FORMATION OF ZINC PHOSPHATE COMPOSITE FILM LAYER EXCELLENT IN HIGH SPEED PRESS FORMABILITY ON ZINC-CONTAINING METAL PLATED STEEL SHEET

摘要

PURPOSE:To form a zinc phosphate composite film layer excellent in high speed press formability on a Zn-contg. metal plated steel sheet by subjecting the surface of a Zn-contg. metal plated steel sheet to activating treatment and thereafter treating it by a soln. of chemical conversion treatment having a specified compsn. CONSTITUTION:A galvanized steel sheet or a galvannealed steel sheet is previously treated by an Ni or Co ion-contg. soln. or a Ti colloidal aq. soln. to activate its surface. Next, it is treated by a soln. of chemical conversion treatment contg. 10 to 30g/l of phosphoric acid ions, 1.0 to 15g/l of nitric acid ions, 0.1 to 8.0g/l of Zn ions, 0.1 to 8.0g/l of at least one kind of metallic ions among Fe, Ni, Mn, Co, Ca and Mg and at least one kind of fluoride ions and complex fluoride ions by 0.1 to 3.0g/l expressed in terms of fluorine ions or moreover, in which nitrous acid ions contain a reaction accelerator such as inorganic peroxide and hydrogen peroxide, the weight ratio of Zn ions to the other metallic ions is regulated to (0:1: 1) to (10: 1) and the acid ratio of the total acidity to free acidity is regulated to (8:1) to (30:1).