High-temperature-resistant high-remanence rare earth permanent magnet material and preparation process thereof

Abstract

The application belongs to the field of new materials, and specifically discloses a high-temperature-resistant high-remanence rare earth permanent magnet material and a preparation process thereof. The raw materials comprise, by weight, 24-34 parts of neodymium, 4-7 parts of dysprosium, 0.1-0.5 parts of lutetium (in the form of lutetium fluoride nano powder), 0.5-2 parts of niobium, 0.3-1 part of molybdenum, 58-68 parts of iron, 0.9-1.3 parts of boron, 0.2-0.8 parts of gallium oxide and 0.1-0.6 parts of copper. The grain boundary thermal stability is optimized through lutetium fluoride / niobium / molybdenum synergy, and the defects of traditional neodymium-iron-boron magnets, such as fast high-temperature remanence attenuation and poor coercive force temperature coefficient, are overcome by combining deep cooling treatment with argon-hydrogen mixed atmosphere step sintering process. The obtained magnet has a remanence retention rate of more than 87% at 250 DEG C, and a long-term aging magnetic flux loss of less than 2.5% at 200 DEG C, and is suitable for high-temperature scenes such as automobile motor rotors. A surface plasma electrolytic oxidation coating can further endow excellent corrosion resistance.

Description

Technical Field

[0001] The invention belongs to the field of novel rare earth-containing permanent magnetic materials, and specifically discloses a high-temperature-resistant and high-remanence rare earth permanent magnetic material and a preparation process thereof. Background Art

[0002] Current commercial rare earth permanent magnet materials (mainly NdFeB) face severe challenges in high temperature applications. Although traditional high remanence magnets have excellent magnetic properties at room temperature (such as Br≥1.4T, Hcj≥20kOe), their main phase Nd2Fe 14 The Curie temperature (Tc≈312°C) and magnetocrystalline anisotropy field (Ha) of B decay rapidly at high temperatures, leading to two major technical bottlenecks: First, when the operating temperature exceeds 180°C, due to the oxidation of the grain boundary phase and the growth of the main phase grains, the remanence Br decays at a rate of >0.12% / °C. After 500 hours of aging at 200°C, the remanence retention rate is generally less than 80%. For example, the magnet temperature of the electric vehicle drive motor can reach 200-220°C under peak load conditions. At this time, the magnetic flux is not The reversible loss is as high as 8-12%, forcing designers to overuse the volume of the magnet to compensate for performance degradation. Secondly, the coercive force temperature coefficient β (Hcj) deteriorates to above -0.6% / ℃, and the anti-demagnetization ability decreases significantly at high temperatures. A typical manifestation is that the coercive force attenuation rate of spacecraft magnetic bearings exceeds 10% when in service at 200℃. It is necessary to rely on expensive heavy rare earth (dysprosium, terbium) doping to improve stability. Existing technology usually adds 8-12wt% dysprosium or terbium to partially replace neodymium to form (Nd,Dy)2Fe 14 Although the B hard magnetic phase can improve the high-temperature coercivity, it causes three side effects: the addition of heavy rare earth reduces the remanence Br by 0.15-0.2T, the material cost surges by more than 300%, and the segregation of excessive heavy rare earth at the grain boundaries accelerates the high-temperature oxidation process.

[0003] To alleviate these issues, the industry has attempted to introduce elements such as niobium and aluminum to strengthen grain boundaries or employ multi-component alloying, but with limited success. Niobium powder additions exceeding 2.5 parts per million form coarse NbFe₂ phases, which fragment magnetic domains and reduce coercivity. While gallium oxide (Ga₂O₃) can lower sintering temperatures, its unmodified oxygen ion mobility leads to increased oxygen diffusion at high-temperature grain boundaries. While copper powder alone promotes liquid-phase sintering, it degrades thermal stability due to the formation of a low-melting-point Cu-Fe phase. More critically, existing technologies are severely inadequate for extreme high-temperature environments (≥250°C). Applications such as oil drilling sensors and nuclear reactor control mechanisms require magnets to exhibit a remanent magnetization (Br) of ≥1.25T and a coercivity decay rate of <5% after aging at 250°C for 1000 hours. However, conventional NdFeB magnets exhibit a Br decay rate below 1.1T under these conditions, resulting in a coercivity loss exceeding 15%, forcing the system to employ forced cooling or compromise power density. Therefore, there is an urgent need to develop a new type of rare earth permanent magnet material. Through innovative component design and preparation process, high-temperature remanence retention of >88% and coercive force temperature coefficient optimized to within -0.3% / ℃ under the premise of low cost and low heavy rare earth dosage can be achieved, thus completely breaking through the performance boundary of the 180-250℃ temperature zone. Summary of the Invention

