High-current copper-aluminum bus fitting terminal coating and preparation method and application thereof

Abstract

The invention belongs to the technical field of electric power fitting surface treatment, and particularly provides a high-current copper-aluminum bus fitting terminal coating and a preparation method and application thereof, and the fitting terminal coating sequentially comprises a substrate layer and a composite layer from inside to outside; the substrate layer is a silver layer I; the composite layer comprises a hard layer and a second silver layer filled in a hard layer framework, the hard layer is of a latticed structure, the minimum repeating units of the lattices of the hard layer are parallelogram lattices, and the hard layer is made of tungsten carbide or titanium carbide or tungsten or molybdenum. The prepared coating is high in bonding strength, stable in performance, free of peeling and falling off and capable of effectively meeting the requirement for the service life of the hardware fitting terminal. Meanwhile, excellent conductivity, wear resistance and corrosion resistance can be provided; in addition, the cold spraying technology is simple in process, rapid in forming, efficient and high in powder utilization rate, and the existing coating preparation and field repair requirements can be effectively met.

Description

Technical Field

[0001] The present invention belongs to the technical field of surface treatment of electric power fittings, and particularly relates to a coating for terminals of large-current copper-aluminum busbar fittings, a preparation method and an application thereof Background Art Large-current busbars are key conductive components indispensable in modern power systems, and the performance of their connection terminals is directly related to the stability, reliability and safety of the electrical system. In the fields of power transmission, rail transit, industrial automation, etc., large-current busbars undertake the core function of efficient electric energy transmission. As the key interface of large-current busbars, the comprehensive electrical and mechanical properties of the surface of connection terminals are of great significance for improving the overall system performance

[0002] Conduction between connection terminals is achieved by mechanical contact. In order to improve the conductivity and reduce the contact resistance, a silver coating is usually prepared on the surface of the connection terminals. Due to the service conditions of terminal components often accompanied by high-frequency vibration and thermal cycles from room temperature to a maximum of 200 °C, the silver coating is prone to fretting wear and contact fatigue failure, resulting in rapid consumption or peeling of the coating, seriously weakening the electrical properties and mechanical integrity of the contact surface, and ultimately threatening the safe operation of the entire electrical system

[0003] In the prior art, terminal coatings are often prepared by traditional electroplating methods, but electroplating methods have problems such as low bonding strength and easy peeling of the coating; CN110760783A discloses a method for improving the wear resistance of terminals of aluminum alloy electric power fittings, and uses thermal spraying technologies such as plasma spraying to prepare terminal coatings, so that the safety, chemical and mechanical properties, service life and surface properties of the fittings are comprehensively improved. However, thermal spraying has problems such as too high heat input and high porosity, which affect the mechanical and conductive properties of the substrate

[0004] CN110042389A discloses a process for laser cladding a silver layer on the surface of terminals of large-current aluminum busbar fittings. This process can obtain a dense silver coating with good bonding effect with the substrate. However, laser cladding technology still belongs to a high-energy beam preparation process. Due to its inherent characteristics of rapid heating and cooling, the coating may still undergo oxidation and formation of pores, which is not conducive to maintaining the high conductivity of the raw material powder. In addition, too large heat input may also cause deformation of the substrate of the terminal of the fitting, resulting in out-of-tolerance dimensions and scrapping. Moreover, due to the extremely high reflectivity of silver, in engineering practice, the laser cladding process usually can only use silver alloy for cladding, which also has an adverse effect on the conductivity of the coating. Finally, the processing efficiency of the laser cladding process is usually low and cannot meet the technical requirements of on-site large-area construction. Therefore, although laser cladding technology has certain advantages in terms of coating density and bonding force, it still faces many challenges in improving the conductive performance of the coating, reducing substrate thermal deformation, and construction efficiency

