A356.2 aluminium alloy is widely used in aerospace and automotive lightweight applications. However, accurateprediction and control of its casting performance remain technically challenging. In this study, an improved process wasdeveloped by optimizing the feeding strategy of molten aluminium and the addition sequence of auxiliary materials (Ti andSi). The synergistic effects of the cooling rate and rare earth (RE) and strontium (Sr) modifications on the refinement of thesolidification microstructure of A356.2 alloys were systematically investigated. Scanning electron microscopy (SEM) andoptical microscopy (OM) characterization reveal that the cooling rate is the dominant factor in microstructure refinement.The grain size of α-Al under water cooling is significantly smaller than that under natural cooling. The addition of REalone markedly refines α-Al grains and promotes the formation of fibrous eutectic silicon. Notably, the interaction betweenRE and Sr shifts from synergistic to antagonistic under water-cooling conditions, resulting in a coarser and more uniformgrain morphology with incomplete modification of eutectic silicon.