CN110919006B - Controllable back pressure metal powder equal-channel angular extrusion device and method - Google Patents
Controllable back pressure metal powder equal-channel angular extrusion device and method Download PDFInfo
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- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/20—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces by extruding
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- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/20—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces by extruding
- B22F2003/202—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces by extruding with back pressure
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/20—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces by extruding
- B22F2003/208—Warm or hot extruding
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Abstract
A controllable back pressure metal powder equal channel angular extrusion device and a controllable back pressure metal powder equal channel angular extrusion method are disclosed, the device comprises an extrusion die system, a hydraulic system and a PLC system, an upper female die and a lower female die in the extrusion die system are buckled to form two extrusion cavity channels which form included angles with each other and have the same cross section size, a vertical oil cylinder of the hydraulic system is used as a mold locking cylinder, two horizontal oil cylinders alternately exchange roles between a back pressure cylinder and a working cylinder, and the back pressure is regulated and controlled through a proportional valve. The method comprises the following steps: setting and applying a mold locking force, and regulating and controlling the temperature; feeding a working cylinder at a maximum system oil pressure and a set extrusion speed, forming extrusion by the back pressure cylinder at a set back pressure, obtaining a maximum extrusion force according to a change curve of the back pressure and the extrusion force, debugging a PLC program by taking the set back pressure as a basis and the maximum extrusion force as a target, obtaining a controllable back pressure, and realizing equal-channel extrusion forming under the condition of constant maximum extrusion force; when the working cylinder reaches the limited position, the back pressure cylinder and the working cylinder exchange roles, and the subsequent pass extrusion process is completed until the end.
Description
Technical Field
The invention belongs to the technical field of large plastic deformation of materials, and particularly relates to a controllable back pressure metal powder equal-channel angular extrusion device and method.
Background
The large plastic deformation technology can perform deformation with high strain rate at a lower temperature, and can be used for preparing fine crystal materials which have mechanical properties (Curie temperature, Debye temperature, electromagnetism, elastic modulus, diffusion coefficient and the like), high strength, high plasticity and the like different from those of the traditional materials.
Equal Channel Angular Pressing (ECAP) is an important large plastic deformation technology, and metal materials enter from one end of a channel and are extruded from the other end of the channel after passing through an angle under the pressure action of a punch through two die channels which form an angle with each other and have the same cross section size. Under the action of the corner of the channel of the die, the metal material generates strong shearing deformation when passing through the corner. Therefore, the ECAP can effectively refine the microstructure of the metal material and improve the comprehensive mechanical property of the material.
Compared with the traditional plastic processing technology of the metal material, the ECAP can ensure that the cross section area and the cross section shape of the metal material are not changed in the deformation process, and the plastic deformation area is smaller, so that the repeated orientation and uniform shearing deformation of the material can be realized only by lower working pressure, which is beneficial to accumulating larger plastic deformation energy in the material and fully refining the grain structure. For the traditional plastic deformation technology, the change of the cross section shape of the material before and after deformation is large, repeated deformation processing is difficult to perform, and large plastic deformation amount cannot be accumulated. Therefore, the grain structure refinement by the conventional plastic deformation technique is insufficient, and it is difficult to refine the grains to submicron and below dimensions.
ECAP as a very effective grain refining method can obviously improve the comprehensive performance of the material, has very wide application prospect, and has the technical advantages mainly expressed in the following aspects:
the strength of the deformed material is obviously improved compared with the material under the traditional plastic deformation technology, the usage amount of the material can be reduced, and the purpose of reducing the weight is achieved.
Secondly, crystal grains can be effectively refined, the plasticity is improved, and the subsequent processing performance and the part forming performance are improved.
And thirdly, the plastic forming can be carried out on the material with poor plasticity, for example, the metal material with the HCP lattice structure has poor plasticity, and the material plasticity can be improved without reducing the strength of the material through applying back pressure, controlling the deformation temperature and other suitable ECAP process conditions.
Different types of textures and grain size distributions can be obtained through different deformation paths, and a material with relatively ideal texture and grain distribution can be obtained by adjusting an extrusion process, so that the aim of simultaneously improving the strength and the plasticity of the material is fulfilled.
