Sintered neodymium-iron-boron magnet and preparation method thereof

Abstract

The invention provides a sintered neodymium-iron-boron magnet and a preparation method thereof. The sintered neodymium-iron-boron magnet comprises main phase crystal grains, a first crystal boundary and a second crystal boundary, the first crystal boundary and the second crystal boundary are adjacent to the main phase crystal grains, the second crystal boundary comprises an Nd2Fe15Ga2 crystal phase, and the atomic number percentage of rare earth elements in the first crystal boundary is larger than that of rare earth elements in the second crystal boundary. The Nd2Fe15Ga2 crystal phase in the second crystal boundary has high magnetic anisotropy energy, a magnetic domain wall can be effectively pinned, so that the coercive force of the magnet is improved, and good magnetic performance can still be kept in the presence of the Nd2Fe15Ga2 crystal phase. Compared with an Nd6Fe13Ga phase, the Nd2Fe15Ga2 crystal phase in the second grain boundary needs to consume more Fe elements and less rare earth elements, so that a rare earth-rich phase is formed in the first grain boundary, and the utilization efficiency of the rare earth elements is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of magnets, and in particular to a sintered NdFeB magnet and a preparation method thereof. Background Art

[0002] Sintered NdFeB magnets have high comprehensive magnetic properties and are widely used in electric motors for new energy vehicles and generator sets for wind power generation. The traditional way to improve the comprehensive magnetic properties of sintered NdFeB magnets is to add heavy rare earth elements to them, but heavy rare earth elements have disadvantages such as high prices and shortages. Therefore, in recent years, we have been exploring the preparation of sintered NdFeB magnets with high magnetic properties without using heavy rare earths. The current mainstream method is to prepare a low-B and high-Ga sintered magnet by adjusting the content of B and Ga elements in the alloy, and to adjust the content of Nd6Fe in the grain boundary phase of the magnet. 13 The generation and distribution of Ga phase are regulated to obtain magnets with high coercivity.

[0003] Currently regulating Nd6Fe 13 During the formation of the Ga phase, it tends to form in the triangular grain boundary region, causing the rare earth elements and Fe elements to be fixed in the triangular grain boundary region. The fixation of Fe elements in the triangular grain boundary region helps to reduce the ferromagnetism of the grain boundary phase and has a positive effect on the improvement of magnetic properties. However, the pinning of rare earth elements in the triangular grain boundary region reduces their mobility, resulting in a decrease in the proportion of rare earth elements entering the grain boundary phase between the main phase grains. This process reduces the utilization efficiency of rare earth elements. This means that there is still much room for improvement in the control of the grain boundary phase of Ga-containing magnets. Summary of the Invention

[0004] The main purpose of the present invention is to provide a sintered NdFeB magnet and a preparation method thereof, so as to solve the problem in the prior art that the utilization efficiency of rare earth elements in the sintered NdFeB magnet is low, resulting in low coercive force and remanence of the sintered NdFeB magnet.

[0005] In order to achieve the above object, according to one aspect of the present invention, a sintered NdFeB magnet is provided. The sintered NdFeB magnet comprises a main phase grain and a first grain boundary and a second grain boundary adjacent to the main phase grain. The second grain boundary comprises Nd2Fe 15 Ga2 crystal phase, and the atomic percentage of the rare earth element in the first grain boundary is greater than the atomic percentage of the rare earth element in the second grain boundary.

[0006] Furthermore, the element composition of the sintered NdFeB magnet includes, by mass percentage, 30.25-31.00% of R element, 0.8-1.0% of B element, 0.5-0.7% of Ga element, and the balance of T element; R element is a rare earth element, and T element is a transition metal element of Group VIII.

[0007] Furthermore, the above-mentioned R element is a combination of Nd element and a first element, and the mass ratio of Nd element to the first element is 1:(0.3~0.35); the first element is selected from any one or more of Pr element, La element and Ce element; and / or, the sintered NdFeB magnet also includes 0.01~0.4% of M element, M element is selected from any one or more of Group IIIA elements, Group IB elements, Group IVB elements, and Group VB elements, preferably M element is selected from any one or more of Cu element, Al element, Nb element and Zr element; and / or, T element is Fe element; or, T element is Fe element and Co element.

[0008] Furthermore, the elemental composition of the first grain boundary includes, by atomic percentage, 60-70% of R element, 15-17% of T element, 2-5% of Ga element and the balance of M element; and / or, the elemental composition of the second grain boundary includes, by atomic percentage, 18-22% of R element, 9-11% of Ga element and the balance of T element, and the second grain boundary includes Nd2Fe 15 Ga2 crystal phase; and / or, the elemental composition of the main phase grains includes 10 to 12% of R elements, 0.5 to 0.7% of Ga elements and the balance of T elements.

[0009] Furthermore, the average grain size of the main phase grains is 4 to 5 μm; and / or the average width of the first grain boundary is 10 to 12 nm.

[0010] According to another aspect of the present invention, a method for preparing the aforementioned sintered NdFeB magnet is provided, the method comprising: preparing metal raw materials according to the element types and mass ratios in the sintered NdFeB magnet to be prepared, and then sequentially performing smelting, rapid solidification, crushing, shaping, sintering and aging treatment to obtain the sintered NdFeB magnet; wherein the aging treatment temperature is 455-475°C and the aging treatment time is 2-5 hours.

