A method for improving the mechanical properties of a hypereutectic Al–Si alloy by introducing the α-Al phase

Abstract The low ductility of hypereutectic Al–Si alloys, which is attributed to the coarse primary silicon particles in the microstructure, limits their application potential. The mechanical properties of hypereutectic Al–Si alloys strongly depend on the size and morphology of the primary Si. This study focused not only on the effect of the primary Si content, but also on the ductile α-Al phase, which does not occur in the microstructure of hypereutectic Al–Si alloys when using traditional alloying methods. We propose a novel method which allows introducing the α-Al phase in order to improve the mechanical properties of hypereutectic Al–Si alloys, e.g., the hardness, tensile strength, and ductility. The formation of the α-Al phase and a refinement of the primary Si were simultaneously achieved via an unconventional method, which is based on mixing a high-temperature molten Al–Si alloy with low Si content into a low-temperature semi-solid Al–Si alloy with high Si content. The resulting alloy showed an improved ductility, hardness and tensile strength compared to a traditionally-cast Al–Si alloy with the same nominal Si content.