Neodymium iron boron alloy powder for preparing non-parallel magnetic circuit sintered magnet and preparation method of neodymium iron boron alloy powder

Abstract

The invention discloses neodymium-iron-boron alloy powder for preparing a non-parallel magnetic circuit sintered magnet and a preparation method of the neodymium-iron-boron alloy powder, and belongs to the technical field of magnetic materials. The average particle size of the alloy powder ranges from 5 micrometers to 8 micrometers, powder particles are in a round cake shape, the ratio of the average diameter to the average thickness ranges from 1.3 to 1.6, and the hydrogen content is smaller than 200 ppm. The preparation method comprises the following steps: smelting and quickly hardening alloy raw materials to obtain a casting sheet; carrying out hydrogen absorption-dehydrogenation treatment for controlling the hydrogen absorption amount on the cast sheet to obtain low-hydrogen crushed powder; and performing jet milling on the hydrogen decrepitation powder under the grinding pressure of 0.3-0.4 MPa to obtain the powder. The powder has specific morphology and extremely low hydrogen content, abnormal shrinkage in the easy magnetization axis direction in the sintering process can be effectively inhibited, and the shrinkage ratio difference of a pressed blank formed by using the powder in three directions after sintering is smaller than 5%. When the powder is used for preparing non-parallel magnetic circuit sintered magnets such as a radiation magnetic ring, a quadrupole magnetic ring, a sextupole magnetic ring or an octupole magnetic ring, the yield is remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of magnetic materials, and particularly relates to a neodymium iron boron alloy powder for preparing a non-parallel magnetic circuit sintered magnet and a preparation method thereof. BACKGROUND

[0002] Compared with the traditional electrically excited motor, the permanent magnet motor has the advantages of simple structure, small size, light weight, low loss, high efficiency, high power factor, etc., and is widely used in aerospace, national defense, industrial and agricultural production and daily life. The rotor structure of the existing neodymium iron boron permanent magnet motor is mostly of the magnetic tile / bar insertion type or the inlaid type: the sintered neodymium iron boron tiles after magnetization are inlaid in the frame structure of soft magnetic material to splice into a ring. However, the magnetic tile splicing ring has the following problems: the magnetic field direction in the single piece magnet is consistent, the magnetic field strength of the magnetic tile splicing ring is unevenly distributed along the outer circle, which leads to poor dynamic balance of the splicing magnetic ring, large transition area between the magnetic poles, and noise and vibration of the motor. For example, the magnetic ring spliced by 8 pieces of magnetic tiles has a magnetic field direction difference of nearly 45° between two adjacent magnetic tiles (as shown in FIG. 1), which leads to discontinuous magnetic field distribution and obvious magnetic field jumping phenomenon, increases the friction and noise of the motor during operation, and reduces the efficiency. Figure 1

[0003] In recent years, the developed radial magnetic ring / multi-pole magnetic ring has overcome the above-mentioned shortcomings of the splicing magnetic ring, and can replace the traditional tile-shaped block. The magnetic field direction of the radial magnetic ring (as shown in FIG. 2) is continuously distributed in a radial state with the ring center as the center, the magnetic field in the whole magnetic ring is continuously and uniformly distributed, and there is no magnetic pole transition area, which greatly reduces the noise and heat generated by the vibration caused by the magnetic field jumping during the operation of the motor, and significantly improves the operating efficiency of the motor. The multi-pole magnetic ring (as shown in FIG. 3) further improves the surface magnetic field strength of the magnetic ring by forming a Halbach magnetic circuit in the magnetic ring, and the maximum surface magnetism can be more than 1.2 times that of the splicing and radial magnetic ring. Figure 2 Figure 3

[0004] At present, the radial magnetic ring and the multi-pole magnetic ring are mainly prepared by bonding, hot pressing and sintering. Among them, the bonding process is the simplest, but the surface magnetic field strength of the prepared magnetic ring is the lowest; the hot pressing process can prepare a radial magnetic ring with high surface magnetism, but its production efficiency is low; the sintering process has the potential to prepare various radial magnetic rings and multi-pole magnetic rings. However, in the sintering preparation process, due to the non-uniform shrinkage of the neodymium iron boron alloy powder (as shown in FIG. 4) in three-dimensional directions, the forming yield of the magnetic ring is not ideal, which restricts the large-scale application of the technology. Figure 4

[0005] ​​​​Therefore, developing a Nd-Fe-B alloy powder with small difference in three-dimensional shrinkage ratio during sintering and suitable for preparing non-parallel magnetic circuit sintered magnets (such as radial magnetic rings and multi-pole magnetic rings) and a preparation method thereof, so as to significantly improve the yield of the magnets, has become a key technical problem to be solved in the field. SUMMARY

[0006] To solve the above technical problems, the present application provides a Nd-Fe-B alloy powder for preparing non-parallel magnetic circuit sintered magnets and a preparation method thereof.

