CN114453581B - Powder metallurgy high-strength high-conductivity aluminum material and preparation method thereof - Google Patents
Powder metallurgy high-strength high-conductivity aluminum material and preparation method thereof Download PDFInfo
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- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 title claims abstract description 114
- 229910052782 aluminium Inorganic materials 0.000 title claims abstract description 55
- 239000000463 material Substances 0.000 title claims abstract description 54
- 238000002360 preparation method Methods 0.000 title claims abstract description 14
- 238000004663 powder metallurgy Methods 0.000 title claims abstract description 13
- 239000000843 powder Substances 0.000 claims abstract description 98
- 238000005245 sintering Methods 0.000 claims abstract description 29
- 238000000034 method Methods 0.000 claims abstract description 28
- 239000002245 particle Substances 0.000 claims abstract description 28
- 238000002156 mixing Methods 0.000 claims abstract description 12
- 238000002490 spark plasma sintering Methods 0.000 claims abstract description 9
- 230000001590 oxidative effect Effects 0.000 claims abstract description 4
- 239000002344 surface layer Substances 0.000 claims abstract description 3
- 238000010438 heat treatment Methods 0.000 claims description 18
- 238000000498 ball milling Methods 0.000 claims description 14
- 238000003825 pressing Methods 0.000 claims description 13
- 230000008569 process Effects 0.000 claims description 11
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 10
- 229910002804 graphite Inorganic materials 0.000 claims description 10
- 239000010439 graphite Substances 0.000 claims description 10
- 238000001816 cooling Methods 0.000 claims description 9
- 229910018072 Al 2 O 3 Inorganic materials 0.000 claims description 8
- 239000000919 ceramic Substances 0.000 claims description 5
- 239000011521 glass Substances 0.000 claims description 5
- 238000012216 screening Methods 0.000 claims description 4
- 238000011049 filling Methods 0.000 claims description 3
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- 238000006243 chemical reaction Methods 0.000 claims 1
- 239000002994 raw material Substances 0.000 abstract description 5
- 238000005275 alloying Methods 0.000 abstract description 4
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- 229910001295 No alloy Inorganic materials 0.000 description 1
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- 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
- B22F3/10—Sintering only
- B22F3/105—Sintering only by using electric current other than for infrared radiant energy, laser radiation or plasma ; by ultrasonic bonding
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/02—Making metallic powder or suspensions thereof using physical processes
- B22F9/04—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/04—Making non-ferrous alloys by powder metallurgy
- C22C1/05—Mixtures of metal powder with non-metallic powder
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C21/00—Alloys based on aluminium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C32/00—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ
- C22C32/001—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ with only oxides
- C22C32/0015—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ with only oxides with only single oxides as main non-metallic constituents
- C22C32/0036—Matrix based on Al, Mg, Be or alloys thereof
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
- C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
- C23C8/10—Oxidising
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- 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
- B22F3/10—Sintering only
- B22F3/105—Sintering only by using electric current other than for infrared radiant energy, laser radiation or plasma ; by ultrasonic bonding
- B22F2003/1051—Sintering only by using electric current other than for infrared radiant energy, laser radiation or plasma ; by ultrasonic bonding by electric discharge
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/02—Making metallic powder or suspensions thereof using physical processes
- B22F9/04—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling
- B22F2009/043—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling by ball milling
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/25—Process efficiency
Abstract
The invention discloses a powder metallurgy high-strength high-conductivity aluminum material and a preparation method thereof, wherein the preparation method comprises the following steps: the first step, preparing powder and sieving, preparing spherical pure aluminum powder, and sieving to obtain two kinds of powder with particle size ranges of ultrafine powder and coarse powder, wherein the particle size of the ultrafine powder is less than 3 mu m, and the particle size of the coarse powder is distributed in the range of 5-10 mu m; second, pre-oxidizing the powder to oxidize the surface layer of the powder and form Al on the surface of the powder 2 O 3 A film; thirdly, mixing powder, namely mixing the pre-oxidized superfine aluminum powder and coarse pure aluminum powder, wherein the superfine pure aluminum powder accounts for 50-100%, and the coarse pure aluminum powder accounts for 0-50%; if the powder is completely ultra-fine pure aluminum powder, the step is skipped; and fourthly, sintering, namely preparing the high-strength high-conductivity aluminum material through spark plasma sintering. The method does not depend on addition of alloying elements, reduces the cost of raw materials, does not obviously reduce the conductivity of the aluminum material while improving the strength of the aluminum material, and prepares the aluminum material with high strength, high conductivity and low density.
