CN106607468B - A kind of differential-velocity extrusion manufacturing process of magnesium alloy high-performance cup shell - Google Patents

Abstract

The invention discloses a differential speed extrusion forming method for a magnesium alloy high-performance cup-shaped part, which relates to the technical field of metal plastic processing and forming; a combined die is adopted, including a "T"-shaped upper die and a "U"-shaped lower die. The interior of the "T"-shaped upper die is a cylindrical cavity, and the "T"-shaped upper die is installed on the "U"-shaped lower die. The section of the formed revolving body cavity is "mountain"-shaped. The bottom of the "mountain" shaped extrusion cavity adopts dislocated "ladder" differential extrusion steps. After three stages of deformation: the first is the coarse deformation stage similar to the cylindrical pier in the axial direction; the second is the large deformation stage of radial extrusion; the third is the shear deformation stage of angular extrusion. Magnesium alloy cup-shaped parts are extruded by "mountain"-shaped extrusion chamber and "ladder" differential extrusion steps with dislocated bottom, which greatly improves the forming ability of magnesium alloy materials, obtains high-density structure and great plastic deformation The grain refinement effect is remarkable, and the effect of eliminating the bimodal distribution of grains on the wall of the cup-shaped part is obvious, which shortens the production process of the high-performance magnesium alloy cup-shaped part.

Description

A Differential Speed Extrusion Forming Method of Magnesium Alloy High Performance Cup

technical field

The invention relates to the technical field of metal plastic processing and forming, in particular to a differential extrusion forming method for extrusion forming and modification of magnesium alloy materials.

Background technique

Cup-shaped components are one of the most representative structural forms in the fields of aerospace, national defense, transportation, etc., and are typical parts of reverse extrusion technology. For the manufacture of cup-shaped parts, most of them use reverse extrusion forming technology. Reverse extrusion technology is an advanced less-cutting processing technology, which not only improves the shape and dimensional accuracy of forgings, saves metal materials, but also because of the metal fiber streamline The profiling improves the mechanical properties of this type of parts. It has the characteristics of "high efficiency, high quality, and low energy consumption". It has high use value in technology and economy, and has become a hot research topic at home and abroad.

Magnesium alloy cup-shaped parts adopt the traditional reverse extrusion forming method, which requires multi-pass upsetting and drawing to achieve the ideal fine-grain strengthening effect. The production efficiency is low and the anisotropy of the formed component is obvious. The circumferential and axial The tensile strength varies greatly. Therefore, it is of great significance to research and develop new forming methods for high-strength and tough magnesium alloy cups.

The published Chinese patent number is ZL201410820158.3, and the patent name is "Annular Channel Angle Extrusion Mold and Method for Magnesium Alloy Cup-Shaped Components", which is a new forming method for preparing cup-shaped components, which belongs to the category of large plastic deformation. Compared with the traditional reverse extrusion method, it has great technical advantages. The average equivalent plastic strain of the formed parts can reach more than 2 times that of the traditional reverse extrusion. The forming force is small, the deformation is large, and the equivalent plastic strain distribution of the formed parts is more accurate. Even, it has a certain role and effect on the refinement of the cup-shaped component grains and the improvement of the mechanical properties.

However, the study found that the cup-shaped parts formed by the patent "Annular Passage Angle Extrusion Forming Die and Method for Magnesium Alloy Cup-shaped Components", the cylinder wall is on the surface perpendicular to the metal flow direction, and the grains are typical bimodal grains distributed. The bimodal grain distribution means that the metal is flattened and elongated under the action of the conical boss in the extrusion cavity, some of the original coarse grains are significantly refined, and some of the coarse grains are distributed in strips. This is very similar to the grain distribution pattern after equal channel angular pressing (ECAP). The bimodal distribution of grains causes the axial tensile fracture mechanism of the cup-shaped wall sample to be a mixed fracture mechanism in which the ductile fracture of the fine-grained band is accompanied by the brittle cleavage fracture of the coarse-grained band, which reduces to a certain extent Plastic and mechanical properties of cups. Obviously, the bimodal distribution of grains on the wall restricts the development and production practice of high-strength cup-shaped parts. From this point of view, there are certain technical limitations in the patent "Mold and Method for Angular Extrusion Forming of Annular Channel of Magnesium Alloy Cup-Shaped Components".

Contents of the invention

The purpose of the present invention is to provide a differential extrusion forming method for magnesium alloy high-performance cup-shaped parts. This method can obtain greater average equivalent strain, improve the effect of grain refinement, and greatly reduce the angular extrusion of the annular channel. The cylinder wall of the press-formed cup-shaped part exhibits a bimodal grain distribution, which reduces the occurrence rate of the mixed tensile fracture mechanism of the cylinder wall.

