Preparation method of high-temperature-stable sintered neodymium-iron-boron permanent magnet material

Abstract

The application provides a preparation method of high-temperature-stability sintered neodymium-iron-boron permanent magnet material. x B y Co a M b Fe 100‑x‑y‑a‑b The main phase alloy powder with a chemical composition as shown in the formula RE c B d Co e M f Fe 100‑c‑d‑e‑f The auxiliary phase alloy powder with a chemical composition as shown in the formula Re c B d Co e M f Fe 100‑c‑d‑e‑f is used as raw material, and after mixing, orientation compression, sintering and tempering are sequentially performed to obtain the high-temperature-stability sintered neodymium-iron-boron material. The application uses double alloy to introduce the auxiliary phase and boron-rich phase in the grain boundary to generate alloying reaction, regenerate a new main phase shell layer, and stabilize the main phase and inhibit the generation of impurity phase by using the cobalt concentration difference between the two phases, so that the high-cobalt sintered neodymium-iron-boron magnet with high temperature stability can be prepared, and the method is easy to control and suitable for batch production.

Description

Technical Field

[0001] This invention relates to the field of rare earth permanent magnet materials technology, and in particular to a method for preparing high-temperature stable sintered NdFeB permanent magnet materials. Background Technology

[0002] Since their emergence in the 1960s, rare-earth permanent magnet materials have experienced rapid development in research, production, and application, currently reaching the third generation: neodymium iron boron (NdFeB). Compared to the previous two generations of rare-earth permanent magnet materials, NdFeB permanent magnets possess high remanence, high energy product, and high intrinsic coercivity, making them the most magnetically powerful permanent magnet materials discovered worldwide. However, their poor temperature stability severely limits their application in high-temperature motors, precision instruments, and other fields. To meet the high-temperature stability requirements of industries such as new energy vehicles and national defense, developing NdFeB permanent magnet materials with high temperature stability is of great significance.

[0003] Studies have shown that when Co is added to a magnet, Co atoms generally replace Fe atoms, preferentially occupying RE2Fe. 14 The 8j1 crystal position of compound B reduces negative exchange interactions and strengthens the 3d-3d metal atom exchange interactions; RE2Co 14 The 3d-3d exchange coupling in B is RE2Fe 14 Three times the amount of B increases the Curie temperature and reduces the remanence temperature coefficient, becoming an important means of improving the temperature stability of magnets. However, when the Co content is high, RE(Fe,Co)2, RE(Fe,Co)3, RE(Fe,Co)4B, and RE2(Fe,Co) appear. 17 Impurities and other phases. The coercivity of sintered NdFeB is a structure-sensitive parameter. The ideal microstructure of sintered NdFeB materials should be: uniform thin-area grain boundaries encapsulating RE2Fe. 14 The B-phase main grains are fine and uniformly distributed. The presence of impurity phases deteriorates the microstructure of the magnet. Among them, RE(Fe,Co)2 is a soft magnetic phase that precipitates along the grain boundaries, weakening the magnetic isolation between the main phase grains and negatively impacting the magnet's coercivity. Furthermore, the presence of impurity phases reduces the proportion of the main phase, lowering the magnet's remanence. Therefore, suppressing impurity phases in high-cobalt magnets and fabricating magnets with both high performance and high temperature stability presents a challenge. Summary of the Invention

[0004] The technical problem solved by this invention is to provide a method for preparing sintered NdFeB magnets. The NdFeB permanent magnet material prepared in this application has high temperature stability, as well as high coercivity and high remanence.

[0005] In view of this, this application provides a method for preparing high-temperature stable sintered NdFeB permanent magnet materials, comprising:

[0006] The main phase alloy powder with the composition shown in formula (I) and the auxiliary phase alloy powder with the composition shown in formula (II) are mixed and then subjected to orientation pressing, sintering and tempering in sequence to obtain high temperature stability sintered NdFeB permanent magnet material.

[0007] RE x B y Co a M b Fe 100-x-y-a-b (I),

[0008] In formula (I), RE is selected from one or more of Dy, Tb, Pr, Nd, La, Ce, Y and Ho;

[0009] M is selected from one or more of Al, Cu, Ga, Si, Sn, Ge, Zr, Ti, and Zn;

[0010] 29≤x≤34, 1.0≤y≤1.8, 10≤a≤30, 0.1≤b≤2.0;

[0011] RE c B d Co e M f Fe 100-c-d-e-f (II),

[0012] In formula (II), RE is selected from one or more of Dy, Tb, Pr, Nd, La, Ce, Y and Ho;

[0013] M is selected from one or more of Al, Cu, Ga, Si, Sn, Ge, Zr, Ti, and Zn;

[0014] 29≤c≤70, 0≤d≤2, 0≤e<a≤20, 0.1≤f≤50.

