Electroplastic effect in AZ31B magnesium alloy sheet through uniaxial tensile tests

The electroplastic effect in AZ31B magnesium alloy sheet was investigated through uniaxial tensile tests. In order to show the athermal effect of the electrical pulses, two types of uniaxial tensile tests at the same testing temperature were carried out： uniaxial tension in environmental cabinet and uniaxial tension with electrical pulses. In addition, the distribution of temperature field in the cross-section area during uniaxial tension with electrical pulses was simulated. The results show that the distribution of temperature field along the cross-section area is homogeneous. By comparing the true stress？true strain curves of AZ31B alloy under uniaxial tensile tests, the athermal effect with electrical pulses was confirmed. The microstructure evolution after the uniaxial tension was studied by optical microscopy. The results indicate that the electrical pulses induced dynamic recrystallization plays an important role in the decrease of flow stress. Finally, a flow stress model of AZ31B sheet taking the influence of electroplastic effect into account was proposed and validated. The results demonstrate that the calculated data fit the experimental data well.

The Stamping Formability of AZ31 Magnesium Alloy Sheet Improved by Equal-channel Angular Pressing

Equal channel angular pressing （ECAP） processing and annealing were applied to the AZ31 magnesium alloy sheets to evaluate the potential improvement in the mechanical properties and formability. The ECAP experiment was conducted at 300 ℃ in a die having an included angle of 90o between two channels by the BCZ route with the sheets rotated by 90°about the normal axis of plate plane. The tensile tests and conical cup tests were conducted at various temperatures from 20 to 250 ℃. The experimental results indicated that improving the working temperatures could lead to the soft in the material and the enhancement of ductility. Comparatively, the ECAPed AZ31 alloy sheets showed the lower yield strength and smaller conical cup value （CCV） than the unECAPed counterpart in the room temperature. The difference in yield strength between them became small in the elevated temperature, but the ECAPed samples still had the smaller CCV value, implying the improved formability. The texture of the AZ31 alloy sheets could be modified by ECAP and the decrease in the yield strength and more uniform deformation realized in the material, so the formability of AZ31 alloy sheets was improved.

Deformation Behavior and Microstructure Evolution of AZ31 Mg Alloy by Forging-Bending Repeated Deformation with Multi-pass Lowered Temperature

In this study, AZ31 Mg alloy was processed by a new severe plasticity deformation methodology with multi-pass lowered temperature, and the deformation behavior and microstructure evolution were investigated by finite element method and electron back-scattered diffraction technique and hardness. The results show that with the increase of deformation pass, the strain gradually springs, and its interval distribution tends to homogenize. Meanwhile, the effective strain increases dramatically with the shear force sudden upgrade in the deformation process. Moreover, the new deformation technique can refine grain size remarkably. With the passes on, {10-12} tensile twins behavior and the pyramidal < c + a > slip are triggered more frequently, leading to the completeness of dynamic recrystallization (DRX) gradually, which weaken and disperse the basal texture obviously. Besides, the standard deviation of hardness is getting smaller, and the maximum can reach 78.40 HV on average, which can be attributed to the even large strain distribution, complete DRX, and the high geometrically necessary dislocation.

Experimental Exploration of Electrical Pulse-Assisted Roller Hemming of AZ31B Magnesium Alloy Sheet

The purpose of this research is to explore the feasibility of roller hemming of AZ31 B magnesium alloy sheet. During the test, a special experimental setup considering the current flow and insulation was designed and employed. For the sake of simplicity, the flat surface-straight edge hemming style was selected. Electrical pulses were introduced in the pre-hemming and final hemming processes. The results show that when hemming at 448 K with hemming speed of 30 mm/min, AZ31 B magnesium alloy sheet was successfully hemmed with excellent perceived quality. No recoil/warp defect, cracking or springback was observed. Electrical pulses induced dynamic recrystallized grains were observed along the grain boundaries in the severely deformed area, which is of great importance to the improvement of the ductility of the material. The hardness was slightly increased after hemming with electrical pulses, and this fact could improve the friction resistance performance of the hemmed part.