脉冲电场下超薄稀土镁合金板冷轧变形机理研究

Magnesium alloy sheets and strips with high ductility have the huge potential in the automotive industry and sophisticated electronic products, which was regarded as green engineering materials in 21st century. Due to the hexagonal lattice of magnesium, leading to poor room temperature formability and strong planar anisotropy, grain refinement and texture modification are two promising approaches to enhance the ductility of Mg alloys. In this study, continuous cold rolling based on the electro-plastic effect was used to prepare the high ductility of ultra thin Mg alloys sheets containing rare earth (RE) elements (thickness ≤ 0.3 mm). The deformation mechanisms of plasticity and recrystallization behavior were fundamentally investigated. The influence of RE elements on the main deformation mechanisms based on the electro-plastic effect such as dislocation glide, twinning and shear bands was systematically investigated. Integrated large strain hot rolling and electro-plastic cold rolling were employed to produce the ultra thin Mg alloys sheets containing RE elements. Quantitative analysis of the deformation mechanisms to the contribution of the strain and low temperature dynamic recrystallization were explored based on the model of strain energy distribution from the Crystal Plasticity Finite Element Method (CPFEM). This study aims to elucidate the mechanism of enhancement ductility of Mg alloys by electro-plastic effect and low temperature dynamic recrystallization, laid on the theoretical and technical foundation for the production the high ductility of ultra thin Mg alloys sheets by means of microstructure and texture control with high strain accommodation in single pass, and without the intermediate annealing during cold rolling.

高延展性镁合金薄板带在汽车及高端电子信息产品中有着重要的应用潜力，被誉为“21世纪绿色工程结构材料”。镁属六方晶系，室温塑性变形能力差且各向异性强，晶粒细化和织构改性是解决该问题的有效途径。本项目拟采用电塑性连续冷轧变形制备高延展性稀土镁合金超薄板材（厚度≤ 0.3 mm），以塑性变形机制和再结晶行为作为主要研究对象，对电塑性冷轧变形增韧机理、变形机制的定量分析及低温动态再结晶机制进行基础科学研究。具体内容包括：通过大变形量热轧开坯，再进行电塑性冷轧变形；研究稀土元素在脉冲电场下冷轧变形对各主要变形机制（滑移、孪晶和剪切带）的影响；定量分析各变形机制对形变的贡献量和低温动态再结晶及织构随机化机制。本项目旨在揭示电塑性变形增韧机理和低温动态再结晶机制，通过微观组织和织构的综合调控实现镁合金板材单道次大变形量的轧制变形，免除冷轧过程中间退火工艺，为制备高延展性稀土镁合金超薄板奠定理论和技术基础

镁合金作为最轻的金属结构材料，在航空航天、汽车、电子产品等领域具有很好的应用前景。由于室温成形性能差，加工成本高，目前镁合金的商业化应用还十分有限。镁合金的成形性能和它的微观组织和织构取向密切相关。研究表明，采用特种加工手段和添加稀土元素（RE）是优化镁合金织构的两种有效手段。然而，前者由于设备的复杂性，在大规模应用上存在困难，后者则由于稀土元素价格较高而难以实现商业化应用。. 本研究通过脉冲电流来辅助镁合金的加工，探索了利用脉冲电流来改善镁合金的加工性能和优化其晶体学织构的可行性。利用电子背散射衍射（EBSD）和粘塑性自洽（VPSC）模拟等技术对加工过程中合金的微观组织和织构演变进行了表征与分析，重点探讨了脉冲电流对镁合金的塑性变形和再结晶机制的影响。首先，通过对比单道次小应变量的传统温轧和电致塑性轧制，研究了脉冲电流对AZ31镁合金孪生行为的影响。发现了脉冲电流对孪生类型、孪生分数以及孪生变体选择的影响规律。其次，系统对比了AZ31镁合金在多道次小应变量的传统温轧和在电致塑性轧制过程中的微观组织和织构演变。通过分析两种轧制制度下材料在孪生、剪切带、动态再结晶（DRX）等行为上的差异，对脉冲电流改善AZ31镁合金轧制性能的现象做出了合理的解释。对比了Mg-1Gd合金在有无电场作用下冷轧变形微观组织和织构取向分析。最后，研究了经室温预轧制的AZ31板材、Mg-1Gd合金在电脉冲处理、箔材轧制过程中的微观组织和织构演变。从理论上解释了脉冲电流对AZ31、Mg-1Gd合金的再结晶形核和晶核长大过程的影响。本研究证明了脉冲电流可以作为改善AZ31、Mg-Gd稀土镁合金轧制性能和优化其织构的有效手段。本研究的实验结果可以为镁合金电致塑性加工工艺的优化提供参考。. 项目完成了预定的研究目标，已发表学术论文7篇，其中SCI收录7篇，获得授权国家发明专利2件，申请发明专利1件。培养博士研究生1名，硕士研究生2名。