Strengthening Mechanism and Anisotropy of Mechanical Properties of Si3N4p/Al-Mg-Si Composites Fabricated by Sintering and Extrusion

The Si3N4p reinforced Al-Mg-Si (Si3N4p/6061Al) composites with various Si3N4p contents were fabricated by hot pressing sintering and hot extrusion. The strengthening mechanism was clarified, and the effects of Si3N4p on microstructure, mechanical properties and anisotropy were investigated. The results showed that Si3N4p, Mg2Si phase, and lots of micropores distributed in as-sintered ingots, and hot extrusion effectively reduced the number of micropores. The Si3N4p was well boned with Al matrix, and no defect or reaction product existed on the interface. Both dynamic recovery and dynamic recrystallization took place during hot extrusion, and the addition of Si3N4p refined the grain structure by promoting the particle stimulated nucleation effect. The main texture of as-extruded composites was brass, while its intensity was gradually weakened with the increase of Si3N4p content. The tensile strength and wear resistance were enhanced by the addition of Si3N4p due to the strengthening mechanisms of load transfer, grain refining, and dislocation strengthening. The extruded composite without Si3N4p exhibited the strong anisotropy of tensile properties and planar anisotropy. Since the addition of Si3N4p was beneficial to refine the grain structure and weaken the intensity of brass, both the tensile properties anisotropy and planar anisotropy were significantly reduced.