A high-coercivity mixed rare earth permanent magnet material based on a multi-step diffusion method and a preparation method thereof

Abstract

The application discloses a high-coercivity mixed rare earth permanent magnet material based on a multi-step diffusion method and a preparation method thereof, and comprises the following steps: (1) adopting a smelting, strip casting, hydrogen decrepitation, airflow milling and sintering technology to prepare a sintered mixed rare earth permanent magnet material; (2) preparing two types of diffuser powders, the first type of diffuser being a light rare earth or an alloy thereof, and the second type of diffuser being a heavy rare earth or an alloy thereof; (3) selecting the first type of diffuser to perform vacuum diffusion treatment; (4) selecting the second type of diffuser to perform vacuum diffusion treatment; and (5) continuing to perform low-temperature tempering treatment, so as to finally obtain the high-coercivity mixed rare earth permanent magnet material. The application aims at solving the problem of low coercivity of the mixed rare earth permanent magnet material, preparing the high-coercivity mixed rare earth permanent magnet material, and realizing commercial application of the mixed rare earth permanent magnet material.

Description

Technical Field

[0001] This invention relates to the field of rare earth permanent magnets, specifically to a high coercivity hybrid rare earth permanent magnet material based on a multi-step diffusion method and its preparation method. Background Technology

[0002] As the most powerful magnetic material currently available, neodymium iron boron (NdFeB) rare earth permanent magnets are widely used in the automotive industry, medical devices, wind power generation, electronics, aerospace, and other fields. However, the rapid growth in demand for NdFeB permanent magnets has led to the overconsumption of major rare earth (RE) raw materials such as neodymium (Nd), praseodymium (Pr), dysprosium (Dy), and terbium (Tb). Furthermore, obtaining these rare earth raw materials requires separation, refining, and purification processes, which inevitably cause environmental pollution. Mixed rare earths, by reducing the complex separation and purification processes, offer significant economic advantages when applied to rare earth permanent magnets. They also effectively address the problem of large-scale stockpiling of other rare earth raw materials such as lanthanum (La) and cerium (Ce), thus promoting the balanced utilization of rare earth resources.

[0003] Taking the Bayan Obo mixed rare earth as an example, La and Ce account for over 75%, while other rare earth elements such as Nd and Pr account for a smaller proportion. Because the tetragonal hard magnetic main phase composed of La and Ce has poor intrinsic magnetic properties, (La,Ce)₂Fe 14 The magnetocrystalline anisotropy field H of phase B A and saturation magnetization M s Both were significantly lower than (Nd,Pr)2Fe 14 Phase B. This results in rare-earth permanent magnet materials prepared directly from mixed rare earth elements having magnetic properties far lower than traditional neodymium iron boron magnets prepared from neodymium-praseodymium alloys, especially with significantly lower coercivity, even <1kOe, making it difficult to meet commercial requirements.

[0004] The low coercivity of mixed rare-earth permanent magnet materials mainly stems from two factors. Intrinsically, due to the high proportions of La and Ce in the mixed rare-earth materials, the tetragonal hard magnetic principal phase has a low H content. A It is not conducive to the coercivity of the magnet; in terms of external factors, permanent magnets prepared by mixing rare earths are prone to generating a large amount of REFe2 phase and high-melting-point RE2O3 oxide phase, which is not conducive to the sintering and densification of the magnet. At the same time, the lack of low-melting-point rare earth-rich grain boundary phases makes it impossible to isolate the exchange coupling between adjacent hard magnetic main phases, resulting in low coercivity of the magnet.

[0005] Grain boundary diffusion technology is an effective method to improve the coercivity of NdFeB permanent magnet materials. The traditional approach involves coating the surface of a sintered NdFeB magnet with pure rare earth elements or their alloys, followed by a diffusion and aging process to allow the surface diffusion source to penetrate the magnet's interior. This modifies the composition of the hard magnetic main phase and optimizes the composition and distribution of the grain boundary phase, thereby improving the magnet's coercivity. However, for mixed rare earth permanent magnet materials, the interaction of multiple rare earth elements leads to a more complex composition and distribution of the hard magnetic main phase and grain boundary phase. Traditional grain boundary diffusion methods have limited diffusion depth, resulting in limited increases in coercivity. Therefore, designing easily diffuseable mixed rare earth permanent magnet material matrices and effective grain boundary diffusion methods are crucial for solving the problem of low coercivity in mixed rare earth permanent magnet materials. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a high coercivity hybrid rare earth permanent magnet material based on a multi-step diffusion method and its preparation method.

