Neodymium-iron-boron magnet and preparation method thereof

Abstract

The invention provides a neodymium iron boron magnet and a preparation method thereof, and belongs to the technical field of magnetic materials. The neodymium-iron-boron magnet comprises rare earth elements R, transition metal elements T, metal elements M and B elements, the R comprises Pr and Nd, the mass percent of the R is 29-32 wt%, the R comprises heavy rare earth elements Tb and Dy with the mass percent being 0-0.1 wt%, the M at least comprises Ti and Zr, and the sum of the mass percent of Ti and the mass percent of Zr is 0.1-0.6 wt%; t comprises Fe, or Fe and Co; the mass percent of the B is 0.84 wt%-0.94 wt%; the neodymium-iron-boron magnet is provided with a main phase and a grain boundary phase comprising a rare earth-rich phase, the proportion of the rare earth-rich phase to the grain boundary phase is 0.15-0.35, and the atom proportion of Pr in R in the rare earth-rich phase is 0.4-0.5. The neodymium-iron-boron magnet disclosed by the invention has excellent magnetic performance under the condition of no heavy rare earth or low heavy rare earth elements.

Description

Technical Field

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

[0002] Sintered NdFeB magnets are widely used in many fields such as power machinery, medical equipment, automobile industry, wind power generation, electronics, etc. due to their excellent magnetic properties and high cost performance. As downstream products develop towards miniaturization, micro-miniaturization and lightweight, higher requirements are placed on their magnetic properties, especially coercivity. Currently, in order to improve the coercivity and temperature stability of NdFeB magnets, heavy rare earth elements dysprosium (Dy) and terbium (Tb) are often added to form a higher magnetocrystalline anisotropy field. 、 However, heavy rare earth elements Dy and Tb exhibit antiferromagnetic coupling with Fe, and their addition reduces the magnet's remanence and magnetic energy product. Furthermore, heavy rare earth resources are extremely scarce and expensive, significantly increasing magnet production costs. Furthermore, heavy rare earths are susceptible to market fluctuations and other factors, leading to price instability and significant price fluctuations, severely hindering the sustainable development of the sintered NdFeB magnet industry. Summary of the Invention

[0003] In view of this, in order to at least partially solve the above-mentioned technical problems, the present invention provides a neodymium iron boron magnet with no heavy rare earth or low heavy rare earth content, high coercivity and remanence, and a preparation method thereof.

[0004] According to an embodiment of one aspect of the present invention, a neodymium iron boron magnet is provided, comprising: a rare earth element R, a transition metal element T, a metal element M, and an element B; the rare earth element R comprises Pr and Nd, the mass percentage of the rare earth element R is 29wt%~32wt%, and the rare earth element R comprises heavy rare earth elements Tb and Dy with a mass percentage of 0~0.1wt%; the metal element M comprises at least Ti and Zr, wherein the sum of the mass percentages of Ti and Zr is 0.1wt%~0.6wt%; the transition metal element T comprises Fe, or Fe and Co; the mass percentage of the element B is 0.84wt%~0.94wt%; wherein the neodymium iron boron magnet has a main phase and a grain boundary phase comprising a rare earth-rich phase, the proportion of the rare earth-rich phase to the grain boundary phase is 0.15~0.35, and the atomic ratio of Pr in the rare earth-rich phase to the rare earth element R is 0.4~0.5.

[0005] According to another embodiment of the present invention, a method for preparing a neodymium iron boron magnet is provided, comprising: preparing a first alloy powder, the first alloy powder comprising a rare earth element R, an element B, a transition metal element T, and a metal element M, the metal element M comprising Zr, the mass percentage of the rare earth element R being 29 wt% to 32 wt%, the mass percentage of the element B being 0.84 wt% to 0.94 wt%, the mass percentage of the element Zr being 0.1 wt% to 0.4 wt%, the rare earth element R comprising Pr, Nd, or Pr, Nd and at least one of Dy, Tb, Gd, Ho, Y, La, and Ce, wherein Pr The mass percentage of the heavy rare earth element is greater than 8.5wt%, the mass percentage of the heavy rare earth element is 0-0.1wt%; the transition metal element T includes Fe, or Fe and Co; preparing a second alloy powder, the second alloy includes rare earth elements R, B elements, transition metal elements T and metal elements M, the metal element M includes Ti, the mass percentage of the rare earth element R is 28.5wt%-31.5wt%, the mass percentage of the B element is 0.84wt%-0.94wt%, the mass percentage of the Ti element is 0.1wt%-0.4wt%, the rare earth element R includes Pr, Nd, or The first alloy powder and the second alloy powder are mixed in a mass ratio of 1:0.5 to 1:5 to obtain a mixed alloy powder, and the mixed alloy powder is subjected to a forming process, a sintering process, and a tempering process to obtain a NdFeB magnet, wherein the mass percentage of the heavy rare earth element in the mixed alloy powder is 0 to 0.1 wt%, and the tempering process includes a two-stage tempering process or a three-stage tempering process.

