Cyanide-free electroplating solution suitable for silver-tungsten alloy co-deposition and plating layer preparation method and application

Abstract

The invention relates to a cyanide-free electroplating solution suitable for silver-tungsten alloy co-deposition and a plating layer preparation method and application, and belongs to the technical field of metal electroplating. The silver-tungsten alloy electroplating solution comprises the following components according to the concentration: 1.2-2.0 g / L of silver nitrate; the concentration of 5, 5-dimethyl hydantoin (DMH) is 25-30 g / L; 3.0 to 3.5 g / L of tungstate; 20 to 25 g / L of citrate; 7-8 g / L of carbonate; and the pH value of the electroplating solution is 10.5-11.5. A cyanide-free electroplating system is constructed, sodium citrate is introduced as an auxiliary coordination agent, metal ions in a plating solution can be effectively stabilized through the strong complexing capacity of the sodium citrate, and the stability of the plating solution is enhanced; and the hydrolytic sensitivity of tungstate radicals is reduced in an alkaline interval. And the co-deposition of the silver-tungsten alloy can be realized in one step only by adopting a direct-current power supply.

Description

Technical Field

[0001] This invention belongs to the field of electroplating technology, and relates to an electroplating technology for co-deposition of silver-tungsten alloy coatings. Specifically, it relates to a cyanide-free electroplating solution suitable for co-deposition of silver-tungsten alloys, a coating preparation method, and its application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Silver plating, due to its excellent conductivity, oxidation resistance, and contact reliability, is widely used in critical components and conductive parts of high-voltage switches and circuit breakers, as well as busbar connectors and conductors, where high electrical performance is required. However, pure silver plating also faces problems such as sulfidation discoloration, poor hardness, high mechanical wear, and severe arc erosion during actual service, leading to increased contact resistance, overheating at connection points, and shortened service life. Therefore, to improve the shortcomings of pure silver plating in terms of hardness, wear resistance, sulfidation resistance, and arc erosion resistance, elements such as nickel, antimony, tin, copper, palladium, and tungsten are usually added to improve and enhance the performance of the silver plating. For example, adding antimony results in a silver-antimony alloy plating, whose hardness (up to 2-3 times that of pure silver) and wear resistance are significantly improved while maintaining good conductivity; adding tungsten results in a silver-tungsten alloy plating, which benefits from silver's excellent conductivity (resistivity as low as 1.59 × 10⁻⁶). -8 The coating combines the advantages of Ω·m with the high strength, high hardness, and high melting point (3422℃) of tungsten, and also possesses comprehensive properties such as high conductivity, excellent wear resistance, resistance to arc erosion, and high-temperature stability. These coatings are crucial in the arc contacts of various medium and high voltage circuit breakers and contactors, ensuring the safe interruption of power grid operations.

[0004] There are various methods for preparing silver alloy coatings, mainly divided into two categories: electroplating and physical / chemical deposition. Among these, electroplating is the most widely used and economical method in industry, a process for depositing silver alloy coatings on the surface of an object using electrochemical methods. Tungsten has a very negative deposition potential (WO4). 2- / W) is approximately -1.05V; while the standard electrode potential of silver (Ag) + The voltage of [Ag(CN)2] is +0.799V, a difference of nearly 1.85V. This causes silver to preferentially precipitate in large quantities in aqueous solution, while tungsten is difficult to reduce, making it difficult to prepare co-deposited silver-tungsten alloy coatings under conventional conditions. To overcome this obstacle, traditional processes commonly use highly toxic cyanides (such as KCN) as strong coordinating agents for silver, forming a stable [Ag(CN)2]2. -The complex reduces the reduction potential of silver to approach the deposition potential of tungsten, thereby achieving co-deposition. However, cyanide is highly toxic, not only in the electroplating process, but also in the post-electroplating treatment of wastewater containing cyanide, which has problems such as great difficulty, high environmental risk and the like, seriously restricting the development and application of the technology, and an environmentally friendly alternative process is urgently needed to be developed.

