Aluminum-zinc plated steel sheet and method for producing the same

1. A method for producing an aluminum-zinc plated steel sheet, comprising a step of forming a covering film not containing resin through applying an aqueous surface regulator onto a plated steel sheet and drying the aqueous surface regulator on the plated steel sheet, the aqueous surface regulator having a pH of 7.5 to 10 and containing a basic compound (A) of transition metal other than cobalt and chromium, a cobalt compound (B), and water,

the basic compound (A) of the transition metal including at least one selected from a group consisting of ammonium salts, carbonates, chlorides, ammonium carbonate, alkali metal carbonates, amine salts, and diethanolamine salts,

wherein the plated steel sheet includes a steel sheet and a plating layer, the plating layer containing zinc and aluminum,

wherein a percentage of a total amount of a phosphorus compound and a fluorine compound in the covering film is 1% by mass or less, and

wherein a mass ratio of an amount of cobalt contained in the cobalt compound (B) to a total amount of the basic compound (A) is within a range of 1/25 to 1/1000.

2. The method for producing the aluminum-zinc plated steel sheet according to claim 1 , wherein

a peak metal temperature of the plated steel sheet in drying the aqueous surface regulator on the plated steel sheet is within a range of 40 to 200° C.

3. The method for producing the aluminum-zinc plated steel sheet according to claim 1 , wherein

the aqueous surface regulator consists of the basic compound (A), the cobalt compound (B), water, and at least one of an acidic component and a basic component for adjusting a pH.

4. The aluminum-zinc plated steel sheet produced by the method according to claim 1 , comprising:

the plated steel sheet including the steel sheet and the plating layer, and

the covering film that covers the plated steel sheet,

the covering film containing:

a basic compound of transition metal other than cobalt and chromium, derived from the basic compound (A) in the aqueous surface regulator; and

metallic cobalt, or metallic cobalt and a cobalt compound, derived from the cobalt compound (B) in the aqueous surface regulator,

the basic compound of the transition metal including at least one selected from a group consisting of ammonium salts, carbonates, chlorides, ammonium carbonate, alkali metal carbonates, amine salts, and diethanolamine salts,

an amount of the covering film per one side of the plated steel sheet being within a range of 0.01 to 0.8 g/m 2 ,

an amount in terms of mass of transition metal other than cobalt in the covering film per one side of the plated steel sheet being within a range of 4 to 400 mg/m 2 , and

an amount in terms of mass of cobalt in the covering film per one side of the plated steel sheet being within a range of 0.1 to 20 mg/m 2 .

5. The aluminum-zinc plated steel sheet according to claim 4 , wherein

the amount in terms of mass of cobalt in the covering film is greater than 0.5 mg/m 2 and not greater than 20 mg/m 2 .

6. The aluminum-zinc plated steel sheet according to claim 4 , wherein

a percentage of aluminum in the plating layer is within a range of 1% by mass to 75% by mass.

7. The aluminum-zinc plated steel sheet according to claim 6 , wherein

the plating layer contains magnesium, and

a percentage of magnesium in the plating layer is greater than 0%/o by mass and not greater than 6.0% by mass.

8. The aluminum-zinc plated steel sheet according to claim 6 , wherein

the plating layer contains Si so that a percentage by mass of Si to aluminum in the plating layer is within a range of 0.1% to 10%.

9. The aluminum-zinc plated steel sheet according to claim 6 , wherein

the plating layer contains at least one of: Ni in an amount of greater than 0% by mass and not greater than 1% by mass of the plating layer; and Cr in an amount of greater than 0% by mass and not greater than 1% by mass of the plating layer.

10. The aluminum-zinc plated steel sheet according to claim 6 , wherein

the plating layer contains at least one of: Ca in an amount of greater than 0% by mass and not greater than 0.5% by mass of the plating layer; Sr in an amount of greater than 0% by mass and not greater than 0.5% by mass of the plating layer; Y in an amount of greater than 0% by mass and not greater than 0.5% by mass of the plating layer; La in an amount of greater than 0% by mass and not greater than 0.5% by mass of the plating layer; and Ce in an amount of greater than 0% by mass and not greater than 0.5% by mass of the plating layer.

11. The aluminum-zinc plated steel sheet according to claim 4 , wherein

the transition metal in the basic compound includes zirconium.

12. The aluminum-zinc plated steel sheet according to claim 4 , wherein

the transition metal in the basic compound is at least one selected from a group consisting of zirconium, vanadium, molybdenum, and niobium.

13. The aluminum-zinc plated steel sheet according to claim 4 , wherein the basic compound of transition metal other than cobalt and chromium includes at least one selected from basic zirconium, basic zirconyl, basic zirconyl salts, basic zirconium carbonate, basic zirconyl carbonate, basic zirconium carbonate salts, and basic zirconyl carbonate salts.

14. The aluminum-zinc plated steel sheet according to claim 4 , wherein the basic compound of transition metal other than cobalt and chromium includes at least one selected from ammonium zirconyl carbonate, potassium zirconyl carbonate, sodium zirconyl carbonate, ammonium zirconium carbonate, potassium zirconium carbonate, and sodium zirconium carbonate.