A composite plating process

Abstract

This invention belongs to the field of electroplating technology. It provides a composite electroplating process that uses an environmentally friendly, cyanide-free free chlorine system plating solution. Combined with nanoparticle reinforcement and laser cladding post-treatment technology, it effectively solves the problems of high pollution, high coating stress, poor wear resistance and easy cross-contamination in traditional processes. It can obtain a multi-layer composite coating with strong adhesion, wear resistance and corrosion resistance, with significant environmental advantages and excellent comprehensive performance.

Description

Technical Field

[0001] This invention relates to the field of electroplating technology, and more particularly to a composite electroplating process. Background Technology

[0002] Composite electroplating technology, as an important surface treatment method, is widely used in precision electronics, high-end decorative products, and wear-resistant parts. Traditional composite electroplating processes typically involve the sequential deposition of multiple metal layers, such as nickel, copper, and silver, to achieve a balance of protection, conductivity, and aesthetics. However, in actual production, this type of process still faces several long-standing technical challenges that have not been effectively resolved.

[0003] First, the environmental and safety issues of plating bath systems are prominent. Many existing processes rely on plating baths containing cyanide to achieve coating uniformity and adhesion. However, cyanide is highly toxic, posing a threat to the health of operators, while wastewater treatment is costly and places a heavy burden on the environment. Although the industry has attempted to develop cyanide-free electroplating systems, they often cannot match traditional cyanide-containing processes in terms of coating quality and process stability, limiting their widespread application.

[0004] Secondly, stress matching and adhesion control between multilayer coatings present a significant challenge. Differences in thermal expansion coefficients and crystallization behavior between different metal layers can easily lead to internal stress at the interface, causing coating warping, microcracks, and even peeling. This problem is particularly pronounced under temperature variations or mechanical loads. While existing technologies attempt to alleviate stress through additives or heat treatment, the effects are limited, the process window is narrow, and adjustments are highly dependent on experience.

[0005] Furthermore, the problem of limited functionality in coatings is becoming increasingly prominent. While conventional electroplated silver layers possess good conductivity and luster, their low hardness and insufficient wear resistance make them unsuitable for the surface durability requirements of high-end industrial parts. Although some studies have attempted to introduce composite particles to enhance the coating, issues such as particle dispersion and bonding strength with the metal matrix remain unresolved, often at the expense of other coating properties.

[0006] Finally, cross-contamination and quality control during the process are also major challenges. Residual metal ions from previous processes can easily contaminate subsequent plating baths, affecting the lifespan of the plating solution and the purity of the coating. Existing control measures mostly rely on strict inter-tank cleaning and isolation, which not only increases equipment complexity and production costs but also extends the production cycle.

[0007] In summary, current composite electroplating technology still suffers from problems such as poor environmental performance, difficulty in stress control, limited functionality, and cumbersome processes. There is an urgent need to develop a new electroplating process that can achieve greener, more stable, and more efficient industrial applications while ensuring the overall performance of the coating. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a composite electroplating process.

[0009] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a composite electroplating process, comprising the following steps: The workpiece can be subjected to chemical degreasing, electrolytic degreasing, pickling, nickel plating, neutralization, alkaline copper plating, activation, pre-plating silver, silver plating and laser cladding post-treatment in sequence; The nickel plating solution contains nickel chloride, nickel sulfate, boric acid, and stress reliever; The alkaline copper plating solution contains copper salts and free sodium salts; The pre-plating silver solution contains silver ions and free chlorine; The silver plating solution contains silver ions, free chlorine, nano-molybdenum disulfide particles, and a sulfur content regulator.

[0010] Furthermore, the electrolytic degreasing is divided into two steps: the first step has a current of 18~22A, a time of 8~12min, and a temperature of 50~60℃; the second step has a current of 13~17A, a time of 3~7min, and a temperature of 50~60℃.

[0011] Furthermore, in the nickel plating solution, the concentration of nickel chloride is 40~70 g / L, the concentration of nickel sulfate is 200~280 g / L, the concentration of boric acid is 40~60 g / L, the concentration of stress reliever is 0.5~2 g / L, and the pH of the nickel plating solution is 3.5~4.4; the stress reliever is saccharin and / or sodium dodecyl sulfate.

