Effects of ageing treatment on corrosion behavior of 7075 aluminum alloy coated by micro arc oxidation (MAO)

The effects of ageing treatment on corrosion behavior of 7075 aluminum alloy coated by MAO have been investigated. The results suggest that precipitates (GPI, GP II zones, η and η’) formed after ageing play a significant role on the thickness, porosity and corrosion resistance of MAO coating. After MAO coating is deteriorated during corrosion test, TEM observations show that coarse and discontinuously distributed precipitates at grain boundary contribute to the electrochemical corrosion resistance. HAADF-STEM images and EDS maps exhibit that the Mg segregation at grain boundary decreases with increasing the ageing time which reduces the stress corrosion cracking (SCC) susceptibility.