In order to solve the existing problems of the background technology, the present invention adopts the following technical solutions:

A method for differential extrusion forming of a magnesium alloy high-performance cup-shaped part, the sequence comprising:

(1) bar blanking;

(2) Homogenizing heat treatment to form a magnesium alloy blank;

(3) Preparation before forming: heating the magnesium alloy blank to the forming temperature and keeping it warm, and preheating the differential extrusion molding die as a whole to above the forming temperature of the magnesium alloy blank and keeping it warm; An upper mold assembly connected to the upper structure of the press, a lower mold assembly connected to the lower structure of the press, and a combined die; the upper mold assembly includes an upper template connected to the upper workbench of the press, The connected upper die set and the built-in punch of the upper die set; the upper template is assembled on the upper workbench of the press with fastening bolts, and the upper end of the punch is placed on the inner center line of the upper die set , the upper end of the punch is positioned by a cylindrical pin, and the upper die seat cover and the upper template are fixed by hexagon socket bolts around it, so that the punch is firmly fastened in the upper die seat cover; the combined die includes, "T" Shaped upper die and "U" shaped lower die, the inside of the "T" shaped upper die is a cylindrical cavity, which fits with the gap of the punch, and the upper end of the "T" shaped upper die is provided with an annular cone surface, Cooperate with the taper surface at the upper end of the cavity of the lower die seat sleeve; the inside of the "U"-shaped lower die is a rotary cavity; the "T"-shaped upper die is installed in the rotary cavity of the "U"-shaped lower die Inside, the cross-sectional shape formed by the revolving body cavity and the cylindrical cavity is a "mountain"-shaped extrusion cavity; the lower mold assembly includes the lower template seat cover, the lower backing plate and the lower template; the lower mold seat cover The inside of the cavity is a cylindrical cavity, and the inside of the cavity is matched with the combined die. The upper end of the cavity is closed with a ring-shaped tapered surface to limit the force of the upper die; the lower die seat sleeve and the lower backing plate are fixed from top to bottom. on the lower template.

(4) Install the mold: Install the mold after preheating and heat preservation on the press; inject oil agent and graphite lubricant into the inner cavity of the combined die, and at the same time, from the small hole at the top of the upper die to the "mountain" shape Inject oil agent and graphite lubricant into the extrusion cavity; put the magnesium alloy blank that has been homogenized and heat-treated into the cylindrical cavity of the upper die of the combined die;

(5) Forming process: the press drives the upper mold plate, upper mold seat cover and punch of the upper mold assembly to move downward, and the extruded magnesium alloy blank flows and deforms along the cavity in the "mountain"-shaped extrusion cavity; the magnesium alloy blank Under the action of the pressure of the cylindrical punch, it undergoes three stages of deformation: one is the coarse deformation stage similar to the cylindrical pier in the axial direction; the other is the large deformation stage of radial extrusion; as the press drives the punch to continue to squeeze The metal begins to be extruded radially along the bottom of the "mountain"-shaped extrusion cavity. During this process, the metal flows through the differential extrusion zone and then shrinks and squeezes into the extrusion channel with a smaller inner diameter; the third is the corner extrusion Shear deformation stage: the press drives the punch to continue to squeeze the metal downwards into the rounded area at the bottom of the "mountain"-shaped extrusion cavity, and the metal flows upward along the axial direction of the die wall under the action of shear stress, forming a magnesium alloy cup shape parts of the cylinder wall;

(6) After the extrusion is completed: stop the downward movement of the upper worktable of the press; tighten the fastening bolts connecting the upper die set and the lower die set, and loosen the tightening joints between the lower die set, the lower backing plate and the lower die. Fix the bolts; the upper worktable of the press moves upwards in the opposite direction, driving the punch to rise and separate from the cup-shaped part, and at the same time, the upper template drives the lower mold seat to rise and separate from the combined die; the ejector cylinder acts on the ejector rod through the hydraulic cylinder , the magnesium alloy cup is ejected from the combined die.

