Ultrasound assisted in-situ casting technique for synthesizing small-sized blocky Al3Ti particles reinforced A356 matrix composites with improved mechanical properties

The in-situ 5 wt% Al3Ti/A356 composites with high strength and good ductility were prepared from A356-K2TiF6 system by an ultrasound assisted in-situ casting technique at 800 °C. The microstructures and mechanical properties of ultrasonic-treated (UT) and non-ultrasonic (NU) samples were examined. It was found that Si element had a solubility of 9-11 at. % in the in-situ formed Al3Ti particle-reinforcement and this solution tendency was proved by a first-principles calculation. In the ultrasonic fields, the in-situ Al3Ti particles were changed from rod-like to blocky in morphology with a reduced average size of 4 μm. Also, Al3Ti particles were distributed uniformly in the matrix and most of which located inside the α-Al crystals. Owing to the nucleating effect and uniform distribution of Al3Ti, both the equiaxed transition from long columnar dendrite structure and refining of α-Al crystals occurred in the UT sample, which contributed to the improvement of both strength and ductility. Compared with T6-A356, the yield strength, ultimate tensile strength and elongation of the T6-UT sample were improved by 12.0%, 27.2% and 313.3%, respectively. Furthermore, the mechanisms of the improved mechanical properties, including the strength and ductility, of the composites were investigated in this research.