Electromagnetic vibrations, which are generated by simultaneous imposition of a static magnetic field and an alternating electric field, are considered to lead to the formation and collapse of cavities even in a molten metal, and then achieve the refinement of solidified structure. In order to refine the microstructure of AZ31B magnesium alloy, the electromagnetic vibration (EMV) process has been applied. Fine equiaxed grains can be obtained when AZ31B alloys are solidified at a frequency interval of ca. 500 up to 2000 Hz. The difference in electrical resistivity between the solid and liquid in mushy zone originates uncoupled motion, which breaks dendrite into fragments, destroys the crystallographic orientations, and yields deformation twins. Effective refinement occurs when the leading solid is driven to move out the operation scope of solute redistribution area where the solute cannot be piled up to generate a constitutionally undercooled region that always destabilizes.
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