Neodymium-iron-boron magnet and preparation method thereof

Abstract

The invention discloses a neodymium iron boron magnet and a preparation method thereof. The neodymium-iron-boron magnet I comprises main phase crystal grains, a triangular crystal boundary region and a two-particle crystal boundary region, and the main phase crystal grains, the triangular crystal boundary region and the two-particle crystal boundary region all comprise MB2 particles; m is selected from one or more of Nb, Zr and Ti; the MB2 particles in the triangular grain boundary region account for less than 90% of the MB2 particles in the neodymium-iron-boron magnet I in quantity; the number ratio of the MB2 particles in the two-particle grain boundary region to the MB2 particles in the neodymium iron boron magnet I is greater than 10%; the number ratio of the two-particle grain boundary region to MB2 particles in the neodymium-iron-boron magnet I is greater than 5%; and the content of M in the neodymium-iron-boron magnet I is 0.1 wt%-1.5 wt%. The neodymium-iron-boron magnet I and the neodymium-iron-boron magnet II both have excellent residual magnetism, coercive force and squareness and are high in flexibility in the aspects of composition and performance adjustment, and the neodymium-iron-boron magnet I can effectively improve the grain boundary diffusion effect and improve the utilization rate of heavy rare earth.

Description

Technical Field

[0001] The invention relates to a neodymium iron boron magnet and a preparation method thereof. Background Art

[0002] Neodymium iron boron (NdFeB) permanent magnets are among the most advanced permanent magnet materials currently available, finding widespread application in new energy vehicle main drive motors, industrial motors, and various household appliances. The trend toward miniaturization and lightweighting of motors places higher demands on the magnetic properties of NdFeB permanent magnets. Therefore, the continuous search for new methods and technologies to manufacture high-performance NdFeB permanent magnets and improve their magnetic properties and temperature characteristics is of great significance.

[0003] Heavy rare earth (HRE) grain boundary diffusion effectively increases the coercivity of magnets and is currently the primary method for producing the high-temperature magnets required for permanent magnet motors. The HRE diffusion process involves multiple diffusion mechanisms, leading to a significant concentration of HRE on the magnet surface, forming an excessively thick shell around the primary phase grains near the magnet surface. This results in a significant waste of the valuable HRE diffusion source, a significant decrease in the magnet's remanence, insufficient coercivity improvement, and compromised overall magnetic properties. Summary of the Invention

[0004] In order to solve the above-mentioned problems in grain boundary diffusion technology, the present invention proposes a NdFeB magnet and a preparation method thereof. Both NdFeB magnet I and NdFeB magnet II have excellent remanence, coercive force and squareness, and are highly flexible in composition and performance adjustment. In addition, NdFeB magnet I can effectively improve the effect of grain boundary diffusion and increase the utilization rate of heavy rare earth.

[0005] The present invention discloses a neodymium iron boron magnet I, which includes main phase grains, triangular grain boundary regions and two-grain grain boundary regions, wherein the main phase grains, the triangular grain boundary regions and the two-grain grain boundary regions all include MB2 particles; M is one or more selected from Nb, Zr and Ti;

[0006] The MB2 particles in the triangular grain boundary region account for less than 90% of the MB2 particles in the NdFeB magnet 1; the MB2 particles in the two-particle grain boundary region and the main phase grains account for more than 10% of the MB2 particles in the NdFeB magnet 1; the MB2 particles in the two-particle grain boundary region account for more than 5% of the MB2 particles in the NdFeB magnet 1;

[0007] The content of M in the NdFeB magnet I is 0.1wt%-1.5wt%, where the content refers to the mass percentage of the element in the NdFeB magnet I.

[0008] The main phase grains, triangular grain boundary regions and two-grain grain boundary regions in the present invention are all conventionally defined in the art. A two-grain grain boundary region is a region formed between two adjacent main phase grains, and a triangular grain boundary region is a region formed between three or more main phase grains.

[0009] After repeated studies, the inventors discovered that by regulating the number of MB2 particles in triangular grain boundaries and two-particle grain boundaries, the remanence, coercivity, and squareness of NdFeB magnets can be significantly improved. Furthermore, the use of the NdFeB magnet I of the present invention can enhance the effectiveness of grain boundary diffusion. This is likely because the MB2 particles in the grain boundaries can expand the channels for grain boundary diffusion, increasing the diffusion rate of heavy rare earth elements. Furthermore, the MB2 particles at the edges of the main phase grains can suppress the thickness of the heavy rare earth shell formed on the surface of the main phase grains, thereby improving the utilization rate of the heavy rare earth elements.

[0010] In the present invention, the number of MB2 particles in the triangular grain boundary region preferably accounts for 50%-80% of the total number of MB2 particles in the NdFeB magnet I, for example, 68%, 74% or 78%.

[0011] In the present invention, the number of MB2 particles in the two-grain grain boundary region and the main phase grains preferably accounts for 20%-50% of the MB2 particles in the NdFeB magnet I, for example, 22%, 26% or 32%.

[0012] In certain specific embodiments of the present invention, the NdFeB magnet I comprises the following components: 24wt%-33wt% of RL, where RL is a light rare earth element and includes Nd; 0.7wt%-1.2wt% of B; 0.1wt%-1wt% of M; and the balance Fe.

