镁合金孪生诱导动态再结晶/微裂纹竞相形成机理研究

During high strain rate rolling (HSRR) of magnesium alloys, dynmiac recrystallization and micocrack are mainly related to twinning, but the interactions among them are not clear. Aiming to study the competition mechanism of twinning-induced dynamic recrystallization/microcrack, the plain strain compression test is used to simulate HSRR processing in this project. The accommodation strain and dislocation model are applied to calculate the local stress-strain arising from deformation twinning. The effects of deformation condition on twinning behavior and local stress-strain arising from deformation twinning are investigated. Considering the local strains arising from deformation twinning, the energy balance equation is built to obtain the critical shear strain for twinning-induced dynamic recrystallization. Taking local stresses arising from deformation twinning into account, the critical shear stress for twinning-induced microcrack is gotten using crack nucleation model. The micostructural plastic mechanics model, associating with the deformation conditions and the local stress-strain arising from deformation twinning, is established on the basis of dislocation multiplication. Then, the competition mechanism of twinning-induced dynamic recrystallization/microcrack is revealed. Finally, the optimized HSRR technology is confirmed by HSRR experiment coupling the micostructural plastic mechanics model. Under the optimized HSRR technology, the twinning-induced dynamic recrystallization can be promoted and microcrack is inhibited. The implementation of this project can aid to discover new technical method and principles for high efficient short process rolling technology and potentially solve the issue that the industrial applications of thermomechanically processed Mg sheet alloys are significantly restricted.

镁合金高应变速率轧制过程中，孪生行为对动态再结晶和微裂纹都会产生重要影响，但三者之间的相互作用有待进一步研究。本项目拟采用平面应变压缩试验模拟高应变速率轧制过程，研究孪生诱导动态再结晶／微裂纹的竞相形成机理。项目运用协调应变和位错模型计算孪生局部应力-应变，研究变形条件对孪生行为及孪生局部应力-应变的影响；考虑孪生局部应变构建能量平衡方程获得孪生诱导动态再结晶临界剪切应变，考虑孪生局部应力运用裂纹形核模型确定孪生诱导微裂纹临界剪切应力；基于位错增值构建与变形条件和孪生局部应力-应变相关的微观塑性力学模型，探明孪生诱导动态再结晶／微裂纹竞相形成机理；最后，利用微观塑性力学模型结合高应变速率轧制实验确定孪生诱导动态再结晶抑制微裂纹的高应变速率轧制工艺。项目的展开为探索高效短流程轧制新工艺方法与原理提供理论支持，有望突破镁合金板材塑性加工产业化发展的瓶颈。

镁合金高应变速率轧制过程中，孪生行为对动态再结晶和微裂纹都会产生重要影响，但三者之间的相互作用有待进一步研究。本项目通过展开平面应变实验和高应变速率轧制实验，采用电子衍射背散色技术和透射电子显微镜等对高应变速率变形过程中的组织演变进行分析，通过力学理论建模分析局部应力-应变分布对孪生、再结晶和微裂纹的影响。发展了判定孪生变体选择方法，精确预测了孪生、再结晶、裂纹等微结构产生的临界条件，构建了孪生局部应力场的微观力学模型，揭示了孪生、再结晶和微裂纹的竞争机制；发现了边裂初生裂纹形成与再结晶机制之间的关系，构建了边裂二次开裂的模型，揭示了边裂形成的潜在机制；提出中高应变速率轧制调控孪晶/再结晶的强韧化方法，构建了考虑晶粒尺寸和孪晶对材料强度叠加影响的本构模型；基于微观力学模型耦合粘塑性多晶体自洽模型（VPSC）仿真镁合金塑性成形过程，探明了织构和再结晶等组织演变与流变行为间的交互作用机理；基于斯密特因子和临界剪切应力，建立组织、变形模型与力学性能之间的联系，揭示了高应变速率的轧制的构性关系。项目研究成果为探索高效短流程轧制新工艺方法与原理提供理论支持，有望突破镁合金板材塑性加工产业化发展的瓶颈。