Molten Metal Flow through Solid Network in Semi-Solid Al–Si Alloy

Abstract

Based on Darcy’s equation, permeability was measured for the flow of molten metal through solid network in order to evaluate slurry fluidity in semi-solid casting process. An experimental apparatus is constructed to control the morphology of globular and dendrite structure for varied fraction of solid and applied pressure. Semi-solid AC4CH alloys with 7 mass% silicon content have been squeezed by argon gas at pressure of 0.50 MPa to force liquid phase through a filter. The fraction of solid is varied from 0 to as high as 0.55. Filtrate weight ratio and gauge pressure are shown to reach to each constant value with pressurizing time of 20 s. At low fraction of solid, permeability depends strongly upon solid morphology, i.e. dendrite structure yields the lower permeability due to large friction factor. Liquid movement through α solid phase network prevails under the formation of cake layer on the filter surface with most fractions of solid and with the fraction more than 0.33 for the dendritic and globular structure of the slurry, respectively. For the globular structure, on the other hand, liquid motion in the filter becomes important for fraction of solid less than 0.33.