KR102589870B1 - Manufacturing method of rare earth sintered magnet - Google Patents

Abstract

The object of the present invention is to apply a slurry of a low melting point metal (TM) or a low melting point metal compound (TMX) to the surface of a sintered magnet to first diffuse the low melting point metal into the inside of the sintered magnet, and then to spread the heavy rare earth metal on the surface of the sintered magnet again. A rare earth permanent magnet manufacturing method that can effectively diffuse into the inside of the sintered magnet when the heavy rare earth metal (RE) diffuses from the grain boundary of the sintered magnet by applying a compound (REX) slurry to secondary diffusion of the heavy rare earth metal into the sintered magnet. It is provided.

Description

Manufacturing method of rare earth permanent magnet {Manufacturing method of rare earth sintered magnet}

In the present invention, after primary diffusion of a low melting point metal into the inside of the sintered magnet, the medium rare earth metal is then secondary diffusion into the inside of the sintered magnet, so that the medium rare earth metal can effectively diffuse into the inside of the sintered magnet when it diffuses from the grain boundary of the sintered magnet. This relates to a method of manufacturing rare earth permanent magnets.

Recently, as energy reduction and environmentally friendly green growth projects have emerged as new issues, the automobile industry is using hybrid vehicles that use internal combustion engines using fossil raw materials in parallel with a motor or hydrogen, an environmentally friendly energy source, as alternative energy to generate electricity. Research on fuel cell vehicles that generate electricity and drive motors is actively underway.

Since these environmentally friendly cars are driven using electrical energy, permanent magnet motors and generators are inevitably used. In terms of magnetic materials, rare earth permanent magnets that exhibit higher residual magnetic flux density and stable coercive force are used to further improve energy efficiency. The demand for magnets is increasing.

In addition, in order to improve the fuel efficiency of automobiles, it is necessary to realize lightweight and miniaturization of automobile parts. For example, in the case of motors, in order to realize lightweight and miniaturization, in addition to motor design technology, the permanent magnet material is ferrite, which was previously used. It is essential to replace the magnets with rare earth permanent magnets that exhibit better magnetic performance.

Demand for rare earth (NdFeTmB) sintered magnets is gradually increasing for motors such as hybrid cars, and it is required to further increase the coercive force (Hcj). In order to increase the coercive force (Hcj) of rare earth (NdFeTmB) sintered magnets, a method of substituting part of Nd with Dy or Tb is known, but the resources of Dy and Tb are scarce and ubiquitous, and these elements The problem is that the residual magnetic flux density (Br) or maximum energy product ((BH)max) of the rare earth (NdFeTmB) sintered magnet decreases due to the substitution of

Recently, in order to solve this problem, medium rare earth metal powder is applied to the surface of the sintered magnet and heat treated to spread it along the grain boundaries of the sintered magnet, and finally diffuses into the grains, forming a medium rare earth diffusion layer inside the crystal grains. The process is being applied.

The formation of a medium rare earth metal diffusion layer inside the sintered magnet acts as a mechanism to suppress reverse magnetic domain nucleation, which causes demagnetization when the permanent magnet is exposed to a reverse magnetic field, and is the latest technology to dramatically improve the coercivity compared to the amount of medium rare earth metal powder used. It's technology.

However, during the grain boundary diffusion process of the heavy rare earth metal, when the heavy rare earth metal applied to the magnet surface diffuses and penetrates into the magnet, it must diffuse along narrow grain boundaries of several nm, resulting in a uniform composition distribution of the heavy rare earth from the magnet surface to the inner center. There is a problem that it cannot be maintained. This is because only a portion of the heavy rare earth metal that quickly penetrated through the magnet surface at the beginning of grain boundary diffusion penetrates into the interior along narrow grain boundaries, and as the penetration progresses, the diffusion rate gradually slows down, so the distribution of heavy rare earth metal in the magnet after grain boundary diffusion is completed is reduced. When measured, a non-uniform distribution of heavy rare earth composition is formed, with a high heavy rare earth concentration on the surface of the magnet and almost no heavy rare earth inside.

In this way, the uneven distribution of heavy rare earth metals inside the sintered magnet causes severe residual stress inside the magnet and causes the coercive force and thermal demagnetization characteristics to not be sufficiently improved in terms of magnetic properties.

Korean Patent Publication No. 10-1534717 (registered on July 1, 2015)

The present invention is intended to solve the problem of non-uniform grain boundary diffusion of heavy rare earth metal applied for the magnetic properties of rare earth permanent magnets, which is a prior art. By effectively diffusing heavy rare earth metal from the inside of the magnet to the center, the coercive force and heat of the rare earth permanent magnet are improved. The aim is to provide a method for manufacturing rare earth permanent magnets that can improve magnetic properties.

Specifically, a low melting point metal (TM) or low melting point metal compound (TMX) slurry is applied to the surface of the sintered magnet to first diffuse the low melting point metal into the crystalline boundary of the sintered magnet, and then a heavy rare earth metal compound is again spread on the surface of the sintered magnet. (REX) Provides a rare earth permanent magnet manufacturing method that can effectively diffuse into the inside of the sintered magnet when the heavy rare earth metal (RE) diffuses from the grain boundary of the sintered magnet by applying slurry to secondary diffusion of the heavy rare earth metal into the sintered magnet. It is done.

