Effects of electromagnetic stirring and superheat on the microstructural characteristics of Al-Si-Fe alloy

Semisolid metal (SSM) processing is getting momentum to be the preferred fabrication route for near or net-shaped castings. For SSM processing of Al-Si alloys, there are two important microstructural features which influence the properties of finished products. These are the size and morphology of the primary alpha-Al phase and the eutectic matrix which consists of silicon, aluminum, and intermetallic phases. The presence of iron is beneficial to reduce the soldering effects in permanent mold castings, but it is unfavorable due to formation of a range of intermetallic phases. The casting parameters play an important role in avoiding the segregation of thin platelets of Fe-intermetallic, which is detrimental to mechanical properties. In this context, it is of particular interest to see the effects of melt stirring on the formation of eutectic silicon flakes and iron-based intermetallics during SSM processing. The effects of process parameters such as cooling rate and superheat are investigated on the morphology and size distribution of eutectic silicon and iron-based intermetallics during application of electromagnetic stirring (EMS). It is concluded that melt stirring not only alters the morphology of alpha-Al phase to rosette or globule shape, but also refines the eutectic silicon and iron-intermetallics. (c) 2006 Elsevier B.V. All rights reserved.