Microstructure and high temperature mechanical properties of Al₃Ti/A356 aluminum matrix composite by in-situ reaction

Al₃Ti/A356 composites were prepared through melt stirring in-situ reaction method by adding K₂TiF₆ salt into the melt of A356 aluminum alloy. The effects of Al₃Ti content on microstructure and tensile properties of as-cast A356 aluminum alloy at room temperature and high temperature were studied. The results showed that the as-cast microstructure of the Al₃Ti/A356 composites mainly consists of α-Al, eutectic Si, and (Al, Si)₃Ti phases. With the increase of the K₂TiF₆ salt addition amount, the (Al, Si)₃Ti phase gradually increased, and its shape changes from large block and rod-like to small block. Meanwhile, the refining effect of eutectic Si in the matrix was more significant. In composites that produce different Al₃Ti, the room temperature tensile strength and yield strength of 2wt%Al₃Ti/A356 composites are the highest, which were 179.7 MPa and 74.1 MPa, respectively. At 350℃, the tensile strength and yield strength of 6wt%Al₃Ti/A356 composite are 22.1% and 12.6% higher than that of A356 aluminum alloy, reaching 66.3 MPa and 57.9 MPa, respectively. The tensile strength of the composite reaches or exceeds that of some Al-Si alloys used for the automotive piston in service. It shows that Al₃Ti/A356 composite material has the potential to be used as a new heat resistant aluminum alloy in automobile engine.