Neodymium-iron-boron magnet material and method for producing same

Abstract

The application belongs to the technical field of rare earth permanent magnet materials, and particularly relates to a neodymium-iron-boron magnet material and a preparation method thereof. The magnet material is composed of PrNd 26.0-30.0%, B 0.88-0.98%, Co 0.25-0.45%, Zr 0.15-0.30%, Ga 0.15-0.30%, Al 0.05-0.15%, Cu 0.15-0.30%, Ca 0.05-0.25%, Sr 0.03-0.15%, Ba 0.02-0.10% and the balance of Fe. In the preparation, the main alloy is first smelted in a deficient amount and is powdered, the remaining components and alkaline earth metals are coated on the surface of the powder by evaporation, and then the magnet is obtained through forming, sintering and tempering. The application realizes high remanence, high coercivity, high squareness and excellent batch consistency without using heavy rare earths.

Description

Technical Field

[0001] This invention belongs to the field of rare earth permanent magnet materials technology, specifically relating to a neodymium iron boron magnet material and its preparation method. Background Technology

[0002] Since its introduction in the 1980s, neodymium iron boron (NdFeB) permanent magnet materials have rapidly become the dominant product in the field of permanent magnet materials due to their excellent magnetic properties, and are widely used in new energy vehicle drive motors, wind power generation, industrial servo systems, consumer electronics, and medical devices. With the rapid development of the new energy vehicle industry, the performance requirements of drive motors for permanent magnets are increasingly stringent. High remanence and energy product are needed to meet the high power density requirements of motors, as well as sufficiently high coercivity to ensure the motor's resistance to demagnetization under high-temperature conditions. Simultaneously, the magnets must possess high squareness to ensure the stability and consistency of motor operation. However, meeting all these performance requirements simultaneously in current technologies still faces numerous technical challenges.

[0003] To improve the coercivity of NdFeB magnets, the most common technique in the industry is to add heavy rare earth elements such as dysprosium and terbium. Heavy rare earth elements can significantly improve the anisotropic field of the magnet, thereby enhancing coercivity. However, the antiferromagnetic coupling between heavy rare earth elements and iron leads to a significant decrease in remanence and maximum energy product. More importantly, dysprosium and terbium are scarce globally, expensive, and highly volatile in price. Over-reliance on heavy rare earth elements not only significantly increases the manufacturing cost of magnets but also poses considerable risks to the supply chain. Therefore, developing high-performance NdFeB magnets with no or low levels of heavy rare earth elements has become a hot research topic in the industry.

[0004] Without adding heavy rare earth elements, researchers have attempted to improve coercivity and squareness by optimizing the main phase composition, adding various trace elements, and improving the preparation process. For example, they have improved the grain boundary structure by adding elements such as gallium, copper, aluminum, and zirconium; refined the grains using rapid solidification casting, hydrogen crushing, and air jet milling; and controlled the distribution of the grain boundary phase through multi-stage tempering heat treatment. However, these methods still have significant shortcomings in the existing technology. On the one hand, although the addition of conventional trace elements can improve magnetic properties to some extent, the improvement in coercivity is limited, usually failing to reach the level of Hcj≥1400kA / m, and squareness often decreases with the increase in coercivity, resulting in a seesaw effect of "high coercivity, low squareness" or "high squareness, low coercivity". On the other hand, the composition and distribution of the grain boundary phase in the existing preparation process are difficult to control precisely, leading to large fluctuations in product performance during mass production, especially in large-scale production, where the consistency of magnetic flux is difficult to guarantee.

[0005] In summary, achieving high remanence, high coercivity, high squareness, and excellent batch consistency simultaneously without the addition of heavy rare earth elements is a pressing technical challenge in the field of NdFeB magnet materials. Summary of the Invention

[0006] The purpose of this invention is to provide a neodymium iron boron magnet material and its preparation method, so as to solve the technical problems of existing non-heavy rare earth neodymium iron boron magnets that are difficult to achieve both high coercivity and high squareness, and have poor batch consistency, and to achieve the comprehensive performance goals of high remanence, high coercivity, high squareness and excellent batch consistency.

[0007] To achieve the above objectives, the present invention provides the following technical solution: The first aspect of the present invention provides a neodymium iron boron magnet material, which is composed of the following components in mass percentage: PrNd 26.0-30.0%, B 0.88-0.98%, Co 0.25-0.45%, Zr 0.15-0.30%, Ga 0.15-0.30%, Al 0.05-0.15%, Cu 0.15-0.30%, Ca 0.05-0.25%, Sr 0.03-0.15%, Ba 0.02-0.10%, and Fe balance.

[0008] Furthermore, the total content of Ca, Sr, and Ba is 0.2–0.4 wt%, and the ratio of the total mass of Ca, Sr, and Ba to the total mass of Ga and Cu is (0.5–1.0):1.

