A RTB-Si-MA rare earth permanent magnet

Abstract

The present invention provides an R-T-B-Si-M-A series rare earth permanent magnet, which mainly comprises the following components in the following mass ratio: R 29.0%-32.8%, B 0.9%-0.98%, Si 0.01%-0.1%, M 0.05%-2%, and A 0.2%-1%. The present invention adds a specified amount of Si and appropriate amounts of Cu and Ga to the R-T-B series rare earth permanent magnet, thereby increasing the remanence and coercive force, and significantly improving the consistency of the remanence and coercive force of the magnet during mass production.

Description

Technical Field

[0001] The invention relates to an RTB-Si-MA series rare earth permanent magnet, belonging to the field of rare earth magnets. Background Art

[0002] In recent years, rare earth permanent magnets containing an R2T14B primary phase have been widely used in servo motors, wind turbines, energy-saving air-conditioning compressors, and new energy vehicles due to their high remanence and magnetic energy product. In pursuit of low-cost, high remanence, and high coercivity, researchers and manufacturers have gradually discovered that, in addition to utilizing heavy rare earth elements, improving the purity of the primary phase, reducing the content of impurities to increase remanence, and reducing the ferromagnetism of the grain boundary phase to increase coercivity are the main approaches to producing high-performance rare earth permanent magnets.

[0003] Adding a small amount of Cu or Ga improves the wettability of the grain boundaries, thereby increasing the coercivity (as in References 1 and 2), but the remanence will be significantly reduced. Since the rare earth grain boundary phase rich in Cu and Ga has a low melting point and is easily oxidized, the effective content will be reduced throughout the preparation process. At the same time, Cu and Ga cause the enrichment phase transformation of the grain boundary phase to occur too quickly, increasing the difficulty of control and hindering the improvement of product performance consistency during mass production. Special hydrogen cracking processes or more stringent sintering and aging conditions are often required.

[0004] In addition, since C lowers the melting point of the rare earth-rich phase and increases the solubility of Fe, it not only easily causes abnormal grain growth and poor squareness during sintering, but also enhances the ferromagnetism of the rare earth-rich grain boundary phase, leading to deterioration of coercivity. Therefore, controlling the carbon content is also a key method for the production of high-performance rare earth permanent magnets. Summary of the Invention

[0005] The object of the present invention is to overcome the deficiencies of the prior art and to provide an RTB-Si-MA rare earth permanent magnet containing a trace amount of Si.

[0006] The technical solution adopted in the present invention is:

[0007] An RTB-Si-MA rare earth permanent magnet mainly includes components with the following mass ratios:

[0008]

[0009] The remainder is T and unavoidable impurities;

[0010] R is selected from at least one element of the following: Nd, Pr, Dy, Tb, Ho, La, Ce, Pm, Sm, Eu, Gd, Er, Tm, Yb, Lu or Y;

[0011] The M is selected from at least one of the following elements: Al, Sn, Ge, Ag, Au, Bi, Mn, Nb, Ti, Hf, Zr or Cr;

[0012] The T is selected from at least one element of Fe and Co;

[0013] The A is at least one element selected from Ga and Cu.

[0014] Si has a good binding force with impurity elements such as O, S, and P, which can reduce the content of impurity elements in the main phase and increase remanence. At the same time, the compound formed by Si has a high melting point. Si enters the grain boundary phase such as R6T13(Ga,Cu)1, which can slow the phase transformation rate, thereby avoiding the problem of reduced magnet consistency caused by different positions in the sintering or aging furnace not reaching the set temperature at the same time. It improves the adaptability of mass production and has a certain effect of inhibiting grain growth. Combined with the low-carbon control process, it effectively ensures the high coercivity and squareness of the magnet.

[0015] To improve detection accuracy, inductively coupled plasma mass spectrometry (ICP-MS) can be used to detect the Si content in the material, with a detection accuracy of up to 10 ppb. The Si content in Si-rich regions can be measured using WDS in a field emission electron probe microscope (EPMA) or scanning electron microscope (EDS), with a detection limit of around 100 ppm.

