A synchrotron X-ray radiography study of dendrite fragmentation induced by a pulsed electromagnetic field in an Al-15Cu alloy

An in situ technique for studying the effect of a pulsed electromagnetic field on dendrite fragmentation behavior based on synchrotron X-ray imaging has been developed, involving the passage of an oscillating current through a foil specimen placed in a static magnetic field. In all cases, the application of a pulsed electromagnetic field to an array of Al-15 wt.%Cu dendrites led to an increase in dendrite fragmentation rate. The induced movement of inter-dendritic liquid between the primary and secondary dendrite arms even at high solid fraction led to instabilities in the local temperature-concentration-curvature equilibrium and the rapid remelting of the most vulnerable microregions. The new in situ methodology provides a basis for the optimization of pulsed electromagnetic field parameters to enhance grain refining performance for specific alloys and casting conditions.