JP6717231B2 - Method for manufacturing sintered RTB magnet - Google Patents

Description

The present invention relates to a method for producing an RTB-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.

R-T-B based sintered magnet of the R 2 _T 14 _B type compound as a main phase is known as the most powerful magnet in the permanent magnet, a voice coil motor of a hard disk drive (VCM), electrical It is used for various motors such as motors for automobiles (EV, HV, PHV, etc.), motors for industrial equipment, and home electric appliances.

Since the intrinsic coercive force H _cJ (hereinafter, simply referred to as “H _cJ ”) of the R-T-B system sintered magnet decreases at high temperature, irreversible thermal demagnetization occurs. In order to avoid irreversible thermal demagnetization, when used for a motor or the like, it is required to maintain high H _cJ even at high temperatures.

It is known that in the RTB-based sintered magnet, H _cJ is improved by substituting a part of R in the main phase with a heavy rare earth element RH(Dy, Tb). In order to obtain high _HcJ at high temperature, it is effective to add a large amount of heavy rare earth element RH to the RTB-based sintered magnet. However, the R-T-B based sintered magnet, replacing light rare-earth element RL as R a (Nd, Pr) in the heavy rare-earth element _RH, while _{the H cJ} is improved, the residual magnetic flux density _{B r} (hereinafter, simply " B _r )) is reduced. Further, since the heavy rare earth element RH is a rare resource, it is required to reduce the amount used.

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 the heavy rare earth element RH to the RTB-based sintered magnet, RH and alloys of various metals M are RTB-based sintered in Patent Documents 1 and 2. A method of increasing the H _cJ of an _RTB -based sintered magnet by efficiently diffusing RH and M into the _RTB -based sintered magnet by heat-treating the magnet while being present on the surface of the magnet is _proposed. It is disclosed.

JP, 2008-263179, A JP, 2011-14668, A

Since the R-T-B based sintered magnet contains highly reactive R, it is easily oxidized and corroded in the air, and has a weak point in corrosion resistance. For this reason, an ordinary RTB-based sintered magnet is put to practical use in a state where a corrosion resistant coating such as a metal coating or a resin coating 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 secure the corrosion resistance of the magnet during the period from the manufacturing of the magnet to the embedding in the component. For this reason, various simple corrosion resistance improving techniques have been proposed, but they require a special process only for improving the corrosion resistance.

Embodiments of the present invention can achieve both an improvement in _HcJ and an improvement in corrosion resistance of an _RTB -based sintered magnet without adding a special step for improving corrosion resistance. Provided is a method for manufacturing a sintered magnet.

In an exemplary embodiment, a method for manufacturing an RTB-based sintered magnet according to the present disclosure is an RTB-based sintered magnet (R is a rare earth element, T is Fe or Fe and Co, and B is boron. ) Is prepared, and an RLRHM1 alloy (RL is Nd and/or Pr, RH is Dy and/or Tb, M1 is Al, Cu, Fe, Ga, Co) on the surface of the RTB-based sintered magnet. , Ni, Zn, one or more selected from the group consisting of Ni, Zn, and M2 compound (M2 is one or more selected from the group consisting of Al, Li, Fe, and Cu, and the M2 compound is M2 fluoride and/or M2. Oxide) powder and a heat treatment step at a temperature equal to or lower than the sintering temperature of the R-T-B system sintered magnet, wherein the RLRHM1 alloy contains RL+RH in an amount of 50 atomic% of the entire RLRHM1 alloy. As described above, M1 is 10 atomic% or more of the entire RLRHM1 alloy, and RL and RH are included in an atomic ratio of RL:RH=96:4 to 10:90, and the melting point of the RLRHM1 alloy is below the temperature of the heat treatment. Yes,
In the heat treatment, the powder of the RLRHM1 alloy and the powder of the M2 compound 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. It is performed in the state of doing.

In one embodiment, the M2 compound is Al fluoride.

In one embodiment, the M2 compound is Al ₂ O ₃ .

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

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

The present inventor has, as a process capable of achieving both _HcJ improvement and corrosion resistance improvement of an _RTB -based sintered magnet, an RLRHM1 alloy and an M2 compound (M2 is Al on the surface of the RTB-based sintered magnet). , Li, Fe, Cu, and at least one selected from the group consisting of Li, Fe and Cu, and the M2 compound and M2 fluoride and/or M2 oxide) are present, and it has been found that it is effective to perform the heat treatment.

