WO2019181249A1

WO2019181249A1 - Method for producing r-t-b system sintered magnet

Info

Publication number: WO2019181249A1
Application number: PCT/JP2019/004166
Authority: WO
Inventors: 倫太郎石井; 國吉　太
Original assignee: 日立金属株式会社
Priority date: 2018-03-23
Filing date: 2019-02-06
Publication date: 2019-09-26
Also published as: JPWO2019181249A1; JP7276132B2; CN110537235B; CN110537235A

Abstract

The present invention is a method for producing an R-T-B system sintered magnet that has a specific composition and satisfies formula (1). This method for producing an R-T-B system sintered magnet comprises: a step for forming an alloy that satisfies the composition of the R-T-B system sintered magnet with use of a starting material Co that has a maximum thickness of 2 mm or less; a step for forming an alloy powder from the alloy; a molding step for obtaining a molded body by molding the alloy powder; a sintering step for obtaining a sintered body by sintering the molded body; and a heat treatment step for subjecting the sintered body to a heat treatment. (1): 14(B)/10.8 < (T)/55.85 (In the formula, (B) represents the content of B expressed in terms of mass%; and (T) represents the content of T (T is composed of Fe and Co) expressed in terms of mass%.)

Description

Method for producing RTB-based sintered magnet

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

The RTB-based sintered magnet (R is at least one of rare earth elements and always contains Nd, and T is at least one kind of transition metal element and always contains Fe) is the highest among permanent magnets. It is known as a high-performance 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 R ₂ T ₁₄ B compound and a grain boundary phase located at the grain boundary portion of the main phase. The main phase, R ₂ T ₁₄ B compound, is a ferromagnetic material having high magnetization, and forms the basis of the characteristics of the RTB-based sintered magnet.

The _RTB -based sintered magnet has irreversible thermal demagnetization because the coercive force H _cJ (hereinafter sometimes simply referred to as “H _cJ ”) decreases at high temperatures. Therefore, especially when used for a motor for an electric vehicle, it is required to have a high _HcJ even under a high temperature.

Conventionally, in order to improve _HcJ , heavy rare earth elements RH such as Dy and Tb have been added in a large amount to an RTB-based sintered magnet. However, when a large amount of the heavy rare earth element RH is added, _HcJ is improved, but there is a problem that the residual magnetic flux density B _r (hereinafter sometimes simply referred to as “B _r ”) is lowered. Therefore, in recent years, while suppressing a decrease in B _r by causing thickening of the RH in the outer shell surface from the main phase crystal grains by diffusing RH inside the R-T-B based sintered magnet, high H _A method for obtaining _cJ has been proposed.

However, Dy has problems such as unstable supply and price fluctuations because it originally has a small amount of resources and its production area is limited. Therefore, without using much as possible RH such as Dy (i.e., to minimize the amount), while suppressing the decrease in B _r, it is required to obtain a high H _cJ.

In Patent Document 1, an R ₂ Fe ₁₇ phase is formed by lowering the amount of B than that of a normal RTB alloy and containing one or more metal elements M selected from Al, Ga, and Cu. Of the transition metal rich phase (R ₆ T ₁₃ M) generated from the R ₂ Fe ₁₇ phase as a raw material, while maintaining the Dy content and reducing the coercive force. It is described that a high RTB system rare earth sintered magnet can be obtained.

In addition, as described above, _RTB -based sintered magnets are most often used for motors, and in particular for improving high temperature stability in order to ensure high-temperature stability in applications such as motors for electric vehicles. However, along with these characteristics, the squareness ratio H _k / H _cJ (hereinafter sometimes 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 tends to occur. Therefore, an _RTB -based sintered magnet having high H _cJ and high H _k / H _cJ is required. In the field of R-T-B based sintered magnet, typically, H _k is a parameter to be measured to determine the H _k / H _cJ is, J (intensity of magnetization) -H (field intensity ) In the second quadrant of the curve, the H-axis reading at a position where J is 0.9 × J _r (J _r is the residual magnetization, J _r = B _r ) is used. A value _obtained by dividing 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

The RTB-based rare earth sintered magnet described in Patent Document 1 can obtain a high H _cJ while reducing the Dy content, but a general _RTB -based sintered magnet (R There is a problem that it is difficult to improve H _k / H _cJ as compared with the case where the B amount is larger than the stoichiometric ratio of the ₂ T ₁₄ B type compound. Specifically, in a general _RTB -based sintered magnet, H _k is about 90% of H _cJ (that is, H _k / H _cJ is about 90%). On the other hand, the RTB-based rare earth magnet described in Patent Document 1 has a high _HcJ , and therefore has a higher H _k value than a general _RTB -based sintered magnet. However, there is a problem that it is difficult to _increase H _k / H _cJ to 90% or more.

Therefore embodiments of the present invention to provide Dy, while reducing the content of RH of Tb or the like, a method for manufacturing the R-T-B based sintered magnet having a high H _cJ and high H _k With the goal.

Aspect 1 of the present invention
R: 28.5-33.0% by mass (R is at least one rare earth element and includes at least one of Nd and Pr),
B: 0.85 to 0.91% by mass,
Ga: 0.2 to 0.7% by mass,
Co: 0.1 to 0.9% by mass,
Cu: 0.05 to 0.50 mass%,
Al: 0.05 to 0.50% by mass, and Fe: 61.5% by mass or more,
An RTB-based sintered magnet manufacturing method that satisfies the following formula (1):

14 [B] /10.8 <[T] /55.85 (1)
([B] is the B content in mass%, [T] is the T in mass% (T is the content of Fe and Co))

Using raw material Co having a maximum thickness of 2 mm or less, producing an alloy satisfying the composition of the RTB-based sintered magnet, producing an alloy powder from the alloy,
A molding step of molding the alloy powder to obtain a molded body;
Sintering step for obtaining a sintered body by sintering the molded body;
A heat treatment step for heat-treating the sintered body;
Is a method for producing an RTB-based sintered magnet.

