JP2002025815A - Method of manufacturing r-t-b sintered magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an R-Fe-B sintered magnet, which is more reduced in oxygen content and residual carbon content and more improved in magnetic characteristics than ones formed through a usual dry method, where the magnet is manufactured through a R-T-B sintered magnet manufacturing method, in which R-T-B sintered magnet material alloy powder subjected to a surface treatment is molded into a body, and the molded body is sintered and thermally treated for the formation of the R-Fe-B sintered magnet. SOLUTION: A R-T-B sintered magnet alloy coarse powder; which contains an R2T14B intermetallic compound (R denotes, at least one of rare earth elements containing Y, and T is Fe or Fe and Co) serving as the main phase and being in an amount of 99.5 to 99.99 pts.wt. and 0.01 to 0.5 pts.wt. ethylene carbonate and/or propylene carbonate are added and mixed together, the mixture is atomized into fine powder whose surface is covered with ethylene carbonate and/or propylene carbonate, the fine powder is molded into a body, and the body is sintered and thermally treated for the manufacture of the R-T-B sintered magnet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an R ₂ T ₁₄ B type intermetallic compound (R is at least one rare earth element including Y, and T is Fe or Fe and Co). The present invention relates to a method for producing a sintered TB magnet.

[0002]

2. Description of the Related Art R-T-B sintered magnets (R is at least one kind of rare earth element containing Y, T is Fe or Fe
And Co) are frequently used in various magnet application product fields (such as home appliances, computer peripherals or automobiles). The demand for downsizing, speeding up, or improving the performance of these magnet-applied products is becoming increasingly severe, and there is a demand for further improving the performance of RTB-based sintered magnets.

[0003] RTB-based sintered magnets usually melt,
A manufacturing process in which the RTB-based alloy obtained by casting is roughly pulverized to about 20 to 500 μm, then finely pulverized to about 1 to 20 μm, molded in a magnetic field, and then sintered, heat treated and surface treated. It is manufactured by.

[0004] Conventionally, a predetermined amount of an additive is added to a coarse alloy powder for an RTB-based sintered magnet to be subjected to fine pulverization and mixed, followed by dry fine pulverization. A predetermined amount of an additive is added to the alloy fine powder for the TB-based sintered magnet and mixed to improve the formability, the magnetic field orientation or the oxidation resistance so that the RT-B-based sintered magnet can be used. Various proposals have been made to improve production efficiency, magnetic characteristics, and the like. (Japanese Patent 60
JP-184602, JP-A-60-184603, JP-A-60-184
184604, JP-A-4-214803 and JP-A-4-214803
-214804). Fatty acids such as stearic acid, fatty acid salts such as zinc stearate, amino acid compounds, polyoxyethylene compounds, paraffin, camphor and the like as additives for improving the formability of alloy coarse powder for RTB based sintered magnets Has been proposed. It has also been proposed to add a fatty acid such as oleic acid, a fatty acid ester, a higher alcohol, a polyethylene glycol, a liquid polymer such as liquid polypropylene, or a borate ester for the purpose of improving the magnetic field orientation or the magnetic field orientation and moldability. I have. Further, for the purpose of improving the oxidation resistance or the oxidation resistance and the moldability, it has been proposed to add a fatty acid, a fatty acid ester, a neutral phosphate, a silicone oil or the like. These additives may be used in combination of two or more.

[0005] A method of mixing and mixing a predetermined amount of an additive and a raw material alloy powder for an RTB based sintered magnet to coat the surface of the raw material alloy powder is roughly classified into a wet method and a dry method. You. In the wet method, for example, a predetermined amount of a raw material alloy coarse powder, an organic solvent and an additive are weighed and then charged into a ball mill or the like and finely pulverized, or a predetermined amount of a dry finely pulverized raw material alloy fine powder, an organic solvent and an additive are measured. Are mixed, the prepared slurry-like mixture is dried, and the solvent is removed to remove the RT-
The surface of the raw material alloy fine powder for the B-based sintered magnet is coated with the additive. On the other hand, in the dry method, for example, after mixing a predetermined amount of a raw material alloy coarse powder and an additive, and then dry-pulverizing with a jet mill or the like, an RTB-based sintered magnet is obtained by the impact energy at the time of the fine pulverization. The additive is coated on the surface of the raw material alloy powder for use. The dry method has an advantage that workability is excellent because the coating process is simpler.