[0015] Preferably, the main phase molecules of the high-temperature stable sintered NdFeB are RE2(Fe,Co). 14 B.

[0016] Preferably, the auxiliary phase alloy powder is 0.5 to 30 wt% of the total of the main phase alloy powder and the auxiliary phase alloy powder.

[0017] Preferably, the particle size of the main phase alloy powder is 1-5 μm, and the particle size of the auxiliary phase alloy powder is 1-5 μm.

[0018] Preferably, the magnetic field strength of the orientation compression molding is 1.0 to 2.0 T, and the pressure is 100 to 200 MPa.

[0019] Preferably, the sintering process specifically includes:

[0020] The oriented magnets are first sintered at 900–1100℃ for 1–6 hours, then the temperature is lowered to 800–1000℃ and held for 0.5–2 hours, and finally raised to 900–1100℃ and held for 0.5–2 hours.

[0021] Preferably, the preparation method of the main phase alloy powder and the auxiliary phase alloy powder is as follows:

[0022] The main phase alloy casting and the auxiliary phase alloy casting are first subjected to hydrogen crushing and then subjected to air jet milling.

[0023] Preferably, the hydrogen pressure for hydrogen decomposition is independently selected from 0.1 to 0.5 MPa, the hydrogen absorption time is independently selected from 2 to 5 h, the dehydrogenation temperature is independently selected from 300 to 500 °C, and the dehydrogenation time is independently selected from 4 to 8 h.

[0024] Preferably, the hydrogen content in the powder obtained by hydrogen crushing is independently less than 1500 ppm, and the average particle size of the powder is independently selected from 100 to 250 μm.

[0025] Preferably, the tempering process involves first holding the material at 800–1000°C for 2–4 hours, and then holding it at 450–600°C for 2–4 hours.

[0026] This application provides a method for preparing high-temperature stable sintered NdFeB permanent magnet materials, which uses chemical compositions as shown in formula RE x B y Co a M b Fe 100-x-y-a-b The main phase alloy powder shown has the following chemical composition as shown in Formula Re c B d Co e M f Fe 100-c-d-e-f Using the auxiliary phase alloy powder shown as raw material, firstly, magnets are prepared using two alloy powders with different cobalt contents: the main phase and the auxiliary phase. The cobalt content in the auxiliary phase alloy powder is lower than that in the main phase alloy. During sintering, due to the concentration difference of cobalt in the two powders, cobalt in the higher concentration region at the grain boundaries diffuses into the lower concentration main phase grains. Secondly, when the boron content of the main phase alloy powder is higher than 1.0 wt%, a boron-rich phase (Re) is generated. 1+ε The cobalt and rare earth elements introduced into the auxiliary phase (Fe4B4) react with the boron-rich phase to generate a new cobalt-containing main phase RE2(Fe,Co). 14 B. The above two methods can suppress the formation of impurity phases by cobalt and rare earth elements in the grain boundaries, and increase the cobalt content in the main phase grains, thereby improving the temperature stability of the magnet.

[0027] In summary, this invention, through the selection of appropriate elemental compositions and proportioning design, can control the microstructure of the obtained rapid-solidifying alloy castings, resulting in fine columnar crystals, without the need for special casting equipment. The process is easy to control and suitable for large-scale production. The method provided by this invention simultaneously improves the remanence and coercivity of the neodymium iron boron permanent magnet material, exhibiting excellent overall performance. Attached Figure Description

[0028] Figure 1 A schematic diagram illustrating the preparation principle of the high-temperature stability sintered NdFeB permanent magnet material provided by this invention. Detailed Implementation

[0029] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0030] In view of the problem that the cobalt-containing impurity phase in the existing NdFeB magnet is detrimental to the magnetic performance of the magnet, this application utilizes a dual main phase approach (high cobalt phase and low cobalt phase), and uses the boron-rich phase to form a cobalt-containing main phase with Co in the grain boundaries, thereby suppressing the formation of impurity phases and allowing more Co elements to enter the main phase grains to form RE2(Fe,Co). 14 B. The higher the Co content in the grains, the better the temperature stability of the magnet. Specifically, this invention discloses a method for preparing a high-temperature-stability sintered NdFeB permanent magnet material, including:

[0031] The main phase alloy powder with the composition shown in formula (I) and the auxiliary phase alloy powder with the composition shown in formula (II) are mixed and then subjected to orientation pressing, sintering and tempering in sequence to obtain high temperature stability sintered NdFeB permanent magnet material.

