Multi-mechanism constitutive model for uniaxial ratchetting of extruded AZ31 magnesium alloy at room temperature

A multi-mechanism macroscopic phenomenological constitutive model is established to characterize the uniaxial ratchetting of extruded AZ31 magnesium (Mg) alloy at room temperature in the framework of small deformation. Because the uniaxial ratchetting of the alloy depends greatly on the strong basal texture and different deformation mechanisms (i.e., dislocation slipping, twinning and detwinning) and presents apparent tensioncompression asymmetry, two separated yield functions and different hardening rules are used in the proposed model regarding to different deformation mechanisms. That is, the traditional von Mises yield criterion and a flow rule in power-law form are used for the plasticity contributed by dislocation slipping, while the Cazacu-Barlat-Plunkett (CPB) yield criterion extended with a back stress tensor and an internal variable f (i.e., twin volume fraction) is employed to express the plastic deformation induced by twinning/detwinning. In addition, the modified Armstrong-Frederick (A-F) kinematic hardening models are adopted to reflect the strain hardening features contributed by different plastic mechanisms, and the interaction among different plastic mechanisms is considered in the developed constitutive model. The reproduced uniaxial ratchetting of extruded AZ31 Mg alloy by the proposed multi-mechanism constitutive model is in a good agreement with the corresponding experimental results obtained at room temperature, which validates the reasonability and capability of the proposed model.