A high-thermal-conductivity r-t-b rare earth permanent magnet and a method for manufacturing the same

Abstract

The application discloses a kind of high thermal conductivity R-T-B rare earth permanent magnet and preparation method thereof, to R-T-B main alloy is added rich R auxiliary alloy, and high thermal conductivity additive powder is added simultaneously, obtain the magnet material with larger thermal conductivity;The mass ratio of main alloy, auxiliary alloy is 7.5~49:1;High thermal conductivity additive powder mass dosage is 0.1wt.%~5.0wt.% of the total mass of main alloy, auxiliary alloy.The application increases the thermal conductivity of magnet by adding the additive with higher thermal conductivity than R-T-B, accelerates the dissipation of magnet heat, reduces the temperature when magnet is used.Compared with the traditional method of adding insulation phase to improve the resistivity and resistance temperature coefficient of magnet, the application can effectively inhibit the loss of magnetic performance of motor magnet in alternating magnetic field.

Description

Technical Field

[0001] This invention relates to a high thermal conductivity RTB rare earth permanent magnet and its preparation method. Background Technology

[0002] RTB rare-earth permanent magnets are magnetic materials composed of rare-earth elements, transition elements, and boron. Among them, Nd₂Fe₂... 14 Theoretical maximum energy product (BH) max Up to 512kJ / m 3 (64.3 MGOe), magnetocrystalline anisotropic field H A Approximately 7.3T, saturation magnetic polarization J S With a charge of approximately 1.60T, it features high coercivity and high energy product and is widely used in fields such as electronics, machinery, transportation, and aerospace.

[0003] Permanent magnet materials used in permanent magnet motors include Sm-Co magnets and RTB magnets. While Sm-Co magnets have a high Curie temperature and good temperature stability, their high content of Sm and Co metals, coupled with the scarcity and high price of Sm in rare earth ores and the high price of Co as a strategic metal, limit their application. RTB rare earth permanent magnets, on the other hand, offer high magnetic properties, do not contain the strategic metal cobalt, and are relatively inexpensive, thus gaining widespread use. However, RTB rare earth permanent magnets have a low Curie temperature, their magnetic properties are significantly affected by temperature, and eddy current losses during motor operation cause the magnet to heat up, thus reducing its magnetic performance.

[0004] The resistivity of RTB rare-earth permanent magnets is approximately 150 μΩ·cm. When a motor applies a changing magnetic field to the magnet, eddy currents cause Joule heating, which heats up the magnet. As the permanent magnet temperature rises, its magnetic properties decrease, ultimately leading to a reduction in motor efficiency.

[0005] To address this decline in magnetic performance, some existing technologies employ adding an insulating phase to the magnet to increase its resistivity and temperature coefficient of resistance, thereby suppressing eddy current heating. However, neodymium iron boron magnetic materials have a thermal conductivity of 89 W / (m·K). After mixing with an insulating phase, the thermal conductivity is poor, making it difficult to dissipate heat during motor operation. This leads to heat accumulation in the magnet, causing its temperature to rise and ultimately resulting in a decrease in magnet performance. Summary of the Invention

[0006] The purpose of this invention is to provide an RTB rare-earth permanent magnet with good thermal conductivity and its manufacturing method, applicable to the field of electric motors. The principle is as follows: during motor operation, the heat of the magnet is transferred to the outside via the cooling water or fan inside the motor. If the thermal conductivity of the magnet can be increased, the efficiency of heat transfer to the outside can be improved, thereby reducing the magnet temperature and achieving the goal of reducing magnetic loss. Therefore, adding additive powder with high thermal conductivity to improve the thermal conductivity of the magnet and timely dissipate heat to reduce the temperature during motor operation is another method to improve the magnet performance of permanent magnets in electric motors.

[0007] The technical solution adopted in this invention is:

[0008] A method for preparing a high thermal conductivity RTB rare-earth permanent magnet, the method comprising:

[0009] The main alloy raw materials and auxiliary alloy raw materials are taken according to the composition ratio. The main alloy SC sheet and auxiliary alloy SC sheet are prepared by vacuum induction melting and strip spinning, respectively. The main alloy SC sheet and auxiliary alloy SC sheet are used to prepare alloy powder. The alloy powder is mixed with high thermal conductivity additive powder. The resulting mixed powder is molded into a magnet blank by an orientation magnetic field. After vacuum sintering, it is subjected to aging treatment to obtain the high thermal conductivity RTB rare earth permanent magnet.

