Neodymium-iron-boron double plating layer surface protection method

Abstract

The application discloses a surface protection method of a Nd-Fe-B double-plating layer, which comprises the following steps: after a Nd-Fe-B part is subjected to mechanical treatment of surface physical defects and surface oil removal treatment, the Nd-Fe-B part is subjected to ultrasonic treatment in an acid pickling solution; then, a copper layer is deposited on the surface of the Nd-Fe-B part by a physical gas deposition method or a magnetron sputtering method, wherein part of copper atoms diffuse into a surface layer of the Nd-Fe-B part and are distributed in grain boundaries; and a nickel layer is electroplated on the copper layer deposited on the surface of the Nd-Fe-B part. The application optimizes boundary microstructure by depositing the copper layer, and on the other hand, the double-plating layer is preferentially selected to replace a three-layer plating layer structure, so that magnetic shielding generated by the plating layer is reduced; and the new surface protection with high corrosion resistance is realized, which does not affect surface adhesion and greatly reduces loss of magnetic performance or even does not cause loss of magnetic performance.

Description

Technical Field

[0001] This invention belongs to the field of NdFeB surface protection technology, and relates to a NdFeB double-coating surface protection method. Background Technology

[0002] Neodymium iron boron (NdFeB) rare-earth permanent magnets are widely used in various types of motors. However, the multiphase structure of NdFeB and the differences in chemical properties between its phases result in inherently insufficient corrosion resistance. If corrosion occurs, the binding medium between the main phase grains inside the magnet disappears, causing the main phase grains to detach, and in severe cases, leading to pulverization and failure of the magnet. Therefore, the development of corrosion protection technology for NdFeB rare-earth permanent magnets significantly restricts their application.

[0003] Currently, improving the corrosion resistance of NdFeB materials involves two aspects: enhancing the material's inherent corrosion resistance and applying a protective coating to the material's surface. Surface coating protection has become a research hotspot due to its ease of operation, controllable cost, relatively simple process, and unrestricted mass production.

[0004] Currently, surface coating protection for sintered NdFeB magnets is mainly achieved through methods such as electroplating, electroless plating, organic coating, and physical vapor deposition. Among these, electroplated Ni-based alloys are widely used due to their excellent high-temperature resistance, oxidation resistance, corrosion resistance, decorative properties, and good mechanical properties such as compressive strength, bending strength, and impact resistance. However, the electroplating process is prone to introducing impurities and continuously generating H2 during the plating process; furthermore, the ferromagnetic nature of the nickel plating layer can create a magnetic shielding effect on magnets. Existing data shows that these factors can lead to a reduction in magnetic properties of more than 5%. Summary of the Invention

[0005] The technical problem solved by this invention is to provide a method for surface protection of neodymium iron boron double coating, which reduces the magnetic shielding generated by the nickel coating, reduces the loss of its magnetic properties, or even eliminates the loss of magnetic properties.

[0006] This invention is achieved through the following technical solution:

[0007] A method for surface protection using a NdFeB double-coating, characterized by comprising the following operations:

[0008] 1) After the NdFeB components undergo surface physical defect mechanical treatment and surface degreasing treatment, they are subjected to ultrasonic treatment in pickling solution;

[0009] The pickling solution includes at least citric acid, ammonia, and urea; after pickling, the grain boundary phase on the surface of the NdFeB component is exposed and a passivation film is formed.

[0010] 2) A copper layer with a thickness of 4–6 μm is deposited on the surface of the NdFeB component by physical vapor deposition or magnetron sputtering; some copper atoms diffuse into the NdFeB surface and are distributed in the grain boundaries.

[0011] 3) Electroplating a nickel layer on the deposited copper layer of the NdFeB component, with a nickel layer thickness of 3.5–15.5 μm.

[0012] The mechanical treatment of the surface physical defects is to perform grinding and polishing. After grinding, the edge radius R of the NdFeB component is less than 0.5mm.

[0013] The surface degreasing treatment involves immersing the neodymium iron boron component in a phosphorus-free degreasing solution and ultrasonically cleaning it for 180–300 seconds.

