KR20240088038A - Manufacturing method of rare earth sintered magnet - Google Patents

Abstract

In the present invention, a low-melting point metal sheet is adhered to the surface of a sintered body made of a rare earth alloy, a heavy rare earth metal compound slurry is applied in that order, and then grain boundary diffusion is performed to improve the temperature coefficient of residual magnetic flux density and coercive force, which are magnetic properties depending on temperature. provides.

Description

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

The present invention relates to a method of manufacturing a rare earth permanent magnet, and in particular, to the surface of a sintered body made of a rare earth alloy, by adhering a low-melting point metal sheet to the surface, applying a heavy rare earth metal compound slurry, and then grain boundary diffusion to determine the residual magnetic flux density, which is a magnetic characteristic depending on temperature. This relates to a method of manufacturing rare earth permanent magnets with improved temperature coefficient and coercive force.

Demand for NdFeB sintered magnets is gradually increasing for use in motors such as hybrid cars, and it is required to further increase its coercive force (Hcj). In order to increase the coercive force (Hcj) of the NdFeB sintered magnet, 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 replacement of these elements is necessary. The problem is that the residual magnetic flux density (Br) or maximum energy product ((BH)max) of the NdFeB sintered magnet decreases due to this.

Dy or Tb bonded to the surface of the magnet is sent into the sintered body through the grain boundaries of the sintered body, and diffuses from the grain boundaries into each particle of the main phase Re2Fe14B (Re is a rare earth element). . This is called grain boundary diffusion. During grain boundary diffusion, the Re-rich phase at the grain boundary is liquefied by heating, so the diffusion speed of Dy or Tb in the grain boundary is much faster than the diffusion speed from the grain boundary into the interior of the columnar particle.

By using this difference in diffusion rate to adjust the heat treatment temperature and time, it is possible to achieve a state in which the concentration of Dy or Tb is high only in the area (surface area) extremely close to the grain boundaries of the columnar particles in the sintered body throughout the entire sintered body. there is.

Since the coercive force (Hcj) of the NdFeB sintered magnet is determined depending on the state of the surface area of the columnar particles, the NdFeB sintered magnet with crystal grains with a high concentration of Dy or Tb in the surface area has a high coercive force.

In addition, when the concentration of Dy or Tb increases, the residual magnetic flux density (Br) of the magnet decreases, but since such area is only the surface area of each columnar particle, the residual magnetic flux density (Br) of the columnar particles as a whole hardly decreases. No. In this way, NdFeB sintered magnets with high coercive force (Hcj) and residual magnetic flux density (Br) that do not substitute Dy or Tb, and high-performance magnets with little change can be manufactured. This method is called the grain boundary diffusion method.

An industrial manufacturing method of NdFeB sintered magnets by the grain boundary diffusion method, in which a fine powder layer of Dy or Tb fluoride or oxide is formed on the surface of the NdFeB sintered magnet and heated, or a powder of Dy or Tb fluoride or oxide is formed on the surface of the NdFeB sintered magnet. There is a method of embedding a NdFeB sintered magnet in a mixed powder of perhydrogenated Ca powder and heating it.

Even before the grain boundary diffusion method described above became known, high-temperature demagnetization was reduced by diffusing at least one type of Tb, Dy, Al, or Ga near the surface of the NdFeB-based sintered magnet (Patent Document 1). ), or by depositing at least one of Nd, Pr, Dy, Ho, and Tb on the surface of the NdFeB sintered magnet to prevent deterioration of magnetic properties due to processing deterioration (patent document 2). It is proposed.

[Patent Document 1] Japanese Patent Publication No. 01-117303 [Patent Document 2] Japanese Patent Publication No. 62-074048 [Patent Document 3] Korean Patent 10-1447301

The present invention relates to a method for manufacturing rare earth permanent magnets, xwt%RE-ywt%B-zwt%TM-bal.wt%Fe (RE=rare earth element, TM=3d transition element, x=28-35, y= After adhering a low-melting point metal sheet to the surface of a sintered body made of a rare earth alloy with a composition of 0.5~1.5, z=0~15, applying slurry of a medium rare earth metal compound in that order, grain boundary diffusion is performed to measure the residual magnetic flux density, which is a magnetic property according to temperature. We provide rare earth permanent magnets with improved number and coercivity.

