Simultaneous Enhancement of Strength–Ductility and Heat Resistance in Al‐Cu‐Mn Alloys Through Sn‐Mediated Precipitation and Ni/Ca‐Induced Grain‐Boundary Engineering

Giga‐casting, a near‐net‐shape manufacturing process widely used in sectors such as new energy vehicles and aerospace, demands aluminum alloys with high integration, efficiency, and comprehensive performance. However, traditional die‐cast alloys still face two core bottlenecks: the strength–ductility trade‐off and high‐temperature microstructural instability, with limited progress in synergistic optimization of these properties. This study proposes a multiscale strategy to synchronously tailor grain boundaries and intragranular precipitates by introducing Ni/Ca and Sn into an Al‐Cu‐Mn matrix. Ni/Ca forms ultrafine eutectic structures that evolve into thermally stable spherical particles after T6 treatment, effectively pinning grain boundaries and promoting intergranular bridges. These bridges enhance boundary cohesion and enable coordinated plastic deformation. During thermal exposure, Ni and Ca segregate at θ‐Al 2 Cu and T Mn phase interfaces, inhibiting precipitate coarsening. Simultaneously, Sn refines θ′ precipitates by reducing interfacial mismatch, boosting strength. The synergy between Sn and Ni/Ca delivers complementary benefits: Sn enhances intragranular precipitation to offset strength loss from Ni/Ca, whereas Ni/Ca improves grain boundary stability and ductility to counteract embrittlement from Sn. This approach overcomes performance trade‐offs, yielding an alloy with high strength (yield strength 346 MPa, tensile strength 461 MPa), excellent ductility (14.1% elongation), and 76% strength retention after prolonged exposure at 300°C. The work offers a novel microstructural design concept for developing high‐performance aluminum alloys suited to giga‐casting under high‐temperature conditions.