Description
Technical Field
The invention relates to the field of high-strength high-conductivity aluminum alloy, in particular to a powder metallurgy high-strength high-conductivity aluminum material and a preparation method thereof.
Background
The mechanical strength and the electrical conductivity are two important indexes for measuring the performance of the metal conductor material, the high mechanical strength is beneficial to bearing the self weight and resisting the external mechanical load, and the good electrical conductivity can reduce the electric energy loss and improve the transmission efficiency. However, the two key indicators strength and conductivity are often in an inverted relationship, i.e., an increase in one indicator often results in a decrease in the other.
Pure aluminum has the advantages of low density, high conductivity, low cost and the like, has wide application prospects in industries such as power electronics, aerospace and the like, but has low strength, and greatly limits the application range of the pure aluminum as a metal conductor. For example, in the field of power transmission, aluminum steel-cored wires are commonly used for overhead power transmission lines due to insufficient strength of pure aluminum, and the addition of a high-density steel core greatly increases the structural weight of the wire.
In order to improve the strength of the aluminum material, two methods are generally used. One method is to obtain various grades of aluminum alloys by adding alloying elements. This method can greatly improve the strength of the alloy by the principles of solid solution strengthening, second phase precipitation strengthening, and the like, but also causes several problems: (1) After the alloy elements are added, lattice distortion is generated on an aluminum matrix, electrons are obviously scattered, and the conductivity of the alloy is reduced; (2) The addition of alloying elements increases the cost of raw materials and increases the difficulty of smelting, processing and recycling of the aluminum alloy. For example, the aluminum alloys for overhead conductors with designations 6201 and 6101, after the processes of solution treatment, cold drawing, artificial aging and the like, the strength can reach 250-330MPa, but the conductivity is only 57-52% IACS, which is much lower than that of pure aluminum.
Another strengthening method is to adopt the violent plastic deformation technology to refine the grain size (d) of the material on the premise of not changing the chemical components of the aluminum material. According to the classical Hall-Petch relation, when the grain size of the material is refined to the ultra-fine grain (d < 1 μm) or nano-grain (d < 100 nm) range, the strength of the material can be greatly improved. However, the aluminum materials obtained by such techniques typically contain a large number of dislocations and low-angle grain boundaries, and these structural defects also significantly reduce the electrical conductivity of the material. In addition, the micro-nano structures are thermodynamically unstable, and crystal grain growth can occur in the actual service process, so that the performance of the material is degraded.
The invention develops a new method, and the powder metallurgy technical route is adopted to prepare the high-strength high-conductivity aluminum material with adjustable performance. Firstly, pre-oxidized superfine aluminium powder (the size of powder particles, D is less than 3 mu m) and coarse aluminium powder (D is less than 5 mu m and less than 10 mu m) are mixed according to a certain proportion, and then the mixture can be successfully prepared by the discharge plasma sintering technologyHigh strength, high conductivity, low density aluminum material (tensile strength > 120MPa, conductivity > 58% IACS, density ≤ 2.7g/cm 3 ). Compared with other methods, the method has the characteristics of low raw material cost, simple preparation process, outstanding material performance and the like, and is suitable for mass production.
Disclosure of Invention
The invention aims to break through the inverted relation of strength and conductivity of the aluminum material, and aims at solving the problems of complex preparation process, high raw material cost and the like of the high-strength high-conductivity aluminum alloy.