In order to achieve the above-described object, the method for manufacturing rare earth permanent magnets according to the present invention is xwt%RE-ywt%B-zwt%TM-bal.wt%Fe (RE=rare earth element, TM=3d transition element) , x = 28 to 35, y = 0.5 to 1.5, z = 0 to 15), a sintering step (S1) of manufacturing a sintered magnet, which is a rare earth permanent magnet with a composition; A sintered magnet processing step (S2) of processing the sintered magnet to the size standard of the desired product; A low melting point metal (TM) slurry or a low melting point metal compound (TMX) slurry having a melting temperature of the alloy material in the range of 650 to 1100° C. is uniformly applied to the surface of the processed sintered magnet. Melting point metal compound (TMX) slurry application step (S3); The sintered body with the low melting point metal (TM) slurry or low melting point metal compound (TMX) slurry applied to the surface is charged into a heating furnace and the low melting point metal (TM) slurry or low melting point metal compound as the coating material is placed in a vacuum or inert gas atmosphere. (TMX) low melting point metal diffusion step (S4) in which the low melting point metal (TM) separated from the slurry is first diffused into the sintered magnet; A heavy rare earth metal compound (REX) coating step (S5) of coating the heavy rare earth metal compound (REX) slurry on the surface of the low melting point metal diffused sintered magnet; A heavy rare earth metal diffusion step in which a sintered magnet coated with the heavy rare earth metal compound (REX) slurry is charged and the heavy rare earth metal compound (REX) is decomposed in a vacuum or inert gas atmosphere to secondary diffuse the heavy rare earth metal into the sintered magnet. (S6); An additional heat treatment step (S7) in which the sintered magnet in which the heavy rare earth metal is diffused is subjected to additional heat treatment in the range of 400 to 1000° C. in a vacuum or inert gas atmosphere; It is characterized by including.

In the method of manufacturing a rare earth permanent magnet according to the present invention, in the heavy rare earth metal compound (REX) coating step, the heavy rare earth metal (RE) contains at least one of the rare earth elements at 10 at.% ( It is characterized in that it contains more than 10 parts by weight, based on 100 parts by weight of rare earth metal powder in the sintering step (S1).

In the method of manufacturing a rare earth permanent magnet according to the present invention, the low melting point metal (TM) or low melting point metal compound (TMX) used as the coating material is Co, Cu, Al, Ga, Nb. , Ti, Mo, V, Zr, and Zn.

In the method of manufacturing a rare earth permanent magnet according to the present invention, X in the heavy rare earth metal compound (REX) used as the coating material is characterized in that it contains at least one of hydrogen, oxygen, and fluorine.

In the method of manufacturing a rare earth permanent magnet according to the present invention, X in the low melting point metal compound (TMX) used as the coating material is characterized in that it contains at least one of hydrogen, oxygen, and fluorine.

In the method for producing a rare earth permanent magnet according to the present invention, the low melting point metal (TM) slurry or low melting point metal compound (TMX) slurry in the low melting point metal (TM) or low melting point metal compound (TMX) application step (S3). The method of applying is one of spraying, dipping, plating (electroless, electrolytic), and deposition methods.

In the method of manufacturing a rare earth permanent magnet according to the present invention, the method of applying the heavy rare earth metal compound (REX) in the heavy rare earth metal compound coating step (S5) is characterized by one of spraying, dipping, and deposition methods.

In the method for manufacturing rare earth permanent magnets according to the present invention, RE=Nd, Pr, La, Ce, Ho, Dy, Tb, or more rare earth metals are included.

In the method of manufacturing a rare earth permanent magnet according to the present invention, the heavy rare earth metal compound used in the application step of the heavy rare earth metal compound (REX) slurry is characterized by being one or more of Ho-compound, Dy-compound, and Tb-compound. do.

In the method for manufacturing rare earth permanent magnets according to the present invention, the low melting point metal (TM) or low melting point metal compound (TMX) slurry contains 35 to 55 wt% of low melting point metal (TM) or low melting point metal compound (TMX) and 45 to 55 wt% of alcohol. It is characterized by mixing 65wt%.

In the method of manufacturing a rare earth permanent magnet according to the present invention, the heavy rare earth metal compound (REX) slurry is characterized by mixing 35 to 55 wt% of the heavy rare earth metal compound and 45 to 65 wt% of alcohol.

In the method of manufacturing a rare earth permanent magnet according to the present invention, in the step of applying the low melting point metal (TM) or low melting point metal compound (TMX) slurry or heavy rare earth metal compound (REX) slurry, the permanent magnet is heated to a temperature of 100 ° C. or lower. It is characterized by: Preferably, it is heated in the temperature range of 60 to 80°C.

In the method of manufacturing a rare earth permanent magnet according to the present invention, the low melting point metal (TM) or low melting point metal compound (TMX) slurry or heavy rare earth metal compound (REX) slurry is supplied as droplets using a metering pump, and the supplied liquid It is characterized by atomizing the enemy using ultrasonic waves and applying it more than once.

