Prediction of the solidification path of Al-4.37Cu-27.02Mg ternary eutectic alloy with a unified microsegregation model coupled with Thermo-Calc

An extended unified microsegregation model with solid back diffusion effects and five different dendrite morphologies was used to investigate the solidification path of Al-4.37Cu-27.02Mg (wt.%) ternary eutectic alloy at different cooling rates and solid back diffusion coefficients, coupled with Thermo-Calc. It was indicated that the cooling rates (R_f) had no obvious effect on the solidification path which was (L + α) → (L + α + T) → (L + α + B + T); but the solid back diffusion coefficient (φ) had a great effect on the solidification path, which evolved gradually from (L + α) → (L + α + T) → (L + α + B + T) into (L + α) → (L + α + T) when Φ increased from 0 to 1. The volume fractions of primary α phase (V_α), binary eutectic (V_2E) and ternary eutectic (V_3E) at each solidification path were calculated. It was shown that V_2E decreased with the increase of R_f whereas V_3E increased and V _α was almost invariant. The dependence of V_2E, V_3E and R_f were determined by linear regression analysis given as: V_2E = -2.5lgR_f + 47.5; V_3E = 6.4lgR_f + 47. Increase in U lead to increases in V_A and V_2E and decrease in V_3E. The predicted soldification paths and volume fractions of Al-4.37Cu-27.02Mg ternary eutectic alloy at different cooling rates were in good agreement with experimental results.