A terbium-free sintered neodymium-iron-boron permanent magnet and a method for producing the same

Abstract

The application provides a terbium-free sintered neodymium-iron-boron permanent magnet and a preparation method thereof, and belongs to the technical field of permanent magnets.The terbium-free sintered neodymium-iron-boron permanent magnet is obtained by mixing a base alloy cast piece with a specific composition, a dysprosium alloy cast piece with a specific composition and dysprosium oxide, and sequentially performing hydrogen crushing, airflow milling, orientation forming, sintering and tempering treatment.The dysprosium alloy cast piece and the dysprosium oxide are used as auxiliary alloys, the microstructure of the base alloy cast piece can be controlled through the hydrogen crushing process, the airflow milling process and the sintering process and the tempering treatment process, and finally, the terbium-free high-performance neodymium-iron-boron permanent magnet is prepared, the scarce rare earth resource terbium is saved to a certain extent, the production cost is reduced, and the balanced utilization of the rare earth resource is promoted.

Description

Technical Field

[0001] This invention relates to the field of high-performance permanent magnet technology, specifically to a terbium-free sintered NdFeB permanent magnet and its preparation method. Background Technology

[0002] Existing sintered NdFeB permanent magnets that meet the ultra-high performance (Hcj > 30) requirements in GB / T13560-2017 typically require the addition of large amounts of heavy rare earth terbium to improve coercivity. Terbium is expensive, approximately six times the price of dysprosium, resulting in high production costs for ultra-high performance sintered NdFeB permanent magnets. Although utilizing existing grain boundary diffusion technology to prepare sintered NdFeB permanent magnets can reduce terbium usage to some extent, it is still unavoidable, which is detrimental to the protection of terbium and other heavy rare earth elements. In the context of sustainable resource development, the development of terbium-free ultra-high performance sintered NdFeB permanent magnets is of great significance. Summary of the Invention

[0003] The purpose of this invention is to provide a terbium-free sintered NdFeB permanent magnet and its preparation method. The terbium-free sintered NdFeB permanent magnet prepared by the method of this invention avoids the use of expensive heavy rare earth terbium resources and can meet the ultra-high performance requirements in GB / T13560-2017.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0005] This invention provides a method for preparing terbium-free sintered NdFeB permanent magnets, comprising the following steps:

[0006] A base alloy casting is provided, wherein the base alloy casting comprises, by mass fraction: M 1 24.5-25%, M 2 1.2-2%, Dy 5-6%, B 0.88-0.92%, balance Fe; the M 1 For Pr and Nd; the M 2 It is Ti and Co, or Ti, Co and M 3 The M 3 It is one or more of Cu, Ga, Zr and V;

[0007] A dysprosium alloy casting is provided, wherein the composition of the dysprosium alloy casting, by mass fraction, comprises: M 4 32-42%, Co 2-4%, B 0.6-0.8%, Ti 0.1-0.2%, balance Fe; the M 4 For Nd and Dy, the M 4 The mass ratio of Nd to Dy is (1-X):X, where X is 0.6 to 0.9;

[0008] The base alloy casting, dysprosium alloy casting, and dysprosium oxide are mixed and then subjected to hydrogen crushing, air jet milling, orientation forming, sintering, and tempering treatments in sequence to obtain terbium-free sintered NdFeB permanent magnets.

[0009] Preferably, the M 1 The mass ratio of Pr to Nd in the medium is (65-70):(30-35).

[0010] Preferably, the M 2 The mass ratio of Ti to Co is (0.1–0.3):(1.0–1.8).

[0011] Preferably, the mass ratio of the dysprosium alloy casting to dysprosium oxide is (27-30):1, and the total mass of the dysprosium alloy casting and dysprosium oxide is 6-10% of the mass of the base alloy casting.

[0012] Preferably, the hydrogen crushing includes sequential hydrogen absorption and dehydrogenation treatments; the temperature of the hydrogen absorption treatment is 315–325°C, and the holding time is 40–50 min; the temperature of the dehydrogenation treatment is 615–625°C, and the holding time is 4–6 h.