In the method of manufacturing a rare earth permanent magnet according to the present invention, the ultrasonic waves are used to atomize low melting point metal (TM) or low melting point metal compound (TMX) slurry or heavy rare earth metal compound (REX) slurry through a carrier gas at a distance of 0.8 to 2 m/. It is characterized in that it is applied to the surface of the permanent magnet at least once at a speed of sec.

In the method of manufacturing a rare earth permanent magnet according to the present invention, the ultrasonic waves are used to atomize low melting point metal (TM) or low melting point metal compound (TMX) slurry or heavy rare earth metal compound (REX) slurry through a carrier gas at a distance of 0.8 to 2 m/. When applied to the surface of a permanent magnet at a speed of sec, it is applied more than once to have a whirlwind-shaped directionality.

In the method of manufacturing a rare earth permanent magnet according to the present invention, the low melting point metal (TM) or low melting point metal compound (TMX) slurry or the heavy rare earth metal compound (REX) slurry is applied in the form of droplets by ultrasonic waves, and then It is characterized by heating a permanent magnet coated with rare earth metal compound (REX) slurry to a temperature of 100°C or lower.

In the method of manufacturing a rare earth permanent magnet according to the present invention, the low melting point metal (TM) or low melting point metal compound (TMX) slurry is applied in the form of droplets by ultrasonic waves, and then the low melting point metal (TM) or low melting point metal compound (TMX) slurry is applied in the form of droplets. A permanent magnet coated with compound (TMX) slurry is heated to a temperature of 100°C or lower, and a medium different from the low melting point metal (TM) or low melting point metal compound (TMX) slurry previously applied to the surface of the heated permanent magnet is applied. It is characterized by applying a rare earth metal compound (REX) slurry and heating the permanent magnet to which the heavy rare earth metal compound (REX) slurry is applied to a temperature of 100°C or lower.

The present invention applies a low melting point metal (TM) slurry or a low melting point metal compound (TMX) slurry to the surface of a sintered magnet to first diffuse the low melting point metal into the inside of the sintered magnet, and then spread the heavy rare earth metal compound to the surface of the sintered magnet again. (REX) By applying the slurry to secondarily diffuse the heavy rare earth metals into the sintered magnet, the low melting point metal is first diffused to the grain boundaries of the sintered magnet, thereby reducing the rare earth metal rich phase (Nd-rich) and the low melting point metal present at the grain boundaries. By combining metals, the melting point of the rare earth metal-rich phase (Nd-rich) of the sintered magnet can be lowered, and the rare earth metal-rich phase (Nd-rich) with this lowered melting point can exist continuously and uniformly at the grain boundaries. When the heavy rare earth metal (RE) separated from the secondarily applied heavy rare earth metal compound (REX) spreads to the grain boundaries of the sintered magnet, it effectively diffuses into the inside of the sintered magnet, improving the coercive force and thermal demagnetization characteristics. There is an effect.

Hereinafter, the present invention will be described in more detail. Hereinafter, “upward,” “downward,” “front,” and “rear” and other directional terms are defined based on the states shown in the drawings.

[Manufacturing method]

(1) Step of manufacturing sintered magnet (S1)

As a raw material powder, a powder made of a rare earth alloy is prepared. The rare earth alloy is at least one selected from RE=Nd, Pr, La, Ce, Ho, Dy, Tb, and Fe, TM=Co, Cu, Al, Ga, Nb, Ti, Mo, V, Zr, and Zn. When B is at least one type selected from one or more 3d transition metals, RE-Fe alloy, RE-Fe-TM alloy, RE-Fe-B alloy, or RE-Fe-TM-B alloy may be mentioned. More specifically, Nd-Fe-B alloy, Nd-Fe-Co alloy, Nd-Fe-Co-B alloy, etc. can be mentioned. Powders made of known rare earth alloys used in rare earth sintered magnets can be used as the raw material powder.

Raw material powder is xwt%RE-ywt%B-zwt%TM-bal.wt%Fe (RE=rare earth element, TM=3d transition element, x=28~35, y=0.5~1.5, z=0~15) It is an alloy of composition.

Raw material powder made of an alloy of the desired composition is melted and cast ingots or thin bodies obtained by rapid solidification are pulverized with a grinding device such as a jet mill, atritamil, ball mill, or vibrating mill, or gas atomized. It can be manufactured using the same atomization method. Powder obtained by a known powder production method or powder produced by an atomization method may be further pulverized and used. By appropriately changing the grinding conditions or manufacturing conditions, the particle size distribution of the raw material powder and the shape of each particle constituting the powder can be adjusted. The shape of the particle is not particularly important, but the closer it is to a true sphere, the easier it is to become densified, and the more easily the particle rotates when a magnetic field is applied. By using the atomization method, powder with a high degree of sphericity can be obtained.

In the process of coarsely crushing the manufactured alloy strip, the strip is charged into a vacuum furnace, evacuated, and maintained in a hydrogen atmosphere at room temperature for more than 2 hours to absorb hydrogen into the strip, and then heated to 600°C in a vacuum atmosphere to heat the inside of the strip. Remove hydrogen present in.