[0007] This invention provides a method for preparing a high coercivity hybrid rare-earth permanent magnet material based on a multi-step diffusion method, comprising the following steps:

[0008] (1) Sintered mixed rare earth permanent magnet materials were prepared by using melting, spinning, hydrogen breaking, air jet milling and sintering techniques;

[0009] (2) Two types of dispersants are prepared: the first type of dispersant is light rare earth or its alloy, and the second type of dispersant is heavy rare earth or its alloy.

[0010] (3) The first type of diffusing agent in step (2) is used to perform vacuum diffusion treatment on the sintered mixed rare earth permanent magnet material prepared in step (1). The amount of the first type of diffusing agent is less than 3% of the mass of the selected sintered mixed rare earth permanent magnet material. The vacuum diffusion treatment is as follows: diffusion temperature 600-950℃, diffusion time 1-6h.

[0011] (4) The second type of diffusing agent in step (2) is then used to perform vacuum diffusion treatment on the sintered mixed rare earth permanent magnet material after step (3) to obtain the treated mixed rare earth permanent magnet material; the amount of the second type of diffusing agent is less than 1% of the mass of the selected sintered mixed rare earth permanent magnet material; the vacuum diffusion treatment is: diffusion temperature 800~950℃, diffusion time 2~10h;

[0012] (5) The mixed rare earth permanent magnet material obtained in step (4) is further subjected to low-temperature tempering treatment at a tempering temperature of 450-650℃ and a tempering time of 0.5-5h to finally obtain a high coercivity mixed rare earth permanent magnet material.

[0013] Furthermore, the composition of the sintered mixed rare earth permanent magnet material described in step (1) is [A1-a (Ce 1-x MM x ) a ] b Fe bal R c B d Ga e Al f A represents one or both of the rare earth elements Nd or Pr; Ce represents cerium; MM represents the mixed rare earth elements associated with Bayan Obo, whose mass composition is: Ce: 50-60%, La: 20-35%, Pr: 5-10%, Nd: 10-20%, other elements and unavoidable impurities ≤2%; Fe represents iron; R represents one or more of the alloying elements Co, Ni, Cu, Mo, Nb, Si, Ti, V or Zr; B represents boron; Ga represents gallium; Al represents aluminum, and by mass percentage, 0.5≤a≤1, 0.5≤x≤0.95, 30≤b≤35, 0.2≤c≤3, 0.80≤d≤1, 0.2≤e≤2, 0.1≤f≤1, 0.4≤e+f≤2.5.

[0014] Preferably, 0.7≤a≤1, 0.7≤x≤0.85, 31≤b≤32.5, 0.7≤c≤1.5, 0.88≤d≤0.95, 0.3≤e≤0.6, 0.2≤f≤0.7, and 0.5≤e+f≤1.3.

[0015] Furthermore, in step (2), the first type of dispersant component is A1. g M1 1-g A1 is one or more of the rare earth elements Nd, Pr, Ce, or La, wherein when A1 is multiple rare earth elements, the total mass percentage of Nd or Pr is higher than 60%, and M1 is one or more of Al, Cu, or Ga; the second type of dispersant component is A1. h A2 i M2 1-h-i A1 is one or more of the rare earth elements Nd, Pr, Ce or La. Similarly, when A1 is multiple rare earth elements, the total mass percentage of Nd or Pr is higher than 60%. A2 is one or two of the rare earth elements Dy or Tb. M2 is one or more of Al, Cu, Ga or H. In terms of mass percentage, 0.6≤g≤1, 0.4≤h≤0.8, 0.1≤i≤0.6.