[0010] The main alloy raw material comprises the following components by mass fraction:

[0011] R1: 29wt.%~32wt.%, where R1 is one or more of Nd, Pr, Dy, Tb, Ho, and Gd;

[0012] B: 0.9 wt.% to 1.1 wt.%;

[0013] M: 0.1–5 wt.%, M is at least one of Cu, Al, Ga, Zn, and Sn;

[0014] The balance is T and other unavoidable impurities, where T is Fe or a mixture of Fe and other transition metals, preferably Fe or Fe and Co. When T contains Co, it is preferred that more than 75.0 wt.% of T is Fe.

[0015] The auxiliary alloy raw material comprises the following components by mass fraction:

[0016] R2: 70 wt.% to 90 wt.%, R2 is at least one of Nd and Pr;

[0017] X: 10wt.%~30wt.%, where X is one or more of Al, Cu, and Ga;

[0018] Preferably, R1 contains at least one of Nd and Pr, and at least one of Dy, Tb, Ho, and Gd, wherein the mass percentage of at least one of Dy, Tb, Ho, and Gd in R1 is 0.2% to 25% of the total content of R1.

[0019] Preferably, R2 is Nd and Pr, and more preferably, the mass percentage of Nd in R2 is 55-85% of the total R2 content.

[0020] The high thermal conductivity additive powder is a powder particle with a thermal conductivity higher than that of NdFeB (89 W / m·K), and the powder particle size is less than 10 μm, preferably less than 2 μm, and more preferably 0.1-2 μm; the purity is 99 wt.% or more.

[0021] In the alloy powder, the mass ratio of the main alloy to the auxiliary alloy is 7.5 to 49:1, preferably 9 to 49:1, and more preferably 9 to 19:1.

[0022] The high thermal conductivity additive powder is used in an amount of 0.1 wt.% to 5.0 wt.% (preferably 0.1 wt.% to 3.0 wt.%) of the alloy powder.

[0023] The amount of high thermal conductivity additive powder added is 0.1-5 wt.%, and preferably 0.1-3 wt.%. If the amount exceeds 5 wt.%, the magnet cannot achieve a favorable density by ordinary vacuum sintering, resulting in deterioration of magnetic properties.

[0024] In the method of this invention, a R-rich auxiliary alloy is added in an amount of 2 wt.% to 12 wt.%, preferably 5 to 10 wt.%. If the amount is less than 2 wt.%, sintering becomes difficult, and the density of the magnet is not fully increased. If the amount exceeds 12 wt.%, satisfactory magnetic properties may not be obtained.

[0025] The preferred auxiliary alloy raw material is:

[0026] R2: 80~85wt.%, X: 15~20wt.%.

[0027] Auxiliary alloys can improve the wetting angle between the grain boundary phase and the main phase grains.

[0028] Preferably, the high thermal conductivity additive powder is one or both of CuCrZr powder and diamond powder.

[0029] In the sintered magnet of the present invention, the CuCrZr powder or diamond powder preferably has a particle size of less than 2 μm. Particle sizes smaller than 0.1 μm may not have a significant effect on increasing thermal conductivity, while particle sizes larger than 10 μm may interfere with the compactness of the magnet and reduce its performance.

[0030] The fine dispersion of chromium-zirconium-copper particles and diamond powder within the sintered body ensures relatively high thermal conductivity of the magnet in the temperature range equal to or below the Curie point. This is likely because the thermal conductivity of CuCrZr powder and diamond powder is higher than that of R2Fe. 14 Compound B.

[0031] The alloy powder is prepared by separately hydrogenating the main alloy SC sheet and the auxiliary alloy SC sheet, then mixing them, and finally preparing the alloy powder by air jet milling.

[0032] Furthermore, the average particle size of the obtained alloy powder is 0.01-10 μm, more preferably 0.1-5 μm, and most preferably 2-4 μm.

[0033] The orientation magnetic field is preferably used for molding to obtain a blank under a magnetic field of 800-2000 kA / m (more preferably 1300-2000 kA / m) and a pressure of 90-150 MPa (more preferably 100-120 MPa).

[0034] The vacuum sintering is preferably carried out in a vacuum at 1050-1200℃ to form the blank.

