Graphene coated copper-based rare earth copper alloy and silver alloy contact preparation method

Abstract

The invention relates to a preparation method of a graphene-coated copper-based rare earth copper alloy and silver alloy contact, which is characterized in that the conductivity, oxidation resistance and mechanical strength of a material are remarkably improved by optimizing a graphene coating process of a copper matrix, combining rare earth element alloying to enhance the copper-based performance and adopting a gradient thermal compounding technology to prepare the silver alloy contact. By the adoption of the technical scheme, magnesium oxide is adopted for assisting annealing, a high-pollution electroplating solution is replaced, the environmental load is reduced, then a graphene coating layer grows on the surface of the copper powder in an in-situ catalytic mode, oxidation and grain coarsening of a copper matrix during high-temperature machining can be restrained, the thermal stability of the material is improved, and the service life of the material is prolonged. According to the method, the copper alloy and the silver layer are combined, alloying treatment of lanthanide rare earth and transition metal is combined, the lanthanide rare earth can refine grains and purify grain boundaries, solid solution strengthening of the transition metal is combined, the strength, abrasion resistance and creep resistance of the alloy are further optimized, then the copper alloy and the silver layer are subjected to hot pressing through the gradient hot pressing technology, the adhesive force of the silver layer is enhanced, and the problem of silver layer stripping is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of composite materials, and particularly to a preparation method of a graphene-coated copper-based rare earth copper alloy and a silver alloy contact. Background Art

[0002] Copper alloy contact materials are widely used in fields such as power switches, relays, and electronic connectors due to their excellent electrical conductivity, thermal conductivity, and mechanical strength. To improve their arc erosion resistance, oxidation resistance, and contact reliability, existing technologies usually adopt surface silver plating or modification means such as adding graphene, but there are still the following key problems.

[0003] Limitations of the graphene coating process: For the chemical vapor deposition method, a patent with the publication number CN202310371265.1 discloses a preparation method of a graphene-coated nano-copper particle composite material, in which hydrocarbon gas is introduced into the copper melt to directly generate graphene. Although this process can achieve in-situ coating, high temperature easily leads to structural defects (such as vacancies and wrinkles) in graphene; for the electroplating method, a patent with the patent number CN202410892862.3 discloses a metal graphene composite material, its preparation method, application, and a graphene precursor: using a graphene oxide (GO)-nickel oxide composite to coat copper powder, which requires complex reduction treatment and residual oxygen impurities, resulting in an increase in the resistivity of the composite material and insufficient electrical conductivity.

[0004] Performance bottleneck of copper-based alloys: Insufficient high-temperature oxidation resistance, conventional copper alloys (such as Cu-Cr-Zr) are prone to form an oxide layer during long-term high-temperature service, increasing the contact resistance; and the application of rare earth elements is single. In existing technologies, a patent with the patent number CN201910460452.0 discloses a preparation method of a copper-based alloy contact, which only refines the grains by adding a single rare earth (such as La or Ce), and does not synergistically regulate the interfacial behavior with graphene, resulting in a contradiction between strength and electrical conductivity.

[0005] Disadvantages of the silver alloy composite process: High electroplating / sputtering cost, traditional silver layer composites rely on electroplating. A patent with the publication number CN110983290A discloses a preparation method of a graphene-coated copper alloy composite material, using electroplating or sputtering, with weak adhesion of the silver layer (<80 MPa), and the energy consumption accounts for more than 30% of the production cost. Summary of the Invention

[0006] Object of the present invention: To overcome the defects of the existing technology, the present invention provides a preparation method of a graphene-coated copper-based rare earth copper alloy and a silver alloy contact. By optimizing the graphene coating process of the copper matrix, combining rare earth element alloying to enhance the properties of the copper matrix, and innovatively using a gradient thermal composite technology to prepare the silver alloy contact, the electrical conductivity, oxidation resistance, and mechanical strength of the material are significantly improved.

