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

Abstract

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 α-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.