Regulating the microstructure of Ti@TiAlSi core-shell structured reinforcing particles endows Al–Si alloy matrix composites with high strength and ductility

Forming spherical core-shell (CS) structured reinforcing particles, consisting of a Ti core and a surrounding TiAlSi intermetallic shell, by in situ reaction between Ti and Al matrix is a promising approach to overcome the strength-ductility trade-off in particle reinforced Al–Si matrix composites. However, the phase constituent and microstructure of the shells are highly sensitive to the Al–Si alloy composition and processing parameters of the powder thixoforming method. Therefore, the effects of Si content and partial remelting temperature on the microstructure of CS particles and the tensile properties of the resultant composites were investigated in this study. The results indicate that uniform and compact shell can be achieved only by the τ2-phase reaction layer generated during partial remelting. To form the τ2 phase, the Si content in the liquid phase of the semisolid billet prior to thixoforming must be higher than 10.3 wt.%. This can be achieved through adjusting the Si content in the Al–Si alloy matrix or/and partial remelting temperature. Moreover, the Ti core radius to shell thickness ratio of ∼1.5 was proposed to achieve the composites with both high strength and ductility. These findings are helpful for designing the microstructure and fabricating CS particles reinforced metal matrix composites with excellent comprehensive mechanical properties.