Abstract:

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 χ (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.

Key words: Indium, Precipitation, Microstructure, HRTEM, 3DAP