Corrosion resistance of pre-coated aluminum sheets after forming

Abstract

Pre-coated aluminum sheets are superior in cost performance and productivity compared to aluminum sheets coated after press forming. Functional pre-coated aluminum sheets, with superior surface characteristics such as lubricity and corrosion resistance have been increasingly used in electrical and other industrial fields. In this paper, the function of corrosion resistance was taken up among these surface functions. And the effects of the glass transition temperatures of the films on the corrosion resistance of pre-coated aluminum sheets before and after forming were investigated. The corrosion resistances after forming of polyester pre-coated aluminum sheets with three different glass transition temperatures were investigated by salt spray test. It was found that corrosion resistances of the film with glass transition temperatures higher than the forming temperature were low. In the samples with low corrosion resistance after forming, whitening of the film was observed. The corrosion reaction resistance values after forming of polyester pre-coated aluminum sheets with three different glass transition temperatures were also measured by electrochemical impedance spectroscopy test. It was found that corrosion reaction resistance values of the film with high glass transition temperatures showed the small values after stretching. It could recognize correlation in above two test results. After forming, micro cracks could be observed only in the sample with high glass transition temperature. This micro cracks made the corrosion resistance of the samples decrease.