[0012] Furthermore, the nickel plating process involves a current of 10-15A, a voltage of 4.6-5.1V, a temperature of 50-55℃, and a time of 40-60min. After nickel plating is completed, a gradient heat treatment process is used to release the residual stress of the plating layer. The specific steps of the gradient heat treatment process are as follows: first, the temperature is raised to 150-160℃ at a heating rate of 2-3℃ / min and held for 0.5-1h; then, the temperature is raised to 400-410℃ at a heating rate of 5-6℃ / min and held for 1-2h; finally, the temperature is raised to 480-500℃ at a heating rate of 2-3℃ / min and held for 0.5-1h.

[0013] Furthermore, in the alkaline copper plating solution, the concentration of copper salt is 20~50g / L, and the concentration of free sodium salt is 10~40g / L; The copper salt is one or more of cuprous cyanide, copper sulfate, and copper pyrophosphate; The free sodium salt is one or more of sodium pyrophosphate, sodium citrate, sodium tartrate, and sodium hydroxide; The pH of the alkaline copper plating solution is 12.8~13.2, the current for alkaline copper plating is 2.4~2.6A, the temperature is 50~55℃, and the time is 40~50min.

[0014] Furthermore, in the pre-plating silver solution, the silver ion concentration is 1~3g / L and the free chlorine concentration is 80~110g / L; The free chlorine is derived from one or more of sodium chloride, potassium chloride, ammonium chloride, and sodium trichloroacetate; The voltage for the pre-plating of silver is 7~8V, the current is 28~32A, the temperature is 20~25℃, and the time is 40~60s.

[0015] Furthermore, in the silver plating solution, the silver ion concentration is 10~30g / L, the free chlorine concentration is 120~150g / L, the concentration of nano molybdenum disulfide is 5~20g / L, and the sulfur content is 5~50ppm. The free chlorine is derived from one or more of sodium chloride, potassium chloride, ammonium chloride, and sodium trichloroacetate; The sulfur content regulator is sodium thiosulfate and / or mercaptobenzothiazole.

[0016] Furthermore, the silver plating current is 12~20A, the voltage is 1.6~1.8V, the processing time is 80~85min, and the temperature is 20~25℃.

[0017] Furthermore, the particle size of the nano-molybdenum disulfide is 0.1~0.5μm.

[0018] Furthermore, the laser power of the laser cladding post-processing is 500~2000W, and the scanning speed is 5~20mm / s.

[0019] As can be seen from the above technical solution, compared with the prior art, the beneficial effects of the present invention are as follows: In terms of environmental protection and safe production, this invention completely eliminates the highly toxic cyanide widely used in traditional electroplating processes, adopting a free chlorine system based on alkali metal chloride salts. This fundamentally eliminates the health threats posed by cyanide to operators and its potential environmental hazards. This system is not only low in toxicity and easy to handle, but also maintains excellent plating solution stability and coating uniformity, achieving a balance between green production and high performance.

[0020] In terms of the overall performance of the coating, by introducing nano-molybdenum disulfide particles and co-depositing them with silver, a uniformly dispersed reinforcing phase was formed in the metal matrix, significantly improving the microhardness and wear resistance of the coating. This allowed the silver layer to not only maintain good conductivity and aesthetics but also to withstand mechanical friction and repeated operations. The subsequent laser cladding process caused micro-area remelting on the coating surface, which not only eliminated inherent defects such as porosity and microcracks during electrodeposition and reduced porosity but also formed a strong metallurgical bonding interface between the coating and the substrate, as well as between coatings themselves, greatly improving the density, adhesion, and overall durability of the coating.

