Method for plating silver on surface of aviation fastener

Abstract

The invention relates to the technical field of metal surface treatment, in particular to a method for plating silver on the surface of an aviation fastener. The method comprises the following procedures of ultrasonic oil removal, first activation, nickel electroplating impact, second activation, silver electroplating, two times of water washing and drying, and a silver electroplating solution comprises the following components: 30-40 g / L of silver nitrate, 40-50 g / L of potassium carbonate, 15-20 g / L of a complexing agent, 1-3 g / L of an accelerant, 0.5-1 g / L of a surfactant, 0.6-0.9 g / L of a brightener, 5-6 g / L of a stabilizer, a pH regulator and pure water. The method for plating silver on the surface of the aviation fastener has the advantages of being simple in technological process, convenient to operate, high in efficiency, environmentally friendly and the like, meanwhile, the obtained silver plating layer and the fastener are good in binding force, and the method has the advantages of being good in discoloration prevention capacity, high in glossiness, good in coating compactness and the like.

Description

Technical Field

[0001] The present application relates to the technical field of metal surface treatment, and in particular to a method for silver plating the surface of aviation fasteners. Background Art

[0002] Silver has good electrical and thermal conductivity, and it has the best electrical conductivity among all metals. In addition, metallic silver also has high chemical stability and corrosion resistance, and has good chemical stability in most organic acids, strong bases and salt solutions. Based on these excellent properties of silver, the preparation of silver coatings occupies a very important position in coating production.

[0003] Stainless steel is a commonly used engineering material. Due to its excellent self-passivation performance, a suitable transition layer is required to form a silver-plated layer with good bonding strength on the surface. Patent CN 104404580B discloses a pretreatment method for improving the bonding strength of cyanide-free silver plating of stainless steel, which uses nickel plating and copper plating as transition layers to improve the bonding strength of cyanide-free silver plating of stainless steel. However, due to the diffusion of copper in silver, this system will change color at high temperatures.

[0004] At present, the surface anti-corrosion treatment of aviation fasteners usually adopts nickel and chromium electroplating, but under extreme conditions, these traditional coatings are prone to microcracks, leading to accelerated local corrosion. Silver plating has become a potential effective way to improve the corrosion resistance of aviation fasteners due to its good electrical conductivity and smooth surface. However, traditional silver plating processes often have problems such as slow deposition rate, poor density of silver plating layer, poor anti-discoloration performance, poor glossiness, and poor coating adhesion. Summary of the invention

[0005] The purpose of the present application is to provide a method for silver plating the surface of aviation fasteners in view of the deficiencies of the current technology. The method for silver plating the surface of aviation fasteners of the present application has the advantages of simple process flow, convenient operation, high efficiency, and green environmental protection. At the same time, the obtained silver-plated layer has good bonding strength with the fastener, has good anti-discoloration ability, high gloss and good coating density.

[0006] The present application provides a method for silver plating the surface of aviation fasteners, which adopts the following technical solution: A method for silver plating on the surface of aviation fasteners comprises the following steps: ultrasonic degreasing→first activation→electroplating impact nickel→second activation→electroplating silver→two water washings→drying, wherein the electroplating silver refers to placing the stainless steel aviation fasteners after the second activation into an electroplating silver plating solution for electroplating, wherein the electroplating silver plating solution comprises the following components: 30-40 g / L silver nitrate, 40-50 g / L potassium carbonate, 15-20 g / L complexing agent, 1-3 g / L accelerator, 0.5-1 g / L surfactant, 0.6-0.9 g / L brightener, 5-6 g / L stabilizer, pH regulator and pure water, wherein the pH of the electroplating silver plating solution is 6-6.7, and the temperature is 40-45°C; the electroplating time of the electroplating silver is 30-50 minutes, and the cathode current density is 0.3-0.5 A / dm 2 .

