Method for producing hot-dip Al-Zn-Mg-Si plated steel sheet and method for producing coated steel sheet

Abstract

To provide a manufacturing method of a hot dipping Al-Zn-Mg-Si-based plated sheet steel having an excellent surface appearance, by suppressing generation of a surface defect caused by dross in a plating bath.SOLUTION: A manufacturing method includes a step for immersing a base steel sheet into a plating bath having a composition containing Al:40-70 mass%, Si:1.2-4 mass% and Mg:1-6 mass%, and having a residue comprising Zn and inevitable impurities, and a bath temperature of the plating bath satisfies following formula (1): plating bath temperature(°C)≤600-4.5MMg-5.5MSi...(1), where, MMg: content (mass%) of Mg in the plating bath, MSi: content (mass%) of Si in the plating bath.SELECTED DRAWING: None

Description

[Technology Field]

[0001] The present invention relates to a method for producing a molten Al-Zn-Mg-Si plated steel sheet and a painted steel sheet, which suppress the occurrence of surface defects caused by dross in the plating bath and have excellent surface appearance. [Background technology]

[0002] Hot-dip Al-Zn plated steel sheets exhibit high corrosion resistance among hot-dip galvanized steel sheets because they combine the sacrificial corrosion protection of Zn with the high corrosion resistance of Al. For example, Patent Document 1 discloses a hot-dip Al-Zn plated steel sheet containing 25 to 75% by mass of Al in the plating layer. Due to its excellent corrosion resistance, demand for hot-dip Al-Zn plated steel sheets has been growing in recent years, mainly in the building materials sector such as roofs and walls that are exposed to the outdoors for long periods, and in the civil engineering and construction sector such as guardrails, wiring and piping, and soundproof walls.

[0003] The plating layer of a hot-dip Al-Zn plated steel sheet consists of a main layer and an alloy layer at the interface between the base steel sheet and the main layer. The main layer is mainly composed of a portion where Zn is supersaturated and Al has solidified in dendrites (the dendrite portion of the α-Al phase) and the remaining portion of the dendrite gaps (interdendrites), and has a structure in which multiple α-Al phases are stacked in the direction of the plating layer thickness. Due to this characteristic film structure, the corrosion progression path from the surface becomes complex, making it difficult for corrosion to easily reach the base steel sheet, and hot-dip Al-Zn plated steel sheets can achieve superior corrosion resistance compared to hot-dip galvanized steel sheets with the same plating layer thickness.

[0004] Furthermore, there is a known technology that aims to further improve corrosion resistance by incorporating Mg into the plating layer of molten Al-Zn plating. As a technology relating to molten Al-Zn plated steel sheets containing Mg (molten Al-Zn-Mg-Si plated steel sheets), for example, Patent Document 2 discloses an Al-Zn-Mg-Si plated steel sheet containing Sr, in which the plating layer contains an Al-Zn-Si alloy containing Mg, the Al-Zn-Si alloy containing 45 to 60% by weight of elemental aluminum, 37 to 46% by weight of elemental zinc, and 1.2 to 2.3% by weight of elemental silicon, and the concentration of Mg is 1 to 5% by weight.

[0005] Furthermore, as a technique for incorporating Mg into the plating layer, Patent Document 3 discloses a hot-dip Al-Zn plated steel sheet that aims to enhance corrosion resistance and protective effect after the underlying steel sheet is exposed by incorporating a certain amount of Mg and Ca into the plating layer. Furthermore, Patent Document 4 discloses an Al-based plated steel sheet that improves the corrosion resistance of flat plates and end faces by forming a coating layer containing, by mass%, Mg: 1-15%, Si: 2-15%, and Zn: 11-25%, with the remainder being Al and unavoidable impurities, thereby defining the size of the Mg2Si phase present in the plating layer. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Special Publication No. 46-7161 [Patent Document 2] Patent No. 5020228 [Patent Document 3] Patent No. 5000039 [Patent Document 4] Japanese Patent Publication No. 2002-12959 [Overview of the project] [Problems that the invention aims to solve]

[0007] While the corrosion resistance of the hot-dip Al-Zn plated steel sheets disclosed in the aforementioned references 2 to 4 can be improved by adding Mg, Mg is an easily oxidized element, and therefore, the Mg contained in the plating bath sometimes generates oxides (top dross) near the bath surface. In addition, in the case of hot-dip plating in which the base steel sheet is immersed, iron-containing oxides (bottom dross) sometimes occur over time, becoming unevenly distributed in the bath or at the bottom of the plating bath. These dross deposits adhere to the surface of the plating layer, causing convex defects and impairing the appearance of the plating layer surface. Therefore, it was desirable to minimize their occurrence as much as possible.