Using hydrogen-treated powder that has completed coarse grinding, it is manufactured into a uniform, fine powder with an average particle diameter ranging from 1 to 10.0㎛ by grinding using jet mill technology in a nitrogen or inert gas atmosphere.

Since the finer the raw material powder, the easier it is to increase the packing density, the maximum particle size is preferably 5.0 μm or less.

A lubricant can be added to the raw material powder. When a mixture containing a lubricant is used, each particle constituting the raw material powder is likely to rotate when a magnetic field is applied, and the orientation is likely to be improved. Lubricants can be used in various materials and forms (liquid, solid) that do not substantially react with the raw material powder. For example, liquid lubricants include ethanol, machine oil, silicone oil, and castor oil, and solid lubricants include metal salts such as zinc stearate, hexagonal boron nitride, and wax. The amount of lubricant added is in the range of 0.01 mass% to 10 mass% based on 100 g of raw material powder for liquid lubricants, and in the range of 0.01 mass% to 5 mass% based on the mass of raw material powder for solid lubricants.

In order to obtain a powder compact of the desired shape and size, a mold for molding of the desired shape and size is prepared. The mold for molding can be one that has conventionally been used in the production of compacted compacts used as materials for sintered magnets, and typically has a die and an upper and lower punch. In addition, cold isostatic press can be used.

When the raw material powder is filled into the mold for molding, current is applied to the magnets located on the left and right sides of the mold in a nitrogen atmosphere to generate a magnetic field, thereby performing compression molding while maintaining the direction of the completely oriented powder. Manufacture molded bodies.

The molded body obtained by magnetic field molding is charged into a sintering furnace and sufficiently maintained in a vacuum atmosphere and below 400°C to completely remove remaining impure organic substances.

Sinter again under the sintering conditions: temperature 900°C to 1200°C, holding time: 0.5 to 3 hours, atmosphere: vacuum, argon, etc. Preferably, the temperature range is 1,000 to 1,100°C, and the holding time is preferably 1 to 2 hours and 30 minutes.

(2) Processing the sintered magnet to a predetermined size (S2)

The sintered magnet is processed into a magnet with a size of 12.5*12.5*5mm.

After immersing the processed magnet into predetermined sizes in an alkaline degreaser solution, the oil on the surface of the magnet was removed by rubbing it with a ceramic ball with a diameter of 2 to 10, and the remaining magnet was thoroughly cleaned with distilled water several times. Remove the degreaser completely.

(3) Low melting point metal (TM) slurry or low melting point metal compound (TMX) slurry application step (S3)

Applying low melting point metal (TM) slurry or low melting point metal compound (TMX) slurry to the surface of the processed sintered magnet is to diffuse the low melting point metal (TM) into the grain boundaries inside the magnet.

The grain boundary of the sintered magnet contains a rare earth metal-rich phase (Nd-rich). The rare earth metal-rich phase (Nd-rich) has a high content of rare earth metals, a low content of Fe, and transition metals such as Cu, Al, Ga, Nb, It is a multi-element alloy element that combines oxygen with rare earth metals such as Zr. Due to this composition ratio, the rare earth metal-rich phase (Nd-rich) melts at a lower temperature than the main phase RE ₂ Fe ₁₄ B. A common method of controlling the melting temperature of the rare earth metal-rich phase (Nd-rich) is to additionally add low melting point elements.

The present invention applies a low melting point metal (TM) slurry or a low melting point metal compound (TMX) slurry to the surface of the sintered magnet to lower the melting temperature of the rare earth metal-rich phase (Nd-rich) present at the grain boundary of the sintered magnet. This is to diffuse metal (TM) into the grain boundaries inside the magnet.

The melting temperature of the low melting point metal (TM) is preferably 1,100°C or lower, and more preferably in the temperature range of 650 to 1,100°C. Additionally, it is preferable that low melting point metal (TM) or low melting point metal compound (TMX) does not react with rare earth metals.

Low melting point metal compounds (TMX) are one or more of hydroxide, fluoride, and oxide powders.

In the slurry, the low melting point metal compound (TMX) powder, which is a solid powder, contains hydrogen (H), fluorine (F), and oxygen (O) in the form of a compound, which is decomposed and discharged when heated for grain boundary diffusion as described later. Decomposed gases such as hydrogen, oxygen, and fluorine also contribute to refining particles. Cu, Al, Ga, Nb, Zr, etc., which are low melting point metals (TM) decomposed by heating, decompose and diffuse into grain boundaries.

The average particle size of the solid powder used in the present invention is preferably 5 ㎛ or less, preferably 4 ㎛ or less, more preferably 3 ㎛ or less. If the particle size is too large, alloying with the matrix structure is difficult to occur when heated. Problems arise in the adhesion of the formed surface layer to the matrix tissue. The smaller the particle diameter, the more dense the surface layer is formed after heating. In order to use the surface layer as a corrosion prevention film, it is better to have a smaller particle size. Therefore, there is no particular lower limit for the particle size, and if cost is not considered, ultrafine particles of several tens of nm are ideal, but the average particle size of the most desirable metal powder for practical use is about 03 ㎛ to 3 ㎛.

