Self-sealing anodization approach to enhance micro-Vickers hardness and corrosion protection of a die cast Al alloy

Die cast, high-Si content ADC12 Al alloy samples were successfully anodized without surface cracks. This was accomplished with a 0.3 M sulfuric acid electrolyte with a high concentration of sodium aluminate. During anodization, the AlO2- anions were attracted to the positively-charged Al substrate and deposited in the cracks formed by un-oxidized Si islands within the ADC12. Anodic films prepared in electrolytes with a high concentration of AlO2- drastically enhanced surface morphology, thickness uniformity, Vickers hardness, and corrosion behavior in comparison with anodic film prepared without AlO2- concentration. The simultaneous sealing mechanism by AlO2- anions during anodization is reported in detail.