Abstract: In this work, the effect of Cu addition and heat treatment schemes on the microstructural evolution, mechanical properties, and corresponding strengthening mechanism of cast Al-Li-Mg alloy were investigated. Results indicate that the dendritic segregation would be induced after the introduction of Cu, and a well-designed two-stage solution treatment could effectively dissolve secondary phases. With Cu addition, aging hardening responses of the alloys were accelerated, accompanied by a continuous increase in the volume fraction of both S'-Al₂CuMg and Al₃Li phases, which enhanced the precipitation strengthening effect. Furthermore, in Cu-containing alloys, both the coarsening of Al₃Li phases and the expansion of Al₃Li-precipitation free zones (PFZ) were inhibited during the aging process. However, severe strain accumulation was found at the interface between the coalesced S' phase and α-Al matrix, which reduced the ductility of the alloy. A good combination of strength and ductility (YS = 308 MPa, UTS = 428 MPa, EL = 5.0 %) was obtained in the Al-2.5Li-2Mg-1Cu-0.12Zr alloy aged at 175 °C for 32 h due to the narrowed Al₃Li-PFZ and the synergistic strengthening of Al₃Li and S' phase. This work is expected to provide guidelines for designing novel cast Al-Li alloys with wider applications.

Key words: Cast Al-Li alloy, Cu addition, Heat treatment, Al₃ Li, Al₂ CuMg, Strength mechanisms