Inclusive anisotropy and texture analyses of AZ91 Mg sheets subjected to various passes of elevated-temperature constrained groove pressing

Constrained groove pressing (CGP) is a kind of sheet severe plastic deformation method suitable for enhancing the strengths of light alloys for various applications such as aerospace and automotive industries. In this research, the annealed AZ91 Mg alloy sheets were subjected to three CGP cycles at 300°C. Subsequently, optical microscopy, scanning electron microscopy, x-ray diffraction, and tensile tests for various directions were performed. Initially, there was a basal texture with a maximum intensity of 3.4 multiple random distribution and several β-Mg₁₇Al₁₂ particles as the second phase in the annealed sheet. As an important achievement of employing the CGP operation, the 1-passed sample represented a superior elongation of 35.7%, maximum yield strength of 141.0 MPa, and maximum ultimate tensile strength of 231.0 MPa in the rolling direction. These were mainly due to, the grain refinement, enhancing the fiber texture in the transverse direction, and controlling the basal texture. However, the experimental results revealed that the basal texture during the second and third passes of the operation could not be controlled. The main preferred orientation was changed from ( 06 6 ¯ 1 ) ⊥ ND ( Normal Direction ) fiber for the annealed sheet to ( 0001 ) ⊥ ND fiber for the CGPed sheets. It is also interesting to note that based on an anisotropy analysis, the 1-passed sample was the most isotropic worksheet, making this specimen a suitable blank for secondary metal forming processes, in comparison with the other CGPed samples. Fractography also indicated that the fracture mechanism varied among ductile, brittle, and mixed modes for workpieces subjected to different passes of the process.