Aspect 2 of the present invention is the method for producing an RTB-based sintered magnet according to aspect 1, wherein the maximum thickness of the raw material Co is 100 μm to 1 mm.

Aspect 3 of the present invention is the _{RTB according} to aspect 1 or 2, wherein the obtained _RTB -based sintered magnet satisfies H _cJ ≧ 1500 kA / m and H _k ≧ 1400 kA / m. It is a manufacturing method of a system sintered magnet.

Aspect 4 of the present invention is the aspect 4 according to any one of the aspects 1 to 3, wherein Dy and Tb in the R are 0% by mass or more and 0.5% by mass or less of the entire RTB-based sintered magnet. This is a method of manufacturing an RTB-based sintered magnet.

According to the manufacturing method according to the embodiment of the present invention, while reducing the content of RH, it is possible to produce the R-T-B based sintered magnet having a high H _cJ and high H _k.

FIG. 1A is a schematic perspective view of a plate-shaped raw material Co, and FIG. 1B is a projection view of the raw material Co from the direction of the arrow 1A in FIG. Is a modification of FIG. 2A is a schematic perspective view of a plate-shaped raw material Co having a wedge shape on one side, and FIG. 2B is a projection view of the raw material Co from the direction of arrow 2A in FIG. 2A. is there. FIG. 3A is a schematic perspective view of a thin plate-like raw material Co bent in a wave shape, and FIG. 3B is an outline of the raw material Co obtained by extending the raw material Co of FIG. 3A into a flat plate shape. FIG. 3C is a perspective view, and FIG. 3C is a projection view of the raw material Co from the direction of arrow 3A in FIG. 4A is a schematic enlarged perspective view of granular raw material Co, and FIG. 4B is a projection view of raw material Co from the direction of arrow 4A in FIG. 4A. FIG. 5A is a schematic perspective view of the rod-shaped raw material Co, and FIG. 5B is a projection view of the raw material Co from the direction of the arrow 5A in FIG. 6 (a) is a schematic perspective view of a rod-shaped raw material Co, FIG. 6 (b) is a schematic cross-sectional view taken along the line YY ′ of FIG. 6 (a), and FIG. FIG. 7 is a projection view of a raw material Co from the direction of an arrow 6A in FIG. FIG. 7 is a graph plotting the magnetic properties (H _k -B _r ) of a sintered magnet manufactured using a raw material Co having a maximum thickness of 10 mm. FIG. 8 is a graph plotting the magnetic properties (H _k −B _r ) of a sintered magnet manufactured using a raw material Co having a maximum thickness of 2 mm. 9, the increase in H _k of the sintered magnet of changing the maximum thickness of the material Co from 10mm to 2 mm, is a graph plotting against B amount. FIG. For sintered magnet having a composition of 14, the maximum thickness of the material Co used is a graph plotting the H _k of the sintered magnet produced by using it. FIG. For sintered magnet having a 16 composition, the maximum thickness of the material Co used is a graph plotting the H _k of the sintered magnet produced by using it. FIG. For sintered magnet having a composition of 17, the maximum thickness of the material Co used is a graph plotting the H _k of the sintered magnet produced by using it. FIG. For sintered magnet having a composition of 18, the maximum thickness of the material Co used is a graph plotting the H _k of the sintered magnet produced by using it. FIG. For sintered magnet having a composition of 22, the maximum thickness of the material Co used is a graph plotting the H _k of the sintered magnet produced by using it.

The embodiment described below exemplifies a manufacturing method of an RTB-based sintered magnet for embodying the technical idea of the present invention, and the present invention is not limited to the following.

As a result of intensive studies, the present inventors have determined the form of the raw material Co in the production of an RTB-based sintered magnet having a specific composition range as specified below, particularly an extremely narrow specific range of B content. It has been found that the magnetic properties of the finally obtained RTB-based sintered magnet can be improved by controlling.

As the raw material Co, one having a Co content of 50% by mass or more can be used. As a generally available raw material Co, a thin plate-like or block-like Co material is known. As the thin plate-like raw material Co, there is electrolytic Co produced by electrolysis, and the maximum thickness is about 3 mm. As the block raw material Co, one having a thickness of 10 mm or more is available.
Since the raw material Co used as the raw material of the sintered magnet is completely melted during the production of the alloy, it is considered unnecessary to thin or pulverize the commercially available raw material Co. It wasn't. However, the present inventors dare to maximize the production of RTB-based sintered magnets having a specific composition range, particularly a very narrow specific range of B content, even if the raw material Co is dissolved. by processing a thickness up to 2 mm, in which found that the value of H _k of the sintered magnet of the final product can be greatly 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 embodiment of 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: 28.5-33.0% by mass (R is at least one rare earth element and includes at least one of Nd and Pr),
B: 0.85 to 0.91% by mass,
Ga: 0.2 to 0.7% by mass,
Co: 0.1 to 0.9% by mass,
Cu: 0.05 to 0.50 mass%,
Al: 0.05 to 0.50% by mass, and Fe: 61.5% by mass or more,
The following formula (1) is satisfied.