[0016] Unlike conventional methods that add elements such as Cu and Ga, which reduce remanence Br and magnetic energy product (BH)max, the present invention incorporates a trace amount of Si, i.e., less than 0.1 wt.%. Because Si is a non-magnetic element, its content is relatively low, and its content in the main phase is even lower, minimizing its magnetic dilution effect. Furthermore, Si can react with impurities such as P and S to form high-melting-point rare earth compounds, which are dispersed in the grain boundary phase. This not only improves the purity and saturation magnetization of the main phase, but also provides a certain pinning effect, inhibiting grain growth and facilitating the achievement of higher density at higher sintering temperatures. Therefore, the trace addition of Si in the present invention actually increases Br and (BH)max.

[0017] From the existing literature report, Cu, Ga add and improve the wettability of rare earth rich grain boundary phase, but also reduce its melting point, thus the grain boundary phase transformation rate increases.And the temperature history of different regions in sintering or aging furnace is different, near the heating unit (molybdenum belt) region, the temperature rise rate is fast, and the high temperature holding time is longer than the region of batch magnet core, and the region where phase change is too early is also prone to grain boundary phase growth and thus uneven distribution, so that the consistency of magnet magnetic properties decreases, and difficulty increases on engineering production. Si element and rare earth, Fe, Cu, Ga often form compounds with higher melting points, which delay grain boundary phase transformation. Before the regional grain boundary phase near the heating unit grows up, enough phase transformations also occur in the grain boundary phase of the core, and the consistency of grain boundary phase structure and magnetic properties of different regions in the furnace is improved. In the present invention, by setting a certain amount of Cu and Ga, the wettability of rare earth rich grain boundary phase is improved, and when Si is avoided to form compounds with impurity elements such as P, S, and O, it is separated out at the grain boundary and directly contacts with the grains to produce too high mismatch energy, thereby reducing coercivity. At the same time, it avoids the problem that excessive Cu and Ga content leads to an increase and growth of grain boundary phases, and even causes excessive rotation of main phase grains during sintering, resulting in insufficient reduction of remanence.

[0018] It should be noted that the Si content of pure iron raw materials, which currently account for more than 50% of rare earth permanent magnet components, is within 30ppm. Rare earth metals such as PrNd, which contain around 30% by weight, also have a Si content within 150ppm. Other metals such as Co and Cu all have Si contents below 10ppm. Therefore, rare earth magnets with Si contents of less than 0.01wt% can be easily produced.

[0019] In the present invention, Si is added as a single element raw material. Alternatively, FeSi alloys or other alloys and compounds can be added, or raw materials containing a certain amount of Si impurities can be added as a single element. In short, as long as the final magnet contains the necessary amount of Si, it is sufficient.

[0020] Preferably, the main phase of the RTB-Si-MA rare earth permanent magnet is an R2T14B compound, and the grain boundary phase between the main phases contains a Si-rich region with a Si content of 0.02 wt.% to 2.0 wt.%.

[0021] Preferably, the Si-rich region contains at least one of Ga and Cu elements, and the total mass fraction of the Ga and Cu elements is 0.05 wt.% to 10 wt.%.

[0022] Preferably, the Si-rich region contains at least one of P and S elements, and the total mass fraction of the P and S elements is 5 wt.% to 20 wt.%.

[0023] The carbon content of the RTB-Si-MA rare earth permanent magnet is controlled to be between 0.02% and 0.15% by weight. The present invention requires controlling the carbon content of the magnet to be between 0.02% and 0.15% by weight to achieve the desired effect. Generally speaking, carbon, particularly Br, is derived from antioxidants and lubricants added during the preparation process to prevent powder oxidation, improve powder fluidity, and ensure stable magnetic properties. The carbon content of the magnet can be easily reduced by controlling the amount of additives used and the exhaust time before vacuum sintering.

[0024] Preferably, R is selected from at least one of the following elements: Nd, Pr, Dy, and Tb.

[0025] Preferably, the M is selected from at least one of the following elements: Al, Ti, and Zr.

