High-strength aluminum-based plated steel sheet with excellent corrosion resistance and weldability and manufacturing method

Abstract

The present invention relates to a high-strength aluminum-based plated steel sheet having excellent corrosion resistance and weldability, and a manufacturing method thereof. An aluminum-based plated steel sheet according to one aspect of the present invention includes an austenitic base steel sheet containing 70% by area or more of an austenitic structure, and an aluminum-based plating layer formed on the base steel sheet, wherein the base steel sheet contains 80% by area or more of ferrite in a surface layer portion, which means a region from the interface with the plating layer toward a depth of 100 μm toward the inside of the base steel sheet, and the aluminum-based plating layer can have a composition including, by weight, 2-12% Si, 5-30% Zn, 0.1-5% Mn, with the balance being Al and unavoidable impurities.

Description

[Technical field]

[0001] The present invention relates to a high-strength aluminum-based plated steel sheet having excellent corrosion resistance and weldability, and a manufacturing method thereof. [Background technology]

[0002] 2. Description of the Related Art In order to ensure the corrosion resistance of steel sheets, plated steel sheets, the surface of which is plated, are widely used.

[0003] In order to manufacture plated steel sheets, a cold-rolled full hard steel sheet is annealed, and then the steel sheet is immersed in a plating bath at a temperature similar to that of the plating bath so that the plating solution is immersed on the surface of the steel sheet. Meanwhile, in the case of representative high strength steel sheets, such as dual phase (DP) steel and transformation induced plasticity (TRIP) steel, which contain a large amount of hard structure such as martensite inside, the strength and elongation of the steel sheet are significantly reduced by the annealing heat treatment, so that it may be technically difficult to obtain a plated steel sheet having a high strength-elongation balance (TS×El).

[0004] Also, widely used plated steel sheets include galvanized steel sheets with a Zn-based plating layer and aluminum-based plated steel sheets with an aluminum-based plating layer. Galvanized steel sheets with Zn-based plating have a lower corrosion potential than iron-based steel sheets, and exhibit a so-called sacrificial corrosion protection property in which Zn corrodes first instead of iron, and are therefore evaluated as steel sheets with excellent corrosion resistance. However, a Zn-based plating layer has a low melting point and a low viscosity of the molten plating solution, which causes the molten plating solution to penetrate into microcracks that occur during welding, resulting in the formation of cracks, known as liquid metal embrittlement (LME). Aluminum plating has a higher melting point than Zn, so there is a relatively low risk of welding liquor embrittlement occurring, but aluminum plating only ensures corrosion resistance by blocking contact between the air and the base steel sheet, and does not have electrochemical corrosion protection properties such as sacrificial corrosion protection, as does zinc plating. As a result, when the base steel sheet is in contact with the atmosphere, it may become difficult to suppress corrosion, which may cause cracks in the coating layer. Therefore, aluminum coating is considered to have inferior corrosion resistance compared to zinc coating, and an Al-Zn-based coating layer to which a certain amount of Zn is added has been proposed to improve the corrosion resistance of such aluminum coating. However, such an Al-Zn-based coating layer cannot completely solve the problem of weld liquor embrittlement, and therefore there is still a demand for a technical solution to simultaneously solve the problems of corrosion resistance and weld liquor embrittlement.

[0005] In addition, if sufficient alloying does not occur between the plating film and the base steel sheet, the adhesion between the base steel sheet and the plating film will be insufficient, and the plating film may peel off. Summary of the Invention [Problem to be solved by the invention]

[0006] According to one aspect of the present invention, there is provided a high-strength aluminum-based plated steel sheet that is free from the problem of weld liquor embrittlement and has excellent corrosion resistance, and that can minimize loss of strength due to heat treatment before plating.

[0007] According to another aspect of the present invention, there is provided a high-strength aluminum-based plated steel sheet having excellent adhesion between a base steel sheet and a plating film.

[0008] The technical problem of the present invention is not limited to the above content. A person having ordinary skill in the art to which the present invention pertains will have no difficulty in understanding further problems of the present invention from the entire content of the specification of the present invention. [Means for solving the problem]

[0009] An aluminum-based plated steel sheet according to one aspect of the present invention includes an austenitic base steel sheet containing 70% by area or more of an austenitic structure and an aluminum-based plating layer formed on the base steel sheet, wherein the base steel sheet contains 80% by area or more of ferrite in a surface layer portion, which means a region from the interface with the plating layer toward a depth of 100 μm toward the inside of the base steel sheet, and the aluminum-based plating layer can have a composition including, by weight, 2-12% Si, 5-30% Zn, 0.1-5% Mn, with the balance being Al and unavoidable impurities.

