Grain refinement and the microstructure evolution of Mg–9Al–5Ca alloy solidified under permanent magnetic stirring

Abstract To achieve the grain refinement of the as-cast Mg–9Al–5Ca alloy and understand the microstructure evolution during the grain refinement process, the permanent magnetic stirring(PMS) was applied to the solidification process of the alloy and the water-quenched experiment was carried out. The experimental results show that, the as-cast microstructure of Mg–9Al–5Ca alloy can be refined by PMS, and the better effect of grain refinement could be obtained with the increase of stirring rate. After applied PMS, the cooling of the melt is improved and the whole solidification time of the alloy is reduced. During the solidification process with PMS, there are more dendrite fragments produced in the melt and more initial dendrite grains at mold wall detached due to the forced convection, and then the grains would gradually grow into the fine and rose-like grains, which lead to the grain refinement of the as-cast alloy.