[0014] The grinding and polishing is carried out using a vibratory polishing machine. Brown corundum abrasive stones and sodium silicate additive solution are added to the vibratory polishing machine, and then neodymium iron boron components are placed in for polishing and grinding.

[0015] The sodium silicate additive solution is prepared by adding 0.1-0.4% triethanolamine, 0.2-0.8% boric acid, and 0.01-0.05% ethylenediaminetetraacetic acid to sodium silicate by mass percentage.

[0016] Take 15%–25% sodium hydroxide, 30%–35% sodium carbonate, 4%–5% sodium metasilicate pentahydrate, 3%–15% sodium dodecyl sulfate, 20%–25% alkyl-substituted dicarboxylate, 2%–3% isomeric fatty alcohol alkoxylate, and 0.5%–1.0% layered crystalline disilicate; dissolve thoroughly in water to prepare a phosphorus-free oil removal solution.

[0017] During ultrasonic cleaning, the ultrasonic power is 1500-2000W and the ultrasonic frequency is 35-40KHz.

[0018] The pickling solution comprises, by mass fraction, 6%–10% citric acid, 3%–5% sodium nitrate, 0.2%–0.4% ammonia and 1.5%–3.5% urea;

[0019] The cleaning method is ultrasonic-assisted cleaning, with the cleaning temperature controlled between 20 and 30°C and the cleaning time controlled between 60 and 180 seconds.

[0020] The magnetron sputtering operation for depositing the copper layer includes:

[0021] 1) After installing the copper target, start the air compressor, water chiller, and voltage regulator, turn on the argon gas and adjust the pressure;

[0022] 2) Preheat and evacuate; vacuum level reaches 5*10 ～3After the heater is turned on and heated to 100-200°C, the vacuum level reaches 5*10. ～4 Pa activates the ionization vacuum gauge;

[0023] 3) Purge with argon gas, 99.995% purity, and a flow rate of 50–200 sccm; adjust the vacuum to 1 Pa–3 Pa and perform copper deposition.

[0024] 4) After deposition is complete, remove the sample.

[0025] The electroplated nickel layer includes the following operations:

[0026] 1) Surface activation treatment of pre-deposited layer:

[0027] The neodymium iron boron component was immersed in dilute sulfuric acid with a volume concentration of 3% to 10% and stirred at room temperature for 30 to 60 seconds.

[0028] 2) Electroplated nickel layer

[0029] The neodymium iron boron component was removed and placed in an electroplating solution as a cathode for electroplating. The electroplating solution contained 200 g / L to 350 g / L of nickel sulfate, 30 g / L to 55 g / L of nickel chloride, 5 g / L to 20 g / L of magnesium sulfate, 5 g / L to 15 g / L of sodium chloride, 35 g / L to 60 g / L of boric acid, and 2 g / L to 5 g / L of ammonia water, with a pH of 3.8 to 5.0.

[0030] The anode is a high-purity nickel ball with a purity >99.9%, and the electroplating current density is 0.3–0.8 A / dm². 2 The temperature is 45℃~55℃, and the electroplating time is 3600s~7200s;

[0031] 3) Cleaning

[0032] After electroplating, rinse multiple times with distilled or deionized water, then clean with hot water at 45℃~55℃, and finally dry with hot air at 20~60℃.

[0033] Compared with the prior art, the present invention has the following beneficial technical effects:

[0034] The NdFeB double-coating surface protection method provided by this invention first optimizes the boundary microstructure of NdFeB by depositing a copper layer using physical vapor deposition or magnetron sputtering, and then performs surface electroplating with nickel. On the one hand, copper atoms can easily diffuse into the NdFeB surface layer and distribute in the grain boundaries. The atoms can not only promote the compactness of the magnet surface layer, but also prevent further corrosion of the sintered NdFeB magnet while ensuring the bonding force between the deposited layer and the substrate. On the other hand, the copper atoms are mainly distributed in the grain boundaries, which improves the microstructure of the grain boundary phase to a certain extent and can promote the improvement of the magnetic properties of the sintered NdFeB magnet. Moreover, the present invention electroplating nickel metal on the copper deposited layer avoids the NdFeB substrate from directly contacting and corroding with chloride ions in the nickel plating solution, and avoids the NdFeB substrate from directly contacting impurity elements introduced during the electroplating process.

