Research On Extrusion Forming Technology For Magnesium Alloy Large Diameter Ring Component

As sealing and fastening connectors,large ring parts are widely used in aerospace,petroleum,chemical and other fields.In order to meet the urgent requirement of lightweight separation ring of Jetron rocket,ZK60 magnesium alloy was selected to prepare large-size thin-walled ring parts,and a new continuous flip extrusion process of curved busbar channel was proposed to solve the difficult problem that it is difficult to couple the traditional ring preparation method with the formability of magnesium alloy materials.First of all,in order to ensure the performance of the forming components,the material opening is completed by a new upsetting process with large aspect ratio,and then,on the basis of the mechanical analysis of the new process by using the principal stress method,the metal flow characteristics in the forming process of large thin-walled ring parts are mastered.Based on the evaluation factor of deformation uniformity,the forming process parameters and die structure parameters are optimized,and the process plan of multiple overturning forming is established.Finally,physical experiments are carried out to verify the success of large-scale thin-walled ring components.The main conclusions are as follows:1.Based on the analysis of the research status and the characteristics of upsetting process of large height-diameter ratio bar,a new upsetting process of large height-diameter ratio bar is put forward by binding the upper end of billet,increasing the outlet of guide zone and changing the shape of cushion,which makes the metal in the difficult deformation zone and the metal in the deformation zone flow synchronously.The shape of the cushion is the main factor affecting the uniformity of upsetting deformation.For the purpose of large plastic deformation and improving deformation uniformity,equivalent strain and equivalent strain S.D.The value is the objective function,and the die structure parameter ? is optimized by numerical simulation.The results show that under the simulated conditions of forming temperature 380 ?,extrusion speed 1.5mm s-1 and friction coefficient 0.3,when the die structure parameter ? is 3 °,the deformation dead zone at the bottom of the billet is obviously reduced,and the overall deformation of the billet is more uniform.Based on this,a blank forming die for large magnesium alloy ring parts is designed.The material properties increased from tensile strength 281.6MPa,yield strength 135.4MPa,elongation 15.8% to tensile strength 284.5MPa,yield strength 145.7MPa,elongation 19.6%.2.Based on the upper bound method,the mechanical analysis and theoretical calculation of different deformation sections or zones in the extrusion process of magnesium alloy large diameter ring members are carried out,and the theoretical calculation formulas of velocity field and strain rate field under the upper limit method are derived.By analyzing the extrusion forming characteristics of magnesium alloy large diameter ring parts,single-pass deformation and forming defects such as "warping" and billet accumulation,the extrusion forming process of magnesium alloy large diameter ring parts is determined.At the same time,the force of the ring blank extrusion process is analyzed by the principal stress method,and the extrusion process of magnesium alloy large diameter ring parts is simulated by DEFORM-3D and the parameters are optimized.The results show that considering the structural size of the formed parts and the single deformation allowed by the new process,the billet needs to be flipped and extruded four times,and the expanding force formula and the maximum pressure formula with the taper angle ? of the inner concave die as independent variables are derived.Taking ?= 20°,23°and25°as examples,compared with the Deform-3D finite element simulation results,the error is less than 10%.Finally,the extrusion process parameters are as follows: the extrusion speed is 1mm s-1,and the taper angle of the inner concave die is 23°.3.According to the blank-making process plan and forming process plan of magnesium alloy large-diameter ring parts,the blank-making and forming experiments of magnesium alloy large-diameter ring parts were carried out.The experimental results show that the change trend of punch pressure is basically consistent with the results of finite element simulation,and there are no obvious defects such as fracture and folding,and the forming quality is good.It opens up a new way to realize the short process and low cost manufacturing of large size magnesium alloy thin-walled rings.4.The tensile strength of the formed parts is 290.9MPa,the yield strength is156.6 MPa,and the elongation is 24.2%.Compared with the punching blank,the tensile strength increases by 6.4MPa,the yield strength increases by about 10.9MPa,and the elongation increases by about 4.6%.The strength and plasticity of the formed parts have been greatly improved,mainly due to the better refinement of the structure under the joint action of DDRX and CDRX.After aging treatment with 170°heat preservation for 12 hours,the average tensile strength is 288.9 MPa,the average yield strength is 168.2 MPa,and the average elongation is25.1%.5.The homogenized structure is backward extruded after upsetting deformation,and the obvious "necklace" structure is formed.at this time,the grain size shows a bimodal distribution,and the average grain size is significantly refined,about 71.4?m.The coarse deformed grains in the formed parts were elongated and distributed in a long strip along the extrusion direction.The grain size was further refined and the average grain size decreases to37.3?m.