Small-size high-coercivity rare earth permanent magnet material and preparation method thereof

Abstract

This invention discloses a small-sized, high-coercivity rare-earth permanent magnet material and its preparation method. It includes the following steps: (1) preparing a neodymium iron boron magnet with at least one dimension ≤ 5 mm, or processing an existing magnet to achieve at least one dimension ≤ 5 mm; (2) [The process is described in the original text, but the translation is incomplete.] ‑3 (2) Heat treatment at Pa to reduce surface oxidation; (3) Rapidly cool the heat-treated sample using a quenching process; (4) Temper the sample; (5) Process and surface treat the sample surface to obtain a small-sized, high-coercivity rare-earth permanent magnet material product with continuous grain boundary phase. This invention introduces micro-stress between grain boundaries and grains through rapid cooling, and then promotes element diffusion into the grains to form continuous grain boundaries under conditions slightly higher than the original heat treatment temperature, effectively achieving magnetic isolation between the main phase grains, thereby improving the coercivity of cerium-rich rare-earth permanent magnet materials.

Description

Technical Field

[0001] This invention relates to the field of rare earth permanent magnet materials, specifically to a small-sized, high-coercivity rare earth permanent magnet material and its preparation method. Background Technology

[0002] Nd-Fe-B possesses advantages such as high magnetic energy product and high cost-effectiveness, making it the most widely used rare-earth permanent magnet material. With the increasing demand for clean energy sources such as wind power and the promotion of electromagnetically driven electric vehicles, the demand for NdFeB rare-earth permanent magnets continues to grow.

[0003] The main technical indicators for measuring the performance of neodymium iron boron permanent magnets include remanence B. r Maximum energy product (BH) max Coercivity H c And Curie temperature T c After years of effort, based on relatively mature alloy composition design theories and optimized preparation processes, B r It has reached 1.555T, which is over 96% of the theoretical value; (BH) max It has reached 474 kJ / m 3 This is over 92% of the theoretical value. And H... c Although some improvement has been achieved, it is still only the theoretical value (H). A The low coercivity (1 / 10 to 1 / 3) of Nd results in poor temperature stability in Nd magnets, significantly limiting their application in precision instruments, aerospace, and other fields. Therefore, improving the coercivity and temperature stability of NdFeB magnets is crucial for expanding their application range. In particular, improving the coercivity of cerium-rich magnets, prepared by partially replacing Nd with the high-abundance rare-earth element cerium (Ce), is currently a key challenge for industrial application.

[0004] Optimizing the heat treatment process to form a continuous rare-earth-rich grain boundary phase in the magnet, thereby achieving demagnetization exchange coupling of the main phase grains, is an important way to improve the coercivity of the magnet. However, some literature reports that due to the excessive iron content in the grain boundary phase, the main phase grains exhibit strong magnetic exchange coupling, resulting in generally low coercivity of the magnet. The literature also reports that introducing some iron-rich grain boundary phases into the grain boundary phase consumes excess iron elements in the grain boundaries, reduces the iron content in the grain boundaries, weakens or even eliminates the magnetic exchange coupling between the main phase grains, and improves the coercivity of the magnet. In addition, constructing a wider and more continuous grain boundary phase can also improve the magnetic isolation effect of the grain boundary phase, thereby improving the coercivity of the magnet. In cerium-rich magnets, the presence of the REFe2 phase replaces a large amount of the rare-earth-rich grain boundary phase, and due to its poor wettability, it often exists in the form of agglomerated tripartite grain boundary phases or independent grains. Conventional heat treatment is difficult to improve this phenomenon, resulting in limited improvement in coercivity and limited heat treatment effect. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a small-sized, high-coercivity rare-earth permanent magnet material and its preparation method, specifically including the following steps:

[0006] (1) Sample size processing: Cerium-rich magnets with at least one dimension ≤5mm are directly prepared by sintering or hot pressing and hot deformation processes, or existing cerium-rich magnets are processed to achieve at least one dimension ≤5mm.

[0007] (2) Vacuum heat treatment: under a vacuum degree of less than 4×10 -3 Heat treatment of cerium-rich magnets under Pa conditions reduces surface oxidation.

