Apparent viscosity of semi-solid AZ91D alloy at steady state

The rheological behavior of semi-solid AZ91D at steady state is studied using a Couette type viscometer. The results show that the apparent viscosity of semi-solid AZ91D at the steady state increases with the solid fraction increasing, and goes up sharply when the solid fraction reaches a certain value, which is called critical fraction. The apparent viscosity of semi-so lid AZ91D at the steady state takes on a distinct downtrend with the shearing rate increasing, which indicates a strong shear thinning property. In addition, the critical solid fraction becomes higher at larger shearing rate, owing to the more globular shape of the solid particles. Based on the experiment results, an empirical equation is built as that, relating the steady state apparent viscosity of semi-solid AZ91D with the solid fraction fs and shearing rate γ: ηapp=10.74exp(6.95fs)γ-0.86.