Neodymium-iron-boron permanent magnet material electroplating process

Abstract

The invention belongs to the technical field of neodymium-iron-boron rare earth permanent magnets, and relates to an electroplating process for a neodymium-iron-boron permanent magnet material. In the aspect of component design, through combination of rare earth elements (such as PrNd, Ce, Gd and the like) and other alloy elements (Cu, Al, Co and the like) in a specific proportion, the basic performance of the neodymium iron boron permanent magnet material is optimized. According to the elaborate design, the magnetic performance and corrosion resistance of the material are improved, the hydrogen content is reduced to be smaller than 8 ppm, the hydrogen embrittlement risk is effectively reduced, multiple factors such as the coating thickness, the surface appearance, the corrosion resistance, the magnetic performance and the coating binding force are comprehensively considered, electroplating 30 min under the condition of 3 A / dm < 2 > is the optimal process condition, and the electroplating cost is reduced. The condition can ensure that the material has good corrosion resistance, can also prevent the coating from being too thick and defects, and ensures that the comprehensive performance of the material meets the actual application requirement.

Description

Technical Field

[0001] The present invention belongs to the technical field of neodymium iron boron rare earth permanent magnets and relates to an electroplating process for neodymium iron boron permanent magnet materials. Background Art

[0002] Neodymium iron boron magnets (NdFeB) are one of the most widely used high-performance magnets at present, and they play an important role in fields such as electric vehicles, wind turbines, and consumer electronics. However, the disadvantages of hydrogen in neodymium iron boron magnets cannot be ignored, and these disadvantages are mainly reflected in aspects such as material properties, cost, and environmental impact.

[0003] First of all, the hydrogen content in neodymium iron boron magnets has a significant impact on their magnetic properties. The presence of hydrogen will reduce the coercivity and remanence of neodymium iron boron magnets, thereby weakening their magnetism. Coercivity refers to the ability of a magnet to resist an external magnetic field, while remanence refers to the magnetization intensity that a magnet can still maintain after demagnetization. These two indicators are crucial for the application of neodymium iron boron magnets, especially for devices that require high stability and strong magnetic fields. Therefore, the presence of hydrogen not only reduces the performance of neodymium iron boron magnets but also may affect their application in key fields.

[0004] Secondly, the presence of hydrogen in neodymium iron boron magnets will increase production costs. In order to ensure the quality of neodymium iron boron magnets, manufacturers need to take additional measures to control the hydrogen content. This includes using high-purity raw materials, optimizing the production process, and conducting strict inspections and quality control. These measures undoubtedly increase production costs, making the price of neodymium iron boron magnets relatively high and restricting their application in some cost-sensitive markets.

[0005] In addition, the presence of hydrogen will also have a negative impact on the corrosion resistance of neodymium iron boron magnets. Neodymium iron boron magnets themselves have certain brittleness and are prone to oxidation, and the presence of hydrogen will exacerbate this problem. Hydrogen can penetrate into the grain boundaries of neodymium iron boron magnets, resulting in stress concentration inside the material, thereby accelerating the aging and corrosion of the material. This is a serious challenge for devices that need to work stably for a long time, because the early failure of the material may lead to equipment failure or safety accidents. Summary of the Invention

[0006] The purpose of the present invention is to address the above-mentioned problems existing in the prior art and propose an electroplating process for neodymium iron boron permanent magnet materials based on the optimization of hydrogen content.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] An electroplating process for neodymium iron boron permanent magnet materials, the process comprising the following steps:

[0009] S1. Ultrasonically clean the neodymium iron boron permanent magnet material, and then perform alkaline degreasing;

[0010] S2. After alkaline degreasing, conduct high-temperature water washing, and then perform pickling treatment.

[0011] S3. After pickling treatment, conduct water washing, and then perform activation treatment.

[0012] S4. After activation treatment, perform nickel plating treatment, and finally conduct water washing, filtration, and drying.

[0013] In the above electroplating process for Nd-Fe-B permanent magnet materials, the composition and mass percentage content of the Nd-Fe-B permanent magnet materials are as follows: 15 - 25% PrNd, 5 - 15% Ce, 1 - 2% Gd, 0.1 - 0.2% Cu, 0.1 - 0.25% Nd, 0.5 - 1.0% Al, 0.25 - 0.35% Co, 0.85 - 0.95% B, and the balance is Fe and inevitable impurities.

