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%.