Mushy Zone Coarsening in an AlCu30 Alloy Accelerated by a Rotating Magnetic Field

Annealing experiments were performed on a near-eutectic Al-30 wt pct Cu alloy held in temperature gradients from 0.1 to 3 K/mm for annealing times of 10 to 500 minutes, with and without the application of rotating magnetic fields. After annealing, metallographic analysis was carried out on sections of the samples with a constant fraction solid of 10 pct. X-ray tomography was also used to create three-dimensional (3-D) reconstructions of the microstructures with a spatial resolution of approximately 1 μm. The specific surface area was measured in two dimensions and three dimensions, as well as the local curvature distribution on the 3-D reconstructed images. The microstructures show clearly that fluid flow accelerates coarsening of the mush and that the temperature gradient has a pronounced and unexpected influence on the coarsening kinetics.