Specific permeability of partially solidified dendritic networks of Al-Si alloys

Abstract

Porous dendritic networks of Al-4 pet Si and Al-4 pct Si-0.25 pet Ti alloys with volume fraction solid,g _sA > 0.628 were prepared by removing the segregated interdendritic liquid from partially solidified samples of the alloys. In the equiaxed samples, available channels for flow were predominately between the grains. Specific permeabilities of the porous dendritic networks were measured with a triaxial cell permeameter. Measured values of specific permeability were 1 × 10^-9 to 3.5 × 10^-11 cm² in the Al-4 pet Si alloy for volume fractions solid of 0.655 to 0.94, respectively. Specific permeabilities in Al-4 pct Si-0.25 pct Ti alloy were 4.82 × 10^-10 to 7.6 × 10^-11 cm² for volume fractions solid of 0.628 to 0.837, respectively. For equivalent volume fractions solid, the measured specific permeabilities were consistently lower for the grain refined samples. Flow through the porous dendritic networks obeys D’Arcy’s law and equations derived from the capillaric flow model for volume fraction liquid less than ∼0.35.