethylolalkyl acid can be copolymerized to self-emulsify and dissolve in water (water dispersion) to obtain the above-mentioned (a) anionic polyurethane resin having ester bonds. In this case, dimethylolalkyl acids with 2 to 6 carbon atoms can be cited as examples, and more specifically, dimethylolacetic acid, dimethylolpropionic acid, dimethylolbutyric acid, dimethylolheptanoic acid, and dimethylolhexanoic acid can be cited.

[0193] Furthermore, for the epoxy resin with a bisphenol backbone described in (b) above, known epoxy resins can be used. Examples include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol AD ​​type epoxy resin, and bisphenol S type epoxy resin. These epoxy resins can be obtained by reacting bisphenol compounds such as bisphenol A, bisphenol F, bisphenol AD, and bisphenol S with epichlorohydrin in the presence of an alkaline catalyst. Component [A] preferably includes a bisphenol A type epoxy resin or a bisphenol F type epoxy resin, and more preferably, a bisphenol A type epoxy resin. The epoxy resin with a bisphenol backbone described in (b) can be dispersed in a liquid such as water using known methods to obtain a chemical conversion treatment solution.

[0194] The aforementioned resin components function as adhesives for the aforementioned chemical conversion coatings. However, the aforementioned (a) anionic polyurethane resin with ester bonds, which constitutes the adhesive, is flexible and therefore can prevent the chemical conversion coating from being damaged (peeled) during processing. The aforementioned (b) epoxy resin with a bisphenol backbone can improve the adhesion between the epoxy resin and the galvanized steel plate substrate and the upper primer coating.

[0195] The chemical conversion coating contains a total of 30-50% by mass of the aforementioned resin component. If the content of the aforementioned resin component is less than 30% by mass, the adhesive effect of the chemical conversion coating is reduced; if it exceeds 50% by mass, the function of the inorganic components, such as the inhibitory effect, is reduced. From the same viewpoint, the content of the aforementioned resin component in the chemical conversion coating is preferably 35-45% by mass.

[0196] Furthermore, in the aforementioned resin composition, the content ratio ((a):(b)) of the anionic polyurethane resin having ester bonds in (a) and the epoxy resin having a bisphenol backbone in (b) must be in the range of 3:97 to 60:40 by mass. This is because if (a):(b) is outside this range, the flexibility and adhesion of the chemically converted film decrease, resulting in insufficient corrosion resistance. From the same viewpoint, (a):(b) is preferably 10:90 to 55:45.

[0197] It should be noted that, depending on the required performance, the above-mentioned resin components may include resins other than (a) anionic polyurethane resins with ester bonds and (b) epoxy resins with bisphenol backbones (other resin components). There are no particular limitations on the above-mentioned other resin components; for example, at least one or a combination of two or more selected from acrylic resins, silicone acrylic resins, alkyd resins, polyester resins, polyalkylene resins, amino resins, and fluoropolymers may be used.

[0198] When the above-mentioned resin composition contains other resins, the total content of the above-mentioned (a) anionic polyurethane resin having ester bonds and the above-mentioned (b) epoxy resin having a bisphenol backbone is preferably 50% by mass or more, more preferably 75% by mass or more. This is because it more reliably achieves a reduction in flexibility and better adhesion as a chemically treated film.

[0199] In addition, the above-mentioned chemical conversion coating contains 2-10% by mass of vanadium compounds, 40-60% by mass of zirconium compounds, and 0.5-5% by mass of fluorine compounds as inorganic compounds.

[0200] By including these compounds, the corrosion resistance of chemical conversion coatings can be improved.

[0201] The aforementioned vanadium compounds, when added to the chemical conversion treatment solution, function as rust inhibitors. By being contained within the chemical conversion coating, these vanadium compounds dissolve moderately in a corrosive environment, combining with zinc ions and other plating components that also dissolve in the corrosive environment to form a dense protective coating. This protective coating not only improves the corrosion resistance of the flat surfaces of the steel plate but also further enhances its resistance to defects, damage to the coating caused by processing, and corrosion occurring from the cut end towards the flat surface.

[0202] Examples of the aforementioned vanadium compounds include vanadium pentoxide, metavanadate, ammonium metavanadate, vanadium trichloride, vanadium trioxide, vanadium dioxide, magnesium vanadate, vanadium acetylacetonate, and vanadium acetylacetonate. Among these vanadium compounds, tetravalent vanadium compounds or tetravalent vanadium compounds obtained through reduction or oxidation are particularly preferred.

[0203] Furthermore, the vanadium compound content in the aforementioned chemically converted coating is 2–10% by mass. This is because if the vanadium compound content in the aforementioned chemically converted coating is less than 2% by mass, the corrosion resistance will decrease due to insufficient inhibitory effect. On the other hand, if the vanadium compound content exceeds 10% by mass, the moisture resistance of the chemically converted coating will decrease.

[0204] The zirconium compound is included in the above-mentioned chemical conversion coating. Through reaction with the plated metal or coexistence with the resin component, it is expected that the strength and corrosion resistance of the chemical conversion coating will be improved. In addition, the zirconium compound itself helps to form a dense chemical conversion coating with good coating properties, so a barrier effect can be expected.

[0205] Examples of zirconium compounds include zirconium sulfate, zirconium carbonate, zirconium nitrate, zirconium lactate, zirconium acetate, and zirconium chloride neutral salts.

[0206] Furthermore, the zirconium compound content in the aforementioned chemically converted coating is 40–60% by mass. This is because if the zirconium compound content in the aforementioned chemically converted coating is less than 40% by mass, it leads to a decrease in the strength and corrosion resistance of the chemically converted coating. If the zirconium compound content exceeds 60% by mass, the chemically converted coating becomes brittle, and under strict processing conditions, the chemically converted coating will be damaged and peeled off.

[0207] The aforementioned fluorine compound is included in the chemical conversion coating and acts as an adhesive agent to the coated coating. As a result, the corrosion resistance of the chemical conversion coating is improved.

[0208] As the aforementioned fluorine compounds, fluoride salts such as ammonium salts, sodium salts, and potassium salts, or fluoride compounds such as ferrous fluoride and ferric fluoride can be used. Among these, fluoride salts such as ammonium fluoride, sodium fluoride, and potassium fluoride are preferred.

