Effect of Na3AlF6 contents in refining flux on 3D characteristics of pore and mechanical properties of recycled Al-Mg-Si alloy

Abstract

Fluoride is an essential and effective component in solid refining flux due to its ability to dissolve Al2O3. In this paper, the effects of Na3AlF6 content in refining flux on the pores and mechanical properties of recycled Al-Mg-Si alloy was investigated by tensile testing, scanning electron microscope (SEM) and Synchrotron radiation X-ray computed tomography (SRXCT). The results show that addition of Na3AlF6 transformed the shrinkage pores with large-sized irregular-shaped to highly spherical hydrogen pores, resulting in a significant reduction in pore volume fraction. When the refining flux with 5% Na3AlF6 is added to the melt, the volume fraction and average equivalent diameter of pores in the recycled alloy decreased by 84% and 23.2%, respectively, compared to those flux of without Na3AlF6. Furthermore, adding Na3AlF6 improves pore distribution uniformity while reducing the equivalent diameter of the largest pore by 83.7%. Although increasing Na3AlF6 content slightly increases pore equivalent diameter, it significantly reduces both larger pores (Equivalent diameter ≥20 μm) and their proportion. Moreover, the elongation of recycled Al gradually increases with higher Na3AlF6 content and reaches up to 21%, which is 40% higher than that without Na3AlF6. This improvement can be attributed primarily to reduced size and sphericity of shrinkage pores.