[0016] Furthermore, in step (3), the first type of dispersant is subjected to vacuum diffusion treatment 1 to 3 times, and the composition of the dispersant is different in each vacuum diffusion treatment.

[0017] Furthermore, during the vacuum diffusion process described in steps (3) and (4), the vacuum level inside the cavity is maintained at ≤10. -3Pa.

[0018] It should be noted that the smelting, belt spinning, hydrogen blasting, air jet milling, and sintering processes used in the preparation of the sintered mixed rare earth permanent magnet material of this invention are all well-known technologies in the field. For example, the smelting temperature usually needs to be higher than the temperature of the material with the highest melting point in the batch, and the belt spinning temperature is generally controlled to be 1-5 m / s for the copper rollers. Hydrogen blasting typically involves loading the rapidly solidifying spun sheets into a stainless steel tank and evacuating the vacuum to below 10°C. -2 Pa, followed by heating and holding with high-purity hydrogen gas. Nitrogen gas is generally chosen as the medium for gas flow milling. Sintering is typically carried out at a temperature range of 1000–1100℃ for 1–4 hours.

[0019] The present invention also provides a high coercivity hybrid rare earth permanent magnet material prepared by the multi-step diffusion method.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1) This invention addresses the problem of low coercivity in mixed rare earth permanent magnet materials, aiming to realize the commercial application of mixed rare earth permanent magnet materials. It can fully leverage the advantages of mixed rare earth MM, significantly reduce the cost of magnet raw materials, alleviate the large-scale stockpiling of high-abundance rare earths such as La and Ce, and effectively balance the utilization of rare earth resources.

[0022] 2) This invention designs the composition of the initial mixed rare-earth permanent magnet material to control the low boron content while introducing Ga and Al elements. The content of high-melting-point, high-oxygen rare-earth oxides in the prepared initial sintered magnet is reduced, and a new RE / Ga / Al-rich grain boundary phase is generated, increasing the grain boundary diffusion channels and facilitating diffusion. This is a prerequisite for preparing high-coercivity mixed rare-earth permanent magnet materials.

[0023] 3) This invention designs a multi-step diffusion method. First, low-melting-point light rare earth elements or their alloys are selected for grain boundary diffusion. These diffusers, upon entering the magnet, can form a Nd / Pr-rich magnetized shell on the epitaxial layer of the main phase grains, while simultaneously forming new grain boundary phases, providing channels for subsequent diffusion and improving diffusion efficiency. Depending on the initial magnet composition design and the requirements for the final magnet's coercivity and other magnetic properties, one or more vacuum diffusion processes can be performed as needed, selecting different diffusion sources, diffusion temperatures, and diffusion times. Subsequently, heavy rare earth elements or their alloys are selected for grain boundary diffusion. Since heavy rare earth elements (Dy / Tb) are not easily found in RE6 (Fe, Ga, Al, Cu),... 14In the grain boundary phase, more Dy / Tb enters the main phase, forming a Dy / Tb-rich magnetically hardened shell. The formation of this double-hard magnetic shell significantly improves the coercivity of the diffused magnet. Simultaneously, the multi-step diffusion method effectively solves the problem of heavy rare earth element (Dy / Tb) waste caused by the excessive accumulation at grain boundaries in traditional grain boundary diffusion. The final tempering process further forms RE6 (Fe,Ga,Al,Cu). 14 The continuous non-ferromagnetic grain boundary phase can effectively isolate the short-range exchange coupling between hard magnetic main phase grains, and finally prepare a high coercivity hybrid rare earth permanent magnet material.

[0024] 4) This invention fully leverages the interactive effects of multiple rare earth elements (La, Ce, Nd, Pr, Dy, Tb) and non-rare earth elements (Cu, Ga, Al, Co, Ni, Mo, Nb, Ti, etc.). Based on sintering-multi-step diffusion-tempering processes, a heterogeneous structure is constructed. This heterogeneity is not only manifested in the double hard magnetic shell and core region inside the main phase grains, but also in the various grain boundary phase regions formed at different preparation stages. This achieves the reduction and utilization of heavy rare earth elements Dy and Tb, and realizes the high-value utilization of Bayan Obo mixed rare earth. Detailed Implementation

[0025] The present invention will be further described and illustrated below with reference to specific embodiments. The embodiments described are merely examples of the content of this disclosure and do not limit the scope of the invention. The technical features of each embodiment in the present invention can be combined accordingly, provided that there is no mutual conflict.