[0008] In view of these circumstances, the present invention aims to provide a method for manufacturing a hot-dip Al-Zn-Mg-Si plated steel sheet and a method for manufacturing a painted steel sheet that suppress the occurrence of surface defects caused by dross in the plating bath and have excellent surface appearance. [Means for solving the problem]

[0009] The inventors, in an effort to solve the above problems, conducted research and found that the more Mg and Si contained in the plating bath, the lower the melting point of the plating bath, indicating a quantitative relationship between the Mg and Si content and the melting point. In addition, they focused on the fact that oxides near the surface of the plating bath (top dross) and iron-containing oxides unevenly distributed in or at the bottom of the plating bath (bottom dross) tend to occur more easily at higher plating bath temperatures. After further intensive research, they set the composition of the plating bath within a certain range and established a relationship between the Mg and Si content and the plating bath temperature: "Plating bath temperature (°C) ≤ 600-4.5M Mg -5.5M Si By satisfying the relationship (1) ..., the surface and internal temperatures of the plating bath can be lowered to an appropriate range, thereby suppressing the occurrence of top dross and bottom dross mentioned above and achieving excellent surface appearance.

[0010] This invention is based on the above findings, and its gist is as follows. 1. The process includes immersing a base steel sheet in a plating bath having a composition containing Al: 40-70% by mass, Si: 1.2-4% by mass, and Mg: 1-6% by mass, with the remainder being Zn and unavoidable impurities. A method for producing a molten Al-Zn-Mg-Si plated steel sheet, characterized in that the bath temperature of the plating bath satisfies the following formula (1). Plating bath temperature (°C) ≤ 600 - 4.5M Mg -5.5M Si ...(1) M Mg : Mg content in the plating bath (mass%), M Si Si content (mass%) in the plating bath

[0011] 2. The method for producing a molten Al-Zn-Mg-Si plated steel sheet according to claim 1, characterized in that the plating bath further contains Sr: 0.01 to 0.2% by mass.

[0012] 3. The method for producing a molten Al-Zn-Mg-Si plated steel sheet according to claim 1 or 2, characterized in that the plating bath further contains one or more elements selected from Cr, Mn, V, Mo, Ti, Ca, Ni, Co, Sb, and B in a total amount of 0.01 to 10% by mass.

[0013] 4. A method for manufacturing a coated steel sheet, characterized by comprising the step of forming a coating film directly or via an intermediate layer on a molten Al-Zn-Mg-Si plated steel sheet obtained by the manufacturing method described in any one of claims 1 to 3. [Effects of the Invention]

[0014] The present invention provides a method for producing a molten Al-Zn-Mg-Si plated steel sheet and a painted steel sheet that suppress the occurrence of surface defects caused by dross in the plating bath and have excellent surface appearance. [Brief explanation of the drawing]

[0015] [Figure 1] This diagram illustrates the relationship between the amount of Al and Fe dissolved in an Al-Fe-Zn alloy and the temperature.

Embodiment for Carrying Out the Invention

[0016] (Method for Manufacturing a Molten Al-Zn-Mg-Si System Plated Steel Sheet) The method for manufacturing a molten Al-Zn-Mg-Si system plated steel sheet of the present invention (hereinafter sometimes simply referred to as "the manufacturing method of the present invention") will be described. The method for manufacturing a molten Al-Zn-Mg-Si system plated steel sheet of the present invention includes a step of immersing a base steel sheet in a plating bath having a composition containing 40 to 70% by mass of Al, 1.2 to 4% by mass of Si, and 1 to 6% by mass of Mg, with the balance being Zn and inevitable impurities. It is characterized in that the bath temperature of the plating bath satisfies the following formula (1). Plating bath temperature (°C) ≤ 600 - 4.5M Mg -5.5M Si ···(1) By the above-described manufacturing method, the generation of surface defects due to dross in the plating bath can be suppressed. As a result, the obtained molten Al-Zn-Mg-Si system plated steel sheet has good surface appearance.

