High-performance low-gallium sintered permanent magnet and preparation method thereof

Abstract

This invention discloses a method for preparing a high-performance low-gallium sintered permanent magnet. The method involves cutting a sintered magnet blank, which has undergone vacuum sintering and vacuum primary aging treatment, into thin magnetic sheets. These sheets are then fed into a continuous tunnel furnace for low-temperature secondary aging treatment to obtain the high-performance low-gallium sintered permanent magnet. The Ga content in the raw materials of the magnet is 0.01 wt.% to 0.1 wt.%. This invention adds a low Ga content to the sintered R-T-B magnet, which can improve the surface defects of the main phase grains, enhance the temperature characteristics of the magnet, and increase the Hcj of the magnet without significantly reducing the Br content. The low Ga content reduces the production cost of Ga-containing magnets. Simultaneously, cutting the magnet after primary aging into thin sheets of a certain thickness accelerates the heating and cooling of the magnet. Furthermore, production using the continuous tunnel furnace described in this invention reduces the secondary aging time of the product, improving production efficiency.

Description

Technical Field

[0001] This invention belongs to the field of sintered permanent magnet manufacturing, and specifically provides a method for manufacturing high-performance low-gallium sintered permanent magnets and a composition design. Background Technology

[0002] Sintered NdFeB materials are widely used in various fields such as information technology, medical equipment, and transportation due to their high remanence, high coercivity, and high energy product. However, with the increasing number of applications, the operating temperature requirements for magnets are also becoming more stringent. Therefore, improving the operating temperature of magnets is one of the important technological developments for sintered magnets. Sintered permanent magnets with high coercivity have a low coercivity temperature coefficient and relatively small irreversible flux loss. Therefore, improving the coercivity of magnets can improve the high-temperature performance of sintered magnets and increase their operating temperature.

[0003] Previous studies have shown that adding Ga can improve the temperature characteristics of sintered magnets. Furthermore, appropriate Ga addition can increase the coercivity (Hcj) of the magnet without significantly reducing its remanence (Br). This is because adding Ga to sintered magnets can generate Nd6Fe. 13 The nonferromagnetic Ga phase uniformly coats the main phase grains, increasing the decoupling effect between the main phase grains. In existing technologies, the Ga addition amount is typically 0.2-2 wt%. Furthermore, due to Nd6Fe... 13 The Ga phase has a high content of rare earth elements, making it susceptible to oxidation; therefore, the Nd6Fe content should be reduced. 13 The proportion of Ga phase in the grain boundary phase. Furthermore, it was found that the aging temperature range for achieving optimal performance in sintered NdFeB magnets with high Ga content is narrower than that for those with low Ga content. For practical production, a wider range is desirable for ease of manufacturing. Moreover, with resource depletion, raw material prices are gradually rising, with Ga alloys reaching over 3000 yuan per kilogram, significantly increasing the production cost of sintered magnets with high Ga content. Considering all these factors, inventing a sintered magnet with low Ga content could not only optimize magnet performance and facilitate production but also save on production costs.

[0004] Furthermore, research indicates that excessive aging temperature or aging duration can lead to Nd6Fe 13 The decreased continuity of the Ga phase distribution leads to a deterioration in magnet performance. Therefore, it is necessary to develop an aging method that can reduce the aging temperature and time of the magnet, and to employ rapid cooling after aging to maintain the consistency of the internal structure of the magnet, resulting in uniform performance. However, rapid cooling from high temperatures can easily cause high stress and severe cracking within the magnet; therefore, it is also necessary to develop a rapid cooling method applicable to low-temperature aging. Summary of the Invention

[0005] To address the problems of poor corrosion resistance, high production cost, and short aging time required for high Ga-RTB sintered magnets, this invention provides a high-performance low-gallium sintered permanent magnet and its preparation method.

[0006] The technical solution adopted in this invention is:

[0007] A method for preparing a high-performance low-gallium sintered permanent magnet, the method comprising: cutting a sintered magnet blank that has undergone vacuum sintering and vacuum first-stage aging treatment into magnet sheets, and then feeding the magnet sheets into a continuous tunnel furnace for low-temperature second-stage aging treatment to prepare the high-performance low-gallium sintered permanent magnet, wherein the Ga content in the raw material of the magnet is 0.01wt.% to 0.1wt.% (preferably 0.05 to 0.08wt%).

[0008] Further, the preferred method is as follows: raw materials of each element are taken according to the composition ratio, wherein the content of Ga is 0.01wt.% to 0.1wt.% (preferably 0.05 to 0.08wt%), alloy rapid solidification sheets are prepared by vacuum induction melting and strip spinning, alloy rapid solidification sheets are hydrogen crushed and air jet milled to obtain alloy powder, alloy powder is pressed into shape by orientation forming and isostatic pressing, the formed magnet is vacuum sintered and high temperature first-stage aging treatment to obtain sintered magnet blank, magnet blank is cut into magnet thin slices, and then magnet thin slices are sent into continuous tunnel furnace for low temperature second-stage aging treatment to prepare the high performance low gallium sintered permanent magnet.

