Interdendritic fluid flow in Al—7%Si alloys modified with sodium and antimony

Abstract

The interdendritic fluid flow was studied for Na- and Sb-modified Al-7%Si alloy castings. The residual liquid in the solidifying alloys was poured into a tube at different liquid fractions and the ratio of apparent permeability to viscosity of the residual liquid (K/μ) was calculated from the liquid flow rate and pressure using D'Arcy's equation. Interdendritic fluid flow occurs at fraction liquid from 0.8 to 0.3. The K/μ ratio is proportional to the square of the fraction liquid and remains unchanged by Sb-modification at the same fraction liquid. The ratio for Na-modified alloys decreases at the same fraction liquid, possibly due to an expanded hydraulic radius. The apparent permeability is proportional to the 2.5th power of the hydraulic radius, which depends on the geometry of dendrites. The K/μ ratio of Na-modified alloy decreases with an increase in the viscosity of the residual liquid.