基于合金枝晶凝固微观偏析统一模型, 导出一种新的描述三元合金单相凝固路径的解析模型. 该模型具有统一性, 不仅可涵盖平衡、非平衡和准平衡3种极限凝固路径模式, 而且可考虑任意凝固相的反扩散、冷速和枝晶几何形貌等因素的影响. 通过对 Al-1.0Cu-6.3Mg, Al-1.49Si-0.64Mg和Al-1.49Si-2.90Mg(质量分数, %)合金在不同凝固反扩散条件下凝固路径的实例计算, 证明了本文三元合金单相凝固路径统一解析模型与算法的可行性.
Accurate prediction for the solidification path of a multicomponent alloy and the amounts of the secondary phases presented under a given solidification condition is critical in understanding and controlling the performances of the solidified alloy materials/parts. The degree of freedom of a single-phase solidification in multicomponent alloys is at least more than one, whilch brings some difficulty in accurate predicting of the solidification path. A new analytical model for predicting a single-phase solidification paths in ternary alloys was developed based on a previously proposed unified microsegregation model for dendrite solidification of binary alloys. The present unified analytical model can not only include the three limiting solidification conditions of equilibrium, nonequilibrium and paraequilibrium solidification, but also take into account of any solid diffusion coefficient, dendrite geometrical morphologies and solidification rates, etc. The algorithms for calculating the solidification paths of ternary alloys was closely coupled with a commercial software package/database of Thermo-Calc via its TQ6-interface in order to directly access to the thermodynamic data. The availability of the proposed analytical model for predicting the primary solidification paths of ternary alloys were demonstrated by the sample computations on Al-1.0Cu-6.3Mg, Al-1.49Si-0.64Mg and Al-1.49Si-2.90Mg alloys under different solidification conditions of solid back diffusion. It was found that the solidification conditions affect the solidification paths significantly. For an alloy, especially with a nominal composition far away from the ternary eutectic point, different solid back diffusion conditions and solidification rate can result in different amounts and even different kinds of secondary phase.
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