Preparation method of R-T-B rare earth permanent magnet

Abstract

The invention discloses a preparation method of an R-T-B rare earth permanent magnet, and the method comprises the following steps: 1, coating with a coating: coating an S1 region on the surface of a permanent magnet substrate with a first coating to obtain a first coating region S1, and coating an S2 region on the surface of the permanent magnet substrate with a second coating to obtain a second coating region S2; the first coating area S1 is smaller than or equal to S, the second coating area S2 is smaller than or equal to S, S is the magnet surface area where the coating face is located, and the first coating and the second coating are composed of one or more components of pure metal containing Dy and / or Tb, hydride, fluoride and oxide; and 2, carrying out grain boundary diffusion treatment on the magnet obtained in the step 1, and carrying out aging treatment after cooling to obtain the R-T-B rare earth permanent magnet. The method has the advantages that diffusion of heavy rare earth in a grain main phase can be reduced, the use amount of the heavy rare earth is reduced, and the coercive force of a selected area can be further enhanced.

Description

Technical Field

[0001] The invention relates to the technical field of rare earth permanent magnet preparation, in particular to a method for preparing an RTB rare earth permanent magnet. Background Art

[0002] RTB rare earth permanent magnets, with their high remanence, high coercivity, and large magnetic energy product, are widely used in modern industry and electronics, including in computers, automated control systems, motors and generators, magnetic resonance imaging (MRI), audio components, material sorting equipment, and communications equipment. With the development of new applications and increasingly demanding and changing application conditions, the demand for products with high coercivity is increasing. Coercivity is one of the key properties of permanent magnets, and improving it has long been a key topic in both rare earth permanent magnet research and theoretical studies.

[0003] RTB rare earth permanent magnet material main phase Nd2Fe 14 The saturation magnetic induction intensity of B is very high, about 1.61T (16.1kGs), and the theoretical magnetic energy product can reach 512 KJ / m 3 , Nd2Fe 14 B has a very high anisotropy field (HA), and its theoretical limit of coercivity is as high as 70kOe. However, the actual Nd-Fe-B magnet is composed of the main phase Nd2Fe 14 The coercive force of the magnet is only one tenth to one half of the theoretical value, and the remanence and magnetic energy product of the magnet are mainly composed of the magnetic phase Nd2Fe 14 B determines the coercive force, which is mainly determined by the Nd-rich phase and microstructure. From the perspective of the demagnetization mechanism of sintered NdFeB materials, the coercive force is mainly the nucleation mechanism of the demagnetization domain at the grain boundary. This determines that the boundary structure and physical properties of the magnetic phase play an important role in the coercive force of the magnet. The methods to improve the coercive force are also focused on improving HA and improving the boundary phase structure. The main methods include: 1. Adding heavy rare earth elements to the alloy to increase the anisotropy field (HA); 2. Powder optimization, using a double liquid alloying method and adding micron and nano powders of heavy rare earth elements or compounds to achieve effective control of the material microstructure, especially the grain boundaries, to improve the coercive force of the magnet; 3. Performing grain boundary diffusion treatment of heavy rare earth on the magnet to improve the coercive force.

[0004] Grain boundary diffusion method is to send Dy and Tb attached to the surface of the magnet into the interior of the sintered body through the grain boundary of the sintered body under high temperature conditions, and diffuse from the grain boundary to the main phase R2Fe 14B (R is a rare earth element) inside each particle. The use of this method can greatly reduce the use of heavy rare earth elements and significantly improve the magnetic properties of the magnet. Since heavy rare earth diffuses from the surface of the magnet to the center of the magnet, the diffused heavy rare earth elements are distributed in a gradient from the surface to the center of the magnet, and this distribution is also affected by the supply of heavy rare earth on the surface. Generally speaking, there is a problem of oversupply of heavy rare earth uniformly coated on the surface of the magnet. On the one hand, on any cross-section of the magnet, the proportion of the main phase is high and the proportion of the grain boundary phase is small. A large part of the coated heavy rare earth is absorbed by the main phase, which is not conducive to the penetration of heavy rare earth along the grain boundary into the interior of the magnet; on the other hand, during the operation of the motor, the reverse demagnetization effect of the excitation coil on the magnet is not uniform, and the strong demagnetization effect is also mainly concentrated on the edge of the magnet. Strengthening the coercive force of the edge part of the magnet is beneficial to improving the anti-demagnetization ability of the magnet and saving the amount of heavy rare earth. Researchers in this field have adopted the method of selective diffusion to improve the anti-demagnetization ability of the magnet and reduce the amount of heavy rare earth.