[0013] Preferably, the air jet milling is carried out in the presence of a lubricant, the mass of which is 1.5 to 2.5‰ of the mass of the coarse powder obtained after hydrogen crushing; the grinding pressure of the air jet milling is 5.9 to 6.1 MPa, and the powder output speed is 145 to 155 kg / h; the particle size d50 of the fine powder obtained after air jet milling is 2.5 to 3 μm.

[0014] Preferably, the orientation forming is carried out under conditions of magnetic induction intensity of 1.3–1.5T and forming pressure of 3–6 MPa; the density of the green body obtained after orientation forming is 3.85–3.95 g / cm³. 3 .

[0015] Preferably, the sintering operating conditions include: vacuum degree < 5.5 × 10⁻⁶. -3 Pa, temperature 1077~1080℃, heat preservation time 4~6h.

[0016] Preferably, the tempering process includes a first tempering process, a second tempering process, and a third tempering process performed sequentially;

[0017] The conditions for the first tempering treatment include: vacuum degree < 8 × 10⁻⁶ -3 Pa, temperature 800~850℃, heat preservation time 2~3h;

[0018] The conditions for the second tempering treatment include: vacuum degree < 5 × 10⁻⁶ -3 Pa, temperature 890~920℃, heat preservation time 4~5h;

[0019] The conditions for the third tempering process include: vacuum degree < 5.5 × 10⁻⁶. -3 Pa, temperature 490~520℃, heat preservation time 5~7h.

[0020] The present invention provides a terbium-free sintered NdFeB permanent magnet prepared by the preparation method described in the above technical solution.

[0021] This invention provides a method for preparing terbium-free sintered NdFeB permanent magnets, comprising the following steps: providing a basic alloy casting, wherein the basic alloy casting comprises, by mass fraction: M 1 24.5-25%, M 2 1.2-2%, Dy 5-6%, B 0.88-0.92%, balance Fe; the M 1 For Pr and Nd; the M 2 It is Ti and Co, or Ti, Co and M 3 The M 3 The alloy is one or more of Cu, Ga, Zr, and V; a dysprosium alloy casting is provided, wherein the composition of the dysprosium alloy casting comprises, by mass fraction: M 4 32-42%, Co 2-4%, B 0.6-0.8%, Ti 0.1-0.2%, balance Fe; the M 4 For Nd and Dy, the M 4 The mass ratio of Nd to Dy is (1-X):X, where X is 0.6-0.9. The base alloy casting, dysprosium alloy casting, and dysprosium oxide are mixed and sequentially subjected to hydrogen crushing, air jet milling, orientation forming, sintering, and tempering to obtain a terbium-free sintered NdFeB permanent magnet. In this invention, the use of Ti in the base alloy casting is beneficial for grain refinement and improved temperature stability. This invention uses dysprosium alloy casting and dysprosium oxide as auxiliary alloys. The microstructure of the base alloy casting can be controlled through the hydrogen crushing, air jet milling, sintering, and tempering processes to finally prepare a terbium-free, high-performance NdFeB permanent magnet. Under the test conditions of the example, its remanence is 13.2 kGs and its coercivity is 32 kOe. Furthermore, the method provided by this invention is suitable for mass production, has good product stability, and can meet the market demand for high-end industrial permanent magnet products. It is especially suitable for use environments with high requirements for temperature stability. More importantly, it saves scarce rare earth resources such as terbium to a certain extent, reduces production costs, and promotes the balanced utilization of rare earth resources. Detailed Implementation

[0022] This invention provides a method for preparing terbium-free sintered NdFeB permanent magnets, comprising the following steps:

[0023] A base alloy casting is provided, wherein the base alloy casting comprises, by mass fraction: M 1 24.5-25%, M 2 1.2-2%, Dy 5-6%, B 0.88-0.92%, balance Fe; the M 1 For Pr and Nd; the M 2 It is Ti and Co, or Ti, Co and M 3 The M 3 It is one or more of Cu, Ga, Zr and V;