Fifthly, the material forming can be carried out at a lower temperature, and further secondary recrystallization coarsening can be effectively inhibited, so that the block material with fine grain scale can be obtained.
However, ECAP has been mainly focused on the laboratory research stage so far, and has relatively few industrial applications, because many factors affect the microstructure and mechanical properties of the metal material during the deformation process, including the following aspects:
firstly, a channel included angle phi and an external angle psi are the most main influence factors, and the channel included angle phi and the external angle psi directly influence the equivalent strain degree of single-pass extrusion; for example, when Φ is 90 °, Ψ is 0 °, 16 °, 37 °, 62 °, 90 °, the shear strain amounts are 1.15, 1.07, 0.99, 0.93, and 0.90, respectively; when phi is 120 degrees, 135 degrees and psi is 0 degrees, the shear strain amounts are 0.66 and 0.48 respectively; it can be seen that when phi is 90 degrees and psi is 0 degree, the shear strain is the largest, when phi is 90 degrees, the deformation resistance borne by the mold is good, and when psi is 0 degree, a dead zone exists at the outer corner of the mold, the friction is large, and a part of non-uniform deformation region exists at the bottom of the sample, so that the effective deformation degree of the region is reduced, and the hardness value is reduced.
Secondly, the temperature is also the most important factor influencing the deformation of the material; for example, as the temperature increases, the grain size gradually increases, and lowering the extrusion temperature can result in higher volume fractions of high angle grain boundaries; for the material difficult to deform, in order to avoid fracture in the extrusion process, the extrusion temperature is generally increased to make the extrusion process smoother; it can be seen that in order to obtain a higher volume fraction of high angle grain boundaries and fine grain structure material, the extrusion temperature is generally reduced as much as possible without breaking the sample.
Thirdly, the back pressure is the most important factor influencing the deformation of the material; the back pressure can provide a hydrostatic pressure environment for the deformation of the material, and the plastic deformation capability of the material can be obviously improved under the action of three-directional pressure, so that the product can be prevented from generating cracks, and the brittle material can be subjected to plastic deformation; after the back pressure is applied, the material can fully fill a dead zone at the outer corner, the shearing zone is closer to a pure shearing deformation state, and the grain refining effect is more obvious; for brittle materials, the application of back pressure can minimize the extrusion temperature, which is beneficial for finer grain structure.
In addition, in the process of extruding the metal powder under ECAP with back pressure, under the action of shearing force and extrusion force, oxide films on the surfaces of powder particles are crushed, mutual welding between powder interfaces is facilitated, and the high-density block material is obtained. Meanwhile, the shearing deformation in the extrusion process is also beneficial to the oxide film on the surface of the powder to be broken, and the oxide particles are uniformly dispersed in the matrix to play a role in strengthening, so that the particle-reinforced compact block material is obtained.
However, the back pressure of most of the existing ECAP equipment with back pressure is invariable, and because the position of the metal shear deformation zone and the friction force between the metal and the die are all in the change, if the actual pressure stress acting on the deformation zone can not be effectively controlled, the structure refinement degree, the relative density, the hardness and the like of the solidified metal powder have great differences, and the consistency of the structure performance and the thermal stability are poor, so that the mechanical properties such as the strength and the plasticity of the material are also reduced.
Disclosure of Invention
Aiming at the problem that the actual pressure stress of a deformation zone cannot be effectively controlled, the invention provides a controllable back pressure metal powder equal-channel corner extrusion device and method, which can realize the condition that the extrusion force of the deformation zone is kept constant, namely under the condition of constant stress, equal-channel extrusion forming is carried out on metal powder under different temperature, extrusion speed and pass conditions, and a block product with good structural property consistency and thermal stability can be obtained; meanwhile, real-time stepless back pressure change can be realized in the equal channel angular extrusion process, so that the extrusion force is changed according to a gradient rule, the size and the performance of internal grains are changed in a gradient manner, and the product with the gradient change of tissues and mechanical properties is prepared.
