JP6733533B2 - Method for manufacturing RTB-based sintered magnet - Google Patents

Description

The present disclosure relates to a method for manufacturing an RTB-based sintered magnet (R is a rare earth element, T is Fe or Fe and Co).

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, and voice coil motor of a hard disk drive (VCM), It is used in various motors such as electric vehicle (EV, HV, PHV, etc.) motors, industrial equipment motors, and home electric appliances.

Since the intrinsic coercive force H _cJ (hereinafter, simply referred to as “H _cJ ”) of the _RTB -based sintered magnet decreases at a 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 when a part of R in the R ₂ T ₁₄ B type compound phase is replaced 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.

Therefore, 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, a fluoride or an oxide of the heavy rare earth element RH, or various metals M or M alloys may be present individually or in a mixed state and allowed to exist on the surface of the sintered magnet, and heat treated in that state to improve coercive force. It has been proposed to diffuse the contributing heavy rare earth element RH into the magnet. Patent Document 1 discloses a method in which powders of R fluoride, R oxyfluoride, and R oxide are brought into contact with the surface of an RTB-based sintered magnet to perform heat treatment to diffuse them into the magnet. doing. Further, the applicant has described in Patent Document 2 that a powder of RLM alloy (M is one or more kinds selected from Cu, Fe, Ga, Co, and Ni) and a powder of RH fluoride are RTB sintered magnets. We proposed a method of reducing RH fluoride by RLM and diffusing only RH into the magnet by allowing it to exist on the surface of and heat treated.

International Publication No. 2006/043348 International Publication No. 2015/163397

In recent years, along with the demand for cost reduction of the R-T-B system sintered magnet, it is desired for the RH diffusion source to have both the cost reduction and the H _cJ improvement effect.

The present disclosure can reduce the cost of a diffusion source for diffusing RH in an R-T-B based sintered magnet, and uses an RH diffusion source having a high H _cJ improvement effect to form an R-T. -A method for manufacturing a B-based sintered magnet is provided.

In an exemplary embodiment, a method of manufacturing an RTB-based sintered magnet according to the present disclosure includes a step of preparing an RTB-based sintered magnet, and a step of preparing the RTB-based sintered magnet. Powder of RLM1M2 alloy (RL is one or more selected from Nd and Pr, M1 and M2 are one or more selected from Cu, Fe, Ga, Co, Ni and Al, and M1=M2 may be M1=M2) on the surface, In the state where a powder of RH fluoride (RH is Dy and/or Tb) and a mixed powder of RH compound powder (diffusion source powder) produced by a recycling process of an RTB magnet are present, And a step of performing heat treatment at a temperature equal to or lower than the sintering temperature of the RTB-based sintered magnet.

In one embodiment, the RH compound powder is an intermediate product produced by a recycling process of an RTB magnet.

In an embodiment, the powder of the RH compound manufactured by the recycling process of the R-T-B magnet is RH carbonate, RH oxalate, RH sulfate, RH phosphate, RH acetate, RH oxide. It is 1 or more types chosen from.

In one embodiment, a ratio of the powder of the RH compound manufactured by the recycling process of the RTB-based magnet in the mixed powder is 5 to 50% by mass.

In one embodiment, the RLM1M2 alloy contains 50 atomic% or more of RL, and the melting point of the RLM1M2 alloy is equal to or lower than the temperature of the heat treatment.

In one embodiment, in the heat treatment, the powder of the RLM1M2 alloy and the mixed powder have a mass ratio of RLM1M2 alloy:mixed powder=96:4 to 50:50 on the surface of the RTB-based sintered magnet. It is done in the state that exists in.

In one embodiment, the mass of the RH element contained in the mixed powder on the surface of the RTB-based sintered magnet is 0.2 to 1.5 with respect to the RTB-based sintered magnet. It is% by mass.

In one embodiment, the method further includes the step of producing the powder of the RH compound by recycling the RTB magnet.

According to the embodiment of the present disclosure, the powder of the RLM1M2 alloy having a reducing effect is used together with the powder of the RH compound that can be generated by the recycling process in the RH fluoride having a high H _cJ improving effect as the RH diffusion source, It is possible to efficiently use rare resources, reduce costs, and manufacture an _RTB -based sintered magnet that can maintain high H _cJ even at high temperatures.

