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.