高强韧镁合金大规格变截面型材的新型非对称反挤压成形机理与组织性能调控

The project is guided by the demand for lightweight of major equipment in key areas, such as national aerospace and orbital transportation. To solve the problem of high deforming resistance, poor forming property, microstructure heterogeneity and non-uniform mechanical properties during preparing large-size variable cross-section profile of high-strength and high-ductility magnesium, we propose a new academic thought of "controlling asymmetry by temperature, stress and strain”. Combined with backward extrusion technology, a novel thought of asymmetric backward extrusion technology about "differential temperature backward extrusion, rotary backward extrusion, gradient strain backward extrusion" is put forward creatively. In this project, the self-developed high-strength and high-ductility Mg-Gd-Y-Zn-Mn alloys are taken as the research object to study the dislocation slip, twinning, recrystallization, and the evolution of the second phase of magnesium alloys during plastic deformation under different temperature, stress and strain fields. The mechanisms of grain refinement, texture weakening, controlling mechanical properties of the high-strength and high-ductility magnesium alloy under complex stress conditions would be clarified. The mechanisms of forming, regulation and controlling in structure and property of high-strength and ductility magnesium alloy would be illuminated through numerical simulation and experimentation. The structure-function relationship among “microstructure-asymmetric deformation-mechanical and forming property” would be established. A novel technique of asymmetric backward extrusion and the accurate regulating and controlling in structure and property would be developed. The technical prototypes of large-size variable cross-section profile preparation in high-strength and ductility magnesium alloy would be obtained, resulting in providing theoretical guidance for the fabricating and processing of high-strength and high-ductility magnesium which are served as key components in China.

本项目以国家航空航天、轨道交通等重点领域重大装备轻量化需求为导向，针对高强韧镁合金大规格变截面型材制备面临的变形抗力高、成形性差及组织性能不均匀等问题，提出“温度控制非对称、应力控制非对称、应变控制非对称”学术思路，融合反挤压技术，创新提出“差温反挤压、旋转反挤压、梯度应变反挤压”新型非对称反挤压技术思想，以自主研发的高强塑Mg-Gd-Y-Zn-Mn镁合金为研究对象，研究镁合金在不同温度场、应力场和应变场下塑性变形过程中位错滑移、孪生、再结晶、第二相演化的微观机理，通过数值模拟与实验相结合，弄清复杂应力条件下高强韧镁合金晶粒细化、织构弱化和强塑性调控规律，阐明高强韧镁合金成形及其组织性能调控机理，建立“非对称变形-微观组织-力学与成形性能”之间的构效关系，发展新型非对称反挤压对组织性能精准调控技术，获得高强韧镁合金大规格变截面型材高效制备技术原型，为高强韧镁合金关重件制备提供理论指导。

随着轨道交通、航空航天和国防军工等现代工业关键领域重大装备升级换代的紧迫需求，兼具轻质、高强韧和耐疲劳的大规格镁合金变截面型材应用潜力巨大。含长周期堆垛有序相（LPSO相）的Mg-Gd-Y-Zn-Mn 高强韧镁合金由于其优异的综合力学性能，可满足重大装备关键构件的服役要求。但是，Mg-RE-TM系高强韧镁合金体系可动滑移系少且合金化程度高，在塑性变形过程中面临变形抗力高、变形织构强、组织性能均匀性差等问题，且传统挤压技术难以满足高强韧镁合金大规格变截面型材的生产需求。非对称加工技术可在镁合金塑性变形过程中引入非对称应力、应变和温度场，有助于镁合金密排六方结构非基面滑移系的启动，具有细化晶粒、弱化织构、变形均匀等特点；结合反向挤压工艺，可优化合金变形抗力，实现高强韧大规格变截面型材的高效制备。.本项目以高强韧Mg-Gd-Y-Zn-Mn合金为研究对象，研究了变形前多级均匀化和预时效等热处理工艺下合金多维多尺度微观组织的演变规律，实现合金中晶粒尺寸、第二相组态、SFs等组织的精准调控；通过研究合金热变形行为，建立了高温变形本构模型及热加工图。结合有限元模拟分析，阐明了非对称挤压工艺对塑性变形过程中金属流动的作用机制和微观组织演变的作用规律，基于优化的非对称变形工艺参数，实现了传统挤压大规格镁合金型材的均质制备。进一步分析了高强韧镁合金在复杂应力场、应变场和温度场的多维非对称物理场耦合作用下的变形机制，制备出高强韧镁合金变截面筒形件，研究了多维非对称反挤压工艺对合金成形性能、微观组织和力学性能的内在联系。明晰了合金时效析出序列演变规律，实现时效沉淀硬化相密度和分布的精确控制。同时，揭示了高强韧镁合金在交变循环应力下裂纹形成及失效机制。本研究为高强韧镁合金大规格关键构件的制备和工程应用提供了理论和技术指导。