[0209] Furthermore, the content of fluorine compounds in the aforementioned chemically converted coating is 0.5% to 5% by mass. This is because if the content of fluorine compounds in the aforementioned chemically converted coating is less than 0.5% by mass, sufficient adhesion in the processing section cannot be obtained, and if the content of fluorine compounds exceeds 5% by mass, the moisture resistance of the chemically converted coating decreases.

[0210] Furthermore, there is no particular limitation on the amount of the chemical conversion coating applied. For example, from the viewpoint of more reliably ensuring corrosion resistance and improving the adhesion of the chemical conversion coating, it is preferable to set the amount of the chemical conversion coating applied to be 0.025 to 0.5 g / m. 2 The adhesion amount of the above chemical conversion film was set to 0.025 g / m. 2 The above measures ensure corrosion resistance more reliably by setting the adhesion amount of the chemical conversion coating to 0.5 g / m. 2 This allows for the suppression of chemical conversion coating peeling.

[0211] The amount of the aforementioned chemical conversion coating can be determined by appropriately selecting a conventional method, such as determining the amount of elements present in the coating by fluorescence X-ray analysis of the coating.

[0212] It should be noted that the method used to form the above-mentioned chemical conversion coating is not particularly limited, and can be appropriately selected according to the required performance and manufacturing equipment. For example, it can be formed by continuously coating the above-mentioned coating film with a chemical conversion treatment solution using a roller coater or the like, and then drying it at a peak metal temperature (PMT) of about 60 to 200°C using hot air, induction heating, or the like. In addition to using a roller coater, the coating of the above-mentioned chemical conversion treatment solution can also be carried out by known methods such as airless spraying, electrostatic spraying, or curtain flow coating machines. Furthermore, as long as the above-mentioned chemical conversion coating contains the above-mentioned resin and the above-mentioned metal compound, it can be either a single-layer film or a multi-layer film, without particular limitation.

[0213] • Coating

[0214] As described above, the coated steel sheet of the present invention has a coating film formed directly or through a chemical conversion coating on the plated film, the coating film having at least a primer coating film.

[0215] Furthermore, in this invention, the primer coating film contains a polyester resin having urethane bonds and an inorganic compound comprising vanadium compounds, phosphoric acid compounds and magnesium oxide.

[0216] The primer coating containing the aforementioned polyester resin with urethane bonds and the aforementioned inorganic compound can improve the adhesion and corrosion resistance of the coating.

[0217] The aforementioned primer coating contains a polyester resin with urethane bonds as its main component. This urethane-bonded polyester resin combines flexibility and strength, thus preventing cracking during processing. It also exhibits high affinity for chemically converted coatings containing urethane resins, thereby particularly contributing to improved corrosion resistance of the processed area.

[0218] It should be noted that the term "main component" here refers to the component with the highest content among all components in the primer coating.

[0219] As the polyester resin having the aforementioned urethane bonds, known resins such as resins obtained by reacting a polyester polyol with a diisocyanate or polyisocyanate having two or more isocyanate groups can be used. Alternatively, a resin obtained by reacting the aforementioned polyester polyol with the aforementioned diisocyanate or the aforementioned polyisocyanate in an excess of hydroxyl groups (urethane-modified polyester resin) can be used, which is then cured using blocked polyisocyanate.

[0220] It should be noted that the aforementioned polyester polyols can be obtained by a known method utilizing the dehydration condensation reaction of polyol components and polyacid components.

[0221] Examples of the aforementioned polyols include diols and polyols with three or more components. Examples of diols include ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, neopentyl glycol, hexanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2-butyl-2-ethyl-1,3-propanediol, methylpropanediol, cyclohexanediol, and 3,3-diethyl-1,5-pentanediol. Examples of polyols with three or more components include glycerol, trimethylolethane, trimethylolpropane, pentaerythritol, and dipentaerythritol. These polyols can be used alone or in combination of two or more.

[0222] The aforementioned polycarboxylic acids are typically polycarboxylic acids, but monocarboxylic acids may be used in combination as needed. Examples of such polycarboxylic acids include phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, 4-methylhexahydrophthalic acid, bicyclo[2,2,1]heptane-2,3-dicarboxylic acid, trimellitic acid, adipic acid, sebacic acid, succinic acid, azelaic acid, fumaric acid, maleic acid, itaconic acid, pyromellitic acid, dimer acids, and their anhydrides, as well as 1,4-cyclohexanedicarboxylic acid, isophthalic acid, tetrahydroisophthalic acid, hexahydroisophthalic acid, and hexahydroterephthalic acid. These polycarboxylic acids can be used alone or in combination of two or more.

[0223] Examples of the aforementioned polyisocyanates include aliphatic diisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and dimer diisocyanate; aromatic diisocyanates such as diphenylmethylene diisocyanate (XDI), isophthalic diisocyanate, toluene diisocyanate (TDI), and 4,4-diphenylmethane diisocyanate (MDI); and cyclic aliphatic diisocyanates such as isophorone diisocyanate, hydrogenated XDI, hydrogenated TDI, and hydrogenated MDI, as well as their adducts, biuret forms, and isocyanurate forms. These polyisocyanates can be used alone or in combination of two or more.

[0224] In addition, the hydroxyl value of the polyester resin having urethane bonds is not particularly limited, but from the viewpoint of solvent resistance and processability, it is preferably 5 to 120 mgKOH / g, more preferably 7 to 100 mgKOH / g, and even more preferably 10 to 80 mgKOH / g.

[0225] Furthermore, from the perspectives of solvent resistance and processability, the number average molecular weight of the aforementioned polyester resin with urethane bonds is preferably 500 to 15,000, more preferably 700 to 12,000, and even more preferably 800 to 10,000.

[0226] The content of the polyester resin with urethane bonds in the primer film is preferably 40 to 88% by mass. If the content of the polyester resin with urethane bonds is less than 40% by mass, its adhesive function as a primer film may be reduced. On the other hand, if the content of the polyester resin with urethane bonds exceeds 88% by mass, the function of the inorganic substances, such as the inhibitory effect, may be reduced.

[0227] Vanadium compounds, as one of the aforementioned inorganic compounds, function as inhibitors. Examples of such vanadium compounds include vanadium pentoxide, metavanadate, ammonium metavanadate, vanadium trichloride, vanadium trioxide, vanadium dioxide, magnesium vanadate, vanadium acetylacetonate, and vanadium acetylacetonate. Among these, tetravalent vanadium compounds or tetravalent vanadium compounds obtained through reduction or oxidation are preferred.