[0035] The neodymium iron boron double-coating surface protection method provided by the present invention replaces the three-layer electroplating structure of bottom nickel plating-copper plating-top nickel plating by depositing a copper layer-top nickel plating double coating, thereby reducing the magnetic shielding generated by the nickel plating layer; it achieves a new type of surface protection with high corrosion resistance that does not affect the surface adhesion and at the same time greatly reduces the loss of its magnetic properties, or even does not produce any loss of magnetic properties. Attached Figure Description

[0036] Figure 1 A schematic diagram of the NdFeB matrix before boundary optimization;

[0037] Figure 2 A schematic diagram of the NdFeB matrix after boundary optimization. Detailed Implementation

[0038] The present invention will be further described in detail below with reference to embodiments. These descriptions are for illustrative purposes only and are not intended to limit the scope of the invention.

[0039] A method for surface protection using a NdFeB double-coating, characterized by comprising the following operations:

[0040] 1) After the NdFeB components undergo surface physical defect mechanical treatment and surface degreasing treatment, they are subjected to ultrasonic treatment in pickling solution;

[0041] The pickling solution includes at least citric acid, ammonia, and urea; after pickling, the grain boundary phase on the surface of the NdFeB component is exposed and a passivation film is formed.

[0042] 2) A copper layer with a thickness of 4–6 μm is deposited on the surface of the NdFeB component by physical vapor deposition or magnetron sputtering; some copper atoms diffuse into the NdFeB surface and are distributed in the grain boundaries.

[0043] 3) Electroplating a nickel layer on the copper layer deposited on the neodymium iron boron component, with a nickel layer thickness of 3.5–15.5 μm.

[0044] Specific implementation examples are given below.

[0045] A method for surface protection using neodymium iron boron double-coating includes the following steps:

[0046] Step 1: Pre-treatment of NdFeB components

[0047] 11) Surface mechanical treatment

[0048] First, address the surface physical defects of the NdFeB components after machining. A vibratory polishing machine is preferred for grinding and polishing. Add brown corundum abrasive and sodium silicate additive solution (0.4% triethanolamine, 0.8% boric acid, and 0.05% ethylenediaminetetraacetic acid by mass percentage), and place the NdFeB components in for polishing and grinding. The edge radius R of the parts after grinding should ideally be less than 0.5mm.

[0049] 12) Surface degreasing treatment

[0050] A phosphate-free oil removal solution with low alkalinity, strong emulsifying power, and strong oil dispersing ability is used.

[0051] By mass fraction, take 15%–25% sodium hydroxide, 30%–35% sodium carbonate, 4%–5% sodium metasilicate pentahydrate, 3%–15% sodium dodecyl sulfate (K12), 20%–25% alkyl-substituted dicarboxylate (DG), 2%–3% isomeric fatty alcohol alkoxylate (EH), and 0.5%–1.0% layered crystalline disilicate; dissolve thoroughly in water to prepare a phosphorus-free oil-removing solution.

[0052] Specifically, take 20% sodium hydroxide, 35% sodium carbonate, 4% sodium metasilicate pentahydrate, 12% sodium dodecyl sulfate (K12), 25% alkyl substituted dicarboxylate (DG), 3% isomeric fatty alcohol alkoxylate (EH), and 1.0% layered crystalline disilicate; dissolve these ingredients thoroughly in water to prepare a phosphorus-free oil removal solution.

[0053] Pour the phosphate-free degreasing solution into the ultrasonic cleaner (inner tank dimensions 800mm*640mm*350mm), place the neodymium iron boron component inside, ultrasonic power: 2000W, ultrasonic frequency: 40KHz; ultrasonic cleaning 180S~300s.

[0054] 13) Pickling

[0055] The pickling solution contains 6%–10% citric acid, 3%–5% sodium nitrate, 0.2%–0.4% ammonia, and 1.5%–3.5% urea by mass fraction. The cleaning method is ultrasonic-assisted cleaning. The cleaning temperature is controlled between 20 and 30°C, and the cleaning time is controlled between 60 and 180 seconds.