[0005] Existing technologies all have limitations. Patent application CN106128678A employs a method of first coating the surface of an RTB rare earth permanent magnet with one or more rare earth fluorides, rare earth oxides, or rare earth hydrides, followed by a diffusion process using Dy vapor. This method mitigates over-penetration of heavy rare earths into the main phase to a certain extent, saving heavy rare earth usage. However, this method involves cumbersome Dy plate arrangement and is unable to control the heavy rare earth supply to selected areas of the magnet. Patent application CN115763042A discloses a method for preparing a grain boundary diffusion magnet comprising alternately arranged coated and uncoated regions. This method reduces over-penetration of heavy rare earths into the uncoated regions, saving heavy rare earth usage to a certain extent. However, there are still issues with over-penetration of heavy rare earths into the main phase from the coated regions, as well as over-penetration of Dy or under-penetration of Tb in the uncoated regions. Because even in the non-coated area, Dy in the coated area can still reach the non-coated area in the form of vapor and cause over-penetration, while Tb can only reach the non-coated area from the coated area through the grain boundary channel without vapor. The area of ​​the non-coated area cannot be too large, otherwise there will be a problem of insufficient Tb penetration.

[0006] Therefore, the existing RTB rare earth permanent magnet preparation method needs to be further improved. Summary of the Invention

[0007] The purpose of the present invention is to overcome the above-mentioned deficiencies and disclose to the public a method for preparing RTB rare earth permanent magnets. The method comprises combining the coating and diffusion of heavy rare earth diffusion sources in selected areas of the magnet, thereby reducing the diffusion of heavy rare earth in the main phase of the grains and the amount of heavy rare earth used, and can further enhance the coercive force of the selected areas. The preparation method is simple and suitable for mass production.

[0008] The technical solution of the present invention is achieved as follows: A method for preparing an RTB rare earth permanent magnet comprises the following steps: Step 1, coating: coating the permanent magnet substrate surface S1 area with a first coating to obtain a first coating area S1, wherein the first coating is composed of one or more components of pure metal, hydride, fluoride, and oxide containing Dy and / or Tb; coating the permanent magnet substrate surface S2 area with a second coating to obtain a second coating area S2, wherein the second coating is composed of one or more components of pure metal, hydride, fluoride, and oxide containing Dy and / or Tb, and contains at least one of pure metal and hydride of Dy; the first coating area S1≤S, the second coating area S2≤S, and S is the magnet surface area where the coating surface is located; Step 2: The magnet obtained in step 1 is subjected to grain boundary diffusion treatment, and then cooled and subjected to aging treatment to obtain an RTB rare earth permanent magnet.

[0009] Preferably, in the step 1, there is an overlapping area S12 between the first coating area S1 and the second coating area S2, and there is an area S0 on S that is not covered by any coating, and 0≤S12≤S, 0≤S0≤0.5S.

[0010] Preferably, the coating region is located on a surface perpendicular to the orientation direction of the RTB rare earth permanent magnet.

[0011] Preferably, two surfaces perpendicular to the orientation direction of the RTB rare earth permanent magnet are both coated with the coating.

[0012] Preferably, the first coating and the second coating further include an organic solution required for coating.

[0013] Preferably, the hydride component containing Dy and / or Tb is R 1-a-b T a X b , wherein R is one or more of the heavy rare earth elements Dy, Tb, and Ho; T is one or more of La, Ce, Pr, Nd, Gd, Al, Cu, Ga, Co, Fe, Nb, Ti, and Zr; X is one or more of H, O, N, C, and B; a and b are weight percentages, 0wt.%≤a<20wt.%, 0wt.%≤b<5wt.%.

[0014] Preferably, the coating mass of the heavy rare earth element in the first coating is 0.05-0.5% of the mass of the magnet in the area where it is located, and the coating mass of the heavy rare earth element in the second coating is 0.2-1.0% of the mass of the magnet in the area where it is located.

[0015] Preferably, in step 1, the coating method of the first coating and the second coating is PVD vapor deposition, spraying or screen printing.

[0016] Preferably, in the step 2, the grain boundary diffusion treatment is as follows: the diffusion temperature of the grain boundary diffusion treatment is 800-950°C, the diffusion time is 8-48h, and the diffusion heating process includes a heat preservation process at 200-600°C, and the heat preservation time is controlled to be 2-6h. After the diffusion is completed, the magnet is rapidly cooled, and the cooling temperature is 60-90°C.

[0017] Preferably, in step 2, the aging treatment process is as follows: the aging treatment temperature is 400-700°C, the aging treatment time is 2-10h, and after the aging is completed, the magnet is rapidly cooled at a cooling temperature of 60-90°C.