[0005] In the prior art, 5,5-dimethylhydantoin (DMH) is used as a main complexing agent to construct a cyanide-free electroplating system, and nickel salt, silver salt and tungsten salt are used to prepare an electroplating solution, thereby obtaining an electroplating layer containing nickel, silver and tungsten. However, the technology needs to use a pulse reverse plating brush plating process, which is a multiple deposition process that continuously interrupts and circulates: silver is deposited at a positive potential, tungsten acid root ions are deposited at a reverse potential, and metallic tungsten is reduced to achieve co-deposition of Ag-W alloy. In the electroplating process, metallic nickel is used as an inducer, and tungsten is deposited together with the metallic nickel to form a heteropoly acid or an intermediate, thereby being induced to precipitate, achieving co-deposition of silver, nickel and tungsten. Although silver and nickel and tungsten are deposited at the negative electrode, the actual process is that silver and nickel and tungsten are deposited separately at the cathode. Silver is mainly deposited at a positive potential, and when switched to a negative potential, the deposition of silver is inhibited or stopped, while nickel and tungsten begin to deposit on the surface covered by silver, and the obtained is a composite plating layer in which Ni-W alloy particles are embedded in a silver matrix. In addition, the pulse reverse plating process has strict requirements on the waveform, frequency, duty cycle, peak current / voltage and other parameters of the pulse, and any slight change will greatly affect the relative deposition rate of the three metals and the composition of the plating layer. On the other hand, since the deposition of Ni-W needs to be carried out at a relatively negative potential, the hydrogen evolution reaction will be very intense, resulting in very low current efficiency, thereby causing the plating layer to be prone to problems such as porosity, looseness and poor adhesion. Therefore, the technology has extremely high requirements on the power supply equipment, control system and process parameters of electroplating, and it is difficult to control the quality of the plating layer, resulting in a significantly higher investment and maintenance cost than conventional direct current electroplating, increasing the input cost of plating production in large-scale production, and increasing the difficulty of process control, thereby facing great challenges in economic efficiency and popularization in actual industrial applications. SUMMARY

[0006] To solve the above technical problems, the purpose of the present application is to provide a cyanide-free electroplating solution and a plating layer preparation method and application suitable for silver-tungsten alloy co-deposition. The electroplating solution suitable for silver-tungsten alloy co-deposition uses DMH as a complexing agent and sodium citrate as an auxiliary complexing agent to enhance the stability of metal ions in the plating solution, thereby eliminating the use of toxic cyanide complexing agents and constructing a cyanide-free electroplating system. By accurately optimizing the ion concentration ratio of silver and tungsten in the plating solution, the purpose of adjusting and narrowing the deposition potential difference is achieved, thereby realizing the preparation of a silver-tungsten co-deposition alloy plating layer.

[0007] The application adopts a pre-nickel plating manner, which not only realizes the induction effect of nickel on tungsten deposition and enhances the adhesion of the plating layer, but also avoids the problem of the decline of the conductive performance of the silver alloy plating layer caused by the doping of nickel element in the silver tungsten alloy plating layer. The application realizes one-step co-deposition of the silver tungsten alloy by adopting a direct current plating manner, thereby ensuring the compactness and uniformity of the silver tungsten alloy plating layer. In order to achieve the above-mentioned purpose, the technical scheme of the application is as follows: In a first aspect, a cyanide-free electroplating solution suitable for silver tungsten alloy co-deposition, wherein the components and concentrations include: Silver nitrate 1.2-2.0 g / L; 5,5-dimethyl hydantoin (DMH) 25-30 g / L; Tungstate 3.0-3.5 g / L; Citrate 20-25 g / L; Carbonate 7-8 g / L; The pH of the electroplating solution is 10.5-11.5.

[0008] Optionally, the tungstate includes one or more of sodium tungstate and potassium tungstate.

[0009] Optionally, the citrate includes one or more of potassium citrate and sodium citrate.

[0010] Optionally, the carbonate includes one or more of potassium carbonate and sodium carbonate.

[0011] Optionally, it further includes a pH adjuster, and the pH adjuster includes one or more of sodium hydroxide and potassium hydroxide.

[0012] In a second aspect, a preparation method of a silver tungsten alloy co-deposition plating layer includes the following steps: S1, degreasing and deoxidizing film on the surface of the electroplating substrate; S2, pre-plating nickel on the surface of the electroplating substrate to obtain a nickel-plated substrate; S3, connecting the nickel-plated substrate to a working electrode, immersing it in the above-mentioned silver tungsten alloy electroplating solution for plating, and adjusting the current density to 0.5-1 mA / cm 2 , and the electroplating time is 60-80 min.

[0013] Optionally, in S1, the electroplating substrate is a copper substrate, or an aluminum substrate with a surface modified with copper.

[0014] Optionally, in S1, the method for degreasing and deoxidizing film includes immersing the electroplating substrate in a 10 vol% H2SO4 solution for 5-10 min, and then washing it with deionized water and drying.

[0015] Optionally, in S2, the method for pre-plating nickel includes: connecting the electroplating substrate to the pre-plating nickel working electrode and immersing it in the electroplating nickel solution for plating.