[0009] The temperature of the low-temperature secondary aging treatment is 450-600℃, and the holding time is 20min-2h, preferably 0.5-1.5h.

[0010] During the low-temperature secondary aging process, the continuous tunnel furnace can be used in air, nitrogen, or argon, preferably under nitrogen or argon purging protection.

[0011] Because sintered magnets with low Ga content have good corrosion resistance, they can be tempered in an air environment, preferably under nitrogen and argon blowing. This saves vacuuming time compared to traditional two-stage tempering. At the same time, the thin sheet products are continuously produced under a conveyor belt, which has the characteristics of rapid heating and cooling, resulting in a significant improvement in magnet production efficiency.

[0012] Traditional secondary aging is carried out in a sintering furnace at a temperature of 450-600℃ for 2-8 hours. However, the actual processing time is much longer than the holding time because it requires a longer vacuuming period. Generally, the vacuum is first reduced to 1 Pa, which takes 1-1.5 hours. Then, the material is heated to the aging temperature, which typically takes 1-3 hours. After reaching the aging temperature, it is held for another 2-8 hours, and then nitrogen is introduced for air cooling to 50-60℃, which takes 0.5-2 hours. Therefore, processing a batch of incoming material takes a considerable amount of time.

[0013] This invention employs a continuous tunnel furnace for secondary aging treatment under atmospheric pressure, eliminating the need for vacuuming and heating, enabling continuous feeding and significantly improving work efficiency. Furthermore, the secondary aging treatment time is substantially reduced compared to existing technologies, with holding time within 2 hours. After secondary aging, the magnet can be air-cooled, allowing for rapid cooling and maintaining the consistency of the magnet's internal structure, thus resulting in uniform magnet performance.

[0014] Furthermore, the preferred method for the low-temperature secondary aging process is as follows: the magnet sheet is placed at the inlet of the continuous tunnel furnace and transported to the secondary aging chamber by the conveyor belt. The magnet undergoes low-temperature secondary heat treatment in the secondary aging chamber. After the treatment, the magnet leaves the secondary aging chamber from the outlet by the conveyor belt and is then cooled to a temperature below 60°C.

[0015] Preferably, the continuous tunnel furnace is equipped with high-temperature resistant plastic baffles at both the inlet and outlet to give the continuous tunnel furnace a certain degree of airtightness, which can reduce heat loss, reduce the escape of nitrogen or argon gas, improve gas utilization, and save costs.

[0016] Preferably, the secondary aging chamber adopts a subsidence type cavity, and the bottom surface of the secondary aging chamber is lower than the height of the inlet and outlet. In other words, the height of the conveyor belt within the secondary aging chamber is lower than the height of the conveyor belt at the inlet and outlet. After entering the inlet of the continuous tunnel furnace, the conveyor belt decreases in height and enters the secondary aging chamber. The passage time of the magnetic sheet within the secondary aging chamber, i.e., the holding time of the secondary aging process, is controlled by the length of the secondary aging chamber and the conveyor speed. Then, the conveyor belt rises in height, passes through the outlet, and enters the cooling chamber for cooling.

[0017] The function of the settling chamber is to reduce the escape of nitrogen and argon and improve the utilization rate of nitrogen and argon during the secondary aging treatment under the protection of argon or nitrogen.

[0018] Preferably, the magnet is cooled in a cooling chamber. The cooling method can be natural cooling in the air or accelerated cooling by blowing air. It is preferred to use accelerated cooling by blowing air.

[0019] Furthermore, the high-performance low-gallium sintered permanent magnet preferably comprises the following components by mass fraction:

[0020] Ga: 0.01 wt.% to 0.1 wt.%, preferably 0.05 to 0.08 wt%.

[0021] R: 28wt.% to 32wt.%, where R is selected from one or more of Pr, Nd, Dy, Tb, Gd, and Ho, preferably containing Pr and Nd, and more preferably containing Nd at 65% or more of the R content;

[0022] B: 0.9 wt.% to 1.1 wt.%

[0023] M: M is M1, or a mixture of M1 and M2, wherein M1 is one or two of the elements Al, Cu, Ti, Zr, and Nb, and M2 is at least one of the elements Si, Zn, Sn, Ge, Ag, V, W, and Mo; the content of M1 is 0.5 wt.% to 4.5 wt.%, preferably 1.5 wt.% to 4.5 wt.%, and when M contains M2, the content of M2 is 0.1% to 2.0 wt.%.