[0007] Technical solution of the present invention: A preparation method of graphene-coated copper-based rare earth copper alloy, comprising the following steps: Step S1: Raw material pretreatment, mixing pure copper powder and magnesium oxide powder evenly according to a mass ratio of 97:3, and annealing under argon protection to form a uniform dispersion system; Step S2: In-situ growth of graphene, introducing a methane / hydrogen mixed gas with a volume ratio of 1:5 into the mixed powder obtained in step S1, reacting at a temperature of 750 - 900 °C and a pressure of 10 - 50 Pa, and catalytically cracking on the surface of the copper powder to generate a graphene coating layer; Step S3: Alloying treatment, mixing the graphene-coated copper powder with lanthanide rare earths and trace transition metals evenly, and obtaining an alloy ingot after melting, isostatic pressing to destroy the graphene-coated copper particle structure, and sintering; Step S4: Hot rolling forming, hot rolling the alloy ingot obtained in step S3 and performing aging treatment to obtain a copper alloy.

[0008] Further, in step S1, the annealing is carried out in an environment of 800 - 1000 °C for 1 - 2 hours.

[0009] Further, in step S3, the lanthanide rare earth component contains at least two of La, Ce, and Pr. Isostatic pressing is carried out at 150 - 170 MPa, and sintering is carried out at 920 - 950 °C for 1 - 2 hours under hydrogen protection.

[0010] Furthermore, in step S3, the total content of La, Ce, and Pr in the lanthanide rare earth is 0.1 - 0.5 wt%, the Ni content in the trace transition metal is 0.2 - 0.8 wt%, and the Co content is 0.1 - 0.3 wt%.

[0011] Further, in step S4, the aging treatment is carried out at 200 - 300 °C for 2 - 4 hours.

[0012] Another object of the present invention is to provide a preparation method of a silver alloy contact, comprising the preparation method according to any one of claims 1 - 4, characterized in that it includes gradient hot pressing and compounding: performing multi-stage hot pressing on a silver alloy strip and the copper alloy strip obtained after the above hot rolling forming in an inert atmosphere to form a metallurgical bonding interface between the silver layer and the copper base; [[ID=2,5]]The multi-stage hot pressing process includes two stages. In the first stage, the hot pressing temperature is 300 - 350 °C and the pressure is 10 - 15 MPa; in the second stage, the hot pressing temperature is 400 - 450 °C and the pressure is 17 - 20 MPa.

[0013] Further, it also includes surface treatment: after the composite material obtained by gradient hot pressing and compounding is electrolytically polished, it is passivated with a nitric acid-phosphoric acid mixed solution to form a dense oxide film.

[0014] Further, the silver alloy strip includes 95 wt% of Ag, 3 wt% of Sn, and 2 wt% of Bi.

[0015] The beneficial effects of the technical solution of the present invention are as follows: Graphene is in-situ grown to reinforce the copper matrix, and rare earth elements are combined to optimize the alloy properties. Finally, it is compounded with a silver alloy to form a high-performance contact material. In this solution, magnesia-assisted annealing is used to replace the highly polluting electroplating solution, reducing the environmental load. Subsequently, 1-3 layers of graphene coating are in-situ catalytically grown on the surface of copper powder, which can inhibit the oxidation and grain coarsening of the copper matrix during high-temperature processing, improve the thermal stability of the material, and combine the alloying treatment of lanthanide rare earths and transition metals. Lanthanide rare earths can refine grains and purify grain boundaries, and combined with the solid solution strengthening of transition metals, further optimize the strength, wear resistance, and creep resistance of the alloy, enabling the material to significantly improve its mechanical properties while maintaining high electrical conductivity. Finally, a high-performance copper alloy material is obtained by hot rolling forming, and then the copper alloy and the silver layer are hot-pressed through a gradient hot-pressing process to enhance the adhesion of the silver layer and avoid the problem of silver layer peeling. Description of the Drawings

[0016] Figure 1 It is a flowchart of the steps of a specific embodiment of the present invention. Detailed Embodiments

[0017] Next, the technical solutions in this embodiment will be clearly and completely described in conjunction with the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present invention.

[0018] The present invention provides a method for preparing a graphene-coated copper-based rare earth copper alloy, which is prepared according to the following steps: Step S1: Pretreatment of raw materials. Pure copper powder with a particle size of 50-200 nm and magnesia powder are mixed evenly at a mass ratio of 97:3; annealed at 800-1000 °C for 1-2 hours under argon protection to form a homogeneous dispersion system.