[0021] In terms of stress control and quality stability, the unique gradient heat treatment process effectively relaxes the internal stress accumulated between different metal layers due to differences in thermal expansion coefficients by precisely controlling the heating rate and holding temperature. This avoids problems such as warping and cracking of the coating due to stress release during use, ensuring the long-term reliability of the product under high temperature or temperature cycling conditions. Simultaneously, by establishing comprehensive physical isolation and chemical cleaning barriers between each plating tank and employing an online monitoring system for real-time feedback control of key process parameters, cross-contamination of metal ions is greatly suppressed, ensuring the long lifespan and high purity of the plating solution, thereby achieving a high degree of consistency in coating composition and quality.

[0022] In summary, this invention, through the systematic integration and collaborative innovation of multiple technologies, simultaneously solves multiple challenges such as environmental protection, functionality, reliability, and stability. The resulting composite coating has excellent wear and corrosion resistance, high bonding strength, excellent conductivity, and long-lasting aesthetics, making it particularly suitable for high-end application scenarios with extremely high requirements for surface performance. Detailed Implementation

[0023] This invention provides a composite electroplating process, comprising the following steps: The workpiece can be subjected to chemical degreasing, electrolytic degreasing, pickling, nickel plating, neutralization, alkaline copper plating, activation, pre-plating silver, silver plating and laser cladding post-treatment in sequence; The nickel plating solution contains nickel chloride, nickel sulfate, boric acid, and stress reliever; The alkaline copper plating solution contains copper salts and free sodium salts; The pre-plating silver solution contains silver ions and free chlorine; The silver plating solution contains silver ions, free chlorine, nano-molybdenum disulfide particles, and a sulfur content regulator.

[0024] In this invention, the chemical degreasing step is as follows: the workpiece is immersed in a solution containing an alkaline degreasing agent at 40~50°C to remove oil stains from the surface of the substrate.

[0025] In this invention, the electrolytic degreasing is divided into two steps. In the first step, the current is 18~22A, preferably 20A; the time is 8~12min, preferably 10min; and the temperature is 50~60℃, preferably 55℃. In the second step, the current is 13~17A, preferably 15A; the time is 3~7min, preferably 5min; and the temperature is 50~60℃, preferably 55℃.

[0026] In this invention, the pickling step is as follows: the workpiece is immersed in a dilute hydrochloric acid solution to remove the oxide film and rust on the surface of the substrate.

[0027] In this invention, the nickel plating solution contains nickel chloride at a concentration of 40-70 g / L, preferably 50-60 g / L, and more preferably 55 g / L; nickel sulfate at a concentration of 200-280 g / L, preferably 220-260 g / L, and more preferably 240 g / L; boric acid at a concentration of 40-60 g / L, preferably 45-55 g / L, and more preferably 50 g / L; a stress reliever at a concentration of 0.5-2 g / L, preferably 1 g / L; and a nickel plating solution with a pH of 3.5-4.4, preferably 4.0. The stress reliever is saccharin and / or sodium dodecyl sulfate.

[0028] In this invention, the nickel plating current is 10~15A, preferably 12A; the voltage is 4.6~5.1V, preferably 5.0V; the temperature is 50~55℃, preferably 52℃; and the time is 40~60min, preferably 50min. After nickel plating is completed, a gradient heat treatment process is used to release the residual stress of the plating layer. The specific steps of the gradient heat treatment process are as follows: first, the temperature is raised to 150-160℃, preferably 155℃, at a heating rate of 2-3℃ / min, and held for 0.5-1h; then, the temperature is raised to 400-410℃, preferably 405℃, at a heating rate of 5-6℃ / min, and held for 1-2h; finally, the temperature is raised to 480-500℃, preferably 490℃, at a heating rate of 2-3℃ / min, and held for 0.5-1h.

[0029] In this invention, the neutralization step is as follows: the workpiece is placed in a weakly alkaline solution for treatment to neutralize the residual acid.

