R-FE-B SINTERED MAGNET, PREPARATION METHOD AND USE THEREOF

Abstract

An RFeB sintered magnet, and a preparation method therefor and use thereof are provided. The surface of the RFeB sintered magnet has an oxide adhesive layer, and is obtained by means of the heat preservation and heat treatment of an RFeB magnet having a composite diffusion layer on the surface thereof. The heat treatment comprises alternately carrying out a low-temperature heat treatment at 750? C.-830? C. and a high-temperature heat treatment at 830? C.-970? C., and a neodymium iron boron green body having the oxide adhesive layer on the surface thereof is obtained. The grain boundary diffusion of the RFeB magnet is optimized, and the coercive force distribution of the magnet is improved. The RFeB sintered magnet can be used in the field of automobiles, wind power generation, household electric motors, medical apparatuses or mobile communication appliances.

Claims

1. A sintered RFeB magnet, wherein the surface of the sintered RFeB magnet has an oxide adhesive layer; and Hcj on the surface of the sintered RFeB magnet in an orientation direction of the magnet is H1, Hcj from the surface of the magnet along the orientation direction of the magnet to a position 2.00?0.02 ?mm inside the magnet is H2, and the difference between H1 and H2 is not more than 50 kA/m; preferably, the H1 and the H2 have a relationship as shown in formula (I): $\begin{array}{cc}H2-H1?50\mathrm{kA}/m& \left(I\right)\end{array}$

2. The sintered RFeB magnet as claimed in claim 1, wherein the oxide adhesive layer has a thickness of less than 20 ?m, preferably less than or equal to 10 ?m; preferably, the oxide adhesive layer comprises at least one of zirconium oxide, calcium oxide, aluminum oxide, and holmium oxide.

3. The sintered RFeB magnet as claimed in claim 1, wherein the sintered RFeB magnet is obtained by subjecting an RFeB magnet blank to a temperature holding heat treatment; the RFeB magnet blank comprises an RFeB magnet and a composite diffusion layer, the composite diffusion layer being disposed on the surface of the RFeB magnet; and after the composite diffusion layer is subjected to the temperature holding heat treatment, a metal oxide therein forms an oxide adhesive layer; preferably, the temperature holding heat treatment comprises alternately performing a low-temperature heat treatment and a high-temperature heat treatment; preferably, the low-temperature heat treatment has a temperature range of 750? C.-830? C.; preferably, the high-temperature heat treatment has a temperature range of 830? C.-970? C.; preferably, the oxide adhesive layer can be removed by means of non-mechanical grinding; and preferably, the RFeB magnet blank comprises an RFeB magnet and a composite diffusion layer, the composite diffusion layer being disposed on the surface of the RFeB magnet.

4. The sintered RFeB magnet as claimed in claim 1, wherein a thickness in an orientation direction of the RFeB magnet is Z, and Z is greater than or equal to 3.95 ?mm; preferably, Z is not less than 3.95 ?mm and not greater than 15.05 ?mm; preferably, a dimensional tolerance of Z is ?0.05 ?mm, for example, ?0.03 ?mm; preferably, in the RFeB magnet, R is selected from any one or more of rare earth elements Nd, Pr, Tb, Dy, Gd and Ho; preferably, in the RFeB magnet, R has a content of 27 wt %-34 wt %; preferably, in the RFeB magnet, B has a content of 0.8 wt %-1.3 wt %; preferably, the RFeB magnet further comprises Fe and M, wherein M is selected from at least one of Ti, V, Cr, Mn, Co, Ga, Cu, Si, Al, Zr, Nb, W, and Mo; and preferably, in the RFeB magnet, M has a content of 0 wt %-5 wt %.

5. The sintered RFeB magnet as claimed in claim 1, wherein the composite diffusion layer has a total thickness of less than 200 ?m; preferably, the composite diffusion layer comprises a heavy rare earth element, and preferably comprises a heavy rare earth element, a metal oxide, an organic solid, and optionally a solvent present or absent; preferably, the heavy rare earth element is selected from at least one of metal dysprosium, metal terbium, dysprosium hydride, terbium hydride, dysprosium fluoride, terbium fluoride, dysprosium oxide, and terbium oxide; preferably, the metal oxide is selected from at least one of zirconium oxide, calcium oxide, aluminum oxide, and holmium oxide; preferably, the organic solid is selected from at least one of rosin-modified alkyd resin, thermoplastic phenolic resin, urea-formaldehyde resin, and polyvinyl butyral; preferably, the solvent is selected from at least one of an alcohol solvent, an ether solvent, and an aromatic hydrocarbon solvent, preferably an alcohol solvent, such as ethanol; preferably, the composite diffusion layer comprises an RH layer and an RL layer, wherein the RH layer comprises a heavy rare earth, an organic solid, and optionally a solvent present or absent; the RL layer comprises a metal oxide, an organic solid, and optionally a solvent present or absent; preferably, the number of each of the RH layer and the RL layer is independently at least 1; preferably, the RH layer and the RL layer are alternately disposed in sequence; preferably, when the RH layer and the RL layer are alternately disposed, an outer layer far from the surface of the RFeB magnet is preferably the RL layer; preferably, the RH layer has a single-layer thickness selected from 0.5 ?m-40 ?m; preferably, the RL layer has a single-layer thickness selected from 0.5 ?m-15 ?m; and preferably, the weight of the composite diffusion layer is 0.1 wt %-3 wt % of the weight of the RFeB magnet.