The principle of the present invention is: a combined die structure is designed, the "T" shaped upper die cavity and the "U" shaped lower die inner cavity jointly form a "mountain" shaped revolving body cavity, especially the bottom of the cavity adopts "Ladder" differential extrusion steps. The length of the step is a, the height is h, the horizontal inclination angle of the transition zone between the upper and lower adjacent steps is α, and the radius of the transition circle is r. The so-called differential speed means that there is a misalignment difference in the longitudinal direction between the "step" step on the lower end surface of the "T"-shaped upper die and the "step" step in the inner cavity of the "U"-shaped lower die corresponding to the lower position. When the metal flows through this area during the pressing process, the upper and lower surfaces of the metal flow along the steps, and the flow velocity forms a differential velocity. Considering the law of metal flow, the present invention adopts the vertical dislocation distance of the upper and lower "ladder" steps as half a step length a/2 (after Deform-3D finite element simulation, the average equivalent plastic strain is the largest when the dislocation distance is a/2).

By controlling the process parameters (number of steps, step length-to-height ratio a/h, transition zone inclination α) to change the stress on the magnesium alloy billet during extrusion deformation, thereby controlling the metal stress state, equivalent variables, and grains The degree of refinement, plastic deformation and organizational uniformity, etc. After the metal flows through the "ladder" differential extrusion steps, the upper and lower surfaces of the metal are subjected to the shear stress of the extrusion steps; at the same time, due to the dislocation difference between the upper and lower "ladder" radial extrusion steps, the metal squeezes in this area. When pressing, the extrusion speeds on the upper and lower surfaces are inconsistent, and torque and shear stress will also be generated inside the metal; in addition, the extrusion area formed by the "stepped" radial extrusion steps has a large entrance diameter and a small exit diameter, and the metal is squeezed into This area is also subjected to the axial extrusion force of the "stepped" radial extrusion step.

These three factors together change the stress state of the metal, resulting in greater plastic deformation on the surface and inside of the metal, increasing the average equivalent strain, obtaining a higher dense structure, and a remarkable effect of microstructure refinement. The extrusion step effectively increases the number of deformations of the metal during the extrusion process, and greatly breaks the microstructure of the cup-shaped parts in the traditional reverse extrusion process into flat and slender strips, making the distribution of large and small grains more uniform, and eliminating the need for The effect of bimodal distribution of grains is obvious.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. 1 is a schematic diagram of the working state of the mold when the blank is extruded in the embodiment provided by the present invention;

Fig. 2 is a schematic diagram of the working state of the die when the billet is to be extruded in the embodiment provided by the present invention;

Figure 3-1 is a schematic diagram of the assembly of the combined die in the embodiment provided by the present invention;

Figure 3-2 is a partially enlarged schematic diagram of the lower end of the combined die cavity in the embodiment provided by the present invention;

Figure 4-1 is a schematic diagram of the "ladder" differential radial extrusion step in the embodiment provided by the present invention;

Figure 4-2 is a schematic diagram of the dislocated "ladder" differential radial extrusion step in the embodiment provided by the present invention;

Fig. 5 is a schematic diagram of the extruded and deformed metal flow zones of the extruded part in the embodiment provided by the present invention;

Fig. 6 is the schematic diagram of the extruded magnesium alloy cup-shaped member in the embodiment provided by the present invention;

Fig. 7 is the metallographic microstructure of the wall part of the cup-shaped part formed by the corner extrusion of the annular channel in the prior art;

Fig. 8 is the metallographic microstructure of the wall part of the cup-shaped part formed by differential extrusion according to the embodiment provided by the present invention;

Reference signs:

1-upper template; 2-upper mold seat cover; 3-lower mold seat cover; 4-"T"-shaped upper die; 5-"U"-shaped lower die; 6-lower backing plate; 7-lower template; 8-straight pin; 9-rod; 10-screw; 11-top block; 12-punch; 13-compression spring; 14-fastening bolt; 15-vertical hole; 16-"mountain" shaped extrusion cavity; 17-differential extrusion step; 18-annular boss.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, and are not intended to limit the present invention.

Please refer to Fig. 1-Fig. 6, this specific embodiment adopts the following technical scheme: a kind of differential extrusion molding die of magnesium alloy high-performance cup-shaped part, comprises the upper die assembly that is connected with the superstructure of press machine, and press machine The lower mold assembly connected to the lower structure and the combined die.

Please refer to Fig. 1-Fig. 2, the upper mold assembly includes: the upper template 1 connected with the upper structure of the press, the upper mold seat cover 2 connected with the upper template 1 and the built-in punch 12 of the upper die seat cover . The upper end of the punch 12 is placed in the inner center of the upper die seat cover 2 .