[0024] The balance is T and other unavoidable impurities, wherein T is at least one of Fe and Co; preferably Fe or Fe and Co; when T is Fe and Co, the Fe content is preferably more than 90% of the T content;

[0025] Furthermore, the high-performance low-gallium sintered permanent magnet has the following microstructure: within a range of 0-10 μm from the magnet surface, the proportion of rare earth oxide RO phase in the grain boundary R-rich phase is less than 20 vol.%, and the oxygen content is 500 PPM to 900 PPM; below a depth of 15 μm from the magnet surface, the proportion of rare earth oxide RO phase in the grain boundary R-rich phase is less than 0.01 vol.%, and the oxygen content is ≤400 PPM.

[0026] When the rare earth oxide RO phase of the low-Ga content sintered magnet is subjected to low-temperature secondary aging in a tunnel furnace in an air atmosphere, it is produced in small amounts or not at all on the product surface and does not affect the magnet performance. When the magnet is subjected to low-temperature secondary treatment in a nitrogen or argon atmosphere, the proportion of the rare earth oxide RO phase in the grain boundary R-rich phase within a distance of 0-10 μm from the magnet surface is less than 0.01 vol.%, and the oxygen content is ≤600 PPM.

[0027] The high-performance low-gallium sintered permanent magnet prepared by this invention has a Ga content ≤0.1wt.%, and the Ga element is mainly distributed in the grain boundary phase; the M1 magnet is at least one of Al, Cu, Ti, Zr and Nb elements, which can increase the wettability between the magnet grain boundary phase and the main phase grains and optimize the defects of the main phase grains; increasing the M1 element content can improve the grain boundary structure and improve the performance of the low-gallium sintered magnet.

[0028] Furthermore, in the method, the melting temperature in the vacuum induction melting and belt spinning is 1450-1480℃, and the alloy quick-setting sheet is obtained by holding the belt spinning at 1400-1430℃.

[0029] The alloy quick-setting sheet has a thickness of ≤0.5mm, preferably 0.2mm-0.35mm; the alloy powder refined by air jet milling has a surface area density (SMD) of 2.5-4.5μm, preferably 2.5-3.5μm.

[0030] The magnetic field for orientation forming is 1.7-2.0T, which enables the magnetic powder to form the same orientation during the pressing process.

[0031] The vacuum sintering temperature is 1030–1100℃, and the vacuum degree inside the furnace is 10 after reaching the highest sintering temperature. -2 -10 -5 Pa, the holding time is 4-12h; the temperature for high-temperature first-level aging treatment is 750-950℃, and the holding time is 2-10h.

[0032] The thickness of the magnet sheet is generally 1 to 5 mm.

[0033] The beneficial effects of this invention are as follows: adding a low content of Ga to the sintered RTB magnet can improve the surface defects of the main phase grains, enhance the temperature characteristics of the magnet, and increase the Hcj of the magnet without significantly reducing the Br content. Studies have shown that when the Ga content in the magnet is too high, it can cause Nd6Fe in the grain boundary phase. 13 The reduced proportion of Ga transition phase decreases the corrosion resistance of the magnet. Furthermore, with the development and utilization of resources, the price of raw materials continues to rise, and the unit price of Ga alloy has increased to over 3000 yuan per kilogram. Therefore, this invention can reduce the production cost of Ga-containing magnets. Simultaneously, cutting the magnets after primary aging into thin sheets of a certain thickness can accelerate the heating and cooling of the magnets, and with the continuous tunnel furnace production described in this invention, the secondary aging time of the product can be reduced, improving production efficiency. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the continuous tunnel furnace device of the present invention.

[0035] Figure 2 This is a scanning electron microscope image of the magnet in Example 1.

[0036] Figure 3 This is a scanning electron microscope image of the magnet in Comparative Example 1. Detailed Implementation

[0037] The technical solution of the present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the conditions set in the embodiments.

[0038] This invention provides a method for preparing a high-performance, low-ga RTB magnet. A metal alloy with a purity of 99% or higher is prepared according to an elemental formula, wherein…

[0039] Ga: 0.01wt.%≤Ga≤0.1wt.%,

[0040] R: 28wt.% ≤ R ≤ 32wt.%, where R is selected from at least one rare earth element from Pr, Nd, Dy, Tb, Gd, and Ho.

[0041] B: 0.9wt.%≤B≤1.1wt.%,

[0042] M: M is M1, or a mixture of M1 and M2, wherein M1 is one or more of Al, Cu, Ti, Zr, and Nb, and M2 is at least one of Co, Si, Zn, Sn, Ge, Ag, V, W, and Mo; 0.5 wt.% ≤ M1 ≤ 4.5 wt.%, preferably 1.5 wt.% ≤ M1 ≤ 4.5 wt.%, and when M contains M2, 0.1 ≤ M2 ≤ 2.0 wt.%.

