JP2857824B2 - Rare earth-iron permanent magnet manufacturing method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a rare earth-iron permanent magnet. 2. Description of the Related Art Conventionally, the following three methods have been used to manufacture R-Fe-B magnets.
The exact method has been reported. (1) Sintering method based on powder metallurgy (Reference Document 1) (2) A quenched thin strip manufacturing apparatus used for manufacturing an amorphous alloy, quenched flakes having a thickness of about 30 μm, and Making a magnet by a resin bonding method (Reference 2) (3) A method in which the same flake used in the method of (2) is subjected to a mechanical orientation treatment by a two-stage hot press method (Reference 2). M.Sagawa, S.Fujimura, N.Togawa, H.Yama
moto and Y.Matsuura; J.Appl.Phys.Vol.55 (6), 15 Maro
h 1984, P2083 Reference 2. RWLee; Appl.Phys.Lett.Vol.46 (8), 15
April 1985, P790. The above prior art will be described with reference to the literature.
First, in the sintering method (1), an alloy ingot is produced by melting and casting, and is then pulverized into magnet powder having a particle size of about 3 μm. The magnet powder is kneaded with a binder serving as a molding aid, and is press-molded in a magnetic field to complete a compact. The compact is sintered in argon at a temperature of around 1100 ° C. for 1 hour and then quenched to room temperature. After sintering, if heat treatment is performed at a temperature of about 600 ° C., the coercive force is further improved. [0005] (2) First, a quenched ribbon of an R-Fe-B alloy is produced at an optimum rotation speed of a quenched ribbon manufacturing apparatus. The obtained ribbon has a ribbon shape with a thickness of 30 μm, and polycrystals having a diameter of 1000 mm or less are gathered. The ribbon is brittle and easily broken, and since the crystal grains are distributed isotropically, it is magnetically isotropic. If the ribbon is adjusted to an appropriate particle size, kneaded with a resin and press-molded, it is possible to achieve a filling of about 85% by volume at a pressure of about 7 ton / cm ² . [0006] The manufacturing method of (3) is a method in which a quenched ribbon or a strip of ribbon is preliminarily heated at about 700 ° C. in a vacuum or an inert atmosphere at a temperature of about 700 ° C. Put in. Uniaxial pressure is applied when the ribbon reaches the desired temperature. Although temperature and time are not specified, T = 725 ± 25
C. and a pressure of about P to 1.4 ton / cm ² are suitable. At this stage, the magnets are generally isotropic, although slightly oriented in the pressing direction. The next hot press is performed in a large area mold. Most commonly at 700 ° C
Press for 0.7 seconds at 0.7 ton. Then, the sample becomes half the initial thickness, the easy axis of magnetization is oriented parallel to the pressing direction, and the alloy becomes anisotropic. These steps are a two-stage hot-pressing procedure
This method is dense and anisotropic by this method
R-Fe-B magnets can be manufactured. In addition, the crystal grain of the ribbon ribbon made by the first melt spinning method is set to be smaller than the grain size when it shows the maximum coercive force, and the crystal grain becomes coarse later during hot pressing. Keep the optimum particle size. [0007] In the prior art described above,
Although R-Fe-B magnets can be manufactured for the time being, manufacturing methods using these technologies have the following disadvantages. In the sintering method (1), it is essential to make the alloy into a powder.However, since the R-Fe-B alloy is very active against oxygen, oxidization becomes excessive when powdered, resulting in sintering. The oxygen concentration in the body will inevitably increase. Also, when molding the powder, a molding aid such as zinc stearate must be used, which is removed in advance in the sintering process. Will remain. This carbon significantly reduces the magnetic performance of R-Fe-B. A molded body after the addition of a molding aid and press molding is called a green body. It is very brittle and difficult to handle. Therefore, it is a great disadvantage that it takes a considerable amount of time to neatly arrange them in the sintering furnace.
