During the late stage of solidification, liquid metal flows through the mushy zone to compensate for the volume change associated with the liquid-to-solid transformation. This shrinkage induced flow critically affects the formation of defects, such as hot tears, gas porosity and micro- and macro-segregation. In this work, in-situ X-ray radiography experiments were carried out at the P05 beamline at the Petra III synchrotron (Germany) to measure the flow within the mushy zone and the evolution of hot tears in AlCu and AlCuFe alloys. The flow was tracked by adding a small amount of Pb to the alloys so that Pb droplets formed as a fine-scale emulsion in the liquid Al. By tracking the movement of thousands of Pb droplets into and through the inter-dendritic regions during solidification and applying a simple analysis, we calculated the liquid velocity at each time step. The evolution of hundreds of hot tears was characterized by analysing their nucleation, growth and merging behaviour and the results related to the solidification conditions and the presence of Fe-rich intermetallics growing in the interdendritic channels.

Moderated by: Daan Maijer / Michel Billet