[0043] The balance is T and other unavoidable impurities, wherein T is at least one of Fe and Co.

[0044] First, the prepared raw materials are melted in a vacuum spinning furnace at a temperature of 1450-1480℃, and then spun at a temperature of 1400-1430℃ to prepare alloy rapid solidification sheets with a thickness of ≤0.5mm, preferably 0.2-0.35mm. The rapid solidification sheets are then hydrogen-crushed and air-jet milled to produce powder with an SMD of 2.5-4.5μm, preferably 2.5-3.5μm. The powder is then pressed into shape in an orientation field of 1.7-2.0T. The formed blank is then densified by high-temperature sintering at 1030-1100℃ and aged at 750-950℃ to produce a blank magnet.

[0045] To rapidly heat the magnets and reduce aging time, the raw magnet blanks are cut into 1-5mm thick magnet sheets and subjected to low-temperature secondary aging in a continuous tunnel furnace. The secondary aging temperature is 450-600℃, and the holding time is 20min-2h. The oxygen content inside the continuous tunnel can be adjusted by introducing gas, and the speed of the conveyor belt in the continuous tunnel furnace can be changed by adjusting the motor output power, thereby controlling the secondary aging time.

[0046] During the low-temperature secondary aging process, the continuous tunnel furnace can be used in air, nitrogen, or argon, preferably under nitrogen or argon purging protection.

[0047] The low-temperature secondary aging process is as follows: the magnet sheet is placed at the feed port of the continuous tunnel furnace and transported to the secondary aging chamber by the conveyor belt. The magnet undergoes low-temperature secondary heat treatment in the secondary aging chamber. After the treatment, the magnet leaves the secondary aging chamber from the discharge port by the conveyor belt and is then cooled to a temperature below 60°C.

[0048] The continuous tunnel furnace is equipped with high-temperature resistant plastic baffles at both the inlet and outlet, which gives the continuous tunnel furnace a certain degree of sealing, reduces heat loss, and also reduces the escape of nitrogen or argon gas, thereby improving gas utilization and saving costs.

[0049] In this embodiment of the invention, the secondary aging chamber preferably adopts a settling-type cavity, such as... Figure 1 As shown, the bottom surface of the secondary aging chamber should be lower than the height of the inlet and outlet, meaning the height of the conveyor belt inside the secondary aging chamber should be lower than the height of the conveyor belt at the inlet and outlet.

[0050] Figure 1 In the process, the magnetic sheet is placed in a loading tray, placed on a conveyor belt, and enters the continuous tunnel furnace through the inlet. After entering the inlet, the conveyor belt descends, and the sheet enters the secondary aging chamber. The bottom of the secondary aging chamber is lower than the inlet and outlet. The secondary aging chamber is equipped with an auxiliary heating device to preheat the material to the aging temperature. The magnetic sheet undergoes low-temperature secondary aging treatment in the secondary aging chamber, which can be carried out in an air atmosphere or by introducing nitrogen or argon gas through a protective gas inlet located at the bottom of the secondary aging chamber, under nitrogen or argon protection.

[0051] The time the magnetic sheet spends in the secondary aging chamber is controlled by adjusting the conveyor speed, which is also the holding time for the secondary aging process. Then, the conveyor belt rises in height, sending the magnetic sheet out of the discharge port and into the cooling chamber for cooling.

[0052] The function of the settling chamber is to reduce the escape of nitrogen and argon and improve the utilization rate of nitrogen and argon during the secondary aging treatment under the protection of argon or nitrogen.

[0053] The magnet is cooled in a cooling chamber. The cooling method can be natural cooling in the air or accelerated cooling by blowing air, with accelerated cooling by blowing air being preferred. The cooling chamber may be equipped with a cooling fan for blowing air cooling.

[0054] In the embodiments, for comparison purposes, the hydrogen breaking, air jet milling, sintering, and first-stage aging were all performed using the same methods; the continuous tunnel furnace used the same motor output power, and the second-stage aging time was 1.5 hours. The performance of the obtained finished products was analyzed, and the cross-section of the thin-film products was observed using a scanning electron microscope.

[0055] Example 1:

[0056] A sintered RTB magnet is composed of the following components:

[0057] Ga: 0.05wt%

[0058] R: 29.6wt%

[0059] B: 0.95wt%

[0060] M: 2.6wt%

[0061] Fe: 65.05 wt%

[0062] Co: 1.0wt%

[0063] R consists of 22.5 wt% Nd and 7.1 wt% Pr; B represents boron; M consists of M1, which is composed of 1.35 wt% Al, 0.4 wt% Cu, 0.45 wt% Ti, 0.2 wt% Zr and 0.2 wt% Nb; Fe represents iron; and Co represents cobalt.

