Neodymium-iron-boron magnet composite modification method

Abstract

The application discloses a neodymium-iron-boron magnet composite modification method, which comprises the following steps: S1, preparing a modified neodymium-iron-boron base body, wherein the neodymium-iron-boron base body comprises 0.13-0.18 wt% of Ga and 0.08-1.02 wt% of Cu; S2, magnetron sputtering deposition of a double-alloy diffusion source, wherein the target material is a Dy-Ho double-alloy target material, and the atomic ratio of Dy to Ho is 1:1; S3, short-time high-temperature vacuum diffusion, heating to 920-980 DEG C, holding for 30 min, secondary aging treatment at 480-520 DEG C for 3 h, and then air quenching to obtain a neodymium-iron-boron magnet; and S4, adopting a chemical plating or electroplating process to deposit a high-phosphorus nickel plating layer on the surface of the neodymium-iron-boron magnet, so as to shorten the heavy rare earth diffusion time and reduce energy consumption under the premise of ensuring diffusion depth, reduce the use amount of expensive Dy while ensuring high coercivity, and form a passivation film in the neodymium-iron-boron magnet to improve corrosion resistance.

Description

Technical Field

[0001] This invention relates to the field of rare earth permanent magnet material preparation technology, specifically to a method for composite modification of neodymium iron boron magnets. Background Technology

[0002] Neodymium iron boron (NdFeB) magnets are widely used due to their excellent magnetic properties, but their inherent poor corrosion resistance and insufficient coercivity at high temperatures are the main bottlenecks limiting their application in extreme environments.

[0003] Existing technologies typically employ the following methods, but all have significant drawbacks: 1. Traditional grain boundary diffusion technology (coating or vapor deposition) suffers from the following drawbacks: the diffusion process usually requires prolonged holding at high temperatures (900~1200℃) (typically 6~10 hours or even longer), resulting in extremely high energy consumption, low production efficiency, and low utilization rate of traditional heavy rare earth elements (Dy / Tb), leading to high costs. 2. Traditional surface electroplating protection (such as zinc plating, nickel plating) suffers from the following drawbacks: it only forms a physical barrier on the magnet surface. Once the coating has pinholes or scratches, the Nd-rich phase inside the substrate is highly susceptible to intergranular corrosion, causing the coating to bulge and peel off, failing to fundamentally solve the problem of grain boundary corrosion sensitivity.

[0004] Existing technologies often treat "improving coercivity (diffusion)" and "improving corrosion resistance (electroplation)" as two separate processes. There is a lack of a synergistic process that can utilize matrix composition to improve diffusion kinetics (thereby shortening diffusion time) and simultaneously achieve grain boundary self-passivation. Summary of the Invention

[0005] To overcome the shortcomings of the above-mentioned related technologies, this application provides a method for composite modification of neodymium iron boron magnets, which shortens the diffusion time of heavy rare earth elements and reduces energy consumption while ensuring diffusion depth; reduces the amount of expensive Dy while ensuring high coercivity; and forms a passivation film inside to improve corrosion resistance.

[0006] The technical solution adopted by this invention to solve the technical problem is: a method for composite modification of neodymium iron boron magnets, comprising the following steps:

[0007] S1, prepare a modified NdFeB matrix, wherein the modified NdFeB matrix comprises 0.13~0.18wt% Ga and 0.08~1.02wt% Cu;

[0008] S2, a magnetron sputtering deposition dual alloy diffusion source, with a Dy-Ho dual alloy target material, wherein the atomic ratio of Dy to Ho is 1:1;

[0009] S3, short-time high-temperature vacuum diffusion, heating to 920~980℃, holding time 25-35min, secondary aging treatment at 480~520℃, followed by gas quenching and cooling, to obtain NdFeB magnets;

[0010] S4 uses chemical plating or electroplating processes to deposit a high-phosphorus nickel plating layer on the surface of a neodymium iron boron magnet.

