CN117497276A - R-T-Ga-B rare earth permanent magnet based on selective region grain boundary diffusion and preparation method thereof - Google Patents
R-T-Ga-B rare earth permanent magnet based on selective region grain boundary diffusion and preparation method thereof Download PDFInfo
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- 229910001172 neodymium magnet Inorganic materials 0.000 claims description 14
- 229910052771 Terbium Inorganic materials 0.000 claims description 10
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- 229910052733 gallium Inorganic materials 0.000 description 1
- 239000003292 glue Substances 0.000 description 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
- H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
- H01F1/047—Alloys characterised by their composition
- H01F1/053—Alloys characterised by their composition containing rare earth metals
- H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
- H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
- H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
- H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
- H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
- H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
- H01F41/0293—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets diffusion of rare earth elements, e.g. Tb, Dy or Ho, into permanent magnets
Abstract
The invention discloses an R-T-Ga-B rare earth permanent magnet based on selective area grain boundary diffusion and a preparation method thereof. The Ga in the diffusion source is melted by utilizing the waste heat of the magnet, and the diffusion source is bonded; the shielding layer can shield the non-corner area and insulate heat, so that powder on the shielding layer is prevented from being bonded, and recovery is facilitated. The invention uses dry powder spraying, does not add organic adhesive, reduces the introduction of impurities such as C and the like, and inhibits the deterioration of the surface performance and microstructure of the magnet. The diffusion source is simple to recycle and the utilization ratio is high. The corner regions ensure coercivity by increasing the Ga content by diffusion, while the core ensures relatively low Ga, ensures high remanence, and improves the overall performance of the magnet.
Description
Technical Field
The invention relates to an R-T-Ga-B rare earth permanent magnet based on selective region grain boundary diffusion and a preparation method thereof, belonging to the field of rare earth magnets.
Background
Grain boundary diffusion is a new technology developed in recent years, can obviously improve the coercive force of the R-T-B rare earth permanent magnet under the condition of ensuring that the magnet has high remanence, and is a common method for preparing the high-performance R-T-B rare earth permanent magnet.
The grain boundary diffusion treatment is to coat a diffusion source layer containing heavy rare earth elements on the surface of the magnet, and then heat the magnet to a specified temperature for a period of time. Heavy rare earth elements in the diffusion source on the surface of the magnet at the high temperature stage diffuse towards the inside of the magnet along the crystal boundary R-rich direction, and a shell layer with a high anisotropic field is formed on the surface of the main phase crystal grain of the magnet. Grain boundary diffusion is therefore a way to increase the coercivity of the magnet by increasing the anisotropic field at the surface of the primary phase grains.
Common ways of disposing a diffusion source at the grain boundary include vacuum physical sputter deposition (PVD), spraying, printing, and the like. PVD equipment is expensive and production efficiency is low, while heavy rare earth utilization is often less than 50wt.% due to space sputtering problems. The spraying and printing process needs to mix the powder containing heavy rare earth source with a certain organic binder, spray or print the mixture on the surface of the product, then heat and solidify the mixture, and the organic binder introduces a large amount of carbon and other impurity elements, which can cause the deterioration of the surface layer of the magnet after diffusion, and often needs to grind off the surface layer, resulting in a large waste of raw materials. Meanwhile, certain harmful gases are volatilized in the use and curing process of the organic binder, so that the environmental-friendly treatment cost of a workshop is increased; the expiration date of the organic additive also adversely affects the recycling and stability of the diffusion source. Furthermore, spraying and printing often set up indiscriminate diffusion sources for areas on the workpiece tray, resulting in significant wastage of diffusion sources when the magnets are not able to meet a full tray.
In addition, because the corner area of the magnet is most likely to demagnetize in the actual operation of the motor, the requirement of selective area diffusion is provided, and the heavy rare earth diffusion is only carried out in the corner area of the magnet to increase the coercive force, thereby reducing the use amount of the heavy rare earth and improving the cost performance of the product.
