Microstructure, texture, and strain-hardening behavior of extruded Mg–Gd–Zn alloys

Abstract

The effect of Zn content on the microstructure, texture, mechanical properties and strain-hardening behavior of extruded Mg–2Gd–xZn (x = 0, 1, 2 and 3 wt%) sheets was investigated. Evaluation of texture revealed that while all of the alloys exhibited weak textures, the texture component was altered from a basal to a non-basal one by the addition of Zn. A typical transverse direction (TD) split texture with basal poles rotated about 40° from the normal direction (ND) toward TD was observed for the Zn-containing alloys, the effect being more pronounced at higher Zn contents. Furthermore, the Mg–2Gd–1Zn alloy exhibited the weakest texture due to solute drag imposed by co-segregation of Zn and Gd atoms at grain boundaries. Addition of Zn also resulted in a general increase in yield stress, ultimate tensile strength and elongation along the extrusion direction from 99 to 172 MPa, 178 to 263 MPa, and 25 to 35% for Mg–2Gd and Mg–2Gd–3Zn alloys, respectively. However, increasing Zn content was accompanied by an initial decrease in anisotropy of mechanical properties and strain-hardening behavior, followed by an increase at higher Zn contents. This was due to the difference of orientation of basal planes with regard to tension direction. As a result, lower yield stress, higher elongation and strain-hardening capacity was obtained along TD (with higher Schmid factor for basal slip) compared to ED. It was concluded that excellent mechanical properties and low anisotropy can be achieved in the Mg–2Gd–1Zn alloy.