[0014] Preferably, the mass ratio of Pr to Nd is 1:0.2 - 2.

[0015] In the above electroplating process for Nd-Fe-B permanent magnet materials, the surface roughness Ra value of the Nd-Fe-B permanent magnet materials is ≤ 0.8 μm.

[0016] In the above electroplating process for Nd-Fe-B permanent magnet materials, alkaline degreasing is carried out using an alkaline degreasing working solution at 40 - 60°C. The alkaline degreasing working solution includes the following raw materials in parts by mass: 5 - 8 parts of sodium hydroxide, 40 - 60 parts of sodium carbonate, 50 - 80 parts of sodium phosphate dodecahydrate, and 500 - 800 parts of water.

[0017] In the above electroplating process for Nd-Fe-B permanent magnet materials, pickling treatment is carried out using nitric acid pickling with a concentration of 5 - 15 wt%, and 0.1 - 0.3 wt% of thiourea is added to the nitric acid.

[0018] In the above electroplating process for Nd-Fe-B permanent magnet materials, activation treatment is carried out using an activation solution. The activation solution includes ammonium fluoride and sulfosalicylic acid with a mass ratio of 1:(2 - 2.5).

[0019] In the above electroplating process for Nd-Fe-B permanent magnet materials, during the nickel plating process, the electroplating solution includes the following raw materials in parts by mass: 230 - 250 nickel sulfate hexahydrate, 25 - 35 parts of nickel chloride hexahydrate, 25 - 35 parts of boric acid, 0.1 - 0.2 part of sodium dodecyl sulfate, 0.5 - 1.5 parts of saccharin, and 800 - 900 parts of water.

[0020] In the above electroplating process for Nd-Fe-B permanent magnet materials, the nickel plating process is divided into a pre-plating stage and a main plating stage. Among them, in the pre-plating stage, a current density of 5 - 8 A / dm 2 is applied for 0.5 - 1.5 min, and in the main plating stage, a current density of 2 - 4 A / dm 2Electroplating is carried out at a current density for 25 - 35 minutes.

[0021] In the above - mentioned electroplating process of Nd - Fe - B permanent magnetic material, for water washing, first use deionized water at 60 - 70 °C to wash for 5 - 8 minutes, and then use deionized water at 25 - 30 °C to wash for 5 - 6 minutes.

[0022] In the above - mentioned electroplating process of Nd - Fe - B permanent magnetic material, after electroplating nickel treatment, the coating thickness of the Nd - Fe - B permanent magnetic material is 18 - 22 μm, and the hydrogen content is less than 8 ppm.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. In terms of composition design, the present invention optimizes the basic properties of Nd - Fe - B permanent magnetic materials through the combination of specific ratios of rare - earth elements (such as PrNd, Ce, Gd, etc.) and other alloy elements (Cu, Al, Co, etc.). This elaborate design not only improves the magnetic properties and corrosion resistance of the material itself, but also reduces the hydrogen content to less than 8 ppm, effectively reducing the risk of hydrogen embrittlement.

[0025] 2. The present invention adopts a method of ultrasonic cleaning combined with alkaline degreasing. Using an alkaline solution at 40 - 60 °C to conduct preliminary cleaning treatment on Nd - Fe - B can more effectively remove surface grease and other pollutants, providing a clean workpiece surface for subsequent processes. Compared with traditional methods, this method is more environmentally friendly and efficient.

[0026] 3. In the pickling process of the present invention, nitric acid with a concentration of 5 - 15 wt% is used and thiourea is added as a corrosion inhibitor. This improvement can effectively control the pickling degree, avoid over - corrosion, and at the same time ensure that the material surface is clean and residue - free. In addition, for the activation treatment, a compound solution of ammonium fluoride and sulfosalicylic acid is used. Compared with the activation method using a single chemical substance, it can more significantly improve the surface activity of the workpiece and enhance the coating adhesion.

[0027] 4. The present invention proposes a two - stage electroplating strategy in the electroplating nickel stage: applying a higher current density in the pre - plating stage to quickly form a basic coating, and using a lower current density in the main - plating stage to ensure the coating quality. This staged electroplating method can not only accelerate the production process, but also ensure that the final coating thickness is uniform and the appearance is bright, reaching the ideal thickness range of 18 - 22 μm. Brief Description of the Drawings

[0028] Figure 1 It is the hydrogen desorption rate diagram of Nd - Fe - B magnets with different pickling times in Examples 1 - 3; a. Example 1; b. Example 2; c. Example 3.

