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

摘要

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.