[0035] The aging process includes a first-stage aging process in a vacuum at 850-1000°C, followed by cooling in an argon atmosphere, and then a second-stage aging process in a vacuum at 400-600°C.

[0036] The preferred processing time for Level 1 timeliness is 3 to 6 hours; the preferred processing time for Level 2 timeliness is 3 to 6 hours.

[0037] This invention also provides a high thermal conductivity RTB rare-earth permanent magnet prepared by the above method, having R2T 14 Type B crystals have a main crystal phase and a grain boundary phase structure, wherein the grain boundary phase consists of 0.05-20 v% powder phase (preferably 0.5-5.0 v% powder phase) and the balance being a R-rich phase. The R-rich phase is uniformly distributed along the main crystal phase, with a thickness of <0.1 μm, typically around 2-3 nm. The powder phase is a high thermal conductivity additive powder that can be uniformly distributed within the grain boundary phase, exhibiting good adhesion to other phases and resisting detachment.

[0038] The high thermal conductivity RTB rare-earth permanent magnet preferably comprises the following components:

[0039] R: 25-32 wt.%, R is one or more of Nd, Pr, Dy, Tb, Ho, and Gd, and necessarily contains at least one of Nd and Pr.

[0040] B: 0.8-1.0 wt.%

[0041] M: 0.1-3.0 wt.%, M is at least one of Cu, Al, Ga, Zn, and Sn; and necessarily contains at least one of Al, Cu, and Ga;

[0042] Powder phase: 0.1-3.0 wt.%

[0043] The balance is T and other unavoidable impurities.

[0044] The impurities include O, C, N, Si, Cl, etc.

[0045] This invention adds a nitrogen-rich auxiliary alloy (II) to the RTB main alloy (I) and simultaneously adds additive powders with high thermal conductivity. During sintering, this pins grain boundaries, preventing grain growth and refining the grains. This increases the overall thermal conductivity of the sintered magnet.

[0046] The RTB rare earth permanent magnet provided by the present invention has a thermal conductivity of 89 W / (m·K) or higher at 20℃, and preferably a thermal conductivity of 100 W / (m·K) or higher at 20℃.

[0047] The RTB rare earth sintered magnet provided by this invention has optimized magnetic properties, improved magnet coercivity and thermal conductivity, and can reduce the temperature of RTB rare earth permanent magnets during use, thereby reducing magnetic loss. It effectively solves the problem of magnet heating during motor operation leading to performance degradation, and improves the stability of the product during use. Therefore, it can be used in the field of motor manufacturing.

[0048] Compared to existing technologies, the present invention allows for the low-cost manufacture of magnets with high coercivity and high thermal conductivity that reduces heat buildup due to eddy currents under operating conditions where the magnet is exposed to an alternating magnetic field (e.g., in an electric motor). Therefore, a low-loss RTB sintered body characterized by high thermal conductivity and controlled eddy current generation can be obtained.

[0049] The method of the present invention is suitable for manufacturing low-loss sintered magnets with a thermal conductivity of at least 100 W / (m·K), especially at least 120 W / (m·K), without sacrificing magnet properties.

[0050] This invention increases the thermal conductivity of the magnet by adding an additive with a higher thermal conductivity than RTB, thereby accelerating heat dissipation and lowering the magnet's operating temperature. Compared to traditional methods of adding an insulating phase to increase the magnet's resistivity and temperature coefficient of resistance, this invention effectively suppresses the loss of magnetic properties of the motor magnet under an alternating magnetic field. Attached Figure Description

[0051] Figure 1 A diagram of the experimental setup for measuring the magnetic loss of a magnet under an alternating magnetic field. Figure 1Figure a shows the experimental setup for measuring the magnetic loss of a magnet, and Figure b shows the internal structure of the induction coil.

[0052] Figure 2 The image shown is the backscattered image of Comparative Example 2, measured by SEM.

[0053] Figure 3 The image shows the backscattered image of Example 6, measured by SEM. Detailed Implementation

[0054] The technical solution of the present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0055] Thermal conductivity is a measure of a material's ability to conduct heat. It refers to the amount of heat transferred per unit time through a unit horizontal cross-sectional area when the temperature gradient is 1℃ / m vertically downwards. It can be expressed as:

[0056]

[0057] E: Calorific value (W)

[0058] t: time (sec)

[0059] λ: Thermal conductivity (W / (m·K))

[0060] A: Area (m²) 2 )

[0061] l: Length (m)

[0062] θ: Temperature (K)

[0063] The preparation of RTB rare-earth sintered magnets will now be explained. In short, the sintered magnet is prepared as follows: it is pulverized in nitrogen atmosphere by a jet of gas.

