Comparative Study on Road and Outdoor Exposure Test on Corrosion Resistance of Painted Aluminum Sheet for Automobiles

Currently, weight reduction in automobiles is a serious concern and application of aluminum sheet is accelerated to meet this purpose. Inevitably, the painted aluminum sheet is required to have a good corrosion resistance. So it is necessary to evaluate the corrosion resistance of painted panels in short period of time.

We thought that the outdoor exposure test in severe conditions was the best test for judging corrosion resistance of painted aluminum panel, and conducted the road tests of 4 routes in Japan and outdoor exposure test in Okinawa for two years and compared them to each other. The following resuts were obtained;

1. (1)
   Atmosphere of outdoor exposure site was as follows;

Outdoor exposure test accelerated the deterioration of paint film and simultaneous under paint film corrosion 4∼5 times faster than the road test. The form of deterioration of paint film and corrosion of the base matal after outdoor exposure was identical with that of the road test.

1. (2)
   Corrosion resistances of the painted panel were affected directly by those of the base metal. The order of corrosion resistance was as follows;

1. (3)
   The corrosion resistance of painted panels was affected by the pretreatment. Chromic chromate and HF added zinc phosphate were excellent.
2. (4)
   After the test, the paint film was removed and the surface of the base metal was investigated. This method enabled a more detailed investigation and evaluation of painted aluminum panel.