[0064] Its preparation method includes the following steps:

[0065] The raw materials are smelted according to the component ratio, and the smelting temperature is controlled at 1470℃. After all the raw materials are melted, the solution temperature is reduced to 1400℃ and then poured onto a copper roller at 1400℃. The strip is then spun to obtain 0.2mm-0.35mm fast-setting sheets.

[0066] The obtained quick-setting sheets were crushed by hydrogen absorption and dehydrogenated at 550°C to obtain magnetic powder.

[0067] Antioxidant and lubricant were added to the magnetic powder and mixed evenly, and then air jet milling was performed to obtain fine powder with SMD of 2.5μm-3.5μm;

[0068] Under a nitrogen protective atmosphere, the fine powder was oriented and pressed into shape. The orientation magnetic field was 1.8T, and the isostatic pressing pressure was 180MPa, resulting in a density of 4.2 g / cm³. 3 The green magnet blank.

[0069] The magnet blank was vacuum sintered at 1050℃ for 8 hours, then cooled in the furnace to below 100℃ and then subjected to a first-stage aging treatment. The first-stage aging temperature was 850℃ and the treatment time was 5 hours to obtain the sintered magnet blank.

[0070] The sintered magnet blanks are machined and cut into 25mm*20mm*5mm magnet slices, which are then placed in a continuous tunnel furnace for secondary aging treatment. The secondary aging temperature is 500℃, and the treatment time is 1.5 hours. The treatment time is controlled by adjusting the speed of the conveyor belt in the secondary aging chamber. The secondary aging chamber of the continuous tunnel furnace is a settling chamber, and the magnets are protected by argon gas within the chamber.

[0071] After leaving the secondary aging treatment chamber, the magnet enters the cooling chamber and is cooled to below 70°C using air cooling to obtain the finished magnet.

[0072] The finished magnet obtained in this embodiment was tested using the NIM-62000 rare-earth permanent magnet standard measuring device; the cross-sectional microstructure of the finished magnet was observed using a scanning electron microscope, and the results are as follows. Figure 2 As shown.

[0073] Comparative Example 1

[0074] A sintered RTB magnet is composed of the following components:

[0075] Ga: 1.5wt%

[0076] R: 29.3wt%

[0077] B: 0.98wt%

[0078] M: 1.6wt%

[0079] Fe: 65.82 wt%

[0080] Co: 0.8wt%

[0081] R consists of 22.8 wt% Nd and 6.5 wt% Pr; B represents boron; M consists of M1, which is composed of 1.0 wt% Al, 0.2 wt% Cu, 0.1 wt% Ti, and 0.3 wt% Zr; Fe represents iron; and Co represents cobalt.

[0082] Its preparation method includes the following steps:

[0083] The raw materials are smelted according to the component ratio, and the smelting temperature is controlled at 1475℃. After all the raw materials are melted, the solution temperature is lowered to 1410℃ and kept at 1410℃ before being poured onto a copper roller. The resulting sheet is a quick-setting sheet of 0.2mm-0.35mm.

[0084] The obtained quick-setting sheets were crushed by hydrogen absorption and dehydrogenated at 550°C to obtain magnetic powder.

[0085] Antioxidant and lubricant were added to the magnetic powder and mixed evenly, and then air jet milling was performed to obtain fine powder with SMD of 2.5μm-3.5μm;

[0086] Under a nitrogen protective atmosphere, the fine powder was oriented and pressed into shape. The orientation magnetic field was 1.8T, and the isostatic pressing pressure was 180MPa, resulting in a density of 4.2 g / cm³. 3 The green magnet blank.

[0087] The magnet blank was vacuum sintered at 1050℃ for 8 hours, then cooled in the furnace to below 100℃ and then subjected to a first-stage aging treatment. The first-stage aging temperature was 850℃ and the treatment time was 5 hours to obtain the sintered magnet blank.

[0088] The sintered magnet blanks are machined and cut into 25mm*20mm*5mm magnet slices, which are then placed in a continuous tunnel furnace for secondary aging treatment at a temperature of 500℃ for 1.5 hours, finally yielding the finished magnet. The secondary aging chamber of the continuous tunnel furnace is a settling-type cavity, and the magnets are protected by argon gas within the chamber.

[0089] The finished magnet obtained in this embodiment was tested using the NIM-62000 rare-earth permanent magnet standard measuring device; the cross-sectional microstructure of the finished magnet was observed using a scanning electron microscope, and the results are as follows. Figure 3 As shown.

