Neodymium-iron-boron magnet and preparation method thereof

Abstract

The invention relates to a neodymium-iron-boron magnet and a preparation method thereof. The preparation method comprises the following steps that first auxiliary alloy powder RexMy and heavy rare earth powder are mixed to obtain diffusion alloy powder; mixing the second auxiliary alloy powder RexMy with the neodymium-iron-boron main alloy powder to prepare a neodymium-iron-boron matrix; placing the diffusion alloy powder on the surface of the neodymium-iron-boron substrate, and performing diffusion treatment and tempering treatment to obtain a neodymium-iron-boron magnet; wherein Re is selected from Pr and / or Nd, M is selected from at least one of Al, Cu or Ga, x and y are mass fractions, x is larger than or equal to 50% and smaller than or equal to 80%, y is larger than or equal to 20% and smaller than or equal to 50%, the mass fraction of first auxiliary alloy powder RexMy in the diffusion alloy powder is W1, the mass fraction of second auxiliary alloy powder RexMy in the neodymium iron boron matrix is W2, and the ratio of W1 to W2 is 10: 1-25: 1. According to the preparation method of the neodymium-iron-boron magnet, the intrinsic coercive force of the neodymium-iron-boron magnet can be improved, and the utilization rate of heavy rare earth elements can be effectively increased.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic materials, and particularly to a neodymium iron boron magnet and a preparation method thereof. Background Art

[0002] Due to its excellent comprehensive magnetic properties, the neodymium iron boron magnet is widely used in high-end fields such as aerospace, microwave communication technology, automotive industry, instrumentation, medical devices, and wind power, variable frequency compressors, hybrid power, etc. However, the neodymium iron boron magnet has the problem of insufficient intrinsic coercivity.

[0003] Currently, the intrinsic coercivity can be improved by the grain boundary diffusion process (GBD), that is: diffusing a diffusion source containing heavy rare earth elements (HRE) such as Dy and Tb into the interior of the neodymium iron boron magnet, increasing the proportion of the grain boundary phase and optimizing the distribution of the grain boundary phase, weakening the magnetic coupling between adjacent Nd2Fe 14 B grains. At the same time, the replacement of Nd atoms by HRE can form a (Nd, HRE)2Fe 14 B shell on the surface of the Nd2Fe 14 B grains, providing a higher anisotropy field, which helps to improve the intrinsic coercivity of the neodymium iron boron magnet.

[0004] However, during the diffusion process, it is easy to form an overly thick (Nd, HRE)2Fe 14 B shell (exceeding 15 nm). The overly thick shell cannot further improve the intrinsic coercivity of the neodymium iron boron magnet, wastes heavy rare earth resources, and even forms an anti-core / shell structure, resulting in the deterioration of the magnetic properties of the neodymium iron boron magnet. Therefore, reducing the formation of the overly thick (Nd, HRE)2Fe 14 B shell is of great significance for further improving the intrinsic coercivity of the neodymium iron boron magnet and improving the utilization rate of heavy rare earths. Summary of the Invention

[0005] Based on this, in view of the above problems, it is necessary to provide a neodymium iron boron magnet and a preparation method thereof. Using the preparation method of the neodymium iron boron magnet can not only improve the intrinsic coercivity of the neodymium iron boron magnet, but also effectively improve the utilization rate of heavy rare earth elements.

[0006] A preparation method of a neodymium iron boron magnet includes the following steps:

[0007] Mixing the first auxiliary alloy powder Re x M y with the heavy rare earth powder to obtain a diffusion alloy powder;

[0008] Mixing the second auxiliary alloy powder Re x M y with the neodymium iron boron master alloy powder and preparing it into a neodymium iron boron matrix;

[0009] Place the diffusion alloy powder on the surface of the NdFeB matrix, and perform diffusion treatment and tempering treatment to obtain an NdFeB magnet;

[0010] Among them, Re is selected from at least one of Pr and / or Nd, M is selected from at least one of Al, Cu or Ga, x and y are mass fractions, and 50% ≤ x ≤ 80%, 20% ≤ y ≤ 50%, and the first auxiliary alloy powder Re x M y in the diffusion alloy powder has a mass fraction of W1, and the second auxiliary alloy powder Re x M y in the NdFeB matrix has a mass fraction of W2, and W1:W2 = 10:1 - 25:1.

[0011] In one embodiment, the mass fraction W1 of the first auxiliary alloy powder Re x M y in the diffusion alloy powder is 10% - 60%;

[0012] And / or, the mass fraction W2 of the second auxiliary alloy powder Re x M y in the NdFeB matrix is 0.5% - 3%.

[0013] In one embodiment, in the step of placing the diffusion alloy powder on the surface of the NdFeB matrix, the mass ratio of the diffusion alloy powder to the NdFeB matrix is 0.5:100 - 1.5:100.

[0014] In one embodiment, the particle sizes of the first auxiliary alloy powder and the second auxiliary alloy powder are each independently selected from 1 μm - 4 μm.

