Preparation method of high-performance neodymium-iron-boron magnet

Abstract

The invention discloses a preparation method of a high-performance neodymium-iron-boron magnet, and belongs to the field of high-performance magnet production, and the preparation method comprises the following steps: S1, preparing an alloy rapid hardening sheet; s2, hydrogen decrepitation; s3, powder is prepared through an airflow mill; s4, stirring and mixing: mixing the fine powder obtained in S3 on a powder mixing machine for 4-8 hours; s5, orientation forming, sintering and post-processing are carried out, a sintered neodymium iron boron blank is obtained, the sintering temperature is 1050-1100 DEG C, and the sintering time is 6-8 h; s6, grinding and cutting the sintered neodymium-iron-boron blank to prepare a magnetic sheet; s7, evaporation is carried out in a vacuum evaporation furnace, and during evaporation, an evaporation source firstly passes through the metal mask plate and then is evaporated to the magnetic sheet; and S8, the evaporated magnetic sheet is naturally cooled and then subjected to heat treatment, and the neodymium-iron-boron magnet is obtained. According to the invention, selective area accurate diffusion of diffusion areas with different shapes and sizes, different diffusion layer thicknesses and different shapes can be realized. And on the other hand, the evaporation source attached to the metal mask plate in the evaporation process can be recycled.

Description

Technical Field

[0001] The present invention relates to the production of high-performance magnets, and more particularly, to a method for preparing high-performance neodymium iron boron magnets. Background Art

[0002] High-performance magnets require a magnetic energy product (BHmax) ≥ 45MGOe, a coercive force (Hc) ≥ 20kOe, and can withstand operating temperatures above 200°C. In order to improve the coercive force and high-temperature resistance, in the production of high-performance magnets, grain boundary diffusion is performed in the process steps after magnet sintering because it can significantly improve the coercive force, save heavy rare earths, and significantly save material costs. Therefore, it becomes a very critical step in the subsequent processing of the magnet after sintering.

[0003] The demagnetization process of a magnet is related to the macroscopically uneven distribution of the internal demagnetization field. Micromagnetic simulation results show that the macroscopic demagnetization field is mainly distributed on the surfaces of the two poles of the oriented magnet. During the reverse demagnetization process, the grain boundary phases and grains near the corners of the pole surface are preferentially flipped. For magnets with complex shapes or large sizes, there are always areas that are most susceptible to demagnetization, and magnetization reversal starts preferentially in some weak areas. In theory, grain boundary diffusion should be used mainly to increase the coercive force of the weak parts of the magnet. In 2020, in response to the differences in anti-demagnetization requirements at different locations during the application of permanent magnet motors, some companies proposed to carry out different degrees of heavy rare earth grain boundary diffusion at different parts of the magnet. However, the current selective diffusion scheme is basically carried out by coating (the sputtering method has been abandoned because it cannot be selected), but the coating method cannot accurately control the position of the selected area. At the same time, the thickness of the coating process is uneven and cannot be accurately controlled, and heterogeneous diffusion cannot be accurately achieved. Summary of the Invention

[0004] In view of the above problems, the present invention provides a method for preparing a high-performance NdFeB magnet, which aims to improve at least one of the problems mentioned in the background art.

[0005] A method for preparing a high-performance NdFeB magnet comprises the following steps:

[0006] S1, preparing alloy quick-setting sheets: melting the prepared raw materials under an argon atmosphere, and then pouring them onto a rotating copper roller to prepare alloy quick-setting sheets with a thickness of 0.2 to 0.4 mm. The melting temperature is 1450 to 1500° C., and the casting temperature is 1400 to 1450° C.;

[0007] S2, hydrogen crushing: Use a rotary hydrogen crushing furnace to hydrogen crush the alloy quick-solidified sheet to coarsely crush it into alloy hydrogen crushed powder with particles below 500μm;

[0008] S3, air flow milling: grinding the alloy hydrogen powder into fine powder with an average particle size of 2.0 to 3.2 μm;

[0009] S4 stirring and mixing: the fine powder of S3 is mixed on a powder mixer for 4 to 8h;

[0010] S5, orientation forming, sintering, and post-processing to obtain sintered NdFeB blanks, the sintering temperature is 1050-1100°C, and the sintering time is 6-8h;

[0011] S6, the sintered NdFeB blank is polished, cut and made into magnetic sheets;

[0012] S7, evaporation is performed in a vacuum evaporation furnace. During evaporation, the evaporation source first passes through the metal mask plate and then evaporates onto the magnetic sheet.

