Low-heavy-rare-earth high-coercive-force permanent magnet and preparation method thereof

Abstract

The invention discloses a low-heavy-rare-earth high-coercivity permanent magnet, which comprises the following magnet components: RcFe with the balance being MdTieGafBg, and is prepared from a multi-alloy mixture consisting of a main alloy R1wFe with the balance being HxGayBz and N auxiliary alloys RnaFe with the balance being Bb. The preparation method of the sintered neodymium-iron-boron magnet comprises the steps of burdening, cast piece mixing, metal Ga adding, hydrogen decrepitation, jet milling, oriented pressing, sintering and aging treatment, wherein the first stage is high-temperature sintering, the sintering temperature is 1060-1100 DEG C, the second stage is 850-950 DEG C high-temperature aging, the third stage is 550-650 DEG C medium-temperature aging, the fourth stage is 450-550 DEG C low-temperature aging, and the sintered neodymium-iron-boron magnet is prepared. The method has the advantages that the addition amount of heavy rare earth can be effectively reduced while the material performance can be improved, the grain structure of the magnet is improved through the four-stage sintering aging heat treatment process, and the coercive force of the magnet is obviously improved.

Description

Technical Field

[0001] The invention relates to the technical field of NdFeB magnet preparation, in particular to a low-heavy rare earth high-coercivity permanent magnet and a preparation method thereof. Background Art

[0002] Since the advent of sintered NdFeB rare earth permanent magnets in 1983, product performance, material formulation, production process and equipment have developed rapidly. While developing, the rare earth permanent magnet industry has also encountered some problems, such as the uneven scale and technology research and development level of production enterprises, the high production costs of some enterprises, and the serious waste of rare earth resources, especially heavy rare earth resources. With the continuous promotion and application of grain boundary diffusion technology, this phenomenon has been greatly improved. However, for some products that cannot be produced using grain boundary diffusion technology, such as large-size UH and high coercive force products with a minimum size of more than 15mm, some companies often need to add more heavy rare earth elements such as dysprosium and zirconium to produce them, and for some customers who require products without dysprosium and zirconium, they are unable to supply them in batches.

[0003] The existing permanent magnet preparation method has the following shortcomings:

[0004] (1) By simply mixing and stirring two or more alloy powders with similar organizational components to produce magnets with different performance requirements, this method is not very helpful in reducing the amount of heavy rare earth and improving the performance of the material. For example, in the patent application with application publication number CN106782978A, a magnet with a third performance index is prepared by mixing two different alloy powders. Each single alloy has a highly similar organizational structure, and the performance of all materials obtained after mixing in different proportions is usually the sum of the linear proportional values ​​of the performance of each alloy and the weight, which cannot reduce the usage of heavy rare earth Dy and Tb in the final material.

[0005] (2) Mixing the added rare earth metal (alloy) hydride (fluoride) with conventional alloy powder, because the amount added is too small, it is difficult to ensure the consistency of the mixed powder composition, and the consistency of the material microstructure and final performance cannot be ensured. For example, in the patent application with application publication number CN106601464A, the process method of mixing the main phase alloy powder with the heavy rare earth metal (alloy) powder and the ultrafine powder according to a certain proportion cannot ensure the uniform mixing of the two powders because the powder mixing heat treatment and stirring process are used when the addition ratio is small at one time, and the final material microstructure consistency is poor, which easily leads to unsatisfactory performance consistency of the finished product, especially small products.

[0006] (3) The versatility of the specially designed auxiliary alloy with a high total rare earth content is poor, and the compositional design of the auxiliary alloy is not significantly different from that of the main alloy, resulting in an ineffective improvement in performance. For example, in the patent application with the publication number CN115083707A, the compositional design differences between the main and auxiliary alloys are not obvious, and the elements in the formula of the auxiliary alloy are relatively close to the rare earth elements and non-rare earth elements in the main alloy, making it difficult to achieve the ideal goal of grain boundary regulation and reconstruction.

