1992 Volume 78 Issue 6 Pages 902-909
Cold model and stirring experiments of Al-10 mass% Cu semi-solid alloys on continuous cooling were carried out to investigate factors affecting viscosity and the relationship between apparent viscosity and stirring condition of semi-solid metals.
In the cold model experiments, the suspension viscosity of sphere particles was lower than that of irregular shape particles, and decreased with widening of particle size distribution. These behaviors were explained well by the equation proposed by MORI-OTOTAKE which is a function of particle shape, the critical fraction solid for fluidity and the fraction solid of suspension. The measured apparent viscosity of Al-10 mass% Cu semi-solid alloys was regressed with this equation. The regression curves were well fitted with the measured values, and the coefficients of regressed equations depended on solidification rate and shear rate. The apparent viscosity increased with increasing solidification rate and decreasing shear rate. The critical fraction solid for fluidity increased with decreasing solidification rate and increasing shear rate. These results depended on the shapes of suspended particles in semi-solid metals. In case of the dendritic structures with many arms or the network structures, the viscosity was increased and the critical fraction solid was decreased. The apparent viscosity equation of Al-10mass% Cu semi-solid alloy is proposed as follows,
ηa=ηLa{1+2.41×105C1/3γ-4/3/2[1/fs-1/(0.72-8.82C1/3γ-1/3)]}(Pa·s).