[0004] In order to solve the above-mentioned problems in the prior art, the present invention discloses a high-temperature resistant and high-remanence rare earth permanent magnet material and a preparation process thereof.

[0005] To achieve the above objectives, the present invention includes the following technical solutions.

[0006] A high-temperature resistant and high-remanence rare earth permanent magnet material, comprising the following raw materials in parts by weight:

[0007] Main rare earth phase: neodymium (Nd) 24–34 parts, dysprosium (Dy) 4–7 parts, lutetium (Lu) 0.1–0.5 parts;

[0008] High melting point strengthener: niobium powder (Nb) 0.5–2 parts, molybdenum powder (Mo) 0.3–1 parts;

[0009] Matrix phase: iron (Fe) 58–68 parts, boron (B) 0.9–1.3 parts;

[0010] Sintering aids: gallium oxide (Ga2O3) 0.2–0.8 parts, copper powder (Cu) 0.1–0.6 parts.

[0011] Furthermore, in the above-mentioned permanent magnetic material, the lutetium (Lu) is added in the form of lutetium fluoride (LuF3) nanopowder with a particle size of ≤500 nm.

[0012] Furthermore, in the above-mentioned permanent magnetic material, the particle sizes of the molybdenum powder and the niobium powder are both ≤2 μm.

[0013] The application further discloses a process for preparing the permanent magnet material.

[0014] (a) smelting Fe, Nd, Dy and B into an alloy ingot under the protection of argon;

[0015] (b) adding LuF3, Nb, Mo and Ga2O3 into the alloy ingot, and performing secondary smelting in a vacuum induction furnace;

[0016] (c) after hydrogen crushing to 200-400 mu m, performing air flow milling to 1.8-3.2 mu m;

[0017] (d) performing press forming under a magnetic field of 2.0-2.8 T, and a pressure of 180-280 MPa;

[0018] (e) performing step-by-step sintering under a protective gas atmosphere:

[0019] stepped temperature rising: 400 DEG C * 1h → 800 DEG C * 1h → 1080-1120 DEG C * 4h;

[0020] slow cooling stage: cooling to 200 DEG C at a speed of 0.3-0.8 DEG C / min, and then air cooling.

[0021] Further, in the process, after the secondary smelting of step (b), deep cooling treatment is added: the alloy ingot is immersed in liquid nitrogen (-196 DEG C) for 1h, and then restored to room temperature.

[0022] Further, in the process, in the sintering of step (e), argon-hydrogen mixed gas (Ar:H2 volume ratio = 95:5) is introduced, and the flow rate is 20-50 mL / min.

[0023] The application further discloses application of the permanent magnet material in a high-temperature motor magnetic pole, and in a 220 DEG C environment: remanence Br≥1.35 T, and coercive force Hcj≥18 kOe.

[0024] The application further discloses a corrosion-resistant magnet unit based on the permanent magnet material, and an Al2O3-ZrO2 composite ceramic layer with a thickness of 15-40 mu m is formed on the surface of the magnet through plasma electrolytic oxidation.

[0025] Compared with the prior art, the application has the following outstanding beneficial effects:

[0026] The application discloses a high-temperature-resistant high-remanence rare earth permanent magnet material and a preparation process thereof, and realizes three beneficial effects through innovative component design and process control.

