JP2579787B2 - Manufacturing method of permanent magnet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a permanent magnet containing a rare earth element, a transition metal, and boron as basic components, and a method for producing the same.

[Prior Art] Permanent magnets are one of important electric and electronic materials used in a wide range of fields from various home electric appliances to peripheral peripheral devices of large computers. With the recent demand for miniaturization and higher efficiency of electric products, permanent magnets are also required to have higher performance. Typical permanent magnets currently used are alnico, hard ferrite and rare earth-transition metal based magnets. In particular, rare earth (hereinafter,
Abbreviated as R. R-Co-based permanent magnets and R-Fe-B-based permanent magnets, which are transition metal (hereinafter abbreviated as TM) -based magnets, have high magnetic performance. I have.

Conventionally, as a method for producing these R-TM-B-based permanent magnets, there is a method disclosed in the following literature.

(1) A method based on sintering based on powder metallurgy. (References 1 and 2) (2) A quenched thin body device used to manufacture an amorphous alloy, which is made by quenching a thin piece having a thickness of about 30 μm and then using the resin bonding method to form a magnet by a melt spinning method. Resin bonding method using quenched flakes. (References 3 and 4) (3) A method in which the quenched flakes used in the method (2) are subjected to mechanical orientation treatment by a two-stage hot press. (References 4 and 5) Here, Reference 1; Japanese Unexamined Patent Publication No. 59-46008 Reference 2; M. Sagawa, S. Fujimura, N. Togawa, H. Yamamoto and
Y. Matuura; J. Appl. Phys. Vol. 55 (6) 15 March 1984 p2
083 Literature 3: JP-A-59-211549 Literature 4: RWLee; Appl. Phys. Lett. Vol. 46 (8) 15 April
1985 p790 Literature 5; JP-A-60-100402 Next, the details of the above-mentioned conventional method will be described.

In the sintering method of (1), an alloy ingot is prepared by melting and casting, and pulverized to obtain a magnet having an appropriate particle size (several μm). The magnet powder is kneaded with a molding aid binder, and is press-molded in a magnetic field to form a compact. This compact is sintered in argon at a temperature of around 1100 ° C. for about 1 hour and quenched to room temperature. Thereafter, heat treatment is performed at a temperature of about 600 ° C. to improve the coercive force.

In the resin bonding method using the quenched flakes by the melt spinning method (2), first, a quenched ribbon of the R-TM-B alloy is manufactured at an optimum rotation speed of the quenched ribbon manufacturing apparatus. The obtained ribbon having a thickness of about 30 μm is a collection of crystals having a diameter of 1000 ° or less, and is brittle and easily broken, and the crystal grains are distributed isotropically. For this reason, no magnetic anisotropy is obtained and the magnetic layer is isotropic. The flakes are pulverized to an appropriate size, kneaded with a resin, and pressed to obtain a bonded magnet. At this time, about 85% by volume can be filled with a pressure of about 7 t / cm ² .

In the method (3), the quenched ribbon or strip obtained in (2) is placed in graphite or another heat-resistant press mold preheated at about 700 ° C. in a vacuum or an inert atmosphere. Uniaxial pressure is applied when the flakes reach the desired temperature. Although the temperature and pressure are not specified, 725 ± 25 ° C. and about 1.4 t / cm ² are suitable as conditions for obtaining sufficient plasticity. At this stage, the axis of easy magnetization of the magnet is oriented slightly in the pressing direction, but is isotropic as a whole. The second hot pressing is performed in a mold having a large area. Generally, pressing is performed at 700 ° C. and 0.7 t / cm ² for several seconds. Then, the magnet becomes almost the first half, the easy axis of magnetization is oriented parallel to the pressing direction, and the magnet becomes anisotropic. By this method, an R-TM-B permanent magnet having anisotropy can be obtained.

The grain size of the quenched ribbon produced by the first melt spinning method should be smaller than the grain size when it shows the maximum coercive force, and the grain size will increase during subsequent hot pressing. To obtain the optimum particle size.

However, in this method, at a high temperature, for example, 800 ° C. or higher, the crystal grains are remarkably coarsened, whereby the coercive force is extremely reduced, and it is not a practical permanent magnet.

[Problems to be Solved by the Invention] By using the above-mentioned conventional technology, R-TM-B
Although system-based permanent magnets can be manufactured, these manufacturing methods have the following disadvantages.

In the sintering method (1), it is essential to turn the alloy into a powder. However, the R-TM-B alloy is very active against oxygen, so that the surface area is reduced when the powder is processed. As a result, the oxidation becomes severe and the oxygen concentration in the sintered body is inevitably increased. Also, when molding the powder, a molding aid such as, for example, zinc stearate must be used. Although this is removed in advance in the sintering process, a small percentage remains in the magnet in the form of carbon.
This carbon is undesirable because it lowers the magnetic performance of the R-TM-B magnet.

The molded body after the addition of the 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 arrange them neatly in the sintering furnace.

Also, in order to obtain an anisotropic magnet, press molding must be performed in a magnetic field, and a large device such as a magnetic field power supply and a coil is required.

