High-performance sintered neodymium-iron-boron magnet and preparation method thereof

Abstract

The invention belongs to the technical field of rare earth permanent magnet materials, and particularly relates to a high-performance sintered neodymium-iron-boron magnet and a preparation method thereof. The high-performance sintered neodymium-iron-boron magnet comprises, by mass, 30%-33% of R, 0.80%-0.95% of B, 0.05%-0.8% of Ga, 0.05%-2.0% of M, 1.0%-1.5% of Co and 60%-68% of Fe, R is Pr and Nd, M is one or more of Cu, Al, Nb and Zr, the atomic percent meets the condition that [Fe] + [Co]-14 and [B] is larger than 1.5 and smaller than 3, by controlling element components and content of the neodymium-iron-boron magnet and combining an efficient preparation method, the organization structure of the magnet is optimized, grain boundary phase distribution of the magnet is improved, and the magnetic performance of the neodymium-iron-boron magnet is improved. And the neodymium-iron-boron magnet with relatively good magnetic performance is obtained.

Description

Technical Field

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

[0002] NdFeB is a rare earth permanent magnet compound composed of rare earth metal neodymium, metallic element iron, non-metallic element boron and a small amount of added elements. It has made a sensation in the world for its extremely high "magnetic energy product" and is called the "magnet king" due to its excellent magnetic properties. It is currently the strongest permanent magnet in the world. Its BHmax value is 5 to 12 times that of ferrite magnets and 3 to 10 times that of alnico magnets; its coercive force is equivalent to 5 to 10 times that of ferrite magnets and 5 to 15 times that of alnico magnets; its potential magnetic performance is extremely high and it can absorb heavy objects equivalent to 640 times its own weight.

[0003] In addition to having extremely high magnetic properties and maximum magnetic energy product, NdFeB magnets also have excellent mechanical processing properties. They can be cut into different shapes and drilled. They are hard, stable, and cost-effective. They are widely used in many fields such as electronic communications, metallurgical manufacturing, geological exploration, health care, transportation, and aerospace. However, NdFeB magnets have poor temperature performance, large magnetic losses when used at high temperatures, low maximum operating temperatures, and are prone to rust. At the same time, with the continuous rise in raw material prices, the cost requirements for NdFeB magnets are also getting higher and higher, especially the use of heavy rare earth elements has a greater impact on the cost of magnets. Summary of the invention

[0004] The purpose of the present invention is to provide a high-performance sintered NdFeB magnet in view of the above technical problems. By optimizing the magnet structure and improving the magnet grain boundary phase distribution, better magnetic properties are obtained, while reducing the use of heavy rare earth elements and lowering the magnet production cost.

[0005] The high-performance sintered NdFeB magnet in the technical solution of the present invention comprises the following components in mass percentage: R: 30-33%, B: 0.80-0.95%, Ga: 0.05-0.8%, M: 0.05-2.0%, Co: 1.0-1.5%, Fe: 60-68%, R is Pr and Nd, and M is one or more of Cu, Al, Nb, and Zr.

[0006] Furthermore, the atomic percentage of the high performance sintered NdFeB magnet satisfies 1.5<[Fe]+[Co]-14[B]<3.

[0007] By adding Ga and combining the atomic percentage relationship of Fe, Co and B, the magnet forms the main phase R 2 Fe 14 In addition to the B phase and the Nd-rich phase, an antiferromagnetic R6 Fe 13 The Ga phase can inhibit the formation of amorphous ferromagnetic materials. This phase is continuously distributed between grain boundaries, which can remove the exchange coupling between grains and greatly improve the coercive force of the magnet.

[0008] Furthermore, the Ga content in the above high performance sintered NdFeB magnet is 0.5-0.6%.

[0009] When the Ga content is too low, R 6 Fe 13 When the Ga content is too high, the R 6 Fe 13 The distribution of Ga phase between grain boundaries becomes poor, which in turn causes the magnetic properties to decrease. Therefore, reasonable control of Ga content can reduce production cost investment on the basis of obtaining the best magnet performance.

[0010] The present invention also provides a preparation method of the high-performance sintered NdFeB magnet, including batching, smelting, hydrogen cracking to obtain coarse powder, stirring the coarse powder, jet milling to obtain fine powder, stirring the fine powder, molding, sintering and aging.

[0011] Furthermore, the smelting temperature is 1440-1480°C.

