Neodymium-iron-boron magnets and their manufacturing methods and applications

Abstract

The present invention provides a neodymium iron boron magnet and its manufacturing method and application, the magnet is R2(Fe,M) 14 The magnet includes main phase crystal grains and a grain boundary phase having a B structure, and the grain boundary phase includes a double grain boundary between two main phase crystal grains and a triangular grain boundary composed of three or more gaps between the main phase crystal grains, in which M includes Cu, Ga, and / or Al, and R is at least one rare earth element including Nd. By adjusting the compounding ratio of the components of elements such as Cu, Ga, and Al, the distribution pattern in the magnet, and the grain size of the crystal grains, a magnet with relatively high magnetic Br and Hcj can be obtained.

Description

Detailed Description of the Invention

[0001] This application claims priority from a prior application bearing patent application number 202111616641.6 and entitled "Neodymium Iron Boron Magnet, Its Manufacturing Method and Application," filed with the State Intellectual Property Office of China on December 27, 2021. The above prior application is incorporated herein by reference in its entirety.

[0002] [Technical Field] The present invention relates to the field of neodymium-iron-boron magnets, and more particularly to neodymium-iron-boron sintered magnets, their manufacturing methods, and applications.

[0003] [Background technology] NdFeB-based sintered permanent magnet materials are currently the permanent magnetic functional materials with the highest overall magnetic performance and the widest range of applications. Known as the modern "king of magnets," they are an important supporting material for promoting the development of related fields such as energy and information. Since their emergence in the 1980s, NdFeB-based sintered magnets have been widely used in many fields, including the automotive industry, medical devices, electronic information, and aerospace, due to their excellent magnetic performance and extremely low cost performance, providing important support for the development of intelligent, miniaturized, and lightweight products in related fields. In recent years, as the performance of NdFeB-based sintered magnets has continued to improve, their application fields have also continued to expand.

[0004] Neodymium-iron-boron sintered permanent magnet materials must have high coercivity to ensure stable magnetic field output under high-temperature conditions. Traditionally, heavy rare earth (Dy / Tb) raw materials have been added to the smelting process to improve magnet coercivity. Due to the scarce and expensive reserves of heavy rare earth resources, large-scale utilization of heavy rare earth resources not only fails to support sustainable mining and utilization, but also significantly increases magnet production costs. Furthermore, the addition of heavy rare earth metals reduces the remanence of the magnet, further reducing the magnetic field strength provided by the magnet to the air, which is detrimental to the weight and size of related equipment.

[0005] To improve magnet performance while reducing the amount of heavy rare earths such as terbium and dysprosium used, dual-alloy technology, grain refinement technology, and grain boundary diffusion technology have attracted the industry's attention. Currently, grain refinement technology and grain boundary diffusion technology are the most widely used. Grain refinement technology controls the process parameters of the smelting and milling processes to obtain a relatively small particle size of jet-milled powder, which is then matched with the corresponding sintering system, ultimately achieving the goal of finely controlling the magnet particle size, thereby reducing defects in the crystal grains inside the magnet and improving the magnet's coercivity.

[0006] Grain boundary diffusion technology involves coating the surface of a magnet with a diffusion source containing terbium and dysprosium elements by methods such as dip coating or spray coating. The terbium and dysprosium elements then diffuse into the interior of the magnet through the grain boundary phase, replacing Nd in the neodymium-rich phase at the grain boundaries and forming (Dy / Tb)2Fe around the main phase crystal grains. 14 B is formed to improve the anisotropy of the grain boundary, thereby achieving the purpose of improving the coercive force.

[0007] Grain refinement and grain boundary diffusion can be used alone or in combination. When combined, grain refinement determines the final performance of the magnet. When grain refinement is used, the magnet's grain size becomes finer, the surface area of ​​the main phase crystal grains increases, the surface energy rises, and activity becomes greater. This makes it difficult to eliminate adsorption to impurity elements such as C, S, O, and N, which not only degrades performance but also makes it more likely for abnormal grain growth to occur, further degrading magnetic performance. The presence of abnormally grown crystal grains in the magnet also significantly reduces the effectiveness of grain boundary diffusion.

[0008] Patent document CN106252012A proposes a method of sintering NdFeB magnets by first holding the temperature at 20°C below the sintering temperature for 0-1 hour, then raising the temperature to the sintering temperature and holding for 3-6 hours, then naturally cooling to 700-800°C, and then raising the temperature to 0-20°C above the sintering temperature and holding for 5-8 hours, thereby producing a magnet with fine grains, uniform density, low heavy rare earth content, and high performance NdFeB magnets, while preventing abnormal grain growth. However, despite the fine grain size requirements, the sintering temperature is high and the holding time is long, still posing a risk of abnormal grain growth. The overall sintering cycle is long, resulting in low mass production efficiency.

[0009] Summary of the Invention In order to improve the above technical problems, the present invention provides a high-performance neodymium-iron-boron magnet, the magnet is R2(Fe,M) 14 The alloy comprises main phase crystal grains and a grain boundary phase having a B structure, the grain boundary phase comprising a bigrain boundary between two main phase crystal grains and a triangular grain boundary formed by gaps between three or more main phase crystal grains, wherein M comprises Cu, Ga, and / or Al, and R is at least one rare earth element including Nd.

[0010] According to an embodiment of the present invention, R includes Nd and further includes at least one rare earth element selected from the group consisting of Y, La, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Sc.