[0030] In this invention, the concentration of copper salt in the alkaline copper plating solution is 20-50 g / L, preferably 30-40 g / L, and more preferably 35 g / L; the concentration of free sodium salt is 10-40 g / L, preferably 20-30 g / L, and more preferably 25 g / L. The copper salt is one or more of cuprous cyanide, copper sulfate, and copper pyrophosphate; The free sodium salt is one or more of sodium pyrophosphate, sodium citrate, sodium tartrate, and sodium hydroxide; The pH of the alkaline copper plating solution is 12.8~13.2, preferably 13; the current for alkaline copper plating is 2.4~2.6A, preferably 2.5A; the temperature is 50~55℃, preferably 52℃; and the time is 40~50min, preferably 45min.

[0031] In this invention, the activation step is to briefly treat the workpiece in an acidic activation solution or a solution containing a surfactant to remove the extremely thin oxide film on the surface and enhance the adhesion of the subsequent coating.

[0032] In this invention, the silver ion concentration in the pre-plating silver solution is 1~3g / L, preferably 2g / L, and the free chlorine concentration is 80~110g / L, preferably 90~100g / L; The free chlorine is derived from one or more of sodium chloride, potassium chloride, ammonium chloride, and sodium trichloroacetate; The voltage for the pre-plating of silver is 7~8V, the current is 28~32A, preferably 30A; the temperature is 20~25℃, preferably 23℃; and the time is 40~60s, preferably 50s.

[0033] In this invention, the silver plating solution has a silver ion concentration of 10-30 g / L, preferably 15-25 g / L, and more preferably 20 g / L; a free chlorine concentration of 120-150 g / L, preferably 130-140 g / L; a nano-molybdenum disulfide concentration of 5-20 g / L, preferably 10-15 g / L; and a sulfur content of 5-50 ppm, preferably 10-40 ppm, and more preferably 20-30 ppm. The free chlorine is derived from one or more of sodium chloride, potassium chloride, ammonium chloride, and sodium trichloroacetate; The sulfur content regulator is sodium thiosulfate and / or mercaptobenzothiazole.

[0034] In this invention, the silver plating current is 12~20A, preferably 15A; the voltage is 1.6~1.8V, preferably 1.7V; the processing time is 80~85min, preferably 82min; and the temperature is 20~25℃, preferably 23℃.

[0035] In this invention, the particle size of the nano-molybdenum disulfide is 0.1~0.5μm, preferably 0.2~0.4μm, and more preferably 0.3μm.

[0036] In this invention, the laser power of the laser cladding post-processing is 500~2000W, preferably 1000~1500W, and the scanning speed is 5~20mm / s, preferably 10~15mm / s.

[0037] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention. Example 1

[0038] Chemical degreasing: Immerse the workpiece in a solution containing sodium carbonate at 45°C for 15 minutes to thoroughly remove surface oil. After removal, rinse thoroughly with deionized water.

[0039] Electrolytic degreasing: Step 1 (cathode electrolysis): current 20A, temperature 55℃, treatment for 10 minutes; Step 2 (anodic electrolysis): current 15A, temperature maintained at 55℃, treatment for 5 minutes; after completion, rinse thoroughly with deionized water.

[0040] Pickling: Immerse the workpiece in a 10% (v / v) dilute hydrochloric acid solution at room temperature for 2 minutes to thoroughly remove the surface oxide film and rust. After removal, rinse thoroughly with deionized water.

[0041] Nickel plating: Prepare the nickel plating solution: Add 55 g / L nickel chloride, 240 g / L nickel sulfate, 50 g / L boric acid, and 1 g / L stress reliever saccharin to deionized water, stir well, and adjust the pH to 4.0. Control the current at 12 A, the voltage at 5.0 V, and the temperature at 52 °C, and electroplat for 50 minutes. After electroplating, remove the workpiece and rinse it thoroughly with deionized water. Perform gradient heat treatment: raise the temperature to 155 °C at a rate of 2.5 °C / min and hold for 45 minutes; then raise the temperature to 405 °C at a rate of 5.5 °C / min and hold for 1.5 hours; finally, raise the temperature to 490 °C at a rate of 2.5 °C / min and hold for 45 minutes, then cool with the furnace.

[0042] Neutralization: Place the workpiece in a 5% (w / v) weakly alkaline sodium carbonate solution and treat at room temperature for 2 minutes to completely neutralize the residual acid, then rinse with deionized water.

