| Magnesium alloy which is the lightest metal materials attracts a broad attention inmodern manufacturing industry. As AZ31B alloy has advantages of high ductility andstrength, it has been widely used in a variety of applications. As AZ31B magnesium alloy’sdiversity mode of deformation, the deformation mechanism is fairly complex. So theresearches on the low cycle fatigue behavior and deformation mechanisms of magnesiumalloy are significant for the prediction of low cycle fatigue behavior that characterized bycyclic plastic deformation behavior.In this paper, the cyclic deformation behavior of AZ31B magnesium alloy at differentstrain amplitudes and frequencies under asymmetric strain-controlled loading wasinvestigated. Based on deformation mechanism analysis, the reason for cyclic hardening andasymmetry of the hysteresis loops was discussed. The experimental results showed that at lowstrain amplitude, the hysteresis loop has a symmetric characteristic. As strain amplitudeincreases, the loops become very asymmetric. The cyclic hardening rate is lower at lowamplitude than that at high amplitude, but its relative rate in the whole cyclic deformationprocess is much higher. The magnesium alloy’s relative rate in the whole cyclic deformationat low frequency is higher than that at high frequency. As frequency increases, the cyclicdeformation stress becomes smaller, especially in the large strain amplitude condition.These macroscopic mechanical behaviors are mainly due to the differences ofmicroscopic mechanisms. When the strain amplitude is small, the basal plane slip is the maindeformation mechanism, followed by tensile twinning as a supplement; In the large strainamplitude, the role of dislocations with twins increase, and the extension twinning-detwinningis becoming dominant role, resulting in increasing the proportion of tensile twins in the entirelife. With increasing frequency, the tendency of twins will increase, the proportion of cylinderdislocations reduces.It was suggested that the extension twinning-detwinning plays an important role incyclic deformation, However, its contribution to the plastic magnitude is limited in the alloywith low intensity of crystals orientation distribution. |
