Abstract
Anodic oxide films formed on aluminum by anodizing in alkaline solution is generally recognized to show higher protective performance against dissolution under alkaline environmental conditions. In this study, electrochemical impedance spectroscopy (EIS) was applied to evaluate the time variations of charge transfer resistance, Rct for the anodically oxidized aluminum during the immersion in alkaline environment. Also SEM, FIB-SIM, and TEM observations were employed to investigate pit morphology for each stage of the dissolution process. It was found that the films formed by anodizing in sodium carbonate (Na2CO3, pH=11.5) solution showed higher resistance against alkaline dissolution than the films formed in ammonium tartrate ((NH4)2C4H4O6, pH=6.7) solution or sulfuric acid (H2SO4, pH=0.0) , because of the high corrosion performance of the barrier layer. The Rct increased as the thickness of the barrier layer increased.
