Composition Driven Redistribution of Feeding Mechanisms in Hypoeutectic Al–Si–Mg Alloys

This study provides a systematic quantitative assessment of the influence of silicon (5–9 wt.%) and magnesium (0–0.6 wt.%) on the solidification behavior and feeding mechanisms of hypoeutectic Al–Si–Mg casting alloys. Cooling curve analysis combined with first-derivative and ΔT (Tw − Tc) evaluation was used to determine characteristic solidification temperatures, including the liquidus, dendrite coherency, rigidity, and solidus temperatures, enabling the precise delineation of feeding regions. Increasing silicon content reduced all characteristic temperatures, while magnesium addition exerted a more pronounced effect on rigidity and solidus temperatures, significantly redistributing the relative contributions of mass, interdendritic, and burst feeding. In particular, magnesium addition systematically expanded the interdendritic feeding interval and reduced the burst-feeding range, promoting earlier dendrite interlocking and restricting melt flow during late-stage solidification. Quantitative temperature ratio analysis revealed that magnesium plays a dominant role in shifting feeding toward interdendritic-controlled flow, especially in low-Si alloys. Sand Hourglass testing confirmed that this redistribution directly correlated with increased shrinkage porosity, with the highest porosity observed in the AlSi9Mg0.6 alloy. The results establish a quantitative link between alloy composition, feeding redistribution, and porosity susceptibility, providing a practical framework for optimizing the design and casting performance of Al–Si–Mg alloys.