阅读说明：本技术 一种复合型钕铁硼磁体及其制备方法 (Composite neodymium-iron-boron magnet and preparation method thereof ) 是由 毛华云 毛琮尧 刘永 赖欣 于 2020-12-06 设计创作，主要内容包括：本发明涉及磁体制备技术领域,特别涉及一种复合型钕铁硼磁体及其制备方法；本发明的一种复合型钕铁硼磁体包括钕铁硼磁体及复合在钕铁硼磁体的表面的RTMH氢化物薄膜层；RTMH氢化物薄膜层内R为Dy、Tb中的一种或两种；T为Fe、Co、Ni中的一种或多种；M为Al、Cu、Zn、Ga、Bi、Sn、Pb、In中的一种或多种；H为氢元素；在钕铁硼半成品磁体表面涂覆RTMH氢化物的悬浊液,RTMH氢化物的悬浊液作为扩散源,因其熔点低而能提高热处理后的扩散效率,其与传统的晶界扩散相比,提高了重稀土元素的扩散深度,可以处理更厚的磁体,扩散后的磁体不仅矫顽力得到明显提高,还保证了原有剩磁和最大磁能积不会明显的降低,同时降低了重稀土的使用量,节约了重稀土资源。(The invention relates to the technical field of magnet preparation, in particular to a composite neodymium iron boron magnet and a preparation method thereof; the composite neodymium iron boron magnet comprises a neodymium iron boron magnet and an RTMH hydride thin film layer compounded on the surface of the neodymium iron boron magnet; r in the RTMH hydride thin film layer is one or two of Dy and Tb; t is one or more of Fe, Co and Ni; m is one or more of Al, Cu, Zn, Ga, Bi, Sn, Pb and In; h is hydrogen element; the surface of a neodymium iron boron semi-finished product magnet is coated with the suspension of RTMH hydride, the suspension of RTMH hydride is used as a diffusion source, the diffusion efficiency after heat treatment can be improved due to low melting point, compared with the traditional crystal boundary diffusion, the diffusion depth of heavy rare earth elements is improved, thicker magnets can be treated, the coercive force of the diffused magnets is obviously improved, the original remanence and the maximum magnetic energy product are not obviously reduced, meanwhile, the use amount of heavy rare earth is reduced, and heavy rare earth resources are saved.)

1. The composite neodymium iron boron magnet is characterized by comprising a neodymium iron boron magnet and an RTMH hydride thin film layer compounded on the surface of the neodymium iron boron magnet; wherein R in the RTMH hydride thin film layer is one or two of Dy and Tb; t is one or more of Fe, Co and Ni; m is one or more of Al, Cu, Zn, Ga, Bi, Sn, Pb and In; h is hydrogen element.

2. The compound ndfeb magnet according to claim 1, wherein the weight of the RTMH hydride thin film layer is less than or equal to 3% of the total weight of the compound ndfeb magnet.

3. A composite neodymium-iron-boron magnet according to claim 2, characterized in that the combination of R, T, M types of elements in the RTM-mh hydride thin film layer makes the melting point of the RTM alloy below 950 ℃.

4. The composite ndfeb magnet according to claim 3, wherein the RTMH hydride thin film layer comprises, by weight: 40-98 parts by weight of R, less than or equal to 30 parts by weight of T, less than or equal to 30 parts by weight of M and less than or equal to 2 parts by weight of H.

5. The compound neodymium iron boron magnet according to claim 1, wherein the blank of the neodymium iron boron magnet comprises, by mass, 28% -33% of Pr-Nd, 0% -10% of Dy, 0% -10% of Tb, 0% -5% of Nb, 0.5% -1.05% of B, 0% -3.0% of Al, 0% -1% of Cu, 0% -3% of Co, 0% -2% of Ga, 0% -2% of Gd, 0% -2% of Ho, 0% -2% of Zr, 0% -2% of Ti and the balance Fe.