[Preparation of sintered R-T-B base material]
An RTB-based sintered magnet base material, which is a target of diffusion of the heavy rare earth element RH, is prepared. In this specification, for the sake of clarity, the RTB-based sintered magnet, which is the target of diffusion of the heavy rare earth element RH, may be strictly referred to as the RTB-based sintered magnet base material. The term "RTB-based sintered magnet" is intended to include such "RTB-based sintered magnet base material". Known materials can be used as the RTB-based sintered magnet base material, and have, for example, the following compositions.
Rare earth element R: 12 to 17 atom%
B (some of B (boron) may be substituted with C (carbon)): 5 to 8 atom%
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): 0-2 atom%
T (transition metal element mainly containing Fe and optionally containing Co) and unavoidable 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 it may contain a heavy rare earth element. When a heavy rare earth element is contained, it is preferable to contain at least one of Dy and Tb.

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

[RLRHM1 alloy]
RL of the RLRHM1 alloy 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 in an amount of 50 atomic% or more of the entire RLRHM1 alloy, M1 in an amount of 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 below the temperature of the diffusion heat treatment.

As RL, Nd and/or Pr which has a high effect of reducing the M2 compound is used. 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 to the diffusion heat treatment temperature described below or less and does not adversely affect the magnet characteristics. To do.

It is believed that the RLRHM1 alloy serves both as a diffusing agent that supplies RH that diffuses into the magnet to enhance H _cJ and as a reducing agent that reduces the M2 compound. On the side where RH is less than 96:4, that is, when RH is less than 4 atomic% of RL+RH, RH sufficient to improve H _cJ cannot be supplied. When RL:RH 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 it is difficult to exert the effect of improving H _cJ. ..

The RLRHM1 alloy is preferably melted during the diffusion heat treatment in order to sufficiently diffuse the RH into the magnet and reduce the M2 compound. Therefore, the melting point of the RLRHM1 alloy is preferably equal to or lower than the temperature of the diffusion heat treatment, but for that purpose, M1 needs 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 quenching method such as a roll quenching method and an atomizing method, and a method of crushing an ingot of the RLRHM1 alloy. The particle size of the powder of the RLRHM1 alloy is preferably 500 μm or less, more preferably 10 to 300 μm. In the present disclosure, the particle size of 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 type particle size distribution measuring device manufactured by Microtrac Bell).

[M2 compound]
The M2 compound is one or more fluorides and/or oxides selected from the group consisting of Al, Li, Fe and Cu. It is considered that M2 diffuses inside the magnet through the grain boundary together with RH. Typical examples of the M2 compound are AlF ₃ , Al ₂ O ₃ , LiF, FeF ₃ , CuF ₂ and the like. Among these typical examples, Al compounds are preferable. These compounds have a large effect of improving the coercive force H _cJ as compared with other compounds. Any method may be used for producing the M2 compound, and a commercially available M2 compound can be used. The particle size of the M2 compound is preferably 100 μm or less.

According to the study of the present inventors, the powder of the RLRHM1 alloy is present on the surface of the RTB-based sintered magnet together with the powder of the M2 compound and heat-treated to obtain the RTB-based sintered magnet. It was found that both improvement of _{HcJ and} improvement of corrosion resistance can be achieved.

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

The binder and the solvent should be those that are substantially removed from the surface of the RTB-based sintered magnet by thermal decomposition or evaporation at a temperature equal to or lower than the melting point of the diffusion aid in the subsequent heating process of the heat treatment. There is no particular limitation as long as it is sufficient. Examples of the binder include polyvinyl alcohol, ethyl cellulose, polyester and the like. Further, the powder of the RLRHM1 alloy and the powder of the M2 compound may be present on the surface of the RTB-based sintered magnet in a mixed state, or may be present separately.

In the method of the present disclosure, since the melting point of the RLRHM1 alloy is equal to or lower than the heat treatment temperature, the RLRHM1 alloy is melted during the heat treatment, and the surface of the R-T-B system sintered magnet has RH as the R-T-B system sintered magnet. It becomes easy to diffuse inside. Before the powder of the RLRHM1 alloy and the powder of the M2 compound are present on the surface of the RTB-based sintered magnet, a special cleaning treatment such as pickling is performed on the surface of the RTB-based sintered magnet. You don't have to. Of course, it does not exclude performing such a cleaning process. Further, even if the surface of the RLRHM1 alloy powder particles is slightly oxidized, there is almost no effect on the diffusion of RH and the effect of reducing the M2 compound.

