Compressive deformation behavior of ultrafine-grained Mg-3Zn-1.2Ca-0.6Zr alloy at room temperature

Abstract

In this study, ultrafine-grained (UFG) Mg-3Zn-1.2Ca-0.6Zr alloy is prepared by a novel extrusion-shear (ES) process. The microstructure, twinning and dislocation evolution of UFG Mg-3Zn-1.2Ca-0.6Zr alloy under compressive deformation at room temperature are studied by electron back-scattering diffraction and transmission electron microscopy techniques. According to the results, the compressive deformation follows a sequence of the three stages in which the work hardening rate first decreases, then increases, and finally decreases, inducing the tensile {101̅2} twinning in UFG alloy. With the coordinated deformation of twinning and dislocation slip, the compressive yield strength and rupture strain of UFG alloy reach 206 MPa and 20.9%, respectively. With the increase of strain rate, the interaction between the twin and the dislocation slip promotes deformation, resulting in a continuous increase in the twin boundary fraction and dislocation density. Furthermore, the {0001} basal texture intensity first increases and then decreases, and basal poles appear separated. When the twin nucleation is saturated, the twins make almost no contribution to grain refinement and plastic deformation, and the dislocation mechanism is dominant in the later stage. As the dislocation density gradually increases, the formation of dislocation cells reduces the work hardening rate.