[0056] This invention selects a weaker organic acid system to reduce damage to the substrate during the pickling process; the organic acid cleaning system utilizes H...+ Under conditions where ions react with alkaline metal oxides, the addition of ammonia to the citric acid solution enhances the removal of iron oxide by generating highly soluble ferrous ammonium citrate and ferric ammonium citrate double salts through the complexation of citric acid. This also prevents the formation of Fe(OH)3 precipitate with a very small solubility product. Furthermore, the addition of nitrates, in synergy with citric acid, accelerates the dissolution of surface contaminants, thereby effectively improving the cleaning effect.

[0057] Preferably, 0.1% urea is added to the ammonium citrate solution to achieve rapid passivation of the newly cleaned surface. After passivation, the sample surface is composed of metal oxides, metal hydroxides, a small amount of elemental metals and water of crystallization to form a passivation film, which effectively improves the phenomenon that the neodymium-rich phase of NdFeB corrodes in the solution and causes the outer surface to become porous, and its corrosion resistance is greatly improved.

[0058] Step 2: Deposit copper layer using physical vapor deposition or magnetron sputtering.

[0059] Taking magnetron sputtering as an example, the coating equipment can be composed of a vacuum chamber, a rotating system, a frame, an oil-free vacuum system, a cooling system, a pneumatic system, and an electrical system.

[0060] Specifically, the selected magnetron sputtering coating machine has a vacuum chamber size greater than φ1000mm*1200mm, a film thickness non-uniformity ≤5%, and an ultimate vacuum degree ≤5.0*10. ～4 Vacuum chamber pressure holding: Vacuum degree ≤5Pa after system pump shutdown and power off for 12 hours; Power supply: DC 1000W (1 unit), RF: 600W; Bias voltage: 0~200V negative bias voltage, continuously adjustable; Heating temperature: Adjustable from room temperature to 350℃, automatic temperature control, temperature control accuracy better than 1%; Gas flow control: Ar~1000sccm; O2~100sccm; N2~100sccm, accuracy better than 1%; Gas pressure control range: 10Pa~1×10 ～5 Pa;

[0061] The main steps of radio frequency magnetron sputtering include vacuuming, vacuum heating, target washing, ion cleaning, film formation, cooling, unloading, and cleaning.

[0062] 21) Place the sample to be plated on the rotating rack and install the rotating rack into the vacuum chamber holder; install the copper target to be sputtered into the cathode target holder; turn on the air compressor, water chiller, and voltage regulator, turn on the argon gas and adjust the pressure, and turn on the rotating rack, setting the rotation speed to 5-30 rpm.

[0063] 22) Preheat and evacuate; vacuum level reaches 5*10 ～3 The heater is turned on (100-200℃). After heating is completed, the vacuum level reaches 5*10. ～4Pa activates the ionization vacuum gauge;

[0064] 23) Purge with argon gas, argon purity 99.995%, argon flow rate 50-200 sccm; adjust the main valve to achieve a vacuum of 1 Pa-3 Pa;

[0065] 24) Turn on the RF sputtering power supply to start operation, ignite and adjust the RF power to 20W~160W; turn on the DC sputtering power supply switch; the workpiece holder should have a rotating device, and its rotation speed should be continuously adjustable; apply a negative bias voltage of 0~200V to the workpiece holder, continuously adjustable (accuracy 1V); perform sputtering deposition to the required thickness according to the set process parameters; the automatic control range of the working pressure is 10Pa~1×10 ～1 Pa, the automatic control accuracy of working pressure is 1%;

[0066] 25) After deposition is complete, remove the NdFeB component.

[0067] This invention deposits copper atoms onto a NdFeB substrate to form a dense copper layer, optimizing the boundary microstructure of the NdFeB substrate (see [link]). Figure 1 , Figure 2 (Comparison diagram before and after boundary optimization is shown). By adjusting the operating voltage and discharge current of the sputtering equipment, a copper deposition layer with good adhesion was obtained; the copper film thickness reached about 5 μm with the change of deposition time; and the deposition process was not limited by the shape of the part. At the same time, since the grain boundary phase in the surface area of ​​the NdFeB substrate is exposed after cleaning, some copper atoms can easily diffuse into the NdFeB surface layer; copper atoms can not only promote the compactness of the magnet surface layer and ensure the adhesion between the deposition layer and the substrate, but also improve the microstructure of the grain boundary phase by mainly distributing copper atoms in the grain boundaries, which can promote the improvement of magnetic properties.

