Abstract: The uniaxial ratcheting behaviors of an extruded AZ31B magnesium alloy was investigated with a series of compression-compression cyclic stress-controlled experiments at ambient temperature. Effects of different mean stresses on the ratcheting stress and its evolution were examined. The mechanism of dominant plastic deformation under mean stress and its effect on the ratcheting behavior in the process of cyclic deformation were discussed. Results show that remarkable ratcheting behavior occurs in the extruded AZ31B magnesium alloy in the process of compression-compression cycles. Instead of the dislocation slip, the twinning-detwinning mechanism plays a key role in the formation of ratcheting strain and determines the rate of ratcheting strain. When the mean stress is 0, -45, -75, -135 MPa, the ratcheting strain formed in the cyclic process increases with the increase of the compressive mean stress, and tends to be stable after a certain number of cycles. The ratcheting strain rate decreases sharply with the increase of the number of cycles until it remains unchanged.

Key words: ratcheting behavior, stress-controlled, mean stress, deformation mechanism, AZ31B