IMPROVEMENT FOR CORROSION RESISTANCE OF ZINC PLATING

摘要

PURPOSE:To improve the corrosion resistance of zinc plating by treating the surface of a zinc plated steel plate with an aq. soln. of ammonium chloride then subjecting the same to a tin substitution treatment, and if necessary, to a chromating treatment. CONSTITUTION:A zinc plated steel plate is immersed for 2-10 minutes in a soln. of 10-30 deg.C such as an aq. soln. of NH4Cl 4 of 2-10wt.% concns. After the stuck NH4Cl soln. is rinsed away, it is immersed for 5-30 minutes in a soln. of 10- 30 deg.C such as an aq. soln. of tin chloride or tin sulfate of 1.0-20g/l concns, whereby it is subjected to a tin substitution treatment. The substitution of zinc by tin is regulated to 1-5wt.% of the entire zinc. To this end, DC electrolysis of 10-100mA/dm2 is effected. If necessary, the steel plate is chromated by using an aq. soln. of CrO3 of 5-30g/l, whereby the corrosion resistance of the zinc plated surface is improved.