High remanence sintered neodymium-iron-boron permanent magnet and method for producing the same

Abstract

This invention discloses a high-remanence sintered NdFeB permanent magnet and its preparation method. The preparation method includes: uniformly mixing a main phase alloy powder with an auxiliary phase alloy powder having an iron content of 70wt%-85wt%, followed by orientation pressing to form a green blank; subjecting the green blank to sintering and tempering heat treatment to obtain a sintered blank; attaching diffusion source powder to the surface of the sintered blank, and performing diffusion heat treatment to obtain the high-remanence sintered NdFeB permanent magnet. This invention introduces a high-iron auxiliary phase and excess rare earth and boron elements between grains to undergo metallurgical reactions and generate a new main phase, which can increase the proportion of ferromagnetic phase in the magnet.

Description

Technical Field

[0001] This invention belongs to the field of rare earth permanent magnet materials technology, specifically relating to a high remanence sintered NdFeB permanent magnet and its preparation method. Background Technology

[0002] Since their introduction in the 1980s, neodymium iron boron (NdFeB) permanent magnets have been an irreplaceable core functional material in high-tech fields such as medical instruments, automobiles, and industrial motors due to their high remanence, high coercivity, and high cost-effectiveness. In the field of new energy drive motors, the use of sintered NdFeB permanent magnets can significantly reduce the amount of magnetic material used, shrink the size and weight of the motor, and simultaneously improve the energy-to-mechanical-energy conversion efficiency, resulting in a substantial improvement in energy efficiency compared to ordinary permanent magnets. Recently, with the new development trend of drive motors evolving from round wire windings to flat wire windings, the fill factor and current density of the stator copper wire assembly slots have increased significantly, requiring sintered NdFeB permanent magnets with the highest possible remanence (magnetic moment) to be matched in the rotor.

[0003] Remanence, a key magnetic performance indicator of sintered NdFeB permanent magnets, has a theoretical upper limit of 1.61T. Currently, the remanence of sintered NdFeB permanent magnets produced using existing processes typically ranges from 1.20 to 1.47T. Furthermore, conventional surface protection processes in the later stages of magnet production can cause minor damage to the remanence, making further enhancement extremely difficult. The remanence of sintered NdFeB permanent magnets is closely related to factors such as magnet density, orientation, the proportion of ferromagnetic phase, and the volume fraction of positive magnetic domains. Increasing the proportion of ferromagnetic phase is widely recognized as the most direct and effective method to improve remanence. Therefore, in magnet manufacturing, reducing the rare earth content in the raw material formulation is commonly used to enhance remanence. When the magnet is composed entirely of the neodymium iron boron ferromagnetic main phase, its remanence reaches its maximum. At this time, the rare earth content is close to a positive fraction of 26.8% (mass ratio). However, since the preparation process of sintered neodymium iron boron permanent magnets is based on powder metallurgy, extensive practice has shown that when the rare earth content of the raw material is lower than 29% (mass ratio) and approaches a positive fraction, the powder sintering process will find it difficult to achieve liquid phase sintering and shrinkage due to the lack of sufficient intergranular phase, resulting in the magnet not being fully densified.

[0004] In summary, upgrading and improving the manufacturing process of sintered NdFeB permanent magnets, while ensuring the densification of the magnets during sintering, is the only way to increase the remanence of the magnets and meet the performance requirements of NdFeB magnets for the development of new motors. This has profound significance for promoting the rapid development of the rare earth permanent magnet field. Summary of the Invention

[0005] The main objective of this invention is to provide a high remanence sintered NdFeB permanent magnet and its preparation method, so as to overcome the shortcomings of the prior art.

[0006] To achieve the aforementioned objectives, the technical solutions adopted in the embodiments of the present invention include:

[0007] This invention provides a method for preparing a high-remanence sintered NdFeB permanent magnet, comprising:

[0008] The main phase alloy powder is uniformly mixed with the auxiliary phase alloy powder with an iron content of 70wt%-85wt%, and then oriented and pressed to form a green blank; the green blank is then sintered and tempered to obtain a sintered blank.