[0007] Therefore, the existing permanent magnet preparation methods need to be further improved. Summary of the Invention

[0008] The purpose of the present invention is to make up for the above deficiencies and disclose to the society a low heavy rare earth high coercivity permanent magnet and its preparation method, which can improve the material performance while effectively reducing the addition amount of heavy rare earths, and improve the magnetic grain structure of the magnet through a four-stage sintering and aging heat treatment process, significantly enhancing the coercivity of the magnet.

[0009] The technical solution of the present invention is realized as follows:

[0010] A low heavy rare earth high coercivity permanent magnet, comprising the following steps:

[0011] The magnet composition of the neodymium iron boron permanent magnet is R c Fe 余量 M d Ti e Ga f B g , where c, d, e, f, g are the mass percentages of the corresponding elements, and the sum of the mass ratios of c, d, e, f, g and the balance is 100%, and 29 ≤ c ≤ 35, 0.65 ≤ d ≤ 3.15, 0.1 ≤ e ≤ 0.5, 0.2 ≤ f ≤ 0.7, 0.85 ≤ g ≤ 1.05, and the balance is Fe and inevitable impurity elements; R is a rare earth element, M is a non-rare earth element, and the average Fe content in the 6:13:1 phase of the neodymium iron boron permanent magnet is controlled at 57% - 61%;

[0012] The neodymium iron boron permanent magnet is a multi-alloy mixture composed of a main alloy and N auxiliary alloys, N ≥ 1, the main alloy accounts for 80% to 99.5% of the mass ratio of the multi-alloy mixture, and the auxiliary alloy accounts for 0.5% to 20% of the mass ratio of the multi-alloy mixture;

[0013] The main alloy composition is R1 w Fe 余量 H x Ga y B z, where w, x, y, and z are the mass percentages of the corresponding elements, and the sum of the mass percentages of w, x, y, z, and the balance is 100%, and 28.5 ≤ w ≤ 33.5, 0.7 ≤ x ≤ 3.2, 0.1 ≤ y ≤ 0.5, 0.86 ≤ z ≤ 1.1. The balance is Fe and inevitable impurity elements, R1 is a rare earth element, and H is a non-rare earth element;

[0014] The composition of the auxiliary alloy is Rn a Fe 余量 B b , where a and b are the mass percentages of the corresponding elements, and the sum of the mass ratios of a, b, and the balance is 100%, and 35 ≤ a ≤ 50, 0.3 ≤ b ≤ 0.8. The balance is Fe and inevitable impurity elements, and Rn is a rare earth element.

[0015] Preferably, in the composition of the magnet, the R is one or more of La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er, and the M is at least one of Co, Cu, Al, Nb, Zr, Sn, and Bi.

[0016] Preferably, in the composition of the main alloy, the R1 is one or more of La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er, and the H is at least two of Co, Cu, Al, Zr, Nb, Ti, Sn, and Bi and must contain Ti.

[0017] Preferably, in the composition of the auxiliary alloy, the Rn is one or more of La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er.

[0018] A method for preparing a low heavy rare earth and high coercivity permanent magnet, comprising the following steps:

[0019] Step 1: According to the formula, prepare the main and auxiliary alloy ingredients, and perform vacuum induction melting respectively to obtain main alloy cast sheets and auxiliary alloy cast sheets with a thickness of 0.1 mm - 0.5 mm;

[0020] Step 2: Mix the main alloy cast sheets and N auxiliary alloy cast sheets, N ≥ 1, add metallic Ga, and perform hydrogen crushing to obtain hydrogen crushed coarse powder;

[0021] Step 3: Add an antioxidant to the hydrogen crushed coarse powder, stir for 30 minutes, and then perform jet milling to obtain fine powder with a particle size of 2.5 - 4.0 microns. After adding an antioxidant and a lubricant to the fine powder, stir;