The technical scheme of the invention is as follows:
a preparation method of a powder metallurgy high-strength high-conductivity aluminum material comprises the following steps:
the first step, preparing powder and sieving, preparing spherical pure aluminum powder, sieving to obtain two kinds of powder with particle size ranges of ultrafine powder and coarse powder, wherein the particle size of the ultrafine powder is less than 3 mu m, and the particle size of the coarse powder is distributed in the range of 5-10 mu m; the size of the powder plays an important role in the strength and the electric conductivity of the material, and the undersize can cause the sintering performance of the material to be poor and simultaneously reduce the strength and the electric conductivity; and an excessive size may result in a decrease in the strength of the material. In addition, the particle size difference between the ultrafine powder and the coarse powder should be appropriate to avoid the fine powder not filling the gaps between the coarse powders. In view of the above, the particle sizes of the above-described optimum ultrafine powder and coarse powder are given.
Second, pre-oxidizing the powder to oxidize the surface layer of the powder and form Al on the surface of the powder 2 O 3 A film; the purpose of this step is to form Al on the powder surface 2 O 3 Film of Al 2 O 3 The film is amorphous Al 2 O 3 Amorphous Al in the subsequent sintering process 2 O 3 Will be transformed into gamma-Al 2 O 3 And the powder becomes a particle reinforced phase, so that the microstructure thermal stability of the powder in the subsequent sintering process can be improved, and the strength of the block material can be improved. In addition, al on the surface of atomized aluminum powder 2 O 3 Thickness of the film2nm-4nm, adding a powder pre-oxidation step to enable Al to be in a range of 2 O 3 The thickness of the film is saturated, so that the number of particle reinforced phases in the sintered sample is increased, and the strength of the sample is improved.
Thirdly, mixing powder, namely mixing the pre-oxidized superfine aluminum powder and coarse pure aluminum powder, wherein the superfine pure aluminum powder accounts for 50-100%, and the coarse pure aluminum powder accounts for 0-50%; if the powder is completely ultra-fine pure aluminum powder, the step is skipped;
and fourthly, sintering, namely preparing the high-strength high-conductivity aluminum material through spark plasma sintering.
In particular, the second step is specifically: uniformly spreading superfine pure aluminum powder or coarse pure aluminum powder in a ceramic square boat, then putting the square boat into a box-type resistance furnace at the temperature of 100-200 ℃, keeping the temperature for 30min, then taking out the square boat, uniformly stirring the aluminum powder by using a glass rod, putting the square boat into the box-type resistance furnace again, repeating the process for 3-5 times, finally taking out the square boat, and placing the square boat in an air environment to cool the square boat to room temperature.
Particularly, in the third step, a planetary ball mill is used for mixing powder, pre-oxidized superfine pure aluminum powder and crude pure aluminum powder are placed into a ball milling tank according to a certain volume fraction ratio, then a ball with the diameter not larger than 3mm is placed into the ball milling tank, the mass ratio of the ball to the aluminum powder is 5.
In particular, the fourth step is specifically: firstly, uniformly filling graphite paper in the inner wall of a graphite mould, then putting a certain mass of powder into the mould, and compacting the powder by using an upper pressing head and a lower pressing head; putting the mold filled with the powder into an SPS sintering furnace, vacuumizing at room temperature, and when the vacuum degree in the furnace is less than 10 -2 After Pa, pressurizing at the speed of 5MPa/min to enable the pressure intensity to reach 25MPa; when the vacuum degree is less than 10 -3 After Pa, starting heating at the speed of 100 ℃/min, heating to 400 ℃, and keeping the temperature for 20min; then increasing the pressure to 50MPa at the speed of 5MPa/min, and continuing to keep the temperature for 20min; increasing pressure to 50-100MPa at speed of 5MPa/min, increasing temperature to 500-600 deg.C at speed of 50 deg.C/min, sintering for 15-30min, stopping heating, cooling to 100 deg.C, unloading, and coolingCooling to room temperature and taking out. Because the specific surface area of the ultrafine powder is large, gas is easily adsorbed on the surface of the powder, so that sintering is difficult, and a compact sample is difficult to obtain; through the stepped pressurization and heating sintering, the method is beneficial to fully removing gas on the surface of the powder and improving the compactness of a sample. A powder metallurgy high-strength high-conductivity aluminum material is prepared by the preparation method.
