JP2018142641A - Method for manufacturing r-t-b based sintered magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an R-T-B based sintered magnet which is increased in intrinsic coercive force and corrosion resistance.SOLUTION: A method for manufacturing an R-T-B based sintered magnet comprises the steps of: preparing an R-T-B based sintered magnet; and performing a thermal treatment at a sintering temperature or below in a state in which powder of RLRHM1 alloy (RL represents Nd and/or Pr, RH represents Dy and/or Tb, M1 represents one or more kinds selected from Al, Cu, Fe, Ga, Co, Ni and Zn) and powder of M2 compound (M2 represents one or more kinds selected from Al, Li, Fe and Cu, and the M2 compound is M2 fluoride and/or M2 oxide) are present on the surface of the magnet. The alloy includes RL+RH at 50 atom% or more to a whole amount thereof, and M1 at 10 atom% or more, provided that the atomic ratio of RL and RH is given by RL:RH=96:4-10:90. The alloy has a melting point equal to or below the temperature of the thermal treatment. The thermal treatment is performed in a state in which the alloy powder and the M2 compound powder are present on the surface of the magnet at a mass ratio given by Alloy:M2 compound=97:3-80:20.SELECTED DRAWING: None

Description

The present invention relates to a method for producing an R-T-B based sintered magnet (R is a rare earth element, T is Fe or Fe and Co, and B is boron) having an R ₂ T ₁₄ B type compound as a main phase.

An RTB-based sintered magnet mainly composed of an R ₂ T ₁₄ B-type compound is known as the most powerful magnet among permanent magnets. It is used for various motors such as motors for automobiles (EV, HV, PHV, etc.), motors for industrial equipment, and home appliances.

The _RTB -based sintered magnet has irreversible thermal demagnetization because its intrinsic coercive force H _cJ (hereinafter simply referred to as “H _cJ ”) decreases at high temperatures. In order to avoid irreversible thermal demagnetization, when used for motors, etc., it is required to maintain a high _HcJ even at high temperatures.

It is known that the RTB-based sintered magnet improves _HcJ when a part of R in the main phase is replaced with a heavy rare earth element RH (Dy, Tb). In order to obtain high _HcJ at a high temperature, it is effective to add a large amount of heavy rare earth element RH in the RTB-based sintered magnet. However, when the light rare earth element RL (Nd, Pr) is substituted as R in the RTB-based sintered magnet with the heavy rare earth element RH, H _cJ is improved, while the residual magnetic flux density B _r (hereinafter simply “ There is a problem that “B _r ”) is reduced. Further, since the heavy rare earth element RH is a rare resource, it is required to reduce the amount of use thereof.

In recent years, so as not to reduce the B _r, to improve the H _cJ of the R-T-B based sintered magnets have been studied with less heavy rare-earth element RH. For example, as a method for effectively supplying and diffusing heavy rare earth elements RH to an RTB-based sintered magnet, Patent Documents 1 and 2 disclose that RH and alloys of various metals M are RTB-based sintered. There is a method in which RH and M are efficiently diffused into the _RTB -based sintered magnet by heat treatment in the state of being present on the surface of the magnet, thereby increasing the _HcJ of the _RTB -based sintered magnet. It is disclosed.

JP 2008-263179 A JP 2011-14668 A

  Since the RTB-based sintered magnet contains R having high reactivity, it is easily oxidized and corroded in the atmosphere, and has a weak point in terms of corrosion resistance. For this reason, an ordinary RTB-based sintered magnet is put to practical use in a state where a corrosion-resistant film such as a metal film or a resin film is formed on the surface thereof.

  On the other hand, when a magnet is used by being embedded in a component, such as an IPM (Interior Permanent Magnet) motor, it is not necessary to form a corrosion-resistant coating on the surface of the magnet. However, it is necessary to ensure the corrosion resistance of the magnet in the period from when the magnet is manufactured to when it is embedded in the component. For this reason, various simple corrosion resistance improvement techniques have been proposed, but they require a special process only for improving the corrosion resistance.