In order to achieve the purpose, the invention adopts the following technical scheme: a controllable back pressure metal powder equal channel angular extrusion device comprises an extrusion die system, a hydraulic system and a PLC system; the extrusion die system comprises a supporting base, a top plate, a lower backing plate, an upper backing plate, a lower substrate, an upper female die and a lower female die; the lower base plate is horizontally and fixedly arranged on the upper surface of the supporting base, the lower base plate is horizontally and fixedly arranged above the lower base plate, a ceramic heating plate mounting groove is reserved between the lower base plate and the lower base plate, and a ceramic heating plate is mounted in the ceramic heating plate mounting groove; the upper base plate is horizontally arranged right above the lower base plate, the upper base plate and the lower base plate are in abutting contact fit, the upper base plate is horizontally and fixedly connected above the upper base plate, a ceramic heating plate mounting groove is also reserved between the upper base plate and the upper base plate, and a ceramic heating plate is mounted in the ceramic heating plate mounting groove; the top plate is horizontally and fixedly connected to the upper surface of the upper base plate; the lower female die is horizontally clamped on the upper surface of the lower substrate, the upper female die is horizontally clamped on the lower surface of the upper substrate, the upper female die and the lower female die are buckled together, a first extrusion cavity channel and a second extrusion cavity channel which form an included angle with each other and have the same section size are formed between the upper female die and the lower female die, and the first extrusion cavity channel and the second extrusion cavity channel are communicated with each other at a corner; the hydraulic system comprises a first horizontal oil cylinder, a second horizontal oil cylinder, a vertical oil cylinder and a hydraulic station; the first horizontal oil cylinder is fixedly arranged on the outer side of the first extrusion cavity channel, the first horizontal oil cylinder is superposed with the central axis of the first extrusion cavity channel, a first extrusion male die rod body is coaxially and fixedly arranged at the end part of a piston rod of the first horizontal oil cylinder, and the first extrusion male die rod body is matched with the first extrusion cavity channel; the second horizontal oil cylinder is fixedly arranged on the outer side of the second extrusion cavity channel, the second horizontal oil cylinder is superposed with the central axis of the second extrusion cavity channel, a second extrusion male die rod body is coaxially and fixedly arranged at the end part of a piston rod of the second horizontal oil cylinder, and the second extrusion male die rod body is matched with the second extrusion cavity channel; the vertical oil cylinder is fixedly arranged right above the top plate, a piston rod of the vertical oil cylinder faces downwards, and the end part of a piston rod of the vertical oil cylinder is fixedly connected with the upper surface of the top plate; the first horizontal oil cylinder, the second horizontal oil cylinder and the vertical oil cylinder are all supplied with oil by a hydraulic station, proportional valves are arranged on oil supply pipelines between the first horizontal oil cylinder and the hydraulic station and between the second horizontal oil cylinder and the hydraulic station, and the flow and the pressure of the first horizontal oil cylinder and the second horizontal oil cylinder are regulated and controlled through the proportional valves; the first horizontal oil cylinder and the second horizontal oil cylinder alternately exchange roles, and when the first horizontal oil cylinder is used as a working cylinder, the second horizontal oil cylinder is used as a back pressure cylinder; when the second horizontal oil cylinder is used as a working cylinder, the first horizontal oil cylinder is used as a back pressure cylinder; the vertical oil cylinder is used as a mold locking cylinder; when the first horizontal oil cylinder or the second horizontal oil cylinder is used as a back pressure cylinder, regulating and controlling the back pressure through a proportional valve; the PLC system is provided with a touch screen, and control instructions are executed on the touch screen.
