Effect of Chemical Composition on Apparent Viscosity of Semi-solid Alloys

Abstract

Stirring experiments of Al, Cu and Fe-based semi-solid alloys on continuous cooling were carried out to investigate the effect of chemical composition on the apparent viscosity of semi-solid alloy slurries. The apparent viscosity for these alloys increased with increasing solidification rate and decreasing shear rate, and the critical fraction of solid for fluidity increased with decreasing solidification rate and increasing shear rate. The equation for apparent viscosity η_a of semi-solid alloy was proposed as follows:
η_a=η_La{1+(αρ_mC^1/3γ^−4/3)/[2(1/f_s−1/(0.72−βC^1/3γ^−1/3))]}    (Pa · s)
α=2.03×10²(X/100)^1/3
β=19.0(X/100)^1/3
where η_La is the apparent viscosity of liquid, ρ_m is the density of alloy, C is the solidification rate, γ is the shear rate and f_s the fraction of solid. The α and β values depended on chemical composition of alloys and became larger with increasing solute content X. These results were explained by the shape parameter value of suspended particles and the volume fraction of liquid trapped between suspended particles in semi-solid alloys.