In the embodiment of the present invention, R-T-B can achieve both improvement of _{HcJ and} improvement of corrosion resistance of an R-T-B type sintered magnet without adding a special step for improving the corrosion resistance. A method for producing a sintered magnet is provided.

In the exemplary embodiment, the manufacturing method of the RTB-based sintered magnet of the present disclosure includes an RTB-based sintered magnet (R is a rare earth element, T is Fe or Fe and Co, and B is boron. ) And an RLRHM1 alloy (RL is Nd and / or Pr, RH is Dy and / or Tb, M1 is Al, Cu, Fe, Ga, Co) , One or more selected from the group consisting of Ni, Zn) and an M2 compound (M2 is one or more selected from the group consisting of Al, Li, Fe, Cu), and the M2 compound is M2 fluoride and / or M2 And a heat treatment at a temperature lower than the sintering temperature of the RTB-based sintered magnet, and the RLRHM1 alloy contains RL + RH at 50 atomic% of the entire RLRHM1 alloy. M1 is now RLR M1 alloy entire 10 atomic% or more, and, the RH and RL RL: RH = 96: 4~10: contains an atomic ratio of 90, and the melting point of the RLRHM1 alloy is less than the temperature of the heat treatment,
In the heat treatment, the RLRHM1 alloy powder and the M2 compound powder are present on the surface of the RTB-based sintered magnet in a mass ratio of RLRHM1 alloy: M2 compound = 97: 3 to 80:20. To be done.

  In one embodiment, the M2 compound is Al fluoride.

In certain embodiments, the M2 compound is _Al 2 _{O 3.}

According to the embodiment of the present disclosure, both the _HcJ improvement and the corrosion resistance improvement of the _RTB -based sintered magnet can be achieved without adding a special process for improving the corrosion resistance.

It is a graph which shows the relationship between the amount of wear by the PCT test of a RTB system sintered magnet, and M2 compound.

As a process that can achieve both improvement of _HcJ and corrosion resistance of the R-T-B system sintered magnet, the present inventor has developed an RLRHM1 alloy, M2 compound (M2 is Al on the surface of the R-T-B system sintered magnet). It has been found that it is effective to perform a heat treatment in the presence of one or more selected from the group consisting of Li, Fe, Cu, M2 compound and M2 fluoride and / or M2 oxide).

[Preparation of RTB-based sintered magnet base material]
An RTB-based sintered magnet base material to be diffused of the heavy rare earth element RH is prepared. In this specification, for the sake of easy understanding, an RTB-based sintered magnet that is an object of diffusion of the heavy rare earth element RH may be strictly referred to as an RTB-based sintered magnet base material. The term “RTB-based sintered magnet” includes such an “RTB-based sintered magnet base material”. As this RTB-based sintered magnet base material, a known material can be used, for example, having the following composition.
Rare earth element R: 12-17 atom%
B (a part of B (boron) may be substituted with C (carbon)): 5 to 8 atomic%
Additive element M ′ (selected from the group consisting of Al, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Pb, and Bi At least one): 0 to 2 atomic%
T (a transition metal element mainly composed of Fe and may contain Co) and inevitable impurities: balance

  Here, the rare earth element R is mainly a light rare earth element RL (at least one element selected from Nd and Pr), but may contain a heavy rare earth element. In addition, when a heavy rare earth element is contained, it is preferable that at least one of Dy and Tb is included.

  The RTB-based sintered magnet base material having the above composition is manufactured by an arbitrary manufacturing method. The RTB-based sintered magnet base material may be sintered, or may be subjected to cutting or polishing.

[RLLRHM1 alloy]
In the RLRHM1 alloy, RL is Nd and / or Pr, RH is Dy and / or Tb, and M1 is one or more selected from the group consisting of Al, Cu, Fe, Ga, Co, Ni, and Zn. . The RLRHM1 alloy contains RL + RH at 50 atomic% or more of the entire RLRHM1 alloy, M1 at 10 atomic% or more of the entire RLRHM1 alloy, and RL and RH in an atomic ratio of RL: RH = 96: 4 to 10:90. RL: RH is preferably 90:10 to 20:80. The melting point of the RLRHM1 alloy is lower than the temperature of the diffusion heat treatment.

