Neodymium-iron-boron permanent magnet and preparation method and application thereof

Abstract

The invention discloses a neodymium-iron-boron permanent magnet, which comprises the following magnet components: RcFe with the balance being MdZreCufGagBh, and is prepared from a multi-alloy mixture consisting of a main alloy R1vFe with the balance being HwCuxGayBz and N auxiliary alloys RnaFe with the balance being Bb, the preparation method of the sintered neodymium-iron-boron permanent magnet comprises the steps that burdening, cast piece mixing, metal Ga adding, hydrogen decrepitation and nano Cu powder adding are conducted, then jet milling, oriented pressing, vacuum sintering and aging treatment are conducted, the first-stage sintering temperature is 1060-1100 DEG C, the second-stage sintering temperature is 1040-1080 DEG C, the third-stage aging treatment temperature is 850-950 DEG C, the fourth-stage aging treatment temperature is 450-650 DEG C, and the sintered neodymium-iron-boron permanent magnet is prepared. The method has the advantages that the grain boundary fluidity and the grain boundary phase thickness can be increased to optimize the grain boundary distribution of the magnet, the purpose of regulating and controlling the magnetism of the grain boundary phase is achieved, the demagnetizing coupling effect between grains is improved, and the consistency of the material structure and the product performance is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of neodymium iron boron magnet preparation, and specifically to a neodymium iron boron permanent magnet, a preparation method thereof, and an application thereof. Background Art

[0002] As the "king of magnets" in current industrial applications, since the invention of sintered neodymium iron boron magnets in 1983, after more than 40 years of rapid development, the material properties have been greatly improved. The application fields have covered various industrial motors, wind power generation, new energy vehicles, consumer electronics, medical treatment, etc., and are still expanding. The total global demand is increasing at about 20% per year. Currently, the main problems to be solved mainly include the imbalance between the growing demand and the utilization of rare earth resources, the low utilization rate of heavy rare earths, and the slow progress in the development of ultra-high performance magnets.

[0003] Therefore, numerous neodymium iron boron enterprises have increased their R & D investment and continuously optimized the material formula cost. Inexpensive high-abundance rare earth metals lanthanum and cerium have been widely used in neodymium iron boron magnets, and the material cost has been greatly reduced. However, there are also some problems, such as large rare earth losses during the production process, resulting in a certain amount of waste and causing fluctuations in material properties.

[0004] The existing preparation of neodymium iron boron magnets mainly has the following deficiencies:

[0005] 1. In the process of adding rare earth metal (alloy) hydrides during powder making, the disadvantage is that the proportion lost in the ultrafine powder during the jet milling process is relatively large, the proportion is uncontrollable, and it causes a certain degree of waste, and the performance consistency is poor. As mentioned in the literature (Effect of DyFe on the Microstructure and Magnetic Properties of Sintered NdFeB. Rare Earths. Vol. 41, No. 3, June 2020, pp. 10 - 16. Article ID: 1004 - 0277(2020)03 - 0010 - 07), adding the commonly used raw material DyFe alloy powder before and after jet milling. The disadvantage of this addition method is that the DyFe alloy powder is easily pulverized to an extremely fine particle size during the jet milling process and is extremely easy to enter the ultrafine powder, resulting in the waste of the heavy rare earth Dy. 79.73 Fe 20.27

[0006] ​2. The process of grinding the added rare earth metal (alloy) hydride into fine powder separately and then adding it will also result in partial loss to the ultrafine powder. At the same time, the fine particle size of the rare earth metal (alloy) fine powder is difficult to control, and it is easy to absorb oxygen, leading to oxidation, impurities and other abnormalities. For example, in the patent application with the publication number CN 104064346A, in the process method of mixing the main phase alloy powder, heavy rare earth alloy powder and ultrafine powder according to a certain ratio, the heavy rare earth alloy powder and ultrafine powder are prepared or collected separately and then added. There is a great risk of oxidation impurities in the process. At the same time, when the non-rare earth Fe element is introduced into the grain boundary phase by the heavy rare earth alloy and reaches a certain proportion, it will have a negative effect on the magnet performance.

