Coarsening mechanisms during isothermal holding of a dendritic Al-10wt%Cu alloy

In-situ isothermal coarsening experiments have been carried out by high-resolution tomography on a dendritic Al-10wt% Cu alloy at a constant temperatures. The rate of coarsening and the coarsening mechanisms are investigated. Three coarsening mechanisms are observed to occur in different parts of the sample. These mechanisms are small arm melting (SAM mechanism) to the benefit of larger ones, interdendritic groove advancement (IGA mechanism) towards the dendrite tips and coalescence of the dendrite tips and groove advancement leading to entrapment of liquid droplets and tubes (CGA mechanism). These mechanisms are similar to those reported in the literature, but analysis of the coarsening rate based on 3D observations of the morphology of the dendrite arms shows that short-range diffusion can explain the rapid evolution of the microstructure. Therefore, improved models are required to adequately resemble the observed coarsening rates.