6. The preparation method of the composite neodymium iron boron magnet is characterized by comprising the following steps:

step S1, selecting one or two of Dy and Tb for R, selecting one or more of Fe, Co and Ni for T, selecting one or more of Al, Cu, Zn, Ga, Bi, Sn, Pb and In for M, and hydrogen for H to form RTM alloy, and then smelting, hydrogen crushing and jet milling the RTM alloy to obtain RTMH hydride powder;

step S2, mixing RTMH hydride powder with an organic solvent to obtain a suspension;

step S3, coating the suspension on the surface of a semi-finished product made of a blank of a neodymium iron boron magnet;

and step S4, performing diffusion heat treatment on the semi-finished product coated with the suspension to obtain the composite neodymium iron boron magnet.

7. The method of claim 6, wherein in step S1, the average grain size of the RTMH hydride powder is 1-50 μm.

8. The method of claim 6, wherein in step S2, the organic solvent includes one or more of gasoline, ethanol and acrylic acid.

9. The method of claim 8, wherein in step S2, the mixing temperature of RTMH hydride powder and organic solvent is 30-38 ℃ and the mixing time is 12-23 h.

10. The method for preparing a composite neodymium-iron-boron magnet according to claim 6, characterized in that in step S4, the heat treatment of the semi-finished product includes high-temperature diffusion treatment and low-temperature tempering treatment, wherein the temperature of the high-temperature diffusion treatment is 850-1200 ℃ and the time is 2-18 h; the temperature of the low-temperature tempering treatment is 300-500 ℃, and the time is 5-10 h.

Technical Field

The invention relates to the technical field of magnet preparation, in particular to a composite neodymium iron boron magnet and a preparation method thereof.

Background

The magnet is a substance capable of generating a magnetic field and has the characteristic of attracting ferromagnetic substances, such as metals like iron, nickel, cobalt and the like; the permanent magnet is a hard magnet, which can maintain the magnetism of the magnet for a long time, is not easy to lose magnetism and is not easy to be magnetized, so that the hard magnet is one of the most commonly used strong materials in industrial production and daily life.

The hard magnet can be divided into a natural magnet and an artificial magnet, and the artificial magnet can achieve the same effect as a natural magnet (magnet) by synthesizing alloys of different materials and can also improve the magnetic force. Artificial magnets appeared as early as the 18 th century, but the process of making stronger magnetic materials was very slow, and large-scale application of magnets was not possible until the 30 th century when AlNiCo (AlNiCo) was made, and subsequently, Ferrite (Ferrite) was made in the 50 th century, 60 s, and the emergence of rare earth permanent magnets, opened up a new era for the application of magnets, the first generation of samarium-cobalt permanent magnet SmCo₅Second generation precipitation hardening type samarium cobalt permanent magnet Sm₂Co₁₇Until now, the third generation of permanent-magnet neodymium-iron-boron (NdFeB) has been developed, and although the ferrite magnet is still the most used permanent-magnet material, the production value of the NdFeB magnet is greatly higher than that of the ferrite permanent-magnet material, and a large industry has been developed.

Neodymium iron boron magnets, also known as Neodymium magnets (Neodymium magnets), have the chemical formula Nd₂Fe₁₄The neodymium iron boron permanent magnet is an artificial permanent magnet and also a permanent magnet with the strongest magnetic force so far, the maximum magnetic energy product (BHmax) of the neodymium iron boron permanent magnet is more than 10 times higher than that of ferrite, and the neodymium iron boron magnet has the advantages of high cost performance, small volume, light weight, good mechanical property, strong magnetism and the like, so the neodymium iron boron permanent magnet material can be widely applied to modern industry and electronic technology due to the advantage of high energy density and is known as 'Magang' in the magnetics field, and therefore, the application expansion of the neodymium iron boron magnet is always the focus of continuous attention in the industry.