[0011] Furthermore, the sintering temperature is 1070-1090° C.; and / or the sintering time is 5.5-7 hours.

[0012] Furthermore, the temperature of the sintering treatment is 595-615° C. higher than the temperature of the aging treatment.

[0013] Furthermore, the average thickness of the quick-setting product is 0.2-0.3 mm; and / or the average particle size of the crushed product is 2.9-3.3 μm; and / or the average density of the molded product is 3.5-4.0 g / cm 3 .

[0014] Furthermore, the sintering and aging treatments are carried out at a vacuum degree of less than 1.0×10 -3Paozhong carried out.

[0015] Applying the technical solution of the present invention, the Nd2Fe 15 Ga2 crystal phase has high magnetic anisotropy energy, which can effectively pin the magnetic domain wall, thereby increasing the coercive force of the magnet, and Nd2Fe 15 The existence of Ga2 crystal phase can still maintain good magnetic properties. 15 Ga2 crystal phase compared to Nd6Fe 13 The Ga phase consumes more Fe and fewer rare earth elements, and helps more rare earth elements enter the first grain boundary, forming a rare earth-rich phase in the first grain boundary, thereby helping to improve the utilization efficiency of rare earth elements and helping to reduce the iron content in the first grain boundary, which in turn helps to further improve the overall performance of the magnet. The atomic percentage of rare earth elements in the first grain boundary is greater than the atomic percentage of rare earth elements in the second grain boundary, which helps to promote the stability of the magnetic domain walls between grains, enhance the magnetic resistance of the grain boundary phase, and further improve the residual magnetic properties of the magnet. In addition, the improvement in the utilization rate of rare earth elements helps to reduce the content of rare earth elements in sintered NdFeB magnets, thereby helping to reduce the cost of sintered NdFeB magnets. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0017] Figure 1 shows the HADDF diagram of the first grain boundary in the magnet of Example 1 of the present application and the corresponding element distribution diagram;

[0018] Figure 2 shows the HADDF diagram of the second grain boundary in the magnet of Example 1 of the present application and the corresponding element distribution diagram;

[0019] Figure 3 shows the SAED pattern of the second grain boundary in the magnet of Example 1 of the present application;

[0020] Figure 4 shows the HADDF diagram of the second grain boundary in the magnet of Comparative Example 1 of the present application and the corresponding element distribution diagram;

[0021] Figure 5 The SAED pattern of the second grain boundary in the magnet of Comparative Example 1 of the present application is shown. DETAILED DESCRIPTION

[0022] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0023] As analyzed in the background technology of this application, the utilization efficiency of rare earth elements in sintered NdFeB magnets in the prior art is low, resulting in low coercivity and remanence of the sintered NdFeB magnets. In order to solve the above problems, this application provides a sintered NdFeB magnet and a preparation method thereof.

[0024] In a typical embodiment of the present application, a sintered NdFeB magnet is provided. The sintered NdFeB magnet includes a main phase grain and a first grain boundary and a second grain boundary adjacent to the main phase grain. The second grain boundary includes Nd2Fe 15 Ga2 crystal phase, and the atomic percentage of the rare earth element in the first grain boundary is greater than the atomic percentage of the rare earth element in the second grain boundary.

[0025] Nd2Fe in the second grain boundary of this application 15 Ga2 crystal phase has high magnetic anisotropy energy, which can effectively pin the magnetic domain wall, thereby increasing the coercive force of the magnet, and Nd2Fe 15 The existence of Ga2 crystal phase can still maintain good magnetic properties. 15 Ga2 crystal phase compared to Nd6Fe 13 The Ga phase consumes more Fe and fewer rare earth elements, and helps more rare earth elements enter the first grain boundary, forming a rare earth-rich phase in the first grain boundary, thereby helping to improve the utilization efficiency of rare earth elements and helping to reduce the iron content in the first grain boundary, which in turn helps to further improve the overall performance of the magnet. The atomic percentage of rare earth elements in the first grain boundary is greater than the atomic percentage of rare earth elements in the second grain boundary, which helps to promote the stability of the magnetic domain walls between grains, enhance the magnetic resistance of the grain boundary phase, and further improve the residual magnetic properties of the magnet. In addition, the improvement in the utilization rate of rare earth elements helps to reduce the content of rare earth elements in sintered NdFeB magnets, thereby helping to reduce the cost of sintered NdFeB magnets.

[0026] In one embodiment of the present application, the element composition of the above-mentioned sintered NdFeB magnet includes, by mass percentage: 30.25-31.00% of R element, 0.8-1.0% of B element, 0.5%-0.7% of Ga element, and the balance of T element; R element is a rare earth element, and T element is a transition metal element of Group VIII.

[0027] Controlling the content of R element within the above range helps to make the magnet maintain sufficient magnetic induction intensity and pass appropriate Nd2Fe 15The distribution of Ga2 phase improves the coercive force; controlling the content of Ga, B and T elements within the above range is helpful to regulate the phase in the grain boundary phase and promote the Nd2Fe 15 The formation of Ga2 phase helps to improve the overall magnetic properties.