[0032] RE x B y Co a M b Fe 100-x-y-a-b (I),

[0033] In formula (I), RE is selected from one or more of Dy, Tb, Pr, Nd, La, Ce, Y and Ho;

[0034] M is selected from one or more of Al, Cu, Ga, Si, Sn, Ge, Zr, Ti, and Zn;

[0035] 29≤x≤34, 1.0≤y≤1.8, 10≤a≤30, 0.1≤b≤2.0;

[0036] Re c B dCo e M f Fe 100-c-d-e-f (II),

[0037] In formula (II), RE is selected from one or more of Dy, Tb, Pr, Nd, La, Ce, Y and Ho;

[0038] M is selected from one or more of Al, Cu, Ga, Si, Sn, Ge, Zr, Ti, and Zn;

[0039] 29≤c≤70, 0≤d≤2, 0≤e<a≤20, 0.1≤f≤50.

[0040] A schematic diagram illustrating the mechanism for preparing high-temperature-stability sintered NdFeB permanent magnets in this application is shown below. Figure 1 As shown, the magnet contains a high-cobalt main phase and a low-cobalt main phase, with a lower cobalt content in the low-cobalt main phase. During sintering, Co atoms in the high-cobalt main phase migrate to the grain boundaries. Due to the Co concentration difference, cobalt in the higher concentration regions of the grain boundaries diffuses into the lower concentration grains of the low-cobalt main phase. Furthermore, the Co that migrates from the grains to the grain boundaries undergoes a metallurgical reaction with the boron-rich phase surrounding the main phase grains, forming a new main phase. These two mechanisms can suppress the formation of impurity phases from cobalt and rare earth elements in the grain boundaries, increase the cobalt content in the main phase grains, and improve the temperature stability of the magnet.

[0041] In this invention, in Formula I, x is preferably 30-33, more preferably 31-32; y is preferably 1.2-1.8, more preferably 1.4-1.6, and most preferably 1.5; a is preferably 10-28, more preferably 16-22, and most preferably 20; b is preferably 0.1-0.5, more preferably 0.2-0.4, and most preferably 0.3.

[0042] In this invention, in Formula II, c is preferably 30-60, more preferably 45-55, and most preferably 50; d is preferably 0-1, more preferably 0-0.8, and most preferably 0.4; e is preferably 5-15, more preferably 8-12, and most preferably 10; f is preferably 0.5-40, and more preferably 1-25.

[0043] In this invention, the average particle size of the main phase alloy powder and the auxiliary phase alloy powder is preferably 2 to 5 μm, more preferably 3 to 4 μm.

[0044] In this invention, the method for preparing the main phase alloy powder preferably includes:

[0045] The main phase alloy castings were hydrogen-crushed and then subjected to air jet milling.

[0046] In this invention, the preferred method for preparing the main phase alloy casting includes:

[0047] The alloy raw materials are melted and then rapidly solidified to obtain the main phase alloy casting.

[0048] This invention does not impose any special limitations on the smelting method; any smelting method well-known to those skilled in the art can be used, where the alloy raw materials are batched according to the pre-obtained composition and then smelted. In this invention, the vacuum degree during the rapid solidification process is preferably less than 10. -2 Pa, the rotation speed is preferably 1.8 to 3.0 m / s, more preferably 2.0 to 2.5 m / s; the pouring temperature is preferably 1200 to 1500℃, more preferably 1300 to 1400℃, and most preferably 1350℃.

[0049] In this invention, the hydrogen pressure during the hydrogen crushing process is preferably 0.1–0.4 MPa, more preferably 0.2–0.3 MPa; the hydrogen absorption time is preferably 2–5 h, more preferably 3–4 h; the dehydrogenation temperature is preferably 320–500 °C, more preferably 350–450 °C, and most preferably 400 °C; the dehydrogenation is preferably vacuum dehydrogenation; and the dehydrogenation time is preferably 4–8 h, more preferably 5–7 h, and most preferably 6 h.

