Microstructure and Mechanical Properties of Mn-Sr Modified Iron Containing Al-Si Alloys

Iron is considered as the harmful impurity in recycling of aluminium alloys. Presence of iron results in formation of brittle intermetallics compounds in these alloys. The size, shape, and distribution of brittle iron intermetallic particles significantly influence the mechanical properties of these alloys. In this study, chemical modification method such as the combined addition of Mn and Sr to the melt was used to modify the morphology of iron intermetallics in Al-Si alloys. Al-75i with 0.6%Fe and Al-75i with 2% Fe alloys were prepared by melting and casting. Subsequently these alloys were modified with the addition of Mn and Sr. SEM-FIB was used for 3D visualisation of iron intermetallic particles in modified alloys. Microstructural results show that the addition of Mn and Sr resulted in modifying the plate-like brittle intermetallics to flower/star-shaped intermetallic compounds. Tensile test results show that the increase in iron from 0.6 to 2% significantly decreased the tensile strength and elongation of the alloy. Modification of Al-7Si-2Fe with Mn and Sr improved the tensile strength and elongation compared to Al-7Si-0.6Fe and this improvement is due to morphological modification of intermetallic compounds with Mn and Sr.