[0064] (I) RTB main alloy,

[0065] (II) R-rich auxiliary alloys and;

[0066] Mix with (III) CuCrZr powder or diamond powder;

[0067] The mixture is shaped into a molded body in a magnetic field; the molded body is then sintered and heat-treated. As described above, R is at least one of Nd, Pr, Dy, Tb, Ho, and Gd; M is at least one of Cu, Al, Ga, Zn, and Sn; T is Fe or a mixture of Fe and other transition metals; and B is boron.

[0068] It is recommended to add (III) additive powder, CuCrZr powder or diamond powder, after the pulverization step. CuCrZr and diamond powders have a particle size of 0.1-5 μm. Powders with excessively small particle sizes will be sieved out by the sorting wheel during the air jet milling process. The preferred additive powder size is 0.1-2 μm, which allows for better bonding with grain boundaries. Furthermore, CuCrZr or diamond powders have greater hardness than the main phase alloy and auxiliary alloy. If they are crushed together with the main phase alloy and auxiliary alloy in nitrogen, the powder particle size may become too small, reducing material utilization.

[0069] The amount of CuCrZr powder or diamond powder added is 0.1-5 wt.%, and preferably 0.1-3 wt.%. If the amount exceeds 5 wt.%, the magnet cannot achieve a favorable density by ordinary vacuum sintering, and special sintering such as hot isostatic pressing (HIP) must be used, which leads to deterioration of magnetic properties.

[0070] When CuCrZr powder or diamond powder is added, it can have a maximum size of 5 μm, preferably a maximum size of 2 μm. The above process ensures the uniform dispersion of the CuCrZr powder phase or diamond powder phase in the sintered body, thereby increasing the thermal conductivity of the sintered body.

[0071] In the method of this invention, a R-rich auxiliary alloy (II) is added in an amount of 2 wt.% to 12 wt.%, preferably 5 to 10 wt.%, which is essentially composed of 70 wt.% to 90 wt.% R and 10 wt.% to 30 wt.% X; wherein R is at least one of Nd and Pr, and X is one or more of Al, Cu, and Ga. If the amount is less than 2 wt.%, sintering becomes difficult, and the density of the magnet is not fully increased. If the amount exceeds 12 wt.%, satisfactory magnetic properties may not be obtained.

[0072] The RTB master phase alloy powder (I) used here is the matrix alloy of the magnet (or the alloy that forms the master phase of the magnet) and is essentially composed of 29 wt.% to 32 wt.% R, 0.9 wt.% to 1.1 wt.% B, 0 to 5 wt.% M, and the balance being T and other unavoidable impurities, wherein R is at least one of Nd, Pr, Dy, Tb, Ho, and Gd, M is at least one of Cu, Al, Ga, Zn, and Sn, and T is Fe or a mixture of Fe and other transition metals. It contains R2Fe 14 B. An alloy with an intermetallic compound as the main phase. The amount of alloy powder (I) added is the weight percentage of (II) and powder (III) plus the amount of the remainder reaching 100%.

[0073] According to the method of the invention, an RTB sintered magnet is prepared by pulverizing (I) and (II) in nitrogen gas by jet gas flow; mixing and combining the pulverized material and (III); shaping the mixture into a molded body in a magnetic field; sintering and heat-treating. In a preferred embodiment, the mixture is pulverized in nitrogen gas flow by jet gas flow to an average particle size of 0.01-10 μm, more preferably 0.1-5 μm, and most preferably 3-4 μm. The pulverized mixture is then shaped under a magnetic field of 800-2000 kA / m, especially 1300-2000 kA / m, and a pressure of 90-150 MPa, especially 100-120 MPa. The molded blank is sintered in vacuum at 1050-1200 °C, and the heat treatment step includes a first-stage aging treatment in vacuum at 850-1000 °C, cooling in an argon atmosphere, and a second-stage aging treatment in vacuum at 400-600 °C. Thus, an RTB sintered magnet is obtained.

