Effects of in-situ γ-Al2O3 particles and heat treatment on the microstructure and mechanical properties of A356 aluminium alloy

Abstract

It is well known that the mechanical properties of hypoeutectic Al–Si alloys are influenced by the size, morphology and distribution of primary α-Al and eutectic Si crystals. In the present study, the effect of in-situ γ-Al2O3 particles and heat treatment on the size and morphology of the primary α-Al dendrites and eutectic Si phases in A356 alloy has been investigated. The as-cast and solution treatment samples were characterized by scanning electron microscopy (SEM). Microstructural analyses demonstrated that primary α-Al was significantly refined by in-situ γ-Al2O3 particles. The secondary dendrite arm space (SDAS) of unrefined α-Al is about 25μm. The SDAS decreases to 11μm when the content of in-situ γ-Al2O3 particles is 0.6%. In addition, the eutectic Si structure was modified from coarse needle-like/platelet-like structure to short plate-like structure and some discrete particles. The mechanical properties were investigated by tensile test with various concentrations of γ-Al2O3 particles. It was found that the ultimate tensile strength (UTS) and elongation (El) increased by 41% and 137%, respectively, due to decreasing SDAS of primary α-Al dendrites and modifying eutectic Si crystals. Moreover, the change of mechanical properties corresponds to the evolution of microstructure.