Atomized droplet solidification as an equiaxed growth model

The solidification of an atomized Al–10 wt.%Cu 250 μm diameter droplet is studied using microprobe analysis. The averaging map of the Cu content reveals segregation taking place at the scale of the droplet. An explanation is given using a new model developed to track the development of the growth front defined between a mushy zone and an undercooled extradendritic liquid. It is found that segregation is due to the diffusion of Cu in the undercooled extradendritic liquid ahead of the growing mushy zone. The model is also shown to be comparable with the description given in the literature for the solidification of an equiaxed grain formed in casting. As a consequence, droplet solidification is believed to be a model system for the study of equiaxed solidification. The model is also able to distinguish clearly between recalescence and remelting events taking place upon solidification of the undercooled melt, as well as their location within the droplet. This was not the case with previously developed equiaxed solidification models.