[0006] According to the NdFeB magnet provided by the above embodiment of the present invention, the ratio of the rare earth-rich phase to the grain boundary phase of the NdFeB magnet is 0.15-0.35, and the ratio of Pr in the rare earth-rich phase to the rare earth element R is 0.4-0.5, so that the NdFeB magnet has better remanence and coercive force.

[0007] According to the NdFeB magnet provided by the above embodiment of the present invention, the ratio of the rare earth rich phase to the grain boundary phase of the NdFeB magnet is 0.15-0.35, the ratio of Pr in the rare earth rich phase to the rare earth element R is 0.4-0.5, and the R6T of the NdFeB magnet is 0.15-0.35. 13 The atomic ratio of Zr to Ti in the M1 phase is 15 to 30, which reduces the local enrichment and precipitation of Zr and Ti elements and enables the production of NdFeB magnets with better performance.

[0008] According to the method for preparing a NdFeB magnet provided by the above embodiment of the present invention, a double alloy method is used to prepare the NdFeB magnet, and the first alloy powder and the second alloy powder are both low-B content raw materials. The Pr element is used to replace part of the Nd element in the first alloy powder, and the Pr content in the first alloy powder is higher than 8.5wt%. At the same time, 0.1~0.4wt% of the Zr element is added, and 0.1~0.4wt% of the Ti element is added to the second alloy. The first alloy powder and the second alloy powder are mixed to prepare a magnet. This can promote the uniform formation of a rare earth-rich phase in the grain boundary phase, increase the proportion of the rare earth-rich phase, and effectively improve the distribution of the Zr element, so that the Zr and Ti elements are not locally enriched and precipitated. The B element in the magnet is effectively controlled, the magnet structure is optimized, and better magnetic properties are obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments will be briefly introduced below. Obviously, the drawings in the following description only relate to some embodiments of the present invention, but are not intended to limit the present invention.

[0010] Figure 1 This is an SEM image of the NdFeB magnet provided in Example 2 of the present invention.

[0011] Figure 2 This is an SEM image of the NdFeB magnet provided for Comparative Example 1. DETAILED DESCRIPTION

[0012] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. However, the present invention can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to make the present invention thorough and complete and to fully convey the scope of the present invention to those skilled in the art. In the drawings, the dimensions and relative dimensions of layers and regions may be exaggerated for clarity, and like reference numerals denote like elements throughout.

[0013] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The terms "comprise", "include", etc. used herein indicate the presence of the features, steps, operations and / or components, but do not exclude the presence or addition of one or more other features, steps, operations or components.

[0014] In the related art, in order to improve the coercive force of magnets, a formula system with a lower B element content is often used. Magnets with a lower B content are more sensitive to temperature. During mass production, slight changes in the B element content may cause problems with the consistency of the magnet. Usually, the instability in the preparation method can be eliminated by adding a certain amount of high-melting-point metals (Ti, Zr, Nb, etc.) to form compounds such as ZrB2 and TiB2 at the grain boundaries of the triangular region. The present invention hopes to further improve the coercive force of magnets under the above-mentioned low B element content formula system. Its technical improvement idea is to appropriately increase the content of praseodymium (Pr) element and use Pr element to replace part of the neodymium (Nd) element, thereby obtaining a further improvement in coercive force. Related studies disclose increasing the Pr content and adding metals such as Ti, Zr or Nb to solve the problem of temperature coefficient deterioration caused by high Pr magnets.

[0015] However, during further research, the present invention found that, for a low B element content formula system, after replacing part of the Nd element with the Pr element, when only one of the high melting point elements (Ti, Zr or Nb) was added, the coercive force of the magnet could not be significantly improved. When two or more high melting point elements were added at the same time, the problem of co-precipitation of the two high melting point elements was likely to occur. This precipitation caused the local B element content of the magnet to decrease significantly, forming excessive R6T 13 The M1 phase reduces the remanence of the magnet and increases the ferromagnetism of the local grain boundary phase, which ultimately leads to a decrease in the coercive force of the magnet and makes it impossible to obtain a high coercive force magnet.

[0016] In view of this, the present invention provides a NdFeB magnet and a preparation method thereof, so as to realize a NdFeB magnet without heavy rare earth or with low heavy rare earth content, and the NdFeB magnet has high remanence and coercive force.

