Neodymium-iron-boron permanent magnet and method for producing the same

Abstract

The application discloses a neodymium-iron-boron permanent magnet and a preparation method thereof. The neodymium-iron-boron permanent magnet is in the shape of a cuboid, the height direction of the neodymium-iron-boron permanent magnet is the orientation direction, and the height of the neodymium-iron-boron permanent magnet is greater than or equal to 8 mm. The content of heavy rare earth elements at the top corner of the neodymium-iron-boron permanent magnet is greater than 0.65 wt%, the content of heavy rare earth elements at the edge of the neodymium-iron-boron permanent magnet is greater than 0.43 wt%, the content of heavy rare earth elements at the outer layer of the neodymium-iron-boron permanent magnet is greater than or equal to 0.22 wt%, and the content of heavy rare earth elements at the core of the neodymium-iron-boron permanent magnet is greater than or equal to 0.003 wt%. The content of heavy rare earth elements at the top corner is greater than that at the edge, the content of heavy rare earth elements at the edge is greater than that at the outer layer, and the content of heavy rare earth elements at the outer layer is greater than that at the core. The neodymium-iron-boron permanent magnet has a large size in the orientation direction and good heat demagnetization resistance.

Description

Technical Field

[0001] This invention relates to a neodymium iron boron permanent magnet and its preparation method. Background Technology

[0002] With Nd2Fe 14 R-Fe-B type rare earth sintered magnets with B-type compounds as the main phase have high magnetic properties and are widely used in new energy vehicle motors, humanoid robots, wind turbines, variable frequency air conditioner motors, consumer electronics products and other fields.

[0003] During operation, permanent magnet motors are prone to high-temperature demagnetization on the outer surface of the permanent magnet, especially in the corner areas, which is particularly noticeable for large-sized oriented diffusion permanent magnets. Currently, some high-end fields have increasingly higher requirements for the thermal demagnetization resistance of permanent magnets, and also require higher energy densities.

[0004] CN119230277A discloses a method for pressure-assisted enhanced grain boundary diffusion in sintered NdFeB magnets. After sintering, the NdFeB magnet undergoes low-temperature pre-aging and cooling to room temperature. The pre-aged magnet is then sliced, pre-diffusion treatment is performed, rare-earth diffusion source coating is applied, non-rare-earth diffusion source pressure bonding is applied, and diffusion heat treatment is completed. The composition of the sintered NdFeB magnet matrix is ​​RE x M y B z Fe 100-x-y-z .

[0005] CN116230348B discloses a method for preparing low-temperature coefficient sintered Nd-Fe-B permanent magnet materials, which obtains LRE-based materials through processes such as batching, rapid solidification and belt spinning, hydrogen breaking, and air jet milling. a1 HRE b1 Co c1 Cu d1 Fe bal M e1 B f1 Rare earth-poor alloy powder; obtained by following the processes of batching, rapid solidification and belt spinning, hydrogen crushing and air jet milling, etc., with an LRE composition. a2 HRE b2 Co c2 Cu d2 Fe bal M e2 B f2 The rare earth-rich alloy powder is prepared; the rare earth-poor alloy powder and the rare earth-rich alloy powder are mixed; the uniformly mixed powder is oriented and shaped, and then isostatically pressed to obtain a green blank; the green blank is sintered in a vacuum sintering furnace and tempered under a protective atmosphere or vacuum.

[0006] The aforementioned neodymium iron boron permanent magnets have relatively weak resistance to thermal demagnetization. Summary of the Invention

[0007] One object of the present invention is to provide a neodymium iron boron (NdFeB) permanent magnet having a large size in the orientation direction and good resistance to thermal demagnetization. Further, this NdFeB permanent magnet has a low absolute value of its remanence temperature coefficient, a low absolute value of its intrinsic coercivity temperature coefficient, and a low magnetic moment thermal decay rate. Another object of the present invention is to provide a method for preparing a NdFeB permanent magnet that improves the resistance to thermal demagnetization of NdFeB permanent magnets with a large size in the orientation direction. Further, the NdFeB permanent magnet obtained by this method has low absolute values ​​of its remanence temperature coefficient and intrinsic coercivity temperature coefficient, and a low magnetic moment thermal decay rate.

[0008] The present invention achieves the above objectives through the following technical solutions.

[0009] On one hand, the present invention provides a neodymium iron boron permanent magnet, which is rectangular in shape, wherein the height direction of the neodymium iron boron permanent magnet is its orientation direction, and the height of the neodymium iron boron permanent magnet is ≥8mm;

[0010] The heavy rare earth element content at the apex of the neodymium iron boron permanent magnet is >0.65wt%, the heavy rare earth element content at the edges of the neodymium iron boron permanent magnet is >0.43wt%, the heavy rare earth element content at the outer layer of the neodymium iron boron permanent magnet is ≥0.22wt%, and the heavy rare earth element content at the core of the neodymium iron boron permanent magnet is ≥0.003wt%.

[0011] Among them, the content of heavy rare earth elements at the top corner is greater than that at the edge, which is greater than that at the outer layer, which is greater than that at the core.

[0012] In the neodymium iron boron permanent magnet of the present invention, preferably, the heavy rare earth element is selected from one or more of Dy and Tb;

[0013] The content of heavy rare earth elements at the apex of the neodymium iron boron permanent magnet is ≤1.00wt%, the content of heavy rare earth elements at the edges of the neodymium iron boron permanent magnet is ≤0.80wt%, the content of heavy rare earth elements at the outer layer of the neodymium iron boron permanent magnet is ≤0.50wt%, and the content of heavy rare earth elements at the core of the neodymium iron boron permanent magnet is ≤0.10wt%.

[0014] According to the neodymium iron boron permanent magnet of the present invention, preferably, the |α of the neodymium iron boron permanent magnet is... Br ≤0.115% / ℃

[0015] |α Hcj ≤0.463% / ℃;

[0016] Where, α Br= [(Br1-Br0) / Br0] / (T1-T0); where Br1 is the remanence of the neodymium iron boron permanent magnet measured at temperature T1 according to the test method specified in GB / T-3217-2013 "Magnetic Test Method for Permanent Magnet (Hard Magnetic) Materials", in kGs; Br0 is the remanence of the neodymium iron boron permanent magnet measured at temperature T0 according to the test method specified in GB / T-3217-2013 "Magnetic Test Method for Permanent Magnet (Hard Magnetic) Materials", in kGs; T1 is in °C, and T0 is in °C;

[0017] Where, α Hcj = [(Hcj1-Hcj0) / Hcj0] / (T1-T0); where Hcj1 is the intrinsic coercivity of the neodymium iron boron permanent magnet measured at temperature T1 according to the test method specified in GB / T-3217-2013 "Magnetic Test Method for Permanent Magnet (Hard Magnetic) Materials", in kOe; Hcj0 is the intrinsic coercivity of the neodymium iron boron permanent magnet measured at temperature T0 according to the test method specified in GB / T-3217-2013 "Magnetic Test Method for Permanent Magnet (Hard Magnetic) Materials", in kOe; T1 is in °C, and T0 is in °C.

[0018] According to the neodymium iron boron permanent magnet of the present invention, preferably, the thermal decay rate of the magnetic moment of the neodymium iron boron permanent magnet is ≤1.35%;

[0019] The thermal attenuation rate of the magnetic moment is calculated using the following formula:

[0020] Magnetic moment thermal decay rate = (m0-m1) / m0×100%;

[0021] Wherein, m0 is obtained by testing using the following method:

[0022] The neodymium iron boron permanent magnet was saturated with magnetization to obtain the magnetized magnet. At 20°C, the magnetic flux of the magnetized magnet was measured using a magnetometer and then converted into a magnetic moment to obtain the magnetic moment of the untreated neodymium iron boron permanent magnet, denoted as m0, with the unit being μVsm.

[0023] m1 was obtained by testing using the following method:

[0024] The neodymium iron boron permanent magnet was placed perpendicularly to the orientation of a 1.5 mm thick aluminum plate. It was then kept at 150 °C for 2 hours in a high-temperature test chamber to obtain a heat-treated magnet. After the heat-treated magnet was naturally cooled to 20 °C, the magnetic flux of the heat-treated magnet was measured using a magnetometer. The magnetic flux was converted into a magnetic moment to obtain the magnetic moment of the heat-treated neodymium iron boron permanent magnet, denoted as m1, with units of μVsm.

[0025] On the other hand, the present invention provides a method for preparing the above-mentioned neodymium iron boron permanent magnet, comprising the following steps:

[0026] S1) The fine powder is mixed with the grain boundary modifier and then shaped to obtain a green body;

[0027] S2) The blank is sintered and then cooled to obtain the magnet to be diffused;

[0028] S3) Wrap the surface of the magnet to be diffused with diffusion metal foil to obtain the diffusion precursor;

[0029] S4) The diffusion precursor is diffused to obtain neodymium iron boron permanent magnets;

[0030] The fine powder contains alloy fine powder, which has the composition shown in formula (I):

[0031] R a T b B c M d N e (I);

[0032] Wherein, R is selected from one or more of La, Ce, Pr, Nd, Ho, Gd, Dy and Tb; T is selected from one or more of Fe and Co; M is selected from one or more of Ti, Ni, V, Nb, Zr, Hf, Mo and W; N is selected from one or more of Al, In, Sn, Zn and Ga, and must contain Ga;

[0033] 28.5≤a≤33, 0.85≤c≤1.0, 0.20≤d≤0.95, 0.30≤e≤0.95, b=100-acde; a~e represent the weight fractions of each element respectively;

[0034] The grain boundary modifier comprises a modified alloy having a composition as shown in formula (II):

[0035] Cu x Bi y Mg z (II);

[0036] 60≤x≤80, 10≤y≤30, 3≤z≤20; x~z represent the weight fractions of each element respectively;

[0037] The diffusion metal foil comprises a first metal foil, a second metal foil, and heavy rare earth powder, wherein the heavy rare earth powder is dispersed between the first metal foil and the second metal foil; the melting point of the first metal foil is lower than that of the second metal foil; and the heavy rare earth powder is selected from one or more of dysprosium, terbium, dysprosium fluoride, terbium fluoride, dysprosium hydride, terbium hydride, terbium-containing alloys, and dysprosium-containing alloys.