[0068] Step 3: Electroplating nickel layer

[0069] 31) Surface activation treatment of pre-deposited layer

[0070] Immerse the neodymium iron boron component in a 3%–10% volume concentration of dilute sulfuric acid and stir gently at room temperature for 30–60 seconds.

[0071] 32) Electroplated nickel layer

[0072] The electroplating solution comprises nickel sulfate, sodium chloride, nickel chloride, boric acid, magnesium sulfate, ammonia, and water. The components are: nickel sulfate (200g / L~350g / L), nickel chloride (30g / L~55g / L), magnesium sulfate (5g / L~20g / L), sodium chloride (5g / L~15g / L), boric acid (35g / L~60g / L), and ammonia (2g / L~5g / L). The selected current density is 0.3~0.8A / dm². The selected pH is 3.8~5.0. The selected temperature is 45℃~55℃. The selected electroplating time is 3600s~7200s.

[0073] The electroplating process uses an STP~100A / 12V.R high-frequency power supply, with an input of AC220V / 1PH and an output of 100A / 12V. It is equipped with a multi-stage time relay for the rectified power supply; one stage controls the total operating time, while the other 1-5 stages are turned on and off according to the process sequence. The current output for different stages can also be controlled by changing the potentiometer value. The anode uses high-purity nickel balls (purity > 99.9%).

[0074] 3) Cleaning

[0075] After electroplating, the sample is cleaned with distilled or deionized water. After rinsing several times, it is washed twice with hot water and then dried with hot air.

[0076] This invention electroplats nickel metal onto a copper deposition layer, avoiding the direct contact between the NdFeB substrate and chloride ions in the nickel plating solution, which would easily lead to corrosion by chloride ions and thus a significant decrease in the magnetic properties of the NdFeB parts after electroplating; it also avoids direct contact between the NdFeB substrate and impurity elements introduced during the electroplating process.

[0077] The following test data illustrates the loss of magnetic properties of the three-layer electroplating coating of the present invention, which consists of a double plating layer and a bottom layer of nickel plating, a copper plating layer, and a top layer of nickel plating.

[0078] One of the comparisons of magnetic properties or magnetic property loss

[0079]

[0080] Comparison of magnetic properties or magnetic property losses (Part 2)

[0081]

[0082] Comparison of magnetic properties or magnetic property losses (Part 3)

[0083]

[0084] Therefore, the double-coating of the present invention reduces the loss of magnetic properties of NdFeB components.

[0085] The following is a comparison of the corrosion resistance of the double-layer plating produced by this invention with that of a bottom layer nickel-copper plating-top layer nickel plating:

[0086] project Double-layer coating structure Three-layer coating structure Self-corrosion current density <![CDATA[1.8*10 ～7 A / cm 2 ]]> <![CDATA[5.3*10 ～6 A / cm 2 ]]> 48-hour salt spray test results The sample is intact The sample is intact 96-hour salt spray test results The sample is intact The sample is intact Results of 120 hours of salt spray resistance The sample is intact Rust spots began to appear on the sample. Results of 168 hours of salt spray resistance Rust spots began to appear on the sample. / Results Comparison better generally

[0087] Thus, it can be seen that the present invention achieves a novel surface protection with high corrosion resistance that does not affect the surface adhesion, while greatly reducing the loss of its magnetic properties, or even causing no loss of magnetic properties.

[0088] The embodiments given above are preferred examples for implementing the present invention, and the present invention is not limited to the above embodiments. Any non-essential additions or substitutions made by those skilled in the art based on the technical features of the present invention are within the protection scope of the present invention.