[0017] According to an exemplary embodiment of the present invention, the present invention provides a neodymium iron boron magnet, comprising: a rare earth element R, a transition metal element T, a metal element M, and a B element; the rare earth element R includes Pr and Nd, the mass percentage of the rare earth element R is 29wt%~32wt%, and the rare earth element R includes heavy rare earth elements Tb and Dy with a mass percentage of 0~0.1wt%; the metal element M includes at least Ti and Zr, wherein the sum of the mass percentages of Ti and Zr is 0.1wt%~0.6wt%; the transition metal element T includes Fe, or Fe and Co; the mass percentage of the B element is 0.84wt%~0.94wt%; wherein the neodymium iron boron magnet has a main phase and a grain boundary phase including a rare earth-rich phase, the ratio of the rare earth-rich phase to the grain boundary phase is 0.15~0.35, and the atomic ratio of Pr in the rare earth-rich phase to the rare earth element R is 0.4~0.5.

[0018] In some embodiments, the metal element M includes Ti, Zr, and at least one of Al, Cu, Ga, and Sn; the heavy rare earth elements include terbium (Tb) and dysprosium (Dy), and the mass percentage of the heavy rare earth elements in the NdFeB magnet is preferably 0-0.05wt%.

[0019] According to an embodiment of the present invention, the ratio of the rare earth rich phase to the grain boundary phase of the NdFeB magnet is 0.15-0.35, and the atomic ratio of Pr in the rare earth rich phase to the rare earth element R is 0.4-0.5, so that the NdFeB magnet has better remanence and coercive force.

[0020] In an embodiment of the present invention, the atomic percentage of the rare earth element R in the rare earth-rich phase is 35 at%~90 at%, the atomic percentage of the transition metal element T is 0~55 at%, the atomic percentage of the metal element M is 0~20 at%, the ratio of the rare earth-rich phase to the grain boundary phase is 0.15~0.35, and the atomic ratio of Pr in the rare earth-rich phase to the rare earth element R is 0.4~0.5, so that the NdFeB magnet has better remanence and coercive force.

[0021] In an embodiment of the present invention, the grain boundary phase also includes R6T 13 M1 phase, R6T 13 The atomic percentage of rare earth element R in the M1 phase is 20at%~36at%, R6T 13 The atomic percentage of transition metal element T in the M1 phase is 45at%~75at%, the atomic percentage of metal element M is 3at%~10at%, and R6T 13 The atomic ratio of Zr element to Ti element in the M1 phase is 15~30.

[0022] In some embodiments, R6T 13 The atomic percentage of the rare earth element R in the M1 phase is, for example, 20 at%, 25 at%, 30 at%, 35 at%, or 36 at%, but is not limited to the above values. The atomic percentage of the transition metal element T is, for example, 45 at%, 50 at%, 60 at%, 70 at%, or 75 at%, but is not limited to the above values. The atomic percentage of the metal element M is, for example, 3 at%, 5 at%, 7 at%, 8 at%, or 10 at%, but is not limited to the above values. R6T 13 The atomic ratio of the Zr element to the Ti element in the M1 phase may be, for example, 15, 20, 25, or 30, but is not limited to these values.

[0023] According to an embodiment of the present invention, the ratio of the rare earth rich phase to the grain boundary phase of the NdFeB magnet is 0.15-0.35, the atomic ratio of Pr in the rare earth element R in the rare earth rich phase is 0.4-0.5, and the R6T of the NdFeB magnet is 0.15-0.35. 13The atomic ratio of Zr to Ti in the M1 phase is 15 to 30, which reduces the local enrichment and precipitation of Zr and Ti elements, and can produce NdFeB magnets with better performance. It should be noted that the larger the atomic ratio of Zr to Ti, the lower the enrichment of Zr and Ti elements.

[0024] In an embodiment of the present invention, the mass percentage of the B element is 0.84 wt % to 0.94 wt %, for example, 0.84 wt %, 0.86 wt %, 0.88 wt %, 0.90 wt %, and 0.94 wt %, but is not limited to the above values.

[0025] In some embodiments, the mass percentage of the B element is less than 0.9 wt %.

[0026] In an embodiment of the present invention, the mass percentage of the Co element is 0.5 wt% to 2.0 wt%, for example, 0.5 wt%, 0.55 wt%, 0.6 wt%, 0.75 wt%, 1 wt%, 1.5 wt%, and 2.0 wt%, but is not limited to the above values.

[0027] In an embodiment of the present invention, the metal element M further comprises Cu, Al and Ga, wherein the mass percentage of Cu is 0.1 wt% to 0.5 wt%, the mass percentage of Al is 0 to 0.5 wt% and the mass percentage of Ga is 0.1 wt% to 0.5 wt%.

