Study On Forming Process And Microstructures And Properties Of Double(single) Layer Square Tube Based On Extrusion-continuous Shearings Of Al/Mg Round Tube Billet

Compared with other metal materials,Mg and Mg alloys have many advantages,such as high specific strength and stiffness,electromagnetic shielding and radiation resistance.Therefore,Mg and Mg alloys have extremely important application value and broad application prospects.However,Mg alloys have some disadvantages such as low absolute strength,poor plastic deformation ability and difficult plastic processing at room temperature,which restrict the wide application of magnesium alloys.In addition,Mg alloys have very active chemical properties,the oxide film formed is loose and porous,which cannot provide sufficient protection to the matrix and is not suitable for many corrosive environments.The corrosion of Mg alloys has become a key problem limiting its application.Based on the previous research and DEFORM-3D numerical simulation analysis,direct extruding-continuous shear forming process was proposed in this paper,and the double（single）layer square profile was successfully prepared.Finite element numerical simulation,microstructure evolution,mechanical properties,bonding layer morphology and texture evolution of the prepared thin-walled double（single）layer square tube were analyzed,and the conclusions were as follows:1.In the process of square tube forming,the maximum mesh distortion occurs in the continuous shear deformation zone,the change from round tube to square tube is mainly due to the die structure.When the forming temperature is 400℃,the maximum temperature rise of square tube forming process is about 12℃,there is concentrated equivalent stress in the corner position and continuous shear region of the square profile.The load increases with the increase of friction factor and extrusion speed and decreases with the increase of extrusion temperature,the billet inside and outside wall velocity of flow at different position are different,combined multiple simulation analysis,the optimum process parameters were obtained:extrusion speed of 1 mm/s,the friction factor of 0.1,the forming temperature is 400℃.2.Combined with the optimum parameters to carry out physical experiments,the expected results were not obtained for square profile.Aiming at the defects such as unshaped square profile and damage in corner area,the method of intermittent extrusion forming is proposed,using this way double layer（single）square profile was successfully achieved.Microstructure,macro-texture,tensile experiments,fracture analysis and mechanical properties were analyzed,the results are as follows:the grain is obviously refined,the grain size is about 10um in the forming zone,the texture strength is optimized,and its yield strength is about 130MPa,the tensile strength is about 235MPa in the process,there were homogeneous and small dimples at the tensile fracture;the hardness of the matrix Mg alloy is about 65HV,the matrix Al alloy is about 53HV,the hardness of the Al/Mg interface region is about 188HV.The texture strength of the prepared square tube decreases with the increase of temperature.3.Through intermittent extrusion continuous shear forming preparation of Al/Mg square shaped interface analysis found that with the increase of deformation temperature,the interface effect becomes better,the more significant the metallurgical effect.XRD analysis found that the bonding layer near Mg intermetallic compounds are mainly Al₁₂Mg₁₇,nearly Al side is mainly Al₃Mg₂;some defects occur at corner position because the large stress concentration and the offset of the mandrel mold.Heat preservation at300℃for 1h and 2h respectively.the thickness of the diffusion layer increased to 23um,which the thickness of the bonding layer was 13um.After 2h,the thickness of the diffusion layer increased to 43um,which the thickness of the binding layer was 13um.4.EBSD analysis of magnesium matrix in Al/Mg composite square tube shows that:the recrystallization,Schmidt factor,texture strength and twinning are different in different forming regions and temperatures.The recrystallization degree is relatively full in the forming region of 400℃,SF value is about 0.3 in continuous shear region.With the formation of square tubes,the twinning disappears in sizing region.The grain orientation deflects along the extrusion direction,the texture strength decreases with the increase of temperature.