Deformation Behavior And Microstructure Evolution Of AZ80 Magnesium Alloy Under Pulsed Current

Magnesium alloys have various applications in the areas of automotive,aerospace,medical,chemical and other engineering application because of their low density,high specific strength and excellent damping shock absorption.However,when the magnesium alloys are formed at room temperature,they have poor formability because of basal and prismatic slip can not coordinate the strain along the direction of C-axis in grains.Improving the plasticity of magnesium alloy has become an important research direction of magnesium alloy production and processing industry.Related studies have shown that applying high density pulsed current to magnesium alloys can weaken texture by promoting dynamic recrystallization and improve formability.However,whether the high-frequency and low-density pulsed current can improve the plasticity of magnesium alloys by improving the strain coordination capability of the microstructure of magnesium alloys is less researched.Based on the above research background,AZ80 magnesium alloy has been used in uniaxial tensile tests at room temperature,high temperature and pulsed current deformation conditions.Through quasi-in-situ EBSD analysis and theoretical calculations,the deformation behavior and microstructure evolution of AZ80magnesium alloy under high-frequency and low-density pulsed current were systematically studied.Firstly,based on the uniaxial tensile tests of AZ80 magnesium alloy under room temperature,high temperature and pulsed current deformation conditions,through the comparison between pulsed current deformation group with room and high temperature deformation group,it is found that the Joule heating effect and the pure electric effect together improve the plasticity of AZ80 magnesium alloy,including the improvement of elongation,the decrease of flow stress and microhardness and the change of fracture mode.Secondly,based on the characterization results of quasi-in-situ EBSD,this thesis explores the microstructure evolution of AZ80 magnesium alloy under different deformation conditions,and comparatively analyzes the differences in behavior of alloy on the subgrain boundary proliferation,twinning and geometrically necessary dislocation evolution,and expounds the mechanism of pulsed current to improve the forming properties of AZ80 magnesium alloy.Thirdly,this thesis has studied the twinning behavior in regions with higher twin fraction under different deformation conditions,combined with the distribution characteristics of geometrically necessary dislocations,by comparing the pulsed current deformation group with room and high temperature deformation group,the effect of pulsed current on the decrease of twin fraction and geometrically necessary dislocation density was expounded,and the mechanism of pulsed current reducing the flow stress of AZ80 magnesium alloy was revealed.Finally,based on the theoretical calculation of the pure electric effect,it is concluded that the dislocations per unit length in AZ80 magnesium alloy are additionally affected by 4.1×10~-77 N electron wind force,which theoretically explains the effect of pulsed current on the strain coordination ability of AZ80 magnesium alloy.