[0013] Wherein, the NdFeB magnet I preferably further includes T, and T is one or more selected from Cu, Al and Ga.

[0014] The T content is preferably 0-2.1 wt %, where the T content refers to the mass percentage of the element in the NdFeB magnet I. The T content in the above range is beneficial to the formation of MB2 particles, which may be because Cu, Al or Ga will form a 6:13:1 phase at the grain boundary. For example, when the element is Ga, the 6:13:1 phase is Nd6Fe 13 Ga phase. The 6:13:1 phase will consume some of the B element, and the T element content in the above range can ensure the formation of MB2 particles.

[0015] The Cu content is preferably 0-0.7 wt %, for example 0.2 wt %, where the content refers to the mass percentage of the element in the NdFeB magnet I.

[0016] The Al content is preferably 0-0.7 wt%, for example 0.08 wt%, where the Al content refers to the mass percentage of the element in the NdFeB magnet I.

[0017] The Ga content is preferably 0-0.7 wt%, for example 0.19 wt%, where the Ga content refers to the mass percentage of the element in the NdFeB magnet I.

[0018] Wherein, the NdFeB magnet I preferably also includes Co.

[0019] The content of Co is preferably 0-2 wt%, for example 1 wt%, where the content refers to the mass percentage of the element in the NdFeB magnet I.

[0020] Wherein, the NdFeB magnet I preferably also includes Dy and / or Tb.

[0021] The Dy content is preferably 0-1.5 wt%, more preferably 0.1 wt%-0.15 wt%, for example 0.12 wt%, where the Dy content refers to the mass percentage of the element in the NdFeB magnet I.

[0022] The Tb content is preferably 0-1.5 wt%, more preferably 0.1 wt%-0.15 wt%, for example 0.12 wt%, where the content refers to the mass percentage of the element in the NdFeB magnet I.

[0023] Wherein, the RL preferably also includes one or more of La, Ce, Pr, Sm, Gd, Ho and Y.

[0024] The content of RL is preferably 29wt%-32wt%, for example 30.14wt%, where the content refers to the mass percentage of the element in the NdFeB magnet I.

[0025] The B content is preferably 0.8 wt%-1.1 wt%, for example 0.96 wt%, where the B content refers to the mass percentage of the element in the NdFeB magnet I.

[0026] In the present invention, the content of M is preferably 0.1 wt%-1 wt%, for example 0.4 wt%, where the content refers to the mass percentage of the element in the NdFeB magnet I.

[0027] In the present invention, the Zr content is preferably 0-1 wt%, for example 0.4 wt%, where the content refers to the mass percentage of the element in the NdFeB magnet I.

[0028] In the present invention, the Nb content is preferably 0-1 wt%, for example 0.4 wt%, where the content refers to the mass percentage of the element in the NdFeB magnet I.

[0029] In the present invention, the Ti content is preferably 0-1 wt%, for example 0.4 wt%, where the Ti content refers to the mass percentage of the element in the NdFeB magnet I.

[0030] In the present invention, the shape of the MB2 particles is, for example, one or more of spherical, needle-shaped, rod-shaped and flake-shaped, preferably rod-shaped and / or flake-shaped.

[0031] In the present invention, the particle size of the MB2 particles is preferably less than 500 nm, more preferably less than 200 nm. When the MB2 particles are spherical, the particle size of the MB2 particles refers to the diameter of the spherical MB2 particles. When the MB2 particles are flake-shaped, needle-shaped, or rod-shaped, the particle size of the MB2 particles refers to the minimum distance between two points passing through the center of the MB2 particle.

[0032] In the present invention, the number of MB2 particles is counted, for example, by counting the number of MB2 particles in multiple scanning electron microscope backscatter (BSE) images of the NdFeB magnet to obtain a distribution ratio of the MB2 particles. The number of MB2 particles is counted by counting the number of MB2 particles in different regions of at least ten BSE images magnified 10,000x to calculate the distribution ratio of the MB2 particles.

[0033] The present invention also provides a method for preparing a NdFeB magnet I, comprising the following steps: subjecting the raw materials to sequential smelting, casting, hydrogen crushing treatment, air flow milling, pressing, sintering, and aging treatment to obtain the magnet; wherein the hydrogen crushing treatment sequentially comprises the steps of hydrogen absorption, dehydrogenation, and cooling;

[0034] The content of M in the raw material is 0.1wt%-1.5wt%, where the content refers to the mass percentage of the element in the raw material; M is one or more selected from Nb, Zr and Ti.

[0035] In certain specific embodiments of the present invention, the raw material includes the following components: 24wt%-33wt% of RL, RL is a light rare earth element and RL includes Nd; 0.7wt%-1.2wt% of B; 0.1wt%-1wt% of M; and the balance is Fe.

[0036] Wherein, the raw material preferably further includes T, and T is one or more selected from Cu, Al and Ga.

[0037] The T content is preferably 0-2.1 wt %, where the T content refers to the mass percentage of the element in the raw material. The T content in the above range is beneficial to the formation of MB2 particles, which may be because Cu, Al or Ga will form a 6:13:1 phase at the grain boundary. For example, when the element is Ga, the 6:13:1 phase is Nd6Fe 13 Ga phase. The 6:13:1 phase will consume some of the B element, and the T element content in the above range can ensure the formation of MB2 particles.

