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

Abstract

Stirring experiments of Al, Cu and Fe semi-solid alloys on continuous cooling were carried out to investigate the effect of chemical composition and stirring conditions on the apparent viscosity of semi-solid metals.
The apparent viscosity of every alloy increased with increasing solidification rate and decreasing shear rate and the critical fraction solid for fluidity increased with decreasing solidification rate and increasing shear rate. The equation for apparent viscosity η_a of semi-solid alloy is proposed as follows,
η_a=η_La{1+αρ_mC^1/3γ^-4/3/2[1/ƒ_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 solidification rate, γ is shear rate and ƒ_S is fraction solid. The α, 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 trapped liquid volume in suspended particles in semi-solid metals.