Strengthening mechanism and anisotropy of mechanical properties of Si3N4p/Al-Mg-Si composites fabricated by sintering and extrusion

Highlights: • Si₃N₄p/6061Al interface was in a good bonding status without any reaction product or defect. • Load transfer, grain refining, and dislocations were the main strengthening mechanisms. • Si₃N₄p greatly reduced the anisotropy by weakening the intensity of brass and refining the grains. 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.