[0013] S8. After the evaporation, the magnetic sheet is naturally cooled and then heat treated to obtain the NdFeB magnet.

[0014] Optionally, in S1, the raw material is based on the base alloy R a T (1-a-b-c) M b B c The composition is configured, wherein R is one, two or three of Nd, Pr and Ce, T is Fe and Co, the mass ratio of Fe and Co is (60-140):1, M is one or more of Cu, Al and Ga and one or two of Ti and Zr, the mass fraction of c is 0.90wt%-0.95wt%; a is 29.5-32wt%; and b is 2.5-3wt%.

[0015] Optionally, in S1, the raw material is based on the base alloy PrNd 22 Ce8Cu 0.15 Ga 0.05 Zr 0.2 Ti 0.15 Co 0.3 B 0.93 Fe bal Configuration of components.

[0016] Optionally, in S6, the size of the magnetic sheet is 20*20*10-15 mm, and the thickness direction is the direction of easy magnetization.

[0017] Optionally, in S5, the orientation pressing is carried out under a magnetic field of 1.8 to 2 T, and isostatic pressing is carried out under a pressure of 200 to 250 MPa; the first-level tempering in the post-treatment is 800 to 920° C., and the tempering time is 2 to 4 hours; the second-level tempering temperature is 460 to 540° C., and the tempering time is 4 to 6 hours.

[0018] Optionally, in S7, the vacuum evaporation furnace includes a furnace body, which is composed of a furnace bottom, a furnace body and a furnace cover. The furnace bottom, the furnace body and the furnace cover form a furnace cavity. A crucible is installed at the center of the bottom of the furnace cavity, a metal mask plate is arranged above the crucible, and a magnetic sheet to be evaporated is arranged above the metal mask plate.

[0019] Optionally, in S7, the first vapor source is placed in a crucible, the magnetic sheet is placed in an evaporation furnace, a metal mask is placed in the evaporation furnace, vacuum is drawn, and then the designated area of the magnetic sheet is selectively diffused through the mask. The distance between the mask and the magnetic sheet is 0.5 to 1.5 mm, the evaporation temperature is 1350°C to 1500°C, and the evaporation thickness is 1 to 5 μm.

[0020] Optionally, S7 includes the following steps:

[0021] S71, placing the first vapor source in a crucible, placing the magnetic sheet in a vapor deposition furnace, placing a metal mask in the vapor deposition furnace, evacuating the furnace, and then performing selective diffusion on the eight corners of the magnetic sheet. The distance between the mask and the magnetic sheet is 0.5-1.5 mm, the evaporation temperature is 1350°C-1500°C, and the vapor deposition thickness is 1-5 μm.

[0022] S72, replace the metal mask plate and / or replace the first vapor source in the crucible with a second vapor source, evacuate the crucible, and then align.

[0023] Optionally, in S7, the first vapor source is Dy 0.8 Fe 0.2 , the second vapor source is Pr-Al-Cu.

[0024] Optionally, in S8, the first stage of heat treatment is performed at a temperature of 800-900° C. for 2-4 hours, and the second stage of heat treatment is performed at a temperature of 500-600° C. for 2-3 hours.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention can achieve selective and precise diffusion of diffusion areas of different shapes and sizes, different diffusion layer thicknesses, and different shapes. In addition, the evaporation source attached to the metal mask during the evaporation process can be recycled. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0028] Figure 1It is a schematic diagram of the overall structure of the evaporation furnace of the present invention;

[0029] Figure 2 This is a schematic diagram of the principle of selected area diffusion of the present invention;

[0030] Figure 3 This is a schematic diagram of the selected area diffusion area in Example 1 of the present invention;

[0031] Figure 4 This is a schematic diagram of the heterogeneous diffusion area in the selected area according to embodiment 2 of the present invention. Figure 1 ;

[0032] Figure 5 This is a schematic diagram of the heterogeneous diffusion area of the evaporation selected area in Example 2 of the present invention. Figure 2 .

[0033] Explanation of the accompanying reference numerals: 1. crucible, 2. metal mask plate, 3. magnetic sheet, 4. furnace body, 5. furnace cavity. DETAILED DESCRIPTION

[0034] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to a fixed connection, an indirect connection via an intermediate medium, internal communication between two components, or an interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0035] In the description of the present invention, it should be understood that the terms "upper," "lower," "front," "back," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like, indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They do not indicate or imply that the devices or elements referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limiting the present invention. In the description of the present invention, "plurality" means two or more, unless otherwise specifically specified.

