Study On Extrusion-shear Expanding Forming Process And Microstructure Properties Of Magnesium Alloy Thin-walled Tube

Magnesium is the lightest metal structural materials in engineering applications and has broad application prospects.Extrusion processing is the most common production methods of magnesium alloy tube.By expanding the diameter of the tube forming,the volume of the forming equipment can be reduced and the production cost can be reduced.On the basis of the previous research,a new severe plastic deformation method of magnesium alloy tube,namely extrusion-shear and expansion forming process(TESE)which combines the three processes.The differences in mechanical properties and microstructure between TESE tubes and ordinary tubes were investigated by means of finite element simulation of forming experiment,microstructure characterization and mechanical properties test.The differences in mechanical properties and microstructure between TESE tubes and ordinary formed tubes were investigated by means of finite element simulation of forming experiment,microstructure characterization and mechanical properties test.The evolution of microstructure in TESE process and the influence of different process parameters(temperature and shear Angle)on the forming of tubes were investigated.The main conclusions are as follows:1.During the TESE forming process,the load value increases with the increase of stroke,then it tends to a constant value when enters the stable extrusion stage.The increase of forming temperature and the decrease of friction will lead to the decrease of the load under the same stroke.The maximum diameter expansion ratio of TESE process can reach3 but when the diameter expansion ratio is 2.5,the phenomenon of uneven flow and the distribution uniformity of damage value become worse and a large number of cracks may occur in some areas of the tube.When the speed increases,the temperature in the deformation zone and the tube forming zone increases and the homogeneity of temperature field distribution becomes worse.The decrease of the shear angle will increase the strain of the tube.with the decrease of the shear angle,the strain homogeneity will also decrease and the shear corner is the position of the maximum strain in the whole deformation zone.2.Compared with the Direct Extrusion tubes,the grain size of the tubes formed by TESE is finer and the distribution is more homogeneous.The fracture morphology of tubes formed by ordinary extrusion is poor and the mechanical properties of TESE tubes are better than those of tubes formed by Direct extrusion.the addition of the expanding shear section can effectively weaken the basal texture of the tube,promote the degree of dynamic recrystallization,and make more grains in the soft orientation.3.In the process of TESE forming,homogeneous and fine equiaxed grains are formed after crushing and recrystallization.With the progress of deformation,the strength of the basal texture is weakened.the proportion of the recrystallized grains is increased and the SF value of the substrate slip system is increased.The {10-12} tensile twins appear in the TESE forming process and the twins disappear in the forming tube.4.With the decrease of shearing Angle,the grain size of the tube becomes smaller and the homogeneity becomes worse.When the shear angle is 130°,the strength and hardness value of the tube is the highest.With the decrease of the shear angle,the basal texture deflects and the dispersion of the pole figure is strengthened.When the shear angle is140°and 130°,the mean value of SF of the basal plane slip system is above 0.3.when the shear angle is 150°,the mean value of SF of the basal plane slip system is only 0.25.5.Within a certain temperature range,the increase of temperature leads to the increase of grain size.The temperature has little effect on the hardness value of the tube and results in the decrease of the strength of the basal texture.The temperature rise within a certain range will also promote the degree of tube recrystallization.The recrystallization ratio of the tube reaches more than 90%,and only a small part of the grains are in the state of substructure and deformation when Forming at 440?.The average SF value of the basal plane slip system is the highest when Forming at 410?.According to the mechanical properties and microstructure,the two factors considered(temperature and shear Angle)were comprehensively analyzed and the shear Angle was 140°,Temperature 410? is the best process parameter.