Search Results

A co-operative program initiated by the Automotive Aluminum Alliance and supported by USAMP continues to pursue the goal of establishing an in-laboratory cosmetic corrosion test for finished aluminum auto body panels that provides a good correlation with in-service performance. The program is organized as a task group within the SAE Automotive Corrosion and Protection (ACAP) Committee. Initially a large reservoir of test materials was established to provide a well-defined and consistent specimen supply for comparing test results. A series of laboratory procedures have been conducted on triplicate samples at separate labs in order to evaluate the reproducibility of the various lab tests. Exposures at OEM test tracks have also been conducted and results of the proving ground tests have been compared to the results in the laboratory tests. Outdoor tests and on-vehicle tests are also in progress. An optical imaging technique is being utilized for evaluation of the corrosion.

The pretreatment of aluminum sheet material in preparation for further paint application can be challenging due to the presence of a thick oxide layer. The composition of the oxide layer is primarily aluminum oxide, but it may also contain magnesium that is typically dispersed unevenly throughout the oxide layer. Zinc-phosphate systems remove much of the oxide layer on aluminum, but questions remain on the extent of removal of the oxide layer by zirconium oxide-based pretreatments and how these oxide layers may affect the zirconium oxide-based pretreatment deposition on aluminum. Several methods have been used to characterize the coating of zirconium oxide-based pretreatments on aluminum. Scanning electron microscopy at very high magnification reveals a coating on aluminum that is significantly different in morphology than the same coating chemistry on steel substrates.