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, manufacturing a rare earth alloy having a composition of x=28-35, y=0.5-1.5, z=0-15; Grinding the prepared alloy to a size of 1.0 ~ 5.0㎛ or less; Magnetizing the pulverized alloy by magnetic field orientation and compression molding; Sintering the magnetized alloy; cleaning the sintered body; Adhering a low melting point metal sheet to the surface of the cleaned sintered body; Applying a slurry obtained by mixing a heavy rare earth compound with a liquid solvent to the surface of a low-melting point metal sheet adhered to the sintered body; charging the sintered body coated with the low-melting-point metal sheet and heavy rare earth metal compound slurry into a heating furnace and diffusing the heavy rare earth elements onto the grain boundaries of the sintered body in a vacuum or inert gas atmosphere; A stress relief heat treatment step of charging the sintered body in which the heavy rare earth metal is diffused into the grain boundaries of the alloy into a heating furnace and performing stress relief heat treatment in a vacuum or inert gas atmosphere; It is characterized in that it consists of a final heat treatment step of heat treatment after the stress relief heat treatment step.

In the method of manufacturing a rare earth permanent magnet according to the present invention, the low melting point metal sheet is one of Cu, Al, and Ga.

In the method of manufacturing a rare earth permanent magnet according to the present invention, the thickness of the low melting point metal sheet is 1 to 60㎛. Preferably it is 1 to 10㎛, more preferably 1 to 6㎛.

The method for manufacturing a rare earth permanent magnet according to the present invention is characterized in that the sintered body and the low melting point metal sheet are bonded using an adhesive prepared by mixing PVP (Polyvinylpyrrolidone) or PVA (Polyvinyl alcohol) with a liquid solvent.

The liquid solvent is ethanol.

In the method for manufacturing rare earth permanent magnets according to the present invention, the heavy rare earth compounds include Gd-Hydride, Gd-Fluoride, Nd-Hydride, Ho-Fluoride, Ho-Hydride, Dy-Hydride, Dy-Fluoride, Tb-Hydride, Tb- It is characterized as one of the fluoride powders.

In the method for producing a rare earth permanent magnet according to the present invention, the slurry is characterized by mixing solid powder of a heavy rare earth compound and a liquid solvent at a ratio of 40 to 60% by volume: 40 to 60% by volume.

In the method of manufacturing a rare earth permanent magnet according to the present invention, the xwt%RE-ywt%B-zwt%TM-bal.wt%Fe (RE=rare earth element, TM=3d transition element, A rare earth alloy with a composition of ∼1.5, z=0∼15) is characterized in that it contains one or more rare earth metals among RE=Nd, Pr, La, Ce, Ho, Dy, and Tb.

In the method of manufacturing a rare earth permanent magnet according to the present invention, the xwt%RE-ywt%B-zwt%TM-bal.wt%Fe (RE=rare earth element, TM=3d transition element, ∼1.5, z=0∼15), and is characterized in that it contains one or more 3d transition metals among TM=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, 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 impurity organic substances.

Sinter again under the sintering conditions: temperature 900°C to 1200°C, holding time: 2 to 8 hours, atmosphere: vacuum, argon, etc. Preferably, the temperature range is 1,000 to 1,100°C, and the holding time is preferably 4 to 6 hours.

In the method of manufacturing a rare earth permanent magnet according to the present invention, the step of diffusing the heavy rare earth metal into the grain boundary phase of the alloy is characterized in that the diffusion temperature is in the range of 400 to 1000°C 1 to 10 times or more.

In the method of manufacturing a rare earth permanent magnet according to the present invention, the sludge coating layer remaining on the surface after the grain boundary diffusion treatment is removed, and then stress relief heat treatment is performed at a temperature of 400 to 1,000°C for 2 to 15 hours. Preferably, stress relief heat treatment is performed at a temperature of 850 to 950°C for 8 to 12 hours. More preferably, stress relief heat treatment is performed at 900°C for 10 hours.