[0026] It should be noted that magnets prepared with very low impurity content in raw materials and strict process control have low impurities such as P, S, and O. With limited microscopic detection capabilities, it is not necessarily possible to detect Si-rich regions containing impurity elements such as P, S, and O 100% of the time. At the same time, in magnets with less Si content, the detection probability of Si-rich regions themselves will also decrease, but the presence of Si elements improves the magnet's local resistance to contamination or interference from impurities such as P, S, and O. The effect of trace Si element addition can be judged by improving the consistency of magnetic properties.

[0027] The beneficial effects of the present invention are mainly reflected in: the present invention improves the remanence and coercivity of the magnet by adding a specified amount of Si and an appropriate amount of Cu and Ga to the RTB-based rare earth permanent magnet, and significantly improves the consistency of the remanence and coercivity of the magnet during mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the method for testing the consistency of magnetic properties; samples are taken at different positions in the sintering furnace, and the average value and standard deviation are calculated after the performance is measured.

[0029] Figure 2 The cross-sectional microstructure of the magnet and the composition of the grain boundary phase were observed using SEM (JEOL Ltd.) and EDS.

[0030] Figure 3 The microstructure of experimental samples 4 and 5;

[0031] Figure 4 is the microstructure of experimental sample 21;

[0032] Figure 5 The microstructure of experimental sample 23;

[0033] Figure 6ICP-MS test results for experimental sample 28;

[0034] Figure 7 This is the microstructure of experimental sample 32. DETAILED DESCRIPTION

[0035] The present invention is further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto:

[0036] The raw alloy (spin-off sheet) is cast using the strip-off method. Various raw materials and master alloys are placed in a medium-frequency induction melting furnace in a certain order and vacuum-heated to melt. After refining for several minutes, the melt temperature is controlled within a set range using power regulation. The crucible is tilted at a certain rate to pour the melt into a tundish and continuously conveyed to a water-cooled copper roller for rapid solidification and cooling. By adjusting the cooling water temperature and flow rate as well as the surface roughness of the copper roller, a rapidly solidified sheet (spin-off sheet) with a thickness of approximately 0.3 mm and a microstructure dominated by columnar crystals is obtained.

[0037] The spun-off flakes are preferably crushed by hydrogen crushing and air flow grinding to achieve the desired particle size.

[0038] The hydrogen crushing is to utilize the hydrogen absorption and expansion of the strip sheet to produce cracks and then cause intergranular and transgranular fractures. Since the hydrogen absorption rate and hydrogen absorption amount of the main phase and the rare earth-rich grain boundary phase are different, the proportion of fracture along the grain boundary phase is greatly increased, which is conducive to obtaining single crystal powder. Hydrogen crushing is to expose the strip sheet to a reactor with a certain pressure of hydrogen, and the general hydrogen pressure is 0.01~0.09Mpa. Since hydrogen absorption is an exothermic reaction, the reactor must be cooled during the hydrogen absorption process, and cooling water spraying is preferably used. After the hydrogen absorption is completed, the excess hydrogen and the hydrogen adsorbed in the alloy are removed by increasing the temperature in the reactor and the vacuum pump group to improve the stability of the powder.

[0039] Jet milling uses high-speed airflow to drive coarse powders into collisions with a target or with each other, achieving further crushing. Gases can include nitrogen, argon, helium, and mixtures containing small amounts of hydrogen or oxygen. The classifying wheel and cyclone classifier in the jet mill control the final powder particle size, preferably achieving a D50 < 5.4 μm as measured by an airflow-dispersed laser particle size analyzer.

[0040] The fine powder is mixed with a certain amount of lubricant and antioxidant and then subjected to magnetic field orientation molding in an orientation press. In order to reduce the amount of additives used and thus the introduction of carbon impurities, one embodiment of the present invention is to use fine powder with a D50 greater than 4.5 microns to ensure powder fluidity and reduce powder activity. At the same time, under the same orientation field, the powder can obtain the greatest possible rotational driving force to achieve a high degree of orientation. When using additives such as lubricants and antioxidants, additives with high volatility and low degreasing temperature are selected from known lubricants to achieve maximum removal of carbon atoms before sintering and high-temperature insulation.