[0015] In one embodiment, the NdFeB master alloy powder satisfies at least one of the following conditions:

[0016] (1) The molecular formula of the NdFeB master alloy powder is R a T b B c , where R is selected from at least one of Dy, Tb, La, Ce, Pr or Nd, T is selected from at least one of Fe, Co, Al, Si, Cu, Nb, Zr or Ga, a, b, c are mass fractions, and 28% ≤ a ≤ 32%, 67% ≤ b ≤ 71%, 0.85% ≤ c ≤ 1.0%;

[0017] (2) The particle size of the NdFeB master alloy powder is 2 μm - 4 μm.

[0018] In one embodiment, the heavy rare earth powder satisfies at least one of the following conditions:

[0019] (1) The heavy rare earth powder is selected from at least one of Dy or Tb;

[0020] (2) The particle size of the heavy rare earth powder is 10 μm - 30 μm.

[0021] In one embodiment, in the step of diffusion treatment, the temperature is 850 °C - 950 °C, and the heat preservation time is 6 h - 30 h.

[0022] In one embodiment, during the heating-up process of the diffusion treatment, the heating rate at 500 °C - 800 °C is < 2 °C / min.

[0023] In one embodiment, in the step of tempering treatment, the temperature is 430 °C - 530 °C, and the heat preservation time is 3 h - 6 h.

[0024] A neodymium iron boron magnet prepared by the preparation method of the neodymium iron boron magnet as described above.

[0025] In the preparation method of the present invention, by simultaneously using the auxiliary alloy powder Re x M y in the neodymium iron boron matrix and the diffusion alloy powder, and regulating the proportion of the auxiliary alloy powder Re x M y in the neodymium iron boron matrix and the diffusion alloy powder, the grain boundary phase of the neodymium iron boron matrix and the melting speed of the diffusion alloy powder are the same or similar during the diffusion treatment, and the heating rate can be slowed down.

[0026] Therefore, every time a part of the diffusion alloy powder melts, this part of the heavy rare earth element will be brought into the interior of the neodymium iron boron matrix by the melted grain boundary phase. Thus, the diffusion of the heavy rare earth element in the neodymium iron boron matrix is carried out step by step, which can avoid the massive enrichment of the molten heavy rare earth element on the surface of the neodymium iron boron matrix. Furthermore, not only can the diffusion depth of the heavy rare earth element in the neodymium iron boron matrix be increased, the thickness of the (Nd, HRE)2Fe 14 B shell layer in the neodymium iron boron magnet be reduced, and the intrinsic coercivity of the neodymium iron boron magnet be improved, but also the utilization rate of the heavy rare earth element can be effectively increased. Detailed implementation manners

[0027] For the convenience of understanding the present invention, the present invention will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. On the contrary, the purpose of providing these embodiments or examples is to make the understanding of the disclosure content of the present invention more thorough and comprehensive.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this invention belongs. The terms used in the specification of the present invention are for the purpose of describing specific embodiments or examples only and are not intended to limit the present invention. The optional range of the term "and / or" used herein includes any one of two or more related listed items, and also includes any and all combinations of the related listed items. The any and all combinations include combinations of any two related listed items, any more than two related listed items, or all related listed items.

[0029] The present invention provides a method for preparing a neodymium-iron-boron magnet, comprising the following steps:

[0030] S1, mixing a first auxiliary alloy powder Re x M y with a heavy rare earth powder to obtain a diffusion alloy powder, and mixing a second auxiliary alloy powder Re x M y with a neodymium-iron-boron master alloy powder and preparing it into a neodymium-iron-boron matrix;

[0031] S2, placing the diffusion alloy powder on the surface of the neodymium-iron-boron matrix, and performing diffusion treatment and tempering treatment to obtain a neodymium-iron-boron magnet.

[0032] Wherein, Re is selected from Pr and / or Nd, M is selected from at least one of Al, Cu or Ga, x and y are mass fractions, and 50% ≤ x ≤ 80%, 20% ≤ y ≤ 50%, and the mass fraction of the first auxiliary alloy powder Re x M y in the diffusion alloy powder is W1, and the mass fraction of the second auxiliary alloy powder Re x M y in the neodymium-iron-boron matrix is W2, and W1:W2 = 10:1 - 25:1.

[0033] It should be noted that the ratio of W1 to W2 is not the mass ratio of the first auxiliary alloy powder Re x M y to the second auxiliary alloy powder Re x M y , but the multiple ratio of the mass fractions. In the present invention, the mass fraction W1 of the first auxiliary alloy powder Re x M y in the diffusion alloy powder is preferably 10% - 60%, and the mass fraction W2 of the second auxiliary alloy powder Re x M y in the neodymium-iron-boron matrix is preferably 0.5% - 3%. That is, when W1 is preferably 20% and W2 is preferably 1%, W1:W2 = 20:1.