[0006]

However, when the work of coating the surface of the raw material alloy powder with the additive is performed by the conventional dry method, the oxygen content and residual amount of the RTB based sintered magnet finally obtained are finally obtained. The carbon content increases, and at the same time the magnetic properties decrease,
This is a factor that hinders the high performance of the TB sintered magnet.

[0007] Therefore, the problem to be solved by the present invention is to form a material by coating the surface of a raw alloy powder for RTB based sintered magnets by a new dry method, and then perform sintering and heat treatment. According to the method of manufacturing an RTB based sintered magnet, an R-Fe having reduced oxygen content and residual carbon content and improved magnetic properties as compared with the case of using a conventional dry method.
-To provide a B-based sintered magnet.

[0008]

According to the present invention, which solves the above-mentioned problems, there is provided an R ₂ T ₁₄ B-type intermetallic compound (R is at least one kind of rare earth element containing Y, and T is Fe or Fe and Co). 99.5 to 99.99 parts by weight of an RTB based sintered alloy alloy powder having a main phase of) and 0.01 to 0.5 parts by weight of ethylene carbonate and / or propylene carbonate are added and mixed.
This is a method for producing an RTB-based sintered magnet in which the powder is finely pulverized into fine powder whose surface is coated with ethylene carbonate and / or propylene carbonate, and then subjected to molding, sintering and heat treatment. The present inventors have determined the type and amount of additive obtained by the dry method, the moldability, the magnetic field orientation and the oxidation resistance of the raw material powder whose surface is coated with the additive, and the R-T obtained finally. The correlation between the oxygen content, the residual carbon content, and the magnetic properties of the -B-based sintered magnet was studied diligently. as a result,
A polar organic additive (propylene carbonate C ₄ O ₃ H or ethylene carbonate C) as an additive having a low residual carbon content and having excellent adsorptivity (coating property) to the raw material powder surface
_{3 O 3 H 4)} is selected, adding a predetermined amount of the raw material fines, by mixing, as compared with the case of using the conventional dry method, it reduces the amount of residual carbon and the oxygen content after sintering Found that it can be suppressed. That is, propylene carbonate C ₄ O ₃ H or ethylene carbonate C ₃ O ₃ H _{4 having} strong polarity is used.
Is adsorbed on the raw material fine powder to cover the surface, the hygroscopicity is significantly reduced, the oxygen content of the raw material fine powder and the sintered body can be suppressed lower than in the case of using the conventional dry method, and propylene carbonate C ₄ O ₃ H Alternatively, it has been found that the residual carbon content after sintering can be suppressed low because the carbon content in ethylene carbonate C ₃ O ₃ H ₄ is small. In particular, the ratio of the number of carbon atoms (Nc) to the sum of the number of carbon atoms (Nc) and the number of oxygen atoms (No) satisfies the relationship of [Nc / (Nc + No)] ≦ 2/3 and the relative dielectric constant at room temperature is Propylene carbonate C ₄ O of 10 or more
It is preferable to use ₃ H or ethylene carbonate C ₃ O ₃ H ₄ . The relative dielectric constant is preferably 10 or more, more preferably 20 or more. If the relative dielectric constant is less than 10, the adsorptive power (coverability) on the surface of the raw material powder decreases, and when it comes into contact with the atmosphere, heat or ignition is instantaneously generated, making it difficult to stably perform industrial production. In this case, it is necessary to once recover the raw material fine powder in a confidential container and then gradually oxidize the raw material fine powder to stabilize the raw material fine powder. The oxygen content of the finally obtained RTB based sintered magnet is as follows: Very high. When [Nc / (Nc + No)] is more than 2/3, the residual carbon content is equivalent to that obtained by the conventional dry method and there is no significant difference. Therefore, it is preferable that the relationship [Nc / (Nc + No)] ≦ 2/3 is satisfied. .