[0029] Figure 2 It is the microscopic image of the Nd - Fe - B magnet in Example 1 after pickling with different pickling times.

[0030] Figure 3 Microscopic images of the NdFeB magnets after pickling for different pickling times in Example 2.

[0031] Figure 4 Microscopic images of the NdFeB magnets after pickling for different pickling times in Example 3.

[0032] Figure 5 Surface comparison of the coatings under different electroplating processes for Example 1 and Examples 4 - 9.

[0033] Figure 6 Coating thickness diagrams under different electroplating processes for Example 1, Examples 5 - 6, and Examples 8 - 9; (a) Current density - thickness; (b) Electroplating time - thickness. Detailed implementation manners

[0034] The following are specific embodiments of the present invention, which further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0035] Example 1:

[0036] S1. Gently process the N35 NdFeB permanent magnet material with 400 - mesh fine sandpaper in a small - amplitude circular motion. After grinding, ensure that the surface roughness Ra value ≤ 0.8 μm.

[0037] The composition and mass percentage content of the N35 NdFeB permanent magnet material are: 10% Pr, 10% Nd, 10% Ce, 1.5% Gd, 0.15% Cu, 0.20% Nd, 0.8% Al, 0.3% Co, 0.92% B, and the balance is Fe and unavoidable impurities.

[0038] S2. Vertically suspend the ground NdFeB permanent magnet material in an ultrasonic cleaning tank and inject anhydrous ethanol solution with a concentration ≥ 99.7% until the workpiece is completely submerged. Utilize the cavitation effect generated by high - frequency vibration to remove residual micron - level metal debris and organic pollutants on the surface. The ultrasonic frequency is fixed at 30 kHz, the power output is adjusted to 150 W, the cleaning temperature is maintained at room temperature (25 ± 3 °C), and the treatment time is 3 minutes.

[0039] S3. Prepare an alkaline degreasing working solution according to the following mass parts: 6 parts of sodium hydroxide, 50 parts of sodium carbonate, 70 parts of sodium phosphate dodecahydrate, and 800 parts of water. Completely immerse the NdFeB permanent magnet material in the degreasing tank and then start the constant - temperature system to stabilize the solution temperature at 50 °C. At the same time, precisely adjust the pH value to the range of 9.0 - 9.5 by dropping formic acid solution. During the treatment process, turn on the mechanical swing arm to drive the workpiece to move at a frequency of 15 times per minute, and take it out after 5 minutes.

[0040] S4. Rinse the NdFeB permanent magnet material with deionized water at 60°C for 1 minute to ensure that there is no residue of degreaser on the workpiece surface, avoiding affecting subsequent processes. Then rinse the workpiece with deionized water at 25°C room temperature. On the one hand, further wash away the residual impurities, and on the other hand, reduce the workpiece temperature to prepare for pickling. The rinsing time is about 1 minute, and the water flow rate is moderate to ensure thorough cleaning of the surface.

[0041] S5. Prepare a pickling solution containing 10 wt% nitric acid, and add 0.2% mass fraction of thiourea as a corrosion inhibitor. After vertically immersing the NdFeB permanent magnet material into the acid tank, start the air stirring system and continuously blow in compressed air at a flow rate of 0.5 m 3 / min to ensure that the solution uniformly contacts the surface of the NdFeB permanent magnet material. Precise control the treatment time at 30 seconds at room temperature environment. Finally, the hydrogen content of the NdFeB is less than 2.5 ppm, and take it out in time to avoid over-corrosion of the substrate.

[0042] S6. Vertically suspend the pickled NdFeB permanent magnet material in the ultrasonic cleaning tank, inject deionized water until the NdFeB permanent magnet material is completely immersed, and perform secondary ultrasonic treatment with the same parameters of 30 kHz / 150W as the primary cleaning.

[0043] S7. Completely immerse the NdFeB permanent magnet material in the activation solution and let it stand at room temperature for 30 seconds. The activation solution is composed of 18 g / L sulfosalicylic acid and 8 g / L ammonium fluoride compounded.