[0010] A method for producing an aluminum-based plated steel sheet according to another aspect of the present invention includes the steps of: preparing an austenitic base steel sheet containing 70% or more by area of ​​an austenitic structure; annealing the austenitic base steel sheet under conditions in which the soaking zone temperature and the dew point temperature are 750 to 870°C and -5 to 20°C, respectively; and immersing the heat-treated austenitic base steel sheet in a coating bath having a composition containing 2 to 12% Si, 5 to 30% Zn, 0.1 to 3% Mn, the balance being Al and unavoidable impurities, and maintained at a temperature of 550 to 650°C, to perform hot-dip coating. Effect of the Invention

[0011] According to the present invention, by using an austenitic high Mn steel as the base steel sheet, it is possible to solve the problem of strength reduction caused by structural transformation even during heat treatment before plating, and by controlling the composition of the plating layer and making the surface layer of the base steel sheet consisting of an austenitic structure into a ferritic structure, it is possible to significantly improve corrosion resistance as well as resistance to weld liquor embrittlement. In addition, by including Mn in the plating layer, it is possible to prevent a decrease in the adhesive strength between the plating layer and the base steel sheet. [Brief description of the drawings]

[0012] [Figure 1] 1 is a graph showing tensile curves before and after plating for a comparative example and an example of the invention. [Diagram 2] 3 is a photograph showing the welded portions of Comparative Example 1 and Invention Example 2. [Diagram 3] 1 is a photograph taken after evaluating the corrosion resistance of Comparative Example 1 and Invention Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present invention will be described in detail below.

[0014] The inventors of the present invention have found that when an austenitic steel is used as the base steel sheet for a plated steel sheet, deterioration of material properties such as strength and elongation can be prevented by heat treatment before plating, and therefore it is possible to produce a high-strength plated steel sheet that can maintain TS×El at a high level. Based on this finding, they have arrived at the present invention.

[0015] The austenitic steel sheet, which is the base steel sheet of the plated steel sheet of the present invention, may contain an austenite structure at 70% or more on an area basis (meaning the ratio in a region including the surface layer portion described later). Since austenite is a stable structure even at room temperature, transformation to other structures can be minimized even when heated, and as a result, changes in physical properties before and after heating can be minimized. Since a higher austenite ratio in the steel sheet of the present invention is more advantageous, there is no particular upper limit, and the ratio of the austenite structure may be 100%. According to one embodiment of the present invention, the ratio of the austenite structure in the microstructure of the steel sheet may be 80% or more. The remaining structure other than austenite is not particularly limited, and may include one or more of various structures that can appear inside steel materials, such as ferrite, bainite, martensite, and pearlite. A commercially available steel sheet that satisfies the structure conditions of the present invention is TWIP (TWin Induced Platicity) steel.

[0016] According to one embodiment of the present invention, the surface layer portion of the base steel sheet of the present invention may contain ferrite as a main structure. That is, by making the structure of the surface layer portion a ferrite structure, it is possible to suppress the occurrence of microcracks, and thereby to suppress the occurrence of weld liquor embrittlement caused by the penetration of the molten coating layer into the cracks during welding. In the present invention, the surface layer portion refers to a region from the surface of the base steel sheet to a depth of 100 μm. In one embodiment of the present invention, the ratio of ferrite in the surface layer portion may be 80% or more on an area basis, and the surface layer portion may be composed of a single phase of ferrite.

[0017] In one embodiment of the present invention, the ratio of each of the above structures may be that obtained when observing a cross section of a steel plate cut in the thickness direction.

[0018] In the present invention, as a method for obtaining a steel sheet with an austenitic structure, a high Mn steel sheet having a high Mn content can be used as a base steel sheet. In the present invention, the high Mn steel means a steel having a Mn content of 5% by weight or more. In the following description of the composition of the steel sheet and the coating layer in the present invention, it should be noted that the unit of content is based on weight unless otherwise specified. Mn is a representative austenite stabilizing element, and by setting the content to 5% or more, the ratio of austenite in the steel sheet can be maintained at the target level in the present invention. However, if the Mn content is excessive, problems such as non-coating and deterioration of coating adhesion may occur, so the upper limit of the Mn content can be determined to be 25%. In one embodiment of the present invention, the range of the Mn content can be determined to be 15 to 20%.