[0028] In one embodiment of the present application, the above-mentioned R element is a combination of Nd element and a first element, and the mass ratio of Nd element to the first element is 1:(0.3~0.35); the first element is selected from any one or more of Pr element, La element and Ce element, and preferably the first element is Pr element; and / or, the sintered NdFeB magnet further includes 0.01~0.4% of M element, M element is selected from any one or more of Group IIIA elements, Group IB elements, Group IVB elements, and Group VB elements, and preferably M element is selected from any one or more of Cu element, Al element, Nb element and Zr element; and / or, T element is Fe element; or, T element is Fe element and Co element.

[0029] Controlling the mass ratio of Nd to the first element within the above range helps optimize the coercivity and remanence properties of the magnet. Pr increases coercivity, while Nd enhances remanence. The combination of the two enhances their synergistic effect, further improving the coercivity and remanence of the magnet. The addition of M further optimizes the properties of the grain boundary phase, promoting the formation of a non-magnetic, chemically stable grain boundary phase, thereby further improving the coercivity of the magnet.

[0030] In order to further improve the coercive force of the magnet, in one embodiment of the present application, the element composition of the above-mentioned sintered NdFeB magnet includes, by mass percentage: 30.25-31.00% of R element, 0.8-1.0% of B element, 0.5%-0.7% of Ga element, 67-67.16% of Fe element, 0.13-0.92% of Co element, 0.06% of Nb element, 0.05-0.15% of Zr element, 0.01-0.06% of Al element, and 0.05-0.1% of Cu element.

[0031] In one embodiment of the present application, the mass proportion of Fe element in the sintered NdFeB magnet is not less than 67%.

[0032] Fe is a ferromagnetic metal with a high saturation magnetization. Controlling the mass ratio of Fe in sintered NdFeB magnets within the above range helps to improve the remanence of the magnet.

[0033] In one embodiment of the present application, the elemental composition of the first grain boundary includes, by atomic percentage, 60-70% of R element, 15-17% of T element, 2-5% of Ga element, and the balance of M element; preferably, the atomic number of Fe element in the elemental composition of the first grain boundary is less than 10%; and / or, by atomic percentage, the elemental composition of the second grain boundary includes, by atomic percentage, 18-22% of R element, 9-11% of Ga element, and the balance of T element, and the second grain boundary includes Nd2Fe 15 Ga2 crystal phase; and / or, the elemental composition of the main phase grains includes 10 to 12% of R elements, 0.5 to 0.7% of Ga elements and the balance of T elements.

[0034] Controlling the concentration of the R element in the first grain boundary within the above range helps to improve the chemical stability of the first grain boundary, reduce oxidation inside the magnet, and at the same time improve the coercive force through the pinning mechanism and enhance the anti-demagnetization ability of the magnet. Controlling the concentration of the T element in the first grain boundary within the above range helps to reduce the magnetism inside the first grain boundary, thereby helping to improve the coercive force of the magnet. Controlling the concentration of the Ga element and the M element in the first grain boundary within the above range helps to optimize the structure of the first grain boundary phase and further improve the coercive force and residual magnetic properties. Controlling the concentration of the R element, Ga element and T element in the second grain boundary within the above range helps to form a stable Nd2Fe 15 Ga2 crystal phase, thus helping to improve the overall performance of the magnet. Controlling the concentration of each element in the main phase grains within the above range helps to further improve the remanence and coercive force of the magnet.

[0035] In one embodiment of the present application, the main phase grains are completely surrounded by the first grain boundary phase and the second grain boundary phase, wherein the first grain boundary is the grain boundary between two main phase grains, and wherein the second grain boundary is the grain boundary surrounded by more than three main phase grains.

[0036] In order to further improve the coercive force and remanence of the magnet, in one embodiment of the present application, the R element in the second grain boundary is composed of 13.2-15% of Nd element and 5.7-7% of Pr element in terms of atomic percentage.

[0037] In one embodiment of the present application, the average grain size of the main phase grains is 4-5 μm; and / or the average width of the first grain boundary is 10-12 nm.

[0038] By controlling the average grain size of the main phase grains and the average width of the first grain boundary within the above ranges, the microstructure of the magnet is optimized, thereby contributing to further improving the coercive force and remanence properties of the magnet.

[0039] By calculating Nd2Fe 15 The structure of Ga2 phase, the unit cell is a rhombohedral structure, the unit cell parameters are This phase is a ferrimagnetic phase with a total magnetization intensity of 31.24 μB / fu, and the number of Ga atoms in the structure is located at the 18h position in the crystal structure.

[0040] In one embodiment of the present application, the coercive force of the sintered NdFeB magnet is 16.35-17.57 kOe; and / or the remanence of the sintered NdFeB magnet is 13.01-13.46 kGs.

[0041] In another typical embodiment of the present application, a method for preparing the aforementioned sintered NdFeB magnet is provided, the preparation method comprising: preparing metal raw materials according to the element types and mass ratios in the sintered NdFeB magnet to be prepared, and then sequentially performing smelting, rapid solidification, crushing, shaping, sintering and aging treatment to obtain a sintered NdFeB magnet; wherein the aging treatment temperature is 455-475°C, and the aging treatment time is 2-5 hours.

[0042] Controlling the temperature and time of aging treatment within the above range is helpful to 15 The formation of Ga2 crystal phases results in heavy rare earth-free magnets with high magnetic properties. This process reduces the amount of rare earths used in the formulation, simplifies the process flow, and lowers the production cost of heavy rare earth-free magnets. It also improves the efficiency of rare earth element utilization in the existing preparation of high-performance heavy rare earth-free magnets.