[0007] 3. The general-purpose of the specially designed auxiliary alloy with a high total rare earth content is poor, and the compositional design of the auxiliary alloy is not significantly different from that of the main alloy, and the performance improvement effect is not good. For example, in the patent application with the publication number CN 115083707A, the compositional design of the main and auxiliary alloys is not significantly different. The elements in the formula of the auxiliary alloy are close to the rare earth elements and non-rare earth elements of the main alloy, and it is difficult to achieve the goal of ideal grain boundary regulation and reconstruction.

[0008] Therefore, the existing preparation of NdFeB magnets needs to be further improved. Summary of the Invention

[0009] The purpose of the present invention is to make up for the above deficiencies and disclose a NdFeB permanent magnet and its preparation method to the society. It adopts the design of an auxiliary alloy with low boron and high total rare earth content. During the preparation process, metal Ga is added to the raw materials, and nano-Cu powder is added during the jet milling process, which can increase the grain boundary fluidity and the thickness of the grain boundary phase to optimize the grain boundary distribution of the magnet, achieve the purpose of regulating the magnetism of the grain boundary phase, improve the demagnetization coupling effect between grains, and adopt a four-stage sintering and aging heat treatment process, which can effectively control the size of the triple crystals, increase the thickness of the narrow grain boundary, and improve the tissue consistency of the material.

[0010] The technical solution of the present invention is realized as follows:

[0011] A NdFeB permanent magnet, the magnet composition of the NdFeB permanent magnet is R c Fe 余量 M d Zr e Cu f Ga g B h, where c, d, e, f, g, h are the mass percentages of the corresponding elements, the sum of the mass ratios of c, d, e, f, g, h and the balance is 100%, and 28.5 ≤ c ≤ 31.5, 0.5 ≤ d ≤ 3, 0.15 ≤ e ≤ 0.6, 0.15 ≤ f ≤ 0.6, 0.15 ≤ g ≤ 0.6, 0.84 ≤ h ≤ 0.97, and the balance is Fe and inevitable impurity elements; R is a rare earth element, and M is a non-rare earth element;

[0012] The neodymium iron boron permanent magnet described is a multi-alloy mixture composed of a main alloy and N auxiliary alloys, N ≥ 1, the mass ratio of the main alloy in the multi-alloy mixture is 85% to 99.5%, and the mass ratio of the auxiliary alloy in the multi-alloy mixture is 0.5% to 15%;

[0013] The main alloy composition is R1 v Fe 余量 H w Cu x Ga y B z , where v, w, x, y, z are the mass percentages of the corresponding elements, the sum of the mass percentages of v, w, x, y, z and the balance is 100%, and 28 ≤ v ≤ 31, 0.65 ≤ w ≤ 3.6, 0.05 ≤ x ≤ 0.35, 0.05 ≤ y ≤ 0.35, 0.85 ≤ z ≤ 0.98, and the balance is Fe and inevitable impurity elements, R1 is a rare earth element, and H is a non-rare earth element;

[0014] The auxiliary alloy composition is Rn a Fe 余量 B b , where a, b are the mass percentages of the corresponding elements, the sum of the mass ratios of a, b and the balance is 100%, and 35 ≤ a ≤ 50, 0.3 ≤ b ≤ 0.8, and the balance is Fe and inevitable impurity elements, Rn is a rare earth element.

[0015] Preferably, in the magnet composition, the R is one or more of La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and the M is at least one of Co, Al, Nb, Ti, Sn, Bi.

[0016] Preferably, in the main alloy composition, the R1 is one or more of La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and the H is at least two of Co, Al, Zr, Nb, Ti, Sn, Bi and must contain Zr.