[0018] The advantages of the present invention compared with the prior art are: The present invention adopts the method of coating heavy rare earth in selected areas to carry out grain boundary diffusion, which can achieve diffusion and penetration of the coating layer into the coated area of ​​the magnet and also achieve diffusion and penetration into the non-coated area. In particular, the Dy mixture coating achieved good penetration into the non-coated area and reduced the residual magnetization of the magnet. When maintaining a certain amount of heavy rare earth coating on the magnet, the selective coating method reduces the coating area of ​​the heavy rare earth and increases the accumulation of heavy rare earth per unit area in the coated area of ​​the magnet. This can improve the concentration gradient of heavy rare earth diffusion, facilitate the continuous diffusion of heavy rare earth into the interior of the magnet, and further improve the coercive force of the magnet. In addition, it also avoids the dispersed distribution of heavy rare earth and thin coating caused by uniform coating of heavy rare earth. Thin coating makes the coated heavy rare earth more susceptible to oxidation and significantly reduces the diffusion effect. The present invention performs combined coating and diffusion of heavy rare earth on selected areas of the magnet, reduces the diffusion of heavy rare earth in the main phase of the grain, reduces the amount of heavy rare earth used, and further enhances the coercive force of the selected area. The preparation method is simple and can be mass-produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of a magnet coated with a heavy rare earth diffusion source coating according to Example 1 of the present invention; Figure 2 This is a schematic diagram of a magnet coated with a heavy rare earth diffusion source coating according to Example 2 of the present invention; Figure 3 This is a schematic diagram of a magnet coated with a heavy rare earth diffusion source coating according to Example 3 of the present invention; Figure 4 This is a schematic diagram of a magnet coated with a heavy rare earth diffusion source coating according to Example 4 of the present invention; Figure 5 This is a schematic diagram of a magnet coated with a heavy rare earth diffusion source coating according to Example 5 of the present invention. DETAILED DESCRIPTION

[0020] The present invention is described in further detail below: A method for preparing an RTB rare earth permanent magnet comprises the following steps: Step 1: Coating: An RTB rare earth permanent magnet is selected as the substrate and processed into the desired shape and size, with the orientation direction aligned with the thickness direction, and then cleaned. A first coating is applied to the surface S1 of the permanent magnet substrate to obtain a first coating region S1. The first coating is composed of one or more components of pure metals, hydrides, fluorides, and oxides containing Dy and / or Tb. A second coating is applied to the surface S2 of the permanent magnet substrate to obtain a second coating region S2. The second coating is composed of one or more components of pure metals, hydrides, fluorides, and oxides containing Dy and / or Tb, and contains at least one pure metal or hydride of Dy. The first coating region S1 ≤ S, and the second coating region S2 ≤ S, where S is the surface region of the magnet where the coating surface is located. The coating methods for the first and second coatings are PVD vapor deposition, spray coating, or screen printing, preferably screen printing.

[0021] Step 2: The magnet obtained in step 1 is subjected to grain boundary diffusion treatment, and then subjected to aging treatment after cooling to obtain an RTB rare earth permanent magnet. The grain boundary diffusion treatment is as follows: the diffusion temperature of the grain boundary diffusion treatment is 800-950°C, the diffusion time is 8-48h, and during the diffusion heating process, a heat preservation process is included at 200-600°C, and the heat preservation time is controlled to be 2-6h. After the diffusion is completed, the magnet is quenched, preferably using high-purity Ar gas for air cooling, and the cooling temperature is 60-90°C. The aging treatment process is as follows: the aging treatment temperature is 400-700°C, the aging treatment time is 2-10h, and after the aging is completed, the magnet is quenched, preferably using high-purity Ar or high-purity N2 gas for air cooling, and the cooling temperature is 60-90°C.

[0022] In the step 1, the first coating area S1 and the second coating area S2 have an overlapping area S12, and there is an area S0 on S that is not covered by any coating, and 0≤S12≤S, 0≤S0≤0.5S.

[0023] The above-mentioned coating area is located on the surface perpendicular to the orientation direction of the RTB rare earth permanent magnet. Preferably, both surfaces perpendicular to the orientation direction of the RTB rare earth permanent magnet are coated with the coating.

[0024] Among them, the hydride component containing Dy and / or Tb is R 1-a-b T a X b, wherein R is one or more of the heavy rare earth elements Dy, Tb, and Ho; T is one or more of La, Ce, Pr, Nd, Gd, Al, Cu, Ga, Co, Fe, Nb, Ti, and Zr; X is one or more of H, O, N, C, and B; a and b are weight percentages, 0wt.%≤a<20wt.%, 0wt.%≤b<5wt.%.

[0025] The first coating and the second coating further include an organic solution required for coating. The organic solution can be one or more components of organic substances such as alcohols, ketones, aldehydes, ethers, esters, resins, amines, hydrocarbons, etc. Preferably, the organic solution is an alcohol, such as ethanol.

[0026] The coating mass of the heavy rare earth element in the first coating is 0.05-0.5% of the mass of the magnet in the area where it is located, and the coating mass of the heavy rare earth element in the second coating is 0.2-1.0% of the mass of the magnet in the area where it is located.

[0027] Explanation of the definition of magnet mass in the region: Given a magnet with dimensions L×W×H (mm) and a mass of M, the coated surface of the magnet is L×W (area S), the heavy rare earth coating area on S is S1 (or S2), and the mass of the coated heavy rare earth is m (m can be calculated by weighing the magnet before and after coating). m / M is the ratio of the heavy rare earth coating mass to the mass of the entire magnet. For a given coating thickness, the value of m fluctuates significantly depending on the coating area S1 (or S2), making it difficult to control this value. For experimental convenience, the mass percentage cannot be based on the total magnet weight M. Instead, the mass N of the magnet in the region covered by the coating, including area S1 (or S2), must be calculated, and then m / N is calculated. m / N is the percentage of the heavy rare earth coating mass m in the coating to the mass N of the magnet in the region covered by the coating, where N = M*S1 / S (or N = M*S2 / S).