14 [B] /10.8 <[T] /55.85 (1)
([B] is the B content in mass%, and [T] is the T content in mass%)

With 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. Therefore, an RT-Ga phase is generated at the two-grain 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 ₃ type crystal structure. In addition, 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 a relatively large amount of Cu and Al is contained in an RTB-based sintered magnet, R ₆ T _13-δ (Ga _1-xy Cu _x Al _y ) _{1 + δ} may be obtained. is there.
Below, each composition is explained in full detail.

(R: 28.5-33.0% by mass)
R is at least one of rare earth elements and includes at least one of Nd and Pr. The content of R is 28.5 to 33.0% by mass. R is may become difficult to densification during sintering is less than 28.5% by mass may main phase proportion exceeds 33.0% by weight can not be obtained a high B _r drops . The content of R is preferably 29.5 to 32.5% by mass. If R is in such a range, higher _Br can be obtained.

R may contain RH such as Dy and Tb. However, in the embodiment of the present invention, by controlling the content of B, Ga, Co, etc., the content of RH is reduced, and the _RTB -based sintering having high H _cJ and high H _k is _achieved. A magnet can be obtained. That is, according to the embodiment of the present invention, the content of RH, more specifically, the content of Dy and Tb (total content) may be suppressed extremely low. Specifically, Dy and Tb in R may be 0% by mass or more and 0.5% by mass or less of the entire RTB-based sintered magnet. Here, “Dy and Tb in R” means that the content of Dy and Tb (0 to 0.5 mass%) is a part of the content of R (28.5 to 33.0 mass%). Means. Further, “0 mass% or more and 0.5 mass% or less of the entire RTB-based sintered magnet” means Dy and Tb when the entire RTB-based sintered magnet is 100 mass%. It means that the total content of is 0% by mass or more and 0.5% by mass or less.

Dy and Tb may include only one or both. That is, when the total content of Dy and Tb is limited to 0 to 0.5% by mass, Dy is contained but Tb is not contained (Tb content is 0% by mass). It may be 0 to 0.5% by mass or less. Similarly, when Tb is contained but Dy is not contained (Dy content is 0% by mass), the Tb content may be 0 to 0.5% by mass or less. When both Dy and Tb are contained, the total content of the Dy content and the Tb content is 0 to 0.5% by mass or less.
Preferably, the total content of Dy and Tb is 0 to 0.3% by mass, and most preferably, both Dy and Tb are not contained (the total content of Dy and Tb is 0% by mass).

(B: 0.85 to 0.91 mass%)
The content of B is 0.85 to 0.91% by mass. If B is less than 0.85% by mass, R ₂ T ₁₇ phase may be produced and high H _cJ may not be obtained. If it exceeds 0.91% by mass, the amount of R—T—Ga phase produced is small. _Therefore, there is a possibility that high _HcJ cannot be obtained. The content of B is preferably 0.87 to 0.91% by mass, and a higher effect of improving _HcJ can be obtained.

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

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

Here, [B] is the B content expressed in mass%, and [T] is the T content expressed in mass%. T is Fe and Co. Therefore, [T] can be rewritten as follows.

[T] = [Fe] + [Co]

Here, [Fe] and [Co] are the contents of Fe and Co in mass%, respectively.

By satisfying the formula (1), the B content is smaller than that of a general RTB-based sintered magnet. A general RTB-based sintered magnet has [T] /55.85 (so that an R ₂ T ₁₇ phase, which is a soft magnetic phase, is not generated in addition to an R ₂ T ₁₄ B phase, which is a main phase. The atomic weight of Fe is less than 14 [B] /10.8 (the atomic weight of B) ([T] is the content of T expressed in mass%). The RTB-based sintered magnet of the embodiment of the present invention differs from a general RTB-based sintered magnet in that [T] /55.85 is more than 14 [B] /10.8. It is defined by equation (1) so as to increase. 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 0.7% by mass)
The Ga content is 0.2 to 0.7% by mass. If Ga is less than 0.2% by mass, the amount of RT-Ga phase produced is so small that the R ₂ T ₁₇ phase cannot be lost and high H _cJ may not be obtained. It will be present unnecessary Ga exceeds 0.7 weight%, there is a possibility that B _r decreases to decrease the main phase proportion.

(Co: 0.1 to 0.9% by mass)
The Co content is 0.1 to 0.9% by mass. In the RTB-based sintered magnet according to the embodiment of the present invention, the addition of Co can suppress the formation of R ₆ T ₁₃ B ₁ formed when the molded body is sintered. B _r , high H _cJ , and high H _k are obtained. However, Co is not possible to suppress the generation of _R 6 _T 13 _{B 1} is less than 0.1 wt%, there may not be to improve the _{H k,} the content of Co is more than 0.9 mass% When the molded body during sintering will be generated by the _R 2 _{T 17} _{phase, H cJ} and _{H k} may be reduced.

(Cu: 0.05 to 0.50 mass%)
The Cu content is 0.05 to 0.50 mass%. If Cu is less than 0.05% by mass, high H _cJ may not be obtained, and if it exceeds 0.50% by mass, sinterability may deteriorate and high H _cJ may not be obtained.

(Al: 0.05 to 0.50 mass%)
The Al content is 0.05 to 0.50 mass%. By containing Al, _HcJ can be improved. Al is usually contained in an amount of 0.05% by mass or more as an unavoidable impurity in the production process, but may be contained in an amount of 0.50% by mass or less in total of the amount contained as an inevitable impurity and the amount intentionally added. Good.

(Fe: 61.5% by mass or more)
The content of Fe in the sintered magnet is 61.5% by mass or more and is an amount satisfying the above-described formula (1). When the content of Fe is less than 61.5% by mass may greatly _{B r} drops. Preferably, Fe is the balance.