[0017] Preferably, in the auxiliary alloy composition, the Rn is one or more of La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er.

[0018] A preparation method of a neodymium-iron-boron permanent magnet, comprising the following steps:

[0019] Step 1: According to the formula, perform the main and auxiliary alloy batching, and respectively carry out vacuum induction melting to obtain a main alloy cast sheet and an auxiliary alloy cast sheet with a thickness of 0.1 mm - 0.5 mm;

[0020] Step 2: Mix the main alloy cast sheet and N kinds of auxiliary alloy cast sheets, N≥1, add metal Ga, and perform hydrogen crushing to obtain hydrogen-crushed coarse powder;

[0021] Step 3: Add an antioxidant and nano-Cu powder to the hydrogen-crushed coarse powder, stir for 30 minutes, then carry out jet milling to obtain fine powder with a particle size of 2.5 - 4.0 microns. After adding an antioxidant and a lubricant to the fine powder, stir;

[0022] Step 4: Put the fine powder into the press operation box under nitrogen protection for orientation pressing. The oxygen content in the press system is <0.05%, the orientation field >1.8 T, and the pressing density is 3.8 - 4.4 g / cm 3 , after isostatic pressing at 180 MPa, put it into the furnace for vacuum sintering and aging treatment;

[0023] Step 5: Sintering and aging treatment: The first-stage high-temperature sintering temperature is 1060 - 1100 °C, and the heat preservation time is 2 - 8 h. The second-stage high-temperature sintering temperature is 1040 - 1080 °C, and the heat preservation time is 2 - 8 h. The third-stage aging treatment temperature is 850 - 950 °C, and the heat preservation time is 2 - 5 h. The fourth-stage aging treatment temperature is 450 °C - 650 °C, and the heat preservation time is 4 - 8 h, to obtain a sintered neodymium-iron-boron permanent magnet.

[0024] Preferably, in the step 2, the mixing weight ratio of the main alloy cast sheet and the auxiliary alloy cast sheet is: 85% - 99.5%: 0.5% - 15%.

[0025] Preferably, in the step 2, the addition amount of metal Ga is 0.1% - 0.5% of the weight of the mixture.

[0026] Preferably, in the step 3, the addition amount of nano-Cu powder is 0.1% - 0.3% of the weight of the mixture.

[0027] Preferably, in the step 3, the addition amount of the antioxidant in the hydrogen-crushed coarse powder is 0.1% of the weight of the mixture; the addition amount of the antioxidant and the lubricant in the fine powder is 0.05% of the weight of the mixture.

[0028] The neodymium-iron-boron permanent magnet is applied to wind turbines, 3C consumer electronic products, and linear motors.

[0029] The advantages of the present invention compared with the prior art are:

[0030] The NdFeB permanent magnet of the present invention adopts a main and auxiliary alloy phase structure. Among them, the main alloy mainly obtains the Nd2Fe 14 B main phase. The auxiliary alloy is designed with a low boron and high total rare earth content, and only contains three elements: boron, rare earth metal, and iron. While forming a certain main phase, it provides a large proportion of rare earth-rich phase as the main source of the grain boundary phase.

[0031] For the preparation method of the NdFeB permanent magnet of the present invention, by adding grain boundary additives (metal Ga and nano Cu powder), a low melting point RE-Cu-Ga phase is formed within the grain boundary phase, which can promote the flow of the rare earth-rich grain boundary phase during aging, increase the thickness of the grain boundary phase, and improve the demagnetization coupling effect. And use metal Ga to construct the phase-forming environment of the 6:13:1 non-ferromagnetic phase at the grain boundary, increase the grain boundary fluidity and the thickness of the grain boundary phase to optimize the grain boundary distribution of the magnet, achieve the purpose of regulating the magnetism of the grain boundary phase, and improve the demagnetization coupling effect between grains.

