Improved mechanical properties of mechanically milled Mg₂Si particles reinforced aluminum-matrix composites prepared by hot extrusion

From the viewpoints of particle refinement and homogeneous distributions of reinforcing phase, this work proposed a novel method to prepare Al/Mg₂Si composites. Mg₂Si particles were synthesized by solid-state reactions of Mg and Si powder mixtures at a high temperature, and then refined by mechanical milling (MM) for 12-36 h. Subsequently, the MMed Mg₂Si particles were incorporated into Al powder followed by hot extrusion for consolidation. The effect of milling time on microstructure and mechanical properties of the Al/Mg₂Si composites was investigated. As the milling time increased, the average size of the Mg₂Si particles in the composites became smaller, but the grain sizes of Al matrix remained almost unchanged. The hot-extrusion process was found to eliminate some particle agglomerations and promote size reduction and uniform dispersion of Mg₂Si particles in the Al matrix. The elastic modulus, yield strength, ultimate tensile strength (UTS), and wear resistance of the composites increased by 8%, 14%, 8.5%, and 38.2%, respectively, with increasing the milling time from 12 h to 36 h, but the elongation decreased by 41%. Furthermore, the hot-extruded Al/Mg₂Si composites exhibited high strength and ductility, for example, the UTS and elongation of the composites with 15 wt% Mg₂Si particles MMed for 36 h increased by 43% and 91%, respectively, compared to conventionally cast Al/Mg₂Si composites. The predicated elastic modulus by the Halpin-Tsai model is close to the experimental results. Moreover, the thermal mismatch strengthening is the dominate strengthening mechanism to improve the yield strength of the Al/Mg₂Si composites.