A study on the self-sealing process of anodic films on aluminum by EIS

The electrochemical behaviors of anodized aluminum in neutral NaCl and Na2SO4 solutions were studied using electrochemical impedance spectroscopy (EIS). The results reveal that there is a self-sealing process for unsealed anodic film in neutral NaCl and Na2SO4 solutions. The resistance of the porous layer (Rp) and the capacitance of the barrier layer (CPEb) increase and the capacitance of the porous layer (CPEp) decreases with immersion time in the initial stage. Corrosion resistance provided by the anodic film is improved by the self-sealing process of the porous layer. However, chloride ions have an opposite effect. The improving effect of the self-sealing process on film resistance is decreased with the increase of chloride concentration of the solution.