Research On Gas Bulging Forming And Simulation Of AZ31B Magnesium Alloy Sheet

Magnesium alloys are widely used in automobile,electron,avigation and spaceflight fields and so on for their low density,high specific strength,specific rigidity,excellent electromagnetic shielding and mechanical processing.However,the application of magnesium alloys is restricted by their poor formability at room temperature due to the hexagonal close packed(hcp) structure.So it is necessary to study the hot stretch property and superplasticity,the gas bulging forming of hemispheroid and its finite element simulation of magnesium alloys for providing technical supports of plastic processing.AZ31B magnesium alloy sheets with high properties were prepared by extruding and cross rolling.The results of hot tensile test showed that the tensile strength is 240～263MPa, yield strength is 110～175MPa,specific elongation is 23～25%,the anisotropy of magnesium alloy thin sheet is improved by cross rolling.The stretch experiment shows that at 698K,the specific elongation of AZ31B magnesium alloy thin sheet is more than 200%,the maximum specific elongation can reach 321%when the strain rate between 6.6×10^-4s^-1 and 6.6×10^-5s^-1.The magnesium alloy sheets exhibit favorable superplasticity performance and the flow stress is 3～12MPa,the strain rate sensitivity coefficient is 0.31～0.44.And then confirm the processing parameters of gas bulging forming:such as temperature and strain rate.A pressure-time curve of AZ31B magnesium alloy sheet was gotten through the simulation by using the software MSC.MARC.And then got the real curve in the experimentation.The experiment of superplastic gas bulging forming shows that,the limit high diameter ratio(H/R) is 0.86,the maximal attenuation radio is 63.25%of magnesium alloy sheets when the temperature is 698K and the strain rate is 5×10^-4s^-1.In the process of bulging forming,the thickness of piece thinning gradually as the height increases,thinning of the top is the maximal,and it is the position where the most easy to crack.The dominant deformation mechanism is grain boundary glide(GBS) by the SEM of fracture of the bulging pieces,and the major coordination mechanism is dislocation creep and atomic diffusion.