Microalloying-driven asynchronous precipitation for elevated-temperature strengthening in Al–Si–Cu–Ni alloy

A multi-microalloyed Al–12Si–4.5Cu–2Ni alloy strengthened with Sc, Zr, V, and Er was developed via squeeze casting and two-stage heat treatment. The alloy exhibited excellent mechanical strength at both room and elevated temperatures, retaining an average tensile strength of 143.8 MPa at 350 °C. Nanoscale L1₂-Al₃M (M=Sc, Zr, Er) precipitates and refined intermetallics (Al₃Ni, Al₇Cu₄Ni, Al₈Cu₄Sc) provided dual strengthening through intragranular hardening and intergranular pinning. Aging induced dense GP zones and θ″/θ′ precipitates, whose coarsening was effectively suppressed by solute drag effects from Sc, V, and Er. Thermodynamic simulations and Transmission electron microscope (TEM) analysis revealed asynchronous precipitation behavior: θ′ (Al₂Cu) formed earlier than β″ (Mg₂Si), despite faster Mg diffusion. First-principles calculations showed a much higher defect formation energy for Mg₂Si (11.27 eV) than for Al₂Cu (1.42 eV), confirming its delayed nucleation and enhanced thermal stability. The coarsening rate of θ′ and β″ precipitates was significantly reduced (1.62×10⁻²⁷ and 2.9×10⁻²⁸ m/s) compared to conventional alloys. This work demonstrates that composite microalloying, combined with tailored heat treatments, enables asynchronous precipitation and improves the high-temperature performance of Al–Si–Cu–Ni alloys.