[0009] Diffusion source powder is attached to the surface of the sintered blank and subjected to diffusion heat treatment to obtain high remanence sintered NdFeB permanent magnets.

[0010] Furthermore, the chemical formula of the main phase alloy powder is RE1 by mass percentage. a B b M1 c Fe 100-a-b-c RE1 includes one or more of Pr, Nd, Dy, Tb, La, Ce, Y, Ho or Gd, B is boron, M1 includes one or more of Cu, Al, Ga, Co, Zr, Ti, Fe is iron, and 28.5≤a≤31, 0.94≤b<1.1, 0.5≤c≤4;

[0011] The chemical formula of the auxiliary phase alloy powder is RE2 by mass percentage. x Fe y B z M2 j RE2 includes at least one of Pr and Nd, Fe is iron, B is boron, and M2 includes one or more of Cu, Al, Ga, Co, Zr, and Ti; 10≤x≤20, 70≤y≤85, 0.2≤z≤0.9, 0≤j≤4, and satisfies x+y+z+j=100.

[0012] Furthermore, the mass ratio of the main phase alloy powder to the auxiliary phase alloy powder is 85-95:15-5.

[0013] Furthermore, the conditions for the tempering heat treatment include: a first-stage heat treatment at a temperature of 900℃ to 1000℃ for a time of 0.5 hours to 2 hours; a second-stage heat treatment at a temperature of 750℃ to 900℃ for a time of 0.5 hours to 2 hours; and a third-stage heat treatment at a temperature of 480℃ to 550℃ for a time of 1 hour to 4 hours.

[0014] Furthermore, the chemical formula of the diffusion source powder is RE3 by mass percentage. m M3 nRE3 includes at least one of Pr, Nd, Dy, Tb, and Ho, and M3 is at least one of Al, Cu, and Ga, and simultaneously satisfies 40≤m≤60 and m+n=100.

[0015] In the preparation process of this invention, the green blank is sintered and tempered to form a sintered blank, which includes main phase particles, the main phase particles are wrapped with a regenerated main phase shell, and iron-rich soft magnetic phase particles are distributed between the regenerated main phase shell. Then, the iron-rich soft magnetic phase particles are diffused by a diffusion source powder of a specific composition to transform the iron-rich soft magnetic phase particles into weak magnetic phase particles, and the weak magnetic phase particles are filled with diffusion source components.

[0016] The present invention also provides a high remanence sintered NdFeB permanent magnet, which is manufactured by the aforementioned method.

[0017] Furthermore, the high remanence sintered NdFeB permanent magnet includes main phase particles, which are wrapped with a regenerated main phase shell, and weak magnetic phase particles are distributed between the regenerated main phase shell, with diffusion source components filling the spaces between the weak magnetic phase particles; wherein, the weak magnetic phase particles are weak magnetic 6:13:1 phases, and the 6:13:1 phase refers to a weak magnetic phase formed by rare earth elements, iron elements, and metallic elements (copper, aluminum, or gallium) in an atomic ratio of 6:13:1.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) This invention utilizes a dual alloy to introduce a specially designed high-iron-content auxiliary phase alloy component. Combined with the particle size distribution of the powder, it can undergo a metallurgical reaction with excess rare earth and boron elements between the crystals during sintering and tempering heat treatment to generate a new main phase, thereby increasing the proportion of ferromagnetic phase in the magnet to a certain extent, thus achieving the purpose of preparing high remanence NdFeB permanent magnets.

[0020] (2) The introduction of the high iron content auxiliary phase alloy in this invention achieves the purpose of reducing the overall rare earth content of the magnet. At the same time, since the high iron content auxiliary phase alloy specially designed in this invention can also be used as a sintering phase, it helps to promote the liquid phase sintering and densification process of the magnet. Therefore, it overcomes the problem that NdFeB magnetic powder particles in low rare earth content systems are difficult to sinter and densify.