[0228] The vanadium compound added to the primer coating can be the same as or different from the vanadium compound added to the chemically converted coating. It is believed that the vanadate compound reacts with vanadate ions gradually dissolved from externally infiltrated moisture, forming a well-adhesive passive coating that protects the exposed metal and provides rust prevention.

[0229] The content of the vanadium compound in the primer film is not particularly limited, but from the viewpoint of achieving both corrosion resistance and moisture resistance, it is preferably 4 to 20% by mass. If the content of the vanadium compound is less than 4% by mass, the inhibitory effect will decrease, which may lead to a decrease in corrosion resistance. If the content of the vanadium compound exceeds 20% by mass, it may lead to a decrease in the moisture resistance of the primer film.

[0230] Phosphoric acid compounds, including one of the aforementioned inorganic compounds, also function as inhibitors. Examples of such phosphoric acid compounds include phosphoric acid, ammonium salts of phosphoric acid, alkali metal salts of phosphoric acid, and alkaline earth metal salts of phosphoric acid. Alkali metal salts of phosphoric acid, such as calcium phosphate, are particularly preferred.

[0231] The content of the aforementioned phosphoric acid compound in the primer film is not particularly limited, but from the viewpoint of achieving both corrosion resistance and moisture resistance, it is preferably 4 to 20% by mass. If the content of the aforementioned phosphoric acid compound is less than 4% by mass, the inhibitory effect will decrease, which may lead to a decrease in corrosion resistance. If the content of the aforementioned phosphoric acid compound exceeds 20% by mass, it may lead to a decrease in the moisture resistance of the primer film.

[0232] Magnesium oxide, one of the aforementioned inorganic compounds, produces Mg-containing products due to initial corrosion. As a poorly soluble magnesium salt, it has the effect of stabilization and improved corrosion resistance.

[0233] The content of magnesium oxide in the aforementioned primer coating is not particularly limited, but from the viewpoint of achieving both corrosion resistance and corrosion resistance of the processed part, it is preferably 4 to 20% by mass. If the content of magnesium oxide is less than 4% by mass, the aforementioned effect is reduced, which may lead to a decrease in corrosion resistance. If the content of magnesium oxide exceeds 20% by mass, the flexibility of the aforementioned primer coating is reduced, and sometimes the corrosion resistance of the processed part is reduced.

[0234] In addition, the aforementioned primer coating may also contain components other than the polyester resin with urethane bonds and inorganic compounds mentioned above.

[0235] For example, crosslinking agents used in forming primer films can be cited. These crosslinking agents react with the aforementioned polyester resins having urethane bonds to form crosslinked coatings; examples include... Azoline compounds, epoxy compounds, melamine compounds, isocyanate compounds, carbodiimide compounds, silane coupling agent compounds, etc., and two or more crosslinking agents can be used in combination. Among these, from the viewpoint of corrosion resistance of the processed part of the obtained coated steel sheet, blocked polyisocyanate compounds are preferred. Examples of blocked polyisocyanates include those in which the isocyanate groups of the polyisocyanate compound are blocked using alcohols such as butanol, oximes such as methyl ethyl ketone oxime, lactams such as ε-caprolactam, diketones such as acetoacetate diester, imidazoles such as imidazole and 2-ethylimidazole, or phenols such as m-cresol.

[0236] Furthermore, the aforementioned primer coating may also contain various well-known components commonly used in the coatings industry, as needed. Specifically, examples include various surface modifiers such as leveling agents and defoamers, dispersants, anti-settling agents, UV absorbers, light stabilizers, silane coupling agents, titanate coupling agents, and other additives, coloring pigments, filler pigments, gloss materials, curing catalysts, and organic solvents.

[0237] The thickness of the primer film is preferably 1.5 μm or more. This is because by making the thickness of the primer film 1.5 μm or more, it is possible to more reliably obtain the effect of improved corrosion resistance and improved adhesion to the topcoat film formed on the chemically converted film and the primer film.

[0238] There are no particular limitations on the method used to form the primer film described above. Furthermore, for the coating method of the coating composition constituting the primer film, it is preferable to apply the coating composition using a roller coater, curtain coating, or similar methods. After applying the coating composition, sintering can be performed using heating methods such as hot air heating, infrared heating, or induction heating to obtain the primer film. The sintering process typically sets the maximum plate temperature to approximately 180–270°C and can be carried out within this temperature range for approximately 30 seconds to 3 minutes.

[0239] Furthermore, for the coating film constituting the coated steel sheet of the present invention, it is preferable to further form an upper coating film on the aforementioned primer coating film.

[0240] The above-mentioned top coating film can not only give the coated steel plate color, gloss, and surface appearance, but also improve various properties such as processability, weather resistance, chemical resistance, pollution resistance, water resistance, and corrosion resistance.

[0241] There are no particular limitations on the composition of the above-mentioned top coating film. The material, thickness, etc. can be appropriately selected according to the required performance.

[0242] For example, the above-mentioned topcoat film can be formed using polyester resin-based coatings, silicone polyester resin-based coatings, polyurethane resin-based coatings, acrylic resin-based coatings, fluoropolymer resin-based coatings, etc.

[0243] Furthermore, the aforementioned top coating film may contain appropriate amounts of titanium dioxide, iron oxide red, mica, carbon black, or other various coloring pigments; aluminum powder, mica, and other metallic pigments; filler pigments composed of carbonates, sulfates, etc.; various microparticles such as silica particles, nylon resin beads, and acrylic resin beads; curing catalysts such as p-toluenesulfonic acid and dibutyltin dilaurate; wax; and other additives.

[0244] Furthermore, from the viewpoint of achieving both appearance and processability, the thickness of the aforementioned top coating is preferably 5 to 30 μm. When the thickness of the aforementioned top coating is 5 μm or more, the color appearance can be stabilized more reliably, and when the thickness of the aforementioned top coating is 30 μm or less, the reduction in processability (the generation of cracks in the top coating) can be suppressed more reliably.

[0245] The coating method for forming the above-mentioned top coating film is not particularly limited. For example, the coating composition can be applied using a roller coater, curtain coating, or other methods. After applying the coating composition, sintering can be performed by heating means such as hot air heating, infrared heating, or induction heating to form the top coating film. The sintering process typically sets the maximum plate temperature to about 180–270°C and can be carried out within this temperature range for about 30 seconds to 3 minutes.

