Abstract: Squeeze casting was employed to form Al-Si-Cu-Ni alloy ingots with a distinct addition of Gd and Yb. Moreover, individual T6 heat treatment was conducted to obtain the optimal parameters. With 0.1 Gd and 0.1 Yb composite addition, the Al-7Si-4Cu-1Ni-0.5Mn-0.5Mg alloy exhibited an excellent ultimate tensile strength (UTS) of 276 MPa (25 °C) and 102 MPa (350 °C). With individual T6 heat treatment (480 °C × 6 h and 180 °C × 8 h), the additional UTS, including 378 MPa (25 °C) and 116 MPa (350 °C), had been achieved. Squeeze casting combined with appropriate T6 heat treatment processes served as a reliable strategy for upgrading mechanical properties in several aspects: grain refinement strengthening, dislocation strengthening, second-phase strengthening, and precipitation strengthening. The synergistic effects of microscale and nanoscale phases were fundamental factors to ensure the deformation resistance and dislocations were hindered by second phases, precipitated phases, stacking faults, and twins. Additionally, around 10-20 nm Mg₂Si and L1₂-Al₃(Gd/Yb) dispersed phases were promoted in enhancing the deep properties of the α-Al matrix. The synergistic strengthening of the α-Al matrix and distinct phases at grain boundaries undoubtedly contributes to the mechanical properties.

Key words: Microalloying, Squeeze casting, Microstructure, Mechanical properties, 350 °C