The rare earth element R, in particular the heavy rare earth element RH, has a problem that the supply is not stable and the price fluctuates greatly because the resource abundance is small and the production area is limited. .. Therefore, in recent years, rare earth elements R are separated and recovered from used waste magnets, magnet scraps discharged as defectives during the production process, magnet processing scraps discharged as cutting scraps and grinding scraps, and used as a magnet raw material. Recycling technology for reuse is developing. The inventor considered that if an RH compound produced in a recycling process is used as a diffusion source, rare RH can be effectively used and the cost of the diffusion source can be reduced. Therefore, when a method of mixing an RH compound having a high H _cJ improving effect with an RH compound generated in the recycling step and using this as a diffusion source was examined, both RLM1M2 alloys having excellent reducing ability were present on the magnet surface. The present invention has been completed by discovering that the RH fluoride and the RH compound produced in the recycling step can be reduced by the heat treatment so that the RH can be diffused in the magnet. In the present specification, a substance containing RH is referred to as a “diffusion agent”, and a substance that reduces the RH of the diffusing agent into a diffusible state is referred to as a “diffusion aid”.

[Preparation of sintered RTB magnet 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 the present specification, for the sake of clarity, an RTB-based sintered magnet, which 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 "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%
Additional 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 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 R-T-B system sintered magnet base material may be as-sintered or may be subjected to cutting or polishing.

[Diffusing agent]
As the diffusing agent, powder of RH fluoride (RH is Dy and/or Tb) is mixed with the RH compound generated in the recycling process of the RTB magnet. Hereinafter, this mixed powder is referred to as a diffusion source powder for the sake of clarity. Specifically, for example, at least one selected from RH carbonate, RH oxalate, RH sulfate, RH phosphate, RH acetate, and RH oxide. Of these, RH carbonate, RH oxalate and RH oxide are preferable. Further, it is preferable that the RH of the RH fluoride and the RH of the RH compound produced in the recycling step are the same kind.

Techniques for recovering the rare earth element R from waste magnets of RTB magnets, magnet scraps, magnet processing scraps, and the like have been developed (International Publication No. 2013/018710). According to such a recovery technique, a rare earth oxide separated from Fe and Co can be obtained by performing various treatments on the waste magnet of the RTB-based magnet. When the rare earth oxide thus obtained is dissolved in an acid and solvent extraction is performed, a solution of the heavy rare earth RH (RH solution) can be obtained by separating it from other rare earth elements R. When carbonate, oxalic acid, sulfuric acid, sulfate, phosphoric acid or phosphate is added to the RH solution as a precipitant, RH carbonate, RH oxalate, RH sulfate or RH phosphate is precipitated respectively. Further, when these precipitates are fired, RH oxide is generated. The powder of the RH compound thus obtained is preferably used as a RH diffusion source in the present disclosure by being mixed with RH fluoride. In a normal recycling process, thereafter, these RH compounds are reduced to RH metal by molten salt electrolysis or the like and used as a raw material of an RTB magnet. Conventionally, it has not been used as a magnet raw material (diffusing agent) in the state of an intermediate product in such a recycling process. By using such an intermediate product as the RH diffusion source, there is a merit that raw materials can be procured at a low cost in the diffusion step, and a subsequent reduction step can be omitted in the recycling step. That is, by adopting the method of the present disclosure, the cost can be double reduced in the diffusion process and the recycling process.

In addition, the Dy-Fe alloy or the Tb-Fe alloy used for diffusing the heavy rare earth element from the outside with respect to the R-T-B system magnet comes into contact with the R-T-B system magnet during the diffusion process. In some cases, the magnet may be discarded in a state where it contains the light rare earth element R such as Nd. A technique for recovering the heavy rare earth element RH from such a used RH diffusion alloy has also been developed (International Publication No. 2014/115876). Therefore, the RH compound can be similarly obtained from the used RH diffusion alloy.

