Sintered neodymium-iron-boron magnet and preparation method thereof

Abstract

The invention provides a sintered neodymium-iron-boron magnet and a preparation method thereof. The sintered neodymium-iron-boron magnet comprises a neodymium-iron-boron sintered body and a heavy rare earth layer, wherein the heavy rare earth layer comprises heavy rare earth and an oxide; part or all of the surface of the neodymium-iron-boron sintered body is covered by the heavy rare earth layer, and heavy rare earth is distributed in an area, at least 3.5 mm deep from the surface, of the neodymium-iron-boron sintered body covered by the heavy rare earth layer; the oxide is one or more of aluminum oxide, silicon oxide, calcium oxide, magnesium oxide, zirconium oxide, copper oxide and zinc oxide, and the heavy rare earth is one or more of dysprosium, terbium, holmium and gadolinium. At least one part of the surface of the neodymium-iron-boron sintered body is covered with the heavy rare earth layer containing the oxide, when the heavy rare earth is diffused at a high temperature, the heavy rare earth enters the neodymium-iron-boron sintered body, the oxide is high in melting point, relatively thick and left on the surface of the neodymium-iron-boron sintered body, the effect of a spacer is achieved, magnet adhesion can be effectively prevented when the heavy rare earth is diffused, and the service life of the magnet is prolonged. And the preparation of the magnet is more convenient, and industrial application is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic materials, and more specifically, to a sintered neodymium iron boron magnet and a preparation method thereof. Background Art

[0002] Sintered neodymium iron boron magnets are the permanent magnetic materials with the strongest comprehensive magnetic properties in the world today. With their excellent properties and cost performance that exceed those of traditional permanent magnetic materials, they are widely used in fields such as energy, transportation, machinery, medical treatment, computers, and household appliances, playing an important role in the national economy. Among the technical indicators of magnetic materials, the magnetic energy product is the most important. The magnetic energy product represents the energy size of the external magnetic field generated by the magnet per unit volume. A high magnetic energy product means that a smaller magnet can output greater power on the motor. Neodymium iron boron is an important rare earth permanent magnetic material with characteristics such as high magnetic energy product, high coercivity, light weight, and low cost, and is the magnet with the highest cost performance so far. The emergence of neodymium iron boron has promoted the development of magnetic devices towards high efficiency, miniaturization, and light weight.

[0003] However, in order to meet the application requirements in high-temperature environments, heavy rare earths Tb or Dy are usually added to neodymium iron boron to improve the coercivity of the magnet. However, the abundance of heavy rare earths is low and the price is extremely expensive. Therefore, the heavy rare earth grain boundary diffusion technology has emerged. It is to coat the surface of the magnet with diffusion agents such as heavy rare earth metals, compounds, or alloys, and then through diffusion heat treatment, the heavy rare earth elements penetrate into the interior of the magnet. This process focuses on strengthening the weak grain surface, thereby achieving the effect of reducing the amount of heavy rare earths. However, in the actual production process, magnets are stacked closely together. When the heavy rare earth source liquefies during high-temperature diffusion, the products are extremely easy to stick together and difficult to separate, affecting the product qualification rate. And some neodymium iron boron manufacturers, in order to prevent product adhesion during diffusion, adopt the method of using spacers, that is, one layer of product and one layer of high-temperature resistant spacer, which increases the operation difficulty, reduces the efficiency, and increases the investment at the same time.

[0004] The patent with the publication number of 112086256A discloses an R-Fe-B series rare earth sintered magnet, which improves the heavy rare earth diffusion effect by using silicon materials. The patent with the publication number of 1688000A adds nano-oxides to the grain boundary phase to improve the coercivity of the sintered magnet. However, the above methods all have the problem that they cannot solve the problem of magnet adhesion during heavy rare earth diffusion and are difficult to be applied industrially. Summary of the Invention

[0005] The main object of the present invention is to provide a sintered neodymium iron boron magnet and a preparation method thereof, so as to solve the problem that magnets are prone to adhesion during heavy rare earth diffusion in the prior art.

[0006] To achieve the above object, according to one aspect of the present invention, there is provided a sintered neodymium iron boron magnet, comprising a neodymium iron boron sintered body and a heavy rare earth layer, the heavy rare earth layer comprising a heavy rare earth and an oxide; wherein, part or all of the surface of the neodymium iron boron sintered body is covered by the heavy rare earth layer, and the heavy rare earth is distributed in a region at least 3.5 mm deep from the surface of the neodymium iron boron sintered body covered with the heavy rare earth layer; wherein, the oxide is one or more of alumina, silica, calcium oxide, magnesium oxide, zirconium oxide, copper oxide and zinc oxide, and the heavy rare earth is one or more of dysprosium, terbium, holmium and gadolinium.

[0007] Further, the weight ratio of the heavy rare earth layer to the neodymium iron boron sintered body is (0.01 - 5):100; and / or by weight percentage, the heavy rare earth layer comprises 1 - 15% of the oxide and 85 - 99% of the heavy rare earth; preferably, by area percentage, 60 - 100% of the surface of the neodymium iron boron sintered body is covered by the heavy rare earth layer.