[0074] Examples 1-5 and Comparative Example 1

[0075] In Examples 1-5, the RTB magnet master alloy was prepared by weighing predetermined amounts of Nd (at least 99 wt.% purity), Dy (at least 99 wt.% purity), Fe (at least 99 wt.% purity), Al, and an iron-boron alloy; high-frequency melting in an argon atmosphere; and rapid cooling in an argon atmosphere using a rapid solidification sheet technique. The alloy was obtained by tape spinning. The composition of the resulting RTB magnet master alloy SC sheet was: 25 wt.% Nd, 3 wt.% Dy, 0.2 wt.% Al, 1 wt.% B, 0.01 wt.% C, with the balance being Fe. The master alloy SC sheet was then crushed by hydrogen absorption to obtain hydrogen-broken master alloy powder. Hydrogen absorption crushing included absorbing hydrogen at room temperature until the pressure in the hydrogenation chamber did not change, and then heat-treating in a vacuum at 550°C for 2 hours to release hydrogen.

[0076] A praseodymium-neodymium alloy, Al, and Cu of at least 99 wt.% purity were weighed and melted at high frequency in an argon atmosphere, followed by rapid cooling in an argon atmosphere using a rapid solidification sheet technique. The alloy was obtained by tape spinning. The resulting auxiliary alloy SC sheet had the following composition: 55 wt.% Nd, 30 wt.% Pr, 10 wt.% Al, and 5 wt.% Cu. Hydrogenation was then performed to obtain hydrogenated auxiliary alloy powder.

[0077] RTB magnet main alloy hydrogen-rich powder and R-rich auxiliary alloy hydrogen-rich powder were mixed at a weight ratio of 9:1 and pulverized by an air jet mill in N2 gas. The powder mixture and CuCrZr powder were weighed at weight ratios of 99:1, 49:1, 97:3, 19:1, and 9:1, respectively, and mixed in a three-dimensional rotary mixer. The resulting fine powder had an average particle size of 2-5 μm.

[0078] Fine powder was poured into a mold and oriented in a magnetic field of 1750 kA / m, and shaped under a pressure of 105 MPa perpendicular to the magnetic field direction. The resulting molded body was sintered at 1080 °C in a vacuum atmosphere for 4 hours, cooled, and then aged for 3 hours at 900 °C in an argon atmosphere (first stage), cooled, and then aged for 4 hours at 600 °C in an argon atmosphere (second stage). Permanent magnet materials with different compositions were thus prepared.

[0079] Comparative Example 1 was prepared using the same procedure as above, except that CuCrZr powder was not added to Comparative Example 1.

[0080] The magnetic and thermal conductivity of the sintered magnets prepared in Examples 1-5 and Comparative Example 1 were measured. The results are shown in Table 1.

[0081] Table 1

[0082]

[0083] As shown in Table 1, compared with magnets without CuCrZr powder, in magnets with added CuCrZr powder, the remanence (Br) decreases slightly with increasing CuCrZr powder content, while the coercivity (Hcj) remains essentially unchanged or increases in some cases. Simultaneously, the thermal conductivity of the magnet also increases accordingly. However, when the CuCrZr powder content exceeds 5%, the magnet density decreases, and pores appear within the magnet, leading to a decline in its magnetic properties.

[0084] Each magnet obtained from the above procedure is processed into a rectangular prism sheet of 20mm × 20mm × 5mm (thickness). It is first saturated with magnets, and then the magnetic flux is measured. The magnets are then fitted into a simulated motor structure composed of silicon steel sheets and AC coils, as shown in the simulation structure. Figure 1 As shown, the magnet sample to be tested was placed between a cuboid box composed of silicon steel sheets and an AC coil. The magnet and the bottom surface of the silicon steel sheet box, as well as the top of the AC coil, were placed in close contact. Cooling water pipes passed parallel through the silicon steel sheets, transferring heat through the sheets to cool the magnet. The cooling water flow rate was controlled at a certain speed, and the AC coil was run at the same power and time. Finally, the magnetic flux of the sample was tested, and the magnetic loss after operation was calculated. The results are shown in Table 2. Table 2 shows that the addition of CuCrZr powder increases the thermal conductivity of the magnet, thus facilitating heat transfer and reducing magnetic loss.

