Neodymium-iron-boron remelting magnetic powder and preparation method thereof, cold and hot shock resistant neodymium-iron-boron magnet and preparation method and application thereof

Abstract

The invention relates to neodymium iron boron remelting magnetic powder and a preparation method thereof, a cold and hot shock resistant neodymium iron boron magnet and a preparation method and application thereof, the neodymium iron boron remelting magnetic powder comprises an Nd2Fe14B magnetic powder matrix, an additive, a fluxing agent and a lubricant, and the additive comprises silicon nitride and / or silicon carbide. The additive contained in the neodymium-iron-boron remelting magnetic powder provided by the invention has high thermal conductivity, so that the neodymium-iron-boron magnet prepared from the neodymium-iron-boron remelting magnetic powder has more heat conduction paths, and the transfer speed of heat energy in the magnet can be further improved; further, internal stress caused by uneven cold and heat of the interior and the exterior under cold and hot impact is relieved; and meanwhile, the additive also has a relatively low expansion coefficient, so that the problems that the magnetic performance is reduced and the surface of the magnet is cracked due to the change of a crystal structure when the interior of the magnet is subjected to alternate cold and heat impact due to an overlarge thermal expansion coefficient can be effectively avoided.

Description

Technical Field

[0001] The invention relates to the technical field of NdFeB magnet preparation, and in particular to NdFeB remelted magnetic powder and a preparation method thereof, a cold and hot shock resistant NdFeB magnet and a preparation method and application thereof. Background Art

[0002] NdFeB material is a basic functional material with a wide range of uses. In the long-term development process, it has become the material basis for computer technology, aerospace technology, communication technology, transportation (automobile) technology, home appliance technology, human health and health care technology, etc.

[0003] NdFeB materials mainly include sintered NdFeB and bonded NdFeB due to different processes. Sintered NdFeB is sintered at high temperature with air or hydrogen as the medium, which can obtain fine grains and excellent magnetic properties, but it is a brittle material itself, and it will break when a certain force is applied. At the same time, sintered NdFeB needs to be sintered at high temperature during the manufacturing process, and the process time is long, so the production cycle is long, so the cost is relatively high. Bonded NdFeB uses compression molding technology, so its mechanical strength and toughness are better than sintered NdFeB, which is very suitable for making small magnets with complex shapes and high precision. However, bonded NdFeB usually uses a binder, so the mechanical strength of bonded NdFeB is limited, but the manufacturing process of bonded NdFeB is simple, and the molding process can be carried out at room temperature, so the production cycle is short, the cost is low, and the loss rate of the product is low, which is suitable for mass production. Therefore, bonded NdFeB has better performance and lower cost than sintered NdFeB, and its application field is wider.

[0004] At present, there is no good NdFeB material resistant to cold and hot shock in actual large-scale production at home and abroad. With the popularization of new energy vehicles, the application environment of magnets is becoming more and more demanding, especially the requirements for magnets under cold and hot shock environments. At present, the heat resistance of NdFeB materials has been improved only by adding heat-resistant materials. For example, CN117542641A discloses a heat-resistant NdFeB material and a preparation method thereof, which discloses a preparation method of a heat-resistant NdFeB magnet. The NdFeB magnet is modified by optimizing the composition, optimizing the process, optimizing the surface modification of magnetic powder, and optimizing the heat-resistant polyurethane elastomer binder, so that the prepared NdFeB magnet still maintains high magnetic properties at a higher temperature; for another example, CN114806157A discloses a NdFeB magnetic composite material and a preparation method thereof, and the NdFeB magnetic composite material includes the following components: heat 2-9 parts by weight of plastic resin, 90-95 parts by weight of surface modified NdFeB magnetic powder, 1-3 parts by weight of reactive compatibilizer, 0.1-0.5 parts by weight of antioxidant and 0.3-1 parts by weight of lubricant are used. The NdFeB magnetic powder is subjected to surface silicon coating, silane coupling agent grafting modification and stabilizer functional grafting, so as to significantly improve the problem of high-temperature oxidation of the NdFeB magnetic powder. Moreover, through the bridging effect of the reactive compatibilizer, the compatibility between the thermoplastic resin matrix and the NdFeB magnetic powder and the thermal stability during processing are effectively enhanced, so as to ensure that the NdFeB magnetic composite material has good magnetic properties and is also conducive to improving the heat resistance and mechanical properties of the composite material.

