Effect of Minor Sc Addition on the Microstructure Evolution of Al–Cu–Li–Mg Alloy During Homogenization with Different Cooling Modes

The microstructure evolution and mechanical properties of Al–3.92Cu–1.10Li–0.68Mg–0.32Ag–0.23Mn–0.35Zn–0.11Zr and Al–3.92Cu–1.12Li–0.76Mg–0.29Ag–0.24Mn–0.24Zn–0.12Zr–0.083Sc (wt%) alloys during homogenization with different cooling modes were comprehensively studied. It was clearly revealed that the minor Sc addition refined the grains of as-cast Al–Cu–Li–Mg alloys through the formation of primary Al 3 (Sc, Zr) phases during the solidification process, and induced Sc enrichment in the θ (Al 2 Cu) eutectic. After the homogenization treatment, the majority of coarse nonequilibrium eutectic phases at the grain boundaries dissolved into the α-Al matrix, leading to the relatively uniform distribution of each element. Sc-added alloy after homogenization treatments possessed more superior strength and ductility than Sc-free alloy. Compared to the furnace cooling mode, the air cooling mode could inhibit the precipitation of micron-sized coarse T 1 (Al 2 CuLi) phase and improve the mechanical properties of the alloys. After homogenization, the continuous Al 2 Cu phase in the as-cast Sc-added alloy dissolved and transformed to an array of W-(Al, Cu, Sc) ternary phase, which was identified as Al 6 Cu 6 Sc with the body-centered tetragonal structure. The appearance of spherical Al 6 Cu 6 Sc particle could not damage the mechanical properties of Al–Cu–Li–Mg alloys after the homogenization treatment. The tensile strength, yield strength and elongation of Sc-added alloy after the homogenization by air cooling were 390 MPa, 265 MPa and 10.8%, respectively. The investigation of Al 6 Cu 6 Sc phase offered a potential avenue to produce high-quality Sc-added 2xxx series alloys. Graphic Abstract