Effects of Ti particles and T6 heat treatment on the microstructure and mechanical properties of A356 alloy fabricated by compocasting

Abstract

In this study, the effects of the addition of Ti powder and T6 heat treatment on the microstructure and the mechanical properties of A356-based composite containing 0.5, 1.5, and 5 wt% Ti fabricated by compocasting were studied. Stirring was carried out at a temperature of 610 °C with a stirring speed of 300 rpm for 10 min. The solution treatment was done at a temperature of 540 °C for 2 h. Then, age hardening was conducted at 170 °C for 7 h. The microstructures and mechanical properties of samples after T6 heat treatment were investigated. After the addition of titanium powder, a reaction layer created on the surface of the titanium powder by diffusion of Ti atoms across the Al melt/Ti interface. Increasing the weight percent of the Ti particles resulted in an increment of silicon nucleation and a decrement of the silicon size. Also, the porosity content increased with increasing the weight percent of Ti. The eutectic Si structure was transformed from a coarse needle-like structure to a short plate-like one by T6 heat treatment. Among all samples, the A356/0.5 wt% Ti composite after the T6 showed the highest ultimate tensile strength (UTS) (306.9 MPa). Compared to the A356 alloy, the hardness and tensile strength of the A356/0.5 wt% Ti composite improved more than 83% and 53%, respectively, due to the presence of Ti and Al3Ti phases. For the A356/Ti composites, the fracture surface was mainly covered by cleavage features.