On the origin of non-basal texture in extruded Mg-RE alloys and its implication for texture engineering

The work aims to investigate the formation and transformation mechanism of non-basal texture in the extruded Mg alloys. With this purpose a pure Mg as reference and eight Mg-Gd binary alloys with the Gd concentration ranging from 0.5 wt.% to 18 wt.% were prepared for extrusion. This study shows that the basal fiber texture in pure Mg transited into RE (rare earth) texture in diluted Mg-Gd alloys and into the abnormal C-texture in high-concentration Mg-Gd alloys. In pure Mg, discontinuous dynamic recrystallization plays a predominant role during the extrusion process, resulting in the formation of a typical basal fiber texture. Alloying with high concentration of Gd impedes the dynamic recrystallization process, facilitating the heterogeneous nucleation of shear bands as well as the dynamic recrystallization within shear bands. Dynamic recrystallized grains within shear bands nucleate with a similar orientation to the host deformed parent grains and gradually tilt their c-axis to the extrusion direction during growth by absorbing dislocations, leading to the formation of either the RE-texture orientation or the C-texture orientation, depending on the stored energy within shear bands. The analysis aided by IGMA and TEM characterization reveals that the shear bands originate from the extensive but heterogeneous activation of pyramidal Ⅰ slip. Tensile tests illustrate a close correlation between the fracture elongation and texture types. A comprehensive understanding of the formation and transformation mechanism of different texture components in Mg alloys holds significant importance for the design of high-performance Mg alloys by texture engineering.