Method for removing nickel-plated layer on copper and copper alloy matrix

Abstract

The invention belongs to the technical field of metal surface treatment, and particularly relates to a method for removing a nickel-plated layer on a copper and copper alloy matrix. In order to reduce the use of reserve salt and cyanide in the nickel stripping solution, main components of the nickel stripping solution comprise a composite nickel stripping agent composed of ethylenediamine, ethylenediamine tetraacetic acid, ammonium persulfate and citric acid and a composite corrosion inhibitor composed of benzotriazole and sodium molybdate, the pH value of the nickel stripping solution is 3-6, the nickel stripping temperature is 50-85 DEG C, the nickel stripping speed is 1-2 microns / h, and the nickel stripping time is 2-3 hours. And after the nickel layer is removed, the surface of the copper alloy matrix is very smooth and free of the defects of floating, pitting and the like.

Description

Technical Field

[0001] This invention belongs to the field of metal surface treatment technology, and in particular relates to a method for removing nickel plating layers from copper and copper alloy substrates. Background Technology

[0002] Nickel plating on metal substrates offers numerous advantages, with the following core characteristics: ① Excellent coating uniformity: Deposition occurs without an external electric field, relying on a chemical reduction reaction. The coating thickness is unaffected by the shape of the part, allowing for uniform coatings even on complex parts, deep cavities, and blind holes. ② Hardness and wear resistance: The plated hardness is approximately 400HV-500HV, which can reach 500HV-900HV after heat treatment. ③ Non-magnetic / low-magnetic: High-phosphorus nickel plating (phosphorus content >10%) has an amorphous structure and is non-magnetic, meeting the non-magnetic requirements of aerospace and electronics fields. ④ Good environmental performance: It does not contain highly toxic substances such as cyanide and hexavalent chromium, complying with RoHS and other environmental standards. It can replace some polluting electroplating processes and is therefore widely used in various fields.

[0003] When the nickel plating layer is substandard, it needs to be removed. Currently, in military enterprises in the aviation and aerospace fields, most companies still use chemical methods containing cyanide and anti-staining salts to remove substandard nickel layers. This is mainly divided into nickel layer removal on copper alloy substrates and nickel layer removal on steel substrates. The method of removing substandard nickel layers using highly toxic substances such as cyanide and anti-staining salts is the most common. The main formulas for removing nickel layers are shown in Table 1.

[0004] Table 1. Main solution formulations for nickel layer removal

[0005] During the stripping process of substandard nickel plating on copper and copper alloy substrates, defects such as mottled appearance, pitting, and rough surface often occur. With increasingly stringent environmental protection requirements and the ban on anti-contamination salts and cyanides, there is an urgent need to develop a nickel stripping method that is less polluting and more environmentally friendly. Summary of the Invention

[0006] To address the above problems, the present invention provides a method for removing nickel plating layers from copper and copper alloy substrates, comprising the following steps: removing nickel plating layers from copper and copper alloy substrates using a nickel stripping solution, wherein the main components of the nickel stripping solution are ethylenediamine, ethylenediaminetetraacetic acid, a composite nickel stripping agent, and a composite corrosion inhibitor, wherein the composite nickel stripping agent is ammonium persulfate and citric acid, and the composite corrosion inhibitor is benzotriazole and sodium molybdate;

[0007] The concentrations of each component in the nickel stripping solution are as follows: ethylenediamine 100ml / L-200ml / L, ethylenediaminetetraacetic acid 10g / L-20g / L, composite nickel stripping agent 35g / L-115g / L, and composite corrosion inhibitor 1.2g / L-6.5g / L;

[0008] Furthermore, in the composite nickel stripping agent, ammonium persulfate is 20g / L-80g / L, and citric acid is 15g / L-35g / L;

[0009] Furthermore, in the composite corrosion inhibitor, benzotriazole is 0.2 g / L-1.5 g / L, and sodium molybdate is 1 g / L-5 g / L;

[0010] The pH of the nickel stripping solution should be 3-6, and can be fine-tuned using acetic acid. The nickel stripping temperature should be 50℃-85℃, and the nickel stripping rate should be 1μm / s. min -2μm / min

[0011] The present invention has the following beneficial effects:

[0012] This invention does not contain highly toxic substances such as anti-dyeing salts, chromic anhydride, or cyanide, and is an environmentally friendly nickel stripping method. Ammonium persulfate is a strong oxidizing agent, and its oxidation mechanism is closely related to the solution pH. When pH < 7, the decomposition mechanism of ammonium persulfate is mainly as follows:

