A Cu / Ni / Ag composite coating, its preparation method and application

Abstract

This invention discloses a Cu / Ni / Ag composite coating, its preparation method, and its applications. The composite coating, from the inside out, comprises: a nickel underlayer in direct contact with the copper alloy substrate; a nickel intermediate layer plated on top of the nickel underlayer; and a silver surface layer plated on top of the nickel intermediate layer. This invention utilizes the nickel underlayer to achieve strong interfacial bonding, and the nickel intermediate layer provides stress buffering, diffusion blocking, and mechanical support, fundamentally solving the problems of wrinkling, bulging, and peeling that easily occur in traditional direct silver plating on copper under electro-thermal-mechanical coupling. In the method of this invention, each functional layer can be prepared through a reasonable process sequence and parameter control, requiring no complex equipment and exhibiting excellent process feasibility and repeatability.

Description

Technical Field

[0001] This invention belongs to the field of surface strengthening technology for electrical engineering materials, specifically relating to a Cu / Ni / Ag composite coating, its preparation method, and its application. Background Technology

[0002] In electrical equipment such as medium and high voltage circuit breakers and disconnect switches, copper alloys (such as CuCo2Be) are widely used as the base material for key electrical contact components such as contact fingers due to their excellent electrical and thermal conductivity. To ensure low and stable contact resistance and to take advantage of the excellent electrical conductivity and certain arc resistance of silver (Ag), a layer of silver is commonly plated on the surface of copper alloy contact fingers in industry.

[0003] However, in actual long-term service, especially under the combined effects of mechanical friction from frequent switching on and off, high-temperature arc erosion, and thermal cycling, we have found that silver layers directly plated on copper (Cu) are prone to some problems. First, the interdiffusion between Cu and Ag is intensified under the heat of the arc, easily forming a poor-performing diffusion layer at the interface. Second, the difference in thermal expansion coefficients between Cu and Ag makes the interface susceptible to fatigue damage under repeated thermal stress. These factors together lead to the common phenomena of silver layer wrinkling, bulging, and even localized detachment failure. Once the plating fails, it directly leads to increased contact resistance and excessive temperature rise, and in severe cases, it can cause welding at the contact points, threatening the safe operation of the equipment.

[0004] To improve adhesion, existing technologies employ a pre-plated nickel undercoat. However, a single thin nickel undercoat is insufficient in buffering and blocking the effects of intense arc thermal shock and mechanical shear stress. The overall wear resistance and arc erosion resistance of the coating depend more on the silver layer itself, offering limited improvement.

[0005] Therefore, how to fundamentally improve the interfacial bonding from the perspective of coating structure design, and simultaneously enhance the surface's resistance to friction and arc erosion, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing copper alloy finger surfaces, such as easy wrinkling and peeling of silver plating and insufficient resistance to arc erosion, by providing a novel Cu / Ni / Ag composite coating, its preparation method, and its applications. The Cu / Ni / Ag composite coating of this invention, through the design of a specific double-layer nickel intermediate structure, significantly enhances the bonding strength between the coating and the substrate, and effectively improves the overall mechanical support and arc erosion resistance of the coating.

[0007] Specifically, the Cu / Ni / Ag composite coating of the present invention comprises, from the inside out: a nickel (Ni) underlayer in direct contact with the copper alloy substrate; a nickel (Ni) intermediate layer plated on the nickel underlayer; and a silver (Ag) top layer plated on the nickel intermediate layer. The copper alloy substrate is chromium-zirconium copper, silver-copper, or a zirconium-copper alloy.

[0008] The nickel (Ni) underlayer is directly plated onto a clean, activated copper alloy substrate. Its main function is to provide a strong metallurgical bond with the copper substrate, laying a solid adhesion foundation for the entire plating system.

[0009] A nickel (Ni) interlayer is plated on top of a nickel underlayer. Unlike a single thin underlayer, this invention features a dense nickel interlayer with a certain thickness. Firstly, it serves as a primary stress buffer and diffusion barrier layer, effectively preventing atomic interdiffusion between the copper substrate and the surface silver layer, and alleviating stress caused by differences in thermal expansion coefficients. Secondly, it acts as a strong support layer, providing a robust "base" for the surface silver layer, improving the overall coating's resistance to mechanical friction and arc impact deformation.

[0010] The silver (Ag) outermost layer provides the excellent electrical conductivity and a certain degree of resistance to arc erosion necessary for equipment operation. Supported by a robust nickel interlayer, the silver layer's performance can be more stable and sustained.

[0011] Furthermore, the thickness of the nickel underlayer is 0.5-3 μm, the thickness of the nickel intermediate layer is 2-10 μm, and the thickness of the silver surface layer is 3-15 μm. This thickness ratio ensures optimal performance while also considering production costs and efficiency.

