Effect of Silicon Percentage on the Casting Quality and Surface Finish of Al-Si Alloys

The effect of varying silicon content, i.e., 5%, 10%, 15%, and 20%, on aluminum-silicon (Al-Si) alloy surface finish and casting quality is studied in this research. Al-Si alloys are widely used in the automotive and aerospace industries due to their excellent mechanical properties, castability, and thermal stability. Al-Si alloys were melted and cast under controlled atmosphere in sand or graphite molds, and their surface defects, roughness, tensile strength, grain structure, and hardness were determined. The results indicated that tensile strength and hardness increase with an increase in silicon content, which ranges from 180 MPa and 60 Vickers at 5% Si to 270 MPa and 95 Vickers at 20% Si, respectively. Increased percentages of silicon, however, also led to increased surface roughness and coarser grain sizes, which increased from 2.5 µm to 5.0 µm. Porosity and shrinkage were more prominent surface defects in intermediate compositions (10–15% Si). The findings suggest that while increased silicon improves mechanical performance, smoothness on the surface is compromised. Therefore, the perfect percentage of silicon to be determined must be decided on the basis of the specific application; higher percentages are required in components which play a very significant role in providing strength, and lower percentages in finishes.