[0005] As a new surface engineering technology, cold spraying has the unique advantage of realizing the preparation of metal coatings under normal or low temperature conditions. Compared with traditional thermal spraying and laser cladding technologies, the cold spraying process has the characteristics of low heat input, small substrate deformation, high coating density, and the coating can maximally maintain the characteristics of raw materials. With the cold spraying process and through gradient material design, it is expected to fundamentally solve the problems of poor wear resistance, easy peeling, and limited coating conductivity existing in the surface coating preparation of large-current busbar fittings terminals. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a coating for large-current copper-aluminum busbar fittings terminals, a preparation method and an application thereof. The prepared coating has a relatively high bonding strength, stable coating performance, does not peel off, and can effectively meet the service life requirements of the fittings terminals.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is: a coating for large-current copper-aluminum busbar fittings terminals, the coating of the fittings terminals from the inside to the outside is successively a base layer and a composite layer; The base layer is a first silver layer; The composite layer includes a hard layer and a second silver layer filled in the hard layer framework. The structure of the hard layer is grid-shaped, and the smallest repeating unit of the hard layer grid is a parallelogram grid. The component of the hard layer is tungsten carbide or titanium carbide or tungsten or molybdenum.

[0008] In a preferred embodiment, the second silver layer is a nanotwinned layer.

[0009] In a preferred embodiment, the horizontal or vertical distance between the parallel sides of the smallest repeating unit of the hard layer grid is 3-6 mm.

[0010] In a preferred embodiment, the ratio of the horizontal width of the smallest repeating unit of the second silver layer to the horizontal width of the adjacent hard layer grid border is 5-7.

[0011] In a preferred embodiment, the thickness of the first silver layer is 100-300 μm; the thickness of the hard layer is 100-500 μm, and the thickness of the second silver layer is 100-500 μm. The surfaces of the hard layer and the second silver layer are at the same height.

[0012] In a preferred embodiment, the particle size of the silver powder of the first silver layer is 10-20 μm; the particle size of the raw material powder of the hard layer is 30-50 μm; the particle size of the nano silver powder of the second silver layer is <1 μm, the fluidity of the nano silver powder is <40 s / 50 g, and the grain size inside the powder is 20 nm-500 nm.

[0013] The present invention also provides a preparation method for a coating of large-current copper-aluminum busbar fittings terminals, including the following steps: S1. Pretreat the surface of the substrate of the large-current busbar fitting terminal; S2. Using silver powder as the raw material, prepare a first silver layer on the surface of the fitting terminal substrate through a cold spraying process to form a base layer; S3. Cover the spraying area of the preset second silver layer with a mask. The mask is grid-shaped. Use the cold spraying process to spray and prepare a hard layer grid on the surface of the first silver layer; S4. Cover the surface of the hard layer grid with a mask. The mask is grid-shaped. The hollow area of the hard layer grid is not covered with a mask. Use the cold spraying process to spray and fill the second silver layer on the surface of the first silver layer and inside the hard layer grid to complete the preparation of the composite layer.

[0014] In a preferred solution, the overlapping rate of the minimum repeating unit of the hard layer grid and the minimum repeating unit of the second silver layer < 20%.

[0015] In a preferred solution, the cold spraying process for preparing the base layer and the composite layer is as follows: the working gas is one or more of air, nitrogen, and helium; the spraying pressure of the cold spraying is 1 - 7.5 Mpa; the spraying temperature of the cold spraying is 200 - 800 °C; the gas velocity of the cold spraying is 800 - 1200 m / s; the ambient temperature of the spraying is -5 °C - 45 °C, and the spraying distance of the cold spraying is 10 - 70 mm.

[0016] The present invention also provides an application of the preparation method of the coating for the large-current copper-aluminum busbar fitting terminal, applying the above coating preparation method for the fitting terminal to the preparation of the large-current busbar fitting terminal or the surface repair of the large-current busbar fitting terminal.

[0017] The large-current copper-aluminum busbar fitting terminal coating, preparation method, and application provided by the present invention have the following beneficial effects: 1. The cold spraying process for preparing the silver coating adopted by the present invention is based on the principle of aerodynamics. Using a high-pressure gas source to drive solid particles to a very high speed to impact the surface of the substrate, causing severe plastic deformation, and thus depositing on the surface of the substrate to form a coating. The coating obtained by this process has a relatively high bonding strength, stable coating performance, will not peel off, and can effectively meet the service life requirements of the fitting terminal.

[0018] 2. The cold spraying process adopted by the present invention has the advantages of relatively low process temperature and less heat input, will not cause thermal deformation of the workpiece and damage to the material structure, thus effectively ensuring sufficient contact surface between terminals and reducing the contact resistance; at the same time, the coating prepared by cold spraying is dense and has a low porosity, and can provide excellent electrical conductivity and corrosion resistance.

