Effect of Barrier Layer on Corrosion Resistance of Porous-Type Anodic Films Formed on AA2055 Al–Cu–Li Alloy and Pure Aluminum

Abstract

It is known that typical porous-type anodic films formed on aluminum and its alloys consist of two layers, i.e. a thick porous layer and thin barrier layer. However, the effect of the two layers on corrosion resistance of the anodic film is still not clear, which prevents a thorough understanding of the protection mechanism of the anodic film, thereby limiting the potential to further optimize the anodizing treatment. Herein, an electrochemical barrier layer thinning (EBLT) process was employed to reduce the thickness of the barrier layer of the porous-type anodic films formed on an AA2055 Al–Cu–Li alloy and pure aluminum. Then the structure and composition of the anodic films before and after immersion in a NaCl solution were studied in a comparison manner. It was found that the EBLT process evidently decreased the corrosion resistance of the anodic films formed on AA2055 alloy and pure aluminum. Thus, it was conclusively validated that the barrier layer of the porous-type anodic film played a decisive role in controlling the corrosion resistance of anodized aluminum and aluminum alloys prior to post sealing.