Please refer to Fig. 3-1, the combined die includes a "T" shaped upper die 4 and a "U" shaped lower die 5. The inside of the "T"-shaped upper die 4 is a cylindrical cavity, which fits with the punch 12 in a gap. Surface limit fit. The inside of the "U" shaped lower die 5 is a revolving cavity. The "T"-shaped upper die 4 is installed in the rotary body cavity of the "U"-shaped lower die 5, and the cross-sectional shape formed by the cylindrical cavity and the rotary body cavity is a "mountain"-shaped extrusion cavity 16; "T" The upper end of the concave die 4 is provided with equally spaced vertical holes 15 along the axial direction, which penetrate to the "mountain"-shaped extrusion cavity 16 as lubricant inflow channels.

Please refer to Figure 3-2, the cross-section of the lower end of the "T"-shaped upper die 4 is a "ladder" differential extrusion step 17, and the corresponding lower longitudinal position, in the shape of the "U"-shaped lower die 5 A "ladder" differential extrusion step 17 is also provided on the cavity surface. The outer lower end of the "T" shaped upper die 4 is provided with an annular boss, which is an extrusion sizing band for the inner diameter of the cup-shaped piece. Corresponding to the horizontal position, an annular boss is also set in the cavity of the "U"-shaped lower die 5, which is the extrusion sizing band for the outer diameter of the cup-shaped part. The bottom fillet of the concave model cavity is connected tangentially.

Please refer to Fig. 1 and Fig. 2, the lower mold assembly includes the lower die set 3, the lower backing plate 6 and the lower template 7, the inside of the lower die set 3 is a cylindrical cavity, and the inside of the cavity is combined with the The upper end of the cavity is closed with a ring-shaped conical surface to limit the bearing force on the "T"-shaped upper die 4; the lower die seat cover 3 and the lower backing plate 6 are fixed on the lower template 7 from top to bottom; The combined "T" shaped upper die 4, "U" shaped lower die 5 and lower backing plate 6 are positioned by cylindrical pins 8 and fixed on the lower template 7 with screws 10 from top to bottom.

The middle part of the lower backing plate 6 and the lower formwork 7 is provided with a push rod through hole communicating with the combined "T" shaped upper die 4 and the bottom through hole of the "U" shaped lower die 5. The block 11 is placed in the inner cavity of the combined "U"-shaped lower die 5, and fits with the inner cavity gap, and the upper surface is level with the "ladder" differential extrusion step 17 in the inner cavity of the "U"-shaped lower die 5 Connected, the lower surface is placed on the lower backing plate 6. The lower surface of the top block 11 has a threaded hole, which is threadedly connected with the push rod 9 .

The punch 12, the "T" shaped upper die 4, the through hole of the "U" shaped lower die 5, the ejector rod through hole, the ejector block 11, and the ejector rod 9 are located on the same axis; the ejector rod More than 9 telescopic mode moves up and down in the through hole of combined " T " shape upper die 4 , " U " shape lower die 5 and push rod 9 through holes.

Please refer to Fig. 1 and Fig. 2, the upper structure of the press (not shown in the figure) is connected with the upper template 1 and the lower mold seat cover 3 through the fastening bolt 14, and the compression spring 13 is installed on the fastening bolt 14, which is located in the lower mold Between the upper end of the seat cover 3 and the upper template 1.

Please refer to Fig. 1, Fig. 2, a kind of differential extrusion forming method of magnesium alloy high-performance cup-shaped parts, its steps include:

(1) bar blanking;

(2) Homogenizing heat treatment to form a magnesium alloy billet.

(3) Preheat the differential extrusion die shown in Figure 1 and Figure 2 to a magnesium alloy forming temperature of 30°C to 50°C and keep it warm for 2 hours, and heat the magnesium alloy billet to a forming temperature of 350°C and keep it warm for 2 to 4 hours . Assemble the differential extrusion die on the press as shown in Figure 1.

(4) Loosen the bolt 14 connecting the upper template 1 and the lower mold seat cover 3, and the upper workbench slider (not shown in the figure) of the press rises to drive the upper mold assembly: the upper template 1, the upper die seat cover 2, the punch The head 12 rises together with the slider, so that the punch 12 is separated from the inner cavity of the combined die; starting from the "T" shaped upper die 4 cylindrical inner cavity of the combined die, inject a certain amount of oil into the inner cavity graphite lubricant, and inject a certain amount of graphite lubricant into the "mountain" shaped extrusion chamber of the combined die from the lubricant hole at the upper end of the "T"-shaped upper die 4; The 350°C magnesium alloy billet is put into the cylindrical inner cavity of the "T"-shaped upper die 4;

(5) The sliding block of the worktable on the press moves downward, driving the punch 12 to squeeze the magnesium alloy billet in the inner cavity of the combined die at an axial speed of 0.5-5 mm/s, so that the magnesium alloy billet is combined Flow extrusion in the " mountain " shape extrusion cavity 16 of formula die, (as shown in Figure 1). Since the diameter of the blank is smaller than the cylindrical inner cavity of the "T"-shaped upper die 4, under the pressure of the punch 12, the metal is first upset and deformed to fill the cylindrical inner cavity of the "T"-shaped upper die 4 , the lower end of the metal is subsequently deformed, and as the punch 12 continues to move downward, the metal billet is finally filled in the "mountain"-shaped extrusion cavity 16.

