The role of Si incorporation on the anodic growth of barrier-type Al oxide

Abstract For Al alloys (e.g. Al-Si series) surface treatment like anodizing is a necessary step for applications in aggressive environments. Si-surface enrichment caused by processing can alter importantly the anodizing process. Model alloys with Si supersaturated in Al layer grown by PVD have been used to investigate the effect of the Si content on the anodizing process. Different Si concentrations of 0, 4, 7, 10 at.% are considered and compared. The morphology and in-depth microstructure of the oxides are derived for the different Si contents and anodizing potentials. Si was found to have a dramatic effect on the void and defect formation during barrier Al oxides growth even for Si concentrations as low as 4 at.%. Importantly, the anodizing oxide layer appears to be heterogeneous in the cross section, with Si accumulation close to the metal oxide interface while pure Al oxide is first formed as a barrier on the top surface.