Finally, adding a certain amount of Ga element can improve the coercive force of the sintered NdFeB. However, excessive addition of the rare earth element has adverse effects such as reduced remanence, so that the addition of the appropriate amount of Ga content in a magnet key region has great application value.
Disclosure of Invention
Aiming at the technical problems of organic carbon impurity problem, effective recovery problem of diffusion source, high equipment complexity and the like in the traditional grain boundary diffusion process, the invention provides an R-T-Ga-B rare earth permanent magnet based on selective area grain boundary diffusion and a preparation method thereof.
The technical scheme adopted by the invention is as follows:
an R-T-Ga-B rare earth permanent magnet based on selective regional grain boundary diffusion, the magnet comprising the following components in mass fraction:
r: 28.5-35 wt%, wherein R consists of R1 and RH, the RH content is 0.2-10.0 wt% of the mass of the magnet, RH is at least one of Dy and Tb, and RH accounting for 0.2-2.0 wt% of the mass of the magnet is added into the magnet in a grain boundary diffusion manner; r is R1, the balance of R1 is at least one of Nd, pr, la, ce, er, gd, sm, tm, lu,
B：0.85~1.1wt.%，
m:0.1 to 8.0wt.%, M comprises one or more of Al, cu, zr, ti, nb, V, cr, ni, mo, zn, W,
ga: 0.4-0.8 wt.%, wherein Ga accounting for 0.2wt.% or more of the mass of the magnet is added to the magnet in a grain boundary diffusion manner;
the balance of T and other unavoidable impurities, wherein T is Fe or Fe and Co;
the magnet has at least one surface layer A, wherein the average heavy rare earth content and Ga content of the surface layer A are higher than the average heavy rare earth content and Ga content of the whole magnet, and the average carbon content of the surface layer A is lower than the average carbon content of the whole magnet.
The surface layer A is a surface layer region ranging from 0.2 to 0.6mm in depth from the surface of the magnet to the core.
The R-T-Ga-B rare earth permanent magnet based on optional region grain boundary diffusion is preferably prepared by the following method:
(1) Coating a diffusion source on a diffusion surface selected area of a neodymium iron boron magnet matrix, wherein the diffusion source is mixed dry powder of heavy rare earth and metal Ga, the heavy rare earth is pure metal or hydride containing at least one of heavy rare earth elements Dy and Tb, the selected area coating is to coat the diffusion source on corner areas of the diffusion surface, and the diffusion source is not coated on non-corner areas;
the corner area is a surface area in a width range of 0-Xmm from the edge of the diffusion surface, X is 0.5-2, and the non-corner area is a surface area outside the width range of Xmm from the edge;
(2) And (3) performing diffusion treatment on the magnet with the selected area coated with the diffusion source, wherein the diffusion temperature is 800-1000 ℃, the heat preservation time is 6-30 h, cooling and tempering to obtain the R-T-Ga-B rare earth permanent magnet based on the selective area grain boundary diffusion.
The invention also provides a preparation method of the R-T-Ga-B rare earth permanent magnet based on selective region grain boundary diffusion, which comprises the following steps:
(1) Coating a diffusion source on a diffusion surface selected area of a neodymium iron boron magnet matrix, wherein the diffusion source is mixed dry powder of heavy rare earth and metal Ga, the heavy rare earth is pure metal or hydride containing at least one of heavy rare earth elements Dy and Tb, the selected area coating is to coat the diffusion source on corner areas of the diffusion surface, and the diffusion source is not coated on non-corner areas;
the corner area is a surface area in a width range of 0-Xmm from the edge of the diffusion surface, X is 0.5-2, and the non-corner area is a surface area outside the width range of Xmm from the edge;
(2) And (3) performing diffusion treatment on the magnet with the selected area coated with the diffusion source, wherein the diffusion temperature is 800-1000 ℃, the heat preservation time is 6-30 h, cooling and tempering to obtain the R-T-Ga-B rare earth permanent magnet based on the selective area grain boundary diffusion.
