Abstract:This study focused on modifying heat treatment schemes to enhance the mechanical properties of sand cast Al-2Li-2Cu-0.5Mg-0.2Sc-0.2Zr alloy. Different three-stage solution treatment schemes ((460 °C, 32 h) + (520 °C, 24 h) + (530/540/550 °C, 4/12/24/32 h)) and aging temperatures (125, 175, 225 °C) were designed for comparison. The microstructure evolutions were analyzed by optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that the three-stage solution treatment of (460 °C, 32 h) + (520 °C, 24 h) + (530 °C, 12 h) could dissolve most of the secondary phases. The TEM results illustrated that fine δ''''(Al₃Li) particles were homogeneously distributed in the matrix after aging at 175 °C for 8 h, accompanied by a small amount of lath-shaped S′(Al₂CuMg) and plate-like T₁(Al₂CuLi) phases. The best comprehensive properties of yield strength of 376 MPa, ultimate tensile strength of 458 MPa and elongation of 4.1% were obtained by the optimal heat treatment scheme ((460 °C, 32 h) + (520 °C, 24 h) + (530 °C, 12 h) + (175 °C, 8 h)).

Key words: Al-Li-Cu alloys; sand-casting; heat treatment; precipitation; microstructure; mechanical properties