[0016] Optionally, the components and concentrations contained in the nickel plating solution include: Nickel sulfate 200~250g / L; can be added in the form of NiSO4•6H2O; Nickel chloride 8~12 g / L; can be added in the form of NiCl2•6H2O; Magnesium sulfate 10~20 g / L; can be added in the form of MgSO4•7H2O; Sodium citrate 15~20g / L; can be added in the form of C6H5Na3O7•2H2O; Boric acid 15~25g / L.

[0017] Optionally, in S2, the working electrode is the negative electrode, the positive electrode is connected to the nickel plate, and the current density is adjusted to 3~5 mA / cm². 2 The pre-plating time for nickel is 30-40 minutes.

[0018] Optionally, in S3, the working electrode is the negative electrode.

[0019] Optionally, in S, the temperature is room temperature.

[0020] Thirdly, the silver-tungsten alloy co-deposited coating prepared by the above-mentioned method includes a pre-plated nickel layer and a silver-tungsten alloy coating covering the surface of the pre-plated nickel layer.

[0021] Optionally, the thickness of the pre-plated nickel layer is 20-30 μm.

[0022] Optionally, the thickness of the silver-tungsten alloy coating is 140-150 μm.

[0023] Fourthly, the application of the aforementioned silver-tungsten alloy co-deposited coating.

[0024] Optionally, the application includes applications at high-voltage circuit breaker contacts or switch arc contact points.

[0025] The beneficial effects of this invention are as follows: (1) Using 5,5-dimethylhydantoin (DMH) as the main coordinating agent, the cyanide used in traditional electroplating is completely replaced, and cyanide-free deposition of silver-tungsten alloy coating is achieved. This fundamentally avoids the problems of using and disposing of highly toxic substances, greatly reduces environmental and health risks, and is in line with the development trend of green electroplating.

[0026] (2) By precisely designing and optimizing the concentration ratio of silver ions and tungstate ions, the deposition potentials of the two in the plating solution tend to be close, so that stable and controllable co-deposition of silver and tungsten can be achieved under conventional DC electroplating conditions, and a silver-tungsten alloy coating with adjustable composition is obtained. The method is scientific and has good reproducibility.

[0027] (3) By adopting the pre-nickel plating process, the nickel layer’s inductive effect on tungsten deposition is utilized, which significantly improves the bonding force between the subsequent silver-tungsten alloy coating and the substrate. At the same time, the nickel layer is only used as a transition layer and does not participate in alloying during the subsequent co-deposition process, thus avoiding the incorporation of nickel elements into the silver-tungsten coating and effectively ensuring the inherent high conductivity of the silver alloy coating.

[0028] (4) The entire electroplating process only requires a DC power supply to achieve co-deposition of silver-tungsten alloy in one step, without the need for complex pulse or periodic reversing equipment. The process is simple, the parameters are easy to control, and the operation is convenient, which helps to reduce equipment investment and operating costs. It has good process stability and prospects for large-scale production application. Attached Figure Description

[0029] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0030] The diagram exaggerates the spacing or dimensions between parts to show their positions; the diagram is for illustrative purposes only.

[0031] Figure 1 This is the XPS analysis result of Example 1 in the specific implementation of this application.

[0032] Figure 2 The above are the SEM analysis results of Example 1 in the specific implementation of this application.

[0033] Figure 3 The hardness analysis results are for Example 1 in the specific implementation of this application.

[0034] Figure 4 This is the XPS analysis result of Comparative Example 1 in the specific implementation of this application.

[0035] Figure 5 This is the SEM analysis result of Comparative Example 1 in the specific implementation of this application.

[0036] Figure 6 The hardness analysis results are for Comparative Example 1 in the specific embodiments of this application. Detailed Implementation

[0037] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0038] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0039] One or more embodiments of the present invention provide a cyanide-free electroplating solution suitable for co-deposition of silver-tungsten alloys, wherein the components and concentrations include: Silver nitrate 1.2~2.0 g / L; 5,5-Dimethylhydantoin (DMH) 25~30 g / L; Tungstate 3.0~3.5 g / L; Citrate 20~25 g / L; Carbonate 7~8 g / L; The pH of the electroplating solution is 10.5~11.5.

[0040] Of the above components, 5,5-dimethylhydantoin (DMH) serves as the main ligand, reacting with Ag... + [Ag(DMH)2] is formed. + A cyanide-free electroplating system was constructed using main complexes; citrate was used as an auxiliary ligand, and its strong complexing ability could effectively stabilize metal ions in the plating solution and enhance the stability of the plating solution; given the hydrolytic sensitivity of tungstate, the pH value of the plating solution was strictly controlled within the alkaline range of 10.5–11.5.