[0043] In one embodiment of the present application, the temperature of the sintering treatment is 1070-1090° C.; and / or the time of the sintering treatment is 5.5-7 hours.

[0044] Controlling the temperature and time of the sintering treatment within the above ranges helps to promote the diffusion of various elements and control the size of the main phase grains within an appropriate range, thereby helping to improve the coercive force and remanent magnetic properties of the magnet.

[0045] In order to further promote Nd2Fe 15 The formation of Ga2 crystal phase improves the coercive force and remanent magnetic properties of the magnet. In one embodiment of the present application, the temperature of the above-mentioned sintering treatment is 595-615°C higher than the temperature of the aging treatment.

[0046] In one embodiment of the present application, the average thickness of the quick-setting product is 0.2-0.3 mm; and / or the average particle size of the crushed product is 2.9-3.3 μm; and / or the average density of the molded product is 3.5-4.0 g / cm 3 .

[0047] Controlling the average thickness of the rapid-solidification product within the above range helps to quickly freeze the alloy's microstructure during solidification, thereby helping to improve the uniformity of the alloy's composition. Controlling the average particle size of the crushed product within the above range facilitates a more uniform density distribution during the forming stage, reducing the porosity within the material and improving the density and consistency of the magnet. Controlling the average density of the molded product within the above range helps to improve the mechanical strength and magnetic properties of the magnet.

[0048] In order to improve the purity of the magnet, in one embodiment of the present application, the above sintering and aging treatments are carried out at a vacuum degree of less than 1.0×10 -3 Paozhong carried out.

[0049] The beneficial effects of the present application will be further illustrated below with reference to examples.

[0050] Example 1

[0051] Step 1: Calculate by mass percentage according to the composition ratio R 30.25 B 0.9 Fe 67.16 Co 0.82 Nb 0.06 Zr 0.15 Al 0.06 Cu 0. 1Ga 0.5 The ingredients are prepared, the R elements are Nd elements and Pr elements, and the mass ratio of Nd elements to Pr elements is 1:0.33. Under vacuum, a quick-setting thin sheet with an average thickness of 0.25 mm is obtained through a melting furnace.

[0052] Step 2: Place the quick-setting sheet in a hydrogen crushing furnace for hydrogen crushing and dehydrogenation to obtain coarse particle powder with a particle size of millimeter level.

[0053] Step 3: The coarse powder particles are subjected to air flow milling to obtain fine powder with an average particle size of 3.0 μm.

[0054] Step 4: Orient the obtained fine powder in a press with a magnetic field strength greater than 1.5T to obtain an average density of 3.7g / cm 3 magnet blanks.

[0055] Step 5: When the vacuum degree is lower than 0.1×10 -4The blank was sintered at 1070°C for 5.5 h under a temperature of 1070°C. The blank was then aged at 465°C for 2 h. The sintering temperature was 605°C higher than the aging temperature. Argon was introduced into the blank for furnace cooling to obtain a sintered NdFeB magnet. The sintered NdFeB magnet included main phase grains, first grain boundaries, and second grain boundaries. The specimens were characterized by a transmission electron microscope (TEM) (Talos F200X). G2) measured the atomic ratios of the elements in the main phase grains, the first grain boundaries and the second grain boundaries. Calculated by the atomic percentage of the first grain boundary, the element composition of the first grain boundary included 16.01% Fe, 15.92% Cu, 2.46% Ga, 26.33% Pr and 39.28% Nd; calculated by the atomic percentage of the second grain boundary, the element composition of the second grain boundary included 5.7% Pr, 13.2% Nd, 9.5% Ga, 1.4% Co and 70.2% Fe; calculated by the atomic percentage of the main phase grains, the element composition of the main phase grains included 85.71% Fe, 1.83% Co, 0.7% Cu, 0.56% Ga, 4.02% Pr and 7.18% Nd. The results were obtained by transmission electron microscopy (TEM) (Talos F200XG2) measured the grain size of the main phase grains and the width of the first grain boundary, and calculated the average grain size of the main phase grains and the average width of the first grain boundary. The average grain size of the main phase grains was 4.68 μm; the average width of the first grain boundary was 10.01 nm.

[0056] Example 2

[0057] The difference from Example 1 is that the mass proportion of Ga element in the ingredients is 0.7%, the mass proportion of Zr element is 0.05%, the mass proportion of Al element is 0.01%, and the mass proportion of Cu element is 0.05%;

[0058] Step 1: Calculate by mass percentage according to the composition ratio R 30.25 B 0.9 Fe 67.16 Co 0.82 Nb 0.06 Zr 0.05 Al 0.01 Cu 0.05 Ga 0.7 The ingredients are prepared, the R elements are Nd elements and Pr elements, and the mass ratio of Nd elements to Pr elements is 1:0.33. Under vacuum, a quick-setting thin sheet with an average thickness of 0.25 mm is obtained through a melting furnace.

[0059] Step 2: Place the quick-setting sheet in a hydrogen crushing furnace for hydrogen crushing and dehydrogenation to obtain coarse particle powder with a particle size of millimeter level.

[0060] Step 3: The coarse powder particles are subjected to air flow milling to obtain fine powder with an average particle size of 3.0 μm.

[0061] Step 4: Orient the obtained fine powder in a press with a magnetic field strength greater than 1.5T to obtain an average density of 3.7g / cm 3 magnet blanks.