[0007] By adopting the above technical solutions, ultrasonic degreasing: remove grease and dirt on the surface of fasteners through ultrasonic vibration to ensure the surface is clean and provide a good foundation for subsequent electroplating. First activation: Activator treatment enhances the metal activity on the surface of fasteners and improves its bonding with the coating. Electroplating impact nickel: Form a uniform nickel plating layer on the surface of stainless steel to enhance the bonding between the coating and the substrate and provide better adhesion for subsequent silver plating. Second activation: Further activate the surface to ensure good activity of the nickel layer, which is conducive to the deposition of the subsequent silver layer. Electroplating silver: Put the activated fasteners into the electroplating silver plating solution. Under the action of electric current, silver ions are reduced and deposited on the surface of the fasteners to form a silver plating layer. 2 water washings: Remove the residual plating solution and other impurities on the surface of the fasteners to ensure the purity of the coating. Drying: Remove moisture by heating to dry the coating and complete the entire silver plating process. In the electroplating silver plating solution, silver nitrate: As the source of silver ions, it is the main component of silver plating. Potassium carbonate: As a conductive agent, it increases the conductivity of the plating solution. Complexing agent: forms a complex with silver ions, reduces the precipitation potential of silver ions, slows down the deposition rate, and helps the formation of nanocrystals. Accelerator: contains rare earth elements such as cerium and lanthanum, increases the polarizability of the plating solution and the cathode overpotential, reduces the resistivity of the coating, and improves the antioxidant properties. Surfactant: increases the activity of the nickel layer surface, making it easier to be plated with a silver layer. Brightener: contains imide and lactam with unsaturated bonds, broadens the current density range of the plating solution, improves the anti-discoloration ability and glossiness of the coating, and makes the coating reach a mirror finish. Stabilizer: improves the stability of the silver plating solution and prevents the decomposition or precipitation of the plating solution. pH regulator: adjusts and maintains the pH value of the plating solution between 6-6.7 to ensure the chemical balance of the plating solution. Pure water: as a solvent, provides the basic environment of the plating solution. These steps and components work together to make the silver plating process efficient, environmentally friendly, and the coating quality excellent. Specifically: Strong bonding: through two activations and impact nickel layer treatments, the bonding between the coating and the substrate is significantly improved. Strong anti-discoloration ability: The use of brightener and accelerator makes the coating have better anti-discoloration ability. High gloss: The effect of brightener makes the coating reach mirror brightness. Good density: The use of complexing agent and rare earth elements makes the coating more uniform and dense, reduces internal stress and corrosion rate. Green and environmental protection: The overall process is simple, easy to operate, and reduces environmental pollution. In summary, the method of silver plating on the surface of aviation fasteners achieves efficient and high-quality silver plating effects through fine process design and reasonable component ratio.

[0008] Preferably, the brightener is composed of polybutene diimide, δ-pentene lactam and phthalimide in a mass ratio of 4:3:4-6.

[0009] By adopting the above technical scheme, the brightener plays a vital role in the silver electroplating process. It widens the current density range of the plating solution through the imide and lactam containing unsaturated bonds, thereby effectively improving the anti-discoloration ability and glossiness of the silver deposit layer, making the coating reach mirror brightness, and refining the grains of the silver plating layer to the nanometer level, reducing the internal stress of the coating. Polybutene diimide: This ingredient helps to improve the brightness and fineness of the coating during the electroplating process. Through its structural characteristics, it can form a protective film on the surface of the coating to prevent the coating from oxidative discoloration. δ-pentene lactam: As a lactam compound, δ-pentene lactam plays a role in refining grains during the electroplating process, making the coating more uniform and smooth, thereby improving the glossiness and corrosion resistance of the coating. Phthalimide: It may help stabilize the metal ions in the plating solution through its chemical properties, promote more uniform deposition, and thus improve the quality of the coating. The combination of polybutene diimide, δ-pentene lactam and phthalimide, through their respective chemical characteristics and synergistic effects, works together in the electroplating process, so that the coating not only achieves a mirror effect in appearance, but also shows higher corrosion resistance and lower internal stress in physical properties. This combination optimizes the comprehensive performance of the coating, making it more suitable for use in high-demand fields such as aviation fasteners.

[0010] Preferably, the complexing agent is composed of 5,5-dimethylhydantoin and thiosemicarbazide in a mass ratio of 3:1-3.