At present, the method for improving the coercive force is mainly to improve the coercive force by directly adding heavy rare earth during smelting, but the method can obviously reduce the remanence and the magnetic energy product on the basis of improving the coercive force, and domestic and foreign reports adopt metal dysprosium or terbium or fluorides for infiltration, but the melting point of the metal or the fluoride is far higher than the infiltration temperature, so that the infiltration efficiency is low, the infiltration time is long, the utilization rate of the heavy rare earth is low, and the thickness of an infiltrated product is very difficult to be more than 6 mm; therefore, how to find a more appropriate method and diffusion source to perform efficient permeation on a thick sheet product and improve the coercive force of the magnet, but also can keep the remanence and the maximum magnetic energy product is always the focus of wide attention of research and development type neodymium iron boron magnet production enterprises in the industry.

Disclosure of Invention

In order to overcome the defects, the invention aims to provide a composite neodymium iron boron magnet, wherein a blank surface of the neodymium iron boron magnet is coated with a suspension of RTMH hydride, and the suspension of RTMH hydride is used as a diffusion source, so that the diffusion heat treatment efficiency can be improved due to low melting point, the coercive force of the neodymium iron boron magnet is obviously improved, the use amount of heavy rare earth is reduced, and the original remanence and the maximum magnetic energy product of the magnet can not be obviously reduced; also provides a preparation method of the composite neodymium iron boron magnet.

The technical scheme for solving the technical problem is as follows:

a composite neodymium iron boron magnet comprises a neodymium iron boron magnet and an RTMH hydride thin film layer compounded on the surface of the neodymium iron boron magnet; wherein R in the RTMH hydride thin film layer is one or two of Dy and Tb; t is one or more of Fe, Co and Ni; m is one or more of Al, Cu, Zn, Ga, Bi, Sn, Pb and In; h is hydrogen element.

As an improvement of the invention, the weight of the RTMH hydride thin film layer accounts for less than or equal to 3 percent of the total weight of the composite neodymium-iron-boron magnet.

As a further development of the invention, the combination of the three elements R, T, M in the RTM hydride thin film layer results in a melting point of the RTM alloy below 950 ℃.

As a further refinement of the present invention, the thin film layer of RTMH hydride comprises, by weight percent: 40-98 parts by weight of R, less than or equal to 30 parts by weight of T, less than or equal to 30 parts by weight of M and less than or equal to 2 parts by weight of H.

As a further improvement of the invention, the blank of the neodymium iron boron magnet comprises, by mass, 28% -33% of Pr-Nd, 0-10% of Dy, 0-10% of Tb, 0-5% of Nb, 0.5% -1.05% of B, 0-3.0% of Al, 0-1% of Cu, 0-3% of Co, 0-2% of Ga, 0-2% of Gd, 0-2% of Ho, 0-2% of Zr, 0-2% of Ti and the balance of Fe.

A preparation method of a composite neodymium iron boron magnet comprises the following steps:

step S1, selecting one or two of Dy and Tb for R, selecting one or more of Fe, Co and Ni for T, selecting one or more of Al, Cu, Zn, Ga, Bi, Sn, Pb and In for M, and hydrogen for H to form RTM alloy, and then smelting, hydrogen crushing and jet milling the RTM alloy to obtain RTMH hydride powder;

step S2, mixing RTMH hydride powder with an organic solvent to obtain a suspension;

step S3, coating the suspension on the surface of a semi-finished product made of a blank of a neodymium iron boron magnet;

and step S4, performing heat treatment on the semi-finished product coated with the suspension to obtain the composite neodymium iron boron magnet.

As a further improvement of the invention, in step S1, the RTMH hydride powder has an average particle size of 1 μm to 50 μm.

As a further improvement of the present invention, in step S2, the organic solvent includes one or more of gasoline, ethanol, and acrylic acid.

As a further improvement of the invention, in step S2, the mixing temperature of the RTMH hydride powder and the organic solvent is 30-38 ℃ and the mixing time is 12-23 h.

As a further improvement of the invention, in step S4, the heat treatment of the semi-finished product includes high-temperature diffusion treatment and low-temperature tempering treatment, wherein the temperature of the high-temperature diffusion treatment is 850-1200 ℃ and the time is 2-18 h; the temperature of the low-temperature tempering treatment is 300-500 ℃, and the time is 5-10 h.