[0027] 1. Improved high-temperature magnetic stability: The introduction of lutetium fluoride nanopowder fundamentally suppresses magnetic attenuation caused by high-temperature oxidation, enabling the magnet to maintain over 87% remanence even at extreme temperatures of 250°C. The coercivity temperature coefficient is optimized to an industry-leading level of nearly -0.3% / °C. The synergistic addition of molybdenum and niobium further forms a high-temperature stable phase, effectively blocking thermal perturbations of the magnetic moment and reducing the flux loss rate at 200°C to less than one-quarter that of conventional materials.

[0028] 2. Process innovation ensures highly reproducible performance: Sintering in an argon-hydrogen mixed atmosphere reduces grain boundary oxygen content. Combined with liquid nitrogen cryogenic pretreatment and a two-stage heat treatment system, this not only improves alloy ingot crushing efficiency but also eliminates internal stress, bringing magnet density close to the theoretical limit. This wide process window allows magnet performance to significantly outperform traditional methods even at low-temperature sintering of 1080°C, significantly reducing energy consumption and production complexity.

[0029] 3. Application performance and economic benefits are simultaneously improved. In automotive drive motor rotor applications, the magnets demonstrate excellent torque stability and power retention at 220°C, completely resolving the magnetic degradation problem under peak load in electric vehicles. The surface plasma electrolytic oxidation coating further imparts resistance to salt spray corrosion, meeting the demands of harsh environments such as offshore platforms. More importantly, lutetium fluoride partially replaces expensive dysprosium and terbium, reducing heavy rare earth usage by over 30%. This significantly reduces material costs while maintaining performance, laying the foundation for industrialization and promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Comparison results of Hcj(20℃) (kOe) room temperature coercivity in magnetic properties test;

[0031] Figure 2 Comparison results of Br retention (%) in magnetic performance test;

[0032] Figure 3 Comparison of magnetic flux loss (%) at 250℃×500h in high temperature aging stability;

[0033] Figure 4 High temperature aging stability medium density (g / cm 3 ) comparison. DETAILED DESCRIPTION

[0034] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0035] Examples 1-5

[0036] 1. Raw material ratio (parts by weight):

[0037] Nd 30 parts, Dy 5 parts, LuF3 nanopowder (containing Lu 0.3 parts, particle size 300nm), Nb 1.2 parts (particle size 1.5μm), Mo 0.6 parts (particle size 1.8μm)

[0038] Fe 65 parts (purity > 99.95%), B 1.1 parts (purity > 99.5%), Ga2O3 0.4 parts (particle size 0.8μm), Cu 0.3 parts (particle size 5μm)

[0039] 2. Preparation process:

[0040] First smelting: Fe, Nd, Dy and B are placed in a vacuum induction furnace and vacuumed to 5×10 -3 Pa, filled with argon to 0.05MPa, smelted at 1550℃ for 20 minutes, and cast into alloy ingots;

[0041] Second smelting: crush the alloy ingot into blocks <10mm, add LuF3, Nb, Mo, Ga2O3, and Cu, and smelt at 1480℃ for 15 minutes in the same equipment;

[0042] Cryogenic treatment: Soak in liquid nitrogen (-196°C) for 1 hour, then return to room temperature for 2 hours;

[0043] Hydrogen crushing: put the alloy ingot into the reactor, evacuate the reactor and introduce hydrogen to 0.15MPa, heat it to 300℃ to absorb hydrogen for 2 hours, then heat it to 600℃ to dehydrogenate for 1 hour to obtain coarse powder with a particle size of 200-350μm;

[0044] Jet milling: crush the coarse powder to 2.0-2.8μm (measured D50=2.5μm) under nitrogen protection;

[0045] Magnetic field forming: In a 2.2T vertical magnetic field, pressurize at 10MPa / s to 230MPa and maintain pressure for 60 seconds;

[0046] Segmented sintering:

[0047] Step heating: 400℃×60min (heating rate 5℃ / min) → 800℃×60min (8℃ / min) → 1100℃×240min (10℃ / min);

[0048] Atmosphere control: introduce Ar:H2=95:5 mixed gas (flow rate 35mL / min);

[0049] Slow cooling program: reduce the temperature to 200℃ at 0.6℃ / min and then cool in the furnace;

[0050] Two-stage heat treatment:

[0051] Level 1: 900°C x 60 min → forced air cooling to 400°C (cooling rate 30°C / min);

[0052] Second stage: 500℃×120min → slowly cool to room temperature (1℃ / min).

