JP7087830B2 - Manufacturing method of RTB-based sintered magnet - Google Patents

Description

The present invention relates to a method for manufacturing an RTB-based sintered magnet used for a motor or the like.

R-TB-based sintered magnets (R is at least one of the rare earth elements and always contains Nd. T is Fe or Fe and Co, B is boron) are household / industrial motors and electricity. It is used in products such as drive motors for automobiles (EVs) and hybrid vehicles (HEVs) and motors for electric power steering (EPS), and contributes to their miniaturization and higher performance. The permanent magnets used for these require highly heat-resistant materials with little demagnetization even in a high-temperature environment. One method of improving heat resistance is to improve coercive force. Generally, by adding heavy rare earth elements such as Dy and Tb, coercive force is increased and irreversible demagnetization at high temperature is suppressed. ing. However, if a large amount of heavy rare earth elements is added, the saturated magnetic polarization decreases, which leads to a decrease in the residual magnetic flux density _Br . In addition, since heavy rare earth elements are raw materials with high resource risk, it is required to reduce the amount used.

Therefore, in recent years, it has been studied to improve _HcJ of RTB-based sintered magnets by using less heavy rare earth elements. For example, a heavy rare earth element fluoride or oxide or various metal M or M alloys can be present on the surface of a sintered magnet individually or mixed and heat-treated in that state to contribute to an increase in coercive force. It has been proposed to diffuse heavy rare earth elements into magnets. By this method, in addition to the reduction of heavy rare earth elements, the decrease of the residual magnetic flux density _Br is suppressed.

Further, even when the heavy rare earth element is not contained, for example, the grain boundary structure of the RTB-based sintered magnet is modified by diffusing the alloy containing Nd (Patent Documents 1 and 2), and the coercive force H. It has been proposed to improve _cJ .

In Patent Document 1, R1i-M1j (R1 is a rare earth element containing Y and Sc, M1 is Al, Si, C, P, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Ge, Zr, One or more selected from Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W, Pb, Bi, 15 <j≤99, i is the balance.) And 70 volumes of intermetal compound phase. Disclosed is a method of heat-treating and diffusing an alloy powder containing% or more in a state of being present on the surface of an RTB-based sintered magnet. Patent Document 2 discloses a method in which an adhesive is applied to the surface of an RTB-based sintered magnet, and a powder of an alloy or compound of a heavy rare earth element, which is at least one of Dy and Tb, is attached and heat-treated. Has been done.

Japanese Unexamined Patent Publication No. 2008-263179 International Publication No. 2018/030187

The present inventors have investigated a method of heat-treating and diffusing an RM alloy powder as described in Patent Document 1 in a state of being present on the surface of an RTB-based sintered magnet. It was found that a plurality of convex portions having a height of 0.1 to 0.5 mm may be generated on the surface of the sintered body. Further investigation revealed that the convex portion has a composition in which a liquid phase generated by melting the RM alloy and a liquid phase generated from the RTB-based sintered magnet are mixed, and the mixture of the liquid phases solidifies. It turned out that it was a raised metal pool. If there is a metal pool, the processing accuracy is lowered in the subsequent process, so that the process of removing the metal pool is increased and the productivity is lowered.

In addition, the powder of the RM alloy or compound is easily oxidized, and since the powder is active, there is a risk of heat generation and burning, so care should be taken when handling the powder in the manufacturing process of the RTB-based sintered magnet. I needed it.

The embodiments of the present disclosure make it possible to suppress the generation of metal pools without deteriorating the magnetic properties, and to make the powder less combustible and easier to handle.

The method for producing an RTB-based sintered magnet of the present disclosure is, in an exemplary embodiment, R (R is at least one of rare earth elements and always contains at least one of Nd and Pr) -T ( T is a transition metal element mainly containing Fe and may contain Co.)-A step of preparing a B-based sintered magnet material and RM (R is at least one of rare earth elements, Nd and M is one or more selected from Al, Cu, Zn, Ga, Fe, Co, and Ni, which always contains at least one of Pr.) The step of preparing the alloy powder and the average thickness on the particle surface of the RM alloy powder. A step of forming an R—OH layer having a thickness of 0.5 μm or more and 3 μm or less, and a step of applying the RM alloy powder having the R—OH layer formed on the surface of the RTB-based sintered magnet material. And the step of performing a heat treatment on the RTB-based sintered magnet material coated with the RM alloy powder on which the R—OH layer is formed.

In one embodiment, the step of forming the R—OH layer is formed by exposing the RM alloy powder to an atmosphere having a temperature of 20 ° C. or higher and 150 ° C. or lower and a relative humidity of 60% or higher and 100% or lower.

According to the embodiment of the present disclosure, it is possible to suppress the generation of metal pools without deteriorating the magnetic properties, and it is possible to make the powder less combustible and easier to handle.