[0038] The Cu content is preferably 0-0.7 wt%, for example 0.2 wt%, where the content refers to the mass percentage of the element in the raw material.

[0039] The Al content is preferably 0-0.7 wt%, for example 0.08 wt%, where the Al content refers to the mass percentage of the element in the raw material.

[0040] The Ga content is preferably 0-0.7 wt%, for example 0.19 wt%, where the Ga content refers to the mass percentage of the element in the raw material.

[0041] Wherein, the raw material preferably also includes Co.

[0042] The content of Co is preferably 0-2 wt%, for example 1 wt%, where the content refers to the mass percentage of the element in the raw material.

[0043] Wherein, the raw material preferably further includes Dy and / or Tb.

[0044] The Dy content is preferably 0-1.5 wt%, more preferably 0.1 wt%-0.15 wt%, for example 0.12 wt%, where the content refers to the mass percentage of the element in the raw material.

[0045] The Tb content is preferably 0-1.5 wt%, more preferably 0.1 wt%-0.15 wt%, for example 0.12 wt%, where the content refers to the mass percentage of the element in the raw material.

[0046] Wherein, the RL preferably also includes one or more of La, Ce, Pr, Sm, Gd, Ho and Y.

[0047] The content of RL is preferably 29 wt%-32 wt%, for example 30.14 wt%, where the content refers to the mass percentage of the element in the raw material.

[0048] The B content is preferably 0.8 wt%-1.1 wt%, for example 0.96 wt%, where the content refers to the mass percentage of the element in the raw material.

[0049] In the present invention, the content of M is preferably 0.1 wt%-1 wt%, for example 0.4 wt%, where the content refers to the mass percentage of the element in the raw material.

[0050] In the present invention, the content of Zr is preferably 0-1 wt%, for example 0.4 wt%, where the content refers to the mass percentage of the element in the raw material.

[0051] In the present invention, the Nb content is preferably 0-1 wt%, for example 0.4 wt%, where the content refers to the mass percentage of the element in the raw material.

[0052] In the present invention, the content of Ti is preferably 0-1 wt%, for example 0.4 wt%, where the content refers to the mass percentage of the element in the raw material.

[0053] In the present invention, the smelting temperature is preferably 1500-1560°C, more preferably 1500-1540°C.

[0054] In the present invention, the vacuum degree of the smelting is, for example, 5×10 -2 Pa.

[0055] In the present invention, the smelting device is, for example, a high-frequency vacuum induction melting furnace.

[0056] In the present invention, the casting temperature is preferably 1350-1560°C, more preferably 1420-1460°C.

[0057] In the present invention, the casting method is, for example, a rapid solidification sheet casting method.

[0058] In the present invention, the thickness of the alloy sheet obtained after casting is preferably 0.2-0.4 mm, for example 0.35 mm.

[0059] In the present invention, the hydrogen absorption pressure is, for example, 0.085 MPa.

[0060] In the present invention, the dehydrogenation temperature is preferably 450-550°C.

[0061] In the present invention, the dehydrogenation, for example, includes the following steps: dehydrogenation is performed under conditions of simultaneous vacuuming and temperature increase.

[0062] In the present invention, preferably, the particle size of the powder obtained after the jet milling treatment is 1-8 μm.

[0063] In the present invention, preferably, the jet milling treatment is carried out in an atmosphere containing 20-50 ppm of oxidizing gas.

[0064] Here, the oxidizing gas refers to oxygen and / or water vapor.

[0065] In the present invention, the pressure of the jet milling treatment is preferably 0.4-1 MPa, for example 0.68 MPa.

[0066] In the present invention, the magnetic field strength during the pressing process is preferably 0.7-2.5T, for example 1.8T.

[0067] In the present invention, the compression molding is preferably performed under an inert atmosphere, such as a nitrogen atmosphere.

[0068] In the present invention, the temperature of the sintering treatment is preferably 900-1200°C, for example 1085°C.

[0069] In the present invention, the sintering treatment time is preferably 3-24 hours, for example 6 hours.

[0070] In the present invention, the aging treatment preferably includes primary aging treatment and secondary aging treatment in sequence.

[0071] The temperature of the primary aging treatment is preferably 600-980°C, for example 900°C.

[0072] The temperature of the secondary aging treatment is preferably 400-600°C, for example 520°C.

[0073] The present invention also provides a NdFeB magnet I, which is prepared according to the preparation method of the NdFeB magnet I described above.

[0074] The present invention also provides a neodymium iron boron magnet II, which includes main phase grains, triangular grain boundary regions and two-grain grain boundary regions, wherein the main phase grain surfaces include heavy rare earth shells; the main phase grains, the triangular grain boundary regions, the two-grain grain boundary regions and the heavy rare earth shells all include MB2 particles; M is one or more selected from Nb, Zr and Ti; and the content of M in the neodymium iron boron magnet II is 0.1wt%-1.5wt%;

[0075] N Cell ≥5%; N Cell is the sum of the number of the main phase grains and the MB2 particles in the heavy rare earth shell;

[0076] Among them, C shell / C core ≥1.05; C shell is the concentration of heavy rare earth in the heavy rare earth shell, C coreis the concentration of heavy rare earth in the center of the main phase grain.