[0024] A dysprosium alloy casting is provided, wherein the composition of the dysprosium alloy casting, by mass fraction, comprises: M 4 32-42%, Co 2-4%, B 0.6-0.8%, Ti 0.1-0.2%, balance Fe; the M 4 For Nd and Dy, the M 4 The mass ratio of Nd to Dy is (1-X):X, where X is 0.6 to 0.9;

[0025] The base alloy casting, dysprosium alloy casting, and dysprosium oxide are mixed and then subjected to hydrogen crushing, air jet milling, orientation forming, sintering, and tempering treatments in sequence to obtain terbium-free sintered NdFeB permanent magnets.

[0026] This invention provides a basic alloy casting, wherein the basic alloy casting comprises, by mass fraction: M 1 24.5-25%, M 2 1.2-2%, Dy 5-6%, B 0.88-0.92%, balance Fe; preferably including: M 1 24.5%–24.8%, M 2 1.3–1.65%, Dy 5–5.5%, B 0.89–0.9%, balance Fe; specifically, M 1 24.5%, M 2 1.3%, Dy 5%, B 0.9%, balance Fe; or it can be M 1 24.5%, M 2 1.65%, Dy 5%, B 0.9%, balance Fe. In this invention, the M 1 For Pr and Nd, the M 1 The preferred mass ratio of Pr to Nd is (65-70):(30-35), more preferably 70:30. In this invention, the M... 2 It is Ti and Co, or Ti, Co and M 3 The M 3The component is one or more of Cu, Ga, Zr, and V, specifically Ga, or Cu, Ga, and Zr. The preferred mass ratio of Cu, Ga, and Zr is (0.08–0.12):(0.28–0.32):(0.13–0.17), more preferably 0.1:0.3:0.15; the M... 2 The preferred mass ratio of Ti to Co is (0.1–0.3):(1.0–1.8), more preferably (0.1–0.15):1. In this invention, when the M 2 Contains M 3 At that time, the M 2 M 3 The content of [agent] is preferably 10-35 wt%, more preferably 11.5-33.3 wt%. The present invention preferably obtains a basic alloy material according to the composition of the basic alloy casting, and then rapidly solidifies the basic alloy material to obtain the basic alloy casting. In the present invention, the conditions for preparing the rapid solidification casting of the basic alloy casting preferably include: refining the basic alloy material at 1460-1500℃ for 5-10 min, then cooling it to 1405-1415℃ at a rate of 8-12℃ / min, holding it at that temperature for 5-10 min, and then casting; wherein, the refining temperature is further preferably 1480℃, the refining time is further preferably 8 min, the casting temperature is further preferably 1410℃, and the holding time before casting is further preferably 8 min; the copper roller speed is preferably 37-43 rpm, more preferably 40 rpm; the thickness of the basic alloy casting is preferably 2-3 mm.

[0027] This invention provides a dysprosium alloy casting, wherein the composition of the dysprosium alloy casting, by mass fraction, comprises: M 4 32-42%, Co 2-4%, B 0.6-0.8%, Ti 0.1-0.2%, balance Fe; preferably including: M 4 38.5%, Co 3%, B 0.6%, Ti 0.1%, balance Fe. In this invention, the M... 4 For Nd and Dy, the M 4The mass ratio of Nd to Dy is (1-X):X, where X is 0.6-0.9, preferably 0.6-0.7. Preferably, the dysprosium alloy material is prepared according to the composition of the dysprosium alloy casting, and the dysprosium alloy material is rapidly solidified and cast to obtain the dysprosium alloy casting. In this invention, the conditions for preparing the rapidly solidified dysprosium alloy casting preferably include: refining the dysprosium alloy material at 1480-1530℃ for 5-10 min, then cooling it to 1420-1440℃ at a rate of 8-12℃ / min, holding it at that temperature for 5-10 min, and then casting; wherein, the refining temperature is further preferably 1510℃, the refining time is further preferably 8 min, the casting temperature is further preferably 1430℃, and the holding time before casting is further preferably 8 min; the copper roller speed is preferably 37-43 rpm, more preferably 40 rpm; the thickness of the dysprosium alloy casting is preferably 2-3 mm.