[0021] (3) After increasing the proportion of ferromagnetic phase in the magnet, the present invention further precisely designed a specific diffusion source alloy by matching the composition content and process window of the weak magnetic 6:13:1 phase. During the diffusion modification process, the phase transformation of the iron-rich soft magnetic phase can be achieved, avoiding the problem of reduced coercivity caused by the introduction of too much iron. Moreover, the high remanence NdFeB permanent magnet products prepared by the present invention have good performance consistency, the process flow is easy to control, and it is suitable for mass production. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the formation process of a high remanence sintered NdFeB permanent magnet in one embodiment of this application.

[0024] Figure 2 The graph shows the Rietveld refinement calculation results of the XRD results of the magnet powders in Example 1 and Comparative Example 1.

[0025] Explanation of reference numerals in the attached figures: 1. Main phase particles, 2. High iron content auxiliary phase particles, 3. Regenerated main phase shell, 4. Iron-rich soft magnetic phase particles, 5. Weakly magnetic phase particles, 6. Diffusion source component. Detailed Implementation

[0026] To overcome the shortcomings of existing technologies, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. This invention mainly provides a high-remanence sintered NdFeB permanent magnet and its preparation method. By introducing a high-iron auxiliary phase and excess rare earth and boron elements between grains to undergo metallurgical reactions and generate a new main phase, the proportion of ferromagnetic phase in the magnet is increased. Furthermore, by designing a specific diffusion source alloy, a phase transformation of the iron-rich soft magnetic phase is achieved during the diffusion modification process, thereby enhancing the coercivity of the magnet. The following will further explain and illustrate this technical solution, its implementation process, and its principles.

[0027] One aspect of this invention provides a method for preparing a high-remanence sintered NdFeB permanent magnet, comprising:

[0028] The main phase alloy powder is uniformly mixed with the auxiliary phase alloy powder with an iron content of 70wt%-85wt%, and then oriented and pressed to form a green blank; the green blank is then sintered and tempered to obtain a sintered blank.

[0029] Diffusion source powder is attached to the surface of the sintered blank and subjected to diffusion heat treatment to obtain high remanence sintered NdFeB permanent magnets.

[0030] In some preferred embodiments, the chemical formula of the main phase alloy powder is RE1 by mass percentage. a B b Mi c Fe 100-a-b-cRE1 includes one or more of Pr, Nd, Dy, Tb, La, Ce, Y, Ho or Gd, B is boron, M1 includes one or more of Cu, Al, Ga, Co, Zr, Ti, Fe is iron, and 28.5≤a≤31, 0.94≤b<1.1, 0.5≤c≤4;

[0031] The chemical formula of the auxiliary phase alloy powder is RE2 by mass percentage. x Fe y B z M2 j RE2 includes at least one of Pr and Nd, Fe is iron, B is boron, and M2 includes one or more of Cu, Al, Ga, Co, Zr, and Ti; 10≤x≤20, 70≤y≤85, 0.2≤z≤0.9, 0≤j≤4, and satisfies x+y+z+j=100.

[0032] In some preferred embodiments, the mass ratio of the main phase alloy powder to the auxiliary phase alloy powder is 85-95:15-5.

[0033] In some preferred embodiments, the average particle size of the main phase alloy powder is 3 micrometers to 5 micrometers, and the average particle size of the auxiliary phase alloy powder is 0.5 micrometers to 2 micrometers.

[0034] In some preferred embodiments, the orientation magnetic field strength for orientation forming is 1.8 to 2.0 T.

[0035] In some preferred embodiments, the sintering conditions include: a sintering temperature of 1020℃~1100℃ and a sintering time of 2 hours~5 hours.

[0036] In some preferred embodiments, the tempering heat treatment conditions include: a first-stage heat treatment at a temperature of 900℃ to 1000℃ for a time of 0.5 hours to 2 hours; a second-stage heat treatment at a temperature of 750℃ to 900℃ for a time of 0.5 hours to 2 hours; and a third-stage heat treatment at a temperature of 480℃ to 550℃ for a time of 1 hour to 4 hours.

