Microstructures and Mechanical Properties of In-Situ Al3Ti/2024 Aluminum Matrix Composites Fabricated by Ultrasonic Treatment and Subsequent Squeeze Casting

Squeeze casting is a near net shaping technology which is advantageous to refining the microstructures and improving the mechanical properties. In the present work, in-situ Al3Ti/2024 Aluminum matrix composites with different amount of Al3Ti reinforcements were successfully fabricated by ultrasonic treatment and subsequent squeeze casting. The effects of specific pressure and the amount of reinforcements on microstructures and mechanical properties were studied. The results show that when the specific pressure is increased from 0 to 150 MPa, the average grain sizes of alpha-Al matrix are decreased by 39.8%, and the yield strength and compressive strength are increased by 16.8% and 22.9%, respectively. However, severe segregations of eutectic structures were generated under an excessive specific pressure of 200 MPa, which also results in deterioration in the mechanical strength. The mass fraction of Al3Ti phases has significant influence on morphology of eutectic structures. When the mass fraction of Al3Ti phases is increased from 4 to 16 wt%, the eutectic structures was changed from continuous network to dispersed structures gradually. The compressive strength was increased from 611.2 to 712.0 MPa (increased by 16.5%), as the Al3Ti content increasing from 0 to 16 wt%. However, as the mass fraction of Al3Ti phases increased, the variation in the yield strength is not monotonically increasing.