Extruded polycrystalline pure magnesium (Mg) with fine grain size (~1.2 µm) exhibits ductility of over 100% at room temperature, in spite of the presence of a strong basal texture. In this study, a set of complementary in-situ characterisation techniques over multiple-length scales were utilised to reveal the deformation modes enabling such ductility. Synchrotron X-ray diffraction results show that the elastic lattice strain of fine-grained sample for tensile elongation up to ~55% is 3–10 times lower than that in the coarse-grained sample, indicating the absence of significant strain accumulation inside fine grains and potential inter-granular deformation in bulk. In-situ scanning electron microscopy validates the predominant operation of the inter-granular deformation, and it further reveals that the inter-granular deformation occurs by the relative sliding between groups of grains having similar orientations. The deformation resulting from such sliding is substantial, and it is accommodated by the rotation of grains located between slid grouped grains, from hard to softer orientations to allowing dislocation slip to readily occur. The accommodating mode of dislocation slip is further supported by in-situ transmission electron microscopy observations. Dislocations glide readily to, and annihilate at, grain boundaries. The observations and direct evidences presented herein suggest that the major deformation mode is sliding between grouped grains that is accommodated by grain rotation and dislocation slip, in contrast to dislocation slip in coarse-grained Mg. The coordinated deformation processes postpone the occurrence of localised stress concentration and greatly increases the ductility of pure Mg at room temperature.

尽管存在很强的基础纹理，但具有细晶粒尺寸（〜1.2 µm）的挤出多晶纯镁（Mg）在室温下仍具有超过100％的延展性。在这项研究中，利用了一组在多长度尺度上互补的原位表征技术来揭示实现这种延展性的变形模式。同步加速器X射线衍射结果表明，拉伸伸长率高达〜55％的细颗粒样品的弹性晶格应变比粗颗粒样品的弹性晶格应变低3-10倍，这表明细颗粒内部没有明显的应变积累和潜在的晶粒间变形。原位扫描电子显微镜证实了晶粒间变形的主要作用，并且进一步揭示了晶粒间变形是通过具有相似取向的晶粒组之间的相对滑动而发生的。由这种滑动引起的变形是很大的，并且通过位于滑动的成组的晶粒之间的晶粒的旋转从硬到软的取向到容易发生位错滑移而容纳了变形。原位进一步支持错位滑移的容纳方式透射电子显微镜观察。位错容易滑到并消除晶界。本文提供的观察和直接证据表明，与粗粒Mg中的位错滑移相反，主要变形模式是在晶粒旋转和位错滑移所适应的成组晶粒之间滑动。协调的变形过程推迟了局部应力集中的发生，并大大提高了纯镁在室温下的延展性。