Formation of Abnormal Texture and Anisotropy Weakening Mechanism of Mg-Gd-Y-Zn-Zr Sheets by Rotary Forward Extrusion

In this work, the effect of rotary forward extrusion technique on the development of texture structure and mechanical anisotropy of Mg-12Gd-4Y-2Zn-0.4Zr sheets is studied. The experiments were carried out using a large-sized alloy (phi 330 x 1100 mm) at an extrusion temperature of 460 degrees C and a high extrusion ratio (10.18). The average grain size of the alloy gradually decreases from 126.3 mu m to 10 mu m with increasing cumulative stress during rotary forward extrusion, the size of the second phase also decreases significantly and is uniformly distributed. At the same time, an abnormal texture (an abnormal extrusion texture with c-axis parallel to extrusion direction) parallel to the extrusion direction (ED) was formed by the rotation of < 0001 > grains, which was caused by the rotation of the basal plane along the principal stress axis driven by the continuous non-basal plane slip under high stress conditions. Dynamic recrystallized (DRX) also plays an essential role in the formation of the abnormal texture, where the DRX process produces a proportion of grains with the nucleation orientation < 0001 > . The subsequent preferential growth of these grains further promotes the rotation of the majority of grains oriented in the < 0001 > direction. Although the nucleation phase of DRX contributes to the formation of abnormal texture, the preferred growth stage of grains has a greater influence on the abnormal texture. In addition, due to the introduction of strong shear stresses, the degree of buckling and fragmentation of the Long Period Stacking Ordered (LPSO) phase is enhanced in all directions, which in turn reduces the morphological differences in different directions, ultimately leading to a significant weakening of mechanical anisotropy. This weakening of mechanical anisotropy is closely related to the homogeneity of the grain size and the differences in the morphology of the LPSO phases.