[0019] In addition to Mn, the base steel sheet may further contain, although not necessarily limited to, C: 0.4 to 0.8%, Al: 0.5 to 3%, and B: 50 ppm or less.

[0020] The C is an element that stabilizes austenite, and if the C content is low, there is a problem that austenite is not sufficiently formed, and conversely, if the C content is excessive, there is a problem that weldability is reduced. Therefore, taking these points into consideration, in one embodiment of the present invention, the C content can be determined to be 0.4 to 0.8%. In another embodiment of the present invention, the C content can be determined to be 0.5 to 0.6%.

[0021] Moreover, the above-mentioned Al is added in an amount of 0.4% or more as an element effective in preventing the occurrence of hydrogen embrittlement. If the Al content is excessive, it may cause a problem of nozzle clogging during continuous casting, so the upper limit of the Al content is set to 3%. In one embodiment of the present invention, the range of the Al content can be set to 0.5 to 1.5%.

[0022] Although not essential, B may be added to increase the strength of the base steel sheet. However, if the B content is excessive, problems such as non-plating occurring and reduced plating adhesion may occur, so the upper limit of the B content may be set to 50 ppm. In the present invention, B is an optional element and may not be added (i.e., it may contain 0%), but in one embodiment, the lower limit may be set to 5 ppm.

[0023] The austenitic high Mn steel sheet of the present invention may further contain, in addition to the above-mentioned elements, elements such as Ti, Nb, Mo, etc., in a total amount of 0.5% or less, if necessary.

[0024] According to an embodiment of the present invention, the base steel sheet may be a hot-rolled steel sheet or a cold-rolled steel sheet, but the type is not particularly limited.

[0025] The present invention also specifically limits the composition of the plating layer in order to prevent weld liquor embrittlement and increase adhesion of the plating layer. The plating layer according to one embodiment of the present invention may have a composition consisting of 0.7-5% Si, 1.5-15% Zn, 0.1-1.5% Mn, and the balance being Al and unavoidable impurities.

[0026] In the coating layer, Si plays a role in suppressing the growth of the Al-Fe alloy layer during hot-dip coating, and when 0.7% or more is added, excessive growth of the Al-Fe alloy layer can be suppressed, thereby ensuring coating adhesion. However, when Si is excessive, exceeding 5%, the growth of the Al-Fe alloy layer is excessively suppressed, and there is a risk of weld liquor embrittlement occurring. That is, the Al-Fe alloy layer can suppress the prevention of the molten coating layer from flowing into the inside of the base steel sheet, so in one embodiment of the present invention, it is intended to avoid excessive suppression of the growth of the Al-Fe alloy layer due to the addition of an excessively high content of Si.

[0027] In addition, Zn is added to the coating layer to impart sacrificial corrosion protection to the aluminum-based coating layer, and is added at 1.5% or more. However, if the Zn content is excessive, the melting point of the molten coating layer decreases and the fluidity increases, which is likely to cause weld liquor embrittlement, so the value is limited to 15% or less.

[0028] In the present invention, Mn is added in an amount of 0.1% or more to increase the coating adhesion. However, if the Mn content exceeds 1.5%, the formation of the Al-Fe alloy phase is inhibited, which may cause weld liquor embrittlement, so the upper limit of the Mn content is set to 1.5%. In the present invention, Mn can be derived from the coating bath, but since a high Mn steel sheet is used, a considerable amount of Mn can diffuse into the base steel sheet and be included in the coating layer.

[0029] In one embodiment of the present invention, the coating layer may further contain 10 to 60% Fe. Fe is formed by a reaction between the base steel sheet and the coating bath when the coating bath comes into contact with the base steel sheet, and is contained in the coating layer, and may be contained in a range of up to 60%. There is no particular lower limit for the content, but when considering normal operating conditions, the Fe content of the coating layer may be determined to be 10% or more.

[0030] In the present invention, Mg can be added in an amount of up to 2.5% if necessary in order to improve the corrosion resistance of the plating layer.

[0031] In one embodiment of the present invention, in addition to the above-mentioned elements, the plating layer may further contain Cr, Mo, Ni, etc., in a total content of 0.5% or less.

[0032] Hereinafter, the method for producing a high-strength aluminum-based plated steel sheet of the present invention will be described.

[0033] First, a step of preparing an austenitic base steel sheet is carried out. The characteristics of the austenitic base steel sheet are as described above.