[0011] By adopting the above technical scheme, the complexing agent forms a stable complex with silver ions, thereby changing the precipitation potential of silver ions and slowing down the deposition rate, which is conducive to the formation of nanocrystals and makes the coating more delicate and uniform. 5,5-Dimethylhydantoin is a white crystal that is easily soluble in water and ethanol and has good complexing properties, especially when combined with silver ions. It forms a stable complex and significantly shifts the precipitation potential of silver ions negatively, thereby reducing the deposition rate, which is conducive to the formation of nanocrystals and makes the coating more delicate and uniform. Semicarbazide can form a complex with silver ions. Although its specific mechanism of action is different from that of 5,5-dimethylhydantoin, the combination of the two can further optimize the performance of the coating. The mixed use of 5,5-dimethylhydantoin and semicarbazide can produce a synergistic effect, further improve the complexing effect, and make the precipitation of silver ions more uniform and delicate. This combination not only helps to refine the grains, but also improves the gloss and anti-discoloration ability of the coating, so that the coating can achieve a mirror-bright effect and enhance its corrosion resistance. In summary, the combined effect of 5,5-dimethylhydantoin and thiosemicarbazide in the silver electroplating process is to optimize the deposition process of silver ions by forming a stable complex, thereby improving the quality of the coating, making it more delicate, uniform and having good optical and anti-corrosion properties.

[0012] Preferably, the promoter is composed of cerium nitrate and lanthanum nitrate in a mass ratio of 1:1-2.

[0013] By adopting the above technical scheme, cerium nitrate can make the static potential of the plating solution shift positively, thereby improving the polarization degree. By improving the polarization degree, cerium nitrate helps to reduce the resistivity of the coating. Cerium nitrate can enhance the anti-oxidation performance of the coating and extend the service life of the coating. Lanthanum nitrate can significantly reduce the microscopic grains, making the coating more uniform and dense. As the coating becomes more uniform and dense, lanthanum nitrate helps to improve the bonding between the coating and the substrate. The refined grain structure and higher bonding force work together to reduce the corrosion rate of the coating and improve the corrosion resistance. When cerium nitrate and lanthanum nitrate work together, the quality of the coating can be further improved. Their synergistic effect makes the coating not only have lower resistivity and better anti-oxidation performance, but also have higher bonding force and finer grain structure. This combination can optimize the overall performance of the coating, so that it exhibits excellent corrosion resistance and conductivity in practical applications. In short, cerium nitrate and lanthanum nitrate, as accelerators, play a vital role in the silver plating process on the surface of aviation fasteners, and through their synergistic effect, the quality and performance of the coating are significantly improved.

[0014] Preferably, the surfactant is composed of fatty acid glyceride and sodium dodecylbenzene sulfonate in a mass ratio of 3:1-2.

[0015] By adopting the above technical solution, the surfactant can form a thin film on the surface of liquid and solid, reduce the surface tension or interfacial tension of water and other solution systems, so that the plating solution can be more easily and evenly distributed on the surface to be plated. By reducing the surface tension, the surfactant helps to improve the uniformity of the coating and ensure that the silver coating covers the entire surface of the fastener more uniformly, thereby improving the quality and aesthetics of the coating. The surfactant can increase the activity of the surface of the plated impact nickel layer, making it easier to be plated with a silver layer, thereby improving the bonding between the coating and the substrate. Fatty acid glyceride: This is a non-ionic surfactant with good emulsification, dispersing and wetting properties. It can form a stable micelle structure in the plating solution, which helps to improve the stability of the plating solution and the uniformity of the coating. Sodium dodecylbenzene sulfonate: This is an anionic surfactant with strong detergency and emulsification properties. It can significantly reduce the surface tension of water, thereby improving the spreadability and adhesion of the plating solution on the surface of the fastener. When the two work together, the non-ionic properties of fatty acid glycerides and the anionic properties of sodium dodecylbenzene sulfonate combine to form a more stable micelle structure in the plating solution, further improving the dispersibility and uniformity of the plating solution, thereby optimizing the silver plating effect. This combination not only improves the bonding strength of the coating, but also enhances the glossiness and anti-discoloration ability of the coating, making the silver coating more dense and beautiful.

[0016] Preferably, the stabilizer is potassium phenyl sulfide; and the pH adjuster is sodium carbonate.

