Twinning characteristic in tension of magnesium alloys and its effect on mechanical properties

• An “unusual” Hall-Petch strengthening effect was revealed in tension of Mg alloys.
• This is attributed to the different twinning activation modes in coarse and fine grained samples.
• Twin chains were promoted by high geometric compatibility factor, low boundary angle and small grain size.

Twinning is an important deformation mechanism for Mg alloys and it generally nucleates from grain boundaries (GBs). When grains are refined, the fraction of GBs will largely increase, which may affect the activation mode of twinning. The present study aims to understand the characteristic of twinning in tension of fine and coarse grained Mg alloys and its effect on mechanical behavior. The experimental results showed that crossed twin lamellae were present within grains in coarse-grained (CG) sample, whereas long twin chains or twin bands crossing many grains were dominant in fine-grained (FG) sample. Because of the different activation mode of twinning, FG sample did not exhibit obviously higher yield strength compared to CG sample. Statistical analyses indicated that the high geometric compatibility factor, low angle boundary misorientation and fine grain size are favorable factors for the formation of twin chains or twin bands in FG sample.

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