Particularly, the average grain size of the high-strength high-conductivity aluminum material is less than or equal to 6 mu m, and a large amount of Al is distributed on the grain boundary 2 O 3 And (3) granules.
In particular, the high-strength and high-conductivity aluminum material has tensile strength of more than 120MPa, electric conductivity of more than 58 percent IACS and density of less than or equal to 2.7g/cm 3 。
Compared with the prior art, the invention has the following remarkable advantages:
firstly, the invention uses pure aluminum powder for sintering, the inside of the structure is clean, no alloy element is added, and the conductivity of the aluminum material is only equal to the intrinsic conductivity, the grain boundary density and the Al of the aluminum 2 O 3 The quantity is related; the aluminum material with fine grains is obtained by sintering the mixed powder of the superfine aluminum powder and the coarse powder, so that the strength of the aluminum material is improved. In addition, the reinforcing mechanism does not depend on the addition of alloying elements, the cost of raw materials is reduced, and the conductivity of the alloy is not obviously reduced while the strength is improved.
Secondly, the invention uses pure aluminum powder for sintering, and the density of the aluminum material is less than or equal to 2.7g/cm 3 。
Thirdly, the preparation process is simple, and the high-strength and high-conductivity aluminum material can be obtained without heat treatment and large plastic deformation. Through step-type pressurization and heating, the gas on the surface of the powder can be fully removed, the vacuum degree in the sintering process is maintained, and a sintered sample is compact.
Fourthly, the grain sizes of the samples sintered by the ultrafine powder and the coarse powder are close to the original grain size of the powder, so that the sample sintered by the ultrafine powder has small grain size and Al 2 O 3 The number is large, the strength is high, the grain boundary density is high, and the conductivity is low; and the coarse powder sintered sample has low strength and high conductivity. According to the mixing law, the strength and the electric conductivity of the aluminum material can be regulated and controlled by regulating and controlling the proportion of the superfine aluminum powder and the coarse aluminum powderAnd the performance of the aluminum material is adjustable and controllable.
Fifthly, the invention controls the Al on the powder surface by pre-oxidizing the powder 2 O 3 Film of Al 2 O 3 The film is amorphous Al 2 O 3 Amorphous Al in the subsequent sintering process 2 O 3 Will be transformed into gamma-Al 2 O 3 And the particles become a particle reinforced phase, so that the strength of the sample is improved.
Drawings
FIG. 1 is a SEM image of high strength and high conductivity aluminum material prepared in example 1 of the present invention;
FIG. 2 is a SEM image of the high-strength and high-conductivity aluminum material prepared in example 2 of the present invention;
FIG. 3 is a tensile engineering stress-strain curve of high strength and high conductivity aluminum material prepared by examples 1,2 and 3 of the present invention.
Detailed Description
The invention is further defined in the following, but not limited to, the figures and examples in the description.
Example 1:
the first step is as follows: powder making
Superfine pure aluminum powder with the particle size of less than 3 mu m is prepared by a gas atomization method under the Ar gas environment, and the powder purity is 99.9 percent.
The second step is that: powder pre-oxidation
10g of superfine pure aluminum powder is uniformly paved in a ceramic square boat with the diameter of 100mm x 50mm x 20mm, then the square boat is placed in a box-type resistance furnace with the temperature of 100 ℃, the square boat is taken out after heat preservation for 30min, the aluminum powder is uniformly stirred by a glass rod and then is placed back in the box-type resistance furnace, the process is repeated for 5 times, and finally the square boat is placed in an air environment and cooled to the room temperature.
The third step: mixed powder
This step is skipped since all ultra-fine pure aluminum powders are used for sintering.
