The Role of Silicon During Solidification Process of Cast Al-Si-Mg Alloys

Hypoeutectic Al-Si-Mg alloys are among the most widely used casting materials in the automotive and aerospace industries due to their low density, high strength-to-weight ratio, corrosion resistance, and good castability. A critical challenge during solidification is shrinkage porosity, which arises from insufficient feeding and significantly reduces casting reliability. While the role of silicon in altering the phase diagram of Al-Si-Mg alloys is well-understood, its direct impact on feeding behavior has not been previously quantified in detail. In this study, the influence of silicon content (5-9 wt.%) on feeding ability was systematically investigated using thermal analysis (TA). By analyzing cooling curves, first derivatives, and ΔT curves, key solidification temperatures, including the liquidus, dendrite coherency, rigidity, and solidus, were precisely identified. For the first time, these data were used to quantitatively define all five feeding regions (liquid, mass, interdendritic, burst, and solid feeding) as a function of silicon content. The results demonstrate that increasing the Si content decreases the liquidus and dendrite coherency temperatures, raises the rigidity and solidus temperatures, and shortens the overall feeding ranges, particularly the interdendritic region (~32 °C reduction). This novel TA-based quantification of feeding regions provides insights that extend beyond classical phase diagram interpretation. The findings confirm that higher Si contents improve feeding ability by narrowing the freezing range and reducing the risk of porosity, while also providing a unique dataset for validating casting simulation software. The results also confirm that increasing the silicon content enhances feeding ability and improves castability by narrowing the freezing range and promoting more uniform solidification in Al-Si-Mg alloys. The study therefore bridges fundamental solidification science with industrial practice, supporting improved alloy design and defect control in Al-Si-Mg castings.