[0005] It can be seen that the current NdFeB magnets only achieve improved heat resistance by adding heat-resistant materials. In some actual applications, NdFeB magnets not only need to be heat-resistant, but also need to be able to effectively cope with alternating hot and cold shocks. The most effective solution to solve the problem of NdFeB magnets coping with hot and cold shocks is to improve the thermal conductivity and thermal expansion coefficient of the magnets themselves. Therefore, under the premise of ensuring good magnetic properties of NdFeB magnets, further improving the anti-hot and cold shock properties of bonded NdFeB materials is an important part of improving product competitiveness.

[0006] Therefore, how to improve the NdFeB magnets while ensuring good magnetic properties to further improve the thermal shock resistance of bonded NdFeB materials is an important part of improving product competitiveness and is also a problem that needs to be solved urgently. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a NdFeB remelted magnetic powder and a preparation method thereof, a NdFeB magnet resistant to cold and hot shocks and a preparation method and application thereof. The additives included in the NdFeB remelted magnetic powder provided by the present invention have high thermal conductivity, so the NdFeB magnet prepared by using the NdFeB remelted magnetic powder will have more heat conduction paths, which can further improve the transfer speed of heat energy inside the magnet, and then be used to alleviate the internal stress caused by uneven cold and heat inside and outside under cold and hot shocks; at the same time, the additives themselves also have a lower expansion coefficient, which can effectively avoid the problem of reduced magnetic properties caused by changes in the crystal structure when the magnet is responding to alternating cold and hot shocks due to excessive thermal expansion coefficients, as well as cracking problems on the surface of the magnet.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a NdFeB remelted magnetic powder, wherein the NdFeB remelted magnetic powder comprises Nd2Fe 14 B. Magnetic powder matrix, additives, flux and lubricant;

[0010] The additives include silicon nitride and / or silicon carbide.

[0011] The present invention adds silicon nitride and / or silicon carbide as additives to Nd2Fe 14 In the B magnetic powder matrix, the above additives have the characteristics of high strength, oxidation resistance and corrosion resistance. In addition, they also have the characteristics of high specific modulus, high thermal conductivity, high temperature resistance and thermal stability. Therefore, the above additives are combined with Nd2Fe 14 The NdFeB magnet prepared by mixing the obtained NdFeB remelted magnetic powder with B magnetic powder matrix will have excellent properties under the conditions of resistance to cold and hot shock.

[0012] As a preferred technical solution of the present invention, the flux includes any one of yttrium oxide, cerium oxide or dysprosium oxide, or a combination of at least two thereof, preferably yttrium oxide.

[0013] Preferably, the lubricant comprises any one of aluminum oxide, calcium carbonate or calcium stearate or a combination of at least two thereof, preferably aluminum oxide.

[0014] In a second aspect, the present invention further provides a method for preparing the NdFeB remelted magnetic powder according to the first aspect, the preparation method comprising the following steps:

[0015] Nd2Fe 14 The B magnetic powder matrix, additives, flux and lubricant are first mixed, vacuum smelted to obtain gold castings, and then ball milled to obtain NdFeB remelted magnetic powder;

[0016] The additives include silicon nitride and / or silicon carbide.

[0017] As a preferred technical solution of the present invention, the raw materials of the NdFeB remelted magnetic powder include, by weight:

[0018] Nd2Fe 14 B magnetic powder matrix 500-3000 parts;

[0019] For example, 500, 800, 1000, 1200, 1500, 1800, 2000, 2200, 2500, 2800 or 3000 copies, etc.;

[0020] Additives 20-50 parts;

[0021] For example, 20, 25, 30, 35, 40, 45 or 50 copies;

[0022] Flux 10-100 parts;

[0023] For example, 10, 20, 30, 40, 50, 60, 70, 80, 90 or 100 copies, etc.;

[0024] 1-10 parts of lubricant;

[0025] For example, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 portions, etc.