[0038] According to the preparation method of the present invention, preferably, the grain boundary modifier further includes a coating agent, wherein the coating agent is selected from one or more of C8-C13 unsaturated monohydric alcohols, aluminate coupling agents, C5-C12 aliphatic alkanes, polymeric diols, and amide compounds;

[0039] The mass ratio of the coating agent to the modified alloy is 1:(3-9);

[0040] The particle size D of the modified alloy 50 The wavelength is 35–55 nm.

[0041] The amount of the grain boundary modifier is 0.5 to 1.5 wt% of the fine powder mass.

[0042] According to the preparation method of the present invention, preferably, the first metal foil is selected from one or more of tin foil and lead foil, and the second metal foil is selected from one or more of aluminum foil and copper foil;

[0043] The first metal foil is in contact with the magnet to be diffused;

[0044] The amount of the heavy rare earth powder is 0.25 to 0.75 wt% of the mass of the magnet to be diffused.

[0045] According to the preparation method of the present invention, preferably, a diffusion metal foil is used to completely cover all surfaces of the magnet to be diffused; the diffusion metal foil is heated to melt the first metal foil, and then cooled to fix the diffusion metal foil on the surface of the magnet to be diffused, thereby obtaining a diffusion precursor.

[0046] According to the preparation method of the present invention, preferably, the particle size D of the fine powder is... 50 The diameter is 2.5–4.0 μm, D 90 / D 10 It ranges from 2.5 to 4.

[0047] According to the preparation method of the present invention, preferably, the diffusion precursor is prepared under a pressure < 5 × 10⁻⁶. -2 A first-stage diffusion process is performed at a pressure of Pa and a temperature of 800–1200 °C to obtain a first-stage diffuser; the first-stage diffuser is then cooled to obtain a cooled first-stage diffuser; the cooled first-stage diffuser is then subjected to a pressure of <5 × 10⁻⁶ Pa. -2A secondary diffusion process is carried out at a temperature of 450–650 °C to obtain a secondary diffuser; the secondary diffuser is then cooled to obtain a neodymium iron boron permanent magnet.

[0048] The neodymium iron boron permanent magnets of the present invention have appropriate heavy rare earth element content in each part, which can improve the thermal demagnetization resistance of large-size neodymium iron boron permanent magnets, reduce the absolute value of the Br temperature coefficient and the absolute value of the Hcj temperature coefficient of large-size neodymium iron boron permanent magnets, and reduce the thermal decay rate of the magnetic moment of large-size neodymium iron boron permanent magnets. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the process of fully enclosing the magnet to be diffused.

[0050] Figure 2 This is a schematic diagram showing the positions of the apex, edges, outer layer, and core of a neodymium iron boron permanent magnet.

[0051] The attached figures are labeled as follows:

[0052] 1-Upper concave chuck; 2-Lower concave chuck; 3-Second diffusion metal foil; 4-Magnet to be diffused; 5-First diffusion metal foil; 101-Peak corner; 102-Edge; 103-Outer layer; 104-Core. Detailed Implementation

[0053] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0054] Neodymium iron boron permanent magnets

[0055] The neodymium iron boron (NdFeB) permanent magnet of this invention is cuboid in shape. The height direction of the NdFeB permanent magnet is its orientation direction. The height of the NdFeB permanent magnet is greater than or equal to 8 mm; preferably, it is greater than or equal to 10 mm. The height of the NdFeB permanent magnet can be less than or equal to 30 mm; preferably, it is less than or equal to 20 mm. The content of heavy rare earth elements varies in different parts of the NdFeB permanent magnet of this invention. This invention has found that controlling the content of heavy rare earth elements in different parts of the NdFeB permanent magnet within a certain range helps to improve the thermal demagnetization resistance of large-size NdFeB permanent magnets, and reduces the absolute values ​​of the Br temperature coefficient, Hcj temperature coefficient, and magnetic moment thermal decay rate of large-size NdFeB permanent magnets.

[0056] The length of the neodymium iron boron permanent magnet can be 20-100 mm; preferably 30-80 mm; more preferably 50-60 mm.

[0057] The width of the neodymium iron boron permanent magnet can be 5 to 50 mm; preferably 10 to 40 mm; more preferably 15 to 30 mm.

[0058] The neodymium iron boron permanent magnets of the present invention contain different amounts of heavy rare earth elements at their apex, edges, outer layer, and core. Specifically, the heavy rare earth element content at the apex is greater than that at the edges, which is greater than that at the outer layer, which is greater than that at the core.

[0059] The heavy rare earth element can be selected from one or more of Dy and Tb. Preferably, the heavy rare earth element is Tb.

[0060] The content of heavy rare earth elements in different parts of a neodymium iron boron permanent magnet can be measured using X-ray fluorescence spectrometry. Specifically, samples obtained from different parts of the neodymium iron boron permanent magnet can be crushed into powder and then measured using X-ray fluorescence spectrometry. The sample can be a cube. The dimensions of the cube can be 4mm × 4mm × 4mm.

[0061] The sampling position of the sample at the apex can be a cube formed by extending 4 mm in the length, width and height directions of the NdFeB permanent magnet, starting from the apex of the NdFeB permanent magnet.

[0062] The sampling location for the edge sample can be a cube formed by extending 4mm from the edge of a 4mm-long neodymium iron boron permanent magnet to the two faces adjacent to that edge. Preferably, the edge is the edge in the height direction of the neodymium iron boron permanent magnet.

[0063] The sampling location for the outer layer sample is a cube formed by extending 4mm into the core of the NdFeB permanent magnet from the center of one surface of the NdFeB permanent magnet as the starting surface. Preferably, this surface is perpendicular to the orientation direction of the NdFeB permanent magnet.

[0064] The orientation of the sample at the core is a cube formed by extending 2mm vertically from several centers of the neodymium iron boron permanent magnet to each of the six surfaces of the neodymium iron boron permanent magnet.

[0065] The heavy rare earth element content at the apex of the neodymium iron boron permanent magnet is >0.65 wt%; preferably, the heavy rare earth element content is ≥0.68 wt%; more preferably, the heavy rare earth element content is ≥0.75 wt%; most preferably, the heavy rare earth element content is ≥0.78 wt%. The heavy rare earth element content at the apex is ≤1.00 wt%; preferably, the heavy rare earth element content is ≤0.90 wt%; more preferably, the heavy rare earth element content is ≤0.85 wt%; most preferably, the heavy rare earth element content is ≤0.80 wt%.

[0066] The heavy rare earth element content at the edges of the neodymium iron boron permanent magnet is >0.43 wt%; preferably, the heavy rare earth element content is ≥0.44 wt%; more preferably, the heavy rare earth element content is ≥0.50 wt%; most preferably, the heavy rare earth element content is ≥0.52 wt%. The heavy rare earth element content at the edges is ≤0.80 wt%; preferably, the heavy rare earth element content is ≤0.60 wt%; more preferably, the heavy rare earth element content is ≤0.55 wt%.

[0067] The outer layer of the neodymium iron boron permanent magnet contains ≥0.22 wt% heavy rare earth elements; preferably, ≥0.25 wt%; more preferably, ≥0.26 wt%. The outer layer contains ≤0.50 wt% heavy rare earth elements; preferably, ≤0.40 wt%; more preferably, ≤0.27 wt%.

[0068] The heavy rare earth element content in the core of the neodymium iron boron permanent magnet is ≥0.003 wt%; preferably, the heavy rare earth element content is ≥0.007 wt%; more preferably, the heavy rare earth element content is ≥0.01 wt%. The heavy rare earth element content in the core is ≤0.10 wt%; preferably, the heavy rare earth element content is ≤0.05 wt%; more preferably, the heavy rare earth element content is ≤0.015 wt%.

[0069] Controlling the content of heavy rare earth elements at the apex, edges, outer layer, and core of NdFeB permanent magnets within the aforementioned range helps improve the thermal demagnetization resistance of large-size NdFeB permanent magnets, and reduces the absolute values ​​of the Br temperature coefficient, Hcj temperature coefficient, and magnetic moment thermal decay rate of large-size NdFeB permanent magnets. Furthermore, it can also reduce the amount of heavy rare earth elements used.

[0070] The neodymium iron boron permanent magnet of the present invention |α Br |≤0.115% / ℃; Preferably, |α Br |≤0.110% / ℃; more preferably, |α Br |≤0.105% / ℃.