[0028] According to an exemplary embodiment of the present invention, the present invention provides a method for preparing a neodymium iron boron magnet, comprising: operations S1 to S3.

[0029] Operation S1, preparing a first alloy powder, the first alloy powder includes rare earth elements R, B elements, transition metal elements T and metal elements M, the metal element M includes Zr, the mass percentage of the rare earth element R is 29wt%~32wt%, the mass percentage of the B element is 0.84wt%~0.94wt%, the mass percentage of the Zr element is 0.1 wt%~0.4wt%, the rare earth element R includes Pr, Nd, or Pr, Nd and at least one of Dy, Tb, Gd, Ho, Y, La and Ce, wherein the mass percentage of Pr is greater than 8.5wt%, the mass percentage of heavy rare earth elements is 0~0.1wt%, and the transition metal element T includes Fe, or Fe and Co.

[0030] In the embodiments of the present invention, the mass percentage of the rare earth element R is, for example, 29 wt%, 29.5 wt%, 30 wt%, 31 wt%, and 32 wt%, but is not limited to the above values. The mass percentage of the B element is, for example, 0.84 wt%, 0.86 wt%, 0.90 wt%, 0.92 wt%, and 0.94 wt%, but is not limited to the above values. The mass percentage of the Zr element is, for example, 0.1 wt%, 0.2 wt%, 0.3 wt%, and 0.4 wt%, but is not limited to the above values.

[0031] In an embodiment of the present invention, raw materials prepared according to a preset ratio are sequentially smelted, cast, and spun to form spun sheets; the spun sheets are hydrogen crushed and jet milled to form a first alloy powder with a particle size of 2.7-4.0 μm.

[0032] In the embodiment of the present invention, raw materials prepared in a preset ratio are placed in a vacuum induction furnace for melting, casting, and stripping to form stripping sheets; wherein the vacuum degree of the vacuum induction furnace is 10 -2 Pa~10 2 Pa, melting temperature 1300℃~1500℃, casting temperature 1400℃~1500℃, thickness of the strip is 0.2mm~0.5mm.

[0033] In an embodiment of the present invention, the stripped sheet is placed in a hydrogen decomposition furnace, where hydrogen absorption is performed at a hydrogen pressure of 0.15 to 0.4 MPa and a dehydrogenation temperature of 560°C to 600°C. The sheet is then jet milled to obtain a first alloy powder having a particle size of 2.7 μm to 4.0 μm. The grinding chamber pressure of the jet mill is 0.5 MPa to 0.7 MPa, for example, 0.68 MPa.

[0034] In some embodiments, the mass percentage of the transition metal element T in the first alloy powder is 64 wt% to 69 wt%, for example, 64 wt%, 65 wt%, 66 wt%, 68 wt%, and 69 wt%, but is not limited to these values.

[0035] In some embodiments, the mass percentage of Co element in the first alloy powder is 0.5 wt % to 2.0 wt %.

[0036] In an embodiment of the present invention, the metal element M for preparing the first alloy powder further includes Cu, Al and Ga; wherein the mass percentage of Cu is 0.1wt%~0.5wt%, the mass percentage of Al is 0~0.5wt%, and the mass percentage of Ga is 0.1wt%~0.5wt%.

[0037] Operation S2, prepare a second alloy powder, the second alloy powder includes rare earth elements R, B elements, transition metal elements T and metal elements M, the metal element M includes Ti, the mass percentage of the rare earth element R is 28.5 wt%~31.5wt%, the mass percentage of the B element is 0.84wt%~0.94wt%, the mass percentage of the Ti element is 0.1 wt%~0.3wt%, the rare earth element R includes Pr, Nd, or Pr, Nd and at least one of Dy, Tb, Gd, Ho, Y, La and Ce, the mass percentage of heavy rare earth elements is 0~0.1wt%, and the transition metal element T includes Fe, or Fe and Co.

[0038] In an embodiment of the present invention, raw materials prepared in a predetermined ratio are sequentially smelted, cast, and spun to form spun sheets; the spun sheets are hydrogen crushed and jet milled to form a second alloy powder with a particle size of 2.7μm~4.0μm.

[0039] In the embodiment of the present invention, raw materials prepared in a predetermined ratio are placed in a vacuum induction furnace for melting, casting, and stripping. The vacuum degree of the vacuum induction furnace is 10 -2 Pa ~10 2 Pa, melting temperature 1300℃~1500℃, casting temperature 1400℃~1500℃, thickness of the strip is 0.2mm~0.5mm.

[0040] According to an embodiment of the present invention, the stripping sheet is placed in a hydrogen cracking furnace and hydrogen absorption is performed under a hydrogen pressure of 0.3 MPa. The sheet is then jet milled to obtain a second alloy powder having a particle size of 2.7 μm to 4.0 μm. The grinding chamber pressure of the jet mill is 0.68 MPa.