[0028] After obtaining the base alloy casting and the dysprosium alloy casting, the present invention mixes the base alloy casting, the dysprosium alloy casting, and dysprosium oxide, and sequentially performs hydrogen crushing, air jet milling, orientation forming, sintering, and tempering treatments to obtain a terbium-free sintered NdFeB permanent magnet. In the present invention, the dysprosium oxide is preferably dysprosium oxide powder, and the average particle size of the dysprosium oxide powder is preferably 20-50 μm, more preferably 30-40 μm. In the present invention, the mass ratio of the dysprosium alloy casting to dysprosium oxide is preferably (27-30):1, more preferably (29-30):1, and the total mass of the dysprosium alloy casting and dysprosium oxide is preferably 6-10% of the mass of the base alloy casting, more preferably 6-8%.

[0029] This invention involves mixing the aforementioned basic alloy casting, dysprosium alloy casting, and dysprosium oxide, followed by hydrogen crushing to obtain coarse powder. In this invention, the hydrogen crushing preferably includes sequential hydrogen absorption and dehydrogenation treatments; the temperature of the hydrogen absorption treatment is preferably 315–325°C, more preferably 318–320°C, and the holding time is preferably 40–50 min, more preferably 43–45 min; the temperature of the dehydrogenation treatment is preferably 615–625°C, more preferably 618–620°C, and the holding time is preferably 4–6 h, more preferably 4.5–5 h. After the dehydrogenation treatment, this invention preferably cools to room temperature to obtain coarse powder. This invention does not have a specific limitation on the particle size of the coarse powder.

[0030] After obtaining coarse powder, the present invention further processes the coarse powder into fine powder by air jet milling. In this invention, the air jet milling is preferably carried out in the presence of a lubricant, preferably a grease-based lubricant, and the mass of the lubricant is preferably 1.5–2.5‰ of the mass of the coarse powder, more preferably 1.8–2‰. The grinding pressure of the air jet milling is preferably 5.9–6.1 MPa, more preferably 6 MPa, and the powder output speed is preferably 145–155 kg / h, more preferably 145–150 kg / h. In this invention, the particle size d50 of the fine powder is preferably 2.5–3 μm, more preferably 2.8 μm.

[0031] After obtaining the fine powder, the present invention performs orientation molding on the fine powder to obtain a green body. In the present invention, the orientation molding is preferably carried out under conditions of a magnetic induction intensity of 1.3–1.5T and a molding pressure of 3–6 MPa, the magnetic induction intensity is further preferably 1.4T, and the molding pressure is further preferably 4–6 MPa. In the present invention, the density of the green body is preferably 3.85–3.95 g / cm³. 3 More preferably 3.9 g / cm³ 3 In an embodiment of the present invention, the orientation forming is specifically performed in a magnetic field press.

[0032] After obtaining the green blank, the present invention sintersulates the green blank to obtain the sintered material. In the present invention, the sintering conditions preferably include: a vacuum degree preferably <5.5 × 10⁻⁶. -3 Pa, more preferably 5 × 10 Pa -3 Pa; the preferred temperature is 1077–1080℃, more preferably 1079–1080℃; the preferred holding time is 4–6 h, more preferably 4.5–5 h. In this invention, the heating rate from room temperature to the required sintering temperature is preferably 4–6℃ / min, more preferably 5℃ / min. In this invention, after the holding period during sintering is completed, the temperature is preferably reduced to 80–90℃ at a rate of 4–6℃ / min to obtain the sintered material; more preferably, it is reduced to 90℃ at a rate of 5℃ / min to obtain the sintered material. In an embodiment of this invention, the sintering is specifically carried out in a sintering furnace.