[0032] In addition, by adopting a four-stage sintering and aging heat treatment process, the size of the triple junction grains can be effectively controlled, the thickness of the narrow grain boundary can be increased, the material structure consistency can be improved, and the product performance consistency can be improved. Description of the Drawings

[0033] Figure 1 is the main alloy component table of the examples and comparative examples of the present invention;

[0034] Figure 2 is the auxiliary alloy component table of the examples and comparative examples of the present invention;

[0035] Figure 3 is the main and auxiliary alloy composition and grain boundary regulation element combination table of the examples and comparative examples of the present invention;

[0036] Figure 4 is the sintering and aging treatment process table in the comparative experiment of the present invention;

[0037] Figure 5 is the performance index table of the comparative experiment of the present invention;

[0038] Figure 6 is the magnet microstructure diagram of Example 1 of the present invention;

[0039] Figure 7 is the magnet microstructure diagram of the comparative group of the present invention. Detailed Description of the Invention

[0040] The present invention will be further described in detail below:

[0041] A NdFeB permanent magnet, the magnet component of the NdFeB permanent magnet is R c Fe 余量 M d Zr eCu f Ga g B h , wherein, c, d, e, f, g, h are the mass percentages of the corresponding elements, the sum of the mass ratios of c, d, e, f, g, h and the balance is 100%, and 28.5 ≤ c ≤ 31.5, 0.5 ≤ d ≤ 3, 0.15 ≤ e ≤ 0.6, 0.15 ≤ f ≤ 0.6, 0.15 ≤ g ≤ 0.6, 0.84 ≤ h ≤ 0.97, and the balance is Fe and inevitable impurity elements; R is a rare earth element, and M is a non-rare earth element;

[0042] The neodymium iron boron permanent magnet described is a multi-alloy mixture composed of a main alloy and N auxiliary alloys, N ≥ 1, the mass ratio of the main alloy in the multi-alloy mixture is 85% to 99.5%, and the mass ratio of the auxiliary alloy in the multi-alloy mixture is 0.5% to 15%;

[0043] The main alloy composition is R1 v Fe 余量 H w Cu x Ga y B z , wherein v, w, x, y, z are the mass percentages of the corresponding elements, the sum of the mass percentages of v, w, x, y, z and the balance is 100%, and 28 ≤ v ≤ 31, 0.65 ≤ w ≤ 3.6, 0.05 ≤ x ≤ 0.35, 0.05 ≤ y ≤ 0.35, 0.85 ≤ z ≤ 0.98, and the balance is Fe and inevitable impurity elements, R1 is a rare earth element, and H is a non-rare earth element;

[0044] The auxiliary alloy composition is Rn a Fe 余量 B b , wherein, a, b are the mass percentages of the corresponding elements, the sum of the mass ratios of a, b and the balance is 100%, and 35 ≤ a ≤ 50, 0.3 ≤ b ≤ 0.8, and the balance is Fe and inevitable impurity elements, Rn is a rare earth element.

[0045] In the magnet composition described, the R is one or more of La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and the M is at least one of Co, Al, Nb, Ti, Sn, Bi.

[0046] In the main alloy composition described, the R1 is one or more of La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and the H is at least two of Co, Al, Zr, Nb, Ti, Sn, Bi and must contain Zr.

[0047] In the described secondary alloy composition, Rn is one or more of La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er.

[0048] A method for preparing a neodymium-iron-boron permanent magnet, comprising the following steps:

[0049] Step 1: According to the formula, perform primary and secondary alloy batching, and respectively conduct vacuum induction melting to obtain primary alloy cast sheets and secondary alloy cast sheets with a thickness of 0.1 mm - 0.5 mm.

[0050] Step 2: Mix the primary alloy cast sheets and N secondary alloy cast sheets, where N ≥ 1, add metallic Ga, and perform hydrogen decrepitation to obtain hydrogen-decrepitated coarse powder; the mixing weight ratio of the primary alloy cast sheets to the secondary alloy cast sheets is: 85% - 99.5% : 0.5% - 15%, and the addition amount of metallic Ga is 0.1% - 0.5% of the weight of the mixture.

