Fe-Pb合金凝固多相体系内偏析形成过程的三维数值模拟

基于Eulerian-Eulerian方法和流体体积技术,建立了三维多相流体动力学凝固模型,并将其与质量、动量、溶质和热焓守恒方程相耦合,对Fe-Pb合金侧向凝固过程进行了数值模拟.首先,分析了分布面积二次梯度((SPb))和浓度二次梯度((CPb))对偏析模式的影响,结果表明:液、气两相的流动相变使偏析模式表现为上端X形下端V形,X偏析由气相相变驱动力和多取向相变作用下的"散射"形成;ttc时,随(SPb)和(CPb)曲线降低,X偏析的下偏析角增大,上偏析角和V偏析角减小,Pb收得率增大,有利于获得含量稳定弥散的凝固组织.此外,还研究了液、气两相交互流动下通道偏析的形成机理,结果表明:通道偏析仅存在于流动-相变交互作用(ul·cl和ug·cg)为负值的区域,该区域的流动扰动抑制合金的局部凝固,促进偏析通道生长;流动-相变交互作用负值越小,偏析通道持续增长越稳定.模拟结果与实验结果相符合,验证了模型的准确性.

Three-dimensional modelling and numerical simulation on segregation during Fe-Pb alloy solidification in a multiphase system

The three-dimensional mathematical model for a three-phase flow during its horizontai solidification is studied using fluid dynamics method based on Eulerian-Eulerian and volume of fraction methods, in which the mass, momentum, species, and enthalpy conservation equations of the Fe-Pb alloy solidification process are solved simultaneously. Effects of Pb area quadratic gradient (∇ (∇S_Pb)) and Pb concentration quadratic gradient (∇ (∇C_Pb)) on the segregation formation are investigated. Results show that the segregation mode is manifested as X-segregates in the upper and V-segregates in the lower part during flow-solidification of liquid phase and gas phase. The X-segregates result from the phase transformation driving force of gas phase and “scattering” is due to the orientation of phase transition. When t >t_c the lower ∇ (∇S_Pb) and ∇ (∇C_Pb) curves cause a larger yielding rate of Pb with a larger down angle of X-segregates and a smaller up angle of X-segregates and V-segregates. All these are favorable for the formation of a well-dispersed microstructure. In addition, the gas-liquid two-phase flow interaction term has an effect on channel segregation, showing that channels occur only in the region where the flow-phase transition interaction term (u_l·∇c_l and u_g·∇c_g) is negative. With a negative flow-phase transition interaction term the increase in flow velocity due to the flow perturbation and flow-phase transition interaction becomes more negative, thus the channel continues to grow and tends to be stable. Calculated results show good agreement with experimental data.
Keywords：multiphase solidificationformation of X-segregateschannel segregationnumerical simulation