[0022] Step 4: Place the fine powder in a press operating box under nitrogen protection for orientation pressing. The oxygen content in the press system is < 0.05%, the orientation field > 1.8 T, and the pressing density is 3.8 - 4.4 g / cm 3, after isostatic pressing at 180MP, it is put into the furnace for vacuum sintering and aging treatment;

[0023] Step Five: Sintering and Aging Treatment: The first stage is high-temperature sintering, the sintering temperature is 1060 - 1100 °C, and the holding time is 2 - 10 hours. The second stage is high-temperature aging, the aging treatment temperature is 850 - 950 °C, and the holding time is 2 - 6 hours. The third stage is medium-temperature aging, the aging treatment temperature is 550 - 650 °C, and the holding time is 2 - 8 hours. The fourth stage is low-temperature aging, the aging treatment temperature is 450 - 550 °C, and the holding time is 2 - 8 hours, obtaining the sintered neodymium iron boron magnet.

[0024] Preferably, in the second step, the mixing weight ratio of the master alloy cast sheet and the auxiliary alloy cast sheet is: 80% - 99.5% : 0.5% - 20%.

[0025] Preferably, in the second step, the addition amount of metal Ga is 0.1% - 0.5% of the weight of the mixture.

[0026] Preferably, in the third step, the addition amount of the antioxidant in the coarse powder after hydrogen crushing is 0.1% of the weight of the mixture; the addition amounts of the antioxidant and the lubricant in the fine powder are 0.05% of the weight of the mixture.

[0027] The advantages of the present invention compared with the prior art are:

[0028] The present invention combines the master alloy and the auxiliary alloy. Through the master alloy, the main phase Nd2Fe 14 B is mainly obtained. While forming a certain main phase, the auxiliary alloy provides a relatively large proportion of the rare earth-rich phase as the main source of the grain boundary phase. The addition of Ga at the grain boundary introduces a low melting point at the grain boundary, constructing a phase formation environment of the 6:13:1 non-ferromagnetic phase at the grain boundary, increasing the grain boundary fluidity and the grain boundary phase thickness to optimize the grain boundary distribution of the magnet, achieving the purpose of regulating the magnetism of the grain boundary phase, and improving the demagnetization coupling effect between grains.

[0029] The preparation method of the present invention uses a "1 + 3" four-stage sintering and aging heat treatment process to improve the grain structure of the magnet, significantly enhancing the coercivity of the magnet. After the component design of the auxiliary alloy and the aging treatment at three temperatures of high, medium, and low, the Fe content of the 6:13:1 phase at the grain boundary decreases, and the grain boundary phase REFex also significantly decreases, resulting in significant improvements in both the coercivity and the Curie temperature of the magnet. Description of the Drawings

[0030] Figure 1 is the microstructure diagram of the permanent magnet of the present invention;

[0031] Figure 2 is the component table of the master alloy in the embodiment of the present invention;

[0032] Figure 3It is the table of secondary alloy components in the embodiments of the present invention;

[0033] Figure 4 It is the table of the main and secondary alloy compositions and the combination of grain boundary control elements in the embodiments of the present invention;

[0034] Figure 5 It is the composition table of the comparative examples of the present invention;

[0035] Figure 6 It is the sintering and aging treatment process table in the comparative experiments of the present invention;

[0036] Figure 7 It is the performance index table of the comparative experiments of the present invention;

[0037] Figure 8 It is the comparative graph of the Curie temperature test experiment of the present invention. Detailed Description of the Invention

[0038] The present invention will be further described in detail below:

[0039] A low heavy rare earth and high coercivity permanent magnet, comprising the following steps:

[0040] The magnet composition of the NdFeB permanent magnet is R c Fe 余量 M d Ti e Ga f B g , where c, d, e, f, g are the mass percentages of the corresponding elements, the sum of the mass ratios of c, d, e, f, g and the balance is 100%, and 29 ≤ c ≤ 35, 0.65 ≤ d ≤ 3.15, 0.1 ≤ e ≤ 0.5, 0.2 ≤ f ≤ 0.7, 0.85 ≤ g ≤ 1.05, and the balance is Fe and unavoidable impurity elements; R is a rare earth element, and M is a non-rare earth element; the R is one or more of La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and the M is at least one of Co, Cu, Al, Nb, Zr, Sn, Bi. The average Fe content in the 6:13:1 phase of the NdFeB permanent magnet is controlled at 57% - 61%.