[0051] Step 3: Add an antioxidant and nano-Cu powder to the hydrogen-decrepitated coarse powder, stir for 30 minutes, then perform jet milling to obtain fine powder with a particle size of 2.5 - 4.0 microns, and stir after adding the antioxidant and lubricant to the fine powder; the addition amount of nano-Cu powder is 0.1% - 0.3% of the weight of the mixture. The addition amount of the antioxidant in the hydrogen-decrepitated coarse powder is 0.1% of the weight of the mixture. The addition amounts of the antioxidant and lubricant in the fine powder are 0.05% of the weight of the mixture.

[0052] Step 4: Place the fine powder into a press operation box under nitrogen protection for orientation pressing, with the oxygen content in the press system < 0.05%, the orientation field > 1.8 T, and the pressing density of 3.8 - 4.4 g / cm 3 , after isostatic pressing at 180 MPa, put it into the furnace for vacuum sintering and aging treatment;

[0053] Step 5: Sintering and aging treatment: The first-stage high-temperature sintering temperature is 1060 - 1100 °C, with a holding time of 2 - 8 h, the second-stage high-temperature sintering temperature is 1040 - 1080 °C, with a holding time of 2 - 8 h, the third-stage aging treatment temperature is 850 - 950 °C, with a holding time of 2 - 5 h, and the fourth-stage aging treatment temperature is 450 °C - 650 °C, with a holding time of 4 - 8 h, to obtain a sintered neodymium-iron-boron permanent magnet. Preferably, the first-stage high-temperature sintering temperature is higher than the second-stage high-temperature sintering temperature.

[0054] The described neodymium-iron-boron permanent magnet is applicable to wind turbines, 3C consumer electronic products, and linear motors.

[0055] The preparation method of the present invention uses a "2+2" four-stage sintering and aging heat treatment process to improve the grain structure of the magnet, that is, a two-stage sintering process + a two-stage aging heat treatment process. Specifically, the high-temperature sintering is carried out in two stages. In the first high-temperature stage (1060-1100°C), the green body can be quickly densified at high temperature to remove harmful impurities therein. In the second sub-high-temperature stage (1040-1080°C), the purpose is to construct the grain boundary phase structure so that the added metal Ga and nano Cu powder at the grain boundary can better fuse with the main phase grains at the grain boundary, preparing for the formation of the subsequent 6:13:1 phase. At the same time, the size of the triple junction grains can be effectively controlled, the thickness of the narrow grain boundary can be increased, the consistency of the material structure can be improved, and the consistency of the product performance can be improved.

[0056] The purpose of adding metal Ga in the preparation method of the present invention is to provide a phase formation environment for constructing the 6:13:1 phase at the grain boundary. The Ga added during hydrogen crushing is mainly located at the grain boundary and forms the 6:13:1 phase with the rare earth in the auxiliary alloy added previously. The 6:13:1 phase is: Nd6Fe 13 Ga1, traditional Nd2Fe 14 The formation of B (2:14:1 phase) in Nd2Fe14B depends on boron as a structure stabilizer. Under low boron conditions, the vacancies of B may lead to the instability of the 2:14:1 phase structure, and other elements (such as Ga) are needed to fill or reconstruct the crystal lattice. The atomic radius of Ga is close to that of Fe, and it is easy to replace the Fe site. The difference in the electronic structure of Ga (p-block element) and Fe (d-block) changes the local chemical bonding and can promote the formation of new phases.

[0057] The 6:13:1 phase has a tetragonal structure similar to that of 2:14:1, but the lattice parameters are adjusted due to the incorporation of Ga. The occupation of the Fe site by Ga can lead to the expansion of the unit cell, reduce the symmetry, and form the stoichiometry of Nd6Fe 13 Ga1. Ga preferentially replaces specific sublattice positions of Fe (such as 8j or 16k positions), changing the local electron density and magnetic exchange interaction, thereby stabilizing the new phase.