First, a slurry is prepared by mixing a liquid solvent with a mixture of solid powders of low melting point metal (TM) or low melting point metal compound (TMX).

Low melting point metal (TM) or low melting point metal compound (TMX) slurry is kneaded by mixing 35 to 55 wt% of low melting point metal (TM) or low melting point metal compound (TMX) and 45 to 65 wt% of alcohol. The liquid solvent may be ethanol.

The method of applying low melting point metal (TM) slurry or low melting point metal compound (TMX) slurry is one of spraying, dipping, plating (electrolytic, electrolytic), and deposition methods.

The spraying application method heats the permanent magnet to a temperature of 100°C or lower in the application step of the low melting point metal (TM) slurry or low melting point metal compound (TMX) slurry prepared above. Preferably, it is heated in the temperature range of 60 to 80°C.

Low melting point metal (TM) or low melting point metal compound (TMX) slurry is supplied as droplets using a metering pump, the supplied droplets are atomized using ultrasound, and the low melting point metal (TM) or low melting point atomized using ultrasound is atomized. The metal compound (TMX) slurry is applied to the surface of the permanent magnet at least once through a carrier gas at a speed of 0.8 to 2 m/sec. When applied, it may have a swirl-like directionality.

After the application, the applied permanent magnet is heated to a temperature of 100°C or lower.

(4) Grain boundary diffusion step (S4) of low melting point metal (TM)

The applied low melting point metal (TM) or low melting point metal compound (TMX) is decomposed by heating.

In order to diffuse the decomposed low melting point metal (TM) into the grain boundaries inside the magnet, the coated material is charged into a heating furnace and heated in an argon atmosphere at a temperature increase rate = 1°C/min. for 2 to 12 hours at a temperature of 700 to 1,000°C. While maintaining the low melting point metal (TM) or low melting point metal compound (TMX), it decomposes into low melting point metal (TM) and diffuses into the magnet to proceed with the penetration reaction.

Preferably, it is maintained at a temperature of 850 to 950°C for 2 to 12 hours.

(5) Heavy rare earth metal compound (REX) slurry coating step (S5)

Applying a medium rare earth metal compound to the surface of a magnet where low melting point metal (TM) is diffused is intended to improve coercive force by diffusing the medium rare earth metal to the grain boundaries inside the magnet.

Previously, when the low melting point metal (TM) is diffused into the grain boundaries of the sintered magnet, the low melting point metal (TM) diffused into the grain boundaries combines with the rare earth metal rich phase (Nd-rich) to form the rare earth metal rich phase (Nd-rich). The melting point is further lowered, and the rare earth metal-rich phase (Nd-rich) with a low melting point exists continuously and uniformly at the grain boundaries, allowing the rare earth metal to diffuse into the interior of the sintered magnet during grain boundary diffusion after application of the rare earth metal. It is effective in doing so.

The heavy rare earth metal compound (REX) is one or more of hydroxide, fluoride, and oxide powder. In the heavy rare earth metal compound (REX), the heavy rare earth metal (RE) contains at least 10 at.% (10 parts by weight, based on 100 parts by weight of the rare earth metal powder in the sintering step (S1)) of at least one rare earth element.

The average particle size of the rare earth metal compound (REX) used in the present invention is preferably 5 ㎛ or less, preferably 4 ㎛ or less, more preferably 3 ㎛ or less. If the particle size is too large, alloying with the matrix structure occurs when heated. It is difficult for this to occur, and problems arise in the adhesion of the formed surface layer to the matrix tissue. The smaller the particle diameter, the more dense the surface layer is formed after heating. In order to use the surface layer as a corrosion prevention film, it is better to have a smaller particle size. Therefore, there is no particular lower limit for the particle size, and if cost is not considered, ultrafine particles of several tens of nm are ideal, but the average particle size of the most desirable metal powder for practical use is about 03 ㎛ to 3 ㎛.

First, a slurry is prepared by mixing a solid powder of a heavy rare earth metal compound (REX) with a liquid solvent.

The rare earth metal compound (REX) slurry is kneaded by mixing 35 to 55 wt% of the rare earth metal compound (REX) and 45 to 65 wt% of alcohol. The liquid solvent may be ethanol.

The method of applying the heavy rare earth metal compound (REX) slurry is characterized by one of spraying, dipping, and deposition methods.

The application method by spraying heats the permanent magnet to a temperature of 100°C or lower in the application step of the prepared heavy rare earth metal compound (REX) slurry. Preferably, it is heated in the temperature range of 60 to 80°C.

Heavy rare earth metal compound (REX) slurry is supplied as droplets using a metering pump, the supplied droplets are atomized using ultrasonic waves, and the medium rare earth metal compound (REX) slurry atomized using ultrasonic waves is transported 0.8 to 2 m through a carrier gas. Apply to the surface of the permanent magnet at least once at a speed of /sec. When applied, it may have a swirl-like directionality.