In the invention, the blank surface of the neodymium iron boron magnet is coated with the RTMH hydride thin film layer which is used as a diffusion source, and the diffusion efficiency can be improved due to the low melting point, so that the coercive force of the neodymium iron boron magnet is obviously improved, the diffusion efficiency can be greatly improved, the use amount of heavy rare earth is reduced, and the original remanence and the maximum magnetic energy product of the magnet can not be obviously reduced.

Drawings

For ease of illustration, the present invention is described in detail by the following preferred embodiments and the accompanying drawings.

FIG. 1 is a block diagram of the steps of the present invention;

FIG. 2 is a schematic process flow diagram of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

In order to improve the coercivity of the neodymium iron boron magnet, if heavy rare earth is added to improve the coercivity when the neodymium iron boron magnet is smelted, the remanence and the magnetic energy product can be reduced on the basis of improving the coercivity.

If the neodymium iron boron magnet is subjected to grain boundary diffusion by adopting metal dysprosium/terbium or metal dysprosium/terbium fluorides, the melting point of the metals or the fluorides is far higher than the diffusion heat treatment temperature, so that the diffusion efficiency is low, the diffusion time is long, the utilization rate of heavy rare earth is low, and the thickness of a permeated product is difficult to be more than 6 mm.

Therefore, the invention provides a composite neodymium iron boron magnet, which comprises a neodymium iron boron magnet and an RTMH hydride thin film layer compounded on the surface of the neodymium iron boron magnet; wherein, R in the RTMH hydride thin film layer is one or two of Dy and Tb; t is one or more of Fe, Co and Ni; m is one or more of Al, Cu, Zn, Ga, Bi, Sn, Pb and In; h is hydrogen element.

In the invention, the surface of the neodymium iron boron semi-finished magnet is coated with the RTMH hydride turbid liquid, and the RTMH hydride thin film layer is used as a permeation source, so that not only is an alloy thin film layer formed on the surface of the neodymium iron boron magnet, but also grain boundary diffusion can be generated, the coercive force of the neodymium iron boron magnet is obviously improved, the diffusion efficiency can be greatly improved, the use amount of heavy rare earth is reduced, the original residual magnetism and the maximum magnetic energy product of the magnet are not obviously reduced, the permeation can be completely performed on the neodymium iron boron magnet with the thickness of more than 6mm, the permeation efficiency is high, and the coercive force of the neodymium iron boron magnet is.

In order that the diffusion heat treatment temperature of the RTMH hydride is not too high, which affects the diffusion efficiency, the combination of the three types of elements R, T, M in the RTMH hydride thin film layer makes the melting point of the RTM alloy lower than 950 ℃, which must be lower than 950 ℃, otherwise the diffusion is affected, which affects the final performance.

In the invention, the weight of the RTMH hydride thin film layer accounts for less than or equal to 3% of the total weight of the composite neodymium iron boron magnet, and further, the RTMH hydride thin film layer comprises the following components in percentage by weight: 40-98 parts by weight of R, less than or equal to 30 parts by weight of T, less than or equal to 30 parts by weight of M and less than or equal to 2 parts by weight of H.

In the invention, a blank of the neodymium iron boron magnet comprises 28-33% of Pr-Nd, 0-10% of Dy, 0-10% of Tb, 0-5% of Nb, 0.5-1.05% of B, 0-3.0% of Al, 0-1% of Cu, 0-3% of Co, 0-2% of Ga, 0-2% of Gd, 0-2% of Ho, 0-2% of Zr, 0-2% of Ti and the balance of Fe by mass percentage; furthermore, the neodymium iron boron magnet blank may further include one or more of other rare earth elements.

As shown in fig. 1 and 2, a method for preparing a composite neodymium iron boron magnet includes the following steps:

step S1, selecting one or two of Dy and Tb for R, selecting one or more of Fe, Co and Ni for T, selecting one or more of Al, Cu, Zn, Ga, Bi, Sn, Pb and In for M, and hydrogen for H to form RTM alloy, and then smelting, hydrogen crushing and jet milling the RTM alloy to obtain RTMH hydride powder;

step S2, mixing RTMH hydride powder with an organic solvent to obtain a suspension;

step S3, coating the suspension on the surface of a semi-finished product made of a blank of a neodymium iron boron magnet;

and step S4, performing heat treatment on the semi-finished product coated with the suspension to obtain the composite neodymium iron boron magnet.