[0026] Preferably, the raw materials of the NdFeB remelted magnetic powder include, by weight:

[0027]

[0028] In the present invention, by regulating the content of each component in the NdFeB remelted magnetic powder, the magnetic properties of the NdFeB magnet resistant to thermal shock prepared from the NdFeB remelted magnetic powder can be regulated. If there are too many additives and too much non-magnetic material is added, although the thermal shock resistance of the NdFeB magnet will be improved to a certain extent, it will also lead to a decrease in the overall magnetic properties of the magnet itself; if there are too few additives, the thermal shock resistance of the magnet will be reduced, it will be easy to crack, and the corresponding use requirements will not be met.

[0029] Preferably, the temperature of the vacuum smelting is 900°C-1100°C, such as 900°C, 950°C, 1000°C, 1050°C or 1100°C, etc., preferably 950°C-1000°C.

[0030] Preferably, the vacuum smelting is performed under an inert atmosphere.

[0031] Preferably, the gas used for the inert atmosphere includes argon.

[0032] It should be noted that the present invention does not impose any specific requirements or restrictions on the vacuum smelting time. 14 The B magnetic powder matrix becomes molten and all the raw materials are mixed evenly. For example, the vacuum smelting time can be 2 hours.

[0033] Preferably, the rotation speed of the ball mill is 200r / min-600r / min, for example, 200r / min, 250r / min, 300r / min, 350r / min, 400r / min, 450r / min, 500r / min, 550r / min or 600r / min, etc., preferably 250r / min-450r / min.

[0034] In the present invention, the particle size distribution of the NdFeB remelted magnetic powder can be regulated by adjusting the rotation speed of the ball mill to 200r / min-600r / min. If the ball mill rotation speed is too high, the particle size of the remelted magnetic powder is smaller, and the magnetic properties of the prepared magnet are reduced; if the ball mill rotation speed is too low, the particle size is too large, which will also lead to a reduction in the magnetic properties of the prepared magnet.

[0035] Preferably, the ball milling time is 2h-5h, such as 2h, 3h, 4h or 5h, etc., preferably 2h-3h.

[0036] Preferably, after the ball milling, screening is also included.

[0037] Preferably, the mesh size of the sieve used for the sieving is 250-350 mesh, such as 250 mesh, 300 mesh or 350 mesh.

[0038] In a third aspect, the present invention further provides a thermal shock resistant NdFeB magnet, which comprises the NdFeB remelted magnetic powder, a binder and a curing agent as described in the first aspect.

[0039] The present invention uses NdFeB remelted magnetic powder as raw material. Since the powder is pre-mixed with additives including silicon nitride and / or silicon carbide, after being combined with a binder and a curing agent, the thermal conductivity of the prepared NdFeB magnet can be increased and the expansion coefficient can be reduced, thereby having better resistance to thermal shock. Under the conditions of alternating hot and cold, the internal crystal structure will not undergo significant changes to affect the magnetic properties, nor will cracks be generated on the surface to reduce its service life.

[0040] As a preferred technical solution of the present invention, the binder includes any one of epoxy resin, phenol-formaldehyde resin or aromatic petroleum resin or a combination of at least two thereof, preferably epoxy resin.

[0041] Preferably, the curing agent includes any one of a silane coupling agent, diethylenetriamine or hexahydropyridine or a combination of at least two thereof, preferably a silane coupling agent.

[0042] It should be noted that the present invention does not make any specific requirements or special limitations on the silane coupling agent. Any silane coupling agent commonly used by those skilled in the art is applicable to the present invention, for example, KH550 and the like.

[0043] In a fourth aspect, the present invention further provides a method for preparing the thermal shock resistant NdFeB magnet according to the third aspect, the preparation method comprising the following steps:

[0044] The NdFeB remelted magnetic powder, the binder and the curing agent are mixed for a second time, pressed and thermally cured to obtain a NdFeB magnet resistant to thermal shock.

[0045] As a preferred technical solution of the present invention, the raw materials of the thermal shock resistant NdFeB magnet include, by weight:

[0046] 500-3000 parts of NdFeB remelted magnetic powder;

[0047] For example, 500, 800, 1000, 1200, 1500, 1800, 2000, 2200, 2500, 2800 or 3000 copies, etc.;

[0048] 10-18 parts of binder;

[0049] For example, 10, 11, 12, 13, 14, 15, 16, 17 or 18 portions, etc.;

[0050] 2-6 parts of curing agent;

[0051] For example, 2, 3, 4, 5 or 6 portions, etc.

