Synergistic Effect of In-Situ Al-7075/Al₃Ti Metal Matrix Composites Prepared via Stir-Assisted Ultrasonic Melt Processing Under Dynamic Nucleation

Abstract: Owing to the high propensity for particle agglomeration, the fabrication of aluminum matrix composites with uniform distribution using casting routes is extremely difficult. In this study, the in-situ development of the Al₃Ti reinforcing phase by employing stir-assisted ultrasonic treatment was utilized to improve the homogeneity, wettability, and thermodynamic stability of the reinforcing particles in an Al-7075 alloy matrix. The in-situ Al₃Ti particles acted as heterogeneous nucleation sites and facilitated grain refinement to form a non-dendritic globular structure compared with the dendritic cells of the base alloy. The grain size of the α-Al dendrites reduced from 160 µm to 65, 50, and 40 µm with the addition of 2, 5, and 7 wt% Al₃Ti, respectively. The reduction in the porosity of the composites and the improvement of the particle homogenization were due to cavitation-induced de-agglomeration and the degassing effect. The formation of a robust and clean interface between the Al₃Ti particles and Al alloy via ultrasonic vibration improved the integrity of the composites compared with that of the base alloy. The thermal expansion mismatch between the Al₃Ti particles and Al alloy contributed significantly to the improved mechanical properties of the composites. Graphic Abstract: [Figure not available: see fulltext.].