[0012] Furthermore, the nickel underlayer is obtained by electroplating with Watt's nickel plating solution; the nickel intermediate layer is obtained by electroplating with a nickel sulfamate system. The nickel intermediate layer obtained by electroplating with a nickel sulfamate system has a low-stress, dense nickel layer.

[0013] Furthermore, the silver surface layer is obtained through a cyanide silver plating process or a non-cyanide silver plating process.

[0014] The present invention also provides a method for preparing the Cu / Ni / Ag composite coating as described above, comprising the following steps: S1. Pre-treat the surface of the copper alloy substrate. Specifically, thoroughly chemically degrease and acid-wash to activate the copper alloy substrate, ensuring that the surface is free of contamination and fully activated.

[0015] S2. Electroplating a nickel underlayer onto the pretreated copper alloy substrate; using a Watt nickel plating solution with good adhesion, applying a low current density, and electroplating for a short time to form a thin, dense, and highly adhesive nickel underlayer.

[0016] S3. Electroplating a nickel intermediate layer on the surface of the nickel substrate; on the nickel substrate, switching to a nickel sulfamate plating bath that can obtain a low-stress, high-density coating. By controlling appropriate current density, temperature and pH value, a nickel intermediate layer that meets the thickness and performance requirements is plated.

[0017] S4. Electroplating a silver layer on the surface of the nickel intermediate layer; on the nickel intermediate layer, using a stable cyanide silver plating process or an environmentally friendly non-cyanide silver plating process, plating a silver layer of the required thickness.

[0018] S5. Clean and dry the workpiece after plating.

[0019] Furthermore, in step S2, the nickel plating substrate is treated with Watt's nickel plating solution, with a current density of 0.5-2.0 A / dm² and a time of 1-5 minutes.

[0020] Furthermore, in step S3, the nickel plating intermediate layer uses a nickel sulfamate plating solution with a current density of 1.0-4.0 A / dm², a temperature of 50-60℃, and a pH value of 3.5-4.5.

[0021] Furthermore, in step S4, the electroplated silver surface layer uses a cyanide silver plating solution, wherein the silver ion concentration is 15-25 g / L, the free potassium cyanide concentration is 60-90 g / L, and the current density is 0.3-0.8 A / dm².

[0022] The present invention also provides an application of the Cu / Ni / Ag composite coating prepared by the aforementioned method in copper alloys for touch fingers.

[0023] The present invention also provides an electrical contact component, wherein the surface of the copper alloy contact base has a Cu / Ni / Ag composite coating as described above, prepared by the aforementioned preparation method.

[0024] Compared with the prior art, the present invention has the following advantages: 1. This invention designs a layered composite structure of "Cu / Ni (bottom layer) / Ni (intermediate layer) / Ag (top layer)," utilizing a nickel bottom layer to achieve strong interfacial bonding, and using a nickel intermediate layer to provide stress buffering, diffusion blocking, and mechanical support. This fundamentally solves the problems of wrinkling, bulging, and peeling that easily occur when silver plating is directly applied to copper under electro-thermal-mechanical coupling, significantly improving the structural integrity and reliability of the plating in complex service environments.

[0025] 2. This invention, by utilizing the robust support provided by the dense nickel interlayer, effectively enhances the resistance to plastic deformation of the surface silver layer. This significantly suppresses material migration and loss when the composite coating is subjected to mechanical friction and high-temperature arc erosion, thereby simultaneously achieving a synergistic improvement in the contact's resistance to friction and wear and its resistance to arc erosion, thus extending the service life of the electrical contacts.

[0026] 3. The dense nickel interlayer with a certain thickness in this invention can effectively block the interdiffusion of atoms between the copper substrate and the silver surface layer, avoid the formation of brittle phases at the interface, and ensure the chemical and structural stability of the contact interface after long-term service or thermal aging, providing a key guarantee for maintaining low and stable contact resistance.

[0027] 4. The composite coating structure involved in this invention is entirely based on a mature electroplating process. Each functional layer can be prepared by reasonable process sequence and parameter control, without the need for complex equipment. It has excellent process feasibility and repeatability, making it easy to promote and apply in existing production systems and achieve stable manufacturing of high-performance contact products. Attached Figure Description

[0028] Figure 1 This is a cross-sectional schematic diagram of the composite coating structure prepared in Example 1 of the present invention; Wherein: 1-copper alloy substrate; 2-nickel bottom layer; 3-nickel intermediate layer; 4-silver top layer. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the scope of protection of the invention.