(6) The slide block of the worktable on the press continues to move downward until the magnesium alloy cup-shaped component of the required size is obtained, and the downward movement of the slide block of the worktable on the press is stopped.

(7) Tighten the bolts 14 connecting the upper template 1 and the lower mold seat cover 3, and loosen the fastening bolts at the joint between the lower template 7 and the lower die seat cover 3; Reverse upward movement, driving the punch 12 to move upward and disengage from the magnesium alloy cup forming part, the fastening bolt 14 drives the lower die seat sleeve 3 and the "T"-shaped upper die 4 of the combined die, and the "U"-shaped die Lower die 5 breaks away from.

(8) The ejector rod 9 is pushed upward by the ejector cylinder (not shown in the figure) of the hydraulic press, and the extruded magnesium alloy cup is formed and the upper die 4 of the "T" shape is concaved from the "U" shape. The cavity of the mold 5 is ejected; the upper die 4 of the "T" shape is removed, and it is installed in the cavity of the lower die 5 of the "U" shape.

(9) The slider of the upper workbench of the press moves downward, driving the lower die seat cover 3 to move downward until the bottom of the lower die seat The bolts that formwork 7 is connected with lower mold seat cover 3 are tightened.

(10) Repeating the steps (4) to (9) can continuously complete the differential extrusion forming of the cup-shaped piece.

Example:

Take the preparation of an AZ31 magnesium alloy cup with an outer diameter of 200 mm and an inner diameter of 170 mm as a specific example.

The blank size used is H=360mm, diameter D ₁ =80mm, inner cavity diameter D ₂ of the "T"-shaped upper die 4 =90mm, D ₁ <D ₂ . The whole mold is preheated to 400°C for 2 hours, and the magnesium alloy billet is heated to the forming temperature of 350°C and held for 2 to 4 hours. The extrusion speed of the punch is 1 mm/s.

As shown in Fig. 3-1, 4 to 8 vertical holes are provided at the upper end of the "T"-shaped upper die 4 along the axial direction to serve as small holes for the lubricant.

As shown in Figure 3-2, the length L2 of the sizing belt of the "T"-shaped upper die 4 is 8.8mm, and the length L1 of the sizing belt of the "U"-shaped lower die 5 is 24mm; it is beneficial to metal flow and supply Considering the angle of extrusion force as large as possible, the connection surface between the sizing belt at the lower end of the "T"-shaped upper die 4 and the horizontal bottom surface is an inclined plane, and the inclined plane is 45° to the horizontal direction. The "T"-shaped upper die 4 and the "U" The annular boss 18 of " shape lower die 5 is connected with the channel wall with an inclined plane, and the angle between the inclined plane and the vertical or horizontal channel wall is 45°, and the height of the boss is about 5mm; " U " shape lower die 5 The radius of the bottom fillet in the cavity is R=20mm, so as to facilitate the large shear deformation of the metal in the bottom fillet area. The inclination angles of all the transition slopes not specified in the "mountain" shaped extrusion cavity wall shown in Figure 3-2 are 45°.

Please refer to Figure 4-1. Figure 4-1 shows the "step" differential extrusion step 17 at the bottom of the "mountain" shaped extrusion chamber 16, the step length a=6mm, height h=4mm, transition circle radius r=4mm , the number of steps takes a value of 3 to 4. Considering that it is beneficial for the metal to be extruded forward one by one along the steps during the extrusion process without forming dead angles, folds and folds, the inclination angle between the connection of adjacent horizontal steps and the horizontal direction is 45°; Please refer to Figure 4-2, the differential extrusion steps 17 on the lower end surface of the "T" shaped upper die 4 and the corresponding differential extrusion steps 17 in the cavity of the "U" shaped lower die 5 have a longitudinal direction Misalignment difference, the misalignment difference is the length of half a step a/2=3mm. The inclination angles of all the transition slopes not specified in the "mountain" shaped extrusion cavity wall shown in Figure 3-2 are 45°.

