Preparation of a novel ultra-high strength Al–Si–Cu–Ni alloy at room/elevated temperature by squeeze casting combined with a new heat treatment process

In this paper, the microstructure evolution and properties of squeeze-cast Al–8Si-1.5Cu–1Ni-0.5Mg-0.5Mn-0.2V-0.2Ti-0.2Zr alloy (hereafter, Al–Si–Cu–Ni alloy for short) were investigated under various solution processes, evaluating the mechanical properties at room and elevated temperatures for both as-cast and T6-treated states. The results showed that following the optimal two-stage solution (i.e., solution at 510 ​°C for 6 ​h ​+ ​solution at 530 ​°C for 8 ​h) and subsequent aging at 190 ​°C for 10 ​h, referred to as the S530-T6 treatment, the Al–Si–Cu–Ni alloy exhibited excellent room/high temperature performance. The ultimate tensile strength (UTS), yield strength (YS) and elongation of the alloy at room temperature were 410 ​MPa, 368 ​MPa and 1.5 ​%, and the UTS, YS and elongation of alloy at 300 ​°C were 177 ​MPa, 170 ​MPa and 6 ​%, respectively. The increase in strength at room temperature is mainly attributed to the spheroidization of eutectic silicon and the precipitate strengthening aroused from uniformly dispersed nano-sized Q-Al₄Cu₂Mg₈Si₇, σ-Al₅Cu₆Mg₂ and θ′-Al₂Cu phases, while the increase in strength at high temperature is due to the formation of heat-resistant Ni-rich phases and the improvement of the micromorphology of high melting point intermetallic compounds.