Molten Zn-Al alloy-plated steel sheet and manufacturing method thereof

摘要

A molten Zn-Al alloy-plated steel sheet with excellent blackening resistance and corrosion resistance, and a manufacturing method thereof are provided. On at least one surface of the steel sheet, a molten Zn-Al alloy plating layer is formed having a composition comprising, in mass%, Al: 3.0-6.0%, Mg: 0.2-1.0% and Ni: 0.01-0.10%, the remainder consisting of Zn and unavoidable impurities, and further, a chemical conversion film containing molybdates is formed as the upper layer of said molten Zn-Al alloy plating layer. By this means, the surface of the plating layer has a structure containing, by surface area ratio, 1-50% of a Zn-Al-Mg ternary eutectic, and, by means of the material / structure of the plating layer and also the chemical conversion film containing molybdates formed on the upper layer of said plating layer, this molten Zn-Al alloy plated steel sheet has excellent blackening resistance and corrosion resistance.