JP7021577B2 - Manufacturing method of RTB-based sintered magnet - Google Patents

Description

The present disclosure relates to a method for manufacturing an RTB-based sintered magnet.

RTB-based sintered magnets (R is at least one of rare earth elements and always contains Nd, T is at least one of transition metal elements and always contains Fe) have the highest performance among permanent magnets. It is known as a magnet, and is used in various motors such as voice coil motors (VCM) for hard disk drives, motors for electric vehicles (EV, HV, PHV, etc.), motors for industrial equipment, and home appliances.

The RTB-based sintered magnet is mainly composed of a main phase composed of an _R2 T ₁₄ B compound and a grain boundary phase located at a grain boundary portion of this main phase. The main phase, R ₂ T ₁₄ B compound, is a ferromagnetic material with high magnetization and forms the basis of the characteristics of RTB-based sintered magnets.

In the RTB-based sintered magnet, the coercive force H _cJ (hereinafter, may be simply referred to as "H _cJ ") decreases at a high temperature, so that irreversible demagnetization occurs. Therefore, especially when used in a motor for an electric vehicle, it is required to have a high _HcJ even at a high temperature.

Conventionally, in order to improve H _cJ , a large amount of heavy rare earth element RH such as Dy and Tb has been added to the R—TB based sintered magnet. However, when a large amount of the heavy rare earth element RH is added, H _cJ is improved, but there is a problem that the residual magnetic flux density _Br (hereinafter, may be simply referred to as “ _Br ”) is lowered. Therefore, in recent years, RH is diffused from the surface of the _RTB -based sintered magnet to the inside to concentrate RH in the outer shell of the main phase crystal grains, thereby suppressing the decrease in Br and increasing the H. A method for obtaining _cJ has been proposed.

However, Dy has problems such as unstable supply and price fluctuations due to the fact that the amount of resources is originally small and the production area is limited. Therefore, it is required to obtain high H _cJ while suppressing the decrease of _Br without using RH such as Dy as much as possible (reducing the amount used as much as possible).

In Patent Document 1, the amount of B is lower than that of a normal RTB alloy, and R ₂ F ₁₇ M is contained by containing one or more kinds of metal elements M selected from Al, Ga, and Cu. By forming a phase and sufficiently securing the volume ratio of the transition metal rich phase (R ₆ T ₁₃ M) generated from the R ₂ Fe ₁₇ phase as a raw material, the coercive force while suppressing the content of Dy. It is described that a high-grade RTB-based rare earth sintered magnet can be obtained.

In addition, as mentioned above, the applications where RTB-based sintered magnets are most used are motors, and improvement of _HcJ is very effective to ensure high-temperature stability, especially in applications such as motors for electric vehicles. However, along with these characteristics, the square ratio H _k / H _cJ (hereinafter, may be simply referred to as H _k / H _cJ ) must also be high. If H _k / H _cJ is low, it causes a problem that demagnetization is likely to occur. Therefore, there is a demand for an RTB-based sintered magnet having a high H _cJ and a high H _k / H _cJ . In the field of RTB-based sintered magnets, in general, H _k , which is a parameter to be measured for obtaining H _k / H _cJ , is J (magnetization strength) −H (magnetic field strength). In the second quadrant of the curve), the H-axis reading at the position where J is 0.9 × _Jr ( _Jr is the residual magnetization, _Jr = _Br ) is used. The value obtained by dividing this H _k by H _cJ of the demagnetization curve (H _k / H _cJ = H _k (KA / m) / H _cJ (KA / m) × 100 (%)) is defined as the square ratio.

International Publication No. 2013/008756

In the R-TB-based rare earth magnet described in Patent Document 1, although a high _HcJ can be obtained while reducing the Dy content, a general R-TB-based sintered magnet ( _R2 T) can be obtained. ₁₄ There is a problem that H _k / H _cJ is lowered as compared with (the amount of B is larger than the ratio of the chemical quantity theory of the B-type compound).

Therefore, an object of the present invention is to provide a method for producing an RTB-based sintered magnet having a high H _cJ and a high H _k / H _cJ while reducing the content of RH.