After the application, the applied permanent magnet is heated to a temperature of 100°C or lower.

(5) Grain boundary diffusion step

The applied rare earth metal compound (REX) is decomposed by heating.

In order to diffuse the decomposed heavy rare earth metal into the grain boundaries inside the magnet, the coated material is charged into a heating furnace, heated in an argon atmosphere at a temperature increase rate = 1°C/min., and maintained at a temperature of 700 to 1,000°C for 2 to 12 hours. Rare earth metal compounds (REX) decompose into medium rare earth metals and diffuse into the magnet, causing a penetration reaction to proceed.

Preferably, it is maintained at a temperature of 800 to 900°C for 2 to 12 hours.

By heating in this way, the grain boundary diffusion method can be easily performed, and the sintered magnet can be highly characterized, that is, the residual magnetic flux density (Br) and maximum energy product ((BH)max) can be maintained at a higher state than before the grain boundary diffusion treatment. It can be converted to high coercivity (Hcj). The fact that the grain boundary diffusion method is highly effective for thin magnets is consistent with previous reports. It is particularly effective for thicknesses of 5 mm or less.

(6) Stress relief heat treatment and final heat treatment step

After the grain boundary diffusion treatment, it is rapidly cooled to room temperature, the inside of the diffusion furnace is maintained in a vacuum atmosphere, the diffused magnet is heated to a temperature in the range of 400 to 1000°C and heat treatment is performed for 1 to 10 hours, and then rapidly cooled to room temperature.

Hereinafter, more specific embodiments of the present invention will be described using test examples.

[Examples 1 to 8]

In the present invention, after manufacturing a sintered rare earth magnet with a composition of 31%RE-1%B-2%TM-Bal.Bal.%Fe (where RE = rare earth element, TM = 3d transition element), the sintered magnet is sintered at 12.5%. It was processed into a magnet with a size of *12.5*5mmT, and the following grain boundary diffusion process was performed to improve the coercive force characteristics of the sintered magnet.

After immersing the sintered magnet in an alkaline degreaser solution, the oil on the surface of the magnet was removed by rubbing it with a ceramic ball measuring 2 to 10 mm. Then, the sintered magnet was thoroughly washed several times with distilled water to remove any remaining degreaser. completely removed.

In Examples 1 to 6, Cu and Al powders from High Purity Chemicals (Japan) were used as the low melting point metal powder applied to the surface of the sintered magnet, and the average particle size of the low melting point metal powder was approximately 3 ㎛. In order to apply low melting point metal powder, a slurry is prepared by mixing low melting point metal powder and alcohol in a ratio of 50 parts by weight: 50 parts by weight, and then the prepared low melting point metal slurry is atomized using ultrasonic waves on the surface of the sintered magnet. When applied to the surface of a permanent magnet at a speed of 0.8 to 2 m/sec through a carrier gas, it was applied in a whirl-like direction.

In order to diffuse the applied low melting point metal into the grain boundaries inside the magnet, the coated material was charged into a heating furnace and heated at a temperature increase rate of 1°C/min. in an argon atmosphere to spread into the magnet while maintaining the temperature at 900°C for 6 hours.

Example 1 was 0.2 parts by weight of Cu, Example 2 was 0.4 parts by weight of Cu, Example 5 was 0.2 parts by weight of Al, and Example 6 was 0.4 parts by weight of Al, and the final heat treatment was not performed after application and diffusion.

In Example 3, 0.2 parts by weight of Cu was applied, in Example 4, 0.4 parts by weight of Cu, in Example 7, 0.2 parts by weight of Al, and in Example 8, 0.4 parts by weight of Al was applied, spread, and then subjected to final heat treatment at 500° C. for 2 hours. This is an example.

Comparative system 1 was subjected to final heat treatment at 500°C for 2 hours after sintering without additional spreading of low melting point metal.

The characteristics of Examples 1 to 8 used for diffusion were measured as residual magnetic flux density (Br) of 14.4 kG and coercive force (Hcj) of 14.5 kOe as in Comparative Example 1, and the low melting point metal of Examples 1 to 8 was measured as a magnet for which diffusion was completed. Table 1 shows the results of evaluating the magnetic properties after processing the surface again to remove the residual diffusion layer.

In Examples 1 and 2, the coercive force after grain boundary diffusion tended to decrease as the amount of Cu metal applied increased after the grain boundary diffusion treatment of Cu element. It is believed that as Cu is added to the rare earth metal-rich phase, the melting temperature is lowered and the rare earth metal-rich phase is aggregated at the triple point of the grain boundary, lowering the coercive force. This indirectly shows that the low melting point metal has diffused into the grain boundary.

Examples 3 and 4 are the results of increasing the coercive force by controlling the rare earth metal-rich phase through final heat treatment after diffusing the Cu element. Compared to Comparative Example 1, an improvement in coercivity of 0.6 kOe was confirmed in the specimen in which 0.2% Cu was diffused.

