中文摘要：

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Rf和固相反扩散系数F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＋a）→（L＋a＋T）→（L＋a＋b＋T）;固相反扩散系数对合金的凝固路径影响较大,当F由0逐渐增大至1时,合金的凝固路径由（L＋a）→（L＋a＋T）→（L＋a＋b＋T）逐渐过渡为（L＋a）→（L＋a＋T）;随着Rf的降低,显微组织中初生相体积分数Va基本不变,两相共晶体积分数V2E增大而三相共晶体积分数V_（3E）减少,上述参数满足：V_（2E）=-2.5lg Rf＋64.9,V3E=2.5lg Rf＋22.12,F的增加使得显微组织中的Va和V2E变大而V3E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.

英文摘要：

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 AlCu, 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 ofthe 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 Rfhad no obvious effect on the solidification path which was（L＋a）→（L＋a＋T）→（L＋a＋b＋T）; but the solid back diffusion coefficient F had a great effect on the solidification path, which evolved gradually from（L＋a）→（L＋a＋T）→（L＋a＋b＋T） into（L＋a）→（L＋a＋T） when F increased from 0 to 1. The volume fractions of primary a phase Va, 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 Rfwhereas V_（3E）increased and Va was almost invariant. The dependence of V_（2E）, V_（3E）and Rfwere determined by linear regression analysis given as： V_（2E）=-2.5lg Rf＋64.9, V3E=2.5lg Rf＋22.12. The increase in F led to increases in Va and V_（2E）and decrease in V_（3E）. The predicted solidification paths and volume fractions of Al-6.32Cu-25.13 Mg ternary eutectic alloy a