It is a schematic diagram which shows the thickness of the RM alloy, the R-OH outer shell layer, and the R-OH outer shell layer in the cross section of the RM alloy powder. It is sectional drawing of the RM alloy powder which has been subjected to the hydroxylation treatment. It is a relationship diagram of the metal accumulation occurrence frequency and the average thickness of the R—OH layer. It is a relationship diagram of the coercive force increase amount ΔH _cJ of the RTB-based sintered magnet after the diffusion heat treatment and the average thickness of the R—OH layer.

As a result of the study, the present inventors have applied RM alloy powder to the surface of the RTB-based sintered magnet material and heat-treated it to diffuse R and M into the sintered magnet material. It has been found that the generation of metal pools can be suppressed by forming an R—OH layer (hydroxyl film layer) on the particle surface of the RM alloy powder by exposing the RM alloy powder to a moist atmosphere. Then, they have found that by setting the thickness of the R—OH layer (hydroxyl film layer) within a specific range, it is possible to suppress the generation of metal pools without deteriorating the magnetic properties. It was also found that the formation of the R—OH layer makes it difficult for the powder to burn and makes it easier to handle.

<RTB-based sintered magnet material>
First, an RTB-based sintered magnet material to be diffused is prepared. As the RTB-based sintered magnet material, a known magnet material can be used. The RTB-based sintered magnet material has, for example, the following composition.
Rare earth element R: 12 to 17 atomic% (R is at least one of the rare earth elements and always contains at least one of Nd and Pr),
B (part of B may be substituted with C) 5-8 atomic%,
Select from the group consisting of additive elements M'(Al, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Pb, and Bi. At least one species): 0-5 atomic%,
T (a transition metal element mainly containing Fe, which may contain Co) and irreversible impurities: balance.

Here, the rare earth element R always contains at least one of Nd and Pr, but may contain at least one of La and Ce, for example, and may contain at least one of Dy and Tb, for example.

The RTB-based sintered magnet material having the above composition is produced by any known production method. The RTB-based sintered magnet material may be in a state of being sintered, or may be cut or polished. The shape and size of the RTB-based sintered magnet material are arbitrary.

<RM alloy powder>
Next, RM alloy powder (R is at least one of rare earth elements and always contains at least one of Nd and Pr, M is one or more selected from Al, Cu, Zn, Ga, Fe, Co and Ni. ) Is prepared. R of the RM alloy powder always contains at least one of Nd and Pr, but may contain at least one of La and Ce, for example, and may contain at least one of Dy and Tb, for example. R is 25 atomic% or more of the total RM alloy powder, preferably 50 atomic% or more of the total RM alloy powder. M is preferably one or more selected from Al, Cu, Ga, Fe, and Co.

The method for producing the RM alloy powder is not particularly limited. The ingot produced by the casting method may be pulverized, or may be produced by a known atomization method.

Then, an R—OH layer is formed on the surface of the powder particles with respect to the RM alloy powder. This makes it possible to suppress metal accumulation. The method of forming the R—OH layer is carried out by exposing the RM alloy powder to a moist atmosphere. The R component on the particle surface of the RM alloy powder reacts with the moisture in the atmosphere, and the R—OH layer is formed only on the outer shell portion of the RM alloy powder. Even if the R-OH layer is uniformly formed on the surface of the powder particles, the RM alloy is melted by heating to a temperature higher than the melting point of the RM alloy, which is the center of the powder particles, and the R-OH is formed. It is possible to pass through the layer and diffuse into the RTB-based sintered magnet material. Further, the formation of the R—OH layer stabilizes the RM alloy powder and makes it difficult to burn, which facilitates the handling of the powder in the manufacturing process of the RTB-based sintered magnet. The method of exposing to a moist atmosphere is performed by, for example, holding in an atmosphere having a temperature of 20 ° C. or higher and 150 ° C. or lower and a relative humidity of 60% or higher and 100% or lower in a constant temperature and humidity chamber. The step of forming the R—OH layer is formed by, for example, exposing the atmosphere to the atmosphere for 2 hours to 200 hours.

The RM alloy formed on the surface of the RM alloy powder particles (the outer shell layer of RM) and the RM alloy in the center of the RM alloy powder particles are R by using an electron microscope or the like. By observing the cross-sectional structure of the -M alloy powder, it can be distinguished from the difference in contrast due to the difference in composition.