[0037] In some preferred embodiments, the chemical formula of the diffusion source powder is RE3 by mass percentage. m M3 n RE3 includes at least one of Pr, Nd, Dy, Tb, and Ho, and M3 is at least one of Al, Cu, and Ga, and simultaneously satisfies 40≤m≤60 and m+n=100.

[0038] In some preferred embodiments, the conditions for the diffusion heat treatment include: holding at 900°C to 950°C for 4 to 10 hours, followed by holding at 480°C to 550°C for 1 to 4 hours.

[0039] like Figure 1 As shown, in this embodiment of the invention, the main phase alloy powder and the high-iron content auxiliary phase alloy powder are uniformly mixed, and then oriented and pressed to form a green blank. The green blank includes main phase particles 1 and high-iron content auxiliary phase particles 2 distributed between the main phase particles. The green blank is then sintered and densified so that the main phase particles 1 are wrapped with a regenerated main phase shell layer 3, and iron-rich soft magnetic phase particles 4 are distributed between the regenerated main phase shell layers 3. Finally, a diffusion heat treatment is performed to transform the iron-rich soft magnetic phase particles 4 into weakly magnetic phase particles 5, and the weakly magnetic phase particles 5 are filled with diffusion source components 6, thereby obtaining a high remanence sintered NdFeB permanent magnet.

[0040] In a specific implementation of this invention, a method for preparing a high-remanence sintered NdFeB permanent magnet is also provided, comprising the following steps:

[0041] 1) Melting the main phase alloy and the auxiliary phase alloy with high iron content;

[0042] 2) The main phase alloy and the high-iron-content auxiliary phase alloy are separately powdered;

[0043] 3) Mix the main phase alloy powder and the high-iron content auxiliary phase alloy powder evenly in a specific ratio;

[0044] 4) The mixed powder is oriented and pressed to form a green body;

[0045] 5) The green blanks are sintered and tempered to obtain fired blanks;

[0046] 6) Prepare a specific diffusion source alloy and then prepare the diffusion source alloy into diffusion source powder;

[0047] 7) The diffusion source powder is attached to the surface of the sintered blank and subjected to diffusion heat treatment to obtain a high remanence sintered NdFeB permanent magnet.

[0048] In some preferred embodiments, the powdering process includes rapid solidification casting, hydrogen crushing, and air jet milling.

[0049] Another aspect of the present invention provides a high remanence sintered NdFeB permanent magnet, which is manufactured by the aforementioned method.

[0050] In some preferred embodiments, the high remanence sintered NdFeB permanent magnet includes main phase particles, which are wrapped with a regenerated main phase shell, and weak magnetic phase particles are distributed between the regenerated main phase shell, and diffusion source components are filled between the weak magnetic phase particles.

[0051] The technical solution of the present invention will be further explained and described below with reference to specific embodiments and accompanying drawings, so as to enable those skilled in the art to fully understand the present invention. However, this explanation and description are not a further limitation on the technical solution of the present invention. Any simple numerical substitutions and conventional adjustments made on the basis of the present invention are all within the protection scope of the present invention.

[0052] Example 1

[0053] A rapidly solidified alloy casting with a main phase is prepared by melting according to the proportions of each element, wherein the chemical formula of the main phase is Nd by mass percentage. 30.5 B 0.94 Al 0.1 Cu 0.1 Ga 0.5 Zr 0.1 Co 0.5 Fe 67.26 The chemical formula of the auxiliary phase with high iron content, expressed as Pr by mass percentage, is... 15 Fe 84 B 0.8 Cu 0.1 Al 0.1 .

[0054] The main phase alloy and the auxiliary phase alloy were separately powdered. The rapidly solidified cast sheet was subjected to hydrogen absorption at room temperature and a hydrogen pressure of 0.2 MPa for 3 hours, and then vacuum dehydrogenated at a temperature of 450℃ for 10 hours to obtain hydrogen-broken powder. Subsequently, the hydrogen-broken powder was further crushed by an air jet mill to obtain magnetic powder.