Due to these drawbacks, generally speaking, the production of R-Fe-B based sintered magnets requires not only expensive equipment but also poor production efficiency and high magnet production costs. I will. Therefore, it cannot be said that this is a manufacturing method that can sufficiently bring out the low raw material cost of the R-Fe-B-based magnet. The production methods (2) and (3) use a vacuum melt spinning apparatus. This device is currently very productive and expensive. In (2), the product is low energy product because it is isotropic in principle, and the squareness of the hysteresis loop is not good, which is disadvantageous in terms of temperature characteristics and use. Method (3) is a unique method that uses hot pressing in two stages, but it is unavoidable that it will be very inefficient when considering mass production. The method for producing an R-Fe-B magnet according to the present invention solves these disadvantages, and an object thereof is to obtain a rare earth-iron permanent magnet of high performance and low cost. In the present invention, R (where R is at least one of the rare earth elements including Y): 8 to 30 atomic%, boron (B): 2 to 8 atomic%, Co: 50 atomic% or less, A
1: A first step of melting and casting an iron-based alloy containing 15 atomic% or less, and hot-working the cast ingot obtained in the first step by pressing in one direction at a temperature of 500 ° C. or more. A second step of refining crystal grains, orienting the easy axis of magnetization in a specific direction, and magnetically making it anisotropic. A method for producing a rare-earth-iron-based permanent magnet, wherein the product (BH) max is 4.1 MGOe or more. It is preferable that the method further includes a step of performing a heat treatment at a temperature of 250 ° C. or more before or after the hot working. As described above, the sintering method and the quenching method, which are the existing methods for producing rare earth-iron permanent magnets, have major drawbacks such as difficulty in powder control by pulverization and poor productivity. In order to remedy these drawbacks, the present inventors have started research on magnetization in a bulk state.
In the composition region described above (the composition is limited to a lower boron region than in the above document), it has been found that sufficient coercive force can be obtained only by performing heat treatment in a cast state because the crystal grains are refined. Further, hot working is easy, and the C axis (easy axis of magnetization) of the crystal grains is oriented in the rolling direction by the hot working , and can be made anisotropic without using a magnetic field.
Magnetic energy product obtained found Rukoto. According to this method, the anisotropy by hot working is not two steps as in the quenching method shown in Reference Document 2, but only one step, and the coercive force after working is greatly increased due to finer grains. It has a completely different phenomenon . Further, since it is not necessary to pulverize the cast ingot, it is not necessary to perform strict atmosphere control as in the sintering method, and the equipment cost is greatly reduced. For research on magnetizing in a bulk state,
There is reference 3, Hiroaki Miho (The Japan Institute of Metals, Autumn 1985 lecture, lecture number (544)).
_16.2 Fe _50.7 Co _22.6 V _1.3 B _{9.2 This} is a small sample sucked up by dissolving in the air by blowing argon gas with a composition of _9.2. . Usually the casting will be a main phase Nd ₂ Fe ₁₄ B phase is coarsened in this composition, the anisotropy by hot working but can, as a permanent magnet
That sufficient coercive force is difficult to obtain We have experimentally confirmed. To obtain a sufficient coercive force in normal casting, it is essential that claim 1 is a low B composition, such as shown in the present invention. [0013] The composition of the conventional R-Fe-B magnets is, R ₁₅ Fe ₇₇ B _8, as represented by reference 1 has been optimized. This composition has shifted to the side richer in R and B as compared with the composition R _11.7 Fe _82.4 B _{5.9 in} which the main phase R ₂ Fe ₁₄ B compound is made in atomic percentage. This is explained from the fact that in order to obtain a coercive force, not only a main phase but also a non-magnetic phase such as an Rrich phase and a Brich phase are required. However, in the composition according to the present invention, the peak value of the coercive force exists at the point where the amount of B shifts to the smaller side. In this composition range, the coercive force is drastically reduced in the case of the sintering method, so that it has not been a problem so far. However, in conventional casting methods, only the composition range of the first aspect of the present invention, a high coercive force is obtained, sufficient coercive force on the side rich the mainstream composition B of the sintered process conversely can not be obtained. These points can be considered as follows. First, whether using the sintering method or the casting method, the coercive force mechanism itself follows the nucleation model. This can be seen from the fact that both initial magnetization curves show a steep rise like SmCo ₅ . The coercive force of this type of magnet is basically based on a single domain model. That is, in this case,