The design of the above-mentioned "ladder" differential radial extrusion steps is mainly used to squeeze the metal entering the bottom of the "mountain"-shaped cavity 16 to change its stress state and increase deformation. There are three main effects:

First, when the metal flows through the "ladder" radial differential extrusion step 17, it interacts with the boss of the differential extrusion step 17, and the upper and lower surfaces of the metal are subjected to the shear force of the differential extrusion step 17;

The second is that the "ladder" differential radial extrusion step is a channel with a large entrance and a small exit. During the metal extrusion process, the metal will be subjected to the axial extrusion force of the extrusion step;

The third is that there is a dislocation difference in the longitudinal direction of the upper and lower differential extrusion steps. This dislocation difference not only increases the number of repeated extrusion deformations of the metal up and down during the metal extrusion process, but also because the metal is in contact with the dislocation steps. The difference in flow velocity generates a certain torque inside the metal, making it also subject to shear stress.

The "ladder" differential extrusion step 17 of the present invention changes the stress state of the metal and greatly increases the plastic deformation of the extruded metal. Because the microstructure of cup-shaped parts in the traditional reverse extrusion process is flat and slender grains, the anisotropy of the structure is relatively large, and the grains on the side wall of the extrusion part in the annular channel corner extrusion process are bimodally distributed, which weakens the extrusion process. The comprehensive performance of the pressed piece, and the design of the "ladder" differential extrusion step of the present invention greatly breaks the slender large grains, makes the size of the grains more uniform, and eliminates the dual mode of grains. The distribution effect is obvious.

Please refer to FIG. 5 . FIG. 5 is a schematic diagram of metal flow zones when the extruded metal is deformed according to the present invention. Under the action of the pressure of the cylindrical punch, the magnesium alloy blank undergoes three stages of deformation: one is the coarse deformation stage similar to the cylindrical pier in the axial direction; the other is the large deformation stage of radial extrusion. As the press drives the punch 12 to continue to extrude downward, the metal begins to extrude radially along the bottom of the "mountain"-shaped extrusion cavity 16, and enters the "step" differential radial extrusion zone; during this process, The metal passes through the differential extrusion zone and then shrinks and extrudes into the extrusion channel with a smaller inner diameter; the third is the shear deformation stage of angular extrusion. As the press drives the punch to continue to squeeze downward, the metal changes from radial flow to axial flow in the fillet deformation zone, resulting in great shear deformation.

Compared with the traditional extrusion method of the magnesium alloy cup-shaped piece and the corner extrusion forming method of the annular channel, the present invention has the following beneficial effects:

(1) Improve the formability of magnesium alloys. Magnesium alloy is a low plasticity material, and it is very easy to crack even if it is formed at high temperature. The "mountain"-shaped extrusion chamber of the invention effectively increases the internal hydrostatic pressure of the extruded piece, and greatly improves the plasticity of the magnesium alloy material.

(2) A high-density structure is obtained, the grain refinement effect is more significant, and a larger average equivalent strain is obtained, and the deformation strengthening effect is more significant. The "step" differential extrusion step at the bottom of the "mountain"-shaped extrusion chamber of the present invention greatly increases the number of repeated extrusion deformations of the metal in the "step" differential radial extrusion zone, making the metal Repeatedly interacting with the misplaced "ladder" differential extrusion steps, the surface and interior are subjected to more shear force and axial extrusion force, which changes the internal stress state of the magnesium alloy material and produces a huge Deformation amount. After the metal undergoes the "step" differential extrusion zone and the subsequent bottom fillet shear deformation zone, the internal pores of the extrusion can be welded to a great extent, the internal cast structure of the deformed body can be broken, and the grains can be refined to Submicron and even nanoscale, forming a large-angle grain boundary structure, obtaining a high-density structure, and greatly enhancing the deformation strengthening effect of magnesium alloy materials.

(3) The effect of eliminating the bimodal distribution of grains is obvious, and the incidence of mixed tensile fracture mechanism of the tube wall of the formed part is effectively reduced. The microstructure of the wall of the traditional reverse extrusion cup is elongated and slender grains with obvious anisotropy. The grains on the wall of the cup-shaped part formed by the angular extrusion of the annular channel are distributed in two modes, which reduces the plasticity and mechanical properties of the cup-shaped part to a certain extent. The present invention aims at these deficiencies of the above-mentioned process, and repeatedly squeezes and breaks the coarse grains and the elongated slender grains through the dislocated "ladder" differential extrusion steps, thereby greatly reducing the radial grain size of the cylinder wall. Modal distribution can effectively improve the comprehensive mechanical properties of cup-shaped components.