[0085] Table 2

[0086]

[0087] Examples 6-9 and Comparative Example 2

[0088] The RTB main alloy hydrogen-burst powder and the R-rich auxiliary alloy hydrogen-burst powder prepared in Examples 1-5 were mixed at a weight ratio of 9:1 and pulverized by an air jet mill in N2 gas. This powder mixture and diamond powder were weighed at weight ratios of 99:1, 49:1, 97:3, and 19:1 and mixed in a three-dimensional rotary mixer. The resulting fine powder had an average particle size of 2-5 μm. The fine powder was poured into a mold and oriented in a magnetic field of 1750 kA / m and shaped under a pressure of 105 MPa perpendicular to the magnetic field direction. The shaped body was sintered at 1080 °C in a vacuum atmosphere for 4 hours, cooled, and aged for 3 hours at 900 °C in an argon atmosphere (first stage), cooled, and aged for 4 hours at 600 °C in an argon atmosphere (second stage). Permanent magnet materials with different compositions were thus prepared.

[0089] Comparative Example 2 was prepared using the same procedure as above, except that diamond powder was not added to Comparative Example 2.

[0090] The magnetic properties, thermal conductivity, and resistivity of the sintered magnets prepared in Examples 6-9 and Comparative Example 2 were measured. The results are shown in Table 3.

[0091] Table 3

[0092]

[0093] Each magnet obtained from the above procedure was processed into a 20mm × 20mm × 5mm (thickness) cuboid sheet. It was first saturated with magnets, and then the magnetic flux was measured. The magnets were then placed in a simulated structure, and cooling water was controlled at a certain flow rate. An AC coil was then run at the same power and for the same duration. Finally, the magnetic flux of the sample was tested, and the magnetic loss after operation was calculated. The results are shown in Table 4.

[0094] Table 4

[0095]

[0096]

[0097] Table 3 shows that compared to magnets without diamond powder, the thermal conductivity of magnets with added diamond powder increases and the resistivity decreases with increasing diamond powder content. Table 4 confirms that although the magnet resistivity decreases and generates more heat, the increased thermal conductivity from the addition of diamond powder lowers the magnet temperature, thus reducing magnetic loss. Furthermore, the scanning electron microscope images of Comparative Example 2 and Example 6 samples show that in Example 6, the added diamond powder is uniformly dispersed within the magnet (the dark dots in the image represent diamond powder), thereby increasing the magnet's thermal conductivity.

[0098] Examples 10-13, Comparative Example 3

[0099] The RTB main alloy hydrogen-burst powder and R-rich auxiliary alloy hydrogen-burst powder prepared in Examples 1-5 were mixed at weight ratios of 49:1, 19:1, 9:1, and 7:1, respectively, and pulverized by an air jet mill in N2 atmosphere. The mixtures of different component powders and diamond powder were weighed at a weight ratio of 97:3 and mixed in a three-dimensional rotary mixer. The resulting fine powder had an average particle size of 2-5 μm. The fine powder was poured into a mold and oriented in a magnetic field of 1750 kA / m and shaped under a pressure of 105 MPa perpendicular to the magnetic field direction. The shaped body was sintered at 1080 °C in a vacuum atmosphere for 4 hours, cooled, and aged for 3 hours at 900 °C in an argon atmosphere (first stage), cooled, and aged for 4 hours at 600 °C in an argon atmosphere (second stage). Permanent magnet materials with different compositions were thus prepared.

[0100] Comparative Example 3 was prepared using the same procedure as above, except that no auxiliary alloy powder was added to Comparative Example 3.

[0101] The magnetic and thermal conductivity of the sintered magnets prepared in Examples 10-13 and Comparative Example 3 were measured. The results are shown in Table 5.

[0102] Table 5

[0103]

[0104]

[0105] As shown in Table 5, compared with magnets without auxiliary alloys, in magnets with added auxiliary alloys, the coercivity (Hcj) first increases and then decreases with increasing auxiliary alloy content, while the remanence (Br) changes relatively little. However, when the auxiliary alloy content increases to 12.5 wt.%, the remanence (Br) decreases significantly. This is because the addition of auxiliary alloys can improve the wetting angle between the main phase and the grain boundary phase, allowing the Nd-rich phase to distribute better along the main phase grain boundaries and refining the grains. However, excessive auxiliary alloys reduce the remanence of the magnet.