[0017] In the method for manufacturing a molten Al-Zn-Mg-Si system plated steel sheet of the present invention, although not particularly limited, from the viewpoints of manufacturing efficiency and quality stability, a continuous molten plating facility is usually adopted. Note that the type of the base steel sheet used for the molten Al-Zn-Mg-Si system plated steel sheet of the present invention is not particularly limited. For example, a pickled and descaled hot-rolled steel sheet or steel strip, or a cold-rolled steel sheet or steel strip obtained by cold-rolling them can be used. Also, the conditions of the pretreatment step and the annealing step are not particularly limited, and any method can be adopted.

[0018] In the method for manufacturing a molten Al-Zn-Mg-Si system plated steel sheet of the present invention, the plating bath has a composition containing 40 to 70% by mass of Al, 1.2 to 4% by mass of Si, and 1 to 6% by mass of Mg, with the balance being Zn and inevitable impurities. Thereby, a molten Al-Zn-Mg-Si system plating having a desired composition can be formed.

[0019] The Al content in the plating bath is set to 40 to 70% by mass, preferably 45 to 65% by mass, based on a balance between the corrosion resistance of the obtained molten Al-Zn-Mg-Si plated steel sheet and the operating surface. If the Al content in the plating bath is at least 40% by mass, sufficient dendrite solidification of Al occurs in the formed plating layer. As a result, the main layer of the plating layer (the layer formed on the interfacial alloy layer in the plating layer) mainly contains supersaturated Zn and consists of a portion where Al has dendrite-solidified (the α-Al phase dendrite portion) and the remaining portion of the dendrite gap (the interdendrite portion), and a structure with excellent corrosion resistance can be ensured in which the dendrite portions are stacked in the direction of the plating layer thickness. Furthermore, the more of these α-Al phase dendrite portions that are stacked, the more complex the corrosion progression path becomes, making it more difficult for corrosion to easily reach the underlying steel sheet, thus improving corrosion resistance. To obtain even higher corrosion resistance, it is preferable to set the Al content in the plating bath to 45% by mass or more. On the other hand, if the Al content in the plating bath exceeds 70% by mass, the amount of Zn, which has a sacrificial corrosion protection effect against Fe, decreases, and the corrosion resistance deteriorates. For this reason, the Al content in the plating bath should be 70% by mass or less. Furthermore, if the Al content in the plating bath is 65% by mass or less, even if the amount of plating deposited decreases and the underlying steel plate is more likely to be exposed, the sacrificial corrosion protection effect against Fe is still present, and sufficient corrosion resistance can be obtained. For this reason, it is preferable that the Al content in the plating bath be 65% by mass or less.

[0020] Furthermore, the Si in the plating bath is added to the plating bath for the purpose of suppressing the growth of the interfacial alloy layer formed at the interface with the underlying steel sheet in the obtained molten Al-Zn-Mg-Si plated steel sheet, and consequently for the purpose of improving corrosion resistance and workability, and is inevitably contained in the main layer of the plating layer. Specifically, when the plating treatment is performed with Si contained in the plating bath, as soon as the steel sheet is immersed in the plating bath, the Fe on the surface of the steel sheet and the Al and Si in the bath undergo an alloying reaction, and Fe-Al and / or Fe-Al-Si compounds are formed in the plating layer. The formation of this Fe-Al-Si interfacial alloy layer can suppress the growth of the interfacial alloy layer. When the Si content in the plating bath is 1.2% by mass or more, in addition to the above-mentioned suppression effect of top dross and bottom dross being significantly exhibited, sufficient suppression of the growth of the interfacial alloy layer becomes possible. On the other hand, when the Si content in the plating bath exceeds 4%, workability decreases and the Si phase that becomes the cathode site is more likely to precipitate. While the precipitation of the Si phase can be suppressed by increasing the Mg content, this method leads to increased manufacturing costs and makes it more difficult to control the composition of the plating bath. For this reason, the Si content in the plating bath is set to 4% or less. Furthermore, from the standpoint of enjoying a higher level of suppression of top dross and bottom dross, and suppressing the growth of the interfacial alloy layer and the precipitation of the Si phase, it is more preferable to set the Si content in the plating bath to 2-4%, and particularly preferable to 2.3-3.5%.