[0008] Further, the neodymium iron boron sintered body is Re α Fe 100-α-β-γ B β M γ , wherein, Re is a light rare earth element, which is one or more of La, Ce, Pr, Nd, Sm and Eu; M is an additive element, which is one or more of Ti, V, Cr, Ni, Zn, Ga, Ge, Al, Zr, Nb, Co, Cu, Ag, Sn, W, Pb, Bi and Pd; α, β and γ are the weight percentages of the respective constituent elements, 28 ≤ α ≤ 35, 0.8 ≤ β ≤ 1, 0 ≤ γ ≤ 5.

[0009] According to another aspect of the present invention, there is provided a method for preparing the above sintered neodymium iron boron magnet of the present invention, comprising the following steps: Step S1, preparing a neodymium iron boron sintered body and a heavy rare earth diffusion source; Step S2, mixing the oxide with the heavy rare earth diffusion source to obtain a heavy rare earth layer mixture; Step S3, coating the heavy rare earth layer mixture on part or all of the surface of the neodymium iron boron sintered body to obtain a coated magnet; Step S4, performing heavy rare earth diffusion treatment on the coated magnet to obtain a sintered neodymium iron boron magnet.

[0010] Further, in Step S1, the heavy rare earth diffusion source is an RT alloy, wherein R is one or more of dysprosium, terbium, holmium and gadolinium, and T is one or more of cobalt, aluminum, copper and gallium; preferably, the average particle size of the heavy rare earth diffusion source is 2 - 10 μm; preferably, the heavy rare earth diffusion source is prepared by the following steps: melting the raw materials of the heavy rare earth diffusion source to form a cast sheet or an ingot, performing hydrogen crushing, and then grinding using a jet mill or a ball mill to obtain the heavy rare earth diffusion source.

[0011] Further, in step S2, the average particle size of the oxide is 5 - 30 μm, preferably 5 - 10 μm; and / or the weight ratio of the oxide to the heavy rare earth diffusion source is (0.01:0.99) - (0.15:0.85), preferably (0.05:0.95) - (0.1:0.9).

[0012] Further, in step S3, the weight ratio of the heavy rare earth layer mixture to the NdFeB sintered body is (0.01 - 5):100; preferably, the heavy rare earth layer mixture is mixed with an organic solvent and a binder to obtain a suspension, and the suspension is coated on part or all of the surface of the NdFeB sintered body and dried to obtain a coated magnet; preferably, the solid content of the suspension is 20 - 80%.

[0013] Further, in step S4, the diffusion treatment includes: heating the coated magnet, then performing thermal diffusion, and finally performing aging treatment; preferably, the diffusion treatment is carried out under vacuum or inert gas protection.

[0014] Further, the heating temperature is 350 - 450 °C and the time is 1 - 5 h; and / or the thermal diffusion temperature is 700 - 1000 °C and the time is 10 - 50 h; and / or the aging treatment includes: cooling the coated magnet after thermal diffusion to below 100 °C, then heating it to 400 - 600 °C and holding for 3 - 10 h.

[0015] Further, the difference between the thermal diffusion temperature and the holding temperature of the aging treatment is 300 - 400 °C; and / or the difference between the thermal diffusion time and the holding time of the aging treatment is 10 - 20 h.

[0016] Applying the technical solution of the present invention, at least a part of the surface of the NdFeB sintered body is covered with a heavy rare earth layer containing an oxide. During the preparation process of the above magnet, when the heavy rare earth diffuses at high temperature, the heavy rare earth enters the interior of the NdFeB sintered body, while the oxide has a relatively high melting point and is relatively thick, remaining on the surface of the NdFeB sintered body to play a spacer role, which can effectively prevent the magnets from sticking during the heavy rare earth diffusion, making it more convenient for magnet preparation and facilitating industrial application. Specific Embodiments

[0017] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0018] As described in the background art of the present invention, there is a problem that magnets are prone to adhesion during the heavy rare earth diffusion of NdFeB magnets in the prior art. To solve the above problem, in a typical embodiment of the present invention, a sintered NdFeB magnet is provided, which includes a NdFeB sintered body and a heavy rare earth layer, and the heavy rare earth layer includes heavy rare earth and an oxide; wherein, part or all of the surface of the NdFeB sintered body is covered by the heavy rare earth layer, and the NdFeB sintered body with the heavy rare earth layer covering it has heavy rare earth distributed in a domain at least 3.5 mm deep from the surface; wherein, the oxide is one or more of aluminum oxide, silicon oxide, calcium oxide, magnesium oxide, zirconium oxide, copper oxide and zinc oxide, and the heavy rare earth is one or more of dysprosium, terbium, holmium and gadolinium.

[0019] In the present invention, by covering at least a part of the surface of a conventional NdFeB sintered body with the heavy rare earth layer containing an oxide of the present invention, during the high-temperature diffusion of the heavy rare earth, the heavy rare earth enters the magnet while the oxide remains on the surface of the magnet. This method can effectively prevent the problem of magnet adhesion during the heavy rare earth diffusion. The present invention limits the application of the above several oxides because the melting points of the above oxides are relatively high, and they can maintain a relatively large particle size during the heavy rare earth diffusion process, so as to better prevent magnet adhesion and at the same time will not have an adverse impact on the magnetic properties of the magnet.