[0041] Optionally, the tungstate includes one or more of sodium tungstate and potassium tungstate; the reduction potentials of silver and tungsten are theoretically calculated using the Nernst equation, the ion concentration ratio of the two in the plating solution is optimized, and the co-deposition potential difference is reduced by utilizing the regulating effect of the ligand on the metal deposition potential, thus providing a thermodynamic basis for realizing silver-tungsten co-deposition.

[0042] Optionally, the citrate includes one or more of potassium citrate and sodium citrate; the citrate ion contains a plurality of -COO groups. - Groups can also react with Ag + Simultaneously, citrate ions possess strong complexing ability, preferentially binding with WO4. 2-The formation of stable heteropolyacid complexes (such as phosphotungstic acid-like structures) effectively prevents tungstate ions from contacting silver ions, thereby fundamentally avoiding the formation of silver-tungsten precipitation and achieving silver-tungsten co-deposition. Furthermore, citrate has good buffering capacity in the alkaline range (pH 8-12). The above formulation has a pH as high as 10.5-11.5, and citrate can stabilize this strongly alkaline environment, offsetting the local pH increase caused by cathode hydrogen evolution during electroplating, and ensuring the stability of DMH and tungstate ions.

[0043] Optionally, the carbonate includes one or more of potassium carbonate and sodium carbonate; the CO3 in the carbonate... 2- Can be used with Ag + It forms an unstable [Ag(CO3)] - Transition complexes can dynamically regulate the reduction rate of silver ions on the surface. In synergy with DMH / citrate, they can make the coating crystals more delicate and smooth. At the same time, they can also act as pH buffers, provide a large number of conductive ions, improve current efficiency, make the current distribution more uniform, improve the uniformity of coating thickness, and reduce the tank voltage to save energy.

[0044] Optionally, a pH adjuster may also be included, comprising one or more of sodium hydroxide and potassium hydroxide; it is mainly used to adjust the pH of the initial electroplating solution, maintain strong alkaline conditions, and ensure the normal operation of the core ligand (DMH), tungstate, and the entire buffer system.

[0045] One or more embodiments of the present invention provide a method for preparing a silver-tungsten alloy co-deposited coating, comprising the following steps: S1. Degrease and remove oxide film from the surface of the electroplated substrate; S2. Pre-plat nickel onto the surface of the electroplating substrate to obtain a nickel-plated substrate; S3. Connect the nickel-plated substrate to the working electrode and immerse it in the above-mentioned silver-tungsten alloy electroplating solution for plating, adjusting the current density to 0.5~1 mA / cm². 2 The electroplating time is 60~80 min.

[0046] In the above process, the induced co-deposition effect of nickel on tungsten deposition is first utilized to further promote the co-deposition of silver-tungsten alloy, and the nickel layer is used to promote the deposition of silver-tungsten alloy.

[0047] Optionally, in S1, the electroplating substrate is a copper substrate, or it can be an aluminum substrate with a copper-modified surface.

[0048] Optionally, in S1, the degreasing and oxide film removal methods include: immersing the electroplated substrate in a 10 vt% H2SO4 solution for 5-10 min, then rinsing with deionized water and drying; avoiding oxides or lipids from affecting the adhesion of the coating to the substrate surface, or even affecting the conductivity of the electroplated substrate surface, promoting the formation of a smooth and dense coating, and reducing internal defects.

[0049] Optionally, in S2, the method of pre-plating nickel includes: connecting the electroplating substrate to the pre-plating nickel working electrode and immersing it in the electroplating nickel solution for plating; the nickel in the pre-plated nickel layer acts as an inducer to promote the deposition of tungsten, thereby promoting the co-deposition of silver-tungsten alloy; at the same time, it avoids the problem of decreased conductivity of silver alloy coating caused by nickel doping in silver-tungsten alloy coating.

[0050] Optionally, the components and concentrations contained in the nickel plating solution include: Nickel sulfate 200~250 g / L; can be added in the form of NiSO4•6H2O; Nickel chloride 8~12 g / L; can be added in the form of NiCl2•6H2O; Magnesium sulfate 10~20 g / L; can be added in the form of MgSO4•7H2O; Sodium citrate 15~20 g / L; can be added in the form of C6H5Na3O7•2H2O; Boric acid 15~25 g / L.

[0051] Optionally, in S2, the working electrode is the negative electrode, the positive electrode is connected to the nickel plate, and the current density is adjusted to 3~5 mA / cm². 2 The pre-plating time for nickel is 30-40 minutes, forming a homogeneous pre-plated nickel layer.