[0041] There is no particular restriction on the pressure and the pressing process during molding. The preferred density of the green compact is 3.6 to 4.5 g / cm 3 Optionally, the molded green compact is further subjected to cold isostatic pressing to eliminate cracks inside the green compact.

[0042] Sintering is generally carried out in a vacuum environment, preferably 10^-3 to -4Pa. Due to the discharge of additives and impurity gases in the low-temperature section of the heating process, the instantaneous pressure may reach 10^-1Pa. In addition, in order to reduce the volatilization of rare earth on the surface of the compact during the high-temperature insulation section of sintering, a small amount of inert gas such as Ar gas can also be introduced at the back end of sintering. The general target sintering temperature is 950-1150℃, and the temperature is kept for 3-24h. In order to achieve low-temperature discharge of gas impurities and improve the temperature uniformity in the sintering furnace, the heating process is carried out in steps and kept at multiple temperatures for a period of time.

[0043] Sintered magnets generally undergo at least one heat treatment at a temperature 100°C below the sintering temperature. Preferably, the magnets are kept at 900°C for 3 hours, cooled to room temperature, and then kept at 500°C for 4 hours to further increase their coercivity. To improve product processing performance, the cooling rate can be slowed after heat treatment to reduce internal stress.

[0044] Samples were taken from the magnet using wire-cut electric discharge, double-end grinding, and centerless grinding. The sample size was a Φ10*10mm cylinder. The machining rate was moderately reduced to ensure the verticality, concentricity, and dimensional accuracy of the product.

[0045] The mean and standard deviation of Br and Hcj mentioned in each embodiment are based on Figure 1 Nine samples were taken from the front, middle and back of the sintering furnace respectively. The demagnetization curves of Φ10*10mm magnets at 20℃ were measured using NIM16000 to obtain 27 Br and Hcj values. The average and arithmetic standard deviation were then calculated.

[0046] ICP-OES and ICP-MS were used to measure the mass fraction of Si above and below 0.1 wt.%.

[0047] Example 1:

[0048] The main materials are PrNd metal with a purity of more than 99.5wt%, Dy and Tb with a purity of more than 99.9wt%, electrolytic copper, electrical pure iron, and low-carbon boron. Other trace elements are added in the form of pure metals and Fe alloys. The Si content of all raw materials is less than 30PPM. The alloy is produced by smelting and spinning strips to produce a strip sheet with a thickness of 0.3mm.

[0049] The alloy was crushed under a hydrogen pressure of 0.09 MPa and heated to 580°C for dehydrogenation. After cooling, 0.08 wt% zinc stearate was added to the crude alloy powder and mixed for 3 hours. The crude alloy powder was further crushed using a nitrogen jet mill to obtain a fine powder with a D50 of 4.6-4.8 microns.

[0050] 0.03wt% of an organic lubricant (Magnetic Powder Protection Lubricant 3#, produced by Tianjin Yuesheng New Materials Research Institute) is added to the fine powder and compacted in a magnetic field. The orientation field is a static magnetic field of 1.9T, and the compacted density is 3.9-4.1g / cm3. From hydrogen decomposition to entering the sintering furnace, all storage and transportation are carried out in an argon atmosphere, ensuring that even with a small amount of additives, the oxygen content of the magnet is kept low.

[0051] The compact was sintered in a vacuum environment at 1050-1080℃ for 4.5h. The sintering temperature was slightly adjusted according to the composition to obtain a density of >7.5g / cm 3 The minimum requirement is that the grain size of the main phase cannot be greater than 15 microns. The sintering temperature is controlled by vacuum degree. When the vacuum degree is greater than 7*10^-3Pa, the heat preservation is started to ensure that the additives are completely removed at the lowest possible temperature. After the vacuum degree is restored, the temperature is continued to rise to the target sintering temperature. After the sintering is completed, the furnace is first cooled to 870℃, and then argon is injected to cool to 700℃. Then, the internal fan is turned on to force cooling to room temperature. The magnet is kept at 900℃ for 3h and cooled to room temperature. It is then kept at 500℃ for 4h and cooled to complete the heat treatment and cooled with argon.

