Work hardening behavior of the extruded and equal-channel angularly pressed Mg-Li-Zn alloys under tensile and shear deformation modes

The flow and work hardening behaviors of extruded and equal-channel angularly pressed (ECAPed) Mg-6Li-1Zn (LZ61) and Mg-12Li-1Zn (LZ121) alloys were studied by tensile and shear punch testing methods. It was shown that the Kocks-Mecking type plots for tensile and shear deformation of both alloys, exhibited similar work hardening (WH) stages in both extruded and ECAPed conditions. WH rates were found to be lower for the ECAPed materials, due to a reasonably uniform and well-refined microstructure. In the case of hcp LZ61 alloy, textural studies showed that the extruded fiber-type texture was replaced by a typical ECAP texture, in which basal planes rotated about 45° to the extrusion axis. This was found to be responsible for the lower tensile strength and higher shear strength in the ECAPed material, as compared to the extruded condition. For the bcc LZ121 alloy, it was observed that the grain refinement achieved after ECAP increases the strength and ductility in both tensile and shear deformation, compared with those of extruded condition. Stage II of the Kocks-Mecking plot in both shear and tensile deformation of LZ121 was eliminated most likely due to stacking fault energy improvement caused by higher Li content of the Mg lattice structure. The shear punch testing (SPT) method was found to yield the flow and WH curves similar to those obtained in tensile testing.