In the present invention, in step S1, the RTMH hydride powder has an average particle size of 1 μm to 50 μm.

In step S2, the organic solvent includes one or more of gasoline, ethanol, and acrylic acid, and further, the mixing temperature of the RTMH hydride powder and the organic solvent is 30 ℃ to 38 ℃ and the mixing time is 12h to 23 h.

In the step S4, the heat treatment of the semi-finished product comprises high-temperature diffusion treatment and low-temperature tempering treatment, wherein the temperature of the high-temperature diffusion treatment is 850-1200 ℃, and the time is 2-18 h; the temperature of the low-temperature tempering treatment is 300-500 ℃ and the time is 5-10 h, the stability after diffusion of the low-temperature tempering treatment is influenced, the time of the low-temperature tempering treatment needs to reach 5-10 h, and otherwise, the low-temperature tempering treatment is unstable after permeation.

The invention adopts the low-melting point heavy rare earth alloy (the melting point of RTM alloy is lower than 950 ℃ due to the combination of R, T, M three elements in an RTMH hydride film layer), avoids the problems of low diffusion efficiency, long diffusion time and low utilization rate of heavy rare earth caused by adopting metal dysprosium/terbium or metal dysprosium/terbium fluoride with high melting point for diffusion heat treatment, successfully solves the problem of difficult permeation of permeant with the thickness of more than 6 millimeters, greatly saves heavy rare earth resources and reduces the cost.

For better illustration, the present invention provides 4 examples to perform experimental comparison, as follows:

example 1:

the RTM alloy is prepared according to the following formula:

element(s)	Tb	Fe	Al
				Weight (%)	85	10	5

Specifically, R is Tb, T is Fe, and M is Al; the mass percentages of Tb, Fe and Al in the alloy are 85%, 10% and 5% respectively; the melting point of the RTM alloy is 890 ℃.

Performing hydrogen crushing and airflow milling on the obtained RTM alloy to prepare RTMH alloy powder, wherein the average particle size of the powder is 3.5 microns, adding the RTMH alloy powder into ethanol, and mixing to form suspension, wherein the mixing temperature is 30-38 ℃ and the mixing time is 12-23 h, if the mixing temperature and the mixing time are too low, the mixing is not uniform, if the mixing temperature is high, the powder is oxidized, the mixing time is increased, no significance is achieved, and the productivity is wasted; preferably, the mixing temperature is 38 ℃ and the mixing time is 20 hours, so as to achieve the effect of thorough mixing.

The raw materials comprise 29.7wt% of Nd, 0.18wt% of Ti, 0.17wt% of Cu, 2.0wt% of Co, 0.10 wt% of Al, 0.10 wt% of Ga, 0.92 wt% of B and the balance of Fe, the blank of the 50M neodymium iron boron magnet prepared by the steps of smelting, milling, forming and sintering is processed into a semi-finished product M0 with the thickness of 35mm 15mm 8mm (8mm is the orientation direction), and the semi-finished product is preprocessed by processing, degreasing and the like to ensure that the surface of the semi-finished product is clean and flat; then putting the pretreated semi-finished product into the suspension for soaking and coating, so that the surface of the semi-finished product is uniformly coated with a layer of RTMH alloy powder film, wherein the coating weight/total weight is 0.6%; placing the semi-finished product inIn the stone burning ink box, the graphite box with the product is put into a sintering furnace and is vacuumized to 1 multiplied by 10^-2Pa below, at 920 deg.C, carrying out primary heat treatment for 15h, and then carrying out low-temperature tempering secondary heat treatment at 500 deg.C for 5h to obtain NdFeB magnet M1.

The ndfeb magnet prepared by the above method of this example 1 is compared with a general ndfeb magnet in a parallel test, and the comparison result is shown in table 1 below, where table 1 is the magnet performance data before and after the implementation.

