JPH065410A - Rare earth element-fe-b anisotropic permanent magnet having excellent thermal stability - Google Patents

Abstract

PURPOSE:To obtain a rare earth-Fe-B permanent magnet having excellent thermal stability in addition to compatible two factors of thin wall and yet high performances. CONSTITUTION:The anisotropic permanent magnet meets the requirements for the chemical compositions in the items (A)-(F) enumerated as follows to make the magnet anisotropic by hot plastic processing and heat-treating the columnar crystal structure in the mean particle diameter not exceeding 30mum. That is, (A) this permanent magnet contains 12-18 atomic % of exceeding two kinds of rare earth elements including Y. (B) At least 1-3 atomic % of Dy is contained in the rare earth elements. 4-6 atomic % of B is contained in said permanent magnet. 0.02-2 atomic % of Ag is contained in the same. O is restricted to the level not exceeding 0.004 atomic %. Residual part: Fe and indispensable impurities.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare earth element-Fe-B type anisotropy permanent magnet, and in particular, it has excellent heat stability and high performance despite its thin wall, and has optimum characteristics for automobiles, for example. The present invention relates to a rare earth element-Fe-B-based anisotropy-permanent magnet that exhibits the above-mentioned effect.

[0002]

2. Description of the Related Art Magnetic materials are important electric and electronic materials used in a wide range of fields from permanent magnets to various electric products for general household use to peripheral end devices of large computers. Recently, downsizing of motors,
Higher performance has been promoted and thinner permanent magnets
High performance is required.

On the other hand, also in the automobile field, exhaust gas regulations,
In order to meet social demands such as reduction of fuel consumption, further miniaturization and higher performance of automobile parts are demanded, and as a part thereof, realization of high performance magnets for automobiles is strongly desired. However, unlike other general household electric appliances and computers, automobile parts are forced to be used in a high temperature and humid environment, and how to maintain high performance in such an environment is a permanent magnet for automobiles. It becomes an important point whether or not the characteristics of can be satisfied.

In recent years, rare earth magnets have been attracting attention as a third permanent magnet after ferrite magnets and alnico magnets. These rare earth magnets are expected to exhibit excellent magnetic properties that can contribute to miniaturization and higher precision of electric products and precision instruments, and are making active progress in both physical property research and production technology. Of these, especially expected in recent years is a rare earth element-transition element-B system such as Nd-F.
It is a permanent magnet such as e-B or Pr-Fe-B. The permanent magnet composition of the present invention contains a rare earth element-Fe-B as a basic component,
Among the rare earth elements, Pr and Dy are contained as essential components, and Ag is contained as a fourth component as an essential component. The evaluation thereof will be described later in detail, but in the following description, for the sake of convenience, the rare earth elements will be described. -Fe-B system (hereinafter sometimes abbreviated as R-Fe-B system magnet) 3
The original magnet will be taken up as a representative example.

By the way, initially, the following two methods were studied as the method for producing the R-Fe-B magnet. The first method is, for example, a sintering method based on powder metallurgy as disclosed in Japanese Patent Laid-Open No. 59-46008, but it requires powdering of the alloy prior to the sintering step, and it becomes powdery. Are more susceptible to oxidation, the oxygen introduced during sintering has a negative effect on the magnetic performance, and the magnetic performance deteriorates due to the inclusion of carbon based on the molding aid added during sintering. The former green body (green body) has low strength and has some drawbacks such as poor handleability,
The properties expected of R-Fe-B magnets have not been fully exhibited.

The second method is a method of forming a quenched thin piece and then forming a bonded magnet by using a thermoplastic resin or the like, which is not accompanied by the above-mentioned drawbacks but is low in productivity and isotropic in principle. Therefore, the maximum energy product [hereinafter sometimes referred to as (BH) _max ], which is the product of the residual magnetic flux density (Br) and the coercive force (iHc), is low, and the squareness is not good, which is a drawback. . Therefore, as a means for positively anisotropy, it has been considered to subject the quenched thin piece to a two-step hot press treatment (mechanical orientation treatment) (for example, JP-A-59-211549 and JP-A-60-100402). etc). However, this is not a practical method considering the necessity of mass production because the productivity will be lower.