[0246] Furthermore, the coated steel sheet of the present invention is similar to the hot-dip galvanized Al-Zn-Si-Mg steel sheet of the present invention described above, characterized in that, within a range of 50 mm removed from both ends of the steel sheet surface (coating surface), the height difference of the steel sheet surface for every 1 mm length is less than 10 μm.

[0247] When the height difference on the surface of the coating is less than 10 μm, there are no wrinkle-like defects, and an excellent surface appearance can be obtained.

[0248] As described above, the aforementioned wrinkled defect refers to a defect where the surface of the coating film becomes wrinkled and uneven due to Mg-based oxides. This appears as a white striped pattern on the coating film surface. Therefore, suppressing wrinkled defects means making the striped pattern visually undetectable. Thus, by controlling the height difference within a 1mm range on the steel plate surface, i.e., the coating surface, to within 10μm, the striped pattern becomes visually undetectable, resulting in an excellent surface appearance. From the same perspective, the height difference within a 1mm range on the steel plate surface is preferably within 5μm.

[0249] It should be noted that the above-mentioned steel plate surface refers to the outermost surface of the steel plate, and in the case of coated steel plates, it refers to the coating surface.

[0250] Here, the height difference on the steel plate surface refers to the difference between the height of the highest point and the lowest point on the steel plate (on the coating) when the direction perpendicular to the surface of the base steel plate (the film thickness direction) is set as the height.

[0251] In addition, the method for obtaining the height difference within a 1mm range on the coating surface is similar to that for the coated surface described above. It can be obtained by using a laser microscope to measure the height difference within a 1mm range at any 100 locations on the coated steel plate and calculating the average of the measured values.

[0252] Furthermore, within a 50mm area removed from both ends of the aforementioned steel plate surface, as a reason for controlling the height difference of the steel plate surface, it is generally difficult to control the amount of coating in the center of the steel plate at both ends, and the cooling rates are also different, thus reducing the likelihood of wrinkle-like defects. In addition, this is because the ends of such steel plates are often trimmed before use, so surface appearance is hardly an issue.

[0253] For the method of controlling the height difference of the coating surface per 1 mm length of the above-mentioned steel plate surface to be less than 10 μm, it is important to suppress the height difference of the above-mentioned coating surface. This can be achieved by adjusting the content ratio of Mg to Mn in the above-mentioned coating film, or by performing other surface treatments to suppress the height difference.

[0254] The method for manufacturing coated steel sheets of the present invention is a method for manufacturing coated steel sheets on which a coating is formed directly or indirectly through chemical conversion of a coated film.

[0255] Furthermore, in the manufacturing method of the present invention, the aforementioned chemical conversion coating contains a resin component and an inorganic compound. The resin component contains a total of 30-50% by mass of (a): an anionic polyurethane resin having ester bonds and (b): an epoxy resin having a bisphenol backbone. The content ratio of (a) to (b) ((a):(b)) is in the range of 3:97 to 60:40 by mass. The aforementioned inorganic compound contains 2-10% by mass of a vanadium compound, 40-60% by mass of a zirconium compound, and 0.5-5% by mass of a fluorine compound.

[0256] The aforementioned coating film has at least a primer film containing a polyester resin and an inorganic compound, wherein the polyester resin has urethane bonds, and the inorganic compound includes a vanadium compound, a phosphoric acid compound, and magnesium oxide.

[0257] The formation of the above-mentioned coating film includes a hot-dip coating process, in which the base steel plate is immersed in a coating bath containing Al: 45-65% by mass, Si: 1.0-4.0% by mass and Mg: 1.0-10.0% by mass, with the remainder consisting of Zn and unavoidable impurities.

[0258] It should be noted that the conditions for the above-mentioned hot-dip galvanizing process are the same as those described in the hot-dip galvanized Al-Zn-Si-Mg steel sheet of the present invention.

[0259] Example

[0260] [Example 1: Samples 1-28]

[0261] Samples 1 to 28 of hot-dip Al-Zn-Si-Mg series steel sheets were prepared by using a 0.8 mm thick cold-rolled steel sheet manufactured using conventional methods as the base steel sheet, and by performing degreasing, annealing and plating treatments using a continuous hot-dip plating equipment.

[0262] It should be noted that the composition of the plating bath used in the manufacture of hot-dip Al-Zn-Si-Mg series steel sheets was varied within the range of Al: 45–65 wt%, Si: 1.5–2.5 wt%, Mg: 1.0–4.5 wt%, Mn: 0.00–1.0 wt%, Sr: 0.00–1.0 wt%, B: 0.00–0.05 wt%, Ca: 0.00–1.0 wt%, Cr: 0.00–0.2 wt%, Ti: 0.00–0.2 wt%, and V: 0.00–0.2 wt%. Furthermore, the bath temperature was controlled at 590°C when Al was 45–55 wt% and at 630°C when Al was 65 wt%, and the immersion temperature of the base steel sheet was controlled to be the same as the plating bath temperature. Furthermore, the plating process is carried out under conditions where the board temperature is cooled to 520–500°C in 3 seconds.

[0263] In addition, regarding the adhesion amount of the coating, it was controlled at 85±5 g / m² per single side in samples 1-23 and 27-28. 2 In samples 24–26, the concentration was controlled at 50–125 g / m² per single side. 2 .

[0264] <Evaluation>

[0265] The following evaluations were conducted on the samples of hot-dip galvanized Al-Zn-Si-Mg steel sheets obtained as described above. The evaluation results are shown in Table 1.

[0266] (1) Composition of the coating (adhesion amount, composition, X-ray diffraction intensity)

[0267] A 100mm diameter hole was punched in each plated sample. After sealing the non-test surfaces with tape, the plating was dissolved and peeled off using a mixture of hydrochloric acid and hexamethylenetetramine as specified in JIS H0401:2013. The amount of plating film attached was calculated based on the mass difference of the samples before and after peeling. The calculated results, i.e., the amount of plating film attached, are shown in Table 1.

[0268] The stripping solution was then filtered, and the filtrate and solid components were analyzed separately. Specifically, the components other than insoluble Si were quantified by performing ICP emission spectroscopy analysis on the filtrate.

[0269] In addition, the solid components were dried and ashed in a furnace at 650°C, and then dissolved by adding sodium carbonate and sodium tetraborate. The melt was further dissolved with hydrochloric acid, and the solution was analyzed by ICP emission spectroscopy to quantify the insoluble Si. The Si concentration in the coated film was calculated by adding the soluble Si concentration obtained from filtrate analysis to the insoluble Si concentration obtained from solid component analysis. The calculated results, i.e., the composition of the resulting coated film, are shown in Table 1.