[0071] α Br This represents the temperature coefficient of remanence. α Br= [(Br1-Br0) / Br0] / (T1-T0); where Br1 is the remanence of the neodymium iron boron permanent magnet measured at temperature T1 according to the test method specified in GB / T-3217-2013 "Magnetic Test Method for Permanent Magnet (Hard Magnetic) Materials", in kGs; Br0 is the remanence of the neodymium iron boron permanent magnet measured at temperature T0 according to the test method specified in GB / T-3217-2013 "Magnetic Test Method for Permanent Magnet (Hard Magnetic) Materials", in kGs; T1 is in °C, and T0 is in °C. According to one embodiment of the present invention, T0 is 20 °C, and T1 is 150 °C.

[0072] The neodymium iron boron permanent magnet of the present invention |α Hcj |≤0.463% / ℃; Preferably, |α Hcj |≤0.460% / ℃; more preferably, |α Hcj |≤0.455% / ℃; Most preferably, |α Hcj |≤0.451% / ℃.

[0073] α Hcj α represents the temperature coefficient of intrinsic coercivity. Hcj = [(Hcj1-Hcj0) / Hcj0] / (T1-T0); where Hcj1 is the intrinsic coercivity of the neodymium iron boron permanent magnet measured at temperature T1 according to the test method specified in GB / T-3217-2013 "Magnetic Test Method for Permanent Magnet (Hard Magnetic) Materials", in kOe; Hcj0 is the intrinsic coercivity of the neodymium iron boron permanent magnet measured at temperature T0 according to the test method specified in GB / T-3217-2013 "Magnetic Test Method for Permanent Magnet (Hard Magnetic) Materials", in kOe; T1 is in °C, and T0 is in °C. According to one embodiment of the present invention, T0 is 20 °C, and T1 is 150 °C.

[0074] The thermal decay rate of the magnetic moment of the neodymium iron boron permanent magnet of the present invention is ≤1.35%; preferably, the thermal decay rate of the magnetic moment is ≤1.00%; more preferably, the thermal decay rate of the magnetic moment is ≤0.55%.

[0075] The thermal decay rate of the magnetic moment is calculated using the following formula:

[0076] Magnetic moment thermal decay rate = (m0-m1) / m0×100%;

[0077] Wherein, m0 is obtained by testing using the following method:

[0078] The neodymium iron boron permanent magnet was saturated with magnetization to obtain the magnetized magnet. At 20°C, the magnetic flux of the magnetized magnet was measured using a magnetometer and then converted into a magnetic moment to obtain the magnetic moment of the untreated neodymium iron boron permanent magnet, denoted as m0, with the unit being μVsm.

[0079] m1 was obtained by testing using the following method:

[0080] The neodymium iron boron permanent magnet was placed perpendicularly to the orientation of a 1.5 mm thick aluminum plate. It was then kept at 150 °C for 2 hours in a high-temperature test chamber to obtain a heat-treated magnet. After the heat-treated magnet was naturally cooled to 20 °C, the magnetic flux of the heat-treated magnet was measured using a magnetometer. The magnetic flux was converted into a magnetic moment to obtain the magnetic moment of the heat-treated neodymium iron boron permanent magnet, denoted as m1, with units of μVsm.

[0081] The magnetic flux is converted into magnetic moment using the following formula:

[0082]

[0083] Where m represents the magnetic moment value; k HH R represents the coil coefficient; HH R represents the coil resistance. FM Φ represents the resistance of the magnetometer; Φ represents the magnetic flux.

[0084] <Preparation Method of Neodymium Iron Boron Permanent Magnets>

[0085] The method for preparing the neodymium iron boron permanent magnet of the present invention includes the following steps: S1) modification and forming; S2) sintering; S3) coating with diffusion metal foil; and S4) diffusion. In some embodiments, it further includes P1) preparing alloy sheets; P2) preparing coarse powder; and P3) preparing fine powder.

[0086] Modification and molding steps

[0087] This invention involves mixing fine powder with a grain boundary modifier, and then molding it to obtain a green body.

[0088] The fine powder contains alloy fine powder. In some embodiments, the fine powder also contains an antioxidant. The particle size D of the fine powder 50 The particle size can be 2.5–4.0 μm; preferably 3.0–3.8 μm; more preferably 3.4–3.6 μm. The D of the fine powder... 90 / D 10 It can be 2.5 to 4; preferably 3 to 3.9; more preferably 3.5 to 3.8.

[0089] The alloy powder of the present invention has the composition shown in formula (I):

[0090] R a T b B c M d N e (I).

[0091] R is selected from one or more of La, Ce, Pr, Nd, Ho, Gd, Dy, and Tb; preferably, R is selected from one or more of La, Ce, Pr, and Nd. More preferably, R is selected from one or more of Pr and Nd. Most preferably, R is Pr and Nd. The mass ratio of Pr to Nd can be 25:(60-90); preferably 25:(65-85); more preferably 25:(70-80).

[0092] a represents the weight parts of R. 28.5 ≤ a ≤ 33; preferably, 29 ≤ a ≤ 32; more preferably, 30 ≤ a ≤ 31.

[0093] T is selected from one or more of Fe and Co. Preferably, T is Fe or Co.

[0094] b represents the weight fraction of T. b = 100 - acde. In some embodiments, 65 ≤ b ≤ 69.5; preferably, 66 ≤ b ≤ 68.5; more preferably, 67 ≤ b ≤ 68.

[0095] The Fe content can be 64 to 68 parts by weight; preferably 64.5 to 67 parts by weight; more preferably 65 to 65.5 parts by weight.

[0096] The content of Co can be 0.5 to 3 parts by weight; preferably 1 to 2.5 parts by weight; more preferably 1.8 to 2.3 parts by weight.

[0097] B represents boron. c represents the weight parts of B. 0.85≤c≤1.0; preferably, 0.90≤c≤0.98; more preferably, 0.95≤c≤0.96.

[0098] M is selected from one or more of Ti, Ni, V, Nb, Zr, Hf, Mo, and W. In some embodiments, M is Ti and V. In other embodiments, M is Ti, Zr, and Ni. In still other embodiments, M is Ti, Nb, Hf, and Mo.

[0099] d represents the weight fraction of M. 0.20≤d≤0.95; preferably, 0.30≤d≤0.70; more preferably, 0.35≤d≤0.50.

[0100] The Ti content can be 0.05 to 0.5 parts by weight; preferably 0.08 to 0.3 parts by weight; more preferably 0.1 to 0.15 parts by weight.

[0101] The content of V can be 0.03 to 0.4 parts by weight; preferably 0.05 to 0.3 parts by weight; more preferably 0.1 to 0.15 parts by weight.

[0102] The Zr content can be 0.03 to 0.4 parts by weight; preferably 0.05 to 0.3 parts by weight; more preferably 0.1 to 0.15 parts by weight.

[0103] The Ni content can be 0.03 to 0.4 parts by weight; preferably 0.05 to 0.3 parts by weight; more preferably 0.1 to 0.15 parts by weight.

[0104] The Nb content can be 0.03 to 0.4 parts by weight; preferably 0.05 to 0.3 parts by weight; more preferably 0.1 to 0.15 parts by weight.

[0105] The Hf content can be 0.03 to 0.4 parts by weight; preferably 0.05 to 0.3 parts by weight; more preferably 0.1 to 0.15 parts by weight.

[0106] The content of Mo can be 0.01 to 0.15 parts by weight; preferably 0.03 to 0.1 parts by weight; more preferably 0.05 to 0.07 parts by weight.

[0107] N is selected from one or more of Al, In, Sn, Zn, and Ga, and must contain Ga. Preferably, it also contains Al and Zn. More preferably, it also contains In.

[0108] e represents the weight parts of N. 0.30≤e≤0.95; preferably, 0.40≤e≤0.70; more preferably, 0.45≤e≤0.60.

[0109] The content of Ga can be 0.05 to 0.4 parts by weight; preferably 0.1 to 0.3 parts by weight; more preferably 0.2 to 0.25 parts by weight.

[0110] The Al content can be 0.01 to 0.3 parts by weight; preferably 0.03 to 0.2 parts by weight; more preferably 0.05 to 0.08 parts by weight.

[0111] The Zn content can be 0.03 to 0.4 parts by weight; preferably 0.05 to 0.3 parts by weight; more preferably 0.1 to 0.15 parts by weight.

[0112] The In content can be 0.03 to 0.4 parts by weight; preferably 0.05 to 0.3 parts by weight; more preferably 0.1 to 0.15 parts by weight.

[0113] Preferably, the alloy powder of the present invention does not contain Cu.

[0114] The antioxidant can be composed of diethylformamide, dipropylene glycol dimethyl ether, and butylated hydroxytoluene. The content of diethylformamide can be 25–50 wt%, preferably 35–45 wt%. The content of dipropylene glycol dimethyl ether can be 20–40 wt%, preferably 25–35 wt%. The content of butylated hydroxytoluene can be 20–40 wt%, preferably 25–35 wt%. The content of the antioxidant can be 0.01–0.2 wt% of the alloy powder mass, preferably 0.05–0.15 wt%, more preferably 0.08–0.1 wt%.

[0115] The grain boundary modifier of the present invention comprises a modified alloy. Preferably, it further comprises a coating agent. The mass ratio of the coating agent to the modified alloy can be 1:(3-9); preferably 1:(4-8); more preferably 1:(5-7).