[0052] The content of each element was tested by ICP, while the C content was tested by carbon-sulfur analyzer and expressed as mass percentage, as shown in the following table:

[0053] No. Nd Pr Dy Tb Fe Al Co Cu Ga Si B Ti C 1 23.25 7.75 0 0 bal 0 0.5 0.12 0.15 0.0003 0.95 0 0.03 2 23.25 7.75 0 0 bal 0 0.5 0.12 0.15 0.005 0.95 0 0.04 3 23.25 7.75 0 0 bal 0 0.5 0.12 0.15 0.01 0.95 0 0.03 4 23.25 7.75 0 0 bal 0 0.5 0.12 0.15 0.05 0.95 0 0.04 5 23.25 7.75 0 0 bal 0 0.5 0.12 0.15 0.1 0.95 0 0.04 6 23.25 7.75 0 0 bal 0 0.5 0.12 0.15 0.11 0.95 0 0.03 7 23.25 7.75 0 0 bal 0 0.5 0.12 0.15 0.2 0.95 0 0.03 8 24 8 0 0 bal 0 0.5 0.12 0.15 0.05 0.95 0 0.03 9 22.5 7.5 1 0 bal 0 0.5 0.12 0.15 0.05 0.95 0 0.04 10 22.875 7.625 0 0.5 bal 0 0.5 0.12 0.15 0.05 0.95 0 0.03 11 23.25 7.75 0 0 bal 0.2 0.5 0.12 0.15 0.05 0.95 0 0.03 12 23.25 7.75 0 0 bal 0.2 0 0.12 0.15 0.05 0.95 0 0.04 13 23.25 7.75 0 0 bal 0.2 0 0.25 0.3 0.05 0.95 0 0.03 14 23.25 7.75 0 0 bal 0.2 0 0.25 0.3 0.05 0.95 0.2 0.03

[0054] In addition, the oxygen content tested by the oxygen analyzer is between 400 and 600 ppm, and sometimes a certain amount of impurity elements such as La, Ce, and Cr will be detected. Since they have a high solid solubility in the raw materials, it is difficult to ensure that they are completely zero.

[0055] Samples were taken from the magnet using wire EDM, double-end grinding, and centerless grinding. The sample size was Φ10*10mm cylindrical. The demagnetization curve of the sample was measured using NIM16000 and the Br, Hcj, and SQ values ​​were obtained. The performance is shown in the following table:

[0056]

[0057] The impact of typical Si content on performance and consistency is shown in the following table: Figure 2 shown.

[0058] The cross-sectional microstructure of the magnet and the composition of the grain boundary phase were observed using SEM (JEOL) and EDS. The special microstructures of Experiments 4 and 5 are shown in Figure 3 , the grain boundary phase composition is shown in the following table:

[0059]

[0060] It can be seen that the grain boundary phase between the main phases contains a Si-rich region with a Si content of 0.35 wt.% to 1.99 wt.%.

[0061] Combining the energy spectrum of the Si-rich grain boundary phase and the magnetic properties of samples No. 1 to 5, it is clear that Si can absorb the P and S impurities in the main phase, increasing the remanence of the magnet. Furthermore, the high-melting-point rare earth compounds formed by Si and impurities such as P and S, when dispersed in the grain boundary phase, can inhibit grain growth and thus increase the coercive force of the magnet.

[0062] Conclusion: With the addition of an appropriate amount of Si (above 0.01wt.% and below 0.10wt.%), the Br and Hcj of the magnets increase slightly, and the SQ increases significantly. At the same time, the consistency of the magnetic properties of magnets at different positions in the same batch of sintering furnaces is significantly improved. When the Si content exceeds a certain amount, the magnetic properties of the magnets will deteriorate significantly. At the same time, a small amount of Si addition does not affect the effect of adding other elements. For example, adding a certain amount of Dy and Tb will increase the coercive force and reduce the remanence accordingly, but the squareness and consistency of the magnetic properties remain at a high level when the Si addition amount is 0.05wt.%.

