MODELING THE DEVELOPMENT OF MICROSEGREGATION DURING SOLIDIFICATION OF AN AL-CU-MG-SI ALLOY

In the as-cast state, wrought aluminium alloys present chemical heterogeneities, the so-called microsegregations, which are due to the partitioning of alloying elements between liquid and solid during solidification. While most of the experimental characterizations of solute distribution reported in the literature are dealing with fully solidified material, this paper presents results related to the build-up of microsegregation during the solidification of an aluminium alloy. The features of the corresponding cumulative distributions are presented and then discussed by comparing them to predictions made with a numerical programme which takes into account both the build-up of the main solutes in the liquid and their diffusion in the solid during the solidification. From this comparison, it is concluded that the build-up of microsegregation during the solidification of aluminium alloys could be described as a phenomenon which occurs in a spherical elementary volume element the diameter of which equals the dendrite arm spacing, and which is not greatly affected by the structural coarsening during solidification. The discrepancies between the calculated and measured cumulative distributions at low solid fraction are associated with a bias of the experimental distributions due to the physical noise of X-ray emission.