Aspect 1 of the present invention is
R: 29.5 to 35.0% by mass (R is at least one rare earth element and contains at least one of Nd and Pr),
B: 0.80 to 0.91% by mass,
It contains Ga: 0.2 to 1.0% by mass, and T: 61.5 to 69.5% by mass (T is Fe and Co, and 90 to 100% by mass of T is Fe).
A method for manufacturing an RTB-based sintered magnet that satisfies the following formula (1).

[T] /55.85>14 [B] /10.8 (1)
([T] is the content of T shown in% by mass, and [B] is the content of B shown in% by mass)

The process of preparing alloy powder and
The molding process of molding the alloy powder to obtain a molded body, and
The molded body is heated at a first sintering temperature in the range of 1010 ° C. to 1030 ° C. and a first sintering time in the range of 12 hours to 36 hours to obtain a first sintered body. 1 sintering process and
The first sintered body is in the range of 990 ° C to 1020 ° C, and is in the range of 17 hours to 41 hours at the second sintering temperature which is 10 ° C or more lower than the first sintering temperature. In the second sintering step of obtaining a second sintered body by heating in a second sintering time that is 5 hours or more longer than the first sintering time.
A heat treatment step of heating the second sintered body at a heat treatment temperature in the range of 400 ° C. to 800 ° C.
Is a method for manufacturing an RTB-based sintered magnet including.

Aspect 2 of the present invention is the second sintering step in which the second sintering temperature is in the range of 990 ° C to 1010 ° C and is 20 ° C or more lower than the first sintering temperature. This is a method for manufacturing an RTB-based sintered magnet according to the above.

According to the production method of the present invention, it is possible to produce an RTB-based sintered magnet having a high H _cJ and a high H _k / H _cJ while reducing the RH content.

The embodiments shown below exemplify a method for manufacturing an RTB-based sintered magnet for embodying the technical idea of the present invention, and do not limit the present invention to the following.

As a result of diligent studies by the present inventors, the present invention is used in the production of an RTB-based sintered magnet having a specific composition range as defined below, particularly a very narrow specific range of B content. By performing the binding process in two stages (first sintering step and second sintering step) and appropriately controlling the sintering conditions (temperature and time) of the first sintering step and the second sintering step. It has been found that the magnetic properties of the finally obtained RTB-based sintered magnet can be improved.
The manufacturing method according to the embodiment of the present invention will be described in detail below.

<RTB-based sintered magnet>
First, the RTB-based sintered magnet obtained by the manufacturing method according to the present invention will be described.

(Composition of RTB-based sintered magnet)
The composition of the RTB-based sintered magnet according to this embodiment is
R: 29.5 to 35.0% by mass (R is at least one rare earth element and contains at least one of Nd and Pr),
B: 0.80 to 0.91% by mass,
It contains Ga: 0.2 to 1.0% by mass, and T: 61.5 to 69.5% by mass (T is Fe and Co, and 90 to 100% by mass of T is Fe), and is described below. Equation (1) is satisfied.

[T] /55.85>14 [B] /10.8 (1)
([T] is the content of T shown in% by mass, and [B] is the content of B shown in% by mass)

Due to the above composition, the amount of B is smaller than that of a general RTB-based sintered magnet, and Ga and the like are contained, so that an RT-Ga phase is generated at the two-particle grain boundary. High H _cJ can be obtained. Here, the RT-Ga phase is typically an Nd ₆ Fe ₁₃ Ga compound. The R ₆ T ₁₃ Ga compound has a La ₆ Co ₁₁ Ga type ₃ crystal structure. Further, the R ₆ T ₁₃ Ga compound may be an R ₆ T _13-δ Ga _{1 + δ} compound (δ is typically 2 or less) depending on the state. For example, when the RTB-based sintered magnet contains a relatively large amount of Cu and Al, it may be R ₆ T _13-δ (Ga _1-xy Cu _x Al _y ) _{1 + δ} . be.
Each composition will be described in detail below.

(R: 29.5 to 35.0% by mass)
R is at least one of the rare earth elements and contains at least one of Nd and Pr. The content of R is 29.5 to 35.0% by mass. If _R is less than 29.5% by mass, it may be difficult to densify during sintering, and if it exceeds 35.0% by mass, the main phase ratio may decrease and high Br may not be obtained. .. The content of R is preferably 29.5 to 33.0% by mass. If _R is in such a range, a higher Br can be obtained.

