Method for manufacturing an electro-galvanized steel sheet excellent in bare corrosion resistance and adaptability to chromating, and product thereof

Abstract

In a Zn-ion based acidic galvanizing bath containing at least one additive selected from the group consisting of: ______________________________________ (a) Cr.sup.3.sup.+ 50 - 700 ppm, (b) Cr.sup.6.sup.+ 50 - 500 ppm, (c) Cr.sup.3.sup.+ and Cr.sup.6.sup.+ 50 - 700 ppm, in which Cr.sup.6.sup.+ being 500 ppm at the maximum, (d) In ion 10 - 3,000 ppm, and (e) Zr ion 10 - 2,500 ppm; and: (f) Co ion 50 - 10,000 ppm, ______________________________________ A steel sheet is subjected to an electro-galvanizing treatment to form a first galvanizing layer on the surface thereof; and then, said electro-galvanized steel sheet with said first galvanizing layer formed thereon to a conventional chromate treatment. With a view to further increasing the amount of deposited chromate on said chromated electro-galvanized steel sheet, said electro-galvanized steel sheet with said first galvanizing layer formed thereon is subjected to another electro-galvanizing treatment in a conventional acidic galvanizing bath containing zinc only to form a second galvanizing layer consisting exclusively of at least 0.2 g/m.sup.2 zinc on said first galvanizing layer; and then, said electro-galvanized steel sheet with said first and said second galvanizing layers formed thereon is subjected to a conventional chromate treatment.

Dependencies are inferred from the claim text.