[0007] To solve the above technical problems, the present application adopts the following technical solutions:

[0008] In the first aspect, the present application provides a Nd-Fe-B alloy powder for preparing non-parallel magnetic circuit sintered magnets, wherein the average particle size D50 of the powder is 5-8 μm, the powder particles are in the shape of a circular disc or an approximate circular disc, the ratio of the arithmetic mean diameter to the arithmetic mean thickness of the particles is 1.3-1.6 under observation by a scanning electron microscope, and the hydrogen content of the powder is not more than 200 ppm.

[0009] This morphology combined with extremely low hydrogen content is proved to effectively inhibit abnormal shrinkage along the easy magnetization axis (c-axis) direction during sintering, so that the linear shrinkage rate difference of the compact in three directions after sintering is less than 5%, which lays a foundation for high-precision forming of complex magnetic circuit magnets.

[0010] Preferably, the linear shrinkage rate S （a / b / c） The calculation formula is: ; the shrinkage rate difference is defined as the maximum value of the absolute values of the differences between the linear shrinkage rates in three directions, that is, |S a -S b |, |S a -S c |, |S b -S c |} max .

[0011] wherein the dimensions of the compact along the a, b and c directions are defined as L 0（a / b / c） , and the dimensions of the sintered body along the a, b and c directions are defined as L 1（a / b / c） ; Preferably, to achieve the above-mentioned powder properties, the present application optimizes the alloy composition. The composition of the powder is represented by the general formula RE a Fe b M c B dREaMbBcMd, wherein RE is selected from one or more of Pr, Nd, Dy, Tb, Gd, Ho, Ce, Y, M is selected from one or more of Cu, Ga, Al, Zr, Nb, Ti, Zn, Sn, a, b, c, d are mass percentages of the corresponding elements, and satisfy: 30.5≤a≤32, 0.8≤c≤1.5, d=1.54-a / 50, b=100-a-c-d.

[0012] Further, in the rare earth elements RE, the mass percentage of Nd is more than 50% of the total amount of RE, the total mass percentage of Gd, Ce and Ho is not more than 20% of the total amount of RE, the total mass percentage of Dy and Tb is not more than 12% of the total amount of RE, and the mass percentage of Y is not more than 7% of the total amount of RE.

[0013] Further, in the additive elements M, the total content of Cu, Ga, Al, Zn and Sn is more than 70% of the total amount of M, and the total content of Zr, Nb and Ti is more than 20% of the total amount of M.

[0014] Preferably, the main phase RE2Fe 14 The mass percentage of B is preferably more than 95% to ensure excellent magnetic properties.

[0015] In a second aspect, the present application provides a preparation method of the above neodymium-iron-boron alloy powder. The method comprises the following key steps: (1) alloying raw materials prepared according to the designed composition are melted and rapidly solidified to obtain alloy cast pieces; (2) the alloy cast pieces are subjected to hydrogen absorption and hydrogen desorption treatment to obtain hydrogen-containing powder with hydrogen content less than 200 ppm; (3) the hydrogen-containing powder is subjected to air jet milling at a grinding pressure of 0.3-0.4 MPa to obtain the neodymium-iron-boron alloy powder.

[0016] Preferably, in step (1), the roller surface linear velocity of the rapid solidification is 0.8-1.2 m / s, the average thickness of the obtained alloy cast pieces is 200-300 μm, and the average width of the RE2Fe 14 The average width of the B main phase columnar crystal is 4-6 μm.

[0017] Preferably, in step (2), the hydrogen supply amount in the hydrogen absorption stage is 70%-80% of the saturated hydrogen absorption amount of the alloy cast pieces, and the hydrogen desorption temperature is 600-650℃.