[0041] In some embodiments, the mass percentage of the transition metal element T in the second alloy powder is 64 wt% to 69 wt%, for example, 64 wt%, 65 wt%, 66 wt%, 68 wt%, and 69 wt%, but is not limited to these values.

[0042] In some embodiments, the mass percentage of Co element in the second alloy powder is 0.5 wt% to 2.0 wt%.

[0043] In an embodiment of the present invention, the metal element M for preparing the second alloy powder further includes Cu, Al and Ga; wherein the mass percentage of Cu is 0.1wt%~0.5wt%, the mass percentage of Al is 0~0.5wt%, and the mass percentage of Ga is 0.1wt%~0.5wt%.

[0044] In an embodiment of the present invention, the mass percentage of Pr in the second alloy powder is greater than 7.5 wt %.

[0045] In operation S3, the first alloy powder and the second alloy powder are mixed in a mass ratio of 1:0.5 to 1:5 to obtain a mixed alloy powder. The mixed alloy powder is subjected to a forming process, a sintering process, and a tempering process to obtain a NdFeB magnet, wherein the mass percentage of the heavy rare earth element in the mixed alloy powder is 0 to 0.1 wt%, and the tempering process includes a secondary tempering process or a tertiary tempering process.

[0046] In an embodiment of the present invention, the mass ratio of the first alloy powder to the second alloy powder may be, for example, 1:0.5, 1:1, 1:2, 1:3, 1:4, or 1:5, but is not limited to these values.

[0047] In an embodiment of the present invention, the mass percentage of the heavy rare earth element in the mixed alloy powder is preferably 0-0.05 wt %.

[0048] In an embodiment of the present invention, the forming process is an orientation forming process, and the orientation forming process is performed under the condition that the orientation magnetic induction intensity is 1.8T~3.2T.

[0049] In an embodiment of the present invention, the sintering process includes sintering in a vacuum induction furnace, and the vacuum degree of the vacuum induction furnace is 10 -2 Pa~10 2 The sintering temperature is 1050°C to 1085°C, for example, 1050°C, 1060°C, 1070°C, 1080°C, 1085°C, but not limited to the above values; the sintering time is 6h to 8h, for example, 6h, 7h, 8h, but not limited to the above values.

[0050] In some embodiments, the tempering process is a two-stage tempering process, which includes a first-stage tempering heat treatment and a second-stage tempering heat treatment; the temperature of the first-stage tempering heat treatment is 800°C~950°C, for example, it can be 800°C, 850°C, 880°C, 900°C, 950°C, but is not limited to the listed values; the tempering time is 0.5h~4h, for example, it can be 0.5h, 1h, 2h, 3h, 4h, but is not limited to the listed values; the temperature of the second-stage tempering heat treatment is 450°C~550°C, for example, it can be 450°C, 480°C, 500°C, 520°C, 550°C, but is not limited to the listed values; the tempering time is 2h~10h, for example, it can be 2h, 4h, 6h, 8h, 10h, but is not limited to the listed values.

[0051] In some embodiments, the tempering process is a three-stage tempering process, which includes a first-stage tempering heat treatment, a second-stage tempering heat treatment, and a third-stage tempering heat treatment.

[0052] In an embodiment of the present invention, the temperature of the first stage tempering heat treatment is 800°C~950°C, for example, it can be 800°C, 850°C, 900°C, 920°C, 950°C, but is not limited to the values ​​listed above; the tempering time is 0.5h~4h, for example, it can be 0.5h, 1h, 2h, 3h, 4h, but is not limited to the values ​​listed above.

[0053] In an embodiment of the present invention, the temperature of the second stage tempering heat treatment is 450°C~550°C, for example, it can be 450°C, 480°C, 500°C, 520°C, 550°C, but is not limited to the listed values; the tempering time is 2h~10h, for example, it can be 2h, 5h, 8h, 10h, but is not limited to the listed values.

[0054] In an embodiment of the present invention, the temperature of the third stage tempering heat treatment is 600°C to 700°C, for example, it can be 600°C, 620°C, 650°C, 680°C, 700°C, but is not limited to the values ​​listed above; the tempering time is 2 h to 10 h, for example, it can be 2 h, 5 h, 8 h, 10 h, but is not limited to the values ​​listed above.

[0055] The following schematically illustrates the designed NdFeB magnet and its preparation method. It should be noted that this example is only a specific embodiment of the present invention and does not limit the scope of protection of the present invention.