[0090] Example 2

[0091] A sintered RTB magnet is composed of the following components:

[0092] Ga: 0.05wt%

[0093] R: 29.6wt%

[0094] B: 0.95wt%

[0095] M: 2.6wt%

[0096] Fe: 65.05 wt%

[0097] Co: 1.0wt%

[0098] R consists of 22.5 wt% Nd and 7.1 wt% Pr; B represents boron; M consists of M1, which is composed of 1.35 wt% Al, 0.4 wt% Cu, 0.45 wt% Ti, 0.2 wt% Zr and 0.2 wt% Nb; Fe represents iron; and Co represents cobalt.

[0099] Its preparation method includes the following steps:

[0100] The raw materials are smelted according to the component ratio, and the smelting temperature is controlled at 1470℃. After all the raw materials are melted, the solution temperature is reduced to 1400℃ and then poured onto a copper roller at 1400℃. The strip is then spun to obtain 0.2mm-0.35mm fast-setting sheets.

[0101] The obtained quick-setting sheets were crushed by hydrogen absorption and dehydrogenated at 550°C to obtain magnetic powder.

[0102] Antioxidant and lubricant were added to the magnetic powder and mixed evenly, and then air jet milling was performed to obtain fine powder with SMD of 2.5μm-3.5μm;

[0103] Under a nitrogen protective atmosphere, the fine powder was oriented and pressed into shape. The orientation magnetic field was 1.8T, and the isostatic pressing pressure was 180MPa, resulting in a density of 4.2 g / cm³. 3 The green magnet blank.

[0104] The magnet blank was vacuum sintered at 1050℃ for 8 hours, then cooled in the furnace to below 100℃ and then subjected to a first-stage aging treatment. The first-stage aging temperature was 850℃ and the treatment time was 5 hours to obtain the sintered magnet blank.

[0105] The sintered magnet blanks are machined and cut into 25mm*20mm*5mm magnet slices, which are then placed in a continuous tunnel furnace for secondary aging treatment at a temperature of 500℃ for 1.5 hours, finally yielding the finished magnet product. The secondary aging chamber of the continuous tunnel furnace is a settling chamber, and the atmosphere within the chamber is air.

[0106] The finished magnet obtained in this embodiment was tested using the NIM-62000 rare earth permanent magnet standard measuring device.

[0107] Example 3:

[0108] A sintered RTB magnet is composed of the following components:

[0109] Ga: 0.05wt%

[0110] R: 29.6wt%

[0111] B: 0.95wt%

[0112] M: 2.6wt%

[0113] Fe: 65.05 wt%

[0114] Co: 1.0wt%

[0115] R consists of 22.5 wt% Nd and 7.1 wt% Pr; B represents boron; M consists of M1, which is composed of 1.35 wt% Al, 0.4 wt% Cu, 0.45 wt% Ti, 0.2 wt% Zr and 0.2 wt% Nb; Fe represents iron; and Co represents cobalt.

[0116] Its preparation method includes the following steps:

[0117] The raw materials are smelted according to the component ratio, and the smelting temperature is controlled at 1470℃. After all the raw materials are melted, the solution temperature is reduced to 1400℃ and then poured onto a copper roller at 1400℃. The strip is then spun to obtain 0.2mm-0.35mm fast-setting sheets.

[0118] The obtained quick-setting sheets were crushed by hydrogen absorption and dehydrogenated at 550°C to obtain magnetic powder.

[0119] Antioxidant and lubricant were added to the magnetic powder and mixed evenly, and then air jet milling was performed to obtain fine powder with SMD of 2.5μm-3.5μm;

[0120] Under a nitrogen protective atmosphere, the fine powder was oriented and pressed into shape. The orientation magnetic field was 1.8T, and the isostatic pressing pressure was 180MPa, resulting in a density of 4.2 g / cm³. 3 The green magnet blank.

[0121] The magnet blank was vacuum sintered at 1050℃ for 8 hours, then cooled in the furnace to below 100℃ and then subjected to a first-stage aging treatment. The first-stage aging temperature was 850℃ and the treatment time was 5 hours to obtain the sintered magnet blank.

[0122] The sintered magnet blanks are machined and cut into 25mm*20mm*5mm magnet slices, which are then placed in a continuous tunnel furnace for secondary aging treatment at a temperature of 520℃ for 1.5 hours, finally yielding the finished magnet. The secondary aging chamber of the continuous tunnel furnace is a settling-type cavity, and the magnets are protected by argon gas within the chamber.

[0123] The finished magnet obtained in this embodiment was tested using the NIM-62000 rare earth permanent magnet standard measuring device.

