Abnormal texture formation and mechanical anisotropy of pre-aging extruded Mg-Gd-Y-Zn-Zr alloy with large-scale

Abstract

In order to further explore the effect of pre-aging treatment on large-scale alloys, a pre-aging extruded Mg-9.32Gd-4.02Y-2.16Zn-0.48Zr (wt.%) alloy with large extrusion ratio (ER = 19.5) and extrusion temperature of 450 °C in large-scale (Φ308 mm × 800 mm) was investigated in this paper. It exhibited good properties and a more pronounced anisotropy. The comprehensive performance in the 45° direction was the best. The extrusion direction (ED) presented a high strength, while the transverse direction (TD) showed poor strength and ductility contemporaneously. The main results of strength anisotropy were the alignment orientation of the long-period stacking ordered (LPSO), fine grain strengthening, and texture strengthening. The c-axis of most of the grains in TD samples was perpendicular to the direction of applied stress because of the abnormal <0001>//ED texture, which reduced the ductility. In addition, the formation mechanism of abnormal texture has also been studied. The higher extrusion temperature reduced the critical shear stress (CRSS) of the non-basal slip system, and the higher strain promoted the rotation of the base plane along the principal stress axis under the operation of continuous non-basal slip, resulting in the abnormal <0001>//ED texture due to lattice rotation. On the other hand, dynamic recrystallization (DRX) also greatly affected the generation of the abnormal texture. Firstly, DRX produced a proportion of grains with a nucleation orientation of <0001>, then the subsequent preferential growth of DRX grains led to the vast majority of grains with an orientation tending towards <0001>. However, the former has less effect on abnormal texture than the latter.