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

Abstract

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 Á/1wt.% Á/Cu, and Al Á/10wt.% Á/Cu with various amounts of the grain refiner TiB 2 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. #

A New Equiaxed Solidification Predictor from a Model of Columnar Growth

“…This finding is also in agreement with the new predictor. Similar bottom-cooled directional solidification experiments on Al-1%Cu and Al-10%Cu, carried out by Rerko et al, 29) showed that, in the absence of grain refiners, the dilute alloy was completely columnar, the concentrated alloy completely equiaxed. Previously, Griffiths et al had also noted 30) that the size of the equiaxed zone increased with nominal Cu concentration in a series of Al-Cu alloy ingots solidified vertically downwards in order to promote convection in the bulk liquid.…”

Fluid flow and microstructure formation in a rotating magnetic field during the directional solidification process

“…The influence of the fluid flow in the solidification process on the solidification microstructure has aroused extensive interest in the field of material physics [1][2][3]. The basic effect of the fluid flow is to change the solute distribution and the heat transfer condition at the front of solid-liquid interface.…”

Influence of melt convection on the columnar to equiaxed transition and microstructure of downward unsteady-state directionally solidified Sn–Pb alloys

“…In both cases experimentally examined, the solute was denser than the solvent, thus inducing a denser solute-enriched melt in the mushy zone and ahead of the growth interface. Under these conditions, it is expected that no natural convection occurs, since both the temperature and compositional gradients have a stabilizing effect on the density stratification [14][15][16].…”