[0009] This invention incorporates three alkaline earth metals—calcium, strontium, and barium—into neodymium iron boron magnet materials. These three metals have extremely low solid solubility in iron and neodymium, and at the sintering and tempering temperatures of neodymium iron boron, they hardly enter the main Nd₂Fe phase. 14Instead of being a B-type lattice metal, it is repelled to the grain boundary region, forming low-melting-point compounds with the neodymium-rich phase at the grain boundary. When a single alkaline earth metal is added, its distribution at the grain boundary is often uneven, easily forming discontinuous island-like phases, with limited magnetic isolation effect on adjacent main phase grains. When calcium, strontium, and barium are added in combination, due to the differences in atomic radius and chemical activity of the three elements, they form segregated layers of different thicknesses during grain boundary solidification. This composite segregated structure makes the non-magnetic phase at the grain boundary more continuous and complete, thus more effectively cutting off the magnetic exchange coupling between the main phase grains and improving coercivity without adding heavy rare earth elements. At the same time, the compounds formed by calcium, strontium, and barium with iron are all paramagnetic or weakly magnetic, and will not form antiferromagnetic coupling with iron like heavy rare earth elements, so the loss of remanence is minimal. In addition, the combined addition of the three alkaline earth metals can lower the melting point of the neodymium-rich phase at the grain boundary, improve the fluidity during liquid phase sintering, and make the grain boundary thin layer more straight and uniform, which has a direct effect on improving the squareness of the demagnetization curve. When the total mass ratio of Ca, Sr, and Ba to Ga and Cu is controlled within the range of 0.5–1.0:1, the segregation of alkaline earth metals in the grain boundary region and the modification effect of Ga and Cu on the grain boundary phase achieve optimal synergy. Ga and Cu can lower the melting point of the neodymium-rich phase at the grain boundary and improve its wettability, while an appropriate amount of alkaline earth metals are uniformly distributed in this liquid phase, making the solidified non-magnetic phase at the grain boundary continuous, intact, and of moderate thickness.

[0010] A second aspect of this invention provides a method for preparing the aforementioned neodymium iron boron magnet material, comprising the following steps: (1) Preparation of main alloy: The main alloy is prepared by batching the materials according to the following proportions: 70-90% of PrNd content, 60-80% of Ga content, 60-80% of Cu content, and the full amount of B, Co, Zr, Al and Fe. After melting, the main alloy sheet is made by rapid solidification casting process. The main alloy sheet is then subjected to hydrogen crushing treatment and air jet milling to obtain main alloy powder. (2) Preparation of alloy for vapor deposition: The remaining PrNd, Cu, Ga and all of Ca, Sr and Ba from step (1) are melted in an inert atmosphere to form an alloy for vapor deposition, and the alloy for vapor deposition is made into a vapor deposition source material. (3) Vacuum vapor deposition coating: The main alloy powder obtained in step (1) is placed on the sample stage of the vacuum vapor deposition equipment, and the vapor deposition source material obtained in step (2) is placed in the evaporation source. The material is heated and evaporated under vacuum conditions, so that the vapor deposition source material is vaporized and deposited on the surface of the main alloy powder particles to form a coating layer. (4) Orientation forming: The main alloy powder coated with the vapor deposition alloy layer obtained in step (3) is pressed into shape in an orientation magnetic field to obtain a green blank; (5) Sintering: Vacuum sintering of the green blank to obtain sintered magnets; (6) Multi-stage tempering: The sintered magnet is subjected to multi-stage tempering to obtain neodymium iron boron magnet material.

[0011] Further, in step (1), the proportion of PrNd is 75-85% of the total PrNd content in the final magnet composition, the proportion of Ga is 65-75% of the total Ga content in the final magnet composition, and the proportion of Cu is 65-75% of the total Cu content in the final magnet composition.

[0012] Furthermore, in the rapid solidification casting process described in step (1), the linear speed of the copper roller is 1 to 5 m / s, and a main alloy sheet with a thickness of 0.2 to 0.5 mm is obtained.

[0013] Further, the hydrogen crushing treatment is as follows: hydrogen is absorbed at a hydrogen pressure of 0.1-0.3 MPa for 1-5 hours, and then dehydrogenated at 500-600℃ for 2-5 hours; the air jet milling is carried out under a protective atmosphere, and the particle size D50 of the main alloy powder is controlled to be 3.0-4.5 μm, and (D90-D10) / D50 ≤ 1.2, and the oxygen content ≤1200ppm.

[0014] In this invention, D10, D50, and D90 are all well-known and commonly used particle size characteristics in the field of rare earth permanent magnet powder and air jet milling. They conform to the national standard GB / T 19077 "Particle Size Analysis by Laser Diffraction" and the conventional laser particle size distribution definition in the NdFeB industry, and are all based on the cumulative distribution of particle volume. D10, D50, and D90 are characteristic particle sizes based on volumetric cumulative distribution: D10 is the particle size corresponding to a 10% volumetric cumulative distribution, D50 is the median particle size corresponding to a 50% volumetric cumulative distribution, and D90 is the particle size corresponding to a 90% volumetric cumulative distribution. (D90-D10) / D50 is the particle size distribution span, used to characterize the uniformity of powder particle size.

