Convection and Macrosegregation in Al-19Cu Alloy Directionally Solidified Through an Abrupt Contraction in Cross-section: A Comparison With Al-7Si
Journal of Crystal Growth
Hypoeutectic Al-19 wt. % Cu alloys were directionally solidified in cylindrical molds that featured an abrupt cross-section decrease 9.5 to 3.2 mm in diameter). Thermo-solutal convection and cross-section-change-induced shrinkage flow effects on macrosegregation were investigated. Dendrite clustering and extensive radial macrosegregation was seen, particularly in the larger cross-section before contraction. This alloy shows positive longitudinal macrosegregation near the contraction followed by negative macrosegregation right after it; the extent of macrosegregation, however, decreases with increasing growth speed. The degree of thermo-solutal convection was compared to another study investigating directional solidification of Al-7 wt. % Si  in order to study the effect of solutal expansion coefficient on macrosegregation. An interesting change of the radial macrosegregation profile, attributable to the area-change-induced-shrinkage flow, was observed very close to the contraction. A two-dimensional model accounting for both shrinkage and thermo-solutal convection was used to simulate solidification, the resulting steepling as well as axial and radial macrosegregation. The experimentally observed macrosegregation associated with the contraction during directional solidification was well predicted by the numerical simulations.
Ghods, M.; Lauer, M.; Grugel, R. N.; Tewari, Surendra N.; and Poirier, D. R., "Convection and Macrosegregation in Al-19Cu Alloy Directionally Solidified Through an Abrupt Contraction in Cross-section: A Comparison With Al-7Si" (2017). Chemical & Biomedical Engineering Faculty Publications. 119.
Ghods M, Lauer M, Grugel RN, Tewari SN, Poirier DR. Convection and macrosegregation in Al-19Cu alloy directionally solidified through an abrupt contraction in cross-section: A comparison with Al-7Si. J Cryst Growth. 2017;459:135-145.
This work was supported by NASA Grant NX10AV40G and NNX14AM18G. M. Lauer would like to acknowledge support from the Sandia National Laboratories Campus Executive Fellowship program.