(4) The process parameters are highly controllable, and magnesium alloy cup-shaped components with different performance requirements and specifications can be extruded. By controlling the process parameters of the "ladder" differential extrusion steps: the number of steps, the length-to-height ratio of steps a/h, and the inclination angle of the transition zone α, the stress on the magnesium alloy billet during extrusion deformation can be changed, thereby controlling the metal Stress state, equivalent variable, degree of grain refinement, plastic deformation and microstructure uniformity, etc.

(5) Shorten the production process of the high-performance magnesium alloy cup: before the traditional reverse extrusion forming high-performance magnesium alloy cup, the blank is a slender cylinder, which must pass through the rough blank of the multi-pass cylindrical pier, the present invention It can directly extrude a billet with a height-to-diameter ratio greater than 3 without buckling, thereby eliminating the pier roughening process. Direct use of axial pressure, radial pressure, and tangential shearing force can obtain great plastic deformation, help to break dendritic structure and impurities, greatly improve the deformation strengthening effect of magnesium alloy materials, and obtain hardness High-performance magnesium alloy cup-shaped parts with low anisotropy, relatively uniform structure, significantly refined grains, and more excellent comprehensive mechanical properties.

(6) Through the simulation comparison of Deform-3D finite element simulation software, it has been verified that the novel differential extrusion cup of the present invention can obtain a larger amount of plastic deformation, and more metals are involved in the plastic deformation process. deformed flow. In terms of simulation parameter settings, the material imported is the parameter model of AZ80, the temperature is 380°C, the grid is divided into 20000, the punch speed is 1mm/s, and the friction coefficient is 0.25. From the simulation results, it can be seen intuitively that the average equivalent strain value (AVG) of the cup-shaped piece formed by the angular extrusion of the annular channel is 4.01, while the average equivalent strain value (AVG) of the novel differential extrusion cup-shaped piece of the present invention As high as 4.89, it is obvious that the average equivalent strain value of the new differential extrusion cup of the present invention is significantly greater than that of the annular channel angular extrusion. Thus, it is confirmed that the cup-shaped article prepared by the novel differential extrusion method of the present invention can obtain a larger amount of plastic deformation. In terms of the degree of deformation, it can be visually observed from the cloud image that the color of the outer wall and inner wall of the differential extrusion is almost the same, while the corner extrusion of the annular channel gradually decreases from the outside to the inside. This shows that the multi-step differential extrusion method can make the metal "squeeze through" during the plastic deformation process, that is to say, it can make as much metal as possible participate in the flow of greater deformation during the plastic deformation process.

(7) Through experiments and microstructure analysis and comparison, it is verified that the novel differential extrusion forming method of the present invention has an obvious effect on eliminating the bimodal distribution of crystal grains. The AZ31 magnesium alloy cup-shaped piece (the specific example adopted in the above-mentioned specific embodiment part) with an outer diameter of 200mm and an inner diameter of 170mm was obtained by using the annular channel corner extrusion forming method and the differential extrusion forming method of the present invention respectively, and the molded part was dissected , respectively take the surface of the sample cylinder wall perpendicular to the metal flow direction (the bottom end surface of the sample) to observe the microstructure under the Zeiss metallographic microscope. Metallographic and microstructure photographs of the extruded cup wall part perpendicular to the metal flow direction. From the metallographic microstructure photos, it can be seen intuitively that the bimodal distribution of crystal grains on the wall of the cup-shaped part after the new differential extrusion forming method is obviously eliminated.

(8) The present invention provides a short-flow, high-performance, and highly controllable manufacturing method for magnesium alloy cup-shaped components, and provides a reference for preparing ultra-fine-grained high-performance cup-shaped components. With the improvement of the lightweight level of aerospace, national defense and military, transportation and other equipment, the requirements for combat technical indicators such as speed, reliability, and carrying capacity are also increasing. 1. The demand for ultra-fine-grained high-performance magnesium alloy cups with more excellent comprehensive mechanical properties is increasing, and the requirements for comprehensive performance are getting higher and higher. The application prospect of the present invention will be better and better.

It will be apparent to those skilled in the art that the invention is not limited to the details of the above-described exemplary embodiments, but that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Accordingly, the embodiments should be regarded in all points of view as exemplary and not restrictive, the scope of the invention being defined by the appended claims rather than the foregoing description, and it is therefore intended that the scope of the invention be defined by the appended claims rather than by the foregoing description. All changes within the meaning and range of equivalents of the elements are embraced in the present invention.