[0019] 3. Compared with traditional processes, for the coating prepared by the cold spraying process in the present invention, the deposited particles are not significantly affected by heat, and the original powder's organizational structure and physical and chemical properties can be well retained. There is basically no oxidation, component burning loss, or grain growth. The tissue composition is uniform, with excellent surface formability and surface quality, and almost no burrs, bubbles, or cracks, thus effectively avoiding the increase in current impedance caused by coating non-uniformity.

[0020] 4. In the present invention, silver layer one is used as the base layer, and the hard layer and the nano-twinned silver layer are used as the surface layer. Among them, with the hard layer grid with high hardness value and high conductivity as the skeleton, it plays a supporting role during the service of the fitting terminal, helps to disperse the load during the wear process, effectively prevents the accumulation of plastic deformation on the surface of the metal matrix, and can also effectively ensure the conductive performance of the coating. In addition, the present invention also prepares the nano-twinned silver layer with a fine crystal structure by using raw materials of nano size and high-speed impact, which can effectively improve the surface hardness of the fitting terminal, and thus improve its wear resistance. Therefore, the adjacent structure of the tungsten carbide grid skeleton and the nano-twinned silver layer can better ensure the stability of the inner layer structure, so as to maintain the long-term good high-conductivity performance and high-wear resistance performance of the fitting terminal and its coating, and can significantly improve the service life of the fitting terminal.

[0021] 5. The cold spraying technology is used for silver layer preparation. The whole process is simple, with rapid prototyping, high efficiency, and high powder utilization rate, and can effectively meet the existing coating requirements.

[0022] 6. In the prior art, repairing the coating of the large-current copper-aluminum bus fitting terminal requires returning to the factory for repair, which has problems of difficult transportation and long cycle. The cold spraying technology adopted in the present invention can repair this fitting on-site, with a rapid response. The chemical composition and microscopic organizational structure of the coating can be consistent with the raw materials, effectively ensuring the service performance of the coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described below in conjunction with the drawings and embodiments: Figure 1 It is the structure diagram of the coating of the present invention; Figure 2 It is the structure schematic diagram of the composite layer; In the figure: fitting terminal 1, base layer 2, composite layer 3, hard layer 31, silver layer two 32. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0025] Example 1: A method for preparing a coating on a large - current aluminum busbar fitting terminal, the steps are as follows: S1. Pretreat the surface of the substrate of the large - current busbar fitting terminal. Mechanically polish the surface of the substrate to make it flat, and then clean the surface of the substrate with acetone.

[0026] S2. Using silver powder as the raw material, prepare a first silver layer on the surface of the fitting terminal substrate through a cold - spraying process to form a base layer.

[0027] The thickness of the first silver layer is 100 - 300μm; the particle size of the silver powder in the first silver layer is 10μm - 20μm.

[0028] S3. Cover the spraying area of the preset second silver layer with a mask. The mask is grid - shaped, and use the cold - spraying process to spray and prepare a hard - layer grid on the surface of the first silver layer. The component of the hard layer is tungsten carbide.

[0029] S4. Cover the surface of the hard - layer grid with a mask. In this embodiment, the mask covers the surface of the already - sprayed tungsten carbide coating. The mask is grid - shaped, and the hollow area of the hard - layer grid is not covered with a mask. Use the cold - spraying process to spray and fill the second silver layer on the surface of the first silver layer and inside the hard - layer grid to complete the preparation of the composite layer.

[0030] The minimum repeating unit of the hard - layer grid is a parallelogram grid; the second silver layer is a nano - twin layer.

[0031] The horizontal or vertical distance between the parallel sides of the minimum repeating unit of the hard - layer grid is 8 - 12mm.

[0032] The ratio of the horizontal width of the minimum repeating unit of the second silver layer to the horizontal width of the adjacent hard - layer grid border is 5 - 7.

[0033] The thickness of the hard layer is 100 - 500μm, the thickness of the second silver layer is 100 - 500μm, and the surface heights of the hard layer and the silver surface layer are the same.

