Microstructure and properties of as-cast Al-4.5Cu-1.5Mg alloy refined with Ti-supported TiC nanoparticles via ultrasonic-assisted addition

A novel Ti-supported TiC nanoparticle (NP) refiner (TiC/Ti) was fabricated by high-energy ball milling and successfully introduced into molten Al via ultrasonic assistance. The effects of the refiner on the microstructure and mechanical properties of the as-cast Al-4.5Cu-1.5Mg alloy were investigated, and the refinement mechanism was discussed. With the addition of 0.2 wt% TiC/Ti refiner, the microstructure of the as-cast Al-4.5Cu-1.5Mg alloy was transformed from coarse dendritic crystals to fine grains, and the average grain size of α (Al) decreased from 415 μm to 88 μm. During the refinement process, the uniformly distributed TiC NPs or small clusters promoted the nucleation of α (Al) on the surface of TiC along the specific orientation Al (111)//TiC (111) and Al (−111)//TiC (−111), which further resulted in the refinement of the grains, the increase in solute Cu/Mg atoms in α (Al) and the improvement of the intergranular eutectic (α (Al) + θ (Al2Cu) + S (Al2CuMg) and block θ (Al2Cu)) phases. These microstructural improvements enhanced the Vickers hardness, yield strength and tensile strength of Al-4.5Cu-1.5Mg to 102 HV, 125 MPa and 249 MPa, which were 13.4%, 68.9% and 39.8% greater than those of the unrefined alloys, respectively.