[0020] In a preferred embodiment, the weight ratio of the heavy rare earth layer to the NdFeB sintered body is (0.01 - 5):100, so that the heavy rare earth can diffuse more fully into the NdFeB sintered body, further improving the magnetic properties while preventing magnet adhesion; and / or by weight percentage, the heavy rare earth layer includes 1 - 15% of the oxide and 85 - 99% of the heavy rare earth, so as to avoid adhesion caused by too low a proportion of the oxide or deterioration of the magnetic properties caused by too high a proportion of the oxide resulting in oxygen entering the magnet; preferably, by area percentage, 60 - 100% of the surface of the NdFeB sintered body is covered by the heavy rare earth layer, so as to better dope the heavy rare earth according to needs, reduce the usage of the heavy rare earth, and reduce the production cost of the magnet.

[0021] The NdFeB sintered body can use conventional types. In order to further improve the comprehensive magnetic properties of the finished magnet, in a preferred embodiment, the NdFeB sintered body is Re α Fe 100-α-β-γ B β M γ , where Re is a light rare earth element, which is one or more of La, Ce, Pr, Nd, Sm and Eu; M is an additive element, which is one or more of Ti, V, Cr, Ni, Zn, Ga, Ge, Al, Zr, Nb, Co, Cu, Ag, Sn, W, Pb, Bi and Pd; α, β and γ are the weight percentages of each component element, 28 ≤ α ≤ 35, 0.8 ≤ β ≤ 1, 0 ≤ γ ≤ 5.

[0022] In another typical embodiment of the present invention, there is also provided the preparation method of the above-mentioned sintered neodymium iron boron magnet of the present invention, including the following steps: Step S1, preparing a neodymium iron boron sintered body and a heavy rare earth diffusion source; Step S2, mixing an oxide with the heavy rare earth diffusion source to obtain a heavy rare earth layer mixture; Step S3, coating the heavy rare earth layer mixture on part or all of the surface of the neodymium iron boron sintered body to obtain a coated magnet; Step S4, performing heavy rare earth diffusion treatment on the coated magnet to obtain a sintered neodymium iron boron magnet.

[0023] The present invention first prepares a neodymium iron boron sintered body and a heavy rare earth diffusion source, and then mixes them with an oxide and coats them on part or all of the surface of the neodymium iron boron sintered body to obtain a coated magnet for heavy rare earth diffusion treatment. When high-temperature diffusion occurs, the heavy rare earth diffusion source diffuses into the magnet interior, while the relatively coarser oxide remains on the magnet surface due to its high melting point, playing a role of spacer, which well solves the problem that the magnets are prone to adhesion during diffusion, and obtains a sintered neodymium iron boron magnet without adhesion phenomenon, which is beneficial to improving the magnetic properties of the neodymium iron boron magnet while improving the preparation efficiency, reducing the equipment cost, and realizing industrial application.

[0024] In a preferred embodiment, in Step S1, the heavy rare earth diffusion source is an RT alloy, where R is one or more of dysprosium, terbium, holmium, and gadolinium, and T is one or more of cobalt, aluminum, copper, and gallium, so as to better improve the diffusion rate of the heavy rare earth in the neodymium iron boron sintered body; for a similar purpose, preferably, the average particle size of the heavy rare earth diffusion source is 2 - 10 μm; preferably, the heavy rare earth diffusion source is prepared through the following steps: melting the raw materials of the heavy rare earth diffusion source to form a cast sheet or an ingot, performing hydrogen crushing, and then using a jet mill or a ball mill for grinding to obtain the heavy rare earth diffusion source, which is more convenient for preparation.

[0025] For the purpose of further improving the magnetic properties while preventing the magnets from adhering, in a preferred embodiment, in Step S2, the average particle size of the oxide is 5 - 30 μm, preferably 5 - 10 μm. When the average particle size of the oxide is too low, it may cause the oxygen of the oxide to be brought into the magnet during the heavy rare earth diffusion process, resulting in an increase in the oxygen content of the magnet and deterioration of the magnetic properties. When the average particle size of the oxide is too high, the coating equipment may be easily damaged due to the large particles, affecting the production efficiency of the magnets.

[0026] Correspondingly, the weight ratio of the oxide to the heavy rare earth diffusion source is (0.01:0.99) - (0.15:0.85), preferably (0.05:0.95) - (0.1:0.9). When the proportion of the oxide is too low, adhesion is likely to occur; when it is too high, it may cause the oxygen in a small amount of fine powder to enter the magnet due to the increase in the addition amount, also resulting in an increase in the oxygen content of the magnet and deterioration of the magnetic properties. Therefore, the present invention limits the weight ratio of the oxide to the heavy rare earth diffusion source within the above range.

[0027] In a preferred embodiment, in step S3, the weight ratio of the heavy rare earth layer mixture to the NdFeB sintered body is (0.01 - 5):100; preferably, the heavy rare earth layer mixture is mixed with an organic solvent and a binder to obtain a suspension, and the suspension is coated on part or all of the surface of the NdFeB sintered body and dried to obtain a coated magnet, which is more convenient for the actual preparation process; preferably, the solid content of the suspension is 20 - 80%. Under the above conditions, magnet adhesion can be better prevented while reducing the usage of heavy rare earths. The organic solvent can be a conventional substance in the art, such as absolute ethanol or terpineol; the binder can be a conventional substance in the art, such as PVB or epoxy resin.