Further, in the step (1), the diffusion surface refers to a magnet surface coated with the diffusion source, and may be generally perpendicular to the magnet orientation direction, parallel to the magnet orientation direction, or at any angle to the magnet orientation direction.
Preferably the diffusion surface is two surfaces perpendicular to the direction of orientation of the magnets.
The selective coating of the diffusion surface can be realized by preparing a shielding sheet, wherein the size of the shielding sheet is the size of a non-corner area; the shielding sheet is covered on the non-corner area of the diffusion surface to expose the corner area, so that the selective area coating can be performed.
The selective coating diffusion source is coated by spraying, and the specific spraying operation preferably comprises the following steps:
(1-1) pretreatment before spraying: tightly tiling a flaky neodymium iron boron magnet matrix, preheating to 80-400 ℃ (preferably 80-120 ℃), and placing a shielding layer on the diffusion surface of the magnet after preheating, covering a non-corner area and exposing a corner area;
(1-2) spray melting: spraying a diffusion source to the whole surface of the magnet, melting Ga in the sprayed powder on the corner area by using the waste heat of the magnet, and bonding the diffusion source and the magnet; the diffusion source is mixed dry powder of pure metal or hydride powder containing at least one of heavy rare earth elements Dy and Tb and metal Ga powder;
a spray gun is typically used to spray the diffusion source onto the tray/magnet/shutter blade surface.
In the diffusion source, the mass content of the metal Ga is preferably 10-30wt%.
(1-3) cooling, solidifying and cleaning: introducing cooling gas, cooling and solidifying the diffusion source in the corner area, blowing off excessive diffusion source powder, and recycling; removing the shielding layer;
and (1-4) turning over the magnet, and repeating the steps (1-1) - (1-3) to finish spraying the second surface to obtain the magnet with the selected area coated with the diffusion source.
The compressed gas used in the spray gun is nitrogen or argon.
The cooling gas in the step (1-3) is nitrogen or argon. The cooling gas is compressed gas, the temperature is below 10 ℃, and the preferable temperature is 5-10 ℃.
The excess diffusion source powder is typically the excess powder on the tray on which the magnets are placed, as well as the uncured adhered diffusion source powder on the shielding layer.
The shielding layer can be formed by splicing a plurality of small shielding sheets covering the non-corner areas together, or is formed by hollowing out the whole shielding sheets to expose the non-corner areas, or is formed by adopting a silk screen mode.
Further, the shielding layer is preferably made of a heat insulating material such as alumina, zirconia or a metal material with a heat insulating layer. Alumina and zirconia are excellent heat insulating materials, or metal materials are selected to be overlapped with heat insulating layers to form a plurality of layers of heat insulating materials to be used as shielding layers.
The neodymium-iron-boron magnet matrix is obtained by processing a sintered large neodymium-iron-boron magnet into a required shape and size, cleaning the magnet after surface treatment, and drying.
The surface treatment of the magnet is to remove greasy dirt and rust spots on the surface of the magnet by polishing or acid washing and sand blasting.
The diffusion treatment is typically carried out in a vacuum diffusion furnace.
In the tempering treatment, the tempering temperature is 400-600 ℃ (preferably 480-420 ℃), and the tempering time is 2-10 h (preferably 3-5 h).
The invention firstly preheats the magnet to 80-400 ℃ and the melting point of Ga is lower than 30 ℃, so that the Ga in the diffusion source powder can be melted by utilizing the waste heat of the magnet. The shielding layer is placed on the surface of the magnet before spraying, the shielding layer has the dual functions of shielding non-corner areas and heat insulation, the shielding layer is heat-insulating, ga in diffusion source powder sprayed on the shielding layer can be prevented from melting, the Ga cannot be adhered to the shielding layer, and therefore follow-up recovery is facilitated. After mixing heavy rare earth (Dy/Tb) or heavy rare earth hydride powder with Ga powder in a certain proportion, spraying the powder on the surfaces of a preheated magnet and a shielding layer by compressed gas, melting the Ga powder by using the heat of the magnet, and bonding a diffusion source and the magnet. And blowing off redundant powder by using cooling compressed gas, cooling diffusion source powder and a magnet coated on the corner area at the same time, realizing solidification and adhesion, and repeating the operation to realize two-sided spraying.