[0116] The modified alloy has the composition shown in formula (II):

[0117] Cu x Bi y Mg z (II).

[0118] x represents the weight parts of Cu. 60≤x≤80; preferably, 65≤x≤75; more preferably, 70≤x≤72.

[0119] y represents the weight parts of Bi. 10≤y≤30; preferably, 15≤y≤25; more preferably, 20≤y≤22.

[0120] z represents the weight parts of Mg. 3 ≤ z ≤ 20; preferably, 5 ≤ z ≤ 15; more preferably, 10 ≤ z ≤ 12.

[0121] The coating agent may be selected from one or more of C8-C13 unsaturated monohydric alcohols, aluminate coupling agents, C5-C12 aliphatic alkanes, polymeric diols, and amide compounds. Preferably, the coating agent includes one or more of C8-C13 unsaturated monohydric alcohols, aluminate coupling agents, C5-C12 aliphatic alkanes, polymeric diols, and amide compounds.

[0122] The amount of unsaturated monohydric alcohol used can be 0.5 to 3 parts by weight; preferably 0.8 to 2 parts by weight; more preferably 1 to 1.5 parts by weight.

[0123] Preferably, the unsaturated monohydric alcohol contains 9 to 11 carbon atoms. According to one embodiment of the invention, the unsaturated monohydric alcohol is terpineol.

[0124] The amount of aluminate coupling agent can be 1 to 4 parts by weight; preferably 1.5 to 3 parts by weight; more preferably 2 to 2.5 parts by weight.

[0125] Preferably, the aluminate coupling agent may be selected from one or more of DL-411, DL-411D, and SG-Al821. According to one embodiment of the present invention, the aluminate coupling agent is DL-411.

[0126] The amount of aliphatic alkanes used can be 0.5 to 3 parts by weight; preferably 0.8 to 2 parts by weight; more preferably 1 to 1.5 parts by weight.

[0127] Preferably, the aliphatic alkane contains 7 to 10 carbon atoms; more preferably, it contains 8 to 9 carbon atoms. According to one embodiment of the invention, the aliphatic alkane is n-octane.

[0128] The amount of polymeric diol used can be 1 to 4 parts by weight; preferably 1.5 to 3 parts by weight; more preferably 2 to 2.5 parts by weight.

[0129] Preferably, the polymeric diol is polyethylene glycol. The molecular weight of polyethylene glycol can be 200–600; more preferably 300–500.

[0130] The amount of amide compound used can be 0.5 to 3 parts by weight; preferably 0.8 to 2 parts by weight; more preferably 1 to 1.5 parts by weight.

[0131] Preferably, the amide compound is selected from one or more of dimethylformamide and dimethylacetamide. Preferably, the amide compound is N,N-dimethylformamide.

[0132] Particle size D of the modified alloy 50 It can be 35-55nm; preferably 40-50nm; more preferably 43-46nm.

[0133] The amount of grain boundary modifier can be 0.5 to 1.5 wt% of the fine powder mass; preferably 0.6 to 1.2 wt%; more preferably 0.75 to 0.8 wt%.

[0134] In some embodiments, the step of preparing a grain boundary modifier is also included:

[0135] The modified alloy raw material is melted in a gas atomization vacuum melting furnace to obtain a spherical modified master alloy. The modified master alloy is then subjected to a hydrogenation-dehydrogenation furnace using the HDDR method to form a modified alloy. The modified alloy and a coating agent are stirred to obtain a grain boundary modifier. Stirring can be performed in a planetary mixer under an argon atmosphere. The stirring time can be 10–60 min; preferably 20–40 min. Before stirring the coating agent with the modified alloy, its various components can be mixed uniformly. Nitrogen can be used as the gas source for gas atomization.

[0136] Particle size D of modified master alloy 50The micrometer can be 2.5–5.0 μm; preferably 3.0–4.0 μm; more preferably 3.2–3.6 μm.

[0137] Mixing the alloy fine powder containing the composition of this invention with a grain boundary modifier can increase the thickness of the grain boundary layer of the magnet to be diffused, weaken the exchange coupling effect, and clear the diffusion channel, so that the apex, edge, outer layer and core of the NdFeB permanent magnet have an appropriate content of heavy rare earth elements, thereby improving the heat resistance and demagnetization ability of the NdFeB permanent magnet.

[0138] Molding can include orientation molding and isostatic pressing. Preferably, isostatic pressing is cold isostatic pressing.

[0139] The molding pressure can be 3 to 10 MPa; preferably 4 to 8 MPa; more preferably 5 to 6 MPa.

[0140] The orientation current can be 100–300A; preferably 150–250A; more preferably 200–220A.

[0141] The isostatic pressure can be 150-230 MPa; preferably 170-210 MPa; more preferably 190-200 MPa.

[0142] The isostatic pressing time can be 20–70 s; preferably 30–60 s; more preferably 40–50 s.

[0143] Orientation molding includes the following steps: injecting modified fine powder into the mold cavity of a magnetic field forming press for orientation molding to obtain a pressed preform. The oxygen content in the mold cavity can be lower than 10 ppm; preferably, the oxygen content is lower than 5 ppm. The density of the pressed preform can be 3-6 g / cm³. 3 The preferred value is 4-5 g / cm³. 3 .

[0144] Isostatic pressing includes the following steps: vacuum-packing the preform, and then pressing it in a cold isostatic press to obtain the preform. The oxygen content of the glove box used for vacuum packaging can be less than 40 ppm; preferably, the oxygen content is less than 20 ppm.

[0145] Sintering steps

[0146] The present invention involves sintering a blank and then cooling it to obtain a magnet to be diffused.

[0147] The sintering temperature can be 800–1300℃; preferably 900–1200℃; more preferably 1000–1100℃. The heating time from the initial temperature to the sintering temperature can be 200–500 min; preferably 250–400 min.

[0148] The sintering time can be 5 to 13 hours; preferably 6 to 11 hours; more preferably 8 to 9 hours.

[0149] Sintering can be performed at pressures less than 5 × 10⁻⁶. -2 The sintering is carried out under conditions of Pa; preferably, sintering is performed under a pressure < 1 × 10 Pa. -2 The sintering is carried out under conditions of Pa; more preferably, sintering is carried out under a pressure of 0.5 × 10 Pa. -3 ~2×10 -3 The experiment was conducted under the condition of Pa.

[0150] Cooling can be carried out under the protection of an inert gas. The inert gas can be argon.

[0151] Cooling can be carried out at a pressure of 50 to 90 kPa; preferably, cooling is carried out at a pressure of 60 to 80 kPa; more preferably, cooling is carried out at a pressure of 70 to 75 kPa.

[0152] Cooling can be achieved using air cooling. Specifically, under the condition that the fan speed is 100-400 r / min; preferably 150-300 r / min, the first stage of air cooling is performed to 700-1100℃; preferably 800-1000℃. Under the condition that the fan speed is 600-1000 r / min; preferably 700-900 r / min, the second stage of air cooling is performed to 400-800℃; preferably 500-700℃. Under the condition that the fan speed is 800-1400 r / min; preferably 900-1200 r / min, the third stage of air cooling is performed to 30-80℃; preferably 50-55℃.

[0153] The height of the magnet to be diffused is greater than or equal to 8 mm; preferably, it is greater than or equal to 10 mm. The height of the magnet to be diffused can be less than or equal to 30 mm; preferably, it is less than or equal to 20 mm. The height direction is the orientation direction of the magnet to be diffused.

[0154] The length of the magnet to be diffused can be 20–100 mm; preferably 30–80 mm; more preferably 50–60 mm.

[0155] The width of the magnet to be diffused can be 5 to 50 mm; preferably 10 to 40 mm; more preferably 15 to 30 mm.

[0156] The oxide film on the surface of the sintered body obtained after cooling can be removed, and then magnetic steel sheets can be cut according to the size of the magnet to be diffused. Oil stains on the surface of the magnetic steel sheets are removed, and then they are dried to obtain the magnet to be diffused.

[0157] Steps for wrapping diffusion metal foil

[0158] This invention involves wrapping the surface of the magnet to be diffused with a diffusion metal foil to obtain a diffusion precursor. "Wrapping" refers to the process of tightly adhering and fixing the diffusion metal foil to the surface of the magnet to be diffused.

[0159] The diffusion metal foil of the present invention comprises a first metal foil, a second metal foil, and heavy rare earth powder. The heavy rare earth powder is dispersed between the first metal foil and the second metal foil.

[0160] The melting point of the first metal foil is lower than that of the second metal foil. The first metal foil may be selected from one or more of tin foil and lead foil. Preferably, the first metal foil is tin foil. Preferably, the first metal foil is a metal foil after the oxide layer has been removed. The thickness of the first metal foil may be 10-60 μm; preferably 30-50 μm; more preferably 40-45 μm.

[0161] The second metal foil may be selected from one or more of aluminum foil and copper foil. Preferably, the second metal foil is aluminum foil. Preferably, the surface of the second metal foil has a dense oxide film. The thickness of the second metal foil may be 10-60 μm; preferably 20-50 μm; more preferably 30-40 μm.

[0162] The heavy rare earth powder is selected from one or more of dysprosium metal, terbium metal, dysprosium fluoride, terbium fluoride, dysprosium hydride, terbium hydride, terbium-containing alloys, and dysprosium-containing alloys. Preferably, the heavy rare earth powder is selected from one or more of dysprosium metal and terbium metal. More preferably, the heavy rare earth powder is terbium metal.

