Effects of Fe content on the 3D morphology of Fe-rich phases and mechanical properties of cast Al-Mg-Si alloy

Fe is a common impurity element in recycled aluminum scraps, and adjusting Fe content can effectively promote the effective utilization of recycled aluminum. In this study, Al-Mg-Si-Mn-Fe alloys with different Fe contents were prepared by adding various percentage of aluminum scraps. Synchrotron X-ray tomography technology was used to study the morphological evolution of Fe-rich phases and corresponding effect on mechanical properties of studied alloys. The results showed that as the Fe content increased, the 3D morphology of Fe-rich phases changed from fine Chinese-script and needle-like shapes to coarse Chinese-script structure. Their 3D morphology was mainly composed of thin platelets and curved branches. The increase in Fe content did not significantly change the 3D structure of Fe-rich phases, but increased the volume fraction and volume fraction of large Fe-rich phases. When the Fe content reached 0.35%, the maximum volume and the number of branches of individual phases increased by 182.9% and 142.2%, respectively, compared with the 0.2Fe alloy. With the increase of Fe content, the ductility of alloys gradually decreased, especially when the Fe content exceeded 0.25%. The Fe content had a small effect on the liquidus temperature of alloys, but it changed the initial formation temperature and type of Fe-rich phases. When the Fe content exceeded 0.32%, it promoted the formation of β-Fe phase, which may be the main reason for the significant decrease in ductility of studied alloys with higher Fe content.