[0041] The NdFeB permanent magnet is a multi-alloy mixture composed of a main alloy and N secondary alloys, N ≥ 1, the main alloy accounts for 80% to 99.5% of the mass ratio of the multi-alloy mixture, and the secondary alloy accounts for 0.5% to 20% of the mass ratio of the multi-alloy mixture;

[0042] The main alloy composition is R1 w Fe 余量 H x Ga y B z, where w, x, y, and z are the mass percentages of corresponding elements, the sum of the mass percentages of w, x, y, z, and the balance is 100%, and 28.5 ≤ w ≤ 33.5, 0.7 ≤ x ≤ 3.2, 0.1 ≤ y ≤ 0.5, 0.86 ≤ z ≤ 1.1. The balance is Fe and inevitable impurity elements, R1 is a rare earth element, and H is a non-rare earth element; the said R1 is one or more of La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er, and the said H is at least two of Co, Cu, Al, Zr, Nb, Ti, Sn, and Bi and must contain Ti.

[0043] The composition of the auxiliary alloy is Rn a Fe 余量 B b , where a and b are the mass percentages of corresponding elements, the sum of the mass ratios of a, b, and the balance is 100%, and 35 ≤ a ≤ 50, 0.3 ≤ b ≤ 0.8. The balance is Fe and inevitable impurity elements, Rn is a rare earth element, and the said Rn is one or more of La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er.

[0044] A preparation method of a low heavy rare earth and high coercivity permanent magnet, comprising the following steps:

[0045] Step 1: According to the formula, perform main and auxiliary alloy batching, and respectively carry out vacuum induction melting to obtain main alloy cast sheets and auxiliary alloy cast sheets with a thickness of 0.1 mm - 0.5 mm.

[0046] Step 2: Mix the main alloy cast sheets and N auxiliary alloy cast sheets, N ≥ 1, add metallic Ga, and perform hydrogen decrepitation to obtain hydrogen decrepitated coarse powder; the mixing weight ratio of the main alloy cast sheets and the auxiliary alloy cast sheets is: 80% - 99.5%: 0.5% - 20%, and the addition amount of metallic Ga is 0.1% - 0.5% of the weight of the mixture.

[0047] Step 3: Add an antioxidant to the hydrogen decrepitated coarse powder, stir for 30 minutes, and then carry out jet milling to obtain fine powder with a particle size of 2.5 - 4.0 microns. After adding an antioxidant and a lubricant to the fine powder, stir; the addition amount of the antioxidant in the hydrogen decrepitated coarse powder is 0.1% of the weight of the mixture; the addition amount of the antioxidant and the lubricant in the fine powder is 0.05% of the weight of the mixture.

[0048] Step 4: Put the fine powder into the press operation box under nitrogen protection for oriented pressing. The oxygen content in the press system < 0.05%, the orientation field > 1.8 T, and the pressing density is 3.8 - 4.4 g / cm 3 , after isostatic pressing at 180 MP, put it into the furnace for vacuum sintering and aging treatment;

[0049] Step 5. Sintering and aging treatment: The first stage is high-temperature sintering, with a sintering temperature of 1060 - 1100 °C and a holding time of 2 - 10 hr. The second stage is high-temperature aging, with an aging treatment temperature of 850 - 950 °C and a holding time of 2 - 6 hr. The third stage is medium-temperature aging, with an aging treatment temperature of 550 - 650 °C and a holding time of 2 - 8 hr. The fourth stage is low-temperature aging, with an aging treatment temperature of 450 - 550 °C and a holding time of 2 - 8 hr, to obtain a sintered NdFeB magnet.