Therefore, as a third method, for example, Japanese Patent Laid-Open No. 62-62
-276803, the cast alloy is hot-rolled to make the crystal grains finer and increase the coercive force, and the crystal axes are aligned in a specific direction to achieve magnetic anisotropy. The means to achieve this was developed. However, since there is no constraint from both sides in the plate width direction in the normal rolling method, the central portion of the rolled ingot is spread in the plate width direction, but sufficient density cannot be obtained at the plate width end side, and The orientation of the crystal axis becomes incomplete. Therefore, even if this method is adopted, magnetic anisotropy cannot be immediately obtained in the entire width direction of the plate. Moreover, if an attempt is made to form a desired axial orientation in the entire strip width under the normal hot rolling conditions as described above,
There is also a problem that the alloy composition of the rare earth magnet is greatly limited because a material having a workability capable of coping with this has to be carried out because of a considerable amount of strong working.

Therefore, as a method of solving the drawbacks of the third method, the present inventors encapsulated the alloy ingot in a metal capsule and applied hot plasticity to the metal capsule while applying a constraint from the width direction. A series of methods of working (rolling, casting) and, if necessary, heat-treating after hot working have been proposed and previously filed (JP-A-2-250918-23). The present inventors have previously filed an application for an R-Fe-B based magnet having both properties of being thin and having high performance and having magnetic characteristics higher than those of a sintered magnet (Japanese Patent Application No. 3-81876). ). With the development of these technologies, it has become possible to obtain an anisotropy permanent magnet having excellent magnetic characteristics relatively easily without being restricted from the viewpoint of the material due to processing reasons.

[0009]

As described above, the products that are required to be miniaturized and have high performance as automobile parts are
It is necessary for the permanent magnets used to satisfy both characteristics of thinning and high performance. However, generally, the thinner the magnet, the lower the performance tends to be.
In particular, the magnetic flux tends to decrease as the wall thickness decreases, and the rate of decrease in magnetic force increases as the operating temperature rises. Therefore, how to achieve improvement in initial characteristics and decrease in reduction rate is a permanent magnet for automobile parts. Will be an important point in.

For example, a thin permanent magnet having a thickness of 1 mm or less can be manufactured by a bonded magnet, but it is difficult in terms of magnetic characteristics as described above and cannot be used when high performance is required. On the other hand, in the sintering method, it is difficult to sinter as thin as possible. For example, if a thin magnet with a thickness of 3 mm or less is to be obtained,
Although it is cut out from a large block, the performance is deteriorated due to the thinning, and the desired magnetic characteristics cannot be obtained when the thickness is about 1 mm as shown in Examples below. Regarding thin-walled anisotropic magnets, a method of mechanically polishing the magnets to reduce the wall thickness has been proposed, for example, as disclosed in JP-A-62-192566. However, productivity decline is unavoidable.

The present invention has been made in order to solve the above technical problems, and its purpose is to provide a rare earth element which has both properties of being thin and having high performance, and which is excellent in thermal stability. It is to provide an Fe-B magnet.

[0012]

Means for Solving the Problems The present invention capable of achieving the above-mentioned object is to satisfy the following chemical compositions (A) to (F) and to form a columnar crystal structure having an average grain size of 30 μm or less by hot plasticity. A rare earth element-Fe-B magnet having an average particle diameter of 30 μm or less, which is annealed by processing and heat treatment.

(A) It contains 12 to 18 atomic% of two or more kinds of rare earth elements including Y (however, 50% by weight or more thereof is Pr). (B) Of rare earth elements, at least 1 to 3 atomic% Dy. (C) B is contained at 4 to 6 atomic%. (D) 0.2 to 2 atomic% of Ag is contained. (E) O is suppressed to 0.004 atomic% or less. (F) Balance: Fe and inevitable impurities

[0014]

The present inventors have studied from various perspectives on the realization of a thin permanent magnet having high performance and excellent thermal stability, based on the technology developed so far. As a result, first, in order to improve the thermal stability of the R-Fe-B system magnet, Dy and Tb
It was found that the addition of heavy rare earth elements such as
However, it was also found that the addition of these heavy rare earth elements causes the grain size of the casting to become coarser, as shown in FIG. 1, and that a sufficient high coercive force cannot be obtained. Therefore, the inventors of the present invention have made extensive studies on miniaturization by an additive element, and if Ag is added as the fourth element with respect to the R—Fe—B system, miniaturization of crystal grains of the magnet alloy is achieved. I found that. In addition, by performing heat treatment after hot composition processing, R ₂ Fe ₁₄ B
It was found that the isolation of phases can be promoted, the coercive force can be improved, and as shown in Table 1, the temperature coefficient of coercive force (room temperature to 200 ° C.) is also significantly improved.

