Modeling of thermal and mechanical behavior of a magnesium alloy AZ31 during electrically-assisted micro-tension

Many researchers have used a material response function termed "electroplasticity" to account for the mechanical behavior of metals subjected to electric current during plastic deformation. However, other researchers claimed that the electrically-assisted (EA) deformation behavior of metals could be successfully characterized using thermal-mechanical constitutive models without the need for electroplasticity theories. In order to examine the controversial mechanisms and determine which dominates the flow stress behavior under EA forming, this work established a flow stress model including the effects of strain hardening, rate hardening, thermal softening, solute-dislocation interaction and electron wind, where the latter three effects were assumed to contribute to the stress drop due to electric current. Additionally, an analytic thermal model was also established to capture the temperature variations during EA tension based on the energy balance between the heat generation due to Joule heating, and the heat losses due to conduction and convection. Also, the evolutions of strain rate and strain at specimen center were incorporated into both models to capture the effects of diffuse necking on thermal and mechanical behaviors during EA tension. Uniaxial micro-tension tests were conducted on AZ31 magnesium alloy specimens subjected to continuous electricity with various current densities to verify the proposed models. Results show that the thermal and mechanical models can effectively predict the thermal and mechanical behaviors of the AZ31 magnesium alloy at various current densities in EA micro-tension, respectively. The modeling results also demonstrate that Joule heating is the major factor to affect the deformation behavior under micro-tension subjected to continuous electricity.