[0043] Alkaline copper plating: Add 35g / L of cuprous cyanide and 25g / L of sodium hydroxide to deionized water, stir well, and adjust the pH value to 13.0 to obtain an alkaline copper plating solution; control the current at 2.5A and the temperature at 52℃, and electroplat for 45 minutes; after electroplating, remove the workpiece and rinse it thoroughly with deionized water.

[0044] Activation: Immerse the workpiece in a 10% (v / v) sulfuric acid solution at room temperature for 30 seconds to remove the very thin oxide film on the surface and enhance the adhesion of subsequent coatings. Rinse thoroughly with deionized water.

[0045] Pre-plating silver: Prepare the pre-plating silver solution: 2 g / L silver nitrate (calculated as silver), 100 g / L potassium chloride; control the voltage at 7.5V, the current at 30A, the temperature at 23℃, electroplating for 50 seconds, and then rinse quickly after completion.

[0046] Silver plating: Prepare the silver plating solution: 20 g / L silver nitrate (based on silver), 135 g / L potassium chloride, 12 g / L nano molybdenum disulfide particles (0.3 μm particle size), and sodium thiosulfate to a sulfur content of 25 ppm. Control the current at 15 A, the voltage at 1.7 V, the temperature at 23 °C, and electroplating for 82 minutes with continuous slow stirring.

[0047] Laser cladding: Laser power is 1200W, scanning speed is 12mm / s. Example 2

[0048] Chemical degreasing: Immerse the workpiece in a solution containing sodium carbonate at 50°C for 12 minutes to thoroughly remove surface oil. After removal, rinse thoroughly with deionized water.

[0049] Electrolytic degreasing: Step 1 (cathode electrolysis): current 22A, temperature 60℃, treatment for 8 minutes; Step 2 (anodic electrolysis): current 15A, temperature maintained at 55℃, treatment for 5 minutes; after completion, rinse thoroughly with deionized water.

[0050] Pickling: Immerse the workpiece in a 10% (v / v) dilute hydrochloric acid solution at room temperature for 2 minutes to thoroughly remove the surface oxide film and rust. After removal, rinse thoroughly with deionized water.

[0051] Nickel plating: Prepare the nickel plating solution: Add 60 g / L nickel chloride, 260 g / L nickel sulfate, 55 g / L boric acid, and 0.8 g / L sodium dodecyl sulfate (stress reliever) to deionized water, stir well, and adjust the pH to 3.8. Control the current at 15 A, the voltage at 4.8 V, and the temperature at 55 °C, and electroplat for 55 minutes. After electroplating, remove the workpiece and rinse it thoroughly with deionized water. Perform gradient heat treatment: raise the temperature to 160 °C at a rate of 3 °C / min and hold for 30 minutes; then raise the temperature to 410 °C at a rate of 6 °C / min and hold for 1 hour; finally, raise the temperature to 500 °C at a rate of 3 °C / min and hold for 30 minutes, then cool with the furnace.

[0052] Neutralization: Place the workpiece in a 5% (w / v) weakly alkaline sodium carbonate solution and treat at room temperature for 2 minutes to completely neutralize the residual acid, then rinse with deionized water.

[0053] Alkaline copper plating: Add 30g / L of copper sulfate and 30g / L of sodium pyrophosphate to deionized water, stir well, and adjust the pH value to 12.9 to obtain an alkaline copper plating solution; control the current at 2.4A and the temperature at 55℃, and electroplat for 40 minutes; after electroplating, remove the workpiece and rinse it thoroughly with deionized water.

[0054] Activation: Immerse the workpiece in a 10% (v / v) sulfuric acid solution at room temperature for 30 seconds to remove the very thin oxide film on the surface and enhance the adhesion of subsequent coatings. Rinse thoroughly with deionized water.

[0055] Pre-plating silver: Prepare the pre-plating silver solution: 1.5 g / L silver nitrate (based on silver), 85 g / L ammonium chloride; control the voltage at 8V, the current at 28A, the temperature at 25℃, electroplating for 60 seconds, and then rinse quickly after completion.