Further, even when Fe is the balance, the RTB-based sintered magnet according to the embodiment of the present invention is an inevitable impurity usually contained in didymium alloy (Nd—Pr), electrolytic iron, ferroboron, and the like. Cr, Mn, Si, La, Ce, Sm, Ca, Mg and the like can be contained. Furthermore, O (oxygen), N (nitrogen), C (carbon), etc. can be illustrated as an inevitable impurity in a manufacturing process. In addition, the RTB-based sintered magnet according to the embodiment of the present invention may include one or more other elements (elements added intentionally other than inevitable impurities). For example, as such an element, a small amount (each about 0.1% by mass) 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. Moreover, you may intentionally add the element mentioned as an inevitable impurity mentioned above. Such elements may be included in a total of about 1.0% by mass, for example. At this level, it is possible to obtain an _RTB -based sintered magnet having high _HcJ .

(Magnetic characteristics of RTB-based sintered magnet)
R-T-B based sintered magnet of the present embodiment show a high _{H cJ} and high _{H k.} In _{particular, H cJ} is 1500 kA / m or more, preferably _{H k} is 1400kA / m or _{more, H cJ} is 1520kA / m or more, more preferably _{H k} is 1420kA / m or _{more, H cJ 1530kA} / m or more, H _k is more preferably ₁₄₂₅ kA / m or more, H _cJ is 1550 kA / m or more, and H _k is particularly preferably 1440 kA / m or more. The above magnetic characteristics can also be achieved in an RTB-based sintered magnet in which the contents of Dy and Tb that can be contained in R (rare earth element) are 0.5% by mass or less in total.

<Method for producing RTB-based sintered magnet>
Next, the manufacturing method of the RTB system sintered magnet which concerns on this invention is demonstrated.
The manufacturing method of the RTB-based sintered magnet includes a process for producing an alloy, a process for producing an alloy powder, a forming process, a sintering process, and a heat treatment process.
Hereinafter, each step will be described.

(1) Process for producing an alloy A metal or an alloy (melting raw material) of each element is prepared so as to have a composition of an RTB-based sintered magnet according to an embodiment of the present invention, and an alloy is produced. At this time, the raw material Co to be used is limited to a predetermined dimension, specifically, a maximum thickness of 2 mm or less. Generally, the sintered magnet such B amount is small as defined in the present application, it is possible to improve the H _cJ, it has been considered to be difficult to improve the H _k. However, the present inventors have found that by using the alloy produced on that the maximum thickness of the material Co to 2mm or less, it has been found that the alloy pulverization, thereby improving the H _k of the sintered magnet obtained by sintering. In particular, it is preferable to control the maximum thickness of the material Co in 100 [mu] m ~ 1 mm, it is possible to significantly improve the _{H k.}

Detailed mechanism capable of improving the H _k is unknown, by the maximum thickness of the material Co is limited to 2mm or less, dissolved starting materials Co uniformly and quickly when melting an alloy, its possible It is presumed that the value of H _k of the finally obtained sintered magnet is improved, and as a result, H _k / H _cJ (square ratio) is improved.

Here, the “maximum thickness” of the raw material Co is the thickest part of the thickness of the raw material Co in the case of the raw material Co having a clear “thickness” such as a plate shape. .
For the raw material Co that is not plate-shaped (that is, the shape whose thickness is not clear), the maximum thickness is defined as follows.
In the projection view of the raw material Co projected so as to minimize the area, two parallel lines in contact with the projection view are drawn so as to sandwich the projection view. By changing the angle of the parallel lines in various ways, the distance when the distance between the parallel lines is minimized becomes the maximum thickness of the raw material Co.

(Maximum thickness of Co plate 10)
The “maximum thickness” of various forms of raw material Co will be described with reference to FIGS. In the embodiment of the present invention, not only the plate shape but also the raw material Co such as a particle shape, a rod shape, or a linear shape can be used.
FIG. 1A is a schematic perspective view of a plate-shaped raw material Co (Co plate) 10. In the Co plate 10, the area of the projection view is minimized when projected from the direction of the arrow 1A. FIG. 1B shows a projection view 11 of the Co plate 10 projected from the direction of the arrow 1A. In FIG. 1 (b), the parallel lines _{L 11a} in contact with the projection 11, drawn two so as to sandwich the projection 11. Further, two parallel lines L _11b in contact with the projection diagram 11 were drawn from another angle so as to sandwich the projection diagram 11. A distance T _1a between the first parallel lines L _11a and L _11a is shorter than a distance W _1a between the second parallel lines L _11b and L _11b . Therefore, the maximum thickness of the Co plate 10 is T _1a .

FIG. 1C shows a modification in the case where the surface is curved in the projection view 11 of the Co plate 10 shown in FIG. As shown in FIG. 1C, in the projection diagram 12 of the Co plate having a curved surface, the outline of the projection diagram 12 is curved. Two parallel lines L _12a in contact with the projection 12 are drawn so as to sandwich the projection 12. In addition, two parallel lines L _12b in contact with the projection diagram 12 were drawn from another angle so as to sandwich the projection diagram 12. A distance T _1b between the first parallel line L _12a and the parallel line L _12a is shorter than a distance W _1b between the second parallel lines L _12b and L _12b . Therefore, the maximum thickness of the Co plate 10 is T _1b .