[0036] The terms "first", "second", "third", "fourth", etc. (if any) in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequential order. It should be understood that the numbers used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can, for example, be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0037] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0038] The following specific embodiments are used to describe the technical solution of the present invention in detail. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described in detail in some embodiments.

[0039] Please refer to Figure 1-Figure 2 , Figure 1 This is a schematic diagram of the overall structure of the vapor deposition furnace of the present invention. Figure 2 It is a schematic diagram of the principle of selected area diffusion of the present invention.

[0040] A method for preparing high-performance NdFeB magnets includes a furnace body 4, which comprises a furnace bottom, a furnace body, and a furnace cover. The furnace bottom, furnace body, and furnace cover form a furnace chamber 5. A crucible 1 is mounted at the center of the bottom of the furnace chamber 5. A metal mask 2 is positioned above the crucible 1. A magnetic sheet 3 to be evaporated is positioned above the metal mask 2. The crucible 1 is used to hold an evaporation source.

[0041] By placing a metal mask 2 between the crucible 1 and the magnetic sheet 3 to be deposited, the present invention integrates the evaporation diffusion process with the metal mask 2, enabling precise diffusion of selected areas of varying shapes and sizes, diffusion layer thicknesses, and shapes. Furthermore, the evaporation source attached to the metal mask 2 during the deposition process is recyclable.

[0042] In one or more specific embodiments of the present invention, the different sizes and shapes of the openings of the metal mask plate 2 can realize evaporation patterns in different areas and shapes, thereby achieving "patterning" of evaporation.

[0043] The present invention can also achieve heterogeneous diffusion of the same magnet by replacing the metal mask plate 2 with different openings and different evaporation sources.

[0044] The metal mask plate 2 is detachably connected to the inner wall of the furnace body. The detachable connection method can be achieved by installing a clamp on the inner wall of the furnace body, or by providing a bump on the inner wall of the furnace body and providing a groove corresponding to the bump on the edge of the metal mask plate 2 (this is the non-evaporation area). As long as the metal mask plate 2 can be located above the crucible 1 and below the magnetic sheet 3 in the furnace chamber 5, there is no particular limitation.

[0045] The magnetic sheet 3 can be attached to the metal substrate through electromagnetic attraction. The sheet is then inverted. Once one side of the sheet is deposited, the other side can be attached to complete double-sided deposition. Leveraging the inherent magnetic properties of the sheet, an electromagnetic field can be applied to adhere the sheet to the substrate. Subsequent heat treatment can remove any weakened magnetic properties without affecting performance.

[0046] In one or more specific embodiments of the present invention, the vertical distance between the upper surface of the metal mask plate 2 and the lower surface of the magnetic sheet 3 is 0.5 to 1.5 mm. A distance that is too large will affect the accuracy of the selection, while a distance that is too close will scratch the film on the surface of the magnet once it is applied to the magnetic surface of the magnetic sheet 3. Preferably, the distance is 1 mm.

[0047] In one or more specific embodiments of the present invention, the distance between the metal mask 2 and the crucible 1 is 50-100 cm.

[0048] Those skilled in the art should know that the evaporation furnace of the present invention, like the existing vacuum evaporation furnace, has a heating system configured outside the furnace (which can be a resistance heating method or an induction heating method). The cooling system of the vacuum evaporation furnace will additionally add a cooling part for the magnetic sheet substrate to prevent the magnetic sheet from overheating and deteriorating its inverted magnetic properties.

[0049] Example 1

[0050] A method for preparing a high-performance NdFeB magnet comprises the following steps:

[0051] S1, preparation of sintered NdFeB precise selective diffusion magnetic matrix: preparation of alloy quick solidification sheet: according to the nominal composition of PrNd 22 Ce8Cu 0.15 Ga 0.05 Zr 0.2 Ti 0.15 Co 0.3 B 0.93 Fe balThe matrix alloy raw materials are prepared, the prepared raw materials are melted in an argon atmosphere, and then poured onto a copper roller with a rotation speed of 3m / s to prepare a quick-setting sheet with a thickness of 0.2 to 0.4mm.

[0052] S2, hydrogen crushing: Use a rotary hydrogen crushing furnace to perform hydrogen crushing treatment on the quick-setting sheets, and crush the quick-setting sheets into particles below 500μm.

