Grain refinement of commercial pure Al treated by Pulsed Magneto-Oscillation on the top surface of melt

Commercial pure Al can be refined by Pulsed Magneto-Oscillation（PMO） treatment applied via a plate induction coil above the top surface of the melt. The proportion of the equiaxed zone area increases with decreasing Height to Diameter（H/D） ratios from 3.5 to1.8 and further to 1.0. Meanwhile, it increases and then decreases with increasing peak current for the three kinds of ingots with H/D ratios of 3.5, 1.8 and 1.0, respectively. However, when the H/D ratio decreases to 0.44, the area proportion of equiaxed zone can reach the maximum value with a lower peak current. FEA software simulation indicates that smaller H/D ratio results in larger current density, electromagnetic force and convection on the top surface of the melt, favoring nucleation and subsequent grain formation. Through evaluating Joule heating effect by PMO, it was found that the proper amount of Joule heating benefits grain refinement. Excessive Joule heating can reduce the size of the equiaxed zone and change the growth morphology of the grains.