[0008] (3) Quenching treatment: The heat-treated sample is rapidly cooled using a quenching process;

[0009] (4) Tempering treatment: Temper the rapidly cooled sample;

[0010] (5) The sample surface is processed and surface treated to obtain a small-sized high coercivity rare earth permanent magnet material product with continuous grain boundary phase.

[0011] Specifically, the cerium-rich magnet used in step (1) has the following composition: (Ce x R y A z D 1-x-y-z ) a Fe bal M c M' d B e Where Ce is a rare earth element, R is one or two rare earth elements La and Y, A is one or two rare earth elements Nd and Pr, D is one or more rare earth elements Gd, Ho, Dy and Tb, M represents one or more rare earth elements Al, Ga, Cu and Ti, M' represents one or more rare earth elements Cr, Mn, Mo, Nb, P, Si, Ta, V, Zr, Ni and Co, and B is an element, calculated as a mass percentage, satisfying 0.3≤x≤0.8, 0≤y≤0.35, 0.15≤z≤0.7, 28≤a≤35, 0.3≤c≤3, 0.05≤d≤3, and 0.85≤e≤1.3.

[0012] Specifically, the heat treatment temperature used in step (2) is 600-900℃ and the heat treatment time is 1-5h.

[0013] Specifically, the quenching medium in step (3) is either gas or liquid. The liquid quenching medium requires a temperature of 20 to 60°C, and the gas quenching medium requires a pressure of 0.25 to 2.5 MPa.

[0014] Specifically, the tempering temperature in step (4) is 420–700°C; the tempering time is 3–8 hours.

[0015] The advantages of this invention compared to the prior art are as follows:

[0016] 1) This invention employs a quenching process after the primary heat treatment, introducing interfacial micro-stress and microcracks. This promotes the formation of a more continuous and wider grain boundary phase within the magnet during the secondary tempering process, effectively achieving demagnetizing exchange coupling between grains and thus improving the magnet's coercivity. During quenching, rapid cooling causes inconsistencies in the shrinkage between grains and between grains and grain boundary phases, resulting in residual stress at the interfaces. Furthermore, residual stress also leads to the formation of microcracks. Residual stress and cracks are thermodynamically high-energy states, tending towards energy decrease during tempering. Therefore, this facilitates element diffusion into these interfacial regions during tempering, releasing stress. In this process, grain boundaries also widen and become more continuous.

[0017] 2) This invention addresses the microstructure characteristics of Ce-rich magnets by employing a high-temperature quenching process to introduce a high cooling rate, thereby eliminating a large amount of agglomerated REFe2 phase and providing favorable conditions for the introduction of continuous grain boundary phases during secondary tempering. However, rapid quenching also affects atomic movement, thus requiring slightly higher temperatures and times to compensate for element diffusion and the full formation of grain boundary phases. Therefore, this invention further employs a secondary tempering temperature slightly higher than typical heat treatment temperatures, and a slightly longer tempering holding time.

[0018] 3) When the cooling rate is too fast, microcracks can propagate into large macrocracks, even leading to sample breakage. Crack formation reduces density, resulting in a decrease in the remanence of the magnet. Therefore, this invention has extensively studied the effects of different cooling media, cooling media at different temperatures, magnets with different compositions, and heat treatment temperatures on the coercivity and other magnetic properties of the magnet. Ultimately, it was determined that the technical combination employed in this invention can effectively control the formation of macrocracks.

[0019] 4) Furthermore, during the quenching process, the significant difference in cooling rates between the interior and surface of large-sized magnets can lead to crack initiation and uneven microstructure, reducing magnetic performance indicators such as squareness. Therefore, this invention also conducted extensive experimental research on sample size, ultimately achieving a magnet with uniform microstructure and virtually no macroscopic cracks within the size limits specified in this invention, thus ensuring high coercivity while maintaining other magnetic performance indicators. Detailed Implementation

[0020] The present invention will be further described and illustrated below with reference to specific embodiments. These embodiments are merely examples of the content of this disclosure and do not limit the scope of the invention. The technical features of each embodiment of the present invention can be combined accordingly without conflict.