[0034] After this, the prepared base steel sheet needs to be annealed in a temperature range of 750 to 870 ° C based on the soaking zone. Since austenite is not sufficiently formed below 750 ° C, it is difficult to secure a sufficient austenite phase, and since austenite is sufficiently formed even if the temperature exceeds 870 ° C, further temperature increase is not necessary. At this time, the dew point temperature in the soaking zone needs to be adjusted to -5 to 20 ° C. By controlling the dew point temperature within this range, internal oxidation and decarburization occur appropriately in the surface layer of the steel sheet, and the structure of the surface layer can be controlled to a ferrite structure. That is, Mn and C are listed as elements that stabilize the austenite structure, and the contents of these elements can be greatly reduced in the surface layer by internal oxidation, so that the structure of the surface layer can be controlled to ferrite. When the dew point temperature is less than -5 ° C, it is difficult to cause an internal oxidation reaction in the surface layer, so that it is difficult to maintain the structure of the surface layer as ferrite. In addition, surface oxidation occurs instead of internal oxidation, and a large amount of oxide is generated on the surface, which hinders alloying. Conversely, if the dew point temperature exceeds 20°C, oxidation will occur not only inside the base steel sheet but also on the surface, resulting in a large amount of oxide being distributed on the surface, which will result in poor wettability with the plating bath during plating and poor plating adhesion.

[0035] After this, the heat-treated base steel sheet needs to be immersed in a coating bath at 550 to 650°C for hot-dip coating. If the temperature of the coating bath is less than 550°C, the viscosity of the coating bath increases, resulting in reduced fluidity. If the temperature exceeds 650°C, the life of the sink roll in the coating bath may be shortened and a large amount of dross may be generated. The composition of the coating bath may include Si: 2 to 12%, Zn: 5 to 30%, Mn: 0.1 to 3%, and the balance Al and unavoidable impurities, taking into consideration the composition of the coating layer that is finally formed. In one embodiment of the present invention, Fe may be further included at a content of 4% or less. In addition, in order to ensure the corrosion resistance of the coating layer, Mg may be further included at 5% or less, and Cr, Mo, and Ni may be further included at a total content of 0.5% or less, as described above in the composition of the coating layer.

[0036] When the base steel sheet is immersed in the coating bath, the temperature of the steel sheet can be 550 to 700°C. If the temperature of the steel sheet is too low, sufficient surface quality cannot be obtained, so the temperature of the immersed steel sheet can be 550°C or higher. However, if the temperature is too high, the temperature of the coating bath may increase due to the temperature of the steel sheet, and the amount of elution from the steel sheet may increase, which may reduce the durability of the coating device, so the upper limit of the temperature of the steel sheet can be set at 700°C. In one embodiment of the present invention, the temperature of the steel sheet when immersed can be set to the temperature of the coating bath to the coating bath temperature + 30°C.

[0037] After hot-dip galvanizing the steel sheet by the above-mentioned process, the coating weight can be adjusted by a known coating weight adjustment means such as an air knife to produce a high-strength aluminum-based plated steel sheet. The coating weight is not particularly limited, but is preferably 10 to 100 g / m per side of the steel sheet. 2 can be limited to. EXAMPLES

[0038] The present invention will be described in detail below with reference to examples. However, it should be noted that the examples described below are merely for illustrating and embodying the present invention, and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the claims and matters that can be reasonably inferred therefrom.

[0039] (Example) Example 1 A cold-rolled steel sheet (sheet thickness: 1.2 mm) having the composition (unit: weight %, where the unit of the B content is ppm, and the remaining components not shown are essentially Fe) and structure (unit: area %) shown in Table 1 below was prepared, and the temperature of the soaking zone was heated to 830°C to perform annealing heat treatment. During the annealing heat treatment, the dew point was controlled as shown in Table 2. The heated steel sheet was immersed in a coating bath having the composition (unit: weight %, the remaining components not shown are aluminum) shown in Table 2, which was maintained at a temperature of 620°C. The temperature of the steel sheet before immersion was controlled at 620°C (±3°C) in all examples. After immersion in the coating bath, the steel sheet was coated with 60 g / m2 per side using an air knife. 2 By controlling the coating weight, an aluminum-based plated steel sheet was produced.