[0028] Example 1: A method for preparing an RTB rare earth permanent magnet comprises the following steps: taking an N54 brand RTB rare earth permanent magnet with magnetic properties of Br=14.82 kGs, Hcj=12.23 kOe, and Hk / Hcj=97.6% as a matrix, and cutting the matrix into magnets with specifications of 20×20×5 mm, with the orientation direction being parallel to the thickness direction of 5 mm.

[0029] Metal Tb powder and metal Dy powder are sprayed sequentially on two 20×20 surfaces (two magnet coating surfaces S) perpendicular to the orientation direction to form a magnet coated with metal Tb powder and metal Dy powder in sequence, wherein there is a first coating area S1 formed by coating with metal Tb powder as the first coating material, and a second coating area S2 formed by coating with metal Dy powder as the second coating material, and the relationship S1=S and S2=S is satisfied, where S is the surface area of ​​a single magnet coating surface. After single-sided coating, the weight of the metal Tb powder coated on the first coating area S1 and the metal Dy powder coated on the second coating area S2 are respectively 0.15% and 0.05% of the weight of the magnet in the coated area (the coating amounts account for 0.15% and 0.05% of the weight of the entire magnet, respectively); after double-sided coating, the cumulative weight of Tb coated on the first coating area S1 and Dy coated on the second coating area S2 are respectively 0.3% and 0.1% of the weight of the magnet in the coated area (that is, the coating amounts of Tb and Dy account for 0.3% and 0.1% of the weight of the entire magnet, respectively). In this embodiment, there is an overlapping area S12 between the first coating area S1 and the second coating area S2, S12=S1=S2=S, and S is not covered by any coating area S0=0. In this embodiment, the detailed coverage diagram of the S, S1, S2, S12, and S0 areas is shown in FIG. Figure 1 .

[0030] As comparative example 1-1, the metal Tb powder and the metal Dy powder were uniformly mixed in a mass ratio of 3:1, and then sprayed onto two 20×20 surfaces of the magnet with a single coating. The coating amount was exactly the same as that in Example 1, and the cumulative coating amount of Tb and Dy was 0.4% (the Tb and Dy coating amounts accounted for 0.3% and 0.1% of the weight of the entire magnet, respectively).

[0031] As Comparative Examples 1-2, a magnet was formed by coating metal Dy powder first, then metal Tb powder. The remaining coating areas and coating amounts were identical to those in Example 1. The cumulative coating amount of Dy and Tb was 0.4% (the Tb and Dy coatings accounted for 0.3% and 0.1% of the total magnet weight, respectively).

[0032] As comparative examples 1-3, the metal Tb powder was coated on two 20×20 surfaces of the magnet, with a coating area of ​​S and a cumulative coating amount of 0.4% (the Tb coating amounts on each surface were 0.2% and 0.2% respectively).

[0033] As comparative examples 1-4, the metal Tb powder was coated on two 20×20 surfaces of the magnet, with a coating area of ​​S and a cumulative coating amount of 0.3% (the Tb coating amount on each surface was 0.15% and 0.15% respectively).

[0034] The magnets produced in Example 1 and Comparative Examples 1-1, 1-2, 1-3, and 1-4 were placed in a vacuum diffusion furnace for grain boundary diffusion treatment. The diffusion treatment process was as follows: first, degassing at 200°C for 2 hours, then heating to 900°C and holding for 15 hours, followed by aging at 500°C for 10 hours.

[0035] The magnetic properties of the RTB rare earth permanent magnets were tested before and after treatment, with the results shown in Table 1. The magnetic properties of the entire sample were measured using a BH magnetic performance tester. To test the performance of different regions of the magnet after selective diffusion, the magnets were processed into samples with dimensions of 1 × 1 × H mm (H is the sample thickness, equivalent to the distance between two S-planes perpendicular to the magnet orientation direction, in mm) for the selected coating areas. The magnetic properties of these different microregions were then measured using PFM.

[0036] Table 1 Comparison of magnetic properties of RTB rare earth permanent magnets before and after treatment in Example 1

[0037] As can be seen from Example 1 and Comparative Examples 1-1 and 1-2 in Table 1, for coatings of the same weight of heavy rare earth elements, Tb and Dy, different diffusion source supply methods produce different effects. In Example 1, where Tb is applied first and then Dy, the coercivity reaches 21.58 kOe. In Comparative Example 1-2, where Dy is applied first and then Tb, the coercivity is increased to 19.76 kOe, resulting in the worst coercivity improvement, even lower than the effect of mixing Tb and Dy before coating and diffusion in Comparative Example 1-1. Comparing Example 1 with Comparative Examples 1-3, the coercivity improvement effect of 0.3% Tb + 0.1% Dy in Example 1 is very similar to that of 0.4% Tb in Comparative Examples 1-3, achieving the goal of replacing some Tb with Dy while still achieving the original magnetic performance level.