The fourth step: sintering
Graphite paper with the thickness of 1mm is uniformly padded in the inner wall of a graphite mold, 5g of powder is put into the mold, the powder is sealed by an upper pressing head and a lower pressing head, the inner diameter of the mold is 15.2mm, and the diameter of the pressing head is 15mm. Placing the mold filled with the powder into SPS sinteringVacuumizing at room temperature in a sintering furnace, and when the vacuum degree in the furnace is less than 10 -2 After Pa, pressurizing at the speed of 5MPa/min to enable the pressure to reach 25MPa; when the vacuum degree is less than 10 -3 After Pa, starting heating at the speed of 100 ℃/min, heating to 400 ℃, and keeping the temperature for 20min; then increasing the pressure to 50MPa at the speed of 5MPa/min, and continuously preserving the heat for 20min; keeping the pressure of 50MPa, finally increasing the temperature to 580 ℃ at the speed of 50 ℃/min, sintering for 20min, then stopping heating, cooling to 100 ℃ along with the furnace, unloading and continuously cooling to the room temperature.
SEM morphology photograph of sample prepared by the above method in this example is shown in FIG. 1, the average grain size is about 1.3 μm, and a large amount of Al is distributed on the grain boundary 2 O 3 Particles; the stress-strain curve is shown in FIG. 3, the room-temperature tensile strength is 207MPa, the elongation at break is 12%, and the electrical conductivity is 58.3% IACS.
Example 2:
the first step is as follows: powder making
Preparing pure aluminum powder with the particle size of less than 10 mu m by a gas atomization method in an Ar gas environment, wherein the purity of the powder is not less than 99.9 percent. The powder with different particle sizes is divided into two types of ultra-fine powder and coarse powder through screening by a screen, wherein the ultra-fine powder is pure aluminum powder with the particle size of less than 3 mu m; the coarse powder is pure aluminum powder with the particle size of 5-10 mu m.
The second step is that: powder pre-oxidation
10g of superfine pure aluminum powder is uniformly paved in a ceramic square boat with the thickness of 100mm x 50mm x 20mm, then the square boat is placed in a box-type resistance furnace with the temperature of 100 ℃, the square boat is taken out after heat preservation for 30min, the aluminum powder is uniformly stirred by a glass rod, the process is repeated for 5 times, and finally the square boat is placed in an air environment and cooled to the room temperature. The coarse powder and the superfine powder are processed in the same way
The third step: mixed powder
The powder mixing was performed using a planetary ball mill. Pre-oxidized superfine pure aluminum powder and coarse pure aluminum powder are mixed according to the proportion of 3:1 is put into a ball milling tank. Then placing a ball with the diameter of 3mm into a ball milling tank, wherein the mass ratio of the ball to the aluminum powder is 5:1, the ball milling tank and the ball are made of stainless steel. The ball milling speed is 100rpm, and the ball milling time is 6h.
The fourth step: sintering
And after the materials are mixed, preparing the high-strength and high-conductivity aluminum material by a discharge plasma sintering technology. Graphite paper with the thickness of 1mm is uniformly padded in the inner wall of a graphite mold, 5g of powder is put into the mold, the powder is sealed by an upper pressing head and a lower pressing head, the inner diameter of the mold is 15.2mm, and the diameter of the pressing head is 15mm. Putting the mold filled with the powder into an SPS sintering furnace, vacuumizing at room temperature, and when the vacuum degree in the furnace is less than 10 -2 After Pa, pressurizing at the speed of 5MPa/min to enable the pressure to reach 25MPa; when the vacuum degree is less than 10 -3 After Pa, starting heating at the speed of 100 ℃/min, heating to 400 ℃, and keeping the temperature for 20min; then increasing the pressure to 50MPa at the speed of 5MPa/min, and continuously preserving the heat for 20min; keeping the pressure of 50MPa, finally increasing the temperature to 550 ℃ at a speed of 50 ℃/min, sintering for 20min, then stopping heating, cooling to 100 ℃ along with the furnace, unloading and continuously cooling to the room temperature.
In the present example, the SEM image of the sample prepared by the above method is shown in FIG. 2, and in comparative example 1, the structure of example 2 has large-sized grains, the average grain size is about 2.8 μm, the grain boundary density is low, and Al is present in the structure 2 O 3 Since the content is low, grain boundary strengthening reduces the strength of the sample and increases the conductivity, while reducing crystal defects. The stress-strain curve is shown in FIG. 3, the room-temperature tensile strength is 140MPa, the elongation at break is 27%, and the electrical conductivity is 59.6% IACS.
