KR20190061244A - Method for preparing rare-earth permanent magnet - Google Patents

Abstract

According to an embodiment of the present invention, a rare earth permanent magnet manufacturing method comprises: a preparation step of preparing a rare earth magnet ingot by melting an R-T-B based alloy; a pulverizing step of pulverizing the rare earth magnet ingot to prepare a rare earth magnet powder having an average particle size of 3.0 μm or less (excluding 0); a forming step of forming a rare earth magnet molding by performing magnetic field molding of the rare earth magnet powder in an inert atmosphere; a sintering step of sintering and diffusing the rare earth magnet molding to manufacture a rare earth sintered magnet; and a grain boundary diffusion step of applying a heavy rare earth mixture prepared by mixing a heavy rare earth hydrogen compound and an alcohol on a surface of the rare earth sintered magnet, and diffusing the applied mixture in a vacuum or inert atmosphere to manufacture a rare earth permanent magnet. Thus, magnetic properties of the rare earth permanent magnet are increased.

Description

METHOD FOR PREPARING RARE-EARTH PERMANENT MAGNET BACKGROUND OF THE INVENTION [0001]

The present invention relates to a method of manufacturing a rare earth permanent magnet, and more particularly to a rare earth permanent magnet capable of improving the magnetic properties of a rare earth permanent magnet manufactured by micronizing particles and intergranular diffusion of heavy rare earths into a rare earth permanent magnet And a manufacturing method thereof.

Generally, a rare earth permanent magnet is a magnet having excellent magnetism such as R-Fe-B sintered magnet (where R is a rare earth element such as neodymium (Nd), dysprosium (Dy), terbium The motor is capable of high output and size reduction and is being applied to various fields such as home electric appliances or motor of a vehicle and the application range such as a new energy field such as a generator is gradually increasing as well as an electronic communication field such as a mobile phone.

In particular, with the recent increase in demand for hybrid or electric vehicles, it is expected that the demand for rare earth permanent magnets, which can achieve 3 to 5 times magnetic power improvement compared to conventional ferrite magnets, will be further increased.

The magnetic properties of the rare earth permanent magnet can be represented by the residual magnetic flux density Br and the coercive force HcJ. The residual magnetic flux density can be determined by the columnar fraction, the density and the degree of self orientation of the rare earth permanent magnet, It is related to the microstructure of the magnet and is determined by fine grain size or uniform distribution of grain boundaries.

Therefore, a technology for miniaturizing the size of the particles used in the production of rare earth permanent magnets to improve the coercive force has been developed. However, as the particles are made finer, the oxidation degree is increased and the manufacturing cost is increased. It can not be done.

In addition, the rare earth permanent magnet as described above is likely to generate eddy current inside the rare earth permanent magnet due to the high conductivity and low specific resistance of the magnet, so that the temperature of the permanent magnet is raised. The temperature rise of the rare earth permanent magnet, It is easy to induce a decrease in the magnetization of the rare earth permanent magnet due to the increase of the temperature or to cause irreversible magnetization of the rare earth permanent magnet.

In order to solve the above problems, a technique of intergranular diffusion of heavy rare earth elements such as dysprosium (Dy) or terbium (Tb) has been developed in order to improve the coercive force of rare earth permanent magnets manufactured by conventional sintering.

However, since the cost of heavy rare earth elements is high in the grain boundary diffusion process, manufacturing cost is increased and post-treatment such as surface coating process is required to improve the corrosion resistance after grain boundary diffusion.

Further, when the particles are made finer in order to improve the coercive force of the rare earth permanent magnet, the middle rare earth element is not easily diffused into the grain boundaries.

It should be understood that the foregoing description of the background art is merely for the purpose of promoting an understanding of the background of the present invention and is not to be construed as adhering to the prior art already known to those skilled in the art.