[0034] In the preparation method of the present invention, the first auxiliary alloy powder Re x M y is mixed with the heavy rare earth powder as the diffusion alloy powder, and the second auxiliary alloy powder Re x M y is mixed with the neodymium-iron-boron master alloy powder to prepare a neodymium-iron-boron matrix, so that most of the second auxiliary alloy powder Re x M y is distributed at the grain boundary phase position of the neodymium-iron-boron matrix, thereby playing a role in regulating the melting point of the grain boundary phase of the neodymium-iron-boron matrix. At the same time, by regulating the ratio of the diffusion alloy powder to the first auxiliary alloy powder Re x M y in the neodymium-iron-boron matrix and the second auxiliary alloy powder Re x M y such that during the diffusion treatment, the melting rates of the grain boundary phase of the neodymium-iron-boron matrix and the diffusion alloy powder are the same or similar, and the heating rate can be slowed down.

[0035] Therefore, every time a part of the diffusion alloy powder melts, the heavy rare earth elements in this part will be carried into the interior of the neodymium-iron-boron matrix by the melted grain boundary phase. Thus, the diffusion of the heavy rare earth elements in the neodymium-iron-boron matrix proceeds step by step, which can avoid the massive enrichment of molten heavy rare earth elements on the surface of the neodymium-iron-boron matrix. This can not only increase the diffusion depth of the heavy rare earth elements in the neodymium-iron-boron matrix, reduce the thickness of the (Nd, HRE)2Fe 14 B shell layer in the neodymium-iron-boron magnet, and increase the intrinsic coercivity of the neodymium-iron-boron magnet, but also, with the same content of heavy rare earth elements, more heavy rare earth elements can diffuse into the neodymium-iron-boron matrix, effectively improving the utilization rate of heavy rare earth elements.

[0036] In the present invention, the heavy rare earth powder is preferably an oxide powder of a heavy rare earth, a hydride powder of a heavy rare earth, a fluoride powder of a heavy rare earth, a heavy rare earth alloy powder or a heavy rare earth pure metal powder, more preferably a heavy rare earth pure metal powder, and even more preferably at least one of Dy or Tb.

[0037] Optionally, the particle size of the heavy rare earth powder is preferably 10 μm - 30 μm, which helps to improve its stability, avoid oxidation reactions, and helps to improve the melting effect with the first auxiliary alloy powder during the diffusion treatment; the particle size of the first auxiliary alloy powder is preferably 1 μm - 4 μm, which helps to improve its dispersion uniformity in the heavy rare earth powder and further improve the melting effect.

[0038] In the present invention, the molecular formula of the neodymium-iron-boron master alloy powder is preferably R a T b B c, where R is selected from at least one of Dy, Tb, La, Ce, Pr or Nd, T is selected from at least one of Fe, Co, Al, Si, Cu, Nb, Zr or Ga, a, b, c are mass fractions, and 28% ≤ a ≤ 32%, 67% ≤ b ≤ 71%, 0.85% ≤ c ≤ 1.0%.

[0039] Optionally, the particle size of the neodymium-iron-boron master alloy powder is preferably 2 μm - 4 μm, and the particle size of the second auxiliary alloy powder is preferably 1 μm - 4 μm, which helps to improve the dispersion uniformity in the neodymium-iron-boron master alloy powder.

[0040] Furthermore, by simultaneously controlling the particle sizes of the first auxiliary alloy powder and the second auxiliary alloy powder, the uniform dispersion degrees of the auxiliary alloy powder in the neodymium-iron-boron master alloy powder and in the heavy rare-earth powder can be simultaneously controlled, and then the grain boundary phase of the neodymium-iron-boron matrix and the melting rate of the diffusion alloy powder can be better controlled, improving the diffusion effect of the heavy rare-earth in the neodymium-iron-boron matrix.

[0041] It can be understood that the first auxiliary alloy powder and the second auxiliary alloy powder can be the same or different, and are preferably the same.

[0042] Optionally, after mixing the second auxiliary alloy powder with the neodymium-iron-boron master alloy powder, it is oriented and formed in a magnetic field, and then sintered to obtain a neodymium-iron-boron magnet. Preferably, the mixed powder can be pressed into a formed blank in an orientation magnetic field, and then put into a vacuum sintering furnace for high-temperature sintering to obtain a sintered neodymium-iron-boron blank, and then the blank is processed into a neodymium-iron-boron magnet. Among them, the sintering temperature is preferably 1050 °C - 1100 °C, and the sintering time is preferably 3 h - 10 h. The present invention does not specifically limit the shape of the neodymium-iron-boron magnet. For example, it can be in the shape of a thin sheet.

[0043] After obtaining the diffusion alloy powder and the neodymium-iron-boron matrix, in the step of placing the diffusion alloy powder on the surface of the neodymium-iron-boron matrix, the diffusion alloy powder can be coated on the surface of the neodymium-iron-boron magnet by means of spraying, screen printing, dipping, etc. The mass ratio of the diffusion alloy powder to the neodymium-iron-boron matrix is 0.5:100 - 1.5:100.

