Optimization design of high-temperature resistant hypoeutectic Al7Si alloy via CALPHAD calculations and experimental validation

The hypoeutectic heat-resistant AlSi alloy was optimized through the CALPHAD method combined with experimental verification. Computational results indicate that the copper content variation beyond the range of 0.4–1.0 wt% have a negligible influence on the phase composition and properties of the cast alloys. Within low copper contents (0.4–1.0 wt%), only the Al₃Ni phase forms. As the Ni content increases, the volume fraction of the Al₃Ni phase increases, improving the high-temperature performance of the alloy. Consequently, the Al-7Si-0.5Cu-xNi system was selected for experimental validation. Experimental findings confirmed the formation of a single Al₃Ni strengthening phase, with the variation in its volume fraction showing good agreement with computational predictions. With the increase of Ni content, the volume fraction of Al₃Ni phase increases significantly. The Al₃Ni phase in the as-cast alloys mainly exhibits lamellar and skeletal shape, with a small amount of fibrous shape. During heat treatment, notable microstructural evolution occurs in both Al₃Ni phase and Si phase. The lamellar ε-Al₃Ni in the as-cast microstructure gradually dissolves, resulting in a microstructure predominantly composed of skeletal γ-Al₃Ni phase and fibrous or spherical δ-Al₃Ni. Concurrently, the coarse reticular or lamellar eutectic Si phase mostly transforms into a finer fibrous or spherical morphology. The mechanical properties of the alloy are improved. The room-temperature strength exceeds 310 MPa, the high-temperature ultimate tensile strength (UTS) at 200 °C surpasses 240 MPa, and the UTS at 300 °C is 40 % higher than that of the reference alloy.