The Effect of Phosphate Pretreatment on Underfilm Corrosion of Painted Ni-Zn Alloy Coated Steel Strip

The results of scab corrosion tests conducted upon a painted commercial Ni-Zn alloy coating pretreated with various commercial phosphate chemical treatments are presented. The effect of these chemical treatments upon dry paint adhesion, blistering, and paint adhesion after water immersion (wet paint adhesion) is also shown. The results indicate that significant improvement in paint adhesion and a minimization of underfilm creepage can be effected by phosphate treating the nickel-zinc alloy surface with a zinc phosphate solution rich in manganese and nickel ions.