| Magnesium alloy with lightweight structure, compared with steel andaluminum, has not only high specific strength and stiffness, but also excellentheat dissipation, electromagnetic shielding effectiveness, damping performanceand machinability. Its products are widely used in aerospace, automotive,military and other fields. As a result, it is considered to be the material with themost potential development of the21st century. However, the application anddevelopment of wrought magnesium alloy are greatly restricted because of thehcp structure of magnesium alloy, less slip systems, plas tic deformationcapability and low productivity, etc. At room temperature, it is difficult tomanufacture magnesium alloy parts by conventional plastic forming methods, butthe defects in forming difficulty can be overcome by superplasticity ofmagnesium alloy. This paper focuses on the following aspects.AZ31+Y+Sr magnesium alloy sheet with superplasticity was prepared bycontinuous casting and rolling. The mechanical behavior and microstructurechanges of AZ31+Y+Sr magnesium alloy were studied, and the maximumelongations were measured at different deformation temperatures duringsuperplastic deformation by tensile tests, to find out optimal temperature of thesuperplasticity of AZ31+Y+Sr magnesium alloy sheet under the experimentalconditions and study effects of Y and Sr on the superplasticity of AZ31magnesium alloy sheet. Discuss the mechanism of superplastic deformation ofmagnesium alloy, observing the fracture morphology by scanning electronmicroscopy.Hemispherical bulging experiment can directly reflect the material’ssuperplasticity. In this particle, AZ31+Y+Sr sheet was bulged to hemisphericalparts, and then measured ratio of height to diameter of the parts at differenttemperatures and observed the wall thickness distribution and microstructure. In addition, the AZ31sheet without adding other elements prepared by casting androlling was chosen as comparison. Explore effects of the temperature on thesuperplasticity of the magnesium alloy sheet; determine effects of cavita tion onthe fracture. A large number of cavities are created in the internal structure, andcontinue to grow and generate during the deformation process, eventually leadingto material fracture.The box-shaped bulging die for sheet box-shaped parts of AZ31+Y+Srmagnesium alloy was designed and gas bulging forming experiments werecarried out at the different temperatures. And then the optimal temperature andpressure process were determined. Finally, statistics of the wall thickness andcavities distribution of parts were analyzed, to explore the process that the box-shaped parts approached the die and the difference of microstructure in differentpositions of the parts. Adding rare earth elements further refine the grainstructure and are conducive to the diffus ion creep, which lays the foundations ofgas bulging forming. |
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