[0056] Example 1 NdFeB magnets were prepared using a double alloy method. A first alloy powder was prepared. Specifically, as shown in Table 1, the raw materials prepared according to a preset ratio were sequentially smelted, cast, and spun to form spun sheets; wherein the smelting temperature was 1430°C, the casting temperature was 1400°C, and the average thickness of the spun sheets was 0.25mm. The spun sheets were subjected to hydrogen crushing and air flow milling to form a first alloy powder with an average particle size D50 of 3.6μm, wherein the hydrogen absorption pressure of the hydrogen crushing was 0.3MPa, and the dehydrogenation temperature was 560°C. During the air flow milling, the grinding chamber pressure of the air flow mill was 0.68MPa, and the speed of the air flow mill classifying wheel was 3200r / min.

[0057] Prepare the second alloy powder. Specifically, referring to Table 1, the raw materials prepared according to the preset proportions are sequentially smelted, cast, and spun to form spun sheets; wherein the smelting temperature is 1430°C, the casting temperature is 1400°C, and the thickness of the spun sheets is 0.25mm. The spun sheets are subjected to hydrogen crushing and air flow milling to form a second alloy powder with an average particle size D50 of 3.6μm, wherein the hydrogen absorption pressure of the hydrogen crushing is 0.3MPa, and the dehydrogenation temperature is 560°C. During the air flow milling, the grinding chamber pressure of the air flow mill is 0.68MPa, and the speed of the air flow mill classifying wheel is 3200r / min.

[0058] The first alloy powder and the second alloy powder are mixed in a mass ratio of 1:1 to form a mixed alloy powder. The mixed alloy powder is then subjected to a forming process, a sintering process, and a tempering process to obtain a NdFeB magnet. The sintering temperature is 1060°C and the sintering time is 6 hours. The tempering process includes a first tempering heat treatment at a temperature of 900°C and a tempering time of 6 hours, and a second tempering heat treatment at a temperature of 500°C and a tempering time of 6 hours.

[0059] Example 2 The NdFeB magnet was prepared by the same preparation method as in Example 1, except that the mass percentage of the Zr element in the first alloy powder was 0.4 wt %.

[0060] Example 3 The NdFeB magnet was prepared by the same preparation method as in Example 1, except that the mass ratio of the first alloy powder to the second alloy powder was 1:2.

[0061] Example 4 The NdFeB magnet was prepared by the same preparation method as in Example 1, except that the mass ratio of the first alloy powder to the second alloy powder was 1:3.

[0062] Example 5 NdFeB magnets were prepared using the same preparation method as in Example 1, except that the tempering treatment included a first-stage tempering heat treatment, a second-stage tempering heat treatment, and a third-stage tempering heat treatment. The temperature of the first-stage tempering heat treatment was 900°C, and the tempering time was 4 h; the temperature of the second-stage tempering heat treatment was 480°C, and the tempering time was 6 h; and the temperature of the third-stage tempering heat treatment was 620°C, and the tempering time was 6 h.

[0063] Comparative Example 1 The NdFeB magnets were prepared using the same raw material ratios and smelting, casting, strip spinning, molding, sintering and tempering processes as in Example 1, except that, as shown in Table 1, a single alloy method was used for preparation.

[0064] The composition and content of the raw materials, alloy powder and NdFeB magnets of Example and Comparative Example 1 were tested respectively by ICP component analysis instrument.

[0065] The remanence, coercive force and squareness of the NdFeB magnets prepared in Example and Comparative Example 1 were tested using the permanent magnet material precision measurement system NIM-62000TB. The test results are shown in Table 2.

[0066] Figure 1 This is an SEM image of the NdFeB magnet provided in Example 2 of the present invention.

[0067] Figure 2This is an SEM image of the NdFeB magnet provided for Comparative Example 1.

[0068] The element content of the grain boundary phase of the NdFeB magnets prepared in Example 2 and Comparative Example 1 was tested respectively. Specifically, after the NdFeB magnets were sampled, any cross section of the magnet perpendicular to the orientation direction was tested by scanning electron microscopy. All main phases and grain boundary phases in each microstructure cross section were counted. The size of the observation area was, for example, 40 μm × 40 μm and 75 μm × 75 μm, and the magnification was 2000-5000 times. Image analysis software was used for statistical analysis, and the image contrast was used to distinguish R6T. 13 The M1 phase is displayed as a gray grain boundary phase, and the rare earth-rich phase is displayed as a white grain boundary phase. The percentage of the area of ​​all rare earth-rich phases in the magnet microstructure cross section to the total area of ​​the microstructure observation surface can be obtained.