Examples 5, 6, 7, and 8 are the results of diffusing Al, another low melting point element. It was confirmed that when Al was diffused, the coercivity was improved by 1 kOe compared to Comparative Example 1. However, the Al element is known to reduce the residual magnetic flux density (Br) by diffusing into the main phase, NdFeB, through the grain boundary, and as the application amount increases compared to the case of diffusing Cu as in Examples 7 and 8, the residual magnetic flux density decreases. It can be seen that has decreased by 0.07 and 0.13 kG.

Table 1 below shows the change in magnetic properties according to the diffusion amount for each type of low melting point element.

division apply
matter Application amount diffusion final
heat treatment residual magnetic flux
Density (Br)
(kG) coercivity
(Hcj)
(kOe) Maximum energy product (BH)
(MGOe) Example 1-1 Cu 0.2% O X 14.41 12.63 52.46 Example 1-2 Cu 0.4% O X 14.40 11.04 52.14 Example 1-3 Cu 0.2% O O 14.40 15.27 52.50 Example 1-4 Cu 0.4% O O 14.38 14.76 52.15 Example 1-5 Al 0.2% O X 14.33 13.54 51.81 Example 1-6 Al 0.4% O X 14.33 13.46 51.96 Example 1-7 Al 0.2% O O 14.28 15.60 51.69 Example 1-8 Al 0.4% O O 14.31 15.65 51.96 Comparative Example 1 X X X O 14.40 14.65 51.52

It was found that when a low melting point metal was applied to the surface of the sintered magnet as in Examples 1 to 8 and the low melting point metal diffused into the grain boundaries of the sintered magnet, the coercive force was not significantly affected.

[Examples 11 to 14]

In Examples 11 to 14, the composition ratio of rare earth magnets is the same as Examples 1 to 8, and even the cleaning process is the same.

In Examples 11 to 14, Cu and Al powders from High Purity Chemicals (Japan) were used as the low melting point metal powder applied to the surface of the sintered magnet, and the average particle size of the low melting point metal powder was approximately 3 ㎛. In order to apply low melting point metal powder, a slurry is prepared by mixing low melting point metal powder and alcohol in a ratio of 50 parts by weight: 50 parts by weight, and then the prepared low melting point metal slurry is atomized using ultrasonic waves on the surface of the sintered magnet. When applied to the surface of a permanent magnet at a speed of 0.8 to 2 m/sec through a carrier gas, it was applied in a whirl-like direction.

In order to diffuse the applied low-melting point metal into the grain boundaries inside the magnet, the coated material is placed in a heating furnace and heated in an argon atmosphere at a temperature increase rate of 1°C/min. Maintained at a temperature of 900°C for 6 hours while the low-melting point metal flows into the magnet. was first spread.

Tb-Hydride powder was used as a medium rare earth metal compound, and wet grinding was performed in an alcohol solvent using a zirconia ball of 0.5 pi to control the powder particle size. Tb-Hydride slurry was prepared by uniformly kneading the ratio of pulverized Tb-Hydride and alcohol to 50 parts by weight: 50 parts by weight, respectively. The finally produced Tb-Hydride slurry is atomized using ultrasonic waves on the surface of a sintered magnet where Cu or Al is first diffused, and when applied to the surface of a permanent magnet at a speed of 0.8 to 2 m/sec through a carrier gas, it is oriented in the form of a whirlpool. It was applied to have.

In order to diffuse the applied rare earth compounds into the grain boundaries inside the magnet, the coated material is placed in a heating furnace and heated in an argon atmosphere at a temperature increase rate of 1°C/min. While maintaining the temperature at 900°C for 6 hours, Tb-Hydride is decomposed into Tb. It spread inside the magnet and allowed the penetration reaction to proceed. Subsequently, a final heat treatment was performed at 500°C for 2 hours.

The base materials of Examples 11 to 14 and Comparative Example 2 used for diffusion were measured to have a residual magnetic flux density (Br) of 14.4 kG and a coercive force (Hcj) of 14.5 kOe, and the magnets on which final grain boundary diffusion of Tb, a medium rare earth metal, was completed were again magnets. The results of evaluating the magnetic properties after processing the surface to remove the residual diffusion layer are shown in Table 2.

In Examples 11 and 12, the secondary diffusion effect of Tb, a medium rare earth metal, was shown after increasing the application amount of Cu metal and grain boundary diffusion. Compared to the case without grain boundary diffusion of Cu element in Comparative Example 2, it was confirmed that in Examples 11 and 12, in which Cu element was primary diffused, the residual magnetic flux density was at the same level and the coercive force (Hcj) was improved by approximately 0.9 kOe.

In order to evaluate the internal and external diffusion uniformity during Tb grain boundary diffusion, the specimen was maintained at a temperature of 180 degrees for 2 hours, and then the irreversible thermal demagnetization rate, which confirms the degree to which the magnetic properties of the sintered magnet are demagnetized, was confirmed. Example 11, It was confirmed that the irreversible thermal decay rate in all of Example 12 was improved compared to Comparative Example 2.

This improvement in irreversible thermal demagnetization means that rare earth elements are uniformly diffused to the center of the sintered magnet rather than the effect of improving the coercive force (Hcj), and the primary diffusion of Cu, a low melting point metal, improves the microstructure inside the sintered magnet. Therefore, it can be seen that it is effective in improving the grain boundary diffusion efficiency of rare earth elements in the future.