(B: 0.80 to 0.91% by mass)
The content of B in the sintered magnet is 0.80 to 0.91% by mass. If B is less than 0.80% by mass, _R2 T ₁₇ phase may be generated and high H _cJ may not be obtained, and if it exceeds 0.91% by mass, the amount of R-T-Ga phase produced is small. There is a risk that too high _HcJ cannot be obtained. The content of B is preferably 0.88 to 0.90% by mass, and a higher H _cJ improving effect can be obtained.

Further, the content of B satisfies the following formula (1).

[T] /55.85>14 [B] /10.8 (1)

Here, [T] is the content of T represented by mass%, and [B] is the content of B represented by mass%.

By satisfying the formula (1), the content of B becomes smaller than that of a general RTB-based sintered magnet. In a general RTB _- based sintered magnet, [T] _{/55.85 (} T] / 55.85 ₍ T) / 55.85 (T) / 55.85 (T) / 55.85 (T) / 55.85 ( The atomic weight of Fe) is less than 14 [B] / 10.8 (atomic weight of B) ([T] is the content of T expressed in% by mass). The RTB-based sintered magnet of the embodiment of the present invention is different from the general RTB-based sintered magnet, and [T] /55.85 is higher than 14 [B] /10.8. It is specified by the formula (1) so that the number increases. Since the main component of T in the RTB-based sintered magnet of the embodiment of the present invention is Fe, the atomic weight of Fe was used.

(Ga: 0.2 to 1.0% by mass)
The content of Ga is 0.2 to 1.0% by mass. If Ga is less than 0.2% by mass, the amount of R _— T—Ga phase produced is too small, and the R2T ₁₇ phase cannot be eliminated, and high _HcJ may not be obtained. If it exceeds 1.0% by mass, unnecessary Ga will be present, and the main phase ratio may decrease and _Br may decrease.

(T: 61.5 to 69.5% by mass (T is Fe and Co, and 90 to 100% by mass of T is Fe))
T is at least one of the transition metal elements and always contains Fe.
The content of T in the sintered magnet is 61.5 to 69.5% by mass. Further, when the total amount of T is 100% by mass, 10% by mass or less thereof can be replaced with Co. That is, 90% by mass or more of the total amount of T is Fe. Further, the total amount of T (100% by mass) may be Fe. Corrosion resistance can be improved by containing Co, but if the substitution amount of Co exceeds 10% by mass of Fe, high _Br may not be obtained. The content of T is 61.5% by mass or more, and the above-mentioned formula (1) is satisfied. If the T content is less than _61.5 % by mass or more than 69.5% by mass, Br may be significantly reduced. Preferably, T is the balance.

Further, even when T is the remainder, the RTB-based sintered magnet of the present invention contains Cr, as an unavoidable impurity usually contained in didymium alloy (Nd-Pr), electrolytic iron, ferrobolon and the like. It can contain Mn, Si, La, Ce, Sm, Ca, Mg and the like. Further, as unavoidable impurities in the manufacturing process, O (oxygen), N (nitrogen), C (carbon) and the like can be exemplified. Further, the RTB-based sintered magnet of the present invention may contain one or more other elements (elements intentionally added other than unavoidable impurities). For example, as such elements, a small amount (about 0.1% by mass each) of Ag, Zn, In, Sn, Ti, Ge, Y, H, F, P, S, V, Ni, Mo, Hf, Ta , W, Nb, Zr and the like may be contained. Further, the elements listed as the above-mentioned unavoidable impurities may be intentionally added. Such elements may be contained, for example, about 1.0% by mass in total. With this degree, it is sufficiently possible to obtain an RTB-based sintered magnet having a high _HcJ .

The sintered magnet of the present invention may further contain any other element. Other elements that can be selectively contained in this way are illustrated below.

(Cu: more than 0% by mass, 0.50% by mass or less)
By containing an appropriate amount of Cu, H _cJ can be further improved.
Cu may be contained in an amount of 0.50% by mass or less. The Cu content is preferably 0.05 to 0.50% by mass. When Cu is contained in an amount of 0.05% by mass to 0.50% by mass, H _cJ can be further improved. The Cu content is more preferably 0.05% by mass or more.