[0270] In addition, after cutting each sample into 100mm×100mm dimensions, the coating on the evaluation surface was mechanically scraped off until the substrate steel plate was exposed. The obtained powder was thoroughly mixed, and 0.3g was taken out. The above powder was qualitatively analyzed using an X-ray diffraction apparatus (SmartLab manufactured by Rigaku Co., Ltd.) under the following conditions: X-ray: Cu-Kα (wavelength = 1.54178Å), Kβ ray removal: Ni filter, tube voltage: 40kV, tube current: 30mA, scan speed: 4° / min, sampling interval: 0.020°, divergence slit: 2 / 3°, Soler slit: 5°, detector: high-speed one-dimensional detector (D / teX Ultra). The intensity obtained by subtracting the base intensity from each peak intensity is taken as the diffraction intensity (cps). The diffraction intensity of the (111) plane of Mg2Si (interface spacing d = 0.3668 nm) and the diffraction intensity of the (111) plane of Si (interface spacing d = 0.3135 nm) are measured.

[0271] (2) Surface appearance

[0272] (2-1) Wrinkled defects

[0273] The surface appearance of each hot-dip Al-Zn-Si-Mg steel sheet sample was visually inspected to confirm the presence or absence of wrinkle-like defects. Furthermore, for each sample, 100 random locations were selected from the portion after removing 50mm from both ends of the steel strip. The height difference of the coated surface within a 1mm length was measured using a laser microscope (Keyence Corporation "VK-X3000"). The averaged value was used to quantify the surface shape. Based on the presence or absence of wrinkle-like defects and the surface shape, the state of wrinkle-like defect formation was evaluated according to the following criteria.

[0274] ◎: No wrinkled defects were observed (height difference less than 5μm).

[0275] 〇: No wrinkled defects were observed (height difference less than 10μm).

[0276] ×: Wrinkled defects were observed (height difference exceeding 10μm).

[0277] (2-2) Scum defects

[0278] The surface appearance of each sample of the hot-dip galvanized Al-Zn-Si-Mg steel sheet was confirmed by visual inspection, and the presence or absence of slag defects was evaluated according to the following criteria.

[0279] ○: No granular scum was observed adhering to the surface.

[0280] ×: Observation of granular scum adhesion

[0281] (3) Evaluation of corrosion resistance

[0282] After cutting the obtained hot-dip galvanized Al-Zn-Si-Mg steel sheet samples into 120mm × 120mm sizes, the evaluation surface, within 10mm of each edge, as well as the end faces and non-evaluation surfaces of the samples, were sealed with tape, leaving the evaluation surface exposed at a size of 100mm × 100mm. This sample in this state was used as the evaluation sample. It should be noted that three identical samples were made for this evaluation.

[0283] For the three evaluation samples prepared as described above, the Japanese Automotive Standard Composite Cycle Test (JASO-CCT) was performed. The corrosion acceleration test was carried out from wet to 300 cycles, and then the corrosion reduction of each sample was determined using the methods described in JIS Z 2383 and ISO 8407, and evaluated according to the following criteria.

[0284] ◎: The corrosion loss of all three samples was 45 g / m³. 2 the following

[0285] ○: The corrosion loss of all three samples was 90 g / m³. 2 the following

[0286] ×: Corrosion loss exceeding 90 g / m² for more than one sample 2

[0287]

[0288] As can be seen from the results in Table 1, the surface appearance of each sample in the present invention is superior to that of each sample in the comparative examples.

[0289] [Example 2: Samples 1-34]

[0290] (1) Samples 1 to 34 of hot-dip Al-Zn-Si-Mg series steel sheets were prepared by using a cold-rolled steel sheet with a thickness of 0.8 mm manufactured by conventional methods as the base steel sheet, and by using a continuous hot-dip galvanizing equipment for degreasing, annealing and galvanizing treatment.

[0291] It should be noted that the composition of the plating bath used in the manufacture of hot-dip Al-Zn-Si-Mg series steel sheets was varied within the range of Al: 45–65 wt%, Si: 1.5–2.5 wt%, Mg: 1.0–4.5 wt%, Mn: 0.00–1.0 wt%, Sr: 0.00–1.0 wt%, B: 0.00–0.05 wt%, Ca: 0.00–1.0 wt%, Cr: 0.00–0.2 wt%, Ti: 0.00–0.2 wt%, and V: 0.00–0.2 wt%. Furthermore, the bath temperature was controlled at 590°C when Al was 45–55 wt% and at 630°C when Al was 65 wt%, and the immersion temperature of the base steel sheet was controlled to be the same as the plating bath temperature. Furthermore, the plating process is carried out under conditions where the board temperature is cooled to 520–500°C in 3 seconds.

[0292] In addition, regarding the adhesion amount of the coating, it was controlled to be 85±5 g / m² per single side in samples 1–29 and 33–34. 2 In samples 30-32, the concentration was controlled at 50-125 g / m² per single side. 2 .

[0293] (2) Then, chemical conversion treatment solution was applied to the coating film of each sample of hot-dip Al-Zn-Si-Mg steel plate using a bar coater and dried using a hot air furnace (heating rate: 60℃ / s, PMT: 120℃) to form a chemical conversion coating film, and the surface-treated steel plate samples shown in Table 2 were produced.

[0294] It should be noted that the chemical conversion treatment solutions are prepared by dissolving each component in water as a solvent to form surface treatment solutions A to F. The types of components (resins, metal compounds) contained in the surface treatment solutions are described below.

[0295] (Resin)

[0296] Carbamate resins: SUPERFLEX 130, SUPERFLEX 126 (Daiichi Kogyo Pharmaceutical Co., Ltd.)

[0297] Acrylic resin: VONCOAT EC-740EF (DIC Corporation)

[0298] (Metal compounds)

[0299] Compound P: Aluminum dihydrogen tripolyphosphate

[0300] Si compounds: silicon dioxide

[0301] Compound V: Sodium metavanadate

[0302] Mo compound: molybdic acid

[0303] Zr compounds: potassium zirconium carbonate

[0304] The composition of the prepared chemical conversion treatment solutions A to F and the amount of chemical conversion film formed are shown in Table 1. It should be noted that the concentrations of each component in Table 1 of this specification are the concentrations of the solid components (mass %).

