Effect of heat treatments on microstructure and mechanical properties of sand cast Al-2Li-2Cu-0.5Mg-0.2Sc-0.2Zr alloy

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 degrees C, 32 h) + (520 degrees C, 24 h) + (530/540/550 degrees C, 4/12/24/32 h)) and aging temperatures (125, 175, 225 degrees 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 degrees C, 32 h) + (520 degrees C, 24 h) + (530 degrees C, 12 h) could dissolve most of the secondary phases. The TEM results illustrated that fine delta'(Al3Li) particles were homogeneously distributed in the matrix after aging at 175 degrees C for 8 h, accompanied by a small amount of lath-shaped S'(Al2CuMg) and plate-like T-1(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 degrees C, 32 h) + (520 degrees C, 24 h) + (530 degrees C, 12 h) + (175 degrees C, 8 h)).