[0077] In the present invention, N Cell The statistical method is as follows: randomly select at least 10 photos with a magnification greater than or equal to 5000 times within a depth of 0-50μm from the diffusion surface in the NdFeB magnet II, and count the number of MB2 particles in more than 100 main phase grains and their heavy rare earth shells.

[0078] In the present invention, the center of the main phase grain is a position inside the main phase grain that is far from the grain boundary. Cell ≥10%, more preferably, N Cell 14%, 15%, 20% or 30%.

[0079] In certain preferred embodiments of the present invention, Cshell / Ccore is 1.5-1.6, such as 1.52, 1.53, 1.54 or 1.58.

[0080] In certain specific embodiments of the present invention, the NdFeB magnet II includes the following components: 24wt%-33wt% of RL, RL is a light rare earth element and RL includes Nd; 0.7wt%-1.2wt% of B; 0.1wt%-1wt% of M; 0.1wt%-5wt% of RH, RH is a heavy rare earth element; and the balance is Fe.

[0081] The RH is, for example, Dy and / or Tb.

[0082] Wherein, the content of Dy is preferably 0.1wt%-3wt%

[0083] The content of Tb is preferably 0.1wt%-3wt%.

[0084] In certain specific embodiments of the present invention, the NdFeB magnet II includes the following components: 24wt%-33wt% of RL, where RL is a light rare earth element and includes Nd; 0.7wt%-1.2wt% of B; 0.1wt%-1wt% of M; and the balance of Fe.

[0085] Wherein, the NdFeB magnet II preferably further includes T, and T is one or more selected from Cu, Al and Ga.

[0086] The T content is preferably 0-2.1 wt %, where the T content refers to the mass percentage of the element in the NdFeB magnet II. The T content in the above range is beneficial to the formation of MB2 particles, which may be because Cu, Al or Ga will form a 6:13:1 phase at the grain boundary. For example, when the element is Ga, the 6:13:1 phase is Nd6Fe 13Ga phase. The 6:13:1 phase will consume some of the B element, and the T element content in the above range can ensure the formation of MB2 particles.

[0087] The Cu content is preferably 0-0.7 wt %, for example 0.2 wt %, where the content refers to the mass percentage of the element in the NdFeB magnet II.

[0088] The Al content is preferably 0-0.7 wt%, for example 0.08 wt%, where the Al content refers to the mass percentage of the element in the NdFeB magnet II.

[0089] The Ga content is preferably 0-0.7 wt%, for example 0.19 wt%, where the Ga content refers to the mass percentage of the element in the NdFeB magnet II.

[0090] Wherein, the NdFeB magnet II preferably further includes Co.

[0091] The content of Co is preferably 0-2 wt%, for example 1 wt%, where the content refers to the mass percentage of the element in the NdFeB magnet II.

[0092] Wherein, the NdFeB magnet II preferably also includes Dy and / or Tb.

[0093] The Dy content is preferably 0-1.5 wt%, more preferably 0.1 wt%-0.15 wt%, for example 0.12 wt%, where the content refers to the mass percentage of the element in the NdFeB magnet II.

[0094] The Tb content is preferably 0-1.5 wt%, more preferably 0.1 wt%-0.15 wt%, for example 0.12 wt%, where the content refers to the mass percentage of the element in the NdFeB magnet II.

[0095] Wherein, the RL preferably also includes one or more of La, Ce, Pr, Sm, Gd, Ho and Y.

[0096] The content of RL is preferably 29 wt%-32 wt%, for example 30.14 wt%, where the content refers to the mass percentage of the element in the NdFeB magnet II.

[0097] The B content is preferably 0.8 wt%-1.1 wt%, for example 0.96 wt%, where the B content refers to the mass percentage of the element in the NdFeB magnet II.

[0098] In the present invention, the content of M is preferably 0.1 wt%-1 wt%, for example 0.4 wt%, where the content refers to the mass percentage of the element in the NdFeB magnet II.

[0099] In the present invention, the content of Zr is preferably 0-1 wt%, for example 0.4 wt%, where the content refers to the mass percentage of the element in the NdFeB magnet II.

[0100] In the present invention, the Nb content is preferably 0-1 wt%, for example 0.4 wt%, where the content refers to the mass percentage of the element in the NdFeB magnet II.

[0101] In the present invention, the content of Ti is preferably 0-1 wt%, for example 0.4 wt%, where the content refers to the mass percentage of the element in the NdFeB magnet II.

[0102] In the present invention, the thickness of the heavy rare earth shell is preferably less than 1 μm.

[0103] The present invention also provides a method for preparing a NdFeB magnet II, which is obtained by subjecting the NdFeB magnet I to a grain boundary diffusion treatment.

[0104] In the present invention, preferably, the temperature of the grain boundary diffusion treatment is 800-1100°C, more preferably 800-1000°C, for example 900°C.

[0105] In the present invention, preferably, the grain boundary diffusion treatment time is 6-36 hours, more preferably 12-36 hours, for example 10 hours.

[0106] In the present invention, preferably, a heat preservation treatment step is further included after the grain boundary diffusion treatment.

