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Mg在室温下的强度和塑性较差, 其根源之一在于Mg的{101ˉ2}形变孪晶在极低的应力下即可形核和扩展, 而且研究表明目前应用于镁合金的时效强化法通常无法显著抑制{101ˉ2}形变孪晶. 尽管对Mg 及其合金的力学性能至关重要, 迄今为止, 对{101ˉ2}形变孪晶的形核和扩展的机制仍存在很大争议. 本文首先回顾了有关形变孪晶的定义以及{101ˉ2}孪晶机制的研究历史, 然后着重介绍了最新的基于原位TEM的研究结果: 即Mg的{101ˉ2}形变孪晶迥异于孪晶的经典定义, 它事实上是一种新的室温变形机制, 即塑性的产生可以通过局部的晶胞重构来完成, 而不需要孪晶位错的参与; 由晶胞重构机制所产生的界面为{0002}/{101ˉ0}界面(BP 界面), 而且该界面在三维空间呈现梯田状的不规则形貌. 晶胞重构机制迥异于基于位错的孪晶变形机制, 因此基于对该机制进行抑制的设计思路可能是开发未来高强韧镁合金的关键.

The {101ˉ2} deformation twinning with extremely low activation stress is considered to be one of main reasons for the low strength of magnesium and its alloys at room temperature. In addition, it was found that those generally adopted age-strengthening methods are less effective for magnesium alloys in which postmortem investigation found that {101ˉ2} deformation twinning is still profuse. The formation and propagation mechanism of {101ˉ2} deformation twinning, which are of great importance for designing high strength magnesium alloy, remains elusive or under fervent debate. This paper reviewed the classical definition of deformation twinning, the existing twinning mechanisms, and the recent achievements through in-situ TEM studies on {101ˉ2} deformation twinning. It was found that the {101ˉ2} deformation twinning observed in magnesium are distinct from the classical definition on twinning. It is indeed a brand new room temperature deformation mechanism that can be carried out through unit- cell- reconstruction, without involving twinning dislocations. In addition, the boundaries generated through unit-cell-reconstruction are composed of {0002}/{101ˉ0} interfaces (BP interfaces) and exhibit a terrace-like morphology in 3D space. The unit- cell- reconstruction is essentially different from the traditional dislocation- based twinning mechanism. As a consequence, to develop an effective strengthening strategy based on the nature of this new deformation mechanism would be the key for designing high strength magnesium alloy.