  RL is Nd and / or Pr, which has a high effect of reducing the M2 compound. M1 is one or more selected from the group consisting of Al, Cu, Fe, Ga, Co, Ni, and Zn, which lowers the melting point of the RLRHM1 alloy below the diffusion heat treatment temperature described below and does not adversely affect the magnet properties. To do.

The RLRHM1 alloy is thought to play both the role of a diffusing agent that diffuses in the magnet to improve _HcJ and the role of a reducing agent that reduces the M2 compound. When RH: RH is less than 96: 4, that is, when RH is less than 4 atom% of RL + RH, RH sufficient to sufficiently improve _HcJ cannot be supplied. When RL: RH is on the side where RL is less than 10:90, that is, when RL is less than 10 atomic% of RL + RH, the ability to reduce the M2 compound is insufficient and the effect of improving _HcJ is difficult to be exhibited. .

  In order to sufficiently diffuse RH into the magnet and reduce the M2 compound, the RLRHM1 alloy is preferably melted during the diffusion heat treatment. Therefore, the melting point of the RLRHM1 alloy is preferably equal to or lower than the temperature of the diffusion heat treatment. For this purpose, M1 is required to be 10 atomic% or more of the entire RLRHM1 alloy.

  Any method may be used for producing the RLRHM1 alloy, and examples thereof include a rapid cooling method such as a roll quenching method and an atomizing method, and a method of pulverizing an ingot of the RLRHM1 alloy. The particle size of the RLRHM1 alloy powder is preferably 500 μm or less, and more preferably 10 to 300 μm. In the present disclosure, the particle size of the powder may be measured by, for example, microscopic observation. It can also be measured using a commercially available particle size distribution measuring device (for example, a laser diffraction / scattering particle size distribution measuring device manufactured by Microtrack Bell).

[M2 compound]
The M2 compound is at least one fluoride and / or oxide selected from the group consisting of Al, Li, Fe, and Cu. M2 is considered to diffuse inside the magnet through the grain boundary together with RH. Typical examples of the M2 compound include AlF ₃ , Al ₂ O ₃ , LiF, FeF ₃ , CuF ₂ and the like. Among these typical examples, an Al compound is preferable. These compounds have a greater effect of improving the coercive force H _cJ than other compounds. Any method for producing the M2 compound may be used, and a commercially available M2 compound may be used. The particle size of the M2 compound is preferably 100 μm or less.

According to the study by the present inventors, the RLTHM1 alloy powder is present together with the M2 compound powder on the surface of the RTB-based sintered magnet and heat-treated. It was found that both _HcJ improvement and corrosion resistance improvement can be achieved.

[Application]
Any method may be used in which the powder of the RLRHM1 alloy and the powder of the M2 compound are present on the surface of the RTB-based sintered magnet. For example, a method in which RLRHM1 alloy powder and M2 compound powder are dispersed on the surface of an R-T-B system sintered magnet, and RLRHM1 alloy powder and M2 compound powder are dispersed in a solvent such as pure water or an organic solvent. , A method of immersing an RTB-based sintered magnet and pulling it up, a powder of RLRHM1 alloy and a powder of M2 compound are mixed with a binder or a solvent to produce a slurry, and this slurry is prepared as RTB A method of applying to the surface of a sintered magnet, granulating the RLRHM1 alloy powder and M2 compound powder together with a binder to produce a granulated powder, and applying this granulated powder to the surface of the RTB-based sintered magnet Any of the methods of attaching to can be performed.

  The binder and the solvent should be substantially removed from the surface of the RTB-based sintered magnet by thermal decomposition or evaporation at a temperature lower than the melting point of the diffusion aid in the subsequent heating process. There is no particular limitation. Examples of the binder include polyvinyl alcohol, ethyl cellulose, polyester and the like. The RLRHM1 alloy powder and the M2 compound powder may be present on the surface of the R-T-B system sintered magnet in a state where they are mixed, or may be present separately.