FIG. 1 is a diagram schematically showing an R—OH layer in a cross section of an RM alloy powder and an RM alloy in a central portion. The R—OH layer 2 exists around the RM alloy 1, and the thickness d of the R—OH layer is the thickness of the RM alloy powder in the depth direction from the particle surface. The thickness d of the R—OH layer varies depending on the temperature, humidity and holding time, and the thickness increases as the temperature, humidity and duration increase. The average thickness of the R—OH layer is 0.5 μm or more. If the average thickness is less than 0.5 μm, the effect of suppressing metal accumulation may not be obtained. The thickness of the R—OH layer is 3 μm or less. If the R—OH layer becomes too thick, the proportion of the central portion made of the RM alloy decreases after the formation of the R—OH layer, and the liquid phase component diffused into the RTB-based sintered magnet material decreases. Therefore, it is necessary to increase the total amount of the RM alloy powder adhered to the RTB-based sintered magnet material, which causes a decrease in efficiency.

The particle size of the RM alloy powder is, for example, 500 μm or less. The lower limit of the particle size is preferably 10 μm or more. If the particle size is too small, the proportion of the central portion made of the RM alloy decreases after the formation of the R—OH layer, and the amount of the liquid phase diffused into the RTB-based sintered magnet material decreases. Therefore, it is necessary to increase the total amount of the RM alloy powder adhered to the RTB-based sintered magnet material, which causes a decrease in efficiency.

<Applying process>
The RM alloy powder on which the R—OH layer is formed is applied to the surface of the RTB-based sintered magnet. Any form may be applied. For example, a method of adhering powdered RM alloy powder to an RTB-based sintered magnet material coated with an adhesive by using a fluid dipping method, a processing container containing RM alloy powder. Examples thereof include a method of dipping an RTB-based sintered magnet material and a method of sprinkling RM alloy powder on the RTB-based sintered magnet material. Further, the processing container containing the RM alloy powder may be subjected to vibration, rocking, or rotation, or the RM alloy powder may be allowed to flow in the processing container.

Examples of the pressure-sensitive adhesive that can be used include PVA (polyvinyl alcohol), PVB (polyvinyl vinylidene), PVP (polyvinylpyrrolidone) and the like. When the pressure-sensitive adhesive is a water-based pressure-sensitive adhesive, the RTB-based sintered magnet material may be preheated before application. The purpose of preheating is to remove excess solvent to control the adhesive strength and to uniformly adhere the adhesive. The heating temperature is preferably 60 to 100 ° C. In the case of a highly volatile organic solvent-based pressure-sensitive adhesive, this step may be omitted.

Any method may be used to apply the adhesive to the surface of the RTB-based sintered magnet. Specific examples of the coating include a spray method, a dipping method, and a dispenser coating.

By heat-treating the RTB-based sintered magnet coated with the RM alloy powder on which the R—OH layer is formed, the R component and the M component in the RM alloy powder are removed from the RT. -Diffuse inside the B-based sintered magnet. The heat treatment temperature for diffusion is not more than the sintering temperature of the RTB-based sintered magnet material (for example, 1000 ° C. or less). Further, the temperature is higher than the melting point of the RM alloy powder (for example, 500 ° C. or higher). After the heat treatment, if necessary, a heat treatment at 400 ° C. to 700 ° C. for 10 minutes to 72 hours may be performed.

<Example>
The present disclosure will be described in more detail by way of examples, but the present disclosure is not limited thereto.

First, by a known method, RT- with a composition ratio of Nd = 13.4, B = 5.8, Al = 0.5, Cu = 0.1, Co = 1.1, and the balance = Fe (atomic%). A B-based sintered magnet was produced. By machining this, an RTB-based sintered magnet material having a size of 5 mm × 20 mm × 30 mm was obtained. When the magnetic properties of the obtained RTB-based sintered magnet material were measured by a BH tracer, HcJ was 1035 kA / m and Br was 1.45 T.

Next, an RM alloy powder having a composition ratio of Nd = 37, Tb = 33, and Cu = 30 (atomic%) was prepared by a gas atomizing method. The particle size of the obtained RM alloy powder was 106 μm or less. Subsequently, the RM alloy powder was held in a constant temperature and humidity chamber at a temperature of 80 ° C. and a relative humidity of 90% for 20 hours (hours), 48 hours and 168 hours, respectively, and R- The M alloy powder was subjected to a hydroxylation treatment.

The cross section of the hydroxylated alloy powder was observed with a scanning electron microscope, and the thickness of the R—OH layer was measured. FIG. 2 is a backscattered electron image (composition contrast image) in a cross section of the hydroxylated RM alloy powder. As shown in the backscattered electron image of FIG. 2, a dark contrast RH layer is formed on the surface of the hydroxylated (48h and 168h) RM alloy powder so as to surround the bright contrast RM alloy. Was done.

Next, the average thickness of the R—OH layer was measured. In the measuring method, the thickness of the R-OH layer was measured at 20 points per powder particle, and the average value was taken as the average thickness of the R-OH layer. The average thickness is 0.5 μm for 20h, 1.3 μm for 48h, and 2.3 μm for 168h. The longer the holding time in the constant temperature and humidity chamber, the larger the average thickness of the R-OH layer. rice field.