6. A preparation method of the sintered RFeB magnet as claimed in claim 1, wherein the preparation method comprises the following steps: (1) disposing a composite diffusion layer on the surface of an RFeB magnet by coating to form the RFeB magnet blank; and (2) performing a temperature holding heat treatment on the RFeB magnet blank in vacuum or in an inert gas atmosphere to obtain a sintered magnet having an oxide adhesive layer on the surface thereof; preferably, the temperature holding heat treatment comprises alternately performing a low-temperature heat treatment and a high-temperature heat treatment, wherein the low-temperature heat treatment has a temperature range of 750? C.-830? C., and the high-temperature heat treatment has a temperature range of 830? C.-970? C.; preferably, the total time for the temperature holding heat treatment is more than or equal to 8 h; preferably, the preparation method further comprises performing an aging heat treatment after the temperature holding heat treatment; and preferably, the aging heat treatment comprises quenching to room temperature after the temperature holding heat treatment, then heating to 430? C.-650? C. for an aging treatment, and quenching to room temperature after holding the temperature for 1 h-72 h.

7. The preparation method of the sintered RFeB magnet as claimed in claim 6, wherein the disposing the composite diffusion layer by coating comprises coating the surface of the RFeB magnet with a slurry, and then drying to form the composite diffusion layer; preferably, the coating can be performed by at least one of coating methods such as brush coating, roll coating, dipping, spray coating, and the like; preferably, after the drying, the weight of the RFeB magnet blank is increased by 0.1 wt %-3 wt % compared with that of the RFeB magnet; preferably, the slurry has a solid content of 30 wt %-90 wt %; and preferably, the slurry is selected from an RH layer slurry and/or an RL layer slurry.

8. The preparation method of the sintered RFeB magnet as claimed in claim 6, wherein the RH layer slurry comprises a heavy rare earth element, an organic solid, and a solvent, wherein preferably, the heavy rare earth element, the organic solid, and the solvent are in a mass ratio of (40-70):(3-10):(20-50); preferably, the RL layer slurry comprises a metal oxide, an organic solid, and a solvent, wherein preferably, the metal oxide, the organic solid, and the solvent are in a mass ratio of (30-70):(3-10):(20-50); preferably, a method for preparing the slurry comprises: adding the metal oxide, the heavy rare earth element, and the organic solid to the solvent, and stirring to form a homogeneous slurry; preferably, the RL layer slurry comprises 55 wt % zirconium oxide, 5 wt % rosin-modified alkyd resin, and 40 wt % ethanol; and the RH layer slurry comprises 60 wt % terbium fluoride, 5 wt % rosin-modified alkyd resin, and 35 wt % ethanol; preferably, the RL layer slurry comprises 50 wt % aluminum oxide, 6 wt % rosin-modified alkyd resin, and 44 wt % ethanol; and the RH layer slurry comprises 55 wt % terbium fluoride, 5 wt % rosin-modified alkyd resin, and 40 wt % ethanol; preferably, the coating further comprises coating the surface of the RFeB magnet several times with the slurry; preferably, when the coating with the slurry is performed several times, the slurry may be the same or different, preferably different; preferably, the composite diffusion layer after drying is formed by alternately disposing the RH layer and the RL layer; and preferably, the temperature holding heat treatment or the aging heat treatment is performed in vacuum or in an inert gas atmosphere.

9. Use of the sintered RFeB magnet as claimed in claim 1 in the fields of automobiles, wind power generation, household motors, medical equipment, or mobile communication devices, preferably in the field of new energy automobiles.

10. A motor, wherein the motor comprises the sintered RFeB magnet as claimed in claim 1; preferably, the motor comprises a power output motor, a steering EPS motor, and a micro motor; and preferably, the micro motor comprises an electric water pump motor, a fog lamp motor for steering linkage, a skylight motor, an air conditioner motor, a wiper motor, and the like.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0098] FIG. 1 shows EPMA analysis at different positions on a sintered magnet according to Example 1.