[0028] As described above, the preparation method of the present invention can prevent magnet adhesion during the diffusion of heavy rare earths. Therefore, when performing heavy rare earth diffusion, the sintered bodies with a heavy rare earth layer containing oxides attached to the surface can be stacked without the need for spaced placement, thereby effectively improving production efficiency and reducing equipment costs. In a preferred embodiment, in step S4, the diffusion treatment includes: heating the coated magnet to remove organic substances in the material, then performing thermal diffusion, and finally performing aging treatment; preferably, the diffusion treatment is carried out under vacuum or inert gas protection to better prevent oxygen from entering the magnet and affecting its magnetic properties.

[0029] In order to further improve the diffusion efficiency of heavy rare earths and at the same time improve the comprehensive magnetic properties of the magnet, in a preferred embodiment, the heating temperature is 350 - 450°C and the time is 1 - 5 h; and / or the thermal diffusion temperature is 700 - 1000°C and the time is 10 - 50 h; and / or the aging treatment includes: cooling the coated magnet after thermal diffusion to below 100°C, then heating it to 400 - 600°C and holding for 3 - 10 h.

[0030] In a preferred embodiment, the difference between the thermal diffusion temperature and the holding temperature of the aging treatment is 300 - 400°C; and / or the difference between the thermal diffusion time and the holding time of the aging treatment is 10 - 20 h, thereby further improving the diffusion rate of heavy rare earths.

[0031] Typical but non-limiting, the weight ratio of the heavy rare earth layer to the NdFeB sintered body is 0.01:100, 0.1:100, 0.5:100, 1:100, 1.2:100, 1.5:100, 2:100, 2.5:100, 3:100, 3.5:100, 4:100, 4.5:100, 5:100 or a range value composed of any two of these values.

[0032] Typically but not limited thereto, by weight percentage, the heavy rare earth layer includes oxides in an amount of 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15% or a range value composed of any two of these values, and heavy rare earths in an amount of 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or a range value composed of any two of these values.

[0033] Typically but not limited thereto, by area percentage, 60%, 70%, 80%, 90%, 100% or a range value composed of any two of these values of the surface of the NdFeB sintered body is covered by the heavy rare earth layer.

[0034] Typically but not limited thereto, in step S1, the average particle size of the heavy rare earth diffusion source is 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm or a range value composed of any two of these values.

[0035] Typically but not limited thereto, in step S2, the average particle size of the oxide is 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 15μm, 20μm, 25μm, 30μm or a range value composed of any two of these values; the weight ratio of the oxide to the heavy rare earth diffusion source is 0.01:0.99, 0.02:0.98, 0.04:0.96, 0.05:0.95, 0.06:0.94, 0.08:0.92, 0.1:0.9, 0.12:0.88, 0.14:0.86, 0.15:0.85 or a range value composed of any two of these values.

[0036] Typically but not limited thereto, in step S3, the weight ratio of the heavy rare earth layer mixture to the NdFeB sintered body is 0.01:100, 0.1:100, 0.5:100, 1:100, 1.2:100, 1.5:100, 2:100, 2.5:100, 3:100, 3.5:100, 4:100, 4.5:100, 5:100 or a range value composed of any two of these values.

[0037] Typically but not limited to, in step S4, during the diffusion treatment, the heating temperature is 350 °C, 360 °C, 370 °C, 380 °C, 390 °C, 400 °C, 410 °C, 420 °C, 430 °C, 440 °C, 450 °C or a range value composed of any two of these values, and the time is 1 h, 2 h, 3 h, 4 h, 5 h or a range value composed of any two of these values; the temperature of thermal diffusion is 700 °C, 800 °C, 900 °C, 1000 °C or a range value composed of any two of these values, and the time is 10 h, 20 h, 30 h, 40 h, 50 h or a range value composed of any two of these values; the aging treatment includes: cooling the coated magnet that has undergone thermal diffusion to below 100 °C, and then heating it to 400 °C, 450 °C, 500 °C, 550 °C, 600 °C or a range value composed of any two of these values, and holding for 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h or a range value composed of any two of these values.

[0038] Typically but not limited to, in step S4, during the diffusion treatment, the difference between the temperature of thermal diffusion and the holding temperature of the aging treatment is 300 °C, 310 °C, 320 °C, 330 °C, 340 °C, 350 °C, 360 °C, 370 °C, 380 °C, 390 °C, 400 °C or a range value composed of any two of these values, and the difference in the holding time is 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h or a range value composed of any two of these values.

[0039] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present application.

[0040] Unless otherwise specified, in the following examples and comparative examples, the added element M uses a mixture of Co, Cu, Al, Ga, Zr, and Ti.