[0062] Step 5: When the vacuum degree is lower than 0.1×10 -4 The obtained blank was sintered under Pa at a temperature of 1070°C for 5.5 hours, then aged at 465°C for 2 hours, and finally cooled with the passage of argon to obtain a sintered NdFeB magnet.

[0063] Example 3

[0064] The difference from Example 1 is that the mass proportion of Ga element in the ingredients is 0.8%, the mass proportion of Zr element is 0.05%, the mass proportion of Al element is 0.01%, the mass proportion of Cu element is 0.05%, and the mass proportion of Co element is 0.72%;

[0065] Step 1: Calculate by mass percentage according to the composition ratio R 30.25 B 0.9 Fe 67.16 Co 0.72 Nb 0.06 Zr 0.05 Al 0.01 Cu 0.05 Ga 0.8 The ingredients are prepared, the R elements are Nd elements and Pr elements, and the mass ratio of Nd elements to Pr elements is 1:0.33. Under vacuum, a quick-setting thin sheet with an average thickness of 0.25 mm is obtained through a melting furnace.

[0066] Step 2: Place the quick-setting sheet in a hydrogen crushing furnace for hydrogen crushing and dehydrogenation to obtain coarse particle powder with a particle size of millimeter level.

[0067] Step 3: The coarse powder particles are subjected to air flow milling to obtain fine powder with an average particle size of 3.0 μm.

[0068] Step 4: Orient the obtained fine powder in a press with a magnetic field strength greater than 1.5T to obtain an average density of 3.7g / cm 3 magnet blanks.

[0069] Step 5: When the vacuum degree is lower than 0.1×10 -4The obtained blank was sintered under Pa at a temperature of 1070°C for 5.5 hours, then aged at 465°C for 2 hours, and finally cooled with the passage of argon to obtain a sintered NdFeB magnet.

[0070] Example 4

[0071] The difference from Example 1 is that the mass proportion of the B element in the ingredients is 0.8%, and the mass proportion of the Co element is 0.92%;

[0072] Step 1: Calculate by mass percentage according to the composition ratio R 30.25 B 0.8 Fe 67.16 Co 0.92 Nb 0.06 Zr 0.15 Al 0.06 Cu 0. 1Ga 0.5 The ingredients are prepared, the R elements are Nd elements and Pr elements, and the mass ratio of Nd elements to Pr elements is 1:0.33. Under vacuum, a quick-setting thin sheet with an average thickness of 0.25 mm is obtained through a melting furnace.

[0073] Step 2: Place the quick-setting sheet in a hydrogen crushing furnace for hydrogen crushing and dehydrogenation to obtain coarse particle powder with a particle size of millimeter level.

[0074] Step 3: The coarse powder particles are subjected to air flow milling to obtain fine powder with an average particle size of 3.0 μm.

[0075] Step 4: Orient the obtained fine powder in a press with a magnetic field strength greater than 1.5T to obtain an average density of 3.7g / cm 3 magnet blanks.

[0076] Step 5: When the vacuum degree is lower than 0.1×10 -4 The obtained blank was sintered under Pa at a temperature of 1070°C for 5.5 hours, then aged at 465°C for 2 hours, and finally cooled with the passage of argon to obtain a sintered NdFeB magnet.

[0077] Example 5

[0078] The difference from Example 1 is that the mass proportion of the B element in the ingredients is 1.0%, and the mass proportion of the Co element is 0.72%;

[0079] Step 1: Calculate by mass percentage according to the composition ratio R 30.25 B 1.0 Fe 67.16 Co 0.72 Nb 0.06 Zr0.15 Al 0.06 Cu 0. 1Ga 0.5 The ingredients are prepared, the R elements are Nd elements and Pr elements, and the mass ratio of Nd elements to Pr elements is 1:0.33. Under vacuum, a quick-setting thin sheet with an average thickness of 0.25 mm is obtained through a melting furnace.

[0080] Step 2: Place the quick-setting sheet in a hydrogen crushing furnace for hydrogen crushing and dehydrogenation to obtain coarse particle powder with a particle size of millimeter level.

[0081] Step 3: The coarse powder particles are subjected to air flow milling to obtain fine powder with an average particle size of 3.0 μm.

[0082] Step 4: Orient the obtained fine powder in a press with a magnetic field strength greater than 1.5T to obtain an average density of 3.7g / cm 3 magnet blanks.

[0083] Step 5: When the vacuum degree is lower than 0.1×10 -4 The obtained blank was sintered under Pa at a temperature of 1070°C for 5.5 hours, then aged at 465°C for 2 hours, and finally cooled with the passage of argon to obtain a sintered NdFeB magnet.

[0084] Example 6

[0085] The difference from Example 1 is that the mass proportion of the B element in the ingredients is 1.1%, and the mass proportion of the Co element is 0.62%;

[0086] Step 1: Calculate by mass percentage according to the composition ratio R 30.25 B 1.1 Fe 67.16 Co 0.62 Nb 0.06 Zr 0.15 Al 0.06 Cu 0. 1Ga 0.5 The ingredients are prepared, the R elements are Nd elements and Pr elements, and the mass ratio of Nd elements to Pr elements is 1:0.33. Under vacuum, a quick-setting thin sheet with an average thickness of 0.25 mm is obtained through a melting furnace.