[0012] Furthermore, the particle size of the coarse powder obtained by hydrogen rupture is 200 to 300 μm.

[0013] Furthermore, the rotation speed of the coarse powder stirring and the fine powder stirring is 10-15 rpm / min, and the time is 1-3 hours.

[0014] Furthermore, when the coarse powder is stirred, 0.03-0.08% of antioxidant and 0.02-0.06% of gasoline are added. By adding antioxidant and gasoline, the antioxidant is uniformly adsorbed on the surface of the magnet powder, and the magnet powder is quickly passivated after being covered by the antioxidant, which greatly improves the oxidation resistance and fluidity of the magnet powder.

[0015] Furthermore, the particle size of the fine powder obtained by the jet mill is 3.0-4.0 μm.

[0016] Furthermore, 55-65 ppm oxygen is introduced during the jet milling process to pre-passivate the magnet powder, reduce the probability of oxidation, and improve the magnetic properties of the sintered NdFeB magnet. When the oxygen content is too high, the magnet powder will be over-oxidized, resulting in poor magnet performance. When the oxygen content is too low, the passivation effect on the powder is limited, resulting in more severe oxidation in the subsequent process, thereby affecting the magnet performance.

[0017] Furthermore, when the fine powder is stirred, 0.03-0.08% of an antioxidant by mass of the fine powder and 0.02-0.06% of gasoline by mass of the fine powder are added.

[0018] Furthermore, the molding is carried out by orientation molding in a magnetic field of 1.5 to 2.0 T under nitrogen protection.

[0019] Furthermore, the sintering temperature is 1000-1200° C., and the sintering time is 3-10 hours.

[0020] Furthermore, the aging adopts graded aging, the first aging temperature is 800-900°C, the time is 2-5h, and the second aging temperature is 400-600°C, the time is 3-8h.

[0021] Furthermore, argon gas is introduced for air cooling during sintering and post-aging cooling. 6 F 13 The grain boundary phase formed by the Ga phase is clearer, isolating the main phase grains and removing the exchange coupling between the grains, which is beneficial to improving the coercive force of the magnet.

[0022] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0023] (1) By controlling the element composition and content of NdFeB magnets, combined with an efficient preparation method, the magnet structure is optimized, the magnet grain boundary phase distribution is improved, and NdFeB magnets with better magnetic properties are obtained;

[0024] (2) By adding Ga, combined with Fe and B content, the magnet forms the main phase R 2 Fe 14 B phase, Nd-rich phase and antiferromagnetic R 6 Fe 13 Ga phase can inhibit the formation of amorphous ferromagnetic materials. This phase is continuously distributed between grain boundaries, which can remove the exchange coupling between grains and greatly improve the coercive force of the magnet.

[0025] (3) When the coarse powder and the fine powder are stirred, antioxidants and gasoline are added to make the antioxidants uniformly adsorbed on the surface of the magnet powder. After the magnet powder is covered with the antioxidants, it is quickly passivated, which greatly improves the antioxidant properties and fluidity of the magnet powder.

[0026] (4) After sintering and aging, argon gas is filled and air-cooled to make R 6 F 13 The grain boundary phase formed by Ga phase is clearer, isolating the main phase grains and removing the exchange coupling between grains, which is beneficial to improving the coercive force of the magnet;

[0027] (5) The NdFeB magnet of the present invention reduces the use of heavy rare earth elements and reduces production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1This is a SEM image of the high performance sintered NdFeB magnet obtained in Example 1;

[0029] Figure 2 This is the SEM image of the high performance sintered NdFeB magnet obtained in Comparative Example 1. DETAILED DESCRIPTION

[0030] The technical scheme of the present invention is further described below by specific examples and accompanying drawings. It should be understood that the specific examples described herein are only used to help understand the present invention and are not used for specific limitations of the present invention. The accompanying drawings used herein are only for better illustrating the disclosure of the present invention and do not have a limiting effect on the scope of protection. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used raw materials in the art, and the methods used in the embodiments are all conventional methods in the art.

[0031] The antioxidant used in the following examples and comparative examples is type C antioxidant produced by Ningbo Haotian Rare Earth Chemical Co., Ltd.