[0040] [Table 1]

[0041] [Table 2]

[0042] Table 3 shows the composition of the plating layer of the plated steel sheets obtained for each Example (unit: weight %, remaining components not shown are aluminum), the ferrite ratio of the surface layer (unit: area %), corrosion resistance, weldability, tensile strength (MPa), and plating adhesion. As shown in Table 3, it was confirmed that the austenite ratio of the base steel sheet of the plated steel sheets did not deviate significantly from the value shown in Table 1, which shows the structure of the base steel sheet before plating, and was the same as the type of the remaining structure (not shown in Table 3). However, in the case of Invention Example 3 (Invention Steel 2 was used as the base steel sheet), it was confirmed that ferrite was formed as the remaining structure.

[0043] The corrosion resistance of the plated steel sheets was judged according to the following criteria.

[0044] Each hot-dip aluminum alloy plated steel sheet was placed in a salt spray tester and sprayed with 5% salt water (temperature 35°C, pH 6.8) at 1ml / 80cm per hour. 2 The steel plate was sprayed with the solution, and 2400 hours after the test, the occurrence of red rust was judged. In other words, the steel plate was judged as having no red rust, as "◎ (excellent)", as having red rust on 50% or less of the steel plate surface area, as "○ (good)", and as having red rust on more than 50% of the steel plate surface area, as "× (poor)".

[0045] The weldability of the plated steel sheets was judged according to the following criteria.

[0046] To evaluate weld liquor embrittlement, a Cu-Cr electrode with a tip diameter of 6 mm was used, and welding was performed under the conditions of a welding current of 0.5 kA and a pressure of 4.0 kN. After welding, the length of the LME crack formed on the cross section was measured using a field emission scanning electron microscope (FE-SEM). The measurement results were rated as follows: when the LME crack length was 150 μm or less, it was evaluated as "◎ (excellent)", when the LME crack length was between 150 μm and 500 μm, it was evaluated as "○ (good)", and when the LME crack length exceeded 500 μm, it was evaluated as "× (poor)".

[0047] The plating adhesion was judged according to the following criteria.

[0048] Using an automobile structural sealer, a sealant was applied to a test piece measuring 75mm x 150mm in area with an area of ​​10mm x 40mm and a thickness of 5mm, which was then cured at 175℃ for 25 minutes, and the piece was then bent 90 degrees and visually inspected for sealer peeling. If the sealer was directly attached to the base steel and no peeling occurred between the sealants, it was rated as "Excellent", if the plating layer peeled off but the area ratio of the coating to the sealer was less than 10% it was rated as "Good", and if the area ratio of the plating layer to the sealer was more than 10% it was rated as "Poor".

[0049] [Table 3]

[0050] In Comparative Example 1 and Comparative Example 2, the process conditions meet the ranges specified in the present invention, but the content of C or Mn in the base steel sheet is insufficient, and as a result, the ferrite structure of the surface layer does not fall within the ranges specified in the present invention. As can be seen from Table 3 above, in Comparative Example 1 and Comparative Example 2, in which the ratio of the ferrite structure of the surface layer in the structure of the steel sheet is less than 80%, it is not possible to prevent LME cracks from occurring during welding, and therefore the weldability is deteriorated. In addition, in Comparative Example 2, the content of Zn in the coating layer is insufficient, and therefore the corrosion resistance is also insufficient. In addition, since the ratio of austenite is not high in both Comparative Examples 1 and 2, it is difficult to maintain a high balance (TS×El) between strength and elongation even after heat treatment, and as a result, the values ​​of the strength and elongation balance are only 15,000 MPa% and 13,000 MPa%, respectively, which is not suitable for steel materials that require high strength and elongation.

[0051] In Comparative Examples 3, 5 and 7, the dew point temperature in the soaking zone during annealing was lower than the value specified in the present invention. When the dew point temperature is too low, internal oxidation and decarburization of the steel sheet surface are unlikely to occur, but surface oxidation occurs. As a result, not only is it difficult to maintain a high ratio of ferrite in the surface layer, but the alloying between the coating layer and the steel sheet is insufficient due to the oxides on the surface. As a result, as shown in Table 3, poor weldability and coating adhesion were obtained.

[0052] In Comparative Examples 4 and 6, the dew point temperature was excessively high, and although the ferrite ratio in the surface layer satisfied the conditions of the present invention, an excessive amount of oxide was formed on the surface, resulting in poor plating adhesion.

[0053] As can be seen from the results in Table 3, invention examples 1 to 3, which are compared with the above comparative examples, all had excellent corrosion resistance, weldability, strength-elongation balance, and plating adhesion, all of which satisfied the conditions of the present invention.