[0087] Step 2: Place the quick-setting sheet in a hydrogen crushing furnace for hydrogen crushing and dehydrogenation to obtain coarse particle powder with a particle size of millimeter level.

[0088] Step 3: The coarse powder particles are subjected to air flow milling to obtain fine powder with an average particle size of 3.0 μm.

[0089] Step 4: Orient the obtained fine powder in a press with a magnetic field strength greater than 1.5T to obtain an average density of 3.7g / cm 3 magnet blanks.

[0090] Step 5: When the vacuum degree is lower than 0.1×10 -4 The obtained blank was sintered under Pa at a temperature of 1070°C for 5.5 hours, then aged at 465°C for 2 hours, and finally cooled with the passage of argon to obtain a sintered NdFeB magnet.

[0091] Example 7

[0092] The difference from Example 1 is that the mass proportion of the R element in the ingredients is 31.00%, the mass proportion of the Fe element is 67%, and the mass proportion of the Co element is 0.13;

[0093] Step 1: Calculate by mass percentage according to the composition ratio R 31.00 B 1.0 Fe 67 Co 0.13 Nb 0.06 Zr 0.15 Al 0.06 Cu 0.1 Ga 0.5 The ingredients are prepared, the R elements are Nd elements and Pr elements, and the mass ratio of Nd elements to Pr elements is 1:0.33. Under vacuum, a quick-setting thin sheet with an average thickness of 0.25 mm is obtained through a melting furnace.

[0094] Step 2: Place the quick-setting sheet in a hydrogen crushing furnace for hydrogen crushing and dehydrogenation to obtain coarse particle powder with a particle size of millimeter level.

[0095] Step 3: The coarse powder particles are subjected to air flow milling to obtain fine powder with an average particle size of 3.0 μm.

[0096] Step 4: Orient the obtained fine powder in a press with a magnetic field strength greater than 1.5T to obtain an average density of 3.7g / cm 3 magnet blanks.

[0097] Step 5: When the vacuum degree is lower than 0.1×10 -4 The obtained blank was sintered under Pa at a temperature of 1070°C for 5.5 hours, then aged at 465°C for 2 hours, and finally cooled with the passage of argon to obtain a sintered NdFeB magnet.

[0098] Example 8

[0099] The difference from Example 1 is that the mass proportion of the R element in the ingredients is 30.15%, and the mass proportion of the Co element is 0.92;

[0100] Step 1: Calculate by mass percentage according to the composition ratio R 30.15 B 0.9 Fe 67.16 Co 0.92 Nb 0.06 Zr 0.15 Al 0.06 Cu 0. 1Ga 0.5 The ingredients are prepared, the R elements are Nd elements and Pr elements, and the mass ratio of Nd elements to Pr elements is 1:0.33. Under vacuum, a quick-setting thin sheet with an average thickness of 0.25 mm is obtained through a melting furnace.

[0101] Step 2: Place the quick-setting sheet in a hydrogen crushing furnace for hydrogen crushing and dehydrogenation to obtain coarse particle powder with a particle size of millimeter level.

[0102] Step 3: The coarse powder particles are subjected to air flow milling to obtain fine powder with an average particle size of 3.0 μm.

[0103] Step 4: Orient the obtained fine powder in a press with a magnetic field strength greater than 1.5T to obtain an average density of 3.7g / cm 3 magnet blanks.

[0104] Step 5: When the vacuum degree is lower than 0.1×10 -4 The obtained blank was sintered under Pa at a temperature of 1070°C for 5.5 hours, then aged at 465°C for 2 hours, and finally cooled with the passage of argon to obtain a sintered NdFeB magnet.

[0105] Example 9

[0106] The difference from Example 1 is that the mass proportion of the R element in the ingredients is 31.00%, the mass proportion of the Fe element is 67%, and the mass proportion of the Co element is 0.13;

[0107] Step 1: Calculate by mass percentage according to the composition ratio R 31.00 B 1.0 Fe 67 Co 0.13 Nb 0.06 Zr 0.15 Al 0.06 Cu 0.1 Ga 0.5The ingredients are prepared, the R elements are Nd elements and Pr elements, and the mass ratio of Nd elements to Pr elements is 1:0.33. Under vacuum, a quick-setting thin sheet with an average thickness of 0.25 mm is obtained through a melting furnace.

[0108] Step 2: Place the quick-setting sheet in a hydrogen crushing furnace for hydrogen crushing and dehydrogenation to obtain coarse particle powder with a particle size of millimeter level.

[0109] Step 3: The coarse powder particles are subjected to air flow milling to obtain fine powder with an average particle size of 3.0 μm.

[0110] Step 4: Orient the obtained fine powder in a press with a magnetic field strength greater than 1.5T to obtain an average density of 3.7g / cm 3 magnet blanks.

[0111] Step 5: When the vacuum degree is lower than 0.1×10 -4 The obtained blank was sintered under Pa at a temperature of 1070°C for 5.5 hours, then aged at 465°C for 2 hours, and finally cooled with the passage of argon to obtain a sintered NdFeB magnet.

[0112] Example 10

[0113] The difference from Example 1 is that the mass ratio of the Nd element to the Pr element is 1:0.3, and a sintered NdFeB magnet is finally obtained.

[0114] Example 11

[0115] The difference from Example 1 is that the mass ratio of the Nd element to the Pr element is 1:0.35, and a sintered NdFeB magnet is finally obtained.