[0041] Example 1

[0042] Step S1, the neodymium-iron-boron permanent magnet material alloy with the composition of (Nd, Pr) 30.5 Fe 余 M 1.6 B 0.96 (wt%) is produced into a square blank of 63.5×52×37.5 (mm) according to the neodymium-iron-boron production process, and the above square blank is processed into a semi-finished product of 63.5×52×4.5 mm; the heavy rare earth RT alloy with the composition of Dy 80 Co 10 Cu 5 Al 5 (wt%) is melted into a cast sheet, the cast sheet is hydrogenated and crushed, and then ball-milled to form a heavy rare earth diffusion source powder with an average particle size of 3.0 μm.

[0043] Step S2: Mix Al powder with an average particle size of 5 μm and heavy rare-earth diffusion source powder in a mass ratio of 0.05:0.95 to obtain a heavy rare-earth layer mixture; 2 O 3 Step S3: Add absolute ethanol and PVB to the heavy rare-earth layer mixture to form a slurry with a solid content of 50%. Coat the slurry on a semi-finished square blank with dimensions of 63.5×52×4.5 mm, with the coating weight gain being 1.2% of the weight of the original magnet;

[0044] Step S4: Heat the coated magnet under inert gas protection to 400 °C and hold for 2 hours to remove the magnet organic matter. Then raise the temperature to 900 °C and hold for 20 hours for heavy rare-earth diffusion. Subsequently, cool it to below 100 °C under inert gas protection and then raise the temperature to 500 °C and hold for 5 hours for aging treatment to obtain a sintered neodymium-iron-boron magnet.

[0045] Example 2

[0046] Step S1: Produce a square blank with dimensions of 63.5×52×37.5 (mm) from a neodymium-iron-boron permanent magnet material alloy with a composition of (Nd, Pr)

[0047] Fe 30.5 Fe 余 M 1.6 B 0.96 (wt%) according to the neodymium-iron-boron production process, and process the above square blank into a semi-finished product with dimensions of 63.5×52×4.5 mm. Melt a heavy rare-earth RT alloy with a composition of Dy 80 Co 10 Cu 5 Al 5 (wt%) into ingots. The ingots are hydrogenated and then ball-milled to form heavy rare-earth diffusion source powder with an average particle size of 3.0 μm;

[0048] Step S2: Mix Al powder with an average particle size of 10 μm and heavy rare-earth diffusion source powder in a mass ratio of 0.05:0.95 to obtain a heavy rare-earth layer mixture; 2 O 3 Step S3: Add absolute ethanol and PVB to the heavy rare-earth layer mixture to form a slurry with a solid content of 50%. Coat the slurry on a semi-finished square blank with dimensions of 63.5×52×4.5 mm, with the coating weight gain being 1.2% of the weight of the original magnet;

[0049] Step S4: Heat the coated magnet under inert gas protection to 400 °C and hold for 2 hours to remove the magnet organic matter. Then raise the temperature to 900 °C and hold for 20 hours for heavy rare-earth diffusion. Subsequently, cool it to below 100 °C under inert gas protection and then raise the temperature to 500 °C and hold for 5 hours for aging treatment to obtain a sintered neodymium-iron-boron magnet.

[0050] Step S4: Heat the coated magnet under the protection of inert gas to 400 °C and keep it at a constant temperature for 2 hours to remove the magnet organic matter, then raise the temperature to 900 °C and keep it at a constant temperature for 20 hours for heavy rare earth diffusion, then cool it to below 100 °C under the protection of inert gas, and then raise the temperature to 500 °C and keep it at a constant temperature for 5 hours for aging treatment to obtain a sintered NdFeB magnet.

[0051] Example 3

[0052] Step S1: For the neodymium iron boron permanent magnet material alloy with the composition of (Nd, Pr) 30.5 Fe 余 M 1.6 B 0.96 (wt%), produce a square blank of 63.5×52×37.5 (mm) according to the neodymium iron boron production process, and process the above square blank into a semi-finished product of 63.5×52×4.5 mm; for the heavy rare earth RT alloy with the composition of Dy 80 Co 10 Cu 5 Al 5 (wt%), melt it to form a cast sheet, hydrogenate and crush the cast sheet, and then ball mill it to form a heavy rare earth diffusion source powder with an average particle size of 2 μm;

[0053] Step S2: Mix Al powder with an average particle size of 5 μm 2 O 3 and the heavy rare earth diffusion source powder according to a mass ratio of 0.01:0.99 to obtain a heavy rare earth layer mixture;

[0054] Step S3: Add anhydrous ethanol and PVB to the heavy rare earth layer mixture to form a slurry with a solid content of 50%, and coat the slurry on the 63.5×52×4.5 mm square blank semi-finished product, with the coating weight gain being 1.2% of the original magnet weight;

[0055] Step S4: Heat the coated magnet under the protection of inert gas to 400 °C and keep it at a constant temperature for 2 hours to remove the magnet organic matter, then raise the temperature to 900 °C and keep it at a constant temperature for 20 hours for heavy rare earth diffusion, then cool it to below 100 °C under the protection of inert gas, and then raise the temperature to 500 °C and keep it at a constant temperature for 5 hours for aging treatment to obtain a sintered NdFeB magnet.