[0106] As shown in Table 5, compared with magnets without auxiliary alloys, the thermal conductivity of magnets with added auxiliary alloys increases slightly with the increase of auxiliary alloy content, thereby reducing magnetic loss. However, the increase in thermal conductivity with increasing auxiliary alloy content is not significant and shows a decreasing trend. This may be because the refined grain boundaries become more complex, which reduces the thermal conductivity of the magnet and thus increases the magnetic loss.

[0107] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high thermal conductivity RTB rare-earth permanent magnet, characterized in that... The method is as follows: The main alloy raw materials and auxiliary alloy raw materials are taken according to the composition ratio. The main alloy SC sheet and auxiliary alloy SC sheet are prepared by vacuum induction melting and strip spinning, respectively. The main alloy SC sheet and auxiliary alloy SC sheet are used to prepare alloy powder. The alloy powder is mixed with high thermal conductivity additive powder. The resulting mixed powder is molded into a magnet blank by an orientation magnetic field. After vacuum sintering, it is subjected to aging treatment to obtain the high thermal conductivity RTB rare earth permanent magnet. The main alloy raw material comprises the following components by mass fraction: R1: 29wt.%~32wt.%, where R1 is one or more of Nd, Pr, Dy, Tb, Ho, and Gd; B: 0.9wt.%~1.1wt.%; M: 0.1~5wt.%, M is at least one of Cu, Al, Ga, Zn, and Sn; The balance is T and other unavoidable impurities, where T is Fe or a mixture of Fe and other transition metals; The auxiliary alloy raw material comprises the following components by mass fraction: R2: 70wt.%~90wt.%, R2 is at least one of Nd and Pr; X: 10wt.%~30wt.%, where X is one or more of Al, Cu, and Ga; The high thermal conductivity additive powder is a powder particle with a thermal conductivity higher than that of NdFeB, with a particle size of less than 10 μm and a purity of more than 99 wt.%. In the alloy powder, the mass ratio of the main alloy to the auxiliary alloy is 7.5~49:1; The high thermal conductivity additive powder is used in an amount of 0.1 wt.% to 5.0 wt.% of the alloy powder. The high thermal conductivity additive powder is one or both of CuCrZr powder and diamond powder.

2. The method as described in claim 1, characterized in that... In the alloy powder, the mass ratio of the main alloy to the auxiliary alloy is 9~49:1; The mass amount of the high thermal conductivity additive powder is 0.1 wt.% to 3.0 wt.% of the mass of the alloy powder.

3. The method as described in claim 1, characterized in that... The auxiliary alloy raw material comprises the following components by mass fraction: R2: 80~85wt.%, X: 15~20wt.%.

4. The method as described in claim 1, characterized in that... The high thermal conductivity additive powder has a particle size of less than 2 μm.

5. The method as described in claim 1, characterized in that... The alloy powder is prepared by first hydrogenating the main alloy SC sheet and the auxiliary alloy SC sheet, then mixing them, and finally preparing the alloy powder by air jet milling.

6. The method as described in claim 1, characterized in that... The average particle size of the alloy powder is 0.01-10 μm.

7. The high thermal conductivity RTB rare-earth permanent magnet prepared by the method according to any one of claims 1 to 6, wherein the magnet has an R2T 14 Type B crystal structure consisting of a main crystal phase and a grain boundary phase, wherein the grain boundary phase is composed of 0.05-20 v% of powder phase and the balance of R-rich phase.

8. The high thermal conductivity RTB rare-earth permanent magnet as described in claim 7, characterized in that... The R-rich phase is uniformly distributed along the main crystal phase with a thickness of <0.1μm; the powder phase is a high thermal conductivity additive powder, which is uniformly distributed in the grain boundary phase.

9. The high thermal conductivity RTB rare-earth permanent magnet as described in claim 7, characterized in that... The high thermal conductivity RTB rare-earth permanent magnet comprises the following components: R: 25-32 wt.%, R is one or more of Nd, Pr, Dy, Tb, Ho, and Gd, and necessarily contains at least one of Nd and Pr; B: 0.8-1.0 wt.%; M: 0.1-3.0 wt.%, M is at least one of Cu, Al, Ga, Zn, and Sn; and necessarily contains at least one of Al, Cu, and Ga; Powder phase: 0.1-3.0 wt.%; the powder phase is a high thermal conductivity additive powder; The balance is T and other unavoidable impurities; T is Fe or a mixture of Fe and other transition metals.

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