[0011] Preferably, the modified NdFeB matrix in step S1 further comprises, by mass percentage: 30.5% Pr and Nd, 0.5% Dy, 1.0% B, 1.0% Co, and the balance being Fe, wherein the mass ratio of Pr to Nd is 2:8 to 3:7.

[0012] Preferably, step S1 specifically includes:

[0013] S1.1, Load the prepared raw materials into the vacuum induction melting furnace and evacuate to 5×10 -2 After Pa, argon gas is introduced for protection, heated and melted, refined and poured onto a water-cooled copper roller, and an alloy strip with a thickness of about 0.3 mm is prepared by a rapid solidification process.

[0014] S1.2. The alloy strip is placed into a hydrogen treatment furnace, and after being saturated with hydrogen, it is heated to 550°C to remove hydrogen. Nitrogen is used as the gas source for air jet milling. The sorting wheel speed is set to 4000 rpm, and the average particle size of the powder is controlled to D50=3.5μm.

[0015] S1.3 The powder obtained in S1.2 was placed in a nitrogen-protected glove box, and 0.08wt% zinc stearate was added as a lubricant. It was pressed into shape under an orientation magnetic field of 2.0T, followed by cold isostatic pressing at 200MPa, and then placed in a vacuum sintering furnace. It was held at 1060℃ for 4 hours to sinter and become dense, thus obtaining the modified NdFeB matrix.

[0016] Preferably, step S2 specifically involves pickling, chamfering, and drying the modified NdFeB substrate to remove the surface oxide scale, then placing it in a magnetron sputtering chamber with the base vacuum reduced to <5.0×10⁻⁶. -4 Pa, argon gas is introduced as the working gas, the sputtering power is adjusted to 3.0~5.0kW, the magnet is rotated by the planetary carrier, the sputtering time is controlled to be 0.5~1.5 hours, and a Dy-Ho alloy film with a thickness of 5~8μm is uniformly deposited on the magnet surface.

[0017] Preferably, the heating rate in step S3 is 10℃ / min.

[0018] Preferably, in step S4, the phosphorus content of the high-phosphorus nickel plating is >10wt%, and the thickness is 10~15μm.

[0019] Compared with related technologies, the present invention has the following advantages:

[0020] The coercivity is significantly improved. Compared with the untreated matrix, the intrinsic coercivity Hcj increases from 17kOe to over 20kOe, and the remanence Br decreases only slightly (<1.5%).

[0021] Production efficiency is greatly improved and energy consumption is reduced: the diffusion heat treatment time is shortened from the traditional 6-10 hours to 30 minutes, the diffusion efficiency reaches 95%, and the overall energy consumption is reduced by 40%.

[0022] Corrosion resistance: After neutral salt spray test (NSS), the magnet surface remains rust-free for more than 96 hours (48-72 hours without Ga and Cu). The synergistic protective effect of grain boundary self-passivation and surface coating effectively increases corrosion resistance. Detailed Implementation

[0023] First, those skilled in the art should understand that these embodiments are merely used to explain the technical principles of the embodiments of this application and are not intended to limit the scope of protection of the embodiments of this application. Those skilled in the art can make adjustments as needed to adapt to specific application scenarios.

[0024] The present invention will be further described in detail below with reference to specific embodiments.

[0025] Example 1

[0026] Ingredients: Weigh the raw materials according to the following weight percentages (wt%):

[0027] Pr and Nd: 30.5%, with a mass ratio of Pr to Nd of 25:75.

[0028] Dy: 0.5%

[0029] B: 1.0%

[0030] Co: 1.0%

[0031] Ga: 0.15%

[0032] Cu: 0.10%

[0033] Fe: Balance.

[0034] Step 1: Preparation of modified NdFeB matrix

[0035] Smelting

[0036] The prepared raw materials were loaded into a vacuum induction melting furnace, and a vacuum of 5×10⁻⁶ was applied. -2 After Pa, argon gas is introduced for protection. The mixture is heated and melted, then refined and poured onto a water-cooled copper roller. An alloy strip with a thickness of approximately 0.3 mm is then prepared using a rapid solidification process (StripCasting).