[0011] According to an embodiment of the present invention, the average grain size of the main phase crystal grains of the magnet is 1.8 to 8 μm, preferably 2.5 to 6 μm. Within this grain size range, the magnet exhibits relatively excellent magnetic performance. If the grain size is smaller, less than 1.8 μm, the surface activity of the crystal grains will be greater, making them more likely to adsorb impurities such as O / N and making it difficult for the adsorbed impurities to escape, resulting in a decrease in performance. If the grain size is relatively large, exceeding 8 μm, the internal structural defects of the main phase crystal grains will increase and the grain boundary phase will become relatively diluted, making it difficult to obtain a high-performance NdFeB magnet.

[0012] According to an embodiment of the present invention, the atomic concentration of Cu in adjacent main phase crystal grains is set to [Cu1], and the atomic concentration of Cu at the two-grain boundary is set to [Cu2], and the relationship 1≦[Cu2] / [Cu1]<2 is satisfied.

[0013] According to an embodiment of the present invention, the triangular grain boundaries in a magnet contain Cu-rich regions, the Cu atomic concentration at the triangular grain boundaries is set to [Cu3], satisfying the relationship [Cu3] / [Cu1] ≥ 2, and the grain boundary phase of the Cu-rich regions is a non-magnetic phase. A relatively high content of Cu-rich regions in a magnet significantly reduces the Br of the magnet. In the triangular grain boundaries of the present invention, the regions where the Cu concentration satisfies [Cu3] / [Cu1] ≥ 2 are defined as Cu-rich regions.

[0014] According to an embodiment of the present invention, the ratio of the area of ​​the Cu-rich regions of the triangular grain boundaries to the total area of ​​the grain boundary phase is <5%.

[0015] According to an embodiment of the present invention, the atomic concentration of Ga in adjacent main phase crystal grains is set to [Ga1], and the atomic concentration of Ga at the two-grain boundary is set to [Ga2], and the relationship 1≦[Ga2] / [Ga1]<2 is satisfied.

[0016] According to an embodiment of the present invention, the triangular grain boundaries in the magnet contain Ga-rich regions, the Ga atomic concentration at the triangular grain boundaries is set to [Ga3], and the relationship [Ga3] / [Ga1]≧2 is satisfied; that is, the regions at the triangular grain boundaries where the Ga element concentration satisfies [Ga3] / [Ga1]≧2 are defined as Ga-rich regions, and the grain boundary phase of the Ga-rich regions is a non-ferromagnetic phase, and preferably the ratio of the area of ​​the Ga-rich regions at the triangular grain boundaries to the total area of ​​the grain boundary phase is <5%.

[0017] According to an embodiment of the present invention, the atomic concentration of Al in adjacent main phase crystal grains is set to [Al1], and the atomic concentration of Al at the two-grain boundary is set to [Al2], and the relationship 1<[Al2] / [Al1]<2 is satisfied.

[0018] According to an embodiment of the present invention, the triangular grain boundaries in the magnet contain Al-rich regions, the Al atomic concentration at the triangular grain boundaries is set to [Al3], and the relationship [Al3] / [Al1]≧2 is satisfied. In other words, the Al-rich regions are defined as the regions at the triangular grain boundaries where the Ga concentration satisfies [Al3] / [Al1]≧2. The grain boundary phase in the Al-rich regions is a non-magnetic phase, and preferably the ratio of the area of ​​the Al-rich regions at the triangular grain boundaries to the total area of ​​the grain boundary phase is <5%.

[0019] In the present invention, adjacent main phase crystal grains refer to main phase crystal grains adjacent to a two-grain boundary.

[0020] In conventional magnet manufacturing processes, Cu rarely penetrates into the main phase grains. Instead, it resides primarily in the Nd-rich phase at the grain boundaries, improving hcj and reducing irreversibility. However, too much Cu reduces Br and Hcj performance. A small amount of Al occupies the 8j2 crystal position in the main phase grains, refining the grains. Most of the Al reduces the nodular distribution of the Nd-rich and B-rich phases at the grain boundaries, improving the wetting angle with the main phase and allowing the Nd-rich phase to be more uniformly distributed along the boundaries. A small amount of Ga is present in the main phase grains, concentrating primarily at the grain boundaries, refining the grains and improving the wettability of the grain surfaces. However, because the compounds formed are non-ferromagnetic phases, it is inevitable to add Cu / Ga / Al, etc., to reduce Br. Furthermore, these stable compounds were concentrated in the grain surface layer, inhibiting the substitution reaction of the grain surface component structure by heavy rare earth elements such as Dy / Tb during the diffusion process, directly resulting in a significant decrease in the diffusion Hcj amplification.

[0021] According to an embodiment of the present invention, [Cu2] / [Cu1] is equal to or greater than 1 and less than 2, and more preferably 1.2 to 1.8. Within this atomic concentration ratio range, Cu is distributed relatively uniformly in the surface layers of the main phase crystal grains and within the two-grain boundaries, and Ga and Al also show the same regularity.

[0022] According to an embodiment of the present invention, the high-performance NdFeB magnet further contains transition metal elements such as Mn, Si, Zr, Ti, and Nb. When the transition metal elements are concentrated in the grain boundary phase and have a distribution pattern similar to that of Cu, Ga, and Al within the magnet, i.e., 1≦[Zr2] / [Zr1]<2, and / or 1≦[Ti2] / [Ti1]<2, and / or 1≦[Nb2] / [Nb1]<2, a high-performance magnet can be obtained. [Zr1] represents the atomic concentration of Zr in adjacent main-phase crystal grains, [Zr2] represents the atomic concentration of Zr at the two-grain boundary, [Ti1] represents the atomic concentration of Ti in adjacent main-phase crystal grains, [Ti2] represents the atomic concentration of Ti at the two-grain boundary, [Nb1] represents the atomic concentration of Nb in adjacent main-phase crystal grains, and [Nb2] represents the atomic concentration of Nb at the two-grain boundary.