Claims

1. A method for surface protection using neodymium iron boron double-coating, characterized in that, Includes the following operations: 1) After the NdFeB components undergo surface physical defect mechanical treatment and surface degreasing treatment, they are subjected to ultrasonic treatment in pickling solution; The pickling solution includes at least citric acid, ammonia, and urea; after pickling, the grain boundary phase on the surface of the NdFeB component is exposed and a passivation film is formed. The pickling solution comprises, by mass fraction, 6%–10% citric acid, 3%–5% sodium nitrate, 0.2%–0.4% ammonia and 1.5%–3.5% urea; The cleaning method is ultrasonic-assisted cleaning, with the cleaning temperature controlled between 20 and 30°C and the cleaning time controlled between 60 and 180 seconds. 2) A copper layer with a thickness of 4-6 μm is deposited on the surface of the NdFeB component by magnetron sputtering; some copper atoms diffuse into the NdFeB surface and are distributed in the grain boundaries to improve the microstructure of the grain boundary phase. 3) Electroplating a nickel layer on the deposited copper layer of the NdFeB component, with a nickel layer thickness of 3.5–15.5 μm; The magnetron sputtering operation for depositing the copper layer includes: 21) After installing the copper target, start the air compressor, water chiller, and voltage regulator, turn on the argon gas and adjust the pressure; 22) Preheat and evacuate; vacuum level reaches 5×10 ～3 After the heater is turned on and heated to 100–200°C, the vacuum level reaches 5 × 10⁻⁶. ～4 Pa activates the ionization vacuum gauge; 23) Purge with argon gas, argon purity 99.995%, argon flow rate 50-200 sccm; adjust vacuum to 1 Pa-3 Pa, and perform copper layer deposition; 24) After deposition is complete, remove the sample.

2. The NdFeB double-coating surface protection method as described in claim 1, characterized in that, The mechanical treatment of the surface physical defects is to perform grinding and polishing. After grinding, the edge radius R of the NdFeB component is less than 0.5mm. The surface degreasing treatment involves immersing the neodymium iron boron component in a phosphorus-free degreasing solution and ultrasonically cleaning it for 180–300 seconds.

3. The NdFeB double-coating surface protection method as described in claim 2, characterized in that, The grinding and polishing is carried out using a vibratory polishing machine. Brown corundum abrasive stones and sodium silicate additive solution are added to the vibratory polishing machine, and then neodymium iron boron components are placed in for polishing and grinding. The sodium silicate additive solution is prepared by adding 0.1-0.4% triethanolamine, 0.2-0.8% boric acid, and 0.01-0.05% ethylenediaminetetraacetic acid to sodium silicate by mass percentage.

4. The NdFeB double-coating surface protection method as described in claim 2, characterized in that, Take 15%–25% sodium hydroxide, 30%–35% sodium carbonate, 4%–5% sodium metasilicate pentahydrate, 3%–15% sodium dodecyl sulfate, 20%–25% alkyl-substituted dicarboxylate, 2%–3% isomeric fatty alcohol alkoxylate, and 0.5%–1.0% layered crystalline disilicate; dissolve thoroughly in water to prepare a phosphorus-free oil removal solution. During ultrasonic cleaning, the ultrasonic power is 1500-2000W and the ultrasonic frequency is 35-40KHz.

5. The NdFeB double-coating surface protection method as described in claim 1, characterized in that, The electroplated nickel layer includes the following operations: 1) Surface activation treatment of pre-deposited layer: The neodymium iron boron component was immersed in dilute sulfuric acid with a volume concentration of 3% to 10% and stirred at room temperature for 30 to 60 seconds. 2) Electroplated nickel layer: The neodymium iron boron component was removed and placed in an electroplating solution as a cathode for electroplating. The electroplating solution contained 200 g / L to 350 g / L of nickel sulfate, 30 g / L to 55 g / L of nickel chloride, 5 g / L to 20 g / L of magnesium sulfate, 5 g / L to 15 g / L of sodium chloride, 35 g / L to 60 g / L of boric acid, and 2 g / L to 5 g / L of ammonia water, with a pH of 3.8 to 5.

0. The anode is a high-purity nickel ball with a purity >99.9%, and the electroplating current density is 0.3–0.8 A / dm². 2 The temperature is 45℃~55℃, and the electroplating time is 3600s~7200s; 3) Cleaning: After electroplating, rinse multiple times with distilled or deionized water, then clean with hot water at 45℃~55℃, and finally dry with hot air at 20~60℃.

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