[0037] Flour Milling

[0038] Hydrogen Decomposition (HD): The alloy strip is placed into a hydrogen treatment furnace, saturated with hydrogen, and then heated to 550°C to remove hydrogen.

[0039] Jet milling: Nitrogen gas is used as the gas source for jet milling. The sorting wheel speed is set to 4000 rpm, and the average particle size of the powder is controlled to D50=3.5μm.

[0040] Forming and sintering

[0041] The powder was placed in a nitrogen-protected glove box, and 0.08 wt% zinc stearate was added as a lubricant. It was pressed into shape under an orientation magnetic field of 2.0 T, followed by cold isostatic pressing at 200 MPa to produce a green compact. The green compact was placed in a vacuum sintering furnace and held at 1060 °C for 4 hours to achieve densification, thus obtaining the modified NdFeB matrix.

[0042] Machining

[0043] The modified NdFeB matrix was cut and ground into square magnets with dimensions of 20mm×10mm×5mm, which were used as the matrix magnets to be treated.

[0044] During the process, Ga and Cu are enriched at the grain boundaries, which improves the fluidity and wettability of the grain boundary phase, laying the foundation for subsequent rapid diffusion, and at the same time inducing the formation of corrosion-resistant Nd(Ga,Cu)Ox grain boundary phase.

[0045] Step 2: Magnetron sputtering deposition of Dy-Ho dual alloy film

[0046] Preprocessing

[0047] The base magnet was sequentially immersed in dilute nitric acid (3% concentration), deionized water, and anhydrous ethanol for ultrasonic cleaning to remove surface oil and oxide layer, and then dried with hot air.

[0048] Loading and Evacuation

[0049] Mount the magnet onto the planetary rotating hanger of the magnetron sputtering equipment. Close the furnace door and evacuate the background vacuum to 5.0 × 10⁻⁶. -4 Pa.

[0050] Sputtering parameter settings

[0051] Target material: Dy-Ho alloy target with an atomic ratio of Dy:Ho = 1:1.

[0052] Gas: Introduce high-purity argon (Ar) and adjust the working pressure to 0.5 Pa.

[0053] Power and Time: Turn on the DC power supply and set the sputtering power to 4.0kW. Start the planetary carrier's rotation and revolution (10rpm), and set the sputtering time to 45 minutes.

[0054] Deposition results: A Dy-Ho alloy film was uniformly deposited on the six surfaces of the magnet. The film thickness was approximately 6 μm, as determined by weighing and step measurement.

[0055] Using Dy-Ho (1:1) alloy targets, the coupling mechanism of Ho-assisted Dy is utilized to reduce the amount of expensive Dy used while ensuring high coercivity.

[0056] Step 3: Short-duration high-temperature vacuum diffusion

[0057] Put into the furnace

[0058] After step 2, when the Dy-Ho dual alloy film is deposited by magnetron sputtering, if a wired equipment is used, the next step can be carried out without breaking the vacuum, or the film can be quickly transferred to a high-vacuum heat treatment furnace.

[0059] Rapid spread

[0060] The temperature was increased to 950℃ at a rate of 10℃ / min. The isothermal holding time was controlled to be 30 minutes. At this time, Ga~Cu assisted the flow of liquid phase at the grain boundaries, and Dy-Ho rapidly penetrated inward.

[0061] Cooling: Stop heating and quench the gas with high-pressure argon gas to below 100°C.

[0062] Thanks to the improved grain boundary wettability of Ga~Cu in step S1, Dy-Ho atoms can penetrate along the grain boundary at an extremely fast speed at 920~980℃, reducing the traditional diffusion time of several hours to 30 minutes, and the diffusion efficiency (the proportion of heavy rare earth elements entering the grain boundary) is as high as 95%.