[0038] Example 2: A method for preparing an RTB rare earth permanent magnet comprises the following steps: taking a 52M brand RTB rare earth permanent magnet with magnetic properties of Br=14.51 kGs, Hcj=14.35 kOe, and Hk / Hcj=97.7% as a matrix, and cutting the matrix into magnets with specifications of 20×20×3 mm, with the orientation direction being parallel to the 3 mm thickness direction.

[0039] Hydrogenated Tb powder and hydrogenated Dy powder are coated sequentially on two 20×20 surfaces (two magnet coating surfaces S) perpendicular to the orientation direction to form a magnet coated with hydrogenated Tb powder and hydrogenated Dy powder in sequence, wherein there is a first coating area S1 with hydrogenated Tb powder and a second coating area S2 with hydrogenated Dy powder, and the relationship S1=S, S2=0.5S is satisfied, and S is the surface area of ​​a single magnet coating surface. After single-sided coating, the weight of the hydrogenated Tb powder coated on the first coating area S1 and the hydrogenated Dy powder coated on the second coating area S2 are respectively 0.05% and 0.2% of the weight of the magnet in the coated area (the coating amounts of Tb and Dy account for 0.05% and 0.1% of the weight of the entire magnet); after double-sided coating, the cumulative weight of Tb coated on the first coating area S1 and Dy coated on the second coating area S2 are respectively 0.1% and 0.2% of the weight of the magnet in the coated area (the coating amounts of Tb and Dy account for 0.1% and 0.2% of the weight of the entire magnet). In this embodiment, there is an overlapping area S12 between the first coating coating area S1 and the second coating coating area S2, S12=S2=0.5S, and no coating area S0=0 is covered on the magnet coating surface S. In this embodiment, the detailed coverage diagram of the S, S1, S2, S12, and S0 areas is shown in Figure 2 .

[0040] As Comparative Example 2, the hydrogenated Tb powder and the hydrogenated Dy powder were uniformly mixed in a mass ratio of 1:2, and then printed on the two surfaces of the magnet with a single coating. The printing amount was exactly the same as that in Example 2, and the cumulative printing amount of Tb and Dy was 0.3% (at this time, the Tb and Dy printing amounts accounted for 0.1% and 0.2% of the weight of the entire magnet, respectively).

[0041] The magnets prepared in Example 2 and Comparative Example 2 were placed in a vacuum diffusion furnace for grain boundary diffusion treatment. The diffusion treatment process was as follows: first, degassing at 600°C for 2 hours, then heating to 900°C and holding for 10 hours, followed by aging at 500°C for 6 hours.

[0042] The magnetic properties of the RTB rare earth permanent magnets were tested before and after treatment, and the test results are shown in Table 2.

[0043] Table 2 Comparison of magnetic properties of RTB rare earth permanent magnets before and after treatment in Example 2

[0044] As can be seen from Example 2 and Comparative Example 2 in Table 2, the selectively coated magnet of Example 2 has regions with high and low coercive forces of 20.94 kOe and 18.65 kOe, and the coercive force of the entire magnet is 19.58 kOe, which is between high and low coercive forces and higher than the coercive force of 18.76 kOe of the magnet of Comparative Example 2. The remanence of the magnet of Example 2, 14.39 kGs, is also higher than the remanence of the magnet of Comparative Example 2, 14.34 kGs. This combined selective diffusion method improves the utilization efficiency of Tb and Dy.

[0045] Example 3: A method for preparing an RTB rare earth permanent magnet comprises the following steps: taking a 50H brand RTB rare earth permanent magnet with magnetic properties of Br=14.23 kGs, Hcj=17.16 kOe, and Hk / Hcj=96.5% as a matrix, and cutting the matrix into magnets with specifications of 20×20×1 mm, with the orientation direction being parallel to the thickness direction of 1 mm.

[0046] Tb was printed sequentially on two 20×20 surfaces (two magnet coating surfaces S) perpendicular to the orientation direction. 80 Al 20 (Tb content 80%.wt, Al content 20%.wt), Dy 80 Fe 20 (Dy content 80%.wt, Fe content 20%.wt), formed by Tb 80 Al 20 、Dy 80 Fe 20 The magnets are coated in sequence and formed with Tb 80 Al 20 The first cladding area S1 is composed of Dy 80 Fe 20 The second coating area S2 satisfies the relationship S1=0.25S and S2=0.25S with S, and the overlapping area S12=0 between the first coating area S1 and the second coating area S2 does not cover any coating area S0=0.5S. In this embodiment, the detailed coverage diagram of the S, S1, S2, S12, and S0 areas is shown in Figure 3 After single-sided printing, the first covering area S1 Tb 80 Al 20 The weight of Tb in the second cladding area S2 is proportional to the Dy 80 Fe 20The weight of Dy in the coating area is 0.5% and 1.0% of the weight of the magnet in the coated area respectively (the coating amount accounts for 0.125% and 0.25% of the weight of the entire magnet respectively); after double-sided printing, the cumulative weight of Tb in the first coating area S1 and Dy in the second coating area S2 reaches 1.0% and 2.0% of the weight of the magnet in the printed area respectively (at this time, the cumulative printing amount of Tb and Dy accounts for 0.25% and 0.5% of the weight of the entire magnet respectively).