[0032] Example 1

[0033] The method for preparing the high performance sintered NdFeB magnet of this embodiment comprises the following steps:

[0034] (1) The ingredients are prepared according to the element percentages of Nd: 25.44%, Pr: 6.36%, B: 0.89%, Ga: 0.5%, Zr: 0.15%, Cu: 0.25%, Co: 1.2%, and Fe: 65.21%, and the atomic content [Fe] + [Co] - 14 [B] = 2.36;

[0035] (2) melting at 1450° C. in a vacuum induction furnace, and hydrogen crushing in a hydrogen treatment furnace to obtain a coarse powder with a particle size of 200 μm, adding 0.05% of an antioxidant by weight of the coarse powder and 0.04% of gasoline by weight of the coarse powder to the coarse powder, and stirring for 2 h at a stirring speed of 15 rpm / min;

[0036] (3) introducing 60 ppm oxygen, jet-milling the stirred coarse powder into fine powder with a particle size of 4.0 μm, adding 0.05% antioxidant by weight of the fine powder and 0.04% gasoline by weight of the fine powder to the fine powder, and stirring for 3 h at a stirring speed of 15 rpm / min;

[0037] (4) Under nitrogen protection, the fine powder was oriented and formed in a magnetic field of 1.8 T, sintered at 1065°C for 5 h, aged at 900°C for 2.5 h, and then aged at 485°C for 4.5 h, and argon gas was introduced for air cooling.

[0038] Example 2

[0039] The method for preparing the high performance sintered NdFeB magnet of this embodiment comprises the following steps:

[0040] (1) The ingredients are prepared according to the element percentages of Nd: 24.8%, Pr: 6.2%, B: 0.9%, Ga: 0.5%, Zr: 0.15%, Cu: 0.25%, Co: 1.0%, and Fe: 66.2%, and the atomic content [Fe] + [Co] - 14 [B] = 2.44;

[0041] (2) melting at 1450° C. in a vacuum induction furnace, and hydrogen crushing in a hydrogen treatment furnace to obtain a coarse powder with a particle size of 200 μm, adding 0.05% of an antioxidant by weight of the coarse powder and 0.04% of gasoline by weight of the coarse powder to the coarse powder, and stirring for 2 h at a stirring speed of 15 rpm / min;

[0042] (3) introducing 55 ppm oxygen, jet-milling the stirred coarse powder into fine powder with a particle size of 4.0 μm, adding 0.06% of the weight of the fine powder antioxidant and 0.05% of the weight of the fine powder gasoline to the fine powder, and stirring for 3 h at a stirring speed of 15 rpm / min;

[0043] (4) Under nitrogen protection, the fine powder was oriented and formed in a magnetic field of 1.8 T, sintered at 1090°C for 5 h, aged at 850°C for 2.5 h, and then aged at 500°C for 4.5 h, and argon gas was introduced for air cooling.

[0044] Example 3

[0045] The method for preparing the high performance sintered NdFeB magnet of this embodiment comprises the following steps:

[0046] (1) The ingredients are prepared according to the element percentages of Nd: 26.0%, Pr: 6.5%, B: 0.88%, Ga: 0.5%, Zr: 0.20%, Cu: 0.20%, Co: 1.2%, and Fe: 64.52%, and the atomic content [Fe] + [Co] - 14 [B] = 2.41;

[0047] (2) melting at 1450° C. in a vacuum induction furnace, and hydrogen crushing in a hydrogen treatment furnace to obtain a coarse powder with a particle size of 200 μm, adding 0.06% of an antioxidant by weight of the coarse powder and 0.05% of gasoline by weight of the coarse powder to the coarse powder, and stirring for 2 h at a stirring speed of 15 rpm / min;

[0048] (3) introducing 60 ppm oxygen, jet-milling the stirred coarse powder into fine powder with a particle size of 4.0 μm, adding 0.05% antioxidant by weight of the fine powder and 0.04% gasoline by weight of the fine powder to the fine powder, and stirring for 3 h at a stirring speed of 15 rpm / min;

[0049] (4) Under nitrogen protection, the fine powder was oriented and formed in a magnetic field of 1.8 T, sintered at 1065°C for 6 h, aged at 900°C for 3.0 h, and then aged at 500°C for 5.0 h, and argon gas was introduced for air cooling.

[0050] Example 4

[0051] The only difference between this embodiment and embodiment 1 is that the ingredients in step (1) are Nd: 25.44%, Pr: 6.36%, B: 0.89%, Ga: 0.4%, Zr: 0.15%, Cu: 0.25%, Co: 1.2%, Fe: 65.31%.