[0044] Optionally, in the step of the diffusion treatment, the temperature is preferably 850 °C - 950 °C, and the heat preservation time is preferably 6 h - 30 h. And during the heating process from 500 °C to 800 °C, the heating rate is preferably < 2 °C / min. Thus, the slower heating rate enables the grain boundary phase of the neodymium-iron-boron matrix and the diffusion alloy powder to have enough time to melt synchronously, and then the heavy rare-earth in the diffusion alloy powder can gradually diffuse into the neodymium-iron-boron matrix, avoiding a large amount of molten heavy rare-earth alloy from enriching on the surface of the neodymium-iron-boron matrix.

[0045] Optionally, in the step of tempering treatment, the temperature is preferably 430°C - 530°C, and the heat preservation time is preferably 3h - 6h.

[0046] The present invention also provides a neodymium iron boron magnet prepared by the preparation method of the neodymium iron boron magnet described above. In the neodymium iron boron magnet, (Nd, HRE)2Fe 14 The thickness of the B shell layer is 1nm - 10nm.

[0047] Hereinafter, the neodymium iron boron magnet and its preparation method will be further described through the following specific examples.

[0048] Example 1

[0049] By hydrogen breaking and ball milling treatment, heavy rare earth powder Dy with an average particle size of 20μm is prepared. By melting, hydrogen breaking and ball milling treatment, auxiliary alloy powder Pr with an average particle size of 2.5μm is prepared 70 Al 20 Ga 10 , and by melting, hydrogen crushing and jet milling treatment, neodymium iron boron master alloy powder (PrNd) with an average particle size of 3.1μm is prepared 30.5 Fe 66.9 Co1Cu 0.15 Al 0.2 Ga 0.2 Zr 0.1 B 0.95 .

[0050] The auxiliary alloy powder Pr 70 Al 20 Ga 10 and the neodymium iron boron master alloy powder (PrNd) 30.5 Fe 66.9 Co1Cu 0.15 Al 0.2 Ga 0.2 Zr 0.1 B 0.95 are uniformly mixed in a mass ratio of 2:98. The mixed powder is pressed into a green compact in an orientation magnetic field and then put into a vacuum sintering furnace to be sintered at 1085°C for 7h to obtain a sintered neodymium iron boron green compact. Then the green compact is processed into a thin neodymium iron boron matrix; the heavy rare earth powder Dy and the auxiliary alloy powder Pr 70 Al 20 Ga 10 are uniformly mixed in a mass ratio of 60:40 to obtain a diffusion alloy powder. Among them, the mass fraction ratio of the auxiliary alloy powder in the neodymium iron boron matrix to the auxiliary alloy powder in the diffusion alloy powder is 1:20.

[0051] The diffusion alloy powder is coated on the surface of the thin NdFeB substrate by spraying. Among them, the mass ratio of the diffusion alloy powder to the NdFeB substrate is 1.35:100. The weight of Dy converted from the diffusion alloy powder coated on the surface of the NdFeB substrate accounts for 0.8 wt% of the weight of the thin NdFeB substrate. Then, the coated thin NdFeB substrate is subjected to diffusion treatment and tempering treatment to obtain the NdFeB magnet. Among them, the temperature of the diffusion treatment is 900 °C, the holding time is 20 h, and during the heating process from 500 °C to 800 °C, the heating rate is 1.5 °C / min. The temperature of the tempering treatment is 480 °C, and the holding time is 5 h.

[0052] In this embodiment, the diffusion effect of the heavy rare earth in the NdFeB magnet and the magnetic properties of the NdFeB magnet are shown in Table 1.

[0053] Example 2

[0054] Through hydrogen breaking and ball milling treatment, heavy rare earth powder Dy with an average particle size of 10 μm is prepared. Through melting, hydrogen breaking and ball milling treatment, auxiliary alloy powder Pr with an average particle size of 1 μm is prepared. 70 Al 20 Ga 10 , through melting, hydrogen crushing and jet milling treatment, NdFeB master alloy powder (PrNd) with an average particle size of 2.8 μm is prepared. 30.5 Fe 66.9 Co1Cu 0.15 Al 0.2 Ga 0.2 Zr 0.1 B 0.95 .

[0055] The auxiliary alloy powder Pr 70 Al 20 Ga 10 and the NdFeB master alloy powder (PrNd) 30.5 Fe 66.9 Co1Cu 0.15 Al 0.2 Ga 0.2 Zr 0.1 B 0.95 are uniformly mixed in a mass ratio of 2:98. The mixed powder is pressed into a green compact in an orientation magnetic field and sintered in a vacuum sintering furnace at 1085 °C for 7 h to obtain a sintered NdFeB green compact, and then the green compact is processed into a thin NdFeB substrate; the heavy rare earth powder Dy and the auxiliary alloy powder Pr 70 Al 20 Ga 10 are uniformly mixed in a mass ratio of 60:40 to obtain the diffusion alloy powder. Among them, the mass fraction ratio of the auxiliary alloy powder in the NdFeB substrate to the auxiliary alloy powder in the diffusion alloy powder is 1:20.