In addition, it should be understood that although this specification is described according to implementation modes, not each implementation mode only contains an independent technical solution, and this description in the specification is only for clarity, and those skilled in the art should take the specification as a whole , the technical solutions in the various embodiments can also be properly combined to form other implementations that can be understood by those skilled in the art.

Claims (1)

1. a kind of differential-velocity extrusion manufacturing process of magnesium alloy high-performance cup shell, it is characterised in that：Comprise the following steps：

(1) bar material baiting；

(2) homogenization heat treatment forms magnesium alloy blank；

(3) prepare before shaping：Magnesium alloy blank is heated to forming temperature and is kept the temperature, and differential-velocity extrusion shaping dies is integrally pre- It more than heat to magnesium alloy blank forming temperature and keeps the temperature；The differential-velocity extrusion shaping dies includes the superstructure with forcing press The mold component of connection, the lower die assembly and combined die being connected with forcing press substructure；The mold Component is included built in the cope plate being connected with the upper table of forcing press, the upper mold cover for seat to connect with cope plate and upper mold cover for seat Punch；The cope plate is assemblied in fastening bolt on forcing press upper table, and the upper ends of the punch are in upper mold On the inside center line of cover for seat, punch upper end is by cylinder finger setting, and surrounding is by hexagon socket head cap screw upper mold cover for seat and cope plate It is fixed, punch is made firmly to be anchored in upper mold cover for seat；The combined die includes, and "T"-shaped upper cavity die and " u "-shaped are recessed Mould, "T"-shaped upper cavity die inside are cylindrical mold cavity, and with punch clearance fit, "T"-shaped upper cavity die upper end is equipped with annular and bores End cone face /V coordinates on face, with lower die cover for seat cavity；It is revolving body cavity inside the " u "-shaped lower cavity die；"T"-shaped fovea superior Mould is mounted in the revolving body cavity of " u "-shaped lower cavity die, and the cross sectional shape that revolving body cavity and cylindrical mold cavity collectively constitute is " mountain " font extrusion chamber, extrusion chamber bottom employ " ladder " formula differential-velocity extrusion step, and so-called differential refers to "T"-shaped fovea superior " ladder " step of mould lower face has a with " ladder " step of the recessed mold cavity of the " u "-shaped of corresponding lower position in longitudinal direction Dislocation is poor, and when metal flows through this region in extrusion process, metal upper and lower surface forms differential along step-flow, flow velocity；Institute The lower die assembly stated includes lower template cover for seat, lower bolster and lower template；It is cylindrical mold cavity inside the lower die cover for seat, type Intracavitary portion and combined die clearance fit, cavity upper end is closed up with circular cone, with to upper cavity die /V load；Lower die cover for seat It is fixed on from top to bottom in lower template with lower bolster；

(4), installation mold：Mold after preheating insulation is mounted on forcing press；Finish stone is injected to combined die inner cavity Black lubricant, while finish graphitic lubricant is injected in " mountain " font extrusion chamber from top to bottom from fovea superior die tip aperture；It will Magnesium alloy blank by homogenization heat treatment is put into the upper cavity die cylindrical type intracavitary of combined die；

(5) forming process：Forcing press drives cope plate, upper mold cover for seat and the punch of mold component to move downward, and squeezes magnesium and closes Golden blank is in " mountain " font extrusion chamber along cavity flow deformation；Magnesium alloy blank is under the action of cylindrical punch pressure, warp Cross the deformation of three phases：First, by the upset deformation stage of axial similar cylinder；Second is that the radial compression large deformation stage；With Forcing press drives punch to continue to be pressed down against, and metal starts along " mountain " font extrusion chamber bottom radial compression, during this, metal Undergauge is squeezed into the smaller squeezing passage of internal diameter after flowing through differential-velocity extrusion band；Third, the corner extrusion detrusion stage；Pressure Machine drives punch to continue to be pressed down against metal into " mountain " font extrusion chamber bottom roundings region, and metal is by shear stress edge It cavity plate wall to flow axially upwards, forms the barrel of magnesium alloy cup shell；

(6) after the completion of extrusion molding：Stop moving downward for forcing press upper table；Tighten what cope plate was connected with lower die cover for seat Fastening bolt unclamps lower die cover for seat, lower bolster and the fastening bolt of lower template junction；Forcing press upper table is transported back up It is dynamic, punch is driven to rise and depart from cup shell, while cope plate drives die holder set to rise, and departs from combined die；It is logical It crosses hydraulic cylinder liftout tank to act on mandril, magnesium alloy cup shell is ejected from combined die.