[0305]

[0306] <Evaluation>

[0307] The following evaluations were conducted on the surface-treated steel sheets obtained as described above. The evaluation results are shown in Table 3.

[0308] (1) Composition of the coating (adhesion amount, composition, X-ray diffraction intensity)

[0309] After plating, 100mm φ holes were punched into each sample. The non-test surfaces were sealed with tape, and the plating was dissolved and peeled off using a mixture of hydrochloric acid and hexamethylenetetramine as specified in JIS H 0401:2013. The amount of plating film adhered was calculated based on the mass difference between the samples before and after peeling. The calculated results, i.e., the amount of plating film adhered, are shown in Table 3.

[0310] The stripping solution was then filtered, and the filtrate and solid components were analyzed separately. Specifically, the components other than insoluble Si were quantified by performing ICP emission spectroscopy on the filtrate.

[0311] In addition, the solid components were dried and ashed in a furnace at 650°C, and then dissolved by adding sodium carbonate and sodium tetraborate. The dissolved product was further dissolved in hydrochloric acid, and the solution was analyzed by ICP emission spectroscopy to quantify the insoluble Si. The Si concentration in the coated film was calculated by adding the soluble Si concentration obtained from the filtrate analysis to the insoluble Si concentration obtained from the solid component analysis. The calculated results, i.e., the composition of the resulting coated film, are shown in Table 3.

[0312] In addition, after cutting each sample into 100mm×100mm sizes, the coating on the evaluation surface was mechanically scraped off until the base steel plate was exposed. After thoroughly mixing the obtained powder, 0.3g was taken out and qualitative analysis of the powder was performed using an X-ray diffraction apparatus (SmartLab manufactured by Rigaku Co., Ltd.) under the following conditions: X-ray: Cu-Kα (wavelength = 1.54178Å), Kβ line removal: Ni filter, tube voltage: 40kV, tube current: 30mA, scan speed: 4° / min, sampling interval: 0.020°, diffusion slit: 2 / 3°, Soler slit: 5°, detector: high-speed one-dimensional detector (D / teX Ultra). The intensity obtained by subtracting the base intensity from each peak intensity was used as the diffraction intensity (cps). The diffraction intensities of the (111) plane of Mg2Si (interface spacing d = 0.3668 nm) and the diffraction intensities of the (111) plane of Si (interface spacing d = 0.3135 nm) were measured. The measurement results are shown in Table 3.

[0313] (2) Surface appearance

[0314] (2-1) Wrinkled defects

[0315] The surface appearance of each hot-dip galvanized Al-Zn-Si-Mg steel sheet and surface-treated steel sheet sample was visually inspected to confirm the presence or absence of wrinkle-like defects. Furthermore, for each sample, 100 random locations were selected from the portion after removing 50 mm from both ends of the steel strip. The height difference of the coated film surface within a 1 mm length was measured using a laser microscope (Keyence Corporation "VK-X3000"). The averaged value was used to quantify the surface shape. Based on the presence or absence of wrinkle-like defects and the surface shape, the state of wrinkle-like defect formation was evaluated according to the following criteria.

[0316] ◎: No wrinkled defects were observed (height difference less than 5μm).

[0317] 〇: No wrinkled defects were observed (height difference less than 10μm).

[0318] ×: Wrinkled defects were observed (height difference exceeding 10μm).

[0319] (2-2) Scum defects

[0320] The surface appearance of each sample of the obtained hot-dip Al-Zn-Si-Mg series steel sheet was confirmed by visual observation, and the presence or absence of slag defects was evaluated according to the following criteria.

[0321] ○: No granular scum was observed adhering to the surface.

[0322] ×: Observation of granular scum adhesion

[0323] (3) Resistance to white rust

[0324] After cutting the hot-dip Al-Zn-Si-Mg series steel plates and surface-treated steel plates into 120mm×120mm sizes, the evaluation object surface within 10mm of each edge, as well as the end face of the sample and the non-evaluation object surface, are sealed with tape, exposing the evaluation object surface in a 100mm×100mm size. The sample in this state is used as the evaluation sample.

[0325] Using the above-mentioned evaluation samples, a 90-hour salt spray test as described in JIS Z 2371 was performed, and the evaluation was conducted according to the following criteria.

[0326] ◎: No white rust on the flat surface.

[0327] ○: The area of ​​white rust formation on the flat plate is less than 10%.

[0328] ×: The area of ​​white rust formation on the flat plate is over 10%.

[0329] (4) Evaluation of corrosion resistance

[0330] After cutting the obtained hot-dip galvanized Al-Zn-Si-Mg steel sheets and surface-treated steel sheets into 120mm × 120mm samples, the evaluation surface, within 10mm of each edge, as well as the end faces and non-evaluation surfaces of the samples, were sealed with tape, leaving the evaluation surface exposed at a size of 100mm × 100mm. This sample was then used as the evaluation sample. It should be noted that three identical samples were made for this evaluation.

[0331] For the three evaluation samples prepared as described above, a combined cycle test according to Japanese automotive standards (JASO-CCT) was performed. The corrosion acceleration test was carried out from wet conditions for 300 cycles, after which the corrosion reduction of each sample was determined using the methods described in JIS Z 2383 and ISO 8407, and the evaluation was conducted according to the following criteria.

[0332] ◎: The corrosion loss of all three samples was 30 g / m³. 2 the following

[0333] ○: The corrosion loss of all three samples was 70 g / m³. 2 the following

[0334] ×: Corrosion loss exceeding 70 g / m² for more than one sample 2

[0335]

[0336] As can be seen from the results in Table 3, the surface appearance of each sample in the present invention is superior to that of each sample in the comparative examples.

[0337] [Example 3: Samples 1-37]

[0338] (1) Using a cold-rolled steel sheet with a thickness of 0.8 mm manufactured by conventional methods as the base steel sheet, degreasing, annealing and plating were performed using a continuous hot-dip galvanizing equipment, thereby producing samples 1 to 37 of hot-dip Al-Zn-Si-Mg series steel sheets under the conditions shown in Table 5.