[0063] Step 4: Timeliness Processing

[0064] The magnet was heated to 500°C and held at that temperature for 3 hours for a second-stage aging treatment to optimize the grain boundary phase structure and release stress. It was then allowed to cool naturally to room temperature.

[0065] Secondary aging treatment can eliminate the above defects through defect relaxation (such as dislocation annihilation and decomposition of supersaturated solid solutions), further reducing the probability of the formation of antimagnetic nuclei and improving the stability and repeatability of coercivity.

[0066] Step 5: Surface high-phosphorus nickel composite protection

[0067] Surface activation: Micro-corrosion activation of the diffused magnet surface (using 1% dilute sulfuric acid for 10 seconds).

[0068] Electroless nickel plating: Plating solution formulation: nickel sulfate ~ sodium hypophosphite system. pH value: 4.6-4.8; temperature: 85℃; plating time: 60 minutes.

[0069] Curing: After cleaning and drying, heat-treat in a 150℃ oven for 30 minutes to increase the adhesion of the coating.

[0070] Final state: Obtain a neodymium iron boron magnet with a 12μm thick high phosphorus nickel plating layer (phosphorus content 11%) on the surface.

[0071] The amorphous structure of the high-phosphorus nickel coating and the Nd(Ga,Cu)Ox passivation film inside the substrate complement each other, further improving corrosion resistance.

[0072] Example 2

[0073] Ingredients: Weigh the raw materials according to the following weight percentages (wt%):

[0074] Pr and Nd: 30.5%, with a mass ratio of Pr to Nd of 25:75.

[0075] Dy: 0.5%

[0076] B: 1.0%

[0077] Co: 1.0%

[0078] Ga: 0.18%

[0079] Cu: 0.08%

[0080] Fe: Balance.

[0081] After step 2, when the Dy-Ho dual alloy film is deposited by magnetron sputtering, if a wired equipment is used, the next step can be carried out without breaking the vacuum, or the film can be quickly transferred to a high-vacuum heat treatment furnace.

[0082] Rapid spread

[0083] The temperature was increased to 960℃ at a rate of 10℃ / min. The isothermal holding time was controlled to be 25 minutes. At this time, Ga~Cu assisted the flow of liquid phase at the grain boundaries, and Dy-Ho rapidly penetrated inward.

[0084] Cooling: Stop heating and quench the gas with high-pressure argon gas to below 100°C.

[0085] The rest is the same as in Example 1.

[0086] Objective: To verify that at a slightly higher temperature and with a slightly higher Ga content, the diffusion time can be further shortened, thus demonstrating the tolerance of the process window.

[0087] Comparative Example 1

[0088] Ingredients: No Ga and Cu added, other ingredients are the same as in Example 1.

[0089] Comparative Example 2

[0090] Ingredients: No Ga and Cu added, other ingredients are the same as in Example 1.

[0091] After step 2, when the Dy-Ho dual alloy film is deposited by magnetron sputtering, if a wired equipment is used, the next step can be carried out without breaking the vacuum, or the film can be quickly transferred to a high-vacuum heat treatment furnace.

[0092] diffusion

[0093] The temperature was increased to 900℃ at a rate of 10℃ / min. The temperature was held at this temperature for 8 hours.

[0094] The rest is the same as in Example 1.

[0095] Performance testing

[0096] According to GB / T13560-2017 "Sintered NdFeB Permanent Magnets", the coercivity (Hcj), remanence (Br), diffusion depth (μm) and diffusion efficiency of the magnets prepared in Examples 1, 2, Comparative Examples 1 and 2 were tested.

[0097] The magnets prepared in Examples 1, 2, 1 (Comparative Example), and 2 (Comparative Example) were subjected to corrosion resistance tests according to GB / T10125 / ISO9227.

[0098] Based on Example 1, the energy consumption percentage of Example 2, Comparative Example 1, and Comparative Example 2 was calculated.

