Electroplating method for nickel-tungsten-phosphorus coating

Abstract

The present invention belongs to the field of corrosion protection technology, and specifically relates to a method for electroplating a nickel-tungsten-phosphorus coating. The method provides a nickel-tungsten-phosphorus coating that utilizes direct current (DC) electroplating and pulse electroplating to form two layers of nickel-tungsten-phosphorus coating on a workpiece surface. The structure and properties of the nickel-tungsten-phosphorus coating are controlled by adjusting the current density and temperature of the DC and pulse electroplating processes. Furthermore, a complexing system composed of ethylenediaminetetraacetic acid, sodium oxalate, and malic acid is employed in conjunction with additive-modified nano-alumina to stabilize metal ions in the plating solution, effectively improving the stability of the plating solution and facilitating the formation of a uniform, dense coating structure.

Description

Technical Field

[0001] The invention belongs to the technical field of corrosion prevention, and in particular relates to an electroplating method for a nickel-tungsten-phosphorus coating. Background Art

[0002] Corrosion protection for offshore oil engineering equipment has become a prominent challenge in today's offshore oil equipment sector. In the petrochemical industry, equipment often faces harsh operating conditions such as corrosion, wear, high temperatures, and high pressures, placing extremely high demands on material performance.

[0003] Nickel-tungsten-phosphorus (NTP) coatings are alloy coatings formed through chemical or electroplating methods. They offer excellent wear and corrosion resistance, and a low coefficient of friction, making them important in the aerospace, automotive, electronics, and petrochemical industries. The addition of tungsten can improve coating defects generated during the plating process, thereby enhancing substrate protection. In the electroless nickel-tungsten-phosphorus (NTP) plating formulation, the selection of complexing agents, stabilizers, brighteners, and anti-pinhole agents is crucial, as they directly impact the physical and chemical properties of the plating solution and the coating. However, traditional complexing agents, such as tartaric acid and citric acid, have lower stability constants for the complexes formed between tungstate ions and the complexing agents than between nickel ions and the complexing agents. Consequently, nickel ions in the plating solution preferentially capture the complexing agents, resulting in an increased concentration of free tungstate ions. In a weakly acidic environment, free tungstate ions readily hydrolyze to form WO3·nH2O, impacting the stability of the plating solution. For example, Chinese patent publication number CN109423670A discloses a method for preparing nickel-tungsten-phosphorus alloy plating on the surface of a track copper bar. The main complexing agent used is any one of sodium acetate, sodium citrate or triethanolamine. However, nickel ions and tungstate are simultaneously present in the plating solution, and both need to be deposited under reducing conditions. The reduction potentials differ significantly, and nickel ions are relatively easy to reduce, resulting in preferential reduction of nickel in the plating solution, triggering the decomposition of tungstate. In addition, the phosphorus is derived from sodium hypophosphite. As a reducing agent, the oxidation product produced by sodium hypophosphite reacts with tungstate to form insoluble phosphates, resulting in turbidity in the plating solution. The complexing agent used cannot maintain the stability of the plating solution.

[0004] In addition, the existing electroplating process has poor stability, such as pH value and temperature sensitivity, complex process, and the porosity of the coating obtained by traditional bath electroplating is large, the corrosion resistance is poor, and the coating thickness is uneven and the coating adhesion is poor. The Chinese patent application document with publication number CN107881537A discloses a preparation method of nickel-tungsten-phosphorus alloy plated on beryllium copper surface, which specifically includes degreasing, pickling and polishing, polishing, film peeling, activation, pH adjustment, bath electroplating, dehydration to prevent discoloration, drying and other steps. In addition to pH adjustment and drying, each of the above steps is followed by a water washing step. Therefore, its preparation process is relatively complex, produces a lot of wastewater, and has high technical requirements for operators. During the electroplating process, it is necessary to strictly control parameters such as plating solution composition, temperature, current density, and pH value. In addition, the coating obtained by bath electroplating has the disadvantages of high porosity, poor corrosion resistance, uneven coating thickness, and poor coating adhesion. Summary of the Invention

[0005] In order to solve the technical problems existing in the above-mentioned technology such as poor plating solution stability, high porosity of the plating layer, poor corrosion resistance and poor bonding strength, the purpose of the present invention is to provide an electroplating method for nickel tungsten phosphorus coating.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows:

[0007] A method for electroplating a nickel-tungsten-phosphorus coating comprises the following steps:

[0008] S1: Pre-grind, degrease and activate the workpiece to obtain the workpiece to be plated;

[0009] S2: Hang the workpiece to be plated obtained in step S1 in an electroplating tank, add plating solution, connect a DC power supply for electroplating for 2-3 hours, and then connect a pulse power supply for electroplating for 1-1.5 hours to obtain a plated workpiece;

[0010] S3: rinsing the plated part obtained in step S2 with deionized water and drying it to obtain a workpiece plated with a nickel-tungsten-phosphorus coating;

[0011] The plating solution comprises the following components: a soluble nickel compound, a soluble tungsten compound, a soluble phosphorus compound, a complexing agent, a pH regulator and water; the complexing agent comprises ethylenediaminetetraacetic acid, sodium oxalate and malic acid.