[0047] As Comparative Example 3, the Tb 80 Al 20 、Dy 80 Fe 20 Mix them evenly in a mass ratio of 1:2, and then apply a single coating to the two surfaces of the magnet. The coating amount is exactly the same as in Example 3. 80 Al 20 、Dy 80 Fe 20 The cumulative coating amount of Tb and Dy is 0.75% of the weight of the magnet (ie, the coating amount of Tb and Dy accounts for 0.25% and 0.5% of the weight of the entire magnet, respectively).

[0048] The magnets prepared in Example 3 and Comparative Example 3 were placed in a vacuum diffusion furnace for grain boundary diffusion treatment. The diffusion treatment process was as follows: first, degassing at 400°C for 2 hours, then heating to 900°C and holding for 10 hours, followed by aging at 460°C for 3 hours.

[0049] The magnetic properties of the RTB rare earth permanent magnets were tested before and after treatment, and the test results are shown in Table 3.

[0050] Table 3 Comparison of magnetic properties of RTB rare earth permanent magnets before and after treatment in Example 3

[0051] As can be seen from Example 3 and Comparative Example 3 in Table 3, the selectively coated magnet of Example 3 has regions with high and low coercive forces of 27.83 kOe and 25.66 kOe, and the coercive force of the entire magnet is 26.23 kOe, which is between high and low coercive forces and higher than the coercive force of 25.94 kOe of the magnet of Comparative Example 3. Furthermore, the remanence of the magnet of Example 3, 14.06 kGs, is also higher than the remanence of the magnet of Comparative Example 3, 13.97 kGs. This combined selective diffusion method improves the utilization efficiency of Tb and Dy.

[0052] Example 4: A method for preparing an RTB rare earth permanent magnet comprises the following steps: taking a 48H brand RTB rare earth permanent magnet with magnetic properties of Br=14.02 kGs, Hcj=17.45 kOe, and Hk / Hcj=97.3% as a matrix, and cutting the matrix into magnets with specifications of 20×20×4.5 mm, with the orientation direction being parallel to the thickness direction of 4.5 mm.

[0053] Print TbF3, Pr on two 20×20 surfaces (two magnet coating surfaces S) perpendicular to the orientation direction 10 Tb 70 Cu 20 (Pr content 10%.wt, Tb content 80%.wt, Al content 20%.wt) coating, in which TbF3 and Pr 10 Tb 70 Cu 20 The mass ratio of Tb is 1:1. Then Dy is printed 80 Al 15 Ga5 (Dy content 80%.wt, Al content 15%.wt, Ga content 5%.wt), formed by TbF3, Pr 10 Tb 70 Cu 20 Coating and Dy 80 Al 15 Ga5 composite coated magnet, and formed with TbF3, Pr 10 Tb 70 Cu 20 The coating is the first coating area S1, with Dy 80 Al 15 Ga5 is the second coating area S2, which satisfies the relationship S1=0.5S, S2=0.5S with S, and the overlapping area S12=0.25S between the first coating area S1 and the second coating area S2, and the area not covered by any coating S0=0.25S. The detailed coverage diagram of S, S1, S2, S12, and S0 areas is shown in Figure 4 After single-sided printing, the TbF3 and Pr 10 Tb 70 Cu 20 The weight of Tb in the second cladding area S2 is proportional to the Dy 80 Al 15 The weight of Dy in Ga5 is 0.2% and 0.4% of the weight of the magnet in the coated area respectively (the coating amount accounts for 0.1% and 0.2% of the weight of the entire magnet respectively); after double-sided printing, the cumulative weight of Tb in the first coated area S1 and Dy in the second coated area S2 reaches 0.4% and 0.8% of the weight of the magnet in the printed area respectively (at this time the cumulative printing amount of Tb and Dy accounts for 0.2% and 0.4% of the weight of the entire magnet respectively).

[0054] As comparative example 4, the TbF3 and Pr 10 Tb 70 Cu 20 Mix Tb at a mass ratio of 1:1, then add Dy 80 Al 15 Ga5, forming TbF3, Pr 10 Tb 70 Cu 20 、Dy 80 Al 15 Ga5 coating, so that the mass ratio of Tb and Dy in the coating is 1:2, after mixing evenly, a single coating is printed on the two surfaces of the magnet. The TbF3, Pr 10 Tb 70 Cu 20 、Dy 80 Al 15 The Ga5 ratio is exactly the same as that of the entire magnet printed in Example 4, and the printed amount of Tb and Dy is controlled to be 0.6% of the weight of the entire magnet (i.e., the printed amount of Tb and Dy accounts for 0.2% and 0.4% of the weight of the entire magnet, respectively).

