KR20180068272A - Method for producing rare earth permanent magnet - Google Patents

Abstract

The present invention provides a method of producing a rare earth permanent magnet that can exert an improved coercive force and thermal characteristics by effectively diffusing heavy rare earth elements along the grain boundaries of a sintered magnet. The method of producing a rare earth permanent magnet according to one embodiment of the present invention includes the steps of: preparing an NdFeB sintered magnet; coating a surface of the NdFeB sintered magnet with a grain boundary diffusion material including R hydrate or R fluoride, and RaMb or M, to form a grain boundary diffusion coating layer; and diffusing the grain boundary diffusion material into a grain boundary of the NdFeB sintered magnet by heat treatment, wherein M is a metal having a melting point higher than a heat treatment temperature during the diffusion, R is a rare earth element, and a and b respectively represent atomic percentages which satisfy the following expressions (1) and (2): 0.1 < a < 99.9 (1), and a + b = 100 (2).

Description

METHOD FOR PRODUCING RARE EARTH PERMANENT MAGNET

The present invention relates to a rare earth permanent magnet manufacturing method in which an alloy powder containing a rare earth element is applied and then heat-treated to diffuse rare earth elements into the grain boundaries of a sintered magnet. More particularly, the present invention relates to an alloy powder containing cobalt (Co) To a rare-earth permanent magnet manufacturing method in which the coercive force is improved and the thermal demagnetization property is improved by diffusing the rare earth element into the grain boundaries of the Nd-Fe-B sintered magnet.

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 output of the motor becomes high and the size thereof can be reduced, and the use range thereof is gradually increasing.

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.

On the other hand, the magnetic properties of a magnet can be represented by residual magnetic flux density and coercive force, wherein the residual magnetic flux density is determined by the fraction, the density and the degree of self-orientation of the rare earth permanent magnet column, and the coercive force The coercive force has a definite relation with the microstructure of the microstructure and is determined by the finer grain size or the uniform distribution of grain boundaries.

Accordingly, various other methods for improving the coercive force of the permanent magnets have been proposed. The magnet alloy method is a method of manufacturing a magnet by mixing other alloy powders having two kinds of compositions, forming a magnetic field, and sintering.

This is because the R-Fe-B powder (where R is rare earth) and rare earth elements such as aluminum (Al) and titanium (Ti), including dysprosium (Dy) or terbium (Tb), which are rare earth elements are composed of neodymium (Nd) or praseodymium (Dy) and terbium (Tb) elements of the alloy powder diffuse into the crystal grains in the sintering process. In the sintering process, the alloying powder is mixed with the alloy powders containing molybdenum (Mo) and molybdenum The effect is deteriorated.

Recently, a grain boundary diffusion method is mainly used in which a coating layer containing a rare earth element such as dysprosium (Dy) or terbium (Tb) is formed on the surface of a sintered magnet and then diffused into the inside of the sintered magnet to improve magnetic properties such as coercive force have.

The intergranular diffusion method is roughly divided into two methods according to the coating layer forming method. First, a coating layer is formed by sputtering or vapor deposition of dysprosium (Dy) or terbium (Tb) on the surface of the sintered magnet, There is a problem in that a large cost is consumed in the manufacturing process, the manufacturing cost is increased, and the productivity is poor and mass production is difficult.

The method of applying the dysprosium (Dy) and the terbium (Tb) on the surface of the sintered magnet in the form of oxide or fluoride on the surface of the sintered magnet and then diffusing the phase by grain boundary diffusion is advantageous in that the process is relatively simple and the productivity is excellent. Dy) and terbium (Tb) are diffused by a substitution reaction. Therefore, it is difficult to diffuse large amounts of these elements into the sintered magnet, so that there is a limit to improvement in coercive force. In particular, fluorides and oxides not only interfere with grain boundary diffusion of pure rare earth elements, And remained in the manufactured permanent magnets, thereby limiting the improvement of the coercive force.

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 10-2012-0124039 A (Nov 11, 2012)

Disclosure of Invention Technical Problem [8] Accordingly, the present invention provides a rare earth permanent magnet manufacturing method capable of improving coercive force and thermal characteristics of a rare earth permanent magnet produced by effectively diffusing a heavy rare earth element along a grain boundary of a sintered magnet do.