[0052] Preferably, the raw materials of the thermal shock resistant NdFeB magnet include, by mass:

[0053] 1500-2500 parts of NdFeB remelted magnetic powder;

[0054] 12-16 parts of binder;

[0055] 3-5 parts of curing agent.

[0056] Preferably, the compression molding pressure is 30 MPa-80 MPa, such as 30 MPa, 40 MPa, 50 MPa, 60 MPa, 70 MPa or 80 MPa, etc., preferably 35 MPa-45 MPa.

[0057] Preferably, the thermal curing temperature is 100°C-200°C, such as 100°C, 120°C, 150°C, 180°C or 200°C, etc., preferably 140°C-180°C.

[0058] Preferably, the thermal curing time is 1 h-2 h, for example, 1 h, 1.2 h, 1.5 h, 1.8 h or 2 h.

[0059] As a preferred technical solution of the present invention, the preparation method comprises the following steps:

[0060] 500-3000 parts of NdFeB remelted magnetic powder, 10-18 parts of binder and 2-6 parts of curing agent are mixed for the second time, pressed at 30MPa-80MPa, and then heat cured at 100°C-200°C for 1h-2h to obtain a NdFeB magnet resistant to thermal shock;

[0061] The method for preparing the NdFeB remelted magnetic powder comprises the following steps:

[0062] 500-3000 parts of Nd2Fe 14 A B magnetic powder matrix, 20-50 parts of additives, 10-100 parts of flux and 1-10 parts of lubricant are first mixed, vacuum smelted at 900°C-1100°C under an inert atmosphere to obtain a gold casting sheet, and then ball milled at a speed of 200r / min-600r / min for 2h-5h, and passed through a 250-mesh sieve to obtain NdFeB remelted magnetic powder, wherein the additive includes silicon nitride and / or silicon carbide.

[0063] In a fifth aspect, the present invention further provides an application of a thermal shock resistant NdFeB magnet, wherein the thermal shock resistant NdFeB magnet described in the third aspect is applied to the fields of new energy vehicles, energy-saving electrical appliances or servo motors.

[0064] Compared with the prior art, the present invention has at least the following beneficial effects:

[0065] 1) The NdFeB remelted magnetic powder provided by the present invention includes additives of silicon nitride and / or silicon carbide. The additives themselves have high thermal conductivity and low expansion coefficient. Therefore, the NdFeB magnet prepared using the NdFeB remelted magnetic powder will have the ability to resist thermal shock.

[0066] 2) The NdFeB magnet provided by the present invention is placed at a low temperature of -40°C for 5 minutes and then at a high temperature of 125°C for 5 minutes. This is one cycle. After a total of 500 cycles, the number of sample cracks is ≤8%, which can effectively cope with use in cold and hot shock environments.

[0067] 3) The present invention first uses a remelting process to melt the high thermal conductivity additive into Nd2Fe 14B magnetic powder matrix, so that the two are highly evenly mixed, and then by adjusting the preparation process parameters of the NdFeB magnet, a NdFeB magnet resistant to cold and hot shock is obtained. DETAILED DESCRIPTION

[0068] For the convenience of understanding the present invention, the present invention lists the following embodiments. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0069] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0070] Example 1

[0071] This embodiment provides a NdFeB remelted magnetic powder and a preparation method thereof, a NdFeB magnet resistant to thermal shock and a preparation method thereof, and the preparation method comprises the following steps:

[0072] (1) 2000 parts of Nd2Fe 14 A B magnetic powder matrix, 28 parts of silicon nitride, 15 parts of yttrium oxide and 4 parts of aluminum oxide are first mixed, then smelted into gold castings in a vacuum induction furnace at 980°C in an argon atmosphere, and ball milled at a speed of 300 r / min for 2.5 hours to obtain NdFeB remelted magnetic powder;

[0073] (2) 2000 parts of NdFeB remelted magnetic powder, 15 parts of epoxy resin and 4 parts of KH550 were mixed in the second step, pressed into a Φ10*10 sample column at a pressure of 40 MPa, and heat cured at 160°C for 2 hours to obtain a NdFeB magnet that is resistant to thermal shock.

