Anelastic behavior and phenomenological modeling of Mg ZEK100-O alloy sheet under cyclic tensile loading–unloading

Cyclic tensile loading–unloading tests were carried out with a cyclically incremental strain of 0.03% in a strain range of 0–2% and with cyclically incremental strain of 1% till fracture to investigate the anelastic behavior of annealed Mg ZEK100 alloy sheet. Large hysteresis stress–strain loops were observed in all cyclic loading–unloading tests, which indicate that the annealed Mg ZEK100 alloy sheet exhibits obvious anelastic effect. Due to the fact that twins are easier to produce in transverse direction (TD) than in rolling direction (RD), the alloy shows larger hysteresis loops in TD when applying cyclic loading–unloading. Both true stress and true plastic strain have an effect on the anelastic effect. At a stress, ∼15 MPa higher than the yield strength, the anelastic effect reaches the maximum and the hysteresis loops add an anelastic strain of 0.0018 in RD and 0.003 in TD to the total elastic strain, and consequently lead to a decrease of 30% and 54% in the apparent elastic modulus in RD and TD, respectively. This phenomenon is discussed in terms of the roles of partially reversible twinning and dislocation slip upon unloading and reloading. A novel phenomenological model is developed to describe the anelastic behavior in the Mg alloy, and the calculated hysteresis loops agree well with the experimental ones. Cyclic hardening in the alloy is observed after a certain number of cycles.