5th International Conference on Advances in Solidification Processes (ICASP-5) 5th International Symposium on Cutting Edge of Computer Simulation of Solidification, Casting and Refining (CSSCR-5)

The presence of small amount of the Fe in the Al-Si alloy causes the formation of the platelet-shaped Al5FeSi intermetallic phase, which is detrimental to the alloy mechanical properties. A series of directional solidification experiments on Al-Si-M alloy were performed under diffusion or controlled convection to study the interaction of fluid flow and the formation of the intermetallic phase and their effect on microstructure and segregation[1]. The blocking effort of the intermetallic phase on fluid flow in the mushy zone leads to the decrease of the permeability of the mushy zone both in flow normal and parallel to the primary dendrites and a decreased species transport. A two-phase model is used to study the effect of the intermetallic phase on the fluid flow and segregation. In the two-phase solidification model, the columnar dendrites are approximated by step-wise growing cylinders with constant primary and secondary arm spacing. The growth kinetics of the columnar phase is governed by the diffusion of the rejected solute ahead of the solid-liquid interface. The conservations for mass, enthalpy, momentum and species are solved respectively. The influence of the intermetallic phase on the fluid flow in the mushy zone is approximated with the anisotropic permeability law with an additional coefficient (where represents the impact factor of the intermetallic phase). Due to the insignificant amount of the Fe in the alloy, the simplified binary alloy Al-7%Si alloy is used to perform current simulation. The unidirectional solidification process can be qualitatively reproduced with the two-phase solidification model. Two inward circulation flow pattern ahead of the mushy zone, which induces the strong positive segregation in the center of the sample, is observed. The fluid velocity in the mushy zone is suppressed due to the decrease of the permeability caused by the formation of the intermetallic phase. At the same time, the segregation severity is reduced for the decreasing of the mass transfer in the mushy zone. The decreasing of the velocity will decrease the feeding ability, which makes it more likely to form some pores and porosities. References [1] S. Steinbach, L. Ratke, G. Zimmermann, L. Sturz, A. Roosz, J. Kovács, Y. Fautrelle, O. Budenkova, J. Lacaze, S. Dost, Investigation of the effect of fluid flow on microstructure evolution in Al-Si-Fe alloys: The MICAST project, in: Decennial International Conference on Solidification Processing, 2017.