The Effect of Phosphate Chemistry and Rinsing Conditions on the Corrosion Resistance and the Paint Adhesion of Zinc Coated and Cold Rolled Sheet Steels

A representative selection of commercially available zinc phosphate pretreatments were evaluated over four sheet metal substrates. The intent of the study was to compare cosmetic corrosion resistance and paint adhesion performance of the various sheet metal/phosphate combinations under present cathodic electrocoat and topcoat systems. While laboratory applied pretreatments were used, an attempt was made to duplicate deficient conditions on some specimens by eliminating rinse conditioner and/or chromium rinse. Panels were tested using the High Temperature Chipping Corrosion and Accelerated Outdoor Corrosion cycles. The resulting creepback from scribe and paint loss data were analyzed and used to draw conclusions regarding relative performances of rinse conditions, phosphates and substrates.