High-stability alkaline chemical nickel-phosphorus-copper plating ternary alloy plating solution and plating method

Abstract

The invention discloses a high-stability alkaline chemical nickel-phosphorus-copper plating ternary alloy plating solution and a plating method, and belongs to the technical field of metal surface treatment. According to the method, sodium citrate, sodium pyrophosphate and sodium lactate are compounded to serve as complexing agents, urea and thiourea or lead nitrate are combined to serve as stabilizing agents, the preferential replacement reaction of Cu < 2 + > is effectively inhibited, and uniform codeposition of the Ni-P-Cu ternary alloy is achieved. The plating solution is high in stability under the conditions that the pH is 9.0-10.0 and the temperature is 63-68 DEG C, can be used for preparing a thick plating layer with the copper content being 5% or above and the thickness being larger than or equal to 50 microns, is suitable for various base materials such as magnesium alloy, carbon steel and stainless steel, and has the advantages of being low in energy consumption, wide in application range, excellent in plating layer performance and the like.

Description

Technical Field

[0001] This invention relates to the field of metal surface treatment technology, and in particular to a highly stable alkaline electroless nickel-phosphorus-copper ternary alloy plating solution and plating method. Background Technology

[0002] Electroless nickel-phosphorus plating technology has been widely used in industry. Traditional electroless nickel-phosphorus plating is mostly carried out under acidic conditions. Although it can obtain a coating with high hardness and good corrosion resistance, the plating temperature is high (usually above 85°C), energy consumption is high, and it is not suitable for non-ferrous metals such as aluminum, zinc, and magnesium that are sensitive to acid, or non-metallic substrates such as plastics, because they will react with the acidic plating solution.

[0003] Alkaline electroless nickel-phosphorus plating technology has emerged to address this issue. It can be performed at higher pH values ​​(typically 8-10) and relatively lower temperatures (typically 60-80℃), expanding its applicability to various substrates. However, existing alkaline electroless nickel plating technologies still suffer from two major drawbacks: 1. Poor solution stability: Under alkaline conditions, the reduction potential of nickel ions is more negative, making reaction kinetics more difficult to control. The plating solution is prone to self-decomposition, resulting in a short service life. 2. Poor stability of complexing agents under alkaline conditions: The concentrations of the main salt and reducing agent are limited by the stability of the complexing agent, preventing the use of higher concentrations. Therefore, the thickness of the deposited electroless plating layer is typically around 10-20 μm, making it impossible to prepare thicker electroless plating layers. 3. Limited plating performance: The plating layers are mostly nickel-phosphorus binary alloys with limited functionality. Although some studies have attempted to add copper salts to alkaline plating solutions to prepare composite plating layers, copper ions (Cu... 2+ The reduction potential of ions (+0.34 V) is much more positive than that of nickel ions (Ni). 2+ At -0.25 V, preferential displacement reaction is very likely to occur, forming loose copper nodules with poor adhesion on the substrate or coating surface, or causing instantaneous decomposition of the plating solution, making it impossible to form a uniform and dense ternary alloy coating.

[0004] Therefore, developing an alkaline electroless plating solution that can achieve ternary co-deposition of nickel, phosphorus, and copper while also possessing high stability is a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a highly stable alkaline electroless nickel-phosphorus-copper ternary alloy plating solution and plating method. This plating solution successfully inhibits Cu through a unique complexing agent compounding system. 2+ The preferential substitution precipitation enabled uniform co-deposition of the Ni-P-Cu ternary alloy, resulting in significant stability of the plating bath. Through optimized addition of the main salt, reducing agent, and complexing agent ratios, a relatively thick Ni-P-Cu ternary alloy coating was prepared.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A highly stable alkaline electroless nickel-phosphorus-copper ternary alloy plating solution and plating method, the process flow includes: 1) Preparation of electroless nickel-phosphorus copper plating solution: Prepare an alkaline electroless nickel-phosphorus copper plating solution according to the following formula: Main salt: Nickel sulfate (NiSO4). 6H₂O 8-12 g / L; Copper sulfate NiSO₄. 6H₂O 0.5-1.5g / L Reducing agent: Sodium hypophosphite (NaH2PO2·H2O) 8-12 g / L; Buffer: Sodium acetate (NaAc·3H2O) 4-8 g / L; Complexing agent 1: sodium citrate 8-15 g / L, complexing agent 2: sodium pyrophosphate 15-25 g / L, complexing agent 3: sodium lactate 5-8 ml / L; Stabilizer 1: Urea 0.5-1.5 mg / L; Stabilizer 2: PbNO3 or thiourea 1-2 mg / L; Surfactant: Sodium dodecylbenzenesulfonate 1-2 mg / L.

[0007] 2) In the highly stable alkaline electroless nickel-phosphorus copper plating solution, the addition of high-concentration copper through complexing agents and stabilizers will not cause decomposition of the plating solution.

[0008] Complexing agent 1: sodium citrate 8-15 g / L, complexing agent 2: sodium pyrophosphate 35-45 g / L, complexing agent 3: sodium lactate 5-8 ml / L; Stabilizer 1: Urea 0.5-1.5 mg / L; Stabilizer 2: PbNO3 or thiourea 1-2 mg / L; The amount of stabilizer 1 added corresponds to the amount of copper sulfate added.

