Microstructure refinement of AZ91D alloy solidified with pulsed magnetic field

The effects of a pulsed magnetic field on the solidified microstructure of an AZ31 magnesium alloy were investigated. The experimental results show that the remarkable microstructural refinement is achieved when the pulsed magnetic field is applied to the solidification of the AZ31 alloy. The average grain size of the as-cast microstructure of the AZ31 alloy is refined to 107 mu m. By quenching the AZ31 alloy, the different primary alpha-Mg microstructures are preserved during the course of solidification. The microstructure evolution reveals that the primary alpha-Mg generates and grows in globular shape with pulsed magnetic field, contrast with the dendritic shape without pulsed magnetic field. The pulsed magnetic field causes melt convection during solidification, which makes the temperature of the whole melt homogenized, and produces an undercooling zone in front of the liquid/solid interface, which makes the nucleation rate increased and big dendrites prohibited. In addition, the Joule heat effect induced in the melt also strengthens the grain refinement effect and spheroidization of dendrite arms.