[0052] Optionally, in S3, the working electrode is the negative electrode, which can be electroplated by an electric bath. The process does not involve potential changes, and the coating is deposited on the surface to be plated, resulting in a coating with stronger adhesion, denser crystals, lower porosity, and uniform and controllable thickness.

[0053] Optionally, in S3, the temperature is set to room temperature.

[0054] One or more embodiments of the present invention provide a method for preparing the above-mentioned silver-tungsten alloy co-deposited coating, which includes a pre-plated nickel layer on the surface of an electroplated substrate, wherein the surface of the pre-plated nickel layer is coated with a silver-tungsten alloy coating.

[0055] In the above structures, the silver-tungsten coating obtained after pre-plating nickel exhibits significantly optimized density and continuity in its microstructure.

[0056] Optionally, the thickness of the pre-plated nickel layer is 20-30 μm.

[0057] Optionally, the thickness of the silver-tungsten alloy coating is 140-150 μm; this thickness is based on the maximum electroplating time. If the electroplating time is extended indiscriminately, the coating will peel off, affecting the quality of the electroplated layer.

[0058] Fourthly, the application of the aforementioned silver-tungsten alloy coating.

[0059] Optionally, the application includes high-voltage circuit breaker contacts or switch arc contact areas.

[0060] The present invention will be further described below with reference to specific embodiments.

[0061] Example 1 A silver-tungsten alloy electroplating solution, wherein the components and concentrations are as follows: The concentration of AgNO3 is 1.7 g / L, used to provide silver ions; The concentration of DMH (5,5-dimethylhydantoin) was 26 g / L, which was used as the main ligand. The Na2WO4 concentration is 3.5 g / L, used to provide tungstate ions; The concentration of C6H5Na3O7 is 20 g / L. As an auxiliary ligand, it is mainly used to stabilize tungstate in the electroplating solution and also to maintain pH stability. The K2CO3 concentration is 8 g / L, and its functions include: providing conductive ions and regulating the reduction rate of metal ions. The KOH concentration is 20 g / L, used to provide alkaline conditions, specifically 11 ± 0.5.

[0062] A nickel plating solution, comprising the following components and concentrations: The concentration of NiSO4•6H2O is 400 g / L; The concentration of NiCl2•6H2O is 20 g / L The concentration of MgSO4•7H2O is 32 g / L The concentration of C6H5Na3O7•2H2O is 20 g / L The concentration of boric acid is 20 g / L.

[0063] The concentrations of each component in the electrolyte were calculated using the Nernst equation.

[0064] The method for preparing a silver-tungsten alloy coating using the above electroplating solution includes the following steps: S1. Select a brass part as the electroplating substrate, immerse the electroplating substrate in a 10 vol% H2SO4 solution for 8±2 min, then rinse with deionized water and dry to obtain the copper part to be electroplated.

[0065] S2. Connect the copper part to be electroplated to the negative terminal of the DC power supply, and the nickel plate to the positive terminal of the DC power supply. Place the copper part to be electroplated and the nickel plate in the above-mentioned nickel plating solution, with the submerged area of ​​the copper part in the solution being 6 cm². 2 Make the electroplating surface of the copper part to be electroplated parallel to the surface of the nickel plate and maintain a set distance. Adjust the current to 30mA and pre-plat the copper part with nickel for 30 minutes. Take out the copper part after nickel plating, clean and dry it to obtain the pre-plated nickel copper part.

[0066] S3. Connect the pre-plated nickel-copper part to the negative terminal of the DC power supply, and connect the stainless steel plate to the positive terminal of the DC power supply. Place the pre-plated nickel-copper part and the stainless steel plate into the aforementioned silver-tungsten alloy electroplating solution, ensuring that the surface of the stainless steel plate is parallel to the electroplating surface of the pre-plated nickel-copper part and maintaining a set distance. Adjust the current density to 1 mA / cm². 2 The electroplating time is 60 minutes. After removing the copper part, it is cleaned and dried to obtain a device with a silver-tungsten alloy coating.

[0067] X-ray photoelectron spectroscopy (XPS) analysis was performed on the obtained silver-tungsten alloy co-deposited coating, and the results are as follows: Figure 1 As shown, it can be clearly observed that on the surface of the silver-tungsten coating obtained after introducing the pre-nickel plating process, the tungsten element exhibits complete and distinctive XPS signal peaks, and its binding energy position matches well with the standard peak position of metallic tungsten and its oxide species.