[0013] S2O8 2- +H + →HSO4 - +SO4 - The generated sulfuric acid free radicals have extremely high redox potentials (2.5V-3.1V), enabling them to oxidize elemental nickel in the electroless nickel layer to Ni. 2+ This process disrupts the crystal structure of the nickel layer, causing it to peel off from the substrate surface. Ethylenediamine can act as a pH adjuster, and ethylenediaminetetraacetic acid (EDTA) as a stabilizer. Both EDTA and EDTA also act as complexing agents, exhibiting strong complexing abilities with nickel ions. They work together to form stable, water-soluble complexes, preventing Ni from detaching from the substrate. 2+ Redeposition occurs on the workpiece surface, with citric acid adjusting the pH to the range of 3-5.5. Benzotriazole and sodium molybdate exhibit synergistic corrosion inhibition under acidic conditions, rapidly adsorbing onto the surface of substrates such as copper and iron to form a ligand protective film. Furthermore, they do not react with organic acids in the system to form precipitates, thus synergistically controlling the substrate corrosion rate to an extremely low level.

[0014] This invention provides an environmentally friendly nickel stripping solution that replaces anti-staining salts and cyanide. Wastewater requires no special detoxification treatment; it can be discharged after neutralization and precipitation in acidic or alkaline wastewater. By rationally controlling the nickel stripping speed, the method described in this invention removes the same nickel layer more than 30% faster than processes using anti-staining salts, resulting in high nickel stripping efficiency. By adjusting the composition and content of each component in the nickel stripping solution, the reaction degree and removal speed of the nickel plating on copper and copper alloy substrates are controlled, ensuring smooth nickel layer removal while avoiding defects such as surface blooming and pitting, and preventing corrosion of the copper substrate. This technology has been put into use. Preliminary calculations show a reduction in wastewater treatment volume containing anti-staining salts and cyanide by 10-30 tons per year; a reduction in procurement costs of approximately 30,000-50,000 RMB per year; and savings for enterprises of approximately 50,000-100,000 RMB per year. The number of parts stripped using this method has already reached 1000-2000 pieces in batch production. Attached Figure Description

[0015] Figure 1 This is a photograph of the copper alloy substrate after nickel stripping in Example 1.

[0016] Figure 2 This is a photograph of the copper alloy substrate after nickel stripping in Example 2.

[0017] Figure 3 This is a photograph of the copper alloy substrate after nickel stripping in Example 3;

[0018] Figure 4 This is a photograph of the copper alloy substrate after nickel stripping in Example 4;

[0019] Figure 5 This is a photograph of the copper alloy substrate after nickel stripping in Example 5.

[0020] Figure 6 This is a photograph of the copper alloy substrate after nickel stripping in Example 6. Detailed Implementation

[0021] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. It should be noted that the embodiments described in this invention are only for further explanation and illustration, and not for limiting their application scope. Based on this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this invention.

[0022] In practice, the nickel layer on the copper and copper alloy substrate can be removed according to the process in Table 2.

[0023] Table 2 Nickel removal process on copper and copper alloy substrates

[0024] Example 1

[0025] The nickel stripping solution formula is as follows: ethylenediamine 160 ml / L, ethylenediaminetetraacetic acid 15 g / L, composite nickel stripping agent 40 g / L, composite corrosion inhibitor 2 g / L, the pH of the nickel stripping solution is 4, and the nickel stripping temperature is 80℃. The nickel plating thickness is 15 μm. After treatment in the nickel stripping solution for 9 minutes, the surface of the copper alloy substrate is as follows: Figure 1 As shown, from Figure 1 It can be seen that the surface of the copper alloy substrate is very smooth after nickel stripping, without defects such as blooming or pitting.

[0026] Example 2

[0027] The nickel stripping solution formula is as follows: ethylenediamine 100ml / L, ethylenediaminetetraacetic acid 10g / L, composite nickel stripping agent 35g / L, composite corrosion inhibitor 1.2g / L, the pH of the nickel stripping solution is 6, and the nickel stripping temperature is 50℃. The nickel plating thickness is 15μm. After treatment in the nickel stripping solution for 14 minutes, the surface of the copper alloy substrate is as follows: Figure 2 As shown, from Figure 2 It can be seen that the nickel layer has been completely removed, and there are no defects such as blooming or pitting on the surface of the copper alloy substrate.

