镁合金阶梯变速等温锻造成形的组织演化规律与调控机理

Stepped-speed isothermal forging is an effective way to produce complex magnesium components with high efficiency by superplastic deformation. During this process, microstructure prediction and control is the important measure to refine grain, through which superplastic deformation can be achieved. However, various microstructure evolution mechanism is exists for huge range of speed during stepped-speed forging. Moreover, its behavior becomes more complex for stepped-speed, which changes microstructure evolution rule and mechanism of magnesium alloy. So, research work, such as microstructure evolution rule and control methodology, is in urgent need to be studied..The project is to reveal microstructure evolution rule and mechanism during stepped-speed forging. Compression tests with constant-speed and stepped-speed will be carried out for this goal. And, microstructure evolution models are going to be established by combining influences of deformation conditions, storage energy and initial microstructure. On the other hand, based on microstructure status and its deformation condition of superplastic compression, finite element analysis models for stepped-speed forging will be developed. And, for verification and improving of these models, stepped-speed isothermal forging tests are going to be carried out on isothermal die forging press. Then, influences of temperature and stepped-speed on deformation state and microstructure will be studied. Consequently, microstructure control mechanism can be revealed. Through this way, grain will be refined and superplastic forging is gonging to be achieved. So, magnesium components can be precisely produced during one-step forming. The research findings of this project can provide a theoretical guidance to manufacture complex magnesium components through superplastic compression with high efficiency.

阶梯变速等温锻造是实现复杂镁合金构件高效超塑性成形的有效途径。在阶梯变速锻造过程中，组织预测与调控是使锻件晶粒细化实现超塑性压缩的重要手段。然而，阶梯变速锻造极宽的速度范围导致多种组织演化机制并存，且受阶梯变速的强激励作用组织演化机制与规律变得极为复杂。因此，阶梯变速锻造的组织演化规律与调控机理是亟待解决的难题。.本项目拟通过恒速率与阶梯变速压缩实验，揭示阶梯变速压缩组织演化机制与规律，建立考虑阶梯变速条件、变形存储能与初始组织状态的组织演化模型；探明压缩超塑性的变形与组织条件，在此基础上，建立阶梯变速锻造有限元分析模型，并通过阶梯变速等温锻造工艺实验进行验证与改进；研究温度与阶梯变速路径对组织状态的影响规律与作用机理，探明阶梯变速锻造的组织调控机理，通过变形过程的晶粒细化实现构件一次超塑性成形。本项目的研究成果可为复杂镁合金构件高效超塑性成形提供理论指导。

镁合金是实际应用中最轻的金属结构材料，在航天航空等领域有很好的应用前景。然而由于镁合金滑移系少、导热系数及摩擦系数大等特性，其塑性变形能力较差。目前镁合金高性能锻件大多采用等温模锻成形制造，但仍存在锻件晶粒组织粗大与生产效率低等问题。对此，本项目提出了阶梯变形等温锻造的新思路，选取典型AZ80变形镁合金，研究了铸态AZ80-Ag(国内牌号AQ80)、锻态AZ80镁合金恒速率与变速率压缩流变特性及组织演变规律，发现在中温（523~573K）和中等速率（0.01~0.001/s）变形条件下，材料呈现出晶界滑移的典型超塑性变形特征，其组织状态为细小均匀的双相组织α-Mg+β-Mg17Al12，尺寸均约为1μm。中温中等速率超塑性变形有利于抑制成形过程晶粒组织长大，实现大塑性流变成形，具有较好的工程应用前景，成形制造航天航空、武器装备等领域高性能复杂镁合金锻件。细小组织是超塑性成形的关键因素。在上述工作基础上，本项目进一步研究确定了细化晶粒和扩大超塑性成形工艺窗口的一些措施，包括固溶、时效预处理和阶梯变速锻造，结果表明通过固溶预处理可充分溶解粗大析出相，降低变形抗力，改变孪生机制，改善变形均匀程度；采用过时效预处理可加强PSN效应有效细化晶粒组织；提高初始变形速率（第一阶段）可增大再结晶形核率同时提高生产效率。