[0017] Preferably, the ultrasonic degreasing process conditions are: placing the stainless steel aviation fasteners in a degreasing solution for ultrasonic treatment for 3-5 minutes, the degreasing solution is a sodium hydroxide solution with a mass concentration of 10%, and the degreasing temperature is 50-60°C.

[0018] Preferably, the process conditions for the first activation are: placing the degreased stainless steel aviation fasteners in the first activation liquid for activation for 2-4 minutes to remove the passivation film on the surface of the stainless steel aviation fasteners; the first activation liquid is a 50-60g / L hydrochloric acid solution, and the activation temperature is 40-50°C.

[0019] Preferably, the process conditions for electroplating impact nickel are as follows: the first activated stainless steel aviation fastener is placed in the impact nickel plating solution for electroplating for 5-8 minutes, with a cathode current density of 9-10 A / dm 2 The impact nickel plating solution is 220-250g / L nickel chloride, 4-6g / L boric acid and 80-90g / L hydrochloric acid, and the temperature is 25-30°C.

[0020] By adopting the above technical solution, electroplating impact nickel is a key step, and its main functions are as follows: by forming a uniform nickel-plated layer on the surface of stainless steel, the bonding force between the plating layer and the substrate is enhanced, thereby improving the adhesion of the silver-plated layer. The impact nickel layer can play a pretreatment role, improve the roughness and activity of the stainless steel surface, and is beneficial to the subsequent silver plating process. Electroplating impact nickel works together with the subsequent silver plating steps to make the silver-plated layer more uniform and dense, and improve the overall quality and performance of the plating layer. By improving the bonding force between the plating layer and the substrate, the protective properties of the silver-plated layer (such as corrosion resistance) are enhanced. The impact nickel layer helps to improve the gloss and color of the silver-plated layer, making it more attractive. In summary, electroplating impact nickel plays a vital role in the silver plating process on the surface of aviation fasteners, and significantly improves the performance and quality of the plating layer through synergy with subsequent steps.

[0021] Preferably, the process conditions for the second activation are: placing the stainless steel aviation fasteners plated with impact nickel in a second activation solution for activation for 0.5-1 minute, the second activation solution is a 20-30 g / L sulfuric acid solution, and the activation temperature is 25-30°C.

[0022] In summary, the beneficial technical effects of this application are: 1. Simple process flow: This method simplifies the traditional silver plating process through a series of clear steps (such as ultrasonic degreasing, activation, electroplating, etc.) and reduces the complexity of operation.

[0023] 2. Convenient and efficient operation: The process parameters (such as electroplating time, current density, solution composition ratio) have been optimized to ensure efficient silver plating effect.

[0024] 3. Green and environmentally friendly: The composition and process design of the electroplating silver solution used reduce the emission of harmful substances and meet environmental protection standards.

[0025] 4. Good bonding strength: A uniform nickel plating layer is formed on the stainless steel surface through the nickel plating impact step, which enhances the bonding strength between the silver plating layer and the fasteners.

[0026] 5. Excellent anti-discoloration ability: The unsaturated bond compounds in the brightener effectively improve the anti-discoloration ability and glossiness of the coating, making it achieve a mirror-like bright effect.

[0027] 6. High gloss: Brightener and optimized electroplating parameters work together to make the coating surface smoother and more glossy.

[0028] 7. Coating with good density: The use of complexing agents and rare earth elements promotes the formation of nanocrystals, making the coating structure denser and reducing internal stress.

[0029] 8. Improved antioxidant properties: The rare earth elements in the accelerator improve the antioxidant properties of the coating and extend the service life of the coating.

[0030] 9. Increase surface activity: The addition of surfactants increases the activity of the impact nickel layer surface, which is beneficial to the subsequent silver plating process.

[0031] 10. Improve the stability of the plating solution: The addition of stabilizers ensures the long-term stable use of the silver plating solution and reduces maintenance costs. DETAILED DESCRIPTION

[0032] The embodiments of the present application will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present application and should not be considered as limiting the scope of the present application. In the examples, if specific conditions are not specified, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0033] In the following embodiments, there are two water washes between each process to clean the surface of the aviation fasteners, and the stainless steel aviation fasteners are aerospace stainless steel bolts.

