Rheology of partially solidified AlSi7Mg0.3 and the influence of SiC additions

Abstract

The rheology of a partially solidified AlSi7Mg0.3 alloy and the effect of SiC additions were investigated using a high-temperature, Searle-type viscometer. During continuous cooling, the viscosity increases gradually with increasing fraction of solidified alloy, until a critical fraction of solidified alloy is reached above which the viscosity sharply increases. The viscosity strongly decreases with increasing shear rate. This shear thinning behaviour is dependent on the time used for changing the shear rate. During isothermal holding, the viscosity gradually decreases towards a quasi-steady state value. The kinetics for reaching this value are independent of stirring speed, but are accelerated by the addition of SiC particles. However, the final viscosity does not seem to be affected by the presence of SiC. After stopping the shearing action, the viscosity increases with time. The increase in viscosity is reduced by the presence of SiC. The restoration time between the resumption of stirring and the re-attainment of quasi-steady state viscosity is much shorter than the corresponding holding time at rest.