R ₂ Fe ₁₄ B compound having large crystal magnetic anisotropy is
If it is too large, the grains will have domain walls in the grains, so that the reversal of magnetization easily occurs due to the movement of the domain walls, and the coercive force is small. On the other hand, when the number of particles decreases and becomes smaller than a certain size, the particles have no domain wall and the reversal of magnetization proceeds only by rotation, so that the coercive force increases. That is, in order to obtain an appropriate coercive force, the R ₂ Fe ₁₄ B phase needs to have an appropriate particle size. The particle size is 10 μm
The front and rear are appropriate, and in the case of the sintering type, the particle size can be adjusted by adjusting the powder particle size before sintering. However, in the case of the casting method, the size of the R ₂ Fe ₁₄ B compound is determined at the stage of solidification from melting, so it is necessary to pay attention to the composition and solidification process. In particular, the meaning of the composition is significant. When B exceeds 8 atomic% , the R ₂ Fe ₁₄
The size of the B phase could easily exceeded the 100 [mu] m, it is difficult to obtain a coercive force in the cast state without using a quenching apparatus, such as a reference 2. On the other hand, in the low boron region as described in the first aspect, the particle size can be easily reduced by devising the mold and casting temperature. However, in any case, if the hot working is performed, the main phase R ₂ Fe ₁₄ B phase becomes finer, so that the coercive force increases as compared with before the working. From a different point of view, the region where the coercive force can be obtained in the casting state can be said to be a composition richer in Fe than R ₂ Fe ₁₄ B. In the solidification stage, Fe appears as primary crystals first, and then R ₂ Fe
₁₄ B phase appears. At this time, since the cooling speed is much faster than the equilibrium reaction, R ₂ Fe ₁₄
It solidifies in such a way that the B phase surrounds it. Low in this composition range
Since it is a B region, the Brich phase as seen in a magnet of the typical composition R ₁₅ Fe ₇₇ B ₈ of the sintered type can be almost neglected quantitatively. Heat treatment to diffuse the primary crystal Fe, is related to the Turkey allowed to reach equilibrium, the coercive force is highly dependent on the diffusion of the Fe phase. The means for hot working is not particularly limited.
However, rolling is particularly preferred. This is because the optimal method for improving the processing productivity, which has become a problem in Reference 3, is rolling. Rare earth-iron permanent magnet produced as described above
Is to refine and refine the crystal grains resulting from the manufacturing process.
Example 1 to be described later,
As shown by 2, high magnetic properties, especially (BH) max of 4.1
It has a high magnetic energy product of MGOe or more. Hereinafter, the reasons for limiting the composition of the permanent magnet according to the present invention will be described. As rare earths, Y, La, Ce, P
r, Nd, Sm, Eu, Gd, Tb, Dy, Ho , E
r , Tm, Yb, and Lu are listed as candidates, and one or more of these are used in combination. The highest magnetic performance is obtained with Pr. Therefore, in practice, P
An r, Pr-Nd alloy, Ce-Pr-Nd alloy, or the like is used. Also, a small amount of additional element, for example, heavy rare earth element Dy,
Tb and the like, Al, Mo, Si and the like are effective in improving the coercive force. Main phase of R-Fe-B magnet is R ₂ Fe ₁₄ B. Therefore, when R is less than 8 atomic%, the above compound is no longer formed and a cubic structure having the same structure as that of α-iron is obtained, so that high magnetic properties cannot be obtained. On the other hand, if R exceeds 25 atomic%, the non-magnetic R rich phase increases and the magnetic properties are remarkably deteriorated. B is an essential element for forming the R ₂ Fe ₁₄ B phase, and if it is less than 2 atomic%, a high coercive force cannot be expected because it becomes a rhombohedral R—Fe system. On the other hand, if the content exceeds 8 atomic%, the nonmagnetic phase rich in B increases, and the crystal grains become coarse, making the rolling process difficult. Co is an effective element for increasing the Curie point of the present magnet, and basically replaces the Fe site.
