We studied the microstructure evolution of Mg-4Y-3Nd-2Sm-0.5Zr alloy by quasi-in-situ electron backscatter diffraction (EBSD) along with several strains under compression tests, which provided direct evidence for the influence of different twin-twin geometric structure on the twinning behavior. The results showed that the mechanical properties of the alloy were higher than traditional magnesium alloys (the maximum compressive strength reaches 402.5 MPa) due to the strengthening effect of Sm and Nd elements addition on solution strengthening, precipitation strengthening, and grain refinement. Combined with the quasi-in-situ EBSD technique, two different twin-twin geometric structures, ‘parallel structure’ and ‘cross structure’, were observed directly in the alloy. In the later stage of deformation, for ‘parallel structure’, residual stress and a large number of dislocations mainly existed in the twin boundary and tip position. For the ‘cross structure’, there was a lot of dislocation density in the interior of twins after fusion. The twin growth rate of ‘parallel structure’ was much faster than that of ‘cross structure’ because the stress of twins was mainly concentrated on the tip of twin. When the movement for the tip of twin was blocked, the growth rate of twin would be obviously decreased. Moreover, the ‘cross structure’ was easy to produce closed space. Due to the constraints of surrounding twins, the confined space was easy to stress concentration, thus inhibiting the growth of twins. At the same time, the ‘cross structure’ of twins needed a more external force to continue to deform, which also served as a strengthening structure.

我们通过准原位电子背散射衍射 (EBSD) 以及压缩试验下的几种应变研究了 Mg-4Y-3Nd-2Sm-0.5Zr 合金的微观结构演变，这为不同孪晶几何形状的影响提供了直接证据结对行为的结构。结果表明，由于Sm、Nd元素的添加具有固溶强化、析出强化和晶粒细化等强化作用，该合金的力学性能高于传统镁合金（最大抗压强度达到402.5 MPa）。结合准原位EBSD技术，直接在合金中观察到两种不同的孪生几何结构，“平行结构”和“交叉结构”。在变形后期，对于“平行结构”，残余应力和大量位错主要存在于孪晶界和尖端位置。对于“交叉结构”，融合后的双胞胎内部存在大量位错密度。“平行结构”的双胞胎生长速度比“交叉结构”快得多，因为双胞胎的应力主要集中在双胞胎的尖端。当双胞胎尖端的运动受阻时，双胞胎的生长速度会明显下降。而且，“交叉结构”容易产生封闭空间。由于周围双胞胎的约束，密闭空间容易产生应力集中，从而抑制双胞胎的生长。同时，双胞胎的‘交叉结构’需要更多的外力才能继续变形，这也起到了加强结构的作用。