The evolution of microstructure and mechanical properties at elevated temperature of cast Al-Li-Cu-Mg alloys with Ni addition

The effect of Ni content on the microstructure and mechanical properties at elevated temperature of cast Al-2.5Li-1Cu-1.5Mg-xNi alloys (x = 0, 0.2, 0.4 and 0.8 wt.%) was investigated. The results showed that the main Ni-rich phase in alloys with 0.2 and 0.4Ni addition is Al₃Ni, while the Al₃CuNi intermetallic compounds appear in 0.8Ni alloy. The decrease of amount of solid-solution Cu atoms in matrix, due to Cu-rich phase precipitates adhere on the Ni-containing second particles, would suppress the formation or growth of Precipitations Free Zones (PFZs) is a noteworthy phenomenon. Moreover, 0.2Ni alloy showed the optimization mechanical properties (YS: 322 ± 23 MPa, UTS: 397 ± 7.7 MPa, Elongation: 7.8 ± 1.3%) at 25 ◦C. With the Ni content increases to 0.8 wt.%, the ultimate tensile strength increased by ∼12.6 % and ∼15.4 % compared with the base alloy at 200 and 300 ^◦C, respectively. With test temperature increasing, the evolution of the fracture mode is as followed: intergranular/quasi-cleavage brittle fracture mode → mixing of brittle and ductile fracture mode → voids coalescence fracture mode, corresponding to 25, 200 and 300 ◦C.