[0034] Example 1

[0035] A method for silver plating on the surface of aviation fasteners comprises the following steps: ultrasonic degreasing→first activation→electroplating impact nickel→second activation→electroplating silver→two water washings→drying, wherein the silver plating refers to placing the stainless steel aviation fasteners after the second activation into an electroplating silver plating solution for electroplating, wherein the electroplating silver plating solution comprises the following components: 30 g / L silver nitrate, 40 g / L potassium carbonate, 15 g / L complexing agent, 1 g / L accelerator, 0.5 g / L surfactant, 0.6 g / L brightener, 5 g / L potassium phenyl sulfide, and sodium carbonate is used to adjust the pH of the electroplating silver plating solution to 6 and the temperature to 40°C; the electroplating time of the electroplating silver is 40 minutes, and the cathode current density is 0.4 A / dm 2 , the brightener is composed of polybutene diimide, δ-pentene lactam and phthalimide in a mass ratio of 4:3:4, the complexing agent is composed of 5,5-dimethylhydantoin and semicarbazide in a mass ratio of 3:1, the accelerator is composed of cerium nitrate and lanthanum nitrate in a mass ratio of 1:1, and the surfactant is composed of fatty acid glyceride and sodium dodecylbenzene sulfonate in a mass ratio of 3:1; The process conditions of ultrasonic degreasing are as follows: the stainless steel aviation fastener is placed in a degreasing liquid for ultrasonic treatment for 3 minutes, the degreasing liquid is a sodium hydroxide solution with a mass concentration of 10%, and the degreasing temperature is 50°C; The process conditions of the first activation are: placing the degreased stainless steel aviation fasteners in the first activation solution for activation for 2 minutes to remove the passivation film on the surface of the stainless steel aviation fasteners; the first activation solution is a 60g / L hydrochloric acid solution, and the activation temperature is 50°C; The process conditions of electroplating impact nickel are as follows: the first activated stainless steel aviation fastener is placed in the impact nickel plating solution for electroplating for 5 minutes, and the cathode current density is 10A / dm 2 The impact nickel plating solution is 250g / L nickel chloride, 4g / L boric acid and 80g / L hydrochloric acid, and the temperature is 30°C; The process conditions of the second activation are: placing the stainless steel aviation fasteners plated with impact nickel in the second activation solution for activation for 0.5 minutes, wherein the second activation solution is a 30 g / L sulfuric acid solution and the activation temperature is 25° C.; The drying step is to place the product in an oven at 80° C. and bake for 30 minutes.

[0036] Example 2

[0037] A method for silver plating on the surface of aviation fasteners comprises the following steps: ultrasonic degreasing→first activation→electroplating impact nickel→second activation→electroplating silver→two water washings→drying, wherein the silver plating refers to placing the stainless steel aviation fasteners after the second activation into an electroplating silver plating solution for electroplating, wherein the electroplating silver plating solution comprises the following components: 40 g / L silver nitrate, 50 g / L potassium carbonate, 20 g / L complexing agent, 3 g / L accelerator, 1 g / L surfactant, 0.9 g / L brightener, 6 g / L potassium phenyl sulfide, and sodium carbonate is used to adjust the pH of the electroplating silver plating solution to 6.7 and the temperature to 45°C; the electroplating time of the electroplating silver is 40 minutes, and the cathode current density is 0.4 A / dm 2 , the brightener is composed of polybutene diimide, δ-pentene lactam and phthalimide in a mass ratio of 4:3:6, the complexing agent is composed of 5,5-dimethylhydantoin and semicarbazide in a mass ratio of 3:3, the accelerator is composed of cerium nitrate and lanthanum nitrate in a mass ratio of 1:2, and the surfactant is composed of fatty acid glyceride and sodium dodecylbenzene sulfonate in a mass ratio of 3:2; The process conditions of ultrasonic degreasing are as follows: the stainless steel aviation fastener is placed in a degreasing liquid for ultrasonic treatment for 5 minutes, the degreasing liquid is a sodium hydroxide solution with a mass concentration of 10%, and the degreasing temperature is 50°C; The process conditions of the first activation are: placing the degreased stainless steel aviation fasteners in the first activation solution for activation for 4 minutes to remove the passivation film on the surface of the stainless steel aviation fasteners; the first activation solution is a 50g / L hydrochloric acid solution, and the activation temperature is 40°C; The process conditions of electroplating impact nickel are as follows: the first activated stainless steel aviation fastener is placed in the impact nickel plating solution for electroplating for 8 minutes, and the cathode current density is 9A / dm 2 The impact nickel plating solution is 220g / L nickel chloride, 6g / L boric acid and 90g / L hydrochloric acid, and the temperature is 25°C; The process conditions of the second activation are: placing the stainless steel aviation fasteners plated with impact nickel in the second activation solution for activation for 1 minute, wherein the second activation solution is a 20g / L sulfuric acid solution and the activation temperature is 25°C; The drying step is to place the product in an oven at 80° C. and bake for 30 minutes.