The present invention also provides a rare earth permanent magnet manufacturing method capable of uniformly diffusing a medium rare earth element while improving the grain boundary diffusion rate.

The present invention also provides a rare earth permanent magnet manufacturing method capable of improving the corrosion resistance and omitting the oxide film removing step after grain boundary diffusion.

According to an embodiment of the present invention, a rare earth permanent magnet manufacturing method includes preparing a NdFeB sintered magnet;

A coating step of applying a grain boundary diffusion material containing R hydrate or R fluoride and RaMb or M to the surface of the NdFeB sintered magnet to form a grain boundary diffusion coating layer; And diffusing the intergranular diffusion material to the grain boundary of the NdFeB sintered magnet by heat treatment, wherein M is a metal having a melting point higher than the heat treatment temperature of the diffusion step, R is a rare earth element, b is an atomic percentage and is characterized by satisfying the following equations (1) and (2) simultaneously.

0.1 < a < 99.9 -------------- (1)

a + b = 100 - (2)

The M is preferably a metal having a melting point of 1000 ° C or higher.

More preferably, the R is any one selected from dysprosium (Dy), terbium (Tb), neodymium (Nd), praseodymium (Pr) and holmium (Ho), and M is cobalt .

In the preparing step, the NdFeB sintered magnet is a mixture of 30 to 35 wt% of a rare earth element including dysprosium (Dy), terbium (Tb), neodymium (Nd), praseodymium (Pr), cobalt 0 to 10 wt% of the total weight of the transition metal including aluminum (Al), copper (Cu), gallium (Ga), zirconium (Zr), and niobium (Nb) And the like.

In the coating step, the intergranular diffusion material may include 1 to 7 wt% of cobalt (Co).

In the coating step, the R hydrate is TbH ₂ , TbH ₃ . DyH ₂ , and DyH ₃ , and the R fluoride is any one of TbF ₂ , TbH ₃ . DyF ₂ , and DyF ₃ .

The coating step may be characterized in that the particle diffusion material is coated on the surface of the NdFeB sintered magnet by a spray method, a suspension sticking method or a barrel painting method to form the coating layer.

The intergranular diffusion material preferably contains 10 to 70 wt% of R and is higher than the rare earth element content contained in the NdFeB sintered magnet.

Wherein the coating step comprises: _a melting step of melting the R hydrate or R fluoride and R _a M _b or M to prepare a molten cobalt alloy; A cooling process for cooling the molten cobalt alloy to prepare a cobalt alloy ingot; A pulverizing step of pulverizing the cobalt alloy ingot to prepare a grain boundary diffusion material in a powder state; And a coating process of applying the intergranular diffusion material to the surface of the NdFeB sintered magnet to form the intergranular diffusion coating layer.

The diffusion step may be characterized in that it is heated and diffused at a temperature of 700 to 1,000 DEG C in an inert atmosphere.

According to the embodiment of the present invention, by diffusing a rare earth element together with cobalt (Co) having an excellent corrosion resistance and a high melting point, the thermal sensitivity of the rare earth permanent magnet can be reduced to improve the thermal characteristics, So that the coercive force of the rare-earth permanent magnet can be improved.

In addition, since a separate oxide film removing process for removing the oxide film after grain boundary diffusion of the rare earth permanent magnet manufactured can be omitted, the productivity can be improved and the manufacturing cost can be reduced.

Furthermore, by enabling the uniform grain boundary diffusion of the rare earth element in the sintered magnet, it is possible to make the quality of the produced rare earth permanent magnet uniform.

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 view schematically showing a rare-earth permanent magnet manufacturing method according to an embodiment of the present invention,
3 is a table showing the longitudinal magnetic characteristics and the thermal sensitivity of the rare-earth permanent magnet prepared using the intergranular diffusion material according to various embodiments of the present invention,
FIG. 4 is a table showing the longitudinal magnetic properties and the thermal sensitivity of a rare-earth permanent magnet prepared using various comparative examples including a low melting point metal,
5 is a photograph showing the diffusion state of the rare-earth permanent magnet manufactured according to an embodiment of the present invention in the grain boundary.

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.