[0052] Example 5

[0053] The only difference between this embodiment and embodiment 1 is that the ingredients in step (1) are Nd: 25.44%, Pr: 6.36%, B: 0.89%, Ga: 0.8%, Zr: 0.15%, Cu: 0.25%, Co: 1.2%, Fe: 64.91%.

[0054] Example 6

[0055] The only difference between this embodiment and embodiment 1 is that 40 ppm of oxygen is introduced in step (3), the coarse powder after stirring is jet-milled into fine powder with a particle size of 4.0 μm, 0.05% of antioxidant by weight of the fine powder and 0.04% of gasoline by weight of the fine powder are added to the fine powder, and the mixture is stirred for 3 hours at a stirring speed of 15 rpm / min.

[0056] Example 7

[0057] The only difference between this embodiment and embodiment 1 is that 80 ppm of oxygen is introduced in step (3), the coarse powder after stirring is jet-milled into fine powder with a particle size of 4.0 μm, 0.05% of antioxidant by weight of the fine powder and 0.04% of gasoline by weight of the fine powder are added to the fine powder, and the mixture is stirred for 3 hours at a stirring speed of 15 rpm / min.

[0058] Comparative Example 1

[0059] The only difference between this comparative example and Example 1 is that the ingredients in step (1) are Nd: 25.44%, Pr: 6.36%, B: 0.91%, Ga: 0.5%, Zr: 0.15%, Cu: 0.25%, Co: 1.2%, Fe: 65.19%, and the atomic content [Fe] + [Co] - 14 [B] = 0.62.

[0060] Comparative Example 2

[0061] The only difference between this comparative example and Example 1 is that the ingredients in step (1) are Nd: 25.44%, Pr: 6.36%, B: 0.87%, Ga: 0.5%, Zr: 0.15%, Cu: 0.25%, Co: 1.2%, Fe: 65.23%, [Fe] + [Co] - 14 [B] = 4.11.

[0062] The microstructure test of the NdFeB magnets obtained in Example 1 and Comparative Example 1 was carried out, and the SEM test results are as follows: Figure 1 and Figure 2 As shown, it can be seen that the NdFeB magnet obtained in Example 1 has a more uniform and continuous distribution of grain boundary phase and a thicker grain boundary phase than that in Comparative Example 1; and scanning electron microscope element analysis is performed on different positions of the NdFeB magnet, and the content of each element in the grain boundary phase of the magnet is determined by single-point quantitative analysis, and the physical phase of the intercrystalline triangle zone is determined according to element determination. The test results are shown in Table 1.

[0063] Table 1 Test results of the content of each element in the grain boundary phase of NdFeB magnets

[0064] Phase Pr Nd Fe Ga Cu Example 1-Point 1 <![CDATA[R 6 F 13 Ga phase]]> 14.7 34.4 42.70 3.20 1.32 Example 1-Point 2 <![CDATA[R 6 F 13 Ga phase]]> 18.0 40.2 31.60 4.60 1.54 Example 1-Point 3 <![CDATA[R 6 F 13 Ga phase]]> 15.5 36.4 39.60 4.00 1.21 Example 1-Point 4 Nd-rich phase 23.5 71.2 0.00 0.20 0.15 Comparative Example 1-Point 1 Nd-rich phase 25.08 55.61 8.96 0.25 0.72 Comparative Example 1-Point 2 Nd-rich phase 24.27 50.90 12.44 0.36 0.93 Comparative Example 1-Point 3 Nd-rich phase 24.13 52.71 10.83 0.50 0.75 Comparative Example 1-Point 4 Nd-rich phase 24.69 48.82 14.31 0.64 1.12

[0065] According to the phase of the intergranular triangle region of the NdFeB magnet, it can be seen that the grain boundary phase of the NdFeB magnet prepared in Example 1 forms R 6 F 13 Ga phase and a Nd-rich phase with a high rare earth content, while Comparative Example 1 forms a conventional Nd-rich phase.

[0066] The magnetic properties of the sintered NdFeB magnets obtained in the above embodiments and comparative examples were tested: at room temperature 20°C, the demagnetization curve test equipment NIM-60000 was used to test the remanence (Br), coercive force (HcJ), squareness (Hk / Hcj), and maximum magnetic energy product ((BH)max) of the magnets were obtained. The test results are shown in Table 1.

