“工艺-组织-性能”模拟研究Mg-Gd-Y合金混晶组织

Multimodal Microstructure of Mg-Gd-Y Alloy Through an Integrated Simulation of“Process-Structure-Property”

以Mg-8Gd-3Y-0.5Zr(GW83K)镁合金为研究对象,探索通过调控混晶显微组织来提高其力学性能的途径。将具有混晶组织的合金抽象为一种不同尺寸的晶粒嵌入到晶界中的颗粒复合体模型,在该模型中基体相为晶界,不同的颗粒相是不同尺寸的晶粒;然后基于Taylor关系的非局部塑性理论修正不同粒子嵌入到基体后对基体性能的影响,建立具有混晶组织特征的有限元平面应变细观力学模型。采用该模型模拟了含有混晶组织的GW83K镁合金在拉伸条件下的应力-应变行为,模拟结果对比实验数据验证了模型的有效性。在此基础上,通过真实时空相场模拟出的不同退火工艺下的混晶组织作为力学模型的几何输入参数,建立"工艺参数-混晶组织-力学性能"之间的关系。模拟结果对比发现,具有混晶组织的GW83K镁合金强度随平均晶粒尺寸的变化符合Hall-Petch关系,粗晶含量和分布显著影响着合金的塑性,当合金在623 K下退火90 min后对应的混晶组织可在保持高强度的同时有效提升塑性,为混晶组织的设计提供了参考。

Rare earth Mg alloys containing Gd elements can be used in aerospace,automotive,and other industrial fields owing to their high strength and creep resistance at room and high temperatures.However,the poor ductility of Mg alloys limits their application.Recently,it was discovered that the ductility of Mg alloy can be improved without compromising on its strength if sufficient amount of coarse grains is distributed in fine grains.In this study,taking the Mg-8 Gd-3 Y-0.5 Zr(GW83 K)alloy as an example,an approach for optimizing multimodal microstructures was investigated,which aimed to improve the mechanical properties of alloys.An alloy with a multimodal grain structure can be used as a particulate compound model,in which the grain boundary is considered the matrix,and different-sized grains are treated as different-types of particles embedded into the grain boundary matrix.A 2 D finite element micromechanics model combined with Taylor-based nonlocal plasticity theory,which considers the size effect of the particles,was established to simulate the mechanical response of the multimodal structure Mg alloy in a tensile test.The model was verified through the experimental data of the stress-strain curve.Moreover,the effects of process parameters on the mechanical properties of the GW83 K alloy were further evaluated by combining the grain structure under different annealing processes,simulated from a real spacetime phase-field model as the geometric input of the finite element model.Finally,the relationships between the annealing parameters,multimodal structure,and mechanical properties of the GW83 K alloy were described.The results show that the yield and tensile strengthes of the multimodal GW83 K alloy presented a Hall-Petch relationship with the average grain size.The content and distribution of coarse grains greatly affected the plasticity of the GW83 K alloy.By annealing the GW83 K alloy at 623 K for90 min,better plasticity could be achieved without sacrificing strength,which is helpful in promoting multimodal microstructural design.