[0124] Comparative Example 2

[0125] A sintered RTB magnet is composed of the following components:

[0126] Ga: 1.5wt%

[0127] R: 29.3wt%

[0128] B: 0.98wt%

[0129] M: 1.6wt%

[0130] Fe: 65.82 wt%

[0131] Co: 0.8wt%

[0132] RR consists of 22.8 wt% Nd and 6.5 wt% Pr; B represents boron; M consists of M1, which is composed of 1.0 wt% Al, 0.2 wt% Cu, 0.1 wt% Ti, and 0.3 wt% Zr; Fe represents iron; and Co represents cobalt.

[0133] Its preparation method includes the following steps:

[0134] The raw materials are smelted according to the component ratio, and the smelting temperature is controlled at 1475℃. After all the raw materials are melted, the solution temperature is lowered to 1410℃ and kept at 1410℃ before being poured onto a copper roller. The resulting sheet is a quick-setting sheet of 0.2mm-0.35mm.

[0135] The obtained quick-setting sheets were crushed by hydrogen absorption and dehydrogenated at 550°C to obtain magnetic powder.

[0136] Antioxidant and lubricant were added to the magnetic powder and mixed evenly, and then air jet milling was performed to obtain fine powder with SMD of 2.5μm-3.5μm;

[0137] Under a nitrogen protective atmosphere, the fine powder was oriented and pressed into shape. The orientation magnetic field was 1.8T, and the isostatic pressing pressure was 180MPa, resulting in a density of 4.2 g / cm³. 3 The green magnet blank.

[0138] The magnet blank was vacuum sintered at 1050℃ for 8 hours, then cooled in the furnace to below 100℃ and then subjected to a first-stage aging treatment. The first-stage aging temperature was 850℃ and the treatment time was 5 hours to obtain the sintered magnet blank.

[0139] The sintered magnet blanks are machined and cut into 25mm*20mm*5mm magnet slices, which are then placed in a continuous tunnel furnace for secondary aging treatment at a temperature of 520℃ for 1.5 hours, finally yielding the finished magnet. The secondary aging chamber of the continuous tunnel furnace is a settling-type cavity, and the magnets are protected by argon gas within the chamber.

[0140] The finished magnets were tested using the NIM-62000 rare earth permanent magnet standard measuring device.

[0141] By comparing Example 1 and Comparative Example 1, it can be found that the magnet with low Ga content undergoing low-temperature secondary aging under argon protection has better magnetic properties than the magnet with high Ga content. Furthermore, in comparison... Figure 2 and Figure 3 Microstructure diagram of cross-section of the magnet, revealing... Figure 2 Magnets made from low-gallium magnets show no significant difference in grain boundary phase contrast; while Figure 3The magnet prepared with high Ga content exhibits a high-brightness structure within its grain boundary phase. Analysis revealed that this structure has a high rare-earth content and a high oxygen content, making it prone to oxidation. Therefore, this comparison demonstrates that low-Ga magnets are less susceptible to oxidation.

[0142] Comparing Example 1 and Example 2, it can be found that the performance of the low-Ga magnet undergoing low-temperature two-stage aging treatment in air atmosphere only slightly decreases. This also indicates that the low-Ga magnet has good corrosion resistance.

[0143] Comparing Examples 1 and 3 with Comparative Example 2, it was found that a 20°C increase in the secondary aging temperature had little impact on the performance of low-Ga content magnets, while the performance of high-Ga content magnets deteriorated significantly. This indicates that the aging temperature range for high-Ga content magnets is narrow, and even a 20°C temperature fluctuation can lead to performance degradation, requiring very high temperature control and resulting in difficulty in controlling product quality levels and causing fluctuations. In contrast, the secondary aging temperature range for low-Ga content magnets is wider than that for high-Ga content magnets, and temperature fluctuations have little impact on magnet performance, resulting in better process stability.

[0144] Comparative Example 3

[0145] The magnet proportions, preparation methods, and steps are the same as in Example 1. The difference is that the sintered magnet blanks after the first-stage aging treatment are not machined but sent to a vacuum sintering furnace for a second-stage aging treatment. The second-stage aging temperature is 500℃, and the treatment time is 5 hours. After entering the sintering furnace, the vacuum is first evacuated to 1 Pa for 1-1.5 hours, then heated to 500℃ for 2.5 hours, and then held at that temperature for 5 hours. After the holding period, the magnets are cooled by air cooling with nitrogen gas introduced. There is no specific time for this cooling; the magnets are cooled to 50℃ (for 1 hour). Therefore, with a loading rate of 600 kg per furnace, the total time required is 9-10 hours.

[0146] In Example 1, it takes approximately 8 hours to process 1000 kg in a continuous tunnel furnace.

[0147] Therefore, this application improves the secondary aging process, which increases the work efficiency by about 100% compared to the existing technology.