[0030] Example 1: Preparation of composite coating on the surface of copper-coated fingertip alloy (CuCo2Be) Using high-voltage switch contact copper alloy (CuCo2Be) as the substrate, the preparation steps of its surface composite coating are as follows: (1) Pretreatment: First, place the copper alloy (CuCo2Be) substrate in an alkaline chemical degreasing solution and immerse it at 55-60℃ for 8 minutes. After that, rinse it thoroughly with running water. Then, immerse it in a 15% dilute sulfuric acid solution for surface activation for 20 seconds. After rinsing with water, quickly transfer it to the electroplating tank.

[0031] (2) Electroplated nickel underlayer: A high-adhesion Watt nickel plating solution system was used, which consisted of 260 g / L nickel sulfate, 45 g / L nickel chloride, and 45 g / L boric acid. At room temperature (22±2℃), the cathode current density was controlled at 1.5 A / dm², and electroplating was carried out for 1.5 minutes to form a dense nickel underlayer with a thickness of about 0.8 μm and a strong bond.

[0032] (3) Electroplating of nickel intermediate layer: The workpiece is transferred to a low-stress nickel sulfamate plating bath for plating. The plating bath contains 420 g / L nickel sulfamate, 35 g / L boric acid, and 0.5 mL / L of a special stress reducer (KD-5022 nickel brightener). The process conditions are set as follows: plating bath temperature 52℃, pH value 3.8, current density 3.0 A / dm², and plating time 20 minutes. This process yields a nickel intermediate layer with a thickness of approximately 5 μm, low internal stress, and a dense structure.

[0033] (4) Silver plating layer: After rinsing with pure water, the workpiece is placed in a cyanide silver plating solution. The plating solution provides silver in the form of AgCN at a concentration of 18 g / L, and contains 70 g / L of free KCN and 25 g / L of potassium carbonate. Under room temperature (25±2℃) conditions, electroplating is performed at a current density of 0.7 A / dm² for 30 minutes to finally obtain a silver surface functional layer with a thickness of approximately 8 μm, i.e., the silver plating layer.

[0034] (5) Post-treatment: After electroplating, the workpiece is successively subjected to plating solution recovery, two-stage countercurrent rinsing, and finally dried with 70℃ hot water to complete the entire preparation process.

[0035] Example 2: Preparation of composite coating on the surface of copper-finger alloy (CuCrZr) Using high-voltage switch chromium-zirconium-copper (CuCrZr) contacts as the substrate, the preparation steps of the Ni (bottom layer) / Ni (intermediate layer) / Ag (surface layer) composite coating on its surface are as follows: (1) Pretreatment: The chromium zirconium copper contact finger substrate is soaked in an alkaline chemical degreasing solution (50-60℃) for 5 minutes to remove oil, rinsed with running water; then it is immersed in a 10% dilute sulfuric acid solution for 30 seconds to activate, rinsed with water and quickly transferred to the plating tank.

[0036] (2) Electroplating of nickel underlayer: Using conventional Watt nickel plating solution (nickel sulfate 250 g / L, nickel chloride 40 g / L, boric acid 40 g / L), at room temperature, electroplating was performed for 2 minutes at a cathode current density of 1.0 A / dm² to obtain a nickel underlayer with a thickness of about 1 μm.

[0037] (3) Electroplating of nickel intermediate layer: The workpiece is transferred to a nickel sulfamate plating bath (nickel sulfamate 400 g / L, boric acid 30 g / L). The temperature of the plating bath is controlled at 55℃ and the pH value is 4.0. Electroplating is performed at a current density of 2.5 A / dm² for 25 minutes to obtain a low-stress dense nickel intermediate layer with a thickness of about 6 μm.

[0038] (4) Electroplating silver layer: After rinsing with pure water, the workpiece is placed in a cyanide silver plating solution (silver is added in the form of AgCN, concentration 20 g / L, free KCN concentration 80 g / L, and appropriate amount of potassium carbonate). At room temperature, electroplating is performed at a current density of 0.5 A / dm² for 40 minutes to obtain a silver layer with a thickness of about 12 μm.

[0039] (5) Post-treatment: After electroplating, the workpiece is successively subjected to plating solution recovery, two-stage countercurrent rinsing, and finally dried with 70℃ hot water to complete the entire preparation process.

