Effects of reheating duration on the microstructure and tensile properties of in situ core–shell-structured particle-reinforced A356 composites fabricated via powder thixoforming

A novel in situ core–shell-structured Ti@(Al–Si–Ti) particulate-reinforced A356 composite was synthesized via powder thixoforming. It is noted that there is a significant improvement in toughness of the particulate-reinforced Al matrix composites, and the problems related to fabrication techniques were also solved. The effects of reheating duration at a semisolid temperature of 600 °C on the microstructure and tensile properties of the resulting composites were investigated. The results indicated that a thick, compact Al–Si–Ti intermetallic shell formed around the Ti powders when the reheating time was at 50 min. A composite containing these reinforcing particles exhibited good tensile properties. Its ultimate tensile strength and yield strength (YS) were decreased by only 2.1 and 3.5%, respectively, while its elongation was increased by 167.8% and up to 8.3%, compared to the (Al, Si)3Tip/A356 composite that was thixoformed after the Ti powders had completely reacted. This occurred because the core–shell-structured particles with hard, compact shells exhibited strengthening role comparable to that provided by the monolithic (Al, Si)3Ti intermetallic particles, and the Ti core effectively inhibited or delayed crack propagation by blunting crack tips and severe plastic deformation. In addition, a modified shear lag model that incorporated the indirect strengthening mechanisms and varying shell thicknesses of Al–Si–Ti intermetallics was proposed to successfully predict the YS of the composites.