A micro-model to account for hot tearing susceptibility in Al-Cu alloys

A 3D micro-model has been developed to predict the permeabilities of equiaxed structures during the solidification of Al-Cu alloys. A cellular automaton-finite difference model was used to simulate the morphological development of the grain structures for alloys in the range 0-10wt.%Cu. CFD modelling was then performed to determine the permeabilities of the generated structures. The permeabilities were compared over the composition range at various solid fractions up to 0.75 (which just precedes the onset of eutectic growth in the 10%Cu alloy). With increasing solid fraction, the shape of the permeability-composition plots was found to become inversely related to the so called 'Lambda' hot tearing susceptibility-composition plot reported by several researchers. A minimum in the permeability plots typically occurred at a composition < 1wt.%Cu, the minimum moving to lower Cu values with increasing fraction solid. On the other hand, the shape of the specific solid/liquid interfacial area-composition plot was directly related to that of the Lambda plot. The observations illustrate the importance of gain morphology to permeability in two-phase solid-liquid regions and, also, the importance of interdendritic feeding to alleviating hot tearing.