[0033] After obtaining the sintered material, the present invention performs a tempering treatment on the sintered material to obtain a terbium-free sintered NdFeB permanent magnet. In the present invention, the tempering treatment preferably includes a first tempering treatment, a second tempering treatment, and a third tempering treatment performed sequentially. In the present invention, the conditions for the first tempering treatment preferably include: a vacuum degree preferably <8×10⁻⁶. -3 Pa, more preferably 6 × 10 Pa -3Pa; the temperature is preferably 800-850℃, more preferably 810-820℃; the holding time is preferably 2-2.5h, more preferably 2h. In this invention, the heating rate to the temperature required for the first tempering treatment is preferably 7-9℃ / min, more preferably 8℃ / min; after the holding time in the first tempering treatment is completed, it is preferably cooled to 80-90℃, preferably 90℃, by vacuum self-cooling, and then the second tempering treatment is performed. In this invention, the conditions for the second tempering treatment preferably include: vacuum degree <5×10 -3 Pa, more preferably 4.5 × 10 Pa -3 Pa; the temperature is preferably 890–920℃, more preferably 895–900℃; the holding time is preferably 4–4.5 h, more preferably 4 h. In this invention, the heating rate to the temperature required for the second tempering treatment is preferably 5–7℃ / min, more preferably 6℃ / min; after the holding time in the second tempering treatment is completed, it is preferably cooled to 80–90℃, preferably 90℃, by vacuum self-cooling, and then the third tempering treatment is performed. In this invention, the conditions for the third tempering treatment preferably include: the vacuum degree is preferably <5.5 × 10⁻⁶. -3 Pa, more preferably 4.5 × 10 Pa -3 Pa; the temperature is preferably 490–520℃, more preferably 510–500℃; the holding time is preferably 5–7h, more preferably 5.5–6h. In this invention, the heating rate to the temperature required for the third tempering treatment is preferably 3–5℃ / min, more preferably 4℃ / min; after the holding time in the third tempering treatment is completed, it is preferably cooled to below 40℃ by continuous air cooling with argon gas to obtain terbium-free sintered NdFeB permanent magnets.

[0034] The method provided by this invention can prepare high-performance sintered NdFeB permanent magnets without consuming heavy rare earth terbium, which promotes the balanced utilization of light and heavy rare earth resources, saves production costs, and broadens the application conditions of the product in high-end fields.

[0035] The present invention provides a terbium-free sintered NdFeB permanent magnet prepared by the preparation method described in the above technical solution.

[0036] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0037] Example 1

[0038] The ingredients were formulated and proportioned according to the design. The basic alloy material, by mass fraction, consisted of: 24.5% praseodymium and neodymium (Pr to Nd mass ratio 7:3), 5% Dy, 1% Co, 0.15% Ga, 0.15% Ti, 0.9% B, with the balance being Fe. The basic alloy material was then rapidly solidified and cast to obtain a basic alloy sheet with a thickness of 2–3 mm. The rapid solidification casting conditions included: refining the basic alloy material at 1480℃ for 8 minutes, then cooling it to 1410℃ at a rate of 10℃ / min, holding it at that temperature for 8 minutes, and then casting. The copper roller rotation speed was 40 rpm.

[0039] According to the formula design, the ingredients are prepared, and the composition of the dysprosium alloy material by mass fraction is as follows: Nd:Dy content is 38.5% (of which, the mass ratio of Nd to Dy is 0.4:0.6), Co content is 3%, B content is 0.6%, Ti content is 0.1%, and the balance is Fe. The dysprosium alloy material is subjected to rapid solidification casting to obtain dysprosium alloy casting sheets with a thickness of 2-3 mm. The conditions for rapid solidification casting include: refining the dysprosium alloy material at 1510℃ for 8 min, then cooling it to 1430℃ at a rate of 10℃ / min, holding it at that temperature for 8 min, and then casting; the copper roller speed is 40 rpm.