[0018] It should be noted that the combination of the specific morphology and low hydrogen content makes the alloy powder of the present application have excellent uniformity of shrinkage when sintered. This property is characterized by the fact that after the powder is formed into a standard compact in parallel orientation and sintered, the maximum difference between the linear shrinkage rates in the three orthogonal directions is not more than 5%. This low shrinkage anisotropy in parallel orientation is the key to the fact that the powder of the present application can be used to prepare non-parallel magnetic circuit sintered magnets such as radiation rings, multipole rings, etc. and achieve a high yield. When the powder has achieved uniform shrinkage in parallel orientation, it is formed in a complex non-parallel magnetic field, and the shrinkage behavior of each microzone is coordinated, thereby effectively avoiding deformation and cracking of the magnet due to uneven shrinkage.

[0019] In a third aspect, the present application provides a use of the neodymium iron boron alloy powder in the preparation of a non-parallel magnetic circuit sintered magnet, wherein when the neodymium iron boron alloy powder is formed in parallel orientation and sintered, the maximum difference between the linear shrinkage rates in the length, width and height directions of the obtained sintered body is not more than 5%.

[0020] Further, a method for preparing a non-parallel magnetic circuit sintered magnet comprises the following steps: S1, using the neodymium iron boron alloy powder provided by the present application or the powder prepared by the method of the present application; S2, pressing the powder into a green compact in a non-parallel orientation magnetic field; S3, isostatic pressing the green compact; S4, sintering and heat treating the isostatically pressed green compact to obtain a sintered magnet.

[0021] Preferably, the non-parallel magnetic circuit sintered magnet is a radiation magnetic ring, a quadrupole magnetic ring, a sextupole magnetic ring or an octupole magnetic ring.

[0022] The use of the method of the present application can make the yield of such complex magnetic circuit magnets stable at more than 95%.

[0023] The present application obtains a casting sheet with regular columnar crystal organization through alloy composition design and melting-rapid solidification process, and provides a structural basis for subsequent processes; by controlling the hydrogen absorption amount (70-80% of the saturated hydrogen absorption amount) and the dehydrogenation temperature (600-650℃), the powder hydrogen content is limited below 200ppm, thereby reducing the main phase brittleness and reducing the c-axis contraction tendency caused by hydrogen-induced lattice distortion; on the basis of the low-hydrogen material, a lower pressure of 0.3-0.4 MPa is used for air flow grinding, so as to promote the powder to break along the grain boundary to form a circular cake shape with a diameter to thickness ratio of 1.3-1.6, and make the easy magnetization axis arrange along the thickness direction. The above specific morphology and low hydrogen content characteristics are combined to effectively suppress the abnormal shrinkage of the powder compact along the c-axis direction in the sintering process, and finally make the shrinkage behavior of the compact in the three-dimensional direction consistent, and the shrinkage ratio difference is controlled within 5%, thereby realizing high dimensional accuracy and high yield of non-parallel magnetic circuit magnet forming.

[0024] Compared with the prior art, the present application has the beneficial technical effects that: 1. The sintering shrinkage uniformity is significantly improved: by accurately controlling the hydrogen content of the alloy powder below 200 ppm, and combining the low-pressure air flow grinding process of 0.3 to 0.4 MPa, the powder particles with specific morphology characteristics are successfully obtained, which are approximately circular cake-shaped, and the average diameter to average thickness ratio is kept between 1.3 to 1.6. The special morphology of the powder effectively suppresses the abnormal shrinkage phenomenon along the easy magnetization axis direction during sintering. The parallel oriented compact prepared by using the powder has a linear shrinkage rate difference of less than 5% in the length, width and height directions after sintering, thereby fundamentally solving the technical problems of magnet deformation and poor dimensional accuracy caused by anisotropic shrinkage in the traditional process.

[0025] 2. The yield of complex magnetic circuit magnets is greatly improved: based on the above excellent shrinkage uniformity, the present application is suitable for preparing sintered magnets with non-parallel magnetic circuit such as radial magnetic ring, quadrupole magnetic ring, sextupole magnetic ring, octupole magnetic ring, etc. The actual production data shows that the yield of such magnets prepared by using the powder and method provided by the present application is stable above 95%, which is significantly improved compared with the traditional process (the yield is usually less than 75%), greatly reducing material waste and production cost.

[0026] 3. The powder morphology and performance are controllable: through the coordinated optimization of the melting-rapid solidification process, hydrogen absorption-dehydrogenation process and air flow grinding process, the morphology and physical properties of the final alloy powder particles are accurately controlled, and the process reproducibility is good, which provides a guarantee for the consistency of product quality.