[0067] Table 1 Magnetic properties of sintered NdFeB magnets

[0068] Remanence Br Coercivity Hcj Squareness Hk / Hcj Maximum magnetic energy product (BH)max Example 1 13.90 18.46 97.9 46.89 Example 2 14.07 18.19 99.3 47.62 Example 3 13.68 18.95 98.6 45.26 Example 4 13.97 16.98 98.8 47.15 Example 5 13.25 18.47 97.9 45.98 Example 6 13.89 17.52 97.8 46.58 Example 7 13.92 17.24 97.7 46.75 Comparative Example 1 14.08 16.58 98.7 47.03 Comparative Example 2 13.78 16.85 92.5 45.59

[0069] The sintered NdFeB magnets obtained in Examples 1-3 have good magnetic properties, and a continuous and clear Re6Fe13Ga grain boundary phase is formed inside the magnets. The Ga content in the NdFeB magnets in Example 4 is low, and sufficient Re6Fe13Ga grain boundary phase cannot be formed. 6 Fe 13Ga phase, the grain boundary phase accounts for a small proportion, and the coercive force is low; in Example 5, the Ga content in the NdFeB magnet is relatively high, and the proportion of Re6Fe13Ga grain boundary phase is increased, but the distribution continuity deteriorates, resulting in a decrease in Br; in Example 6, a small air flow rate of oxygen is introduced during air flow milling, which has limited passivation effect on the powder, and subsequent production processes are more susceptible to oxidation, resulting in a decrease in the coercive force of the magnet; in Example 7, a large air flow rate of oxygen is introduced during air flow milling, resulting in excessive oxidation of the magnetic powder, which directly affects the performance of the magnet and reduces the coercive force; in Comparative Example 1, the atomic percentage of B added is too high, [Fe]+[Co]-14[B]<1.5, and the Re6Fe13Ga grain boundary phase cannot be formed, so the coercive force is greatly reduced; in Comparative Example 2, the atomic percentage of B added is too small, [Fe]+[Co]-14[B]>3, and a ferromagnetic phase is formed at the grain boundary, resulting in a deterioration of the magnet structure and a significant deterioration of the magnetic properties.

[0070] Finally, it should be noted that the specific embodiments described herein are merely examples of the spirit of the present invention, and are not intended to limit the implementation methods of the present invention. Those skilled in the art of the present invention may make various modifications or supplements to the described embodiments or replace them in similar ways. It is not necessary and impossible to provide all examples of all implementation methods here. However, these obvious changes or modifications derived from the essential spirit of the present invention still fall within the scope of protection of the present invention, and interpreting them as any additional limitation is contrary to the spirit of the present invention.

Claims

1. A high performance sintered NdFeB magnet, characterized in that: The invention comprises the following components in mass percentage: R: 30-33%, B: 0.80-0.95%, Ga: 0.05-0.8%, M: 0.05-2.0%, Co: 1.0-1.5%, Fe: 60-68%, R is Pr and Nd, and M is one or more of Cu, Al, Nb and Zr.

2. The high performance sintered NdFeB magnet according to claim 1, characterized in that: The atomic percentage of the high performance sintered NdFeB magnet satisfies 1.5<[Fe]+[Co]-14[B]<3.

3. The high performance sintered NdFeB magnet according to claim 1, characterized in that: The Ga content in the high-performance sintered NdFeB magnet is 0.5-0.6%.

4. A method for preparing a high performance sintered NdFeB magnet as claimed in claim 1, characterized in that: The preparation method comprises batching, smelting, hydrogen cracking to obtain coarse powder, stirring the coarse powder, air flow grinding to obtain fine powder, stirring the fine powder, molding, sintering and aging.

5. The preparation method according to claim 4, characterized in that: The particle size of the coarse powder obtained by hydrogen rupture is 200 to 300 μm.

6. The preparation method according to claim 4, characterized in that: When the coarse powder is stirred, 0.03-0.08% of antioxidant by weight of the coarse powder and 0.02-0.06% of gasoline by weight of the coarse powder are added.

7. The preparation method according to claim 4, characterized in that: During the jet milling, 55-65 ppm of oxygen was introduced.

8. The preparation method according to claim 4, characterized in that: The particle size of the fine powder obtained by jet milling is 3.0-4.0 μm.

9. The preparation method according to claim 4, characterized in that: When the fine powder is stirred, 0.03-0.08% of the weight of the fine powder is added with an antioxidant and 0.02-0.06% of the weight of the fine powder is added with gasoline.

10. The preparation method according to claim 4, characterized in that: Argon gas is introduced for air cooling during sintering and post-aging cooling.

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