Effects of Inter-metallic Particles on Corrosion Resistance of Anodic Films on 7A04-T6 Aluminium Alloy

In order to study the effects of inter-metallic particles on the corrosion resistance of anodic films on 7A04-T6 aluminium alloy, the metallographic microstructure of hot extrusion rod of 7A04-T6 aluminium alloy was observed by scanning laser confocal microscopy. The inter-metallic particles were identified by backscattered electron image. The morphologies of the areas with inter-metallic particles were traced before and after anodization and after immersion in exfoliation corrosion liquid for different times. The electrochemical impedance spectroscopy (EIS) was measured. The results indicated that the cavities caused by larger inter-metallic particles in the anodic films on 7A04 aluminium alloy were responsible for the corrosion beneath anodic films, the cracking and final complete failure of anodic films.