[0055] The main phase alloy powder and the auxiliary phase alloy powder were mixed, with the auxiliary phase alloy powder accounting for 5% of the total weight. The mixed powder was then oriented and pressed in a 1.8T magnetic field, and isostatically pressed at 180MPa to obtain a magnet green blank. Afterwards, under atmospheric isolation conditions, the magnet green blank was sent to a vacuum sintering furnace for sintering at 1070℃ for 4 hours. Finally, it was heat-treated at 990℃, 840℃, and 480℃ for 2 hours each to obtain NdFeB sintered blanks.

[0056] Diffusion source powder was prepared according to the ratio of each element, and its chemical formula by mass percentage is Pr. 50 Tb 10 Al 15 Cu 15 Ga 10 Diffusion source powder was attached to the surface of the sintered blank and subjected to diffusion heat treatment. The blank was held at 900℃ for 8 hours and then at 480℃ for 2 hours to obtain a high remanence sintered NdFeB permanent magnet.

[0057] Comparative Example 1

[0058] The neodymium iron boron permanent magnet was prepared according to the method of Example 1, the difference being that the chemical formula mass percentage of the matrix was the same as the nominal composition of the alloy after mixing in Example 1, which was Nd. 28.975 Pr 0.75 B 0.933 Al 0.1 Cu 0.095 Ga 0.475 Zr 0.095 Co 0.5 Fe 68.097 .

[0059] The remanence and coercivity of the magnet products prepared in Example 1 and the comparative example of this invention were tested using a high coercivity permanent magnet measuring instrument (model PFM14.CN) provided by HIRST Corporation. The density was measured using Archimedes' displacement method. The test results are as follows:

[0060] Remanence (kGs) Coercivity (kOe) <![CDATA[Density (g / cm 3 )]]> Example 1 14.78 20.91 7.56 Comparative Example 1 14.45 18.62 7.53

[0061] The magnet products of Example 1 and Comparative Example 1 were crushed, and the powder was subjected to X-ray diffraction. The proportion of the main phase was then calculated using Rietveld precision calculations, and the results are as follows: Figure 2 As shown.

[0062] The above results clearly show that the technical solution proposed in this invention can produce a more compact neodymium iron boron permanent magnet with high remanence.

[0063] Example 2

[0064] A rapidly solidified alloy casting with a main phase is prepared by melting according to the proportions of each element, wherein the chemical formula of the main phase is Nd by mass percentage. 29.5 B 0.98 Al 0.1 Cu 0.2 Ga 0.1 Zr 0.1 Fe 69.02 The chemical formula of the auxiliary phase with high iron content, expressed as Pr by mass percentage, is... 20 Fe 79.4 B 0.5 Ti 0.1 .

[0065] The main phase alloy and the auxiliary phase alloy were separately powdered. The rapidly solidified cast sheet was subjected to hydrogen absorption at room temperature and a hydrogen pressure of 0.2 MPa for 3 hours, and then vacuum dehydrogenated at a temperature of 450°C for 9 hours to obtain hydrogen-broken powder. Subsequently, the hydrogen-broken powder was further crushed using an air jet mill to obtain magnetic powder.

[0066] The main phase alloy powder and the auxiliary phase alloy powder were mixed, with the auxiliary phase alloy powder accounting for 10% of the total weight. The mixed powder was then oriented and pressed in a 2.0T magnetic field, and isostatically pressed at 180MPa to obtain a magnet green blank. Afterwards, under atmospheric isolation conditions, the magnet green blank was sent to a vacuum sintering furnace for sintering at 1080℃ for 4 hours. Finally, it was heat-treated at 1000℃, 850℃, and 500℃ for 2 hours each to obtain NdFeB sintered blanks.