DETAILED DESCRIPTION

[0099] The technical solutions of the present disclosure will be further described in detail with reference to the following specific examples. It should be understood that the following examples are merely exemplary illustrations and explanations of the present disclosure, and should not be construed as limiting the protection scope of the present disclosure.

[0100] Unless otherwise stated, the starting materials and reagents used in the following examples are all commercially available products, or can be prepared by using known methods.

[0101] A method for analyzing grain boundary phase and main phase structures in the present disclosure is as follows: scanning a fracture of a blank by EPMA, processing a CP image of EPMA by using ImagePRO software, and analyzing the width, the length and the like of the grain boundary.

Example 1

[0102] Firstly, a neodymium-iron-boron magnet (RFeB magnet) was provided, and the magnet was processed to form a magnetic sheet. The surface of the magnetic sheet was washed with an acid solution and deionized water, and then dried to obtain a neodymium-iron-boron magnet M1. The magnetic sheet had dimensions of 40 ?mm?20 ?mm?6 ?mm and a dimensional tolerance of ?0.03 mm. The thickness in the orientation direction of the magnet M1 was Z=6 ?mm, and components of M1 are shown in the table below.

[0103] An RH slurry was prepared from terbium hydride as a heavy rare earth element powder, rosin-modified alkyd resin powder as an organic solid, and ethanol with weight percentages of 60 wt %, 5 wt %, and 35 wt %, respectively. An RL slurry was prepared from zirconium oxide as a metal oxide, rosin-modified alkyd resin powder as an organic solid, and ethanol with weight percentages of 55 wt %, 5 wt %, and 40 wt %, respectively. An RH layer, an RL layer, an RH layer, and an RL layer were sequentially disposed on the surface of the magnet by means of dipping and hot air drying to form a composite diffusion layer, so as to obtain an RFeB magnet blank, where the RH layer had a thickness of 20?5 ?m, the RL layer had a thickness of 3?2 ?m, and the composite diffusion layer accounted for 1.2?0.2% by weight of the magnet M1.

[0104] The treated RFeB magnet blank with the composite diffusion layer described above on the surface was placed in a material box for diffusion temperature holding heat treatment in a heat treatment device. The heat treatment process was in a vacuum state, and heating was started when the vacuum degree was less than or equal to 10 Pa. The diffusion heat treatment process was set as follows: [0105] (1) heating: (50-780) ? C.?100 ?min; [0106] (2) low-temperature diffusion heat treatment: 780? C.?240 ?min; [0107] (3) heating: (780-920) ? C.?30 ?min; [0108] (4) high-temperature diffusion heat treatment: 920? C.?240 ?min; [0109] (5) low-temperature diffusion heat treatment: 780?240 ?min (no heating power output during heat treatment at the stage of cooling to 780? C.); [0110] (6) heating: (780-920) ? C.?30 ?min; and [0111] (7) high-temperature diffusion heat treatment: 920? C.?240 ?min.

[0112] The diffusion heat treatment was followed by quenching, and after the quenching was finished, the system was heated to 500? C. for aging treatment (the aging treatment refers to a heat treatment process in which alloy workpieces, after solution treatment, cold plastic formation or casting and forging, are placed at a high temperature or kept at room temperature to maintain the variation in performance, shape and size over time). The temperature was held for 4 h, and then the system was quenched again to room temperature to obtain a sintered magnet M2. The RFeB magnet blanks were in a contact arrangement during the heat treatment, and there was no adhesion of the sintered magnets after diffusion. As tested by energy spectroscopy, a zirconium oxide powder adhesive layer with an average thickness of 5 ?m was formed on the surface of M2.

[0113] The products described above were tested as follows:

TABLE-US-00001 TABLE 1 Comparison of overall performance of sintered magnet M2 and magnet M1 Test method: 7 mm ? 7 mm ? 6 mm samples were taken from the magnet M1 and the magnet M2. Test equipment: NIM-62000 Item Density (g/cm.sup.3) Br (T) Hcj (kA/m) M2 7.52 1.432 2029 M1 7.51 1.443 1209

TABLE-US-00002 TABLE 2 Comparison of Hcj at a position on the surface of sintered magnet M2 and Hcj at a position 2 mm from the surface of the magnet Test method: As shown in FIG. 1, 1 mm ? 1 mm ? 1 mm samples were taken from a position on the surface of the sintered magnet M2 and a position 2 mm from the surface, i.e., H1 and H2, respectively. The difference in Hcj between the positions H1 and H2 was 39 kA/m, and EPMA analysis on the element Tb shows that Tb was mainly distributed on the grain boundary in the field of view 1 selected from the position H1, and a large amount of Tb was not found to enter the main phase. The element Tb was obvious on the grain boundary in the field of view 2 selected from the position H2, and the element Tb was distributed uniformly at the grain boundary after diffusion. Test equipment: PFM06 Item Hcj (kA/m) H1 2051 H2 2012