[0068] The obtained silver-tungsten alloy co-deposited coating was analyzed by scanning electron microscopy (SEM), and the results are as follows: Figure 2 As shown, the coating surface is uniform and smooth, with fine and tightly arranged grains, which further confirms the superior performance of the silver-tungsten alloy electroplating solution in this embodiment.

[0069] Nanoindentation testing (six test points) was performed on the obtained silver-tungsten alloy co-deposited coating, and the hardness of the pre-plated nickel-silver-tungsten coating was measured as follows: Figure 3 As shown, the hardness is HV 230~250. This data not only meets the technical standards, but more importantly, it perfectly matches the densified structure revealed by SEM analysis and the results of XPS confirming the successful introduction of tungsten.

[0070] Comparative Example 1 A silver-tungsten alloy electroplating solution, wherein the components and concentrations are as follows: The concentration of AgNO3 is 1.7 g / L, used to provide silver ions; DMH (5,5-dimethylhydantoin) at a concentration of 26 g / L was used as the main ligand. The Na2WO4 concentration is 3.5 g / L, used to provide tungstate ions; The concentration of C6H5Na3O7 is 20 g / L. As an auxiliary ligand, it is mainly used to stabilize tungstate in the electroplating solution and also to maintain pH stability. The K2CO3 concentration is 8 g / L, and its functions include: providing conductive ions and regulating the reduction rate of metal ions. The KOH concentration is 20 g / L, used to provide alkaline conditions, specifically 11 ± 0.5.

[0071] The method for preparing a silver-tungsten alloy coating using the above electroplating solution includes the following steps: S1. Select a brass part as the electroplating substrate, immerse the electroplating substrate in a 10 vol% H2SO4 solution for 5-10 minutes, then rinse with deionized water and dry to obtain the copper part to be electroplated.

[0072] S3. Connect the copper part to be electroplated to the negative terminal of the DC power supply, and the stainless steel plate to the positive terminal of the DC power supply. Place the copper part to be electroplated and the stainless steel plate into the silver-tungsten alloy electroplating solution, respectively, so that the surface of the stainless steel plate is parallel to the electroplating surface of the copper part to be electroplated, and maintain a set distance. Adjust the current density to 1 mA / cm². 2 The electroplating time is 60 minutes. After removing the copper part, it is cleaned and dried to obtain a device with a silver-tungsten alloy coating.

[0073] X-ray photoelectron spectroscopy (XPS) analysis was performed on the obtained silver-tungsten alloy coating, and the results are as follows: Figure 3 As shown, the signal intensity of tungsten in the unplated nickel sample was significantly lower, even making it difficult to detect effectively. This analytical result clearly verifies the crucial role of the pre-plated nickel layer in promoting the electrochemical deposition of tungsten ions: nickel may optimize the deposition kinetics of tungsten by inducing interfacial electronic structure regulation, thereby achieving stable incorporation and uniform distribution of tungsten in the coating.

[0074] The obtained silver-tungsten alloy coating was analyzed by scanning electron microscopy (SEM), and the results are as follows: Figure 4 As shown, the coating surface is uneven and has obvious defects such as holes.

[0075] Nanoindentation testing (six test points) was performed on the obtained silver-tungsten alloy coating. The average hardness of the unplated nickel-silver-tungsten coating was measured to be HV 120~140. Figure 6 As shown, it is significantly lower than that of Example 1.

[0076] The plating bath electroplating method used in this invention is different from the pulse reverse plating electrobrush plating method involved in the background technology.

[0077] Electroplating is an electrochemical process that uses a plating pen, immersed in a plating solution, as the anode. The pen contacts and moves continuously against the workpiece surface, causing metal ions to discharge and crystallize on the negative electrode (workpiece) surface, forming a metal coating. Because of the relative movement between the plating pen and the workpiece in electroplating, the entire surface does not undergo simultaneous reduction and crystallization of metal ions. Instead, localized areas of the surface experience instantaneous discharge and crystallization upon contact with the pen. The plating solution used in electroplating is typically an aqueous solution of organometallic complexes, with a significantly higher metal particle concentration than in traditional plating baths. Strong acids or alkalis are avoided. The metal ion concentration in the plating solution is relatively high, and the current density is several times or even tens of times higher than in traditional plating baths. Therefore, to overcome the drawback of easy passivation of the anode, the anode used in electroplating is usually an insoluble graphite electrode.