[0058] In the Nd-Fe-B-Ga quaternary system, under the condition of low boron and high gallium, the Gibbs free energy of the 6:13:1 phase is lower than that of the traditional 2:14:1 phase, becoming a thermodynamically more stable phase.

[0059] In addition, the addition of Ga reduces the liquid phase formation temperature, promotes grain boundary diffusion, accelerates atomic rearrangement, and provides kinetic conditions for the nucleation of new phases. The replacement of Fe by Ga can reduce the saturation magnetization of the main phase (because Ga is a non-magnetic element), but the coercivity can be improved by optimizing the grain boundary phase. Ga is enriched at the grain boundary, inhibiting the nucleation of reverse magnetization domains. At the same time, the presence of the 6:13:1 phase can refine the grains and enhance the magnetic hardening ability.

[0060] In the preparation method of the present invention, the purpose of adding metallic nano Cu powder is to refine the crystal grains and enhance the coercivity. The high surface activity and small size of the nano copper powder can serve as heterogeneous nucleation sites to inhibit the abnormal growth of the main phase (Nd2Fe 14 B) crystal grains, refine the microstructure, and thus enhance the coercivity (Hcj). At the same time, the synergistic effect of gallium further stabilizes the grain boundaries and hinders the movement of magnetic domain walls. In addition, adding Cu powder can also optimize the grain boundary phase and magnetic properties. Copper diffuses to the grain boundaries during sintering to form a Cu-rich phase (such as Nd-Cu or Nd-Fe-Cu phase), improve the grain boundary wettability, and reduce grain boundary defects. The previously added gallium can promote the uniform distribution of copper, jointly form a eutectic liquid phase with a low melting point, enhance the grain boundary isolation effect, and reduce the probability of reverse magnetic domain nucleation, thereby achieving the purpose of improving performance.

[0061] The following is a further elaboration in combination with examples and comparative experiments:

[0062] The present invention combines a main alloy and an auxiliary alloy. The main alloy composition is R1 v Fe 余量 H w Cu x Ga y B z , and the auxiliary alloy composition is Rn a Fe 余量 B b . The main alloy component tables of the examples and comparative examples are as Figure 1 shown, and the auxiliary alloy component tables of the examples and comparative examples are as Figure 2 shown. The main and auxiliary alloy compositions and the grain boundary regulation element combination tables of the examples and comparative examples are as Figure 3 shown (in the examples, the added weights of metallic Ga and metallic nano Cu powder are calculated according to the total weight percentage after mixing the main and auxiliary alloys). Raw materials are prepared according to the composition in Figures 1 to 3 , and permanent magnets are prepared according to steps 1 to 4 of the preparation method of the present invention. Then, sintering and aging treatment processes are carried out according to the processes shown in Figure 4 to obtain corresponding permanent magnets (Examples 1-3 and Comparative Examples 1-3). The performance of Examples 1-3 and Comparative Examples 1-3 is tested, and the test results are as Figure 5 shown. It can be seen from Figure 5 that compared with Comparative Examples 1-3, Examples 1-3, through the multi-alloy process and grain boundary addition regulation technology described in this design, combined with the 2+2 type four-stage sintering and aging process, the total material cost in the example formula is equivalent to or lower than that of the comparative examples, but the magnetic properties of the magnets are significantly improved compared with the comparative examples. This formula and process ensure all indexes of magnetic properties while having equivalent or better cost, achieving good results.