(Maximum thickness of Co plate 20 having a wedge-shaped portion)
FIG. 2A is a schematic perspective view of a plate-shaped raw material Co (Co plate) 20 in which one side 25 is formed in a wedge shape (a blade shape whose thickness decreases toward the outside). In the Co plate 20, the area of the projection view is minimized when projected from the direction of the arrow 2A. FIG. 2B shows a projection view 21 of the Co plate 20 projected from the direction of the arrow 2A. In FIG. 2B, two parallel lines L _{2 a} that are in contact with the projection diagram 21 are drawn so as to sandwich the projection diagram 21. In addition, two parallel lines L _2b in contact with the projection diagram 21 were drawn from another angle so as to sandwich the projection diagram 21. Further, two parallel lines L _2c in contact with the projection diagram 21 were drawn from another angle so as to sandwich the projection diagram 21. The distance T _2a between the first parallel lines L _2a and L _2a is the distance W ₂ between the second parallel lines L _2b and L _2b and the distance between the third parallel lines L _2c and L _2c. shorter than the Y _2. Therefore, the maximum thickness of the Co plate 20 is T _2a .

Note that the “thickness” in the projection diagram 21 shown in FIG. 2B includes not only the thickness T _2a but also the thickness of the wedge-shaped portion (for example, the thickness T _2b and T _2c ). However, the “maximum thickness” in the embodiment of the present invention is the thickest T _2a among those thicknesses. This is because the meltability of the raw material Co is considered to be important, and even if it is partially thin, the thick part has the most influence.

(Maximum thickness of Co corrugated plate 30)
FIG. 3A is a schematic perspective view of a thin plate-like raw material Co (Co wave plate) 30 bent in a wave shape. In the case of such a curved raw material Co, first, it is extended and flattened. In the case of the Co corrugated plate 30, one end 30a is pulled in the direction Xa, and the other end 30b is pulled in Xb, and is extended into a flat plate shape as shown in FIG. Called). The maximum thickness obtained with the Co extension plate 35 is the maximum thickness of the Co wave plate 30.

In the Co extension plate 35 shown in FIG. 3B, the area of the projected view is minimized when projected from the direction of the arrow 3A. FIG. 3C shows a projection 31 of the Co extension plate 35 projected from the direction of the arrow 3A. In FIG. 3C, two parallel lines L _{3 a} in contact with the projection diagram 31 are drawn so as to sandwich the projection diagram 31. Further, two parallel lines L _3b in contact with the projection diagram 31 were drawn from another angle so as to sandwich the projection diagram 31. The first parallel line _L _3a, the distance _{T 3} between the _{L 3a,} the second parallel line _L _3b, shorter than the distance _{W 3} between the _{L 3b.} Therefore, the maximum thickness of the Co extension plate 35 and extension before Co-wave plate 30 are both _{T 3.}

Thus, the maximum thickness of the Co corrugated plate 30 is determined by the state of the Co extension plate 35 for the following reason. When the maximum thickness is determined in the state of the Co corrugated plate 30, the distance between the peak portion (upper end) and the valley portion (lower end) of the curve becomes the “maximum thickness”. However, in the embodiment of the present invention, the maximum thickness is an index of the melting property of the raw material Co. If the curved plate is formed from a thin plate, it should exhibit the same meltability as the thin plate when not curved. Therefore, in the embodiment of the present invention, the maximum thickness of the Co wave plate 30 is determined by the state of the Co extension plate 35.

(Maximum thickness of Co particles 40)
FIG. 4A is a schematic perspective view of granular raw material Co (Co particles). In the Co particle 40, the area of the projected view is minimized when projected from the direction of the arrow 4A. FIG. 4B shows a projection 41 of the Co particles 40 projected from the direction of the arrow 4A. In FIG. 4B, two parallel lines L _{4 a} in contact with the projection 41 are drawn so as to sandwich the projection 41. Further, two parallel lines L _4b in contact with the projection diagram 41 were drawn from another angle so as to sandwich the projection diagram 41. Further, two parallel lines L _4c in contact with the projection 41 are drawn from another angle so as to sandwich the projection 41. The distance T _4a between the first parallel lines L _4a and L _4a is the distance W ₄ between the second parallel lines L _4b and L _4b and the distance between the third parallel lines L _4c and L _4c. shorter than the Y _4. Therefore, the maximum thickness of the Co plate 20 is _T4a .

Note that the “thickness” in the projection diagram 41 shown in FIG. 4B includes not only the thickness T _4a but also the thickness of the constricted portion of the Co particles 40 (for example, the thickness T _4b and T _4c ). Can be. However, the “maximum thickness” in the embodiment of the present invention is the thickest T _4a among those thicknesses.

(Maximum thickness of Co bar 50)
FIG. 5A is a schematic perspective view of a rod-shaped raw material Co (Co rod). In the Co bar 50, the area of the projection is minimized when projected from the direction of the arrow 5A. FIG. 5B shows a projection 51 of the Co bar 50 projected from the direction of the arrow 5A. In FIG. 5B, two parallel lines L _{5 a} in contact with the projection 51 are drawn so as to sandwich the projection 51. In addition, two parallel lines L _5b in contact with the projection 51 are drawn from another angle so as to sandwich the projection 51. A distance T _5a between the first parallel lines L _5a and L _5a is shorter than a distance T _5b between the second parallel lines L _5b and L _5b . Therefore, the maximum thickness of the Co bar 50 is _T5a .
Note that the maximum thickness of such a bar corresponds to the minor axis in the cross-sectional view of the bar.