[0028] Example 3

[0029] The nickel stripping solution formula is as follows: ethylenediamine 200ml / L, ethylenediaminetetraacetic acid 20g / L, composite nickel stripping agent 115g / L, composite corrosion inhibitor 6.5g / L, the pH of the nickel stripping solution is 3, and the nickel stripping temperature is 80℃. The nickel plating thickness is 15μm. After treatment in the nickel stripping solution for 8 minutes, the surface of the copper alloy substrate is as follows: Figure 3 As shown, from Figure 3 It can be seen that the nickel layer has been completely removed, and there are no defects such as blooming or pitting on the surface of the copper alloy substrate.

[0030] Example 4

[0031] The nickel stripping solution formula is as follows: ethylenediamine 150 ml / L, ethylenediaminetetraacetic acid 15 g / L, composite nickel stripping agent 60 g / L, composite corrosion inhibitor 3 g / L, the pH of the nickel stripping solution is 4, and the nickel stripping temperature is 65℃. The nickel plating thickness is 15 μm. After treatment in the nickel stripping solution for 10 minutes, the surface of the copper alloy substrate is as follows: Figure 4 As shown, from Figure 4 It can be seen that the nickel layer has been completely removed, and there are no defects such as blooming or pitting on the surface of the copper alloy substrate.

[0032] Example 5

[0033] The nickel stripping solution formula is as follows: ethylenediamine 150 ml / L, ethylenediaminetetraacetic acid 15 g / L, composite nickel stripping agent 60 g / L, composite corrosion inhibitor 3 g / L, the pH of the nickel stripping solution is 5, and the nickel stripping temperature is 65℃. The nickel plating thickness is 15 μm. After treatment in the nickel stripping solution for 12 minutes, the surface of the copper alloy substrate appears as follows: Figure 5 As shown, from Figure 5It can be seen that the nickel layer has been completely removed, and there are no defects such as blooming or pitting on the surface of the copper alloy substrate.

[0034] Example 6

[0035] The nickel stripping solution formula is as follows: ethylenediamine 150 ml / L, ethylenediaminetetraacetic acid 15 g / L, composite nickel stripping agent 60 g / L, composite corrosion inhibitor 6 g / L, the pH of the nickel stripping solution is 4, and the nickel stripping temperature is 80℃. The nickel plating thickness is 15 μm. After treatment in the nickel stripping solution for 9 minutes, the surface of the copper alloy substrate is as follows: Figure 6 As shown, from Figure 6 It can be seen that the nickel layer has been completely removed, and there are no defects such as blooming or pitting on the surface of the copper alloy substrate.

Claims

1. A method for removing a nickel plating layer from a copper or copper alloy substrate, characterized in that, The process includes the following: using a nickel stripping solution to remove the nickel layer from copper and copper alloy substrates. The main components of the nickel stripping solution are ethylenediamine, ethylenediaminetetraacetic acid, a composite nickel stripping agent, and a composite corrosion inhibitor. The composite nickel stripping agent is ammonium persulfate and citric acid, and the composite corrosion inhibitor is benzotriazole and sodium molybdate.

2. The method for removing nickel plating from copper and copper alloy substrates according to claim 1, characterized in that, The concentrations of each component in the nickel stripping solution are as follows: ethylenediamine 100ml / L-200ml / L, ethylenediaminetetraacetic acid 10g / L-20g / L, composite nickel stripping agent 35g / L-115g / L, and composite corrosion inhibitor 1.2g / L-6.5g / L.

3. The method for removing nickel plating from copper and copper alloy substrates according to claim 2, characterized in that, The concentration of ammonium persulfate in the composite nickel stripping agent is 20 g / L-80 g / L, and the concentration of citric acid is 15 g / L-35 g / L.

4. The method for removing nickel plating from copper and copper alloy substrates according to claim 2, characterized in that, The concentration of benzotriazole in the composite corrosion inhibitor is 0.2 g / L-1.5 g / L, and the concentration of sodium molybdate is 1 g / L-5 g / L.

5. The method for removing nickel plating from copper and copper alloy substrates according to claim 1, characterized in that, The pH of the nickel stripping solution is 3-6.

6. The method for removing nickel plating from copper and copper alloy substrates according to claim 5, characterized in that, The pH of the nickel stripping solution was adjusted using acetic acid.

7. The method for removing nickel plating from copper and copper alloy substrates according to claim 1, characterized in that, The nickel stripping temperature is 50℃-85℃, and the nickel stripping speed is 1μm / min-2μm / min.

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