[0040] The dysprosium alloy casting sheet was mixed with dysprosium oxide powder with an average particle size of 30 μm at a mass ratio of 30:1 to obtain an auxiliary alloy; the base alloy casting sheet was mixed with the auxiliary alloy, wherein the auxiliary alloy accounted for 6% of the mass of the base alloy casting sheet; the resulting mixed raw material was subjected to hydrogen absorption treatment at 320℃ for 45 min, and then subjected to dehydrogenation treatment at 620℃ for 5 h, and then cooled to room temperature (25℃) to obtain coarse powder;

[0041] The coarse powder is mixed with a grease lubricant, wherein the grease lubricant accounts for 2‰ of the mass of the coarse powder. The resulting mixture is then subjected to air jet milling to obtain fine powder. The grinding pressure of the air jet milling is 6 MPa, and the powder output speed is 150 kg / h. The particle size d50 of the fine powder is 2.8 μm.

[0042] The fine powder was placed in a magnetic field press and oriented under conditions of a magnetic induction intensity of 1.4T and a molding pressure of 6MPa to obtain a density of 3.9 g / cm³. 3 raw blanks;

[0043] The green blank was placed in a sintering furnace and heated from room temperature to 1080°C at a rate of 5°C / min, while maintaining a vacuum of 4.5 × 10⁻⁶. -3Sintering was carried out under Pa conditions for 5 hours, followed by cooling to 90°C at a rate of 5.5°C / min to obtain the sintered material; then the temperature was increased to 820°C at a rate of 8°C / min, and sintered under a vacuum of 6×10⁻⁶. -3 The first tempering treatment was carried out under Pa conditions for 2 hours, followed by cooling to 90°C under vacuum self-cooling. Then, the temperature was increased to 900°C at a rate of 6°C / min, and the temperature was maintained at 900°C with a vacuum degree of 4.5 × 10⁻⁶. -3 The second tempering treatment was carried out under Pa conditions for 4 hours, followed by cooling to 90°C under vacuum self-cooling, and finally heated to 500°C at a rate of 4°C / min. The temperature was maintained at 500°C and the vacuum degree was 4.5 × 10⁻⁶. -3 The third tempering treatment was carried out under Pa conditions for 6 hours, and the temperature was cooled to below 40°C by continuous air cooling with argon gas to obtain terbium-free sintered NdFeB permanent magnets.

[0044] Three terbium-free sintered NdFeB permanent magnet samples were prepared repeatedly according to the method in Example 1, and then subjected to 20°C. The cylindrical test specifically measured the remanence (Br), coercivity (Hcb), intrinsic coercivity (Hcj), magnetic energy product ((BH)max), reverse magnetic field (Hk) at J=0.9Jr on the J-demagnetization curve of the magnet, and squareness (Hk / Hcj). The specific results are shown in Table 1. Table 1 shows that the terbium-free sintered NdFeB permanent magnet prepared using the method provided by this invention, after testing, has a remanence of 13.2 kGs and an intrinsic coercivity of 32 kOe. Furthermore, Table 1 shows that the terbium-free sintered NdFeB permanent magnet prepared using the method provided by this invention exhibits good product stability.

[0045] Table 1. Performance test results of three terbium-free sintered NdFeB permanent magnet samples in Example 1.

[0046]

[0047] Example 2

[0048] The ingredients were formulated and proportioned according to the design. The basic alloy material, by mass fraction, consisted of: 24.5% praseodymium and neodymium (Pr to Nd mass ratio 7:3), 5% Dy, 1% Co, 0.3% Ga, 0.15% Zr, 0.1% Ti, 0.1% Cu, 0.9% B, with the balance being Fe. The basic alloy material was then rapidly solidified and cast to obtain a basic alloy sheet with a thickness of 2–3 mm. The rapid solidification casting conditions included: refining the basic alloy material at 1480℃ for 8 minutes, then cooling it to 1410℃ at a rate of 10℃ / min, holding it at that temperature for 8 minutes, and then casting. The copper roller rotation speed was 40 rpm.