[0027] 4. High process integration, easy to implement: the preparation method provided by the present application is compatible with the existing neodymium-iron-boron powder production line, does not require complex or expensive additional equipment, and is easy to industrialize and apply. Attached Figure Description

[0028] Figure 1 A schematic diagram of a neodymium iron boron alloy magnetic ring with spliced ​​magnetic rings in the prior art; Figure 2 A schematic diagram of a neodymium iron boron alloy magnetic ring for radiation magnetic rings in the prior art; Figure 3 This is a schematic diagram of a neodymium iron boron alloy magnetic ring for multipole magnetic rings in the prior art; Figure 4 A schematic diagram of ordinary sintered NdFeB alloy powder; Figure 5 Scanning electron microscope image of sintered NdFeB alloy powder in an approximately disc-shaped shape prepared for an embodiment of the present invention; Figure 6 A schematic diagram of the approximately disc-shaped sintered NdFeB alloy powder prepared according to an embodiment of the present invention. Detailed Implementation

[0029] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0030] Many specific details are set forth in the following description to provide a thorough understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below. Furthermore, the term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that excludes other embodiments.

[0031] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0032] Example 1 The sintered NdFeB alloy powder and magnetic ring of the non-parallel magnetic circuit in Example 1 were prepared by the following method: (1) Industrial-grade raw materials PrNd, Dy, Fe, Co, Cu, Al, and FeB are used, according to the designed composition (PrNd) 30.5 Dy 0.8 Cu 0.1 Al 0.2 Ga 0.2 Co 1.0 B 0.92 Fe 余 (wt%) Ingredients; (2) The above alloy raw materials were processed by smelting and rapid solidification casting to obtain an alloy casting sheet with an average thickness of 230 μm. The alloy casting sheet contained a neodymium iron boron main phase (RE2Fe). 14 The average width of the columnar crystals (B phase) is 5.2 μm, the alloy melting temperature is 1460℃, the casting (rapid solidification) temperature is 1445℃, and the linear speed of the copper roller is 1 m / s. (3) The alloy castings obtained by the rapid solidification process are crushed by hydrogen absorption-dehydrogenation process. During the hydrogen absorption stage, the hydrogen supply is controlled to be 70% of the saturated hydrogen absorption. Then, dehydrogenation is carried out at 600℃ so that the hydrogen content of the coarse crushed alloy powder is ≤120ppm. (4) The coarsely crushed alloy powder was placed in an air jet mill and finely ground under an argon atmosphere at a grinding pressure of 0.3 MPa to obtain alloy powder with an average particle size (D50) of 5.02 μm. The powder particles were approximately disc-shaped, with an average diameter 1.3 times the average thickness. Figure 5 As shown; The morphology of powder particles was observed using a scanning electron microscope. No fewer than 500 particles were randomly selected for image analysis. The maximum projected diameter (i.e., diameter) and the thickness perpendicular to the diameter direction of each particle were measured. The arithmetic mean was calculated to obtain the ratio of the average diameter to the average thickness.

[0033] (5) Add an appropriate amount of lubricant to the alloy powder after air jet milling and stir in a mixer for 5 hours. Feed the uniformly mixed NdFeB alloy powder into a radiation magnetic field press for orientation forming. The magnetic field direction is distributed radially along the magnetic ring, and the magnetic field strength is 1.5T. The formed radiation-oriented magnetic ring green blank is subjected to isostatic pressing at 180MPa.

[0034] (6) (Preparation of parallel orientation test compact) Take a portion of the uniformly mixed NdFeB alloy powder and send it into a parallel magnetic field press for orientation forming to obtain a cuboid compact with dimensions of 50mm×40mm×30mm, which is used to test the sintering shrinkage ratio.

[0035] (7) The green blanks after isostatic pressing are subjected to high-temperature sintering and heat treatment: the sintering temperature is 1060℃, the sintering time is 5h, and the blanks are cooled rapidly by a fan after sintering. Then, a two-stage tempering treatment is carried out: the first-stage tempering temperature is 860℃ and the holding time is 3h; the second-stage tempering temperature is 460℃ and the holding time is 3h.