In the method of manufacturing a rare earth permanent magnet according to the present invention, after the stress relief heat treatment, a final heat treatment is performed at a temperature of 400 to 600° C. for 0.5 to 3 hours. Preferably, the final heat treatment is performed at a temperature of 450 to 550°C for 1.5 to 2.5 hours.

According to the method of manufacturing a rare earth permanent magnet according to the present invention, a low melting point metal sheet is adhered to the surface of a sintered body made of a rare earth alloy, and a heavy rare earth metal compound slurry is applied in that order to deposit the heavy rare earth metal on the grain boundaries of the sintered body in a vacuum or inert gas atmosphere. When diffused, the liquid phase in which the low melting point metal is liquefied and the solid phase of the heavy rare earth metal coexist at the diffusion temperature, and the liquid phase of the low melting point metal acts as a solvent, increasing the degree of freedom of the heavy rare earth metal decomposed from the heavy rare earth metal compound and diffusion to the grain boundary. It has the effect of improving performance.

In addition, the sheet of low-melting point metal exists uniformly in a liquid state on the surface of the sintered body, which has the effect of making the diffusion of heavy rare earths into the grain boundary phase of the sintered body uniform across the entire surface of the sintered body.

Figure 1 is a flowchart showing the manufacturing process of the rare earth permanent magnet according to the present invention.

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) Steps for producing rare earth alloy powder

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.

The raw material powder made of an alloy of the desired composition is melted and cast ingots or the thin body obtained by rapid solidification is pulverized by 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 for more than 2 hours to absorb hydrogen into the strip, and then heated to 600°C in a vacuum atmosphere to exist inside the strip. Remove hydrogen.

Using hydrogen-treated powder that has completed coarse grinding, it is manufactured into a uniform, fine powder with an average particle diameter in the range of 1 to 5.0㎛ 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.

(2) Magnetic field orientation and forming steps

A lubricant can be added to the raw 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, a pulse current is applied to the electromagnets located on the left and right sides of the mold for molding in a nitrogen atmosphere to generate a high magnetic field to completely orient the powder, and then a direct current is generated by applying a direct current. A molded body is manufactured by simultaneously performing compression molding while maintaining the direction of the powder that has already been completely oriented by a magnetic field.

(3) Sintering step

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.

The sintered body 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.

(4) Adhesion step of adhering a low melting point metal sheet to the surface of the rare earth sintered body

The low melting point metal is one of Cu, Al, and Ga, and the low melting point metal is a thin sheet. The thickness of the low melting point metal sheet is preferably 1 to 60㎛.

If the low melting point metal sheet is not fixed to the surface of the sintered body, the low melting point metal sheet may be separated from the sintered body when applying the heavy rare earth metal compound slurry, which will be described later.

Therefore, the sintered body and the low melting point metal sheet are bonded using an adhesive.

The adhesive between the sintered body and the low-melting point metal sheet is manufactured by mixing PVP (Polyvinylpyrrolidone) or PVA (Polyvinyl alcohol) with a liquid solvent.

PVP (Polyvinylpyrrolidone) has a vaporization temperature of 217.6°C and the chemical formula (C ₆ H ₉ NO)n, and PVA (Polyvinyl alcohol) has a vaporization temperature and melting point of 228°C and the physical properties of (C2H4O)x.

PVP (Polyvinylpyrrolidone) is dissolved in ethanol, a liquid solvent, at room temperature and applied to the surface of the cleaned sintered body at a thickness of 20 to 70 um to adhere the low melting point metal sheet.

The adhesive components, PVP (Polyvinylpyrrolidone) and PVA (Polyvinyl alcohol), are vaporized and evaporated at the grain boundary diffusion temperature, and the components are composed of carbon, hydrogen, nitrogen, and oxygen, so no residue remains after evaporation, so they have no effect on the surface of the sintered body. It is an ingredient that does not exist.

Liquid solvents are ethanol and alcohol.

(5) Application step of applying heavy rare earth compound slurry to the surface of the low melting point metal sheet adhered to the rare earth sintered body.