[0015] Further, in step (3), the sample stage rotates at a speed of 5–20 r / min, the evaporation time is 30–120 minutes, the evaporation source temperature is 800–1000℃, and the vacuum degree is ≤10. -2 Pa.

[0016] Further, the pressing and molding in the orientation magnetic field described in step (4) includes: pressing and molding in an orientation magnetic field of ≥1.8T, followed by cold isostatic pressing treatment, with a cold isostatic pressing pressure of 200-300MPa and a holding time of 5-15 minutes.

[0017] Furthermore, the vacuum sintering described in step (5) is divided into two stages: first, pre-firing at 1000-1050℃ for 1-3 hours, and then heating up to 1060-1090℃ for 3-6 hours.

[0018] Furthermore, the multi-stage tempering process described in step (6) includes: first holding at 850-950°C for 2-5 hours, and then holding at 450-550°C for 3-8 hours.

[0019] Calcium, strontium, and barium are easily oxidized and volatilized in their molten state at high temperatures, and they also react with crucible materials, leading to reduced yield and inaccurate composition control. This invention employs a step-by-step strategy: only elements other than calcium, strontium, and barium are melted in the main alloy, with praseodymium, neodymium, gallium, and copper added only in partial amounts. The remaining amounts, along with all calcium, strontium, and barium, are melted separately to form a low-melting-point alloy. This low-melting-point alloy is melted in an inert atmosphere. The presence of praseodymium, neodymium, copper, and gallium significantly lowers the alloy's liquidus temperature, and the activity of the alkaline earth metals decreases substantially after alloying, effectively suppressing volatilization losses during the melting process. Subsequently, this low-melting-point alloy is uniformly coated onto the surface of the main alloy powder particles using vacuum evaporation. During the subsequent sintering and heating process, the coating layer melts first to form a continuous liquid phase, which then permeates and diffuses along the grain boundaries. At this point, calcium, strontium, and barium, due to their extremely low solid solubility in the main phase lattice, are repelled to the grain boundaries and combine with neodymium-rich layers at the grain boundaries to form a continuous non-magnetic thin layer. Meanwhile, the added praseodymium-neodymium, copper, and gallium enter the grain boundaries to optimize their composition and structure. The process of this invention utilizes the liquid-phase sintering effect of low-melting-point alloys to significantly improve the continuity and uniformity of the non-magnetic phase at the grain boundaries, thereby achieving synergistic optimization of high coercivity, high squareness, and high remanence without adding heavy rare earth elements.

[0020] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: 1. This invention introduces three alkaline earth metals, calcium, strontium, and barium, into the formulation simultaneously. By utilizing their composite segregation effect in the grain boundary region, a continuous and complete non-magnetic grain boundary thin layer is formed, which effectively isolates the magnetic exchange coupling between the main phase grains, thereby increasing the squareness to over 96% and solving the problem of low squareness in existing heavy rare earth magnets.

[0021] 2. By adopting a process that combines step-by-step batching with vacuum evaporation coating, alkaline earth metals are uniformly deposited on the surface of magnetic powder particles in the form of low-melting-point alloys. This avoids the oxidation and volatilization of alkaline earth metals during the traditional smelting process, making the composition precise and controllable, while ensuring the consistency of magnetic flux in mass production.

[0022] 3. The entire technical solution does not rely on heavy rare earth elements, and the raw material cost is significantly lower than similar products that add dysprosium and terbium. Experiments show that the magnet produced by this invention has a remanence of no less than 1.42T, an intrinsic coercivity of no less than 1440kA / m, and a maximum energy product of no less than 400kJ / m. 3The squareness reaches 96.4%, and the standard deviation of magnetic flux of 4536 products is less than 0.02mWb, demonstrating excellent and stable overall performance. Attached Figure Description

[0023] Figure 1 The image shows the metallographic structure of the main alloy sheet obtained in step (1) of Example 1.

[0024] Figure 2 The image shows the demagnetization curve of the neodymium iron boron magnet material prepared in Example 1.

[0025] Figure 3 The image shows the demagnetization curve of the neodymium iron boron magnet material prepared in Example 2.

[0026] Figure 4 The demagnetization curve of the neodymium iron boron magnet material prepared in Comparative Example 1 is shown.

[0027] Figure 5 The demagnetization curve of the neodymium iron boron magnet material prepared in Comparative Example 2 is shown.

[0028] Figure 6 The demagnetization curve of the neodymium iron boron magnet material prepared in Comparative Example 3 is shown.

[0029] Figure 7 The demagnetization curve of the neodymium iron boron magnet material prepared in Comparative Example 4 is shown.

[0030] Figure 8 The demagnetization curve of the neodymium iron boron magnet material prepared in Comparative Example 5 is shown.

[0031] Figure 9 The demagnetization curve of the neodymium iron boron magnet material prepared in Comparative Example 6 is shown.

[0032] Figure 10 The demagnetization curve of the neodymium iron boron magnet material prepared in Comparative Example 7 is shown. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise specified, the raw materials used in the embodiments are all commercially available products.