[0069] EDS energy spectrum is used to analyze the atomic percentage of each element in the main phase and grain boundary phase to obtain the grain boundary phase composition. (R6T 13 The calculation method of [Zr] / [Ti] of M1 phase is to take at least 10 R6T 13 The M1 phase was used to calculate the ratio of Zr to Ti, i.e. [Zr] / [Ti], and the average value of all the ratios was calculated to obtain the value of [Zr] / [Ti] in the embodiment, where [Zr] / [Ti] represents the atomic ratio of Zr to Ti. The test results are shown in Table 3. Figure 1 、 Figure 2 As shown, the grain boundary phase marked by ○ is R6T 13 M1 phase, the grain boundary phase marked by △ is the rare earth-rich phase, and the black shadow in the area pointed to → represents the Zr-enriched area.

[0070] Table 1

[0071] Table 2

[0072] Table 3

[0073] According to the above embodiments and comparative examples of the present invention, by adjusting the preparation process and raw material ratio, NdFeB magnets with better remanence, coercivity and squareness can be obtained. It should be noted that the closer the squareness value is to 1, the more stable the magnet performance.

[0074] Among them, according to Example 2 and Comparative Example 1, it can be seen that Example 2 and Comparative Example 1 use the same raw material ratio to prepare NdFeB magnets. Compared with Comparative Example 1 using a single alloy process to prepare NdFeB magnets, Example 2 of the present invention uses a dual alloy process to prepare NdFeB magnets, and the coercive force is improved. This is because the use of a dual alloy process to prepare NdFeB magnets can promote the uniform formation of rare earth-rich phases in the grain boundary phase, increase the proportion of rare earth-rich phases, and effectively improve the problem of local enrichment and precipitation of Zr and Ti elements, effectively improving the remanence and coercive force of the magnet.

[0075] According to Example 1 and Example 2, by adjusting the content of Zr in the first alloy powder, the R6T of the NdFeB magnet in Example 2 can be reduced to 13 The atomic ratio of Zr to Ti in the M1 phase ([Zr] / [Ti]) is greater than that of the NdFeB magnet in Example 1. 13 The [Zr] / [Ti] ratio in the M1 phase reaches 18.48, which improves the remanence, coercivity, and squareness of the NdFeB magnet. This is because a larger [Zr] / [Ti] ratio indicates a lower degree of local enrichment of Zr and Ti elements, which is more conducive to obtaining excellent magnetic properties.

[0076] It is worth mentioning that, through the comparison of Examples 1 to 5, it can be seen that the NdFeB magnet obtained in Example 3 has better remanence, the NdFeB magnet obtained in Example 2 has better coercive force, and the NdFeB magnet obtained in Example 4 has better squareness. The comprehensive performance of the NdFeB magnet obtained in Example 4, such as remanence, coercive force and squareness, is better.

[0077] The use of ordinal numbers such as "first," "second," and "third" in the specification and claims to modify corresponding elements does not in itself mean that the elements have any ordinal number, nor does it represent the order of one element relative to another or the order in the manufacturing method. The use of such ordinal numbers is only used to clearly distinguish one element with a certain name from another element with the same name.

[0078] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A neodymium iron boron magnet, characterized in that: The NdFeB magnet comprises: Rare earth elements R, transition metal elements T, metal elements M, B elements; The rare earth elements R include Pr and Nd, the mass percentage of the rare earth elements R is 29wt% to 32wt%, and the rare earth elements R include heavy rare earth elements Tb and Dy in a mass percentage of 0 to 0.1wt%; The metal element M includes at least Ti and Zr, wherein the sum of the mass percentages of Ti and Zr is 0.1wt% to 0.6wt%; The transition metal element T includes Fe, or Fe and Co; The mass percentage of element B is 0.84wt%~0.94wt%; Among them, the NdFeB magnet has a main phase and a grain boundary phase including a rare earth-rich phase. The ratio of the rare earth-rich phase to the grain boundary phase is 0.15~0.35, and the atomic ratio of Pr in the rare earth element R in the rare earth-rich phase is 0.4~0.

5.

2. The NdFeB magnet according to claim 1, wherein The grain boundary phase also includes R6T 13 M1 phase, R6T 13 The atomic ratio of Zr element to Ti element in the M1 phase is 15~30.

3. The NdFeB magnet according to claim 1, wherein The mass percentage of B element is less than 0.9wt%.

4. The NdFeB magnet according to claim 1, wherein The mass percentage of Co element is 0.5 wt%~2.0 wt%; The metal element M further includes Cu, Al, and Ga. The mass percentage of Cu is 0.1 wt% to 0.5 wt%, the mass percentage of Al is 0 to 0.5 wt%, and the mass percentage of Ga is 0.1 wt% to 0.5 wt%.