The present invention seeks to improve the temperature characteristics of the coercive force and residual magnetic flux density by adding a heavy rare earth metal, and simultaneously improves the temperature coefficient of the residual magnetic flux density and the coercive force by adding a heavy rare earth metal using a grain boundary diffusion process. will be.

In order to uniformly apply heavy rare earth to the surface of the low-melting point metal bonded to the rare earth sintered body according to the present invention, the heavy rare earth compound is manufactured by mixing the solid powder of the heavy rare earth compound and the liquid solvent at 40 to 60% by volume: 40 to 60% by volume. Put the rare earth compound slurry in a container and evenly disperse it using a stirrer (magnetic stirrer). After depositing the processed body, the rare earth compounds are evenly applied to the surface of the magnet while holding for 1 to 2 minutes, or applied by spraying method.

The liquid solvent may be alcohol.

The heavy rare earth compounds include Gd-Hydride, Gd-Fluoride, Gd-oxide, Gd-oxyfluoride, Nd-Hydride, Ho-Fluoride, Ho-Hydride, Dy-Hydride, Dy-Fluoride, Tb-Hydride, and Tb-Fluoride powder. There is more than one.

In the slurry, the heavy rare earth compound 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. Gases such as decomposed hydrogen also contribute to miniaturizing particles. Heavy rare earth elements Gd, Nd, Ho, Dy, and Tb decomposed by heating are decomposed 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 size, 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㎛.

(6) Grain boundary diffusion step

The sintered body with the low melting point metal sheet and the applied heavy rare earth compound slurry is charged into a heating furnace to diffuse the heavy rare earth metal into the grain boundaries inside the magnet, and heated in an argon atmosphere at a temperature increase rate = 1°C/min. to 700°C. While maintaining the temperature at ~1,000°C for 1 to 10 hours, the heavy rare earth compound or heavy rare earth metal alloy decomposes into heavy rare earth and diffuses into the magnet to proceed with the penetration reaction.

Preferably, the temperature is maintained at 900°C for 6 hours, at 800°C for 10 hours, or at 850°C for 9 hours.

By heating in this way, the grain boundary diffusion method can be easily carried out, and the sintered magnet can have high characteristics, 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 especially effective for thicknesses of 5 mm or less.

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

After the grain boundary diffusion treatment, the sludge coating layer remaining on the surface is removed, and then stress relief heat treatment is performed at a temperature of 400 to 1,000°C for 2 to 15 hours. Preferably, stress relief heat treatment is performed at a temperature of 850 to 950°C for 8 to 12 hours.

After the stress relief heat treatment, a final heat treatment is performed at a temperature of 400 to 600°C for 0.5 to 3 hours. Preferably, the final heat treatment is performed at a temperature of 450 to 550°C for 1.5 to 2.5 hours.

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

In this example, 32wt%RE-1wt%B-1.5wt%TM-bal.wt%Fe (where RE = rare earth element, TM = 3d transition element, x = 28 to 35, y = 0.5 to 1.5, z = An alloy with a composition of 0 to 15) was melted by induction heating in an argon atmosphere, and then rapidly cooled using a strip casting method to prepare an alloy strip.

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 for more than 2 hours to absorb hydrogen into the strip, and then heated to 600°C in a vacuum atmosphere to exist inside the strip. Hydrogen was removed. Using hydrogen-treated powder that had completed coarse grinding, it was manufactured into a uniform, fine powder with an average particle diameter ranging from 1 to 5.0㎛ by grinding using jet mill technology. At this time, the process of manufacturing the alloy strip into fine powder was performed in a nitrogen or inert gas atmosphere to prevent oxygen contamination and deterioration of magnetic properties.

Magnetic field forming was performed as follows using fine rare earth powder ground by a jet mill. Rare earth powder is filled into a mold in a nitrogen atmosphere, and a direct current magnetic field is applied by electromagnets located on the left and right sides of the mold to orient the rare earth powder in a uniaxial direction. At the same time, compression molding is performed by pressing the upper and lower punches to form a molded body. was manufactured.

The molded body obtained by magnetic field molding was charged into a sintering furnace, maintained sufficiently in a vacuum atmosphere and below 400°C to completely remove any remaining impurity organic matter, and then raised to 1050°C and held for 2 hours to carry out the sintering and densification process.

