本文系统总结了Mg中{10$\bar{1}$2}-{10$\bar{1}$2}双拉伸孪晶及其构成的复合孪晶结构的研究进展。连续多向变形可以显著降低Mg的拉/压不对称性,其基本步骤是连续双向变形,该过程在Mg中激发大量双拉伸孪晶形成,它有36个变体,可分为4个取向差组,其中一组显著择优,无法用Schmid因子(SF)完全解释。一次和二次拉伸孪晶在晶界处或晶内孪晶界处交汇,形成晶间或晶内复合孪晶结构,它们的形成路径具有多样性。SF法则和衡量孪生切变穿越界面的m' 因子,对解释晶间或晶内复合孪晶结构的形成,部分或者完全失效,这对人们揭示较复杂条件下孪晶的形成机理提供了机遇和挑战。建议未来的工作重点围绕模拟晶内复合孪晶结构的形成以及实验观察一次拉伸孪晶间界面和二次拉伸孪晶界的界面结构展开。

This paper summarizes recent research progresses on {10$\bar{1}$2}-{10$\bar{1}$2} double extension twin and its related compound twin structures in Mg. Tension-compression asymmetry of Mg with strong texture can be greatly alleviated through sequential multi-directional deformations, which consist of several sequential bi-axial deformations. There exist 36 possible double extension twin variants, which can be classified into four misorientation groups according to their misorientations with respect to the grain matrix. One of the groups appears with a much higher frequency than the others, which cannot be perfectly explained by Schmid factor (SF) rule. Primary and secondary extension twins form intergranular and intragranular compound twin structures without any one-for-all mechanism. SF rule and m' factor, which evaluates how much twinning shear can pass through an interface, partly or even totally fail to explain the formation of the compound twin structures, presenting challenge to make clear mechanism of twin formation under complex loading conditions. It is suggested that modelling on the formation of intragranular compound twin structure and experimental characterization of interfacial structures of primary twin-twin boundary and secondary twin boundary should be paid much attention in the future.