Studies on tensile behaviour and microstructural evolution of UFG Mg-4Zn-4Gd alloy processed through hot rolling

Abstract

The effect of rolling at elevated temperature on mechanical behaviour of bulk Mg-4Zn-4Gd alloy was investigated. The alloy was subjected to solution treatment at 673K for 24h, followed by flat and cross rolling at elevated temperature (723K). The microstructure of ultrafine grains (less than ~1µm size) was successfully achieved from solutionized sample with grain size ~78µm after the rolling process, which has significantly influenced the mechanical behaviour of the deformed Mg alloy. The yield strength (YS), ultimate tensile strength (UTS), elongation-to-failure (%E) and hardness of a rolled specimen have enhanced maximum up to the value of 276.3 ± 13MPa, 341.3 ± 7MPa, ~26.1% and 74.2 ± 2HV, respectively. The improvement in mechanical properties of processed Mg alloys due to the combined effect of grain refinement and secondary phase (W-phase) distribution into the Mg matrix upon the repetitive rolling process. In addition, the improvement in tensile properties is explained by correlating the dislocation density (ρ), scanning electron (SEM) and transmission electron (TEM) micrographs. The developed intrinsic property of rolled specimens is substantiated by tensile fractography obtained from SEM equipped with energy dispersive X-ray spectroscopy (EDS). Various other microstructural features were also revealed by TEM and X-ray diffraction (XRD) analysis. The anisotropy of various rolled Mg-4Zn-4Gd specimens was also elucidated on the basis of tensile results.