A method for preparing graphene-aluminum matrix composite material by in-situ exfoliating graphite and graphene-aluminum matrix composite material

Abstract

The application discloses a method for preparing graphene aluminum matrix composite material by in-situ exfoliation of graphite and graphene aluminum matrix composite material, and belongs to the technical field of aluminum matrix composite material. Spherical graphite and aluminum powder are mixed, dried under vacuum condition of a binder and an organic solvent, and the mixed powder is sealed in a polyurethane cover and placed into cold isostatic pressing equipment for cold pressing, then is placed into a vacuum heating furnace for vacuum degassing, and finally is extruded through different plastic deformation amounts to prepare graphene aluminum composite materials with different graphene contents. The material can be applied to high-strength and high-toughness aluminum alloy plate and high-strength and high-conductivity aluminum alloy guide rod and the like products as an intermediate alloy of a continuous casting and rolling production line.

Description

Technical Field

[0001] This invention relates to the field of aluminum-based composite materials technology, specifically to a method for preparing graphene aluminum-based composite materials by in-situ exfoliation of graphite and the graphene aluminum-based composite materials themselves. Background Technology

[0002] Graphene is a two-dimensional nanomaterial composed of carbon atoms, exhibiting a single-layer sheet structure with a unique two-dimensional honeycomb crystal structure and extremely high bond strength. Its strength reaches 130 GPa, Young's modulus is approximately 1100 GPa, and fracture strength is approximately 125 GPa. It is the material with the lowest resistivity in the world (resistivity of only about 10 nΩ·m), and its conductivity is about 100 times that of copper. Utilizing graphene's high strength and excellent conductivity, and combining it with pure aluminum or aluminum composite materials to prepare graphene / aluminum composites can effectively improve the strength and conductivity of aluminum cables, achieving a better match between the mechanical and electrical properties of graphene-aluminum alloy cables, thus meeting the market's urgent demand for new aluminum alloy cables with high strength and good conductivity. Current research on graphene dispersion in aluminum matrices largely focuses on how to uniformly disperse graphene within the aluminum matrix. The powder metallurgy process used in this approach has a long processing route and excessively high preparation costs, failing to meet industrialization requirements. Achieving a short-process, low-cost, and high-performance preparation of graphene-aluminum composite materials will be crucial for their industrial application. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing graphene-aluminum matrix composites by in-situ exfoliation of graphite and the graphene-aluminum matrix composites themselves. First, spherical graphite, aluminum powder, binder, and organic solvent are mixed and dried under vacuum conditions. The resulting mixed powder is then sealed in a polyurethane sleeve and placed in a cold isostatic pressing apparatus for cold pressing. Next, it is placed in a vacuum heating furnace for vacuum degassing. Finally, graphene-aluminum matrix composites with different graphene contents are prepared by extrusion with different plastic deformation amounts. This material can be used as an intermediate alloy in continuous casting and rolling production lines for large-scale application in high-strength and high-toughness aluminum alloy plates and high-strength and high-conductivity aluminum alloy guide rods, etc., which is of great significance for the industrialization of graphene-aluminum alloys.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A method for preparing graphene-aluminum matrix composites by in-situ exfoliation of graphite, the method comprising the following steps:

[0006] (1) Mixed drying:

[0007] A certain mass of organic solvent and binder is poured into a stirring drying kettle, and then a certain mass of spherical graphite is added and mixed evenly. After adding aluminum-based powder, a mixed slurry is obtained. The mixed slurry is mixed and dried under stirring and vacuum conditions for a certain time to obtain a uniform mixed powder.

[0008] (2) Cold pressing preforming:

[0009] The mixed powder obtained in step (1) is transferred into a bag under vacuum or nitrogen protection. The bag is placed on an electromagnetic vibration table, filled and vibrated to compact the powder, and then vacuum-sealed. The bag is then placed in a cold isostatic pressing chamber for cold pressing to obtain a graphite aluminum-based rod.

[0010] (3) Vacuum sintering:

[0011] After the graphite aluminum-based rods are removed from the cold isostatic pressing equipment, they are placed in a vacuum sintering furnace for vacuum sintering. After sintering, they are naturally cooled to room temperature, and then the graphite aluminum-based rods are removed and machined for later use.

[0012] (4) Hot extrusion into rods:

[0013] The machined graphene aluminum-based rods are placed in a heat treatment furnace along with the extrusion die and heated at 500-550℃ for 3 hours. After being removed, they are put into an extruder for hot extrusion and finally processed into graphene aluminum-based composite rods of the required diameter (e.g., 1-10mm).

