Effect of grain refinement by ECAP on the corrosion resistance of anodic coating of AA6063 prepared by pulse constant voltage anodizing process

This study investigates the effects of severe plastic deformation and post-deformation aging treatment of AA6063 substrates on the microstructure, corrosion resistance and hydrophobicity of anodic films prepared using a pulse constant voltage process. Equal Channel Angular Pressing (ECAP) was applied to AA6063 substrates for up to six passes, followed by aging thermal treatment. The processed substrates were anodized using a two-step anodizing method under constant pulse voltage and identical electrochemical conditions. The microstructure, corrosion behavior and hydrophobicity of the anodized films were analyzed. Results indicate that six ECAP passes significantly refined the grain size of AA6063, fragmented secondary phase particles, and redistributed them uniformly within the aluminum matrix. Increasing ECAP passes improved the order and uniformity of the anodic film while reducing its average porosity. Potentiodynamic polarization and EIS measurements revealed a mixed corrosion mechanism involving both uniform and pitting corrosion. With more ECAP passes, corrosion resistance increased, and localized pitting corrosion diminished. However, aging treatment of deformed substrates reduced corrosion resistance of the deposited anodic film and increased its susceptibility to localized pitting. Contact angle measurements showed that hydrophobicity improved with increased ECAP passes, with contact angle rising from 96.35° to 126.66° for Al-2P-A and Al-6P-A samples, respectively. Conversely, aging treatment reduced hydrophobicity, with contact angle decreasing from 126.66° to 105.93° for A-6P-A and A-6P-A-A samples, respectively.