Synergistic effects of γ-Al2O3 nanoparticles and fast cooling on the microstructural evolution and mechanical properties of Al-20Si alloys

Abstract

Hypereutectic Al-Si alloys have been applied as structural materials in various fields thanks to their favorable wear resistance, good thermal conductivity and low coefficient of thermal expansion. Nevertheless, such alloys usually have poor strength and ductility because the coarse primary Si and acicular eutectic Si in the matrix can severely degrade the mechanical properties. Thus, the control over the alloy microstructure is crucial in achieving the enhanced mechanical performance. Herein, we demonstrate that the size, distribution and morphology of primary and eutectic Si phases can be changed upon the addition of γ-Al2O3 nanoparticles (NPs) and further tailored by tuning cooing rates. The addition of NPs combined with the fast-cooling treatment can induce the phenomenal refinement and modification of Si phases in Al-20Si alloys. The NP-induced refinement and modification mechanisms have been proposed to elucidate the microstructural evolution of Al-20Si alloys produced at various cooling rates. Results indicate that the Al-20Si alloys with the addition of 2.0 wt% NP produced at the cooling rate of 100 K/s can exhibit the most excellent mechanical properties with their yield strength, ultimate tensile strength, elongation and microhardness improved by 78.0%, 75.5%, 301.7% and 119.3%, respectively, in comparison with Al-20Si alloys produced via the conventional casting route.