[0023] According to an embodiment of the present invention, the high-performance neodymium iron boron magnet is, at a mass ratio of 100%, 27-35% R and 0.8~1.2wt% B and 0 to 3.0 wt% Co, 0.1 to 0.6 wt% Cu, 0.1 to 0.8 wt% Ga, 0-1.0 wt% Al, 60 to 72 wt% T, In this, R is at least one rare earth element including Nd, and T includes Fe and other transition metal elements as well as unavoidable impurity elements, the transition metal elements having the above-mentioned meanings.

[0024] According to an embodiment of the present invention, R includes Nd and at least one rare earth element selected from the group consisting of Y, La, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Sc. Preferably, R is at least one of Nd, Y, Dy, Tb, Ho, La, and Ce, with the total mass of Dy, Tb, and / or Ho accounting for 5 wt% or less of the total mass of the magnet, and the total mass of La, Ce, and / or Y accounting for 3 wt% or less of the total mass of the magnet. If R in a magnet is too high, the neodymium-rich phase of the magnet increases and Br decreases. If R is too low, a uniform and continuous Nd-rich phase for magnetic insulation of the main phase crystal grains cannot be formed in the magnet, resulting in a significant deterioration in the Hcj and squareness of the magnet. R2(Fe,M) composed of rare earth elements such as Pr, Dy, Tb, and Ho is used. 14 The B-based main phase crystal grains have a lower magnetic polarization strength and a superior anisotropy field than Nd, which significantly reduces the Br of the magnet, improves Hcj, and ensures a high Br of the magnet. At the same time, small amounts of heavy rare earth elements such as Dy, Tb, and Ho are used to improve the Hcj of the magnet, and their content in the total magnet composition is ≦5wt%. Rare earth elements such as La, Ce, and Y have significantly lower intrinsic magnetic properties than Nd, are abundant and inexpensive, and can be added in small amounts, and their content in the total magnet composition is ≦3wt%. Preferably, R includes Nd and Pr.

[0025] According to an embodiment of the present invention, the B content is 0.8 to 1.2 wt%, more preferably 0.87 to 1.05 wt%, and even more preferably 0.93 to 1.00 wt%. If the B content is too low, R will be relatively high, the proportion of the R-rich phase formed will be relatively high, and the volume ratio of the main phase crystal grains will be small, resulting in a low magnet Br and unstable Hcj and squareness of the magnet. If the B content is too high, the volume ratio of the B-rich phase will increase significantly, significantly reducing magnetic performance.

[0026] According to an embodiment of the present invention, Co occupies the position of Fe in the main phase crystal grains within the magnet. Co has a smaller atomic magnetic moment than Fe. The addition of Co reduces the Br of the magnet and has a significant effect on the corrosion resistance and temperature resistance of the magnet. Therefore, the Co content is 0-3.0 wt%, and more preferably 0.5-2 wt%. When the Co content is 0, the corrosion resistance and temperature coefficient of the magnet are significantly reduced. However, when the Co content is greater than 3 wt%, the Br is significantly reduced and the Hcj is also significantly reduced. In addition, high Co content increases the brittleness of the magnet, making it more susceptible to processing cracks and resulting in a low product acceptance rate. Furthermore, Co is a strategic metal and is used in large quantities, so there is a very high demand for a stable supply of raw materials.

[0027] According to an embodiment of the present invention, the Cu content is 0.1 to 0.6 wt%, and more preferably 0.2 to 0.5 wt%. If the Cu content is too high, grain growth is suppressed and the grain boundary phase is expanded, reducing the volume ratio of the main phase crystal grains and lowering the Br of the magnet. If the Cu content is too low and no Cu is added, the main phase crystal grains and the B-rich phase of the magnet will become relatively coarse, significantly reducing the magnetic performance of the magnet.

[0028] According to an embodiment of the present invention, the Ga content is 0.1 to 0.8 wt%, and more preferably 0.2 to 0.6 wt%. If the Ga content is too high, grain growth is suppressed and the grain boundary phase expands, reducing the volume ratio of the main phase crystal grains and lowering the Br of the magnet. If the Ga content is too low and no Ga is added, the main phase crystal grains and B-rich phase of the magnet will become relatively coarse, significantly reducing the magnetic performance of the magnet.

[0029] According to an embodiment of the present invention, the Al content is 0 to 1.0 wt%, and more preferably 0.1 to 0.5 wt%. If the Al content is too high, grain growth is suppressed and the grain boundary phase is expanded, reducing the volume ratio of the main phase crystal grains and lowering the Br of the magnet. If the magnet does not contain Al, the main phase crystal grains and the B-rich phase of the magnet will become relatively coarse, significantly reducing the magnetic performance of the magnet.

[0030] According to an embodiment of the present invention, T includes Fe and other transition metal elements, as well as inevitable impurity elements. The other transition metal elements are, for example, Mn, Si, Zr, Ti, Nb, etc., and the inevitable impurity elements are, for example, elements such as C, S, O, and N. Preferably, T includes Fe and / or Ti.

[0031] The present invention further provides a method for producing the above-mentioned neodymium-iron-boron magnet, the method comprising: (a) a smelting process in which the components of the magnet are melted, cast, and cooled to form an alloy sheet; (b) a milling process in which the alloy sheet is crushed into alloy powder; (c) a press molding process in which the alloy powder is press molded under the action of a magnetic field to obtain a billet; (d) a sintering process for sintering the billet, aging it, and manufacturing it to obtain a neodymium-iron-boron magnet.

