Iron Removal from Recycled Al-Si Alloys by Cr, Sr, and Mn Additions

Global aluminium production has been surging in recent years due to its favourable properties, which can be tailored through alloying. To cope with this increasing demand, aluminium production has shifted increasingly towards primary production, as secondary production is restricted by impurity accumulation, particularly iron (Fe). The addition of Fe-bearing intermetallic particle formers, such as manganese (Mn), chromium (Cr), and strontium (Sr), is a potential solution. In contrast to previous studies, which mainly focused on higher-Fe Al-Si alloys, the present work investigates the impact of varying Mn-Cr and Mn-Sr additions on the Fe removal efficiency, defined as the percentage of Fe content in the melt after sedimentation relative to the initial Fe content, the formation of Fe-bearing intermetallic particles and the yield of clean Al following particle sedimentation in low-Fe Al-Si alloys. The experimental work included small-scale melting with 8 kg of Al-11Si-0.5Fe alloys. The study concludes that using Fe-bearing intermetallic particle formers, such as Mn and Cr, is effective for low Fe concentrations in the melt. However, a higher quantity of Mn at constant Cr is necessary for a more efficient reduction of Fe. When comparing Mn-Cr with Mn-Sr additions, Mn-Cr additions improve Fe removal efficiency, whereas Mn-Sr significantly improves the clean aluminium output yield with lower Fe removal efficiency. Further increases in Sr adversely affect particle yield and packing density, with no impact on Fe removal efficiency.