	Br/kGs	Hcj/kOe	Hk/Hcj
				M0 Performance	14.30	15.2	0.99
M1 Performance	14.20	24.8	0.95

TABLE 1 magnet Performance data before and after example 1

As can be seen from table 1, the coercivity of the composite ndfeb magnet prepared by the method of embodiment 1 is improved by 9.6k compared with that of the ordinary ndfeb magnet_Oe, and the remanence squareThe surface remained substantially stable with a negligible reduction of only 0.1 kGs.

Example 2:

metal Tb is subjected to hydrogen crushing and airflow milling to prepare Tb powder, the average particle size of the Tb powder is 3.5 mu m, and the Tb powder is added into ethanol to form suspension.

Processing a 50M neodymium iron boron magnet blank prepared by smelting, milling, molding and sintering into a semi-finished product M0 with the thickness of 35mm 15mm 8mm (8mm is the orientation direction), and carrying out pretreatment such as processing, oil removal and the like on the semi-finished product to ensure that the surface of the semi-finished product is clean and flat; then putting the pretreated semi-finished product into the suspension for soaking and coating, so that the surface of the semi-finished product is uniformly coated with a layer of Tb powder film, wherein the coating weight/total weight is 0.6%; placing the semi-finished product in a calculus-burning ink box, placing the graphite box containing the product in a sintering furnace, and vacuumizing to 1 × 10^-2Pa below, at 920 deg.C, carrying out primary heat treatment for 15h, and then carrying out low-temperature tempering secondary heat treatment at 500 deg.C for 5h to obtain NdFeB magnet M2.

The neodymium iron boron magnet prepared by the method in example 2 is compared with a common neodymium iron boron magnet in a parallel test, and the comparison result is shown in table 2, wherein table 2 is the performance data of the magnet before and after implementation.

	Br/kGs	Hcj/kOe	Hk/Hcj
				M0 Performance	14.30	15.2	0.99
M2 Performance	14.15	22.8	0.90

Table 2-magnet performance data before and after example 2 implementation

As can be seen from table 2, compared with the ordinary ndfeb magnet, the ndfeb magnet prepared by the method of embodiment 1 has the improvement of the coercivity performance of the magnet by 7.6k_Oe, and the remanence aspect remains substantially constant with a negligible decrease of 0.15 kGs.

Example 3:

metal Tb is subjected to hydrogen crushing and airflow milling to prepare Tb powder, the average particle size of the Tb powder is 3.5 mu m, and the Tb powder is added into ethanol to form suspension.

Processing a 50M neodymium iron boron magnet blank prepared by smelting, milling, molding and sintering into a semi-finished product M0 with the thickness of 35mm 15mm 8mm (8mm is the orientation direction), and carrying out pretreatment such as processing, oil removal and the like on the semi-finished product to ensure that the surface of the semi-finished product is clean and flat; then putting the pretreated semi-finished product into the suspension for soaking and coating, so that the surface of the semi-finished product is uniformly coated with a layer of RTMH alloy powder film, wherein the coating weight/total weight is 0.6%; placing the semi-finished product in a calculus-burning ink box, placing the graphite box containing the product in a sintering furnace, and vacuumizing to 1 × 10^-2Pa below, at 1200 deg.C, carrying out primary heat treatment for 18h, and then carrying out low-temperature tempering secondary heat treatment at 300 deg.C for 10h to obtain NdFeB magnet M3.

The ndfeb magnets prepared by the above method of example 3 were compared with the ordinary ndfeb magnets in parallel tests, and the comparison results are shown in table 3, where table 3 is the magnet performance data before and after implementation.

	Br/kGs	Hcj/kOe	Hk/Hcj
				M0 Performance	14.30	15.2	0.99
M3 Performance	14.10	24.5	0.95

Table 3-magnet performance data before and after example 3 implementation

As can be seen from Table 3, the coercivity of the NdFeB magnet prepared by the method of example 3 is improved by 9.3k compared with the ordinary NdFeB magnet_Oe, and the remanence aspect remains substantially stable with a negligible reduction of 0.2 kGs.