The RTB-based magnet to be recycled is not limited to the sintered magnet, but may be a bonded magnet, a hot-worked magnet, magnet powder used for them, or the like. By using the R-T-B magnet generated in the recycling process, it is possible to effectively utilize the rare RH and reduce the cost of the diffusion source. The particle size of the RH compound powder is, for example, 20 μm or less, and the small one is about several 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 particle size distribution measuring device manufactured by Microtrac Bell Co., Ltd.).

The RH fluoride powder may be any powder produced industrially. The particle size of the RH fluoride powder is preferably 100 μm or less. The RH fluoride in the present invention may include RH oxyfluoride, which is an intermediate substance in the production process of RH fluoride.

The ratio of the powder of the RH compound produced by the recycling step of the RTB-based magnet in the diffusion source powder is preferably 5 to 50% by mass, more preferably 10 to 40% by mass. If it is less than 5% by mass, there is a certain effect in terms of efficient use of rare resources, but the effect of cost reduction is low. On the other hand, if it exceeds 50% by mass, many diffusion sources need to be generated in the recycling process, and the supply of raw materials may become unstable. Further, depending on the type of compound, the H _cJ improving effect may be low.

The above-mentioned RH compound may be one prepared by purchasing an RH compound manufactured by a third party through a recycling process of an RTB-based magnet from the third party, or an RTB-based compound. It may be manufactured by performing the magnet recycling process by itself.

[Diffusion aid]
As the diffusion aid, powder of RLM1M2 alloy is used. RL is at least one selected from Nd and Pr, M1 and M2 are at least one selected from Cu, Fe, Ga, Co, Ni, and Al, and M1=M2 may be satisfied. Typical examples of the RLM1M2 alloy are NdCu alloy, NdFe alloy, NdCuAl alloy, NdCuCo alloy, NdCoGa alloy, NdPrCu alloy, NdPrFe alloy and the like. The powder of these alloys is used as a mixture with the above-mentioned diffusion source powder. A plurality of types of RLM1M2 alloy powder and a diffusion source powder may be mixed and used. The method for producing the powder of the RLM1M2 alloy is not particularly limited. In the case of being manufactured by a quenching method or a casting method, in order to improve the pulverizability, it is preferable to set M1≠M2, and to use an alloy of ternary system or more such as NdCuAl alloy, NdCuCo alloy, and NdCoGa alloy. The particle size of the RLM1M2 alloy powder is, for example, 500 μm or less, and the small one is about 10 μm.

In the present disclosure, the RH compound produced by the recycling process is such that the RLM1M2 alloy efficiently reduces the RH compound by heat-treating the RLM1M2 alloy as a diffusion aid together on the surface of the RTB-based sintered magnet. Then, the sufficiently reduced RH diffuses in the RTB-based sintered magnet base material. This makes it possible to greatly improve H _cJ as a diffusion source with a small amount of RH, as in the case of RH fluoride.

[Application]
Any method may be used for allowing the powder of the RLM1M2 alloy and the diffusion source powder to be present on the surface of the RTB-based sintered magnet. For example, a method of spraying the powder of the RLM1M2 alloy and the diffusion source powder on the surface of the RTB-based sintered magnet, or dispersing the powder of the RLM1M2 alloy and the diffusion source powder in a solvent such as pure water or an organic solvent, A method of immersing an R-T-B based sintered magnet in this and pulling it up, a powder of the RLM1M2 alloy and a mixed powder are mixed with a binder or a solvent to prepare a slurry, and this slurry is subjected to the R-T-B based sintering. A method of applying to the surface of the magnet, a method of granulating the powder of the RLM1M2 alloy and the diffusion source powder together with a binder to prepare a granulated powder, and adhering the granulated powder to the surface of the RTB sintered magnet. , And the like. 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 equal to or lower than the melting point of the diffusion aid in the subsequent heating process. However, there is no particular limitation. Examples of the binder include polyvinyl alcohol, ethyl cellulose, polyester and the like. Further, the powder of the RLM1M2 alloy and the diffusion source powder may be present on the surface of the RTB-based sintered magnet in a state where they are mixed, or may be present separately. In the method of the present disclosure, the melting point of the RLM1M2 alloy is equal to or lower than the heat treatment temperature, so that the RLM1M2 alloy melts during the heat treatment, and the surface of the R-T-B system sintered magnet has reduced RH as RT-B. It becomes easy to diffuse inside the system sintered magnet. Therefore, before the powder of the RLM1M2 alloy and the diffusion source powder are present on the surface of the RTB-based sintered magnet, special cleaning such as pickling is performed on the surface of the RTB-based sintered magnet. No action required. Of course, it does not exclude performing such a cleaning process. Further, even if the surface of the RLM1M2 alloy powder particles is slightly oxidized, it has almost no effect on the effect of reducing the diffusion source powder.