[0021] Example 1:

[0022] 1) A size of 50×40×4mm was obtained directly through a sintering process. 3 The sintered magnets, by mass percentage, have a composition of [(Pr 0.2 Nd 0.8 ) 0.6 Ce 0.4 ] 32 Fe bal Cu 0.2 Ga 0.4 Al 0.2 Co 0.8 Zr 0.2 B 0.9 ;

[0023] 2) The prepared magnet was subjected to vacuum heat treatment at a temperature of 750℃ for 2 hours.

[0024] 3) The magnet obtained in step 2) is quenched by oil quenching at 50°C.

[0025] 4) The quenched magnet obtained in step 3) is subjected to tempering treatment at a temperature of 650℃ for 4 hours.

[0026] 5) The magnet obtained in step 4) is subjected to surface treatment to obtain the final small-sized high coercivity rare earth permanent magnet material product with continuous grain boundary phase.

[0027] The NIM6500C permanent magnet characteristic measuring instrument test results show that the magnet's magnetic properties are B. r =12.30kG, H cj =13.50 kOe, (BH) max =34.10MGOe.

[0028] Comparative Example 1:

[0029] The difference between Comparative Example 1 and Example 1 is that step 3) of quenching was not performed; instead, the magnet obtained in step 2) was directly tempered after being cooled in the furnace. Test results from the NIM6500C permanent magnet characteristic measuring instrument showed that the magnet's magnetic properties were B. r =12.20kG, H cj = 12.60 kOe, (BH) max =33.12 MGOe, all lower than in Example 1.

[0030] Comparative Example 2:

[0031] The difference between Comparative Example 2 and Example 1 is that the tempering temperature in step 4) is different; the tempering temperature is 410°C. Test results from the NIM6500C permanent magnet characteristic measuring instrument show that the magnet's magnetic properties are B. r =12.26kG, H cj = 9.73 kOe, (BH) max =32.51 MGOe, all lower than in Example 1.

[0032] Comparative Example 3:

[0033] The difference between Comparative Example 3 and Example 1 is that the quenching medium in step 3) is different; ice water quenching at 0°C is used. The magnet broke after quenching, making performance testing impossible.

[0034] Comparative Example 4:

[0035] The difference between Comparative Example 4 and Example 1 is that the sintered magnet in step 1) has a different size, which is 50×40×30mm. 3 Macroscopic cracks appeared in the magnet after quenching. Test results from the NIM6500C permanent magnet characteristic measuring instrument showed that the magnet's magnetic properties were B. r =12.01kG, H cj = 12.73 kOe, (BH) max =30.23 MGOe, all lower than in Example 1.

[0036] Example 2:

[0037] 1) A size of 50×30×4mm was obtained directly through a sintering process. 3 The sintered magnets, by mass percentage, have the following composition:

[0038] [(Pr 0.2 Nd 0.8 ) 0.65 La 0.05 Ce 0.3 ] 32 Fe bal Cu 0.25 Ga 0.35 Al 0.35 Ti 0.15 Co 0.25 B 0.92 ;

[0039] 2) The prepared magnet was subjected to vacuum heat treatment at a temperature of 700℃ for 3 hours.

[0040] 3) The magnet obtained in step 2) is quenched using water at 20°C;

[0041] 4) Temper the magnet obtained in step 3) at a temperature of 600℃ for 6 hours.

[0042] 5) The magnet obtained in step 4) is subjected to surface treatment to obtain the final small-sized high coercivity rare earth permanent magnet material product with continuous grain boundary phase.

[0043] The NIM6500C permanent magnet characteristic measuring instrument test results show that the magnet's magnetic properties are B. r =12.71kG, H cj = 15.26 kOe, (BH) max =38.10MGOe.

[0044] Comparative Example 5:

[0045] The difference between Comparative Example 5 and Example 2 is that step 3) of quenching was not performed; instead, the magnet obtained in step 2) was directly tempered after being cooled in the furnace. Test results from the NIM6500C permanent magnet characteristic measuring instrument showed that the magnet's magnetic properties were B. r =12.58kG, H cj = 12.58 kOe, (BH) max =36.93 MGOe, all lower than in Example 2.

