Effect of stirring rate on grain morphology of Mg-Al alloy semi-solid structure by phase field lattice Boltzmann simulation

•The semisolid morphology is described by PF-LBM and rigid body rotation model.•The strong forced convection causes velocity difference of melt around the grain.•The velocity difference of melt flow around the grain driving the grain rotating.•The concentrated solute is distributed around the grain by the grain rotation.•The grain growth is inhibited and approaches to sphere by the grain rotation. In order to investigate the effects of stirring rate on semi-solid structure of Mg-Al alloy, a PF-LBM model (Phase Field Lattice Boltzmann model) coupled with a rigid body rotation model were adopted in this work. Grain morphology, grain growth rate and grain rotation at different stirring rates were systematically studied. The results indicated that by driving force of melt flow velocity difference around the grain, the grain rotated during the stirring process, and then solute concentration would present to the low flow areas around the grain, which was caused by the forced convection. The solutes are uniformly distributed around the grain as the grain rotates. As a result, the fine and spherical grain can be obtained owing to the inhibition of grain growth.