Permeability assessment by 3D interdendritic flow simulations on microtomography mappings of Al-Cu alloys

Samples of binary Al-Cu alloys quenched from the mushy state during permeability measurements [Ø. Nielsen, L. Arnberg, A. Mo, H. Thevik, Metall. Mater. Trans. A 30A (1999) 2455-2462] were mapped in 3D using microtomography at the European Synchrotron Radiation Facility. Using 3D image analysis, the tomograms were binarised in order to separate the Al dendrite skeleton from the quenched Al-Al2Cu eutectic, i.e., the interdendritic liquid during the permeability measurement. Subsequently, the complete permeability tensor was calculated for each sample by solving Stokes equations in the 3D tomogram domain constituted by the interdendritic liquid. In general, there is a reasonable agreement between the trace of the calculated permeability tensors and the experimental reference data. Some deviations have been attributed to a tendency for preferential flow channels in one of the samples and to a too small calculation volume compared with the characteristic lengths of the microstructure in one of the samples.