[0044] S8. Configure the electroplating solution raw materials with the following mass parts: 240 parts of nickel sulfate hexahydrate, 30 parts of nickel chloride hexahydrate, 30 parts of boric acid, 0.1 part of sodium dodecyl sulfate, 1.0 part of saccharin, and 850 parts of water. Design the pole pitch to be 20 mm according to the size of the NdFeB permanent magnet material, and an insulating sleeve needs to be installed at the contact point between the fixture and the workpiece to prevent current concentration. The bath temperature is maintained at 50 ± 1°C through the PID temperature control system; adjust the pH to the range of 4.8 - 5.0 by adding ammonia drop by drop. The electroplating process is carried out in two steps: apply a current density of 5 A / dm 2 for 1 minute in the pre-plating stage; apply a current density of 3 A / dm 2 for 30 minutes in the main plating stage. Finally, the coating thickness reaches 20 ± 2 μm, and the hydrogen content is less than 8 ppm.

[0045] S9. Rinse the nickel-plated workpiece with deionized water at 60°C to remove substances such as residual nickel plating solution on the surface. The rinsing time is about 1 minute to ensure surface cleanliness. Then rinse it again with normal temperature deionized water to further clean the surface and reduce the workpiece temperature at the same time. The rinsing time is about 1 minute to ensure that there is no residue on the surface.

[0046] S10. Use filtered and dried compressed air to blow-dry the surface of the workpiece from different angles. The air flow pressure should be moderate to avoid damaging the coating, ensure no water stains remain on the surface, and prevent subsequent rusting or affecting the appearance quality.

[0047] Example 2:

[0048] S1. Gently process the N35 neodymium iron boron permanent magnet material with 400-mesh fine sandpaper in a small circular motion. After grinding, ensure that the surface roughness Ra value ≤ 0.8 μm.

[0049] The composition and mass percentage content of the N35 neodymium iron boron permanent magnet material are as follows: 10% Pr, 10% Nd, 10% Ce, 1.5% Gd, 0.15% Cu, 0.20% Nd, 0.8% Al, 0.3% Co, 0.92% B, and the balance is Fe and unavoidable impurities.

[0050] S2. Vertically suspend the ground neodymium iron boron permanent magnet material in an ultrasonic cleaning tank and inject anhydrous ethanol solution with a concentration ≥ 99.7% until the workpiece is completely immersed. Utilize the cavitation effect generated by high-frequency vibration to remove residual micron-sized metal debris and organic pollutants on the surface. The ultrasonic frequency is fixed at 30 kHz, the power output is adjusted to 150 W, the cleaning temperature is maintained at room temperature (25 ± 3 °C), and the treatment time is 3 minutes.

[0051] S3. Prepare an alkaline degreasing working solution according to the following mass parts: 6 parts of sodium hydroxide, 50 parts of sodium carbonate, 70 parts of sodium phosphate dodecahydrate, and 800 parts of water. After completely immersing the neodymium iron boron permanent magnet material in the degreasing tank, start the constant temperature system to stabilize the solution temperature at 50 °C. At the same time, precisely adjust the pH value to the range of 9.0 - 9.5 by dropping formic acid solution. During the treatment process, turn on the mechanical swing arm to drive the workpiece to move at a frequency of 15 times per minute, and take it out after 5 minutes.

[0052] S4. Rinse the neodymium iron boron permanent magnet material with deionized water at a temperature of 60 °C for 1 minute to ensure no degreasing agent remains on the surface of the workpiece and avoid affecting subsequent processes. Then rinse the workpiece with deionized water at room temperature (25 °C). On the one hand, further wash away the residual impurities; on the other hand, reduce the temperature of the workpiece to prepare for pickling. The rinsing time is about 1 minute, and the water flow rate is moderate to ensure thorough cleaning of the surface.

[0053] S5. Prepare a pickling solution containing 10 wt% concentration of hydrochloric acid, and add 0.2% mass fraction of thiourea as a corrosion inhibitor. Vertically immerse the neodymium iron boron permanent magnet material in the acid tank and start the air stirring system at 0.5 m 3Compressed air is continuously blown in at a flow rate of / min to ensure that the solution uniformly contacts the surface of the NdFeB permanent magnet material. The treatment time is precisely controlled at 30 seconds at room temperature. Finally, the hydrogen content of the NdFeB is less than 2.5 ppm, and it is taken out in time to avoid over-corrosion of the substrate.

[0054] S6. Vertically suspend the pickled NdFeB permanent magnet material in an ultrasonic cleaning tank, inject deionized water until the NdFeB permanent magnet material is completely submerged, and perform secondary ultrasonic treatment with the same parameters of 30 kHz / 150 W as the primary cleaning.