[0019] Step S2: In-situ growth of graphene. A methane / hydrogen mixed gas with a volume ratio of 1:5 is introduced into the mixed powder obtained after annealing in Step S1, and the reaction is carried out at 750-900 °C and 10-50 Pa for 30-60 minutes to catalytically crack and generate a graphene coating on the surface of the copper powder.

[0020] Step S3: Alloying treatment. Mix the graphene-coated copper powder with lanthanide rare earths (La, Ce, Pr, with a total content of 0.1 - 0.5 wt%) and trace transition metals (0.2 - 0.8 wt% Ni, 0.1 - 0.3 wt% Co), perform isostatic pressing under the environment of 150 - 170 MPa, and sinter at 920 - 950 °C for 1 - 2 hours under hydrogen protection to obtain an alloy ingot.

[0021] Step S4: Hot rolling forming. Hot roll the alloy ingot into a strip with a thickness of 0.1 - 0.5 mm at 500 - 600 °C, and perform aging treatment at 200 - 300 °C for 2 - 4 hours to optimize the grain boundary structure, so as to obtain a laminated rare earth copper alloy strip.

[0022] Based on the laminated rare earth copper alloy strip prepared by the above steps, the present invention provides a method for preparing a silver alloy contact, and the specific steps are as follows: Step 1: Gradient hot pressing composite. Stack the silver alloy strip and the laminated rare earth copper alloy strip, and obtain a composite material by using a multi-stage hot pressing process in an inert atmosphere; wherein the Ag content in the silver alloy strip is 95 wt%, the Sn content is 3 wt%, and the Bi content is 2 wt%. The multi-stage hot pressing process is divided into two stages: The first stage: Perform pre-composite treatment of the copper alloy and the silver alloy for 1 - 1.5 hours under the environment of a hot pressing temperature of 300 - 350 °C and a pressure of 10 - 15 MPa to activate the eutectic liquid phase of the silver alloy (Ag - Sn - Bi) and initially fill the interface microvoids. The second stage: Under the environment of a hot pressing temperature of 450 - 500 °C and a pressure of 20 - 25 MPa, promote the mutual diffusion of Cu / Ag atoms, and the treatment time is 2 - 2.5 hours, so that the silver layer and the copper base form a metallurgical bonding interface and improve the bonding strength of the interface. Step 2: Surface treatment. After the composite material obtained by gradient hot pressing composite in Step S1 is electrolytically polished, it is passivated by using a nitric acid - phosphoric acid mixed solution with a pH between 2 - 3 to form a dense oxide film to enhance the corrosion resistance.

[0023] The following is a specific embodiment of a graphene-coated copper-based rare earth copper alloy and a method for preparing a silver alloy contact according to the present invention. Example 1

[0024] A method for preparing a graphene-coated copper-based rare earth copper alloy and a silver alloy contact in this embodiment includes the following steps: Step S1: Raw material pretreatment. Mix 9.7 kg of copper powder and 0.3 kg of magnesium oxide evenly; anneal at 900 °C for 1 hour under argon protection.

[0025] Step S2: In-situ growth of graphene. Methane / hydrogen mixed gas with a volume ratio of 1:5 is introduced into the mixed powder obtained after annealing in Step S1, and the reaction is carried out at 800 °C and 30 Pa for 40 minutes to obtain copper powder coated with graphene.

[0026] Step S3: Alloying treatment. The copper powder coated with graphene is mixed evenly with La-Ce-Pr mixed rare earth with a total content of 0.3 wt% and trace transition metal Ni with a content of 0.5 wt%, and is isostatically pressed at 150 - 170 MPa, and sintered at 920 - 950 °C for 1.5 hours under hydrogen protection.

[0027] Step S4: Hot rolling forming. The alloy ingot is hot rolled into a 0.3 mm strip, and aging treatment is carried out at 250 °C for 3 hours.

