Coarsening of the mushy zone in an AlCu30 alloy accelerated by a rotating magnetic field

Abstract

Annealing experiments were performed on a near-eutectic Al-30wt%30 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 having a constant fraction solid of 10%. X-ray tomography was also used to create three-dimensional reconstructions of the microstructures with a spatial resolution of approximately 1µm. The specific surface area was measured in 2D and 3D, as well as the local curvature distribution on the 3D reconstructed images. The microstructures clearly show that fluid flow accelerates coarsening of the mush, and that the temperature gradient has a pronounced and unexpected influence on the coarsening kinetics, which is explained qualitatively with a simple model of secondary dendrite arm growth.