[0067] Diffusion source powder was prepared according to the ratio of each element, and its chemical formula by mass percentage is Pr. 60 Al 20 Cu 10 Ga 10 Diffusion source powder was attached to the surface of the sintered blank and subjected to diffusion heat treatment. The blank was held at 900℃ for 10 hours and then held at 500℃ for 2 hours to obtain a high remanence sintered NdFeB permanent magnet.

[0068] Comparative Example 2

[0069] The neodymium iron boron permanent magnet was prepared according to the method of Example 2, the difference being that the chemical formula mass percentage of the matrix was the same as the nominal composition of the alloy after mixing in Example 2, which was Nd. 26.55 Pr2B 0.932 Al 0.09 Cu 0.18 Ga 0.09 Zr 0.09 Ti 0.01 Fe 70.058 .

[0070] The remanence and coercivity of the magnet products prepared in Example 2 and Comparative Example 2 of this invention were measured using a high coercivity permanent magnet measuring instrument (model PFM14.CN) provided by HIRST Corporation, and the density was measured using Archimedes' displacement method. The test results are as follows:

[0071]

[0072] The above results clearly show that the technical solution proposed in this invention can produce a more compact neodymium iron boron permanent magnet with high remanence.

[0073] Example 3

[0074] A rapidly solidified alloy casting with a main phase is prepared by melting according to the proportions of each element, wherein the chemical formula of the main phase is Nd by mass percentage. 31 B 1.0 Al 0.1 Cu 0.1 Zr 0.1 Co 0.5 Fe 68.2The chemical formula of the auxiliary phase with high iron content, expressed as Pr by mass percentage, is... 18 Fe 79.8 B 0.7 Al 0.2 Zr 0.1 Ga 1.2 .

[0075] The main phase alloy and the auxiliary phase alloy were separately powdered. The rapidly solidified cast sheet was subjected to hydrogen absorption at room temperature and a hydrogen pressure of 0.2 MPa for 4 hours, and then vacuum dehydrogenated at a temperature of 450°C for 10 hours to obtain hydrogen-broken powder. Subsequently, the hydrogen-broken powder was further crushed using an air jet mill to obtain magnetic powder.

[0076] The main phase alloy powder and the auxiliary phase alloy powder were mixed, with the auxiliary phase alloy powder accounting for 8% of the total weight. The mixed powder was then oriented and pressed in a 1.8T magnetic field, and isostatically pressed at 180MPa to obtain a magnet green blank. Subsequently, under atmospheric isolation conditions, the magnet green blank was sent to a vacuum sintering furnace for sintering at 1060℃ for 4 hours, followed by a 4-hour heat treatment at 980℃, and finally, heat treatments at 880℃ and 520℃ for 2 hours each to obtain a NdFeB sintered blank.

[0077] Diffusion source powder was prepared according to the ratio of each element, and its chemical formula by mass percentage is Pr. 35 Dy 25 Al 10 Cu 15 Ga 15 Diffusion source powder was attached to the surface of the sintered blank and subjected to diffusion heat treatment. The blank was held at 880℃ for 10 hours and then held at 500℃ for 2 hours to obtain a high remanence sintered NdFeB permanent magnet.

[0078] Comparative Example 3

[0079] The neodymium iron boron permanent magnet was prepared according to the method of Example 3, the difference being that the chemical formula mass percentage of the matrix was the same as the nominal composition of the alloy after mixing in Example 3, which was Nd. 28.52 Pr 1.44 B 0.976 Al 0.108 Cu 0.092 Zr 0.1 Co 0.46 Fe 69.128 Ga 0.096 .

[0080] The remanence and coercivity of the magnet products prepared in Example 3 and Comparative Example 3 of this invention were measured using a high coercivity permanent magnet measuring instrument (model PFM14.CN) provided by HIRST Corporation, and the density was measured using Archimedes' displacement method. The test results are as follows:

[0081] Remanence (kGs) Coercivity (kOe) <![CDATA[Density (g / cm 3 )]]> Example 3 14.73 17.65 7.56 Comparative Example 3 14.35 16.37 7.54

[0082] The above results clearly show that the technical solution proposed in this invention can produce a more compact neodymium iron boron permanent magnet with high remanence.