[0040] The Cu / Ni / Ag composite coating structure designed in this invention, by introducing a functionally distinct double-layer nickel interlayer, fundamentally improves the bonding between the coating and the substrate, and synergistically enhances the surface's arc erosion resistance and wear resistance, resulting in a significantly superior overall performance compared to traditional pure silver coatings. To verify the above effects, the Cu / Ni / Ag composite coating samples prepared in Examples 1 and 2 were used as experimental groups, while samples using the same copper alloy substrate (CuCo2Be and CuCrZr) but with a pure silver surface layer of the same thickness directly electroplated on its surface (excluding the nickel underlayer and nickel interlayer) were used as control groups for performance comparison tests. Arc erosion resistance was assessed using an electrical contact material tester, conducting 3000 on / off tests under a DC resistive load and a current of 10A, evaluating the results by measuring the depth of the erosion pit and mass loss; wear resistance was assessed using a reciprocating friction and wear tester, sliding 100 m under a load of 10N and a sliding speed of 0.1 m / s, evaluating the results by measuring the coefficient of friction and wear volume.

[0041] Test results show that, in terms of arc erosion resistance, the traditional pure silver plating has an ablation pit depth of approximately 8.5 μm and a mass loss of approximately 2.8 mg; the composite plating in Example 1 has an ablation pit depth of approximately 5.3 μm and a mass loss of approximately 1.8 mg, representing reductions of approximately 38% and 35%, respectively; and the composite plating in Example 2 has an ablation pit depth of approximately 5.5 μm and a mass loss of approximately 1.9 mg, representing reductions of approximately 35% and 32%, respectively. Regarding wear resistance, the traditional pure silver plating has a coefficient of friction of approximately 0.32 and a wear volume of approximately 5.5 × 10⁻⁶. -4 mm³; the coefficient of friction of the composite coating in Example 1 is approximately 0.24, and the wear volume is approximately 3.0 × 10⁻⁶ mm³. -4 mm³, respectively reduced by approximately 25% and 45%; the composite coating of Example 2 has a friction coefficient of approximately 0.25 and a wear volume of approximately 3.3 × 10 mm³. -4 mm³, respectively reduced by approximately 22% and 40%. The above data indicate that the present invention significantly improves the arc erosion resistance and wear resistance of the composite coating in an electro-thermal-mechanical coupled service environment through the stress buffering, diffusion blocking and mechanical support effects of the double-layer nickel interlayer.

[0042] Although the present invention has been illustrated and described with reference to preferred embodiments, those skilled in the art should understand that various changes and modifications can be made to the present invention without departing from the scope defined by the claims.

Claims

1. A Cu / Ni / Ag composite coating, characterized in that, The composite coating comprises, from the inside out: a nickel underlayer in direct contact with the copper alloy substrate; a nickel intermediate layer plated on top of the nickel underlayer; and a silver surface layer plated on top of the nickel intermediate layer.

2. The Cu / Ni / Ag composite coating according to claim 1, characterized in that, The thickness of the nickel base layer is 0.5-3 μm, the thickness of the nickel intermediate layer is 2-10 μm, and the thickness of the silver surface layer is 3-15 μm.

3. The Cu / Ni / Ag composite coating according to claim 2, characterized in that, The nickel underlayer is obtained by electroplating with Watt's nickel plating solution; the nickel intermediate layer is obtained by electroplating with a nickel aminosulfonate system.

4. The Cu / Ni / Ag composite coating according to claim 2, characterized in that, The silver surface layer is obtained through cyanide silver plating or non-cyanide silver plating processes.

5. The method for preparing the Cu / Ni / Ag composite coating according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Pretreatment of the copper alloy substrate surface. S2. Electroplating a nickel underlayer onto the pretreated copper alloy substrate; S3. Electroplating a nickel intermediate layer onto the surface of the nickel base layer; S4. Electroplating a silver layer onto the surface of the nickel intermediate layer; S5. Clean and dry the workpiece after plating.

6. The method according to claim 5, characterized in that, In step S2, the nickel plating substrate is plated using Watt's nickel plating solution with a current density of 0.5-2.0 A / dm² and a time of 1-5 minutes.

7. The method according to claim 5, characterized in that, In step S3, the nickel plating intermediate layer uses a nickel sulfamate plating solution with a current density of 1.0-4.0 A / dm², a temperature of 50-60℃, and a pH value of 3.5-4.

5.

8. The method according to claim 5, characterized in that, In step S4, the silver plating surface layer uses a cyanide silver plating solution, wherein the silver ion concentration is 15-25 g / L, the free potassium cyanide concentration is 60-90 g / L, and the current density is 0.3-0.8 A / dm².

9. The application of the Cu / Ni / Ag composite coating according to any one of claims 1-4 or the Cu / Ni / Ag composite coating prepared according to any one of claims 5-8 in copper alloys for touch fingers.

10. An electrical contact component, characterized in that, The copper alloy finger substrate contained therein has a Cu / Ni / Ag composite coating as described in any one of claims 1-4 or a Cu / Ni / Ag composite coating prepared in any one of claims 5-8.

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