[0055] S7. Completely immerse the NdFeB permanent magnet material in the activation solution and let it stand for 30 seconds at room temperature. The activation solution is composed of 18 g / L sulfosalicylic acid and 8 g / L ammonium fluoride.

[0056] S8. Prepare the electroplating solution raw materials with the following mass parts: 240 parts of nickel sulfate hexahydrate, 30 parts of nickel chloride hexahydrate, 30 parts of boric acid, 0.1 part of sodium dodecyl sulfate, 1.0 part of saccharin, and 850 parts of water. Design the pole pitch to be 20 mm according to the size of the NdFeB permanent magnet material. Insulating sleeves need to be installed at the contact points between the hanging fixture and the workpiece to prevent current concentration. The temperature of the bath solution is maintained at 50 ± 1 °C through a PID temperature control system; the pH is adjusted to the range of 4.8 - 5.0 by gradually dropping ammonia water. The electroplating process is carried out in two steps: apply a current density of 5 A / dm 2 for 1 minute during the pre-plating stage; apply a current density of 3 A / dm 2 for 30 minutes during the main plating stage. Finally, the coating thickness reaches 20 ± 2 μm and the hydrogen content is less than 8 ppm.

[0057] S9. Rinse the nickel-plated workpiece with 60 °C deionized water to remove substances such as residual nickel plating solution on the surface. The rinsing time is about 1 minute to ensure the surface is clean. Then rinse it again with normal temperature deionized water to further clean the surface and at the same time reduce the temperature of the workpiece. The rinsing time is about 1 minute to ensure there is no residual substance on the surface.

[0058] S10. Use filtered and dried compressed air to blow dry the surface of the workpiece from different angles. The air flow pressure is moderate to avoid damaging the coating, ensure that there is no water stain residue on the surface, and prevent subsequent rusting or affecting the appearance quality.

[0059] Example 3:

[0060] S1. Gently treat the N35 NdFeB permanent magnet material with 400-mesh fine sandpaper in a small circular motion. After polishing, ensure that the surface roughness Ra value ≤ 0.8 μm;

[0061] The composition of the N35 neodymium-iron-boron permanent magnet material and its mass percentage content are as follows: 10% Pr, 10% Nd, 10% Ce, 1.5% Gd, 0.15% Cu, 0.20% Nd, 0.8% Al, 0.3% Co, 0.92% B, and the balance is Fe and inevitable impurities.

[0062] S2. Vertically suspend the polished neodymium-iron-boron permanent magnet material in the ultrasonic cleaning tank, inject anhydrous ethanol solution with a concentration ≥ 99.7% until the workpiece is completely submerged, and use the cavitation effect generated by high-frequency vibration to remove residual micron-sized metal debris and organic contaminants on the surface. The ultrasonic frequency is fixed at 30 kHz, the power output is adjusted to 150 W, the cleaning temperature is maintained at room temperature (25 ± 3 °C), and the treatment time is 3 minutes.

[0063] S3. Prepare the alkaline degreasing working solution according to the following mass parts: 6 parts of sodium hydroxide, 50 parts of sodium carbonate, 70 parts of sodium phosphate dodecahydrate, and 800 parts of water. After completely immersing the neodymium-iron-boron permanent magnet material in the degreasing tank, start the constant temperature system to stabilize the solution temperature at 50 °C, and at the same time precisely adjust the pH value to the range of 9.0 - 9.5 by dropping formic acid solution. During the treatment process, start the mechanical swing arm to drive the workpiece to move at a frequency of 15 times per minute, and take it out after 5 minutes.

[0064] S4. Rinse the neodymium-iron-boron permanent magnet material with deionized water at a temperature of 60 °C for 1 minute to ensure that there is no degreasing agent residue on the workpiece surface to avoid affecting subsequent processes. Then rinse the workpiece with deionized water at room temperature of 25 °C. On the one hand, further wash away the residual impurities, and on the other hand, reduce the workpiece temperature to prepare for pickling. The rinsing time is about 1 minute, and the water flow rate is moderate to ensure thorough cleaning of the surface.