[0034] Example 1 This embodiment provides a neodymium iron boron magnet material composed of the following components by mass percentage: 28.0% PrNd, 0.92% B, 0.35% Co, 0.22% Zr, 0.22% Ga, 0.10% Al, 0.22% Cu, 0.12% Ca, 0.08% Sr, 0.05% Ba, with the balance being Fe and unavoidable impurities.

[0035] The preparation method of the neodymium iron boron magnet material includes the following steps: (1) Preparation of the main alloy: The main alloy is prepared by batching the materials according to the following proportions: 80% (22.4 wt%) of PrNd, 65% (0.143 wt%) of Ga, 65% (0.143 wt%) of Cu, and the total amount of B, Co, Zr, Al, and Fe (B 0.92 wt%, Co 0.35 wt%, Zr 0.22 wt%, Al 0.10 wt%, Fe balance). The above raw materials are placed in a vacuum induction melting furnace and heated to 1000 wt% of the final magnet composition. -2 Melting was carried out under a vacuum of 1480°C for 20 minutes. The molten metal was then poured onto a rotating copper roller at a linear speed of 3.0 m / s to obtain an alloy sheet with a thickness of 0.30 mm.

[0036] Metallographic microstructure photographs of the obtained alloy thin sheets are as follows: Figure 1 As shown in the figure, 3.83 μm and 3.10 μm are the width dimensions of the columnar dendrite arms, and 294.09 μm is the overall thickness dimension of the alloy sheet. It can be seen from the figure that a uniform columnar crystal structure is formed inside the alloy, without coarse equiaxed crystals and α-Fe precipitates. The spacing between the columnar dendrite arms is about 3~4 μm, indicating that a high-quality casting sheet with uniform structure and fine grains has been obtained, which provides a good microstructure basis for the subsequent preparation of high-performance magnets.

[0037] The alloy sheet was placed in a hydrogen decompression furnace and evacuated to a vacuum level of ≤10. -1 After pressing with hydrogen to 0.20 MPa, the pressure was maintained for 3 hours to allow the alloy sheet to absorb hydrogen and become brittle. Then, the temperature was increased to 550 °C at 8 °C / min, and dehydrogenation was carried out under vacuum for 3 hours to obtain coarse powder. The coarse powder was then pulverized by an air jet mill under nitrogen protection, with a classifier speed of 4000 rpm and a pulverizing pressure of 0.7 MPa. The particle size D50 of the main alloy powder was controlled to be 3.8 μm, the particle size distribution (D90-D10) / D50 = 1.15, and the oxygen content was 1100 ppm to obtain the main alloy powder.

[0038] (2) Preparation of alloy for vapor deposition: The remaining PrNd (5.6wt%), Ga (0.077wt%), Cu (0.077wt%) from step (1) and all of Ca (0.12wt%), Sr (0.08wt%), Ba (0.05wt%) are melted in argon protection to form an alloy for vapor deposition. The melting temperature is 1300℃, and the temperature is held for 40 minutes. After casting into ingots, the ingots are crushed into particles with a particle size ≤5mm, which are used as the source material for vapor deposition.

[0039] (3) Vacuum Evaporation Coating: Place the main alloy powder obtained in step (1) on the sample stage of the vacuum evaporation equipment, and place the evaporation source material obtained in step (2) in the evaporation source. Evacuate to a vacuum degree of 5×10⁻⁶. -3 Pa uses electron beam evaporation with an evaporation source temperature of 850℃, a sample stage rotating at 10 r / min, and a evaporation time of 60 minutes to vaporize the evaporation source material and uniformly deposit it on the surface of the main alloy powder particles to form a coating layer.

[0040] (4) Orientation forming: The main alloy powder coated with the vapor deposition alloy layer obtained in step (3) is pressed into shape in an orientation magnetic field of 2.0T with a forming pressure of 20MPa to obtain a green blank. Then the green blank is subjected to cold isostatic pressing treatment with a cold isostatic pressing pressure of 250MPa and a holding time of 10 minutes.

[0041] (5) Sintering: Place the green body obtained in step (4) in a vacuum sintering furnace with a vacuum degree ≤10. -2 Pa, first heat to 1030℃ for pre-firing for 2 hours, then heat to 1075℃ for main firing for 4 hours. After sintering, cool rapidly to room temperature at a cooling rate of 250℃ / min to obtain sintered magnets.

[0042] (6) Multi-stage tempering: The sintered magnet obtained in step (5) is subjected to multi-stage tempering under vacuum conditions: first, it is kept at 900°C for 3 hours, then at 500°C for 5 hours, and then cooled to room temperature with the furnace to obtain neodymium iron boron magnet material.

[0043] Example 2 This embodiment provides a neodymium iron boron magnet material composed of the following components by mass percentage: 27.5% PrNd, 0.90% B, 0.40% Co, 0.25% Zr, 0.25% Ga, 0.12% Al, 0.25% Cu, 0.18% Ca, 0.10% Sr, 0.06% Ba, with the balance being Fe and unavoidable impurities.