Disclosed is a rare earth permanent magnet produced by diffusing a rare-earth element such as dysprosium (Dy) or terbium (Tb) and a metal having a melting point of 1,000 ° C or higher together in a grain boundary of an NdFeB sintered magnet, It is possible to improve the magnetic characteristics such as the coercive force of the rare earth permanent magnet to be formed, reduce the thermal sensitivity, and omit the separate oxide film removing step, thereby simplifying the process.

FIG. 1 is a flowchart illustrating a method of manufacturing a rare-earth permanent magnet according to an embodiment of the present invention, and FIG. 2 is a view schematically showing a method of manufacturing a rare-earth permanent magnet according to an embodiment of the present invention.

1 and 2, a rare-earth permanent magnet manufacturing method according to an embodiment of the present invention includes a step of preparing an NdFeB sintered magnet 10 and a step of forming a grain boundary diffusion coating layer 10 on the surface of the NdFeB sintered magnet 10, And a diffusion step of diffusing the intergranular diffusion material (200).

The preparation step is such that the NdFeB sintered magnet 10 to be manufactured contains 30 to 35 wt% of rare earth elements including dysprosium (Dy), terbium (Tb), neodymium (Nd), praseodymium (Pr), cobalt The sum of the weight ratio of transition metals including aluminum (Al), copper (Cu), gallium (Ga), zirconium (Zr) and niobium (Nb) is 0 to 10 wt%, boron (B) ) Is melted by heating at 1300 to 1550 ° C using a high-frequency melting furnace, and the NdFeB alloy is prepared by strip casting.

When the NdFeB alloy is prepared, the NdFeB alloy is finely ground through hydrogenation and dehydrogenation, and then pulverized using a jet mill to produce NdFeB powder. In this case, the NdFeB powder has a diameter of 3 to 5 μm .

As described above, when the NdFeB powder is prepared, the NdFeB sintered magnet 10 is manufactured by sintering and heat treatment using a magnetic field molding machine in which the magnetic field direction and the forming direction are perpendicular to each other.

The preparation step according to an embodiment of the present invention is preferably performed in an inert atmosphere filled with nitrogen (N) or argon (Ar) gas, because the impurities such as carbon (C) or oxygen This is because the magnetic properties of the NdFeB sintered magnet 10 manufactured by this method can be minimized.

As described above, when the NdFeB sintered magnet 10 is provided, the intergranular diffusion material 200 is applied to the surface of the NdFeB sintered magnet 10 in the coating step to form a grain boundary diffusion coating layer.

The intergranular diffusion material 200 according to an embodiment of the present invention is provided with R hydrate or R fluoride included as a rare earth element and cobalt (Co) or cobalt alloy represented by M or R _a M _b .

R is any rare earth element selected from dysprosium (Dy), terbium (Tb), neodymium (Nd), praseodymium (Pr) and holmium (Ho), M is a metal having a melting point of 1,000 ° C or higher, b is preferably provided so as to satisfy the following equations (1) and (2) at the same time as the atomic percentages.

0.1 < a < 99.9 -------------- (1)

a + b = 100 - (2)

More specifically, in the present invention, the R hydrate is TbH2, TbH3. DyH2, and DyH3, and the R fluoride is TbF2, TbH3. DyF2, and DyF3 were selected, and M was cobalt (Co).

The cobalt (Co) used in the present invention is one of relatively high metals having a melting point of 1,498 DEG C and then melted together with R hydrate or R fluoride as the temperature of the rare earth element is increased for intergranular diffusion of the rare earth element, , Thereby forming a liquid phase intergranular diffusion material having a lowered melting point.

Thus, it is possible to improve the magnetic properties of the rare-earth permanent magnet manufactured by improving dispersibility and facilitating diffusion by increasing the intergranular diffusion speed of the intergranular diffusion material 200 including the rare earth element, So that the quality of the rare-earth permanent magnets can be made uniform.

At this time, when a low melting point metal such as zinc (Zn) or aluminum (Al) having a melting point of less than 700 캜 and a relatively low melting point is used as M, the melting point of dysprosium (Dy) and terbium (Tb) But it does not affect the Curie temperature of the produced magnet and can not improve the thermal demagnetization property.

On the other hand, cobalt (Co) which is a refractory metal used in the present invention has a lower oxidizing power than neodymium (Nd) and has a high Curie temperature, thereby improving magnetic properties at high temperatures. NdFeB It is possible to reduce the thermal sensitivity of a magnet manufactured by replacing the grain boundaries of the sintered magnet 10 with neodymium (Nd) in grain boundaries and to improve corrosion resistance.