[0050] In the preparation method of the present invention, the "1 + 3" four-stage sintering and aging heat treatment process is adopted to improve the grain structure of the magnet, significantly enhancing the coercivity of the magnet. After the design of the co-alloy components and the aging treatment at three temperature levels of high, medium, and low, the Fe content in the 6:13:1 phase is reduced, and the high-Fe grain boundary phase REFex is also significantly reduced, resulting in a significant increase in both the coercivity and Curie temperature of the magnet. The microstructure of the permanent magnet prepared by the preparation method of the present invention is significantly improved. After three-stage aging, the RE6Fe 13 content in the Ga phase of the magnet is significantly reduced, thereby achieving the purpose of greatly improving the material properties, as shown in Figure 1 and Figure 6 .

[0051] The purpose of adding metal Ga in the preparation method of the present invention is to provide a phase-forming environment for constructing the 6:13:1 phase at the grain boundary. The Ga added during hydrogen decrepitation is mainly located at the grain boundary and forms the 6:13:1 phase with the rare earth in the previously added co-alloy. Combining with the three-stage aging process in the "1 + 3" type high-temperature sintering and aging heat treatment process, the iron content in the 6:13:1 phase is adjusted to make it iron-poor, thus becoming a non-magnetic phase, improving its demagnetization coupling effect at the grain boundary, and greatly enhancing the material properties, especially the intrinsic coercivity.

[0052] The 6:13:1 phase is: Nd6Fe 13 Ga1, and the formation of the traditional Nd2Fe 14 B (2:14:1 phase) depends on boron as a structure stabilizer. Under low-boron conditions, the vacancies of B may lead to the instability of the 2:14:1 phase structure, and other elements (such as Ga) are needed to fill or reconstruct the lattice. The atomic radius of Ga is close to that of Fe, and it is easy to replace the Fe site. The difference in the electronic structure of Ga (p-block element) and Fe (d-block) changes the local chemical bonding, which can promote the formation of new phases.

[0053] The 6:13:1 phase has a tetragonal structure similar to that of 2:14:1, but the lattice parameters are adjusted due to the incorporation of Ga. The occupation of the Fe site by Ga can lead to the expansion of the unit cell, reduce the symmetry, and form Nd6Fe 13The stoichiometric ratio of Ga1. Ga preferentially substitutes specific sublattice positions of Fe (such as the 8j or 16k positions), changing the local electron density and magnetic exchange interaction, thereby stabilizing the new phase.

[0054] In the Nd-Fe-B-Ga quaternary system, under the condition of low boron and high gallium, the Gibbs free energy of the 6:13:1 phase is lower than that of the traditional 2:14:1 phase, becoming a thermodynamically more stable phase.

[0055] In addition, the addition of Ga reduces the liquid phase formation temperature, promotes grain boundary diffusion, accelerates atomic rearrangement, and provides kinetic conditions for the nucleation of the new phase. The substitution of Ga for Fe can reduce the saturation magnetization of the main phase (because Ga is a non-magnetic element), but the coercivity is improved by optimizing the grain boundary phase. Ga enriches at the grain boundaries, inhibiting the nucleation of reverse magnetization domains. At the same time, the presence of the 6:13:1 phase can refine the grains and enhance the magnetic hardening ability.

[0056] Furthermore, through the synergistic effect of Ti and Ga, a Ti-Ga-Fe ternary phase is formed, which is dispersedly distributed in the grain boundary phase, pinning the grain boundary movement and hindering the movement of magnetic domain walls, thus enhancing the coercivity; in addition, the high-temperature stability of Ti and the liquid-phase diffusion ability of Ga are complementary, forming a gradient-distributed grain boundary phase during sintering and aging processes, which can optimize the magnetic hardening path.