[0009]

DETAILED DESCRIPTION OF THE INVENTION Propylene carbonate C _{4 as} an additive
The mixture of O ₃ H and / or ethylene carbonate C ₃ O ₃ H ₄ and the raw material alloy coarse powder is obtained by mixing 99.5 to 99.99 parts by weight of the raw material alloy coarse powder and 0.01 to 0.5 part by weight of an additive, for example, in an Ar gas or nitrogen gas atmosphere. Into the mixer held at It is preferable to use a hermetic mixer because the additive has a strong hygroscopic property due to its polarity and there is a concern that moisture may be mixed in the mixing step. The mixing ratio is preferably 99.5 to 99.99 parts by weight of the raw material coarse powder and 0.01 to 0.5 part by weight of the additive, and more preferably 99.9 to 99.98 parts by weight of the raw material coarse powder and 0.02 to 0.1 part by weight of the additive. When the amount of the additive is less than 0.01 part by weight, the effect of reducing the oxygen content is not obtained, and the lubricity of the raw material powder is reduced, and the orientation of the magnetic field is reduced. Maximum energy product of sintered magnet
(BH) max decreases. If the amount of the additive exceeds 0.5 parts by weight, the residual carbon content and the oxygen content increase, and the magnetic properties deteriorate.

The raw material coarse powder mixed with the additives is finely pulverized to an average particle size of 2 to 5 μm using, for example, a jet mill.
If the average particle size is less than 2 μm, the oxygen content increases and the moldability deteriorates significantly. If the average particle size exceeds 5 μm, the coercive force decreases. In order to improve the moldability, it is preferable to mix 99.0 to 99.99 parts by weight of the raw material alloy powder obtained by adding the above-mentioned additives in a predetermined amount and 0.01 to 1.0 part by weight of the stearate, and to subject the mixture to molding. .

The steps of molding, sintering, heat treatment and surface treatment of the RTB based sintered magnet according to the present invention can be carried out under known conditions. The molding is preferably performed by compression molding in a magnetic field, and the molding pressure is 49 to 490 MPa (0.5 to 5 ton / c).
m ² ), and the applied magnetic field strength is 636.6 kA / m (8
kOe) or more is preferred. The sintering is preferably carried out in a vacuum or in an inert atmosphere such as argon gas at 1000 to 1100 ° C. for 1 to 4 hours. The heat treatment after sintering is performed at 700 to 1000 ° C in vacuum or in an inert gas atmosphere such as Ar gas.
Perform the first stage heat treatment by heating and holding for
Perform the second stage heat treatment by heating and holding at 0 to 650 ° C for 1 to 10 hours, and if necessary, further heat and maintain at 400 to 600 ° C and at least 10 ° C lower than the second stage heat treatment temperature. Preferably, the third heat treatment is performed, and then the temperature is cooled to room temperature. In order to improve corrosion resistance, it is preferable to coat the surface of the RTB-based sintered magnet body with electrolytic or electroless Ni plating, Cu plating, Ni-P plating, an electrodeposited epoxy resin film, or the like.

[0012]

The present invention will be described below in more detail with reference to examples, but the present invention is not limited by these examples. (Example 1) High frequency melting, Nd: 24.5 wt%, Pr:
6.8 wt%, Dy: 0.85 wt%, Al: 0.08 wt%, G
a: 0.14 wt%, B: 1.0 wt%, the molten alloy adjusted to the main component composition of the balance Fe is poured onto the surface of a quenching roll of a strip casting device and rapidly solidified to form an R-Fe-B alloy flake. Produced. Next, this alloy flake was heated in an Ar gas atmosphere at 1000 ° C. for 2 hours and then cooled to room temperature. Then, after hydrogen embedding and embrittlement, the mixture was crushed by a Landel mill to obtain a raw material alloy coarse powder. The composition of the main components of the alloy coarse fraction was the same as that of the molten metal. Then, the alloy coarse powder 99.9
5 parts by weight and 0.05 parts by weight of propylene carbonate were charged into a closed mixer and mixed for 15 minutes. Then, finely pulverized in a nitrogen gas stream by a jet mill, average particle size 4.7μm
Was obtained. Next, the applied magnetic field strength was 636.6 kA / m (8 kO
e) Molding was performed in a compression magnetic field under the conditions of a molding pressure of 98 MPa (1.0 ton / cm ² ) to prepare a molded body to be subjected to sintering and a molded body for strength measurement. The compact to be used for sintering is 30mm long x horizontal
15 mm x 16 mm thick, molded body for strength measurement is 30 mm long
It was formed into a shape of × 15 mm in width × 9 mm in thickness. The measurement of the strength of the compact was evaluated by the bending strength by a three-point bending test. Table 2 shows the results. Sintering is 1080 ° C x 2 hours, about 6.7 x 10 ⁴ Pa
(5 × 10 ⁴ Torr) in vacuum and then cooled to room temperature. Next, heat treatment is performed in an Ar gas atmosphere at 900 × 1.
The heating was performed in two stages of heating at 550 ° C. × 1 hour and then cooled to room temperature. Next, the obtained sintered body was processed until the sintered skin disappeared, and the magnetic properties at room temperature were measured with a BH tracer. Table 1 shows the results. Table 1 shows the results of analyzing the oxygen content and the carbon content of the finely pulverized fine powder and the sintered body. According to Tables 1 and 2, the oxygen content and the carbon content of the fine powder and the sintered body of Example 1 are all kept low, and have a molded body strength and high magnetic properties that do not lower the industrial production efficiency. You can see that.