[0032] According to an embodiment of the present invention, the smelting process in step (a) is a conventional technique, such as using a spinning method to produce an alloy sheet. Exemplarily, step (a) is specifically a smelting process, in which the components of the magnet are sufficiently melted into molten alloy steel in a medium-frequency induction smelting furnace in a vacuum or inert gas atmosphere according to the target component ratio, and then rapidly cooled to form an alloy sheet or alloy ingot. Exemplarily, secondary cooling is performed.

[0033] According to an embodiment of the present invention, said step (b) is a milling process, specifically including coarse grinding and fine grinding, and preferably said coarse grinding is selected from hydro-grinding and / or medium grinding.

[0034] Preferably, the pulverization is performed using a jet mill. Preferably, the jet milling is performed in an inert gas atmosphere. Preferably, the inert gas is selected from nitrogen gas, helium gas, etc.

[0035] In the present invention, the above-mentioned hydrogen crushing, medium crushing or jet milling can be carried out by any known operation in the prior art.

[0036] According to an embodiment of the present invention, in step (b), the alloy powder is further screened, such as by grading wheel screening, after pulverization. For example, the SMD particle size of the alloy powder is 1.8-8 μm, preferably 2.5-6 μm, and X90 / X10≦4.5. SMD is the area-average particle size. A smaller SMD indicates a smaller powder particle size, and a larger SMD indicates a larger powder particle size. X90 represents the particle size value corresponding to 90% cumulative distribution, i.e., all particles have particle sizes equal to or smaller than this particle size, and the number of particles larger than this particle size is zero. X10 represents the particle size value corresponding to 10% cumulative distribution, i.e., all particles have particle sizes equal to or smaller than this particle size, and the number of particles larger than this particle size is zero. X90 / X10 represents the particle size distribution of the powder, and a smaller X90 / X10 indicates a more concentrated powder particle size distribution.

[0037] According to an embodiment of the present invention, in step (b), a lubricant needs to be further added during pulverization, and preferably added both before and after jet milling. Adding a lubricant before jet milling can improve the flowability of the powder, adding a lubricant during jet milling can improve the flowability and uniformity of the powder, and adding a lubricant after jet milling can also improve the uniformity and flowability of the powder, facilitating uniform powder filling and pressing.

[0038] Preferably, the lubricant is selected from known agents in the prior art and used in a known amount in order to achieve sufficient and uniform mixing of the powder and ease of molding. Exemplarily, the lubricant is selected from easily volatile organic solvents such as lipids or alcohols, e.g., zinc stearate. Exemplarily, the amount of the lubricant added is 0.1 to 1 wt% of the total mass of the raw materials.

[0039] Preferably, after adding the lubricant, further mixing is required, and the mixing time is preferably 1 to 6 hours.

[0040] The mixing according to the present invention can be carried out using methods known in the art, for example by mixing in a mixer.

[0041] According to an embodiment of the present invention, in step (c), the pressing is carried out in a press die cavity.

[0042] According to an embodiment of the present invention, in step (c), it is necessary to perform alignment magnetization and molding with a magnetic field strength of 2 T or more before press molding, and either coil magnetization or pulse magnetization may be used.

[0043] According to an embodiment of the present invention, in step (c), after press molding, a reverse magnetic field is applied to perform demagnetization.

[0044] According to an embodiment of the present invention, in step (c), the compacted billet may be subjected to a cold isostatic press to further increase the billet density.

[0045] According to an embodiment of the present invention, in step (d), the billet is further heat-treated before sintering. The heat-treatment temperature is 100 to 950°C, preferably 150 to 900°C, and the heat-treatment temperature retention time is 60 to 120 minutes. For example, the heat-treatment temperature is 3 to 6 stages, and the heat-treatment temperature and heat-retention time for each stage may be the same or different. The heat-treatment stages may be performed in an inert gas or in a vacuum. For example, the heat-treatment temperature is 4 stages, and the heat-treatment temperatures are 100 to 200°C, 200 to 550°C, 550 to 700°C, and 700 to 950°C, respectively.

[0046] According to an embodiment of the present invention, in step (d), the sintering treatment has three or more sintering temperature-keeping stages and pre-sintering temperature-raising stages, illustratively 3 to 10 stages, for example 3, 4, 5, 6, 7, 8, 9 or 10 stages, the temperature of the sintering temperature-keeping stage is 950 to 1200°C, preferably 980 to 1070°C, the temperature-keeping time of each stage is 20 to 120 minutes, the temperature-keeping temperature of each sintering treatment may be the same or different, the temperature-keeping time may be the same or different, and the sintering temperature-keeping stage may be performed in an inert gas or in a vacuum.

[0047] For example, the temperature rise rate during each sintering step is 0.5 to 5°C / min, more preferably 1 to 4°C / min, and the temperature rise rate in each temperature rise step may be the same or different.

[0048] According to an embodiment of the present invention, between two adjacent sintering and temperature-keeping processes, the next temperature-raising and temperature-keeping process may be carried out directly after the previous sintering and temperature-keeping process is completed, or cooling may be carried out first after the previous sintering and temperature-keeping process is completed, and then the next temperature-raising and temperature-keeping process may be carried out. The cooling temperature is not limited as long as it is lower than the temperature of the previous sintering and temperature-keeping process, and the number of cooling stages is not particularly limited as long as the required cooling temperature is reached. That is, any random process may be carried out between two adjacent sintering and temperature-keeping processes. For example, after the previous sintering and temperature-keeping process is completed, 1 to 10 stages of cooling may be carried out first, and then the next temperature-raising and temperature-keeping process may be carried out, and the cooling temperatures of the 1 to 10 stages may be the same or different.