[0107] The temperature of the heat preservation treatment is preferably 400-700°C, more preferably 400-600°C, for example 460°C.

[0108] The heat preservation treatment time is preferably 1-6 hours, more preferably 2-4 hours.

[0109] In the present invention, the diffusion source of the grain boundary diffusion treatment is preferably a diffusion source containing Dy and / or Tb.

[0110] The weight gain of the diffusion source is preferably 0.1-1%, for example 0.6%. The weight gain refers to the weight increase ratio of the NdFeB magnet before and after the grain boundary diffusion treatment, i.e., weight gain = 1 - weight of the NdFeB magnet before the grain boundary diffusion treatment / weight of the NdFeB magnet after the grain boundary diffusion treatment.

[0111] Those skilled in the art generally understand that in order to make the NdFeB magnet I suitable for grain boundary diffusion treatment, the NdFeB magnet I can generally be mechanically processed before the grain boundary diffusion treatment.

[0112] The present invention also provides a NdFeB magnet II, which is prepared according to the preparation method of the NdFeB magnet II.

[0113] The present invention also provides an application of the above-mentioned NdFeB magnet II in magnetic steel.

[0114] On the basis of conforming to the common sense in this field, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0115] The reagents and raw materials used in the present invention are commercially available.

[0116] The positive progress effect of the present invention is:

[0117] The NdFeB magnets I and II provided by the present invention both have excellent remanence, coercive force and squareness; and the NdFeB magnet I of the present invention can effectively improve the effect of grain boundary diffusion and increase the utilization rate of heavy rare earth.

[0118] The NdFeB magnets I and II of the present invention have high flexibility in composition and performance adjustment. BRIEF DESCRIPTION OF THE DRAWINGS

[0119] Figure 1 This is a scanning electron microscope backscatter (BSE) image of the NdFeB magnet I of Example 1.

[0120] Figure 2 This is a scanning electron microscope backscattering (BSE) image of the NdFeB magnet II of Comparative Example 1.

[0121] Figure 3 This is a scanning electron microscope backscatter (BSE) image of the NdFeB magnet II of Example 1.

[0122] Figure 4 This is a scanning electron microscope backscattering (BSE) image of the NdFeB magnet II of Comparative Example 1. DETAILED DESCRIPTION

[0123] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or selected according to the product specifications.

[0124] Examples 1-4 and Comparative Examples 1-3

[0125] The element contents in the NdFeB magnets I of Examples 1-4 and Comparative Examples 1-3 are listed in Table 1:

[0126] Table 1

[0127]

[0128] Note: / indicates that the element is not contained.

[0129] The preparation methods of the NdFeB magnets I and II of Examples 1-4 and Comparative Examples 1-3 are as follows:

[0130] The raw materials are sequentially subjected to smelting, casting, hydrogen crushing treatment, air flow milling treatment, pressing, sintering treatment and aging treatment to obtain the product; the hydrogen crushing treatment sequentially includes the steps of hydrogen absorption, dehydrogenation and cooling; the content of M in the raw materials is 0.1wt%-1.5wt%, where the content means the mass percentage of the element in the raw materials; and M is one or more selected from Nb, Zr and Ti.

[0131] Among them, the smelting is carried out at a vacuum degree of 5×10 -2 Pa high-frequency vacuum induction melting furnace, the melting temperature is in the range of 1500-1540 ℃. The casting adopts the rapid solidification casting method to cast the material from the melt into an alloy sheet with a thickness of 0.35mm, wherein the casting temperature is in the range of 1420-1460 ℃. Hydrogen absorption is carried out under the condition of hydrogen pressure of 0.085MPa, and dehydrogenation is carried out under the conditions of simultaneous vacuum and temperature increase, and the dehydrogenation temperature is 550 ℃. The air flow milling treatment is to grind the material from the hydrogen crushing treatment into an atmosphere containing 20-50ppm of oxidizing gas, the oxidizing gas refers to oxygen and / or water vapor, and the pressure of the air flow milling treatment is 0.68MPa. Pressing is carried out in a nitrogen atmosphere, and the magnetic field strength of the press molding is 1.8T. The sintering treatment is to sinter the blank from the press molding at 1085 ℃ for 6h. The aging treatment includes primary aging treatment and secondary aging treatment. The temperature of the primary aging treatment is 900° C., and the temperature of the secondary aging treatment is 520° C. After the aging treatment, the NdFeB magnet I is obtained.

[0132] After machining, NdFeB magnet I is subjected to grain boundary diffusion treatment. A diffusion source containing Tb is used for the grain boundary diffusion treatment. The treatment is performed at 900°C for 10 hours and then at 460°C for 2 hours. The weight gain of the diffusion source is 0.6%. After the grain boundary diffusion treatment, NdFeB magnet II is obtained.

[0133] The obtained NdFeB magnets were tested by using a scanning electron microscope. Figure 1 The backscattered electron microscopy (BSE) image of the NdFeB magnet 1 prepared in Example 1 of the present invention is shown. The black rod-shaped particles are nano-sized MB2 particles. Figure 1The white circle in the middle indicates the MB2 particles in the grain, the white triangle area indicates the MB2 particles in the triangular grain boundary area, and the white rectangle area indicates the MB2 particles in the two-particle grain boundary area.

