Primary Study of the Mechanism for Constant-Current Anodizing of Aluminum in Sulfuric Acid

The anodic oxidation process of aluminum in sulfuric acid has been investigated at constant current. The mechanism for the for-mation of anodic oxidation coating on Al was primarily studied,and the anodizing potential-time relation of Al was analyzed. Re-sults indicate that the potential -time relation of Al anodizing in sulfuric acid was dominated by regular stepped potential,and the regular stepped potential was measured as 0.039 V. Using anodi-zing current density -time curve,the porosity of the anodizing coating was determined to be about 0.1 %. In general,the regu-lar stepped potential was supposed to be related with the thickness of the barrier layer and it increased with increasing thickness of the barrier layer. Moreover,the barrier layer was first formed in the pores and then spread to other area of Al substrate when the barrier layer thickness increased by 1.53 μm.