[0083] Example 4

[0084] A rapidly solidified alloy casting with a main phase is prepared by melting according to the proportions of each element, wherein the chemical formula of the main phase is Nd by mass percentage. 28.5 B 0.94 Al 0.2 Cu 0.2 Zr 0.1 Co 0.5 Fe 69.5 The chemical formula of the auxiliary phase with high iron content, expressed as Pr by mass percentage, is... 18 Fe 79.8 B0.7Cu 0.3 Ga 1.2 .

[0085] The main phase alloy and the auxiliary phase alloy were separately powdered. The rapidly solidified cast sheet was subjected to hydrogen absorption at room temperature and a hydrogen pressure of 0.2 MPa for 3 hours, and then vacuum dehydrogenated at a temperature of 450℃ for 10 hours to obtain hydrogen-broken powder. Subsequently, the hydrogen-broken powder was further crushed by an air jet mill to obtain magnetic powder.

[0086] The main phase alloy powder and the auxiliary phase alloy powder were mixed, with the auxiliary phase alloy powder accounting for 15% of the total weight. The mixed powder was then oriented and pressed in a 1.9T magnetic field, and isostatically pressed at 180MPa to obtain a magnet green blank. Afterwards, under atmospheric isolation conditions, the magnet green blank was sent to a vacuum sintering furnace for sintering at 1100℃ for 4 hours. Finally, it was heat-treated at 1000℃, 900℃, and 550℃ for 2 hours each to obtain NdFeB sintered blanks.

[0087] Diffusion source powder was prepared according to the ratio of each element, and its chemical formula by mass percentage is Pr. 35 Dy 15 Ho 10 Al 10 Cu 10 Ga 20 Diffusion source powder was attached to the surface of the sintered blank and subjected to diffusion heat treatment. The blank was held at 950℃ for 10 hours and then at 550℃ for 2 hours to obtain a high remanence sintered NdFeB permanent magnet.

[0088] Comparative Example 4

[0089] The neodymium iron boron permanent magnet was prepared according to the method of Example 4, the difference being that the chemical formula mass percentage of the matrix was the same as the nominal composition of the alloy after mixing in Example 4, which was Nd. 24.225 Pr 2.7B 0.904 Al 0.17 Cu 0.215 Zr 0.085 Co 0.425 Fe 71.045 Ga 0.18 .

[0090] The remanence and coercivity of the magnet products prepared in Example 4 and Comparative Example 4 of this invention were tested using a high coercivity permanent magnet measuring instrument (model PFM14.CN) provided by HIRST Company, and the density was measured using Archimedes' displacement method. The test results are as follows:

[0091]

[0092] The above results clearly show that the technical solution proposed in this invention can produce a more compact neodymium iron boron permanent magnet with high remanence.

[0093] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0094] This invention introduces a high-iron auxiliary phase and excess rare earth and boron elements between grains to undergo a metallurgical reaction and generate a new main phase, thereby increasing the proportion of ferromagnetic phase in the magnet. A specific diffusion source alloy is designed to achieve a phase transformation of the iron-rich soft magnetic phase during diffusion modification, thus improving the coercivity of the magnet. This method can prepare sintered NdFeB magnets with high remanence and high coercivity. The process is easy to control and suitable for mass production.

[0095] Although the invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that elements of the embodiments can be substituted with substantially equivalents. Furthermore, many modifications can be made without departing from the scope of the invention to adapt particular situations or materials to the teachings of the invention. Therefore, this invention is not intended to be limited to the specific embodiments disclosed for carrying out the invention, but rather is intended to encompass all embodiments falling within the scope of the appended claims. Moreover, unless specifically stated otherwise, any use of the terms first, second, etc., does not indicate any order or importance, but is used to distinguish one element from another.