[0015]

[Table 1]

Next, the alloy composition of the R-Fe-B magnet of the present invention will be described. First, as the rare earth element, a lanthanoid rare earth element containing Y has been widely used so far, but in the present invention, two or more kinds of these containing at least 50 wt% or more of Pr and 1 to 3 atom% of Dy are used. It was concluded that it is useful to construct with rare earth elements. The type of rare earth element used in combination with Pr and Dy is not particularly limited, but among them, Nd, Ce, La, Tb,
It is particularly preferable to use Ho, Y or the like. Among the rare earth elements used in the magnet of the present invention, 50% by weight or more is defined as Pr because Pr exhibits the most excellent magnetic characteristics.

The R-Fe-B system magnet of the present invention contains 1 to 3 atomic% of Dy as a rare earth element.
If it is less than atomic%, the thermal stability effect cannot be obtained, and if it exceeds 3 atomic%, the particle size becomes coarse and the holding power is lowered.
As for the elements other than Pr and Dy, one or a combination of two or more of the above-mentioned rare earth elements other than Pr and Dy may be used, but practically the Pr-Nd alloy is most advantageously used. The rare earth element in the magnet of the present invention may contain a small amount of a rare earth element other than the above, but it should be suppressed to 1% by weight or less.

In the R-Fe-B system magnet of the present invention, R
Is too small, the main phase R ₂ -Fe ₁₄ -B (atomic ratio, for example Pr ₂ Fe
₁₄ B) cannot be formed, a sufficient liquid phase amount (main phase amount) necessary for anisotropy during hot working cannot be obtained, and high performance of the magnet cannot be achieved. From this point of view, the ratio of the rare earth element needs to be 12 atomic% or more. On the other hand, when the upper limit exceeds 18 atom%, R is a non-magnetic phase.
Excessive rich phase is caused, which appears as a decrease in magnetic flux density, and good magnetic characteristics cannot be exhibited.

B must be 4 to 6 atomic%, and if it is less than 4 atomic%, the volume fraction of the main phase will be insufficient and the magnetic flux density will be lowered. On the other hand, regarding the upper limit, R ₂ Fe that does not have magnetic properties
It is required to be 6 atomic% or less from the viewpoint of preventing occurrence decrease in iHc due to the ₄ B ₄ phase.

As described above, Ag is used for achieving the miniaturization of the columnar structure as well as the suppression of the generation of the surface deterioration layer due to the grinding process, thereby exhibiting high performance even if it is thin. is there. In order to achieve the above effect, the addition amount must be 0.2 at% or more, but if it is too much, the non-magnetic grain boundary phase increases and the characteristics are degraded, so it should be 2 at% or less. Is.

In the magnet of the present invention, in addition to the above-mentioned essential components, the balance basically consists of Fe and inevitable impurities. Fe is an essential element for forming the magnetic phase, but a part (for example, about 20% by weight) thereof may be replaced with Co. It is unavoidable that a small amount of O is mixed in each step of the magnet of the present invention, but the O content should be suppressed to 0.004 atomic% or less. That is, O exists in the magnet as a rare earth oxide such as R ₂ O ₃ or RO, and this oxide is nonmagnetic and becomes a magnetic impurity, which hinders reduction of coercive force and isolation of the main phase. Therefore, it is necessary to suppress the O content as much as possible.
From this viewpoint, O must be 0.004 atomic% or less.

In the magnet of the present invention, the average crystal grain size of the columnar crystal structure and the crystal structure after anisotropy are both regulated to 30 μm or less. The reason is as follows. Is. First, as shown in FIG. 2, in order to obtain characteristics equal to or higher than those of the sintered magnet, it is necessary to set the average grain size of the columnar crystal structure after casting to 30 μm or less. When hot plastic working and heat treatment are applied to the ingot, the coercive force is improved, but when excessive heat treatment is performed, the crystal grains become coarse and the coercive force is rather lowered. The average grain size of the crystals of 3 must be 30 μm or less.