[0012] Through the above technical solution, two layers of nickel-tungsten-phosphorus coatings are obtained on the surface of the workpiece using two electroplating methods: direct current plating and pulse plating. The electroplating time and current density of the direct current plating film and the pulse plating film are different, and the structure of the formed coating is different, and the component content is also different. The two-layer film grows in an interlaced manner, effectively reducing defects such as pores and cracks in the coating, blocking the corrosion path of the corrosive medium entering the substrate, and achieving the purpose of good protection of the substrate. The direct current plating process can quickly activate the workpiece, improve the bonding force between the workpiece and the coating, reduce the lattice defects of the coating, and reduce the internal stress of the coating. At the same time, the constant current field can make the metal ions in the plating solution evenly deposited on the cathode surface, obtaining a coating with uniform thickness and density. The pulse plating process can obtain a low-stress coating by adjusting the pulse parameters, and electroplating in the pulse mode helps to form a fine, dense crystal structure, giving the coating good corrosion resistance and mechanical properties.

[0013] The complexing agent is the main factor to balance the precipitation potential of the main salt ions, and it can also ensure the stability of the plating solution system. The complexing system composed of ethylenediaminetetraacetic acid, sodium oxalate and malic acid is used. EDTA forms a stable complex with nickel ions in the plating solution through four carboxyl groups and two amino groups, and slowly dissociates [Ni-EDTA] 2- , maintain free Ni in the plating solution 2+ Concentration stability to avoid high concentration leading to local Ni 2+ The solution also stabilizes tungstate ions, preventing their hydrolysis while also reducing the deposition potential of tungsten and promoting the co-precipitation of tungsten and nickel. Sodium oxalate and EDTA form a "strong-weak combination," providing a buffer when EDTA concentration fluctuates, maintaining the stability of metal ions in the plating bath. Malic acid provides a buffer for the plating bath in a weakly acidic environment, stabilizing its pH. Furthermore, the presence of the α-hydroxyl group in malic acid inhibits the oxidation of hypophosphite by dissolved oxygen in the plating bath, reducing hydrogen evolution and lowering the porosity of the coating. Using EDTA, sodium oxalate, and malic acid as a composite complex system significantly improves the stability of the plating bath and the quality of the coating through a synergistic mechanism of "strong complexation, moderate complexation, and buffering regulation."

[0014] Furthermore, the complexing agent is composed of ethylenediaminetetraacetic acid, sodium oxalate, and malic acid in a mass ratio of 3-8:6-9:10-14.

[0015] Through the above technical solution, excessive EDTA usage increases the solution's resistance, reducing the current density used for electrodeposition. Excessive EDTA also occupies space on the electrode surface, hindering the deposition of tungsten, which has a more negative potential. By controlling the mass ratio of the various components in the complexing agent, the tungsten content in the coating can be effectively increased.

[0016] Furthermore, the complexing agent is composed of ethylenediaminetetraacetic acid, sodium oxalate, and malic acid in a mass ratio of 5-7:7-8:12-14.

[0017] Furthermore, the plating solution includes the following components in parts by mass: 170-200 parts of a soluble nickel compound, 30-50 parts of a soluble tungsten compound, 20-30 parts of a soluble phosphorus compound, 40-50 parts of a complexing agent, 20-30 parts of a pH regulator, and 1000-1500 parts of water.

[0018] Furthermore, the plating solution also includes 30-50 parts by mass of an additive and 10-15 parts by mass of a dispersant, the additive is modified nano-alumina, and the dispersant is one of fatty acid methyl ester ethoxylate sulfonate, sodium dodecyl sulfate, sodium dodecyl phosphate, and sodium dodecylbenzene sulfonate.

[0019] Furthermore, the preparation method of the modified nano-alumina is as follows: (1) dispersing nano-alumina in deionized water, adding vinyltrimethoxysilane, adjusting the pH value to 3-5, heating to 70-80°C, reacting for 3-5 hours, filtering, washing the filter cake, and drying to obtain silanized alumina; (2) mixing water, sodium dodecylbenzenesulfonate and anhydrous ethanol, adding tripropyleneamine, silanized alumina and initiator, heating to 80-100°C, stirring and reacting for 4-5 hours, cooling, filtering, washing, and drying to obtain modified nano-alumina.

[0020] Through the above-mentioned technical solution, nano-alumina is reacted with vinyltrimethoxysilane to introduce double bonds into the nano-alumina. This then undergoes an addition reaction with the double bonds in tripropyleneamine, introducing tertiary amine groups from the tripropyleneamine onto the surface of the nano-alumina to produce modified alumina. When the modified alumina is added to the plating solution, the lone pairs of electrons in the tertiary amine groups on its surface can directly coordinate with the tungstate atoms in the tungstate. Furthermore, under weakly acidic conditions, the protonated tertiary amines form ion pairs with the negatively charged tungstate through electrostatic interactions, thereby stabilizing the tungstate ions. Furthermore, during the tungsten deposition process, some nano-alumina is also deposited on the electrode surface, forming a metal-nonmetal composite film layer, effectively improving the hardness and wear resistance of the coating.