[0046] Example 3:

[0047] 1) A material with dimensions of Ф20×5mm was directly prepared by sintering. 3 The magnet, by mass percentage, has a composition of [(Pr 0.2 Nd 0.8 ) 0.5 Ce 0.5 ] 31.5 Fe bal Cu 0.15 Ga 0.35 Al 0.25 Co 0.35 Zr 0.15 B 0.94 ;

[0048] 2) The prepared magnet was subjected to vacuum heat treatment at a temperature of 690℃ for 5 hours.

[0049] 3) The magnet obtained in step 2) is quenched using high-pressure argon gas at 0.5 MPa;

[0050] 4) Temper the magnet obtained in step 3) at a temperature of 650°C for 8 hours.

[0051] 5) The magnet obtained in step 4) is subjected to surface treatment to obtain the final small-sized high coercivity rare earth permanent magnet material product with continuous grain boundary phase.

[0052] The NIM6500C permanent magnet characteristic measuring instrument test results show that the magnet's magnetic properties are B. r =11.81kG, H cj = 12.14 kOe, (BH) max =29.86MGOe.

[0053] Comparative Example 6:

[0054] The difference between Comparative Example 6 and Example 3 is that step 3) was not performed; instead, the magnet obtained in step 3) was cooled in the furnace and then directly tempered. Test results from the NIM6500C permanent magnet characteristic measuring instrument showed that the magnet's magnetic properties were B. r =11.76kG, H cj = 10.62 kOe, (BH) max =28.72 MGOe, both lower than in Example 3.

[0055] Comparative Example 7:

[0056] The difference between Comparative Example 7 and Example 3 is that the quenching medium in step 3) is different; 0°C ice water is used for quenching. Test results from the NIM6500C permanent magnet characteristic measuring instrument show that the magnet's magnetic properties are B. r =11.65kG, H cj = 11.02 kOe, (BH) max =27.95 MGOe, both lower than in Example 3.

[0057] The embodiments described above 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. It should be noted that 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. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A method for preparing a small-sized, high-coercivity rare-earth permanent magnet material, characterized in that, Includes the following steps: (1) Sample size processing: Cerium-rich magnets with at least one dimension ≤5mm are directly prepared by sintering or hot pressing and hot deformation processes, or existing cerium-rich magnets are processed to achieve at least one dimension ≤5mm. (2) vacuum heat treatment: heat treatment of cerium-rich magnets in an environment with a vacuum degree less than 4x10 -3 Pa to reduce surface oxidation; (3) Quenching treatment: The heat-treated sample is rapidly cooled using a quenching process; (4) Tempering treatment: Temper the rapidly cooled sample; (5) The sample surface is processed and surface treated to obtain a small-sized high coercivity rare earth permanent magnet material product with continuous grain boundary phase.

2. The method according to claim 1, characterized in that, The cerium-rich magnet used in step (1) has the following composition: (Ce x R y A z D 1-x-y-z ) a Fe bal M c M' d B e Where Ce is a rare earth element, R is one or two rare earth elements La and Y, A is one or two rare earth elements Nd and Pr, D is one or more rare earth elements Gd, Ho, Dy and Tb, M represents one or more rare earth elements Al, Ga, Cu and Ti, M' represents one or more rare earth elements Cr, Mn, Mo, Nb, P, Si, Ta, V, Zr, Ni and Co, and B is an element, calculated as a mass percentage, satisfying 0.3≤x≤0.8, 0≤y≤0.35, 0.15≤z≤0.7, 28≤a≤35, 0.3≤c≤3, 0.05≤d≤3, and 0.85≤e≤1.

3.

3. The method of claim 1, wherein, The heat treatment temperature used in step (2) is 600-900℃, and the heat treatment time is 1-5h.

4. The method of claim 1, wherein, The quenching medium in step (3) is either gas or liquid. Liquid quenching medium requires a temperature of 20 to 60°C, while gas quenching medium requires a pressure of 0.25 to 2.5 MPa.

5. The method of claim 1, wherein, The tempering temperature in step (4) is 420–700℃; the tempering time is 3–8h.