[0053] S3, air flow milling: using high pressure nitrogen gas at 0.5-1.0 MPa, by controlling the speed of the sorting wheel, the alloy hydrogen powder is broken into fine powder with an average particle size of 2.95-3.05 μm.

[0054] S4. Stirring and mixing: Add 0.5 kg / ml of lubricant to the obtained micron-sized fine powder, and then mix it on a powder mixer for 4 hours.

[0055] S5, Orientation Molding and Sintering: The mixed powder is oriented and pressed in a 1.8T magnetic field and isostatically pressed at 240MPa to produce a green compact. The green compact is sintered in a vacuum sintering furnace at 1070°C for 5 hours to obtain a sintered magnet. The sintered magnet undergoes a primary tempering temperature of 915°C for 3 hours and a secondary tempering temperature of 650°C for 4 hours to obtain a sintered NdFeB blank.

[0056] S6, the sintered NdFeB blank is polished and cut to form a magnetic sheet 3 with a thickness of 20*20*10 mm, and the magnetic sheet 3 is cleaned, and the 10 mm thickness direction is the easy magnetization direction.

[0057] S7, steam source Dy0.8Fe0.2 is placed Figure 1 The magnetic piece 3 is placed in the crucible 1 Figure 1 The metal mask plate 2 is placed in the evaporation furnace, vacuumed, and then the eight edges of the easily magnetized surface of the magnetic sheet 3 are selectively diffused, as shown in FIG. Figure 3 As shown, the distance between the mask plate 2 and the magnetic sheet 3 is 1 mm, the mask plate is 65 cm away from the evaporation source, the evaporation temperature is 1450°C, and the evaporation thickness is 4.5 μm. The metal mask plate 2 is made of a high-melting-point alloy with a melting point greater than 1500°C.

[0058] S8. After the evaporation, the magnetic sheet 3 is naturally cooled and then heat treated to obtain a NdFeB magnet. The first treatment temperature is 880°C for 3 hours, and the second treatment temperature is 550°C for 2.5 hours.

[0059] The performance of the magnetic sheet 3 of S6 and the NdFeB magnet of S8 were tested respectively, and the results are shown in Table 1 below.

[0060] Comparative Example 1

[0061] Compared with Example 1, the difference lies in S7. In this comparative example, in S7, the metal mask plate 2 is replaced with a screen, the aperture of which is slightly larger than the particle size of the vapor source, and the apertures of the screen are evenly distributed.

[0062] Comparative Example 2

[0063] Compared with Example 1, the difference lies in S7. In this comparative example, in S7, the evaporation method selection area of Example 1 is changed to evaporating Dy0.8Fe0.2 on the entire easy magnetization surface of the magnetic sheet 3 with a thickness of 4.5 μm.

[0064] Table 1

[0065]

[0066]

[0067] Example 2

[0068] Compared with Example 1, the difference is that S7 is: the evaporation source is Dy0.8Fe0.2 and Pr-Al-Cu alloy, and the evaporation steps include S71, S72, S73 and S74;

[0069] S71, steam source is Dy0.8Fe0.2

[0070] S72, the steam source is Pr-Al-Cu alloy.

[0071] S73, such as Figure 4 and Figure 5 As shown in the schematic diagram of the selected heterogeneous diffusion area, the exclusive mask plate for evaporating Dy0.8Fe0.2 is first installed to carry out selective evaporation on the edges of both sides of the magnetic surface; after completion, the diffusion source and exclusive mask plate for evaporating Pr-Al-Cu alloy are replaced to carry out enhanced evaporation in the central area of both sides.

[0072] S74, after the vapor deposition, the magnetic sheet 3 is cooled and then heat treated to obtain a NdFeB magnet. The first stage treatment temperature is 880°C for 3 hours, and the second stage treatment temperature is 550°C for 2.5 hours.

[0073] The performance of the magnetic sheet 3 of S6 and the NdFeB magnet of S8 were tested respectively, and the results are shown in Table 2 below.

[0074] Comparative Example 3

[0075] Compared with Example 2, the difference lies in S7. In this comparative example, in S7, the evaporation sources are all Dy0.8Fe0.2, and the entire surface is evaporated.