The equal-channel angular extrusion method for the controllable back pressure metal powder adopts the equal-channel angular extrusion device for the controllable back pressure metal powder and comprises the following steps of:
the method comprises the following steps: filling metal powder into the first extrusion cavity channel and the second extrusion cavity channel, inputting a mold locking force required to be applied by a vertical oil cylinder and a temperature required to be applied by a ceramic heating plate into the touch screen, executing a mold locking action command of the vertical oil cylinder to tightly buckle the upper female mold and the lower female mold together, and executing a temperature control command to enable the temperature to reach a set requirement;
step two: under the mold locking force of the vertical oil cylinder, the first horizontal oil cylinder serves as a working cylinder to feed at the maximum system oil pressure and the set extrusion speed, the second horizontal oil cylinder serves as a back pressure cylinder to extrude the metal powder by setting back pressure, the change curves of the back pressure and the extrusion force are displayed and stored on a touch screen in real time, the maximum extrusion force is obtained, then PLC program debugging is carried out on the basis of the set back pressure by taking the maximum extrusion force as a target, the controllable back pressure is obtained, the condition that the extrusion force of a deformation area is kept constant is realized, and equal-channel extrusion forming of the metal powder is realized under the condition of the constant maximum extrusion force;
step three: when the first horizontal oil cylinder as a working cylinder reaches a limit position, the first horizontal oil cylinder stops acting, the first horizontal oil cylinder and the second horizontal oil cylinder perform role exchange, then the second horizontal oil cylinder as the working cylinder feeds at the maximum extrusion force and the set extrusion speed, the first horizontal oil cylinder serves as a back pressure cylinder to extrude metal powder with controllable back pressure, and the second horizontal oil cylinder stops acting until the second horizontal oil cylinder reaches the limit position as the working cylinder;
step four: the first horizontal oil cylinder and the second horizontal oil cylinder exchange roles again, the first horizontal oil cylinder is used as a working cylinder to feed at the maximum extrusion force and the set extrusion speed, and the second horizontal oil cylinder is used as a back pressure cylinder to extrude the metal powder at the controllable back pressure;
step five: and repeating the third step and the fourth step until the angular extrusion forming of the controllable back pressure metal powder and other channels is finished after the set pass is reached.
The invention has the beneficial effects that:
the controllable back pressure equal-channel angular extrusion device and method for the metal powder can realize the condition that the extrusion force of a deformation area is kept constant, namely under the condition of constant stress, equal-channel extrusion forming is carried out on the metal powder under the conditions of different temperatures, extrusion speeds and passes, and a block product with good structural property consistency and thermal stability can be obtained; meanwhile, real-time stepless back pressure change can be realized in the equal channel angular extrusion process, so that the extrusion force is changed according to a gradient rule, the size and the performance of internal grains are changed in a gradient manner, and the product with the gradient change of tissues and mechanical properties is prepared.
Drawings
FIG. 1 is a front view of a controlled back pressure metal powder equal channel rotary extrusion apparatus of the present invention;
FIG. 2 is a top view of a controlled back pressure metal powder isopipe extruder apparatus of the present invention;
FIG. 3 is an appearance and morphology diagram of pure aluminum powder particles prepared by an atomization method in the example;
FIG. 4 is a microstructure of the head of a pure aluminum powder sample after a first pass of pressing in the example;
FIG. 5 is a microstructure of a tail portion of a sample of pure aluminum powder after a first pass of pressing in the example;
in the figure, 1-supporting base, 2-top plate, 3-lower backing plate, 4-upper backing plate, 5-lower backing plate, 6-upper backing plate, 7-upper female die, 8-lower female die, 9-ceramic heating plate mounting groove, 10-first extrusion cavity channel, 11-second extrusion cavity channel, 12-first horizontal oil cylinder, 13-second horizontal oil cylinder, 14-vertical oil cylinder, 15-first extrusion male die rod body, and 16-second extrusion male die rod body.
Detailed Description
The invention is described in further detail below with reference to the figures and the specific embodiments.