[0050] In this invention, the hydrogen content of the powder obtained after hydrogen crushing is preferably less than 1500 ppm, and the average particle size of the powder is preferably 100-250 μm, more preferably 150-200 μm, and most preferably 160-180 μm.

[0051] In this invention, the method for preparing the auxiliary phase alloy powder preferably includes:

[0052] The auxiliary phase alloy castings were hydrogen-crushed and then subjected to air jet milling.

[0053] In this invention, the preferred method for preparing the auxiliary phase alloy casting includes:

[0054] The alloy raw materials are melted and then rapidly solidified to obtain the main phase alloy casting.

[0055] This invention does not impose any special limitations on the smelting method; any smelting method well-known to those skilled in the art can be used, where the alloy raw materials are batched according to the pre-obtained composition and then smelted. In this invention, the vacuum degree during the rapid solidification process is preferably less than 10. -2 The preferred rotational speed is 1.8–3.0 m / s, more preferably 2.0–2.5 m / s; the preferred pouring temperature is 900–1500℃, more preferably 1000–1400℃, even more preferably 1100–1300℃, and most preferably 1200℃.

[0056] In this invention, the selection range of process parameters for hydrogen crushing is consistent with that described in the above technical solution, and will not be repeated here; the hydrogen content of the powder obtained after hydrogen crushing is preferably less than 1500 ppm, the average particle size of the powder is preferably 100-250 μm, more preferably 150-200 μm, and most preferably 160-180 μm.

[0057] In this invention, the thickness of the main phase alloy casting and the auxiliary phase alloy casting is preferably 0.1-0.5 mm, more preferably 0.2-0.4 mm, and most preferably 0.3 mm.

[0058] In this invention, the mass of the auxiliary phase alloy powder is preferably 0.5-30% of the total mass of the main phase alloy powder and the auxiliary phase alloy powder, more preferably 1-25%, even more preferably 5-20%, and most preferably 10-15%.

[0059] In this invention, the orientation pressing is preferably performed in a magnetic field; the strength of the magnetic field is preferably 1.5 to 2.0 T, more preferably 1.6 to 1.9 T, and most preferably 1.7 to 1.8 T; the pressure of the isostatic pressing is preferably 150 to 200 MPa, more preferably 160 to 190 MPa, and most preferably 170 to 180 MPa.

[0060] In this invention, the sintering is preferably vacuum sintering. Specifically, the sintering in this invention comprises:

[0061] The oriented magnets are first sintered at 900–1100℃ for 1–6 hours, then the temperature is lowered to 800–1000℃ and held for 0.5–2 hours, and finally raised to 900–1100℃ and held for 0.5–2 hours.

[0062] More specifically, the sintering temperature is preferably 900–1100℃, more preferably 950–1050℃, and most preferably 1000℃; the sintering time is preferably 2–5 hours, more preferably 3–4 hours. The temperature is then lowered to preferably 800–1000℃, and most preferably 900℃, with a holding time of preferably 0.5–2 hours, and most preferably 1 hour; the temperature is then raised back to the sintering temperature with a holding time of preferably 0.5–2 hours, and most preferably 1 hour.

[0063] In this invention, the tempering process involves first holding the material at 800–1000°C for 2–4 hours, and then holding it at 450–600°C for 2–4 hours.

[0064] This invention suppresses the generation of impurity phases in high-cobalt magnets and improves cobalt utilization through two methods, thus preparing a high-temperature stable magnet. Firstly, the magnet is prepared using alloy powders with different cobalt contents in the main phase and auxiliary phase. The cobalt content in the auxiliary phase alloy powder is lower than that in the main phase alloy. During sintering, the cobalt in the high-cobalt main phase diffuses to the grain boundaries (①). Due to the cobalt concentration difference, the cobalt in the higher concentration region of the grain boundaries diffuses into the lower concentration main phase grains (②). Secondly, when the boron content of the main phase alloy powder is not less than 1.0 wt%, a boron-rich phase (RE) is generated. 1+ε The cobalt and rare earth elements introduced into the auxiliary phase (Fe4B4) will react with the boron-rich phase (②) within the designed heat treatment window to generate a new cobalt-containing main phase RE2(Fe,Co). 14 B(③). The above two methods can suppress the formation of impurity phases by cobalt and rare earth elements in the grain boundaries, and increase the cobalt content in the main phase grains, thereby improving the temperature stability of the magnet.