[0063] The neodymium iron boron permanent magnet of the present invention adopts "1+N+2", where "1" refers to the main alloy, "N" refers to N kinds of auxiliary alloys, and "2" refers to the grain boundary additive metals Ga and nano Cu powder. Among them, the main alloy mainly obtains the Nd2Fe 14 B main phase. The auxiliary alloy is designed with low boron and high total rare earth content, and only contains three elements: boron, rare earth metal, and iron. While forming a certain main phase, it provides a large proportion of rare earth-rich phase as the main source of the grain boundary phase. As a preference, multiple auxiliary alloys can be combined, that is, N≥2. Using multiple auxiliary alloys can take into account the material formula cost and performance requirements. By conducting different addition types and proportion adjustment tests, the optimization of material cost and performance can be achieved. By adding Pr-Nd light rare earth auxiliary alloy, the intrinsic coercivity can be improved while the remanence hardly decreases or slightly decreases; while adding a small amount of Dy, Tb heavy rare earth auxiliary alloy can greatly improve the intrinsic coercivity of the material.

[0064] Prepare raw materials according to Example 1, and prepare the permanent magnet according to Steps 1 to 4 of the preparation method of the present invention. Through the first-stage sintering at 1090°C, the second-stage sintering at 1070°C, the third-stage aging heat treatment at 900°C, and the fourth-stage aging heat treatment at 475°C, the permanent magnet of Example 1 is prepared, and the microstructure is observed. The microstructure diagram of the magnet is as follows Figure 6 shown. As a control group, prepare raw materials in the same way as in Example 1, prepare the permanent magnet according to Steps 1 to 4, and through the first-stage sintering at 1080°C, the second-stage aging heat treatment at 900°C, and the third-stage aging heat treatment at 475°C, the permanent magnet of the control group is prepared, and the microstructure is observed. The microstructure diagram of the magnet is as follows Figure 7 shown. By comparing the microstructure diagrams of Example 1 and the control group, it can be found that the grain boundary continuity of the control group is poor, and the rare earth-rich phase aggregated at the triple grain boundary is larger, and the white spots at the triple grain boundary are more and larger; while the grain boundary of Example 1 is more continuous, the triple grain boundary is smaller, and the rare earth-rich phase is less, indicating that more low-melting-point alloy / rare earth-rich phase flows to the surrounding narrow grain boundaries. Adopting the "2+2" sintering and aging heat treatment process of the present invention, that is, adopting a two-stage sintering process + a two-stage aging heat treatment process, can effectively control the size of the triple grain, increase the thickness of the narrow grain boundary, improve the material tissue consistency, and improve the product performance consistency.

[0065] The best embodiments of the present invention have been illustrated, and various changes or modifications made by those of ordinary skill in the art will not depart from the scope of the present invention.

Claims

1. A neodymium iron boron permanent magnet, characterized in that: The magnet composition of the neodymium iron boron permanent magnet is R c Fe 余量 M d Zr e Cu f Ga g B h , where c, d, e, f, g, h are the mass percentages of the corresponding elements, the sum of the mass ratios of c, d, e, f, g, h and the balance is 100%, and 28.5 ≤ c ≤ 31.5, 0.5 ≤ d ≤ 3, 0.15 ≤ e ≤ 0.6, 0.15 ≤ f ≤ 0.6, 0.15 ≤ g ≤ 0.6, 0.84 ≤ h ≤ 0.97, and the balance is Fe and inevitable impurity elements; R is a rare earth element, and M is a non-rare earth element; The neodymium iron boron permanent magnet is a multi - alloy mixture composed of a main alloy and N auxiliary alloys, N≥1. The mass ratio of the main alloy in the multi - alloy mixture is 85% to 99.5%, and the mass ratio of the auxiliary alloy in the multi - alloy mixture is 0.5% to 15%. The main alloy component is R1 v Fe 余量 H w Cu x Ga y B z , where v, w, x, y, z are the mass percentages of the corresponding elements, the sum of the mass percentages of v, w, x, y, z and the balance is 100%, and 28 ≤ v ≤ 31, 0.65 ≤ w ≤ 3.6, 0.05 ≤ x ≤ 0.35, 0.05 ≤ y ≤ 0.35, 0.85 ≤ z ≤ 0.98, the balance is Fe and inevitable impurity elements, R1 is a rare earth element, and H is a non-rare earth element; The secondary alloying component is Rn a Fe 余量 B b , where a and b are the mass percentages of the corresponding elements, the sum of the mass ratios of a, b and the balance is 100%, and 35 ≤ a ≤ 50, 0.3 ≤ b ≤ 0.8, the balance is Fe and inevitable impurity elements, and Rn is a rare earth element.