[0057] The following is further elaborated in combination with examples and comparative experiments:

[0058] The present invention adopts a combination of main and auxiliary alloys. The main alloy composition is R1 w Fe 余量 H x Ga y B z , and the auxiliary alloy composition is Rn a Fe 余量 B b . The main alloy component table in the examples is as Figure 2 shown, and the auxiliary alloy component table in the examples is as Figure 3 shown. The composition of the main and auxiliary alloys and the combination of grain boundary control elements in the examples are as Figure 4 shown, and the composition table of the comparative examples is as Figure 5 shown; raw materials are prepared according to the compositions in Figures 2 to 5 (the weight of added metallic Ga in the examples is calculated according to the total weight percentage after mixing the main and auxiliary alloys), and the permanent magnets are prepared according to steps 1 to 4 of the preparation method of the above-mentioned low heavy rare earth and high coercivity permanent magnet, and then processed according to the sintering and aging treatment process as Figure 6 shown, corresponding to obtaining permanent magnets (Examples 1-3 and Comparative Examples 1-3). The performance of Examples 1-3 and Comparative Examples 1-3 is tested, and the test results are as Figure 7 shown. From Figure 7It can be seen that the performance of the permanent magnet is improved, which is specifically manifested as follows: compared with comparative examples 1 to 3, through the multi-alloy process and grain boundary addition control technology described in this design, combined with the 1+3 four-stage sintering aging process, the contents of heavy rare earth Dy and Tb in the embodiment formula are lower than those in the comparative example, but the magnet performance is equivalent to that in the comparative example, which greatly reduces the material cost while ensuring various indicators of magnetic properties.

[0059] Curie temperature test: the ingredients were prepared according to the formula in Example 1, and steps 1 to 4 were followed to mix, hydrogen crush, jet mill, and orientation press, and then sintered at 1080°C and kept warm for 4 hours; the experimental group was aged in three stages at 900°C + 610°C + 490°C, and the control group was aged in two stages at 900°C + 490°C. After the permanent magnets were obtained, the Curie temperature was tested. The experimental results are shown in Figure 2. Figure 8 As shown, the Curie temperature of the experimental group is 320.86°C, and the Curie temperature of the comparison group is 302.85°C. It can be seen that the Curie temperature can be significantly improved by three-stage aging compared with two-stage aging.

[0060] The best embodiment of the present invention has been described, and various changes or modifications may be made by those skilled in the art without departing from the scope of the present invention.

Claims

1. A low-heavy rare earth high coercivity permanent magnet, characterized in that: It includes the following steps: The magnet composition of the described neodymium iron boron permanent magnet is R c Fe 余量 M d Ti e Ga f B g , where c, d, e, f, g are the mass percentages of the corresponding elements, the sum of the mass ratios of c, d, e, f, g and the balance is 100%, and 29 ≤ c ≤ 35, 0.65 ≤ d ≤ 3.15, 0.1 ≤ e ≤ 0.5, 0.2 ≤ f ≤ 0.7, 0.85 ≤ g ≤ 1.05, and the balance is Fe and inevitable impurity elements; R is a rare earth element, M is a non-rare earth element, and the average Fe content in the 6:13:1 phase of the described neodymium iron boron permanent magnet is controlled within 57% - 61%; The neodymium iron boron permanent magnet is a multi-alloy mixture composed of a main alloy and N auxiliary alloys, where N≥1. The main alloy accounts for 80% to 99.5% of the mass ratio of the multi-alloy mixture, and the auxiliary alloy accounts for 0.5% to 20% of the mass ratio of the multi-alloy mixture; The main alloy components are R1 w Fe 余量 H x Ga y B z , where w, x, y, and z are the mass percentages of the corresponding elements, the sum of the mass percentages of w, x, y, z and the balance is 100%, and 28.5 ≤ w ≤ 33.5, 0.7 ≤ x ≤ 3.2, 0.1 ≤ y ≤ 0.5, 0.86 ≤ z ≤ 1.1, the balance is Fe and inevitable impurity elements, R1 is a rare earth element, and H is a non-rare earth element; The secondary alloying components described are Rn a Fe 余量 B b , where a and b are the mass percentages of the corresponding elements, the sum of the mass ratios of a, b and the balance is 100%, and 35 ≤ a ≤ 50, 0.3 ≤ b ≤ 0.