[0044] The preparation method of the neodymium iron boron magnet material includes the following steps: (1) Preparation of the main alloy: The main alloy is prepared by batching the materials according to the following proportions: 85% (23.375 wt%) of PrNd, 70% (0.175 wt%) of Ga, 70% (0.175 wt%) of Cu, and the total amount of B, Co, Zr, Al, and Fe (B 0.90 wt%, Co 0.40 wt%, Zr 0.25 wt%, Al 0.12 wt%, Fe balance). The above raw materials are placed in a vacuum induction melting furnace and heated to 1000 ppm. -2 Melting was carried out under a vacuum of 1460℃ for 25 minutes. The molten metal was poured onto a rotating copper roller at a linear speed of 2.5 m / s to obtain an alloy sheet with a thickness of 0.35 mm. The alloy sheet was then placed in a hydrogen crushing furnace and evacuated to a vacuum of ≤10 Pa. -1 After pressing with hydrogen to 0.18 MPa, the pressure was maintained for 4 hours to allow the alloy sheet to absorb hydrogen and become brittle. Then, the temperature was increased to 530 °C at a rate of 6 °C / min, and dehydrogenation was carried out under vacuum for 4 hours to obtain coarse powder. The coarse powder was then pulverized by an air jet mill under nitrogen protection, with a classifier speed of 3500 rpm and a pulverizing pressure of 0.65 MPa. The particle size D50 of the main alloy powder was controlled to be 4.0 μm, the particle size distribution (D90-D10) / D50 = 1.18, and the oxygen content was 1050 ppm, thus obtaining the main alloy powder.

[0045] (2) Preparation of alloy for vapor deposition: The remaining PrNd (4.125wt%), Ga (0.075wt%), Cu (0.075wt%) from step (1) and all of Ca (0.18wt%), Sr (0.10wt%), Ba (0.06wt%) were melted in argon protection to form an alloy for vapor deposition. The melting temperature was 1280℃, and the temperature was held for 50 minutes. After casting into ingots, the ingots were crushed into particles with a particle size ≤5mm, which were used as the source material for vapor deposition.

[0046] (3) Vacuum Evaporation Coating: Place the main alloy powder obtained in step (1) on the sample stage of the vacuum evaporation equipment, and place the evaporation source material obtained in step (2) in the evaporation source. Evacuate to a vacuum degree of 3×10 -3 Pa was used for resistance heating evaporation. The evaporation source temperature was 820℃, the sample stage rotated at a speed of 15 r / min, and the evaporation time was 80 minutes. This allowed the evaporation source material to be vaporized and uniformly deposited on the surface of the main alloy powder particles to form a coating layer.

[0047] (4) Orientation forming: The main alloy powder coated with the vapor deposition alloy layer obtained in step (3) is pressed into shape in an orientation magnetic field of 1.9T with a forming pressure of 18MPa to obtain a green blank. Then the green blank is subjected to cold isostatic pressing treatment with a cold isostatic pressing pressure of 280MPa and a holding time of 8 minutes.

[0048] (5) Sintering: Place the green body obtained in step (4) in a vacuum sintering furnace with a vacuum degree ≤10. -2 Pa, first heat to 1040℃ for pre-firing for 2.5 hours, then heat to 1080℃ for main firing for 3.5 hours, and after sintering, rapidly cool to room temperature at a cooling rate of 280℃ / min to obtain sintered magnets.

[0049] (6) Multi-stage tempering: The sintered magnet obtained in step (5) is subjected to multi-stage tempering in an argon atmosphere. First, it is held at 910°C for 2.5 hours, then at 490°C for 6 hours, and then cooled to room temperature in the furnace to obtain neodymium iron boron magnet material.

[0050] Comparative Example 1 The difference between this comparative example and Example 1 is that the NdFeB magnet material in this comparative example is composed of the following components by mass percentage: PrNd 28.0%, B 0.92%, Co 0.35%, Zr 0.22%, Ga 0.22%, Al 0.10%, Cu 0.22%, Sr 0.08%, Ba 0.05%, with the balance being Fe and unavoidable impurities. That is, Ca is not added. The preparation method is the same as in Example 1, except that Ca is not added in step (2).

[0051] Comparative Example 2 The difference between this comparative example and Example 1 is that the NdFeB magnet material in this comparative example is composed of the following components by mass percentage: PrNd 28.0%, B 0.92%, Co 0.35%, Zr 0.22%, Ga 0.22%, Al 0.10%, Cu 0.22%, Ca 0.12%, Ba 0.05%, with the balance being Fe and unavoidable impurities. That is, Sr is not added. The preparation method is the same as in Example 1, except that Sr is not added in step (2).

[0052] Comparative Example 3 The difference between this comparative example and Example 1 is that the NdFeB magnet material in this comparative example is composed of the following components by mass percentage: PrNd 28.0%, B 0.92%, Co 0.35%, Zr 0.22%, Ga 0.22%, Al 0.10%, Cu 0.22%, Ca 0.12%, Sr 0.08%, with the balance being Fe and unavoidable impurities. That is, Ba is not added. The preparation method is the same as in Example 1, except that Ba is not added in step (2).