[0021] Furthermore, the plating bath contains 1 to 6% by mass of Mg. In the resulting molten Al-Zn-Mg-Si plated steel sheet, when the main layer of the plating layer corrodes, Mg is included in the corrosion products, improving the stability of the corrosion products and delaying the progression of corrosion, resulting in improved corrosion resistance. More specifically, the Mg present in the main layer of the plating layer combines with the Si mentioned above to form Mg2Si. This Mg2Si dissolves initially when the plated steel sheet corrodes, so Mg is included in the corrosion products. The Mg in these corrosion products concentrates on the surface of the corrosion products, densifying them and improving the stability of the corrosion products and their barrier properties against external corrosion factors. Here, the reason for setting the Mg content in the plating bath to 1% by mass or more is that by setting the Mg content to 1% by mass or more, a large amount of Mg₂Si can be generated in the plating layer, and an excellent corrosion retardation effect can be obtained. From the same perspective, the Mg content in the plating bath is preferably 2% by mass or more, and more preferably 3% by mass or more. On the other hand, the content of Mg is 6 set to 6 % by mass or less because when the Mg content exceeds 5 %, in addition to the saturation of the corrosion resistance improvement effect, Mg oxides are formed, and the above-mentioned top dross is likely to occur. From the same perspective, the Mg content in the plating bath is preferably

[0022] % by mass or less. On the other hand, in the case of a coated steel sheet using a molten Al-Zn-based plated steel sheet containing Mg as a base, Mg₂Si phases or Mg-Zn compounds (MgZn₂, Mg 32 (Al,Zn) 49(etc.) dissolves in the initial stages of corrosion, and Mg is incorporated into the corrosion products. Corrosion products containing Mg are very stable, and this suppresses corrosion in the initial stages, thereby suppressing large paint film blistering due to selective corrosion of the Zn-rich phase, which is a problem in painted steel sheets using conventional Al-Zn plated steel sheets as a base. As a result, molten Al-Zn plated steel sheets with Mg in the plating layer exhibit excellent post-painting corrosion resistance. If the Mg content in the plating bath is less than 3% by mass, the amount of Mg that dissolves during corrosion is small, and there is a risk that the post-painting corrosion resistance will not improve. Furthermore, if the Mg content in the plating bath exceeds 6% by mass, not only will the effect saturate, but corrosion of the Mg compound will occur, and the solubility of the entire plating layer will increase excessively. As a result, even if the corrosion products are stabilized, their dissolution rate will increase, which may cause large blistering and deterioration of post-painting corrosion resistance. For this reason, in order to stably obtain excellent post-painting corrosion resistance, it is preferable to set the Mg content in the plating bath to 6% by mass or less.

[0023] Furthermore, it is preferable that the plating bath further contains 0.001 to 1.0 mass% of Sr. This is because the inclusion of Sr in the plating bath suppresses the occurrence of wrinkle-like defects and further improves the surface appearance of the resulting molten Al-Zn-Mg-Si plated steel sheet. The aforementioned wrinkle-like defects are defects that form wrinkle-like irregularities on the surface of the plating layer and are observed as whitish streaks on the surface of the plating layer. Since such streak-like defects contain Mg oxide, they are more likely to occur when a large amount of Mg is added to the plating bath. Therefore, in the molten Al-Zn-Mg-Si plated steel sheet of the present invention, by including Sr in the plating bath, Sr is preferentially oxidized over Mg on the surface of the plating layer of the molten Al-Zn-Mg-Si plated steel sheet, thereby suppressing the oxidation reaction of Mg and making it possible to suppress the occurrence of the aforementioned streak-like defects.

[0024] The Sr content in the plating bath is preferably 0.001% by mass or more, as this is to more reliably obtain the effect of suppressing the occurrence of the streak-like defects described above. From a similar viewpoint, the Sr content in the plating bath is more preferably 0.005% by mass or more, even more preferably 0.01% by mass or more, and particularly preferably 0.05% by mass or more. On the other hand, the Sr content in the plating bath is preferably 1.0% by mass or less. If the Sr content is too high, the oxidation of Mg will be suppressed too much, making it difficult to generate the corrosion products caused by Mg2Si described above, and there is a risk that sufficient corrosion resistance cannot be obtained. From a similar viewpoint, the Sr content in the plating bath is preferably 0.7% by mass or less, more preferably 0.5% by mass or less, and particularly preferably 0.3% by mass or less.

[0025] Furthermore, similar to Mg mentioned above, the plating bath preferably contains one or more elements selected from Cr, Mn, V, Mo, Ti, Ca, Ni, Co, Sb, and B in a total amount of 0.01 to 10% by mass, as these elements improve the stability of corrosion products and slow down the progression of corrosion. The reason for setting the total content of the above-mentioned components to 0.01 to 10% by mass is that a sufficient corrosion delaying effect can be obtained without the effect becoming saturated.

