Addressing the strength-ductility trade-off in a cast Al-Li-Cu alloy—Synergistic effect of Sc-alloying and optimized artificial ageing scheme

A dramatic improvement of strength and ductility of cast Al-2.5 Li-1.5 Cu-1 Zn-0.5 Mg-0.15 Zr alloy was obtained by the collaboration of Sc-alloying and optimized ageing scheme. Joint and independent influence of Sc-alloying and different ageing temperatures were investigated. The results revealed that a substantial increase was realized in the hardness of Sc-containing alloy, and the ageing response time was only influenced by ageing temperature. Coarse and heterogeneous δ’(AlLi), wide δ’-precipitation free zones(δ’-PFZs), and a large amount of T1(AlCu Li) precipitates were observed in Sc-containing alloy aged at 175?C, which resulted in superior yield strength and poor elongation. The Sc-containing alloy obtained an excellent combination of ductility(elongation = 8.2 %) and tensile strength(ultimate strength=565 MPa) suffered to 150?C ageing for 64 h. The increase in the elongation was mainly due to the combined effect of grain refining, much finer δ’, and extremely narrow δ’-PFZs(<10 nm), while the higher strength was mainly attributed to the formation of Al(Sc, Zr, Li) composite particles and a large amount of S’(AlCu Mg) phase. However, the enhancement of the different ageing temperature(150?C and 175?C) on the mechanical properties of the alloys without Sc addition was not obvious.