[0163] Heavy rare earth powder particle size D 50 The micrometer can be 0.01–0.10 μm; preferably 0.03–0.08 μm; more preferably 0.05–0.07 μm.

[0164] The amount of heavy rare earth powder can be 0.25-0.75 wt% of the magnet to be diffused; preferably 0.35-0.6 wt%; more preferably 0.4-0.5 wt%.

[0165] The first metal foil comes into contact with the magnet to be diffused.

[0166] Specifically, the present invention uses a diffusion metal foil to completely cover all surfaces of the magnet to be diffused; the diffusion metal foil is heated to melt the first metal foil, and then cooled to fix the diffusion metal foil on the surface of the magnet to be diffused, thus obtaining a diffusion precursor.

[0167] The diffused metal foil can be heated to 260–370°C; preferably 280–350°C; more preferably 300–320°C.

[0168] The diffused metal foil can be held at the above temperature for 1 to 10 seconds; preferably 2 to 8 seconds; more preferably 3 to 6 seconds.

[0169] An inert gas can be used to purge the diffusion metal foil to cool it. Nitrogen can be used as the inert gas.

[0170] A first and a second diffusion metal foil can be used to completely cover all surfaces of the magnet to be diffused. The first diffusion metal foil has a length of L1 and a width of W1; the second diffusion metal foil has a length of L2 and a width of W2; the magnet to be diffused has a length of L, a width of W, and a height of H; then L1 = L, W1 = W + H + H, L2 = L + H + H, and W2 = W. The second diffusion metal foil covers the bottom surface of the magnet to be diffused and its two opposite sides (the sides composed of height and width). The first diffusion metal foil covers the top surface of the magnet to be diffused and its other two sides (the sides composed of height and length).

[0171] In some embodiments, the step of preparing a diffused metal foil is also included:

[0172] The second metal foil is heat-treated in air or an oxygen-rich atmosphere at a temperature of 300–350°C for 1–2 hours to form a dense oxide film on the outer surface of the aluminum foil, thus obtaining the treated second metal foil.

[0173] The first metal foil is immersed in an acid solution and then washed to obtain a washed first metal foil. The water on the washed first metal foil is removed to obtain a treated first metal foil. The acid solution can be a nitric acid solution. The concentration of the acid solution can be 5–30 wt%; preferably 10–20 wt%.

[0174] Heavy rare earth powder is uniformly distributed on a treated second metal foil, and then a treated first metal foil is used to cover the heavy rare earth powder to obtain a diffusion source blank. A roller is used to roll the surface of the diffusion source blank to obtain a diffusion source metal foil. Preferably, under the protection of an inert gas, the heavy rare earth powder is uniformly distributed on the treated second metal foil, and then a treated first metal foil is used to cover the heavy rare earth powder to obtain the diffusion source blank. The inert gas can be selected from one or more of nitrogen, argon, and helium.

[0175] Diffusion steps

[0176] This invention involves diffusing a diffusion precursor to obtain a neodymium iron boron permanent magnet. The diffusion can be carried out in a vacuum heat treatment furnace. Specifically, the diffusion precursor can be placed in a molybdenum box, and then diffusion can be performed in the vacuum heat treatment furnace.

[0177] Specifically, the diffusion precursor is subjected to a pressure < 5 × 10⁻⁶. -2 A first-stage diffusion process is performed at a pressure of Pa and a temperature of 800–1200 °C to obtain a first-stage diffuser; the first-stage diffuser is then cooled to obtain a cooled first-stage diffuser; the cooled first-stage diffuser is then subjected to a pressure of <5 × 10⁻⁶ Pa. -2 A secondary diffusion process is carried out at a temperature of 450–650 °C to obtain a secondary diffuser; the secondary diffuser is then cooled to obtain a neodymium iron boron permanent magnet.

[0178] Preferably, first-order diffusion occurs at pressures < 1 × 10⁻⁶. -2 The diffusion is carried out under conditions of Pa; more preferably, the first-order diffusion is carried out at a pressure of 3 × 10 Pa. -3 ~7×10 -3 The experiment was conducted under the condition of Pa.

[0179] Preferably, the primary diffusion temperature is 850–1100°C; more preferably, the primary diffusion temperature is 900–1000°C.

[0180] The primary diffusion time can be 3 to 10 hours; preferably 4 to 8 hours; more preferably 6 to 7 hours.

[0181] The time required to heat from the initial temperature to the primary diffusion temperature can be 100–400 min; preferably 150–300 min; more preferably 200–250 min.

[0182] The primary diffuser can be cooled in an inert gas atmosphere. The inert gas can be selected from one or more of nitrogen, helium, neon, and argon. According to one embodiment of the present invention, the inert gas is argon.

[0183] The primary diffuser can be cooled at a pressure of 50–200 kPa; preferably, at a pressure of 80–150 kPa; more preferably, at a pressure of 100–120 kPa.

[0184] The primary diffuser can be cooled by air cooling. The air velocity can be 20–80 m / s; preferably 30–70 m / s; more preferably 40–60 m / s.

[0185] The primary diffuser can be cooled to 15–35°C; preferably 20–30°C, to obtain a cooled primary diffuser.

[0186] Preferably, secondary diffusion occurs at pressures < 1 × 10⁻⁶. -2 The secondary diffusion is carried out under conditions of Pa; more preferably, the secondary diffusion is carried out at a pressure of 3 × 10 Pa. -3 ~7×10 -3 The experiment was conducted under the condition of Pa.

[0187] Preferably, the secondary diffusion temperature is 500–600°C; more preferably, the secondary diffusion temperature is 520–580°C.

[0188] The secondary diffusion time can be 2 to 10 hours; preferably 3 to 8 hours; more preferably 5 to 6 hours.

[0189] The time required to heat from the initial temperature to the secondary diffusion temperature can be 70–150 min; preferably 80–120 min; more preferably 100–110 min.

[0190] The secondary diffuser can be cooled in an inert gas atmosphere. The inert gas can be selected from one or more of nitrogen, helium, neon, and argon. According to one embodiment of the present invention, the inert gas is argon.

[0191] The secondary diffuser can be cooled at a pressure of 50 to 200 kPa; preferably, at a pressure of 80 to 150 kPa; more preferably, at a pressure of 100 to 120 kPa.

[0192] The secondary diffuser can be cooled by air cooling. The air velocity can be 20-80 m / s; preferably 30-70 m / s; more preferably 40-60 m / s.

[0193] The secondary diffuser can be cooled to 15–35°C; preferably 20–30°C.

[0194] In some embodiments, the process also includes the steps of fine grinding, cleaning, and drying the diffused magnet obtained after cooling the secondary diffuser.

[0195] Steps for preparing alloy sheets

[0196] This invention involves melting the permanent magnet matrix raw material and then casting it for rapid solidification to obtain an alloy sheet.

[0197] Melting can be carried out under a pressure ≤ 20 Pa; preferably, melting is carried out under a pressure ≤ 10 Pa; more preferably, melting is carried out under a pressure ≤ 6 Pa.

[0198] Rapid casting can be carried out under a pressure ≤20Pa; preferably, rapid casting can be carried out under a pressure ≤10Pa; more preferably, rapid casting can be carried out under a pressure ≤6Pa.

[0199] The casting temperature can be 1200–1650℃; preferably 1300–1600℃; more preferably 1400–1500℃.

[0200] The average thickness of the alloy sheet can be 0.1 to 0.5 mm; preferably 0.2 to 0.3 mm.

[0201] Steps for preparing coarse powder

[0202] This invention involves hydrogen pulverizing alloy sheets to obtain coarse powder.

[0203] Hydrogen absorption can be carried out at a pressure of 0.06 to 0.15 MPa; preferably, hydrogen absorption is carried out at a pressure of 0.08 to 0.12 MPa; more preferably, hydrogen absorption is carried out at a pressure of 0.1 to 0.11 MPa.

[0204] Hydrogen absorption can be carried out at a temperature of 150–250°C; preferably, hydrogen absorption is carried out at a temperature of 160–200°C; more preferably, hydrogen absorption is carried out at a temperature of 170–180°C.

[0205] Dehydrogenation is carried out under vacuum conditions. Vacuum refers to a pressure <10 Pa; preferably, the pressure <1 × 10 Pa. -2 Pa.

[0206] The dehydrogenation temperature can be 450–750°C; preferably 500–700°C; more preferably 550–600°C.

[0207] The dehydrogenation time can be 2 to 8 hours; preferably 3 to 7 hours; more preferably 4 to 6 hours.

[0208] The hydrogen content in the coarse powder is less than 1000 ppm; preferably, the hydrogen content is less than 900 ppm. In some embodiments, the hydrogen content in the coarse powder is 850–900 ppm.

[0209] Steps for preparing fine powder

[0210] The present invention uses air jet milling to obtain fine powder from raw materials including coarse powder.

[0211] Preferably, the raw materials also contain antioxidants.

[0212] The grinding gas source for the air jet mill is an inert gas. Preferably, the gas source is selected from one or more of helium, neon, and argon. More preferably, the gas source is argon.

