基于快速多向锻造和温锻细化晶粒的大型镁合金锻件组织性能调控

Magnesium alloy is particularly favored as its low density in the field which the loss of weight is very important. Current magnesium alloy forging applications are unsatisfactory in these areas, mainly due to the low strength in the magnesium alloy forgings, plus the poor formability at room temperature, limiting its application in the aerospace field. The current methods which improve the strength of magnesium alloys are still difficult to manufacture high-strength magnesium alloy forgings with large size. Recently the international scholars show that the twin deformation is the dominant deformation mechanism during grains refinement process in forging with high speed. In view of this, the applicant puts forward a multi-directional forging with high speed and warm forging method to control the microstructure and properties of magnesium alloys by grain refinement. The {10-12} twin and {10-11}-{10-12} double twin formation mechanism and the role in the formation new grains will be studied during multi-directional forging with high speed using molecular dynamics simulation. The relationship between basal and pyramidal slip, critical resolved shear stress, accumulation energy also will be studied. Make full use of the twinning deformation mechanism in magnesium alloy, promote twinning by changing forging directions, avoid the medium speed range which can not be used to forge magnesium alloy. It can obtain high strength and good plasticity by refine grains. In order to ensure the ultimate high strength in magnesium alloy forgings, the warm forging method is adopted after the grains refinement. In this project, the molecular dynamics method is adopted to study the nature mechanism of grain refinement of magnesium alloys. In addition, the FEM simulations are used to track the performance and the grains evolution during the multi-directional forging with high speed and warm forging process. The experimental process and the observation of the microstructure and mechanical properties are also combined to use in the project. The objective is to reveal the grain refinement mechanism under multi-directional forging with high speed and to explore a control and regulation method about the microstructure and performance of large magnesium alloy forgings by grain refinement to improve the strength and performance. This project will promote the technological progress of large magnesium alloy forgings in China.

镁合金在减重尤为重要航空航天领域受到青睐，镁合金锻件在这些领域应用却未达预期，主要原因之一是镁合金锻件强度较低，室温成形性较低。现存提高镁合金强度方法仍不易制备较大尺寸高强锻件。基于最近国际上对快速锻造孪生为主导晶粒细化这一机制的新认识，提出基于快速多向锻造和温锻细化晶粒的大型镁合金锻件组织性能调控。利用分子动力学研究快速多向锻造拉伸{10-12}孪生和{10-11}-{10-12}双拉伸孪生等形成机制和在形成新晶粒中作用，其与基面和锥面滑移、临界剪切应力、储存能等复杂作用机制，结合有限元模拟、工艺实验和微观组织观察研究晶粒细化关键影响因素。在此基础上，充分利用孪生变形，通过模具快速多向锻造细化晶粒，获得高强度同时拥有良好塑性。细化晶粒后再采用镁合金温锻技术，保证锻件最终高强度，目的是揭示快速多向锻造镁合金晶粒细化机理，探索出细化大型锻件晶粒、提高最终锻件强度的一种共性组织性能调控方法。

镁合金在减重尤为重要航空航天领域受到青睐，镁合金锻件在这些领域应用却未达预期，主要原因之一是镁合金锻件强度和室温成形性较低。项目通过分子动力学、有限元模拟和实验相结合，揭示镁合金锻坯快速多向锻造下晶粒细化的本质物理机理，制备晶粒细化的镁合金锻坯，提高锻坯室温塑性，同时温成形该类承载构件，调控锻件组织和性能，大幅度提高镁合金承载构件力学性能指标。.项目执行过程中围绕上述研究目标，建立了多向锻造的分子动力学模拟模型，研究了镁多向压缩过程中塑性变形行为；阐明了镁中{10-11}压缩孪晶和{10-12}拉伸孪晶的形成机制，孪生过程由孪晶位错运动主导，依靠原子剪切和迁动共同完成；揭示了位错、孔洞、第二相等缺陷对孪晶生长过程的影响规律，位错、孔洞、第二相均可以不同程度地阻碍孪晶生长，其阻碍作用的实质是缺陷与孪晶界上的孪晶位错发生反应，妨碍孪晶位错的正常运动；建立了变形过程中动态再结晶行为的元胞自动机模型，完成了不同变形参数对动态再结晶行为和组织影响的模拟研究。.完成了温度、应变速率和应变程度等对AZ80A、MB15镁合金及轻稀土镁合金Mg-7Gd-2Y-1Zn-0.5Zr多向锻造晶粒细化机制及组织性能影响的研究，结果表明挤压及多向锻造复合工艺分别使AZ80、MB15及Mg-7Gd-2Y-1Zn-0.5Zr镁合金平均晶粒尺寸由74.7µm、20µm、40.2µm细化到9.8µm、4.3µm、0.34µm，屈服强度由108.51MPa、185.65MPa、259.67MPa提高至179.29MPa、195.81MPa、412.60MPa，抗拉强度由258.48MPa、285.54MPa、362.30MPa提高至462.13MPa、434.35MPa、440.07MPa。.在此基础上研究了多向锻造后的细晶锻坯温锻工艺，并在承载结构件进行了相关验证。通过多向锻造及等温锻造技术获得的低成本轻稀土镁合金锻件屈服强度可达到337MPa，抗拉强度达到408MPa，且延伸率为12.2%。该项工作将为低成本镁合金锻件应用奠定了基础。

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