[0056] The diffusion alloy powder is coated on the surface of the thin NdFeB substrate by spraying method. Among them, the mass ratio of the diffusion alloy powder to the NdFeB substrate is 1.35:100. The weight of Dy converted from the diffusion alloy powder coated on the surface of the NdFeB substrate accounts for 0.8 wt% of the weight of the thin NdFeB substrate. Then, the coated thin NdFeB substrate is subjected to diffusion treatment and tempering treatment to obtain the NdFeB magnet. Among them, the temperature of the diffusion treatment is 900 °C, the holding time is 20 h, and during the heating process from 500 °C to 800 °C, the heating rate is 1.5 °C / min, and the temperature of the tempering treatment is 480 °C, and the holding time is 5 h.

[0057] In this embodiment, the diffusion effect of the heavy rare earth in the NdFeB magnet and the magnetic properties of the NdFeB magnet are shown in Table 1.

[0058] Example 3

[0059] The heavy rare earth powder Dy with an average particle size of 20 μm is prepared by hydrogen breaking and ball milling treatment. The auxiliary alloy powder Nd 60 Al 25 Cu 15 , and the main NdFeB alloy powder (PrNd) with an average particle size of 3.1 μm is prepared by melting, hydrogen breaking and jet milling treatment. 30.5 Fe 66.9 Co1Cu 0.15 Al 0.2 Ga 0.2 Zr 0.1 B 0.95 .

[0060] The auxiliary alloy powder Nd 60 Al 25 Cu 15 and the main NdFeB alloy powder (PrNd) 30.5 Fe 66.9 Co1Cu 0.15 Al 0.2 Ga 0.2 Zr 0.1 B 0.95 are uniformly mixed in a mass ratio of 2:98. The mixed powder is pressed into a green compact in an orientation magnetic field and put into a vacuum sintering furnace to be sintered at 1085 °C for 7 h to obtain a sintered NdFeB green compact, and then the green compact is processed into a thin NdFeB substrate; the heavy rare earth powder Dy and the auxiliary alloy powder Nd 60 Al 25 Cu 15Mix evenly at a mass ratio of 60:40 to obtain diffusion alloy powder. Among them, the mass fraction ratio of the auxiliary alloy powder in the NdFeB matrix to the auxiliary alloy powder in the diffusion alloy powder is 1:20.

[0061] Coat the diffusion alloy powder on the surface of the thin NdFeB matrix by spraying method. Among them, the mass ratio of the diffusion alloy powder to the NdFeB matrix is 1.35:100. The weight of Dy converted from the diffusion alloy powder coated on the surface of the NdFeB matrix accounts for 0.8 wt% of the weight of the thin NdFeB matrix. Then, perform diffusion treatment and tempering treatment on the coated thin NdFeB matrix to obtain NdFeB magnets. Among them, the temperature of the diffusion treatment is 900 °C, the holding time is 20 h, and during the heating process from 500 °C to 800 °C, the heating rate is 1.5 °C / min. The temperature of the tempering treatment is 480 °C, and the holding time is 5 h.

[0062] In this example, the diffusion effect of the heavy rare earth in the NdFeB magnet and the magnetic properties of the NdFeB magnet are shown in Table 1.

[0063] Example 4

[0064] Through hydrogen breaking and ball milling treatment, heavy rare earth powder Dy with an average particle size of 20 μm is obtained. Through melting, hydrogen breaking and ball milling treatment, auxiliary alloy powder Pr with an average particle size of 2.5 μm is obtained. 70 Al 20 Ga 10 , through melting, hydrogen crushing and jet milling treatment, NdFeB master alloy powder (PrNd) with an average particle size of 3.1 μm is obtained. 30.5 Fe 66.9 Co1Cu 0.15 Al 0.2 Ga 0.2 Zr 0.1 B 0.95 .

[0065] Mix the auxiliary alloy powder Pr 70 Al 20 Ga 10 and the NdFeB master alloy powder (PrNd) 30.5 Fe 66.9 Co1Cu 0.15 Al 0.2 Ga 0.2 Zr 0.1 B 0.95 Mix evenly at a mass ratio of 0.5:99.5, press the mixed powder into a green compact in an orientation magnetic field, put it into a vacuum sintering furnace and sinter at 1085 °C for 7 h to obtain a sintered NdFeB green compact, and then process the green compact into a thin NdFeB matrix; mix the heavy rare earth powder Dy and the auxiliary alloy powder Pr 70 Al20 Ga 10 Mix evenly at a mass ratio of 87.5:12.5 to obtain diffusion alloy powder. Among them, the mass fraction ratio of the auxiliary alloy powder in the NdFeB matrix to the auxiliary alloy powder in the diffusion alloy powder is 1:25.

[0066] Coat the diffusion alloy powder on the surface of the thin NdFeB matrix by spraying method. Among them, the mass ratio of the diffusion alloy powder to the NdFeB matrix is 0.915:100. The weight of Dy converted from the diffusion alloy powder coated on the surface of the NdFeB matrix accounts for 0.8 wt% of the weight of the thin NdFeB matrix. Then, perform diffusion treatment and tempering treatment on the coated thin NdFeB matrix to obtain NdFeB magnets. Among them, the temperature of the diffusion treatment is 900 °C, the holding time is 20 h, and during the heating process from 500 °C to 800 °C, the heating rate is 1.5 °C / min. The temperature of the tempering treatment is 480 °C, and the holding time is 5 h.