Next, PVA was applied to the entire surface of the RTB-based sintered magnet material as an adhesive by a dipping method on the RTB-based sintered magnet material. The hydroxylated RM alloy powder was attached to the RTB-based sintered magnet material coated with the pressure-sensitive adhesive. The RM alloy powder was spread on the treatment container and adhered to the entire surface of the RTB-based sintered magnet material coated with the adhesive.

The heat treatment for diffusion was performed at 450 ° C. for 2 hours and then at 900 ° C. for 10 hours. Then, the heat treatment was further performed at 490 ° C. for 3 hours.

After the heat treatment was completed, it was visually confirmed whether or not metal pools were generated on the surface of the RTB-based sintered magnet material. There is a case where a metal pool is generated even in one place in one RTB-based sintered magnet material, and there is no case where no metal pool is generated in one place, and the ratio of the metal pool to the total number is generated. Obtained as frequency.

FIG. 3 shows the relationship between the frequency of metal accumulation and the average thickness of the R—OH layer. As shown in FIG. 3, when the hydroxylation treatment was not performed (the average thickness of the R—OH layer was 0 μm), the metal pool was 100%, whereas the hydroxylation treatment was performed for 20 hours (R). When the thickness of the −OH layer is 0.5 μm), the metal pool is 40%, which is significantly reduced. Further, when the hydroxylation treatment was carried out at 48 h (thickness of the R-OH layer was 1.3 μm) and 168 h (thickness of the R-OH layer was 2.3 μm), no metal pool was generated.

FIG. 4 shows the relationship between the increase in the coercive force of the RTB-based sintered magnet after the diffusion heat treatment with respect to the coercive force of the undiffused RTB-based sintered magnet ΔH _cJ and the average thickness of the R—OH layer. Is shown. No decrease in ΔH _cJ was observed even when the R—OH layer was formed by the hydroxylation treatment.

An RTB-based sintered magnet material was prepared in the same manner as in Example 1. Next, an RM alloy powder having a composition ratio of Nd = 46, Tb = 33, and Cu = 21 (atomic%) was prepared by a gas atomizing method. The particle size of the obtained RM alloy powder was 106 μm or less. Subsequently, the RM alloy powder was held in a constant temperature and humidity chamber at a temperature of 80 ° C. and a relative humidity of 90% for 168 hours, and the RM alloy powder was subjected to hydroxylation treatment. .. The average thickness of the R—OH layer formed on the surface of the hydroxylated RM alloy powder was 2.3 μm.

Next, PVA as an adhesive was applied to the entire surface of the RTB-based sintered magnet material as an adhesive by the dipping method in the same manner as in Example 1. The hydroxylated RM alloy powder was attached to the RTB-based sintered magnet material coated with the pressure-sensitive adhesive. The RM alloy powder was spread on the treatment container and adhered to the entire surface of the RTB-based sintered magnet material coated with the adhesive.

The heat treatment for diffusion was performed at 450 ° C. for 2 hours and then at 900 ° C. for 10 hours. Then, the heat treatment was further performed at 490 ° C. for 3 hours.

After the heat treatment was completed, it was visually confirmed whether or not metal pools were generated on the surface of the RTB-based sintered magnet material. As a result, no metal pools were generated when the hydroxylation treatment was performed. In addition, no decrease in ΔH _cJ was observed even after the hydroxylation treatment.

The Nd-Fe-B-based sintered magnet obtained by the method for manufacturing the RT-B-based sintered magnet of the present disclosure is a motor for driving home appliances / industrial motors, electric vehicles (EV) and hybrid vehicles (HEV). And can be used in products such as motors for electric power steering (EPS).

1 ... RM alloy, 2 ... R-OH layer

Claims (2)

R (R is at least one of rare earth elements and always contains at least one of Nd and Pr) -T (T is a transition metal element mainly containing Fe and may contain Co) -B-based firing. The process of preparing the magnet material and
RM (R is at least one of rare earth elements and always contains at least one of Nd and Pr, M is one or more selected from Al, Cu, Zn, Ga, Fe, Co and Ni) alloy powder. The process of preparing and
A step of forming an R—OH layer having an average thickness of 0.5 μm or more and 3 μm or less on the particle surface of the RM alloy powder, and
The step of applying the RM alloy powder on which the R—OH layer is formed to the surface of the RTB-based sintered magnet material, and
A step of heat-treating the RTB-based sintered magnet material coated with the RM alloy powder on which the R—OH layer is formed, and
A method for manufacturing an RTB-based sintered magnet, including the above method. The R— according to claim 1, wherein the step of forming the R—OH layer is formed by exposing the RM alloy powder to an atmosphere having a temperature of 20 ° C. or higher and 150 ° C. or lower and a relative humidity of 60% or higher and 100% or lower. A method for manufacturing a TB-based sintered magnet.

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