[0026] The plating layer contains components of the underlying steel sheet incorporated into the plating through a reaction between the plating bath and the underlying steel sheet during the plating process, as well as unavoidable impurities in the plating bath. The underlying steel sheet components incorporated into the plating may include up to approximately 2% Fe. Examples of other unavoidable impurities in the plating bath include Cu and Zr. It is not possible to distinguish between Fe incorporated from the underlying steel sheet and Fe present in the plating bath for quantitative analysis. While there are no particular limitations on the total content of unavoidable impurities, from the viewpoint of maintaining the corrosion resistance and uniform solubility of the plating, it is preferable that the total amount of unavoidable impurities excluding Fe be 1% by mass or less.

[0027] Furthermore, as described above, the molten Al-Zn-Mg-Si plated steel sheet obtained by the manufacturing method of the present invention has a plating layer consisting of an interfacial alloy layer present at the interface with the base steel sheet and a main layer present on top of the interfacial alloy layer. The composition of the main layer is such that Al and Si are slightly lower on the interfacial alloy layer side, but overall it is almost the same as the composition of the plating bath. Therefore, the composition of the main layer can be controlled with high precision by controlling the composition of the plating bath.

[0028] The present invention provides a method for manufacturing a molten Al-Zn-Mg-Si plated steel sheet, comprising the step of immersing a base steel sheet in the plating bath, wherein the temperature of the plating bath satisfies the following formula (1). Plating bath temperature (°C) ≤ 600 - 4.5M Mg -5.5M Si ...(1)

[0029] In conventional methods for manufacturing molten Al-Zn-Mg plated steel sheets, while the inclusion of Mg improves corrosion resistance, Mg is an easily oxidized element, and therefore, the Mg contained in the plating bath sometimes generates oxides (top dross) near the bath surface. Furthermore, in the case of molten plating where the base steel sheet is immersed, over time, iron-containing oxides (bottom dross) may become free or unevenly distributed in or at the bottom of the plating bath. These drosses, after the plating layer is formed, cause surface defects, resulting in a decrease in the surface appearance of the resulting molten Al-Zn-Mg-Si plated steel sheet. Regarding the generation of bottom dross in or at the bottom of the plating bath, for example, Figure 1 shows a cross-section of the Al-Fe-Zn ternary alloy phase diagram, illustrating the relationship between the dissolution amounts of Al and Fe in an Al-Fe-Zn alloy and temperature, when Zn is 30% by weight. This diagram also shows that the solubility of Fe increases with increasing temperature.

[0030] Therefore, in this invention, a quantitative relationship between the content of Mg and Si in the plating bath and the melting point of the plating bath was derived, based on the fact that the melting point of the plating bath decreases as the content of Mg and Si in the plating bath increases. Furthermore, considering that the occurrence of top dross and bottom dross is suppressed as the plating bath temperature decreases, by combining the above-mentioned quantitative relationship between the content of Mg and Si in the plating bath and the melting point of the plating bath with a temperature at which the dross can be suppressed, the occurrence of top dross and bottom dross can be significantly reduced compared to conventional methods, and the occurrence of surface defects caused by these dross can be suppressed.

[0031] In the method for manufacturing a molten Al-Zn-Mg-Si plated steel sheet according to the present invention, it is preferable that the temperature of the steel sheet when it enters the plating bath (entry temperature) be 20°C or less than or equal to the temperature of the plating bath plus 20°C (plating bath temperature + 20°C). This suppresses the steel sheet temperature from becoming too high during molten plating and reduces the temperature difference with the plating bath temperature, thereby suppressing the formation of large particle sizes of Mg2Si in the plating layer of the resulting molten Al-Zn-Mg-Si plated steel sheet, which can lead to a decrease in workability. From a similar viewpoint, the entry temperature of the steel plate is preferably less than or equal to the temperature obtained by adding 10°C to the temperature of the plating bath (plating bath temperature + 10°C), and preferably less than or equal to the temperature of the plating bath.

[0032] In addition, in the manufacturing method of the present invention, there are no particular limitations other than the bath temperature and the temperature of the plate being entered during the hot-dip plating process, and a hot-dip Al-Zn-Mg-Si plated steel sheet can be manufactured according to a conventional method.