[0009] 3) Preparation of chemical plating solution: Dissolve the weighed nickel sulfate, sodium acetate, and complexing agent 1 in distilled water, filter, and pour into the test tank. Add stabilizer 2 to the tank solution. Measure out complexing agent 3 and mix it with the above solution. Add the weighed copper sulfate and complexing agent 2, stir thoroughly to dissolve, and then dilute with water to 500 mL to obtain solution a. After preparation, place solution a in a water bath and heat to approximately 65°C.

[0010] b) Dilute the pre-weighed, dissolved, and filtered sodium hypophosphite to 500 mL; this is solution b. Heat solution b to approximately 65°C in a water bath. Mix solutions a and b, stir thoroughly, and finally adjust the pH to the specified range with a 10% dilute ammonia solution. The prepared solution is light green, pure, and free of impurities. For electroless plating, heat the above solution to 65°C and then place the sample to be plated inside.

[0011] 4) Implement chemical plating, and control the process conditions as follows: In the initial stage, depending on the intensity of the reaction bubbles, an active sample can be used to accelerate the reaction. The required active sample is a magnesium alloy wire, such as AZ31. When the magnesium alloy wire is brought into contact with the surface of the sample to be plated, a large number of bubbles will be generated on both the magnesium alloy wire and the sample surface. After 3-5 seconds of contact, the magnesium alloy wire can be removed.

[0012] pH 9.0-10.0, temperature 63-68℃ Optimal loading capacity: 0.8-1.0 dm 2 / L Deposition rate is approximately 5-8 μm / h This invention selects different pretreatment processes for different substrates, followed by electroless nickel-phosphorus copper alloy plating. For carbon steel and stainless steel substrates, the following process and procedure are selected: surface sandblasting - degreasing - activation - pre-nickel plating - electroless nickel plating; The pre-plating nickel process is as follows: Nickel chloride (NiCl₂·6H₂O): 240 g / L; Hydrochloric acid (HCl) (ρ=1.17): 200 g / L; Temperature: Room temperature; Current density: 5~8 A / dm³ 2 Time: 3-5 minutes The magnesium alloy substrate is selected using the following process and technology: surface sandblasting - degreasing - activation - pre-nickel plating - electroless nickel plating. The pickling process is as follows: Nitric acid (HNO3) 30 ml / L; Phosphoric acid (H3PO4) 605 ml / L; Temperature: Room temperature; Time: 30-40 s The activation process is as follows: Potassium pyrophosphate (K4P2O7·3H2O) 200 g / L; Sodium carbonate (Na2CO3) 20 g / L; NaF 5 g / L; Temperature: 60-70℃; Time: 2-3 min.

[0013] The beneficial effects of this invention are as follows: This invention utilizes an alkaline electroless nickel plating solution, suitable for electroless plating on metal surfaces with poor acid corrosion resistance. The invention employs composite additives and stabilizers to prevent decomposition of the electroless nickel-phosphorus copper plating solution, thereby increasing the copper content in the coating. The coating prepared by this invention can achieve a copper content of over 5%. Attached Figure Description

[0014] Figure 1 Surface morphology and elemental analysis results of electroless nickel-phosphorus copper plating; Figure 2 Morphology of electroless nickel-phosphorus copper plating; Figure 3Macroscopic morphology of electroless nickel-phosphorus copper plating. Detailed Implementation

[0015] The present invention will be further explained below with reference to specific implementation schemes, but it is not limited to the present invention. The structures, proportions, sizes, etc. shown in the accompanying drawings are only used to complement the content disclosed in the specification, so as to enable those skilled in the art to understand and read, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modification of the structure, change of the proportion relationship or adjustment of the size, without affecting the effect and purpose that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0016] All contents and proportions mentioned are calculated by mass. The samples used were made of magnesium alloy and carbon steel, and were processed into 30cm×30cm test pieces.

[0017] Example 1 Plating bath preparation: Nickel sulfate 8 g / L, copper sulfate 0.5 g / L, sodium hypophosphite 8 g / L, sodium acetate 4 g / L, sodium citrate 8 g / L, sodium pyrophosphate 15 g / L, sodium lactate 5 mL / L, urea 0.5 mg / L, thiourea 1 mg / L, sodium dodecylbenzenesulfonate 1 mg / L. pH adjusted to 9.0, temperature 65℃. Deposition was performed on a carbon steel substrate at a rate of 8 μm / h, resulting in a copper content of 5.2% in the plating layer.

[0018] Example 2 Nickel sulfate 10 g / L, copper sulfate 1.0 g / L, sodium hypophosphite 10 g / L, sodium acetate 6 g / L, sodium citrate 12 g / L, sodium pyrophosphate 20 g / L, sodium lactate 6 mL / L, urea 1.0 mg / L, lead nitrate 1.5 mg / L, sodium dodecylbenzenesulfonate 1.5 mg / L. At pH 9.5 and a temperature of 66℃, a deposition rate of 9 μm / h was achieved on a magnesium alloy substrate, resulting in a copper plating content of 5.5%.

