Apparent Viscosity of Al-10mass%Cu Semi-solid Alloys

Cold model and stirring experiments for Al-10mass%Cu semi-solid alloys by continuous cooling investigated factors affecting viscosity and the relationship between apparent viscosities and stirring conditions of semi-solid alloys. In the cold model experiments, the suspension viscosity of spherical particles was lower than that of irregularly shaped particles, and decreased with the broadening of particle size. These behaviors were explained very well by the equation proposed by Mori-Ototake that defines viscosity as a function of particle shape, the critical fraction of solid for fluidity and the fraction of solid of suspension. The coefficients of this equation were determined by fitting the measured apparent viscosities of Al-10mass%Cu semi-solid alloys using regression method. The measured values were well fitted to the determined curves of this equation. And it has been shown that the determined coefficients varied with solidification rate and shear rate. The apparent viscosity increased with increasing solidification rate and increasing shear rate. The critical fraction of solid for fluidity increased with decreasing solidification rate and increasing shear rate. These results depended on the shapes of suspended particles in semi-solid alloys. In dendritic structures with many arms or network structures, the viscosity was increased and the critical fraction of solid was decreased. The apparent viscosity equation of Al-10mass%Cu semi-solid alloy proposed was: ηa=ηLa{1+(2.41×105C1/3γ−4/3)/[2(1/fs−1/(0.72−8.82C1/3γ−1/3))]} (Pa · s)