Improving the corrosion protection of AA6061 T6–10% Al2O3 using new surface pre-treatments prior to fluoropolymer coatings

The corrosion protection performance of AA6061 T6–10% Al2O3 composite, coated with fluoropolymer, was investigated in 3.5% NaCl. A comparison between epoxy-treated specimens (after applying the same topcoat under scratched conditions) of clear perfluoropolyether (PFPE)-based topcoat with other specimens treated with eight different types of new pre-treatments depends on cerium, manganese, vanadium and molybdenum. The corrosion rates of the epoxy-treated specimens increased dramatically after less than 1 month of exposure in NaCl. Conversely, the new pre-treatments showed outstanding corrosion protection even after 2 months in NaCl. A general model has been used to analyze the impedance data in terms of reactions occurring during the interaction of the coated metals with the environment. Based on this analysis the eight pre-treatments have been ranked in terms of their efficiency in providing corrosion protection by the organic coating. A comparison between impedance results and visual observation over 2 months confirms that AC impedance data can be used efficiently to characterize organic coating/metal systems. It was found that these types of pre-treatments not only improve the protective power against filiform corrosion, but also maintain the adhesion performance within acceptable ranges.