[0053] Comparative Example 4 The difference between this comparative example and Example 1 is that the neodymium iron boron magnet material in this comparative example is composed of the following components by mass percentage: PrNd 28.0%, B 0.92%, Co 0.35%, Zr 0.22%, Ga 0.22%, Al 0.10%, Cu 0.22%, Ce 0.25%, with the balance being Fe and unavoidable impurities. The preparation method is the same as in Example 1, except that Ca, Sr, and Ba are replaced with Ce in step (2).

[0054] Comparative Example 5 The comparative example has the same NdFeB magnet material composition as Example 1. The preparation method is as follows: (1) Preparation of main alloy: The raw materials were prepared according to the total composition of the final magnet (PrNd 28.0%, B 0.92%, Co 0.35%, Zr 0.22%, Ga 0.22%, Al 0.10%, Cu 0.22%, Ca 0.12%, Sr 0.08%, Ba 0.05%, Fe balance). The above raw materials were placed in a vacuum induction melting furnace and heated to 1000 ppm. -2 Melting was carried out under a vacuum of 1480℃ for 20 minutes. The molten metal was poured onto a rotating copper roller at a linear speed of 3.0 m / s to obtain an alloy sheet with a thickness of 0.30 mm. The alloy sheet was then placed in a hydrogen crushing furnace and evacuated to a vacuum of ≤10 Pa. -1 After pressing with hydrogen to 0.20 MPa, the pressure was maintained for 3 hours to allow the alloy sheet to absorb hydrogen and become brittle. Then, the temperature was increased to 550 °C at 8 °C / min, and dehydrogenation was carried out under vacuum for 3 hours to obtain coarse powder. The coarse powder was then pulverized by an air jet mill under nitrogen protection, with a classifier speed of 4000 rpm and a pulverizing pressure of 0.7 MPa. The particle size D50 was controlled to be 3.8 μm, the particle size distribution (D90-D10) / D50 = 1.15, and the oxygen content was 1100 ppm to obtain alloy powder.

[0055] (2) Orientation forming: The alloy powder is pressed into shape in an orientation magnetic field of 2.0T with a forming pressure of 20MPa to obtain a green blank. Then the green blank is subjected to cold isostatic pressing treatment with a cold isostatic pressing pressure of 250MPa and a holding time of 10 minutes.

[0056] (3) Sintering: Place the green blank in a vacuum sintering furnace with a vacuum degree ≤10 -2 Pa, first heat to 1030℃ for pre-firing for 2 hours, then heat to 1075℃ for main firing for 4 hours. After sintering, cool rapidly to room temperature at a cooling rate of 250℃ / min to obtain sintered magnets.

[0057] (4) Multi-stage tempering: The sintered magnet is subjected to multi-stage tempering under vacuum conditions: first, it is kept at 900℃ for 3 hours, then at 500℃ for 5 hours, and then cooled to room temperature with the furnace to obtain neodymium iron boron magnet material.

[0058] Comparative Example 6 The comparative example has the same NdFeB magnet material composition as Example 1. The preparation method is as follows: (1) Preparation of the main alloy: The main alloy is prepared by batching the materials according to the following proportions: 80% (22.4 wt%) of PrNd, 65% (0.143 wt%) of Ga, 65% (0.143 wt%) of Cu, and the total amount of B, Co, Zr, Al, and Fe (B 0.92 wt%, Co 0.35 wt%, Zr 0.22 wt%, Al 0.10 wt%, Fe balance). The above raw materials are placed in a vacuum induction melting furnace and heated to 1000 wt% of the final magnet composition. -2 Melting was carried out under a vacuum of 1480℃ for 20 minutes. The molten metal was poured onto a rotating copper roller at a linear speed of 3.0 m / s to obtain an alloy sheet with a thickness of 0.30 mm. The alloy sheet was then placed in a hydrogen crushing furnace and evacuated to a vacuum of ≤10 Pa. -1 After pressing with hydrogen to 0.20 MPa, the pressure was maintained for 3 hours to allow the alloy sheet to absorb hydrogen and become brittle. Then, the temperature was increased to 550 °C at 8 °C / min, and dehydrogenation was carried out under vacuum for 3 hours to obtain coarse powder. The coarse powder was then pulverized by an air jet mill under nitrogen protection, with a classifier speed of 4000 rpm and a pulverizing pressure of 0.7 MPa. The particle size D50 of the main alloy powder was controlled to be 3.8 μm, the particle size distribution (D90-D10) / D50 = 1.15, and the oxygen content was 1100 ppm to obtain the main alloy powder.

[0059] (2) Mixing of remaining components: Under the protection of argon atmosphere, the remaining PrNd (5.6wt%), Ga (0.077wt%), Cu (0.077wt%) from step (1) and all of Ca (0.12wt%), Sr (0.08wt%), Ba (0.05wt%) are crushed into powder with a particle size ≤5μm and mixed with the main alloy powder obtained in step (1) in a mixer for 4 hours to make the mixture uniform and obtain mixed powder.