[0028] Step S5: Gradient hot pressing composite. The silver alloy strip and the rare earth copper alloy strip are laminated, and a multi-stage hot pressing process is adopted in an inert atmosphere; the Ag content in the silver alloy strip is 95 wt%, the Sn content is 3 wt%, and the Bi content is 2 wt%. The multi-stage hot pressing process is divided into two stages: The first stage: pre-composite treatment of the copper alloy and the silver alloy is carried out at a hot pressing temperature of 350 °C and a pressure of 10 MPa for 1 hour. The second stage: It is carried out at a hot pressing temperature of 450 °C and a pressure of 20 MPa to promote the mutual diffusion of Cu / Ag atoms. The treatment time is 2 hours to form a metallurgical bonding interface between the silver layer and the copper base; after detection, the interface bonding strength reaches 120 MPa.

[0029] Step S6: Surface treatment. After the composite material obtained in Step S5 is electrolytically polished, it is passivated with a nitric acid-phosphoric acid mixed solution with a pH between 2 - 3 to form a dense oxide film to enhance corrosion resistance. Example 2

[0030] Adjust the amount of La-Ce-Pr mixed rare earth taken to be 0.5 wt%, and in the two stages of the multi-stage hot pressing process, the first stage is optimized to a hot pressing temperature of 320 °C and a pressure of 12 MPa; the second stage is optimized to a hot pressing temperature of 480 °C and a pressure of 25 MPa, and the rest are the same as in Example 1; after surface treatment in this example, it is measured that the interface bonding strength is increased to 135 MPa.

Claims

1. A preparation method of graphene-coated copper-based rare earth copper alloy, characterized in that, It includes the following steps: Step S1: Pretreatment of raw materials. Mix pure copper powder and magnesium oxide powder evenly at a mass ratio of 97:3, and perform annealing under argon protection to form a uniform dispersion system; Step S2: In-situ growth of graphene. Pass a methane / hydrogen mixed gas with a volume ratio of 1:5 into the mixed powder obtained in Step S1, react at 750 - 900 °C and a pressure of 10 - 50 Pa, and catalytically crack on the surface of the copper powder to generate a graphene coating layer; Step S3: Alloying treatment. Mix the graphene-coated copper powder with lanthanide rare earths and trace transition metals, form a static pressure mold, and sinter to obtain an alloy ingot; Step S4: Hot rolling forming. Hot roll the alloy ingot obtained in Step S3 and perform aging treatment to obtain a copper alloy.

2. The preparation method of a graphene-coated copper-based rare earth copper alloy according to claim 1, characterized in that, In Step S1, the annealing is carried out in an environment of 800 - 1000 °C for 1 - 2 hours.

3. A method for preparing a graphene-coated copper-based rare earth copper alloy according to claim 1, characterized in that, In Step S3, the lanthanide rare earth component contains at least two of La, Ce, and Pr.

4. A method for preparing a graphene-coated copper-based rare earth copper alloy according to claim 3, characterized in that, In Step S3, the total content of La, Ce, and Pr in the lanthanide rare earth is 0.1 - 0.5 wt%, and the Ni content in the trace transition metal is 0.2 - 0.8 wt%, and the Co content is 0.1 - 0.3 wt%.

5. A method for preparing a graphene-coated copper-based rare earth copper alloy according to claim 1, characterized in that, In Step S4, the aging treatment is carried out at 200 - 300 °C for 2 - 4 hours.

6. A method for preparing a silver alloy contact, comprising the preparation method according to any one of claims 1-5, characterized in that, It also includes gradient hot pressing composite: The silver alloy strip and the copper alloy strip obtained after the above hot rolling forming are metallurgically bonded at the interface between the silver layer and the copper matrix by using a multi-stage hot pressing process in an inert atmosphere; The multi-stage hot pressing process includes two stages. In the first stage, the hot pressing temperature is 300 - 350 °C and the pressure is 10 - 15 MPa; in the second stage, the hot pressing temperature is 450 - 500 °C and the pressure is 20 - 25 MPa.

7. A method for preparing a silver alloy contact according to claim 6, characterized in that, It also includes surface treatment: After the composite material obtained by gradient hot pressing composite is electrolytically polished, it is passivated with a nitric acid - phosphoric acid mixed solution to form a dense oxide film.

8. A method for preparing a silver alloy contact according to claim 7, characterized in that, The silver alloy strip includes 95 wt% of Ag, 3 wt% of Sn, and 2 wt% of Bi.

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