(Maximum thickness of constricted Co bar 60)
FIG. 6A is a schematic perspective view of a rod-shaped raw material Co (constricted Co rod) partially reduced in diameter (that is, partially constricted). As shown in FIG. 6B, in the cross-sectional view (YY ′ line) of the constricted portion 65 of the Co rod 60, the short diameter T _6b of the constricted portion 65 is the short diameter T _6a of the non-constricted portion 66. Smaller.
However, the constricted portion is not reflected in the projection 61 (FIG. 6C) of the Co bar 60 projected from the direction of the arrow 6A where the area of the projection is minimized. Thus, in FIG. 6 (c), the parallel lines _{L 6a} in contact with the projection drawing 61, subtract two so as to sandwich the projection view 61, the parallel lines _L _6a, the distance _{T 6a} between the _{L 6a,} as shown in FIG. 6 This coincides with the “minor axis T _6a of the non-constricted portion 66” shown in FIG. Then, the parallel lines _L _6a, the distance _{T 6a} between the _{L 6a} becomes the maximum thickness of the Co bar 60.

The raw material Co having a maximum thickness of 2 mm or less and the raw materials of other components are melted to produce an alloy. The alloy can be made into flakes, for example, by strip casting.

(2) Step of producing alloy powder In this step, the alloy obtained in the step (1) is pulverized to produce alloy powder.
For example, the obtained alloy (for example, flaky raw material alloy) is hydrogen pulverized so that the size of the coarsely pulverized powder is 1.0 mm or less, for example. Next, the coarsely pulverized powder by pulverizing by a jet mill or the like, for example, the particle size D _{50 (a} value obtained by laser diffraction method using air flow dispersion method (median diameter)) is 3 ~ 7 [mu] m milled powder (Alloy Powder). 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.

(3) Forming step Using the obtained alloy powder, the forming is performed in a magnetic field to obtain a formed body. In the magnetic field molding, a dry alloy method in which a dry alloy powder is inserted into a mold cavity and molded while applying a magnetic field, a slurry in which the alloy powder is dispersed is injected into the mold cavity, Any known forming method in a magnetic field may be used, including a wet forming method of forming while discharging the slurry dispersion medium.

(4) Sintering process The sintered compact (sintered magnet) is obtained by sintering the molded object obtained at the formation process. A known method can be used for sintering the molded body. In addition, in order to prevent the oxidation by the atmosphere at the time of sintering, it is preferable to perform sintering in a vacuum atmosphere or atmospheric gas. The atmosphere gas is preferably an inert gas such as helium or argon.

(5) Heat treatment process It is preferable to heat-treat with respect to the obtained sintered magnet for the purpose of improving a magnetic characteristic. Known conditions can be used for the heat treatment temperature, the heat treatment time, and the like. For example, heat treatment (one-step heat treatment) only at a relatively low temperature (400 ° C. or more and 600 ° C. or less) may be performed, or heat treatment is performed at a relatively high temperature (700 ° C. or more and sintering temperature or less (eg, 1050 ° C. or less)). After performing, heat treatment (two-stage heat treatment) may be performed at a relatively low temperature (400 ° C. or more and 600 ° C. or less). Preferable conditions are as follows: heat treatment at 730 ° C. to 1020 ° C. for 5 minutes to 500 minutes, cooling (after cooling to room temperature or after cooling to 440 ° C. to 550 ° C.), and further at 440 ° C. to 550 ° C. Heat treatment for about 500 minutes to 500 minutes. The heat treatment atmosphere is preferably a vacuum atmosphere or an inert gas (such as helium or argon).

For the purpose of making a final product shape, the obtained sintered magnet may be subjected to machining such as grinding. In that case, the heat treatment may be performed before or after machining. Furthermore, you may surface-treat to the obtained sintered magnet. The surface treatment may be a known surface treatment, and for example, a surface treatment such as Al deposition, electric Ni plating, or resin coating can be performed.

Sintered magnet thus obtained has a high H _cJ and high H _k are obtained had a high squareness ratio.

The composition of the RTB-based sintered magnet is approximately No. 1 in Table 1. The raw materials for each element were blended so that each composition shown in 1 to 23 was obtained. At this time, the raw material Co is Co metal, and the maximum thickness is 10 mm (cube), 4 mm (cube), 2 mm (plate), 1 mm (bar), 425 μm (particle), 100 μm (powder), 5 μm ( Fine powder) was used. The raw material Co of each dimension was prepared by cutting from a block-like Co material. Note that the raw material Co having a maximum thickness of 10 mm (cubic) and 2 mm (plate-like) is a sample No. in Table 1. Used to produce all alloys having a composition of 1 to 23, and other raw materials Co (4 mm (cube), 1 mm (bar), 425 μm (particulate), 100 μm (powder)), 5 μm (fine powder) )) Is a sample No. Used only for the production of alloys having compositions of 14, 16-18, 22.

The blended raw materials were melted and cast by a strip casting method to obtain a flaky alloy having a thickness of 0.2 to 0.4 mm. The obtained flake-like alloy was hydrogen embrittled in a hydrogen-pressurized atmosphere, and then subjected to dehydrogenation treatment in which it was heated and cooled in vacuum to 550 ° C. to obtain coarsely pulverized powder. Next, after adding and mixing 0.04% by mass of zinc stearate as a lubricant with respect to 100% by mass of the coarsely pulverized powder, the obtained coarsely pulverized powder was mixed with an airflow type pulverizer (jet mill device). Then, dry pulverization was performed in a nitrogen stream to obtain finely pulverized powder (alloy powder) having a particle diameter D ₅₀ (median diameter) of 4 μm. The oxygen concentration in the nitrogen gas during pulverization was controlled to 50 ppm or less. The particle size D ₅₀ is a value obtained by a laser diffraction method using an airflow dispersion method.