[0026] Example 1:

[0027] Sintered mixed rare earth permanent magnet materials were prepared using melting, spinning, hydrogen breaking, air jet milling, and sintering techniques. The composition, by mass percentage, was [(Nd...]. 0.2 (Ce 0.3 MM 0.7 ) 0.8 ] 31.5 Fe bal Co 0.6 Cu 0.2 Zr 0.15 B 0.95 Ga 0.3 Al 0.2 Three dispersant powders with different components were prepared, and their components, by mass percentage, were Pr, Pr, and Pr, respectively. 0.77 Ce 0.12 Ga 0.11 (Class I dispersant), Pr 0.95 Al 0.05 (Class I dispersant) and Nd 0.64 Dy 0.25 Ga 0.11(Second type of diffusing agent). Correspondingly, the dosages of the three diffusing agent powders are 2%, 2%, and 0.8% of the mass of the selected sintered mixed rare-earth permanent magnet material, respectively. A three-step diffusion method is employed, the first step being Pr 0.77 Ce 0.12 Ga 0.11 Diffusion, diffusion temperature 850℃, diffusion time 2h; second step Pr 0.95 Al 0.05 Diffusion, diffusion temperature 850℃, diffusion time 1 hour; Step 3 Nd 0.64 Dy 0.25 Ga 0.11 Diffusion was performed at a temperature of 900℃ for 6 hours. The magnet was then subjected to low-temperature tempering at 500℃ for 4 hours to obtain a high-coercivity mixed rare-earth permanent magnet material. Test results from the AMT-4 permanent magnet characteristic measuring instrument showed that the coercivity of the diffused magnet reached 15.5 kOe.

[0028] Comparative Example 1:

[0029] The difference from Example 1 lies in the selection of the dispersant and the diffusion method. A dispersant is prepared, with Nd as a mass percentage. 0.64 Dy 0.25 Ga 0.11 The amount of diffusing agent powder used was 1% of the mass of the selected sintered mixed rare earth permanent magnet material. A one-step diffusion method was used, with a diffusion temperature of 900℃ and a diffusion time of 6 hours. The magnet was then subjected to low-temperature tempering treatment at 500℃ for 4 hours. Test results from the AMT-4 permanent magnet characteristic measuring instrument showed that the coercivity of the diffused magnet was 10.8 kOe, which is much smaller than that of Example 1.

[0030] Example 2:

[0031] Sintered mixed rare earth permanent magnet materials were prepared using melting, spinning, hydrogen breaking, air jet milling, and sintering techniques. The composition, by mass percentage, was [(Nd...]. 0.3 (Ce 0.15 MM 0.85 ) 0.7 ] 31 Fe bal Co 0.85 Cu 0.25 Nb 0.2 Ti 0.2 B 0.88 Ga 0.6 Al 0.7 Two dispersants were prepared, with Nd as the main component, by mass percentage. 0.76 Pr 0.19 Al 0.05 (Class I dispersant) and Pr 0.58 Dy 0.27Cu 0.15 (Second type of diffusing agent). Accordingly, the amounts of the two diffusing agent powders are 2.5% and 0.6% of the mass of the selected sintered mixed rare earth permanent magnet material, respectively. A two-step diffusion method is adopted, the first step being Nd... 0.76 Pr 0.19 Al 0.05 Diffusion, diffusion temperature 850℃, diffusion time 2h; second step Pr 0.58 Dy 0.27 Cu 0.15 Diffusion was performed at 800℃ for 10 hours. The magnet was then subjected to low-temperature tempering at 480℃ for 5 hours to obtain a high-coercivity mixed rare-earth permanent magnet material. Test results from the AMT-4 permanent magnet characteristic measuring instrument showed that the coercivity of the diffused magnet reached 15.3 kOe.

