Effects of Mold Temperature on the Microstructure and Tensile Properties of Ti@(Al-Si-Ti)p/A356 Composite Prepared via Powder Thixoforming

Abstract

A novel A356 Al-based composite reinforced with Ti@(Al-Si-Ti) core-shell-structured particles (Ti@(Al-Si-Ti)p) was prepared utilizing powder thixoforming method. The effects of mold temperature on the microstructures and tensile properties of the composites, as well as the toughening mechanisms, were investigated. The results indicated that the primary α-Al particles gradually coarsened and evolved into large-sized interconnected particles with the rise of mold temperature. Simultaneously, the core-shell structured reinforcements tended to agglomerate and the eutectic Si phases gradually coarsened and became spheroidal. The tensile properties of the synthesized composites firstly increased as the mold temperature rose from 150 °C to 200 °C due mainly to the improvement of the microstructure compactness and the spheroidization of the eutectic Si phases, and then decreased resulting from the coarsening of both the primary particles and eutectic Si phases, the agglomeration of the reinforcing particles and the deteriorated microstructure compactness. The composite thixoformed at 200 °C had an excellent elongation of 8.3% besides high tensile strengths. The excellent ductility can be attributed to decreased crack size in the shell and delayed crack propagation by plastic deformation, and multiplication of secondary cracks in the Ti core that originated from the core-shell structure of the reinforcements.