The invention has the beneficial effects that:
1. the dry powder spraying is used, no organic adhesive is added in the whole process, the introduction of impurities such as C and the like is effectively reduced, and the carbon content of the magnet is conveniently controlled.
2. And regulating and controlling the amount of Ga powder and the powder adhesion amount by utilizing the waste heat of the magnet pretreatment, and finally regulating and controlling the use amount of the heavy rare earth source together with the spraying amount.
3. The shielding layer is used for controlling the powder coating position and the heating position, and the cooling gas is used for cleaning and recycling the redundant powder and cooling the adhered powder, so that the powder coating device is simple and efficient.
4. Compared with the traditional spraying and printing, after the non-coating area is shielded by the shielding layer, the diffusion source powder is only bonded to the specific selected area of the magnet, and the diffusion source powder on the shielding layer is not fused and adhered due to the heat insulation of the shielding layer, so that other powder which is not adhered can be directly recycled, and the flexibility of the manufacturing tool and the sample amount is improved. Compared with the traditional adhesive diffusion source, the diffusion source on the shielding layer after heating and curing has the advantages of high recovery difficulty, additional solvent, unstable recovery quality, simple recovery method of the unutilized diffusion source, no solvent recovery, stable quality, high utilization ratio and small waste.
5. The conventional spraying method is added with an organic additive, so that the carbon content of the surface layer of the magnet is increased after diffusion, the residual magnetism is reduced more, and the macroscopic coercivity Hcj is reduced due to the existence of a degradation layer. The conventional operation is to backgrind to remove the degradation layer, and to increase the coercive force and remanence of the magnet. The diffusion source of the invention does not add organic additives, the total amount of rare earth in the magnet is increased after diffusion, the average mass fraction of C is relatively reduced, the deterioration of the surface layer performance and microstructure of the magnet is inhibited, the surface layer deterioration layer is not required to be removed by regrinding, the diffusion source has better magnetic performance, and the waste of the diffusion source and raw materials is reduced.
6. Research shows that adding a certain amount of Ga into a magnet can obtain Nd 6 Fe 13 Ga phase can raise the coercive force of the magnet. However, excessive addition of Ga does not increase the coercive force any more and leads to a decrease in remanence. Therefore, the Ga content is increased by diffusion in the corner region where the surface layer is most demagnetized to ensure coercive force (demagnetization resistance), while the core ensures relatively low Ga and high remanence, thereby improving the overall performance of the magnet.
7. Compared with the whole-surface spraying of the conventional process, the method for spraying the selected areas reduces the consumption of diffusion sources and reduces the cost on the premise that the magnetic performance meets the requirements of customers.
Drawings
FIG. 1 is a schematic diagram showing the steps of the preparation process of the R-T-Ga-B rare earth permanent magnet based on optional domain grain boundary diffusion according to example 1 of the present invention.
Detailed Description
The sintered bulk neodymium-iron-boron magnet matrix is prepared by adopting the processes of melt-throwing an SC sheet, hydrogen breaking, air flow grinding, orientation forming, isostatic pressing, vacuum sintering and aging.
And machining the aged large neodymium-iron-boron magnet to a required shape and size, and cleaning and drying the magnet after surface treatment to obtain the neodymium-iron-boron magnet matrix.
The schematic diagram of the preparation process steps of the R-T-Ga-B rare earth permanent magnet based on optional region grain boundary diffusion is shown in the figure.
