镁合金中孪晶相关塑性与强韧化的微观机理及多尺度模拟

Driven by the current policy of energy saving and emission reduction, structural weight reduction becomes an unstopping trend. As the lightest structural metal today, Magnesium (Mg) has a lot of potential uses in automobile and national defense applications. However, the wide use of Mg alloys as a structural material is limited by their low strength and toughness, due to the hexagonal close-packed crystal structure of pure magnesium, which cannot provide enough slip systems at room temperature. Twinning is an important deformation mode for the strengthening/toughening, and therefore current project aims to study the twinning related plasticity and strengthening/toughening mechanism in magnesium alloy AZ31 through macro/micro experiments and multiscale simulations. First, using electron microscopy and molecular dynamics, the interaction between microstructure (solute atoms, precipitates, grain boundaries) and twinning will be systematically investigated to reveal the twinning strengthening mechanism and model. Then, the plastic mechanism and model will be introduced into the discrete dislocation dynamics method to produce multiscale software accurately handling the dislocation slip and twinning. Finally, the software will be employed to study the macroscopic mechanical properties of magnesium alloys, especially the influence of alloying elements, grain size, texture and orientation on the twinning deformation and strengthening/toughening property, to establish the physical relationship between microstructure, plastic deformation and strengthening/toughening. Current project will propose some effective methods to improve the mechanical property, and provide theoretical guidance for the structure design and processing technology of magnesium alloys.

在当前节能减排的号召下，结构减重已是形势所趋。镁是现今最轻的金属结构材料，在汽车、国防等领域的应用前景广阔。然而纯镁的密排六方晶体结构中的室温滑移系较少，导致强度较低与韧性较差，阻碍了镁合金的广泛应用。可见孪晶是实现强韧化的重要变形机制，故本项目拟通过宏微观实验观测与多尺度计算手段，深入研究变形镁合金AZ31的孪晶相关塑性及强韧化机理。首先，运用电子显微镜与分子动力学手段，系统地观测、模拟镁合金中固溶原子、析出物、晶界等微结构与孪晶的相互作用，揭示孪晶的强化机制与模型。然后将孪晶相关的塑性机制引入到离散位错动力学中去，开发一个能精确模拟孪晶变形与位错滑移的多尺度软件。最终将该软件用于研究镁合金的宏观力学性能，着重分析合金元素、晶粒尺寸、织构、取向对孪晶变形与强韧性能的影响，建立微结构-塑性变形-强韧化的内在物理关联，并提出改善强韧性能的技术与手段，为镁合金的结构设计与加工工艺提供理论指导。

在当前节能减排的号召下，结构减重已是形势所趋。镁是现今最轻的金属结构材料，但由于强度较低与韧性较差，阻碍了其工程应用。本项目针对镁合金中的孪晶变形开展系统研究，取得了若干创新成果：（1）揭示了镁合金中孪晶与析出相的相互作用机理，发展了孪晶变形的析出强化理论模型，并预测柱面片状析出相对位错和孪晶均有不错的强化效果，可用于工程设计；（2）研究了晶界对孪晶的阻碍效果，并发展了孪晶的晶粒尺寸效应模型，解释了孪晶较强的晶粒尺寸效应；（3）系统研究了镁合金中位错的相互作用，揭示了镁合金中重要的位错反应机制。本项目的创新成果对镁合金力学性能提升和微结构设计提供重要的理论参考和技术指导。研究成果在镁合金研究领域引起重要的学术影响，在国内外重要学术期刊和学术会议发表论文14篇，其中IJP论文3篇、Scripta Materialia论文2篇、Computational Materials Science论文2篇、固体力学学报论文2篇。所发论文得到广泛引用，其中一篇IJP论文2018年至今已被引用43次，并被国际同行称为至今最为重要的模拟（Fan et al. (2018) provide the most in depth simulation study on the phenomenon to date）。项目组成员入选了国家级人才计划和德国洪堡学者，参加学术交流60人次，做邀请报告12场。本项目培养研究生7名，其中1名入选日本JSPS研究员、2名获四川省力学学会学术交流会学生竞赛组二等奖；本科生11名，其中2名获四川大学本科优秀毕业论文。