In situ X-ray imaging of α-Al(FeMn)Si grain evolution during solidification of an Al-Si alloy with electromagnetic stirring

During the solidification of aluminum alloys with high iron concentrations in conjunction with electromagnetic stirring, the electromagnetic force induces movement of precipitated intermetallic grains containing iron. This force is assumed to cause macrosegregation of such compounds, although the movement process is complex due to the additional effects of melt flow on growth kinetics. The present work used in situ X-ray imaging to obtain insights into the macrosegregation process induced by electromagnetic stirring. This imaging was employed to observe the evolution of primary intermetallic α-Al(FeMn)Si grains during the solidification of an Al-10Si-2Fe-2Mn alloy in the presence of a rotating magnetic field. The α-Al(FeMn)Si grains were found to be uniformly distributed in the horizontal direction of the alloy without electromagnetic stirring but tended to congregate at the periphery of the specimen with stirring. In situ X-ray imaging confirmed that electromagnetic stirring also promoted growth of α-Al(FeMn)Si phase grains from the periphery into the center of the alloy. The α-Al(FeMn)Si phase at the sample periphery comprised a single grain, indicating that stirring led to dendrite growth. These observations together with ex situ crystallographic analyses demonstrated that macrosegregation in an Al-10Si-2Fe-2Mn alloy solidified with electromagnetic stirring resulted from grain coarsening of the α-Al(FeMn)Si phase at the sample periphery.