高差速比轧制制备超塑性镁合金的微结构竞争机制及跨尺度仿真研究

High-strain-rate superplasticity can obviously promote the forming efficiency of complex parts and high temperature anti-oxidation of Mg alloys. The high-ratio differential speed rolling is a highly efficient and low-cost process to produce the high-performance Mg alloys, satisfying the significant demands in China national industrial field. However, the plates still have problems regarding edge cracking or surface cracking during the rolling process, and the degradation of superplasticity of the rolled plates can be caused by the grains widely and abnormally growing during hot working, in addition, the precise control of high-strain-rate superplasticity is currently unable to be achieved modulating microstructures and textures. Employing experiments and multi-scale simulations, this project aims at above critical problems and launches following meso-mechanical studies respectively: (1) To identify the competition between recrystallization and fracture related to the rolling process and local deformation domain effects; (2) To clarify the temperature-dependent promotion and pinning effects of precipitates and grain boundaries on grain boundary sliding and migration; (3) To reveal the cooperatively controlled competition between strengthening and superplasticity softening by precipitates, grain boundaries and textures, the coordination mechanisms of the stress concentration resulting from grain boundary sliding, and the cavitation mechanism. Based on above, this project is expected to ascertain the quantitative correlation among the processing parameters, the microstructure and texture features together with evolution, and high-strain-rate superplasticity, and to effectively solve the processing problems, such as finished product rate decreasing, low thermal stability and incapability of precise performance controlling.

高应变速率超塑性能够显著提升镁合金的复杂零件成型效率和高温抗氧化能力。高差速比轧制是一种制备相应性能镁合金的高效率、低成本工艺，符合国家工业界的重大需求。然而，板材在轧制过程中仍然存在边裂或表面开裂问题，且热加工过程中晶粒易异常长大导致轧后板材超塑性衰退，此外，目前无法通过微结构和织构的调控实现高应变速率超塑性的精准控制。本项目拟针对上述关键问题，通过实验及跨尺度仿真，分别开展下列细观力学问题研究：（1）明确轧制工艺及局部变形域效应关联的再结晶与断裂竞争机制；（2）阐明温度依赖下析出相、晶界等因素对晶界滑移、迁移的促进及钉扎机制；（3）揭示析出相、晶界及织构共同控制的强化与超塑性软化竞争机制，以及超塑性晶界滑移的应力集中协调机制及空洞化机制。在此基础上，确定工艺参数、微结构和织构的特征与演化规律、高应变速率超塑性三者间的定量关联，有效解决制备成材率降低、热稳定性差及性能无法精准控制等问题。

高应变速率超塑性能够显著提升镁合金的复杂零件成型效率和高温抗氧化能力。高差速比轧制是一种制备相应性能镁合金的高效率、低成本工艺，符合国家工业界的重大需求。然而，板材在轧制过程中仍然存在边裂或表面开裂问题，且热加工过程中晶粒易异常长大导致轧后板材超塑性衰退，此外，目前无法通过微结构和织构的调控实现高应变速率超塑性的精准控制。本项目针对上述关键问题，通过实验及跨尺度仿真，分别开展了下列力学问题研究：探明了高差速比轧制过程中镁合金内孪生、剪切带、晶界等诱导的再结晶与断裂的竞争机制，以及工艺参数关联的上述竞争机制对织构演化的作用机理；分析了析出相对晶粒热稳定性的影响机制以及析出相诱导的损伤；研究了微结构及织构控制的强化与超塑性软化的机制，分析了超塑性变形过程的应力集中协调及韧性断裂机制。获得了以下科学成果：（1）提出了一种可描述复杂多路径及非线性大变形加载下HCP合金非对称屈服面演化的解析模型及次弹塑性本构关系；（2）发展了可定量关联宏观剧烈塑性成形工艺与微结构及织构演化的跨尺度仿真技术，并基于此技术揭示了粗晶镁合金中再结晶转化对细晶化过程及热加工塑性的作用；（3）从局部应力场角度解释了析出相对晶界运动的钉扎机制，揭示了析出相诱导再结晶与空洞化竞争的原子机制，建立了应力-腐蚀耦合损伤的多物理场仿真框架；（4）在实验和数值上澄清了承受压缩-剪切-拉伸等复合应力载荷、高温及高应变率的镁合金韧性断裂宏观及微观机制，提出了能有效提升镁合金塑性并抑制失效的材料微结构设计方案。所获成果为解决制备成材率低、热稳定性差及性能无法精准控制等问题，提供了理论模型、实验依据和仿真方法。