Research On Deformation Behavior And Mechanism Of Magnesium Alloy By High Rate Forming At Elevated Temperature

As the lightest metal structure material, due to the high specific strength, specificstiffness, good electric-conductive, thermal-conductivity and damping performance,magnesium alloys are widely used in automotive, aerospace, communicationselectronics and national defense and other important fields. The formability at roomtemperature is poor, which is limit the application of magnesium alloy sheet plasticforming. Warm and high rate forming technology can effectively improve formabilityof light and difficult-to-deformation materials. So constitutive and failure model,deformation and failure behaviors, forming limit and fracture mechanism ofmagnesium alloys under warm and high rate forming condition were systematicstudied，which funded by the National Natural Science Foundation of China，it canprovide a theoretical basis for warm and electromagnetic forming technology ofmagnesium alloy.According to the quasi-static tensile test and warm and high speed dynamictensile test with Hopkinson Tensile Bar of AZ31B magnesium alloy，the stress-straincurves of quasi-static and high strain rate under different temperatures were beenobtained. The mechanical property of magnesium alloy under different temperaturesand strain rates were studied. The results showed that temperatures and strain rateswill increase the dynamic softening effect of magnesium alloy materials, adiabatictemperature rise will be produced at high strain rates, adiabatic temperature rise willbe increase with the plastic strain increase. However, microstructure and mechanicalproperties of AZ31B magnesium alloy have an effect with adiabatic temperature riseincrease.The high speed dynamic tensile test based on Hopkinson Tensile Bar of warmAZ31B magnesium alloy, according to the combination of macroscopic andmicroscopic method, the deformation and failure behavior of AZ31B magnesiumalloy under the different temperatures and strain rates were been investigated. Theinfluence law of temperatures and strain rates on the fracture surface morphology andmicrostructure were been discussed. The deformation and fracture behavior and itsmechanism of AZ31B magnesium alloy under the different temperatures and strainrates were been analyzed.According to the quasi-static tensile test with smooth round bar specimens and different notch radius round bar specimens, The fracture strain of the specimensdepends on stress triaxiality will be discovered, the fracture strain decreases withstress triaxiality increases; The fracture strain gradually increases with temperaturesand strain rates increase. The relation of fracture strain and stress triaxiality will beestablished according to the experiment and numerical simulation methods.Combining with the quasi-static tensile test, high temperature dynamic tensiletest and numerical simulation methods, JC constitutive model and failure model ofAZ31B magnesium alloy under the different temperatures and the high strain rateswere been established. Electromagnetic forming process were been simulated with theobtained JC constitutive model and failure model of magnesium alloy sheet atdifferent temperatures，and it also verified with the experimental results. It indicateddeformation of warm electromagnetic forming and the failure behaviors can be gooddescribed by JC constitutive model and failure model ofAZ31B magnesium alloy.Based on the electric field, magnetic field and structure field finite elementanalysis theory and electromagnetic field and structure field coupling method, theelectromagnetic field model and structure model with uniform pressure coil, flat spiralcoil and flat spiral coil combined the driver were been established. Electromagneticforming process of magnesium alloy sheet under the different coils and drivers werebeen analyzed. Magnetic field force distribution, the plastic strain distribution anddeformation contour of different coils were been obtained. The deformation law ofelectromagnetic forming process of magnesium alloy sheet under different coils anddrivers were been established. The influence of temperature on the bulging height ofmagnesium alloy sheet were been analyzed with the uniform pressure coil.Electromagnetic forming limit of magnesium alloy were been analyzed under thedifferent temperatures basing on JC constitutive model and failure model. Themagnesium alloy forming limit diagram under the warm and high velocity was beenestablished. The influence law of discharging voltage, capacitance, temperature andboundary condition parameters on electromagnetic forming limit. The results showedthat temperature is the biggest effect on the magnesium alloy forming performance,the second is the discharge voltage, minimum influence is capacitance.