[0056] Silver plating: Prepare the silver plating solution: 20 g / L silver nitrate (based on silver), 145 g / L free chlorine (provided by a mixture of sodium chloride and sodium trichloroacetate), 8 g / L nano-molybdenum disulfide particles (0.4 μm particle size), and sodium thiosulfate to a sulfur content of 35 ppm. Control the current at 18 A, the voltage at 1.6 V, the temperature at 25 °C, and electroplating for 80 minutes with continuous slow stirring.

[0057] Laser cladding: Laser power is 1500W, scanning speed is 15mm / s. Example 3

[0058] Chemical degreasing: Immerse the workpiece in a solution containing sodium carbonate at 40°C for 20 minutes to thoroughly remove surface oil. After removal, rinse thoroughly with deionized water.

[0059] Electrolytic degreasing: Step 1 (cathode electrolysis): current 18A, temperature 50℃, treatment for 12 minutes; Step 2 (anodic electrolysis): current 13A, temperature maintained at 50℃, treatment for 7 minutes; after completion, rinse thoroughly with deionized water.

[0060] Pickling: Immerse the workpiece in a 10% (v / v) dilute hydrochloric acid solution at room temperature for 2 minutes to thoroughly remove the surface oxide film and rust. After removal, rinse thoroughly with deionized water.

[0061] Nickel plating: Prepare the nickel plating solution: Add 50 g / L nickel chloride, 220 g / L nickel sulfate, 45 g / L boric acid, and 1.5 g / L stress reliever (a mixture of saccharin and sodium dodecyl sulfate) to deionized water, stir well, and adjust the pH to 4.2. Control the current at 10 A, the voltage at 5.1 V, and the temperature at 50 °C, and electroplat for 60 minutes. After electroplating, remove the workpiece and rinse it thoroughly with deionized water. Perform gradient heat treatment: raise the temperature to 155 °C at a rate of 2 °C / min and hold for 60 minutes; then raise the temperature to 400 °C at a rate of 5 °C / min and hold for 2 hours; finally, raise the temperature to 480 °C at a rate of 2 °C / min and hold for 60 minutes, then cool with the furnace.

[0062] Neutralization: Place the workpiece in a 5% (w / v) weakly alkaline sodium carbonate solution and treat at room temperature for 2 minutes to completely neutralize the residual acid, then rinse with deionized water.

[0063] Alkaline copper plating: Add 40 g / L copper pyrophosphate, 20 g / L sodium citrate, and sodium hydroxide to deionized water to adjust the pH to 13.1 to obtain an alkaline copper plating solution; control the current at 2.6 A and the temperature at 50 °C, and electroplat for 50 minutes; after electroplating, remove the workpiece and rinse it thoroughly with deionized water.

[0064] Activation: Immerse the workpiece in a 10% (v / v) sulfuric acid solution at room temperature for 30 seconds to remove the very thin oxide film on the surface and enhance the adhesion of subsequent coatings. Rinse thoroughly with deionized water.

[0065] Pre-plating silver: Prepare the pre-plating silver solution: 3g / L silver nitrate (based on silver), 95g / L sodium chloride; control the voltage at 7V, the current at 32A, the temperature at 20℃, electroplating for 40 seconds, and then rinse quickly after completion.

[0066] Silver plating: Prepare the silver plating solution: 15 g / L silver nitrate (based on silver), 125 g / L potassium chloride, 18 g / L nano molybdenum disulfide particles (0.3 μm particle size), and sodium thiosulfate to a sulfur content of 15 ppm. Control the current at 12 A, the voltage at 1.8 V, the temperature at 20 °C, and electroplating for 85 minutes with continuous slow stirring.

[0067] Laser cladding: Laser power is 1000W, scanning speed is 10mm / s.

[0068] Comparative Example 1

[0069] Similar to Example 1, except that no nano molybdenum disulfide particles were added and the laser cladding process was omitted; only conventional hot water drying and cooling were performed.

