Comparative study on yield behavior and non-associated yield criteria of AZ31B and ZK61 M magnesium alloys

Abstract

The mechanical properties, especially the yield behavior, of AZ31B and ZK61 M magnesium alloys were comparatively investigated in this study. Series of uniaxial tension, uniaxial compression, shear and through-thickness compression (equi-biaxial tension) tests were conducted to obtain yield strengths and Lankford ratios (r values) under different strains and angles to their rolling directions and further the anisotropic characteristics as well as the tension-compression asymmetric features of the materials were analyzed. Furthermore, different yield criteria were adopted to represent yield behaviors of two magnesium alloys and their applicability on such magnesium alloys were compared. Results show that both magnesium alloys show apparent anisotropic and tension-compression asymmetric yield behavior. Compared with AZ31B, ZK61 M performs more remarkably in the anisotropic behavior and more intricately in tension-compression asymmetry and hardening features with changes of angles to the rolling direction and strain. The associated yield criteria of Hill1948, Yld2000-2D and CPB06 cannot concurrently represent anisotropic plastic yield and flow behaviors of AZ31B and ZK61 M magnesium alloys well; while the corresponding yield criteria based on non-associated flow rule can ideally describe these two aspects meantime. Among them, under tension and shear conditions, the non-associated Yld2000-2D criterion provided the most accurate predicting results than the other criteria. Regarding the tension-compression asymmetric characteristics of magnesium alloys, the non-associated model based on the CPB06 was introduced which makes concurrent prediction of tension-compression yield stress and Lankford ratio of these two materials possible. As a result, the comprehensive prediction capability of this model is fairly outstanding among all of three models. This study can provide basis for selection of plastic models, calibration technique and further application in numerical modeling.