[0054] Figure 1 shows the results of tensile tests on Comparative Example 1 (Comparative Example in the drawing) and Invention Example 2 (Invention Example in the drawing). As can be seen from the graph in the drawing, in the case of Invention Example 2, which satisfies the conditions of the present invention, there was almost no decrease in tensile strength and elongation before and after plating. However, in the case of Comparative Example 1, it can be seen that the austenite ratio in the base steel sheet is insufficient, resulting in a large change in strength before and after plating and a small decrease in elongation.

[0055] FIG. 2 is a photograph of the welded portions of Comparative Example 1 and Invention Example 2. As can be seen from the photograph, numerous LME cracks occurred in the welded portion of Comparative Example 1, but no LME cracks were observed in Invention Example 2, demonstrating excellent weldability.

[0056] FIG. 3 shows the results of evaluating the corrosion resistance of Comparative Example 1 and Invention Example 2. As can be seen from the photograph in the drawing, Invention Example 2 exhibited far superior corrosion resistance compared to Comparative Example 1.

[0057] As discussed through the above examples, the advantageous effects of the present invention have been confirmed.

Claims

1. The steel sheet includes an austenitic base steel sheet containing an austenitic structure at 70% by area or more, and an aluminum-based plating layer formed on the base steel sheet, The base steel sheet contains ferrite in an amount of 80% by area or more in a surface layer portion, which means a region extending from an interface with a coating layer toward an interior of the base steel sheet to a depth of 100 μm, The aluminum-based plated steel sheet has a composition containing, by weight, 0.7 to 5% Si, 1.5 to 15% Zn, 0.1 to 1.5% Mn, and the balance being Al and unavoidable impurities.

2. The aluminum-based plated steel sheet according to claim 1, wherein the aluminum-based plating layer further contains, in weight ratios, one or both of elements selected from the group consisting of 10 to 60% Fe and 2.5% or less Mg.

3. The aluminum-based plated steel sheet according to claim 2 , wherein the aluminum-based plating layer further contains Cr, Mo, and Ni in a total content of 0.5 wt % or less.

4. The aluminum-based plated steel sheet according to claim 1, wherein the austenitic base steel sheet contains 5 to 25% by weight of Mn.

5. The aluminum-based plated steel sheet according to claim 1, wherein the austenitic base steel sheet has a composition containing, by weight, Mn: 5 to 25%, C: 0.4 to 0.8%, Al: 0.5 to 3%, B: 50 ppm or less, and the balance being Fe and unavoidable impurities.

6. The aluminum-based plated steel sheet according to claim 5 , wherein the austenitic base steel sheet further contains the elements Ti, Nb, and Mo in a total amount of 0.5 wt % or less.

7. A method for producing the aluminum-based plated steel sheet according to claim 1, comprising the steps of: preparing an austenitic base steel sheet containing 70% or more by area of ​​an austenitic structure; Annealing the austenitic base steel sheet under conditions where the soaking zone temperature and the dew point temperature are 750 to 870° C. and −5 to 20° C., respectively; and The method for producing an aluminum-based plated steel sheet includes a step of immersing the heat-treated austenitic base steel sheet in a plating bath having a composition, by weight, of 2 to 12% Si, 5 to 30% Zn, 0.1 to 3% Mn, the balance being Al and unavoidable impurities, and maintained at a temperature of 550 to 650°C, to perform hot-dip plating.

8. The method for producing an aluminum-based plated steel sheet according to claim 7, wherein the plating bath further contains, by weight ratio, one or both of elements selected from the group consisting of Fe: 4% or less and Mg: 5% or less.

9. The method for producing an aluminum-based plated steel sheet according to claim 7, wherein the plating bath further contains Cr, Mo, and Ni in a total content of 0.5 wt.% or less.

10. The method for producing an aluminum-based plated steel sheet according to claim 7, wherein the temperature of the austenitic base steel sheet when immersed in the plating bath is 550 to 650°C.

11. The method for producing an aluminum-based plated steel sheet according to claim 7, wherein the austenitic base steel sheet contains 5 to 25% by weight of Mn.

12. 8. The method for producing an aluminum-based plated steel sheet according to claim 7, wherein the austenitic base steel sheet has a composition containing, by weight, 5 to 25% Mn, 0.4 to 0.8% C, 0.5 to 3% Al, 50 ppm or less B, and the balance being Fe and unavoidable impurities.

13. The method for producing an aluminum-based plated steel sheet according to claim 12, wherein the austenitic base steel sheet further contains the elements Ti, Nb, and Mo in a total amount of 0.5 wt% or less.

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