Neodymium-iron-boron magnet and preparation method thereof

Abstract

The invention provides a neodymium iron boron magnet and a preparation method thereof. The preparation method comprises the following steps: mixing a neodymium-iron-boron main alloy and an auxiliary alloy, and sintering to obtain a neodymium-iron-boron magnet; wherein the neodymium iron boron main alloy comprises 28 to 32 weight percent of Re, 66 to 72 weight percent of T and 0.85 to 1.0 weight percent of B; wherein Re is a rare earth element; t is selected from one or more of Fe, Co, Al, Cu, Mg, Fe, Co, Nb, Zr and Ga; and the auxiliary alloy comprises 70-90 wt% of Ti and 10-30 wt% of metal with the melting point lower than 900 DEG C. On the basis, negative effects on the magnetic performance of the neodymium-iron-boron magnet cannot be generated, and the mechanical strength of the product can be greatly improved. In addition, the raw materials are low in cost, easy to obtain and more suitable for industrial application.

Description

Technical Field

[0001] The invention relates to the technical field of neodymium iron boron magnets, and in particular to a neodymium iron boron magnet and a preparation method thereof. Background Art

[0002] Sintered NdFeB magnets have excellent comprehensive magnetic properties and are widely used in aerospace, microwave communication technology, automotive industry, instrumentation and medical equipment, etc. In recent years, the promotion speed and application scope of sintered NdFeB magnets in high-end fields such as wind power, variable frequency compressors, and hybrid power have expanded rapidly.

[0003] However, this functional material with excellent magnetic properties and wide application has the disadvantages of poor strength and toughness. This is mainly due to the following reasons: The phase composition of sintered NdFeB permanent magnet material mainly includes the main phase Nd2Fe 14 B. Rare earth-rich phase and boron-rich phase. The main phase is formed by peritectic reaction at about 1200℃ and is the only magnetic phase in the alloy. The melting point of the rare earth-rich phase is 650℃~700℃. It is the last to solidify in the alloy and is located between the solidified main phase grains and distributed along the grain boundaries. It is a thin layer phase covering the main phase grains.

[0004] Sintered NdFeB permanent magnet single crystal has magnetostriction anisotropy and thermal expansion anisotropy. This anisotropy leads to large internal stress, resulting in poor strength and easy fracture. The poor strength and toughness of sintered NdFeB permanent magnet materials often lead to peeling, edge and corner loss during surface treatment after machining and during the use of finished products. With the miniaturization and high precision of magnetic devices, as well as the military, aerospace, high-speed motors and other fields with strong impact and vibration, higher requirements are placed on the mechanical strength of magnetic devices. Therefore, improving the mechanical strength of sintered NdFeB permanent magnet materials has become an urgent requirement.

[0005] In the prior art, the patent application with application number CN202010843895 discloses a high-performance sintered NdFeB magnet and a preparation method thereof, which significantly improves the magnetic properties, corrosion resistance and toughness of the NdFeB magnet by adding heavy rare earth elements, corrosion-resistant metals and carbon nanotubes with excellent strength and flexibility to the NdFeB magnetic powder. However, the reserves of heavy rare earth elements are limited and expensive. In addition, carbon nanotubes are also expensive and difficult to mass produce. The patent application with application number CN202210181432 discloses a preparation method of a high-mechanical-strength sintered NdFeB magnet, which is to mix magnetic powders with different compositions and different average particle sizes but similar performances, so that the coarse powder and the fine powder are reasonably matched, the compact density is improved, and after sintering and tempering heat treatment, the obtained NdFeB magnet has excellent toughness, bending strength and fracture toughness. This method reduces the void defects between the main phase grains through different particle size ratios, reducing the risk of fracture occurring at the defects, but this method does not improve the grain boundary phase of the product, and fracture will still occur in the relatively fragile grain boundary phase.

[0006] It can be seen that the existing technology for preparing sintered NdFeB magnets has the problems of high cost, difficulty in obtaining raw materials, or inability to effectively improve the mechanical strength of the product. Therefore, it is necessary to provide a new method for preparing sintered NdFeB magnets to improve the above problems. Summary of the invention

[0007] The main purpose of the present invention is to provide a NdFeB magnet and a preparation method thereof, so as to solve the problems in the prior art of preparing sintered NdFeB magnets, such as high cost, difficulty in obtaining raw materials, or failure to effectively improve the mechanical strength of the product.