[0213] Coarse powder and antioxidant can be mixed to form a raw material for air jet milling. Mixing can be carried out in a vertical single-screw mixer. The mixing time can be 10–60 min; preferably 20–50 min; more preferably 30–40 min.

[0214] Preparation Example 1

[0215] The modified alloy raw materials are provided according to the composition of the modified alloy.

[0216] The modified alloy raw materials were smelted in a gas atomization vacuum melting furnace using nitrogen as the gas source to obtain spherical modified master alloys. The particle size D of the modified master alloy was determined. 50 The particle size was 3.52 μm. The modified master alloy was subjected to HDDR process in a hydrogenation-dehydrogenation furnace to form a particle size D. 50 It is a modified alloy with a wavelength of 45nm. The elemental composition of the modified alloy is Cu. 70 Bi 20 Mg 10 (by weight)

[0217] Terpineol, aluminate coupling agent DL-411, n-octane, polyethylene glycol 400, and N,N-dimethylformamide were mixed in a weight ratio of 1:2:1:2:1 to obtain the coating agent.

[0218] The modified alloy and coating agent in a weight ratio of 6:1 were stirred in a planetary mixer under an argon atmosphere for 30 minutes to obtain the grain boundary modifier.

[0219] Preparation Example 2

[0220] The first diffusion source foil and the second diffusion foil are both rectangular. The length of the first diffusion foil is L1 and the width is W1; the length of the second diffusion foil is L2 and the width is W2; the length of the magnet to be diffused is L, the width is W, and the height is H; then L1 = L, W1 = W + H + H, L2 = L + H + H, W2 = W.

[0221] The first diffusion source metal foil and the second diffusion metal foil are prepared using the following method:

[0222] Aluminum foil was heat-treated in air at 330°C for 1.5 hours to form a dense oxide film on its outer surface, resulting in the treated aluminum foil. The thickness of the treated aluminum foil was 30 μm.

[0223] Tin foil was immersed in a 15 wt% nitric acid solution for 1 min, followed by ultrasonic cleaning for 2 min to obtain cleaned tin foil. The cleaned tin foil was then dehydrated in ethanol, and finally dried with nitrogen gas at 25°C to obtain treated tin foil. The thickness of the treated tin foil was 40 μm.

[0224] Under argon protection, the particle size D 50 Terbium powder with a particle size of 0.05 μm and a purity of 99.99% was uniformly dispersed on the treated aluminum foil, and then treated tin foil was used to cover the terbium powder to obtain a diffusion source blank. The treated aluminum foil and the treated tin foil were the same size and their edges were aligned. The surface of the diffusion source blank was repeatedly rolled with an embossing roller to obtain a diffusion source metal foil.

[0225] The total mass of terbium powder contained in the first diffusion source metal foil and the second diffusion metal foil is 0.4 wt% of the magnet to be diffused.

[0226] Preparation Example 3

[0227] Except that the total mass of terbium powder contained in the first diffusion source metal foil and the second diffusion metal foil is 0.45 wt% of the magnet to be diffused, the rest is the same as in preparation example 2.

[0228] Example 1

[0229] P1) Producing the raw material for the permanent magnet matrix. The composition of the raw material for the permanent magnet matrix is ​​as follows:

[0230] Pr-Nd (Nd to Pr mass ratio of 75:25) 30.9wt%, B 0.93wt%, Ti 0.2wt%, V 0.1wt%, Al 0.1wt%, Zn 0.1wt%, Ga 0.1wt%, Co 1wt%, and Fe balance.

[0231] The permanent magnet matrix material was melted under a pressure ≤6Pa, and then rapidly solidified by casting under a pressure ≤6Pa to obtain an alloy sheet with an average thickness of 0.23mm. The casting temperature was 1460℃.

[0232] P2) The alloy sheet was subjected to hydrogen absorption at a pressure of 0.1 MPa and a temperature of 180°C, and then dehydrogenated under vacuum (pressure < 10 Pa) and a temperature of 580°C for 4.5 h to obtain coarse powder with a hydrogen content of 895 ppm. Argon gas was used to protect the coarse powder tank during discharge.

[0233] P3) The coarse powder and antioxidant were mixed and stirred in a vertical single-screw mixer for 30 minutes, and then subjected to an air jet mill to obtain fine powder. The amount of antioxidant was 0.09 wt% of the coarse powder mass. The antioxidant was composed of 40 wt% diethylformamide, 30 wt% dipropylene glycol dimethyl ether, and 30 wt% dibutylhydroxytoluene. The grinding gas source for the air jet mill was argon (purity 99.99%). The particle size D of the fine powder was... 50 It is 3.5μm, D 90 / D 10 It is 3.8.

[0234] S1) The fine powder and the grain boundary modifier obtained in Preparation Example 1 were mixed and stirred in a vertical single-screw mixer for 30 min to obtain modified fine powder. The amount of grain boundary modifier was 0.75 wt% of the mass of the fine powder.

[0235] The modified fine powder was injected into the mold cavity of a magnetic field forming press for orientation molding, resulting in a powder with a density of 4.21 g / cm³. 3 The preform is formed under the following conditions: molding pressure of 5.3 MPa, orientation current of 200 A, and oxygen content in the mold cavity of less than 5 ppm.

[0236] The preform is vacuum-packed and then pressed for 40 seconds at 190 MPa in a cold isostatic press to obtain the preform. The oxygen content in the glove box used for vacuum packaging is less than 20 ppm.

[0237] S2) The billet is subjected to a pressure of 1×10 -3The sinter was then sintered at 1060℃ for 8 hours under the following conditions: argon gas was introduced to a pressure of 70 kPa; the temperature was then cooled to 900℃ using a first-stage air cooling system at a fan speed of 200 r / min; to 600℃ using a second-stage air cooling system at a fan speed of 800 r / min; and to 50℃ using a third-stage air cooling system at a fan speed of 1100 r / min, yielding the sintered body. The time to heat the body from the initial temperature to 1060℃ was 300 min.

[0238] The oxide scale on the surface of the sintered body is removed by grinding, and magnetic steel sheets with a length (L) of 50mm, a width (W) of 20mm, and a height (H) of 10mm are cut using multi-wire cutting. The height direction is the orientation direction of the magnet to be diffused. The oil stains on the surface of the magnetic steel sheets are cleaned, and then dried to obtain the magnet to be diffused.

[0239] S3) such as Figure 1 As shown, the second diffusion metal foil 3 of Preparation Example 2 is placed inside the concave chuck 2 of the wrapping fixture, and then the magnet to be diffused 4 is placed in the middle position of the concave chuck 2. The second diffusion metal foil 3 covers the bottom surface and the two opposite sides (the sides composed of height and width) of the magnet to be diffused 4. The tin foil of the second diffusion metal foil 3 is in contact with the magnet to be diffused 4. The first diffusion metal foil 5 of Preparation Example 2 is placed inside the upper concave chuck 1, and then the upper concave chuck 1 is pressed downward so that the first diffusion metal foil 5 covers the upper surface and the other two sides (the sides composed of height and length) of the magnet to be diffused 4. The tin foil of the first diffusion metal foil 5 is in contact with the magnet to be diffused 4.

[0240] The concave chuck 1 and the concave chuck 2 are heated to 320°C and held for 4 seconds to melt the tin foil of the first diffusion metal foil 5 and the second diffusion metal foil 3. The first diffusion metal foil 5 and the second diffusion metal foil 3 then wrap around the magnet 4 to be diffused. Then, nitrogen gas is used to purge the concave chuck 1 and the concave chuck 2 to cool the tin foil of the first diffusion metal foil 5 and the second diffusion metal foil 3, thus obtaining the diffusion precursor.

[0241] S4) In a vacuum heat treatment furnace, the diffusion precursor placed in a molybdenum box is subjected to a pressure of 5 × 10⁻⁶. -3 First-stage diffusion was carried out for 6 hours at a pressure of 910℃ and Pa to obtain the first-stage diffuser. The time to raise the temperature from the initial temperature to 910℃ was 200 min. Argon gas was introduced into a vacuum heat treatment furnace to a pressure of 100 kPa, and then the first-stage diffuser was cooled to 25℃ at a wind speed of 50 m / s to obtain the cooled first-stage diffuser. The cooled first-stage diffuser was then subjected to a pressure of 5 × 10⁻⁶ kPa. -3Secondary diffusion was carried out for 5.5 hours at a temperature of 530℃ and a pressure of 100 kPa to obtain a secondary diffuser. The temperature was increased from the initial temperature to 530℃ in 100 minutes. Argon gas was introduced into a vacuum heat treatment furnace to a pressure of 100 kPa, and then the secondary diffuser was cooled to 25℃ at a wind speed of 50 m / s to obtain the diffused magnet. The diffused magnet was then finely ground, cleaned, and dried to obtain a neodymium iron boron permanent magnet.

[0242] Example 2

[0243] Except for the different composition of the permanent magnet matrix material, the rest is the same as in Example 1. The composition of the permanent magnet matrix material in this example is as follows:

[0244] Pr-Nd (Nd to Pr mass ratio of 75:25) 30.9wt%, B 0.93wt%, Ti 0.1wt%, Zr 0.1wt%, Ni 0.1wt%, Al 0.1wt%, Zn 0.1wt%, In 0.1wt%, Ga 0.1wt%, Co 1.5wt%, and Fe balance.