[0074] Example 2

[0075] This embodiment provides a NdFeB remelted magnetic powder and a preparation method thereof, and a preparation method of a NdFeB magnet resistant to thermal shock. The difference between the preparation method and the embodiment 1 is that in step (1), 500 parts of Nd2Fe 14 A first mixture is performed with B magnetic powder matrix, 50 parts of silicon nitride, 15 parts of yttrium oxide and 4 parts of aluminum oxide, and the remaining preparation methods and parameters are consistent with those in Example 1.

[0076] Example 3

[0077] This embodiment provides a NdFeB remelted magnetic powder and a preparation method thereof, and a preparation method for a NdFeB magnet resistant to thermal shock. The difference between the preparation method and the embodiment 1 is that in step (1), 3000 parts of Nd2Fe 14 A B magnetic powder matrix, 20 parts of silicon nitride, 15 parts of yttrium oxide and 4 parts of aluminum oxide are first mixed to obtain a eutectic material. The remaining preparation methods and parameters are consistent with those in Example 1.

[0078] Example 4

[0079] This embodiment provides a NdFeB remelted magnetic powder and a preparation method thereof, and a preparation method of a NdFeB magnet resistant to thermal shock. The difference between the preparation method and the embodiment 1 is that in step (1), 500 parts of Nd2Fe 14 A B magnetic powder matrix, 28 parts of silicon nitride, 100 parts of yttrium oxide and 4 parts of aluminum oxide are first mixed to obtain a eutectic material. The remaining preparation methods and parameters are consistent with those in Example 1.

[0080] Example 5

[0081] This embodiment provides a NdFeB remelted magnetic powder and a preparation method thereof, and a preparation method for a NdFeB magnet resistant to thermal shock. The difference between the preparation method and the embodiment 1 is that in step (1), 3000 parts of Nd2Fe 14 A B magnetic powder matrix, 28 parts of silicon nitride, 10 parts of yttrium oxide and 4 parts of aluminum oxide are first mixed to obtain a eutectic material. The remaining preparation methods and parameters are consistent with those in Example 1.

[0082] Example 6

[0083] This embodiment provides a NdFeB remelted magnetic powder and a preparation method thereof, and a preparation method of a NdFeB magnet resistant to thermal shock. The difference between the preparation method and the embodiment 1 is that in step (1), 500 parts of Nd2Fe 14 A B magnetic powder matrix, 28 parts of silicon nitride, 15 parts of yttrium oxide and 10 parts of aluminum oxide are first mixed to obtain a eutectic material. The remaining preparation methods and parameters are consistent with those in Example 1.

[0084] Example 7

[0085] This embodiment provides a NdFeB remelted magnetic powder and a preparation method thereof, and a preparation method for a NdFeB magnet resistant to thermal shock. The difference between the preparation method and the embodiment 1 is that in step (1), 3000 parts of Nd2Fe 14 A B magnetic powder matrix, 28 parts of silicon nitride, 15 parts of yttrium oxide and 10 parts of aluminum oxide are first mixed to obtain a eutectic material. The remaining preparation methods and parameters are consistent with those in Example 1.

[0086] Example 8

[0087] This embodiment provides a NdFeB remelted magnetic powder and a preparation method thereof, and a preparation method for a NdFeB magnet resistant to thermal shock. The difference between the preparation method and Example 1 is that in step (1), the rotation speed of the ball mill is 600 r / min, and the other preparation methods and parameters are consistent with Example 1.

[0088] Example 9

[0089] The present embodiment provides a NdFeB remelted magnetic powder and a preparation method thereof, and a preparation method for a NdFeB magnet resistant to thermal shock. The difference between the preparation method and Example 1 is that in step (1), the rotation speed of the ball mill is 200 r / min, and the other preparation methods and parameters are consistent with Example 1.

[0090] Example 10

[0091] This embodiment provides a NdFeB remelted magnetic powder and a preparation method thereof, and a preparation method for a NdFeB magnet resistant to thermal shock. The difference between the preparation method and Example 1 is that in step (1), the ball milling time is 5 hours, and the other preparation methods and parameters are consistent with Example 1.

[0092] Embodiment 11

[0093] This embodiment provides a NdFeB remelted magnetic powder and a preparation method thereof, and a preparation method for a NdFeB magnet resistant to thermal shock. The difference between the preparation method and Example 1 is that in step (1), the ball milling time is 2 hours, and the other preparation methods and parameters are consistent with Example 1.

