| This paper selected AZ31 magnesium alloy which was widely studied as the research object.In order to determine the optimum process parameters of the magnesium alloy cup shell with radial-reverse compound extrusion,FEM was conducted including different cavity structure(double cone channel,hemispherical channel,upper half cone channel,lower half cone channel and flat channel),the height of the work belt to produce shear deformation(h=1mm?h=2mm?h=3mm)and the angle(? =45°? ? =60°),as well as the different aspect ratio of the billet(? =1? ? =2? ? =4).When the cavity structure presented upper half cone channel and the value of the height and the angle of the work belt and the aspect ratio of thr billet were 2,45°,4,respectively,the simulation results showed optimum.Based on the analysis of the FEM,die design,forming load calculation and forming experiments were conducted.The microstructure of the five typical regions of the cup shell formed by radial-reverse compound extrusion was analyzed systematically and the microstructure evolution of the process was obtained.The tensile strength,hardness and other mechanical properties of the cup shell were measured and analyzed.The EBSD experiment was carried out on the bottom and sidewall of the cup shell,and the effect of forming process on the texture of the end wall was analyzed.In view of the Insufficient to the disadvantages of the forming process,a new technology of differential extrusion was put forward.It has certain guiding significance for the production of high strength and toughness magnesium alloy cupshaped parts.Research shows that:(1)The maximum forming load,the average equivalent strain and the maximum value damage were moderate under the upper half cone channel and the value of the height and the angle was 2mm and 45°.What's more,the deformation was more uniform.With the increase of the height of the conical boss,the average equivalent strain and the forming load(2)increased,and the deformation became uneven.Under the condition of aspect ratio of4,the forming load showed smallest,and the average equivalent strain presented largest.In addition,the opening height of the machine was satisfied.(3)The yield strength and elongation of the sidewall of the cup shell with radialbackward compound extrusion were only 149.6MPa,17.3%,respectively.The value of the tensile strength was 285.3MPa and the value of the hardness was 70.91 HB,which was about30% higher than that of the traditional reverse extrusion cup shell.However,the yield strength and elongation decreased.The microstructure of the sidewall showed the double mode of the distribution of the coarse grains and refined grains.After the corner,grain had no obvious preferred orientation,and diffuse nature of alloy increased.What's more,the strong texture disappeared and evenly distributed on the grain,and the metal texture was weaken.(4)The value of the pressure through simulation,the upper limit method and the actual forming experiment was 1.48×106kN,1.93×106kN and 1.63×106kN,respectively.Through the comparison of the three sets of measurements,the value of the simulation was lower than that of the measured and the value of the upper limit method was higher than that of the measured.The deviation of the simulation and the upper limit method was 8.67% and 18.4%,respectively.The equivalent strain of the side wall of the cup through the upper limit method was 2.933 and the value was 2.895 of the simulation.The results were in good agreenment and the accuracy of the formula was verified partly.(4)Based on the radial-backward compound extrusion,a new type of differential stepped channel structure extrusion was put forward.The structure of the die could effectively increase the number of shearing stress of the metal,and obviously increased the equivalent strain,which may eliminate the defects existing in the prior die structure. |
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