EXPERIMENTAL VALIDATION OF CONTINUUM MIXTURE MODEL FOR BINARY ALLOY SOLIDIFICATION

Experiments were performed with binary metal alloys to validate a cont inuum mixture model for alloy solidification. Ingots of two compositio ns, Pb-20%Sn and Pb-40%Sn, were cast in a permanent mold, and the soli dification process was simulated Temperature histories were measured d uring casting, and composition profiles were found in the solidified i ngot. Dendritic arm spacings were found from optical micrographs of th e alloy microstructure and used to determine a constant in. the Blake- Kozeny submodel for the mushy zone permeability in the liquid-solid in teraction ter-m of the momentum equations. Scaling analysis from a pre vious work and a large uncertainty in the permeability constant sugges ted that predictions of the composition are extremely sensitive to the choice of a permeability model. Three simulations of each casting wer e performed using the permeability constant as a parameter, and measur ed temperatures and compositions were compared with predictions based on different model constants. In the region of the liquidus interface, where all of the significant advection of solute takes place, the res ults suggest that the Blake-Kozeny model based on measured dendritic a rm spacings significantly underpredicts the resistance of the dendriti c array to fluid flow.