The production method of the present disclosure does not necessarily exclude that powders (third powder) other than the powders of the RLRHM1 alloy and the M2 compound are present on the surface of the RTB-based sintered magnet, but the third powder is It is necessary to take care so as not to prevent the RH in the M2 compound from diffusing inside the RTB-based sintered magnet. The mass ratio of the powder of “RLRHM1 alloy and M2 compound” to the whole powder existing on the surface of the RTB-based sintered magnet is preferably 70% or more.

According to the manufacturing method of the present disclosure, it is possible to _efficiently improve _HcJ of an _RTB -based sintered magnet with a small amount of RH. The amount of the 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 equal to or lower than the sintering temperature of the RTB-based sintered magnet (specifically, 1000° C. or lower) and higher than the melting point of the RLRHM1 alloy powder. Specifically, the heat treatment temperature is preferably 500° C. or higher at the temperature of the RTB-based sintered magnet. The heat treatment time is, for example, 10 minutes to 72 hours. Further, after the heat treatment for diffusion, if necessary, heat treatment may be further performed at 400 to 700° C. for 10 minutes to 72 hours.

(Experimental example 1)
First, according to 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. A B-type sintered magnet was produced. By machining this, an RTB-based sintered magnet base material having a size of 4.9 mm×10 mm×24.5 mm 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 characteristics of the RTB-based sintered magnet after heat treatment are measured after the surface of the RTB-based sintered magnet is removed by machining. Therefore, according to the R-T-B system sintered magnet base material, the surface was further machined by 0.2 mm each, and the size was measured to be 4.5 mm x 9.6 mm x 24.1 mm. did. Further, when the amount of impurities in the RTB-based sintered magnet base material was separately measured by 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 produced by the atomizing method. The obtained alloy powder 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 applied to two sides of 10 mm×24.5 mm of the R-T-B system sintered magnet base material, and the RH (Tb) amount was 1.0 on both sides of the R-T-B system magnet base material. It was applied so as to be a mass% and dried.

The Mo plate on which the R-T-B based sintered magnet base material was placed was housed in a processing container and covered. This lid does not prevent gas from entering or exiting the container. This was housed 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 from room temperature while evacuation was performed, and the atmospheric pressure and temperature reached the above conditions. After that, the temperature was once lowered to room temperature, the Mo plate was taken out, and the RTB-based sintered magnet was recovered. The recovered RTB-based sintered magnet was returned to the processing container, housed again in the heat treatment furnace, and heat-treated 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 from the room temperature while exhausting the vacuum and the atmospheric pressure and temperature reached the above conditions. After that, the temperature was once lowered to room temperature, and then the RTB-based sintered magnet was collected.

The surface of each of the obtained R-T-B based sintered magnets was polished and removed by 0.2 mm, and 4.5 mm×9.6 mm×24.1 mm sample No. 1 to 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. After ultrasonic cleaning in ethanol for 1 to 7, a pressure cooker test (PCT test) was performed at a temperature of 120° C., a relative humidity of 100% RH and 0.2 MPa for 12 hours×3 cycles.

FIG. 1 is a graph showing the amount of wear of the magnet 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 not coated with the slurry.

From Table 1 and FIG. 1, it was found that the magnet heat-treated by allowing the M2 compound to exist on the surface of the RTB-based sintered magnet base material together with the RHRLM1 alloy can achieve both improvement in H _{cJ and} improvement in corrosion resistance.

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

Claims (3)

A step of preparing an RTB 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 and Zn on the surface of the R-T-B based sintered magnet. 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 the sintering temperature of the R-T-B based sintered magnet in the state of being present;
Including,
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 contains RL and RH in an atomic ratio of RL:RH=96:4 to 10:90, and The melting point of the RLRHM1 alloy is below the temperature of the heat treatment,
In the heat treatment, the powder of the RLRHM1 alloy and the powder of the M2 compound 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 method for producing an RTB-based sintered magnet, which is performed under the following conditions. The method for manufacturing an RTB-based sintered magnet according to claim 1, wherein the M2 compound is Al fluoride. The method for manufacturing an RTB-based sintered magnet according to claim 1, wherein the M2 compound is Al ₂ O ₃ .

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