The shielding layer or the combined shielding layer is prepared according to the size of the final finished magnet, and the shielding layer can be prepared by compounding aluminum oxide, zirconium oxide and metal materials with heat insulation coatings.
And tightly tiling the sheet magnet matrix, preheating to 100-400 ℃, covering the preheated sheet magnet with a shielding layer on the surface perpendicular to the diffusion direction, covering non-corner areas, and exposing corner areas. And then spraying mixed powder containing heavy rare earth and Ga on the surface of the magnet/shielding layer in a spraying mode, wherein the heavy rare earth-containing powder is pure metal and hydride containing at least one of Dy and Tb of the heavy rare earth elements, and removing the shielding sheet after the diffusion source is coated. Turning over the magnet, and repeating the steps to finish the area selection coating of the second surface.
And (3) placing the magnet in a vacuum diffusion furnace, heating to 800-1000 ℃, preserving heat for 6-30 h, and performing high-temperature grain boundary diffusion treatment. And cooling to room temperature after finishing, heating to 400-600 ℃, and preserving heat for 2-10 hours to obtain the final magnet.
The magnet composition was tested using ICP, the carbon content was measured using a carbon element analyzer, and the magnet microstructure and micro-domain composition were analyzed using SEM. The magnet magnetic properties were tested using NIM equipment, 5 samples were tested per group and the average value calculated.
Example 1:
the sintered R-T-B magnet is prepared by adopting the processes of melt-throwing an SC sheet, hydrogen breaking, air flow grinding, orientation forming, isostatic pressing, vacuum sintering and aging, wherein the length, width and height of the sintered magnet are 65mm, 32mm and 43mm, and the direction of 43mm is the orientation direction.
Peeling a single sintered magnet by 1mm by adopting an inner circle slicer, ensuring the surface of the magnet to be flat, cutting into a flaky NdFeB magnet matrix with the length, width and height of 20mm, 10mm and 5.0mm, cleaning and drying, wherein the height direction is the orientation direction of the magnet. The schematic of the preparation process steps for preparing R-T-Ga-B rare earth permanent magnets based on selective region grain boundary diffusion is shown in FIG. 1. According to the shape and size design shielding sheet shown in figure 1, the shielding sheet material is zirconia, the size of the shielding area inside the sheet-shaped magnet is 17mm multiplied by 7mm, the width of the exposed corner area of the magnet is 1.5mm, and the shielding layers are connected and spliced through the reinforcement lines to form an integral shielding layer, so that a shielding workpiece is formed, as shown in figure 1.
The magnets are closely spread on a workpiece tray and enter a drying tunnel for preheating, after the preheating is carried out to 100 ℃, a shielding layer is immediately placed on the magnets, spraying operation is carried out by using a spray gun, and a diffusion source is sprayed on all surfaces of all the magnets, namely the surfaces of the tray/the magnets/the shielding sheets. The diffusion source was a mixed powder of TbH powder and Ga powder, in which the mass content of Ga is shown in table 1. Melting Ga in the spray powder on the corner area by utilizing the waste heat of the magnet, and bonding a diffusion source with the magnet; introducing compressed cooling gas with the temperature of 6 ℃, cooling and solidifying diffusion sources in the corner areas, blowing off excessive diffusion source powder, and sending the powder into a recovery and collection device, wherein the diffusion source powder collected in the recovery and collection device can be directly recovered for use; removing the shielding layer; the resulting diffused and non-diffused regions are shown in fig. 1. Turning over the magnet, and repeating the steps to finish spraying the second surface to obtain the magnet with the selected area coated with the diffusion source.
The weight of the diffusion source is controlled to be 0.42-wt% of the mass of the magnet through the spraying amount and the preheating temperature of the magnet, so that the diffusion source in the selected area is ensured to be sufficient.