[0339] It should be noted that the composition of the plating bath used in the manufacture of hot-dip Al-Zn-Si-Mg series steel sheets was varied within the range of Al: 45–65 wt%, Si: 1.5–2.5 wt%, Mg: 1.0–4.5 wt%, Mn: 0.00–1.0 wt%, Sr: 0.00–1.0 wt%, B: 0.00–0.05 wt%, Ca: 0.00–1.0 wt%, Cr: 0.00–0.2 wt%, Ti: 0.00–0.2 wt%, and V: 0.00–0.2 wt%. Furthermore, the bath temperature was controlled at 590°C when Al was 45–55 wt% and at 630°C when Al was 65 wt%, and the immersion temperature of the base steel sheet was controlled to be the same as the plating bath temperature. Furthermore, the plating process is carried out under conditions where the board temperature is cooled to 520–500°C in 3 seconds.

[0340] In addition, regarding the adhesion amount of the coating, it was controlled to be 85±5 g / m² per single side in samples 1–32 and 36–37. 2 In samples 33–35, the concentration was controlled at 50–125 g / m² per single side. 2 .

[0341] (2) Then, the chemical conversion treatment solution shown in Table 4 was applied to the coating film of each sample of the hot-dip galvanized steel sheet using a bar coater, and dried in a hot air drying oven (to a plate temperature of 90°C) to form an adhesion weight of 0.1 g / m 2 Chemical conversion treatment of the membrane.

[0342] It should be noted that the chemical conversion treatment solution used is a solution with a pH of 8-10 prepared by dissolving the components in water as a solvent. The types of components (resin components, inorganic compounds) contained in the chemical conversion treatment solution are described below.

[0343] (Resin composition)

[0344] Resin A: A mixture of (a) anionic polyurethane resin with ester bonds ("SUPERFLEX 210" manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.) and (b) epoxy resin with a bisphenol backbone ("Yuka Resin RE-1050" manufactured by Yoshimura Oil Chemical Co., Ltd.) in a mass ratio of (a):(b) = 50:50.

[0345] Resin B: Acrylic resin (manufactured by DIC Corporation, "VONCOAT EC-740EF")

[0346] (Inorganic compounds)

[0347] Vanadium compounds: Organovanadium compounds chelated with acetylacetone

[0348] Zirconium compounds: ammonium zirconium carbonate

[0349] Fluorine compounds: ammonium fluoride

[0350] (3) Then, on the chemical conversion coating formed as described above, a primer coating is applied using a bar coater, and sintering is performed at a steel plate temperature of 230°C and a sintering time of 35 seconds, thereby forming a primer coating film with the composition shown in Table 4. Then, on the primer coating film formed as described above, a topcoat coating composition is applied using a bar coater, and sintering is performed at a steel plate temperature of 230°C to 260°C and a sintering time of 40 seconds, thereby forming a topcoat film with the resin conditions and film thickness shown in Table 4, and coated steel plates for each sample are produced.

[0351] It should be noted that the primer coating is obtained by mixing the various components and stirring in a ball mill for approximately 1 hour. The resin components and inorganic compounds constituting the primer film use the following substances.

[0352] (Resin composition)

[0353] Resin α: A resin obtained by curing a urethane-modified polyester resin (obtained by reacting 455 parts by mass of polyester resin and 45 parts by mass of isophorone diisocyanate, with an acid value of 3, a number-average molecular weight of 5600, and a hydroxyl value of 36) using a blocked isocyanate.

[0354] It should be noted that the urethane-modified polyester resin is prepared under the following conditions. In a flask equipped with a stirrer, distillation column, water separator, cooling pipe, and thermometer, 320 parts by mass of isophthalic acid, 200 parts by mass of adipic acid, 60 parts by mass of trimethylolpropane, and 420 parts by mass of cyclohexanediethanol are added. The mixture is heated and stirred, allowing the generated condensation water to distill out of the system, while the temperature is increased from 160°C to 230°C at a constant rate over 4 hours. After reaching 230°C, 20 parts by mass of xylene are slowly added. The condensation reaction continues while maintaining the temperature at 230°C. The reaction is terminated when the acid value drops below 5. After cooling to 100°C, 120 parts by mass of Solvesso 100 (manufactured by ExxonMobil, trade name, a high-boiling-point aromatic hydrocarbon solvent) and 100 parts by mass of butyl cellosolve are added, thereby obtaining a polyester resin solution.

[0355] Resin β: Carbamate-cured polyester resin (manufactured by Kansai Paint Co., Ltd., "Evaclad 4900")

[0356] (Inorganic compounds)

[0357] Vanadium compounds: magnesium vanadate

[0358] Phosphoric acid compound: calcium phosphate

[0359] Magnesium oxide compounds: magnesium oxide

[0360] In addition, for the resins used in the top coating shown in Table 4, the following coatings are used.

[0361] Resin I: Melamine-cured polyester coating (BASF Japan Co., Ltd. "Precolor HD0030HR")

[0362] Resin II: An organosol-based sintered fluoropolymer coating with a polyvinylidene fluoride to acrylic resin mass ratio of 80:20 (manufactured by BASF Japan Co., Ltd., "Precolor No. 8800HR").

[0363]

[0364] <Evaluation>

[0365] The following evaluations were conducted on the samples of coated steel sheets obtained as described above. The evaluation results are shown in Table 5.

[0366] (1) Composition of the coating (adhesion amount, composition, X-ray diffraction intensity)

[0367] After coating, 100mm φ holes were punched into each sample. The non-test surfaces were sealed with tape, and the coating was dissolved and peeled off using a mixture of hydrochloric acid and hexamethylenetetramine as specified in JIS H 0401:2013. The amount of coating adhesion was calculated based on the mass difference between the samples before and after peeling. The calculated results, i.e., the amount of coating adhesion, are shown in Table 5.

[0368] The stripping solution was then filtered, and the filtrate and solid components were analyzed separately. Specifically, the components other than insoluble Si were quantified by performing ICP emission spectroscopy on the filtrate.

[0369] In addition, the solid components were dried and ashed in a furnace at 650°C, and then dissolved by adding sodium carbonate and sodium tetraborate. The dissolved product was further dissolved in hydrochloric acid, and the solution was analyzed by ICP emission spectroscopy to quantify the insoluble Si. The Si concentration in the coated film was calculated by adding the soluble Si concentration obtained from the filtrate analysis to the insoluble Si concentration obtained from the solid component analysis. The calculated results, i.e., the composition of the resulting coated film, are shown in Table 5.