As shown in fig. 1 and 2, a controllable back pressure metal powder equal channel angular extrusion device comprises an extrusion die system, a hydraulic system and a PLC system; the extrusion die system comprises a supporting base 1, a top plate 2, a lower cushion plate 3, an upper cushion plate 4, a lower base plate 5, an upper base plate 6, an upper female die 7 and a lower female die 8; the lower base plate 3 is horizontally and fixedly arranged on the upper surface of the supporting base 1, the lower base plate 5 is horizontally and fixedly arranged above the lower base plate 3, a ceramic heating plate mounting groove 9 is reserved between the lower base plate 3 and the lower base plate 5, and a ceramic heating plate is mounted in the ceramic heating plate mounting groove 9; the upper substrate 6 is horizontally arranged right above the lower substrate 5, the upper substrate 6 and the lower substrate 5 are in abutting contact fit, the upper padding plate 4 is horizontally and fixedly connected above the upper substrate 6, a ceramic heating plate mounting groove 9 is also reserved between the upper padding plate 4 and the upper substrate 6, and a ceramic heating plate is mounted in the ceramic heating plate mounting groove 9; the top plate 2 is horizontally and fixedly connected to the upper surface of the upper backing plate 4; the lower female die 8 is horizontally clamped on the upper surface of the lower substrate 5, the upper female die 7 is horizontally clamped on the lower surface of the upper substrate 6, the upper female die 7 and the lower female die 8 are buckled together, a first extrusion cavity channel 10 and a second extrusion cavity channel 11 which form an included angle with each other and have the same cross-sectional dimension are formed between the upper female die 7 and the lower female die 8, and the first extrusion cavity channel 10 and the second extrusion cavity channel 11 are communicated with each other at a corner; the hydraulic system comprises a first horizontal oil cylinder 12, a second horizontal oil cylinder 13, a vertical oil cylinder 14 and a hydraulic station; the first horizontal oil cylinder 12 is fixedly arranged at the outer side of the first extrusion cavity channel 10, the first horizontal oil cylinder 12 is overlapped with the central axis of the first extrusion cavity channel 10, a first extrusion male die rod body 15 is coaxially and fixedly arranged at the end part of a piston rod of the first horizontal oil cylinder 12, and the first extrusion male die rod body 15 is matched with the first extrusion cavity channel 10; the second horizontal oil cylinder 13 is fixedly arranged at the outer side of the second extrusion cavity channel 11, the second horizontal oil cylinder 13 is overlapped with the central axis of the second extrusion cavity channel 11, a second extrusion male die rod body 16 is coaxially and fixedly arranged at the end part of a piston rod of the second horizontal oil cylinder 13, and the second extrusion male die rod body 16 is matched with the second extrusion cavity channel 11; the vertical oil cylinder 14 is fixedly arranged right above the top plate 2, a piston rod of the vertical oil cylinder 14 faces downwards, and the end part of the piston rod of the vertical oil cylinder 14 is fixedly connected with the upper surface of the top plate 2; the first horizontal oil cylinder 12, the second horizontal oil cylinder 13 and the vertical oil cylinder 14 are all supplied with oil by a hydraulic station, proportional valves are arranged on oil supply pipelines between the first horizontal oil cylinder 12 and the hydraulic station and between the second horizontal oil cylinder 13 and the hydraulic station, and the flow and the pressure of the first horizontal oil cylinder 12 and the second horizontal oil cylinder 13 are regulated and controlled through the proportional valves; the first horizontal oil cylinder 12 and the second horizontal oil cylinder 13 alternately exchange roles, and when the first horizontal oil cylinder 12 is used as a working cylinder, the second horizontal oil cylinder 13 is used as a back pressure cylinder; when the second horizontal oil cylinder 13 is used as a working cylinder, the first horizontal oil cylinder 12 is used as a back pressure cylinder; the vertical oil cylinder 14 is used as a mold locking cylinder; when the first horizontal oil cylinder 12 or the second horizontal oil cylinder 13 is used as a back pressure cylinder, regulating and controlling the back pressure through a proportional valve; the PLC system is provided with a touch screen, and control instructions are executed on the touch screen, such as an emergency stop instruction, a first horizontal oil cylinder extrusion action instruction, a second horizontal oil cylinder extrusion action instruction, a first horizontal oil cylinder backpressure maintaining instruction, a second horizontal oil cylinder backpressure maintaining instruction, a vertical oil cylinder mold locking action instruction and a temperature control instruction; the touch screen can facilitate the data input and display of the PLC system, so that a large number of input and output devices such as buttons, switches, indicator lamps, nixie tubes and the like can be omitted, and input and output points required by the PLC system are greatly reduced; the change curves of the extrusion force and the back pressure can be displayed and stored on the touch screen, and the position of the metal shearing deformation area and the friction force between the metal and the mold are changed, so that the change curves are expressed as follows under the common conditions: the extrusion force is small in the 1/3 process of the stroke, the extrusion force is rapidly increased when the metal powder enters the middle section of the stroke, the extrusion force is basically kept unchanged at the last extrusion force of the stroke, the fact that the actual pressure stress of the deformation area is also changed according to the rule that the actual pressure stress is small in the initial stage, rapidly increased in the middle stage and basically unchanged in the final stage is shown, and the extrusion force is mainly influenced by the plastic deformation force and the back pressure of the deformation area, so that the purpose of equal-channel extrusion forming of the metal powder under the constant stress condition can be achieved through the controllable back pressure.