[0067] In this example, the diffusion effect of the heavy rare earth in the NdFeB magnet and the magnetic properties of the NdFeB magnet are shown in Table 1.

[0068] Example 5

[0069] The difference between Example 5 and Example 1 is that the auxiliary alloy powder Pr 70 Al 20 Ga 10 and the NdFeB master alloy powder (PrNd) 30.5 Fe 66.9 Co1Cu 0.15 Al 0.2 Ga 0.2 Zr 0.1 B 0.95 Mix evenly at a mass ratio of 0.3:99.7; mix the heavy rare earth powder Dy and the auxiliary alloy powder Pr 70 Al 20 Ga 10 Mix evenly at a mass ratio of 94:6 to obtain diffusion alloy powder. Among them, the mass fraction ratio of the auxiliary alloy powder in the NdFeB matrix to the auxiliary alloy powder in the diffusion alloy powder is 1:20.

[0070] In this example, the diffusion effect of the heavy rare earth in the NdFeB magnet and the magnetic properties of the NdFeB magnet are shown in Table 1.

[0071] Example 6

[0072] The difference between Example 6 and Example 1 is that the auxiliary alloy powder Pr 70 Al 20 Ga 10 and the NdFeB master alloy powder (PrNd)30.5 Fe 66.9 Co1Cu 0.15 Al 0.2 Ga 0.2 Zr 0.1 B 0.95 Mix evenly in a mass ratio of 4:96; Mix the heavy rare earth powder Dy and the auxiliary alloy powder Pr 70 Al 20 Ga 10 Mix evenly in a mass ratio of 20:80 to obtain diffusion alloy powder. Among them, the mass fraction ratio of the auxiliary alloy powder in the NdFeB matrix to the auxiliary alloy powder in the diffusion alloy powder is 1:20.

[0073] In this embodiment, the diffusion effect of the heavy rare earth in the NdFeB magnet and the magnetic properties of the NdFeB magnet are shown in Table 1.

[0074] Example 7

[0075] The difference between Example 7 and Example 1 is that during the heating process from 500 °C to 800 °C, the heating rate is 3 °C / min.

[0076] In this embodiment, the diffusion effect of the heavy rare earth in the NdFeB magnet and the magnetic properties of the NdFeB magnet are shown in Table 1.

[0077] Comparative Example 1

[0078] Through hydrogen breaking and ball milling treatment, a heavy rare earth powder Dy with an average particle size of 20 μm is prepared. Through melting, hydrogen crushing and air flow milling treatment, a NdFeB master alloy powder (PrNd) with an average particle size of 3.1 μm is prepared 30.5 Fe 66.9 Co1Cu 0.15 Al 0.2 Ga 0.2 Zr 0.1 B 0.95 .

[0079] Press the NdFeB master alloy powder into a green compact in an orientation magnetic field, put it into a vacuum sintering furnace and sinter at 1085 °C for 7 h to obtain a sintered NdFeB green compact, and then process the green compact into a thin NdFeB matrix.

[0080] Coat the surface of the thin NdFeB matrix with the heavy rare earth powder Dy by spraying method. Among them, the mass ratio of the heavy rare earth powder to the NdFeB matrix is 0.81:100, and the weight of Dy coated on the surface of the NdFeB matrix accounts for 0.8 wt% of the weight of the thin NdFeB matrix; Then, the coated thin NdFeB matrix is subjected to diffusion treatment and tempering treatment to obtain a NdFeB magnet, where the diffusion treatment temperature is 900 °C, the holding time is 20 h, the tempering treatment temperature is 480 °C, and the holding time is 5 h.

[0081] In this comparative example, the diffusion effect of heavy rare earths in the NdFeB magnet and the magnetic properties of the NdFeB magnet are shown in Table 1.

[0082] Comparative Example 2

[0083] Through hydrogen breaking and ball milling treatments, heavy rare earth powder Dy with an average particle size of 20 μm was prepared. Through melting, hydrogen breaking and ball milling treatments, auxiliary alloy powder Pr with an average particle size of 2.5 μm was prepared. 70 Al 20 Ga 10 , and through melting, hydrogen crushing and jet milling treatments, NdFeB master alloy powder (PrNd) with an average particle size of 3.1 μm was prepared. 30.5 Fe 66.9 Co1Cu 0.15 Al 0.2 Ga 0.2 Zr 0.1 B 0.95 .

[0084] The auxiliary alloy powder Pr 70 Al 20 Ga 10 and the NdFeB master alloy powder (PrNd) 30.5 Fe 66.9 Co1Cu 0.15 Al 0.2 Ga 0.2 Zr 0.1 B 0.95 were uniformly mixed at a mass ratio of 2:98. The mixed powder was pressed into a green compact in an orientation magnetic field and then put into a vacuum sintering furnace and sintered at 1085 °C for 7 h to obtain a sintered NdFeB green compact, and then the green compact was processed into a thin NdFeB substrate.