Examples 13 and 14 showed the secondary diffusion effect of rare earth elements after increasing the amount of Al metal applied and grain boundary diffusion. There is no significant difference in the increase in coercivity (Hcj) compared to Comparative Example 2, but it can be seen that the irreversible thermal attenuation rate is improved as the amount of Al applied increases.

This confirmed that primary diffusion of Al, a low melting point metal, is also effective in improving the microstructure of sintered magnets. However, it was confirmed that the primary diffusion of Al tends to diffuse into the crystal grains, so the effect of improving the coercive force (Hcj) and irreversible thermal attenuation rate is small, and the reduction in residual magnetic flux density is relatively large.

Table 2 below shows the effect of applying the low melting point element grain boundary diffusion technology.

division 1st spread Application amount secondary spread Application amount residual magnetic flux
Density (Br)
(kG) coercivity
(Hcj)
(kOe) Maximum energy product (BH)
(MGOe) hot potato
180°C Example 11 Cu 0.2% TbH 1.00% 14.14 28.33 50.80 2.86% Example 12 Cu 0.4% TbH 1.00% 14.14 28.48 50.76 2.52% Example 13 Al 0.2% TbH 1.00% 13.95 27.42 49.46 5.04% Example 14 Al 0.4% TbH 1.00% 13.94 27.49 49.39 3.36% Comparative example 2 X X TbH 1.00% 14.19 27.55 50.48 6.25%

In addition, the present invention is not limited to the above-described embodiments, and appropriate changes can be made without departing from the gist of the present invention. For example, the composition of the raw material powder, the shape and size of the molded body, the magnetic field application speed, sintering conditions, etc. can be appropriately changed.

Claims (7)

xwt%RE-ywt%B-zwt%TM-bal.wt%Fe (RE=rare earth element, TM=3d transition element, x=28∼35, y=0.5∼1.5, z=0∼15) rare earth element A sintering step (S1) of manufacturing a magnetic sintered body;
A sintered magnet processing step (S2) of processing the sintered body to fit the size standard of the desired product;
A low melting point metal (TM) slurry or a low melting point metal compound (TMX) slurry having a melting temperature of the alloy material in the range of 650 to 1100° C. is uniformly applied to the surface of the processed sintered magnet. Melting point metal compound (TMX) slurry application step (S3);
The sintered body with the low melting point metal (TM) slurry or low melting point metal compound (TMX) slurry applied to the surface is charged into a heating furnace and the low melting point metal (TM) slurry or low melting point metal compound as the coating material is placed in a vacuum or inert gas atmosphere. (TMX) The low melting point metal (TM) separated from the slurry is diffused into the grain boundaries of the sintered magnet, and the low melting point metal (TM) combines with the rare earth rich phase (Nd-rich) at the grain boundaries to form a rare earth rich phase (Nd-rich). A low melting point metal diffusion step (S4) of primary diffusion to lower the melting point of;
A heavy rare earth metal compound (REX) coating step (S5) of coating a heavy rare earth metal compound (REX) slurry on the surface of the sintered body of the low melting point metal diffusion step;
The sintered body coated with the heavy rare earth metal compound (REX) slurry is charged, and the heavy rare earth metal compound (REX) is decomposed in a vacuum or inert gas atmosphere to produce the heavy rare earth metal into a sintered magnet with a lowered melting point in the low melting point metal diffusion step (S4). Heavy rare earth metal diffusion step (S6) of secondary diffusion into the grain boundaries;
An additional heat treatment step (S7) of performing additional heat treatment on the sintered magnet in which the heavy rare earth metal is diffused at a temperature ranging from 400 to 1000° C. in a vacuum or inert gas atmosphere; A method of manufacturing a rare earth permanent magnet comprising: delete According to claim 1,
In the low melting point metal (TM) or low melting point metal compound (TMX) used as the coating material, the low melting point metal (TM) is one of Co, Cu, Al, Ga, Nb, Ti, Mo, V, Zr, and Zn. A method of manufacturing a rare earth permanent magnet characterized by containing the above. According to claim 1,
A method of manufacturing a rare earth permanent magnet, wherein in the heavy rare earth metal compound (REX) used as the coating material, X contains at least one of hydrogen, oxygen, and fluorine. According to claim 1,
A method of manufacturing a rare earth permanent magnet, wherein in the low melting point metal compound (TMX) used as the coating material, X contains at least one of hydrogen, oxygen, and fluorine. According to claim 1,
The method of applying the low melting point metal (TM) or low melting point metal compound (TMX) in the low melting point metal (TM) or low melting point metal compound (TMX) application step (S3) includes spraying, dipping, and plating (electroless, A method of manufacturing rare earth permanent magnets, characterized in that it is one of electrolysis) and deposition methods. According to claim 1,
A method of manufacturing a rare earth permanent magnet, characterized in that the method of applying the heavy rare earth metal compound (REX) in the heavy rare earth metal compound coating step (S5) is one of spraying, dipping, and deposition methods.