Permeability of dual structured hypoeutectic aluminum alloys

A mathematical expression to describe the evolution of permeability during equiaxed eutectic solidification of hypoeutectic aluminum alloys has been developed by considering the solidifying microstructure to be a dual structured system consisting of a network of equiaxed, dendritic and eutectic grains. The permeability of hypoeutectic aluminum alloy microstructures was characterized on simulated dendritic/eutectic microstructures predicted using a cellular automaton technique starting from a primary dendritic structure characterized via X-ray microtomographic analysis. The permeability was characterized (i) physically using large-scale analogs of the simulated microstructures and (ii) numerically by predicting the flow through the simulated microstructures. The permeability values determined through physical and numerical modeling are in good agreement with each other and are consistent with the mathematical expression. The proposed permeability expression is valid over the complete solidification range and for a wide range of compositions. The expression reduces to the conventional Carman-Kozeny expression during dendritic solidification and/or dendritic/eutectic solidification with a low density of eutectic grains. However, it deviates from the conventional Carman Kozeny expression as the density of eutectic grains increases. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.