Processing and tensile properties of A356 composites containing in situ small-sized Al₃Ti particulates

This research proposed an in situ casting method for preparing Al₃Ti_p/A356 composites with high strength and good ductility by adding Ti powders into molten A356 at 800 °C. A sampling experiment was firstly carried out to explore the evolution process of Ti powders in the A356 melt. Based on which in situ Al₃Ti_p/A356 composites with 1.5 and 3.0 wt% Ti additions were fabricated respectively. Both the microstructures and tensile properties of samples after T6 heat treatment were investigated. The results showed that blocky Si-substituted Al₃Ti particulates were synthesized in the in situ reaction and the formation of which followed a reaction-peeling model. The utilization ratio of Ti powders in the fabricating process could research 70%. In situ Al₃Ti particulates existed inside the α-Al crystals of A356 alloy, with the size smaller than 10 µm. Both the equiaxed transition from long columnar dendrite structure and refining of α-Al crystals occurred due to the nucleating effect of Al₃Ti. Compared with T6-A356, the yield strength, ultimate tensile strength, and percent elongation of the T6-A356/3.0Ti were improved by 29.2%, 36.0% and 143.6%, respectively. The mechanisms of the improved tensile properties, including the strength and ductility, of the composites were also discussed in this research.