[0038] Example 3

[0039] A method for silver plating on the surface of aviation fasteners comprises the following steps: ultrasonic degreasing→first activation→electroplating impact nickel→second activation→electroplating silver→two water washings→drying, wherein the electroplating silver refers to placing the stainless steel aviation fasteners after the second activation into an electroplating silver plating solution for electroplating, wherein the electroplating silver plating solution comprises the following components: 35 g / L silver nitrate, 45 g / L potassium carbonate, 17 g / L complexing agent, 2 g / L accelerator, 0.8 g / L surfactant, 0.7 g / L brightener, 5.5 g / L potassium phenyl sulfide, and sodium carbonate is used to adjust the pH of the electroplating silver plating solution to 6.3 and the temperature to 43°C; the electroplating time of the electroplating silver is 40 minutes, and the cathode current density is 0.4 A / dm 2 , the brightener is composed of polybutene diimide, δ-pentene lactam and phthalimide in a mass ratio of 4:3:5, the complexing agent is composed of 5,5-dimethylhydantoin and semicarbazide in a mass ratio of 3:2, the accelerator is composed of cerium nitrate and lanthanum nitrate in a mass ratio of 1:1.5, and the surfactant is composed of fatty acid glyceride and sodium dodecylbenzene sulfonate in a mass ratio of 3:1.5; The process conditions of ultrasonic degreasing are as follows: the stainless steel aviation fasteners are placed in a degreasing liquid for ultrasonic treatment for 4 minutes, the degreasing liquid is a sodium hydroxide solution with a mass concentration of 10%, and the degreasing temperature is 55°C; The process conditions of the first activation are: placing the degreased stainless steel aviation fasteners in the first activation solution for activation for 3 minutes to remove the passivation film on the surface of the stainless steel aviation fasteners; the first activation solution is a 55g / L hydrochloric acid solution, and the activation temperature is 45°C; The process conditions of electroplating impact nickel are as follows: the first activated stainless steel aviation fastener is placed in the impact nickel plating solution for electroplating for 6 minutes, and the cathode current density is 9.5A / dm 2 The impact nickel plating solution is 230g / L nickel chloride, 5g / L boric acid and 85g / L hydrochloric acid, and the temperature is 27°C; The process conditions of the second activation are: placing the stainless steel aviation fasteners plated with impact nickel in the second activation solution for activation for 0.8 minutes, wherein the second activation solution is a 25g / L sulfuric acid solution and the activation temperature is 27°C; The drying step is to place the product in an oven at 80° C. and bake for 30 minutes.

[0040] Comparative Example 1 The same as Example 3, except that the brightener is polybutene diimide.

[0041] Comparative Example 2 The same as Example 3, except that the brightener is δ-pentene lactam.

[0042] Comparative Example 3 The same as Example 3, except that the brightener is phthalimide.

[0043] Comparative Example 4 The same as Example 3, except that the complexing agent is 5,5-dimethylhydantoin.

[0044] Comparative Example 5 The same as Example 3, except that the complexing agent is thiosemicarbazide.

[0045] Comparative Example 6 The same as Example 3, except that the surfactant is fatty acid glyceride.

[0046] Comparative Example 7 The same as Example 3, except that the surfactant is sodium dodecylbenzene sulfonate.

[0047] Comparative Example 8 The same as Example 3, except that the promoter is cerium nitrate.

