| Fine-grained and ultrafine-grained materials have many excellent characteristics, which differ from conventional materials, such as significantly improved mechanical propertise and outstanding physical and chemical properties. Thus, more and more grain refinement processes have been deeply studyed. Multi-directional forging(MDF) is a old method for obtaining bulk fine-grained materials but rapidly develops nearly.Firstly, based on the finite element software Defrom-3D, the MDF of cast pure mg was numerically simulated. We can know that Blank early deformation of exercise based mainly on the axial forging, and later dominated mainly transverse tensile, And the strain of the core blank uniformity better than external, in particular the uniformity of forging other than the center of the center plane of the section in both directions is better. Then, through using the multi-directional forging dies which designed by ourselves for the pure Mg’s pre-test, the results are less different than the simulations, and by detecting the performance of pure Mg deformed,multi-directional forging deformation really can canrefine the grain,and the more deformed pass the organization more uniform elongation and corrosion resistanceare also possible.Secondly, we designed the Mg-2Zn-0.2Mn alloy, after the homogenizing annealing processing the bad thermal stability of the alloy was found, for the360℃/8h abnormal grain growth lead to the decline elongation and corrosion resistance. Multi-directional forging the alloy deformation processing stages in the process lower the heat distortion temperature of the grain refinement effect is more obvious,the more distortion you pass the larger grain size, but the grain size increase donly little effect; while effects of temperature and passon the corrosion resistanceis more complex; under multi-directional forging process rather than the insulation under the conditions, and the rmalconditions, as well as for grain refinement deformation temperature uniformity of organization than the deformation passes to be larger, but the influence of the variation inresults:the lower the temperature,the smaller the grains, the more passes, the more homogeneous but no significant difference in grain size;while for corrosion, the higher the temperaturethe greater the pass the better the corrosion resistance of the alloy. And for the sample in the deformation process of250"C-9P after heat treatment were annealed at250℃the detection results again show good bad thermal stability of the alloy, but it also proves the short annealing time for the alloy to enhance corrosion resistance to be helpful.Because of the earlier failure of the mold, we compared the designed mold with the conventional mold, and found our mold’s defects:The inner wall of the mold and the fixation of the interference fit with in the side wall panels of the hexagonal screw there has been stress accelerated failure of theside wall panels;compared to the mold side wall panel while the whole, because the size is too thin,so the resistance to deformation poor, with magnesium alloys when the deformationis not lubricating,the friction increases, resulting in failure prone to creep even; heating and heating plates designed to increase the number of heating the mold, the deformation of the magnesium alloy when change saffect the organization, but also aware of security risks to such anassembly when the experiment.In conclusion, for the experimental results, while not perfect, but also confirmed that the multi-directional forging deformation of magnesium alloy can make grain refinement better, and improve the mechanical properties and corrosion properties, but with the exploring of process, mold improving and the environment in the future to be improved for the experimental focus. |
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