  In the method of the present disclosure, since the RLRHM1 alloy has a melting point lower than the heat treatment temperature, it melts during the heat treatment, and the surface of the R-T-B system sintered magnet has RH of the R-T-B system sintered magnet. It becomes easy to diffuse inside. Special cleaning treatment such as pickling the surface of the R-T-B system sintered magnet before the RLRHM1 alloy powder and the M2 compound powder are present on the surface of the R-T-B system sintered magnet. There is no need to do. Of course, it does not exclude performing such a cleaning process. Further, even if the surface of the RLRHM1 alloy powder particles is somewhat oxidized, there is almost no influence on the diffusion of RH and the effect of reducing the M2 compound.

  Although the manufacturing method of the present disclosure does not necessarily exclude the presence of powder (third powder) other than the powder of RLRHM1 alloy and M2 compound on the surface of the R-T-B system sintered magnet, Care must be taken not to inhibit diffusion of RH in the M2 compound into the interior of the RTB-based sintered magnet. The mass ratio of the “RLLRHM1 alloy and M2 compound” powder in the entire powder existing on the surface of the RTB-based sintered magnet is desirably 70% or more.

According to the manufacturing method of the present disclosure, it is possible to _efficiently improve the _HcJ of the _RTB -based sintered magnet with a small amount of RH. The amount of RH element in the powder present on the surface of the RTB-based sintered magnet is preferably 0.2 to 1.5 mass% with respect to the RTB-based sintered magnet.

[Diffusion heat treatment]
The heat treatment temperature for diffusion is not higher than the sintering temperature of the RTB-based sintered magnet (specifically, for example, 1000 ° C. or lower), and is higher than the melting point of the RLRHM1 alloy powder. Specifically, the heat treatment temperature is preferably 500 ° C. or higher as the temperature of the RTB-based sintered magnet. The heat treatment time is, for example, 10 minutes to 72 hours. Moreover, you may perform the heat processing for 10 minutes-72 hours at 400-700 degreeC as needed after the heat processing for diffusion.

(Experimental example 1)
First, by a known method, the composition ratio Nd = 13.4, B = 5.8, Al = 0.5, Cu = 0.1, Co = 1.1, and the balance = Fe (atomic%) RT -B system sintered magnet was produced. By machining this, a 4.9 mm × 10 mm × 24.5 mm RTB-based sintered magnet base material was obtained. Magnetic properties of the obtained R-T-B based sintered magnet base material where a measured by B-H _{tracer, H cJ} is 1035kA / m, _{B r} was 1.45 T.

  As will be described later, the magnetic properties of the RTB-based sintered magnet after heat treatment are measured after removing the surface of the RTB-based sintered magnet by machining. For this reason, the R-T-B system sintered magnet base material is also measured in accordance with it by further removing the surface by 0.2 mm each by machining to a size of 4.5 mm × 9.6 mm × 24.1 mm. did. Moreover, when the impurity amount of the R-T-B system sintered magnet base material was separately measured with a gas analyzer, oxygen was 810 ppm, nitrogen was 370 ppm, and carbon was 870 ppm.

Next, an alloy having a composition of Nd ₅₇ Tb ₁₃ Cu ₃₀ (atomic%) (melting point: 570 ° C.) was prepared as an RLRHM1 alloy. The alloy is a powder having a particle size of 106 μm or less prepared by an atomizing method. The powder of the obtained alloy and the powder of the M2 compound shown in Table 1 were mixed at a mass ratio of Nd ₅₇ Tb ₁₃ Cu ₃₀ : M2 compound = 90: 10 to obtain a mixed powder (NdTbCu = Nd ₅₇ Tb in Table 1). ₁₃ Cu ₃₀ ). This mixed powder was mixed with polyvinyl alcohol and water to obtain a slurry. This slurry was added to two surfaces of an R-T-B system sintered magnet base material of 10 mm × 24.5 mm, and the amount of RH (Tb) was 1.0 on both surfaces with respect to the R-T-B system magnet base material. It apply | coated so that it might become mass%, and it dried.