The abundance ratio of the RLM1M2 alloy in the powder state and the diffusion source powder on the surface of the RTB-based sintered magnet (before heat treatment) is RLM1M2 alloy:diffusion source powder=96:4 to 50:50 by mass ratio. Preferably, the abundance ratio is RLM1M2 alloy:diffusion source powder=95:5 to 60:40.

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 is equal to or lower than the sintering temperature of the R-T-B based sintered magnet (specifically, for example, 1000° C. or lower) and higher than the melting point of the powder of the RLM1M2 alloy, but specifically, It is preferably 500° C. or higher. The heat treatment time is, for example, 10 minutes to 72 hours. Further, after the heat treatment, if necessary, heat treatment may be further performed at 400 to 700° C. for 10 minutes to 72 hours.

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. A B-type sintered magnet was produced. By subjecting this to machining, an RTB based sintered magnet base material of 6.5 mm×7.4 mm×7.4 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, since 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, RT-T- The surface of the B-based sintered magnet base material was also removed by mechanical processing in accordance with it, and the size was measured to be 6.3 mm×7.0 mm×7.0 mm. TbF ₃ , carbonic acid Tb, oxalic acid Tb, and oxidized Tb were prepared as diffusing agents. A commercially available TbF ₃ was used. Carbonic acid Tb, oxalic acid Tb, and oxidized Tb were experimentally prepared assuming each compound produced in the recycling process of the RTB magnet. Specifically, carbonic acid Tb and oxalic acid Tb are Tb oxides obtained by separating an R-T-B based magnet containing Tb and an RH diffusion source from T in the recycling process of the R-T-B based magnet. Assuming carbonic acid Tb and oxalic acid Tb obtained from the product, it was prepared by imitation from Tb ₄ O ₇ reagent. The Tb ₄ O ₇ reagent was added to 10 vol% hydrochloric acid, dissolved at 60° C., and then filtered. Sodium carbonate or oxalic acid dihydrate was added to the filtrate thus obtained, and the mixture was allowed to stand at 60° C. for 2 hours and then filtered to obtain a precipitate. The precipitate was vacuum dried at 60° C. for 6 hours to obtain a carbonic acid Tb powder or an oxalic acid Tb powder. Furthermore, the obtained Tb carbonate powder was fired in the air at 900° C. for 2 hours to obtain an oxidized Tb powder. The particle size of these powders was a few μm. When the obtained carbonic acid Tb, oxalic acid Tb, and oxidized Tb were analyzed by ICP analysis, the Tb contents were 58.5 mass%, 42.7 mass%, and 14.2 mass%, respectively. Next, a diffusion aid having a composition of Nd ₇₀ Cu ₃₀ (atomic %) was prepared (melting point 520° C.: value shown in binary system phase diagram of Nd—Cu). The diffusion aid was produced by a centrifugal atomization method and had a particle size of 106 μm or less. The obtained diffusing agent powder and diffusion aid powder were mixed with polyvinyl alcohol and pure water at a mixing ratio shown in Table 1 to obtain a slurry. The amount of RH was 0.25% by mass of the slurry on one surface of the 7.4 mm×7.4 mm of the RTB-based sintered magnet base material in a mass ratio to the RTB-based sintered magnet base material. Was applied so that In this example, the slurry was applied to only one diffusion surface of the _RTB -based sintered magnet base material to confirm the effect of improving _HcJ . Actually, it may be one surface or a plurality of surfaces from two surfaces to the entire surface. The RTB-based sintered magnet base material was housed in a processing container and the lid was covered. (This lid does not prevent the gas in and out of the container from entering and exiting.) This was placed in a heat treatment furnace and heat-treated at 400° C. for 2 hours in an Ar atmosphere of 100 Pa and then heated to 900° C. for 10 hours. I went. The heat treatment was performed under the above conditions after the temperature was raised from the room temperature while being evacuated 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 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 the obtained RTB-based sintered magnet was removed by machining to obtain samples 1 to 10 of 6.3 mm×7.0 mm×7.0 mm. The magnetic characteristics of the obtained samples 1 to 10 were measured by a BH tracer to determine the amount of change in _HcJ . The results are shown in Table 1.

