| In the fields of aerospace,national defense and military industry,lightweight has become the most urgent demand to further improve performance and reduce energy consumption.Aluminum alloy has the advantages of good corrosion resistance,low density and excellent mechanical properties.It has become the preferred material for lightweight in aerospace,military industry and other fields.At present,2XXX aluminum alloy and traditional back extrusion process are used to prepare the tail frame,which has low mechanical properties and can not meet the service requirements of the new generation of equipment.Material composition optimization and large plastic deformation are effective ways to improve the mechanical properties of aluminum alloys.In this paper,the new Al Zn mg Cu aluminum alloy developed by Central South University is used as the raw material.Aiming at the difficult problem of material process coupling,a method of preparing large-diameter cylindrical parts with outer longitudinal ribs by cumulative severe plastic deformation is proposed based on the traditional upsetting back extrusion process.Firstly,in order to ensure the high-performance requirements of the flight stability device,the deformation is designed,and the reciprocating upsetting extrusion process is used to complete the material blank opening.Secondly,based on the accurate extrusion process simulated by DEFORM-3D finite element software,the metal flow characteristics in the extrusion process of cylindrical parts with external longitudinal bars are mastered,and the forming process and die structure parameters are optimized with the goal of high-precision forming,In order to realize the integrated shape and property control forming of the new high-strength aluminum alloy tail frame.The main conclusions are as follows:1.Analyze the part drawing and extrusion process characteristics of cylindrical parts with outer longitudinal reinforcement,and formulate the extrusion drawing of cylindrical parts with outer longitudinal reinforcement.Based on the strengthening mechanism of aluminum alloy,the deformation is designed and the size of aluminum alloy bar is determined.According to the characteristics of upsetting forming process,a reciprocating upsetting extrusion process scheme of two upsetting and one extrusion is put forward.On this basis,the die of one fire reciprocating upsetting and extrusion is designed,and the experiment of reciprocating upsetting and extrusion is carried out.2、The precise extrusion forming process of cylindrical parts with outer longitudinal ribs is simulated by DEFORM-3D to master the metal flow characteristics.Taking the deformation uniformity and rib filling fullness as the objective function and the evaluation methods such as straightness and strain cumulative distribution probability,the forming process and die structure parameters are optimized.The optimal parameters are as follows: extrusion speed is 1mm / s,deformation temperature is 440 ° C,punch flow promotion angle is 10 ° and friction factor is0.3.Taking the center point of the rib as the research object,the three-dimensional strain changes of the center point under different flow promotion angles and friction factors of the punch are analyzed.The results show that larger circumferential compressive strain and smaller axial tensile strain can promote the radial flow of metal and improve the filling fullness of the outer longitudinal rib.The upper bound method is used to calculate the deformation parts in different deformation sections or areas in the precise extrusion process of cylindrical parts with outer longitudinal bars,and the theoretical calculation formulas of velocity field and strain rate field are derived.3、According to the extrusion forming process scheme of cylindrical parts with outer longitudinal bars,aiming at high-precision forming,an accurate extrusion forming die is designed,and the forming experiment of cylindrical parts with outer longitudinal bars is carried out.The surface of the formed part is free of defects such as crack and folding,the rib is fully filled,and the forming quality is good.The dimensional accuracy of the formed parts is tested.The measurement results show that the wall thickness difference is 0.96 mm,the straightness of the rib is 1.65 mm,the wall thickness difference of the cylindrical parts is small,the rib is fully filled,and the forming accuracy is high.The rationality of the extrusion forming die structure is verified.4、After reciprocating upsetting extrusion and precise extrusion process,the initial grains are elongated along the extrusion direction,and the coarse grains are surrounded by a large number of fine grains in a "necklace" distribution.The average grain size is significantly refined,about 23 μ m。 After 475 ° C / 3H + 120 ° C / 24 h heat treatment,the grains of the formed parts are coarsened,and the average grain size is increased to 25 μ m。5、The tensile strength of the blank in the initial state is 289 MPa and the elongation is4%;After precise extrusion,the tensile strength of the formed part is 383 mpa and the elongation is 10.6%.Compared with the initial state,the mechanical properties of the formed parts are improved,which is mainly due to the crushing of the coarse second phase in the blank and the significant grain refinement.After 475 ° C / 3H + 120 ° C / 24 h heat treatment,the tensile strength of the blank is significantly increased to 725 MPa,the yield strength is 344 mpa,and the elongation is 15.3%.Compared with the formed part,the tensile strength and yield strength of the heat treated state are significantly increased,which is mainly due to the significant refinement of the second phase in the matrix and the increase of precipitation. |
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