KR 10-1516567 B1 (2015.05.15)

Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made to solve the above-mentioned problems, and provides a rare-earth permanent magnet manufacturing method excellent in magnetic properties capable of manufacturing a rare earth permanent magnet excellent in magnetic properties such as magnetic flux density and coercive force.

The technical objects to be achieved by the present invention are not limited to the above-mentioned technical problems and other technical subjects which are not mentioned can be clearly understood by those skilled in the art from the description of the present invention.

A method of manufacturing a rare earth permanent magnet according to an embodiment of the present invention includes: preparing a rare earth magnet ingot by melting an R-T-B type alloy; Pulverizing the rare earth magnet ingot to prepare a rare earth magnet powder having an average particle size of 3.0 탆 or less (excluding 0); A forming step of forming the rare earth magnet powder by magnetic field shaping the rare earth magnet powder in an inert atmosphere; A sintering step of sintering and diffusing the rare earth magnet compact to produce a rare earth sintered magnet; And a grain diffusion step of applying a heavy rare earth mixture prepared by mixing a heavy rare earth metal hydride compound and an alcohol on the surface of the rare earth sintered magnet and spreading it in a vacuum or an inert atmosphere to produce a rare earth permanent magnet.

In the preparation step, the rare earth magnet ingot is produced by strip casting 27 to 36 wt% of R, 0 to 5 wt% of T, 0 to 2 wt% of B, and the balance Fe and other unavoidable impurities in a vacuum or an inert atmosphere .

(Where R is a rare earth element, T is a transition metal, and B is boron).

The preparation step may be characterized in that the rare earth magnet ingot is ground in an oxygen concentration atmosphere of 2,000 ppm or less so that the average particle size of the rare earth magnet powder is 1.0 to 3.0 탆.

Preferably, in the intergranular diffusion step, the heavy rare earth hydrogen compound is provided in powder form having at least one of Nd-H compound, Dy-H compound and Tb-H compound and having an average particle size of 1.0 to 5.0 μm Do.

Wherein the intergranular diffusion step comprises a step of preparing a rare earth metal mixture in which the heavy rare earth mixture in a slurry state is prepared by mixing 10 to 70 weight of a solvent with respect to 100 weight parts of the heavy rare earth hydrogen compound; And applying a rare earth mixture while applying the heavy rare earth mixture to the surface of the rare earth sintered magnet; And a rare earth diffusion process in which the rare earth sintered magnet is charged into a furnace of a vacuum or an inert atmosphere and diffused to produce the rare earth permanent magnet.

Preferably, the rare earth permanent magnet is manufactured by diffusing the heavy rare-earth diffusion process at a temperature of 700 to 950 ° C for 1 to 30 hours.

More preferably, the heavy rare earth diffusion process is performed at a temperature of 800 to 900 ° C for 1 to 30 hours to produce the rare earth permanent magnet.

The method for manufacturing a rare-earth permanent magnet according to an embodiment of the present invention includes the steps of: after the intergranular diffusion step, heat treatment in an inert atmosphere at a temperature of 700 to 900 DEG C for 1 to 30 hours to remove stress of the rare earth permanent magnet; .

More preferably, the heat treatment step is a heat treatment in an inert atmosphere at a temperature of 800 to 900 DEG C for 1 to 30 hours to remove the stress of the rare earth permanent magnet.

More preferably, the rare earth permanent magnet manufacturing method according to an embodiment of the present invention may further include a cleaning step of removing foreign matter adhering to the surface of the rare earth sintered magnet before the grain diffusion step.

According to the embodiment of the present invention, it is possible to improve the magnetic characteristics such as magnetic flux density and coercive force by increasing the grain yield of heavy rare earth elements while refining the particles of the rare earth permanent magnet to be produced.

In addition, there is an effect that the production cost can be reduced by reducing the amount of rare earths being used.