[0070] Test group: Workpieces prepared by the electroplating process of Example 1 (material: C17200 beryllium copper, size: 50mm×50mm×1mm).

[0071] Control group: Workpieces prepared using the electroplating process of Comparative Example 1, similar to those in Example 1.

[0072] Test environment: temperature 23±2℃, relative humidity 50±10%.

[0073] 1. Coating adhesion strength test (Test standard: ASTM B571) Method: The sample was placed in a muffle furnace preheated to 300 ± 5℃ and held for 30 minutes. Then, it was immediately removed and quenched in deionized water at room temperature (25℃).

[0074] Results: Sample 1: After 3 cycles, the silver-plated surface showed no blistering, wrinkling, or peeling. No abnormalities were observed at the edges using a 10x optical microscope. The sample was deemed to have excellent bonding strength and passed the test.

[0075] Comparative Example 1 Sample: After the second cycle, slight but visible wrinkling and fine blistering appeared in the edge area of ​​the sample. This was determined to be due to insufficient bonding strength, and the test failed.

[0076] 2. Abrasion resistance test (Test standard: ASTM D4060) Testing equipment: Taber 5155 abrasion testing machine Test parameters: Additional load is 500 gf, rotation speed is 60 rpm, and total friction revolutions are 1000 revolutions.

[0077] Evaluation method: Weigh the sample before and after the test (mg). The smaller the mass loss, the better the wear resistance.

[0078] Results: The average mass loss of the sample in Example 1 was 2.8 mg, while the average mass loss of the sample in Comparative Example 1 was 15.4 mg. Therefore, the wear resistance of the coating of the present invention is 5.5 times that of the comparative example, which directly proves that the co-deposited nano-molybdenum disulfide particles have a significant wear-enhancing effect.

[0079] 3. Coating porosity test (Test standard: ASTM B741) Method: Clean the sample with alcohol and air dry it, then place it in a container of concentrated nitric acid (density 1.42 g / cm³). 3 The sample was placed in the upper part of the desiccator and sealed. It was exposed to nitric acid vapor at room temperature (23°C) for 2 hours. The sample was then removed, rinsed with deionized water, and dried. The sample was observed and counted under a 20x optical microscope, with the area per unit area (1 cm²) counted. 2 The number of spots (pores) inside the substrate metal caused by corrosion.

[0080] Results: The average number of pores in the sample of Example 1 was 3 pores / cm2 The extremely low porosity indicates a very dense coating. The average pore number of the sample in Comparative Example 1 was 28 pores / cm². 2 Therefore, this invention, through laser cladding post-treatment, enables the micro-area remelting of the coating surface, effectively sealing the pores and micro-cracks generated by electrodeposition, reducing the porosity by 89%, and greatly improving the corrosion resistance and protective properties of the coating.

[0081] 4. Contact resistance test (Test standard: ASTM B667) Test equipment and parameters: Four-terminal contact resistance tester, probe material is gold-plated tungsten steel, contact pressure is 50cN, open circuit voltage is 20 mV (to avoid breaking down the surface film).

[0082] Test results: The average contact resistance of the sample in Example 1 was 1.05 mΩ, and the average contact resistance of the sample in Comparative Example 1 was 1.12 mΩ. Both exhibited excellent conductivity. After introducing nano-molybdenum disulfide into the coating of this invention, the contact resistance did not deteriorate; on the contrary, it showed a slight advantage due to the denser coating and smoother surface, fully meeting the electrical performance requirements of high-end electrical connectors.

[0083] 5. Micro Vickers hardness test (Test standard: ASTM E384) Test equipment and parameters: Micro Vickers hardness tester, load of 25 gf (0.245 N), holding time of 15 seconds.

[0084] Test results: The average micro Vickers hardness of the sample in Example 1 was 125 HV, while the average micro Vickers hardness of the sample in Comparative Example 1 was 65 HV. The hardness of the coating of the present invention is nearly twice that of the comparative example. This quantitatively demonstrates the dispersion strengthening effect of the nano-molybdenum disulfide particles, explaining the fundamental reason for its significantly improved wear resistance.