The equal-channel angular extrusion method for the controllable back pressure metal powder adopts the equal-channel angular extrusion device for the controllable back pressure metal powder and comprises the following steps of:
the method comprises the following steps: filling metal powder into the first extrusion cavity channel 10 and the second extrusion cavity channel 11, inputting a mold locking force P1 required to be applied by the vertical oil cylinder 14 and a temperature required to be applied by the ceramic heating plate into the touch screen, executing a mold locking action command of the vertical oil cylinder to tightly lock the upper female mold 7 and the lower female mold 8 together, and executing a temperature control command to enable the temperature to reach a set requirement;
step two: under the clamping force P1 of the vertical oil cylinder 14, the first horizontal oil cylinder 12 serves as a working cylinder to feed at the maximum system oil pressure and the set extrusion speed V1, meanwhile, the second horizontal oil cylinder 13 serves as a back pressure cylinder to extrude the metal powder at the set back pressure P2, the change curves of the back pressure and the extrusion force are displayed and stored on a touch screen in real time, the maximum extrusion force P0 is obtained, then, on the basis of the set back pressure P2, the PLC program debugging is carried out by taking the maximum extrusion force P0 as a target, the controllable back pressure P20 is obtained, the condition that the extrusion force of a deformation area is kept constant is realized, namely, equal-channel extrusion forming is carried out on the metal powder under the condition of the constant maximum extrusion force P0;
step three: when the first horizontal oil cylinder 12 serving as a working cylinder reaches a limit position, the first horizontal oil cylinder 12 stops acting, the first horizontal oil cylinder 12 and the second horizontal oil cylinder 13 are exchanged in roles, then the second horizontal oil cylinder 13 serving as the working cylinder feeds with a maximum extrusion force P0 and a set extrusion speed V1, the first horizontal oil cylinder 12 serving as a back pressure cylinder extrudes metal powder with a controllable back pressure P20, and the second horizontal oil cylinder 13 stops acting until the second horizontal oil cylinder 13 serving as the working cylinder reaches the limit position;
step four: the first horizontal cylinder 12 and the second horizontal cylinder 13 are exchanged in roles again, the first horizontal cylinder 12 is used as a working cylinder to feed with the maximum extrusion force P0 and the set extrusion speed V1, and the second horizontal cylinder 13 is used as a back pressure cylinder to extrude the metal powder with the controllable back pressure P20;
step five: and repeating the third step and the fourth step until the angular extrusion forming of the controllable back pressure metal powder and other channels is finished after the set pass is reached.
In this embodiment, the metal powder is pure aluminum powder, and the chemical components thereof are: si (0.1%), Fe (0.15%), Cu (0.02%), O (0.25), wherein the components of Si, Fe, Cu and Al are consistent with the standard components of commercial pure aluminum, but because the aluminum powder has larger specific surface area, an oxide layer is generated on the surface in the atomization preparation process, and therefore, the content of oxygen is higher. As shown in fig. 3, in order to show the appearance of the pure aluminum powder particles prepared by the atomization method, the sizes thereof are different, and the initial average size of the particles is about 35 μm, and the observation of the microstructure shows that each aluminum powder particle comprises a plurality of grains, and the grains are substantially equiaxed and have an average diameter size of about 6.36 μm.