The present invention will be described in more detail with reference to the following examples, but the following examples are not intended to limit the present invention, and any change in design can be made without departing from the spirit of the preceding and following claims. It is included in the technical scope.

[0024]

EXAMPLES Alloy ingots (Nos. 1 to 14) having the compositions shown in Table 2 were manufactured by high frequency melting. At this time, the starting raw material is electrolytic iron having a purity of 99.9% by weight as Fe, B is a ferroboron alloy, rare earth elements and other additive elements have a purity of
99.9% by weight of each was used. Then, it was cast by a copper mold to form fine columnar crystals having an average particle size of 30 μm or less.

[0025]

[Table 2]

Next, the alloy ingot was cut and enclosed in an iron capsule, and the total rolling reduction was 76 at 950 ° C. while restraining it from the width direction.
% Hot rolling was performed. Subsequently, heat treatment was performed at 1000 ° C for 6 hours (first step) and 480 ° C for 2 hours (second step), and the magnetic properties and average grain size of the obtained magnet alloy and coercive force temperature coefficient (room temperature to 200 ° C) )investigated. The results are shown in Table 3, and it can be seen that the crystals to which Dy and Ag are added at the same time can make the crystals finer and the iHc and the temperature coefficient of coercive force are improved.

[0027]

[Table 3]

Next, the composition (atomic ratio) of Pr ₁₃ Dy ₂ Fe ₇₇ B ₇ Ag ₁
And 10KOe of alloy powder having an average particle size of 3 μm
99.999% after pressure molding at 1.5ton / cm ^{2 in} magnetic field
Sintered in pure Ar gas (250 Torr) for 10 hours at 1070 ℃,
Further, an aging heat treatment was performed at 530 ° C. for 1 hour to obtain a sintered magnet. Using the obtained sintered magnet and the magnet of No. 13 (invention product) shown in Table 2, the thickness was 3, 1, 0.5, 0.3 (m
m) was ground and the magnetic properties of each were investigated.
The results are shown in Table 4, and it can be seen that the present invention has a small degree of processing deterioration.

[0029]

[Table 4]

[0030]

As described above, according to the present invention, by adding Dy and Ag in combination to the rare earth element-Fe-B system, it is possible to achieve the refinement of the crystal grains, and even if the thickness is 3 μm or less, it is satisfactory. A permanent magnet having excellent magnetic properties and excellent thermal stability was obtained. Further, the permanent magnet according to the present invention is optimal as a permanent magnet for automobile parts because of its characteristics.

[Brief description of drawings]

FIG. 1 is a graph showing the influence of the amount of Dy added on the ingot particle size and magnetic properties.

FIG. 2 is a graph showing the relationship between ingot grain size and magnetic characteristics.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsukasa Yuri 1-5-5 Takatsukadai, Nishi-ku, Kobe City Kobe Steel Research Institute, Kobe Steel Research Institute

Claims (2)

[Claims] 1. A columnar crystal structure satisfying the following chemical compositions (A) to (F) and having an average grain size of 30 μm or less is anisotropy by hot plastic working and heat treatment: 30 μm or less A rare earth element-Fe-B system anisotropy permanent magnet having excellent thermal stability, characterized by having an average particle size of (A) Two or more kinds of rare earth elements including Y (however, 50% by weight)
The above is Pr) in an amount of 12 to 18 atomic%. (B) Of the rare earth elements, at least 1 to 3 atomic% is Dy
Is. (C) B is contained at 4 to 6 atomic%. (D) 0.2 to 2 atomic% of Ag is contained. (E) O is suppressed to 0.004 atomic% or less. (F) Balance: Fe and inevitable impurities 2. The thickness in the anisotropy direction is 0.5 to 3 mm, the maximum energy product is 25 MGOe or more, the coercive force is 20 KOe or more, and the coercive force temperature coefficient from room temperature to 200 ° C.
The anisotropic permanent magnet according to claim 1, which has a content of -0.5% / ° C or more.