[0036] (8) Perform necessary machining on the sintered and heat-treated NdFeB radiant magnetic rings to achieve the specified dimensional accuracy. (Note: The cuboid blank is used for performance testing; see the subsequent "Performance Testing and Effect Comparison" section.) Example 2 The main difference between the preparation method of the non-parallel magnetic circuit sintered Nd-Fe-B alloy powder and magnetic ring of Example 2 and Example 1 is that: 1. The average thickness of the alloy cast sheet prepared by the melting and rapid quenching and tape casting process is 200 μm, and the average width of the Nd-Fe-B main phase columnar crystal in the cast sheet is about 4.68 μm; 2. The hydrogen supply amount in the hydrogen absorption stage is 75% of the saturated hydrogen absorption amount, so that the hydrogen content of the obtained coarse broken alloy powder is ≤160 ppm; 3. The average particle size (D50) of the alloy powder obtained after the jet mill is 5.63 μm, and the powder particle shape is approximately a circular disc. Using the same scanning electron microscope image analysis method as in Example 1, the ratio of the arithmetic mean diameter to the arithmetic mean thickness of the particles is 1.4.

[0037] 4. According to the same method as step (6) of Example 1, a parallel oriented cuboid test compact is prepared.

[0038] Example 3 The difference between Example 3 and Example 1 is that in the hydrogen absorption-dehydrogenation process, the hydrogen supply amount in the hydrogen absorption stage is controlled to be 80% of the saturated hydrogen absorption amount, so that the hydrogen content of the final hydrogen broken powder is ≤200 ppm. A parallel oriented cuboid test compact is also prepared.

[0039] Example 4 The difference between Example 4 and Example 1 is that in the jet mill process, the grinding gas is argon, and the grinding pressure is 0.4 MPa. A parallel oriented cuboid test compact is also prepared.

[0040] Example 5 The difference between Example 5 and Example 1 is that in the jet mill process for preparing the Nd-Fe-B alloy powder, the jet mill grinding gas is argon, and the grinding pressure is 0.35 MPa. A parallel oriented cuboid test compact is also prepared.

[0041] Example 6 The non-parallel magnetic circuit sintered Nd-Fe-B alloy powder and quadrupole ring of Example 6 are prepared by the following method: (1) Using industrial raw materials PrNd, Dy, Fe, Co, Cu, Al, FeB, the ingredients are designed as follows (PrNd) 30.5 Dy 0.8 Cu 0.1 Al 0.2 Ga 0.2 Co 1.0 B 0.92 Fe 余 (wt%); (2) The prepared alloy is melted and rapidly solidified to obtain a cast sheet with an average thickness of 230 μm. The average width of the Nd-Fe-B columnar crystals in the alloy cast sheet is 5.2 μm. The melting temperature of the alloy is 1460 °C, and the pouring temperature is 1445 °C. The rotating speed of the copper roller is 1 m / s. (3) The cast sheet obtained by the melting-rapid solidification process is subjected to a hydrogen absorption-dehydrogenation process. The hydrogen supply amount in the hydrogen absorption stage is 70% of the saturated hydrogen absorption amount. The dehydrogenation temperature is 600 °C, so that the hydrogen content of the crushed alloy powder is ≤120 ppm. (4) The crushed alloy powder is placed in a jet mill device and finely ground in an argon atmosphere while maintaining a grinding pressure of 0.3 MPa. The obtained alloy powder has an average particle size (D50) of 5.02 μm. The powder particles are approximately disc-shaped, and the diameter is 1.3 times the thickness. (5) An appropriate amount of lubricant is added to the alloy powder after the jet milling, and the mixture is stirred in a mixer for 5 h. (6) (Preparation of parallel orientation test compacts) A portion of the mixed powder is fed into a parallel magnetic field press for orientation molding to obtain a cuboid compact with a size of 50 mm x 40 mm x 30 mm, which is used for testing the sintering shrinkage ratio. (7) The mixed alloy powder is fed into a four-pole orientation magnetic field press for molding. The magnetic poles are designed with an outer sleeve and four groups of magnetic poles built-in. The included angle between adjacent magnetic poles is 90° to form a magnetic field strictly distributed along four radial directions. (8) After magnetic field calibration, orientation pressing is performed in a stable four-pole magnetic field with a magnetic field strength of 1.8 T to obtain a four-pole magnetic ring green compact. The four-pole magnetic ring green compact after molding is subjected to 200 MPa isostatic pressing. (9) The green compact after isostatic pressing is subjected to high-temperature sintering and heat treatment. The sintering temperature is 1060 °C, and the sintering time is 5 h. After sintering, rapid cooling is performed using a fan. Subsequently, two-stage tempering treatment is performed. The first-stage tempering treatment temperature is 860 °C, and the holding time is 3 h. The second-stage tempering treatment temperature is 460 °C, and the holding time is 3 h. (10) The four-pole magnetic ring after sintering and heat treatment is subjected to mechanical processing to achieve the specified dimensional accuracy.