Example 3:
the first step is as follows: powder making
Preparing pure aluminum powder with the particle size of less than 10 mu m by a gas atomization method in an Ar gas environment, wherein the purity of the powder is not less than 99.9 percent. The powder with different particle sizes is divided into two types of ultra-fine powder and coarse powder through screening by a screen, wherein the ultra-fine powder is pure aluminum powder with the particle size of less than 3 mu m; the coarse powder is pure aluminum powder with the particle size of 5-10 mu m.
The second step: powder pre-oxidation
10g of superfine pure aluminum powder is uniformly paved in a ceramic square boat with the thickness of 100mm x 50mm x 20mm, then the square boat is placed in a box-type resistance furnace with the temperature of 100 ℃, the square boat is taken out after heat preservation for 30min, the aluminum powder is uniformly stirred by a glass rod, the process is repeated for 5 times, and finally the square boat is placed in an air environment and cooled to the room temperature. The coarse powder is processed in the same way as the ultra-fine powder.
The third step: mixed powder
The powder mixing was performed using a planetary ball mill. Pre-oxidized superfine pure aluminum powder and coarse pure aluminum powder are mixed according to the proportion of 1:1 is put into a ball milling tank. Then placing a ball with the diameter of 3mm into a ball milling tank, wherein the mass ratio of the ball to the aluminum powder is 5:1, the ball milling tank and the ball are made of stainless steel. The ball milling speed is 100rpm, and the ball milling time is 6h.
The fourth step: sintering
And after the mixing is finished, preparing the high-strength and high-conductivity aluminum material by using a spark plasma sintering technology. Graphite paper with the thickness of 1mm is uniformly padded in the inner wall of a graphite mould, 5g of powder is put into the mould, the powder is sealed by an upper pressing head and a lower pressing head, the inner diameter of the mould is 15.2mm, and the diameter of the pressing head is 15mm. Putting the mold filled with the powder into an SPS sintering furnace, vacuumizing at room temperature, and when the vacuum degree in the furnace is less than 10 -2 After Pa, pressurizing at the speed of 5MPa/min to enable the pressure to reach 25MPa; when the vacuum degree is less than 10 -3 After Pa, starting heating at the speed of 100 ℃/min, heating to 400 ℃, and keeping the temperature for 20min; then increasing the pressure to 50MPa at the speed of 5MPa/min, and continuing to keep the temperature for 20min; keeping the pressure of 50MPa, finally increasing the temperature to 525 ℃ at the speed of 50 ℃/min, sintering for 20min, then stopping heating, cooling to 100 ℃ along with the furnace, unloading and continuously cooling to the room temperature.
The sample prepared in this example by the above-mentioned method had an average crystal grain size of about 5.2 μm, a tensile strength at room temperature of 121MPa, an elongation at break of 48%, and an electrical conductivity of 60.3% IACS. The stress-strain curve is shown in fig. 3.
Table 1 shows the tensile strength and conductivity of examples 1,2, and 3 and conventional cast high purity aluminum (purity 99.9%), and it can be seen that the present invention improves strength without significantly reducing conductivity, and achieves a good combination of strength and conductivity.
TABLE 1
| Test specimen | Tensile strength/MPa | Conductivity/% IACS |
| Example 1 | 207 | 58.3 |
| Example 2 | 140 | 59.6 |
| Example 3 | 121 | 60.3 |
| Conventional casting high-purity aluminum (purity 99.9%) | 60 | 62.6 |
The above embodiments are only used for illustrating the design idea and features of the present invention, and the purpose of the present invention is to enable those skilled in the art to understand the content of the present invention and implement the present invention accordingly, and the protection scope of the present invention is not limited to the above embodiments. Therefore, all equivalent changes or modifications based on the principles and design concepts disclosed herein are intended to be included within the scope of the present invention.
