Influence of AlTiB Grain Refinement and AlSr Modification in Fe-Contaminated Secondary AlSi7Mg0.3 Alloys

Abstract Fe contamination is a major limitation in the upcycling of secondary Al-Si casting alloys. Inevitable Fe contamination during recycling processes, such as automotive shredding, promotes the formation of brittle Fe-rich intermetallic compounds that severely compromise ductility. In this work, the effectiveness and limitations of conventional industrial melt treatments AlTi5B1 grain refinement and AlSr5 modification were systematically evaluated. The synergistic effects of these additions on the microstructure evolution and mechanical properties of AlSi7Mg0.3 alloys with increasing Fe contents (0.1, 1.3 and 3.8 wt.%) were assessed. A Taguchi experimental design was applied to assess each individual treatment and combined influence on the size, morphology, and distribution of Fe-rich intermetallic phases. Quantitative image analysis, supported by ANOVA, revealed that optimized additions (3 wt.% AlTi5B1 and 0.5 wt.% AlSr5) effectively reduce the size of Fe-rich intermetallics and promote the formation of less detrimental α-AlFeSi phases at high Fe levels. However, these microstructural modifications were insufficient to prevent severe embrittlement. Tensile properties, particularly ductility, remained low, and fracture behavior was dominated by the high-volume fraction of brittle intermetallic phases. The results demonstrate that while conventional grain refinement and modification treatments can partially mitigate Fe-related degradation, they are insufficient for the upcycling of highly Fe-contaminated secondary aluminum alloys within a circular economy framework. Graphical Abstract