[0116] Example 12

[0117] The difference from Example 1 is that the mass ratio of the Nd element to the Pr element is 1:0.4, and a sintered NdFeB magnet is finally obtained.

[0118] Example 13

[0119] The difference from Example 1 is that the temperature of the aging treatment is 475° C., and the temperature of the sintering treatment is 595° C. higher than the temperature of the aging treatment, and finally a sintered NdFeB magnet is obtained.

[0120] Example 14

[0121] The difference from Example 1 is that the sintering temperature is 1080° C., which is 615° C. higher than the aging temperature, and finally a sintered NdFeB magnet is obtained.

[0122] Example 15

[0123] The difference from Example 1 is that the sintering temperature is 1090° C., which is 625° C. higher than the aging temperature, and finally a sintered NdFeB magnet is obtained.

[0124] Comparative Example 1

[0125] The difference from Example 1 is that the aging treatment is cancelled, and a sintered NdFeB magnet is finally obtained. The sintered NdFeB magnet includes main phase grains, a first grain boundary and a second grain boundary. In terms of atomic percentage of the first grain boundary, the elemental composition of the first grain boundary includes 47.6% Fe element, 24.53% Nd element, 17.62% Pr element, 2.46% Ga element, 4.55% Cu element and 3.24% Co element; in terms of atomic percentage of the second grain boundary, the elemental composition of the second grain boundary includes 20.7% P r element, 34.2% Nd element, 34.9% Ga element, 1.0% Co element, 4.3% Fe element and 4.9% Cu element; in terms of the percentage of the number of atoms of the main phase grains, the elemental composition of the main phase grains includes 86.20% Fe element, 0.92% Co element, 0.3% Cu element, 0.66% Ga element, 4.56% Pr element and 7.36% Nd element, the average grain size of the main phase grains is 5.21μm; the average width of the first grain boundary is 2.0nm.

[0126] Comparative Example 2

[0127] The difference from Example 1 is that the aging treatment temperature is 450°C, and a sintered NdFeB magnet is finally obtained. The sintered NdFeB magnet includes main phase grains, a first grain boundary and a second grain boundary. In terms of the atomic percentage of the first grain boundary, the element composition of the first grain boundary includes 54.30% Fe element, 19.43% Nd element, 17.58% Pr element, 2.16% Ga element, 4.52% Cu element and 2.01% Co element; in terms of the atomic percentage of the second grain boundary, the element composition of the second grain boundary includes The main phase grains are composed of 20.7% Pr, 34.2% Nd, 34.9% Ga, 4.3% Co and 5.9% Fe elements; in terms of the percentage of the number of atoms of the main phase grains, the elemental composition of the main phase grains includes 87.20% Fe, 1.92% Co, 0.5% Cu, 0.34% Ga, 4.56% Pr and 5.48% Nd elements; the average grain size of the main phase grains is 5.02 μm; the average width of the first grain boundary is 5.3 nm.

[0128] Comparative Example 3

[0129] The difference from Example 1 is that the aging treatment temperature is 510°C, and a sintered NdFeB magnet is finally obtained. The sintered NdFeB magnet includes main phase grains, a first grain boundary and a second grain boundary. In terms of atomic percentage of the first grain boundary, the elemental composition of the first grain boundary includes 53.78% Fe element, 20.33% Nd element, 18.72% Pr element, 1.96% Ga element, 3.95% Cu element and 1.26% Co element; in terms of atomic percentage of the second grain boundary, the elemental composition of the second grain boundary includes 18.58% Pr element, 34.44% Nd element, 2.03% Ga element, 1.17% Co element and 43.78% Fe element; in terms of the percentage of the number of atoms of the main phase grains, the elemental composition of the main phase grains includes 86.52% Fe element, 2.01% Co element, 1.0% Cu element, 0.39% Ga element, 4.76% Pr element and 5.32% Nd element, the average grain size of the main phase grains is 4.72μm; the average width of the first grain boundary is 8.7nm.

[0130] Performance Testing

[0131] Coercivity and remanence were measured at room temperature using a NIM-62000 instrument manufactured by the China Institute of Metrology. All test samples were polished cubes measuring 8mm x 8mm x 4mm. When using the NIM-62000, the samples were first saturated with a 5T pulsed magnetic field.

[0132] The coercive force and remanence of the sintered NdFeB magnets prepared in the examples and comparative examples were tested. The test results are shown in Table 1.

[0133] Table 1

[0134]

[0135]

[0136] Figure 1 The HADDF diagram of the first grain boundary in the magnet of Example 1 of the present application and the corresponding element distribution diagram, wherein Figure (1a) is the HADDF diagram of the first grain boundary, Figure (1b) is the Fe element distribution diagram, Figure (1c) is the Ga element distribution diagram, Figure (1d) is the Cu element distribution diagram, Figure (1e) is the Nd element distribution diagram, and Figure (1f) is the Pr element distribution diagram. Figure 1 It can be seen that the first grain boundary is enriched with Cu and Ga elements.

[0137] Figure 2The HADDF diagram of the second grain boundary in the magnet of Example 1 of the present application and the corresponding element distribution diagram, wherein, from top to bottom, they are the HADDF diagram of the second grain boundary, the Fe element distribution diagram, the Ga element distribution diagram, the Nd element distribution diagram, and the Pr element distribution diagram; Figure 3 is the SAED pattern of the second grain boundary in the magnet of Example 1 of the present application; Figure 2 and Figure 3 It can be seen that the second grain boundary contains Nd2Fe 15 Ga2 crystal phase.

