<p>To achieve a superior balance between the strength and ductility for elevated-temperature applications, the effect of trace Ni addition (0.2-0.3 wt.%) on the microstructure and mechanical properties of A357 alloy was investigated in this study. The microstructure was observed by optical microscope, SEM and TEM. The tensile testing at different temperatures was carried out to examine the influence of Ni-microalloying on strengthening. The aging-precipitation hardness curves and DSC heat-flow curves were analyzed to discuss the influence of Ni-microalloying on aging-precipitation behavior. The results demonstrate that Ni-microalloying leads to the formation of eutectic Al₃Ni and Al₅FeNi intermetallic compounds at the eutectic grain boundaries, which increases boundary brittleness and consequently decreases the room-temperature strength in the as-cast state. However, during solution treatment, a significant finding is the precipitation of a great amount of nano-Al₃Ni particles in the matrix, which substantially increase the increment of room-temperature yield strength at T4 state. Ni-microalloying exhibits a negligible influence on the strength increment induced by the subsequent aging treatment. Critically, the aging hardening curves and DSC heat-flow curves reveal that Ni effectively hinders the phase transformations of β″ → β′ and β′ → β, as it increases the formation activation energies of β′ and β phases. Consequently, Ni-microalloying remarkably improves both room-temperature and elevated-temperature strength. This enhanced high-temperature performance is attributed to the synergistic effect of the grain boundary eutectic compounds, and nanoscale Al₃Ni dispersoids, and the retardation of the β″ → β′ transformation during thermal exposure.</p>