On the Preparation and Properties of Al-7Si-0.4Mg Matrix Composites Reinforced by In-situ Intragranular Al₃Ti and Intergranular TiB₂

In particulate reinforced Al matrix composites (PRAMCs), the micro-sized ceramic particles tend to segregate at the α-Al grain boundary, resulting in a sharp drop in the ductility of the composite and thus restricting its application. It is promising to improve the ductility of the TiB2-containing composites while maintaining high strength by introducing the intragranular Al3Ti particles to replace part of TiB2 particles. In the present work, (Al3Ti+TiB2)/Al-7Si-0.4Mg composites were prepared by using the ultrasound assisted in-situ casting. The results showed that most of modified Al3Ti particles were inside the α-Al grains while TiB2 particles were mainly located at the α-Al grain boundaries. Under the ultrasonic stirring, both particles were uniformly distributed in the Al alloy matrix. Compared with Al-7Si-0.4Mg alloy, the (3Al3Ti+2TiB2)/Al-7Si-0.4Mg composite exhibited the best comprehensive mechanical properties, and its yield strength, ultimate tensile strength, and elongation (254MPa, 310MPa, and 3.8%) were improved by 21.0%, 21.6%, and 111%, respectively. This work provides a novel composite design approach to achieve a strength-ductility synergetic improvement.