(Al: more than 0% by mass, 0.50% by mass or less)
By containing an appropriate amount of Al, H _cJ can be further improved.
Al may be contained in an amount of 0.50% by mass or less. The Al content is preferably 0.05 to 0.50% by mass. When Al is contained in an amount of 0.50% by mass or less, H _cJ can be further improved. Al can usually be contained in an amount of 0.05% by mass or more as an unavoidable impurity in the manufacturing process, but even if it is contained in an amount of 0.5% by mass or less in total of the amount contained in the unavoidable impurity and the amount intentionally added. good. The Al content is more preferably 0.05% by mass or more.

(Magnetic characteristics of RTB-based sintered magnet)
The sintered magnet according to the present invention exhibits high H _cj and high H _k / H _cJ . In particular, it is preferable that H _cj is 1400 kA / m or more and H _k / H _cJ is more than 85, and it is more preferable that H _cj is more than 1500 kA / m and H _k / H _cJ is more than 85. Further, H _k is preferably 1200 kA / m or more, and more preferably 1230 kA / m or more.

<Manufacturing method of RTB-based sintered magnet>
Next, a method for manufacturing the RTB-based sintered magnet according to the present invention will be described.
The method for producing an RTB-based sintered magnet includes a step of preparing an alloy powder, a forming step, a first sintering step, a second sintering step, and a heat treatment step.
Hereinafter, each step will be described.

(1) Step of preparing alloy powder Metals or alloys of each element are prepared so as to have the above composition, and flake-shaped alloys are produced by using these by a strip casting method or the like.
The obtained flake-shaped alloy is pulverized with hydrogen, and the size of the coarsely pulverized powder is set to, for example, 1.0 mm or less. Next, by finely pulverizing the coarsely pulverized powder with a jet mill or the like, for example, the finely pulverized powder (alloy powder) having a particle size D50 (value (median diameter) obtained by the laser diffraction method by the air flow dispersion method) of 3 to 7 μm. ). A known lubricant may be used as an auxiliary agent for the coarsely pulverized powder before jet mill pulverization, and the alloy powder during and after jet mill pulverization.

(2) Molding step Molding is performed in a magnetic field using the obtained alloy powder to obtain a molded product. Molding in a magnetic field is a dry molding method in which a dry alloy powder is inserted into the cavity of a mold and molded while applying a magnetic field. A slurry in which the alloy powder is dispersed is injected into the cavity of the mold. Any known in-field molding method may be used, including a wet molding method in which the slurry is molded while discharging the dispersion medium.

(3) Sintering step A sintered body (sintered magnet) is obtained by sintering the molded body obtained in the molding step. In the present invention, a sintered magnet is manufactured by performing two-step sintering (first sintering step and second sintering step). Further, in both the first and second sintering steps, sintering is performed at a sintering temperature lower than the general sintering temperature and a sintering time longer than the general sintering time.

(3-1) First Sintering Step In the first sintering step, the molded body is first sintered in the range of 12 hours to 36 hours at the first sintering temperature in the range of 1010 ° C to 1030 ° C. Heat at the sintering time. As a result, the first sintered body is obtained.
The general sintering conditions are a sintering temperature of 1040 to 1060 ° C. and a sintering time of about 4 hours to 6 hours. That is, the first sintering temperature of the first sintering step of the present invention is about 10 to 50 ° C. lower than the general sintering temperature, and the first sintering time is compared with the general sintering time. It is about 2 to 8 times longer.

(3-2) Second Sintering Step In the second sintering step, the first sintered body is in the range of 990 ° C to 1020 ° C, and the second sintering temperature is 10 ° C or more lower than the first sintering temperature. Sinter at the sintering temperature. The sintering time (second sintering time) is in the range of 17 hours to 41 hours, and the heating is performed longer than the first sintering time by 5 hours or more. As a result, a second sintered body (sintered magnet) is obtained.
In the sintering conditions of the second sintering step of the present invention, the second sintering temperature is further lower than the first sintering temperature, which is lower than the general sintering temperature, and the second sintering time is general. Longer than the sintering time Even longer than the first sintering time. Preferably, in the second sintering step, the second sintering temperature is in the range of 990 ° C to 1010 ° C and is 20 ° C or more lower than the first sintering temperature. It is possible to produce an RTB-based sintered magnet having a higher H _cJ and a higher H _k / H _cJ while reducing the content of RH.