In the embodiment, the upper female die 7, the lower female die 8, the first extrusion male die rod body 15 and the second extrusion male die rod body 16 are all made of H13 hot work die steel, and the heat treatment hardness is HRC 49-52. The first extrusion cavity channel 10 and the second extrusion cavity channel 11 are the same in size and are both 12mm multiplied by 120mm, and clearance fit of H7/g6 is adopted between the first extrusion male die rod body 15 and the first extrusion cavity channel 10 and between the second extrusion male die rod body 16 and the second extrusion cavity channel 11. In order to take account of the larger pass deformation degree and the problem of dead zone, the channel included angle phi is 90 degrees, and the external angle psi is 16 degrees. The range of the mold locking force P1 of the vertical oil cylinder 14 is 300-2000 KN, the range of the main pressure exerted by the first horizontal oil cylinder 12 and the second horizontal oil cylinder 13 is 0-500 KN, the range of the back pressure P2 exerted by the first horizontal oil cylinder 12 and the second horizontal oil cylinder 13 is 10-50 KN, the range of the extrusion speed V1 is 0.1-10 mm/s, and the temperature control range of the ceramic heating plate is 0-999 ℃.
In practice, the temperature was set to 100 ℃ and the maximum pressing force P0 was set to 10KN, pure aluminum powder samples were pressed in a total of four passes, and the density of each pass was measured by the drainage method and the hardness was measured by the microhardness tester, with the results shown in the following table:
TABLE 1 Density and mechanical Properties of the individual samples
As is clear from fig. 4 and 5, the microstructure at the head of the sample is not different from the microstructure at the tail of the sample, and the microstructures are uniform, that is, the pure aluminum powder can be agglomerated only by the first-pass extrusion, the relative density of the pure aluminum powder can reach more than 96%, the relative density of the pure aluminum powder can reach 99% after the four-pass extrusion, and the agglomerated sample has higher strength than the aluminum material.
The embodiments are not intended to limit the scope of the present invention, and all equivalent implementations or modifications without departing from the scope of the present invention are intended to be included in the scope of the present invention.
Claims (1)
1. A controllable back pressure metal powder equal channel angular extrusion method adopts a controllable back pressure metal powder equal channel angular extrusion device, and the device comprises an extrusion die system, a hydraulic system and a PLC system; the extrusion die system comprises a supporting base, a top plate, a lower backing plate, an upper backing plate, a lower substrate, an upper female die and a lower female die; the lower base plate is horizontally and fixedly arranged on the upper surface of the supporting base, the lower base plate is horizontally and fixedly arranged above the lower base plate, a ceramic heating plate mounting groove is reserved between the lower base plate and the lower base plate, and a ceramic heating plate is mounted in the ceramic heating plate mounting groove; the upper base plate is horizontally arranged right above the lower base plate, the upper base plate and the lower base plate are in abutting contact fit, the upper base plate is horizontally and fixedly connected above the upper base plate, a ceramic heating plate mounting groove is also reserved between the upper base plate and the upper base plate, and a ceramic heating plate is mounted in the ceramic heating plate mounting groove; the top plate is horizontally and fixedly connected to the upper surface of the upper base plate; the lower female die is horizontally clamped on the upper surface of the lower substrate, the upper female die is horizontally clamped on the lower surface of the upper substrate, the upper female die and the lower female die are buckled together, a first extrusion cavity channel and a second extrusion cavity channel which form an included angle with each other and have the same section size are formed between the upper female die and the lower female die, and the first extrusion cavity channel and the second extrusion cavity channel are communicated with each other at a corner; the hydraulic system comprises a first horizontal oil cylinder, a second horizontal oil cylinder, a vertical oil cylinder and a hydraulic station; the first horizontal oil cylinder is fixedly arranged on the outer side of the first extrusion cavity channel, the first horizontal oil cylinder is superposed with the central axis of the first extrusion cavity channel, a first extrusion male die rod body is coaxially and fixedly arranged at the end part of a piston rod of the first horizontal oil cylinder, and the first extrusion male die rod body is matched with the first extrusion cavity