[0085] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A composite electroplating process, characterized in that, Includes the following steps: The workpiece can be subjected to chemical degreasing, electrolytic degreasing, pickling, nickel plating, neutralization, alkaline copper plating, activation, pre-plating silver, silver plating and laser cladding post-treatment in sequence; The nickel plating solution contains nickel chloride, nickel sulfate, boric acid, and stress reliever; The alkaline copper plating solution contains copper salts and free sodium salts; The pre-plating silver solution contains silver ions and free chlorine; The silver plating solution contains silver ions, free chlorine, nano-molybdenum disulfide particles, and a sulfur content regulator.

2. The composite electroplating process according to claim 1, characterized in that, The electrolytic degreasing process consists of two steps: the first step uses a current of 18-22A, a time of 8-12 minutes, and a temperature of 50-60℃; the second step uses a current of 13-17A, a time of 3-7 minutes, and a temperature of 50-60℃.

3. The composite electroplating process according to claim 2, characterized in that, In the nickel plating solution, the concentration of nickel chloride is 40~70 g / L, the concentration of nickel sulfate is 200~280 g / L, the concentration of boric acid is 40~60 g / L, the concentration of stress reliever is 0.5~2 g / L, and the pH of the nickel plating solution is 3.5~4.4; the stress reliever is saccharin and / or sodium dodecyl sulfate.

4. The composite electroplating process according to any one of claims 1 to 3, characterized in that, The nickel plating process involves a current of 10-15A, a voltage of 4.6-5.1V, a temperature of 50-55℃, and a time of 40-60 minutes. After nickel plating is completed, a gradient heat treatment process is used to release the residual stress of the plating layer. The specific steps of the gradient heat treatment process are as follows: first, the temperature is raised to 150-160℃ at a heating rate of 2-3℃ / min and held for 0.5-1h; then, the temperature is raised to 400-410℃ at a heating rate of 5-6℃ / min and held for 1-2h; finally, the temperature is raised to 480-500℃ at a heating rate of 2-3℃ / min and held for 0.5-1h.

5. The composite electroplating process according to claim 4, characterized in that, In the alkaline copper plating solution, the concentration of copper salt is 20~50g / L and the concentration of free sodium salt is 10~40g / L. The copper salt is one or more of cuprous cyanide, copper sulfate, and copper pyrophosphate; The free sodium salt is one or more of sodium pyrophosphate, sodium citrate, sodium tartrate, and sodium hydroxide; The pH of the alkaline copper plating solution is 12.8~13.2, the current for alkaline copper plating is 2.4~2.6A, the temperature is 50~55℃, and the time is 40~50min.

6. The composite electroplating process according to claim 5, characterized in that, In the pre-plating silver solution, the silver ion concentration is 1~3g / L and the free chlorine concentration is 80~110g / L; The free chlorine is derived from one or more of sodium chloride, potassium chloride, ammonium chloride, and sodium trichloroacetate; The voltage for the pre-plating of silver is 7~8A, the current is 28~32A, the temperature is 20~25℃, and the time is 40~60s.

7. The composite electroplating process according to claim 1 or 6, characterized in that, The silver plating solution has a silver ion concentration of 10-30 g / L, a free chlorine concentration of 120-150 g / L, a nano molybdenum disulfide concentration of 5-20 g / L, and a sulfur content of 5-50 ppm. The free chlorine is derived from one or more of sodium chloride, potassium chloride, ammonium chloride, and sodium trichloroacetate; The sulfur content regulator is sodium thiosulfate and / or mercaptobenzothiazole.

8. The composite electroplating process according to claim 7, characterized in that, The silver plating process involves a current of 12-20A, a voltage of 1.6-1.8V, a processing time of 80-85 minutes, and a temperature of 20-25℃.

9. The composite electroplating process according to claim 7, characterized in that, The particle size of the nano-molybdenum disulfide is 0.1~0.5μm.

10. The composite electroplating process according to claim 8 or 9, characterized in that, The laser power of the laser cladding post-processing is 500~2000W, and the scanning speed is 5~20mm / s.