[0014] In step (1) above, the organic solvent is one or more of anhydrous methanol, anhydrous ethanol and acetone, and the mass fraction of the organic solvent in the mixed slurry is 20-40 wt%; the binder is one or two of polyamide and paraffin, and the mass fraction of the binder in the mixed slurry is 0.1-5 wt%.

[0015] In step (1) above, the median particle size of the spherical graphite is 0.5-15μm, the purity is above 99.5%, the oxygen content is ≤500ppm, and the water content is ≤800ppm; the mass fraction of spherical graphite in the mixed slurry is 5%-15%.

[0016] In step (1) above, the aluminum-based powder has a particle size range of 5-15 μm, a purity of ≥99.5%, an oxygen content ≤1000 ppm, and a water content ≤500 ppm. The aluminum-based powder is pure aluminum powder, aluminum alloy powder, or aluminum-based composite material powder.

[0017] In step (1) above, during the mixing and drying process, the vacuum degree of mixing and stirring is 500Pa-1KPa, the mixing and drying time is 6-12h, and the drying temperature is 70-120℃.

[0018] In step (2) above, the holding pressure of the cold isostatic pressing is 150-210 MPa, and the holding time is 2-5 min.

[0019] In step (2) above, the bag material is polyurethane or rubber, and the inner diameter of the bag is 140mm-200mm.

[0020] In step (3) above, during the vacuum sintering process, the vacuum degree is greater than 10 Pa, the sintering temperature is 600-650℃, and the holding time is 100-200 min.

[0021] The design mechanism of this invention is as follows:

[0022] 1. This invention uses spherical graphite mixed with aluminum-based powder, which is easy to cold press into shape. The graphite-aluminum-based round rod has high density, and the graphite is evenly dispersed inside the aluminum matrix. Compared with flake graphite, spherical graphite can further reduce the contact area between carbon and aluminum matrix. Under cold pressing, it can achieve contact and bonding between aluminum, which plays a key role in the density of cold pressing.

[0023] 2. The present invention uses additives such as alcohols, polyamides or paraffin binders to further bond the spherical aluminum-based powder with the spherical graphite particles, thereby reducing the agglomeration of graphite particles during cold pressing or hot extrusion deformation.

[0024] 3. This invention further achieves in-situ exfoliation of spherical graphite by adjusting the amount of spherical graphite added, the graphite particle size, and the large plastic deformation of aluminum-based powder processing. During the large deformation of the extrusion, the axial grains of the graphite are significantly elongated and the radial grains are gradually refined, which greatly improves the mechanical properties of the graphene aluminum-based composite material and makes its electrical properties basically equivalent to those of pure aluminum conductors.

[0025] 4. The preparation process of this invention is short and low-cost, and can be used as an intermediate alloy in continuous casting and rolling production lines for large-scale application in products such as high-strength and high-toughness aluminum alloy plates and high-strength and high-conductivity aluminum alloy rods.

[0026] 5. The preparation equipment of this invention is simple, easy to operate, has relaxed conditions, produces less pollution, saves energy, uses simple and readily available raw materials, has a high graphite addition amount, and has low application cost after dilution. It also has a significant scale effect. Furthermore, the content of graphene exfoliated in situ can be controlled by controlling the amount of deformation.

[0027] The advantages and beneficial effects of this invention are as follows:

[0028] 1. This invention uses spherical graphite as raw material, mixes and dries it with aluminum-based powder, cold isostatically presses it into shape, and then vacuum sintersects it to further remove internal gases from the aluminum matrix, resulting in high density. Then, through large plastic deformation hot extrusion, the spherical graphite is exfoliated in situ in layers to produce a graphene-aluminum-based composite material. The carbon content of this composite material can reach more than 10%, and it can be used as an intermediate alloy product in aluminum alloy continuous casting and rolling production lines, which has the potential advantage of greatly reducing the production cost of graphene-carbon aluminum alloy final products.

[0029] 2. This invention provides a method for adding a high content (5%-15%) of graphite to an aluminum matrix. By adding spherical graphite of a certain particle size, the contact area between carbon and the aluminum matrix is ​​further reduced. Under the cold pressing action of the graphite-aluminum matrix mixed powder, better contact and bonding between aluminum can be achieved, which plays a key role in the density of cold pressing and can make up for the shortcomings of the prior art. Attached Figure Description

[0030] Figure 1 The images show cross-sectional crystal phase photographs and graphs of graphene size statistical analysis of the 9.5mm graphene aluminum rod in Example 2; where: (a) cross-sectional crystal phase photograph; (b) graph of graphene size statistical analysis.