[0042] Example 7 Example 7 aims to prepare a six-pole magnetic ring. The difference between the preparation method of Example 7 and that of Example 6 is as follows: 1. The magnetic field press is designed with an outer sleeve and six groups of magnetic poles built-in. The included angle between adjacent magnetic poles is 60° to ensure that the magnetic field is distributed along six radial directions.

[0043] 2. Orientation molding is performed in a stable six-pole magnetic field with a magnetic field strength of 1.9 T. The subsequent processing steps (including the preparation of parallel test compacts) are the same as those of Example 6.

[0044] Example 8 Example 8 aims to prepare an octupole magnetic ring, the preparation method of which is different from that of Example 6 in that: 1. The magnetic field press adopts a design of an outer sleeve with 8 groups of built-in magnetic poles, and the included angle between the magnetic poles is 45° to ensure that the magnetic field is distributed along the eight radial directions.

[0045] 2. The orientation forming is performed in a stable octupole magnetic field of 2.0 T. The subsequent processing steps (including the preparation of parallel test compacts) are the same as those of Example 6.

[0046] Comparative Example 1 The sintered neodymium-iron-boron alloy powder and the magnetic ring of Comparative Example 1 are prepared by the following method: (1) Industrial raw materials PrNd, Dy, Fe, Co, Cu, Al, FeB are used to prepare the alloy according to the designed composition (PrNd) 30.5 Dy 0.8 Cu 0.1 Al 0. 2Ga 0.2 Co 1.0 B 0.92 Fe 余 (wt%) are prepared; (2) The alloy is prepared by melting and rapid solidification to obtain a cast sheet with an average thickness of 180 μm, the average width of the neodymium-iron-boron columnar crystals in the alloy cast sheet is 4.5 μm, the alloy melting temperature is 1460 °C, the casting temperature is 1445 °C, and the copper roller rotation speed is 1 m / s; (3) The cast sheet obtained by the melting-rapid solidification process is subjected to hydrogen absorption-dehydrogenation process, the hydrogen supply amount in the hydrogen absorption stage is saturated hydrogen absorption, and the dehydrogenation temperature is 750 °C, so that the hydrogen content of the coarse broken alloy powder is ≤600 ppm; (4) The coarse broken alloy powder is ground by air jet milling process in an argon atmosphere, and the grinding pressure is kept at 0.5 MPa to obtain an alloy powder with an average particle size of 3.64 μm, and the powder particle shape is spherical, as shown in Figure 4 ; (5) The air-jet-milled alloy powder is added with a lubricant and stirred in a mixer for 5 h; (6) (Preparation of parallel orientation test compacts) Part of the mixed powder is sent into a parallel magnetic field press for orientation forming to obtain a cuboid compact with a size of 50 mm x 40 mm x 30 mm, which is used for testing the sintering shrinkage ratio; (7) Another part of the mixed neodymium-iron-boron alloy powder is sent into a radial magnetic field press for orientation forming, and the magnetic field strength is 1.5 T. The formed radial magnetic ring is subjected to 180 MPa isostatic pressing treatment; (8) After isostatic pressing, high temperature sintering is performed, the sintering temperature is 1060°C, the sintering time is 5h, and after the sintering is completed, fast cooling is performed by using a fan. The tempering process adopts a two-stage heat treatment process; the first stage heat treatment temperature is 860°C, the holding time is 3h; the second stage heat treatment temperature is 460°C, the holding time is 3h; (9) The sintered neodymium-iron-boron magnetic ring is subjected to mechanical processing, and the processing reaches the specified dimensional accuracy.

[0047] Comparative Example 2: The difference between Comparative Example 2 and Comparative Example 1 is that in the hydrogen absorption-dehydrogenation process adopted by Comparative Example 2, the hydrogen supply amount in the hydrogen absorption stage is 90% of the saturated hydrogen absorption amount, and the dehydrogenation temperature is 750°C, so that the hydrogen content of the coarse broken and crushed alloy powder is ≤650ppm. A parallel orientation cuboid test compact is also prepared.

[0048] Comparative Example 3: The difference between Comparative Example 3 and Comparative Example 1 is that in the hydrogen absorption-dehydrogenation process adopted by Comparative Example 3, the hydrogen supply amount in the hydrogen absorption stage is 60% of the saturated hydrogen absorption amount, so that the hydrogen content of the coarse broken and crushed alloy powder is ≤200ppm. A parallel orientation cuboid test compact is also prepared.