1 is a flowchart illustrating a method of manufacturing a rare-earth permanent magnet according to an embodiment of the present invention,
FIG. 2 is a table showing magnetic properties of various embodiments and comparative examples manufactured according to an embodiment of the present invention,
3 is a table showing magnetic properties and thermal potatoes according to the average particle size of the heavy rare earth hydrogen compound.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments. For reference, the same numbers in this description refer to substantially the same elements and can be described with reference to the contents described in the other drawings under these rules, and the contents which are judged to be obvious to the person skilled in the art or repeated can be omitted.

1 is a flowchart illustrating a method of manufacturing a rare-earth permanent magnet according to an embodiment of the present invention.

As shown in FIG. 1, a rare earth permanent magnet manufacturing method according to an embodiment of the present invention includes preparing a rare earth magnet ingot by melting an RTB-based alloy and pulverizing the rare earth magnet ingot to prepare a rare earth magnet powder A sintering step of sintering and diffusing the rare earth magnet compact to produce a rare earth sintered magnet, and a step of diffusing the rare earth magnet to form a rare earth permanent magnet by applying a rare earth magnet mixture do.

The preparation step is to strip cast the remainder Fe and other unavoidable impurities by 27 to 36 wt% of R (rare earth element), 0 to 5 wt% of T (transition metal), 0 to 2 wt% of B (boron) .

It is preferable that the rare earth magnet ingot is provided in a vacuum or an inert atmosphere because the oxygen content of the rare earth magnet ingot is minimized to improve the magnetic properties of the rare earth permanent magnet produced by facilitating the diffusion of the rare earth element thereafter There is.

When the rare earth magnet ingot is provided as described above, the rare earth magnet ingot is reacted by exposing the rare earth magnet ingot to hydrogen gas, followed by vacuum evacuation while raising the temperature to about 600 ° C to release hydrogen. Then, The rare earth magnet powder is produced using a milling apparatus. At this time, the average particle size of the rare earth magnet powder is preferably 3.0 탆 or less.

The reason for this is that when the average particle size of the rare earth magnet powder to be produced exceeds 3.0 탆, the effect of improving the coercive force due to the grain refinement of the rare earth permanent magnet to be produced is insignificant.

More preferably, the average particle size of the rare earth magnet powder in the pulverization step is preferably 1.0 to 3.0 占 퐉, because when the rare earth magnet powder is pulverized to less than 1.0 占 퐉, the pulverizing time and speed are increased, But also has a problem of oxidation due to excessive refinement of the particles, so that it is preferable to limit the range to the above range.

At this time, it is preferable to carry out the pulverization step in an atmosphere having an oxygen concentration of 2,000 ppm or less because, as described above, as the concentration of oxygen increases, the magnetic properties of rare earth permanent magnets produced may deteriorate.

As described above, when the rare earth magnet powder is provided, the rare earth magnet powder is filled in an inactive mold in the molding step, and a direct current magnetic field is applied to the electromagnets disposed on both sides of the mold to align and simultaneously compress the rare earth magnet powder, .

When the rare-earth magnet compact is provided as described above, the rare-earth magnet compact is charged into the sintering furnace in the sintering step, and the furnace is heated in a vacuum or inert atmosphere at a temperature of about 400 ° C. to completely remove the remaining impurity organic matter. Sintered for about 2 hours to produce a rare earth sintered magnet.

Preferably, the rare-earth permanent magnet manufacturing method according to an embodiment of the present invention may further include a cleaning step of removing foreign matter of the rare-earth sintered magnet before the grain diffusion step.

More specifically, the cleaning step includes an oil removal process of dipping the rare earth sintered magnet in an alkali degreasing solution and then removing oil on the surface by using a ceramic ball having a diameter of 5 to 10 mm, a washing process of removing the remaining degreasing agent by distilled water, A rare earth sintering process in which a rare earth sintered magnet having a degreasing agent removed thereon is dipped in a nitric acid solution at a concentration of 1 to 10% Remove any foreign matter adhering to the surface of the magnet.