[0008] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, a method for preparing a NdFeB magnet is provided, the preparation method comprising: mixing a NdFeB main alloy and an auxiliary alloy and sintering them to obtain a NdFeB magnet; wherein the NdFeB main alloy comprises: 28-32wt% Re, 66-72wt% T and 0.85-1.0wt% B; wherein Re is a rare earth element; T is selected from Fe and one or more of Co, Al, Cu, Mg, Fe, Co, Nb, Zr and Ga; the auxiliary alloy comprises: 70-90wt% Ti and 10-30wt% of a metal having a melting point below 900°C.

[0009] Furthermore, the amount of the auxiliary alloy is 0.1-0.5% by weight of the NdFeB main alloy.

[0010] Furthermore, the sintering includes a first stage sintering and a second stage sintering performed sequentially, and the processing temperature of the first stage sintering is lower than the processing temperature of the second stage sintering; preferably, the processing temperature of the first stage sintering is 20 to 80° C. lower than the processing temperature of the second stage sintering.

[0011] Furthermore, the rare earth element is selected from one or more of Dy, Tb, Ho, Gd, La, Ce, Pr or Nd; preferably, the metal with a melting point below 900° C. is selected from Al and / or Cu.

[0012] Furthermore, the treatment temperature of the first stage sintering is 1040-1070°C, and the treatment time is 4-8h; preferably, the treatment temperature of the second stage sintering is 1090-1120°C, and the treatment time is 4-8h; further preferably, after the first stage sintering is completed, the system temperature is cooled to 600-800°C and then heated to the treatment temperature of the second stage sintering for the second stage sintering.

[0013] Furthermore, the NdFeB main alloy has a powdery state, and an average particle size is 2 to 4 μm.

[0014] Furthermore, the auxiliary alloy has a powdery state, and an average particle size is 0.5 to 1 μm.

[0015] Furthermore, after sintering, the preparation method also includes the step of tempering the sintered material in two stages; preferably, the first tempering temperature is 850-950°C, and the first tempering insulation time is 2-5h; preferably, the second tempering temperature is 430-530°C, and the second tempering insulation time is 3-6h.

[0016] Furthermore, after mixing and before sintering, the preparation method also includes the step of pressing the mixture of the NdFeB main alloy and the auxiliary alloy in an oriented magnetic field with a magnetic field strength of ≥1.4T.

[0017] In order to achieve the above object, according to one aspect of the present invention, there is provided a NdFeB magnet prepared by the above-mentioned method for preparing a NdFeB magnet.

[0018] Compared with other metal elements, Ti has good processing toughness and ductility, and has excellent bending and compressive strength, which can make up for the defect of poor strength of the neodymium-rich phase at the grain boundary of NdFeB. The metal with low melting point not only has good toughness, but more importantly, it has good wettability. The auxiliary alloy formed by Ti and low melting point metal elements has a melting point of 700℃~1000℃, and has good fluidity during high temperature sintering, so that Ti can be evenly distributed in the outer grain boundary position of the main phase of NdFeB during the sintering process. This will not have a negative impact on the magnetic properties of NdFeB magnets, and can also greatly improve the mechanical strength of the product. In addition, the above-mentioned raw material cost of the present invention is low, and it is easier to obtain, and is more suitable for industrial applications. DETAILED DESCRIPTION

[0019] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0020] As described in the background section of this application, the prior art has the problems of high cost, difficulty in obtaining raw materials, or inability to effectively improve the mechanical strength of the product when preparing sintered NdFeB magnets. In order to solve this problem, the present application provides a method for preparing NdFeB magnets, which comprises: mixing a NdFeB main alloy and an auxiliary alloy for sintering to obtain a NdFeB magnet; wherein the NdFeB main alloy comprises: 28-32wt% Re, 66-72wt% T and 0.85-1.0wt% B; wherein Re is a rare earth element; T is selected from Fe and one or more of Co, Al, Cu, Mg, Fe, Co, Nb, Zr, and Ga; and the auxiliary alloy comprises: 70-90wt% Ti and 10-30wt% of a metal having a melting point below 900°C.

[0021] The inventors found that the typical microstructure of sintered NdFeB magnet material is that the Nd-rich grain boundary phase wraps the main phase grains. Among them, the main phase grains are typical intermetallic compounds, lacking plasticity, but with high strength and hardness; while the Nd-rich phase has a certain plasticity, but its strength and hardness are much lower than the brittle main phase grains. Such a structure makes it inevitable that when NdFeB breaks, the cracks will extend along the weak Nd-rich phase, making the final fracture appear as intergranular fracture, resulting in poor mechanical strength of the sintered NdFeB magnet material.