[0085] The heavy rare earth powder Dy was coated on the surface of the thin NdFeB substrate by spraying. Among them, the mass ratio of the heavy rare earth powder to the NdFeB substrate was 0.81:100, and the weight of Dy coated on the surface of the NdFeB substrate accounted for 0.8 wt% of the weight of the thin NdFeB substrate; then the coated thin NdFeB substrate was subjected to diffusion treatment and tempering treatment to obtain the NdFeB magnet. Among them, the temperature of the diffusion treatment was 900 °C, the holding time was 20 h, and during the heating process from 500 °C to 800 °C, the heating rate was 1.5 °C / min, and the temperature of the tempering treatment was 480 °C, and the holding time was 5 h.

[0086] In this comparative example, the diffusion effect of heavy rare earths in the NdFeB magnet and the magnetic properties of the NdFeB magnet are shown in Table 1.

[0087] Comparative Example 3

[0088] The heavy rare earth powder Dy with an average particle size of 20 μm was prepared by hydrogen decrepitation and ball milling, and the auxiliary alloy powder Pr with an average particle size of 2.5 μm was prepared by melting, hydrogen decrepitation and ball milling. 70 Al 20 Ga 10 The neodymium-iron-boron master alloy powder (PrNd) with an average particle size of 3.1 μm was prepared by melting, hydrogen crushing and jet milling. 30.5 Fe 66.9 Co1Cu 0.15 Al 0.2 Ga 0.2 Zr 0.1 B 0.95 。

[0089] The neodymium-iron-boron master alloy powder was pressed into a green compact in an orientation magnetic field and then sintered in a vacuum sintering furnace at 1085 °C for 7 h to obtain a sintered neodymium-iron-boron green compact, which was then machined into a thin neodymium-iron-boron substrate; the heavy rare earth powder Dy and the auxiliary alloy powder Pr 70 Al 20 Ga 10 were uniformly mixed in a mass ratio of 60:40 to obtain a diffusion alloy powder.

[0090] The diffusion alloy powder was coated on the surface of the thin neodymium-iron-boron substrate by spraying. Among them, the mass ratio of the diffusion alloy powder to the neodymium-iron-boron substrate was 1.33:100. The weight of the diffusion alloy powder coated on the surface of the neodymium-iron-boron substrate, converted to Dy, accounted for 0.8 wt% of the weight of the thin neodymium-iron-boron substrate; then the coated thin neodymium-iron-boron substrate was subjected to diffusion treatment and tempering treatment to obtain a neodymium-iron-boron magnet. Among them, the temperature of the diffusion treatment was 900 °C, the holding time was 20 h, and during the heating process from 500 °C to 800 °C, the heating rate was 1.5 °C / min, and the temperature of the tempering treatment was 480 °C, and the holding time was 5 h.

[0091] In this comparative example, the diffusion effect of the heavy rare earth in the neodymium-iron-boron magnet and the magnetic properties of the neodymium-iron-boron magnet are shown in Table 1.

[0092] Comparative Example 4

[0093] The difference between Comparative Example 4 and Example 1 is that the auxiliary alloy powder Pr 70 Al 20 Ga 10 and the neodymium-iron-boron master alloy powder (PrNd) 30.5 Fe 66.9 Co1Cu 0.15 Al 0.2 Ga 0.2 Zr 0.1 B 0.95Mix evenly at a mass ratio of 1:99; mix the heavy rare earth powder Dy and the auxiliary alloy powder Pr 70 Al 20 Ga 10 Mix evenly at a mass ratio of 95:5 to obtain the diffusion alloy powder. Among them, the mass fraction ratio of the auxiliary alloy powder in the neodymium iron boron matrix to the auxiliary alloy powder in the diffusion alloy powder is 1:5.

[0094] In this comparative example, the diffusion effect of the heavy rare earth in the neodymium iron boron magnet and the magnetic properties of the neodymium iron boron magnet are shown in Table 1.

[0095] In the above examples and comparative examples, a permanent magnet material was used to measure the magnetic properties of the thin neodymium iron boron matrix with a B-H meter, and an ICP test method was used to test the content of the heavy rare earth diffused into the neodymium iron boron magnet.

[0096] The utilization rate of the heavy rare earth in the neodymium iron boron magnet was characterized by the ratio of the content of the heavy rare earth diffused into the neodymium iron boron magnet to the content of the heavy rare earth coated on the neodymium iron boron magnet.