[0245] Example 3

[0246] Except for the different composition of the permanent magnet matrix material, the rest is the same as in Example 1. The composition of the permanent magnet matrix material in this example is as follows:

[0247] Pr-Nd (Nd to Pr mass ratio of 75:25) 30.9wt%, B 0.96wt%, Nb 0.1wt%, Ti 0.1wt%, Hf 0.1wt%, Mo 0.05wt%, Al 0.05wt%, Zn 0.1wt%, In 0.1wt%, Ga 0.2wt%, Co 2wt%, and Fe balance.

[0248] Example 4

[0249] Except that the amount of grain boundary modifier is 1 wt% of the fine powder mass, the rest is the same as in Example 1.

[0250] Example 5

[0251] Except that the first and second diffusion metal foils are the same as those in Example 3, the rest are the same as in Example 1.

[0252] Example 6

[0253] Except for step S4), which differs from Example 1, the rest of the steps are the same as in Example 1. Step S4) of this example is as follows:

[0254] In a vacuum heat treatment furnace, the diffusion precursor placed in a molybdenum box is subjected to a pressure of 5 × 10⁻⁶. -3 First-stage diffusion was carried out at 860℃ and Pa for 6 hours to obtain the first-stage diffuser. The time to raise the temperature from the initial temperature to 860℃ was 200 min. Argon gas was introduced into a vacuum heat treatment furnace to a pressure of 100 kPa, and then the first-stage diffuser was cooled to 25℃ at a wind speed of 20 m / s to obtain the cooled first-stage diffuser. The cooled first-stage diffuser was then subjected to a pressure of 5 × 10⁻⁶ kPa. -3 Secondary diffusion was carried out for 5.5 hours at 500℃ and Pa to obtain a secondary diffuser. The time to raise the temperature from the initial temperature to 500℃ was 100 minutes. Argon gas was introduced into a vacuum heat treatment furnace to a pressure of 100 kPa, and then the secondary diffuser was cooled to 25℃ at a wind speed of 20 m / s to obtain the diffused magnet. The diffused magnet was then finely ground, cleaned, and dried to obtain a neodymium iron boron permanent magnet.

[0255] Comparative Example 1

[0256] Except for the different composition of the permanent magnet matrix material, the rest is the same as in Example 1. The composition of the permanent magnet matrix material in this comparative example is as follows:

[0257] Pr-Nd (Nd to Pr mass ratio of 75:25) 30.9wt%, B 0.96wt%, Ti 0.1wt%, Ga 0.1wt%, Co 0.5wt%, and Fe balance.

[0258] Comparative Example 2

[0259] Except for the different composition of the permanent magnet matrix material, the rest is the same as in Example 1. The composition of the permanent magnet matrix material in this comparative example is as follows:

[0260] Pr-Nd (Nd to Pr mass ratio of 75:25) 30.9wt%, B 0.96wt%, Ti 0.2wt%, Al 0.1wt%, Co 0.5wt%, and Fe balance.

[0261] Comparative Example 3

[0262] Except for the composition of the permanent magnet matrix raw material and the S1 step, the rest is the same as in Example 1.

[0263] The composition of the permanent magnet matrix material in this comparative example is as follows:

[0264] Pr-Nd (Nd to Pr mass ratio of 75:25) 30.9wt%, B 0.93wt%, Ti 0.2wt%, V 0.1wt%, Al 0.1wt%, Zn 0.1wt%, Ga 0.1wt%, Co 1wt%, Cu 0.1wt%, and Fe balance.

[0265] In step S1 of this comparative example, the grain boundary modifier was replaced with the lubricant n-octane, and the amount of lubricant used was 0.1 wt% of the fine powder mass.

[0266] Comparative Example 4

[0267] The magnet to be diffused was prepared using the method in Example 1. Terbium metal was melted and rapidly solidified to prepare terbium metal castings. The terbium metal castings were crushed under hydrogen absorption at 1 atm to prepare coarse terbium powder. The coarse terbium powder was crushed into fine terbium powder by an argon gas flow mill. The fine terbium powder was mixed with terpineol at a mass ratio of 1:2 and vacuum stirred to obtain terbium slurry.

[0268] Terbium slurry was coated onto the upper and lower surfaces of the magnet to be diffused to obtain the diffusion precursor. The amount of terbium used was 0.4 wt% of the mass of the magnet to be diffused.

[0269] In a vacuum heat treatment furnace, the diffusion precursor is subjected to a pressure of 5 × 10⁻⁶. -3 First-stage diffusion was carried out for 6 hours at a pressure of 910℃ and Pa to obtain the first-stage diffuser. The time to raise the temperature from the initial temperature to 910℃ was 200 min. Argon gas was introduced into a vacuum heat treatment furnace to a pressure of 100 kPa, and then the first-stage diffuser was cooled to 25℃ at a wind speed of 50 m / s to obtain the cooled first-stage diffuser. The cooled first-stage diffuser was then subjected to a pressure of 5 × 10⁻⁶ kPa. -3 Secondary diffusion was carried out for 5.5 hours at a temperature of 530℃ and a pressure of 100 kPa to obtain a secondary diffuser. The temperature was increased from the initial temperature to 530℃ in 100 minutes. Argon gas was introduced into a vacuum heat treatment furnace to a pressure of 100 kPa, and then the secondary diffuser was cooled to 25℃ at a wind speed of 50 m / s to obtain the diffused magnet. The diffused magnet was then finely ground, cleaned, and dried to obtain a neodymium iron boron permanent magnet.

[0270] Comparative Example 5

[0271] Except for not performing grain boundary diffusion on the magnet to be diffused, the process is the same as in Example 1. The magnet to be diffused obtained in this comparative example is a neodymium iron boron permanent magnet.

[0272] Comparative Example 6

[0273] Particle size D of fine powder 50 4.2μm, D 90 / D10 Except for 4.5, the rest are the same as in Example 1.

[0274] Experimental Example

[0275] 1. The magnetic properties of the neodymium iron boron permanent magnets in the examples and comparative examples were tested according to the test methods specified in GB / T-3217-2013 "Magnetic Test Methods for Permanent Magnet (Hard Magnet) Materials". The results are shown in Table 1.

[0276] Table 1

[0277]

[0278]

[0279] Note: Br represents remanence, and Hcj represents intrinsic coercivity.

[0280] 2. The neodymium iron boron permanent magnets prepared by the methods of the examples and comparative examples are saturated and magnetized to obtain magnetized magnets; at 20°C, the magnetic flux of the magnetized magnets is measured using a magnetometer and then converted into magnetic moment to obtain the magnetic moment of the untreated neodymium iron boron permanent magnets, denoted as m0, with units of μVsm.

[0281] The aforementioned neodymium iron boron permanent magnet was placed perpendicularly to the orientation direction on a 1.5mm thick aluminum plate. It was then kept at 150℃ for 2 hours in a high-temperature test chamber to obtain a heat-treated magnet. After the heat-treated magnet was naturally cooled to 20℃, the magnetic flux of the heat-treated magnet was measured using a magnetometer. The magnetic flux was converted into a magnetic moment to obtain the magnetic moment of the heat-treated neodymium iron boron permanent magnet, denoted as m1, with units of μVsm.

[0282] The thermal decay rate of the magnetic moment is calculated using the following formula:

[0283] Magnetic moment thermal decay rate = (m0-m1) / m0×100%.

[0284] The magnetic flux is converted into magnetic moment using the following formula:

[0285]

[0286] Where m represents the magnetic moment value; k HH R represents the coil coefficient; HH R represents the coil resistance. FM Φ represents the resistance of the magnetometer; Φ represents the magnetic flux.

[0287] The results are shown in Table 2.

[0288] Table 2

[0289]

[0290]

[0291] 3. For example Figure 2 As shown, samples were taken from the apex 101, edge 102, outer layer 103, and core 104 of the NdFeB permanent magnets obtained in the examples and comparative examples. The sample size was 4 mm × 4 mm × 4 mm. The samples were crushed into powder, and the Tb content in each part of the sample was measured by X-ray fluorescence spectrometry.

[0292] Specifically, the sampling position of the sample at the apex 101 is a cube formed by extending 4 mm in the length, width and height directions of the NdFeB permanent magnet, starting from the apex 101 of the NdFeB permanent magnet.

[0293] The sampling position of the sample at edge 102 is to take the edge 102 of the neodymium iron boron permanent magnet with a length of 4mm in the height direction as the starting edge, and extend it 4mm to the two faces adjacent to the edge 102 to form a cube.

[0294] The sampling location of the outer layer 103 samples is a cube formed by extending 4mm into the core of the NdFeB permanent magnet, starting from the middle of the upper surface of the NdFeB permanent magnet with a size of 4mm×4mm.

[0295] The sampling positions of the 104 core samples are cubes formed by extending 2mm vertically to each of the six faces of the neodymium iron boron permanent magnet, starting from the geometric center of the neodymium iron boron permanent magnet.

[0296] The results are shown in Table 3.

[0297] Table 3

[0298]

[0299]

[0300] This invention is not limited to the above-described embodiments. Any modifications, improvements, or substitutions that can be conceived by those skilled in the art without departing from the essential content of this invention fall within the scope of this invention.