[0022] Based on this, the inventor proposed to add auxiliary alloy B (including 70-90wt% Ti and 10-30wt% metal elements with a melting point below 900°C) to the main NdFeB alloy A (including 28-32wt% Re, 66-72wt% T and 0.85-1.0wt% B) for sintering. Among them, Ti has good processing toughness and ductility compared with other metal elements, and has excellent bending and compressive strength, which can make up for the defect of poor strength of the original NdFeB grain boundary neodymium-rich phase. The low-melting-point metal not only has good toughness, but more importantly, it has good wettability. The auxiliary alloy formed by Ti and low-melting-point metal elements has a melting point of 700°C to 1000°C, and has good fluidity during high-temperature sintering, and can make Ti evenly distributed in the outer grain boundary position of the NdFeB main phase during the sintering process. This will not have a negative impact on the magnetic properties of the NdFeB magnet, but also greatly improve the mechanical strength of the product. In addition, the raw materials of the present invention have low cost and are easier to obtain, and are more suitable for industrial applications.

[0023] In order to further balance the mechanical strength and magnetic properties of the NdFeB magnet, in a preferred embodiment, the amount of the auxiliary alloy B is 0.1-0.5% by weight of the NdFeB main alloy A, for example, 0.1%, 0.2%, 0.3%, 0.4% or 0.5%. Within this addition amount range, the auxiliary alloy elements are basically distributed at the grain boundary position, and will not have a negative impact on the magnetic properties of the sintered NdFeB magnet.

[0024] In order to further improve the mechanical strength of the NdFeB magnet, in a preferred embodiment, the sintering includes a first stage sintering and a second stage sintering performed in sequence, and the treatment temperature of the first stage sintering is lower than the treatment temperature of the second stage sintering. Ti and Ti alloys have excellent mechanical strength, which can make up for the defect of poor strength of the original NdFeB grain boundary NdFeB rich phase. The first stage sintering temperature is low, so that the auxiliary alloy B can be melted first, flow along the grain boundary phase, and evenly distributed on the surface of the large-grained NdFeB main phase after the magnet is cooled. Then the sintering temperature is increased for the second stage sintering, which can densify the NdFeB main phase, thereby forming a dense microstructure in which the outer layer of the NdFeB main phase is wrapped with a Ti-rich grain boundary phase. Preferably, the treatment temperature of the first stage sintering is 20 to 80 ° C lower than the treatment temperature of the second stage sintering. Based on this, the above two stages of sintering have a better synergistic effect.

[0025] In order to further improve the magnetic properties of the NdFeB magnet, in a preferred embodiment, the rare earth element is selected from one or more of Dy, Tb, Ho, Gd, La, Ce, Pr or Nd. In order to further balance the mechanical strength and magnetic properties of the NdFeB magnet, in a preferred embodiment, the metal with a melting point below 900°C is selected from Al and / or Cu. Compared with other metal elements, the addition of Ti element in conjunction with Al and Cu can further make Ti more evenly distributed at the outer grain boundary position of the NdFeB main phase, so that the NdFeB magnet obtained not only has better mechanical strength, but also better magnetic properties.

[0026] In order to further make up for the defect of poor strength of the neodymium-rich phase at the grain boundary of NdFeB, in a preferred embodiment, the treatment temperature of the first stage sintering is 1040-1070°C, and the treatment time is 4-8h. The treatment temperature of the second stage sintering is 1090-1120°C, and the treatment time is 4-8h. Further preferably, after the first stage sintering is completed, the system temperature is cooled to 600-800°C and then heated to the treatment temperature of the second stage sintering for the second stage sintering. The treatment temperature of the first stage sintering is controlled at 1040-1070°C, which can more smoothly melt the auxiliary alloy B first and flow along the grain boundary phase. After the first stage sintering is completed, the system temperature is cooled to 600-800°C and then heated to the treatment temperature of the second stage sintering for the second stage sintering, so that the magnet can be more evenly distributed on the surface of the large-grained NdFeB main phase after cooling. Then the sintering temperature is increased to 1090-1120°C for the second stage sintering, which can make the NdFeB main phase more compact and form a dense microstructure with a Ti-rich grain boundary phase wrapped in the outer layer of the NdFeB main phase with better performance.

[0027] In order to further improve the uniformity of the performance of the NdFeB magnet, after sintering, the preparation method further includes the step of performing two-stage tempering on the sintered material. Preferably, the first tempering temperature is 850-950°C, and the first tempering holding time is 2-5 hours. The second tempering temperature is 430-530°C, and the second tempering holding time is 3-6 hours.