[0094] Example 12

[0095] The present embodiment provides a NdFeB remelted magnetic powder and a preparation method thereof, and a preparation method of a NdFeB magnet resistant to thermal shock. The difference between the preparation method and Example 1 is that in step (2), 500 parts of NdFeB remelted magnetic powder, 18 parts of epoxy resin and 4 parts of KH550 are mixed in a second step to obtain a blend. The remaining preparation methods and parameters are consistent with those in Example 1.

[0096] Example 13

[0097] The present embodiment provides a NdFeB remelted magnetic powder and a preparation method thereof, and a preparation method for a NdFeB magnet resistant to thermal shock. The difference between the preparation method and Example 1 is that in step (2), 3000 parts of NdFeB remelted magnetic powder, 10 parts of epoxy resin and 4 parts of KH550 are mixed for a second time to obtain a blend, and the remaining preparation methods and parameters are consistent with Example 1.

[0098] Embodiment 14

[0099] This embodiment provides a NdFeB remelted magnetic powder and a preparation method thereof, and a preparation method of a NdFeB magnet resistant to thermal shock. The difference between the preparation method and the embodiment 1 is that in step (1), 2000 parts of Nd2Fe 14 A B magnetic powder matrix, 60 parts of silicon nitride, 15 parts of yttrium oxide and 4 parts of aluminum oxide are first mixed to obtain a eutectic material. The remaining preparation methods and parameters are consistent with those in Example 1.

[0100] Embodiment 15

[0101] This embodiment provides a NdFeB remelted magnetic powder and a preparation method thereof, and a preparation method of a NdFeB magnet resistant to thermal shock. The difference between the preparation method and the embodiment 1 is that in step (1), 2000 parts of Nd2Fe 14 A B magnetic powder matrix, 28 parts of silicon nitride, 110 parts of yttrium oxide and 4 parts of aluminum oxide are first mixed to obtain a eutectic material. The remaining preparation methods and parameters are consistent with those in Example 1.

[0102] Example 16

[0103] This embodiment provides a NdFeB remelted magnetic powder and a preparation method thereof, and a preparation method of a NdFeB magnet resistant to thermal shock. The difference between the preparation method and the embodiment 1 is that in step (1), 2000 parts of Nd2Fe 14 A B magnetic powder matrix, 28 parts of silicon nitride, 15 parts of yttrium oxide and 15 parts of aluminum oxide are first mixed to obtain a eutectic material. The remaining preparation methods and parameters are consistent with those in Example 1.

[0104] Embodiment 17

[0105] This embodiment provides a method for preparing a NdFeB magnet that is resistant to thermal shock. The difference between the preparation method and the embodiment 1 is that the process of preparing the NdFeB remelting magnetic powder is omitted, and 28 parts of silicon nitride, 15 parts of yttrium oxide, and 4 parts of aluminum oxide are directly mixed with 2000 parts of Nd2Fe 14 B magnetic powder matrix, 15 parts of epoxy resin and 4 parts of KH550 were mixed, and the remaining preparation methods and parameters were consistent with those in Example 1.

[0106] Comparative Example 1

[0107] This comparative example provides a NdFeB remelted magnetic powder and a preparation method thereof, and a preparation method of a NdFeB magnet resistant to thermal shock. The difference between the preparation method and Example 1 is that in step (1), yttrium oxide is omitted, and 2000 parts of Nd2Fe 14 The B magnetic powder matrix, 28 parts of silicon nitride and 4 parts of aluminum oxide are first mixed to obtain a blend. The remaining preparation methods and parameters are consistent with those in Example 1.

[0108] Comparative Example 2

[0109] This comparative example provides a method for preparing a neodymium iron boron magnet. The difference between the preparation method and Example 1 is that the process of preparing the remelted neodymium iron boron magnetic powder is omitted, and the addition of silicon nitride, yttrium oxide and aluminum oxide is omitted. 14 The B magnetic powder matrix was directly mixed with 15 parts of epoxy resin and 4 parts of KH550, and the remaining preparation methods and parameters were consistent with those in Example 1.

