Effect of sulfuric acid anodizing time on adhesion and corrosion resistance of 5052 aluminum alloy with two-layer anodized films

To fabricate multi-materials joining between aluminum alloy and engineering plastics for automotive weight reduction, we have developed a two-step anodizing process to improve adhesion and corrosion resistance for 5052 aluminum alloy. The two-step anodizing process consists of phosphoric acid anodizing (PA) followed by sulfuric acid anodizing (SA), with the PA film on the upper layer and the SA film on the lower layer. In this study, the effect of SA anodizing time on adhesion and corrosion resistance was evaluated for the two-step anodizing process on 5052 aluminum alloy. Adhesion was around 17 MPa even when the SA anodizing time was varied. On the other hand, anodic polarization measurements showed that increasing the SA anodizing time resulted in a decrease in corrosion current density and a positive shift in corrosion potential, indicating improved corrosion resistance. In the two-step anodizing process, the morphology and chemical state of the PA film was important for adhesion, and the thickness of the SA film was important for corrosion resistance.