[0048] Comparative Example 9 The same as Example 3, except that the promoter is lanthanum nitrate.

[0049] Performance Testing The silver-plated aviation fasteners prepared in Examples 1 to 3 and Comparative Examples 1 to 9 were subjected to the following performance tests, respectively. The test results are shown in Table 1.

[0050] Anti-discoloration performance test: refer to QJ458-88 for testing; Adhesion test: put the sample into an oven and heat it with the cold oven, keep it at 230℃ for 120min, then quickly put it into 20℃ water for thermal shock test, check the adhesion of the coating after thermal shock, the coating is qualified if there is no peeling, blistering or shedding, then test the parts after thermal shock according to the adhesion test marking method of QJ479-90, the coating is qualified if there is no peeling, blistering or shedding; Appearance evaluation: visually observe whether the silver-plated layer is dense and bright.

[0051] Table 1 Performance test

[0052] Analyzing the data in Table 1, we can see that: 1) The silver-plated layer of the silver-plated aviation fasteners prepared in Examples 1 to 3 has good bonding strength with the fasteners, good anti-discoloration ability, high glossiness and good coating density.

[0053] 2) The performance comparison analysis of the silver-plated aviation fasteners prepared in Example 3 and Comparative Examples 1-3 shows that the brightener is composed of polybutene diimide, δ-pentene lactam and phthalimide in a mass ratio of 4:3:5. The imide and lactam containing unsaturated bonds broaden the current density range of the plating solution, thereby effectively improving the anti-discoloration ability and glossiness of the silver deposit layer, making the coating achieve mirror brightness, and refining the grains of the silver-plated layer to the nanometer level, reducing the internal stress of the coating. The combination of polybutene diimide, δ-pentene lactam and phthalimide, through their respective chemical properties and synergistic effects, acts together in the electroplating process, so that the coating not only achieves a mirror effect in appearance, but also shows higher corrosion resistance and lower internal stress in physical properties. This combination optimizes the comprehensive performance of the coating, making it more suitable for application in high-demand fields such as aviation fasteners.

[0054] 3) The performance comparison analysis of the silver-plated aviation fasteners prepared in Example 3 and Comparative Examples 4-5 shows that the complexing agent is composed of 5,5-dimethylhydantoin and semicarbazide in a mass ratio of 3:2. The complexing agent forms a stable complex with silver ions, thereby changing the precipitation potential of silver ions and slowing down the deposition rate, which is conducive to the formation of nanocrystals and makes the coating more delicate and uniform. The mixed use of 5,5-dimethylhydantoin and semicarbazide can produce a synergistic effect, further improve the complexing effect, and make the precipitation of silver ions more uniform and delicate. This combination not only helps to refine the grains, but also improves the gloss and anti-discoloration ability of the coating, so that the coating can achieve a mirror-bright effect and enhance its corrosion resistance.

[0055] 4) The performance comparison analysis of the silver-plated aviation fasteners prepared in Example 3 and Comparative Examples 6-7 shows that the surfactant is composed of fatty acid glyceride and sodium dodecylbenzene sulfonate in a mass ratio of 3:1.5. The surfactant can form a thin film on the surface of the liquid and the solid, reduce the surface tension or interfacial tension of water and other solution systems, so that the plating solution is more easily and evenly distributed on the surface to be plated. By reducing the surface tension, the surfactant helps to improve the uniformity of the coating, ensure that the silver coating covers the entire surface of the fastener more uniformly, thereby improving the quality and aesthetics of the coating. The surfactant can increase the activity of the surface of the plated impact nickel layer, making it easier to be plated with a silver layer, thereby improving the bonding strength of the coating and the substrate. By combining the non-ionic properties of fatty acid glyceride and the anionic properties of sodium dodecylbenzene sulfonate, a more stable micelle structure can be formed in the plating solution, further improving the dispersibility and uniformity of the plating solution, thereby optimizing the silver plating effect. This combination not only improves the bonding strength of the coating, but also enhances the glossiness and anti-discoloration ability of the coating, making the silver coating more dense and beautiful.

