镁合金晶体塑性本构模型与非均匀孪生变形分析

微结构演化对镁合金材料力学性能有着显著的影响,为了揭示镁合金宏观塑性各向异性特性与非均匀孪生变形的关系,开展了不同路径下的单轴加载试验以及采用含滑移、孪生机制的晶体塑性本构模型对试验条件下的镁合金变形行为进行数值模拟研究.文中本构模型描述了滑移与孪生变形机制以及晶格转动的机制,同时研究采用三维微结构代表性有限元模型,其包含晶粒尺寸、晶向和晶界倾角等微结构参数.研究结果表明,轧制镁合金具有强烈的宏观塑性各向异性行为,并对这种镁合金塑性各向异性行为的模拟结果以及多晶织构的模拟演化结果与试验测量进行对比,结果都基本吻合.对孪生非均匀变形模拟分析表明,镁合金宏观塑性各向异性行为与滑移、孪生变形机制的不同启动组合紧密相关,同时多晶体内应力的非均匀分布受到孪生变形的严重影响.而不同晶粒尺寸的晶粒所发生的孪生变形有比较大的差异,造成孪晶变体在晶粒内的分布极不均匀.该研究可为通过微结构的合理配置来设计和控制材料的力学性能提供理论依据.

Crystal Plasticity Constitutive Model and Analysis of Heterogeneous Deformation by Twinning for Magnesium Alloys

The evolution of microstructure significantly influences the mechanical behaviors of magnesium alloys. To reveal the relation between the plastic anisotropy and the heterogeneous deformation by twinning for Mg alloys, the uniaxial tests with different loading paths were conducted, and the deformation behaviors of Mg alloys were simulated using the crystal plasticity constitutive model, which can nicely describe the different deformation mechanisms of slip, twinning and lattice rotation. A representative volume element of material with the microstructural parameters of grain size, crystal orientation and grain-boundary misorientation angle was adopted. The Mg alloy sheets exhibit considerable plastic anisotropy. The comparison shows excellent agreement between the predicted results and the experimental data of the plastic anisotropic behaviors and polycrystalline textures of Mg alloys. The analysis of heterogeneous deformation by twinning indicates that the plastic anisotropic behaviors of Mg alloys are closely related with different activated combinations of the slip and twinning mechanisms. The inhomogeneous stress distribution in polycrystalline is significantly affected by twinning. However, the deformations by twinning in different sizes of grains are quite different, which results in the inhomogeneous distribution of twinning variants in grains. This research contributes to the design and control of the mechanical properties of magnesium alloys through a further improvement in the microstructure.