[0060] (3) Orientation molding: The mixed powder is pressed into shape in an orientation magnetic field of 2.0T with a molding pressure of 20MPa to obtain a green compact. Then the green compact is subjected to cold isostatic pressing treatment with a cold isostatic pressing pressure of 250MPa and a holding time of 10 minutes.

[0061] (4) Sintering: Place the green blank in a vacuum sintering furnace with a vacuum degree ≤10 -2Pa, first heat to 1030℃ for pre-firing for 2 hours, then heat to 1075℃ for main firing for 4 hours. After sintering, cool rapidly to room temperature at a cooling rate of 250℃ / min to obtain sintered magnets.

[0062] (5) Multi-stage tempering: The sintered magnet is subjected to multi-stage tempering under vacuum conditions: first, it is kept at 900℃ for 3 hours, then at 500℃ for 5 hours, and then cooled to room temperature with the furnace to obtain neodymium iron boron magnet material.

[0063] Comparative Example 7 The difference between this comparative example and Example 1 is that the NdFeB magnet material in this comparative example is composed of the following components by mass percentage: PrNd 28.0%, B 0.92%, Co 0.35%, Zr 0.22%, Ga 0.35%, Al 0.10%, Cu 0.35%, Ca 0.12%, Sr 0.08%, Ba 0.05%, with the balance being Fe and unavoidable impurities. The preparation method is the same as in Example 1.

[0064] Performance testing The magnetic properties of the magnet materials prepared in Examples 1-2 and Comparative Examples 1-7 were tested according to GB / T 3217-2013 "Magnetic Test Methods for Permanent Magnet (Hard Magnetic) Materials". The main test items included: remanence Br, characterizing the magnetic induction intensity retained after saturation magnetization; magnetic coercivity Hcb, characterizing the magnet's ability to resist demagnetization by an external reverse magnetic field; intrinsic coercivity Hcj, characterizing the magnet's inherent resistance to demagnetization; maximum energy product (BH)max, characterizing the maximum magnetic energy stored per unit volume of the magnet; and squareness Hk / Hcj, calculated by the ratio of knee coercivity Hk to intrinsic coercivity Hcj, characterizing the rectangularity of the demagnetization curve; a higher value indicates more stable and consistent magnetic properties. The test results are shown in Table 1. The demagnetization curves of the NdFeB magnet materials prepared in Examples 1-2 and Comparative Examples 1-7 are shown in the figure. Figures 2-10 As shown.

[0065] The horizontal axis of the spectrum represents the magnetic field strength, with units of kOe and kA / m, while the vertical axis represents the magnetic flux density, with units of kGs and T. The spectrum provides key magnetic performance parameters of the magnet, including remanence Br, coercivity Hcb, intrinsic coercivity Hcj, maximum energy product (BH) max, and squareness Hk / Hcj.

[0066] Based on the performance data marked below the graph, it can be seen that the squareness (Hk / Hcj) of the magnets in Examples 1 and 2 of this invention is as high as 96.4%, which is significantly higher than that of the comparative samples (squareness is 88.5% to 93.2%). At the same time, it also has higher intrinsic coercivity (Hcj≥1448 kA / m) and maximum magnetic energy product ((BH)max≥400.5 kJ / m³). The overall magnetic performance is significantly better than that of the comparative samples.

[0067] Table 1 Performance Test Results

[0068] The performance test results above show that Examples 1 and 2 exhibit excellent overall magnetic properties, indicating that the present invention achieves a synergistic improvement in high remanence, high coercivity, high energy product, and high squareness without the addition of heavy rare earth elements. Comparative Example 1 (without Ca), Comparative Example 2 (without Sr), and Comparative Example 3 (without Ba) show a significant decrease in squareness after the absence of one alkaline earth metal in each of the three examples. This demonstrates that Ca, Sr, and Ba are all indispensable; only the combined addition of all three can produce a sufficient synergistic effect of grain boundary segregation, forming a continuous and complete non-magnetic grain boundary phase. Comparative Example 4 replaces Ca, Sr, and Ba with an equal amount of Ce. Although the coercivity is slightly improved compared to Comparative Examples 1-3, the squareness is still far lower than that of Example 1, indicating that Ce cannot replace the unique role of the ternary composite addition of Ca, Sr, and Ba in optimizing grain boundary structure and improving squareness. Comparative Example 5 used a conventional one-time melting process to directly add all components to the main alloy. All magnetic properties were significantly inferior to those of Example 1, with an intrinsic coercivity of only 1265 kA / m and a squareness of only 88.5%. This was because Ca, Sr, and Ba underwent severe oxidation and volatilization during high-temperature melting, resulting in an actual alkaline earth metal content in the final magnet that was far lower than the design value. Furthermore, the oxide inclusions generated by volatilization disrupted the uniformity of the grain boundary structure. Comparative Example 6 used mechanical mixing instead of vacuum evaporation coating. The intrinsic coercivity and squareness were still significantly lower than in Example 1, indicating that vacuum evaporation can achieve uniform coating of Ca, Sr, and Ba on the surface of the main alloy powder, ensuring that the alkaline earth metals are fully segregated to the grain boundary region during sintering. Mechanical mixing cannot achieve the same uniform distribution effect. In Comparative Example 7, excessive Ga and Cu led to an excessively thick grain boundary phase, diluting the volume fraction of the main phase and reducing remanence. Simultaneously, the composition of the grain boundary phase deviated from the optimal range, forming unfavorable precipitates that became demagnetization nucleation sites, resulting in a decrease in both coercivity and squareness.

