Vacuum-assisted HPDC lightweight Al-based entropy alloy with ultrahigh strength and exceptional thermal stability at elevated temperatures

Lightweight and high-strength aluminum (Al) alloys have a wide range of industrial applications. Al alloys with excellent elevated-temperature mechanical properties have been increasingly in demand. In this study, a novel lightweight Al-based entropy alloy (Al 80 Si 8 Mg 4 Cu 4 Zn 4 ) with a density of 2.928 g/cm 3 was calculated with thermodynamic parameters and a calculated phase diagram (CALPHAD) framework. The alloy fabricated by vacuum-assisted high pressure die casting (HPDC) shows ultrahigh specific yield strength at room and elevated temperatures (200°C-400 °C) compared with conventional Al alloys, Al-based entropy alloys, and even additive manufacturing (AM) Al alloys. Specifically, the yield strength reaches 332 MPa and 178 MPa at 300 °C and 400 °C with plasticity exceeding 40 % under compression test. At room temperature, the main strengthening mechanism is solid solution strengthening, while at elevated temperature, the primary strengthening mechanism is Orowan strengthening. The high interconnectivity of the rigid Q-Al 5 Cu 2 Mg 8 Si 6 phase and θ-Al 2 Cu networks play a significant role in strengthening at the elevated temperatures. In addition, the alloy exhibits superior thermal stability. Accordingly, the estimated grain growth exponent n of ∼4.13 indicates the diffusion mechanism of the alloy is grain boundary (GB) diffusion at 300 °C. The stability is mainly attributed to the pinning effect of T-AlZnMgCu phase and the nonequilibrium segregation of Zn and Cu at GB at 300 °C and below. Moreover, stability of the size, volume fraction and hardness of intermetallic compounds (IMCs) underscores the good thermal stability of microstructure. Our findings provide an important route to fabricate the lightweight Al-based entropy alloys components with enhanced room and elevated-temperature mechanical properties by vacuum-assisted HPDC and also could promote the entropy alloy applications.