[0033] (Manufacturing method for painted steel sheets) The present invention's method for manufacturing a coated steel sheet is characterized by comprising the step of forming a coating film directly or via an intermediate layer on a molten Al-Zn-Mg-Si plated steel sheet obtained by the method for manufacturing a molten Al-Zn-Mg-Si plated steel sheet according to the present invention described above. Because the molten Al-Zn-Mg-Si plated steel sheet obtained by the manufacturing method of the present invention is used, the occurrence of surface defects caused by dross in the plating bath can be suppressed, and excellent surface appearance can be achieved.

[0034] The type of coating film and the method of forming the coating film are not particularly limited and can be appropriately selected according to the required performance. For example, methods such as roll coater coating, curtain flow coating, and spray coating can be used. After applying a paint containing an organic resin, it is possible to form a coating film by heating and drying it using means such as hot air drying, infrared heating, or induction heating.

[0035] The intermediate layer is not particularly limited as long as it is formed between the molten Al-Zn-Mg-Si plated steel sheet and the coating film. Examples include chemical conversion coatings and primers such as adhesive layers. The chemical conversion coating can be formed, for example, by chromate treatment or chromium-free chemical conversion treatment, which involves applying a chromate treatment solution or a chromium-free chemical conversion treatment solution and drying it at a steel sheet temperature of 80 to 300°C without washing with water. These chemical conversion coatings may be single-layer or multi-layer; in the case of multi-layer coatings, multiple chemical conversion treatments can be performed sequentially. [Examples]

[0036] (Samples 1-38) Cold-rolled steel sheets with a thickness of 0.5 mm, manufactured by conventional methods, were used as the base steel sheet, and samples 1 to 38 of hot-dip Al-Zn-Mg-Si plated steel sheets were manufactured in a continuous hot-dip galvanizing facility. The composition of the plating bath used in the manufacturing process was approximately the same as that of the plating layer of each sample shown in Table 1, and the measured bath temperature of the plating bath and the right-hand side of the calculated equation (1) (600 - 4.5M) were used. Mg -5.5M Si The values ​​of ) are shown in Table 1.

[0037] (evaluation) Each sample of the molten Al-Zn-Mg-Si plated steel sheet obtained as described above was evaluated as follows. The evaluation results are shown in Table 1.

[0038] (1) Surface appearance For each sample of hot-dip Al-Zn plated steel sheet (650 mm in length x 914 mm in width), the surface of the plating layer was observed visually. The observation results were then evaluated according to the following criteria. ◎: No defects or wrinkle-like defects caused by dross were observed. ○: At least no defects attributable to Dross were observed. △: No wrinkle-like defects were observed at all. ×: Dross-induced defects and wrinkle-like defects were observed.

[0039] [Table 1]

[0040] Table 1 shows that each sample of the present invention has superior surface appearance compared to each sample of the comparative example. [Industrial applicability]

[0041] According to the present invention, it is possible to provide a method for manufacturing a molten Al-Zn-Mg-Si plated steel sheet and a painted steel sheet that suppress the occurrence of surface defects caused by dross in the plating bath and have excellent surface appearance.

Claims

1. immersing a substrate steel sheet in a coating bath containing 40 to 70% by mass of Al, 1.2 to 4% by mass of Si, and 1 to 6% by mass of Mg, with the balance being Zn and unavoidable impurities; A method for producing a hot-dip Al-Zn-Mg-Si coated steel sheet, characterized in that the bath temperature of the coating bath satisfies the following formula (1): Plating bath temperature (℃)≦600-4.5M Mg -5.5M Si ···(1) M Mg : Mg content in the plating bath (mass%), M Si : Si content in the plating bath (mass%)

2. 2. The method for producing a hot-dip Al-Zn-Mg-Si plated steel sheet according to claim 1, wherein the plating bath further contains 0.01 to 0.2 mass % of Sr.

3. 3. The method for producing a hot-dip Al-Zn-Mg-Si coated steel sheet according to claim 1, wherein the coating bath further contains 0.01 to 10 mass% in total of one or more elements selected from Cr, Mn, V, Mo, Ti, Ca, Ni, Co, Sb, and B.

4. 4. A method for producing a coated steel sheet, comprising a step of forming a coating film directly or via an intermediate layer on a hot-dip Al-Zn-Mg-Si-plated steel sheet obtained by the production method according to claim 1.

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