[0065] To further understand the present invention, the preparation method of the high-temperature stability sintered NdFeB permanent magnet material provided by the present invention will be described in detail below with reference to the embodiments. The scope of protection of the present invention is not limited by the following embodiments.

[0066] Example 1

[0067] The main phase rapid solidification alloy castings and auxiliary phase rapid solidification alloy castings were prepared by melting according to the element ratios. The vacuum degree during the preparation of the main phase rapid solidification alloy castings was 3 x 10⁻⁶. -2 Pa, rotation speed 2.0 m / s, casting temperature 1380℃, vacuum degree 3x10 during preparation of the auxiliary phase rapid solidification alloy casting sheet. -2 Pa, rotation speed 2.0 m / s, casting temperature 1350℃, main phase chemical formula mass percentage Nd 29.5 B 1.0 Co 20 Al 0.1 Cu 0.2 Ga 0.1 Zr 0.1 Fe 49.0 The auxiliary phase chemical formula has a mass percentage of Nd. 29.5 B 1.0 Co 10 Al 0.1 Cu 0.2 Ga 0.1 Zr 0.1 Fe 59.0 ;

[0068] The main phase alloy casting and the auxiliary phase alloy casting were separately powdered. The rapidly solidified alloy casting was subjected to hydrogen absorption at room temperature and a hydrogen pressure of 0.2 MPa for 3 hours, and then dehydrogenated under vacuum at 450℃ for 9 hours to obtain hydrogen-crushed powder. The hydrogen-crushed powder was then further crushed using an air jet mill to obtain main phase alloy powder and auxiliary phase alloy powder respectively.

[0069] The main phase alloy powder and the auxiliary phase alloy powder are mixed, with the auxiliary phase alloy powder accounting for 30% of the total weight (main phase alloy powder + auxiliary phase alloy powder). The mixed powder is then oriented and pressed in a 1.8T magnetic field and isostatically pressed under a pressure of 180MPa to obtain a magnet. After that, the magnet is sent to a vacuum sintering furnace for sintering under conditions isolated from the atmosphere. The sintering temperature is 1080℃. After sintering for 4 hours, the temperature is lowered to 980℃ and held for 1 hour, then raised to 1080℃ and held for 1 hour. Finally, it is heat-treated at 900℃ and 500℃ for 2 hours each to obtain a neodymium iron boron permanent magnet.

[0070] Comparative Example 1

[0071] Rapidly solidified alloy castings were prepared by melting and smelting according to the element ratios, with a vacuum degree of 3 x 10⁻⁶ during the preparation process. -2 Pa, rotation speed 2.0 m / s, casting temperature 1380℃, chemical formula mass percentage Nd 29.5 B 1.0 Co 17 Al 0.1 Cu 0.2 Ga 0.1 Zr 0.1 Fe 52.0 The subsequent processes are the same as in Example 1;

[0072] The remanence and coercivity of the products prepared in Example 1 and Comparative Example 1 of this invention were measured using a high coercivity permanent magnet measuring instrument (model PFM14.CN) provided by HIRST Corporation, and the remanence temperature coefficient (20℃~120℃) was calculated. The thermomagnetic curves of 400-900K were measured using a vibrating sample magnetometer (model SQUID) provided by Quantum Design under a magnetic field of 500Oe, and the Curie temperature was determined. The phase ratio was obtained by Rietveld refinement calculation based on the XRD results of the magnet powder. The test results are shown in Table 1.

[0073] Table 1 Performance data of NdFeB permanent magnets prepared in Example 1 and Comparative Example 1

[0074]

[0075] Example 2

[0076] The main phase rapid solidification alloy castings and auxiliary phase rapid solidification alloy castings were prepared by melting according to the element ratios. The vacuum degree during the preparation of the main phase rapid solidification alloy castings was 3 x 10⁻⁶. -2 Pa, rotation speed 2.0 m / s, casting temperature 1340℃, vacuum degree 3x10 during preparation of the auxiliary phase rapid solidification alloy casting sheet. -2 Pa, rotation speed 2.0 m / s, casting temperature 950℃, main phase chemical formula mass percentage Nd 29.5 B 1.2 Co 20 Al 0.1 Cu 0.2 Ga 0.1 Zr 0.1 Fe 48.8 The auxiliary phase chemical formula has a mass percentage of Pr. 60 Co 15 Al 25 ;

[0077] The main phase alloy casting and the auxiliary phase alloy casting were separately powdered. The rapidly solidified alloy casting was subjected to hydrogen absorption at room temperature and a hydrogen pressure of 0.2 MPa for 3 hours, and then dehydrogenated under vacuum at 450℃ for 9 hours to obtain hydrogen-crushed powder. After that, the hydrogen-crushed powder was further crushed by air jet mill to obtain main phase alloy powder and auxiliary phase alloy powder.