The comparative example was sprayed using a conventional spray diffusion source, and likewise was selectively sprayed using a masking layer. Before spraying, the TbH powder was mixed with alcohol and added to the AD gum content of 0.3wt% from Dongguan Yuanzhuo mechanical equipments Co., ltd. After spraying, heating and curing, and after spraying and curing at two selected areas, the weight increase of the diffusion source is 0.42 and wt percent. The diffusion source duty ratio on the shielding layer on the tray was = (17×7)/(20×10) =59.5%, and the actual use ratio of the diffusion source on the corner area of the magnet was 40.5%. The diffusion source with the proportion of 59.5% on the shielding layer cannot be directly recycled due to solidification of the binder in the heating process, alcohol and glue are required to be added for recycling, and organic components in the powder are easy to denature and lose efficacy, so that the stability of the recycled diffusion source powder is difficult to control, and the diffusion quality is influenced. Therefore, when the diffusion source with the additive is added for area selection spraying, the utilization rate of the diffusion source is low, the recovery difficulty is high, the recovery solvent is required to be consumed, and the waste proportion of the diffusion source is high.
And (3) placing the magnet in a vacuum diffusion furnace, heating to 950 ℃, preserving heat for 15 hours, cooling to room temperature after finishing, heating to 520 ℃ and preserving heat for 4 hours.
The overall composition and carbon content of the magnet were measured using an ICP and carbon elemental analyzer, while the magnet was cut out to a thickness of 0.6mm from the surface layer, the composition and carbon content were measured, the magnetic properties of the magnet were measured using NIM equipment, 5 samples were measured for each group and the average value was calculated. Meanwhile, a group of samples are taken respectively, the surface layer is removed by 0.05mm through regrinding, and the magnetic property test is carried out again.
TABLE 1 diffusion matrix and diffusion source composition, average composition carbon content and surface Tb of magnet after diffusion and carbon content
TABLE 2 magnetic Properties of magnets before and after diffusion
Since conventional spraying requires a certain amount of organic additives, the carbon content of the surface layer of the magnet increases after diffusion, resulting in a more decrease in remanence while the macroscopic coercivity Hcj also decreases due to the presence of the deteriorated layer. After the degraded layer was removed by backgrinding by 0.05mm, both coercivity and remanence were improved, and the necessity of removing the degraded layer was also demonstrated from the opposite side. The regrind operation tends to result in waste of diffusion sources and raw materials.
Experiment No.1-4 adopts Tb and Ga to jointly diffuse, does not use organic additives, and reduces the carbon content of the surface layer because the original carbon element is diluted after diffusion. Tb has a better coercive force improving effect than Ga element, so that the Ga content of a diffusion source is smaller and the coercive force is slightly higher. However, a certain amount of Ga can obviously increase the coercive force, and meanwhile, the increase of Ga powder also improves the adhesion effect of a diffusion source and a matrix and promotes element diffusion, so that the coercive force is not obviously reduced. Experiment No.5 shows that the effective Tb content is reduced due to excessive Ga content of a diffusion source, and the coercive force increasing amount is weakened; at the same time, the residual magnetism of the magnet is also significantly reduced compared with other embodiments, since excessive Ga content can lead to reduced residual magnetism. Therefore, the Ga content in the diffusion source is preferably 10-30%.
Example 2:
the sintered R-T-B magnet is prepared by adopting the processes of melt-throwing an SC sheet, hydrogen breaking, air flow grinding, orientation forming, isostatic pressing, vacuum sintering and aging, wherein the length, width and height of the sintered magnet are 65mm, 32mm and 43mm, and the direction of 43mm is the orientation direction.
Peeling a single sintered magnet by 1mm by adopting an inner circle slicer, ensuring the surface of the magnet to be flat, cutting into a flaky NdFeB magnet with the length, width and height of 20mm, 10mm and 5.0mm, cleaning and drying, wherein the height direction is the orientation direction of the magnet. According to the shape and size design shielding sheet shown in figure 1, the shielding sheet material is zirconia, the size of the shielding area inside the sheet-shaped magnet is 18.5mm multiplied by 18.5mm, the width of the exposed corner area of the magnet is 0.75mm, and all shielding layers are connected through a reinforcement line to form an integral shielding layer. The magnet is placed on a workpiece tray and enters a drying tunnel for preheating, and a shielding layer is immediately placed on the preheating for spraying operation. The specific process steps are the same as in example 1. The diffusion source was a mixed powder of DyH powder and Ga powder, the weight fraction of Ga being 15wt.%. The weight of the diffusion source is controlled by the spraying amount and the preheating temperature of the magnet.