Claims (6)
1. A preparation method of a powder metallurgy high-strength high-conductivity aluminum material is characterized by comprising the following steps:
the method comprises the following steps of firstly, preparing powder and screening, preparing spherical pure aluminum powder, and screening to obtain two kinds of powder with particle size ranges of superfine pure aluminum powder and coarse pure aluminum powder, wherein the particle size of the superfine pure aluminum powder is less than 3 mu m, and the particle size of the coarse pure aluminum powder is distributed in the range of 5-10 mu m;
secondly, pre-oxidizing the powder to oxidize the surface layer of the powder and generate amorphous Al on the surface of the powder 2 O 3 A film; the second step is specifically as follows: uniformly spreading the superfine pure aluminum powder or the coarse pure aluminum powder in a ceramic square boat, then putting the square boat into a box-type resistance furnace at the temperature of 100-200 ℃, keeping the temperature for 30min, then taking out the square boat, uniformly stirring the superfine pure aluminum powder or the coarse pure aluminum powder by using a glass rod, putting the square boat into the box-type resistance furnace again, repeating the process for 3 to 5 times, finally taking out the square boat, and placing the square boat in an air environment to cool the square boat to the room temperature;
thirdly, mixing powder, namely mixing the pre-oxidized superfine pure aluminum powder and the crude pure aluminum powder, wherein the superfine pure aluminum powder accounts for 50-100% and the crude pure aluminum powder accounts for 0-50%; if the powder is completely ultra-fine pure aluminum powder, the step is skipped;
fourthly, sintering, namely preparing the high-strength high-conductivity aluminum material by spark plasma sintering, wherein the amorphous Al is 2 O 3 Conversion to gamma-Al 2 O 3 Become a particle reinforced phase, and a large amount of Al is distributed on the grain boundary of the high-strength high-conductivity aluminum material 2 O 3 Particles; the tensile strength of the high-strength high-conductivity aluminum material is more than 120MPa, and the electric conductivity is more than 58 percent IACS.
2. The preparation method of the powder metallurgy high-strength high-conductivity aluminum material as claimed in claim 1, wherein in the third step, a planetary ball mill is used for mixing powder, the pre-oxidized superfine pure aluminum powder and coarse pure aluminum powder are placed into a ball milling tank according to a certain volume fraction ratio, then a ball with the diameter not more than 3mm is placed into the ball milling tank, the mass ratio of the ball to the mixed pure aluminum powder is 5.
3. The preparation method of the powder metallurgy high-strength high-conductivity aluminum material as set forth in claim 1, wherein the fourth step is specifically: firstly, uniformly filling graphite paper in a graphite mouldPutting a certain mass of powder into a die in the inner wall of the die, and compacting the powder by using an upper pressing head and a lower pressing head; putting the mold filled with the powder into an SPS sintering furnace, vacuumizing at room temperature, and when the vacuum degree in the furnace is less than 10 -2 After Pa, pressurizing at the speed of 5MPa/min to enable the pressure to reach 25MPa; when the vacuum degree is less than 10 -3 After Pa, starting heating at the speed of 100 ℃/min, heating to 400 ℃, and keeping the temperature for 20min; then increasing the pressure to 50MPa at the speed of 5MPa/min, and continuing to keep the temperature for 20min; then increasing the pressure to 50-100MPa at the speed of 5MPa/min, finally increasing the temperature to 500-600 ℃ at the speed of 50 ℃/min, sintering for 15-30min, then stopping heating, cooling to 100 ℃ along with the furnace, unloading, cooling to room temperature, and taking out.
4. A powder metallurgy high-strength high-conductivity aluminum material, characterized by being prepared by the preparation method of any one of claims 1 to 3.
5. The powder metallurgy high-strength high-conductivity aluminum material as set forth in claim 4, wherein the average grain size of the high-strength high-conductivity aluminum material is 6 μm or less, and a large amount of Al is distributed on grain boundaries 2 O 3 And (3) granules.
6. The powder metallurgy high-strength high-conductivity aluminum material as claimed in claim 4 or 5, wherein the tensile strength of the high-strength high-conductivity aluminum material is more than 120MPa, the conductivity is more than 58% IACS, the density is less than or equal to 2.7g/cm 3 。
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