Effects of stirring velocity and secondary cooling rate on average grain size and shape factors of AZ91D semi-solid slurry were investigated. Stirring velocities and secondary cooling rate are taken as the dominant factors influencing solidification structure evolution of semi-solid AZ91D alloy. The results reveal that increasing in stirring velocities is beneficial for the refinement of primary phase size and the improvement of the particle roundness

while increasing in secondary cooling rate is helpful for the refinement of the grain size but harmful for the particle roundness. Constitutive equations between solidification structure and stirring velocities as well as secondary cooling rate were presented on the basis of multiple non-linear regression method

providing a reference for preparing desirable semi-solid slurry.