Microstructure And Mechanical Properties Of Rolled AZ31 Alloy Sheets Processed By Electropulsing Treatment

Magnesium alloy has excellent physical and chemical properties,such as low density,high specific strength and stiffness,good electromagnetic shielding and high vibration damping capacity, et al, therefore is of important application value in the automotive,aerospace,electronics and other fields. But the wider application of magnesium alloy is limited due to its hexagonal closed-packed crystal structure, the lack of effectively strengthening phase and its poor forming performance. Grain refinement can effectively improve the strength and plasticity of materials, and is widely used in the magnesium alloy as a reinforcement method.Electropulsing treatment(EPT) is a new method to refine the microstructure and improve the mechanical properties of metal materials. In this study, the high energy electropulsing treatment was used to deal with the rolled AZ31 magnesium alloy in order to improve the microstructure and the mechanical properties. The microstructure evolution of rolled AZ31 alloy sheets with 10%, 15% and 20% rolling reduction were investigated under EPT byVHX-2000 optical microscope and scanning electron microscope equipped with electron backscattered diffraction(EBSD).After EPTed with a pluse-width of 30 μs, a current density of 4.16×109A/m2, a duty ratio of 0.003 and a processing time of 10 min, the average grain size of AZ31 alloy was refined from 150 μm to 20 μm while the tensile strength and the elongation were improved to 265 MPa and 19.7%. The thermal and athermal effect of EPT on the recrystallization during were analyzed. Using the heat electric couple and Fourier heat dissipation model the temperatures of samples under EPT were measured and calculated, at which the rolled Mg alloy sheets were treated to compare effects of EPT and heat treatment on the recrystallization of the deformed Mg alloys. As a result, the EPTed sample was recrystallized completely while the heat treated sample was seldom recrystallized, which revealed that the athermal effect of EPT plays a major role in recrystallization. Furthermore, the mechanism of the athermal effect was also discussed.The electric pulsing carried on the deformed metals will induce an additional Gibbs free energy which will increase the recrystallization driving force of the materials and accelerate their process of recrystallization. In addition, pulse current can increase the recrystallization nucleation rate, quicken the dislocation slipping and climbing, improve the rate of defect migration and ultimately promote the recrystallization process.