[0097] Table 1

[0098]

[0099] As can be seen from Examples 1-7 in Table 1, the content of the heavy rare earth diffused into the neodymium iron boron magnet is more and the diffusion efficiency is higher, indicating that when the neodymium iron boron master alloy powder and the heavy rare earth powder both contain auxiliary alloy powder, it has a better diffusion effect; and, from Examples 1-4 and Examples 5-6, it can be seen that although the mass fraction ratio of the first auxiliary alloy powder in the diffusion alloy powder to the second auxiliary alloy powder in the neodymium iron boron matrix is within a specific range, when the dosage of the second auxiliary alloy powder and the first auxiliary alloy powder is not within the specific range, the ability to control the grain boundary phase of the neodymium iron boron matrix and the melting speed of the diffusion alloy powder decreases, resulting in a decrease in the magnetic properties of the prepared neodymium iron boron magnet; from Example 1 and Example 7, it can be seen that when the heating rate is greater than 2 °C / min, the grain boundary phase of the neodymium iron boron matrix and the diffusion alloy powder do not have enough time to melt synchronously, so that the heavy rare earth elements cannot effectively diffuse into the neodymium iron boron matrix, resulting in a decrease in the magnetic properties of the neodymium iron boron magnet and a too thick shell layer formed.

[0100] In Comparative Example 1, since neither the neodymium iron boron master alloy powder nor the heavy rare earth powder contains auxiliary alloy powder, the diffusion effect of the heavy rare earth in the neodymium iron boron matrix becomes poor.

[0101] In Comparative Examples 2-3, since the neodymium iron boron master alloy powder or the heavy rare earth powder does not contain auxiliary alloy powder, during the diffusion treatment, the difference in the melting speed between the grain boundary phase of the neodymium iron boron matrix and the heavy rare earth powder is large, resulting in a poor diffusion effect of the heavy rare earth in the neodymium iron boron matrix.

[0102] In Comparative Example 4, since the mass fraction ratio of the first auxiliary alloy powder in the diffusion alloy powder to the second auxiliary alloy powder in the NdFeB matrix is not within a specific range, the heavy rare earth and the NdFeB matrix cannot maintain the same melting rate, resulting in unsatisfactory magnetic properties of the prepared NdFeB magnet.

[0103] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0104] The above-described embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent should be subject to the appended claims.

Claims

1. A method for preparing a neodymium iron boron magnet, characterized in that: The following steps are involved: The first auxiliary alloy powder Re x M y Mixing with heavy rare earth powder to obtain diffusion alloy powder; The second auxiliary alloy powder Re x M y Mixing with NdFeB main alloy powder to prepare NdFeB matrix; Placing the diffusion alloy powder on the surface of the NdFeB matrix, and performing diffusion treatment and tempering treatment to obtain a NdFeB magnet; Wherein, Re is selected from Pr and / or Nd, M is selected from at least one of Al, Cu or Ga, x and y are mass fractions, and 50%≤x≤80%, 20%≤y≤50%, and the first auxiliary alloy powder Re in the diffusion alloy powder x M y The mass fraction of the second auxiliary alloy powder Re in the NdFeB matrix is ​​W1. x M y The mass fraction is W2, W1:W2=10:1-25:

1.

2. The method for preparing a NdFeB magnet according to claim 1, wherein: The first auxiliary alloy powder Re in the diffusion alloy powder x M y The mass fraction W1 is 10%-60%; And / or, the second auxiliary alloy powder Re in the NdFeB matrix x M y The mass fraction W2 is 0.5%-3%.

3. The method for preparing a NdFeB magnet according to claim 1, characterized in that: In the step of placing the diffusion alloy powder on the surface of the NdFeB matrix, the mass ratio of the diffusion alloy powder to the NdFeB matrix is ​​0.5:100-1.5:

100.

4. The method for preparing a NdFeB magnet according to claim 1, characterized in that: The particle sizes of the first auxiliary alloy powder and the second auxiliary alloy powder are independently selected from 1 μm to 4 μm.

5. The method for preparing a NdFeB magnet according to claim 1, characterized in that: The NdFeB main alloy powder meets at least one of the following conditions: (1) The molecular formula of the NdFeB main alloy powder is R a T b B c , wherein R is selected from at least one of Dy, Tb, La, Ce, Pr or Nd, T is selected from at least one of Fe, Co, Al, Si, Cu, Nb, Zr or Ga, a, b, c are mass fractions, and 28%≤a≤32%, 67%≤b≤71%, 0.85%≤c≤1.0%; (2) The particle size of the NdFeB main alloy powder is 2 μm-4 μm.

6. The method for preparing a NdFeB magnet according to claim 1, characterized in that: The heavy rare earth powder satisfies at least one of the following conditions: (1) The heavy rare earth powder is selected from at least one of Dy and Tb; (2) The particle size of the heavy rare earth powder is 10 μm-30 μm.

7. The method for preparing a NdFeB magnet according to claim 1, characterized in that: In the diffusion treatment step, the temperature is 850° C.-950° C. and the insulation time is 6 h-30 h.

8. The method for preparing a NdFeB magnet according to claim 7, characterized in that: During the temperature rise process of the diffusion treatment, the temperature rise rate from 500°C to 800°C is less than 2°C / min.

9. The method for preparing a NdFeB magnet according to claim 1, characterized in that: In the step of tempering treatment, the temperature is 430° C.-530° C. and the insulation time is 3 h-6 h.

10. A NdFeB magnet obtained by the method for preparing a NdFeB magnet according to any one of claims 1 to 9.

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