PROCESS FOR PHOSPHATING METAL SURFACE TO MAKE THEREON A ZINC PHOSPHATE COATING FILM

摘要

A metal surface is processed with dipping by a firstzinc phosphating solution in which a fluoride complex and asimple fluoride are contained and a concentration of thissimple fluoride is 200 to 300 mg/l on a basis convertedinto the HF concentration and that of the fluoride complexis in a mole ratio with the simple fluoride converted intothe HF as shown as, [fluoride complex] / [simple fluoride]~ 0.01, and then the surface is processed with spraying bya second zinc phosphating solution in which a simplefluoride concentration is 500 mg/l or less and higher thanthat in said first zinc phosphating solution.Thus, on a metal surface is formed a zinc phosphatecoating film which is suitable for electrodeposition coating,particular for cationic electrodeposition coating, andsuperior in coating film adhesion, corrosion-resistance,particularly resistance for warm brine, and prevention ofscab-corrosion.