[0148] The finished magnets were tested using the NIM-62000 rare earth permanent magnet standard measuring device.

[0149] Comparative Example 4

[0150] The magnet proportions, preparation methods and steps are the same as those in Comparative Example 1, and the secondary aging process of the sintered magnet blank after the first-stage aging treatment is the same as that in Comparative Example 3.

[0151] The finished magnets were tested using the NIM-62000 rare earth permanent magnet standard measuring device.

[0152] The magnet performance results for each embodiment and comparative example are shown in Table 1.

[0153] Table 1. Comparison of Magnet Performance

[0154] Br(kGs) Hcj(kOe) Hk / Hcj Example 1 15.21 17.86 97.3％ Comparative Example 1 12.03 15.45 88.2％ Example 2 14.82 17.45 95.2％ Example 3 15.18 17.79 97.5％ Comparative Example 2 11.62 13.60 85.5％ Comparative Example 3 15.23 17.84 98.0％ Comparative Example 4 15.10 17.52 96.5％

[0155] This invention reduces the Ga content in Ga-containing magnets and employs a continuous tunnel furnace for secondary aging of the product, thereby lowering production costs and improving the oxidation resistance of Ga-containing magnets. Furthermore, using thin-sheet products for low-temperature secondary aging in a continuous tunnel furnace reduces heating and cooling times, maintains product performance consistency, and improves magnet production efficiency.

Claims

1. A method for preparing a low-gallium sintered permanent magnet, characterized in that... The method is as follows: A sintered magnet blank that has undergone vacuum sintering and vacuum first-stage aging treatment is cut into magnet sheets. The magnet sheets are then fed into a continuous tunnel furnace for low-temperature second-stage aging treatment to prepare the low-gallium sintered permanent magnet. The Ga content in the raw material of the magnet is 0.05~0.08 wt.%. The temperature of the low-temperature secondary aging treatment is 450-600 ℃, and the holding time is 20 min-2 h; during the low-temperature secondary aging treatment, the continuous tunnel furnace is in an air, nitrogen or argon atmosphere.

2. The method as described in claim 1, characterized in that... During the low-temperature secondary aging process, the continuous tunnel furnace is in a nitrogen or argon atmosphere.

3. The method as described in claim 1, characterized in that... The low-temperature secondary aging process is as follows: the magnet sheet is placed at the feed port of the continuous tunnel furnace and transported to the secondary aging chamber by the conveyor belt. The magnet undergoes low-temperature secondary heat treatment in the secondary aging chamber. After the treatment, the magnet leaves the secondary aging chamber from the discharge port by the conveyor belt and is then cooled to a temperature below 60°C. The secondary aging chamber adopts a settling chamber, and the bottom surface of the secondary aging chamber is lower than the height of the inlet and outlet.

4. The method as described in claim 3, characterized in that... The magnet is cooled in a cooling chamber by natural cooling in the air or by using a blower to accelerate cooling.

5. The method according to any one of claims 1 to 4, characterized in that... The low-gallium sintered permanent magnet comprises the following components by mass fraction: R: 28 wt.%~32 wt.%, R is selected from one or more of Pr, Nd, Dy, Tb, Gd, and Ho. B: 0.9 wt.%~1.1 wt.% M: M is M1, or a mixture of M1 and M2, wherein M1 is one or two of the elements Al, Cu, Ti, Zr, and Nb, and M2 is at least one of the elements Si, Zn, Sn, Ge, Ag, V, W, and Mo; the content of M1 is 0.5 wt.% to 4.5 wt.%, and when M contains M2, the content of M2 is 0.1 to 2.0 wt.%. The balance is T and other unavoidable impurities, wherein T is at least one of Fe and Co.

6. The method as described in claim 1, characterized in that... The thickness of the magnet sheet is 1~5mm.

7. The low-gallium sintered permanent magnet prepared by the method as described in claim 5, characterized in that... The low-gallium sintered permanent magnet has the following microstructure: within 0-10 μm from the magnet surface, the proportion of rare earth oxide RO phase in the grain boundary R-rich phase is less than 20 vol.%, and the oxygen content is 500 PPM~900 PPM; below 15 μm from the magnet surface, the proportion of rare earth oxide RO phase in the grain boundary R-rich phase is less than 0.01 vol.%, and the oxygen content is ≤400 PPM.

8. The low-gallium sintered permanent magnet prepared by the method as described in claim 5, characterized in that... The low-gallium sintered permanent magnet has the following microstructure: when the magnet is subjected to low-temperature secondary treatment in a nitrogen or argon atmosphere, the proportion of rare earth oxide RO phase in the grain boundary R-rich phase within a range of 0-10 μm from the magnet surface is less than 0.01 vol.%, and the oxygen content is ≤600 PPM.

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