[0110] The particle sizes of the NdFeB remelted magnetic powders prepared in Examples 1-16 and Comparative Example 1 were tested on a particle size tester, and the magnetic properties of the NdFeB magnets prepared in Examples 1-17 and Comparative Example 1-2 were tested on a BH performance tester at room temperature, followed by a hot and cold shock test. The specific test conditions were as follows: placing the powder at a low temperature of -40°C for 5 minutes, and then placing the powder at a high temperature of 125°C for 5 minutes, which was one cycle. After a total of 500 cycles, the powder was cooled to room temperature and the number of cracked samples was observed. The specific test data are shown in Table 1.

[0111] Table 1

[0112]

[0113]

[0114] Note: “ / ” indicates that the preparation of NdFeB remelted magnetic powder was not carried out and the particle size test was not carried out.

[0115] The test results show that:

[0116] (1) It can be seen from Examples 1 to 13 that the present invention includes silicon nitride and / or silicon carbide as additives and adds Nd2Fe 14 B magnetic powder matrix, and then add flux and lubricant to assist, Nd2Fe 14 After the B magnetic powder matrix is ​​melted, it is mixed more evenly with additives, flux and lubricant. The obtained NdFeB remelted magnetic powder is prepared through a specific preparation process to obtain NdFeB magnets that are resistant to cold and hot shocks. It has excellent magnetic properties, especially under the impact of alternating hot and cold. The number of sample cracks is ≤8%, which can effectively cope with the use in cold and hot shock environments.

[0117] (2) It can be seen from Example 1 and Examples 14-16 that the present invention can take into account both the magnetic properties of the NdFeB magnet itself and its resistance to thermal shock by regulating the content of silicon nitride, yttrium oxide and aluminum oxide within a certain range, that is, the overall performance is better. Compared with Example 1, if the addition amount of non-magnetic materials such as silicon nitride, yttrium oxide or aluminum oxide is too much, the magnetic properties (coercive force and remanence) of the NdFeB magnet itself will be slightly reduced.

[0118] (3) It can be seen from Example 1 and Example 17 that if silicon nitride is still added in the present invention, but the process of preparing the NdFeB remelted magnetic powder is omitted, that is, silicon nitride, yttrium oxide and aluminum oxide are directly mixed with Nd2Fe 14 B magnetic powder matrix, epoxy resin and KH550 are mixed. Due to the direct mixing of silicon nitride, silicon nitride is formed on the Nd2Fe 14The dispersibility of B magnetic powder in the matrix becomes worse, and silicon nitride will play a more lubricating role in the magnet, and the thermal shock resistance and magnetic properties of the prepared NdFeB magnet are reduced.

[0119] (4) It can be seen from Example 1 and Comparative Example 1 that the addition of yttrium oxide in the present invention can promote the dispersion of silicon nitride and the densification of remelted magnetic powder. If its addition is omitted, it will lead to silicon nitride agglomeration and uneven internal stress, which will significantly reduce the thermal shock resistance of the NdFeB magnet and the corresponding magnetic properties.

[0120] (5) It can be seen from Example 1 and Comparative Example 2 that if the addition of the additive silicon nitride and the process of preparing the NdFeB remelting magnetic powder are omitted in the present invention, Nd2Fe 14 The B magnetic powder matrix is ​​directly mixed with epoxy resin and KH550, lacking the addition of silicon nitride with high thermal conductivity and low expansion coefficient. The thermal shock resistance of the obtained NdFeB magnet is significantly reduced, and the corresponding magnetic properties are also significantly reduced.

[0121] In summary, the NdFeB remelted magnetic powder provided by the present invention includes additives of silicon nitride and / or silicon carbide. The above-mentioned additives themselves have high thermal conductivity and low expansion coefficient. Therefore, the NdFeB magnet prepared using the NdFeB remelted magnetic powder will have more heat conduction paths, which can further improve the transfer speed of thermal energy, and thus be used to cope with and alleviate the internal stress caused by uneven heat and cold inside and outside under hot and cold shocks. At the same time, its lower expansion coefficient can effectively avoid the problem of reduced magnetic properties caused by excessive thermal expansion coefficient of the magnet when coping with alternating hot and cold shocks, changes in the crystal structure inside, and cracking on the surface of the magnet.