[0053] Examples 2-5

[0054] The following Examples 2-5 are modified relative to Example 1, see Table 1.

[0055]

[0056] Comparative Examples 1-4

[0057] The comparative examples were modified based on Example 1, see Table 2.

[0058]

[0059] Test Example 1

[0060] Magnetic performance test

[0061] 1. Test purpose:

[0062] Verify the influence of raw material composition (Lu / Mo / Nb synergy) and process (Ar / H2 atmosphere) on high-temperature magnetic stability, and quantify the effect of solving the defect of "fast decay of high-temperature remanence".

[0063] 2. Test method:

[0064] Sample preparation:

[0065] Cut each magnet into a Φ10.00±0.05mm × 7.00±0.05mm cylinder

[0066] Axial pulse magnetization (field strength 6.0T, pulse width 10ms)

[0067] 3. Measuring equipment:

[0068] NIM-5000H permanent magnet measuring instrument

[0069] High temperature constant temperature chamber temperature control accuracy: ±0.3℃ (250℃ point)

[0070] 4. Data Collection:

[0071] Each sample was tested three times and the average was taken after removing outliers.

[0072] Br retention rate = Br(250℃) (T) / Br(20℃) (T) × 100%

[0073] 5. Test item interpretation:

[0074] Br (20℃) (T): remanence at room temperature (20℃), unit Tesla (T), reflects the basic magnetization ability of the magnet, the higher the value, the stronger the stored magnetic energy.

[0075] ΔBr*: difference in remanence at room temperature (T) relative to Example 1, negative values indicate performance degradation, used to quantify the impact of component / process changes.

[0076] Hcj (20℃) (kOe): coercivity at room temperature, unit kilo- Oersted (kOe), the higher the value, the stronger the anti-demagnetization ability.

[0077] Br (250℃) (T): remanence at 250℃, directly reflects the high-temperature working stability.

[0078] Br retention rate (%): (Br(250℃) / Br(20℃))x100%, measures the ability to retain magnetic properties at high temperatures, >85% is an industry breakthrough indicator.

[0079] The results are shown in Table 3 and Figure 1 , Figure 2 .

[0080]

[0081] From the data in Table 3, the following conclusions can be drawn:

[0082] 1) Core role of Lutetium (Lu): The Br retention rate of Comparison 1 (without LuF3) is only 81.05%, which is 8% lower than that of Example 1 (89.05%), proving that the fluorine ions produced by the decomposition of LuF3 can significantly inhibit high-temperature grain boundary oxidation. When the Lu content is reduced to 0.1 parts (Example 2), the Br retention rate is still 87.85%, indicating that Lu is still effective at low addition levels.

[0083] 2) Molybdenum / Niobium Synergistic Mechanism: The Hcj(20℃) of Comparison 2 (without Mo) dropped to 20.87 kOe (Example 1 was 26.52 kOe), possibly due to the formation of coarse NbFe2 phases by excessive niobium, which disrupts the magnetic domain; after adjusting the Mo / Nb ratio in Example 4, the Hcj(20℃) dropped to 24.93 kOe.

[0084] 3) Sintering aids are not replaceable: Comparison 3 (Al2O3 / Zn replaces Ga2O3 / Cu) has a Br(20℃) as low as 1.382T, and a density of only 7.28 g / cm 3 , due to the pores generated by the volatilization of zinc, resulting in a sharp increase in high-temperature magnetic flux loss to 15.67% (Example 1 is only 3.21%, see Table 4 below).

[0085] Test Example 2

[0086] High temperature aging stability

[0087] 1. Test purpose:

[0088] Verify the magnetic flux attenuation rate of the material under long-term high-temperature service and solve the irreversible loss problem caused by the "difference in coercive force temperature coefficient".

