The effect of processing parameters on the microstructure and texture evolution of a cup-shaped AZ80 Mg alloy sample manufactured by the rotating backward extrusion

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The rotating backward extrusion (RBE) process is of great potential for producing the high qualitative cup-shaped AZ80 magnesium (Mg) alloy pieces based on the severe plastic deformation (SPD). However, researches on RBE process involving the microstructure and texture development are still pretty limited. Thus, in this work, the RBE process of AZ80 Mg alloy cup-shaped pieces was performed at three temperatures of 573, 613 and 653 K combining with three different rotating revolutions of 5, 50 and 100. Furthermore, the conventional backward extrusion (CBE), i.e. N = 0 in the rotating revolution, was also conducted for comparison. The effects of rotating revolution and processing temperature on the microstructure and texture evolution were studied in detail. The results showed that a relatively refined and homogeneous microstructure could be achieved by the RBE process compared with the CBE process. With the increasing rotating revolutions, the average grain size of the sample was decreased and the dynamical recrystallization (DRX) fraction was increased gradually. As the temperature increasing, the grain size of the cup-shaped samples was gradually increased, and the DRX fraction was also gradually increased for N = 0 and N = 5 samples, while it was almost unchanged for N = 50 and N = 100 samples. The smallest grain size of 3.9 μm and the largest DRX fraction of 99.2% were both obtained at 573 K with N = 100. The grain refinement during the RBE process was mainly caused by the DRX, which was determined by the deformation mechanism including the continuous DRX (CDRX) and discontinuous DRX (DDRX). Decreasing the deformation temperature could promote the generation of dynamic precipitates (DP), increasing rotating revolutions could reduce the size of the DP and make the undissolved eutectic phase (EP) more fragmented. In addition, the strong texture exhibited in the CBE samples could be effectively weakened by increasing the rotating revolution or temperature during the RBE process, owing to the higher proportion of new DRXed grains whose orientations were more random compared to the deformed grains.