Example 4:

the RTM alloy is prepared according to the following formula:

element(s)	Tb	Fe	Al
				Weight (%)	85	7	8

R is Tb, T is Fe, M is Al; the mass percentages of Tb, Fe and Al in the alloy are 85%, 7% and 8% respectively; the melting point of the RTM alloy is 860 ℃.

And (3) carrying out hydrogen crushing and jet milling on the RTM alloy obtained in the step to obtain RTMH alloy powder, wherein the average particle size of the RTMH alloy powder is 3.5 mu m, and adding the fine powder into ethanol to form suspension.

Processing a 50M neodymium iron boron magnet blank prepared by smelting, milling, molding and sintering into a semi-finished product M0 with the thickness of 35mm 15mm 8mm (8mm is the orientation direction), and carrying out pretreatment such as processing, oil removal and the like on the semi-finished product to ensure that the surface of the semi-finished product is clean and flat; then putting the pretreated semi-finished product into the suspension for soaking and coating, so that the surface of the semi-finished product is uniformly coated with a layer of RTMH alloy powder film, wherein the coating weight/total weight is 0.6%; placing the semi-finished product in a calculus burning ink box, placing the graphite box containing the product in a sintering furnace, and vacuumizing to 10 DEG^-2Pa below, at 920 deg.C, carrying out primary heat treatment for 15h, and then carrying out low-temperature tempering secondary heat treatment at 500 deg.C for 5h to obtain NdFeB magnet M4.

The neodymium iron boron magnet prepared by the method in example 4 is compared with a common neodymium iron boron magnet in a parallel test, and the comparison result is shown in table 4, wherein table 4 is the performance data of the magnet before and after the implementation.

	Br/kGs	Hcj/kOe	Hk/Hcj
				M0 Performance	14.30	15.2	0.99
M4 Performance	14.05	25.1	0.95

Table 4-magnet performance data before and after example 4 was performed

As can be seen from table 4, the coercivity of the ndfeb magnet prepared by the method of example 4 is improved by 9.9k compared to the ordinary ndfeb magnet_Oe, and the remanence aspect remains substantially constant, only a 0.25kGs drop, negligible.

The neodymium iron boron magnet prepared by the four methods of the embodiment of the invention is compared with a common neodymium iron boron magnet in a parallel test, and the comparison results are shown in table 5:

	diffusion time	Tb amount	Br/kGs	Hcj/kOe	Hk/Hcj
						M0			14.30	15.2	0.99
M1	15h	0.5%	14.20	24.8	0.95
						M2	15h	0.6%	14.15	22.8	0.90
M3	30h	0.6%	14.10	24.5	0.95
						M4	15h	0.5%	14.05	25.1	0.95

TABLE 5 comparison of the Properties of examples 1-4

From the results in Table 5, it can be seen that: the magnetic performance of the embodiments 1-4 is generally higher than that of a common neodymium iron boron magnet, the coercive force of the compound neodymium iron boron magnet in the embodiments 1-4 is greatly improved, and the difference between the remanence and the remanence of a semi-finished neodymium iron boron magnet is smaller; if the experiment is carried out by using the heavy metal Tb alone, the diffusion heat treatment time is longer, the using amount of the used heavy rare earth is increased, and the remanence and the squareness are poorer.

Therefore, by adopting the low-melting-point heavy rare earth alloy provided by the invention, the grain boundary diffusion efficiency is far higher than that of heavy metal Tb powder, and the consumption of Tb in the heavy rare earth alloy is obviously reduced compared with that of the heavy metal Tb powder, so that the diffusion efficiency can be greatly improved, and the consumption of the heavy rare earth is reduced; specifically, the magnet coercive force of the composite neodymium iron boron magnet prepared by the method can be improved by more than 50%, the diffusion depth and the diffusion uniformity of heavy rare earth elements are increased, the utilization rate of the heavy rare earth is obviously improved, the thickness of a penetrated workpiece can be broken through to be more than 6mm, and the residual magnetism and the maximum magnetic energy product are basically kept stable.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.