Interdendritic fluid flow in a lead-tin alloy

Abstract

Fluid flow through interdendritic channels of a partially remelted Pb-20 pct Sn alloy has been measured. The flow, resulting from gravity forces, was determined for columnar and equiaxed dendritic structures as a function of dendrite arm spacing. The initial interdendritic flow was found to be consistent with Darcy’s law with a tortuosity factor of 4.6. The initial permeability of the dendritic array was found to be a function of the square of the primary dendrite spacing, and a more complex function of secondary dendrite arm spacing. There was little difference in flow rates for columnar and equiaxed structures of similar size. After the initial flow period the flow rate was observed to increase above that defined by Darcy’s law for castings with small dendrite spacings. This was shown to be a result of coarsening of the liquid channels during flow. The observed coarsening process is considered in terms of diffusion controlled ripening.