[0021] Furthermore, the particle size of the nano-alumina is 10-30 nm.

[0022] Furthermore, the mixing mass ratio of water, sodium dodecylbenzenesulfonate and anhydrous ethanol in step (2) is 40-50:7-11:25-40.

[0023] Furthermore, the initiator is one of hydrogen peroxide, sodium persulfate and azobisisobutyronitrile, and the amount of the initiator is 0.7%-1.2% of the mass of tripropyleneamine.

[0024] Furthermore, the mass ratio of the nano-alumina, vinyltrimethoxysilane and tripropyleneamine is 13-17:4-8:3-7.

[0025] Furthermore, the current density of the DC power supply output in step S2 is 18-25A / dm 2 , the electroplating temperature of the DC power supply is 62-75°C.

[0026] Through the above technical solution, the structure and properties of the formed coating are controlled by controlling the current density and plating temperature of DC electroplating. When the current density exceeds the above current density, hydrogen evolution is serious near the electrode, which affects the adhesion of the tungsten-containing complex on the electrode and hinders the deposition of W. At the same time, due to the continuous precipitation of H2 on the electrode surface, the pH value of the solution near it rises rapidly, which is conducive to the deposition of Ni. However, H + The reduction in concentration is not conducive to the deposition of P, and thus will affect the distribution of nickel, tungsten and phosphorus in the coating. At the same time, the precipitated hydrogen will be mixed in the coating to form bubbles or pinholes, thereby affecting the corrosion resistance of the coating.

[0027] Furthermore, the current density of the pulse power output in step S2 is 4-8A / dm 2 The pulse frequency is 1200-1500 Hz, the duty cycle is 20%-30%; the electroplating temperature of the pulse power supply is 72-76°C.

[0028] Through the above-mentioned technical solution, the selection of lower current density and higher pulse frequency helps to obtain a denser and smoother coating and improve the uniformity of the coating, while a smaller duty cycle can reduce the average current density while maintaining the peak current, which helps to avoid the occurrence of hydrogen evolution, reduce the porosity of the coating, and improve the flatness and corrosion resistance of the coating.

[0029] Furthermore, the soluble nickel compound is one of nickel sulfate, nickel chloride and nickel nitrate; the soluble tungsten compound is one of sodium tungstate, potassium tungstate, ammonium tungstate and ammonium metatungstate; the soluble phosphorus compound is sodium hypophosphite; and the pH adjuster is one of glacial acetic acid, sulfuric acid and nitric acid.

[0030] Furthermore, the preparation method of the plating solution is specifically as follows: water is added to a reactor, and a soluble nickel compound, a soluble tungsten compound and a soluble phosphorus compound are added in sequence, each raw material is stirred for 0.3-0.5h after being added, a complexing agent is added in small amounts and multiple times, and after stirring evenly, a pH adjuster is added to adjust the pH value of the solution to 5.7-6.5 to obtain a plating solution.

[0031] Furthermore, the method for preparing the plating solution further comprises adding a dispersant and stirring evenly, adding an additive and stirring evenly to obtain the plating solution.

[0032] In the above technical solution, the pH value of the plating solution will affect the composition and structure of the coating. Studies have found that when the pH value of the plating solution is too low, the tungstate ions in the plating solution are easy to react with the H + Combined with the formation of tungstic acid precipitation, resulting in a decrease in the tungsten content in the coating, and the intensification of the hydrogen evolution reaction on the electrode surface, resulting in an increase in the porosity of the coating, the coating becomes brittle, and the performance decreases; when the pH value of the plating solution is too high, Ni 2+ Easy and OH - Combined with the formation of nickel hydroxide precipitation, the nickel content in the coating is reduced. At the same time, the increase in pH value can accelerate the reduction rate of metal ions and increase the deposition rate, resulting in uneven coating deposition and affecting the density and corrosion resistance of the coating.

[0033] Furthermore, the operations of pre-grinding, degreasing, and activation treatment in step S1 are specifically as follows: grinding the workpiece flat with a polishing machine, cleaning it with deionized water, and then immersing it in an alkaline solution for degreasing, rinsing it with deionized water, and then immersing it in dilute hydrochloric acid until uniform corrosion pits appear on the surface of the workpiece, and then cleaning it with deionized water.

[0034] Furthermore, in the operations of pre-grinding, degreasing and activation treatment, the alkaline solution is a mixed solution of sodium hydroxide and sodium carbonate, the concentration of sodium hydroxide is 0.3-0.4 mol / L, the concentration of sodium carbonate is 0.1-0.2 mol / L, the degreasing temperature is 65-75°C, and the degreasing time is 2.2-3h; the concentration of the dilute hydrochloric acid is 1.0-1.5 mol / L.

[0035] Furthermore, the drying temperature in step S3 is 300-400° C., and the drying time is 2-2.5 hours.

