Cosmetic Corrosion of Aluminum Closure Panels: Lab Testing vs Field Performance

The correlation of lab test results with field performance for painted steel and galvanized steel automotive closure panels is now well established after many years. Although aluminum closure panels have been used on certain vehicles for many years, it has only been in more recent times that their usage has increased to a point where the issue of correlating lab and field corrosion data has become more essential. Many tests in the automotive industry were developed specifically for steel and their applicability to aluminum closures is uncertain. On the other hand, many of the standard corrosion tests used on aluminum were designed for aluminum applications other than automotive, e.g., architectural or packaging, so that the test environment and product requirements were very different. In this paper, a number of standard corrosion tests, including filiform, salt spray and cycling environment, were carried out on AA6111 and AA6016 closure sheet materials for comparison with field data. Analysis of the mode of corrosion failure was made as well as comparison of the extent of corrosion. The reasons for the variations in failure modes and extent of corrosion are discussed.