Visualization of freckle formation induced by forced melt convection in solidifying GaIn alloys

A bottom-up solidification of a Ga–25 wt.%In alloy under the influence of buoyancy-driven and electromagnetically driven convection was investigated by X-ray radioscopy. The main effect of the flow on the solidification is determined by the flow-induced redistribution of solute concentration which results in a change of the growth direction of the dendrites and the preference of secondary branches for an accelerated or decelerated growth. The experiments demonstrate clearly how the interdendritic flow contributes to the formation of spacious segregation freckles.