提升室温塑性是镁合金大规模产业化应用所面临的极大挑战。晶粒细化是提升镁合金塑性的重要手段。然而，晶粒尺寸对镁合金力学行为的影响具有多尺度性，迄今也没有建立起普适的机理来描述晶粒尺寸、微观变形机制、材料宏观塑性三者之间的内禀联系。本项目采用原位扫描电子显微镜/电子背散射衍射、透射电子显微镜、高角度环形暗场扫描透射显微、原位同步辐射X射线衍射等先进实验分析技术研究镁合金变形机制及变形行为的晶粒尺寸效应。重点澄清（1）不同晶粒尺寸下滑移与孪晶、基面滑移与非基面滑移之间相互竞争的关系；（2）晶粒尺寸对晶界两侧变形协调行为的影响；（3）晶粒尺寸对<c+a>位错滑移稳定性的影响；（4）合金元素对镁合金滑移与孪晶的影响这四个科学问题。通过本研究，将建立起镁合金晶粒尺寸与宏观塑性之间的力学本构关系，实现晶粒尺寸-成分-塑性优化匹配，为设计新型镁合金及发展先进塑性加工技术提供理论支持。

Enhancing the room temperature ductility of Mg alloys is very important for their wide application in industry. Grain refinement is a useful way for that purpose. However, the influence of grain size to the mechanical properties for Mg is a multi-scale problem. So Far, there is not a universal theory to describe the relationship of grain size, micro-deformation mechanisms, and macroscopic mechanical properties in Mg. The project will use in situ scanning electron microscopy and electron backscattered diffraction (in situ SEM/EBSD), transmission electron microscopy (TEM), high angle annular dark field scanning transmission microscopy (HAADF-STEM), in situ synchrotron radiation X-ray diffraction (in-situ synchrotron XRD) and other advanced experimental techniques to study deformation mechanisms of Mg, and how these mechanisms are affected by the grain size. We focus on four issues, including (1) how grain size affects the competition between slip and twinning, basal slip and non-basal slip, (2) how grain size affects the slip transfer at grain boundaries, (3) how grain size affects the stability of <c+a> dislocations, (4) the alloying effect. From this project, we aim to establish a general theory to relate grain size and ductility for various Mg alloys. The theory will be useful for new alloy development and improve processing technologies in the future.