[0049] In order to ensure production efficiency, the sintering and heat-keeping stage is preferably controlled within 10 sets.

[0050] In the present invention, the above-mentioned three or more stages of sintering and temperature retention process can achieve a uniform distribution of elements such as Cu, Ga, and Al, and this sintering mode helps elements such as Cu, Ga, and Al to segregate from the grain boundary phase to the main phase crystal grains.

[0051] According to an embodiment of the present invention, in step (d), the aging treatment is performed after the sintering treatment and cooling. Illustratively, the aging treatment includes cooling to room temperature after the sintering treatment is completed, and then performing a temperature increase treatment.

[0052] Preferably, the aging treatment is selected from primary aging treatment or secondary aging treatment.

[0053] Preferably, the conditions for the primary aging treatment are an aging treatment temperature of 500 to 700°C and a temperature holding time of 240 to 420 minutes. Preferably, the secondary aging treatment includes a first aging treatment in which the temperature is raised to 800 to 950°C and the temperature holding time is 180 to 300 minutes, and a second aging treatment in which the temperature is raised to 450 to 600°C after cooling to 200°C or below and the temperature is held for 240 to 360 minutes.

[0054] According to an embodiment of the present invention, a diffusion treatment may also be performed after the sintering process.

[0055] Preferably, the diffusion treatment includes applying a diffusion material to the magnet surface, and performing a vacuum heating diffusion treatment, a diffusion cooling treatment, and a diffusion aging treatment.

[0056] Preferably, the diffusion material is at least one selected from pure metals of Dy and / or Tb, hydrides of Dy and / or Tb, oxides of Dy and / or Tb, hydroxides of Dy and / or Tb, alloys of Dy and / or Tb, fluorides of Dy and / or Tb, and the like, and is illustratively Dy metal.

[0057] Preferably, the diffusion treatment can be carried out by using a method such as vacuum deposition, magnetron sputtering, coating or embedding.

[0058] Preferably, the temperature of the vacuum thermal diffusion treatment is 850 to 950° C., and the time of the vacuum thermal diffusion treatment is 10 to 30 hours.

[0059] Preferably, the temperature of the diffusion cooling is less than 100°C.

[0060] Preferably, the temperature of the diffusion aging treatment is 450 to 600°C, and the time of the diffusion aging treatment is 4 to 8 hours.

[0061] According to embodiments of the present invention, the billet may also be machined to a target size after the sintering process and before the diffusion treatment.

[0062] According to an embodiment of the present invention, after the sintering process and before the diffusion process, the magnet is explicitly cleaned after the billet is machined to the target size to remove any machining debris, machining cutting fluid residue, or machining adhesives from the magnet surface.

[0063] According to an embodiment of this aspect, the cleaning treatment before diffusion can be, but is not limited to, ultrasonic cleaning with pure water and pickling, and the acid can be, but is not limited to, nitric acid, sulfuric acid, citric acid, etc.

[0064] The present invention further provides an application of the above neodymium iron boron magnet for use in motor applications.

[0065] The present invention further provides a motor including the above magnet.

[0066] The present invention further provides applications of the above motor, preferably, the above motor can be applied to new energy vehicles and energy-saving home appliances.

[0067] Beneficial effects of the present invention: The present invention makes it possible to obtain magnets with relatively high Br and Hcj by adjusting the component ratios and distribution of elements such as Cu, Ga, and Al in the magnet, as well as the grain size. The sintering method provided by the present invention, i.e., three or more sintering and temperature-holding stages and a temperature-rising stage before the temperature-holding stage, not only ensures sufficient sintering of the main phase crystal grains and grain boundary phase of the magnet and increases its density, but also suppresses abnormal growth of the main phase crystal grains and prevents the oriented and ordered crystal grains from deflecting during sintering, ensuring the degree of orientation of the magnet and significantly improving the Br of the magnet.

[0068] Within the range of the Cu, Ga, and Al atomic concentration ratios of the present invention (i.e., 1≦[Cu2] / [Cu1]<2, 1≦[Ga2] / [Ga1]<2, 1<[Al2] / [Al1]<2), R2(Fe,M) 14 The formation of the B structure results in a relatively low M concentration at the grain boundaries where the main phase crystal grains meet, resulting in a relatively high Hcj while still maintaining a relatively high remanence. Furthermore, the diffusion process significantly improves Hcj, with the Tb diffusion achieving an Hcj of 880 kA / m or more, and the Dy diffusion achieving an Hcj of 480 kA / m or more. [Brief explanation of the drawings]

[0069] [Figure 1] FIG. 2 is a diagram showing the distribution of Cu in the magnet of Example 1. [Figure 2] FIG. 1 is a diagram showing the distribution of Cu in the magnet of Comparative Example 1.

[0070] [Mode for Carrying Out the Invention] The technical solutions of the present invention will be described in more detail below with reference to specific examples. It should be understood that the following examples are merely for illustrative purposes and should not be construed as limiting the scope of the claims of the present invention. Any technology realized based on the above content of the present invention is included within the scope of the claims of the present invention.

[0071] Unless otherwise specified, all raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0072] Examples 1 and 2 A method for manufacturing a neodymium iron boron magnet, the method comprising the steps of:

[0073] (a) Raw materials were prepared according to the target composition of the magnet in Table 1 below, and smelted using a vacuum induction smelting furnace under Ar gas atmosphere protection. The molten liquid was cast onto a quench roll rotating at a speed of 33 rpm so as to achieve a casting temperature of 1420°C (i.e., strip casting process), and a neodymium-iron-boron alloy sheet was obtained, with the target alloy sheet having an average thickness of 0.22 mm.

