MICROSTRUCTURAL REFINEMENT OF MAGNESIUM ALLOY BY ELECTROMAGNETIC VIBRATIONS

摘要

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 in a molten metal, and then achieve refinement of the solidified structure. In order to refine the microstructure of AZ91D magnesium alloy and pure magnesium (99.9 mass%), the electromagnetic vibration process has been applied. When electromagnetic vibrations are imposed on the melt of AZ91D, primary α-dendrites are refined to approximately 100 μm from 1800 μm at the vibration frequency of 200 Hz. However, the effect of refinement by the electromagnetic vibrations becomes weak at frequencies above 400 Hz. For pure magnesium, the vibration frequency near 500 Hz is the most effective for the refinement of crystal grain in the frequency range from 60 Hz to 5000 Hz. Microstructural refinement under a variation of the frequency shows a similar tendency to hypo- and hyper-eutectic alloys previously reported.