A Study on the Fluidity of the Liquid in the Solid-Liquid Coexisting Zone

Abstract

In order to clarify the fluidity of interdendritic liquid contributing to the formation of macrosegregation and the castability in an ingot, an artificial hole was made in the zone of coexistence of the solid and the liquid so as to make only the liquid flow into the hole. Then the relation among the fluidity of the liquid, the fraction of solid and the dendrite morphology in the solid-liquid coexisting zone was examined. Furthermore the fluidity of the interdendritic liquid was estimated by the effective permeability.
The results on an Al-2.4 wt%Si alloy are summarized as follows:
(1) The fraction of solid at which dendrites begin to form networks is about 31%, and the fraction of solid above which the interdendritic liquid cannot flow is 67%. These fractions of solid are consistent with those at the boundaries between the q₁ and the q₂ zones and between the q₁ and p zones, respectively, which have been previously found from the hydrodynamic examination on the process of solidification by one of the authors.
(2) The effective permeabilities in the fraction of solid of 0.35 and 0.65 are 6.1×10⁻⁴ and 6.2×10⁻⁶ cm/s, respectively. The latter is the value that the seepage of the interdendritic liquid can hardly occur. It is equal to the value that the seepage of water in the soil can be scarcely occurred.
(3) It is practical that the fluidity of the interdendritic liquid is evaluated with the effective permeability obtained by this experimental method, because the effective permeability consists of the viscosity and the density in the liquid and the permeability depending on the dendrite morphology.