After manufacturing the sintered body through the sintering manufacturing process described above, the sintered body was processed into a magnet with a size of 12.5*12.5*5mm.

After immersing the processed magnet 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 degreaser was completely removed by thoroughly washing the magnet several times with distilled water. .

Copper sheets with thicknesses of 6, 10, 60, and 100 um were adhered to the surface of the cleaned sintered body, respectively. At this time, the sintered body and the low-melting-point metal sheet were bonded using an adhesive prepared by mixing PVP (Polyvinylpyrrolidone) or PVA (Polyvinyl alcohol) with a liquid solvent.

Afterwards, the uniformly kneaded Tb Hydride powder slurry was applied on the copper sheet adhered to the surface of the sintered body, with the ratio of Tb Hydride powder and alcohol as a liquid solvent adjusted to 50%:50%, respectively.

The amount of Tb Hydride powder slurry applied was 1.0 parts by weight per 100 parts by weight of the sintered body.

By using the copper sheet, which is a low-melting point metal of the present invention, application is simpler than applying powder, and the low-melting point metal, which is a sheet, exists uniformly in a liquid state on the surface of the sintered body, so that heavy rare earth diffusion on the grain boundaries of the sintered body spreads across the entire surface of the sintered body. There is a uniformity effect throughout.

Afterwards, in order to spread the applied Tb Hydride compound to the grain boundaries inside the magnet, the coated material was placed in a heating furnace and heated in an argon atmosphere at a temperature increase rate of 1°C/min. The Tb Hydride compound was maintained at 900°C for 6 hours. It was decomposed into Tb and diffused inside the magnet, allowing the penetration reaction to proceed. After diffusion treatment, the diffusion layer was removed from the surface, and then stress relief heat treatment was performed at 900°C for 10 hours, followed by final heat treatment at 500°C for 2 hours.

Comparative Example 1 was manufactured in the same manner as Example 1 of the present invention, with the only difference being whether or not a copper sheet was applied.

The properties of the base material used in the diffusion of Examples 1-1 to 1-4 and Comparative Example 1 were measured as Br = 14.4 kG, Hcj = 14.65 kOe, and the magnet for which final grain boundary diffusion was completed was processed again and the remaining surface was The results of evaluating the magnetic properties after removing the diffusion layer are shown in Table 1.

Adhesion of copper sheet to sintered body and comparison of magnetic properties after application of Tb Hydride compound slurry Sample Process conditions magnetic characteristics texture Adhesive sheet thickness (um) Residual magnetic flux density
Br(kG) coercivity
Hcj(kOe) irreversible
Heat Potato (180℃)% Comparative Example 1 - 14.22 28.37 2.52 Example 1-1 Cu Sheet 6 14.23 28.62 1.14 Example 1-2 10 14.19 28.77 1.47 Example 1-3 60 14.22 26.93 3.17 Example 1-4 100 14.12 22.74 21.52

As shown in the magnetic property evaluation results in Table 1, the best magnetic properties were obtained at a copper sheet thickness of 6um. More precisely, an improvement effect of 1.38% was confirmed in irreversible thermal decomposition.

Irreversible thermal demagnetization is more important because it is a value that can evaluate the uniformity of grain boundary diffusion.

In the method for evaluating irreversible thermal demagnetization in Example 1 of the present invention, a magnetic specimen is magnetized using a 3 Tesla magnetic field, and the total flux (F1) of the magnet is measured using a flux meter. Then, the magnetized magnet is placed in an oven heated to 180 degrees and maintained for 2 hours to perform thermal magnetization. After thermal demagnetization, the magnet is cooled to room temperature again and the total flux (F2) is measured. Compare the flux of the magnet measured before and after thermal demagnetization to calculate the thermal demagnetization rate (=(F1-F2)/F1 * 100).

When medium rare earth and light rare earth grain boundary diffusion is used by mixing most low-melting point materials, the residual magnetic flux density decreases significantly, but when copper sheets are used, the residual magnetic flux density is not significantly affected. In other words, residual magnetic flux density is an important characteristic that determines the strength of a magnet, so it can be said to be an advantage.