[0089] 2. Test method:

[0090] Reference magnetic flux Φ0:

[0091] Measured with HT-100 fluxmeter at 25°C (probe accuracy ±0.2%)

[0092] Aging conditions:

[0093] 250℃ aging: vacuum quartz tube packaging (oxygen content <10ppm)

[0094] Loss calculation:

[0095]

[0096] The results are shown in Table 4 and Figure 3 、 Figure 4 .

[0097]

[0098] From the data in Table 4, we can see the high temperature aging stability law:

[0099] The double-defect group (Comparative 4) showed a magnetic flux loss of 18.34% after aging at 250°C for 500 hours, far exceeding the 3.21% of Example 1. The density dropped to 7.21 g / cm 3 (Example 1 is 7.61 g / cm 3 ).

[0100] Application Example 1

[0101] Applied to automobile drive motor rotor

[0102] Test platform: 150kW permanent magnet synchronous motor test bench

[0103] Working conditions: Peak power 220℃ continuous operation, coolant temperature 105℃

[0104] The results are shown in Table 5

[0105]

[0106] High temperature remanence stability:

[0107] The remanence of the magnet in Example 1 is maintained at 1.35T, which is 10.7% higher than that of the commercial N35SH magnet (1.22T), completely solving the magnetic decay problem under peak load.

[0108] Torque output quality:

[0109] The output torque fluctuation rate is only 2.8% (8.3% for traditional magnets), indicating excellent magnetic domain stability at high temperatures and significantly reduced motor vibration and noise.

[0110] Long-term reliability:

[0111] After 1000 hours of continuous operation, the power attenuation is <0.5% (traditional magnets are >3.2%), verifying the material's breakthrough durability under extreme working conditions.

[0112] Conclusion: The magnet of the present invention meets the core requirements of electric vehicle drive motors for high temperature, high power density and low vibration.

[0113] Application Example 2

[0114] Corrosion-resistant magnet unit

[0115] Surface treatment: plasma electrolytic oxidation (electrolyte: NaAlO2 8g / L + Zr(NO3)45g / L)

[0116] Voltage 350V, time 30min, generate Al2O3-ZrO2 composite layer (thickness 28±3μm)

[0117] Salt spray test: 5% NaCl solution, spray at 35±1℃, and place the sample at a 45° tilt.

[0118] The results are shown in Table 6

[0119]

[0120] Al2O3-ZrO2 composite coating (28±3μm) was generated by plasma electrolytic oxidation. Salt spray test showed that:

[0121] 1) Anti-corrosion performance:

[0122] The coated magnet has no visible corrosion spots after 500 hours, and the rust area of ​​the uncoated magnet is greater than 35%;

[0123] 2) Magnetic performance protection:

[0124] After 1000 hours of salt spray, the magnetic flux loss of the coated magnet is only 0.42% (uncoated magnet loses 8.7%), proving that the coating effectively blocks Cl - Erosion of grain boundaries;

[0125] 3) Industrial applicability:

[0126] The electrolyte formula (NaAlO2+Zr(NO3)4) and voltage / time parameters (350V×30min) are feasible for mass production, with a cost increase of less than 5%.

[0127] Conclusion: This technology makes magnets suitable for harsh environments such as marine oil and gas equipment, humidity and high temperature, and their service life is increased by more than 10 times.

[0128] Based on the above embodiments, it can be summarized as follows:

[0129] 1. Breakthrough improvement in high-temperature magnetic properties:

[0130] By introducing LuF3 nanopowder (0.1-0.5 parts), the high-temperature remanence retention is increased from <80% of traditional materials to >87% (measured at 1.32T at 250°C). At the same time, the enhanced effect of Lu's 4f electron spin polarization optimizes the coercive force temperature coefficient to -0.28% / °C (Example 1).

[0131] The synergistic addition of Mo / Nb (Mo 0.3-1 parts / Nb 0.5-2 parts, molar ratio 1:1.2-1.8) suppresses magnetic moment reversal, reducing the magnetic flux loss rate at 200℃×1000h to as low as 1.82% (compared to traditional materials >7.9%).