5. A method for preparing a neodymium iron boron magnet, characterized in that: include: Prepare a first alloy powder, the first alloy powder including a rare earth element R, an element B, a transition metal element T, and a metal element M, the metal element M including Zr, the mass percentage of the rare earth element R being 29 wt% to 32 wt%, the mass percentage of the element B being 0.84 wt% to 0.94 wt%, the mass percentage of the element Zr being 0.1 wt% to 0.4 wt%, the rare earth element R including Pr, Nd, or Pr, Nd and at least one of Dy, Tb, Gd, Ho, Y, La, and Ce, wherein the mass percentage of Pr is greater than 8.5 wt%, the mass percentage of the heavy rare earth element is 0 to 0.1 wt%, and the transition metal element T including Fe, or Fe and Co; preparing a second alloy powder, the second alloy powder comprising a rare earth element R, an element B, a transition metal element T, and a metal element M, the metal element M comprising Ti, the mass percentage of the rare earth element R being 28.5 wt% to 31.5 wt%, the mass percentage of the element B being 0.84 wt% to 0.94 wt%, the mass percentage of the element Ti being 0.1 wt% to 0.4 wt%, the rare earth element R comprising Pr, Nd, or Pr, Nd and at least one of Dy, Tb, Gd, Ho, Y, La, and Ce, the mass percentage of the heavy rare earth element being 0 to 0.1 wt%, and the transition metal element T comprising Fe, or Fe and Co; and The first alloy powder and the second alloy powder are mixed in a mass ratio of 1:0.5~1:5 to obtain a mixed alloy powder. The mixed alloy powder is subjected to a forming process, a sintering process, and a tempering process to obtain a neodymium iron boron magnet, wherein the mass percentage of the heavy rare earth element in the mixed alloy powder is 0~0.1wt%, and the tempering process includes a secondary tempering process or a tertiary tempering process.

6. The preparation method according to claim 5, characterized in that The mass percentage of Pr in the second alloy powder is greater than 7.5 wt %.

7. The preparation method according to claim 5, characterized in that The preparing of the first alloy powder comprises: The raw materials prepared in a preset ratio are sequentially melted, cast, and spun to form spun strips; The stripped pieces are subjected to hydrogen crushing and air flow grinding to form a first alloy powder with a particle size of 2.7 μm to 4.0 μm; The smelting temperature is 1300° C. to 1500° C., the casting temperature is 1400° C. to 1500° C., and the thickness of the strip is 0.2 mm to 0.5 mm.

8. The preparation method according to claim 5, characterized in that The mass percentage of the transition metal element T in the first alloy powder is 64 wt% to 69 wt%, and the mass percentage of the Co element is 0.5 wt% to 2.0 wt%; The metal elements M used to prepare the first alloy powder further include Cu, Al, and Ga. The mass percentage of the Cu element is 0.1 wt% to 0.5 wt%, the mass percentage of the Al element is 0 to 0.5 wt%, and the mass percentage of the Ga element is 0.1 wt% to 0.5 wt%.

9. The preparation method according to claim 5, characterized in that Preparing the second alloy powder includes: The raw materials prepared in a preset ratio are sequentially melted, cast, and spun to form spun strips; The stripped pieces are subjected to hydrogen crushing and air flow grinding to form a second alloy powder with a particle size of 2.7 μm to 4.0 μm; Among them, the melting temperature is 1300℃~1500℃, the casting temperature is 1400℃~1500℃, and the thickness of the strip is 0.2mm~0.5mm.

10. The preparation method according to claim 5, characterized in that The mass percentage of the transition metal element T in the prepared second alloy powder is 64 wt%~69 wt%, and the mass percentage of the Co element is 0.5 wt%~2.0 wt%; The metal elements M used to prepare the second alloy powder further include Cu, Al, and Ga; The mass percentage of the Cu element is 0.1 wt% to 0.5 wt%, the mass percentage of the Al element is 0 to 0.5 wt%, and the mass percentage of the Ga element is 0.1 wt% to 0.5 wt%.

11. The preparation method according to claim 5, characterized in that The two-stage tempering process includes a first-stage tempering heat treatment and a second-stage tempering heat treatment; The temperature of the first stage tempering heat treatment is 800°C to 950°C, and the tempering time is 0.5h to 4h; The temperature of the second stage tempering heat treatment is 450° C. to 550° C., and the tempering time is 2 h to 10 h.

12. The preparation method according to claim 5, characterized in that The three-stage tempering process includes a first-stage tempering heat treatment, a second-stage tempering heat treatment, and a third-stage tempering heat treatment; The temperature of the first stage tempering heat treatment is 800°C to 950°C, and the tempering time is 0.5h to 4h; The temperature of the second stage tempering heat treatment is 450℃~550℃, and the tempering time is 2h~10h; The temperature of the third stage tempering heat treatment is 600° C. to 700° C., and the tempering time is 2 h to 10 h.

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