Nucleation and grain formation of pure Al under Pulsed Magneto-Oscillation treatment

The grain structure of commercially pure Al can be significantly refined by the Pulsed Magneto-Oscillation (PMO) treatment. When PMO was applied to the melt during solidification, the thermal undercooling increased not only near the mold wall but also in the center of the melt. PMO treatment promoted more vigorous convection of the melt, resulting in a significant decrease in the temperature gradient from the mold wall to the center of the casting compared to the case without PMO treatment. The resulting lower temperature gradient led to a more uniform temperature field in the melt, which in turn favored the survival of the Al grains and allowed them to grow rather than remelt. Consideration of the thermal environment during solidification provides a more complete description of the mechanism of grain refinement of pure metals when PMO is applied. (C) 2014 Elsevier B.V. All rights reserved.