Influence of Ti elements on the evolution of microstructure, mechanical properties and thermal stability of Al-Cu alloy

This paper compares the evolution patterns of microstructure, mechanical properties and heat exposure response behavior of alloys with low (0.15 wt%) and high Ti (0.75 wt%) content prepared by conventional casting processes. The results show that the alloy with high Ti content has slightly finer grains and no improvement in the thermal stability of the θ' precipitates compared to the low Ti content alloy. Moreover, after exposing the as-aged alloy to 300 ℃ for 100 h, the high Ti content alloy exhibits higher tensile strength at room temperature, attributing to the reinforcement effect of Al3Ti nanoparticles. The results of geometric phase analysis and transmission electron microscope images reveal that the compressive strain field occurring on the Al3Ti/matrix interface can validly block the movement of dislocations, thus hardening the alloy. Finally, the classical nucleation theory was referred to explain the difference on the thermal exposure response behavior of two alloys with various Ti contents at 300 ℃. With increasing thermal exposure time, the stiffening role of the Al3Ti nanoparticles gradually overcomes the softening behavior caused by the destabilization of coarsened θ' and becomes the dominant factor governing the mechanical properties of the alloy. The theoretical analysis is consistent with the microstructure and the thermal exposure hardness response behavior.