[0069] Batch flux consistency test: Following the method in Example 1, 4536 products were continuously produced, and the magnetic flux of each product was measured using a fluxmeter. The results showed that the magnetic flux distribution was in the range of 8.39–8.46 mWb, with an average value of 8.43 mWb and a standard deviation of 0.018 mWb. This indicates that the manufacturing process of the present invention significantly improves the consistency of batch production.

[0070] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles 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 neodymium iron boron magnet material, characterized in that, It is composed of the following components by mass percentage: PrNd 26.0–30.0%, B 0.88–0.98%, Co 0.25–0.45%, Zr 0.15–0.30%, Ga 0.15–0.30%, Al 0.05–0.15%, Cu 0.15–0.30%, Ca 0.05–0.25%, Sr 0.03–0.15%, Ba 0.02–0.10%, Fe balance; The total content of Ca, Sr, and Ba is 0.2–0.4 wt%, and the ratio of the total mass of Ca, Sr, and Ba to the total mass of Ga and Cu is (0.5–1.0):

1. The preparation method of neodymium iron boron magnet material includes the following steps: (1) Preparation of main alloy: The main alloy is prepared by batching the materials according to the following proportions: 75-85% of PrNd content, 65-75% of Ga content, 65-75% of Cu content, and the full amount of B, Co, Zr, Al and Fe. After melting, the main alloy sheet is made by rapid solidification casting process. The main alloy sheet is then subjected to hydrogen crushing treatment and air jet milling to obtain main alloy powder. (2) Preparation of alloy for vapor deposition: The remaining PrNd, Cu, Ga and all of Ca, Sr and Ba from step (1) are melted in an inert atmosphere to form an alloy for vapor deposition, and the alloy for vapor deposition is made into a vapor deposition source material. (3) Vacuum evaporation coating: the main alloy powder obtained in step (1) is placed on a sample table of a vacuum evaporation device, the evaporation source material obtained in step (2) is placed in an evaporation source, and the evaporation source material is heated and evaporated under vacuum conditions to make the evaporation source material gasify and deposit on the surface of the main alloy powder particles to form a coating layer; the sample table rotates at a speed of 5-20 r / min, the evaporation time is 30-120 minutes, the evaporation source temperature is 800-1000°C, and the vacuum degree is ≤10 -2 Pa; (4) Orientation forming: The main alloy powder coated with the vapor deposition alloy layer obtained in step (3) is pressed into shape in an orientation magnetic field to obtain a green blank; (5) Sintering: Vacuum sintering of the green blank to obtain sintered magnets; (6) Multi-stage tempering: The sintered magnet is subjected to multi-stage tempering to obtain neodymium iron boron magnet material; The remanence of the neodymium-iron-boron magnet material is not less than 1.42T, the intrinsic coercive force is not less than 1440kA / m, and the maximum magnetic energy product is not less than 400kJ / m 3 , and the squareness reaches 96.4%.

2. The neodymium iron boron magnet material according to claim 1, characterized in that, In step (1), the linear speed of the copper roller in the rapid solidification casting process is 1 to 5 m / s, and a main alloy sheet with a thickness of 0.2 to 0.5 mm is obtained.

3. The neodymium iron boron magnet material according to claim 1, characterized in that, The hydrogen crushing process is as follows: hydrogen is absorbed at a hydrogen pressure of 0.1–0.3 MPa for 1–5 hours, followed by dehydrogenation at 500–600 °C for 2–5 hours; the air jet milling is carried out under a protective atmosphere, controlling the particle size D50 of the main alloy powder to be 3.0–4.5 μm, and (D90–D10) / D50 ≤ 1.2, with an oxygen content ≤ 1200 ppm; wherein, D10, D50, and D90 are characteristic particle sizes based on volume cumulative distribution: D10 is the particle size corresponding to a 10% volume cumulative distribution of the powder, D50 is the median particle size corresponding to a 50% volume cumulative distribution of the powder, and D90 is the particle size corresponding to a 90% volume cumulative distribution of the powder.

4. The neodymium iron boron magnet material according to claim 1, characterized in that, Step (4) involves pressing the material in an orientation magnetic field, followed by cold isostatic pressing. The cold isostatic pressing pressure is 200-300 MPa, and the holding time is 5-15 minutes.

5. The neodymium iron boron magnet material according to claim 1, characterized in that, The vacuum sintering described in step (5) is divided into two stages: first, pre-firing at 1000-1050℃ for 1-3 hours, and then heating up to 1060-1090℃ for 3-6 hours.

6. The neodymium iron boron magnet material according to claim 1, characterized in that, The multi-stage tempering process described in step (6) includes: first holding at 850-950℃ for 2-5 hours, and then holding at 450-550℃ for 3-8 hours.

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