Refining of pure aluminum cast structure by surface pulsed magneto-oscillation

A technique termed surface pulsed magneto-oscillation (SPMO) was developed for refining the solidification structure of metals and alloys. Its working principles are to allow an electropulse to pass through a cookie-like induction coil mounted on the top of a mold to produce pulsed electromagnetic fields (EMFs) which are expected to modify the solidification process and structure of ingots. The experimental results showed that an electropulse flowing in the induction coil can make pure aluminum cast structures transform radically from the columnar to equiaxed grains. In order to examine the origin of equiaxed grains, the steel gauze was applied to the mold to hinder the migration of free grains induced by the pulsed electromagnetic fields. Through comparison of cast structures it was showed that the equiaxed grains should originate from the upper surface of the melt and/or top mold wall. And the forced convection induced by the pulsed magneto-oscillation plays a vital role in the formation of cast structure.