[0099] The test results are shown in Table 1.

[0100] Table 1. Performance test results of Examples 1, 2, Comparative Example 1, and Comparative Example 2.

[0101]

[0102] A comparison of Example 2 and Example 1 shows that at a slightly higher temperature and with a slightly higher Ga content, the diffusion time can be further shortened.

[0103] In Comparative Example 1, due to the lack of a low-melting-point, highly wettable channel formed by Ga~Cu, Dy-Ho remained only on the surface within 30 minutes and failed to effectively penetrate into the magnet. Although the coercivity was slightly improved, the corrosion resistance was not as good as in Example 1 because there was no self-passivating phase Nd(Ga,Cu)Ox inside the matrix.

[0104] Compared with Example 1, Comparative Example 2 has a much higher energy consumption, and because there is no self-passivating phase inside the matrix, its corrosion resistance is not as good as that of Example 1.

[0105] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for composite modification of neodymium iron boron magnets, characterized in that: Includes the following steps: S1, prepare a modified NdFeB matrix, wherein the modified NdFeB matrix comprises 0.13~0.18wt% Ga and 0.08~1.02wt% Cu, and the modified NdFeB matrix further comprises, by mass percentage: 30.5% Pr and Nd, 0.5% Dy, 1.0% B, 1.0% Co, and the balance being Fe, wherein the mass ratio of Pr to Nd is 2:8~3:7; S1.1, Load the prepared raw materials into the vacuum induction melting furnace and evacuate to 5×10 -2 After Pa, argon gas is introduced for protection, heated and melted, and after refining, it is poured onto a water-cooled copper roller and prepared into an alloy strip through a rapid solidification process. S1.2, the alloy strip is placed into the hydrogen treatment furnace, and after hydrogen saturation, it is heated to 550°C to remove hydrogen. Nitrogen is used as the gas source for air jet milling. The sorting wheel speed is set to 4000 rpm, and the average particle size of the powder D50 is controlled to be 3.5 μm. S1.3 The powder obtained in S1.2 was placed in a nitrogen-protected glove box, and 0.08wt% zinc stearate was added as a lubricant. It was pressed into shape under an orientation magnetic field of 2.0T, and then subjected to cold isostatic pressing at 200MPa. It was then placed in a vacuum sintering furnace and held at 1060℃ for 4 hours to sinter and densify, thus obtaining a modified NdFeB matrix. S2, a magnetron sputtering deposition dual alloy diffusion source, with a Dy-Ho dual alloy target material, wherein the atomic ratio of Dy to Ho is 1:1; S3, short-time high-temperature vacuum diffusion, heating to 920~980℃, holding time 25~35min, secondary aging treatment at 480~520℃, followed by gas quenching and cooling to obtain NdFeB magnets; S4 uses chemical plating or electroplating processes to deposit a high-phosphorus nickel plating layer on the surface of the neodymium iron boron magnet, with a phosphorus content of >10wt%.

2. The method for composite modification of NdFeB magnets according to claim 1, characterized in that: Step S2 specifically involves pickling, chamfering, and drying the modified NdFeB substrate to remove the surface oxide scale. Afterward, the substrate is placed in a magnetron sputtering chamber, and the base vacuum is evacuated to <5.0 × 10⁻⁶. -4 Pa, argon gas is introduced as the working gas, the sputtering power is adjusted to 3.0~5.0kW, the magnet is rotated by the planetary carrier, the sputtering time is controlled to be 0.5~1.5 hours, and a Dy-Ho alloy film with a thickness of 5~8μm is uniformly deposited on the magnet surface.

3. The method for composite modification of NdFeB magnets according to claim 1, characterized in that: The heating rate in step S3 is 10℃ / min.

4. The method for composite modification of NdFeB magnets according to claim 1, characterized in that: In step S4, the thickness of the high-phosphorus nickel plating is 10~15μm.

Images