As described above, when the rare earth sintered magnet from which the foreign substance is removed is prepared, a rare earth permanent magnet is manufactured by applying and diffusing the heavy rare earth mixture to the surface of the rare earth sintered magnet in the grain boundary diffusion step.

More specifically, a rare earth permanent magnet manufacturing method according to an embodiment of the present invention is a method for manufacturing a rare earth permanent magnet by mixing a heavy rare earth metal hydride compound and a solvent to prepare a slurry- And a rare earth diffusion process in which a rare earth sintered magnet coated with a heavy rare earth element is charged and diffused into a heating furnace in a vacuum or an inert atmosphere to prepare a rare earth permanent magnet.

The process for preparing the heavy rare earth mixture according to one embodiment of the present invention is a process for preparing a heavy rare earth mixture by using a neodymium hydride Nd-H compound, a dysprosium hydride Dy-H compound or a terbium hydride Tb-H compound 10 to 70 parts by weight of a solvent such as an alcohol is mixed with 100 parts by weight of a rare earth hydrogen compound containing at least one of them to prepare a slurry-form heavy rare earth mixture.

More preferably, the process for preparing a heavy rare earth mixture according to an embodiment of the present invention is preferably to prepare a heavy rare earth mixture by mixing a Dy-H compound or a Tb-H compound with a solvent because the Nd- The effect of improving magnetic properties such as coercive force is excellent.

At this time, it is preferable that the heavy rare-earth hydrogen compound has an average particle size of 1.0 to 5.0 mu m because, when it exceeds 5.0 mu m, the intergranular diffusion amount is not smooth and the degree of improvement of magnetic properties such as coercive force is insignificant. There is a problem that the production cost is increased according to the above-mentioned range.

When a solvent is added in an amount of less than 10 parts by weight based on 100 parts by weight of the heavy rare earth hydrogen compound, the viscosity of the heavy rare earth mixture prepared in a slurry state is high and can not be smoothly applied to the surface of the rare earth sintered magnet. The viscosity of the rare earth mixture becomes excessively low to reduce the amount of the middle rare earth mixture applied to the surface of the sintered rare earth sintered magnet so that the amount of rare earth elements diffused into the rare earth sintered magnet is reduced It is preferable that the above range is limited.

When a heavy rare earth mixture is prepared, a heavy rare earth mixture is applied to the surface of the rare earth sintered magnet during the application of the mixture.

When a heavy rare earth mixture is applied to the surface of the rare earth sintered magnet, the rare earth sintered magnet is charged into a furnace of vacuum or inert atmosphere in the middle rare earth diffusion process and diffused to manufacture a rare earth permanent magnet.

At this time, the heavy rare earth diffusion process can be performed at a temperature of 700 to 950 ° C for 1 to 30 hours, more preferably at a temperature of 800 to 900 ° C for 1 to 30 hours.

The reason for this is that the diffusion of heavy rare earths is not smooth at a temperature lower than 700 ° C., and when the temperature exceeds 950 ° C., the coercive force decreases as the crystal grains of the rare earth permanent magnet produced grow, This is because the degree of improvement of the coercive force is highest when it is diffused at a temperature of 800 to 900 ° C.

More preferably, the rare earth permanent magnet manufacturing method according to an embodiment of the present invention further includes a heat treatment step for removing stress by heat treatment in an inert atmosphere at a temperature of 700 to 900 DEG C for 1 to 30 hours after the grain diffusion step Preferably, the heat treatment is performed at a temperature of 800 to 900 DEG C for 1 to 30 hours to remove the stress of the rare earth permanent magnet.

The reason for this is that when the temperature is less than 700 ° C, the stress is removed for a long time, resulting in deteriorated productivity. When the temperature exceeds 900 ° C, the crystal grains of the rare earth permanent magnet grow or diffuse, It is limited to the above range.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings, wherein: And is not intended to limit the technical scope of the present invention.