[0138] Figure 4 The HADDF diagram of the second grain boundary in the magnet of Comparative Example 1 of the present application and the corresponding element distribution diagram, wherein Figure (4a) is the HADDF diagram of the second grain boundary, and Figure (4a) is the distribution diagram of Fe, Ga, Nd and Pr elements;

[0139] Figure 5 This is the SAED pattern of the second grain boundary in the magnet of Comparative Example 1 of the present application, Figure 4 and Figure 5 It can be seen that the second grain boundary in comparison column 1 mainly contains an amorphous rare earth-rich Ga-containing phase.

[0140] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0141] Nd2Fe in the second grain boundary of this application 15 Ga2 crystal phase has high magnetic anisotropy energy, which can effectively pin the magnetic domain wall, thereby increasing the coercive force of the magnet, and Nd2Fe 15 The existence of Ga2 crystal phase can still maintain good magnetic properties. 15 Ga2 crystal phase compared to Nd6Fe 13 The Ga phase consumes more Fe and fewer rare earth elements, and helps more rare earth elements enter the first grain boundary, forming a rare earth-rich phase in the first grain boundary, thereby helping to improve the utilization efficiency of rare earth elements and helping to reduce the iron content in the first grain boundary, which in turn helps to further improve the overall performance of the magnet. The atomic percentage of rare earth elements in the first grain boundary is greater than the atomic percentage of rare earth elements in the second grain boundary, which helps to promote the stability of the magnetic domain walls between grains, enhance the magnetic resistance of the grain boundary phase, and further improve the residual magnetic properties of the magnet. In addition, the improvement in the utilization rate of rare earth elements helps to reduce the content of rare earth elements in sintered NdFeB magnets, thereby helping to reduce the cost of sintered NdFeB magnets.

[0142] The above are merely embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A sintered NdFeB magnet, characterized in that: The sintered NdFeB magnet includes a main phase grain and a first grain boundary and a second grain boundary adjacent to the main phase grain, wherein the second grain boundary includes Nd2Fe 15 Ga2 crystal phase, and the atomic percentage of the rare earth element in the first grain boundary is greater than the atomic percentage of the rare earth element in the second grain boundary.

2. The sintered NdFeB magnet according to claim 1, wherein The element composition of the sintered NdFeB magnet includes, by mass percentage, 30.25-31.00% of R element, 0.8-1.0% of B element, 0.5-0.7% of Ga element, and the balance of T element; The R element is a rare earth element, and the T element is a transition metal element of Group VIII.

3. The sintered NdFeB magnet according to claim 2, wherein The R element is a combination of an Nd element and a first element, and the mass ratio of the Nd element to the first element is 1:(0.3-0.35); the first element is selected from any one or more of a Pr element, a La element, and a Ce element; And / or, the sintered NdFeB magnet further comprises 0.01-0.4% of an M element, wherein the M element is selected from any one or more of Group IIIA elements, Group IB elements, Group IVB elements, and Group VB elements, and preferably, the M element is selected from any one or more of Cu elements, Al elements, Nb elements, and Zr elements; And / or, the T element is Fe; or, the T element is Fe and Co.

4. The sintered NdFeB magnet according to claim 3, wherein Measured in atomic percentage, the elemental composition of the first grain boundary includes 60-70% of R element, 15-17% of T element, 2-5% of Ga element and the balance of M element; And / or, in terms of atomic percentage, the elemental composition of the second grain boundary includes 18-22% of R element, 9-11% of Ga element and the balance of T element, and the second grain boundary includes the Nd2Fe 15 Ga2 crystal phase; And / or, the element composition of the main phase grains includes 10-12% of R element, 0.5-0.7% of Ga element and the balance of T element.

5. The sintered NdFeB magnet according to any one of claims 1 to 4, characterized in that The average grain size of the main phase grains is 4 to 5 μm; and / or the average width of the first grain boundaries is 10 to 12 nm.

6. A method for preparing a sintered NdFeB magnet according to any one of claims 1 to 5, characterized in that: The preparation method comprises: The metal raw materials are prepared according to the element types and mass ratios in the sintered NdFeB magnet to be prepared, and then smelting, rapid solidification, crushing, shaping, sintering and aging treatment are carried out in sequence to obtain the sintered NdFeB magnet; wherein the temperature of the aging treatment is 455-475°C, and the time of the aging treatment is 2-5 hours.

7. The preparation method according to claim 6, characterized in that The sintering temperature is 1070-1090° C.; and / or the sintering time is 5.5-7 hours.

8. The preparation method according to claim 6 or 7, characterized in that The temperature of the sintering treatment is 595-615° C. higher than the temperature of the aging treatment.

9. The preparation method according to any one of claims 6 to 8, characterized in that The average thickness of the quick-setting product is 0.2-0.3 mm; and / or the average particle size of the crushed product is 2.9-3.3 μm; and / or the average density of the molded product is 3.5-4.0 g / cm 3 .

10. The preparation method according to any one of claims 6 to 9, characterized in that The sintering and aging treatments were performed at a vacuum degree of less than 1.0×10 -3 Paozhong carried out.

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