Processing, multiscale microstructure refinement and mechanical property enhancement of hypoeutectic Al–Si alloys via in situ bimodal-sized TiB2 particles

Abstract A comprehensive investigation of the trace additions of in situ novel bimodal-sized (nano and submicron) TiB2 particles on the solidification behavior, microstructure and mechanical property evolution of Al–7Si–4Cu alloys were carried out through remelting and dilution-assisted ultrasonic vibration. The results showed that both the primary α-Al dendrites and eutectic Si structure were greatly refined in the presence of 0.7 wt% bimodal-sized TiB2 particles, with a reduction of 79.0% and 53.7% compared to the base alloy, which is far beyond the efficiency of micron-sized TiB2 particles. Additionally, the average diameter of the θ′ precipitates was greatly reduced by 32.7%. Thermal analysis revealed that the bimodal-sized TiB2 particles sharply shifted the nucleation temperature of primary α-Al from 600.7 °C to 607.1 °C; meanwhile, the corresponding recalescence undercooling decreased by 3.6 °C. More importantly, in contrast with the common dilemma of strength-ductility trade-off, the yield strength and elongation to fracture of the inoculated Al–7Si–4Cu alloy were simultaneously and significantly improved by 26.3% and 71.1%, respectively. In this work, the mechanisms of multiscale microstructure refinement and mechanical property enhancement by bimodal-sized TiB2 particles were systematically discussed.