PURPOSE: To improve the plating adhesion and corrosion resistance by treating a galvanized steel sheet with a soln. contg. a magnesium alkoxide to form a magnesium oxide coating film.
CONSTITUTION: A soln. contg. a magnesium alkoxide is applied on a galvanized steel sheet and heat-treated to form a magnesium oxide coating film of 0.1-10.0g/m2. Besides, ≥1 kind among water, oxygen, oxide ion and hydroxide ion is incorporated into a molten salt bath consisting essentially of a magnesium salt, and a galvanized steel sheet is dipped in the bath to form a magnesium oxide coating film on the surface. Alternately, the galvanized steel sheet is cathodized in a molten salt bath consisting essentially of a magnesium salt and contg. ≥1 kind among water, oxygen, oxide ion and hydroxide ion to form a magnesium oxide coating film on the surface.
NAKAJIMA SEIJI
NAKAKOUJI NAOMASA
MORITO NOBUYUKI
