A large number of anomalous extension twins, with low or even negative twinning Schmid factors, were found to nucleate and grow in a strongly textured Mg-1Al alloy during tensile deformation along the extruded direction. The deformation mechanisms responsible for this behaviour were investigated through electron back-scattered diffraction, grain reference orientation deviation, and slip trace-modified lattice rotation. It was found that anomalous extension twins nucleated mainly at the onset of plastic deformation at or near grain boundary triple junctions. They were associated with the severe strain incompatibility between neighbour grains as a result from the different basal slip-induced lattice rotations. Moreover, the anomalous twins were able to grow with the applied strain due to the continuous activation of basal slip in different neighbour grains, which enhanced the strain incompatibility. These results reveal the complexity of the deformation mechanisms in Mg alloys at the local level when deformed along hard orientations.

中文翻译：

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Mg-1%Al变形过程中不适合孪晶取向的晶粒中形核和延伸孪晶生长的起源

强织构化 Mg-1Al 合金在沿挤压方向拉伸变形过程中，发现大量具有低甚至负孪生 Schmid 因子的反常延伸孪晶成核并生长。通过电子背散射衍射、晶粒参考取向偏差和滑移迹修改晶格旋转研究了造成这种行为的变形机制。研究发现，反常延伸孪晶主要在晶界三联结处或附近塑性变形开始时成核。它们与相邻晶粒之间严重的应变不相容性有关，这是由于不同的基底滑移引起的晶格旋转造成的。此外，由于不同相邻晶粒中基底滑移的持续激活，异常孪晶能够随着施加的应变而生长，从而增强了应变不相容性。这些结果揭示了镁合金沿硬取向变形时局部变形机制的复杂性。