This has the effect of lowering the melting point of Nd-rich by diffusing copper as a low melting point element into the grain boundaries and improving the grain boundary diffusion of medium and light rare earth elements by improving the microstructure and crystal structure of the base crystal grain interface. However, the thickness of the copper sheet is If the thickness exceeds a certain level, the diffusion effect decreases.

In Example 2, all processes were performed under the same conditions except that the heavy rare earth compound was changed to Dy Hydride and applied, and in Comparative Example 2, all processes were performed except that the heavy rare earth compound was changed to Dy Hydride and applied. It was carried out under the same conditions.

The properties of the base material used for diffusion in Examples 2-1 to 2-4 and Comparative Example 2 were measured as Br = 14.4 kG, Hcj = 14.65 kOe, and the magnet for which final grain boundary diffusion was completed was processed again on the surface and the remaining The results of evaluating the magnetic properties after removing the diffusion layer are shown in Table 2.

Adhesion of copper sheet to sintered body and comparison of magnetic properties after application of Dy Hydride compound slurry Sample Process conditions magnetic characteristics texture Adhesive sheet thickness (um) Residual magnetic flux density
Br(kG) coercivity
Hcj(kOe) irreversible
Hot potato (160℃) Comparative Example 2 - 13.86 24.14 6.66 Example 2-1 Cu Sheet 6 13.84 24.62 5.17 Example 2-2 10 13.85 24.25 5.57 Example 2-3 60 13.87 22.66 7.21 Example 2-4 100 13.970 19.74 25.52

As shown in the magnetic property evaluation results in Table 2, the best magnetic properties were obtained at a copper sheet thickness of 6um. More precisely, the best results were obtained in Examples 2-1 to 2-4 and Comparative Example 2 at 5.17% in irreversible thermal demagnetization.

Since irreversible thermal demagnetization is a value that can evaluate the uniformity of grain boundary diffusion, the lower the demagnetization value, the better the magnet.

The magnetic specimen was magnetized using the 3 Tesla magnetic field of Example 2 of the present invention, and the total flux (F1) of the magnet was measured using a flux meter. Then, the magnetized magnet is placed in an oven heated to 160 degrees and maintained for 2 hours to perform thermal magnetization. After thermal demagnetization, the magnet is cooled to room temperature again and the total flux (F2) is measured. Compare the flux of the magnet measured before and after thermal demagnetization to calculate the thermal demagnetization rate (=(F1-F2)/F1 * 100).

In Example 3, all processes were performed under the same conditions except that the heavy rare earth compound was changed to Nd Hydride and applied, and in Comparative Example 3, all processes were performed except that the heavy rare earth compound was changed to Nd Hydride and applied. It was carried out under the same conditions.

The properties of the base material used for diffusion in Examples 3-1 to 3-4 and Comparative Example 3 were measured as Br = 14.4 kG, Hcj = 14.65 kOe, and the magnet for which final grain boundary diffusion was completed was processed again and the remaining surface was processed. The results of evaluating the magnetic properties after removing the diffusion layer are shown in Table 3.

Comparison of magnetic properties after adhering copper sheet to sintered body and applying Nd Hydride compound slurry Sample Process conditions magnetic characteristics texture Adhesive sheet thickness (um) Residual magnetic flux density
Br(kG) coercivity
Hcj(kOe) irreversible
Hot potato (140℃) Comparative Example 3 - - 14.36 16.20 33.52 Example 3-1 Cu Sheet 6 14.37 16.30 30.04 Example 3-2 10 14.36 16.28 30.67 Example 3-3 60 14.36 14.56 34.21 Example 3-4 100 14.39 12.64 40.52

As shown in the magnetic property evaluation results in Table 3, the best magnetic properties were obtained at a copper sheet thickness of 6um. More precisely, the best results were obtained in Examples 3-1 to 3-4 and Comparative Example 3 at 30.04% in irreversible thermal demagnetization.