[0056] Example 4

[0057] Step S1: For the neodymium iron boron permanent magnet material alloy with the composition of (Nd, Pr) 30.5 Fe 余 M 1.6 B 0.96Neodymium-iron-boron permanent magnet material alloy of (wt%), produce a square blank of 63.5×52×37.5 (mm) according to the neodymium-iron-boron production process, and process the above square blank into a semi-finished product of 63.5×52×4.5 mm; The heavy rare earth RT alloy with the composition of Dy 80 Co 10 Cu 5 Al 5 (wt%) is melted to form a cast sheet, the cast sheet is hydrogenated and then ball milled to form a heavy rare earth diffusion source powder with an average particle size of 10 μm;

[0058] Step S2, mix Al 2 O 3 powder with an average particle size of 30 μm and the heavy rare earth diffusion source powder in a mass ratio of 0.15:0.85 to obtain a heavy rare earth layer mixture;

[0059] Step S3, add anhydrous ethanol and PVB to the heavy rare earth layer mixture to form a slurry with a solid content of 50%, and coat the slurry on the square blank semi-finished product of 63.5×52×4.5 mm, with the coating weight increasing by 1.2% of the weight of the original magnet;

[0060] Step S4, heat the coated magnet to 400°C and keep it at a constant temperature for 2 hours under inert gas protection to remove the organic matter of the magnet, then raise the temperature to 900°C and keep it at a constant temperature for 20 hours for heavy rare earth diffusion, then cool it to below 100°C under inert gas protection, and then raise the temperature to 500°C and keep it at a constant temperature for 5 hours for aging treatment to obtain a sintered neodymium-iron-boron magnet.

[0061] Example 5

[0062] Step S1, the neodymium-iron-boron permanent magnet material alloy with the composition of (Nd, Pr) 30.5 Fe 余 M 1.6 B 0.96 (wt%) produces a square blank of 63.5×52×37.5 (mm) according to the neodymium-iron-boron production process, and processes the above square blank into a semi-finished product of 63.5×52×4.5 mm; The heavy rare earth RT alloy with the composition of Dy 80 Co 10 Cu 5 Al 5 (wt%) is melted to form a cast sheet, the cast sheet is hydrogenated and then ball milled to form a heavy rare earth diffusion source powder with an average particle size of 3.0 μm;

[0063] Step S2, mix Al 2 O 3 powder with an average particle size of 10 μm and the heavy rare earth diffusion source powder in a mass ratio of 0.05:0.95 to obtain a heavy rare earth layer mixture.

[0064] Step S3: Add absolute ethanol and PVB to the heavy rare earth layer mixture to form a slurry with a solid content of 50%. Coat the slurry on the semi-finished blank of a 63.5×52×4.5 mm square, and the coating weight gain is 1.2% of the weight of the original magnet.

[0065] Step S4: Heat the coated magnet to 400 °C under inert gas protection and keep it at a constant temperature for 2 hours to remove the organic matter of the magnet. Then raise the temperature to 900 °C and keep it at a constant temperature for 20 hours for heavy rare earth diffusion. Subsequently, cool it to below 100 °C under inert gas protection, and then raise the temperature to 500 °C and keep it at a constant temperature for 5 hours for aging treatment to obtain a sintered NdFeB magnet.

[0066] Example 6

[0067] Step S1: A NdFeB permanent magnet material alloy with the composition of (Nd, Pr) 30.5 Fe 余 M 1.6 B 0.96 (wt%) is used to produce a square blank of 63.5×52×37.5 (mm) according to the NdFeB production process. The above square blank is processed into a semi-finished product of 63.5×52×4.5 mm; A heavy rare earth RT alloy with the composition of Dy 80 Co 10 Cu 5 Al 5 (wt%) is melted into a cast sheet. The cast sheet is hydrogenated and then ball-milled to form a heavy rare earth diffusion source powder with an average particle size of 3.0 μm.

[0068] Step S2: Mix Al 2 O 3 powder with an average particle size of 10 μm and the heavy rare earth diffusion source powder according to a mass ratio of 0.1:0.9 to obtain a heavy rare earth layer mixture.

[0069] Step S3: Add absolute ethanol and PVB to the heavy rare earth layer mixture to form a slurry with a solid content of 50%. Coat the slurry on the semi-finished blank of a 63.5×52×4.5 mm square, and the coating weight gain is 1.2% of the weight of the original magnet.

[0070] Step S4: Heat the coated magnet to 400 °C under inert gas protection and keep it at a constant temperature for 2 hours to remove the organic matter of the magnet. Then raise the temperature to 900 °C and keep it at a constant temperature for 20 hours for heavy rare earth diffusion. Subsequently, cool it to below 100 °C under inert gas protection, and then raise the temperature to 500 °C and keep it at a constant temperature for 5 hours for aging treatment to obtain a sintered NdFeB magnet.

