Microstructure and texture evolution during porthole die extrusion of Mg-Al-Zn alloy

This study reports the formation mechanism of inhomogeneous microstructure in AZ31 Mg alloy extruded by porthole die. Two streamlines corresponding to welding and matrix zones of the extruded profile were focused, and the evolution of microstructure and texture was investigated. The results show that (i) Welding zone streamline: The complete dynamic recrystallization (DRX) occurred after splitting stage, and the microstructure consists of equiaxed grains with several microns. Strong shearing texture is formed during splitting stage, and the c-axis has a deviation with normal direction. Then, the basal plane rotates to be perpendicular with normal direction during the welding stage. The main textures are identified as < 0001 > //ND and {0001} < 11-20 > textures, while the fraction of these two components varies significantly during extrusion process. (ii) Matrix zone streamline: The coarse elongated grains were reserved along the whole streamline, which indicates the occurrence of partial DRX. Moreover, the {10-12} < 10 - 11 > extension twins appear inside the coarse unDRXed grains. The basal plane of unDRXed grains tends to be perpendicular to ED direction with a deviation angle, and the {11-20} < 10 - 10 > texture can also be observed. However, the orientation concentration with certain pattern was not formed for DRXed grains.