Example 2 Instead of the additive of Example 1,
A mixture of 50 parts by weight of ethylene carbonate and 50 parts by weight of propylene carbonate was mixed with 0.05 part by weight, and the raw material alloy crude material of Example 1 was mixed with 9 parts by weight.
The same evaluation as in Example 1 was performed, except that 9.95 parts by weight was mixed and mixed. The results are shown in Tables 1 and 2. Tables 1 and 2 show that good results equivalent to those of Example 1 were obtained.

[0014]

[Table 1]

[0015]

[Table 2]

From Examples 1 and 2, according to the present invention, R-
It can be seen that the oxygen content of the Fe—B based sintered magnet body can be reduced to 0.45 wt% or less and the residual carbon content can be reduced to 0.04 wt% or less.

(Comparative Example 1) In place of the additive of Example 1,
0.05 parts by weight of zinc stearate and the raw material alloy crude of Example 1
The same evaluation as in Example 1 was performed, except that 99.95 parts by weight were mixed and mixed. The results are shown in Tables 1 and 2. From Tables 1 and 2, it can be seen that the fine powder and the sintered body have a higher oxygen content and a higher carbon content than the above-mentioned examples, and the strength of the molded body is reduced. This decrease in the strength of the compact significantly reduced industrial production efficiency. (Comparative Example 2) The room-temperature magnetic properties and the strength of the compact of the R-Fe-B based sintered magnet were measured in the same manner as in Example 1 except that no additive was added. The results are shown in Tables 1 and 2.

Example 3 Nd content: 24.1% by weight, Pr: 6.8% by weight, Dy: 0.85 to which Nd content was reduced by 0.4% by weight as compared with Example 1 and Co was added.
wt%, Al: 0.08 wt%, Ga: 0.14 wt%, B: 1.
An alloy melt adjusted to a main component composition of 0 wt%, Co: 2 wt%, and the balance of Fe was poured onto the surface of a quenching roll of a strip casting apparatus and rapidly solidified to produce an RTB-based alloy flake. Thereafter, in the same manner as in Example 1, the strength of the molded body,
The oxygen content, carbon content, and room temperature magnetic properties of the fine powder and the sintered body were evaluated. As a result, the same values as in Example 1 were obtained for the strength of the compact, the oxygen content and the carbon content of the fine powder and the sintered body. The magnetic properties at room temperature were Br = 1.37 (T) and the coercive force iH
High values of c = 1.33 (MA / m) and (BH) max = 362 (kJ / m ³ ) were obtained.

[0019]

As described above, according to the present invention, the oxygen content and the residual carbon content of the fine powder and the sintered body can be suppressed lower than in the case where the conventional dry method is used. -A T-B based sintered magnet can be provided.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) H01F 1/053 C22C 38/00 303D 1/06 H01F 1/04 H // C22C 38/00 303 1/06 A

Claims (1)

[Claims] 1. An R-T-B system having a main phase of R ₂ T ₁₄ B-type intermetallic compound (R is at least one of rare earth elements including Y and T is Fe or Fe and Co). 99.5 to 99.99 parts by weight of alloy coarse powder for sintered magnets and 0.01 to 0.5 parts by weight of ethylene carbonate and / or propylene carbonate are added,
After mixing, the mixture is then pulverized and the surface is ethylene carbonate and / or
Or a fine powder coated with propylene carbonate, followed by molding, sintering and heat treatment.
A method for producing a B-based sintered magnet.