Alternatives to Electrocoating Aluminum in Automotive Applications

The inherent corrosion resistance of aluminum is much greater than automotive steels. To demonstrate this principle in a fashion acceptable to the automotive industry, a test program was run which incorporated lab, test track and real life trials on both unpainted and painted aluminum and painted steel. The lab program consisted of neutral salt and cyclic corrosion tests. Having demonstrated that aluminum does not need electrocoating for good corrosion integrity, alternatives to electrocoating which would allow primers to be applied only where necessary for esthetic purposes were sought. Several primers were selected for study based upon current automotive usage. Factors such as the degree of pretreatment prior to primer application and the presence of residual lubricant on the metal were evaluated. Laboratory testing of primer on aluminum alloys for both structural members and body skin applications showed that paint performance equivalent to, and in certain cases surpassing, conventional electroprimer could be achieved. Lab testing in this case included filiform corrosion evaluation.