[0036] The plated workpiece is dried at this temperature for 2-2.5 hours. Solid solution hard phase and dispersed hard phase (Ni3P) will precipitate in the coating, which plays an embedding and fixing role. Under the action of these hard phases, the atoms in the coating are not easily stripped off by friction shear force, which can effectively improve the hardness of the coating and obtain better wear resistance.

[0037] Compared with the prior art, the electroplating method of nickel tungsten phosphorus coating provided by the present invention has the following technical advantages:

[0038] (1) The electroplating method of nickel tungsten phosphorus coating provided by the present invention adopts direct current plating and pulse plating to obtain two layers of nickel tungsten phosphorus coating on the surface of the workpiece, and the structure and performance of the nickel tungsten phosphorus coating are controlled by adjusting the current density and temperature of direct current plating and pulse plating;

[0039] (2) The present invention adopts a complex system composed of ethylenediaminetetraacetic acid, sodium oxalate and malic acid, and uses additives to modify nano-alumina to enable the metal ions in the plating solution to exist stably, effectively improving the stability of the plating solution and helping to obtain a uniform and dense coating structure;

[0040] (3) The plating solution provided by the present invention does not contain Fe 3+ 、Cu 2+ 、Ag + Heavy metal ions such as nickel ions can prevent the decomposition of hypophosphite by impurity ions, ensure the smooth redox reaction of phosphate with nickel ions and tungstate, increase the thickness of the coating, and thus improve the corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a cross-sectional electron micrograph of the coating obtained in Example 8;

[0042] Figure 2 This is a surface electron microscope image of the coating obtained in Example 8;

[0043] Figure 3 This is the EDS energy spectrum of the coating prepared in Example 8. DETAILED DESCRIPTION

[0044] The following will be further described in conjunction with specific embodiments, but the present invention is not limited to the following embodiments. Those skilled in the art may make various modifications based on the basic concept of the present invention, but as long as they do not depart from the basic concept of the present invention, they are all within the scope of the present invention.

[0045] In this specific embodiment, the raw materials are all commercially available unless otherwise specified.

[0046] In this specific embodiment, the nickel ion concentration, tungstate ion concentration, hypophosphite ion concentration and solution pH value in the plating solution are detected every 1 hour, and the corresponding chemical components are automatically added to the insufficient part until the nickel tungsten phosphorus coating is completed.

[0047] In this specific embodiment, 50 mm×50 mm×2 mm Q235 steel is used as the substrate (workpiece), and a stainless steel sheet is used as the anode.

[0048] Example 1

[0049] A method for electroplating a nickel-tungsten-phosphorus coating comprises the following steps:

[0050] S1: Pre-grind, degrease, and activate the workpiece: polish the workpiece with a polishing machine, rinse it repeatedly with deionized water for 3 times, and immerse it in a mixed solution of sodium hydroxide and sodium carbonate for degreasing. The degreasing temperature is 65°C, the degreasing time is 3 hours, the concentration of sodium hydroxide is 0.3 mol / L, and the concentration of sodium carbonate is 0.2 mol / L. Rinse it repeatedly with deionized water for 3 times and then immerse it in dilute hydrochloric acid with a concentration of 1.0 mol / L until uniform corrosion pits appear on the surface of the workpiece. Rinse it repeatedly with deionized water for 3 times to obtain the workpiece to be plated.

[0051] S2: Place the plated workpiece obtained in step S1 in the electroplating tank, add the plating solution, and connect the DC power supply at a current density of 18A / dm 2 , electroplating at 75℃ for 2h, then turning on the pulse power supply at a current density of 4A / dm 2 , electroplating for 1.5 h under the conditions of a pulse frequency of 1500 Hz, a duty cycle of 20%, and a temperature of 72° C. to obtain a plated part;

[0052] The plating solution is prepared by adding 1000g of water to a reactor, followed by the addition of 170g of nickel sulfate, 50g of potassium tungstate, and 20g of sodium hypophosphite, stirring for 0.3h after each addition, adding 40g of a complexing agent in four portions, stirring evenly after each addition, adjusting the pH of the solution to 5.7 by adding 20g of glacial acetic acid, adding 10g of fatty acid methyl ester ethoxylate sulfonate, stirring evenly, and adding 30g of modified nano-alumina, stirring evenly, to obtain a plating solution. The complexing agent comprises ethylenediaminetetraacetic acid, sodium oxalate, and malic acid in a mass ratio of 3:6:10.

[0053] The preparation method of modified nano-alumina is as follows: (1) 130g of nano-alumina with a particle size of 10nm is dispersed in 500g of deionized water, 40g of vinyltrimethoxysilane is added, the pH value is adjusted to 3, heated to 70℃, reacted for 5h, filtered, the filter cake is washed, and dried to obtain silanized alumina; (2) 450g of water, 70g of sodium dodecylbenzenesulfonate and 250g of anhydrous ethanol are mixed evenly, 30g of tripropyleneamine, silanized alumina and 0.36g of hydrogen peroxide are added, heated to 80℃, stirred for reaction for 5h, naturally cooled and filtered, the filter cake is repeatedly washed with anhydrous ethanol, and placed in a vacuum drying oven to dry at 60℃ to obtain modified nano-alumina.