[0122] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A neodymium iron boron remelted magnetic powder, characterized in that: The NdFeB remelted magnetic powder includes Nd2Fe 14 B. Magnetic powder matrix, additives, flux and lubricant; The additives include silicon nitride and / or silicon carbide.

2. The NdFeB remelted magnetic powder according to claim 1, characterized in that: The flux comprises any one of yttrium oxide, cerium oxide or dysprosium oxide or a combination of at least two thereof, preferably yttrium oxide; Preferably, the lubricant comprises any one of aluminum oxide, calcium carbonate or calcium stearate or a combination of at least two thereof, preferably aluminum oxide.

3. A method for preparing NdFeB remelted magnetic powder according to claim 1 or 2, characterized in that: The preparation method comprises the following steps: Nd2Fe 14 The B magnetic powder matrix, additives, flux and lubricant are first mixed, vacuum smelted to obtain gold castings, and then ball milled to obtain NdFeB remelted magnetic powder; The additives include silicon nitride and / or silicon carbide.

4. The preparation method according to claim 3, characterized in that: The raw materials of the NdFeB remelted magnetic powder include, by mass: Preferably, the raw materials of the NdFeB remelted magnetic powder include, by weight: Preferably, the temperature of the vacuum smelting is 900°C-1100°C, preferably 950°C-1000°C; Preferably, the vacuum smelting is carried out under an inert atmosphere; Preferably, the rotation speed of the ball mill is 200r / min-600r / min, preferably 250r / min-450r / min; Preferably, the ball milling time is 2h-5h, preferably 2h-3h.

5. A NdFeB magnet resistant to thermal shock, characterized in that: The thermal shock resistant NdFeB magnet comprises the NdFeB remelted magnetic powder as claimed in claim 1 or 2, a binder and a curing agent.

6. The thermal shock resistant NdFeB magnet according to claim 5, characterized in that: The binder comprises any one of epoxy resin, phenol-formaldehyde resin or aromatic petroleum resin or a combination of at least two thereof, preferably epoxy resin; Preferably, the curing agent includes any one of a silane coupling agent, diethylenetriamine or hexahydropyridine or a combination of at least two thereof, preferably a silane coupling agent.

7. A method for preparing a thermal shock resistant NdFeB magnet according to claim 5 or 6, characterized in that: The preparation method comprises the following steps: The NdFeB remelted magnetic powder, the binder and the curing agent are mixed for a second time, and then pressed and thermally cured to obtain a NdFeB magnet resistant to thermal shock.

8. The preparation method according to claim 7, characterized in that: The raw materials of the thermal shock resistant NdFeB magnet include: 500-3000 parts of NdFeB remelted magnetic powder; 10-18 parts of binder; 2-6 parts of curing agent; Preferably, the raw materials of the thermal shock resistant NdFeB magnet include, by mass: 1500-2500 parts of NdFeB remelted magnetic powder; 12-16 parts of binder; 3-5 parts of curing agent; Preferably, the pressure of the compression molding is 30MPa-80MPa, preferably 35MPa-45MPa; Preferably, the temperature of the thermal curing is 100°C-200°C, preferably 140°C-180°C; Preferably, the thermal curing time is 1h-2h.

9. The preparation method according to claim 7, characterized in that: The preparation method comprises the following steps: 500-3000 parts of NdFeB remelted magnetic powder, 10-18 parts of binder and 2-6 parts of curing agent are mixed for the second time, pressed at 30MPa-80MPa, and then heat cured at 100°C-200°C for 1h-2h to obtain a NdFeB magnet resistant to thermal shock; The method for preparing the NdFeB remelted magnetic powder comprises the following steps: 500-3000 parts of Nd2Fe 14 A B magnetic powder matrix, 20-50 parts of additives, 10-100 parts of flux and 1-10 parts of lubricant are first mixed, vacuum smelted at 900°C-1100°C under an inert atmosphere to obtain a gold casting sheet, and then ball milled at a speed of 200r / min-600r / min for 2h-5h, and passed through a 250-mesh sieve to obtain NdFeB remelted magnetic powder, wherein the additive includes silicon nitride and / or silicon carbide.

10. An application of a NdFeB magnet resistant to thermal shock, characterized in that: The thermal shock resistant NdFeB magnets described in claim 5 or 6 are applied to the fields of new energy vehicles, energy-saving electrical appliances or servo motors.

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