Effect of alloy types on the anodizing process of aluminum

Specimens of AA 5083 and AA 6111 (unheat- and heat-treated) were investigated in comparison with the pure aluminum during anodizing in sulfuric acid bath using electrochemical techniques, SEM/EDS and XRF. The alloy type affects the kinetics of anodizing but certain qualitative characteristics and the basic aspects of the anodizing mechanism are similar for the alloys and pure aluminum. We found that for AA 6111 alloy, the stage of rearrangement of the pores during anodizing before the current reaches a steady-state value is missing due to enrichment of the alloying elements at the oxide/metal interface. For alloys under certain anodizing conditions, formation of a resistive film at the bottom of the pores results in decreasing anodizing current. This phenomenon is more prevalent for AA 5083 alloy than for AA 6111. For AA 6111 alloy, the heat treatment affects anodizing kinetics and improves the anodizing efficiency. Understanding the effect of alloy types on anodizing process under various operating conditions (voltage, temperature and sulfuric acid concentration) will enable us to optimize porous oxide structures for improved coating performance in color ability and corrosion resistance.