[0032] Comparative Example 2:

[0033] The difference from Example 2 lies in the selection of the dispersant and the diffusion method. A dispersant is prepared, with Nd as a mass percentage component. 0.76 Pr 0.19 Al 0.05 The amount of diffusing agent powder used was 2.5% of the mass of the selected sintered mixed rare earth permanent magnet material. A one-step diffusion method was used, with a diffusion temperature of 890℃ and a diffusion time of 6 hours. The magnet was then subjected to low-temperature tempering treatment at 480℃ for 5 hours. Test results from the AMT-4 permanent magnet characteristic measuring instrument showed that the coercivity of the diffused magnet was 10.2 kOe, which is much smaller than that of Example 2.

[0034] Example 3:

[0035] Sintered mixed rare earth permanent magnet materials were prepared using melting, spinning, hydrogen crushing, air jet milling, and sintering techniques. The composition, by mass percentage, was (Ce...). 0.2 MM 0.8 ) 32.5 Fe bal Ni 0.25 Cu 0.25 Ti 0.2 B 0.92 Ga 0.4 Al 0.4 Two dispersants were prepared, with the composition being Pr (by mass percentage). 0.94 Al 0.03 Ga 0.03 (Class I dispersant) and Pr 0.75 Tb 0.12 Ga 0.11 H 0.02(Second type of diffusing agent). Accordingly, the amounts of the two diffusing agent powders are 1.5% and 0.8% of the mass of the selected sintered mixed rare earth permanent magnet material, respectively. A two-step diffusion method is adopted, the first step of which involves Pr 0.94 Al 0.03 Ga 0.03 Diffusion, diffusion temperature 800℃, diffusion time 2h; second step Pr 0.75 Tb 0.12 Ga 0.11 H 0.02 Diffusion was performed at a temperature of 900℃ for 6 hours. The magnet was then subjected to low-temperature tempering at 500℃ for 3 hours to obtain a high-coercivity mixed rare-earth permanent magnet material. Test results from the AMT-4 permanent magnet characteristic measuring instrument showed that the coercivity of the diffused magnet reached 14.1 kOe.

[0036] Comparative Example 3:

[0037] The difference from Example 3 is that the composition of the sintered mixed rare earth permanent magnet material is different, with increased B content, decreased Ga content, and decreased Al content. The composition, by mass percentage, is (Ce... 0.2 MM 0.8 ) 32.5 Fe bal Ni 0.25 Cu 0.25 Ti 0.2 B 1.1 The test results from the AMT-4 permanent magnet characteristic measuring instrument show that the coercivity of the diffused magnet is 7.8 kOe, which is much smaller than that of Example 3.

[0038] Comparative Example 4:

[0039] The difference from Example 3 is that the diffusion agent used in the second diffusion step is different; the component is Pr by mass percentage. 0.85 Tb 0.02 Ga 0.11 H 0.02 The amount of diffuser powder used was 0.8% of the mass of the selected sintered mixed rare earth permanent magnet material. The test results of the AMT-4 permanent magnet characteristic measuring instrument showed that the coercivity of the diffused magnet was 10.4 kOe, which was much smaller than that of Example 3.

[0040] This invention designs the composition of the initial mixed rare-earth permanent magnet material and employs a multi-step diffusion method. First, low-melting-point light rare-earth elements or their alloys are used for grain boundary diffusion, followed by heavy rare-earth elements or their alloys. This results in the formation of a double hard magnetic shell rich in Nd / Pr and Dy / Tb within the main phase grains of the mixed rare-earth permanent magnet material. Simultaneously, the multi-step diffusion improves the microstructure of the mixed rare-earth permanent magnet material, forming RE6(Fe,Ga,Al,Cu). 14The continuous non-ferromagnetic grain boundary phase can effectively isolate the short-range exchange coupling between hard magnetic main phase grains, and finally prepare a high coercivity hybrid rare earth permanent magnet material.