Although this compound forms R ₂ Co ₁₄ B , this compound has a small crystal anisotropic magnetic field, and as its amount increases, the coercive force of the magnet as a whole decreases. Therefore, in order to provide a coercive force of 1 k0e or more which can be considered as a permanent magnet, the content is preferably within 50 atomic%. Al is originally an element that is always contained in an alloy when it is melted using an alumina crucible. However, in the present application, the upper limit is particularly set in consideration of the case where it is positively added. Reference 4 Zhang Maocai et al. Proceeding softh
e 8th Intenational Work-shop on Rare Earth Magnets
1985, P541 has the effect of increasing the coercive force. Although this document shows the effect on sintered magnets, the effect exists similarly in cast magnets. However
Since Al is a non-magnetic element, increasing the amount of addition lowers the residual magnetic flux density, and exceeding 15 atomic% results in residual magnetic flux density equal to or lower than that of hard ferrite, so it cannot fulfill its purpose as a rare earth magnet. . Therefore, the addition amount of Al is 15 atoms
% Or less is good. Embodiment 1 FIG. 1 shows an example of a process chart of the manufacturing method according to the present invention. First, an alloy having a desired composition is melted in an induction furnace and cast into a casting mold. Next, various types of hot working are performed to impart anisotropy to the magnet. In this embodiment, not a general casting method but a special dynamic casting method, a liquid dynamic compation method having a large crystal grain fine effect by quenching (references)
5, TSChin et al., J.Appl.Phys.59 (4), 15 February 1986, P
1297) was used. As hot working, any one of (1) extrusion (FIG. 2), (2) rolling (FIG. 3), and (3) stamping (FIG. 4) was performed at 1000 ° C. As for the extrusion, a square mold extrusion was devised so that a force was applied uniaxially. Regarding the strain rate of the rolling process and the stamp, the speed of the stamp was adjusted so as to minimize the strain rate. In either method, the axis of easy magnetization of the crystal is oriented so as to be parallel to the direction in which the alloy is pressed. An alloy having the composition shown in the following table was melted, and a magnet was manufactured by the method shown in FIG. However, the hot working method does not
Various processing methods were used as well as engineering. The hot working method used is also shown in the table. The annealing treatment after hot working was carried out base and 1000 ° C. × 24 hours to. [Table 1] Next, the results are shown. [Table 2] From Table 2, it can be seen that the residual magnetic flux density increased and became magnetically anisotropic in all the hot working methods of extrusion, rolling and stamping. In addition, those that have been subjected to hot rolling,
It has better surface properties than others and is said to be a particularly excellent method.
I can. Embodiment 2 Here, an embodiment using a normal casting method will be introduced. First, the composition shown in Table 3 is melted in an induction furnace and cast into an iron mold.
Columnar crystals are formed. After rolling at a processing rate of about 70% (the other conditions were the same as in Example 1), annealing was performed at 1000 ° C. for 24 hours to magnetically cure the ingot. At this time, the average particle size after annealing is about 1
It was 5 μm. [Table 3] [Table 4] According to Table 4, (BH) max,
It can be seen that iHc also shows a significant increase. This is because the more crystal grains in the processing oriented in a specific direction, squareness of the B-H curve is improved by a large margin. The quenching method of the reference 2, tend to rather iHc is reduced by the processing, therefore, has become a major feature of the (BH) max, greatly increase the iHc present invention. As described above, in particular, the cast ingot is pressed in one direction at a temperature of 500 ° C. or more and hot-worked to refine the crystal grains and specify its easy axis of magnetization. , And the magnetically anisotropically oriented, the easy axis of the crystal grains of the cast ingot is oriented in the pressed direction, so that a permanent magnet excellent in magnetic properties can be manufactured. Become like In addition, since the hot working is completed in one stage, an excellent effect that it is suitable for mass production is exhibited.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a manufacturing process diagram of an R-Fe-B based magnet of the present invention. FIG. 2 is a view showing an orientation treatment of a magnet alloy by hot extrusion. FIG. 3 is a view showing an orientation treatment of a magnet alloy by hot rolling. FIG. 4 is a view showing an orientation treatment of a magnet alloy by hot stamping. [Description of Signs] 1. Hydraulic press 2. Die (mold) 3. Magnetic alloy 4. Arrow 5 indicating pressure. Arrow 6 indicating easy magnetization direction of magnet alloy. Roll 7. Arrow 8 indicating the direction of rotation Arrow 9 indicating the traveling direction of the magnet alloy Substrate 10 Arrow 11 indicating the vertical movement of the stamp Arrow 12 indicating the moving direction of the substrate Stamp

Claims (1)

(57) [Claims] R (where R is at least one of the rare earth elements including Y): 8 to 30 atomic%, boron (B): 2 to 8
A first step of melting and casting an iron-based alloy containing at least 10 atomic%, 50 atomic% of Co, and 15 atomic% or less of A: at a temperature of 500 ° C. or more at a temperature of 500 ° C. or more. Pressurizing in one direction and performing hot working to refine crystal grains, orient the easy axis of the magnetization in a specific direction, and magnetically anisotropically comprise a second step; The process is performed sequentially, and the magnetic energy product (BH) of the magnet
rare earth characterized by max not less than 4.1 MGOe
Manufacturing method of iron-based permanent magnet. 2. The method for producing a rare earth-iron permanent magnet according to claim 1, further comprising a step of performing a heat treatment at a temperature of 250 ° C. or more before or after the hot working.