[0054] S3: Rinse the plated part obtained in step S2 with deionized water three times, and dry it at 300° C. for 2.5 hours to obtain a workpiece plated with a nickel-tungsten-phosphorus coating.

[0055] Example 2

[0056] A method for electroplating a nickel-tungsten-phosphorus coating comprises the following steps:

[0057] S1: Pre-grind, degrease, and activate the workpiece: polish the workpiece with a polishing machine, rinse it repeatedly with deionized water for 5 times, and immerse it in a mixed solution of sodium hydroxide and sodium carbonate for degreasing. The degreasing temperature is 75°C, the degreasing time is 2.2h, the concentration of sodium hydroxide is 0.4mol / L, and the concentration of sodium carbonate is 0.1mol / L. Rinse it repeatedly with deionized water for 5 times and then immerse it in dilute hydrochloric acid with a concentration of 1.5mol / L until uniform corrosion pits appear on the surface of the workpiece. Rinse it repeatedly with deionized water for 5 times to obtain the workpiece to be plated.

[0058] S2: Place the workpiece prepared in step S1 in the electroplating tank, add the plating solution, and connect the DC power supply at a current density of 25A / dm 2 , electroplating at 62℃ for 3h, then turning on the pulse power supply at a current density of 8A / dm 2 , electroplating for 1 h under the conditions of a pulse frequency of 1200 Hz, a duty cycle of 30%, and a temperature of 76°C to obtain a plated part;

[0059] The plating solution preparation method specifically comprises the following steps: adding 1500g of water to a reactor, followed by the sequential addition of 200g of nickel nitrate, 30g of sodium tungstate, and 30g of sodium hypophosphite, stirring each raw material for 0.5h. Adding 50g of a complexing agent in four portions, stirring thoroughly after each addition, and then adding 30g of sulfuric acid (35% by mass) to adjust the pH of the solution to 6.5. Adding 15g of sodium lauryl phosphate and stirring thoroughly, and finally adding 50g of modified nano-alumina and stirring thoroughly to obtain a plating solution. The complexing agent comprises ethylenediaminetetraacetic acid, sodium oxalate, and malic acid in a mass ratio of 8:9:14.

[0060] The preparation method of modified nano-alumina is as follows: (1) 170g of nano-alumina with a particle size of 30nm is dispersed in 500g of deionized water, 80g of vinyltrimethoxysilane is added, the pH value is adjusted to 5, heated to 80℃, reacted for 3h, filtered, the filter cake is washed, and dried to obtain silanized alumina; (2) 500g of water, 110g of sodium dodecylbenzenesulfonate and 400g of anhydrous ethanol are mixed evenly, 70g of tripropyleneamine, silanized alumina and 0.49g of sodium persulfate are added, heated to 100℃, stirred and reacted for 4h, naturally cooled and filtered, the filter cake is repeatedly washed with anhydrous ethanol, and placed in a vacuum drying oven to dry at 70℃ to obtain modified nano-alumina.

[0061] S3: Rinse the plated part obtained in step S2 with deionized water for 5 times, and dry it at 400° C. for 2 hours to obtain a workpiece plated with a nickel-tungsten-phosphorus coating.

[0062] Example 3

[0063] A method for electroplating a nickel-tungsten-phosphorus coating comprises the following steps:

[0064] S1: Pre-grind, degrease, and activate the workpiece: polish the workpiece with a polishing machine, rinse it repeatedly with deionized water 4 times, and immerse it in a mixed solution of sodium hydroxide and sodium carbonate for degreasing. The degreasing temperature is 70°C, the degreasing time is 2.7h, the concentration of sodium hydroxide is 0.35mol / L, and the concentration of sodium carbonate is 0.17mol / L. Rinse it repeatedly with deionized water 4 times and then immerse it in dilute hydrochloric acid with a concentration of 1.3mol / L until uniform corrosion pits appear on the surface of the workpiece. Rinse it repeatedly with deionized water 4 times to obtain the workpiece to be plated.

[0065] S2: Place the workpiece prepared in step S1 in the electroplating tank, add the plating solution, and connect the DC power supply at a current density of 20A / dm 2 , electroplating at 68℃ for 2.5h, then turning on the pulse power supply at a current density of 7A / dm 2 , electroplating for 1.2 h under the conditions of a pulse frequency of 1300 Hz, a duty cycle of 25%, and a temperature of 75°C to obtain a plated part;

[0066] The plating solution is prepared as follows: 1300g of water is added to a reactor, followed by 190g of nickel chloride, 37g of ammonium tungstate, and 25g of sodium hypophosphite. Each raw material is stirred for 0.4h after addition. 46g of a complexing agent is added in four portions, stirring thoroughly after each addition. 25g of nitric acid (35% by mass) is added to adjust the pH of the solution to 6.0. 12g of sodium lauryl sulfate is added and stirred thoroughly. Finally, 42g of modified nano-alumina is added and stirred thoroughly to obtain a plating solution. The complexing agent is composed of ethylenediaminetetraacetic acid, sodium oxalate, and malic acid in a mass ratio of 6:7:13.

