Hardness Behaviour of Secondary A356 Alloys: The Influence of Iron and Manganese

Abstract The rising demand for sustainable materials has led to an increase in the usage of recycled aluminium in the automotive and engineering sectors. However, impurities such as iron, introduced during recycling, can weaken mechanical properties by forming brittle intermetallic phases. This study examines how iron content and manganese addition affect the hardness and microstructure of secondary A356 aluminium alloys. The experimental alloys were produced with Fe levels from 0.080 to 0.586 wt.% and Mn additions up to 0.300 wt.%. Brinell and Vickers microhardness tests were performed to assess overall and local hardness, while microstructure analysis was conducted using scanning microscopy with EDX analysis. Results showed that increasing Fe content slightly raised the hardness due to the formation of Fe-rich Al 5 FeSi intermetallic phases, which are brittle and platelet-shaped. The addition of Mn transformed these phases into more compact α-Al 15 (Fe,Mn) 3 Si 2 morphologies, improving phase distribution. These findings highlight that controlling Fe content and Mn addition is crucial for optimising the hardness and other mechanical properties of recycled A356 alloys and encouraging the sustainable reuse of aluminium materials.