Role of Ti in the microstructure evolutions and mechanical properties of cast Al-2.5Li-1.5Cu-1Zn-0.5Mg(-0.2Zr) alloys

Transition elements are important alloying elements in aluminum alloys, whilst there was a blank of the role of Ti in cast Al-Li-Cu alloys. In this study, the impact of 0.1 and 0.2 wt% Ti additions on A1-2.5Li-1.5Cu-1Zn-0.5Mg(-0.2Zr) alloys has been investigated by microstructure characterizations and tensile tests. The optical microscopy results showed that the grains were significantly refined as the transition elements presented. There was little poisoning phenomenon in the alloys containing both Zr and Ti for the limited holding time during the smelting process. The age-hardening and mechanical properties were prominently enhanced with the addition of Ti and Zr after ageing at 150 C. The results of transmission electron microscopy showed that dispersed and dense theta' (Al2Cu) precipitates distributed in the alloy containing 0.2 wt% Ti, while T-1(Al2CuLi) phases dominated in the alloy containing 0.2 wt% Ti and 0.2 wt% Zr, accompanied by a moderate number of S' (Al2CuMg). The coarsening rates of delta'(Al3Li) and delta'-precipitation free zones (PFZs) decreased gradually with the content of transition elements increasing, but the case in the 0Zr2Ti alloy was abnormal for the interaction between theta' and delta'. The best comprehensive mechanical properties of YS = 374 MPa, UTS= 527 MPa and EL = 7.1% could be obtained by 2Zr2Ti alloy after ageing at 150 degrees C for 64 h. (C) 2021 Published by Elsevier B.V.

Automated summary

This study investigated the impact of titanium on cast Al-Li-Cu alloys and found that titanium addition can significantly refine the grains and improve the age-hardening and mechanical properties of the alloy. Additionally, the interaction between titanium and zirconium in the alloy also affects the formation and coarsening rate of precipitates.