[0370] In addition, after cutting each sample into 100mm×100mm dimensions, the coating on the evaluation surface was mechanically scraped off until the substrate steel plate was exposed. The resulting powder was thoroughly mixed, and 0.3g was taken out. The powder was then subjected to qualitative analysis using an X-ray diffraction apparatus (SmartLab manufactured by Rigaku Co., Ltd.) under the following conditions: X-ray: Cu-Kα (wavelength = 1.54178Å), Kβ line removal: Ni filter, tube voltage: 40kV, tube current: 30mA, scan speed: 4° / min, sampling interval: 0.020°, diffusion slit: 2 / 3°, Soler slit: 5°, detector: high-speed one-dimensional detector (D / teX Ultra). The intensity obtained by subtracting the base intensity from each peak intensity is taken as the diffraction intensity (cps). The diffraction intensity of the (111) plane of Mg2Si (interface spacing d = 0.3668 nm) and the diffraction intensity of the (111) plane of Si (interface spacing d = 0.3135 nm) are measured.

[0371] (2) Surface appearance

[0372] (2-1) Wrinkled defects

[0373] The surface appearance of each sample of the coated steel sheet was visually inspected to confirm the presence or absence of wrinkle-like defects. Furthermore, for each sample, 100 random locations were selected from the portion after removing 50mm from both ends of the steel sheet. The height difference of the coated film surface within a 1mm length was measured using a laser microscope (Keyence Corporation "VK-X3000"). The averaged value was used to quantify the surface shape. Based on the presence or absence of wrinkle-like defects and the surface shape, the state of wrinkle-like defect formation was evaluated according to the following criteria.

[0374] ◎: No wrinkled defects were observed (height difference less than 5μm).

[0375] 〇: No wrinkled defects were observed (height difference less than 10μm).

[0376] ×: Wrinkled defects were observed (height difference exceeding 10μm).

[0377] (2-2) Scum defects

[0378] The surface appearance of each sample of the obtained coated steel sheet was confirmed by visual inspection, and the presence or absence of slag defects was evaluated according to the following criteria.

[0379] ○: No granular scum was observed adhering to the surface.

[0380] ×: Observation of granular scum adhesion

[0381] (3) Evaluation of corrosion resistance

[0382] Each sample of the obtained coated steel sheet was cut into 120mm × 120mm dimensions. Three of the four edges of the evaluation surface, at a distance of 10mm from the edge, as well as the end face and the non-evaluation surface, were sealed with tape. Only one edge was left unsealed, exposing the cut end face. This unsealed edge was used as the evaluation sample. It should be noted that the cutting was performed with the burrs of the cut end face facing towards the evaluation surface.

[0383] The Japanese Automotive Standard Composite Cycle Test (JASO-CCT) was conducted using the samples described above. The corrosion acceleration test was started by wetting the samples, and samples were removed every 20 cycles for washing and drying. The samples were then visually observed, and the number of cycles in which red rust was confirmed to have appeared on the shear end face of the side that was not sealed with tape was evaluated according to the following criteria.

[0384] ◎: The number of cycles for red rust formation in the 3 samples is ≥600.

[0385] ○: The number of cycles for red rust formation in 3 samples is ≥400.

[0386] ×: The number of cycles for red rust formation in more than one sample is less than 400.

[0387]

[0388] As can be seen from the results in Table 5, the samples of the present invention have superior surface appearance and corrosion resistance compared with the samples of the comparative examples.

[0389] Industrial availability

[0390] According to the present invention, a hot-dip galvanized Al-Zn-Si-Mg steel sheet is provided that is free from other defects such as scum defects, has suppressed the generation of wrinkle defects, and has an excellent surface appearance.

[0391] Furthermore, according to the present invention, it is possible to provide surface-treated steel sheets with excellent surface appearance and resistance to white rust, as well as coated steel sheets with excellent surface appearance and excellent corrosion resistance.

Claims

1. A hot-dip plated Al-Zn-Si-Mg system steel sheet, characterized by, A hot-dip plated Al-Zn-Si-Mg system steel sheet having a plated coating film, The plated coating film has a composition containing Al: 45 to 65 mass%, Si: 1.0 to 3.0 mass%, Mg: 1.0 to 10.0 mass%, and Mn: 0.01 to 0.5 mass%, with the remainder consisting of Zn and inevitable impurities. The height difference of the steel sheet surface per 1 mm length is 10 μm or less in the range of 50 mm from both ends of the steel sheet.

2. The hot-dip plated Al-Zn-Si-Mg system steel sheet according to claim 1, characterized by, The content of Mn in the plated coating film is 0.1 to 0.3 mass%.

3. The hot-dip plated Al-Zn-Si-Mg system steel sheet according to claim 1 or 2, characterized by, An alloy layer containing Mn is provided at the interface between the plated coating film and the base steel sheet.

4. The hot-dip plated Al-Zn-Si-Mg system steel sheet according to any one of claims 1 to 3, characterized by, The plated coating film further contains one or two or more selected from B, Ca, Ti, V, Cr, Sr, Mo, In, Sn, Sb, Ce, and Bi in a total of 0.01 to 3.0 mass%.

5. A surface treated steel sheet characterized by, A surface-treated steel sheet having the plated coating film according to any one of claims 1 to 4 and a chemical conversion coating film formed on the plated coating film, The chemical conversion coating film contains at least one resin selected from an epoxy resin, a urethane resin, an acrylic resin, a silicone acrylic resin, an alkyd resin, a polyester resin, a polyalkylene resin, an amino resin, and a fluorine resin, and at least one metal compound selected from a P compound, a Si compound, a Co compound, a Ni compound, a Zn compound, an Al compound, a Mg compound, a V compound, a Mo compound, a Zr compound, a Ti compound, and a Ca compound.

6. A coated steel sheet characterized by, A coated steel sheet having a coating film formed directly or via a chemical conversion coating film on the plated coating film according to any one of claims 1 to 4, The chemical conversion coating film contains a resin component and an inorganic compound, the resin component contains (a) an anionic polyurethane resin having an ester bond and (b) an epoxy resin having a bisphenol skeleton in a total of 30 to 50 mass%, the contained ratio of (a) to (b) ((a):(b)) is in the range of 3:97 to 60:40 in terms of mass ratio, and the inorganic compound contains a vanadium compound in an amount of 2 to 10 mass%, a zirconium compound in an amount of 40 to 60 mass%, and a fluorine compound in an amount of 0.5 to 5 mass%, The coating film has at least a primer coating film containing a polyester resin having a urethane bond and an inorganic compound containing a vanadium compound, a phosphoric acid compound, and magnesium oxide.

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