[0049] According to the formula design, the ingredients are prepared, and the composition of the dysprosium alloy material by mass fraction is as follows: Nd:Dy content is 38.5% (of which, the mass ratio of Nd to Dy is 0.4:0.6), Co content is 3%, B content is 0.6%, Ti content is 0.1%, and the balance is Fe. The dysprosium alloy material is subjected to rapid solidification casting to obtain dysprosium alloy casting sheets with a thickness of 2-3 mm. The conditions for rapid solidification casting include: refining the dysprosium alloy material at 1510℃ for 8 min, then cooling it to 1430℃ at a rate of 10℃ / min, holding it at that temperature for 8 min, and then casting; the copper roller speed is 40 rpm.

[0050] The dysprosium alloy casting sheet was mixed with dysprosium oxide powder with an average particle size of 30 μm at a mass ratio of 30:1 to obtain an auxiliary alloy; the base alloy casting sheet was mixed with the auxiliary alloy, wherein the auxiliary alloy accounted for 6% of the mass of the base alloy casting sheet; the resulting mixed raw material was subjected to hydrogen absorption treatment at 320℃ for 45 min, and then subjected to dehydrogenation treatment at 620℃ for 5 h, and then cooled to room temperature (25℃) to obtain coarse powder;

[0051] The coarse powder is mixed with a grease lubricant, wherein the grease lubricant accounts for 2‰ of the mass of the coarse powder. The resulting mixture is then subjected to air jet milling to obtain fine powder. The grinding pressure of the air jet mill is 6 MPa, and the powder output speed is 145 kg / h. The particle size d50 of the fine powder is 2.8 μm.

[0052] The fine powder was placed in a magnetic field press and oriented under conditions of a magnetic induction intensity of 1.4T and a molding pressure of 6MPa to obtain a density of 3.9 g / cm³. 3 raw blanks;

[0053] The green blank was placed in a sintering furnace and heated from room temperature to 1077°C at a rate of 5°C / min, while maintaining a vacuum of 4.5 × 10⁻⁶. -3 Sintering was carried out under Pa conditions for 5 hours, followed by cooling to 90°C at a rate of 5.5°C / min to obtain the sintered material; then the temperature was increased to 810°C at a rate of 8°C / min, and sintered under a vacuum of 6×10⁻⁶. -3 The first tempering treatment was carried out under Pa conditions for 2 hours, followed by cooling to 90°C under vacuum self-cooling. Then, the temperature was increased to 895°C at a rate of 6°C / min, and the temperature was maintained at 895°C with a vacuum degree of 4.5 × 10⁻⁶. -3 The second tempering treatment was carried out under Pa conditions for 4 hours, followed by cooling to 90°C under vacuum self-cooling, and finally heated to 510°C at a rate of 4°C / min. The temperature was maintained at 510°C and the vacuum degree was 4.5 × 10⁻⁶. -3 The third tempering treatment was carried out under Pa conditions for 6 hours, and the temperature was cooled to below 40°C by continuous air cooling with argon gas to obtain terbium-free sintered NdFeB permanent magnets.

[0054] Three terbium-free sintered NdFeB permanent magnet samples were prepared repeatedly according to the method in Example 2, and then subjected to 20°C. The cylindrical test specifically measured the remanence (Br), coercivity (Hcb), intrinsic coercivity (Hcj), magnetic energy product ((BH)max), reverse magnetic field (Hk) at J=0.9Jr on the J-demagnetization curve of the magnet, and squareness (Hk / Hcj). The specific results are shown in Table 2. Table 2 shows that the terbium-free sintered NdFeB permanent magnet prepared using the method provided by this invention, after testing, has a remanence of 13.2 kGs and an intrinsic coercivity of 32 kOe. Furthermore, Table 2 shows that the terbium-free sintered NdFeB permanent magnet prepared using the method provided by this invention exhibits good product stability.