[0065] S5. Prepare a pickling solution containing 10 wt% concentration of sulfuric acid, and at the same time add 0.2% mass fraction of thiourea as a corrosion inhibitor. Vertically immerse the neodymium-iron-boron permanent magnet material in the acid tank and start the air stirring system to continuously blow in compressed air at a flow rate of 0.5 m 3 / min to ensure that the solution uniformly contacts the surface of the neodymium-iron-boron permanent magnet material. Precise control the treatment time at room temperature environment for 30 seconds. Finally, the hydrogen content of the neodymium-iron-boron is less than 2.5 ppm, and take it out in time to avoid over-corrosion of the substrate.

[0066] S6. Vertically suspend the pickled neodymium-iron-boron permanent magnet material in the ultrasonic cleaning tank, inject deionized water until the neodymium-iron-boron permanent magnet material is completely submerged, and perform secondary ultrasonic treatment with the same parameters of 30 kHz / 150 W as the primary cleaning.

[0067] S7. Completely immerse the neodymium-iron-boron permanent magnet material in the activation solution and let it stand at room temperature for 30 seconds. The activation solution is compounded by 18 g / L of sulfosalicylic acid and 8 g / L of ammonium fluoride.

[0068] S8. Prepare an electroplating solution raw material with the following parts by mass: 240 parts of nickel sulfate hexahydrate, 30 parts of nickel chloride hexahydrate, 30 parts of boric acid, 0.1 part of sodium dodecyl sulfate, 1.0 part of saccharin, and 850 parts of water. Design the pole pitch to be 20 mm according to the size of the NdFeB permanent magnet material. An insulating sleeve needs to be installed at the contact point between the fixture and the workpiece to prevent current concentration. The bath temperature is maintained at 50 ± 1 °C through a PID temperature control system; use ammonia water to gradually adjust the pH to the range of 4.8 - 5.0. The electroplating process is carried out in two steps: apply a current density of 5 A / dm 2 for 1 minute in the pre-plating stage; apply a current density of 3 A / dm 2 in the main plating stage for 30 minutes. The final coating thickness reaches 20 ± 2 μm, and the hydrogen content is less than 8 ppm.

[0069] S9. Rinse the workpiece after nickel plating with deionized water at 60 °C to remove substances such as residual nickel plating solution on the surface. The rinsing time is about 1 minute to ensure the surface is clean. Then rinse again with normal temperature deionized water to further wash the surface and at the same time reduce the temperature of the workpiece. The rinsing time is about 1 minute to ensure there is no residual substance on the surface.

[0070] S10. Use compressed air that has been filtered and dried to blow dry the surface of the workpiece from different angles. The air flow pressure is moderate to avoid damaging the coating, ensure there is no water stain residue on the surface, and prevent subsequent rusting or affecting the appearance quality.

[0071] Example 4:

[0072] The difference from Example 1 is only that in the main plating stage of step S8, apply a current density of 1 A / dm 2 for 30 minutes.

[0073] Example 5:

[0074] The difference from Example 1 is only that in the main plating stage of step S8, apply a current density of 2 A / dm 2 for 30 minutes.

[0075] Example 6:

[0076] The difference from Example 1 is only that in the main plating stage of step S8, apply a current density of 4 A / dm 2 for 30 minutes.

[0077] Example 7:

[0078] The difference from Example 1 is only that in the main plating stage of step S8, apply a current density of 5 A / dm 2 for 30 minutes.

[0079] Example 8:

[0080] The difference from Example 1 is only that in the main plating stage of step S8, electroplating is carried out at a current density of 30 mA / cm 2 for 20 minutes.

[0081] Example 9:

[0082] The difference from Example 1 is only that in the main plating stage of step S8, electroplating is carried out at a current density of 30 mA / cm 2 for 40 minutes.

[0083] Table 1: Hydrogen content of NdFeB permanent magnet materials with different pickling processes in Examples 1 - 3

[0084] Pickling time Example 1 (Nitric acid) Example 2 (Hydrochloric acid) Example 3 (Sulfuric acid) 10s 1.94 ppm 4.14 ppm 4.86 ppm 30s 2.52 ppm 6.65 ppm 6.49 ppm 30s 2.53 ppm 8.35 ppm 10.60 ppm