[0019] Example 3 Nickel sulfate 12 g / L, copper sulfate 1.5 g / L, sodium hypophosphite 12 g / L, sodium acetate 8 g / L, sodium citrate 15 g / L, sodium pyrophosphate 25 g / L, sodium lactate 8 mL / L, urea 1.5 mg / L, thiourea 2 mg / L, sodium dodecylbenzenesulfonate 2 mg / L. At pH 10.0 and a temperature of 68℃, a deposition rate of 9 μm / h was achieved on a stainless steel substrate, resulting in a copper plating content of 5.8%.

[0020] Example 4 The plating solution composition was the same as in Example 1, with pH 9.2, temperature 64°C, deposition rate 5.5 μm / h, and copper content of the plating layer 5.5%.

[0021] Example 5 The plating solution composition was the same as in Example 2, with pH 9.8, temperature 67°C, deposition rate 10 μm / h, and copper content of the plating layer 5.8%.

[0022] Example 6 The plating solution composition was the same as in Example 3, with pH 9.5, temperature 65°C, deposition rate 8 μm / h, and copper content of the plating layer 5.3%.

[0023] Example 7 Pretreatment was performed on the magnesium alloy substrate: sandblasting, degreasing, pickling (nitric acid 30 mL / L, phosphoric acid 605 mL / L, room temperature 40 s), activation (potassium pyrophosphate 200 g / L, sodium carbonate 20 g / L, sodium fluoride 5 g / L, 70℃ 3 min), pre-plating with nickel, followed by chemical plating, resulting in excellent coating adhesion.

[0024] Example 8 Pretreatment of carbon steel substrate: sandblasting, degreasing, activation, and pre-plating with nickel (nickel chloride 240 g / L, hydrochloric acid 200 g / L, current density 6 A / dm³). 2 After 4 minutes, chemical plating was performed, resulting in a coating thickness of 50 μm without peeling or cracking.

[0025] Matters not covered in this invention are common knowledge.

[0026] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A highly stable alkaline electroless nickel-phosphorus-copper ternary alloy plating solution, characterized in that, The highly stable alkaline electroless nickel-phosphorus-copper ternary alloy plating solution comprises the following components and their concentration ranges: Nickel sulfate: 8–12 g / L; Copper sulfate: 0.5–1.5 g / L; Sodium hypophosphite: 8–12 g / L; Sodium acetate: 4–8 g / L; Sodium citrate: 8–15 g / L; Sodium pyrophosphate: 15–25 g / L; Sodium lactate: 5–8 mL / L; Urea: 0.5–1.5 mg / L; Thiourea or lead nitrate: 1–2 mg / L; Sodium dodecylbenzenesulfonate: 1–2 mg / L.

2. The high-stability alkaline electroless nickel-phosphorus-copper ternary alloy plating solution according to claim 1, characterized in that: The highly stable alkaline electroless nickel-phosphorus-copper ternary alloy plating solution has a pH value of 9.0–10.0 and a temperature of 63℃–68℃.

3. A method for applying the highly stable alkaline electroless nickel-phosphorus-copper ternary alloy plating solution according to any one of claims 1 and 2, characterized in that: The electroless nickel-phosphorus copper plating process includes the following steps: a) Dissolve nickel sulfate, sodium acetate, and sodium citrate in water, and filter to obtain solution a; b) Add copper sulfate and sodium pyrophosphate to solution a and stir to dissolve; c) Add sodium lactate, urea, thiourea or lead nitrate, and surfactant, and bring the volume to 500 mL; d) Dissolve sodium hypophosphite in water and heat to 65°C to obtain solution b; e) Mix solution a with solution b, and adjust the pH to 9.0–10.0 with ammonia. f) Immerse the workpiece to be plated in the plating solution for chemical plating.

4. The plating method of the high-stability alkaline electroless nickel-phosphorus-copper ternary alloy plating solution according to claim 3, characterized in that: The substrate is pretreated before plating, including sandblasting, degreasing, activation and pre-plating with nickel.

5. The plating method of the high-stability alkaline electroless nickel-phosphorus-copper ternary alloy plating solution according to claim 4, characterized in that: The pre-plating nickel solution consists of: 240 g / L nickel chloride, 200 g / L hydrochloric acid, and a current density of 5–8 A / dm³. 2 Time: 3–5 minutes.

6. The plating method of the high-stability alkaline electroless nickel-phosphorus-copper ternary alloy plating solution according to claim 3, characterized in that: Initial activation is performed in the plating solution using magnesium alloy wires, with a contact time of 3–5 seconds.

7. The plating method of the high-stability alkaline electroless nickel-phosphorus-copper ternary alloy plating solution according to claim 3, characterized in that: The coating deposition rate is 5–8 μm / h.

8. The plating method of the high-stability alkaline electroless nickel-phosphorus-copper ternary alloy plating solution according to claim 3, characterized in that: The coating is a Ni-P-Cu ternary alloy with a copper content of not less than 5%.

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