The magnetic specimen was magnetized using the 3 Tesla magnetic field of Example 3 of the present invention, and the total flux (F1) of the magnet was measured using a flux meter. Then, the magnetized magnet is placed in an oven heated to 140 degrees and maintained for 2 hours to perform thermal magnetization. After thermal demagnetization, the magnet is cooled to room temperature again and the total flux (F2) is measured. Compare the flux of the magnet measured before and after thermal demagnetization to calculate the thermal demagnetization rate (=(F1-F2)/F1 * 100).

In Example 4, all processes were performed under the same conditions except that the heavy rare earth compound was changed to Pr Hydride and applied, and in Comparative Example 4, all processes were performed except that the heavy rare earth compound was changed to Pr Hydride and applied. It was carried out under the same conditions.

The properties of the base material used in the diffusion of Examples 4-1 to 4-4 and Comparative Example 4 were measured as Br = 14.4 kG, Hcj = 14.65 kOe, and the magnet for which final grain boundary diffusion was completed was processed again on the surface to remain. The results of evaluating the magnetic properties after removing the diffusion layer are shown in Table 4.

Adhesion of copper sheet to sintered body and comparison of magnetic properties after applying Pr Hydride compound slurry Sample Process conditions magnetic characteristics texture Adhesive sheet thickness (um) Residual magnetic flux density
Br(kG) coercivity
Hcj(kOe) irreversible
Hot Potatoes (180℃) Comparative Example 4 - 14.41 17.08 34.17 Example 1-1 Cu Sheet 6 14.42 17.13 31.09 Example 4-2 10 14.40 17.10 31.87 Example 4-3 60 14.42 15.25 35.32 Example 4-4 100 14.48 13.31 41.54

As shown in the magnetic property evaluation results in Table 4, the best magnetic properties were obtained at a copper sheet thickness of 6 μm. More precisely, the best result was obtained in Examples 4-1 to 4-4 and Comparative Example 4 at 31.09% in irreversible heat demagnetization.

The magnetic specimen was magnetized using the 3 Tesla magnetic field of Example 4 of the present invention, and the total flux (F1) of the magnet was measured using a flux meter. Then, the magnetized magnet is placed in an oven heated to 140 degrees and maintained for 2 hours to perform thermal magnetization. After thermal demagnetization, the magnet is cooled to room temperature again and the total flux (F2) is measured. Compare the flux of the magnet measured before and after thermal demagnetization to calculate the thermal demagnetization rate (=(F1-F2)/F1 * 100).

As a result of evaluating the magnetic properties of Examples 1 to 4 of the present invention, preferable results were obtained when the thickness of the copper sheet was 1 to 10 μm in all examples.

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, the sintering conditions, etc. can be appropriately changed.

Claims (4)

Manufacturing a sintered body by sintering rare earth alloy powder;
cleaning the sintered body;
Adhering a low melting point metal sheet to the surface of the sintered body;
Applying a slurry obtained by mixing a heavy rare earth compound with a liquid solvent to the surface of a low-melting point metal sheet adhered to the sintered body;
Adhering the low melting point metal sheet, charging the sintered body coated with slurry into a heating furnace, and diffusing heavy rare earth metal onto the grain boundaries of the sintered body in a vacuum or inert gas atmosphere;
A stress relief heat treatment step of charging the sintered body in which the heavy rare earth metal is diffused into the grain boundaries of the alloy into a heating furnace and performing stress relief heat treatment in a vacuum or inert gas atmosphere;
A method of manufacturing a rare earth permanent magnet, characterized in that it consists of a final heat treatment step of heat treatment after the stress relief heat treatment step. According to claim 1,
A method of manufacturing a rare earth permanent magnet, characterized in that the low melting point metal sheet is one of Cu, Al, and Ga. According to claim 1,
A method of manufacturing a rare earth permanent magnet, characterized in that the thickness of the low melting point metal sheet is 1 to 60㎛. According to claim 1,
The heavy rare earth compound is a permanent rare earth compound, characterized in that one of Gd-Hydride, Gd-Fluoride, Nd-Hydride, Ho-Fluoride, Ho-Hydride, Dy-Hydride, Dy-Fluoride, Tb-Hydride, and Tb-Fluoride powder. Magnet manufacturing method.