[0063] Example 2:

[0064] The main materials are PrNd metal with a purity of 99.5wt% or more, electrolytic copper with a purity of 99.9wt% or more, electrical pure iron, and low-carbon boron. Other trace elements are added in the form of pure metals and Fe alloys. The Si content of all raw materials is less than 30PPM. The alloy is produced by smelting and spinning strips to produce a strip sheet with a thickness of 0.3mm.

[0065] The alloy was crushed under a hydrogen pressure of 0.09 MPa and heated to 580°C for dehydrogenation. After cooling, 0.08 wt% zinc stearate was added to the crude alloy powder and mixed for 3 hours. The crude alloy powder was further crushed using a nitrogen jet mill to obtain a fine powder with a D50 of 4.6-4.8 microns.

[0066] Add 0.03wt% of organic lubricant to the fine powder and press it into shape in a magnetic field. The orientation magnetic field is a static magnetic field of 1.9T and the pressing density is 3.9-4.1g / cm 3 From hydrogen decomposition to entering the sintering furnace, all storage and transportation atmospheres are argon atmosphere, so that even a small amount of additives can control the oxygen content of the magnet to a low level.

[0067] The compact was sintered in a vacuum environment at 1030-1050℃ for 4.5h. The sintering temperature was slightly adjusted according to the composition to obtain a density of >7.5g / cm 3 The minimum requirement is that the grain size of the main phase cannot be greater than 15 microns. The sintering temperature is controlled by vacuum degree. When the vacuum degree is greater than 7*10^-3Pa, the heat preservation is started to ensure that the additives are completely removed at the lowest possible temperature. After the vacuum degree is restored, the temperature is continued to rise to the target sintering temperature. After the sintering is completed, the furnace is first cooled to 870℃, and then argon is injected to cool to 700℃. Then, the internal fan is turned on to force cooling to room temperature. The magnet is kept at 900℃ for 3h and cooled to room temperature. It is then kept at 500℃ for 4h and cooled to complete the heat treatment and cooled with argon.

[0068] The content of each element was tested by ICP, while the C content was tested by carbon-sulfur analyzer and expressed as mass percentage, as shown in the following table:

[0069] No. Nd Pr Dy Tb Fe Al Co Cu Ga Si B Ti C 15 24 8 0 0 bal 0 0.5 0 0.15 0.1 0.98 0.15 0.03 16 24 8 0 0 bal 0 0.5 0 0.2 0.1 0.98 0.15 0.04 17 24 8 0 0 bal 0 0.5 0 1 0.1 0.98 0.15 0.03 18 24 8 0 0 bal 0 0.5 0.1 0 0.1 0.98 0.15 0.04 19 24 8 0 0 bal 0 0.5 0.2 0 0.1 0.98 0.15 0.03 20 24 8 0 0 bal 0 0.5 1 0 0.1 0.98 0.15 0.04 21 24 8 0 0 bal 0 0.5 0.1 0.12 0.1 0.98 0.15 0.03 22 24 8 0 0 bal 0 0.5 0.2 0.3 0.1 0.98 0.15 0.03 23 24 8 0 0 bal 0 0.5 0.4 0.5 0.1 0.98 0.15 0.04 24 24 8 0 0 bal 0 0.5 0.6 0.5 0.1 0.98 0.15 0.03 25 24 8 0 0 bal 0 0.5 0.5 0.6 0.1 0.98 0.15 0.04 26 24 8 0 0 bal 0 0.5 0.8 0.2 0.1 0.98 0.15 0.04 27 24 8 0 0 bal 0 0.5 0.7 0.5 0.11 0.98 0.15 0.04

[0070] Samples were taken from the magnets using wire-cut electrospark cutting, double-end grinding, and centerless grinding. The sample size was Φ10*10mm cylinders. The demagnetization curves of the samples were measured using a NIM16000 and the Br, Hcj, and SQ values ​​were obtained.