[0132] 2. Process innovation ensures performance stability

[0133] Sintering in an Ar / H2 mixed atmosphere (H2 accounts for 5-10%) combined with a two-stage heat treatment (900℃ rapid cooling + 500℃ slow cooling) eliminates internal stress, and the magnet density reaches 7.61 g / cm 3 (close to the theoretical value of 98.5%);

[0134] At the same time, liquid nitrogen cryogenic treatment (-196℃×1h) can improve the performance of alloy ingots and increase the subsequent hydrogen crushing efficiency by 40%.

[0135] 3. Significantly optimized application performance:

[0136] Automotive drive motor rotor: Under high-temperature conditions of 220°C, the residual magnetism is maintained at 1.35T (commercial N35SH is only 1.22T), the torque fluctuation rate is reduced to 2.8% (conventional >8%), and the power attenuation is <0.5% after 1000h.

[0137] Corrosion-resistant magnet unit: The Al2O3-ZrO2 plasma electrolytic oxidation coating (28μm) shows no rust after 1000 hours of salt spray testing, and the magnetic flux loss is only 0.42% (uncoated magnets >8.7%), meeting the requirements of extreme environments such as marine oil and gas equipment.

[0138] 4. Cost and environmental advantages:

[0139] LuF3 replaces 30% heavy rare earth Dy (4-7 parts of Dy, only 0.1-0.5 parts of LuF3), the material cost is reduced by 40%;

[0140] The sintering temperature is reduced to 1080-1120℃ (traditional 1150℃), the energy consumption is reduced by 15%, and the H2 reducing atmosphere reduces heavy metal oxide emissions.

[0141] The above are only a few preferred embodiments of the present application, which are described in more detail and in more detail, but cannot be construed as limiting the scope of the patent of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of protection of the present application.

Claims

1. A high temperature resistant and high remanence rare earth permanent magnet material, characterized in that: It is composed of the following raw materials in parts by weight: Main rare earth phase: neodymium Nd 24–34 parts, dysprosium Dy 4–7 parts, lutetium Lu 0.1–0.5 parts; High melting point strengthener: niobium powder Nb 0.5–2 parts, molybdenum powder Mo 0.3–1 parts; Matrix phase: iron Fe 58–68 parts, boron B 0.9–1.3 parts; Sintering aids: gallium oxide Ga2O3 0.2–0.8 parts, copper powder Cu 0.1–0.6 parts; The lutetium Lu is added in the form of lutetium fluoride LuF3 nanopowder with a particle size of ≤500 nm; The particle sizes of the molybdenum powder and the niobium powder are both ≤2 μm; The preparation process of the above permanent magnetic material comprises the following steps: (a) Fe, Nd, Dy, and B are melted into alloy ingots under argon protection; (b) LuF3, Nb, Mo, Ga2O3, and Cu are added to the alloy ingot and secondary smelting is performed in a vacuum induction furnace; (c) Hydrogen crushing to 200–400 μm, followed by jet milling to 1.8–3.2 μm; (d) Pressing in a magnetic field of 2.0–2.8 T and a pressure of 180–280 MPa; (e) Sintering in sections under a protective gas atmosphere, introducing an argon-hydrogen mixture during sintering.

2. The permanent magnetic material according to claim 1, characterized in that Step (b) After the secondary smelting, cryogenic treatment is added: the alloy ingot is immersed in liquid nitrogen for 1 hour and then returned to room temperature.

3. The permanent magnetic material according to claim 1, characterized in that In step (e), the argon-hydrogen mixture has a volume ratio of Ar:H2 = 95:5 and a flow rate of 20–50 mL / min; The staged sintering of step (e) comprises: Step heating: 400℃×1h → 800℃×1h → (1080–1120℃)×4h; Slow cooling stage: cool to 200℃ at 0.3-0.8℃ / min and then air cool.

4. The use of the permanent magnetic material according to any one of claims 1 to 3 in a high-temperature motor pole, characterized in that: In an environment of 220℃: remanence Br ≥1.35T, coercive force Hcj ≥18 kOe.

5. A corrosion-resistant magnet unit based on the permanent magnetic material according to any one of claims 1 to 3, characterized in that: An Al2O3-ZrO2 composite ceramic layer with a thickness of 15–40 μm is generated on the magnet surface by plasma electrolytic oxidation.

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