[0074] [Table 1]

[0075] (b) The alloy sheet was coarsely crushed by hydro-crushing to obtain powder, and zinc stearate (0.1 wt% of the raw material mass) was added to the powder as a lubricant and mixed for 60 min. The mixed material was then finely crushed in a fluidized bed jet mill using nitrogen gas as the grinding gas. By adjusting equipment parameters such as the rotation speed of the grading wheel and the grinding pressure, a jet-milled powder with a target particle size SMD = 2.5 μm (i.e., alloy powder) was obtained, with an X90 / X10 ratio of 4.2.

[0076] (c) To the jet mill powder of the target particle size obtained by production, zinc stearate was further added as a lubricant in an amount of 0.2 wt% of the raw material mass, and mixed for 120 min. After thorough mixing, the mixture was pressed into a billet with a magnetizing magnetic field strength of 2 T, and then subjected to isostatic pressing in an isostatic pressing machine at a pressure of 180 MPa for 15 s to improve the density of the billet and achieve a density of 4.3 g / cm. 3 The billet was obtained.

[0077] (d) The billet was placed in a sintering furnace and heated in a vacuum, then heated at 150°C and 260°C for 100 minutes each to remove the lubricant, then heated at 600°C and 900°C for 90 minutes each to remove gases, and then subjected to the three-stage sintering and heat-holding process shown in Table 2 below. After the third sintering and heat-holding stage, the billet was cooled directly to room temperature to obtain a sintered body. The specific three-stage sintering and heat-holding process is shown in Table 2 below, and after each sintering and heat-holding stage, the temperature was directly increased to the next heating process.

[0078] [Table 2]

[0079] (e) Secondary aging treatment: The above sintered body was taken, heated to 900°C and kept at that temperature for 180 minutes, then cooled to 200°C, and then further heated to 530°C and kept at that temperature for 240 minutes. After the temperature keeping was completed, the body was cooled to room temperature to obtain a magnet after aging treatment.

[0080] (f) The magnets after aging treatment were processed into sample columns with a standard φ10-10, and the performance of the magnets was measured using a BH device. The specific magnetic performance test results are shown in Table 3.

[0081] [Table 3]

[0082] The vertically oriented surfaces of the magnets produced in Examples 1 and 2 were polished, and the magnet crystal grain size was confirmed using a scanning electron microscope (SEM). The average crystal grain size within the field of view (×2000 magnification) was defined using Image-Pro Plus software analysis, with the maximum crystal grain size defined as the size of the largest crystal grain within the field of view. The number of crystal grains within the ×2000 magnification field of view was counted, and the field area was divided by the number of crystal grains to determine the unit crystal grain area. The crystal grain size was calculated using the circle area formula to determine the average crystal grain size. The crystal grain with the largest area within the field of view was taken, and the crystal grain size was calculated using the circle area formula to determine the maximum crystal grain size. The test results are shown in Table 4.

[0083] The distribution of each component within the magnet was analyzed using a field emission electron probe microanalyzer (FE-EPMA) (JEOL, 8530F). Line scans were performed across the main phase grains, the double grain boundaries, and the triangular grain boundaries to confirm and analyze the differences in the distribution concentrations of elements such as Cu, Ga, and Al in the above areas. The atomic concentrations of Cu, Ga, and Al at a position 0.5 μm inside the main phase grains from the double grain boundaries were defined as [Cu1], [Ga1], and [Al1], respectively. The atomic concentrations of Cu, Ga, and Al at the center of the double grain boundary between two main phase grains were defined as [Cu2], [Ga2], and [Al2], respectively. The average ratio of five pairs of adjacent main phase grains to the double grain boundaries within the field of view was defined as [Cu2] / [Cu1], and the concentration ratio between the two was used to confirm whether the Cu element was relatively uniformly distributed in the main phase grains and the double grain boundaries. In the triangular grain boundaries, the area where the Cu element concentration satisfies [Cu3] / [Cu1] ≥ 2 was defined as a Cu-rich area, and the ratio of the area of ​​the Cu-rich area to the total area of ​​the grain boundary phase was calculated using Image-Pro Plus software. The relative distributions of Ga and Al and the area occupancy of the enriched areas were analyzed using the same analytical method.

[0084] The distribution and structural characteristics of Cu, Ga, and Al measured by the above analytical methods are shown in Table 4 below.

[0085] [Table 4]

[0086] FIG. 1 shows the distribution of Cu in the magnet of Example 1. As can be seen from FIG. 1, Cu is distributed relatively uniformly in the surface layers of the main phase crystal grains and in the two-grain boundaries. Although Cu-rich regions exist in the triangular grain boundaries, the area occupancy of the Cu-rich regions is relatively small, and the concentration of Cu at the triangular grain boundaries is also relatively low.

[0087] Comparative Examples 1-2 (a) Raw materials were prepared according to the target magnet compositions in Table 5 below, and manufactured using a strip casting process to obtain neodymium-iron-boron alloy sheets. The target alloy sheet had an average thickness of 0.22 mm.

[0088] [Table 5]

[0089] The alloy sheet was pulverized and milled using the same process as in Examples 1 and 2, and the alloy powder was press-molded and sintered according to the three-stage temperature-rising and heat-retaining sintering process in Table 6 below. After each sintering and heat-retaining stage was completed, the temperature was raised directly to the next temperature-rising process, and after the third heat-retaining stage was completed, the material was cooled to room temperature and a sintered body was obtained.