And (3) placing the magnet in a vacuum diffusion furnace, heating to 950 ℃, preserving heat for 15 hours, cooling to room temperature after finishing, heating to 520 ℃ and preserving heat for 4 hours.
Table 3 example matrix formulation and diffusion source and weight gain
TABLE 4 average composition after diffusion, dy content, and magnetic Properties
The overall composition of the magnet before and after diffusion was measured using ICP and carbon element analyzer, the magnetic properties of the magnet before and after diffusion were measured using NIM equipment, 5 samples were tested for each group and the average value was calculated.
In Table 4, ΔHcj/kOe refers to the difference in increase in coercivity after diffusion from the corresponding matrix coercivity in Table 3.
As can be seen from the data in Table 3, before diffusion, since Ga element addition can increase the coercive force of the magnet, the coercive force of experiment Nos. 6 and 7 is increased compared with comparative example 3; however, after the Ga content exceeds a certain amount (0.6%), the coercive force is not increased any more, but is slightly lowered as in comparative example 4.
The data in table 4 shows that after diffusion: the diffusion of the heavy rare earth selective area can lead to the increase of the coercive force of the magnet. However, since the Ga content in the matrix of comparative example 3 is low, the Ga content in the magnet after diffusion is only 0.36% and less than 0.4%, and thus the increase in coercive force is limited; and experiment No.9 has the advantages that the heavy rare earth content and Ga content diffused into the magnet are improved by increasing the weight gain, the coercive force is obviously improved, and the increment is similar to that of experiments No.6 and 7. Since the Ga content of the matrix of comparative example 4 was higher, the Ga content after diffusion was further increased beyond 0.8%, resulting in serious deterioration of remanence and also greatly reduced coercivity increment. Therefore, the Ga content in the magnet of the present invention is preferably 0.4 to 0.8wt%.
Experiment No.8 reduced the weight gain, and after the amount of Ga diffusion was reduced, the coercivity gain was improved. However, as the diffusion source weight gain was reduced, the diffusion permeation amount of heavy rare earth Dy was also reduced, and the final coercivity was increased by an amount lower than that of experiments nos. 6 and 7.
Claims (10)
1. An R-T-Ga-B rare earth permanent magnet based on selective regional grain boundary diffusion, characterized in that the magnet comprises the following components in mass fraction:
r: 28.5-35 wt%, wherein R consists of R1 and RH, the RH content is 0.2-10.0 wt% of the mass of the magnet, RH is at least one of Dy and Tb, and RH accounting for 0.2-2.0 wt% of the mass of the magnet is added into the magnet in a grain boundary diffusion manner; r is R1, the balance of R1 is at least one of Nd, pr, la, ce, er, gd, sm, tm, lu,
B：0.85~1.1wt.%，
m:0.1 to 8.0wt.%, M comprises one or more of Al, cu, zr, ti, nb, V, cr, ni, mo, zn, W,
ga: 0.4-0.8 wt.%, wherein Ga accounting for 0.2wt.% or more of the mass of the magnet is added to the magnet in a grain boundary diffusion manner;
the balance of T and other unavoidable impurities, wherein T is Fe or Fe and Co;
the magnet has at least one surface layer A, wherein the average heavy rare earth content and Ga content of the surface layer A are higher than the average heavy rare earth content and Ga content of the whole magnet, and the average carbon content of the surface layer A is lower than the average carbon content of the whole magnet.