[0028] In order to further improve the performance uniformity of NdFeB magnets, in a preferred embodiment, the NdFeB main alloy has a powdery state with an average particle size of 2 to 4 μm. The auxiliary alloy has a powdery state with an average particle size of 0.5 to 1 μm. In some optional embodiments, the above-mentioned NdFeB main alloy and auxiliary alloy can be directly purchased from the market, or they can be prepared by conventional technical means in the art. For example, the raw materials of the NdFeB main alloy and the auxiliary alloy can be mixed according to the stoichiometric ratio and then prepared by a smelting and rapid solidification process to obtain the NdFeB main alloy and the auxiliary alloy. The NdFeB main alloy is crushed by hydrogen crushing and air flow milling to obtain a NdFeB main alloy powder with an average particle size of 2 to 4 μm. The auxiliary alloy is crushed by wet ball milling to obtain an auxiliary alloy powder with an average particle size of 0.5 to 1 μm.

[0029] In order to further improve the performance uniformity of NdFeB magnets, in a preferred embodiment, after mixing and before sintering, the preparation method also includes the step of pressing the mixture of the NdFeB main alloy and the auxiliary alloy in an oriented magnetic field with a magnetic field strength of ≥1.4T.

[0030] The present application also provides a NdFeB magnet prepared by the above-mentioned method for preparing NdFeB magnets. Based on the above reasons, the NdFeB magnet obtained in the present application has greatly improved mechanical strength while meeting conventional magnetic properties.

[0031] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0032] Example 1

[0033] (1) Preparation of NdFeB main alloy (PrNd) by melting and rapid solidification process 30.5 Fe 66.9 Co 1.0 Cu 0.15 Al 0.2 Ga 0. 2Zr 0.1 B 0.95 And auxiliary alloy Ti 85 Al7Cu8;

[0034] (2) crushing the NdFeB main alloy by hydrogen crushing and air flow milling to obtain NdFeB main alloy powder with an average particle size of 3.2 μm;

[0035] (3) grinding and crushing the auxiliary alloy by wet ball milling to obtain auxiliary alloy powder with an average particle size of 0.8 μm;

[0036] (4) adding the auxiliary alloy powder into the NdFeB main alloy powder at a weight ratio of 0.3% and mixing evenly;

[0037] (5) pressing the mixed alloy powder into a blank in an oriented magnetic field with a magnetic field strength of 1.8 T;

[0038] (6) placing the formed blank into a vacuum sintering furnace for two-stage high-temperature sintering, wherein the first sintering temperature is 1050°C, the first sintering heat preservation time is 6 hours, cooling to 700°C after the first sintering heat preservation, and then heating to the second sintering temperature of 1097°C, and the second sintering heat preservation time is 5 hours;

[0039] (7) After the sintering of the blank, the blank is subjected to two-stage tempering treatment, the first tempering temperature is 900°C, the first tempering holding time is 3 hours, the second tempering temperature is 480°C, and the second tempering holding time is 4 hours.

[0040] Example 2

[0041] The only difference from Example 1 is that the auxiliary alloy powder is added to the NdFeB main alloy powder at a weight ratio of 0.1%.

[0042] Example 3

[0043] The only difference from Example 1 is that the auxiliary alloy powder is added to the NdFeB main alloy powder at a weight ratio of 0.5%.

[0044] Example 4

[0045] The only difference from Example 1 is that the auxiliary alloy powder is added to the NdFeB main alloy powder at a weight ratio of 1%.

[0046] Example 5

[0047] The only difference from Example 1 is that the formed blank is placed in a vacuum sintering furnace for two stages of high-temperature sintering, the first sintering temperature is 1097°C, the first sintering insulation time is 6 hours, after the first sintering insulation is completed, it is cooled to 700°C, and then heated to the second sintering temperature of 1050°C, and the second sintering insulation time is 5 hours.

[0048] Example 6

[0049] The only difference from Example 1 is that the formed blank is placed in a vacuum sintering furnace for two stages of high-temperature sintering, the first sintering temperature is 1000°C, the first sintering insulation time is 6 hours, after the first sintering insulation is completed, it is cooled to 700°C, and then heated to the second sintering temperature of 1200°C, and the second sintering insulation time is 5 hours.