[0071] Example 7

[0072] Step S1: The composition is (Nd, Pr) 30.5 Fe余 M 1.6 B 0.96 (wt%) neodymium-iron-boron permanent magnet material alloy, produce a square blank of 63.5×52×37.5 (mm) according to the neodymium-iron-boron production process, and process the above square blank into a semi-finished product of 63.5×52×4.5mm; for the component of Dy 80 Co 10 Cu 5 Al 5 (wt%) heavy rare earth RT alloy is melted into cast sheets, the cast sheets are hydrogenated and crushed, and then ball-milled to form heavy rare earth diffusion source powder with an average particle size of 3.0μm;

[0073] Step S2, mix Al 2 O 3 powder with an average particle size of 5μm and the heavy rare earth diffusion source powder according to a mass ratio of 0.05:0.95 to obtain a heavy rare earth layer mixture;

[0074] Step S3, add absolute ethanol and PVB to the heavy rare earth layer mixture to form a slurry with a solid content of 50%, coat the slurry on the square blank semi-finished product of 63.5×52×4.5mm, and the coating weight gain is 0.01% of the weight of the original magnet;

[0075] Step S4, heat the coated magnet to 350°C under inert gas protection and keep it at a constant temperature for 5 hours to remove the magnet organic matter, then raise the temperature to 700°C and keep it at a constant temperature for 50 hours for heavy rare earth diffusion, then cool it to below 100°C under inert gas protection, and then raise the temperature to 400°C and keep it at a constant temperature for 10 hours for aging treatment to obtain a sintered neodymium-iron-boron magnet.

[0076] Example 8

[0077] Step S1, for the component of (Nd, Pr) 30.5 Fe 余 M 1.6 B 0.96 (wt%) neodymium-iron-boron permanent magnet material alloy, produce a square blank of 63.5×52×37.5 (mm) according to the neodymium-iron-boron production process, and process the above square blank into a semi-finished product of 63.5×52×4.5mm; for the component of Dy 80 Co 10 Cu 5 Al 5 (wt%) heavy rare earth RT alloy is melted into cast sheets, the cast sheets are hydrogenated and crushed, and then ball-milled to form heavy rare earth diffusion source powder with an average particle size of 3.0μm;

[0078] Step S2, mix Al 2 O 3The powder and the heavy rare earth diffusion source powder are proportioned according to a mass ratio of 0.05:0.95 to obtain a heavy rare earth layer mixture;

[0079] In step S3, absolute ethanol and PVB are added to the heavy rare earth layer mixture to form a slurry with a solid content of 50%. The slurry is coated on a square blank semi-finished product of 63.5×52×4.5 mm, and the coating weight gain is 5% of the weight of the original magnet;

[0080] In step S4, the magnet after the above coating is heated to 450°C under the protection of an inert gas and kept at a constant temperature for 1 hour to remove the organic matter of the magnet, then the temperature is raised to 1000°C and kept at a constant temperature for 10 hours for heavy rare earth diffusion, and then cooled to below 100°C under the protection of an inert gas, and then the temperature is raised to 600°C and kept at a constant temperature for 3 hours for aging treatment to obtain a sintered neodymium iron boron magnet.

[0081] Comparative Example 1

[0082] The difference from Example 1 is that in step S2, the average particle size of the Al 2 O 3 powder is 4 μm.

[0083] Comparative Example 2

[0084] The difference from Example 1 is that in step S2, the average particle size of the Al 2 O 3 powder is 35 μm.

[0085] Comparative Example 3

[0086] The difference from Example 1 is that in step S2, the Al 2 O 3 powder and the heavy rare earth diffusion source powder are proportioned according to a mass ratio of 0.00:1.00.

[0087] Comparative Example 4

[0088] The difference from Example 1 is that in step S2, the Al 2 O 3 powder and the heavy rare earth diffusion source powder are proportioned according to a mass ratio of 0.16:0.84.

[0089] The proportion of the surface area of the neodymium iron boron sintered body covered by the heavy rare earth layer, the depth of the heavy rare earth distribution area from the surface of the neodymium iron boron sintered body, the remanence Br, the intrinsic coercivity HcJ, the magnetic energy product (BH)m, and the adhesion of the product after heavy rare earth diffusion of the sintered neodymium iron boron magnets prepared in the above examples and comparative examples are measured. The results are shown in Table 1. Among them, Example 1 is measured twice in parallel. Fluorescence analysis shows that heavy rare earths are distributed in the area at least 3.5 mm deep from the surface of the neodymium iron boron sintered body with a heavy rare earth layer coverage. Element content analysis shows that the heavy rare earth content increases after diffusion in this area.

[0090] Test method:

[0091] Remanence Br, intrinsic coercivity HcJ, magnetic energy product (BH)m: NIM-10000H / 62000TB permanent magnet non-destructive measurement system.

[0092] Table 1

[0093]

[0094]

[0095] It can be seen from the above results that although the product does not stick together after diffusion when the particle size of alumina powder is <5μm, the magnetic property Hcj decreases. The reason is that when the particle size is <5μm, oxygen in the alumina powder will be brought into the magnet during the heavy rare earth diffusion process, resulting in an increase in the oxygen content of the magnet and deterioration of the magnetic properties. When the particle size of the alumina powder is >30μm, the coating equipment is easily damaged due to the large particle size, affecting the production efficiency of the magnet. It can be seen from the above results that the magnetic property Hcj decreases when the particle size of the alumina powder is 5μm and the ratio of the alumina powder is >0.15. The reason is that although the average particle size of the alumina powder is 5μm, there is still a certain proportion of fine powder. When the addition ratio is large, oxygen in the finer alumina powder enters the magnet, resulting in an increase in the oxygen content of the magnet and deterioration of the magnetic properties.