In Example 1, an RTB-based alloy containing 32 wt% of R :, 1 wt% of T, 1 wt% of B, and the balance of Fe and other unavoidable impurities, which does not contain a heavy rare earth element, was dissolved by a vacuum induction heating method, A magnet ingot was produced.

In order to improve the crushability of the rare earth magnet ingot produced, hydrogen was absorbed at a hydrogen atmosphere and at room temperature, and then hydrogen was removed in a vacuum atmosphere at 600 ° C., and then the hydrogen peroxide was removed by a pulverizing method using a jet mill. A rare earth magnet powder was prepared.

At this time, the pulverization step for pulverizing the rare earth magnet ingot was performed in an inert gas atmosphere such as argon or nitrogen to prevent the magnetic properties from being contaminated with oxygen.

The rare earth magnet powder thus prepared is filled in a mold in an inert atmosphere and a direct current magnetic field is applied to the electromagnets located on the left and right of the mold to orient the rare earth magnet powder and compression molding is performed by means of upper and lower punches, Thereby preparing a magnet compact.

The rare-earth magnet compact thus prepared was charged into a sintering furnace and sufficiently maintained at a temperature of 400 ° C or lower in a vacuum atmosphere to completely remove the remaining impure organic matter. The temperature was further raised to 1020 ° C and maintained for 2 hours to sinter and diffuse, .

The rare earth sintered magnet thus prepared was cut into a size of 12.5 mm x 12.5 mm x 5 mm, dipped in an alkali degreasing agent solution, rubbed together with a ceramic ball having a size of 5 to 10 mm, The oil was removed, and the magnet was again cleaned several times with distilled water to completely remove the remaining degreasing agent.

Then, it was immersed in a nitric acid solution diluted with 1 ~ 10% concentration and pickled for 1 ~ 5 minutes to completely remove the rust generated during processing. After pickling, it was transferred again to alcohol and distilled water. The remaining nitric acid was removed and sufficiently dried to prepare a rare earth sintered magnet.

In order to uniformly coat the surface of the rare earth sintered magnet prepared above with a heavy rare earth element, a mixture of rare earth compounds and alcohol in Dy-H was mixed at a ratio of 1: 1, and the mixture was uniformly mixed to prepare a heavy rare earth mixture. And the rare earth sintered magnet was immersed therein for 1 to 2 minutes to uniformly apply the rare earth sintered magnet to the middle rare earth magnet mixture.

Then, a rare earth sintered magnet coated with a heavy rare earth mixture was charged into a heating furnace, heated in an argon atmosphere at a heating rate of 1 ° C / min and diffused into a rare earth sintered magnet in a rare earth sintered magnet while maintaining the temperature at 900 ° C for 5 hours. .

Thereafter, the magnetism was evaluated for a magnet subjected to a stress relieving heat treatment at a temperature of 900 DEG C for 10 hours, and then subjected to a final heat treatment at a temperature of 500 DEG C for one hour

On the other hand, the various examples and comparative examples of Figs. 2 and 3 were prepared under the same conditions as in Example 1, except for the conditions described in Figs. 1 and 2 below.

Figure 2 is a table showing the magnetic properties of various embodiments and comparative examples made in accordance with embodiments of the present invention.

In Comparative Examples 1 to 7 and Comparative Examples 11 to 13, as the average particle size of the rare earth magnet powder exceeds 3.0 탆, the residual magnetic flux density is comparable to that of Examples but coercive force is lowered.

On the other hand, when Comparative Examples 8 to 10 and Examples 9 to 12 are compared, when the temperature range during grain boundary diffusion exceeds 700 to 950 ° C, the coercive force decreases to 21.5 kOe or less. In particular, in Examples 9 to 11, it can be seen that when the grain boundary diffusion is performed at 800 to 900 ° C, the coercive force is improved to 22.0 kOe or more.

Comparing Examples 13 to 17 and Comparative Examples 14 to 16, it can be seen that when the heat treatment temperature exceeds 800 to 900 ° C. in the heat treatment step, the residual magnetic flux density remains the same but the coercive force gradually decreases.

