Investigation on Primary Silicon Precipitation Mechanism in Al-Si Eutectic Alloy under Electromagnetic Field

Microstructures of a eutectic Al-Si alloy in continuous casting either with or without an EMF were investigated using optical microscopy (OM), and scanning electron microscopy (SEM) techniques. Primary silicon and primary aluminum was found coexisted under an EMF. The volume faction and size of primary silicon are decreased, while change from long bar into short equiaxed particles with increasing EMF power. Based on crystallographic orientation analysis using electron backscatter diffraction (EBSD), it is found that primary Si and surround primary Al share no crystallography relationship. Because the Lorntz force Al-Al clusters suffered is larger than that on Al-Al clusters, so Si-Si clusters are segregated in the melt and then nucleate independently.