[0085] It can be seen from Figure 1 that the curve characteristics of different pickling times are roughly the same. The hydrogen content increases after pickling with all three acids. However, the increase in hydrogen content after pickling with nitric acid in Example 1 is less. This is because the strong oxidizing property of nitric acid forms an oxide film on the surface of the NdFeB permanent magnet material, which inhibits the penetration of hydrogen to a certain extent. It can be seen from Figure 2 that the surface of NdFeB after pickling with nitric acid is affected relatively mildly, only corroding the surface and not causing significant damage to the internal grains, and the overall surface is relatively flat. It can be seen from Figure 3 that hydrochloric acid has a stronger corrosive effect on the material. In the figure, not only the rich-neodymium phase has been completely corroded, but the main phase grains have also been corroded. This is attributed to the strong penetration ability of chloride ions in hydrochloric acid. It can be seen from Figure 4 that as the pickling time with sulfuric acid increases, the cracking between the main phase grains becomes more obvious, and the pores and intergranular cracks at the grain boundaries of the NdFeB surface layer continuously increase, and the corrosion depth also becomes deeper and deeper, making the surface layer of NdFeB become a relatively loose structure.

[0086] Figure 5 Effect of current density: At 3 A / dm 2 , the surface is relatively flat; when it rises to 4 A / dm 2 , the graininess increases; at 5 A / dm 2 , pores appear. This is because the high current intensifies the hydrogen evolution side reaction and damages the deposition of the coating. Effect of electroplating time: At 3 A / dm 2 , when the time is extended from 20 min to 40 min, the surface changes from relatively smooth to rough. Generally speaking, electroplating at 3 A / dm 2 for 30 min results in a flat coating surface and better effects.

[0087] It can be seen from Figure 6 that as the current density increases from 2 A / dm 2 to 4 A / dm 2, the coating thickness increased from about 19 μm to over 30 μm, showing an obvious upward trend, indicating that the coating was deposited faster and thicker. When the electroplating time was extended from 20 min to 30 min, the coating thickness was basically stable at about 22 μm, but when it was extended to 40 min, the thickness increased significantly to nearly 48 μm. However, the coating thickness is not the thicker the better, generally not exceeding 25 μm, otherwise it will affect its magnetic properties.

[0088] Table 2: Critical evaluation values of polarization curves after different electroplating processes in Example 1, Examples 5 - 6, and Examples 8 - 9

[0089] Example Ecorr (V) <![CDATA[Icorr (A / cm 2 )]]> Example 1 -0.52 <![CDATA[7.71E -6 > Example 5 -0.66 <![CDATA[1.10E -5 > Example 6 -0.45 <![CDATA[3.20E -6 > Example 8 -0.59 <![CDATA[1.44E -5 > Example 9 -0.33 <![CDATA[1.92E -6 > N35 NdFeB permanent magnetic material -0.85 <![CDATA[1.82E -5 >

[0090] It can be seen from Table 1 that the self - corrosion current density (I corr ) of the sample after nickel plating decreased significantly. When electroplating for 30 min at 3 A / dm 2 , I corr dropped to 7.71E - 6 A / cm 2 , which was about one order of magnitude lower than that of the substrate. At the same time, the self - corrosion potential (E corr ) shifted positively by 0.3 V, indicating that the coating effectively inhibited the corrosion of the substrate. Although high current density (4 A / dm 2 ) or long time (40 min) could further improve the corrosion resistance (I corr reached a minimum of 1.92E - 6 A / cm 2 ), it was likely to cause hydrogen evolution defects or result in an over - thick coating (>25 μm), affecting the magnetic properties. Considering the corrosion resistance, coating thickness and functional properties comprehensively, electroplating for 30 min at 3 A / dm 2 in Example 1 was the optimal process condition, which ensured the corrosion resistance while avoiding the problems of over - thick coating and defects.

[0091] To sum up, in the pickling treatment before electroplating, the effects of different types of acids on the hydrogen content of Nd - Fe - B materials were significantly different. Due to its strong oxidizing property, nitric acid formed an oxide film on the material surface, effectively inhibiting the infiltration of hydrogen, and the hydrogen content of the material increased less after nitric acid pickling. When pickling with hydrochloric acid and sulfuric acid, the hydrogen content of the material increased significantly with the extension of pickling time. However, the effects of various pickling treatments on the magnetic properties of Nd - Fe - B materials were limited. The magnetic induction intensity of the material remained basically stable. Only pickling with nitric acid for 60 s had a slight effect on the magnetic polarization intensity in some areas, but had little effect on the overall magnetic induction intensity, and the remanence was hardly affected. Considering various factors such as coating thickness, surface morphology, corrosion resistance, magnetic properties, and coating adhesion comprehensively, electroplating for 30 min at 3 A / dm 2 was the optimal process condition. This condition could not only ensure the good corrosion resistance of the material but also avoid over - thick coating and defects, ensuring that the comprehensive performance of the material met the actual application requirements.

