An experimental study of cyclic plastic deformation of extruded ZK60 magnesium alloy under uniaxial loading at room temperature

• Ratcheting experiments conducted for the first time involving twinning–detwinning in Mg.
• Long-term ratcheting rate decay identified to follow a power law relationship.
• Three types of cyclic deformation of Mg identified.
• Twinning–detwinning found to be a key cyclic hardening mechanism in Mg.

To experimentally study the role of the twinning/detwinning process in cyclic plastic deformation of Mg alloys, both strain-controlled and stress-controlled cyclic tension–compression experiments were conducted using extruded ZK60 magnesium (Mg) alloy in ambient air. The fully revered strain-controlled experiments had strain amplitudes varying from 0.25% to 4%. Three types of cyclic deformation are identified in light of the involvement of twinning/detwinning. The stress-controlled experiments reveal the cyclic ratcheting behavior of the material. Due to a strong basal texture of the material, no sustainable twinning/detwinning deformation occurs when the stress level is below the twinning or detwinning yield stress. As a result, ratcheting deformation under certain loading conditions is dominated by dislocation slip and is similar to that of other metallic materials. Cyclic twinning and detwinning in a stress-controlled experiment result in significant cyclic hardening. Under stress-controlled loading condition when ratcheting deformation occurs, the ratcheting rate decays with increasing number of loading cycles following a power law fashion regardless of the deformation mechanisms. Strain ratcheting is discussed for deformation involving the twinning/detwinning process and the experimental observations are explained in light of the micromechanisms.