[0041] The above-described embodiments are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. Those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a high coercivity hybrid rare-earth permanent magnet material based on a multi-step diffusion method, characterized in that, Includes the following steps: (1) A sintered mixed rare earth permanent magnet material was prepared by means of smelting, spinning, hydrogen breaking, air jet milling and sintering techniques; the composition of the sintered mixed rare earth permanent magnet material is [A 1-a (Ce 1-x MM x ) a ] b Fe bal R c B d Ga e Al f A represents one or both of the rare earth elements Nd or Pr; Ce represents cerium; MM represents the mixed rare earth elements associated with Bayan Obo, with the following mass composition: Ce: 50~60%, La: 20~35%, Pr: 5~10%, Nd: 10~20%, other elements and unavoidable impurities ≤2%; Fe represents iron; R represents one or more of the alloying elements Co, Ni, Cu, Mo, Nb, Si, Ti, V or Zr; B represents boron; Ga represents gallium; Al represents aluminum. The mass percentages are: 0.5≤a≤1, 0.5≤x≤0.95, 30≤b≤35, 0.2≤c≤3, 0.80≤d≤1, 0.2≤e≤2, 0.1≤f≤1, 0.4≤e+f≤2.

5. (2) Two types of dispersants are prepared. The first type of dispersant is a light rare earth element or its alloy, and the second type of dispersant is a heavy rare earth element or its alloy. In step (2), the composition of the first type of dispersant is Al. g M1 1-g A1 is one or more of the rare earth elements Nd, Pr, Ce, or La, wherein when A1 is multiple rare earth elements, the total mass percentage of Nd or Pr is higher than 60%, and M1 is one or more of Al, Cu, or Ga; the second type of dispersant component is A1. h A2 i M2 1-h-i A1 is one or more of the rare earth elements Nd, Pr, Ce or La; A2 is one or two of the rare earth elements Dy or Tb; M2 is one or more of Al, Cu, Ga or H; and by mass percentage, 0.6≤g≤1, 0.4≤h≤0.8, 0.1≤i≤0.

6. (3) The first type of diffusing agent in step (2) is used to perform vacuum diffusion treatment on the sintered mixed rare earth permanent magnet material prepared in step (1). The amount of the first type of diffusing agent is less than 3% of the mass of the selected sintered mixed rare earth permanent magnet material. The vacuum diffusion treatment is as follows: diffusion temperature 600~950℃, diffusion time 1~6h. (4) The second type of diffusing agent in step (2) is used to perform vacuum diffusion treatment on the sintered mixed rare earth permanent magnet material after step (3) to obtain the treated mixed rare earth permanent magnet material; the amount of the second type of diffusing agent is less than 1% of the mass of the selected sintered mixed rare earth permanent magnet material; the vacuum diffusion treatment is: diffusion temperature 800~950℃, diffusion time 2~10h; (5) The mixed rare earth permanent magnet material obtained in step (4) is further subjected to low-temperature tempering treatment at a tempering temperature of 450~650℃ and a tempering time of 0.5~5h to finally obtain a high coercivity mixed rare earth permanent magnet material.

2. The method for preparing high coercivity hybrid rare-earth permanent magnet materials based on a multi-step diffusion method as described in claim 1, characterized in that, The composition of the sintered mixed rare earth permanent magnet material described in step (1) satisfies the following: 0.7≤a≤1, 0.7≤x≤0.85, 31≤b≤32.5, 0.7≤c≤1.5, 0.88≤d≤0.95, 0.3≤e≤0.6, 0.2≤f≤0.7, 0.5≤e+f≤1.

3.

3. The method for preparing high coercivity hybrid rare-earth permanent magnet material based on a multi-step diffusion method as described in claim 1, characterized in that, In step (3), the first type of dispersant is subjected to vacuum diffusion treatment 1 to 3 times, and the composition of the dispersant is different each time it is vacuum diffused.

4. The method for preparing high coercivity hybrid rare-earth permanent magnet material based on a multi-step diffusion method as described in claim 1, characterized in that, During the vacuum diffusion process described in steps (3) and (4), the vacuum level inside the cavity should be maintained at ≤10. -3 Pa.

5. A high coercivity mixed rare earth permanent magnet material prepared by the preparation method of the high coercivity mixed rare earth permanent magnet material based on the multi-step diffusion method according to any one of claims 1-4.