[0034] The particle size of the raw material powder of the hard layer is 30μm - 50μm; the particle size of the nano - silver powder in the second silver layer is <1μm, the fluidity of the nano - silver powder is <40s / 50g, and the grain size inside the powder is 20nm - 500nm.

[0035] The overlapping rate of the minimum repeating unit of the hard - layer grid and the minimum repeating unit of the second silver layer is <20%.

[0036] The cold spraying process for preparing the base layer and the composite layer is as follows: the working gas is one or more of air, nitrogen, or helium; the spraying pressure of cold spraying is 1 - 7.5 Mpa; the spraying temperature of cold spraying is 200 - 800 °C; the gas velocity of cold spraying is 800 - 1200 m / s; the ambient temperature for spraying is -5 °C - 45 °C, and the spraying distance of cold spraying is 10 - 70 mm.

[0037] Example 2: The difference from Example 1 is that the composition of the hard layer is titanium carbide.

[0038] Example 3: The difference from Example 1 is that the composition of the hard layer is tungsten.

[0039] Example 4: The difference from Example 1 is that the composition of the hard layer is molybdenum.

[0040] Comparative Example 1: A method for preparing a coating on a large current aluminum busbar fitting terminal, the steps are as follows: S1. Pretreat the surface of the base body of the large current busbar fitting terminal. Use mechanical grinding to grind the surface of the base body flat, and then use acetone to clean the surface of the base body.

[0041] S2. Using silver powder as the raw material, prepare a first silver layer on the surface of the fitting terminal base body through the cold spraying process; the thickness of the first silver layer is 100 - 300 μm; the particle size of the silver powder of the first silver layer is 10 μm - 20 μm.

[0042] Comparative Example 2: The difference from Example 1 is that the second silver layer is not a twin crystal structure, and the second silver layer uses the same process and raw materials as the first silver layer.

[0043] Comparative Example 3: The difference from Example 1 is that the horizontal or vertical distance between the parallel sides of the smallest repeating unit of the hard layer grid is 20 mm.

[0044] Comparative Example 4: The difference from Example 1 is that the ratio of the horizontal width of the smallest repeating unit of the second silver layer to the horizontal width of the adjacent hard layer grid border is 10.

[0045] The performance tests of the coatings prepared in Examples 1 - 4 and Comparative Examples 1 - 4 are as follows: Combined with the particularity of the fitting terminal and the actual situation of the cold spraying process, due to the special nature of the spraying object, it is impossible to conduct destructive testing. In order to verify the effectiveness of the spraying process and the quality of the coating, use the same equipment, the same batch of raw material powder, the same process, and prepare accompanying test pieces continuously after spraying the product, and conduct relevant tests.

[0046] 1) Conductivity test The samples prepared by the examples and comparative examples were tested and compared. For the technical solution of the present invention, an eddy current conductivity meter was used to test the conductivity of the silver coating at 20°C ± 5°C with reference to "GB / T 32971-2016 Eddy Current Testing Method for Conductivity of Copper and Copper Alloy". The test results are shown in Table 1.

[0047] 2) Wear resistance test The Brinell hardness was measured with reference to GB / T 231.1-2018 "Metallic materials - Brinell hardness test - Part 1: Test method" to indirectly characterize the wear resistance of the coating. The test results are shown in Table 1.

[0048] 3) Adhesion strength test The adhesion strength of the coating was tested with reference to GB / T 8642 - 2002 "Determination of tensile adhesion strength of thermal sprayed coatings". The test results are shown in Table 1.

[0049]

[0050] Comparing Examples 1 to 4 with Comparative Example 1, it can be seen that the hard layer grid with high hardness value and high conductivity acts as a skeleton during the service of the fitting terminal, which helps to disperse the load during the wear process, effectively prevents the accumulation of plastic deformation on the surface of the metal matrix, and can effectively ensure the conductivity of the coating.

[0051] Comparing Example 1 with Comparative Example 2, it can be seen that the nanoscale raw materials are selected to prepare the nanoscale twin silver layer with a fine grain structure by high-speed impact, which can effectively improve the surface hardness of the fitting terminal and thus improve its wear resistance (hardness).