[0092] In the embodiments herein, for the points within the technical scope claimed by the present invention that are not exhausted by the point values, as well as for the new technical solutions formed by the equivalent substitution of single or multiple technical features in the technical solutions of the embodiments, they are also within the scope claimed by the present invention. At the same time, in all the exemplified or unexemplified embodiments of the present invention, the various parameters in the same embodiment only represent an example (i.e., a feasible solution) of its technical solution, and there is no strict cooperation and limitation relationship between the various parameters. Among them, the parameters can be mutually replaced without violating the axioms and the requirements of the present invention, except as specifically stated.

[0093] The technical means disclosed in the solution of the present invention are not limited to the technical means disclosed by the above technical means, but also include the technical solutions formed by any combination of the above technical features. The above is the specific implementation manner of the present invention. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements are also regarded as the protection scope of the present invention.

[0094] The specific embodiments described herein are only illustrative of the spirit of the present invention. Those skilled in the art to which the present invention pertains can make various modifications or supplements to the described specific embodiments or use similar ways to replace them, but will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A NdFeB permanent magnet material electroplating process, characterized in that: The process comprises the following steps: S1. Ultrasonic cleaning of the NdFeB permanent magnet material, followed by alkaline degreasing; S2, after alkaline degreasing, high temperature water washing, then acid washing, and then secondary ultrasonic cleaning; S3, after pickling, washing with water, and then activation treatment; S4, after the activation treatment, nickel electroplating treatment is performed, and finally the mixture is washed with water, filtered and dried.

2. The electroplating process of NdFeB permanent magnet material according to claim 1, characterized in that: The composition and mass percentage of the NdFeB permanent magnet material are: 15-25% PrNd, 5-15% Ce, 1-2% Gd, 0.1-0.2% Cu, 0.1-0.25% Nd, 0.5-1.0% Al, 0.25-0.35% Co, 0.85-0.95% B, and the balance is Fe and unavoidable impurities.

3. The electroplating process of NdFeB permanent magnet material according to claim 1, characterized in that: The surface roughness Ra value of NdFeB permanent magnet material is ≤0.8μm.

4. The electroplating process of NdFeB permanent magnet material according to claim 1, characterized in that: The alkaline degreasing adopts an alkaline degreasing working solution of 40-60° C., and the alkaline degreasing working solution comprises the following raw materials in parts by weight: 5-8 parts of sodium hydroxide, 40-60 parts of sodium carbonate, 50-80 parts of sodium phosphate dodecahydrate, and 500-800 parts of water.

5. The electroplating process of NdFeB permanent magnet material according to claim 1, characterized in that: The pickling treatment uses nitric acid with a concentration of 5-15wt% to which 0.1-0.3wt% thiourea is added.

6. The electroplating process of NdFeB permanent magnet material according to claim 1, characterized in that: The activation treatment uses an activation solution, which includes ammonium fluoride and sulfosalicylic acid in a mass ratio of 1:(2-2.5).

7. The electroplating process of NdFeB permanent magnet material according to claim 1, characterized in that: The electroplating solution in the nickel electroplating process includes the following raw materials in parts by mass: 230-250 parts of nickel sulfate hexahydrate, 25-35 parts of nickel chloride hexahydrate, 25-35 parts of boric acid, 0.1-0.2 parts of sodium dodecyl sulfate, 0.5-1.5 parts of saccharin, and 800-900 parts of water.

8. The electroplating process of NdFeB permanent magnet material according to claim 1, characterized in that: The nickel electroplating process is divided into a pre-plating stage and a main plating stage. In the pre-plating stage, 5-8A / dm 2 The current density lasts for 0.5-1.5min, and 2-4A / dm is applied in the main plating stage 2 The current density is electroplated for 25-35min.

9. The electroplating process of NdFeB permanent magnet material according to claim 1, characterized in that: Wash with deionized water at 60-70℃ for 50-80min, then wash with deionized water at 25-30℃ for 55-65min.

10. The electroplating process of NdFeB permanent magnet material according to claim 1, characterized in that: After nickel electroplating, the coating thickness of NdFeB permanent magnet material is 18-22μm, and the hydrogen content is less than 8ppm.

Images