基于织构调控的镁合金管材挤剪成形机理与控形控性机制

Microstructures of magnesium alloys for tubes can be refined by equal channel angle pressing,and texture of basal plane would become weaken,but equal channel angle pressing is difficult to be industrialized, and the process is complicated.Fibrous microstructures and strong basal textures may be form by hot extrusion,which would decrease forming qualities of tube made of magnesium alloys.A new type of composite extrusion technology for thin-walled tubes made of magnesium alloys containing rare-earth element yttrium has been presented which combines the traditional direct extrusion and shear deformation(shorted as TES), Which is the combination of extrusion and shear deformation,and the TES process would control the microstructures and properties and shape qualities. In view of the scientific problems of congruent relationships among forming parameters,microstructure-texture and strength-toughness,shape qualities.The TES process of Mg-2Zn-1Mn-1.5Y(ZM21-1.5Y)magnesium alloy with rare earth elements is regarded as the research object in this item.Mathematical models of constitutive and plastic damage and microstructure evolutions and texture evolutions of magnesium alloy will be established based on physical simulations.Macro-micro coupled numerical simulations of TES process and optimization of forming parameters will be done.By means of TES process and EBSD and TEM technologies etc.,the association rules among textures and microstructures and shear stresses and forming parameters will be established and verified,and the regulation mechanisms of textures and microstructures of tubes may be explored.The corresponding relationships between the strength-toughness,shape qualities of tubes and microstructure-texture,forming parameters will be probed.Based on the above rules, the coordination controllablity mechanisms of shapes and performances of TES forming will be constructed.The coordination controllablity system of shapes and performances of TES forming with multi-objective functions and multiple design variables and the macro-micro coupled forming limit diagrams will be established. The significances of this research are to open up a new way to prepare for pipes and section bars made of magnesium alloy with rare earth elements with high forming qualities,and scientific understandings of the relationships between microstructures and properties of magnesium alloy would be promoted,and the project would provide scientific basises and technical foundations for the engineering applications of TES forming technology for tubes made of rare earth magnesium alloys.

镁合金管材等通道挤压可细化组织弱化织构，但工艺复杂；热挤压会形成纤维状组织及强烈的基面织构。项目提出管材(Tube)挤压(Extrusion)剪切(Shear)复合成形技术(简称TES)，可实现组织性能及外形质量的调控。针对TES成形参数、组织演变与强韧性及外形质量的对应关系这一科学问题，以ZM21-1.5Y镁合金的TES成形为研究对象，基于物理模拟建立材料本构及组织演化等模型，进行宏微观耦合的数值模拟和参数优化，通过TES试验结合EBSD及TEM等手段，构建织构-组织-剪切应力-成形参数间的关联关系，探究管材组织织构调控机理；揭示管材的强韧性、外形质量随织构组织、成形参数的演变规律；建立TES管材形/性协同调控机制，提出多目标函数多设计变量的形/性协同调控体系和宏微观耦合的成形极限图。项目开辟了一条制备高质量镁合金管材及型材的新途径，为TES成形技术的工程应用提供科学依据和技术基础。

镁合金薄壁管材正挤压会形成沿挤压方向的带状组织和较强的基面织构，这些织构不利于管材的二次加工(如内高压成形、折角、煨弯等)，严重降低了镁合金管材质量，造成力学性能各向异性；镁管等通道挤压可细化组织并弱化织构，但需要多次挤压、工艺复杂难以工业化；项目提出了镁合金管材挤压剪切成形技术。如：提出了以镁合金管材挤压-剪切成形工艺，也就是以“挤压成形管材+管壁连续多次剪切+整形”为路径加工管材，与普通挤压相比，镁合金管材挤压+管壁连续等通道挤压成形显著细化晶粒，提高了管材的硬度，在挤压过程中产生了大量的位错滑移及压缩孪晶{10-11}和拉伸孪晶{10-12}，变形态组织的比例明显增加；提出了AZ31镁合金薄壁管材挤压-连续剪切弯曲成形工艺和连续变通道挤压-剪切工艺,弱化了成形管材基面织构，细化了晶粒，提高了管材的综合力学性能，坯料受到剪切作用，晶粒c的轴不断向TD方向偏转，最终大部分晶粒的c轴发生了约86°的偏转；提出了将正挤压-剪切-扩径三道工序结合成形镁合金管材,在成形过程中，晶粒经过不断破碎、反复再结晶后形成均匀细小的等轴晶粒,基面织构的强度得到弱化、再结晶晶粒的比例提高以及基面滑移系的SF值增大。. 项目实现了不同镁合金管材挤压剪切工艺和模具结构条件下成形过程的三维动态宏微观耦合的数值模拟；基于数值模拟初步建立了管材织构-组织-成形参数之间的关系；应用数值模拟优化了挤压剪切成形参数，进行了相关试验，采用EBSD、SEM等先进方法研究了管材的组织和织构的演化特征，探索了剪切应变对管材组织织构的调控机理；探究了管材的强韧性及外形质量随织构组织、成形参数的演变规律；构建了挤压剪切成形的镁合金薄壁管材的强韧性及外形质量-织构-组织-成形参数之间的关系。研究成果将提升对镁合金管材挤压剪切成形参数、组织织构与强韧性及外形质量关联规律的科学理解，为镁合金管材挤压剪切成形技术的工程应用提供科学依据和技术基础。. 通过对研究内容和结果的整理，已经形成具有国际先进水平的管材挤压剪切成形理论与技术体系及具有自主知识产权的研究成果，包括在国内外重要期刊上录用、发表学术论文共17篇，被SCI/EI收录16篇。申请具有自主知识产权的发明专利7件，并授权4件；参与国内外会议18人次，并做邀请报告多次，获奖多次，和外国学者交流9次；培养硕士研究生7人；申请人获得人才领域5项。