[0031] Figure 2 The images show the longitudinal section crystal phase photographs and the longitudinal statistical analysis diagram of graphene size for a 9.5mm graphene aluminum rod; where: (a) longitudinal section crystal phase photograph; (b) longitudinal statistical analysis diagram of graphene size. Detailed Implementation

[0032] To further understand the present invention, the present invention is described below with reference to examples. However, the examples are only for further illustrating the features and advantages of the present invention, and are not intended to limit the scope of the claims of the present invention.

[0033] Example 1:

[0034] Weigh 20 kg of anhydrous ethanol, 140 g of polyamide, and 7 kg of spherical graphite powder (D50: 5 μm), and add them separately to a stirred drying vessel. Mix for 2 hours. Then add 63 kg of aluminum powder (D50: 10 μm) to the stirred drying vessel and start the stirring at 35 r / min for 1 hour. After that, turn on the vacuum pump and heating system. When the temperature reaches 100℃, maintain the mixture under a vacuum of less than 10 Pa for 12 hours. After naturally cooling to room temperature, transfer the mixed powder into a polyurethane bag. Place the bag on an electromagnetic vibration table, fill it with the mixture, vibrate to compact it, and then vacuum seal the bag. Place the bag in a cold isostatic pressing chamber and pressurize it at 200 MPa for 3 minutes. After the graphite aluminum rods are removed from the cold isostatic pressing equipment, they are placed in a vacuum sintering furnace for sintering at a temperature of 630℃ for 150 minutes with a vacuum degree greater than 10Pa. After naturally cooling to room temperature, the graphite aluminum rods are removed, machined, and then placed in a heat treatment furnace along with the extrusion die for heating at 520℃ for 3 hours. After being removed, they are put into an extrusion press for hot extrusion and finally processed into graphene aluminum rods with a diameter of 9.5mm.

[0035] Example 2:

[0036] Weigh 15 kg of anhydrous ethanol, 120 g of polyamide, and 5 kg of spherical graphite powder (D50: 3 μm), and add them separately to a stirred drying vessel. Mix for 2 hours. Then add 50 kg of aluminum powder (D50: 8 μm) to the stirred drying vessel and start the stirring at 35 r / min for 2 hours. After that, turn on the vacuum pump and heating system. When the temperature reaches 120℃, maintain the mixture under a vacuum of less than 10 Pa for 10 hours. After naturally cooling to room temperature, transfer the mixed powder into a polyurethane bag. Place the bag on an electromagnetic vibration table, fill it with the mixture, vibrate to compact it, and then vacuum seal the bag. Place the bag in a cold isostatic pressing chamber and pressurize it at 160 MPa for 5 minutes. After the graphite aluminum rods are removed from the cold isostatic pressing equipment, they are sintered in a vacuum sintering furnace at 650℃ for 120 minutes under a vacuum of greater than 10 Pa. After natural cooling to room temperature, the graphite aluminum rods are removed, machined, and then placed in a heat treatment furnace along with the extrusion die at 550℃ for 2 hours. After removal, they are placed in an extrusion press for hot extrusion, ultimately producing graphene aluminum rods with a diameter of 9.5 mm. Figure 1 and Figure 2 The images shown are cross-sectional and longitudinal section crystal phase photographs and graphene size statistical analysis diagrams of the 9.5mm graphene aluminum rod in Example 2, which further illustrate the preparation of graphene aluminum composite material by in-situ exfoliation of graphite with large deformation in the example.

[0037] Example 3:

[0038] Weigh 12 kg of anhydrous ethanol, 80 g of polyamide, and 4 kg of spherical graphite powder (D50: 8 μm), and add them separately to a stirred drying vessel. Mix for 1.5 h. Then add 40 kg of aluminum powder (D50: 12 μm) to the stirred drying vessel and start the stirring at 35 r / min for 2 h. After that, turn on the vacuum pump and heating system. When the temperature reaches 120℃, maintain it under a vacuum of less than 10 Pa for 8 h. After naturally cooling to room temperature, transfer the mixed powder into a polyurethane bag. Place the bag on an electromagnetic vibration table, fill it with the mixture, vibrate to compact it, and then vacuum seal the bag. Place it in the chamber of a cold isostatic press and hold it at 210 MPa for 2 min. After the graphite aluminum rods are removed from the cold isostatic pressing equipment, they are placed in a vacuum sintering furnace for sintering at a temperature of 650℃ for 120 minutes with a vacuum degree greater than 10Pa. After naturally cooling to room temperature, the graphite aluminum rods are removed, machined, and then placed in a heat treatment furnace along with the extrusion die for heating at 550℃ for 2 hours. After being removed, they are put into an extrusion press for hot extrusion and finally processed into graphene aluminum wire with a diameter of 3.05mm.