[0078] The main phase alloy powder and the auxiliary phase alloy powder were mixed, with the auxiliary phase alloy powder accounting for 5% of the total weight (main phase alloy powder and auxiliary phase alloy powder). The mixed powder was then oriented and pressed in a 1.8T magnetic field and isostatically pressed under a pressure of 180MPa to obtain a magnet. Afterwards, the magnet was sintered in a vacuum sintering furnace under atmospheric isolation conditions at a sintering temperature of 1060℃. After sintering for 4 hours, the temperature was lowered to 950℃ and held for 1 hour, then raised to 1060℃ and held for 1 hour. Finally, it was heat-treated at 900℃ and 500℃ for 2 hours each to obtain a neodymium iron boron permanent magnet.

[0079] Comparative Example 2

[0080] The neodymium iron boron permanent magnet was prepared according to the method of Example 2, except that the mass percentage of the main phase chemical formula was Nd. 29.5 B 0.9 Co 20 Al 0.1 Cu 0.2 Ga 0.1 Zr 0.1 Fe 49.1 The auxiliary phase chemical formula has a mass percentage of Pr. 60 Co 15 Al 25 .

[0081] The remanence, coercivity, remanence temperature coefficient (20℃~120℃), Curie temperature, and phase ratio of the iron neodymium boron permanent magnets prepared in Example 2 and Comparative Example 2 were tested according to the methods of Example 1 and Comparative Example 1. The test results are shown in Table 2.

[0082] Table 2 Performance data of NdFeB magnets prepared in Example 2 and Comparative Example 2

[0083]

[0084] Example 3

[0085] The main phase rapid solidification alloy castings and auxiliary phase rapid solidification alloy castings were prepared by melting according to the element ratios. The vacuum degree during the preparation of the main phase rapid solidification alloy castings was 3 x 10⁻⁶. -2 Pa, rotation speed 2.0 m / s, casting temperature 1380℃, vacuum degree 3x10 during preparation of the auxiliary phase rapid solidification alloy casting sheet. -2 Pa, rotation speed 2.0 m / s, casting temperature 1050℃, main phase chemical formula mass percentage Nd 24.8 Ce 4.03 La 1.24 Y 0.93 B 1.1 Cu 0.1 Co 20 Fe 47.8 The auxiliary phase chemical formula has a mass percentage of Pr. 60 Co 15 Cu 25 ;

[0086] The main phase alloy casting and the auxiliary phase alloy casting were separately powdered. The rapidly solidified alloy casting was subjected to hydrogen absorption at room temperature and a hydrogen pressure of 0.2 MPa for 3 hours, and then dehydrogenated under vacuum at 450℃ for 9 hours to obtain hydrogen-crushed powder. After that, the hydrogen-crushed powder was further crushed by air jet mill to obtain main phase alloy powder and auxiliary phase alloy powder.

[0087] The main phase alloy powder and the auxiliary phase alloy powder were mixed, with the auxiliary phase alloy powder accounting for 9% of the total weight (main phase alloy powder + auxiliary phase alloy powder). The mixed powder was then oriented and pressed in a 1.8T magnetic field and isostatically pressed under a pressure of 180MPa to obtain a magnet. Afterwards, the magnet was sintered in a vacuum sintering furnace under atmospheric isolation conditions at a sintering temperature of 1020℃. After sintering for 4 hours, the temperature was lowered to 950℃ and held for 1 hour, then raised to 1020℃ and held for 1 hour. Finally, it was heat-treated at 900℃ and 500℃ for 2 hours each to obtain a neodymium iron boron permanent magnet.

[0088] Comparative Example 3

[0089] The neodymium iron boron permanent magnet was prepared according to the method of Example 3, except that the mass percentage of the main phase chemical formula was Nd. 24.8 Ce 4.03 La 1.24 Y 0.93 B 0.9 Cu 0.1 Co 20 Fe 48.0 The auxiliary phase chemical formula has a mass percentage of Pr. 60 Co 15 Cu 25 .