[0067] The preparation method of modified nano-alumina is as follows: (1) 150g of nano-alumina with a particle size of 20nm is dispersed in 500g of deionized water, 65g of vinyltrimethoxysilane is added, the pH value is adjusted to 4, the mixture is heated to 75℃, the reaction is carried out for 4h, the mixture is filtered, the filter cake is washed, and the mixture is dried to obtain silanized alumina; (2) 480g of water, 85g of sodium dodecylbenzenesulfonate and 310g of anhydrous ethanol are mixed evenly, 45g of tripropyleneamine, silanized alumina and 0.45g of azobisisobutyronitrile are added, the mixture is heated to 90℃, the reaction is stirred for 4.5h, the mixture is naturally cooled and filtered, the filter cake is repeatedly washed with anhydrous ethanol, and the mixture is dried in a vacuum drying oven at 65℃ to obtain modified nano-alumina.

[0068] S3: Rinse the plated part obtained in step S2 with deionized water for 4 times, and dry it at 350° C. for 2.3 h to obtain a workpiece plated with a nickel-tungsten-phosphorus coating.

[0069] Example 4

[0070] The electroplating method of the nickel tungsten phosphorus coating in this embodiment is similar to that in Example 3. The difference between this embodiment and Example 3 is that the complexing agent in this embodiment is composed of ethylenediaminetetraacetic acid, sodium oxalate, and malic acid in a mass ratio of 5:8:12.

[0071] Example 5

[0072] The electroplating method of the nickel tungsten phosphorus coating in this embodiment is similar to that in Example 3. The difference between this embodiment and Example 3 is that the complexing agent in this embodiment is composed of ethylenediaminetetraacetic acid, sodium oxalate, and malic acid in a mass ratio of 7:6:14.

[0073] Example 6

[0074] The electroplating method of the nickel-tungsten-phosphorus coating in this embodiment is similar to that in embodiment 5. The difference between this embodiment and embodiment 5 is that step S2 is specifically: hanging the workpiece to be plated obtained in step S1 in the electroplating tank, adding the plating solution, connecting the DC power supply at a current density of 22A / dm 2 , electroplating at 68℃ for 2.5h, then turning on the pulse power supply at a current density of 8A / dm 2 Electroplating was carried out for 1.2 h under the conditions of a pulse frequency of 1300 Hz, a duty cycle of 25%, and a temperature of 75°C to obtain a plated part.

[0075] Example 7

[0076] The electroplating method of the nickel-tungsten-phosphorus coating in this embodiment is similar to that in embodiment 5. The difference between this embodiment and embodiment 5 is that step S2 is specifically: hanging the workpiece to be plated obtained in step S1 in the electroplating tank, adding the plating solution, connecting the DC power supply at a current density of 18A / dm 2 , electroplating at 68℃ for 2.5h, then turning on the pulse power supply at a current density of 5A / dm 2 Electroplating was carried out for 1.2 h under the conditions of a pulse frequency of 1300 Hz, a duty cycle of 25%, and a temperature of 75°C to obtain a plated part.

[0077] Example 8

[0078] The electroplating method of the nickel tungsten phosphorus coating in this embodiment is similar to that in Example 7. The difference between this embodiment and Example 7 is that the preparation method of the modified nano-alumina is as follows: (1) 155g of nano-alumina with a particle size of 20nm is dispersed in 500g of deionized water, 55g of vinyltrimethoxysilane is added, the pH value is adjusted to 4, the mixture is heated to 75°C, the reaction is carried out for 4h, the mixture is filtered, the filter cake is washed, and the mixture is dried to obtain silanized alumina; (2) 480g of water, 85g of sodium dodecylbenzenesulfonate and 310g of anhydrous ethanol are mixed evenly, 50g of tripropyleneamine, silanized alumina and 0.45g of azobisisobutyronitrile are added, the mixture is heated to 90°C, the reaction is stirred for 4.5h, the mixture is naturally cooled and filtered, the filter cake is repeatedly washed with anhydrous ethanol, and the mixture is dried in a vacuum drying oven at 66°C to obtain the modified nano-alumina.

[0079] Example 9

[0080] The electroplating method of the nickel tungsten phosphorus coating in this embodiment is similar to that in Example 7. The difference between this embodiment and Example 7 is that the preparation method of the modified nano-alumina is as follows: (1) 145 g of nano-alumina with a particle size of 20 nm is dispersed in 500 g of deionized water, 60 g of vinyltrimethoxysilane is added, the pH value is adjusted to 4, the mixture is heated to 75° C., the reaction is carried out for 4 h, the mixture is filtered, the filter cake is washed, and the mixture is dried to obtain silanized alumina; (2) 480 g of water, 85 g of sodium dodecylbenzenesulfonate and 310 g of anhydrous ethanol are mixed evenly, 40 g of tripropyleneamine, silanized alumina and 0.45 g of azobisisobutyronitrile are added, the mixture is heated to 90° C., the reaction is stirred for 4.5 h, the mixture is naturally cooled and filtered, the filter cake is repeatedly washed with anhydrous ethanol, and the mixture is dried in a vacuum drying oven at 65° C. to obtain the modified nano-alumina.