8. The balance is Fe and inevitable impurity elements, and Rn is a rare earth element.

2. A low-heavy rare-earth high coercivity permanent magnet according to claim 1, characterized in that: In the magnet composition, R is one or more of La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and M is at least one of Co, Cu, Al, Nb, Zr, Sn, Bi.

3. A low-heavy rare earth high coercivity permanent magnet according to claim 1, characterized in that: In the main alloy composition, R1 is one or more of La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and H is at least two of Co, Cu, Al, Zr, Nb, Ti, Sn, Bi and must contain Ti.

4. A low-heavy rare earth high coercivity permanent magnet according to claim 1, characterized in that: In the auxiliary alloy composition, Rn is one or more of La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er.

5. The preparation method of a low heavy rare earth and high coercivity permanent magnet according to claim 1, characterized in that: It includes the following steps: Step 1: According to the formula, prepare the main and auxiliary alloy ingredients, and conduct vacuum induction melting respectively to obtain main alloy cast sheets and auxiliary alloy cast sheets with a thickness of 0.1mm - 0.5mm; Step 2: Mix the main alloy cast sheets and N auxiliary alloy cast sheets, where N≥1, add metallic Ga, and perform hydrogen pulverization to obtain hydrogen pulverized coarse powder; Step 3: Add an antioxidant to the hydrogen pulverized coarse powder, stir for 30 minutes, then perform jet milling to obtain fine powder with a particle size of 2.5 - 4.0 microns. After adding an antioxidant and a lubricant to the fine powder, stir; Step 4: Put the fine powder into the press operation box under nitrogen protection for orientation pressing. The oxygen content in the press system is <0.05%, the orientation field > 1.8T, and the pressing density is 3.8 - 4.4 g / cm 3 . After isostatic pressing at 180 MPa, it is put into the furnace for vacuum sintering and aging treatment; Step 5: Sintering and aging treatment: The first stage is high-temperature sintering, with a sintering temperature of 1060 - 1100°C and a holding time of 2 - 10 hours. The second stage is high-temperature aging, with an aging treatment temperature of 850 - 950°C and a holding time of 2 - 6 hours. The third stage is medium-temperature aging, with an aging treatment temperature of 550 - 650°C and a holding time of 2 - 8 hours. The fourth stage is low-temperature aging, with an aging treatment temperature of 450°C - 550°C and a holding time of 2 - 8 hours, to obtain a sintered neodymium iron boron magnet.

6. The preparation method of a low heavy rare earth and high coercivity permanent magnet according to claim 5, characterized in that: In the said Step 2, the mixing weight ratio of the main alloy cast sheet and the auxiliary alloy cast sheet is: 80% - 99.5%: 0.5% - 20%.

7. The preparation method of a low heavy rare earth and high coercivity permanent magnet according to claim 5, characterized in that: In the said Step 2, the addition amount of metallic Ga is 0.1% - 0.5% of the weight of the mixture.

8. The preparation method of a low heavy rare earth and high coercivity permanent magnet according to claim 5, characterized in that: In the said Step 3, the addition amount of the antioxidant in the hydrogen pulverized coarse powder is 0.1% of the weight of the mixture; the addition amount of the antioxidant and the lubricant in the fine powder is 0.05% of the weight of the mixture.

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