The Mg_93.72Gd_5.85Y_0.43 alloy with columnar grains and preferred orientation of [22$4(\_)$5] was selected in this paper, and its deformation mechanism was investigated by room-temperature tensile test, quasi-in-situ observation and Electron Back Scatter Diffraction (EBSD). The results showed that all the columnar grains had the “soft” orientation ([22$4(\_)$5]) for both basal <a> slip system and {10$1(\_)$2} tensile twinning system. At the initial deformation stage (ε ≤ 3%), basal <a> dislocations started to move and crossed grain boundary, forming the basal-basal slip system pairs (B/B). As the deformation increased (ε ≤ 50%), {10$1(\_)$2} tensile twins selectively nucleated in single columnar grain and then expanded and merged rapidly, forming the bands of tensile twins and the basal slip system + tensile twinning-basal slip system pairs (BT/B). At the later deformation stage (ε ≤ 74.5%), the orientation transition brought by tensile twinning triggered the activation of {10$1(\_)$1} compression twins, leading to severe stress concentration and crack nucleation near the large-angle grain boundary and twinning boundary. The evolution of B/B pairs to BT/B pairs driven by grain boundary compatibility stress resulted in relaxation of the stress concentration at grain boundaries and guaranteed the excellent plasticity of the experimental alloy. A modified grain boundary compatibility stress calculation was proposed in this paper and was proved to be more effective in predicating the nucleation of tensile twins than the geometric compatibility factor.

Mg _93.72 Gd _5.85 Y _0.43合金，具有柱状晶粒，且优选取向为[22$4（\_）$本文选择[5]，通过室温拉伸试验，准原位观察和电子背散射衍射（EBSD）研究了其变形机理。结果表明，所有柱状晶粒均具有“软”取向（[22$4（\_）$5]），同时适用于基础<a>滑动系统和{10$\mathrm{1个}（\_）$2}拉伸孪生系统。在初始变形阶段（ε≤3％），基<a>位错开始移动并越过晶界，形成基-基滑移系统对（B / B）。随着变形的增加（ε≤50％），{10$\mathrm{1个}（\_）$2}孪生孪晶选择性地在单个圆柱状晶粒中成核，然后迅速膨胀和融合，形成了孪生孪生带和基底滑移系统+拉伸孪生-基底滑移系统对（BT / B）。在变形后期（ε≤74.5％），拉伸孪生带来的取向转变触发了{10$\mathrm{1个}（\_）$1}压缩孪晶，导致大角度晶界和孪晶界附近出现严重的应力集中和裂纹形核。由晶界相容性应力驱动的B / B对向BT / B对的演化导致晶界处应力集中的松弛，并保证了实验合金的优异可塑性。本文提出了一种改进的晶界相容应力计算方法，并证明了在预测孪晶形核方面比几何相容因子更有效。