[0076] Table 2

[0077]

[0078]

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing high-performance NdFeB magnets, characterized in that: The following steps are involved: S1, preparing alloy quick-setting sheets: melting the prepared raw materials under an argon atmosphere, and then pouring them onto a rotating copper roller to prepare alloy quick-setting sheets with a thickness of 0.2 to 0.4 mm. The melting temperature is 1450 to 1500° C., and the casting temperature is 1400 to 1450° C.; S2, hydrogen crushing: Use a rotary hydrogen crushing furnace to hydrogen crush the alloy quick-solidified sheet to coarsely crush it into alloy hydrogen crushed powder with particles below 500μm; S3, air flow milling: grinding the alloy hydrogen powder into fine powder with an average particle size of 3.0-3.2 μm; S4 stirring and mixing: the fine powder of S3 is mixed on a powder mixer for 4 to 8h; S5, orientation forming, sintering, and post-processing to obtain sintered NdFeB blanks, the sintering temperature is 1050-1100°C, and the sintering time is 6-8h; S6, the sintered NdFeB blank is polished, cut and made into magnetic sheets; S7, evaporation in a vacuum evaporation furnace, during evaporation, the evaporation source first passes through a metal mask plate and then evaporates onto the magnetic sheet; S8. After the evaporation, the magnetic sheet is naturally cooled and then heat treated to obtain the NdFeB magnet.

2. The method for preparing a high performance NdFeB magnet according to claim 1, wherein: In S1, the raw materials are based on the base alloy R a T (1-a-b-c) M b B c The composition is configured, wherein R is one, two or three of Nd, Pr and Ce, T is Fe and Co, the mass ratio of Fe and Co is (60-140):1, M is one or more of Cu, Al and Ga and one or two of Ti and Zr, the mass fraction of c is 0.90wt%-0.95wt%; a is 29.5-32wt%; and b is 2.5-3wt%.

3. The method for preparing a high performance NdFeB magnet according to claim 1, wherein: In S1, the raw materials are based on the base alloy PrNd 22 Ce8Cu 0.15 Ga 0.05 Zr 0.2 Ti 0.15 Co 0.3 B 0.93 Fe bal Configuration of components.

4. The method for preparing a high performance NdFeB magnet according to claim 1, wherein: In S6, the size of the magnetic sheet is 20*20*10~15mm, and the thickness direction is the easy magnetization direction.

5. The method for preparing a high performance NdFeB magnet according to claim 1, wherein: In S5, the orientation pressing is carried out under a magnetic field of 1.8 to 2 T and isostatic pressing is carried out under a pressure of 200 to 250 MPa; the first-level tempering of the post-treatment is 800 to 920°C and the tempering time is 2 to 4 hours; the second-level tempering temperature is 460 to 540°C and the tempering time is 4 to 6 hours.

6. The method for preparing a high performance NdFeB magnet according to claim 1, wherein: In S7, the vacuum evaporation furnace includes a furnace body, which is composed of a furnace bottom, a furnace body and a furnace cover. The furnace bottom, the furnace body and the furnace cover form a furnace cavity. A crucible is installed at the center of the bottom of the furnace cavity, a metal mask plate is arranged above the crucible, and a magnetic sheet to be evaporated is arranged above the metal mask plate.

7. The method for preparing a high performance NdFeB magnet according to claim 6, wherein: In S7, the first vapor source is placed in a crucible, the magnetic sheet is placed in an evaporation furnace, a metal mask is placed in the evaporation furnace, vacuum is drawn, and then selective diffusion is performed on a specific area of the magnetic sheet. The distance between the mask and the magnetic sheet is 0.5 to 1.5 mm, the evaporation temperature is 1350°C to 1500°C, and the evaporation thickness is 1 to 5 μm.

8. The method for preparing a high performance NdFeB magnet according to claim 6, wherein: S7 includes the following steps: S71, placing a first vapor source in a crucible, placing a magnetic sheet in a vapor deposition furnace, placing a metal mask in the vapor deposition furnace, evacuating the furnace, and then performing selective diffusion on a specific area of the magnetic sheet through the mask. The distance between the mask and the magnetic sheet is 0.5 to 1.5 mm, the evaporation temperature is 1350°C to 1500°C, and the vapor deposition thickness is 1 to 5 μm. S72, replacing the metal mask or / and replacing the first evaporation source in the crucible with a second evaporation source, evacuating the crucible, and then performing evaporation again.

9. The method for preparing a high performance NdFeB magnet according to claim 1, wherein: In S7, the first vapor source is Dy 0.8 Fe 0.2 , the second vapor source is Pr-Al-Cu.

10. The method for preparing a high performance NdFeB magnet according to claim 1, wherein: In S8, the first stage of heat treatment is performed at a temperature of 800-900° C. for 2-4 hours, and the second stage of heat treatment is performed at a temperature of 500-600° C. for 2-3 hours.

Images