Coupled Calculation Of The Solidification Paths Of Ternary Eutectic Alloys Based On Thermo-Calc

Microsegregation is a prevalent phenomenon in the solidification process. The research on microsegregation is very important to understand the solidification behavior and predicate the solidification structure. Most of the engineering alloys are multicomponent and multiphase. Therefore, microsegregation modeling for multicomponent and multiphase alloys, and predicting their solidification behaviors and structures have important scientific and engineering significances. The thermodynamic data supplied by the phase diagram is necessary in calculating the microsegregation. But the phase diagrams of multicomponent alloys are very scarce. The CALPHAD method can efficiently solve the above problem, and can be used in various thermodynamic-coupled solidification modeling, including microsegregation, for a multicomponent and multiphase system.The aim of this thesis is to establish an algorithm for calculating the solidification paths of ternary eutectic alloys coupled with Thermo-Calc based on the microsegregation model proposed by our research group, using the numerical calculating method. The main works include:By improving the previous regression algorithm of binary eutectic alloys of our research group, a Thermo-Calc-coupled algorithm is established. Furthermore, the calculation procedure is written using FORTRAN. Using both of the regression and Thermo-Calc-coupled algorithms, the solidification paths of Al-1.5%Si and Al-5%Cu are calculated. And the results are compared with each other.Based on the simplified microsegregation model of ternary eutectic alloys, a Thermo-Calc-coupled algorithm and computer codes in FORTRAN to calculate the solidification paths of ternary eutectic alloys are established. Using the Thermo-Calc-coupled program, the Al-4.5%Cu-1%Si and Al-10%Cu-2.5%Mg are calculated at two different solidification rates. The relations among the liquid concentration, temperature and solid fraction are studied. Meanwhile, a windows-based software for calculating the microsegregation of multicomponent alloys is developed, using VC++. Experiments are conducted with four different compositions in the Al-rich corner of Al-Cu-Si system at four different cooling rates. By analyzing the cooling curves and metallography, the solidification paths are determined. The secondary dendrite arm spacing and the average solidification rates are measured. Based on the experimentally measured data, the solidification paths for the each sample are calculated using the presently developed computer codes. The computed results are comparable to the experiments.