[0055] Table 2 shows the performance test results of three terbium-free sintered NdFeB permanent magnet samples in Example 2.

[0056]

[0057] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a terbium-free sintered NdFeB permanent magnet, comprising the following steps: A base alloy casting is provided, wherein the base alloy casting comprises, by mass fraction: M 1 24.5~25%, M 2 1.2~2%, Dy 5~6%, B 0.88~0.92%, balance Fe; the M 1 For Pr and Nd; the M 2 It is Ti and Co, or Ti, Co and M 3 The M 3 It is one or more of Cu, Ga, Zr and V; the thickness of the base alloy casting is 2~3 mm; A dysprosium alloy casting is provided, wherein the composition of the dysprosium alloy casting, by mass fraction, comprises: M 4 32-42%, Co 2-4%, B 0.6-0.8%, Ti 0.1-0.2%, balance Fe; the M 4 For Nd and Dy, the M 4 The mass ratio of Nd to Dy is (1-X):X, where X is 0.6~0.9; the thickness of the dysprosium alloy casting is 2~3mm; The base alloy casting, dysprosium alloy casting, and dysprosium oxide are mixed and then subjected to hydrogen crushing, air jet milling, orientation forming, sintering, and tempering treatments in sequence to obtain terbium-free sintered NdFeB permanent magnets. The mass ratio of the dysprosium alloy casting to dysprosium oxide is (27~30):1, and the total mass of the dysprosium alloy casting and dysprosium oxide is 6~10% of the mass of the base alloy casting.

2. The preparation method according to claim 1, characterized in that, The M 1 The mass ratio of Pr to Nd in the medium is (65~70):(30~35).

3. The preparation method according to claim 1, characterized in that, The M 2 The mass ratio of Ti to Co is (0.1~0.3):(1.0~1.8).

4. The preparation method according to claim 1, characterized in that, The hydrogen decomposition process includes sequential hydrogen absorption and dehydrogenation treatments; the temperature of the hydrogen absorption treatment is 315~325℃, and the holding time is 40~50min; the temperature of the dehydrogenation treatment is 615~625℃, and the holding time is 4~6h.

5. The preparation method according to claim 1 or 4, characterized in that, The air jet milling is carried out in the presence of a lubricant, the mass of which is 1.5 to 2.5‰ of the mass of the coarse powder obtained after hydrogen crushing; the grinding pressure of the air jet milling is 5.9 to 6.1 MPa, and the powder output speed is 145 to 155 kg / h; the particle size d50 of the fine powder obtained after air jet milling is 2.5 to 3 μm.

6. The preparation method according to claim 1, characterized in that, The orientation forming is carried out under conditions of magnetic induction intensity of 1.3~1.5T and forming pressure of 3~6MPa; the density of the green body obtained after orientation forming is 3.85~3.95g / cm³. 3 .

7. The preparation method according to claim 1, characterized in that, The sintering conditions include: vacuum degree < 5.5 × 10⁻⁶. -3 Pa, temperature 1077~1080℃, heat preservation time 4~6h.

8. The preparation method according to claim 1 or 7, characterized in that, The tempering process includes a first tempering process, a second tempering process, and a third tempering process performed sequentially. The conditions for the first tempering treatment include: vacuum degree < 8 × 10⁻⁶ -3 Pa, temperature 800~850℃, heat preservation time 2~3h; The conditions for the second tempering treatment include: vacuum degree < 5 × 10⁻⁶ -3 Pa, temperature 890~920℃, heat preservation time 4~5h; The conditions for the third tempering process include: a vacuum degree of <5.5×10⁻⁶. -3 Pa, temperature 490~520℃, heat preservation time 5~7h.

9. Terbium-free sintered NdFeB permanent magnets prepared by the preparation method according to any one of claims 1 to 8.

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