[0056] 5) The performance comparison analysis of the silver-plated aviation fasteners prepared in Example 3 and Comparative Examples 8-9 shows that the accelerator is composed of cerium nitrate and lanthanum nitrate in a mass ratio of 1:1.5. When cerium nitrate and lanthanum nitrate act together, the quality of the coating can be further improved. Their synergistic effect makes the coating not only have lower resistivity and better oxidation resistance, but also have higher bonding strength and finer grain structure. This combination can optimize the overall performance of the coating, so that it exhibits excellent corrosion resistance and anti-discoloration ability in practical applications.

[0057] The above embodiments are only used to explain the technical solutions of the present application rather than to limit them. Although the above embodiments provide a specific description of the present application, relevant technical personnel should understand that the specific implementation modes of the present invention can still be modified or replaced by equivalents, and any modifications and equivalent replacements that do not depart from the spirit and scope of the present application should be included in the scope of protection of the present application.

Claims

1. A method for silver plating the surface of aviation fasteners, characterized in that: The method comprises the following steps: ultrasonic degreasing→first activation→electroplating impact nickel→second activation→electroplating silver→two water washings→drying, wherein the electroplating silver refers to placing the stainless steel aviation fasteners after the second activation into an electroplating silver plating solution for electroplating, and the electroplating silver plating solution comprises the following components: 30-40 g / L silver nitrate, 40-50 g / L potassium carbonate, 15-20 g / L complexing agent, 1-3 g / L accelerator, 0.5-1 g / L surfactant, 0.6-0.9 g / L brightener, 5-6 g / L stabilizer, pH regulator and pure water, wherein the pH of the electroplating silver plating solution is 6-6.7, and the temperature is 40-45°C; the electroplating time of the electroplating silver is 30-50 minutes, and the cathode current density is 0.3-0.5 A / dm 2 The brightener is composed of polybutene diimide, δ-pentene lactam and phthalimide in a mass ratio of 4:3:4-6.

2. A method for silver plating the surface of aviation fasteners according to claim 1, characterized in that: The complexing agent is composed of 5,5-dimethylhydantoin and thiosemicarbazide in a mass ratio of 3:1-3.

3. The method for silver plating the surface of aviation fasteners according to claim 1, characterized in that: The promoter is composed of cerium nitrate and lanthanum nitrate in a mass ratio of 1:1-2.

4. The method for silver plating the surface of aviation fasteners according to claim 1, characterized in that: The surfactant is composed of fatty acid glyceride and sodium dodecylbenzene sulfonate in a mass ratio of 3:1-2.

5. The method for silver plating the surface of aviation fasteners according to claim 1, characterized in that: The stabilizer is potassium phenyl sulfide.

6. The method for silver plating the surface of aviation fasteners according to claim 1, characterized in that: The pH regulator is sodium carbonate.

7. The method for silver plating the surface of aviation fasteners according to claim 1, characterized in that: The process conditions of ultrasonic degreasing are as follows: placing the stainless steel aviation fasteners in a degreasing solution for ultrasonic treatment for 3-5 minutes, the degreasing solution is a sodium hydroxide solution with a mass concentration of 10%, and the degreasing temperature is 50-60°C.

8. The method for silver plating the surface of aviation fasteners according to claim 1, characterized in that: The process conditions of the first activation are: placing the degreased stainless steel aviation fasteners in the first activation solution for activation for 2-4 minutes to remove the passivation film on the surface of the stainless steel aviation fasteners; The first activation solution is a 50-60 g / L hydrochloric acid solution, and the activation temperature is 40-50°C.

9. The method for silver plating the surface of aviation fasteners according to claim 1, characterized in that: The process conditions of electroplating impact nickel are as follows: the first activated stainless steel aviation fastener is placed in the impact nickel plating solution for electroplating for 5-8 minutes, and the cathode current density is 9-10A / dm 2 The impact nickel plating solution is 220-250g / L nickel chloride, 4-6g / L boric acid and 80-90g / L hydrochloric acid, and the temperature is 25-30°C.

10. A method for silver plating the surface of an aviation fastener according to claim 1, characterized in that The process conditions of the second activation are: putting the stainless steel aviation fasteners plated with impact nickel into the second activation solution for activation for 0.5-1 minute, the second activation solution is a 20-30g / L sulfuric acid solution, and the activation temperature is 25-30°C.

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