Cyclic deformation and fatigue of extruded ZK60 magnesium alloy with aging effects

Monotonic and fully reversed strain-controlled cyclic deformation experiments were conducted on a ZK60 magnesium (Mg) alloy in as-extruded and T5 aged conditions in ambient air. It was observed that the aging process had a significant influence on the stress-strain response and the fracture stress and strain under both monotonic tension and monotonic compression but a marginal influence on the stabilized cyclic deformation and fatigue of the material. An Electron Backscatter Diffraction (EBSD) analysis revealed that double twins were formed under a large compression strain in the as-extruded Mg but were not observed in the aged state under monotonic compression. A kink point in the strain-life fatigue curve demarcates the influence of twinning-detwinning deformation on fatigue. No twinning occurred throughout the fatigue life of the material when the strain amplitude was lower than the kink point value. With a strain amplitude slightly above the kink point, twinning-detwinning occurred but the process diminished as the loading cycle increased. The aging process enhanced the kink point slightly from a strain amplitude of 0.32% to 0.35%. Only small amount residual twins were observed in the material after fatigue loading when the strain amplitudes were lower than 4%.