The effects of 0.5 wt pct In on Al-3.3Cu-0.8Li alloy were studied. Instead of T1 （Al2CuLi） phase, there was an unknown cubic phase acting as the dominant precipitates in the In-added alloy in T6 temper, which disappeared in T8 temper. The orientation relationship between this phase and matrix was given by SAEDs： （001）p//（001）α, [010]p//[010]α. Both measuring directly from HREM images or calculating from it＇s FFTs gave an close lattice parameter about 0.83 nm. 3DAP composition analysis revealed the presence of Al, Cu and Li in the atomic percentages： 60%Al, 30%Cu and 10%Li. Thus, this cubic phase is considered to be Li-rich γ1 （Al4Cu9） phase or a new phase designated as X （Al5Cu6Li2）. Different from the traditional report providing heterogeneous nucleation sites for the precipitates, In was detected neither around nor in the cubic phase by EDX and 3DAP.
Zhengrong PAN Ziqiao ZHENG Zhongquan LIAO Shichen LI