2. The R-T-Ga-B rare earth permanent magnet based on optional domain grain boundary diffusion according to claim 1, wherein the surface layer a is a surface layer region ranging from 0 to 0.6 in depth from the magnet surface to the core, K being 0.2 to 0.6.
3. The R-T-Ga-B rare earth permanent magnet based on selective area grain boundary diffusion according to claim 1 or 2, characterized in that the magnet is prepared as follows:
(1) Coating a diffusion source on a diffusion surface selected area of a neodymium iron boron magnet matrix, wherein the diffusion source is mixed dry powder of heavy rare earth and metal Ga, the heavy rare earth is pure metal or hydride containing at least one of heavy rare earth elements Dy and Tb, the selected area coating is to coat the diffusion source on corner areas of the diffusion surface, and the diffusion source is not coated on non-corner areas;
(2) And (3) performing diffusion treatment on the magnet with the selected area coated with the diffusion source, wherein the diffusion temperature is 800-1000 ℃, the heat preservation time is 6-30 h, cooling and tempering to obtain the R-T-Ga-B rare earth permanent magnet based on the selective area grain boundary diffusion.
4. A method for preparing an R-T-Ga-B rare earth permanent magnet based on selective regional grain boundary diffusion, characterized in that the method comprises the steps of:
(1) Coating a diffusion source on a diffusion surface selected area of a neodymium iron boron magnet matrix, wherein the diffusion source is mixed dry powder of heavy rare earth and metal Ga, the heavy rare earth is pure metal or hydride containing at least one of heavy rare earth elements Dy and Tb, the selected area coating is to coat the diffusion source on corner areas of the diffusion surface, and the diffusion source is not coated on non-corner areas;
(2) And (3) performing diffusion treatment on the magnet with the selected area coated with the diffusion source, wherein the diffusion temperature is 800-1000 ℃, the heat preservation time is 6-30 h, cooling and tempering to obtain the R-T-Ga-B rare earth permanent magnet based on the selective area grain boundary diffusion.
5. The method of claim 4, wherein in step (1), the corner region is a surface region of the diffusion surface within a width range of 0 to Xmm from the edge, X is 0.5 to 2, and the non-corner region is a surface region outside the width range of Xmm from the edge.
6. The method of claim 4, wherein in step (1), the diffusion surface is a magnet surface coated with a diffusion source, and is a magnet surface perpendicular to, parallel to, or at any angle to the direction of magnet orientation.
7. The method of claim 4, wherein said step (1) is performed by:
(1-1) pretreatment before spraying: tightly tiling a flaky neodymium iron boron magnet matrix, preheating to 80-400 ℃, and placing a shielding layer on the diffusion surface of the magnet after preheating, covering a non-corner area and exposing a corner area;
(1-2) spray melting: spraying a diffusion source to the whole surface of the magnet, melting Ga in the sprayed powder on the corner area by using the waste heat of the magnet, and bonding the diffusion source and the magnet; the diffusion source is mixed dry powder of pure metal or hydride powder containing at least one of heavy rare earth elements Dy and Tb and metal Ga powder;
(1-3) cooling, solidifying and cleaning: introducing cooling gas, cooling and solidifying the diffusion source in the corner area, blowing off excessive diffusion source powder, and recycling; removing the shielding layer;
and (1-4) turning over the magnet, and repeating the steps (1-1) - (1-3) to finish spraying the second surface to obtain the magnet with the selected area coated with the diffusion source.
8. The method of claim 7, wherein the mass content of metal Ga in the diffusion source is 10-30 wt.%.
9. The method of claim 7, wherein the cooling gas in step (1-3) is nitrogen or argon, the cooling gas is compressed gas, and the temperature is below 10 ℃.
10. The method of claim 7, wherein the masking layer is in the form of a plurality of small masking sheets covering non-corner areas that are spliced together; or the whole shielding sheet is hollowed out to expose a plurality of non-corner areas; or adopting a silk screen mode; the shielding layer is made of heat insulation materials.
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