More preferably, the intergranular diffusion material 200 according to an embodiment of the present invention includes 10 to 70 wt% of a rare earth element represented by R, and the content of the rare earth element contained in the NdFeB sintered magnet 10 It is preferable that it is contained at a high level.

The reason is that when the content of the rare earth element in the intergranular diffusion material 200 is less than 10 wt%, the amount of the rare earth element diffused into the grain boundary 100 is small and the improvement of the magnetic property is insignificant. When the content is more than 70 wt% So that the manufacturing cost is increased by raising the cost of the rare-earth permanent magnet manufactured.

When the content of the rare earth element contained in the NdFeB sintered magnet is lower than that of the rare earth element contained in the NdFeB sintered magnet, the diffusion effect is lowered into the crystal grains of the NdFeB sintered magnet, It is desirable to improve the property.

On the other hand, it is preferable that the content of cobalt (Co) is 1 to 7 wt% because if the content of cobalt (Co) is less than 1 wt%, the effect of improving coercive force by cobalt (Co) If it exceeds 7 wt%, the magnetic properties such as the coercive force of the rare-earth permanent magnet, which is rather produced, are lowered as the ratio of the R hydrate or R fluoride formed with the molten cobalt molten compound is lowered. Limit.

The coating step according to one embodiment of the present invention includes _a melting step of melting the R hydrate or R fluoride and R _a M _b or M as described above to prepare a molten cobalt alloy and filling the melted cobalt alloy melt into a mold, And a cobalt alloy ingot is pulverized by using a ball mill to prepare a powdered grain boundary diffusion material 200 and a pulverizing process for preparing a NdFeB sintered magnet 10, To form a grain boundary diffusion coating layer.

At this time, the intergranular diffusion coating layer may be formed by one of the spraying method, the suspension sticking method, and the barrel painting method.

The spraying method is a method in which powdery granular diffusion material 200 is sprayed onto the surface of the NdFeB sintered magnet 10 by spraying with a solvent or the like. In the suspension-adhering method, a powdery intergranular diffusion material Means that the suspension is immersed in the suspension and the NdFeB sintered magnet 10 is immersed in the suspension so that the suspension is lifted while being attached to the surface of the NdFeB sintered magnet 10 and dried.

In the barrel painting method, an adhesive layer is formed by applying an adhesive material such as liquid paraffin to the surface of the NdFeB sintered magnet 10, and a powder of the grain boundary diffusion material 200 in powder form and a metal or ceramic material of about 1 mm in diameter When the NdFeB sintered magnet 10 is charged into the mixture and vibrated and stirred, the intergranular diffusion material 200 is pushed against the adhesive layer by the impact medium, And the grain boundary diffusion material 200 is applied to the surface of the NdFeB sintered magnet 10.

In the present invention, the thickness of the intergrowth diffusion coating layer applied to the surface of the NdFeB sintered magnet 10 is preferably 5 to 150 탆, because when the thickness of the intergrowth diffusion coating layer exceeds 150 탆, Diffusion of the diffusion material 200 becomes difficult, and when the thickness is less than 5 mu m, the effect of improving the coercive force by the grain boundary diffusion treatment can not be sufficiently obtained.

As described above, when the formation of the intergranular diffusion coating layer is completed, the molten intergranular diffusion material 200 is heated to 700-1,000 DEG C in the diffusion step to diffuse the intergranular diffusion material 200 into the grain boundary 100 of the NdFeB sintered magnet 10, A material-diffused grain boundary grain 300 is formed to produce a rare-earth permanent magnet.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

division Nd Pr Dy Tb Co B Al Cu C O Fe wt% 27 One One One 2 One 0.5 0.25 0.01 0.12 Honey.

Table 1 is a table showing the composition of the NdFeB sintered magnet manufactured according to the embodiment of the present invention.

After the intergranular diffusion material 200 having various compositions was applied to the surface of the NdFeB sintered magnet 10 having the composition shown in Table 1, the intergranular diffusion material 200 was heat-treated at 800 ° C for 4 hours to perform grain boundary diffusion, And FIG. 4, respectively.