[0049] Comparative Example 4: The difference between Comparative Example 4 and Comparative Example 1 is that in the airflow mill process adopted by Comparative Example 4, the grinding pressure is 0.5MPa, and spherical neodymium-iron-boron powder particles are obtained. A parallel orientation cuboid test compact is also prepared.

[0050] Comparative Example 5: The difference between Comparative Example 5 and Comparative Example 1 is that in the airflow mill process adopted by Comparative Example 5, the grinding pressure is 0.2MPa, and spherical neodymium-iron-boron powder particles are obtained. A parallel orientation cuboid test compact is also prepared.

[0051] Comparative Example 6: The difference between Comparative Example 6 and Comparative Example 1 is that in Comparative Example 6, a forming method of 4 groups of magnetic poles is adopted, the included angle between the magnetic poles is 90°, the magnetic field is distributed along 4 radial directions, and the magnetic field strength is 1.8T, so that a sintered neodymium-iron-boron quadrupole ring is obtained. The powder preparation and the preparation of the parallel test compact are the same as in Comparative Example 1.

[0052] Comparative Example 7: The difference between Comparative Example 7 and Comparative Example 1 is that in Comparative Example 7, a forming method of 6 groups of magnetic poles is adopted, the included angle between the magnetic poles is 60°, the magnetic field is distributed along 6 radial directions, and the magnetic field strength is 1.9T, so that a sintered neodymium-iron-boron sextupole ring is obtained. The powder preparation and the preparation of the parallel test compact are the same as in Comparative Example 1.

[0053] Comparative Example 8: The difference between Comparative Example 8 and Comparative Example 1 is that the pole forming mode of Comparative Example 8 adopts 8 groups of magnetic poles, and the included angle between the magnetic poles is 45°, which ensures that the magnetic field is distributed along 8 radial directions, and the magnetic field strength is 2.0T, to obtain a sintered neodymium-iron-boron eight-pole magnetic ring. The powder preparation and parallel test compact preparation are the same as those of Comparative Example 1.

[0054] Performance test and effect comparison 1. Shrinkage uniformity test After the parallel oriented cuboid compacts (standard initial size: length L 0(a) = 50 mm, width L 0(b) = 40 mm, height L 0(c) = 30 mm) prepared according to the above method of Examples 1-8 and Comparative Examples 1-8 are subjected to the same sintering and heat treatment, the final sizes in a, b, and c directions are measured respectively, and are recorded as L 1(a) , L 1(b) , and L 1(c) . The linear shrinkage rates S (x) , S 0(x) , and S 1(x) in each direction are calculated according to the formula S 0(x) = (L (a) - L (b) ) / L (c) × 100% (wherein x represents a, b, or c direction). The maximum value of the absolute value of the difference between the shrinkage rates of the three directions is defined as the “shrinkage ratio difference”.

[0055] 2. Magnetic body yield rate test The non-parallel magnetic circuit magnetic rings (radial oriented magnetic rings or four-, six-, and eight-pole magnetic rings) prepared according to the examples and comparative examples are counted, and the proportion of the final qualified products that meet the design size and performance requirements is calculated as the “yield rate”.

[0056] The test results are shown in Table 1.

[0057] Table 1 Performance comparison of neodymium-iron-boron permanent magnet materials after different treatment

[0058] As shown in Table 1, Examples 1-8 are preferred examples. When the saturated hydrogen absorption amount is controlled to be 70%-80% in the hydrogen absorption-dehydrogenation process, the hydrogen content of the hydrogen powder is <200ppm, and the grinding pressure of the jet mill is 0.3-0.4MPa, an approximately circular cake-shaped alloy powder is prepared. The parallel oriented compacts prepared using the powder have a shrinkage ratio difference of less than 5% in the three directions after sintering. When the non-parallel magnetic circuit sintered magnets (including radial magnetic rings, four-pole, six-pole, and eight-pole magnetic rings) are prepared using the above-mentioned powder, the yield rate is higher than 95%.

[0059] In contrast, the comparative examples 1-8 deviated from the preferred conditions of the present application in one or more aspects of hydrogen content control, jet mill pressure or powder morphology, etc. The prepared powders were mostly spherical, the shrinkage ratio of the compacts was significantly increased (all greater than 7%), and the yield of the final magnetic ring was also greatly reduced, generally less than 75%.

