Effect of high shear rate on solidification microstructure of semisolid AZ91D alloy

To investigate the effects of rotation speed and shearing time on morphology of semisolid AZ91D alloy, experimental work was undertaken using a twin-screw slurry maker. The results show that increasing the rotation speed and reasonable time can give rise to substantial grain refinement during continuous shearing stage, which can be attributed to the increasing of effective nucleation rate caused by the extremely uniform temperature due to high shear rate and high degree of turbulence. Comparing with low rotation speed at the same thermal condition, the analysis indicates that the microstructures obtained at high rotation speed are homogenous spherical and fine grains instead of dendritic or rosette and exhibits uniform distribution in the eutectic matrix.