[0096] As can be seen from the above, compared with the comparative examples, at least a part of the surface of the neodymium iron boron sintered body in each embodiment of the present invention is covered with a heavy rare earth layer containing oxides. During the high-temperature diffusion of the heavy rare earth in the preparation process of the above magnet, the heavy rare earth enters the inside of the neodymium iron boron sintered body, while the oxide has a relatively high melting point and is relatively coarse, remaining on the surface of the neodymium iron boron sintered body, acting as a spacer, which can effectively prevent the magnets from sticking together during the heavy rare earth diffusion, making it more convenient for the preparation of the magnets and conducive to industrial application.

[0097] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modifications, equivalent replacements, improvements, 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 sintered NdFeB magnet, characterized in that: It comprises a neodymium iron boron sintered body and a heavy rare earth layer, wherein the heavy rare earth layer comprises heavy rare earth and oxide; Wherein, part or all of the surface of the NdFeB sintered body is covered by the heavy rare earth layer, and the heavy rare earth is distributed in an area of ​​the NdFeB sintered body covered by the heavy rare earth layer at a depth of at least 3.5 mm from the surface; Wherein, the oxide is one or more of aluminum oxide, silicon oxide, calcium oxide, magnesium oxide, zirconium oxide, copper oxide and zinc oxide, and the heavy rare earth is one or more of dysprosium, terbium, holmium and gadolinium.

2. The sintered NdFeB magnet according to claim 1, characterized in that: The weight ratio of the heavy rare earth layer to the NdFeB sintered body is (0.01-5):100; and / or The heavy rare earth layer comprises 1 to 15% of the oxide and 85 to 99% of the heavy rare earth by weight percentage; Preferably, in terms of area percentage, 60-100% of the surface of the NdFeB sintered body is covered by the heavy rare earth layer.

3. The sintered NdFeB magnet according to claim 1 or 2, characterized in that: The NdFeB sintered body is Re α Fe 100-α-β-γ B β M γ ,in, Re is a light rare earth element, which is one or more of La, Ce, Pr, Nd, Sm and Eu; M is an added element, which is one or more of Ti, V, Cr, Ni, Zn, Ga, Ge, Al, Zr, Nb, Co, Cu, Ag, Sn, W, Pb, Bi and Pd; α, β and γ are the weight percentages of the respective constituent elements, 28≤α≤35, 0.8≤β≤1, 0≤γ≤5.

4. The method for preparing a sintered NdFeB magnet according to any one of claims 1 to 3, characterized in that: The following steps are involved: Step S1, preparing a NdFeB sintered body and a heavy rare earth diffusion source; Step S2, mixing the oxide with the heavy rare earth diffusion source to obtain a heavy rare earth layer mixture; Step S3, coating the heavy rare earth layer mixture on part or all of the surface of the NdFeB sintered body to obtain a coated magnet; Step S4, subjecting the coated magnet to a heavy rare earth diffusion treatment to obtain the sintered NdFeB magnet.

5. The preparation method according to claim 4, characterized in that: In step S1, the heavy rare earth diffusion source is an RT alloy, wherein R is one or more of dysprosium, terbium, holmium and gadolinium, and T is one or more of cobalt, aluminum, copper and gallium; Preferably, the average particle size of the heavy rare earth diffusion source is 2 to 10 μm; Preferably, the heavy rare earth diffusion source is prepared by the following steps: melting the raw material of the heavy rare earth diffusion source to form a casting or an ingot, performing hydrogen crushing, and then grinding using a jet mill or a ball mill to obtain the heavy rare earth diffusion source.

6. The preparation method according to claim 4 or 5, characterized in that: In step S2, the average particle size of the oxide is 5 to 30 μm, preferably 5 to 10 μm; and / or The weight ratio of the oxide to the heavy rare earth diffusion source is (0.01:0.99) to (0.15:0.85), preferably (0.05:0.95) to (0.1:0.9).

7. The preparation method according to any one of claims 4 to 6, characterized in that: In the step S3, the weight ratio of the heavy rare earth layer mixture to the NdFeB sintered body is (0.01-5):100; Preferably, the heavy rare earth layer mixture is mixed with an organic solvent and a binder to obtain a suspension, and the suspension is coated on part or all of the surface of the NdFeB sintered body and dried to obtain the coated magnet; Preferably, the solid content of the suspension is 20-80%.

8. The preparation method according to any one of claims 4 to 7, characterized in that In the step S4, the diffusion treatment includes: heating the coated magnet, then performing thermal diffusion, and finally performing aging treatment; Preferably, the diffusion treatment is performed under vacuum or inert gas protection.

9. The preparation method according to claim 8, characterized in that: The heating temperature is 350-450° C. and the heating time is 1-5 hours; and / or The thermal diffusion temperature is 700-1000° C. and the time is 10-50 hours; and / or The aging treatment comprises: cooling the coated magnet after the thermal diffusion to below 100° C., then heating it to 400-600° C., and keeping the temperature for 3-10 hours.

10. The preparation method according to claim 9, characterized in that: The difference between the thermal diffusion temperature and the insulation temperature of the aging treatment is 300-400° C.; and / or the difference between the thermal diffusion time and the insulation time of the aging treatment is 10-20 hours.

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