| 摘要 |
PURPOSE:To form a zinc phosphate conversion film having excellent adhesiveness to paint when coated by treating a steel plate plated with Zn or a zinc alloy with a zinc phosphate soln. of specified composition contg. Mn and Ni ions. CONSTITUTION:A treating bath for forming a zinc phosphate conversion film contg. 0.5-1.5g/l Zn ion, 0.3-3.0g/l bivalent Mn ion, 0.5-4g/l bivalent Ni ion, and 5-30g/l phosphate ion is used as the treating bath when a zinc phosphate conversion film is formed on a steel plate plated with zinc or a zinc alloy. The concn. ratio of the Mn ion to Ni ion in the treating bath is regulated to be in the range A-B-C-D-E in the figure or preferably in the range a-b-c-d-e. The zinc phosphate conversion film having excellent resistance to corrosion and adhesiveness to paint after coating can be formed. |