[0081] Example 10

[0082] The electroplating method for the nickel-tungsten-phosphorus coating in this embodiment is similar to that in Example 8. The difference between this embodiment and Example 8 is that the plating solution is prepared as follows: 1300 g of water is added to a reactor, followed by the sequential addition of 190 g of nickel chloride, 37 g of ammonium tungstate, and 25 g of sodium hypophosphite. Each raw material is stirred for 0.4 h after addition. 46 g of a complexing agent is added in four portions, stirring evenly after each addition. 25 g of nitric acid (35% by mass) is added to adjust the pH of the solution to 5.7. 12 g of sodium lauryl sulfate is added and stirred evenly. 42 g of modified nano-alumina is added and stirred evenly to obtain a plating solution. The complexing agent is composed of ethylenediaminetetraacetic acid, sodium oxalate, and malic acid in a mass ratio of 6:7:13.

[0083] Comparative Example 1

[0084] The electroplating method of the nickel tungsten phosphorus coating in this comparative example is similar to that in Example 8. The difference between this comparative example and Example 8 is that the complexing agent in this comparative example consists of sodium citrate and tartaric acid in a mass ratio of 3:1.

[0085] Comparative Example 2

[0086] The electroplating method of the nickel tungsten phosphorus coating in this comparative example is similar to that in Example 8. The difference between this comparative example and Example 8 is that no additives are added to the plating solution formula of this comparative example.

[0087] Comparative Example 3

[0088] The electroplating method of the nickel-tungsten-phosphorus coating in this comparative example is similar to that in Example 8. The difference between this comparative example and Example 8 is as follows: Step S2 of this comparative example is as follows: a DC power supply is connected at a current density of 32A / dm 2 , electroplating at 68℃ for 2.5h, then turning on the pulse power supply at a current density of 15A / dm 2 Electroplating was carried out for 1.2 h under the conditions of a pulse frequency of 1300 Hz, a duty cycle of 25%, and a temperature of 75°C to obtain a plated part.

[0089] Test Example 1: Performance Test

[0090] Microhardness test: The microhardness of the nickel-tungsten-phosphorus coating was measured using an HVS-1000 digital microhardness tester with a load of 200 g and a loading time of 20 s.

[0091] Adhesion test: The adhesion of the coating is tested according to the thermal shock method in GB / T 5270-2024 "Review of test methods for adhesion strength of electrodeposited and chemically deposited metallic coatings on metal substrates": the sample is placed in a 220°C oven for 1 hour, then removed and immediately quenched in room temperature water. If the coating does not separate from the substrate, such as blistering and flaking, it indicates good adhesion.

[0092] Corrosion resistance test: After cleaning the coating, wipe it dry and dry it in an electric constant temperature blast drying oven until constant weight is reached. Record the weight. Use protective glue to protect the edge and expose a fixed area (8.0 cm 2 ) was immersed in 3.5wt% NaCl solution for 650h. The specimen was removed, cleaned, and dried in a drying oven to constant weight. The post-corrosion mass was recorded. The corrosion rate was calculated by the corrosion weight loss after immersion and expressed in g·m -2 ·a -1 To express.

[0093] Plating solution stability test: Observe each group of plating solutions to see if there are any phenomena such as turbidity, precipitation, stratification, or color change during the electroplating process.

[0094] The test results are shown in Table 1.

[0095] Table 1 Performance test results of nickel-tungsten-phosphorus coating

[0096]

[0097] Combined with the data in Table 1, analysis of the experimental data of Examples 1 to 5 and Comparative Example 1 shows that the complexing agent can stabilize the plating solution and improve the uniformity of the coating. The present invention adopts ethylenediaminetetraacetic acid, sodium oxalate and malic acid in a certain mass ratio to form a synergistic mechanism of "strong complexation-medium complexation-buffering adjustment", which effectively improves the stability of the plating solution and the uniformity of the coating, thereby improving the hardness and corrosion resistance of the coating.

[0098] Analysis of the experimental data of Examples 1 to 4, Examples 6 to 7, and Comparative Example 3 shows that current density is one of the key factors affecting the nickel tungsten phosphorus coating. When the current density range provided by the present invention is exceeded, hydrogen evolution is severe near the electrode, and hydrogen will be doped into the coating to form bubbles or pinholes, thereby affecting the microhardness, bonding strength and corrosion resistance of the coating.

[0099] Analysis of the experimental data of Examples 1 to 4, Examples 8 to 9, and Comparative Example 2 shows that the modified nano-alumina in the present invention is added as an additive to the plating solution to assist the complexing agent in improving the stability of the plating solution, and part of the nano-alumina is deposited on the coating to improve the hardness of the coating.

