MICROSEGREGATION MODELING OF RAPIDLY SOLIDIFIED AL-CU DROPLETS

摘要

X-Ray tomography, Neutron Diffraction experiments and Stereology calculation on Scanning Electron Microscope images were done on Impulse Atomized Al-Cu alloys of (nominal) compositions 4.3 wt%Cu, 5 wt%Cu, 10 wt%Cu and 17 wt%Cu atomized under N_2 and He gas. From the results of these experiments, position of nucleus within an individual droplet and volume percent of initial growth, recalescence and eutectic were determined. These experimental results were used to compare with a solidification model developed to study the microsegregation in rapidly solidifying droplets produced from Impulse Atomization. The model solves the heat balance equation as the droplet loses heat to the atomization gas and phase transformation occurs during solidification. Starting with an off-center nucleation site and an initial user-defined undercooling for the nucleation of the primary phase, the model predicts the thermal history, fraction solidified and microsegregation in the droplet as a function of time. Comparison of prediction with experimental results are used to propose an understanding of the solidification path of the atomized droplets.