Deformation behavior and deformation mechanism evolution of AZ31B magnesium alloy under compression-compression cyclic loading

Abstract

In order to investigate the cyclic deformation behavior in radial direction of extruded AZ31B magnesium alloy, the asymmetric compression-compression cyclic deformation test under strain-controlled was carried out at the strain amplitudes of 0.75%, 1.0%, 2.0% and 4.0%. The results indicate that the hysteresis curves of cyclic deformation show good symmetry at the small strain amplitudes of 0.75% and 1.0%. At the large strain amplitudes of 2.0% and 4.0%, the hysteresis curve shows poor symmetry, and the inflection point appears on the hysteresis curve. With the increase of cycles, the plastic strain amplitude decreases, and all materials exhibit cyclic hardening behavior. The hardening rate during tensile process is much higher than that of compression process at small strain amplitude, however the difference is not obvious at large strain amplitude. The analysis reveals that the effect of dislocation slip is greater on the entire life of magnesium alloy with 〈1120〉 silk texture along the radial orientation at the small strain amplitude. At the wide strain amplitude, the deformation mechanism evolves during the cyclic process with the increase of plastic deformation, the base plane dislocation and tensile twinning of lower critical resolved shear stress(CRSS) can not fully meet the deformation requirements, while the initiation of slip system and residual twinning of higher CRSS cause inflection point of hysteresis curves. The incomplete twinning-detwinning process results in a large number of residual twins in the deformed matrix, which affects the hardening rate during the cyclic deformation process, the fatigue life is reduced in the meantime.

Keywords

• extruded magnesium alloy
• deformation mechanism evolution
• compression-compression loading
• cyclic hardening
• crystal orientation