[0052] Comparing Example 1 with Comparative Examples 3 and 4, it can be seen that the parameters of the composite layer play an important role in the overall improvement of the conductivity, wear resistance and adhesion strength of the coating, which can better ensure the stability of the inner layer structure, so as to maintain the long-term good high conductivity and high wear resistance of the fitting terminal and its coating, and can significantly improve the service life of the fitting terminal.

[0053] The above embodiments are only the preferred technical solutions of the present invention and should not be regarded as limitations on the present invention. The embodiments and the features in the embodiments in this application can be arbitrarily combined with each other without conflict. The protection scope of the present invention should be the technical solutions recorded in the claims, including the equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, the equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A high current copper-aluminum busbar fitting terminal coating, characterized in that: The coating of the hardware terminal is composed of a base layer and a composite layer from the inside to the outside; The base layer is a silver layer 1; The composite layer includes a hard layer and a second silver layer filled in the hard layer skeleton. The structure of the hard layer is grid-shaped, and the minimum repeating unit of the hard layer grid is a parallelogram grid. The composition of the hard layer is tungsten carbide or titanium carbide or tungsten or molybdenum.

2. A high current copper-aluminum busbar fitting terminal coating according to claim 1, characterized in that: The second silver layer is a nano twin layer.

3. A high current copper-aluminum busbar fitting terminal coating according to claim 1, characterized in that: The horizontal or vertical spacing between the parallel sides of the minimum repeating unit of the hard layer grid is 3 to 6 mm.

4. A high current copper-aluminum busbar fitting terminal coating according to claim 3, characterized in that: The ratio of the horizontal width of the minimum repeating unit of the second silver layer to the horizontal width of the adjacent hard layer grid frame is 5-7.

5. The high current copper-aluminum busbar fitting terminal coating according to claim 1, characterized in that: The thickness of the first silver layer is 100-300 μm; the thickness of the hard layer is 100-500 μm, and the thickness of the second silver layer is 100-500 μm. The surface heights of the hard layer and the second silver layer are consistent.

6. The method for preparing a high current copper-aluminum busbar fitting terminal coating according to claim 1, characterized in that: The particle size of the silver powder of the first silver layer is 10-20 μm; the particle size of the raw material powder of the hard layer is 30-50 μm; the particle size of the nano silver powder of the second silver layer is less than 1 μm, the fluidity of the nano silver powder is less than 40s / 50g, and the grain size inside the powder is 20nm-500nm.

7. The method for preparing a high current copper-aluminum busbar hardware terminal coating according to any one of claims 1 to 6, characterized in that: The steps include: S1. Pre-treat the substrate surface of the high-current busbar fitting terminal; S2, using silver powder as a raw material, preparing a silver layer on the surface of the hardware terminal substrate by a cold spraying process to form a base layer; S3, using a mask to cover the spraying area of ​​the preset silver layer 2, the mask is in a grid shape, and using a cold spraying process to spray on the surface of the silver layer 1 to prepare a hard layer grid; S4. Use a mask to cover the surface of the hard layer grid. The mask is in a grid shape. The hollow area of ​​the hard layer grid is not covered by the mask. Use a cold spraying process to spray and fill the silver layer 2 on the surface of the silver layer 1 and in the hard layer grid to complete the preparation of the composite layer.

8. The method for preparing a high current copper-aluminum busbar hardware terminal coating according to claim 7, characterized in that: The overlap rate of the minimum repeating unit of the hard layer grid and the minimum repeating unit of the second silver layer is less than 20%.

9. The method for preparing a high current copper-aluminum busbar hardware terminal coating according to claim 7, characterized in that: The cold spraying process for preparing the base layer and the composite layer is as follows: the working gas is one or more of air, nitrogen, and helium; the spraying pressure of the cold spraying is 1 to 7.5 MPa; the spraying temperature of the cold spraying is 200 to 800°C; the gas velocity of the cold spraying is 800 to 1200 m / s; the ambient temperature of the spraying is -5°C to 45°C, and the spraying distance of the cold spraying is 10 to 70 mm.

10. Application of a method for preparing a coating for a high current copper-aluminum busbar fitting terminal, characterized in that: The method for preparing the coating for the hardware terminal described in claims 7 to 9 is applied to the preparation of a high-current busbar hardware terminal or the surface repair of a high-current busbar hardware terminal.

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