Enhancing Microhardness and Corrosion Resistance of Anodic Oxides Grown on Hypoeutectic Al–Si Alloys Pretreated by Low-Energy High-Current Electron Beams

Anodic oxidation is widely employed in industry to impart high mechanical properties and improve the corrosion resistance of Al-Si alloys. However, compared to pure Al, the high content of Si prevents the growth of a uniform anodic layer, leading to the formation of cracks and porosities within the oxide. In the present work, low-energy high-current electron beam is used as pretreatment of a hypoeutectic Al-Si alloy to enhance the properties of the anodic oxide. Electron beam modified samples showed a fine and homogenous dispersion of Si in the alpha-matrix, together with a content reduction of Si in the treated layer. Hard anodic oxides grown on electron beam pre-treated alloys exhibited a higher microhardness, increased by 65%, and a lower corrosion current density, decreased by 94%. Cross-sectional SEM morphology and EDX elemental maps showed less defective anodic oxides, in contrast with oxide formed on as-cast hypoeutectic Al-Si alloys.