[0134] Figure 2 The scanning electron microscope backscattering (BSE) image of the NdFeB magnet II prepared in Comparative Example 1 of the present invention is shown. The black rod-shaped particles are nano-sized MB2 particles. Figure 2 The white circles in the middle indicate MB2 particles in the triangular grain boundary region and the two-particle grain boundary region, and the white rectangular area indicates MB2 particles in the main phase grains and heavy rare earth shells.

[0135] MB2 particle counts in the NdFeB magnets of Examples 1-4 and Comparative Examples 1-3 were performed by counting MB2 particles in multiple scanning electron microscope backscatter (BSE) images to determine the MB2 particle distribution ratio. The MB2 particle counts were performed by counting MB2 particles in different regions of at least ten BSE images magnified 10,000x, and calculating the MB2 particle distribution ratio.

[0136] Determination of the thickness of the heavy rare earth shell: The determination method is to count the average heavy rare earth shell thickness of more than 100 main phase grains within a depth of 0-50 μm from the diffusion surface in the NdFeB magnet II. The measurement instrument is a scanning electron microscope.

[0137] N Cell The statistical method is as follows: randomly select at least 10 photos with a magnification greater than or equal to 5000 times within a depth of 0-50μm from the diffusion surface in the NdFeB magnet II, and count the number of MB2 particles in more than 100 main phase grains and their heavy rare earth shells.

[0138] Figure 3 is a scanning electron microscope backscattering (BSE) image of the NdFeB magnet II of Example 1, Figure 4 The scanning electron microscope backscattering (BSE) image of the NdFeB magnet II of Comparative Example 1 is shown in FIG. Figure 3 and Figure 4 It can be seen from the figure that the thickness of the heavy rare earth shell layer in Example 1 is less than that in Comparative Example 1.

[0139] Effect Example 1

[0140] The remanence (Br), intrinsic coercivity (Hcj) and demagnetization curve of the NdFeB magnet prepared in Example 1 were tested using a PFM pulsed BH demagnetization curve tester (model PFM14, from Hirst, UK, agent of the Institute of Metrology). The results are shown in the following table.

[0141]

[0142] The Br of the NdFeB magnet I of Examples 1-4 of the present invention can reach more than 13.92 kGs, the Hcj of the NdFeB magnet I can reach more than 15.17 kOe, the Br of the NdFeB magnet II can reach more than 13.8 kGs, and the Hcj of the NdFeB magnet II can reach more than 25.18 kOe, indicating that the NdFeB magnet I and NdFeB magnet II of the present invention both have excellent remanence and coercive force.

[0143] Compared with Examples 1-4, in Comparative Example 1, the number of MB2 particles in the triangular grain boundary region accounts for too high a ratio of the number of MB2 particles in the NdFeB magnet I, and the number of MB2 particles in the two-particle grain boundary region and the main phase grains accounts for too low a ratio of the number of MB2 particles in the NdFeB magnet I, resulting in a significant deterioration in the performance of the NdFeB magnet I. Compared with Examples 1-4, in Comparative Example 2, the number of MB2 particles in the two-particle grain boundary region accounts for too low a ratio of the number of MB2 particles in the NdFeB magnet I, resulting in a significant decrease in the Hcj of the NdFeB magnet II. Compared with Examples 1-4, in Comparative Example 3, the number of MB2 particles in the two-particle grain boundary region accounts for too low a ratio of the number of MB2 particles in the NdFeB magnet I, resulting in a significant decrease in the Hcj of the NdFeB magnet II. Cell If the Hcj is too low, the Hcj of the NdFeB magnet II will be significantly reduced.

[0144] Thus, the NdFeB magnet I of the present invention can effectively improve the effect of grain boundary diffusion and increase the utilization rate of heavy rare earth. The NdFeB magnet I and NdFeB magnet II of the present invention both have excellent remanence, coercivity and squareness, and are highly flexible in composition and performance adjustment.

Claims

1. A neodymium iron boron magnet I, characterized in that: The NdFeB magnet I comprises main phase grains, triangular grain boundary regions and two-grain grain boundary regions, wherein the main phase grains, the triangular grain boundary regions and the two-grain grain boundary regions all comprise MB2 particles; M is one or more selected from Nb, Zr and Ti; The MB2 particles in the triangular grain boundary region account for less than 90% of the MB2 particles in the NdFeB magnet 1; the MB2 particles in the two-particle grain boundary region and the main phase grains account for more than 10% of the MB2 particles in the NdFeB magnet 1; the MB2 particles in the two-particle grain boundary region account for more than 5% of the MB2 particles in the NdFeB magnet 1; The content of M in the NdFeB magnet I is 0.1wt%-1.5wt%, where the content refers to the mass percentage of the element in the NdFeB magnet I.