The obtained alloy powder was mixed with a dispersion medium to prepare a slurry. Normal decane was used as a dispersion medium, and methyl caprylate was mixed as a lubricant. The concentration of the slurry was 70% by mass of the alloy powder and 30% by mass of the dispersion medium, and the lubricant was 0.16% by mass with respect to 100% by mass of the alloy powder. The slurry was molded in a magnetic field to obtain a molded body. The magnetic field during molding was a static magnetic field of 0.8 MA / m, and the applied pressure was 5 MPa. In addition, what was called a right-angle magnetic field shaping | molding apparatus (lateral magnetic field shaping | molding apparatus) in which the magnetic field application direction and the pressurization direction orthogonally cross was used for the shaping | molding apparatus.

The obtained molded body was sintered at 1000 ° C. or higher and 1050 ° C. or lower (a temperature at which densification by sintering was sufficiently selected for each sample) for 4 hours, and then rapidly cooled to obtain a sintered body. The density of the obtained sintered body was 7.5 Mg / m ³ or more. The obtained sintered body was held in vacuum at 800 ° C. for 2 hours, then cooled to room temperature, then held in vacuum at 430 ° C. for 2 hours, and then subjected to a heat treatment to cool to room temperature to obtain an RTB system Sintered magnets (No. 1 to 23) were obtained. Table 1 shows the components of the obtained RTB-based sintered magnet. In addition, each component (except O, N, and C) in Table 1 was measured using a high frequency inductively coupled plasma optical emission spectrometry (ICP-OES). The O (oxygen) content is determined by gas melting-infrared absorption method, the N (nitrogen) content is determined by gas melting-heat conduction method, and the C (carbon) content is determined by combustion-infrared absorption method. Measured using.

Table 2 shows the B amount, the T amount (the sum of the Co amount and the Fe amount), the value of the left side (14 [B] /10.8) of the formula (1), and the right side ([T] /55.85). The value is shown. Table 2 also shows the satisfiability of the formula (1). Here, “◯” means that Expression (1) is satisfied, and “X” means that Expression (1) is not satisfied.

The RTB-based sintered magnets after heat treatment (Sample Nos. 1 to 23) are each machined to prepare samples having a length of 7 mm, a width of 7 mm, and a thickness of 7 mm, and a BH tracer at room temperature (20 The magnetic properties (B _r , H _cJ , H _k , H _k / H _cJ ) of each sample were measured at a temperature of ± 10 ° C. Table 3 shows the measurement results. In H _k / H _cJ (square ratio), H _k is in the second quadrant of the I (magnetization magnitude) -H (magnetic field strength) curve, and I is 0.9 × J _r (J _r is This is the value of H at the position where the value of remanent magnetization, J _r = B _r ).
Sample No. using raw material Co having various maximum thicknesses. Tables 4 to 6 show the measurement results of the magnetic characteristics of 14, 16 to 18, and 22.

Sample No. 1 to 12 do not satisfy the definition of the composition of the sintered magnet according to the embodiment of the present invention. Sample No. In 1-2, 4-5, and 7-10, the amount of B does not satisfy the definition of the present invention. Sample No. 6 and 11, the Ga amount does not satisfy the rule according to the embodiment of the present invention. Sample No. In No. 12, the amount of Co does not satisfy the rule according to the embodiment of the present invention. Sample No. 1 to 3, 5, 8, and 10 do not satisfy the definition of the expression (1). As can be seen from Table 3, most of these samples tend to have a relatively low value of _{HcJ at} any of the maximum thicknesses of the raw material Co, 10 mm and 2 mm.

Sample No. Nos. 13 to 23 satisfy all the requirements for the composition of the sintered magnet according to the embodiment of the present invention. Therefore, sample no. _Nos . 13 to 23 have relatively high values of _{HcJ in} any of the maximum thicknesses of the raw material Co of 10 mm and 2 mm (Table 3).

In each sample, consider the relationship between the maximum thickness of the H _k and the raw material Co. FIG. 7 is a graph plotting the magnetic properties (H _k -B _r ) of a sintered magnet manufactured using a raw material Co having a maximum thickness of 10 mm. FIG. 8 is a graph plotting the magnetic properties (H _k −B _r ) of a sintered magnet manufactured using a raw material Co having a maximum thickness of 2 mm. In FIG. 7 and FIG. The data of 1 to 12 are plotted, and the symbol “●” indicates the sample No. The data of 13 to 23 are plotted.

As can be seen from FIG. 7, when the maximum thickness of the raw material Co is 10 mm, the sample No. In any of 1 to 12 and Samples 13 to 23, the obtained sintered magnet had an H _k of less than 1400 kA / m.
On the other hand, when the maximum thickness of the raw material Co is 2 mm as shown in FIG. In 1 to 12, the H _k of the obtained sintered magnet remained less than 1400 kA / m, but in Samples 13 to 23, the H _k of the obtained sintered magnet was 1400 kA / m or more. .

In each sample, the amount of increase _{H k} when changing the maximum thickness of the material Co from 10mm to 2 mm _{_{(i.e., H k (2mm) -H k}} (10mm)) shown in Table 3. “H _k (10 mm)” and “H _k (2 mm)” in Table 3 and the like mean values of H _k of sintered magnets manufactured using raw material Co having a maximum thickness of 10 mm and 2 mm, respectively. Further, in FIG. 9, the increase amount of H _k is plotted against the B amount.

As is apparent from FIG. 9, in the case of a sintered magnet (sample Nos. 13 to 23) having a B content of 0.85 to 0.91% by mass, the maximum thickness of the raw material Co is reduced to 2 mm or less. The value of _k increased by 80 kA / m or more and reached 1400 kA / m or more.
On the other hand, in the case of a sintered magnet (sample Nos. 1 to 12) with a B content of less than 0.85 mass% or more than 0.91 mass%, even if the maximum thickness of the raw material Co is limited to 2 mm or less, H The amount of increase of _k was less than 10 kA / m, and hardly increased.