[0078] The electroplating process used in the embodiments of this invention is a continuous electrodeposition process, where the coating is deposited uniformly on the surface being plated. Therefore, electroplating in a plating bath results in a coating with stronger adhesion, denser crystals, lower porosity, and controllable uniform thickness. The bonding strength and consistency between the coating and the substrate far exceed those of brush plating used for repair purposes. Furthermore, in large-scale production, the unit cost of electroplating in a plating bath is significantly lower than that of brush plating. Although the initial equipment investment is higher, its automation potential is significant, and it eliminates the need for manual hand-held operation, offering outstanding economic advantages under batch production conditions.

[0079] Comparative Example 2 A silver-tungsten alloy electroplating solution, wherein the components and concentrations are as follows: The concentration of AgNO3 is 1.7 g / L, used to provide silver ions; The concentration of DMH (5,5-dimethylhydantoin) was 26 g / L, which was used as the main ligand. The Na2WO4 concentration is 3.5 g / L, used to provide tungstate ions; The K2CO3 concentration is 8 g / L, and its functions include: providing conductive ions and regulating the reduction rate of metal ions. The KOH concentration is 20 g / L, used to provide alkaline conditions, specifically 11 ± 0.5.

[0080] The difference from Example 1 is that C6H5Na3O7 is not added.

[0081] A nickel plating solution, comprising the following components and concentrations: The concentration of NiSO4•6H2O is 400 g / L; The concentration of NiCl2•6H2O is 20 g / L The concentration of MgSO4•7H2O is 32 g / L The concentration of C6H5Na3O7•2H2O is 20 g / L The concentration of boric acid is 15~25g / L.

[0082] The method for preparing a silver-tungsten alloy coating using the above electroplating solution includes the following steps: S1. Select a brass part as the electroplating substrate, immerse the electroplating substrate in a 10 vol% H2SO4 solution for 8 minutes, then rinse with deionized water and dry to obtain the copper part to be electroplated.

[0083] S2. Connect the copper part to be electroplated to the negative terminal of the DC power supply, and the nickel plate to the positive terminal of the DC power supply. Place the copper part to be electroplated and the nickel plate in the above-mentioned nickel plating solution, with the submerged area of ​​the copper part in the solution being 6 cm². 2 Make the electroplating surface of the copper part to be electroplated parallel to the surface of the nickel plate and maintain a set distance. Adjust the current to 30mA and pre-plat the copper part with nickel for 30 minutes. Remove the copper part after nickel plating, clean and dry it to obtain the pre-plated nickel copper part.

[0084] S3. Connect the pre-plated nickel-copper part to the negative terminal of the DC power supply, and connect the stainless steel plate to the positive terminal of the DC power supply. Place the pre-plated nickel-copper part and the stainless steel plate into the aforementioned silver-tungsten alloy electroplating solution, ensuring that the surface of the stainless steel plate is parallel to the electroplating surface of the pre-plated nickel-copper part and maintaining a set distance. Adjust the current density to 1 mA / cm². 2 The electroplating time is 60 minutes. After removing the copper part, it is cleaned and dried to obtain a device with a silver-tungsten alloy coating.

[0085] Comparative Example 3 A silver-tungsten alloy electroplating solution, wherein the components and concentrations are as follows: The concentration of AgNO3 is 1.7 g / L, used to provide silver ions; DMH (5,5-dimethylhydantoin) at a concentration of 10 g / L was used as the main ligand. The Na2WO4 concentration is 3.5 g / L, used to provide tungstate ions; The concentration of C6H5Na3O7 is 10 g / L. As an auxiliary ligand, it is mainly used to stabilize tungstate in the electroplating solution and also to maintain pH stability. The K2CO3 concentration is 4 g / L, and its functions include: providing conductive ions and regulating the reduction rate of metal ions. The KOH concentration is 20 g / L, used to provide alkaline conditions, specifically 11 ± 0.5.

[0086] The difference from Example 1 is that the concentrations of DMH (5,5-dimethylhydantoin), C6H5Na3O7 and K2CO3 were adjusted.

[0087] A nickel plating solution, comprising the following components and concentrations: The concentration of NiSO4•6H2O is 400 g / L; The concentration of NiCl2•6H2O is 20 g / L The concentration of MgSO4•7H2O is 32 g / L The concentration of C6H5Na3O7•2H2O is 20 g / L The concentration of boric acid is 15~25g / L.

[0088] The method for preparing a silver-tungsten alloy coating using the above electroplating solution includes the following steps: S1. Select a brass part as the electroplating substrate, immerse the electroplating substrate in a 10 vol% H2SO4 solution for 8 minutes, then rinse with deionized water and dry to obtain the copper part to be electroplated.