[0090] The remanence, coercivity, remanence temperature coefficient (20℃~120℃), Curie temperature, and phase ratio of the iron neodymium boron permanent magnets prepared in Example 3 and Comparative Example 3 were tested according to the methods of Example 1 and Comparative Example 1. The test results are shown in Table 3.

[0091] Table 3 Performance data of NdFeB magnets prepared in Example 3 and Comparative Example 3

[0092]

[0093] This invention suppresses the formation of impurity phases and improves cobalt utilization in high-cobalt magnets through two methods to prepare high-temperature stable magnets. First, the magnet is prepared using alloy powders with different cobalt contents in the main phase and auxiliary phase. The cobalt content in the auxiliary phase alloy powder is lower than that in the main phase alloy. During sintering, due to the concentration difference of cobalt in the two powders, cobalt in the higher concentration region at the grain boundaries diffuses into the lower concentration main phase grains. Second, when the boron content of the main phase alloy powder is not less than 1.0 wt%, a boron-rich phase (RE) is generated. 1+ε The cobalt and rare earth elements introduced into the auxiliary phase (Fe4B4) react with the boron-rich phase to generate a new cobalt-containing main phase RE2(Fe,Co). 14 B. The above two methods can suppress the formation of impurity phases by cobalt and rare earth elements in the grain boundaries, and increase the cobalt content in the main phase grains, thereby improving the temperature stability of the magnet.

[0094] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0095] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a high-temperature stable sintered NdFeB permanent magnet material, comprising: After mixing the main phase alloy powder with the composition shown in formula (I) and the auxiliary phase alloy powder with the composition shown in formula (II), the mixture is subjected to orientation pressing, sintering and tempering in sequence to obtain high temperature stability sintered NdFeB permanent magnet material. The auxiliary phase alloy powder comprises 1-20 wt% of the total amount of the main phase alloy powder and the auxiliary phase alloy powder; The sintering process is specifically as follows: The oriented magnets are first sintered at 900~1100℃ for 1~6 hours, then the temperature is lowered to 800~1000℃ and held for 0.5~2 hours, and finally raised to 900~1100℃ and held for 0.5~2 hours. RE x B y Co a M b Feb 100-x-y-a-b (I), In formula (I), RE is selected from one or more of Dy, Tb, Pr, Nd, La, Ce, Y and Ho; M is selected from one or more of Al, Cu, Ga, Si, Sn, Ge, Zr, Ti, and Zn; 29≤x≤34, 1.2≤y≤1.8, 10≤a≤30, 0.1≤b≤2.0; RE c B d Co e M f Feb 100-c-d-e-f (II), In formula (II), RE is selected from one or more of Dy, Tb, Pr, Nd, La, Ce, Y and Ho; M is selected from one or more of Al, Cu, Ga, Si, Sn, Ge, Zr, Ti, and Zn; 29≤c≤70, 0≤d≤2, 0≤e<a≤20, 0.1≤f≤50.

2. The preparation method according to claim 1, characterized in that, The main phase molecules of the high-temperature stable sintered NdFeB are RE2(Fe,Co). 14 B.

3. The preparation method according to claim 1, characterized in that, The particle size of the main phase alloy powder is 1~5μm, and the particle size of the auxiliary phase alloy powder is 1~5μm.

4. The preparation method according to claim 1, characterized in that, The magnetic field strength of the orientation compression molding is 1.0~2.0T, and the pressure is 100~200MPa.

5. The preparation method according to claim 1, characterized in that, The specific preparation methods for the main phase alloy powder and the auxiliary phase alloy powder are as follows: The main phase alloy casting and the auxiliary phase alloy casting are first subjected to hydrogen crushing and then subjected to air jet milling.

6. The preparation method according to claim 5, characterized in that, The hydrogen pressure for hydrogen decomposition is independently selected from 0.1~0.5MPa, the hydrogen absorption time is independently selected from 2~5h, the hydrogen dehydrogenation temperature is independently selected from 300~500℃, and the hydrogen dehydrogenation time is independently selected from 4~8h.

7. The preparation method according to claim 5, characterized in that, The hydrogen content in the powder obtained by hydrogen crushing is independently less than 1500 ppm, and the average particle size of the powder is independently selected from 100~250 μm.

8. The preparation method according to claim 1, characterized in that, The tempering process involves first holding the material at 800-1000℃ for 2-4 hours, and then holding it at 450-600℃ for 2-4 hours.

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