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采用微观偏析统一模型并耦合Thermo-Calc研究了Al-6.32Cu-25.13Mg (质量分数, %)合金在不同冷却速率R_f和固相反扩散系数Φ下的凝固路径. 结果表明: 冷却速率对合金的凝固路径影响较小, 即不同冷却速率下合金的凝固路径均为: (L+α)→(L+α+T)→(L+α+β+T); 固相反扩散系数对合金的凝固路径影响较大, 当Φ由0逐渐增大至1时, 合金的凝固路径由(L+α)→(L+α+T)→(L+α+β+T)逐渐过渡为(L+α)→(L+α+T); 随着R_f的降低, 显微组织中初生相体积分数V_α基本不变, 两相共晶体积分数V_2E增大而三相共晶体积分数V_3E减少, 上述参数满足: V_2E=-2.5lgR_f+64.9, V_3E=2.5lgR_f+22.12, Φ的增加使得显微组织中的V_α和V_2E变大而V_3E变小. 结合实验研究了Al-6.32Cu-25.13Mg合金在上述不同冷却速率下的凝固路径及各相体积分数, 结果显示, 实验结果与模拟结果吻合较好.

The solidification path of alloy reveals the detailed relationship between the solute concentration in liquid and the temperature during the solidification process. The best and most accurate method to predict the solidification path of multicomponent/multiphase alloys is to establish proper microsegregation modeling coupled with phase diagram calculations according to the CALPHAD method. Recently, several alloy systems such as Al-Cu, Al-Mg and Cu-Mg have been developed, which have aroused the interest of many researchers. Up to now, the research about Al-Cu-Mg ternary alloy, especially containing higher Mg content, is relatively rare. The purpose of the present work is to investigate the solidification path of Al-6.32Cu-25.13Mg (mass fraction, %) ternary eutectic alloy at different cooling rates and solid back diffusion coefficients by an extended unified microsegregation model coupled with Thermo-Calc. Solidification experiments and subsequent microstructural characterization are combined with numerical calculation of solidification paths. It was shown that the cooling rates R_f had no obvious effect on the solidification path which was (L+α)→(L+α+T)→(L+α+β+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+β+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+64.9, V_3E=2.5lgR_f+22.12. The increase in Φ led to increases in V_α and V_2E and decrease in V_3E. The predicted solidification paths and volume fractions of Al-6.32Cu-25.13Mg ternary eutectic alloy at different cooling rates were in good agreement with experimental results.