2. The neodymium iron boron permanent magnet according to claim 1, characterized in that: In the magnet composition, R is one or more of La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and M is at least one of Co, Al, Nb, Ti, Sn, Bi.

3. A neodymium iron boron permanent magnet according to claim 1, characterized in that: In the main alloy composition, R1 is one or more of La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and H is at least two of Co, Al, Zr, Nb, Ti, Sn, Bi and must contain Zr.

4. A neodymium iron boron permanent magnet according to claim 1, characterized in that: In the auxiliary alloy composition, Rn is one or more of La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er.

5. The preparation method of a neodymium iron boron permanent magnet according to claim 1, characterized in that: It includes the following steps: Step 1: According to the formula, perform batching of the main and auxiliary alloys, and conduct vacuum induction melting respectively to obtain main alloy cast sheets and auxiliary alloy cast sheets with a thickness of 0.1mm - 0.5mm. Step 2: Mix the main alloy cast sheets and N auxiliary alloy cast sheets, N≥1, add metallic Ga, and perform hydrogen decrepitation to obtain hydrogen - decrepitated coarse powder. Step 3: Add an antioxidant and nano - Cu powder to the hydrogen - decrepitated coarse powder, stir for 30 minutes, then perform jet milling to obtain fine powder with a particle size of 2.5 - 4.0 microns. After adding an antioxidant and a lubricant to the fine powder, stir it. Step 4: Put the fine powder into the press operation box under nitrogen protection for orientation pressing. The oxygen content in the press system is <0.05%, the orientation field > 1.8T, and the pressing density is 3.8 - 4.4 g / cm 3 . After isostatic pressing at 180 MPa, put it into the furnace for vacuum sintering and aging treatment; Step 5: Sintering and aging treatment: The first - stage high - temperature sintering temperature is 1060 - 1100°C, and the holding time is 2 - 8h. The second - stage high - temperature sintering temperature is 1040 - 1080°C, and the holding time is 2 - 8h. The third - stage aging treatment temperature is 850 - 950°C, and the holding time is 2 - 5h. The fourth - stage aging treatment temperature is 450°C - 650°C, and the holding time is 4 - 8h to obtain a sintered neodymium iron boron permanent magnet.

6. The preparation method of a neodymium iron boron permanent magnet according to claim 5, characterized in that: In the step 2, the mixing weight ratio of the main alloy cast sheets and the auxiliary alloy cast sheets is: 85% - 99.5%:0.5% - 15%.

7. The preparation method of a neodymium iron boron permanent magnet according to claim 5, characterized in that: In the step 2, the addition amount of metallic Ga is 0.1% - 0.5% of the mixture weight.

8. The preparation method of a neodymium iron boron permanent magnet according to claim 5, characterized in that: In the step 3, the addition amount of nano - Cu powder is 0.1% - 0.3% of the mixture weight.

9. The preparation method of a neodymium-iron-boron permanent magnet according to claim 5, characterized in that: In the step 3, the addition amount of the antioxidant in the hydrogen - decrepitated coarse powder is 0.1% of the mixture weight; the addition amount of the antioxidant and the lubricant in the fine powder is 0.05% of the mixture weight.

10. The application of a neodymium iron boron permanent magnet according to claim 1, characterized in that: The neodymium iron boron permanent magnet is applied to wind turbines, 3C consumer electronics products, and linear motors.

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