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 degrees C for 6 h + solution at 530 degrees C for 8 h) and subsequent aging at 190 degrees 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 degrees 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, sigma-Al5Cu6Mg2 and theta '-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.