Phosphate chemical conversion treatment

PURPOSE: To form a phosphate chemical conversion treatment film having corrosion preventive effect and excellent adhesive power to the coating film and org. film formed thereon by bringing Zn and Zn alloy plated steel products into contact with a treating liquid of a specified compsn. contg. Zn, phosphate, Mg, etc. CONSTITUTION: Iron and steel product, such as steel sheet, subjected to electrogalvanizing, hot dip Zn coating and Zn alloy plating the brought into contact with the treating liquid having the following compsn. to form the phosphate films having the excellent corrosion preventive effect by itself and the excellent adhesive power to the coating materials and org. films applied thereon. Namely, the compsn. of the treating liquid contains 0.5 to 5.0g/l Zn, 3 to 20g/l phosphate (as P 2 O 5 ) and 0.3 to 3g/l Mg. The weight ratio of Mg/Zn is (0.5 to 10):1, the S value is 0.1 to 0.4. If nitrate is used as an accelerator, the weight ratio of NO 2 :P 2 O 5 is specified to (0.15 to 0.7):1 and if the liquid contains Ni ions, the amt. thereof is confined to ≤1.5g/l. Further, a liquid having the compsn. contg. ≤3g/l fluoride, such as HF, is used at need. COPYRIGHT: (C)1990,JPO