[0100] Test Example 2: Characterization Test

[0101] Morphology test: The cross-sectional morphology and surface morphology of the coating obtained in Example 8 were analyzed and tested using a FEI QUANTA environmental scanning electron microscope (SEM). The test results are shown in Figure 1 、 Figure 2 .

[0102] Composition analysis: The Ni, W, and P elemental compositions of each sublayer of the double-layer film were determined using the energy dispersive spectrometer (EDS) attached to the SEM. Before scanning, the sample was placed in acetone for 1 minute to remove oil. The test results are shown in Figure 3 and Table 2.

[0103] Table 2 Coating composition

[0104]

[0105] Depend on Figure 1 and Figure 2 It can be seen that the double-layer coating film prepared in Example 8 of the present invention has a dense structure, the coating and the substrate, and the coating and the coating are well bonded, and a small amount of aluminum oxide particles are evenly distributed on the surface of the coating.

[0106] Depend on Figure 3It can be seen that the coating prepared in Example 8 of the present invention contains three metal elements, namely nickel, tungsten and phosphorus, and also contains a small amount of aluminum. Therefore, it can be seen that a small amount of nano-aluminum oxide is doped in the coating.

[0107] The above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Persons skilled in the art should not modify the above embodiments without departing from the spirit and scope of the present invention. Any equivalent modifications or alterations made by persons skilled in the art without departing from the technical spirit of the present invention are intended to fall within the scope of protection of the present invention.

Claims

1. A method for electroplating a nickel-tungsten-phosphorus coating, characterized in that: The following steps are involved: S1: Pre-grind, degrease and activate the workpiece to obtain the workpiece to be plated; S2: Hang the workpiece to be plated obtained in step S1 in an electroplating tank, add plating solution, connect a DC power supply for electroplating for 2-3 hours, and then connect a pulse power supply for electroplating for 1-1.5 hours to obtain a plated workpiece; S3: rinsing the plated part obtained in step S2 with deionized water and drying it to obtain a workpiece plated with a nickel-tungsten-phosphorus coating; The plating solution comprises the following components: a soluble nickel compound, a soluble tungsten compound, a soluble phosphorus compound, a complexing agent, a pH regulator and water; the complexing agent comprises ethylenediaminetetraacetic acid, sodium oxalate and malic acid; The plating solution further comprises an additive and a dispersant, wherein the additive is modified nano-alumina, and the dispersant is one of fatty acid methyl ester ethoxylate sulfonate, sodium lauryl sulfate, sodium lauryl phosphate, and sodium dodecylbenzene sulfonate; The preparation method of the modified nano-alumina is as follows: (1) dispersing the nano-alumina in deionized water, adding vinyltrimethoxysilane, adjusting the pH value to 3-5, heating to 70-80°C, reacting for 3-5 hours, filtering, washing the filter cake, and drying to obtain silanized alumina; (2) mixing water, sodium dodecylbenzenesulfonate and anhydrous ethanol evenly, adding tripropyleneamine, silanized alumina and an initiator, heating to 80-100°C, stirring and reacting for 4-5 hours, cooling, filtering, washing, and drying to obtain the modified nano-alumina.

2. The electroplating method of nickel-tungsten-phosphorus coating according to claim 1, characterized in that: The complexing agent is composed of ethylenediaminetetraacetic acid, sodium oxalate and malic acid in a mass ratio of 3-8:6-9:10-14.

3. The electroplating method of nickel-tungsten-phosphorus coating according to claim 1, characterized in that: The plating solution comprises the following components in parts by mass: 170-200 parts of a soluble nickel compound, 30-50 parts of a soluble tungsten compound, 20-30 parts of a soluble phosphorus compound, 40-50 parts of a complexing agent, 20-30 parts of a pH regulator, and 1000-1500 parts of water.

4. The electroplating method of nickel-tungsten-phosphorus coating according to claim 1, characterized in that: The initiator is one of hydrogen peroxide, sodium persulfate and azobisisobutyronitrile, and the amount of the initiator is 0.7%-1.2% of the mass of tripropyleneamine.

5. The electroplating method of nickel-tungsten-phosphorus coating according to claim 1, characterized in that: The mass ratio of the nano-alumina, vinyltrimethoxysilane and tripropyleneamine is 13-17:4-8:3-7.

6. The electroplating method of nickel-tungsten-phosphorus coating according to claim 1, characterized in that: In step S2, the current density output by the DC power supply is 18-25 A / dm2, and the electroplating temperature of the DC power supply is 62-75°C.

7. The electroplating method of nickel-tungsten-phosphorus coating according to claim 1, characterized in that: The current density of the pulse power output in step S2 is 4-8A / dm 2 The pulse frequency is 1200-1500 Hz, the duty cycle is 20%-30%; the electroplating temperature of the pulse power supply is 72-76°C.

8. The electroplating method of nickel-tungsten-phosphorus coating according to claim 1, characterized in that: The drying temperature in step S3 is 300-400° C., and the drying time is 2-2.5 hours.

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