[0060] The above data prove that by limiting the hydrogen content in the hydrogen broken powder, reducing the brittleness of the neodymium iron boron main phase, combined with low pressure jet milling, reducing the breaking of the neodymium iron boron main phase in the vertical c-axis direction during jet milling, the difference in shrinkage ratio of the neodymium iron boron radiation magnetic ring and the multi-pole ring in three directions is effectively reduced, the yield of the neodymium iron boron radiation magnetic ring and the multi-pole ring is significantly improved, and the resource loss and cost waste in the production process are greatly reduced.

[0061] The technical features of the above embodiments can be combined in any way. To make the description concise, not all possible combinations of the technical features in the above embodiments are described, but as long as the combinations of the technical features do not contradict, they should be considered within the scope of the present disclosure.

[0062] It is obvious to those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be considered as exemplary and non-limiting, and the scope of the present application is defined by the appended claims, not the above description, and therefore all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application, and any reference signs in the claims should not be considered as limiting the claims.

[0063] In addition, it should be understood that although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the description of the specification is only for the sake of clarity, and those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that those skilled in the art can understand.

Claims

1. A neodymium iron boron alloy powder for preparing non-parallel magnetic circuit sintered magnets, characterized in that, The powder has an average particle size D50 of 5-8 μm by volume, and the powder particles are disc-shaped or nearly disc-shaped. Statistical observation under a scanning electron microscope shows that the ratio of the arithmetic mean diameter to the arithmetic mean thickness of the particles is 1.3-1.6, and the hydrogen content of the powder does not exceed 200 ppm.

2. The NdFeB alloy powder according to claim 1, characterized in that, The composition of the powder is in the general formula RE a Fe b M c B d The expression indicates that RE is selected from one or more of Pr, Nd, Dy, Tb, Gd, Ho, Ce, and Y, M is selected from one or more of Cu, Ga, Al, Zr, Nb, Ti, Zn, and Sn, and a, b, c, and d are the mass percentages of the corresponding elements, satisfying: 30.5≤a≤32, 0.8≤c≤1.5, d=1.54-a / 50, and b=100-acd.

3. The NdFeB alloy powder according to claim 2, characterized in that, The mass percentage of Nd in RE is more than 50% of the total RE, the combined mass percentage of Gd, Ce, and Ho does not exceed 20% of the total RE, the combined mass percentage of Dy and Tb does not exceed 12% of the total RE, and the mass percentage of Y does not exceed 7% of the total RE.

4. The NdFeB alloy powder according to claim 2, characterized in that, The combined mass percentage of Cu, Ga, Al, Zn, and Sn in M ​​accounts for more than 70% of the total mass of M, while the combined mass percentage of Zr, Nb, and Ti accounts for more than 20% of the total mass of M.

5. The NdFeB alloy powder according to any one of claims 1 to 4, characterized in that, RE2Fe in the powder 14 The mass percentage of the B main phase is 88%–94%.

6. A method for preparing neodymium iron boron alloy powder as described in any one of claims 1 to 5, characterized in that, Includes the following steps: (1) The alloy raw materials according to the designed composition are melted and rapidly solidified to obtain alloy castings; (2) The alloy casting is subjected to hydrogen absorption and dehydrogenation treatment to obtain hydrogen fragments with a hydrogen content of less than 200 ppm; (3) The hydrogen-rich powder is subjected to air jet milling at a pressure of 0.3~0.4 MPa to obtain the neodymium iron boron alloy powder.

7. The method according to claim 6, characterized in that, In step (1), the linear velocity of the rapidly solidifying roller surface is 0.8~1.2 m / s, the average thickness of the resulting alloy casting is 200~300 μm, and the RE2Fe in the casting is... 14 The average width of the B main phase columnar crystals is 4~6 μm.

8. The method according to claim 6, characterized in that, In step (2), the hydrogen supply during the hydrogen absorption stage is 70% to 80% of the saturated hydrogen absorption capacity of the alloy casting, and the dehydrogenation temperature is 600 to 650°C.

9. The use of a neodymium iron boron alloy powder in the preparation of non-parallel magnetic circuit sintered magnets, characterized in that, The neodymium iron boron alloy powder is the neodymium iron boron alloy powder according to any one of claims 1 to 5, and when the neodymium iron boron alloy powder is shaped by parallel orientation and sintered, the maximum difference between the linear shrinkage rates of the resulting sintered body in the length, width and height directions does not exceed 5%.

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