Effect of melt convection and solid transport on macrosegregation and grain structure in equiaxed Al–Cu alloys

Macrosegregation in metal casting can be caused by thermal and solutal melt convection, and the transport of unattached solid crystals. These free grains can be a result of, for example, nucleation in the bulk liquid or dendrite fragmentation. In an effort to develop a comprehensive numerical model for the casting of alloys, an experimental study has been conducted to generate benchmark data with which such a solidification model could be tested. The specific goal of the experiments was to examine equiaxed solidification in situations where sinking of grains is (and is not) expected. The objectives were: (1) experimentally study the effects of solid transport and thermosolutal convection on macrosegregation and grain size distribution patterns; and (2) provide a complete set of controlled thermal boundary conditions, temperature data, segregation data, and grain size data, to validate numerical codes. The alloys used were Al–1wt.%–Cu, and Al–10wt.%–Cu with various amounts of the grain refiner TiB2 added. Cylindrical samples were either cooled from the top, or the bottom. Several trends in the data are apparent and provide good starting points for comparisons to numerical models.