Deformation of extruded ZK60 magnesium alloy under uniaxial loading in different material orientations

The deformation behavior of an extruded ZK60 magnesium (Mg) alloy was investigated experimentally under uniaxial loading in the extrusion direction (ED) and the transverse direction (TD). X-Ray diffractometer (XRD) and electron back scattered diffraction (EBSD) were employed to examine the microstructure evolution using companion specimens. The results indicated that the flow stress and strain hardening rate were strongly affected by the loading directions relative to the initial material orientations. Strong tension-compression asymmetry was exhibited when the loading was applied along the ED. Practically identical stress-strain responses were obtained when the tension/compression was applied in the TD. The difference in tension-compression responses between the ED and TD specimens arises from the distinctive twinning activities, which are inherently related to the initial basal texture. When loading was applied in the ED, copious tension twinning can attained only under compression. However, in the TD, either tension or compression can impose similar amounts of grains under c-axis tension, thus activating tension twinning in both directions. Detailed analyses of strain hardening rate responses under different loading paths were made. The deformation mechanisms associated with different stages of strain hardening rate were discussed with a particular emphasis on the roles of deformation twinning.