channel; the second horizontal oil cylinder is fixedly arranged on the outer side of the second extrusion cavity channel, the second horizontal oil cylinder is superposed with the central axis of the second extrusion cavity channel, a second extrusion male die rod body is coaxially and fixedly arranged at the end part of a piston rod of the second horizontal oil cylinder, and the second extrusion male die rod body is matched with the second extrusion cavity channel; the vertical oil cylinder is fixedly arranged right above the top plate, a piston rod of the vertical oil cylinder faces downwards, and the end part of a piston rod of the vertical oil cylinder is fixedly connected with the upper surface of the top plate; the first horizontal oil cylinder, the second horizontal oil cylinder and the vertical oil cylinder are all supplied with oil by a hydraulic station, proportional valves are arranged on oil supply pipelines between the first horizontal oil cylinder and the hydraulic station and between the second horizontal oil cylinder and the hydraulic station, and the flow and the pressure of the first horizontal oil cylinder and the second horizontal oil cylinder are regulated and controlled through the proportional valves; the first horizontal oil cylinder and the second horizontal oil cylinder alternately exchange roles, and when the first horizontal oil cylinder is used as a working cylinder, the second horizontal oil cylinder is used as a back pressure cylinder; when the second horizontal oil cylinder is used as a working cylinder, the first horizontal oil cylinder is used as a back pressure cylinder; the vertical oil cylinder is used as a mold locking cylinder; when the first horizontal oil cylinder or the second horizontal oil cylinder is used as a back pressure cylinder, regulating and controlling the back pressure through a proportional valve; the PLC system is provided with a touch screen, and control instructions are executed on the touch screen; the method is characterized by comprising the following steps:
the method comprises the following steps: filling metal powder into the first extrusion cavity channel and the second extrusion cavity channel, inputting a mold locking force required to be applied by a vertical oil cylinder and a temperature required to be applied by a ceramic heating plate into the touch screen, executing a mold locking action command of the vertical oil cylinder to tightly buckle the upper female mold and the lower female mold together, and executing a temperature control command to enable the temperature to reach a set requirement;
step two: under the mold locking force of the vertical oil cylinder, the first horizontal oil cylinder serves as a working cylinder to feed at the maximum system oil pressure and the set extrusion speed, the second horizontal oil cylinder serves as a back pressure cylinder to extrude the metal powder by setting back pressure, the change curves of the back pressure and the extrusion force are displayed and stored on a touch screen in real time, the maximum extrusion force is obtained, then PLC program debugging is carried out on the basis of the set back pressure by taking the maximum extrusion force as a target, the controllable back pressure is obtained, the condition that the extrusion force of a deformation area is kept constant is realized, and equal-channel extrusion forming of the metal powder is realized under the condition of the constant maximum extrusion force;
step three: when the first horizontal oil cylinder as a working cylinder reaches a limit position, the first horizontal oil cylinder stops acting, the first horizontal oil cylinder and the second horizontal oil cylinder perform role exchange, then the second horizontal oil cylinder as the working cylinder feeds at the maximum extrusion force and the set extrusion speed, the first horizontal oil cylinder serves as a back pressure cylinder to extrude metal powder with controllable back pressure, and the second horizontal oil cylinder stops acting until the second horizontal oil cylinder reaches the limit position as the working cylinder;
step four: the first horizontal oil cylinder and the second horizontal oil cylinder exchange roles again, the first horizontal oil cylinder is used as a working cylinder to feed at the maximum extrusion force and the set extrusion speed, and the second horizontal oil cylinder is used as a back pressure cylinder to extrude the metal powder at the controllable back pressure;
step five: and repeating the third step and the fourth step until the angular extrusion forming of the controllable back pressure metal powder and other channels is finished after the set pass is reached.
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| CN113828777B (en) * | 2021-10-28 | 2023-07-21 | 四川科匠轻金属材料科技有限公司 | Device and process for preparing high-strength alloy by semi-continuous extrusion of metal powder |
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