Asymmetric tension-compression mechanical behaviors of extruded Mg-4.58Zn-2.6Gd-0.18Zr alloy with double-peak fiber texture

To clarify asymmetric mechanical behaviors of the extruded Mg-4.58Zn-2.6Gd-0.18Zr alloy during room temperature tension and compression, the evolution of microstructure, texture and strain hardening rate were systematically investigated when loading along the extrusion direction (ED). The results found that the as-extruded alloy exhibited <10 1 ̅ 0>-<11 2 ̅ 0> double-peak fiber texture, leading to obvious tension compression yield asymmetry and compressive yield plateau. Fiber texture kept stable and only texture intensity gradually decreased with the increasing tensile strain, while fiber texture was exhausted due to the extension twinning and <0001> texture component was aggravated with the increasing compressive strain. Moreover, twinning parts within grains with <10 1 ̅ 0> fiber texture was re-oriented to the c-axis paralleling to the ED, and that in <11 2 ̅ 0> fiber texture deviated about 30° away from the ED. This soft orientation would be finally rotated to the <0001> paralleling to the ED under the action of basal slip, explaining why the <0001> pole dispersed at first and then concentrated with the increasing compressive strain. Three stages of strain hardening rate were both observed for tensile and compressive tests, while increment of Stage II was only observed under compression. Stage II in compression could be further divided into two parts with different slopes. Such phenomenon was seldom reported in Mg alloys, which was caused by different propagation and re-orientation of extension twinning in double-peak fiber texture, and weakened the effect of twin lamella segmentation with the increasing compressive strain. Findings in this work given us a better understanding of asymmetric tensile-compressive mechanical behaviors of extruded Mg alloys with double-peak fiber texture.