Hitherto, a Zn plated steel obtained by performing plating of a Zn-containing alloy on the surface of a steel has been used in wide fields of, such as automobiles, home appliances, and construction materials. However, since Zn has problems of rising prices, depleting resources, and the like, there is a demand for a plating metal that can replace Zn.
Meanwhile, Al is cheap and also has a rich amount of deposits. Due to excellent corrosion resistance and heat resistance, an aluminum plated steel sheet that is plated with aluminum, similarly to Zn plated steels, is widely used for home appliances, and construction and automobile structural materials.
However, the aluminum plated steel sheet has a problem of a relatively small sacrificial corrosion-preventing action. This is because Al has a characteristic of being easily passivated, particularly, in a dry environment, and the sacrificial corrosion-preventing performance is degraded due to generation of a passive film. Therefore, it has been difficult to replace a zinc plate having an excellent sacrificial corrosion-preventing performance with an aluminum plate of the related art.
In recent years, since there has been a strong demand for a highly corrosion-resistant steel in which corrosion (for example, perforation corrosion) does not occur over a long period of time (for example, for several years) even in a highly corrosive environment, a number of proposals have been made to enhance the corrosion resistance of a hot-dip aluminum alloy plated steel sheet (for example, refer to Patent Documents 1 to 4).
In the proposals, steel sheet compositions or plating bath compositions are devised, and the comprehensive corrosion resistance of a hot-dip aluminum plated steel sheet is improved. Meanwhile, recently, as a result of diversifying uses of hot-dip aluminum plated steel sheets, there have been increasing cases in which hot-dip aluminum plated steel sheets are used after being cut into a necessary shape or severely deformed. Therefore, there is a strong demand for an increase in shear cut edge corrosion resistance and processed part corrosion resistance, that is, improvement of the sacrificial corrosion-preventing performance.
Patent Document 5 discloses an Al plated steel sheet having excellent processed part corrosion resistance and end surface corrosion resistance. However, since the steel sheet includes expensive Zn in the plated layer, the steel sheet is disadvantageous in home appliances, and construction and automobile structural materials in terms of costs.
Patent Document 6 discloses a high-strength Al plated steel sheet having excellent processed part corrosion resistance, but quenching is essential after a pressing process, and versatility is lacking.
Patent Document 7 discloses an aluminum alloy plated steel containing Mg and Ca. However, in the disclosure, the method of attaching a plating layer to a steel is not limited to hot dipping, and no studies have been performed regarding stable manufacturing through industrially advantageous hot dipping.