Claims

1. A method for preparing a high-remanence sintered NdFeB permanent magnet, characterized in that, include: The main phase alloy powder is uniformly mixed with the auxiliary phase alloy powder with an iron content of 70wt%-85wt% and then oriented to form a green blank. The green blank is subjected to sintering and tempering heat treatment to obtain a sintered blank; Diffusion source powder is attached to the surface of the sintered blank and subjected to diffusion heat treatment to obtain high remanence sintered NdFeB permanent magnets; The chemical formula of the main phase alloy powder is RE1 by mass percentage. a B b M1 c Fe 100-a-b-c RE1 includes one or more of Pr, Nd, Dy, Tb, La, Ce, Y, Ho or Gd, B is boron, M1 includes one or more of Cu, Al, Ga, Co, Zr, Ti, Fe is iron, and 28.5≤a≤31, 0.94≤b<1.1, 0.5≤c≤4; The chemical formula of the auxiliary phase alloy powder is RE2 by mass percentage. x Fe y B z M2 j RE2 includes at least one of Pr and Nd, Fe is iron, B is boron, and M2 includes one or more of Cu, Al, Ga, Co, Zr, and Ti; 10≤x≤20, 70≤y≤85, 0.2≤z≤0.9, 0≤j≤4, and satisfies x+y+z+j=100; The chemical formula of the diffusion source powder is RE3 by mass percentage. m M3 n RE3 includes at least one of Pr, Nd, Dy, Tb, and Ho, and M3 is at least one of Al, Cu, and Ga, and simultaneously satisfies 40≤m≤60 and m+n=100; The high remanence sintered NdFeB permanent magnet includes main phase particles and a regenerated main phase shell layer coated on the main phase particles. Weakly magnetic phase particles are also distributed between the regenerated main phase shell layers, and diffusion source components are filled between the weakly magnetic phase particles. The weakly magnetic phase particles are weakly magnetic 6:13:1 phases, and the weakly magnetic 6:13:1 phase formation refers to a weakly magnetic phase formed by rare earth elements, iron elements, and metal elements in an atomic ratio of 6:13:

1. The metal elements are selected from copper, aluminum, or gallium.

2. The method for preparing a high remanence sintered NdFeB permanent magnet according to claim 1, characterized in that: The mass ratio of the main phase alloy powder to the auxiliary phase alloy powder is 85-95:15-5.

3. The method for preparing a high remanence sintered NdFeB permanent magnet according to claim 1, characterized in that: The average particle size of the main phase alloy powder is 3 micrometers to 5 micrometers, and the average particle size of the auxiliary phase alloy powder is 0.5 micrometers to 2 micrometers.

4. The method for preparing a high remanence sintered NdFeB permanent magnet according to claim 1, characterized in that: The orientation magnetic field strength for the orientation forming is 1.8 to 2.0 T.

5. The method for preparing a high remanence sintered NdFeB permanent magnet according to claim 1, characterized in that, The sintering conditions include: a sintering temperature of 1020℃~1100℃ and a sintering time of 2 hours~5 hours.

6. The method for preparing a high remanence sintered NdFeB permanent magnet according to claim 1, characterized in that, The conditions for the tempering heat treatment include: a first-stage heat treatment at a temperature of 900℃ to 1000℃ for a time of 0.5 hours to 2 hours; a second-stage heat treatment at a temperature of 750℃ to 900℃ for a time of 0.5 hours to 2 hours; and a third-stage heat treatment at a temperature of 480℃ to 550℃ for a time of 1 hour to 4 hours.

7. The method for preparing a high remanence sintered NdFeB permanent magnet according to claim 1, characterized in that, The conditions for the diffusion heat treatment include: holding at 900℃~950℃ for 4~10 hours, followed by holding at 480℃~550℃ for 1~4 hours.

8. A high remanence sintered NdFeB permanent magnet, characterized in that, The high remanence sintered NdFeB permanent magnet is made by the method described in any one of claims 1-7.

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