Corrosion Resistance and Paintability of Zinc and Zinc-Alloy Coatings for Automotive Sheet

Electroplated and hot-dip-galvanized coatings have been widely used by the automobile industry for corrosion protection of unexposed surfaces against perforation. There is a growing interest in replacing these essentially pure zinc coatings with thinner, more corrosion resistant zinc-alloy coatings, and also in using the alloy coatings on exposed surfaces to achieve cosmetic-corrosion resistance and improved paint performance. This paper presents the results of various tests conducted to evaluate the performance of several Fe-Zn and Ni-Zn alloy coatings for these services. The coatings were evaluated in over-the-road corrosion tests and indoor “scab” corrosion tests, as well as conventional salt-spray tests.