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

Abstract

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.

Influence of the Regime of Electropulsing-Assisted Machining on the Plastic Deformation of the Layer Being Cut

“…They found the current density threshold to achieve an effective thermal softening for each metallic alloy. Previously, they also published electrically-assisted micro-tension results to describe the thermomechanical behaviour of the AZ31 magnesium alloy under different current densities and, consequently, different joule effects [17]. As a result, the thermal softening was attributed only to the contribution of the joule effect and the change of the material resistivity.…”

Effects of specimen and grain size on electrically-induced softening behavior in uniaxial micro-tension of AZ31 magnesium alloy: Experiment and modeling

“…rather than before the high-rate heating stage (i.e., within 1 s after turning on electricity and showing very high Joule heating rate) [14] for all the tests to avoid some additional effects on the mechanical behavior of AZ31 sheets such as thermal expansion. Also, it should be mentioned that all the tests were performed under a strain rate of 0.01 s -1 until fracture and run at least 3 times for repeatability.…”

“…It was found that the electrically-induced temperature was non-uniformly distributed in the gauge area with the maximum temperature occurring at the center of specimens due to the symmetric configuration of uniaxial tension [14,15]. The maximum temperatures during EA tension were averaged for samples with various grain sizes and specimen sizes, which were plotted against the square of current density.…”

“…In order to account for the electroplastic effect, a well-known mechanism has been usually mentioned in classic works and studies, i.e., the electron-dislocation interaction, leading to a theoretical consideration of the so-called "electron wind force" [12]. However, the athermal effect is complicated and disputable since many recent studies [13,14] claimed that the thermal effect due to Joule heating dominated the EA deformation behavior of various metals, which can be used to model EA flow stress without taking the athermal effect into account. Therefore, more experimental studies associated with EA forming would be needed in future in order to find the main factor and parameter influencing on the electroplastic effect.…”

Electrically-Assisted Tubing Processes for Enhancing Manufacturability of Oxide Dispersion Strengthened Structural Materials for Nuclear Reactor Applications

“…(3) analysis of machine performance under mechanical loading; (4) design of machine electrical setting path and insulation; (5) multi-pass process analysis; (6) design of power transmission system (axial/radial/torque feeding mechanisms), roll bearing system, cooling system, workpiece feeding mechanism, and other related mechanical connection support components; (7) design and optimization of roll profiles/dimensions; (8) analysis and simulation of the rolling process; (9) development of engineering drawings and fabrication; (10) assembly and calibration of the EA tube rolling machine; (11) design and integration of the electrical control system; (12) hardware integration for high power supply electrically-assisted rolling process; (13) induction heating system integration; (14) experimental tests for the new rolling process. Through the process from conceptual design to final machine calibration and experimental tests, there are many technical and physical works that have been implemented and improved for the best performance of the innovative prototype.…”