Cosmetic Corrosion of Painted Aluminum Automotive Body Sheet

In recent years, increasing attention has been given to the need to develop an accelerated laboratory test method(s) for cosmetic corrosion of painted panels that realistically simulate in-service exposure [1,2]. Much of that work has focused on steel substrates. The purpose of this research is to compare the corrosion performance of painted aluminum sheet as determined from various laboratory methods and in-service exposure, and to determine the most realistic accelerated test method. Several aluminum sheet products from the 2xxx, 5xxx, and 6xxx alloy series have been tested. Steel substrates similar to those used in other programs [1,2] have also been included. The results indicate that of the laboratory test methods investigated, ASTM B117, Continuous Salt Spray provides the best correlation with outdoor data for aluminum alloys. For steel, however, ASTM B117 correlates poorly. In addition, there is considerable difference in the relative magnitudes and morphologies of corrosion, and occasionally in the relative rankings, as a function of test method. The influence of alloy composition and zinc phosphate coating weight are also discussed.