[0039] Example 4:

[0040] Weigh 18 kg of anhydrous ethanol, 140 g of polyamide, and 10 kg of spherical graphite powder (D50: 14 μm), and add them separately to a stirred drying vessel. Mix for 2 hours. Then add 60 kg of aluminum powder (D50: 10 μm) to the stirred drying vessel and start the stirring at 35 r / min for 2 hours. After that, turn on the vacuum pump and heating system. When the temperature reaches 120℃, maintain the mixture under a vacuum of less than 10 Pa for 12 hours. After naturally cooling to room temperature, transfer the mixed powder into a polyurethane bag. Place the bag on an electromagnetic vibration table, fill it with the mixture, vibrate to compact it, and then vacuum seal the bag. Place it in a cold isostatic pressing chamber and pressurize it at 200 MPa for 5 minutes. After the graphite aluminum rods are removed from the cold isostatic pressing equipment, they are placed in a vacuum sintering furnace for sintering at a temperature of 630℃ for 150 minutes with a vacuum degree greater than 10Pa. After cooling naturally to room temperature, the graphite aluminum rods are removed, machined, and then placed in a heat treatment furnace along with the extrusion die for heating at 520℃ for 3 hours. After being removed, they are put into an extrusion press for hot extrusion and finally processed into graphene aluminum wire with a diameter of 3.83mm.

[0041] Example 5:

[0042] Weigh 12 kg of anhydrous ethanol, 100 g of polyamide, and 3 kg of spherical graphite powder (D50: 3 μm), and add them separately to a stirred drying vessel. Mix for 2 hours. Then add 50 kg of aluminum powder (D50: 10 μm) to the stirred drying vessel and start the stirring at 35 r / min for 2 hours. After that, turn on the vacuum pump and heating system. When the temperature reaches 120℃, maintain it under a vacuum of less than 10 Pa for 12 hours. After naturally cooling to room temperature, transfer the mixed powder into a polyurethane bag. Place the bag on an electromagnetic vibration table, fill it with the mixture, vibrate to compact it, and then vacuum seal the bag. Place it in a cold isostatic pressing chamber and pressurize it at 200 MPa for 5 minutes. After the graphite aluminum rods are removed from the cold isostatic pressing equipment, they are placed in a vacuum sintering furnace for sintering at a temperature of 630℃ for 150 minutes with a vacuum degree greater than 10Pa. After naturally cooling to room temperature, the graphite aluminum rods are removed, machined, and then placed in a heat treatment furnace along with the extrusion die for heating at 520℃ for 3 hours. After being removed, they are put into an extrusion press for hot extrusion and finally processed into graphene aluminum rods with a diameter of 9.5mm.

[0043] The 1-10mm rods produced in the above embodiments were further diluted in molten aluminum as intermediate alloy masterbatch in a continuous casting and rolling production line. A comparison was made based on a final carbon content of 0.2wt%. The comparative example was existing L3 type hard aluminum wire (GB / T 17048-2017). Mechanical property tensile testing was conducted according to GB / T4909.3-2009, and electrical property resistivity testing was conducted according to GB / T 3048.2-2007. The DC resistivity at 20°C was converted to conductivity expressed in IACS (International Standard for Annealed Copper). The comparison of mechanical and electrical properties is shown in the table below.

[0044] Table 1. Comparison of performance indicators of diluted graphene aluminum wire (3-4mm)

[0045]

[0046]

[0047] In summary, this invention achieves spherical graphite exfoliation by adjusting the graphite content, graphite particle size, and large plastic deformation during aluminum processing within the aluminum matrix. In the initial pre-forming stage of the aluminum powder and graphite powder mixture, compared to flake graphite, spherical graphite, with the same mass fraction, can further reduce the contact area between carbon and the aluminum matrix. Under physical pressure, it enables contact and bonding between aluminum particles, playing a crucial role in achieving high density during cold pressing. Additives such as alcohols and polyamide binders further enhance the adhesion between the spherical aluminum powder and graphite particles, reducing graphite particle agglomeration during cold pressing or hot extrusion deformation. Furthermore, vacuum sintering after cold pressing removes internal gases from the cold-pressed rod, further improving the density of the graphene aluminum rod.