[0071]

[0072]

[0073] The cross-sectional microstructure of the magnet and the composition of the grain boundary phase were observed using SEM (JEOL) and EDS. Figure 4 , the grain boundary phase composition is shown in the following table:

[0074]

[0075] It can be seen that the grain boundary phase between the main phases contains a Si-rich region with a Si content of 0.58 wt.% to 0.9 wt.%.

[0076] The special microstructure of Experiment 23 can be found in Figure 5 , the grain boundary phase composition is shown in the following table:

[0077]

[0078] It can be seen that the grain boundary phase between the main phases contains a Si-rich region with a Si content of 0.47 wt.% to 1.2 wt.%.

[0079] Cu and Ga improve the wettability of the grain boundary phase and the main phase, making the grain boundary phase more uniform. They also encapsulate the Si compounds at the grain boundaries, preventing direct contact with the main phase, thereby increasing the coercivity of the magnet. The magnetic properties of samples No. 15 to 23 show that adding appropriate amounts of Cu and Ga to form Si compounds can simultaneously increase the remanence and coercivity of the magnet.

[0080] Conclusion: Despite the addition of 0.05wt.% Si, performance consistency and squareness optimization were not achieved when the combined Ga and Cu content was less than 0.2wt.%. When the combined Ga and Cu content exceeded 1wt.%, remanence and coercivity decreased significantly, and performance volatility increased. SEM analysis revealed that excessive Ga and Cu can lead to large Ga- and Cu-rich phases, increasing local stray fields and demagnetization fields, leading to performance degradation.

[0081] Example 3:

[0082] The alloy is primarily composed of PrNd metal with a purity of at least 99.5wt%, Tb with a purity of at least 99.9wt%, electrolytic copper, electrical-grade iron, and low-carbon boron. Other trace elements are added in the form of pure metals and Fe alloys. In Experiments 28-31, graphite was used as the carbon raw material. The Si content of all raw materials was kept below 30 ppm. The alloy was produced by smelting and spinning strips to form strip sheets with a thickness of 0.3 mm.

[0083] The alloy was crushed under a hydrogen pressure of 0.09 MPa and heated to 580°C for dehydrogenation. After cooling, 0.08 wt% zinc stearate was added to the crude alloy powder and mixed for 3 hours. The crude alloy powder was further crushed using a nitrogen jet mill to obtain a fine powder with a D50 of 4.6-4.8 microns.

[0084] 0.03 wt% of organic lubricant was added to the fine powder. The addition amount of organic lubricant in experiments 32 and 33 was 0.08 wt% and 0.2 wt% respectively to change the final carbon content of the magnet. The magnet was pressed in a magnetic field. The orientation magnetic field was a static magnetic field of 1.9 T, and the pressing density was 3.9-4.1 g / cm 3From hydrogen decomposition to entering the sintering furnace, all storage and transportation atmospheres are argon atmosphere, so that even a small amount of additives can control the oxygen content of the magnet to a low level.

[0085] The compact was sintered in a vacuum environment at 1030-1050℃ for 4.5h. The sintering temperature was slightly adjusted according to the composition to obtain a density of >7.5g / cm 3 The minimum requirement is that the grain size of the main phase cannot be greater than 15 microns. The sintering temperature is controlled by vacuum degree. When the vacuum degree is greater than 7*10^-3Pa, the heat preservation is started to ensure that the additives are completely removed at the lowest possible temperature. After the vacuum degree is restored, the temperature is continued to rise to the target sintering temperature. After the sintering is completed, the furnace is first cooled to 870℃, and then argon is injected to cool to 700℃. Then, the internal fan is turned on to force cooling to room temperature. The magnet is kept at 900℃ for 3h and cooled to room temperature. It is then kept at 500℃ for 4h and cooled to complete the heat treatment and cooled with argon.

