In magnesium alloys, detwinning typically refers to the phenomenon in which the { \(10\overline{1 }2\) } twins revert to their original orientation before twinning occurs. This study revealed the correlation between detwinning and macroscopic strain-localized banding in AZ31 (Mg-3Al-1Zn-0.3Mn, wt pct) Mg alloy and explored the origin of this correlation. Using digital image correlation (DIC) and in situ X-ray diffraction analysis, a collective detwinning phenomenon occurring alongside macroscopic strain-localized bands was observed. These strain-localized bands formed and propagated repetitively in the gauge part of the specimen during tensile deformation. The heterogeneous deformation was prominent in the yield plateau region of the stress–strain curve, where intensive detwinning was observed. Quantitative assessment of the local strain performed using correlative electron backscatter diffraction–DIC analysis revealed that the detwinning shear significantly contributes to macroscopic strain localization; however, detwinning alone cannot account for the observed strain localization. This study demonstrated that detwinning occurs collectively, inducing the formation and propagation of macroscopic strain-localized bands during tensile deformation.
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