3 is a table showing magnetic properties and thermal potatoes according to the average particle size of the heavy rare earth hydrogen compound.

As can be seen from FIG. 3, when the average particle size of the heavy rare earth hydrogen compound exceeds 1 to 5 μm, the residual magnetic flux density, coercive force and maximum energy efficiency (BHmax) are decreased and the thermal sensitivity is increased It is understood that the thermal demagnetization property is lowered.

Although the present invention has been described with reference to the preferred embodiments thereof, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention as defined in the following claims. It can be understood that

Claims (10)

Preparing a rare earth magnet ingot by melting the RTB alloy;
Pulverizing the rare earth magnet ingot to prepare a rare earth magnet powder having an average particle size of 3.0 탆 or less (excluding 0);
A forming step of forming the rare earth magnet powder by magnetic field shaping the rare earth magnet powder in an inert atmosphere;
A sintering step of sintering and diffusing the rare earth magnet compact to produce a rare earth sintered magnet; And
And a grain boundary diffusion step of applying a heavy rare earth mixture prepared by mixing a heavy rare earth hydrogen compound and an alcohol on the surface of the rare earth sintered magnet and diffusing in a vacuum or an inert atmosphere to produce a rare earth permanent magnet.
The method according to claim 1,
In the preparation step,
The rare earth magnet ingot is produced by strip casting 27 to 36 wt% of R, 0 to 5 wt% of T, 0 to 2 wt% of B, the balance Fe and other unavoidable impurities in a vacuum or inert atmosphere. , And a rare earth permanent magnet.
(Where R is a rare earth element, T is a transition metal, and B is boron).
The method of claim 2,
In the preparation step,
Wherein the rare earth magnet ingot is ground in an oxygen concentration atmosphere of 2,000 ppm or less so that the average grain size of the rare earth magnet powder is 1.0 to 3.0 mu m.
The method according to claim 1,
In the intergranular diffusion step,
Wherein the heavy rare earth hydrogen compound is provided in a state of powder including at least one of Nd-H compound, Dy-H compound and Tb-H compound and having an average particle size of 1.0 to 5.0 탆. Gt;
The method of claim 4,
Wherein the intergranular diffusion step comprises:
Preparing a rare earth metal mixture in which the heavy rare earth mixture in a slurry state is prepared by mixing 10 to 70 weight of a solvent with respect to 100 weight parts of the heavy rare earth hydrogen compound; And
Applying a rare earth mixture while applying the heavy rare earth mixture to the surface of the rare earth sintered magnet; And
A rare-earth permanent magnet manufacturing method comprising the steps of: charging the rare-earth sintered magnet into a heating furnace in a vacuum or an inert atmosphere and diffusing the rare-earth magnet to manufacture the rare-earth permanent magnet.
The method of claim 5,
In the heavy rare earth diffusion process,
Wherein said rare earth permanent magnet is produced by diffusion at a temperature of 700 to 950 DEG C for 1 to 30 hours to produce said rare earth permanent magnet.
The method of claim 6,
In the heavy rare earth diffusion process,
Wherein said rare earth permanent magnet is produced by diffusion at a temperature of 800 to 900 DEG C for 1 to 30 hours to produce said rare earth permanent magnet.
The method according to claim 1,
After the intergranular diffusion step,
Treating the rare earth permanent magnet in an inert atmosphere at a temperature of 700 to 900 DEG C for 1 to 30 hours to remove the stress of the rare earth permanent magnet.
The method of claim 8,
The heat treatment step may include:
Treated in an inert atmosphere at a temperature of 800 to 900 DEG C for 1 to 30 hours to remove the stress of the rare earth permanent magnet.
The method according to claim 1,
Prior to the intergranular diffusion step,
And a cleaning step of removing foreign matter adhering to the surface of the rare earth sintered magnet.

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