[0086] The content of each element was tested by ICP, while the C content was tested by carbon-sulfur analyzer and expressed as mass percentage, as shown in the following table:

[0087] No. Nd Pr Dy Tb Fe Al Co Cu Ga Si B Zr C 28 23.1 7.7 0 5.3 bal 0 3 0.15 0.2 0.06 0.97 0.12 0.02 29 23.1 7.7 0 5.3 bal 0 3 0.15 0.2 0.06 0.97 0.12 0.05 30 23.1 7.7 0 5.3 bal 0 3 0.15 0.2 0.06 0.97 0.12 0.15 31 23.1 7.7 0 5.3 bal 0 3 0.15 0.2 0.06 0.97 0.12 0.2 32 23.1 7.7 0 5.3 bal 0 3 0.15 0.2 0.06 0.97 0.12 0.08 33 23.1 7.7 0 5.3 bal 0 3 0.15 0.2 0.06 0.97 0.12 0.18

[0088] The results of ICP-MS test on experimental sample No. 28 are shown in Figure 6 By comparing the ICP and ICP-MS results, it can be seen that the Si content of NO28-33 samples is around 600ppm, and the addition of lubricant does not cause abnormal loss of Si elements during the magnet manufacturing process.

[0089] Samples were taken from the magnet using wire EDM, double-end grinding, and centerless grinding. The sample size was Φ10*10mm cylindrical. The demagnetization curve of the sample was measured using NIM16000 and the Br, Hcj, and SQ were obtained, as shown in the following table:

[0090]

[0091] The cross-sectional microstructure of the magnet and the composition of the grain boundary phase were observed using SEM (JEOL) and EDS. Figure 7 , the grain boundary phase composition is shown in the following table:

[0092]

[0093] It can be seen that the grain boundary phase between the main phases contains a Si-rich region with a Si content of 0.02 wt.% to 0.96 wt.%.

[0094] Carbon reacts with rare earth elements at grain boundaries to form carbides, reducing the rare earth-rich phase content at the grain boundaries and lowering the coercivity of the magnet. Combining the energy spectrum with the magnetic properties of magnets No. 28 to 33, it can be seen that when the carbon content is high, the Si compounds formed at the grain boundaries cannot play a role in increasing the coercivity of the magnet.

[0095] Conclusion: When the carbon content is higher than 0.15wt.%, the coercivity and squareness of the magnet decrease significantly.

Claims

1. An RTB-Si-MA rare earth permanent magnet, mainly comprising the following components in the following mass ratio: R 29.0%~32.8% B 0.9%~0.98% Si 0.01%~0.1% M 0.05%~2% A 0.2%~1% The remainder is T and unavoidable impurities; R is selected from at least one element of the following: Nd, Pr, Dy, Tb, Ho, La, Ce, Pm, Sm, Eu, Gd, Er, Tm, Yb, Lu or Y; The M is selected from at least one of the following elements: Al, Sn, Ge, Ag, Au, Bi, Mn, Nb, Ti, Hf, Zr or Cr; The T is selected from at least one element of Fe and Co; The A is selected from at least one element of Ga and Cu; the main phase of the RTB-Si-MA rare earth permanent magnet is an R2T14B type compound, and the grain boundary phase between the main phases contains a Si-rich region with a Si content of 0.02wt.% to 2.0wt.%; the Si-rich region contains at least one of Ga and Cu elements.

2. The RTB-Si-MA rare earth permanent magnet according to claim 1, characterized in that The total mass fraction of Ga and Cu elements in the Si-rich region is 0.05 wt.% to 10 wt.%.

3. The RTB-Si-MA rare earth permanent magnet according to claim 1, characterized in that The Si-rich region contains at least one of P and S elements, and the total mass fraction of the P and S elements is 5 wt.% to 20 wt.%.

4. The RTB-Si-MA rare earth permanent magnet according to claim 1, characterized in that The C content in the RTB-Si-MA rare earth permanent magnet is controlled to be 0.02 wt.% to 0.15 wt.%.

5. The RTB-Si-MA rare earth permanent magnet according to claim 1, characterized in that The R is selected from at least one of the following elements: Nd, Pr, Dy, and Tb.

6. The RTB-Si-MA rare earth permanent magnet according to claim 1, characterized in that The M is selected from at least one of the following elements: Al, Ti, and Zr.

Images