| 摘要 |
PURPOSE:To form a zinc phosphate film having good quality without eluting a large amt. of Al into a zinc phosphate treating liquid by forming further a pure Zn plating layer on a steel sheet hot-dipped with a Zn-Al alloy then subjecting the same to a zinc phosphate treatment. CONSTITUTION:A plating layer consisting of pure Zn is further electroplated to 0.5-10mu thickness on the plating layer consisting of Zn-Al alloy in the stage of forming a zinc phosphate film by a zinc phosphate treating liquid on a steel sheet subjected to hot dipping of a Zn-Al alloy contg. 3-5% Al. The steel sheet is thereafter treated with the zinc phosphate treating liquid contg. 0.85-1.7g/l Zn ion, 1.0-2.5g/l Ni ion, 5.5-10g/l PO4 ion, 0.8-1.5g/l NO3 ion and 1.5-5.5g/ lF ion and having <=50ppm accumulated Al ion eluted from the Zn-Al plating layer to form the zinc phosphate film having excellent performance on the Zn-Al plated steel sheet. |