Because of the above disadvantages, generally speaking, R-TM-B
Not only expensive equipment is required for the production of sintered magnets, but also the production efficiency deteriorates and the production cost of the magnets increases. Therefore, it cannot be said that the advantages of the relatively inexpensive R-TM-B magnet can be utilized.

Next, the methods (2) and (3), which use a vacuum melt spinning apparatus, which are currently very poor in productivity and expensive.

Since the method (2) is isotropic in principle, the energy product is low, and the squareness of the hysteresis loop is not good, so that it is disadvantageous in terms of temperature characteristics and use.

In the method (3), an anisotropic magnet can be obtained, but since hot pressing is used in two stages, it will not be denied that it will be extremely inefficient when actually considering mass production. Further, in this method, at high temperatures, for example, at 800 ° C. or higher, the crystal grains are extremely coarsened, whereby the coercive force is extremely reduced, and the magnet does not become a practical permanent magnet.

In addition, permanent magnets are used for motors, generators, chucking, etc., but considering these applications, permanent magnets are rarely used alone, and motors, generators,
In chucking, a yoke such as a soft magnetic material and a shaft of a paramagnetic material are always used together. However, in the prior art, a method has been adopted in which a magnet is manufactured as a single magnet and a yoke or a shaft is attached thereto. In this method, the magnet must be machined with high precision, which is a great limitation in the manufacturing process of the magnet. In particular, motors are often used in a ring shape, and the inner surface processing of this ring-shaped magnet is technically difficult and costly.

The present invention solves the above-mentioned drawbacks of the prior art, and aims at melting and casting a basic process, and by using both hot working and heat treatment, a high performance and low cost R- It is an object of the present invention to provide a method for producing a TM-B permanent magnet.

[Means for Solving the Problems] The present invention relates to a method for producing a permanent magnet containing a rare earth element (including Y), a transition metal, and boron as basic components.
At least a first step of melting and casting the alloy consisting of the basic components, and a state in which the cast ingot obtained in the first step is covered with a soft magnetic material or a material to be used by being joined to a magnet at 500 ° C. Hot working at the above temperature, forming the cast ingot into a desired magnet shape and magnetically anisotropic the second step, and a third step of performing a heat treatment at a temperature of 250 ° C. or more. A method for producing a permanent magnet, comprising:

Further, the present invention provides a method for producing a permanent magnet comprising a rare earth element (including Y), a transition metal and boron as basic components, wherein at least an alloy composed of the basic components is melted to form a soft magnetic material or a magnet. A first step of casting into a mold made of a material to be used for joining, and hot working the cast ingot obtained in the first step at a temperature of 500 ° C. or more together with the mold to obtain the cast ingot. And a third step of performing a heat treatment at a temperature of 250 ° C. or more at a temperature of 250 ° C. or more.

[Operation] As described above, the sintering method and the quenching method, which are the conventional methods of manufacturing the R-TM-B-based permanent magnets, each have difficulty in powder control by pulverization, poor productivity, and restrictions on magnet shape. It has many disadvantages.

In order to improve these disadvantages, the present inventors have focused on the study of magnetic hardening in a bulk state, and in the rare earth element and transition metal, and in the composition range of a magnet containing boron as a basic component,
It has been found that it has a sufficiently high coercive force only by performing a heat treatment after casting, and that it is easily oriented by performing hot working. Hereinafter, this point will be described.

Also magnet using the production method of the present invention, similarly to the magnet using a sintering method in the prior art (1), the initial magnetization curve shows a steep rise as SmCo _5. This indicates that the coercive force mechanism itself is a nucleation type. The coercive force mechanism of this type of magnet is basically described by a single domain model, and the coercive force of a magnet largely depends on its crystal grain size. That is, when the crystal grains of the R ₂ TM ₁₄ B compound phase having a large crystal magnetic anisotropy, which is the main phase of the R-TM-B based magnet, are too large, they have domain walls in the crystal grains, The reversal of magnetization easily occurs due to the movement of the domain wall, and the coercive force decreases. On the other hand, when a crystal grain becomes smaller than a certain critical radius, the crystal grain becomes a single magnetic domain particle having no domain wall, and the reversal of magnetization proceeds only by rotation. Since the rotation of the magnetization requires a larger energy than the movement of the domain wall, a large coercive force can be obtained. That is, it is the main phase in order to obtain a sufficiently large coercive force.
It is necessary to make the crystal grains of the R ₂ TM ₁₄ B compound phase appropriately large.

Although the critical radius is on the order of submicrons, the particle size in the sintering method is about 10 μm. This is because, in the case of the sintering method, the casting ingot goes through a process of once pulverizing, so that if a powder having a critical radius is to be obtained, the surface area increases significantly, and the concentration of oxygen remaining in the sintered body increases. In addition, a sintered body having a particle size close to the critical radius cannot be produced. Conversely, if it is a nucliation type magnet, the growth rate of coarse columnar crystals or equiaxed crystals can be suppressed by adjusting the cooling rate without going through the step of grinding the cast ingot, and the R ₂ TM ₁₄ B compound If the phase crystal grains can be refined, a sufficiently high coercive force can be obtained.

