3D imaging and quantification of porosity and intermetallic particles in strontium modified Al-Si alloys

Abstract

Al-Si alloys are widely used in the automotive and aerospace industries. Porosity is considered to be a major defect in these cast alloys. In this study, the effect of strontium (Sr) modification on porosity formation and intermetallic formation in Al-Si alloys is quantified using X-ray tomography. Quantitative information such as average pore size, shape, pore distribution and intermetallic particle size distribution were evaluated for Sr modified and unmodified Al-Si alloys. Results show that the addition of 400 ppm of Sr increases the porosity by 10% as compared to unmodified Al-Si alloy. Further, Sr addition increases the average equivalent diameter of pores from 2 μm to 18 μm compared to unmodified alloys. A greater number of larger pores were found in the Sr modified alloy, whereas the number of small sized pores was significantly higher in unmodified alloy. The addition of 400 ppm of Sr results in formation of Al-Si-Sr intermetallics with an average equivalent diameter of 4.5 μm. It can be hypothesised that these intermetallic particles act as heterogeneous sites for pore nucleation and significant further growth of porosity in Sr modified alloys.