Enhanced Fe tolerance in recycled Al-7Si-0.3Mg alloys via refining microstructure

Controlling Fe content and resultant Fe-rich intermetallic compound (Fe-rich IMC) is a key issue in aluminum recycling, due to their detrimental effect on ductility. The critical Fe content (0.17wt.% for β-Al5FeSi formation in Al-7Si-0.3Mg alloys) and the achievable Fe tolerance (the maximum Fe content in recycled alloys without abrupt elongation deterioration) were distinguished though the thermodynamic calculation and experimental determination. The contribution of alloying to the maximum elongation (~100%) of Al-7Si-0.3Mg-0.2Fe alloy at a cooling rate of 2°C/s was determined by comparing the effects of individual and overall modification, targeting the Fe-rich IMCs, α-Al, and eutectic Si on mechanical properties. Same microstructural refinement effect achieved by overall alloying modification was obtained through the addition of Sr and accelerated cooling (from 2 to 6℃/s). A 317% improvement in elongation at 0.2wt.% Fe was achieved through this synergistic refinement, demonstrating its superior effectiveness in enhancing ductility. Further microstructure analysis revealed that the secondary dendrite arm spacing (SDAS) is the most critical factor influencing Fe tolerance in this alloy. In contrast, the refinement of Fe-rich IMCs, while beneficial, is not the most critical contributor to improving Fe tolerance. This strategy enables the utilization of high-Fe aluminum scrap, thereby advancing the sustainability of the aluminum recycling industry.