Texture tailoring and microstructure refinement induced by {11-21} and {10-12} twinning in an extruded Mg-Gd alloy

An extruded Mg-17Gd (wt%) alloy with < 0001 > fiber texture was compressed along different directions at room temperature. Electron backscatter diffraction characterization was used to investigate the texture tailoring, twinning and dynamic recrystallization (DRX) behaviors. The results indicate that {10-12} and {11-21} twinning activated. The [0001] pole tilted to compression direction with the strain increasing and twinning dominated the texture transition. Activation of {10-12} twinning can be governed by Schmid law, while it is more appropriate to explain the activation of {11-21} twinning by the basal slip transfer condition in the twinned grains according to the slip trace analysis. In addition, operation of {11-21} twinning can facilitate the nucleation of {10-12} twin in the same grain by changing Schmid factor (SF) in the vicinities of {11-21} twin. Grain refinement occurred in the specimens with large strain and the average grain size decrease from -27 & mu;m to -12 & mu;m. The mechanism of grain refinement can be summarized as follows: the mobility of twin boundaries will be restricted because of the twin-twin and dislocation-twin interaction and converted to random high angle grain boundaries (HAGBs). The random HAGBs offer the nucleation sites and the strain accumulation within twins offer the driving force which facilitate the formation of DRXed grains at random HAGBs. Additionally, the SF difference within parent grain may result in the formation of HAGBs, and these HAGBs can connected the random HAGBs that result from the dislocation-twin interaction which result in the formation of new grains.