2. NdFeB magnet 1 as claimed in claim 1, characterized in that, The MB2 particles in the triangular grain boundary region account for 50%-80% of the MB2 particles in the NdFeB magnet I, for example, 68%, 74% or 78%; And / or, the number ratio of the MB2 particles in the two-grain grain boundary region and the main phase grains to the MB2 particles in the NdFeB magnet I is 20%-50%, for example, 22%, 26% or 32%; And / or, the content of M is preferably 0.1wt%-1wt%, for example 0.4wt%, where the content means the mass percentage of the element in the NdFeB magnet I; And / or, the Zr content is preferably 0-1wt%, for example 0.4wt%, where the content refers to the mass percentage of the element in the NdFeB magnet I; And / or, the Nb content is preferably 0-1wt%, for example 0.4wt%, where the content refers to the mass percentage of the element in the NdFeB magnet I; And / or, the Ti content is preferably 0-1wt%, for example 0.4wt%, where the Ti content refers to the mass percentage of the element in the NdFeB magnet I; and / or, the MB2 particles are shaped, for example, one or more of spherical, needle-shaped, rod-shaped, and flake-shaped, preferably rod-shaped and / or flake-shaped; and / or, when the MB2 particles are in the shape of flakes or spheres, the particle size of the MB2 particles is preferably less than 500 nm, more preferably less than 200 nm; And / or, the NdFeB magnet I comprises the following components: 24wt%-33wt% of RL, RL is a light rare earth element and RL comprises Nd; 0.7wt%-1.2wt% of B; 0.1wt%-1wt% of M; and the balance of Fe; Wherein, the NdFeB magnet I preferably further includes T, where T is one or more selected from Cu, Al and Ga; Wherein, the content of T is preferably 0-2.1wt%, and the content means the mass percentage of the element in the NdFeB magnet I; The Cu content is preferably 0-0.7 wt %, for example 0.2 wt %, where the content refers to the mass percentage of the element in the NdFeB magnet I. Wherein, the content of Al is preferably 0-0.7wt%, for example 0.08wt%, and the content means the mass percentage of the element in the NdFeB magnet I; The Ga content is preferably 0-0.7 wt%, for example 0.19 wt%, where the Ga content refers to the mass percentage of the element in the NdFeB magnet I. Wherein, the NdFeB magnet I preferably further comprises Co; Wherein, the content of Co is preferably 0-2wt%, for example 1wt%, and the content means the mass percentage of the element in the NdFeB magnet I; Wherein, the NdFeB magnet I preferably further comprises Dy and / or Tb; The Dy content is preferably 0-1.5 wt%, more preferably 0.1 wt%-0.15 wt%, for example 0.12 wt%, where the Dy content refers to the mass percentage of the element in the NdFeB magnet I. The Tb content is preferably 0-1.5 wt%, more preferably 0.1 wt%-0.15 wt%, for example 0.12 wt%, where the content refers to the mass percentage of the element in the NdFeB magnet I. Wherein, the RL preferably further comprises one or more of La, Ce, Pr, Sm, Gd, Ho and Y; The content of RL is preferably 29wt%-32wt%, for example 30.14wt%, where the content refers to the mass percentage of the element in the NdFeB magnet I. The B content is preferably 0.8 wt%-1.1 wt%, for example 0.96 wt%, where the B content refers to the mass percentage of the element in the NdFeB magnet I.

3. A method for preparing a NdFeB magnet 1 as claimed in claim 1 or 2, characterized in that: It includes the following steps: The raw materials are sequentially subjected to smelting, casting, hydrogen crushing treatment, air flow milling treatment, pressing, sintering treatment and aging treatment to obtain the product; the hydrogen crushing treatment sequentially includes the steps of hydrogen absorption, dehydrogenation and cooling; The content of M in the raw material is 0.1wt%-1.5wt%, where the content refers to the mass percentage of the element in the raw material; M is one or more selected from Nb, Zr and Ti.