As can be seen from Table 1 and Figs. 3 and 4, when the intergranular diffusion material containing a low-melting metal such as zinc or aluminum is used, the coercive force and the magnetic flux density are improved, but the thermal sensitivity is similar to that of rare earth permanent magnets The characteristics can not be improved.

On the other hand, when the composition of the intergranular diffusion material 200 satisfies the present invention, not only the magnetic properties such as coercive force are excellent, but also the thermal sensitivity is decreased, thereby improving the thermal characteristics of the rare earth permanent magnet manufactured.

At this time, more preferably, the content of cobalt (Co) in the grain boundary diffusion material 200 according to an embodiment of the present invention is preferably 1 to 7 wt%. The reason is that the degree of improvement in thermal characteristics and coercive force is insignificant when the content is less than 1 wt%, and the thermal characteristics and coercive force tend to be decreased when the content exceeds 7 wt%.

5 is a photograph showing the diffusion state of the rare-earth permanent magnet manufactured according to an embodiment of the present invention in the grain boundary.

5, according to an embodiment of the present invention, the grain boundary diffusion material 200 is uniformly distributed along the grain boundaries of the NdFeB sintered magnet 10 to uniformize the quality of the rare earth permanent magnet produced It can be seen that there is an effect.

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

10: NdFeB sintered magnet 100: Grain grain boundary
200: grain boundary diffusion material 300: grain boundary grain diffusion material diffusion

Claims (10)

Preparing a NdFeB sintered magnet;
A coating step of applying a grain boundary diffusion material containing R hydrate or R fluoride and RaMb or M to the surface of the NdFeB sintered magnet to form a grain boundary diffusion coating layer; And
And diffusing the intergranular diffusion material to the grain boundary of the NdFeB sintered magnet by heat treatment,
Wherein M is a metal having a melting point higher than a heat treatment temperature of the diffusion step and R is a rare earth element and a and b are atomic percentages and satisfy the following equations (1) and (2) simultaneously: A method for manufacturing a rare earth permanent magnet.
0.1 < a < 99.9 -------------- (1)
a + b = 100 - (2)
The method according to claim 1,
And M is a metal having a melting point of 1000 ° C or higher.
The method of claim 2,
Wherein R is any one selected from dysprosium (Dy), terbium (Tb), neodymium (Nd), praseodymium (Pr), holmium (Ho), and M is cobalt (Co) Gt;
The method of claim 3,
In the preparation step,
The NdFeB sintered magnet has a weight ratio of rare earth elements including dysprosium (Dy), terbium (Tb), neodymium (Nd) and praseodymium (Pr) of 30 to 35 wt%, cobalt (Co), aluminum (Al) (B), and the balance of iron (Fe), in terms of the weight ratio of the transition metal including transition metal (Cu), gallium (Ga), zirconium (Zr), and niobium Of the rare earth permanent magnet.
The method of claim 3,
In the coating step,
Wherein the intergranular diffusion material contains 1 to 7 wt% of cobalt (Co).
The method of claim 5,
In the coating step,
The R hydrate is TbH ₂ , TbH ₃ . DyH ₂ , and DyH ₃ , and the R fluoride is any one of TbF ₂ , TbH ₃ . DyF ₂ , and DyF ₃ , respectively.
The method according to claim 1,
Wherein the coating step comprises:
Characterized in that the particle diffusion material is coated on the surface of the NdFeB sintered magnet by a spray method, a suspension adhesion method, or a barrel painting method to form the coating layer.
The method of claim 4,
Wherein the intergranular diffusion material comprises:
Characterized in that it contains 10 to 70 wt% of R and is higher than the rare earth element content contained in the NdFeB sintered magnet.
The method of claim 3,
Wherein the coating step comprises:
A melting step of melting the R hydrate or R fluoride and R _a M _b or M to prepare a molten cobalt alloy;
A cooling process for cooling the molten cobalt alloy to prepare a cobalt alloy ingot;
A pulverizing step of pulverizing the cobalt alloy ingot to prepare a grain boundary diffusion material in a powder state; And
And coating the surface of the NdFeB sintered magnet with the intergranular diffusion material to form the intergranular diffusion coating layer.
The method of claim 2,
Wherein the spreading step comprises:
In an inert atmosphere, by heating at a temperature of 700 to 1,000 DEG C to diffuse the rare earth permanent magnet.

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