[0048] Furthermore, the present invention employs cold pressing of graphite and aluminum powder to further solve the problem of aluminum powder oxidation during hot pressing. However, the increased oxygen content in the aluminum matrix will hinder the conductivity of the final aluminum electrical materials.

Claims

1. A method of preparing graphene aluminum matrix composite by in-situ exfoliation of graphite, characterized by: The method includes the following steps: (1) Mixed drying: A certain mass of organic solvent and binder is poured into a stirred drying vessel, then a certain mass of spherical graphite is added and mixed evenly. Aluminum-based powder is then added to obtain a slurry. The slurry is mixed and dried under stirring and vacuum conditions for a certain time to obtain a uniformly mixed powder. The median particle size of the spherical graphite is 0.5-15 μm, with a purity of ≥99.5%, oxygen content ≤500 ppm, and water content ≤800 ppm. The mass fraction of spherical graphite in the slurry is 5%-15%. (2) Cold pressing preforming: The mixed powder obtained in step (1) is transferred into a bag under vacuum or nitrogen protection. The bag is placed on an electromagnetic vibration table, filled and vibrated to compact the powder, and then vacuum-sealed. The bag is then placed in a cold isostatic pressing chamber for cold pressing to obtain a graphite aluminum-based rod. (3) Vacuum sintering: After the graphite aluminum-based rods are removed from the cold isostatic pressing equipment, they are placed in a vacuum sintering furnace for vacuum sintering. After sintering, they are naturally cooled to room temperature, and then the graphite aluminum-based rods are removed and machined for later use. (4) Hot extrusion into rods: The machined graphene aluminum-based rods are placed in a heat treatment furnace along with the extrusion die and heated at 500-550℃ for 3 hours. After being removed, they are put into an extruder for hot extrusion and finally processed into graphene aluminum-based composite rods of the required diameter.

2. The method of claim 1, wherein the in-situ exfoliation of graphite to produce graphene aluminum matrix composite is characterized by: In step (1), the organic solvent is one or more of anhydrous methanol, anhydrous ethanol and acetone, and the mass fraction of the organic solvent in the mixed slurry is 20-40 wt%. The binder is one or two of polyamide and paraffin, and the mass fraction of the binder in the mixed slurry is 0.1-5 wt%.

3. The method of claim 1, wherein the in-situ exfoliation of graphite to produce graphene aluminum matrix composite is characterized by: In step (1), the aluminum-based powder has a particle size range of 5-15 μm, a purity of 99.5% or higher, an oxygen content of ≤1000 ppm, and a water content of ≤500 ppm.

4. The method of claim 3, wherein the in-situ exfoliation of graphite to produce graphene aluminum matrix composite is characterized by: The aluminum-based powder is pure aluminum powder, aluminum alloy powder, or aluminum-based composite material powder.

5. The method of claim 1, wherein the in-situ exfoliation of graphite to produce graphene aluminum matrix composite is characterized by: In step (1), during the mixing and drying process, the vacuum degree of mixing and stirring is 500Pa-1KPa, the mixing and drying time is 6-12h, and the drying temperature is 70-120℃.

6. The method of claim 1, wherein the in-situ exfoliation of graphite to produce graphene aluminum matrix composite is characterized by: In step (2), the holding pressure of the cold isostatic pressing is 150-210 MPa, and the holding time is 2-5 min.

7. The method of claim 1, wherein the in-situ exfoliation of graphite to produce graphene aluminum composites is characterized by: In step (2), the bag material is polyurethane or rubber, and the inner diameter of the bag is 140mm-200mm.

8. The method of claim 1, wherein the in-situ exfoliation of graphite to produce graphene aluminum matrix composite is characterized by: In step (3), during the vacuum sintering process, the vacuum degree is greater than 10 Pa, the sintering temperature is 600-650℃, and the holding time is 100-200 min.

9. A graphene aluminum matrix composite prepared by the method of any one of claims 1-8, wherein: The composite material comprises an aluminum matrix and graphene uniformly distributed in the aluminum matrix, with a graphene content of 5-15 wt.%.

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