Thus, the sample No. 1 satisfying the definition of the composition of the sintered magnet according to the embodiment of the present invention. 13 to 23, by limiting the maximum thickness of the raw material Co used in production to 2 mm or less, it has excellent magnetic properties such that H _cJ is 1500 kA / m or more and H _k is 1400 kA / m or more. I understood. In particular, the effect of limiting the maximum thickness of the raw material Co was remarkable when the B content was 0.85 to 0.91% by mass.

Furthermore, sample no. Examples sintered magnet having a composition of 14 ~ 18, 22, examined the effect of the _{H k} in the case of using a raw material Co with different maximum thicknesses. Table 4 shows sample Nos. Manufactured using raw material Co having a maximum thickness of 10 mm and 4 mm. The measurement results of the magnetic properties of the sintered magnets 14, 16 to 18, 22 are shown. Table 5 shows sample Nos. Manufactured using raw material Co having a maximum thickness of 2 mm and 1 mm. The measurement result of the magnetic characteristic of 16 sintered magnets is shown. Table 6 shows sample Nos. Manufactured using raw material Co having a maximum thickness of 425 μm, 100 μm, and 5 μm. The measurement results of the magnetic properties of the sintered magnets 14, 16 to 18, 22 are shown. 10 to 14 show the sample Nos. For each 14-18,22, the maximum thickness of the material Co, was plotted _{H k} of the sintered magnet produced by using the raw material Co.

As shown in FIG. Regarding No. 14, in the sintered magnet manufactured using the raw material Co having a maximum thickness of 2 mm or less, the H _k was 1420 kA / m or more. Furthermore, when raw material Co having a maximum thickness of 100 μm to 2 mm was used, H _k of the obtained sintered magnet was 1425 kA / m or more.

As shown in FIG. For No. 16, in the sintered magnet manufactured using the raw material Co having a maximum thickness of 2 mm or less, the H _k was 1440 kA / m or more. Further, when the raw material Co having a maximum thickness of 100 μm to 1 mm was used, the H _k of the obtained sintered magnet was 1460 kA / m or more.

As shown in FIG. Regarding No. 17, in the sintered magnet manufactured using the raw material Co having a maximum thickness of 2 mm or less, the H _k was 1460 kA / m or more. Furthermore, when raw material Co having a maximum thickness of 100 μm to 1 mm was used, H _k of the obtained sintered magnet was 1480 kA / m or more.

As shown in FIG. For 18, the sintered magnet maximum thickness was prepared using the following ingredients Co 2 mm, _{H k} became 1465kA / m or more. Furthermore, when raw material Co having a maximum thickness of 100 μm to 1 mm was used, H _k of the obtained sintered magnet was 1485 kA / m or more.

As shown in FIG. For No. 22, in the sintered magnet manufactured using the raw material Co having a maximum thickness of 2 mm or less, the H _k was 1400 kA / m or more. Furthermore, when raw material Co having a maximum thickness of 100 μm to 1 mm was used, H _k of the obtained sintered magnet was 1420 kA / m or more.

From the results of FIGS. 10 to 14, it is possible to improve H _k by setting the maximum thickness of the raw material Co to 2 mm or less, and further, by setting the maximum thickness of the raw material Co to 100 μm to 1 mm, the H _k can be reduced. It turned out that it can improve more.

The present application includes Japanese Patent Application No. 2018-056846 filed on March 23, 2018 and Japanese Patent Application No. 2018-182636 filed on September 27, 2018. Accompanied by claiming priority as a basic application. Japanese Patent Application No. 2018-056846 and Japanese Patent Application No. 2018-182636 are incorporated herein by reference.

10, 20, 30, 40, 50, 60 Raw material Co
Maximum thickness of T _1a , T _1b , T _2a , T ₃ , T _4a , T _5a , T _6a raw material Co

Claims

R: 28.5-33.0% by mass (R is at least one rare earth element and includes at least one of Nd and Pr),
B: 0.85 to 0.91% by mass,
Ga: 0.2 to 0.7% by mass,
Co: 0.1 to 0.9% by mass,
Cu: 0.05 to 0.50 mass%,
Al: 0.05 to 0.50 mass%,
Fe: 61.5% by mass or more,
An RTB-based sintered magnet manufacturing method that satisfies the following formula (1):

14 [B] /10.8 <[T] /55.85 (1)
([B] is the B content in mass%, [T] is the T in mass% (T is the content of Fe and Co))

Using a raw material Co having a maximum thickness of 2 mm or less, producing an alloy satisfying the composition of the RTB-based sintered magnet;
Producing an alloy powder from the alloy;
A molding step of molding the alloy powder to obtain a molded body;
Sintering step for obtaining a sintered body by sintering the molded body;
A heat treatment step for heat-treating the sintered body;
A method of manufacturing an RTB-based sintered magnet.
2. The method for producing an RTB-based sintered magnet according to claim 1, wherein the maximum thickness of the raw material Co is 100 μm to 1 mm.
3. The RTB -based sintered magnet according to claim 1, wherein the obtained RTB -based sintered magnet satisfies H cJ ≧ 1500 kA / m and H k ≧ 1400 kA / m. Method.
The RTB according to any one of claims 1 to 3, wherein Dy and Tb in R are 0% by mass or more and 0.5% by mass or less of the entire RTB-based sintered magnet. Manufacturing method of sintered magnet.