[0090] Secondary aging treatment: The above sintered body was taken, heated to 900°C and kept at that temperature for 180 minutes, then cooled to 200°C, and then further heated to 530°C and kept at that temperature for 240 minutes. After the temperature keeping was completed, the body was cooled to room temperature to obtain a magnet after aging treatment.

[0091] [Table 6]

[0092] The magnetic properties were tested according to the above magnetic properties test method, and the test results are shown in Table 7. The magnet grain size test and element distribution test were also performed according to the above magnet grain size test and element distribution method, and the results are shown in Table 8.

[0093] [Table 7]

[0094] [Table 8]

[0095] *Since Ga and Al were not added to the magnet design composition of Comparative Example 2, "--" indicates that the component concentrations were not compared.

[0096] FIG. 2 shows the distribution of Cu in the magnet of Comparative Example 1. As can be seen from FIG. 2, the Cu concentration in the surface layers of the main phase crystal grains and the two-grain boundaries is relatively low. However, compared with FIG. 1, the relative concentration at the two-grain boundaries is still relatively high. Furthermore, the Cu-rich regions at the triangular grain boundaries have clearly increased, with a relatively high area occupancy rate. In other words, Cu is highly concentrated at the triangular grain boundaries.

[0097] Comparing Examples 1 and 2 with Comparative Examples 1 and 2, the Br of Comparative Example 2 was slightly improved compared to the Br of Examples 1 and 2, but the coercive force Hcj and squareness were significantly reduced. When the component elements of a magnet are within the ranges of the present invention, the overall performance of its Br and Hcj is superior, and it has an excellent squareness Hk / Hcj, ensuring a stable magnetic field output of the magnet.

[0098] Example 3 The difference between Example 3 and Example 1 was that the sintering process was carried out according to the three-stage temperature-rising and temperature-retaining sintering process shown in Table 9 below, and after each stage of sintering and temperature-retaining was completed, the material was cooled to 900°C, and then the next stage of temperature-rising was carried out in step (d).

[0099] [Table 9]

[0100] Comparative Example 3 The difference between Comparative Example 3 and Example 1 was that the sintering process was carried out according to the two-stage temperature increase and temperature retention sintering process shown in Table 10 below, and after the first stage of temperature retention was completed, the material was cooled to 400°C, and then a second stage of temperature increase was carried out in step (d).

[0101] [Table 10]

[0102] The magnets produced in Example 3 and Comparative Example 3 were subjected to magnetic performance tests and analyses of magnet crystal grain size and element distribution. The results of the magnetic performance tests are shown in Table 11, and the crystal grain size and element distribution are shown in Table 12.

[0103] [Table 11]

[0104] [Table 12]

[0105] Comparing Example 3 with Comparative Example 3, the use of the temperature-rising and temperature-holding sintering process of the present invention has a shorter cycle and better magnetic properties than the conventional two-stage sintering process, effectively suppressing abnormal growth of magnet crystal grains, and achieving uniform distribution of Cu, Ga, and Al elements in the main phase crystal grains and the two-grain grain boundaries, with reduced concentration at the triangular grain boundaries.

[0106] Compared to Example 1, Example 3 increases the number of steps in which, after each temperature increase and hold, the material is cooled to below 900°C after each temperature hold, and then the next temperature increase is performed. By using a sintering process that separates the temperature increase and decrease into three stages, abnormal growth of magnet crystal grains is further effectively suppressed and the magnet performance is slightly improved.

[0107] Example 4 The sintered and aged magnets from Example 3 were processed into sheet products measuring 20 mm in length, 20 mm in width, and 5 mm in thickness. A thin film of metallic Dy was applied to the magnet surface using a dip coating process, followed by a diffusion treatment at 900°C for 15 hours. After cooling to a temperature below 100°C, the diffusion temperature was further increased to 500°C and aging treatment was performed for 5 hours. The final magnets were subjected to magnetic performance testing, and the test results are shown in Table 13 below.

[0108] Comparative Example 4 The sintered and aged magnet from Comparative Example 3 was subjected to the same diffusion treatment process as in Example 4, namely, the magnet was processed into a sheet product 20 mm long, 20 mm wide, and 5 mm thick, and a thin film of metallic Dy was applied to the magnet surface using a dip coating process. The magnet was then subjected to a diffusion treatment at 900°C for 15 hours, cooled to below 100°C, and then further heated to 500°C for 5 hours of aging treatment. The final magnet was subjected to a magnetic performance test, and the test results are shown in Table 13 below.

[0109] [Table 13]

[0110] In Table 13, ΔBr and ΔHcj respectively indicate the Br amplification and Hcj amplification of Example 4 relative to Example 3, and the Br amplification and Hcj amplification of Comparative Example 4 relative to Comparative Example 3.

[0111] Comparing the results of Example 4 and Comparative Example 4, it was found that the magnets produced by the method of the present invention using the same diffusion process had better Hcj amplification, better final magnet performance, and a more suitable structure for diffusion.

[0112] Although the embodiments of the present invention have been described above as examples, the scope of the claims of the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc. made by those skilled in the art without departing from the spirit and principles of the present invention are also included within the scope of the claims of the present invention.

