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)₃Ti_p/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.