As can be seen from Table 1, R-T-B based sintered magnet according to the manufacturing method of the present disclosure is H _cJ is greatly improved without the B _r little lowered. That is, even if the RH compound produced in the recycling step is mixed with the RH fluoride as the diffusion source and used, if the RLM1M2 alloy as the diffusion auxiliary is both present on the surface of the RTB-based sintered magnet and heat treated. , RLM1M2 alloy efficiently reduces the RH fluoride and the RH compound generated in the recycling step, and the sufficiently reduced RH diffuses into the R-T-B system sintered magnet base material, thereby serving as a diffusion source. It was found that H _cJ could be greatly improved with a small amount of RH as in the case of using only fluoride. On the other hand, when the diffusion aid was not used, H _cJ could not be significantly improved. Therefore, the RH compound was present together with the RLM1M2 alloy on the surface of the RTB-based sintered magnet and heat-treated. Only in the case, it was found that it diffuses in the magnet and exerts an effect of greatly improving H _cJ .

Since the manufacturing method of the present disclosure can efficiently use rare resources to manufacture an _RTB -based sintered magnet that can maintain a high H _cJ even at high temperatures, a magnet obtained by the manufacturing method. Can be suitably used for a motor of an electric vehicle (EV, HV, PHV, etc.).

Claims (8)

A step of preparing an RTB-based sintered magnet,
RLM1M2 alloy (RL is one or more selected from Nd and Pr, M1 and M2 are one or more selected from Cu, Fe, Ga, Co, Ni and Al on the surface of the RTB sintered magnet. , M1=M2) and a powder of RH fluoride (RH is Dy and/or Tb) and a powder of RH compound produced by the recycling process of the RTB magnet. A step of performing heat treatment at a temperature equal to or lower than the sintering temperature of the R-T-B system sintered magnet in the state of being allowed to stand;
The manufacturing method of the RTB type|system|group sintered magnet containing. The method for producing an RTB-based sintered magnet according to claim 1, wherein the powder of the RH compound is an intermediate product produced by a recycling step of the RTB-based magnet. The powder of the RH compound produced by the recycling process of the R-T-B magnet is selected from RH carbonate, RH oxalate, RH sulfate, RH phosphate, RH acetate and RH oxide. The method for producing an RTB-based sintered magnet according to claim 1 or 2, which is one or more kinds. The R-T- according to any one of claims 1 to 3, wherein a ratio of the powder of the RH compound manufactured by the recycling step of the R-T-B magnet in the mixed powder is 5 to 50% by mass. A method for manufacturing a B-based sintered magnet. The manufacturing of the RTB-based sintered magnet according to claim 1, wherein the RLM1M2 alloy contains 50 atomic% or more of RL, and the melting point of the RLM1M2 alloy is equal to or lower than the temperature of the heat treatment. Method. In the heat treatment, the powder of the RLM1M2 alloy and the mixed powder are present on the surface of the RTB-based sintered magnet in a mass ratio of RLM1M2 alloy:mixed powder=96:4 to 50:50. The method for producing an RTB-based sintered magnet according to claim 1, which is performed. On the surface of the RTB-based sintered magnet, the mass of the RH element contained in the mixed powder is 0.2 to 1.5 mass% with respect to the RTB-based sintered magnet. A method for manufacturing an RTB-based sintered magnet according to claim 1. The method for producing an RTB-based sintered magnet according to claim 1, further comprising a step of producing the powder of the RH compound by recycling an RTB-based magnet.