The first sintering step and the second sintering step may be continuously performed. That is, after the first sintering step is completed, the second sintering step may be performed as it is by cooling from the first sintering temperature to the second sintering temperature. Further, after the completion of the first sintering step, the temperature may be once cooled to room temperature and then raised to the second sintering temperature to perform the second sintering step.
In both the first sintering step and the second sintering step, in order to prevent oxidation due to the atmosphere at the time of sintering, the sintering is preferably performed in a vacuum atmosphere or an atmosphere gas. As the atmosphere gas, it is preferable to use an inert gas such as helium or argon.

(4) Heat treatment step The obtained second sintered body (sintered magnet) is heat-treated for the purpose of improving the magnetic properties. The heat treatment temperature is in the range of 400 ° C. to 800 ° C. Known conditions can be used for the heat treatment time, and the heat treatment can be performed for, for example, 60 minutes to 300 minutes. For example, the heat treatment (one-step heat treatment) may be performed only at a relatively low temperature (400 ° C. or higher and 600 ° C. or lower), or the heat treatment may be performed at a relatively high temperature (700 ° C. or higher and 800 ° C. or lower) and then relatively low. Heat treatment (two-stage heat treatment) may be performed at a temperature (400 ° C. or higher and 600 ° C. or lower). Preferred conditions are heat treatment at 730 ° C. or higher and 1020 ° C. or lower for about 5 to 500 minutes, after cooling (after cooling to room temperature or cooling to 440 ° C. or higher and 550 ° C. or lower), and further at 440 ° C. or higher and 550 ° C. or lower. Heat treatment may be performed for about 1 to 500 minutes. The heat treatment atmosphere is preferably a vacuum atmosphere or an inert gas (helium, argon, etc.).

The obtained sintered magnet may be machined by grinding or the like for the purpose of forming the final product shape. In that case, the heat treatment may be performed before or after machining. Further, the obtained sintered magnet may be surface-treated. The surface treatment may be a known surface treatment, and for example, surface treatment such as Al vapor deposition, electro-Ni plating, and resin paint can be performed.

In the sintered magnet thus obtained, both H _cj and H _k / H _cJ were improved.

The RTB-based sintered magnets are No. 1 in Table 1. Each element was weighed and cast by a strip casting method so as to have the compositions shown in M1 to M4 to obtain a flake-shaped alloy. The obtained flake-shaped alloy was hydrogen embrittled in a hydrogen-pressurized atmosphere, and then dehydrogenated by heating and cooling in a vacuum to 550 ° C. to obtain coarsely pulverized powder. Next, zinc stearate as a lubricant was added to the obtained coarsely pulverized powder in an amount of 0.04% by mass based on 100% by mass of the coarsely pulverized powder, mixed, and then used by an air flow type pulverizer (jet mill device). , Dry pulverization in a nitrogen atmosphere to obtain an alloy powder having a _D50 of 4.3 μm. The component analysis results of the obtained alloy powder are shown in Table 1 No. It is shown in M1 to M4. Each component (other than O, N and C) in Table 1 was measured using high frequency inductively coupled plasma emission spectroscopy (ICP-OES). The O (oxygen) content is a gas melting-infrared absorption method, the N (nitrogen) content is a gas melting-heat conduction method, and the C (carbon) content is a combustion-infrared absorption method. Used and measured.

A liquid lubricant was added to the alloy powder in an amount of 0.3% by mass based on 100% by mass of the finely pulverized powder, mixed, and then molded in a magnetic field to obtain a molded product. As the molding apparatus, a so-called right-angled magnetic field forming apparatus (transverse magnetic field forming apparatus) in which the magnetic field application direction and the pressurizing method direction are orthogonal to each other was used.

The obtained molded body was subjected to a first sintering step, a second sintering step and a heat treatment step under the conditions shown in Table 2 to obtain an RTB-based sintered magnet. For example, the sample No. in Table 2 1 is No. The molded product obtained by molding the M1 alloy powder was heated at a temperature of 1020 ° C. for 24 hours and then cooled to room temperature to obtain a first sintered body, and then the first sintered body was heated to a temperature of 1000 ° C. After heating to room temperature for 36 hours and then cooling to room temperature to obtain a second sintered body, the second sintered body was heated at 800 ° C. for 2 hours, then lowered to 490 ° C., and further heated at 490 ° C. for 3 hours. It was done. Sample No. 2 to 24 are described in the same manner. In addition, sample No. In Nos. 5 to 12, the second sintering step was not performed.