Claims

1. A neodymium-iron-boron magnet, The magnet is R ２ (Fe, M) １４ the alloy comprises main phase crystal grains and a grain boundary phase having a B structure, the grain boundary phase comprising a double grain boundary between two main phase crystal grains and a triangular grain boundary formed by gaps between three or more main phase crystal grains, wherein M comprises Cu, Ga, and Al, and R represents at least one rare earth element including Nd; The neodymium-iron-boron magnet is 100% by mass, 27-35% R and 0.8 to 1.2 wt% B, 0.5 to 3.0 wt% Co; 0.1 to 0.6 wt% Cu; 0.1 to 0.8 wt % Ga; 0.1 to 1.0 wt % Al; 60 to 72 wt % T; wherein R is at least one rare earth element including Nd, T includes Fe and other transition metal elements, as well as unavoidable impurity elements; the transition metal element is at least one of Mn, Si, Zr, Ti, and Nb; The average grain size of the main phase crystal grains of the magnet is 1.8 to 8 μm, The atomic concentration of Cu in adjacent main phase crystal grains is set to [Cu 1 ], and the atomic concentration of Cu at the grain boundary between the two grains is set to [Cu 2 ], and the relationship 1≦[Cu 2 ] / [Cu 1 ]<2 is satisfied; the atomic concentration of Ga in adjacent main phase crystal grains is set to [Ga 1 ], the atomic concentration of Ga at the grain boundary between the two grains is set to [Ga 2 ], and the relationship 1≦[Ga 2 ] / [Ga 1 ]<2 is satisfied; The atomic concentration of Al in adjacent main phase crystal grains is set to [Al 1 ], and the atomic concentration of Al at the two-grain boundary is set to [Al 2 ], and the relationship 1<[Al 2 ] / [Al 1 ]<2 is satisfied; Adjacent main phase grains refer to main phase grains adjacent to a two-grain boundary. Neodymium iron boron magnet.

2. 2. The neodymium-iron-boron magnet according to claim 1, wherein the average grain size of the main phase crystal grains of the magnet is 2.5 to 6 μm.

3. The triangular grain boundaries in the magnet contain Cu-rich regions, the atomic concentration of Cu at the triangular grain boundaries is set to [Cu 3 ], and the relationship [Cu 3 ] / [Cu 1 ]≧2 is satisfied; The triangular grain boundaries in the magnet contain Ga-rich regions, and the atomic concentration of Ga at the triangular grain boundaries is defined as [Ga ３ ] and set it to [Ga ３ ] / [Ga １ ]≧2, The triangular grain boundaries in the magnet contain Al-rich regions, the atomic concentration of Al at the triangular grain boundaries is set to [Al 3 ], and the relationship [Al 3 ] / [Al 1 ]≧2 is satisfied; 2. The neodymium-iron-boron magnet according to claim 1.

4. The ratio of the area of ​​the Cu-rich region of the triangular grain boundary to the total area of ​​the grain boundary phase is <5%, The grain boundary phase of the Ga-rich region is a non-ferromagnetic phase, and the ratio of the area of ​​the Ga-rich region of the triangular grain boundary to the total area of ​​the grain boundary phase is less than 5%; The ratio of the area of ​​the Al-rich region of the triangular grain boundary to the total area of ​​the grain boundary phase is <5%; 4. The neodymium-iron-boron magnet according to claim 3.

5. 2. A method for producing a neodymium-iron-boron magnet according to claim 1, (a) a smelting process in which the components of the magnet are melted, cast, and cooled to form an alloy sheet; (b) a milling process in which the alloy sheet is pulverized into alloy powder; (c) a press molding process in which the alloy powder is press molded under the action of a magnetic field to obtain a billet; (d) a sintering process for sintering, aging, and manufacturing the billet to obtain a neodymium-iron-boron magnet. A method characterized by:

6. In step (b), the SMD particle size of the alloy powder is 1.8-8 μm, and X90 / X10≦4.5; In step (d), the sintering process includes three or more sintering temperature-holding stages and a pre-sintering temperature-raising stage, and the temperature of the sintering temperature-holding stage is 950 to 1200°C; During each sintering step, the temperature rise rate is 0.5 to 5°C / min.

6. The method of claim 5.

7. In step (b), the SMD particle size of the alloy powder is 2.5 to 6 μm; In step (d), the sintering process includes 3 to 10 stages of sintering temperature-holding stages and pre-sintering temperature-raising stages, the temperature of the sintering temperature-holding stages is 980 to 1070°C, and the temperature-holding time of each stage is 20 to 120 minutes; During each sintering step, the temperature rise rate is 1 to 4°C / min. Between each two adjacent stages of sintering and temperature-keeping processes, the next temperature-raising and temperature-keeping process can be carried out directly after the previous stage of sintering and temperature-keeping process is completed, or the previous stage of sintering and temperature-keeping process can be cooled first and then the next temperature-raising and temperature-keeping process can be carried out after the previous stage of sintering and temperature-keeping process is completed, that is, any random process can be arranged between each two adjacent stages of sintering and temperature-keeping process.

7. The method of claim 6.

8. The aging treatment is selected from primary aging treatment or secondary aging treatment, The conditions of the primary aging treatment are that the aging treatment temperature is 500 to 700°C and the heat retention time is 240 to 420 minutes, The secondary aging treatment includes: performing a first aging treatment by increasing the temperature to 800 to 950°C and holding the temperature for 180 to 300 minutes; and performing a second aging treatment by cooling the steel to 200°C or less and then increasing the temperature to between 450 to 600°C and holding the temperature for 240 to 360 minutes.

6. The method of claim 5.

9. After the sintering process, a diffusion treatment may be performed, The diffusion treatment includes applying a diffusion material to the magnet surface, and performing a vacuum heating diffusion treatment, a diffusion cooling treatment, and a diffusion aging treatment; The diffusion material is at least one selected from the group consisting of pure metals of Dy and / or Tb, hydrides of Dy and / or Tb, oxides of Dy and / or Tb, hydroxides of Dy and / or Tb, and fluoride alloys of Dy and / or Tb.

6. The method of claim 5.

10. A motor equipped with the neodymium iron boron magnet according to claim 1. A motor characterized by:

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