TABLE-US-00003 TABLE 3 Comparison of main components of sintered magnet M2 and magnet M1 Test equipment: Spectrometer Test item B Al Co Nd Pr Dy Tb Cu Ga Al Zr Found value of M2, % 0.97 0.17 0.81 22.32 7.24 \ 0.87 0.12 0.1 0.16 0.12 Found value of M1, % 0.98 0.17 0.80 22.29 7.10 \ 0.46 0.11 0.1 0.15 0.12 Note: The balance was Fe.

[0114] The results described above show that in this way, compared with M1, the remanence Br of M2 was only reduced by about 0.011 T, and Hcj was increased by about 820 kA/m. The component test shows that Tb of M2 was increased by about 0.41 wt % compared with M1.

TABLE-US-00004 TABLE 4 Analysis and comparison of contents of elements C and O in sintered magnet M2 and magnet M1 Test equipment: CS analyzer and ONH analyzer Item C (wt %) O (wt %) Found value of M2 0.0537 0.0914 Found value of M1 0.0546 0.0891

[0115] Table 4 shows that, from the analysis and comparison of the contents of elements CSON in the magnets before and after diffusion, the contents of C and O did not show a significant increase, indicating that impurity elements formed by slurries during diffusion did not enter the magnets.

Example 2

[0116] Like the neodymium-iron-boron magnet M1 in Example 1, a magnetic sheet formed had dimensions of 40 ?mm?30 ?mm?8 ?mm and a dimensional tolerance of 0.03 ?mm, and a composite diffusion layer was disposed on the surface: an RH slurry was prepared from terbium fluoride as a heavy rare earth element powder, rosin-modified alkyd resin powder as an organic solid, and ethanol with weight percentages of 55 wt %, 5 wt %, and 40 wt %, respectively. An RL slurry was prepared from aluminum oxide as a metal oxide, rosin-modified alkyd resin powder as an organic solid, and ethanol with weight percentages of 50 wt %, 6 wt %, and 44 wt %, respectively. An RH layer, an RL layer, an RH layer, and an RL layer were sequentially disposed on the surface of the magnet by means of roll coating and hot air drying to form a composite diffusion layer, so as to obtain an RFeB magnet blank with an oxide on the surface, where the RH layer had a thickness of 25?5 ?m, the RL layer had a thickness of 3?2 ?m, and the composite diffusion layer accounted for 0.9?0.2% by weight of the magnet M1.

[0117] The RFeB magnet blank described above was placed in a material box for diffusion temperature holding heat treatment heat treatment in a heat treatment device. A heating process was set as follows: 50-780? C.?100 ?min+780? C.?180 ?min+780-920? C.?30 ?min+920? C.?240 ?min+780?360 min (no heating power output during the heat treatment)+780-920? C.?30 ?min+920? C.?360 ?min. Quenching was then performed, and after the quenching was finished, the system was heated to 520? C. for aging treatment. The temperature was held for 4 h, and then the system was quenched to room temperature to obtain a magnet M3. As tested by energy spectroscopy, an aluminum oxide powder adhesive layer was formed on the surface of M3. The RFeB magnet blanks were in a contact arrangement during the heat treatment, and there was no adhesion of the sintered magnets after diffusion.

TABLE-US-00005 TABLE 5 Comparison of performance of sintered magnet M3 and magnet M1 Item Density (g/cm.sup.3) Br (T) Hcj (kA/m) M3 7.51 1.363 2275 M1 7.52 1.378 1407

[0118] Table 5 shows that in this way, compared with M1, the remanence Br of M3 was only reduced by about 0.015 T, and Hcj was increased by about 868 kA/m.

TABLE-US-00006 TABLE 6 Comparison of Hcj at a position on the surface of sintered magnet M3 and Hcj at a position 2 mm from the surface of the magnet Test method: 1 mm ? 1 mm ? 1 mm samples were taken from a position on the surface of the sintered magnet M3 and a position 2 mm from the surface, and the difference in Hcj between the positions H1 and H2 was 38 kA/m. Test equipment: PFM06 Item Hcj (kA/m) H1 2297 H2 2259

[0119] The exemplary embodiments of the present disclosure have been described above. However, the protection scope of the present disclosure is not limited to the embodiments described above. Any modification, equivalent, improvement, and the like made by those skilled in the art without departing from the spirit and principle of the present disclosure shall fall within the protection scope of the present disclosure.