[0089] S2. Connect the copper part to be electroplated to the negative terminal of the DC power supply, and the nickel plate to the positive terminal of the DC power supply. Place the copper part to be electroplated and the nickel plate in the above-mentioned nickel plating solution, with the submerged area of ​​the copper part in the solution being 6 cm². 2 Make the electroplating surface of the copper part to be electroplated parallel to the surface of the nickel plate and maintain a set distance. Adjust the current to 30mA and pre-plat the copper part with nickel for 30 minutes. Remove the copper part after nickel plating, clean and dry it to obtain the pre-plated nickel copper part.

[0090] S3. Connect the pre-plated nickel-copper part to the negative terminal of the DC power supply, and connect the stainless steel plate to the positive terminal of the DC power supply. Place the pre-plated nickel-copper part and the stainless steel plate into the aforementioned silver-tungsten alloy electroplating solution, ensuring that the surface of the stainless steel plate is parallel to the electroplating surface of the pre-plated nickel-copper part and maintaining a set distance. Adjust the current density to 1 mA / cm². 2 The electroplating time is 60 minutes. After removing the copper part, it is cleaned and dried to obtain a device with a silver-tungsten alloy coating.

[0091] The results of testing the coating composition, microstructure, and Vickers hardness of Examples 1, Comparative Examples 1 to 3 are shown in Table 1.

[0092] Table 1

[0093] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A cyanide-free electroplating solution suitable for co-deposition of silver-tungsten alloys, characterized in that, The components and their concentrations include: Silver nitrate 1.2~2.0 g / L; 5,5-Dimethylhydantoin (DMH) 25~30 g / L; Tungstate 3.0~3.5 g / L; Citrate 20~25g / L; Carbonate 7~8g / L; The pH of the electroplating solution is 10.5~11.

5.

2. The cyanide-free electroplating solution for co-deposition of silver-tungsten alloys as described in claim 1, characterized in that, The tungstate includes one or more of sodium tungstate and potassium tungstate; Alternatively, the citrate may include one or more of potassium citrate and sodium citrate; Alternatively, the carbonate may include one or more of potassium carbonate and sodium carbonate.

3. A method for preparing a silver-tungsten alloy co-deposited coating, characterized in that, Includes the following steps: S1. Degrease and remove oxide film from the surface of the electroplated substrate; S2. Pre-plat nickel onto the surface of the electroplating substrate to obtain a nickel-plated substrate; S3. Connect the nickel-plated substrate to the working electrode and immerse it in the silver-tungsten alloy electroplating solution as described in any one of claims 1-3 for plating, adjusting the current density to 0.5~1 mA / cm². 2 The electroplating time is 60~80 minutes.

4. The method for preparing the silver-tungsten alloy co-deposited coating as described in claim 3, characterized in that, In S1, the electroplating substrate is a copper substrate or an aluminum substrate with copper surface decoration; Alternatively, in S1, the degreasing and oxide film removal methods include: immersing the electroplated substrate in a 10 vol% H2SO4 solution for 5-10 min, then rinsing with deionized water and drying.

5. The method for preparing the silver-tungsten alloy co-deposited coating as described in claim 3, characterized in that, In S2, the method for pre-plating nickel includes: connecting the electroplating substrate to the pre-plating nickel working electrode and immersing it in the electroplating nickel solution for plating. Alternatively, the components and concentrations contained in the nickel plating solution include: Nickel sulfate 200~250g / L; Nickel chloride 8~12 g / L; Magnesium sulfate 10~20g / L; Sodium citrate 15~20g / L; Boric acid 15~25g / L; Alternatively, in S2, the working electrode is the negative electrode, the positive electrode is connected to the nickel plate, and the current density is adjusted to 3~5 mA / cm². 2 The pre-plating time for nickel is 30-40 minutes, forming a homogeneous pre-plated nickel layer.

6. The method for preparing the silver-tungsten alloy co-deposited coating as described in claim 5, characterized in that, In S3, the temperature is room temperature.

7. A silver-tungsten alloy co-deposited coating prepared by a method according to any one of claims 3-6, characterized in that, It includes a pre-plated nickel layer and a silver-tungsten alloy coating covering the surface of the pre-plated nickel layer.

8. The silver-tungsten alloy co-deposited coating as described in claim 7, characterized in that, The thickness of the pre-plated nickel layer is 20-30 μm.

9. The silver-tungsten alloy co-deposited coating as described in claim 7, characterized in that, The thickness of the silver-tungsten alloy coating is 140-150 μm.

10. An application of the silver-tungsten alloy co-deposited coating as described in any one of claims 7-9, characterized in that, The applications include those at high-voltage circuit breaker contacts or switch arc contact points.

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