[0055] The magnets prepared in Example 4 and Comparative Example 4 were placed in a vacuum diffusion furnace for grain boundary diffusion treatment. The diffusion treatment process was as follows: first, degassing at 200°C for 6 hours, then heating to 900°C and maintaining for 24 hours, followed by aging at 500°C for 5 hours.

[0056] The magnetic properties of the RTB rare earth permanent magnets were tested before and after treatment, and the test results are shown in Table 4.

[0057] Table 4 Comparison of magnetic properties of RTB rare earth permanent magnets before and after treatment in Example 4

[0058] As can be seen from Example 4 and Comparative Example 4 in Table 4, the selectively coated magnet of Example 4 has regions with high and low coercive forces of 26.28 kOe, 24.61 kOe, 27.38 kOe, and 23.86 kOe. The coercive force of the entire magnet is 25.53 kOe, which is between high and low coercive forces and higher than the coercive force of 24.47 kOe of the magnet of Comparative Example 4. The remanence of the magnet of Example 4, 13.85 kGs, is also higher than the remanence of the magnet of Comparative Example 4, 13.79 kGs. This combined selective diffusion method improves the utilization efficiency of Tb and Dy.

[0059] Example 5: A method for preparing an RTB rare earth permanent magnet comprises the following steps: taking a 45H brand RTB rare earth permanent magnet with magnetic properties of Br=13.54 kGs, Hcj=17.53 kOe, and Hk / Hcj=98.5% as a matrix, and cutting the matrix into magnets with specifications of 20×20×3.5 mm, with the orientation direction being parallel to the thickness direction of 3.5 mm.

[0060] Print Tb on two 20×20 surfaces (two magnet coating surfaces S) perpendicular to the orientation direction 85 Cu 10 Ti5 (Tb content 85%.wt, Cu content 10%.wt, Ti content 5%.wt) coating, and then printed metal Dy powder to form a Tb 85 Cu 10 Ti5 and metal Dy powder composite coated magnet, and formed with Tb 85 Cu 10 Ti5 is the first coating area S1, and metal Dy powder is the second coating area S2. It satisfies the relationship S1=0.72S, S2=0.21S with S, and the overlapping area S12=0.09S of the first coating area S1 and the second coating area S2, and the area not covered by any coating S0=0.16S. In this embodiment, the detailed coverage diagram of S, S1, S2, S12, and S0 areas is shown in Figure 5 After single-sided printing, the first covering area S1 Tb 85 Cu 10 The weight of Tb in Ti5 and the weight of Dy in the metal Dy powder in the second coating area S2 are 0.125% and 0.5% of the weight of the magnet in the coated area respectively (the coating amount accounts for 0.09% and 0.105% of the weight of the entire magnet respectively); after double-sided printing, the cumulative weight of Tb in the first coating area S1 and Dy in the second coating area S2 reaches 0.25% and 1.0% of the weight of the magnet in the printed area respectively (at this time the cumulative printing amount of Tb and Dy accounts for 0.18% and 0.21% of the weight of the entire magnet respectively).

[0061] As Comparative Example 5, the Tb 85 Cu 10 Ti5 is mixed with metal Dy powder to form Tb 85 Cu 10 The coating of Ti5 and metal Dy powder makes the mass ratio of Tb to Dy in the coating be 6:7. After mixing evenly, it is printed on the two surfaces of the magnet. The Tb printed on the entire magnet is 85 Cu 10The amount of Ti5 and metal Dy powder is the same as the printed amount of the entire magnet in Example 5, that is, the printed amount of Tb and Dy is controlled to be 0.39% of the weight of the entire magnet (after single-sided printing, the printed amount of Tb and Dy accounts for 0.09% and 0.105% of the weight of the entire magnet respectively; after double-sided printing, the printed amount of Tb and Dy accounts for 0.18% and 0.21% of the weight of the entire magnet respectively, and the cumulative amount is 0.39%).

[0062] The magnets prepared in Example 5 and Comparative Example 5 were placed in a vacuum diffusion furnace for grain boundary diffusion treatment. The diffusion treatment process was as follows: first, degassing at 300°C for 3 hours, then heating to 900°C and holding for 12 hours, followed by aging at 500°C for 4 hours.

[0063] The magnetic properties of the RTB rare earth permanent magnets were tested before and after treatment, and the test results are shown in Table 5.

[0064] Table 5 Comparison of magnetic properties of RTB rare earth permanent magnets before and after treatment in Example 5

[0065] As can be seen from Example 5 and Comparative Example 5 in Table 5, the selectively coated magnet of Example 5 has regions with high and low coercive forces of 24.69 kOe, 24.13 kOe, 26.87 kOe, and 23.05 kOe. The coercive force of the entire magnet is 24.55 kOe, which is between high and low coercive forces and higher than the coercive force of 23.24 kOe of the magnet of Comparative Example 5. The remanence of the magnet of Example 5, 13.45 kGs, is also higher than the remanence of the magnet of Comparative Example 5, 13.41 kGs. This combined selective diffusion method improves the utilization efficiency of Tb and Dy.