[0050] Comparative Example 1

[0051] (1) Preparation of neodymium iron boron alloy (PrNd) by melting and rapid solidification process 30.5 Fe 66.9 Co 1.0 Cu 0.15 Al 0.2 Ga 0.2 Zr 0.1 B 0.95 ;

[0052] (2) crushing the NdFeB main alloy by hydrogen crushing and air flow milling to obtain NdFeB alloy powder with an average particle size of 3.2 μm;

[0053] (5) pressing the NdFeB alloy powder into a blank in an oriented magnetic field with a magnetic field strength of 1.8 T;

[0054] (6) placing the formed blank into a vacuum sintering furnace for high-temperature sintering at a sintering temperature of 1097°C and a sintering holding time of 5 hours;

[0055] (7) After the sintering of the blank, the blank is subjected to two-stage tempering treatment, the first tempering temperature is 900°C, the first tempering holding time is 3 hours, the second tempering temperature is 480°C, and the second tempering holding time is 4 hours.

[0056] Comparative Example 2

[0057] The only difference from Example 1 is that the auxiliary alloy component is Zr 85 Al7Cu 8；

[0058] The NdFeB main alloy used in Example 1 and Comparative Example 1 is of the same proportion. The samples in the Example and Comparative Example are respectively tested for magnetic properties using a permanent magnetic material measuring BH instrument, and are respectively processed into standard sizes and tested for bending strength using a universal pressure testing machine. The results are shown in Table 1.

[0059] Table 1

[0060]

[0061]

[0062] It can be seen from the test results that the magnetic properties of the blank are similar to those of the comparative example and the example sample, but the bending strength of the example sample is significantly higher and the mechanical strength is better.

[0063] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a neodymium iron boron magnet, characterized in that: The preparation method comprises: mixing a main NdFeB alloy and an auxiliary alloy and sintering them to obtain the NdFeB magnet; The NdFeB main alloy comprises: 28-32wt% Re, 66-72wt% T and 0.85-1.0wt% B; wherein Re is a rare earth element; T is selected from Fe and one or more of Co, Al, Cu, Mg, Fe, Co, Nb, Zr and Ga; The auxiliary alloy comprises: 70-90wt% of Ti and 10-30wt% of a metal with a melting point lower than 900°C.

2. The method for preparing a NdFeB magnet according to claim 1, wherein: The amount of the auxiliary alloy is 0.1-0.5% of the weight of the NdFeB main alloy.

3. The method for preparing a NdFeB magnet according to claim 1 or 2, characterized in that: The sintering includes a first stage sintering and a second stage sintering performed sequentially, and the processing temperature of the first stage sintering is lower than the processing temperature of the second stage sintering; Preferably, the processing temperature of the first stage sintering is 20-80° C. lower than the processing temperature of the second stage sintering.

4. The method for preparing a NdFeB magnet according to any one of claims 1 to 3, characterized in that: The rare earth element is selected from one or more of Dy, Tb, Ho, Gd, La, Ce, Pr or Nd; Preferably, the metal having a melting point below 900° C. is selected from Al and / or Cu.

5. The method for preparing a NdFeB magnet according to claim 3, characterized in that: The first stage of sintering has a treatment temperature of 1040-1070°C and a treatment time of 4-8 hours; Preferably, the treatment temperature of the second stage sintering is 1090-1120°C, and the treatment time is 4-8h; More preferably, after the first stage sintering is completed, the system temperature is cooled to 600-800° C. and then raised to the processing temperature of the second stage sintering to carry out the second stage sintering.

6. The method for preparing a NdFeB magnet according to any one of claims 1 to 5, characterized in that: The NdFeB main alloy is in powder form with an average particle size of 2 to 4 μm.

7. The method for preparing a NdFeB magnet according to any one of claims 1 to 6, characterized in that: The auxiliary alloy is in powder form, and the average particle size is 0.5 to 1 μm.

8. The method for preparing a NdFeB magnet according to any one of claims 1 to 7, characterized in that: After the sintering, the preparation method further comprises the step of performing two-stage tempering on the sintered material; Preferably, the first tempering temperature is 850-950°C, and the first tempering holding time is 2-5h; Preferably, the second tempering temperature is 430-530° C., and the second tempering holding time is 3-6 hours.

9. The method for preparing a NdFeB magnet according to any one of claims 1 to 8, characterized in that: After the mixing and before the sintering, the preparation method further comprises the step of pressing the mixture of the NdFeB main alloy and the auxiliary alloy in an oriented magnetic field with a magnetic field strength of ≥1.4T.

10. A NdFeB magnet prepared by the method for preparing a NdFeB magnet according to any one of claims 1 to 9.

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