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

In the as-cast state, wrought aluminium alloys present chemical hetero geneities, the so-called microsegregations, which are due to the parti tioning of alloying elements between liquid and solid during solidific ation. While most of the experimental characterizations of solute dist ribution reported in the literature are dealing with fully solidified material, this paper presents results related to the build-up of micro segregation during the solidification of an aluminium alloy. The featu res of the corresponding cumulative distributions are presented and th en discussed by comparing them to predictions made with a numerical pr ogramme which takes into account both the build-up of the main solutes in the liquid and their diffusion in the solid during the solidificat ion. From this comparison, it is concluded that the build-up of micros egregation during the solidification of aluminium alloys could be desc ribed as a phenomenon which occurs in a spherical elementary volume el ement the diameter of which equals the dendrite arm spacing, and which is not greatly affected by the structural coarsening during solidific ation. The discrepancies between the calculated and measured cumulativ e distributions at low solid fraction are associated with a bias of th e experimental distributions due to the physical noise of X-ray emissi on.