The obtained RTB sintered magnet was machined to prepare a sample having a length of 7 mm, a width of 7 mm, and a thickness of 7 mm, and the magnetic characteristics were measured by a BH tracer. The results are shown in Table 3. In addition, H _k is a value of 0.9 × J _r (J _r is residual magnetization, J _r = _Br ) in the second quadrant of the J (magnitude of magnetization) −H (strength of magnetic field) curve. It is the value of H at the position where it becomes.

In the present specification, the quality judgment of H _cJ and H _k / H _cJ is determined by whether or not H _cJ > 1300 kA / m and H _k / H _cJ > 85 are satisfied, respectively. In the present invention, H _cJ and H _k / H _cJ are both high, that is, those satisfying the condition of "H _cJ > 1300 kA / m and H _k / H _cJ >85" are defined as "examples of the present invention", and H _cJ , A "comparative example" is one that does not satisfy the condition of "H _cJ > 1300 kA / m and H _k / H _cJ >85" because one or both of H _k / H _cJ is low.
As shown in Table 3, all of the examples of the present invention (Sample Nos. 1 to 3) satisfy H _cJ > 1300 kA / m and H _k / H _cJ > 85, and have high H _cJ and high H _k / H _cJ. have. On the other hand, sample No. In No. 4, the conditions of the first sintering step, the second sintering step and the heat treatment step satisfy the provisions of the present invention, but since the composition is outside the scope of the provisions of the present invention, a high _{Hk / H cJ is} obtained. Although it has been obtained, since H _cJ is significantly reduced, it does not satisfy the condition of "H _cJ > 1300 kA / m and H _k / H _cJ >85", and high H _cJ and high H _k / H _cJ. Could not be obtained together.
Further, the sample No. 1 in which the first sintering temperature and the first sintering time of the first sintering step are outside the range of the present invention and the second sintering step is not performed is further performed. 5 to 12, sample No. 1 in which the first temperature of the first sintering step is outside the range of the present invention. No. 13-16, the second sintering temperature of the second sintering step is outside the range of the present invention. No. 17 to 20 and No. 1 having the same heating temperature in the first sintering step and the second sintering step. None of 21 to 24 satisfied the condition of "H _cJ > 1300 kA / m and H _k / H _cJ >85", and both high H _cJ and high H _k / H _cJ could not be obtained.

Claims (2)

R: 29.5 to 35.0% by mass (R is at least one rare earth element and contains at least one of Nd and Pr),
B: 0.80 to 0.91% by mass,
It contains Ga: 0.2 to 1.0% by mass, and T: 61.5 to 69.5% by mass (T is Fe and Co, and 90 to 100% by mass of T is Fe).
A method for manufacturing an RTB-based sintered magnet that satisfies the following formula (1).

[T] /55.85>14 [B] /10.8 (1)
([T] is the content of T shown in% by mass, and [B] is the content of B shown in% by mass)

The process of preparing alloy powder and
The molding process of molding the alloy powder to obtain a molded body, and
The molded body is heated at a first sintering temperature in the range of 1010 ° C. to 1030 ° C. and a first sintering time in the range of 12 hours to 36 hours to obtain a first sintered body. 1 sintering process and
The first sintered body is in the range of 990 ° C to 1020 ° C, and is in the range of 17 hours to 41 hours at the second sintering temperature which is 10 ° C or more lower than the first sintering temperature. In the second sintering step of obtaining a second sintered body by heating in a second sintering time that is 5 hours or more longer than the first sintering time.
A method for producing an RTB-based sintered magnet, which comprises a heat treatment step of heating the second sintered body at a heat treatment temperature in the range of 400 ° C. to 800 ° C. The RT according to claim 1, wherein in the second sintering step, the second sintering temperature is in the range of 990 ° C to 1010 ° C and is 20 ° C or more lower than the first sintering temperature. -A method for manufacturing a B-based sintered magnet.