4. The preparation method of NdFeB magnet 1 as claimed in claim 3, wherein The content of M is 0.1wt%-1wt%, for example 0.4wt%, where the content refers to the mass percentage of the element in the raw material; And / or, the Zr content is 0-1 wt%, for example, 0.4 wt%, where the content refers to the mass percentage of the element in the raw material; And / or, the Nb content is 0-1 wt%, for example, 0.4 wt%, where the content refers to the mass percentage of the element in the raw material; And / or, the Ti content is 0-1 wt%, for example, 0.4 wt%, where the content refers to the mass percentage of the element in the raw material; And / or, the smelting temperature is 1500-1560°C, preferably 1500-1540°C; And / or, the vacuum degree of the smelting is 5×10 -2 Pa; And / or, the smelting device is a high-frequency vacuum induction melting furnace; And / or, the casting temperature is 1350-1560°C, preferably 1420-1460°C; And / or, the casting method is a rapid-setting sheet casting method; And / or, the thickness of the alloy sheet obtained after the casting is 0.2-0.4 mm, for example, 0.35 mm; And / or, the hydrogen absorption pressure is 0.085 MPa; And / or, the dehydrogenation temperature is 450-550°C; And / or, the dehydrogenation comprises the following steps: performing dehydrogenation under conditions of simultaneous vacuuming and heating; And / or, the particle size of the powder obtained after the jet milling treatment is 1-8 μm; And / or, the jet milling treatment is carried out in an atmosphere containing 20-50 ppm of an oxidizing gas; wherein the oxidizing gas refers to oxygen and / or water vapor; And / or, the pressure of the jet milling process is 0.4-1 MPa, for example 0.68 MPa; And / or, the magnetic field strength during the pressing is 0.7-2.5 T, for example 1.8 T; And / or, the pressing is performed under an inert atmosphere, for example, a nitrogen atmosphere; And / or, the sintering temperature is 900-1200° C., for example, 1085° C.; And / or, the sintering treatment time is 3-24 hours, for example, 6 hours; And / or, the aging treatment includes primary aging treatment and secondary aging treatment in sequence; wherein the temperature of the primary aging treatment is preferably 600-980°C, for example, 900°C; wherein the temperature of the secondary aging treatment is preferably 400-600°C, for example, 520°C; And / or, the raw material includes the following components: 24wt%-33wt% of RL, RL is a light rare earth element and RL includes Nd; 0.7wt%-1.2wt% of B; 0.1wt%-1wt% of M; and the balance of Fe; Wherein, the raw material preferably further comprises T, and T is one or more selected from Cu, Al and Ga; Wherein, the content of T is preferably 0-2.1wt%, and the content means the mass percentage of the element in the raw material; The Cu content is preferably 0-0.7 wt%, for example 0.2 wt%, where the content refers to the mass percentage of the element in the raw material. The Al content is preferably 0-0.7 wt%, for example 0.08 wt%, where the Al content refers to the mass percentage of the element in the raw material. The Ga content is preferably 0-0.7 wt%, for example 0.19 wt%, where the Ga content refers to the mass percentage of the element in the raw material. Wherein, the raw material preferably further comprises Co; wherein, the content of the Co is preferably 0-2wt%, for example, 1wt%, and the content means the mass percentage of the element in the raw material; The raw materials preferably further include Dy and / or Tb; wherein the content of Dy is preferably 0-1.5wt%, more preferably 0.1wt%-0.15wt%, for example 0.12wt%, and the content means the mass percentage of the element in the raw materials; wherein the content of Tb is preferably 0-1.5wt%, more preferably 0.1wt%-0.15wt%, for example 0.12wt%, and the content means the mass percentage of the element in the raw materials; Wherein, the RL preferably further comprises one or more of La, Ce, Pr, Sm, Gd, Ho and Y; The content of RL is preferably 29 wt%-32 wt%, for example 30.14 wt%, where the content refers to the mass percentage of the element in the raw material. The B content is preferably 0.8 wt%-1.1 wt%, for example 0.96 wt%, where the content refers to the mass percentage of the element in the raw material.

5. A neodymium iron boron magnet I, characterized in that: It is obtained according to the preparation method of the NdFeB magnet 1 according to claim 3 or 4.

6. A neodymium iron boron magnet II, characterized in that: The NdFeB magnet II comprises main phase grains, triangular grain boundary regions and two-grain grain boundary regions, the main phase grain surfaces comprise heavy rare earth shells; the main phase grains, the triangular grain boundary regions, the two-grain grain boundary regions and the heavy rare earth shells all comprise MB2 particles; M is one or more selected from Nb, Zr and Ti; the content of M in the NdFeB magnet II is 0.1wt%-1.5wt%; N Cell ≥5%; N Cell is the sum of the number of the main phase grains and the MB2 particles in the heavy rare earth shell; Among them, C shell / C core ≥1.05; C shell is the concentration of heavy rare earth in the heavy rare earth shell, C core is the concentration of heavy rare earth in the center of the main phase grain.

7. The NdFeB magnet II according to claim 6, characterized in that: N Cell ≥10%, preferably, N Cell 14%, 15%, 20% or 30%; and / or, C shell / C core is 1.5-1.6, such as 1.52, 1.53, 1.54 or 1.58; And / or, the thickness of the heavy rare earth shell layer is less than 1 μm; And / or, the NdFeB magnet II comprises the following components: 24wt%-33wt% of RL, RL is a light rare earth element and RL includes Nd; 0.7wt%-1.2wt% of B; 0.1wt%-1wt% of M; 0.1wt%-5wt% of RH, RH is a heavy rare earth element; and the balance is Fe; Wherein, the RH is, for example, Dy and / or Tb; Wherein, the content of Dy is preferably 0.1wt%-3wt%; The Tb content is preferably 0.1 wt%-3 wt%.

8. A method for preparing the NdFeB magnet II according to claim 6 or 7, characterized in that: The NdFeB magnet 1 as claimed in any one of claims 1, 2 and 5 is subjected to grain boundary diffusion treatment.

9. The method for preparing the NdFeB magnet II according to claim 8, wherein: The temperature of the grain boundary diffusion treatment is 800-1100° C., preferably 800-1000° C., for example 900° C.; And / or, the grain boundary diffusion treatment time is 6-36 hours, preferably 12-36 hours, for example 10 hours; And / or, a heat preservation treatment step is further included after the grain boundary diffusion treatment; wherein the temperature of the heat preservation treatment is preferably 400-700° C., more preferably 400-600° C., for example, 460° C.; wherein the time of the heat preservation treatment is preferably 1-6 hours, more preferably 2-4 hours; And / or, the diffusion source of the grain boundary diffusion treatment is a diffusion source containing Dy and / or Tb; wherein the weight increase of the diffusion source is 0.1-1%, for example, 0.6%.

10. A neodymium iron boron magnet II, characterized in that: It is prepared according to the preparation method of the NdFeB magnet II according to claim 8 or 9.

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