Paintability Performance of Metallic Coated Steels

Eleven coated steel substrates and cold-rolled steel were painted with three automotive paint systems and subjected to three different atmospheric corrosion environments and two different on-vehicle corrosion environments. Exposures were designed to give results indicative of the cosmetic corrosion behavior of these materials when used in exposed automotive body panel applications. Results clearly show that of the twelve materials tested, zinc-base coated steels performed best in all environments studied. A correlation is evident between heavier zinc coatings and longer term cosmetic corrosion resistance. Galvannealed steels offer approximately equivalent cosmetic corrosion resistance at equal coating weights when compared to galvanized steels. Cold-rolled steel does not offer long-term cosmetic corrosion resistance for automotive applications. In addition, a zinc-rich primed exposed surface does not offer a substantial increase in cosmetic corrosion protection in comparison to cold-rolled steel. Results of these exposures were also compared to the results of various accelerated corrosion tests to attempt to establish a correlation between long-term exposures and accelerated methods for evaluation of cosmetic corrosion performance.