[0066] The present invention utilizes a method of combining heavy rare earth coatings in selected areas for grain boundary diffusion. This allows the coating layer to diffuse and penetrate the coated area of ​​the magnet while reducing over-penetration into the coated area. It also allows for diffusion and penetration into the uncoated area (if any). In particular, the applied Dy mixture coating achieves good penetration into the uncoated area and minimizes the decrease in the magnet's remanent magnetization. While maintaining a certain amount of heavy rare earth coating on the magnet, the selective coating method reduces the coated area of ​​the heavy rare earth and increases the accumulation of heavy rare earth per unit area in the coated area of ​​the magnet. This improves the concentration gradient of the heavy rare earth diffusion, facilitates the continuous diffusion of the heavy rare earth into the magnet, and further increases the coercive force of the magnet. Furthermore, it avoids the dispersed distribution of the heavy rare earth and the thin coating layer caused by uniform heavy rare earth coating, which can make the coated heavy rare earth more susceptible to oxidation and significantly reduce the diffusion effect. The present invention performs combined coating and diffusion of heavy rare earth on selected areas of the magnet, thereby reducing the diffusion of heavy rare earth in the main phase of the grain, reducing the amount of heavy rare earth used, and further enhancing the coercive force of the selected area. The preparation method is simple and can be mass-produced.

[0067] The best embodiment of the present invention has been described, and various changes or modifications can be made by those skilled in the art without departing from the scope of the present invention.

Claims

1. A method for preparing an RTB rare earth permanent magnet, characterized by: The following steps are involved: Step 1, coating: coating the permanent magnet substrate surface S1 area with a first coating to obtain a first coating area S1, wherein the first coating is composed of one or more components of pure metal, hydride, fluoride, and oxide containing Dy and / or Tb; coating the permanent magnet substrate surface S2 area with a second coating to obtain a second coating area S2, wherein the second coating is composed of one or more components of pure metal, hydride, fluoride, and oxide containing Dy and / or Tb, and contains at least one of pure metal and hydride of Dy; the first coating area S1≤S, the second coating area S2≤S, and S is the magnet surface area where the coating surface is located; Step 2: The magnet obtained in step 1 is subjected to grain boundary diffusion treatment, and then cooled and subjected to aging treatment to obtain an RTB rare earth permanent magnet.

2. The method for preparing an RTB rare earth permanent magnet according to claim 1, wherein: In the step 1, the first coating area S1 and the second coating area S2 have an overlapping area S12, and there is an area S0 on S that is not covered by any coating, and 0≤S12≤S, 0≤S0≤0.5S.

3. The method for preparing an RTB rare earth permanent magnet according to claim 1, wherein: The coating region is located on the surface perpendicular to the orientation direction of the RTB rare earth permanent magnet.

4. The method for preparing an RTB rare earth permanent magnet according to claim 3, wherein: Two surfaces perpendicular to the orientation direction of the RTB rare earth permanent magnet are coated with the coating.

5. The method for preparing an RTB rare earth permanent magnet according to claim 1, wherein: The first coating and the second coating also include an organic solution required for coating.

6. The method for preparing an RTB rare earth permanent magnet according to claim 1, wherein: The hydride containing Dy and / or Tb has a composition of R 1-a-b T a X b , wherein R is one or more of the heavy rare earth elements Dy, Tb, and Ho; T is one or more of La, Ce, Pr, Nd, Gd, Al, Cu, Ga, Co, Fe, Nb, Ti, and Zr; X is one or more of H, O, N, C, and B; a and b are weight percentages, 0wt.%≤a<20wt.%, 0wt.%≤b<5wt.%.

7. The method for preparing an RTB rare earth permanent magnet according to claim 1, wherein: The coating mass of the heavy rare earth element in the first coating is 0.05-0.5% of the mass of the magnet in the area where it is located, and the coating mass of the heavy rare earth element in the second coating is 0.2-1.0% of the mass of the magnet in the area where it is located.

8. The method for preparing an RTB rare earth permanent magnet according to claim 1, wherein: In the step 1, the coating method of the first coating and the second coating is PVD vapor deposition, spraying or screen printing.

9. The method for preparing an RTB rare earth permanent magnet according to claim 1, wherein: In the step 2, the grain boundary diffusion treatment is as follows: the diffusion temperature of the grain boundary diffusion treatment is 800-950°C, the diffusion time is 8-48h, the diffusion heating process includes a heat preservation process at 200-600°C, and the heat preservation time is controlled to be 2-6h. After the diffusion is completed, the magnet is rapidly cooled, and the cooling temperature is 60-90°C.

10. The method for preparing an RTB rare earth permanent magnet according to claim 1, wherein: In the step 2, the aging treatment process is as follows: the aging treatment temperature is 400-700°C, the aging treatment time is 2-10h, and after the aging is completed, the magnet is rapidly cooled at a cooling temperature of 60-90°C.

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