多轴复合加载下变形镁合金各向异性变形的高通量实验表征与跨尺度本构关系

The anisotropic behavior is the key restriction for the processing and application of wrought magnesium alloys. Quantitative characterization of yield surfaces evolution under multi-axial loading, and clarification the relationship between macroscopic anisotropy and microstructure based on precise constitutive models are the bottleneck problems for the utilization of anisotropic behavior and the improvement of processing technology. Recently it is found by the applicant that, the above mentioned bottleneck problems can be solved by high throughput experiments and multi-scale constitutive models. Therefore, the initial yield surface and evolution of subsequent yield surfaces under multi-axial loading will be tested by means of high throughput experiments for conventional wrought magnesium alloy, novel multi-scale (macro-meso-micro-nano scales) constitutive model based on Integrated Computational Materials Engineering (ICME) will be built, the relationship between macroscopic anisotropy and microstructure under multi-axial loading will be strengthened, the universal evolution of anisotropic behavior will be clarified, the integrated computation of anisotropy during plastic forming process will be performed to improve the processing technology for wrought magnesium alloys.

各向异性行为是制约变形镁合金加工应用最关键的因素之一。如何定量表征多轴复合加载下屈服面演化，并通过精确本构模型澄清宏观各向异性行为与微观组织结构的关系，是弱化并利用各向异性行为，提高其后续变形加工能力的瓶颈问题。申请人最近研究发现，采用高通量实验结合跨尺度本构模型可以有效解决上述瓶颈问题。因此，本项目拟选取常规变形镁合金作为研究对象，采用高通量实验探究多轴复合加载下初始与后继屈服面演化机理，基于集成计算材料工程（ICME），构建新型宏观-介观-微观-纳米跨尺度本构模型，分析多轴复合加载过程中显微组织演变与屈服面形状演化之间的关系，揭示具有普适意义的变形镁合金各向异性行为演化机制，实现其塑性成形过程中各向异性行为的集成计算，为利用该行为优化加工制备工艺建立基础。

各向异性行为是制约变形镁合金加工应用最关键的因素之一，因此，弱化并利用该行为，是提高变形镁合金后续变形加工能力、扩展应用领域的重要途径。本项目针对AZ31变形镁合金的各向异性行为，通过薄板平面双向加载实验、棒材拉—扭复合加载实验，系统研究了AZ31变形镁合金轧制板材、挤压棒材在多向复合加载下各向异性力学性能、swift效应以及显微组织演变，阐明了显微组织对AZ31变形镁合金各向异性演化的一般规律。主要结论分为三部分：1）变形机制演化。通过自由端扭转实验，发现预位错可以促进孪晶的生长，从而增加轴向缩短量；预孪晶有利于激活柱面滑移抑制轴向缩短。在剪切-拉/压复合加载时，滑移和孪生分别为剪切-拉/压实验的主要变形机制。2）定量表征了多轴复合加载下AZ31变形镁合金的等塑性功面和屈服面演化，发现孪晶的启动导致了高硬化率和流变应力，使等塑性功面由凸向凹转变。预拉伸引起的位错强化和对孪晶形核的抑制导致后续屈服面的膨胀，位错强化和取向强化之间的竞争导致后续屈服面的形状变化，后继屈服面向预压方向的旋转是由于基面滑移引起的结构旋转。3）修正了新型畸变强化本构模型，与微观组织演变相结合，分析了塑性变形过程中微观组织演变与各向异性演化之间的关系，模拟并预测了AZ31镁合金单轴加载下屈服面沿 RD/TD 方向演变过程，并通过多向加载实验得到了验证。