  The Mo plate on which this RTB-based sintered magnet base material was placed was accommodated in a processing container and covered. This lid does not prevent the gas from entering or leaving the container. This was accommodated in a heat treatment furnace and heat-treated at 900 ° C. for 10 hours in an Ar atmosphere of 100 Pa. The heat treatment was carried out under the above conditions after the temperature was raised while evacuating from room temperature and the atmospheric pressure and temperature reached the above conditions. Then, after the temperature was lowered to room temperature, the Mo plate was taken out and the RTB-based sintered magnet was collected. The recovered RTB-based sintered magnet was returned to the processing vessel and accommodated again in a heat treatment furnace, and heat treatment was performed at 490 ° C. for 3 hours in a vacuum of 10 Pa or less. This heat treatment was also performed under the above conditions after the temperature was raised while evacuating from room temperature and the atmospheric pressure and temperature reached the above conditions. Thereafter, the temperature was lowered to room temperature, and then the R-T-B sintered magnet was collected.

The surface of the obtained RTB-based sintered magnet was polished and removed by machining by 0.2 mm each, and sample No. 4.5 mm × 9.6 mm × 24.1 mm was removed. 1-7 were obtained. The obtained sample No. The magnetic properties of 1-7 was measured by B-H tracer _was determined _{H cJ} and _{B r.} The results are shown in Table 1.

  Furthermore, sample no. About 1-7, after performing ultrasonic cleaning in ethanol, the pressure cooker test (PCT test) of 12 hours x3 cycles was performed at a temperature of 120 ° C., a relative humidity of 100% RH, and 0.2 MPa.

  FIG. 1 is a graph showing the amount of magnet wear after the PCT test for each type of M2 compound. The amount of wear of the magnet includes the amount of wear on the side surface where the slurry is not applied.

From Table 1 and FIG. 1, it was found that a magnet heat-treated with the M2 compound and the RHRLM1 alloy present on the surface of the RTB-based sintered magnet base material can achieve both improved _{HcJ and} improved corrosion resistance.

The method for producing an RTB-based sintered magnet according to the present invention can provide an RTB-based sintered magnet that improves _HcJ with less heavy rare earth element RH and also has improved corrosion resistance.

Claims (3)

Preparing a R-T-B sintered magnet (R is a rare earth element, T is Fe or Fe and Co, and B is boron);
An RLRHM1 alloy (RL is Nd and / or Pr, RH is Dy and / or Tb, M1 is a group consisting of Al, Cu, Fe, Ga, Co, Ni, Zn on the surface of the RTB-based sintered magnet) And a powder of M2 compound (M2 is one or more selected from the group consisting of Al, Li, Fe and Cu, and M2 compound is M2 fluoride and / or M2 oxide). A step of performing a heat treatment at a temperature equal to or lower than a sintering temperature of the R-T-B system sintered magnet in a state of being present;
Including
The RLRHM1 alloy includes RL + RH at least 50 atomic% of the entire RLRHM1 alloy, M1 at least 10 atomic% of the entire RLRHM1 alloy, and RL and RH in an atomic ratio of RL: RH = 96: 4 to 10:90, and The melting point of the RLRHM1 alloy is equal to or lower than the temperature of the heat treatment,
In the heat treatment, the RLRHM1 alloy powder and the M2 compound powder are present on the surface of the RTB-based sintered magnet in a mass ratio of RLRHM1 alloy: M2 compound = 97: 3 to 80:20. The manufacturing method of the RTB system sintered magnet performed in the state to do.   The method for producing an RTB-based sintered magnet according to claim 1, wherein the M2 compound is Al fluoride. The method for producing an RTB-based sintered magnet according to claim 1, wherein the M2 compound is Al ₂ O ₃ .

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