Formation of the solidified microstructure of Mg–Al–Zn alloy under a low-voltage pulsed magnetic field

Effect of a low-voltage pulsed magnetic field (LVPMF) on the solidified microstructure of Mg–Al–Zn alloy has been investigated. Experimental results show that the solidified structure of Mg–Al–Zn alloy can be remarkably refined and that the morphology of α-Mg is transformed from developed dendrite to fine rosette with the application of LVPMF. Magnetization of the solute and solvent in the diffusion layer cannot account for the formation of the rosette α-Mg under LVPMF. A model for the formation of rosette α-Mg under LVPMF has been developed by analyzing the growth behavior of α-Mg dendrite. Morphology change of α-Mg dendrite under LVPMF is caused by Joule heat concentrated on the dendrite tip. Accumulation of Joule heat on the dendrite tip melts the local dendrite tip and increases the radius of curvature. The increased radius of curvature at the dendrite tip lowers the growth rate and results in the formation of rosette α-Mg.