The present study investigates the effect of cadmium (Cd) addition and the Sr/Cd ratio on the microstructure, solidification behaviour, and mechanical properties of an Al-7Si-0.4Mg cast alloy. Alloys with varying Cd levels (0-1.25 wt.%), with and without Sr modification (0.015 wt.% Sr), were prepared and examined using optical microscopy, deep-etched SEM, EBSD, and thermal analysis. Mechanical behaviour was assessed through tensile, hardness, and impact tests, supported by fractography. The results show that Cd addition alone does not affect dendritic growth, eutectic Si morphology, or solidification characteristics, and are consistent with negligible changes in strength, hardness, and ductility. In contrast, Sr addition transformed eutectic Si from coarse flakes into fine fibrous network, resulting in a 12% increase in ultimate tensile strength and a 62% improvement in elongation. Notably, Cd did not hinder the effect of Sr modification, unlike other trace elements such as Bi, Sb, or B. However, excessive Cd promoted the formation of Al₂Cd₂Si intermetallic compounds, which slightly reduced ductility and toughness. Thermal analysis confirmed that the eutectic growth temperature remained depressed across all Sr/Cd ratios, indicating a stable modification effect. These findings demonstrate that, while Cd alone is ineffective as a modifier, it does not poison Sr modification in Al-Si-Mg alloys. The results are practically significant for recycling-based alloy production, where Cd may be present as an impurity, suggesting that Sr-modification treatments remain effective despite the presence of Cd.