Claims

1. A neodymium iron boron permanent magnet, characterized in that, The neodymium iron boron permanent magnet is rectangular in shape, and the height direction of the neodymium iron boron permanent magnet is its orientation direction. The height of the neodymium iron boron permanent magnet is ≥8mm. The heavy rare earth element content at the apex of the NdFeB permanent magnet is >0.65wt%, at the edges of the NdFeB permanent magnet is >0.43wt%, at the outer layer of the NdFeB permanent magnet is ≥0.22wt%, and at the core of the NdFeB permanent magnet is ≥0.003wt%. Among them, the content of heavy rare earth elements at the top corner is greater than that at the edge, which is greater than that at the outer layer, which is greater than that at the core. The neodymium iron boron permanent magnet is prepared by the following method: S1) The fine powder is mixed with a grain boundary modifier and then shaped to obtain a green body; S2) The blank is sintered and then cooled to obtain the magnet to be diffused; S3) Wrap the surface of the magnet to be diffused with diffusion metal foil to obtain the diffusion precursor; S4) The diffusion precursor is diffused to obtain neodymium iron boron permanent magnets; The fine powder contains alloy fine powder, which has the composition shown in formula (I): R a T b B c M d N e (I); Wherein, R is selected from one or more of La, Ce, Pr, Nd, Ho, Gd, Dy and Tb; T is selected from one or more of Fe and Co; M is selected from one or more of Ti, Ni, V, Nb, Zr, Hf, Mo and W; N is selected from one or more of Al, In, Sn, Zn and Ga, and must contain Ga; 28.5≤a≤33, 0.85≤c≤1.0, 0.20≤d≤0.95, 0.30≤e≤0.95, b=100-acde; a~e represent the weight fractions of each element respectively; The grain boundary modifier comprises a modified alloy having a composition as shown in formula (II): With x Bi y Mg z (II); 60≤x≤80, 10≤y≤30, 3≤z≤20; x~z represent the weight fractions of each element respectively; The diffusion metal foil comprises a first metal foil, a second metal foil, and heavy rare earth powder, wherein the heavy rare earth powder is dispersed between the first metal foil and the second metal foil; the melting point of the first metal foil is lower than that of the second metal foil; and the heavy rare earth powder is selected from one or more of dysprosium, terbium, dysprosium fluoride, terbium fluoride, dysprosium hydride, terbium hydride, terbium-containing alloys, and dysprosium-containing alloys. The first metal foil is selected from one or more of tin foil and lead foil, and the second metal foil is selected from one or more of aluminum foil and copper foil.

2. The neodymium iron boron permanent magnet according to claim 1, characterized in that, The heavy rare earth element is selected from one or more of Dy and Tb; The content of heavy rare earth elements at the apex of the neodymium iron boron permanent magnet is ≤1.00wt%, the content of heavy rare earth elements at the edges of the neodymium iron boron permanent magnet is ≤0.80wt%, the content of heavy rare earth elements at the outer layer of the neodymium iron boron permanent magnet is ≤0.50wt%, and the content of heavy rare earth elements at the core of the neodymium iron boron permanent magnet is ≤0.10wt%.

3. The neodymium iron boron permanent magnet according to claim 1, characterized in that, The neodymium iron boron permanent magnet | α Br |≤0.115% / ℃,| α Hcj ≤0.463% / ℃; in, α Br =[( Br 1 -Br 0 ) / Br 0 ] / ( T 1 -T 0 );in, Br 1 For neodymium iron boron permanent magnets at a temperature of T 1 The remanence measured under the conditions specified in GB / T-3217-2013 "Magnetic Test Methods for Permanent Magnet (Hard Magnet) Materials", is expressed in kGs. Br 0 For neodymium iron boron permanent magnets at a temperature of T 0 The remanence measured under the conditions specified in GB / T-3217-2013 "Magnetic Test Methods for Permanent Magnet (Hard Magnetic) Materials" is expressed in kGs; T1 is expressed in °C and T0 in °C. in, α Hcj =[( Hcj 1 -Hcj 0 ) / Hcj 0 ] / ( T 1 -T 0 );in, Hcj 1 For neodymium iron boron permanent magnets at a temperature of T 1 The intrinsic coercivity measured under the conditions specified in GB / T-3217-2013 "Magnetic Test Methods for Permanent Magnet (Hard Magnet) Materials", is expressed in kOe. Hcj 0 For neodymium iron boron permanent magnets at a temperature of T 0 The intrinsic coercivity measured under the conditions specified in GB / T-3217-2013 "Magnetic Test Methods for Permanent Magnet (Hard Magnet) Materials", is expressed in kOe. T 1 The unit is ℃. T 0 The unit is ℃.

4. The neodymium iron boron permanent magnet according to claim 1, characterized in that, The thermal decay rate of the magnetic moment of the neodymium iron boron permanent magnet is ≤1.35%; The thermal decay rate of the magnetic moment is calculated using the following formula: Magnetic moment thermal decay rate = ( m 0 - m 1 ) / m 0 ×100%; in, m 0 The following method was used for testing: Neodymium iron boron (NdFeB) permanent magnets were saturated with magnetizers to obtain magnetized magnets. The magnetic flux of the magnetized magnets was measured using a fluxmeter at 20°C and then converted into a magnetic moment. This magnetic moment of the untreated NdFeB permanent magnets was then obtained, denoted as […]. m 0 The unit is μVsm; in, m 1 The following method was used for testing: Neodymium iron boron (NdFeB) permanent magnets were placed perpendicularly to the orientation of a 1.5 mm thick aluminum plate. The magnets were then heat-treated by holding them at 150°C for 2 hours in a high-temperature chamber. After naturally cooling the heat-treated magnets to 20°C, the magnetic flux was measured using a fluxmeter. The magnetic flux was then converted into a magnetic moment to obtain the magnetic moment of the heat-treated NdFeB permanent magnet, denoted as . m 1 The unit is μVsm.

5. The method for preparing a neodymium iron boron permanent magnet according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1) The fine powder is mixed with a grain boundary modifier and then shaped to obtain a green body; S2) The blank is sintered and then cooled to obtain the magnet to be diffused; S3) Wrap the surface of the magnet to be diffused with diffusion metal foil to obtain the diffusion precursor; S4) The diffusion precursor is diffused to obtain neodymium iron boron permanent magnets; The fine powder contains alloy fine powder, which has the composition shown in formula (I): R a T b B c M d N e (I); Wherein, R is selected from one or more of La, Ce, Pr, Nd, Ho, Gd, Dy and Tb; T is selected from one or more of Fe and Co; M is selected from one or more of Ti, Ni, V, Nb, Zr, Hf, Mo and W; N is selected from one or more of Al, In, Sn, Zn and Ga, and must contain Ga; 28.5≤a≤33, 0.85≤c≤1.0, 0.20≤d≤0.95, 0.30≤e≤0.95, b=100-acde; a~e represent the weight fractions of each element respectively; The grain boundary modifier comprises a modified alloy having a composition as shown in formula (II): With x Bi y Mg z (II); 60≤x≤80, 10≤y≤30, 3≤z≤20; x~z represent the weight fractions of each element respectively; The diffusion metal foil comprises a first metal foil, a second metal foil, and heavy rare earth powder, wherein the heavy rare earth powder is dispersed between the first metal foil and the second metal foil; the melting point of the first metal foil is lower than that of the second metal foil; and the heavy rare earth powder is selected from one or more of dysprosium, terbium, dysprosium fluoride, terbium fluoride, dysprosium hydride, terbium hydride, terbium-containing alloys, and dysprosium-containing alloys. The first metal foil is selected from one or more of tin foil and lead foil, and the second metal foil is selected from one or more of aluminum foil and copper foil.

6. The preparation method according to claim 5, characterized in that, The grain boundary modifier also includes a coating agent, which is selected from one or more of the following: C8-C13 unsaturated monohydric alcohols, aluminate coupling agents, C5-C12 aliphatic alkanes, polymeric diols, and amide compounds. The mass ratio of the coating agent to the modified alloy is 1:(3-9); The particle size D of the modified alloy 50 The wavelength is 35–55 nm. The amount of the grain boundary modifier is 0.5 to 1.5 wt% of the fine powder mass.

7. The preparation method according to claim 5, characterized in that, The first metal foil is in contact with the magnet to be diffused; The amount of the heavy rare earth powder is 0.25 to 0.75 wt% of the mass of the magnet to be diffused.

8. The preparation method according to claim 7, characterized in that, The diffusion metal foil is used to completely cover all surfaces of the magnet to be diffused; the diffusion metal foil is heated to melt the first metal foil, and then cooled to fix the diffusion metal foil on the surface of the magnet to be diffused, thus obtaining the diffusion precursor.

9. The preparation method according to claim 5, characterized in that, The particle size of the fine powder D 50 The size ranges from 2.5 to 4.0 μm. D 90 / D 10 It ranges from 2.5 to 4.

10. The preparation method according to any one of claims 5 to 9, characterized in that, The diffusion precursor was subjected to a pressure < 5 × 10⁻⁶. -2 A first-stage diffusion process is performed at a pressure of Pa and a temperature of 800–1200 °C to obtain a first-stage diffuser; the first-stage diffuser is then cooled to obtain a cooled first-stage diffuser; the cooled first-stage diffuser is then subjected to a pressure of <5 × 10⁻⁶ Pa. -2 Pa, and secondary diffusion is carried out at a temperature of 450–650 °C to obtain a secondary diffuser; The secondary diffuser is cooled to obtain a neodymium iron boron permanent magnet.

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