In the present invention, the following has been found by using both the composition and hot working.

1) A cast alloy having relatively fine crystal grains can be obtained by making the macrostructure into a columnar crystal.

2) This cast alloy has in-plane anisotropy.

3) The cast alloy is subjected to a heat treatment so that a sufficiently high coercive force is obtained in a bulk state, and an anisotropic magnet can be manufactured.

4) The degree of orientation is significantly increased by hot working the obtained ingot.

From the above points, it is not necessary to go through the above-mentioned steps such as pulverization and sintering, and it is free from productivity problems such as difficulty in powder management.

In the hot working of the R-TM-B permanent magnet, it is indispensable to perform it in a non-oxidizing atmosphere.
Industrially, hot working requires a coating material such as a sheath or a capsule. The magnet and yoke and shaft are integrated by hot working or using such a material for the mold together with the sheath and capsule as the material of the yoke and shaft used for the product. Can be manufactured. This eliminates the need for a step such as inner surface processing for joining with the yoke or the shaft, and significantly reduces steps such as cutting and polishing, which are indispensable in the prior art. In addition, by performing HIP or the like, the adhesion to the yoke is improved.

Hereinafter, a preferable composition range of the permanent magnet according to the present invention will be described.

As rare earth metals, Y, La, Ce, Pr, Nd, Sm, Eu,
Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu are listed as candidates, and one or more of these are used in combination. The highest magnetic properties are obtained with Pr. Therefore, practically, Pr, Pr-Nd, Ce-Pr-Nd alloy and the like are used. Examples of the transition metal include Fe, Co, Ni, and Cu, and one or more of these may be used in combination. Further, a small amount of additional elements, for example, heavy rare earth elements such as Dy and Tb, Al, Si, Mo, and Ga are effective for improving the coercive force.

The main phase of the R-TM-B-based permanent magnet is an R ₂ TM ₁₄ B compound phase. Therefore, when R is less than 8 atomic%, the above compound is no longer formed, and high magnetic performance cannot be obtained. On the other hand, if R exceeds 30 atomic%, the number of non-magnetic R-rich phases increases, and the magnetic properties are significantly reduced. Therefore, the range of R is preferably 8 to 30 atomic%. However, in order to form a cast magnet, preferably 8 to
25 at% is appropriate.

B is an essential element for forming the R ₂ TM ₁₄ B compound phase, and a high coercive force cannot be expected at 2 atomic% or less because it becomes a rhombohedral R-TM system. On the other hand, if it exceeds 28 atomic%, the nonmagnetic phase containing B increases, and the residual magnetic flux density is remarkably reduced. However, as a cast magnet, B is preferably 8 atomic% or less, and if it is more than that, a fine R ₂ TM ₁₄ B compound phase cannot be obtained unless special cooling is performed, and an appropriate coercive force can be obtained. Absent.

Al, Ga and the like show an effect of increasing the coercive force. However,
Since Al and Ga are non-magnetic elements, the residual magnetic flux density decreases as the amount of addition increases, and when Al exceeds 15 atomic%, Ga exceeds 6 atomic%, the residual magnetic flux density becomes lower than that of hard ferrite. Therefore, it cannot fulfill its purpose as a rare earth magnet. Therefore, the addition amount of Al is preferably 15 atomic% or less, and Ga is preferably 6 atomic% or less.

[Examples] Table 1 shows the compositions of the alloys produced by the present invention.

(Example 1) Rare earths, transition metals and boron were weighed so as to have the composition shown in Table 1, and were melted and cast in an induction heating furnace. As shown in FIG. Cover with.
This was subjected to hot-rolling at 950 ° C. The processing rate is about 80%. Thereafter, heat treatment was performed at 1000 ° C. for 24 hours, and cutting and polishing were performed to obtain a yoke-integrated magnet for a voice coil motor in which the yoke 20 was integrated with the magnet 10 as shown in FIG. In the conventional method, both the yoke and the magnet must be polished and bonded, but in the present embodiment, such a step is not required, and the number of steps is greatly reduced. Table 2 shows the magnetic properties of the yoke-integrated magnet. It can be seen that a magnet that can sufficiently withstand practical use has been obtained.

(Example 2) An alloy having the composition shown in Table 1 was melted and cast into an iron mold 3 as shown in FIG.
And subjected to hydrostatic extrusion. Then, heat treatment and cutting and polishing were performed, and as shown in FIG.
Was obtained as a motor yoke integrated magnet. In the conventional method, both the yoke and the magnet must be polished and bonded. However, in the present embodiment, such a step is not required, and in particular, polishing of the inner surface of the magnet is not required, and the number of steps is greatly reduced. Table 3 shows the magnetic properties of the yoke-integrated magnet.

[Effects of the Invention] As described above, according to the method for manufacturing a permanent magnet of the present invention,
Sufficient coercive force can be obtained simply by subjecting the cast ingot to a heat treatment that goes through the steps of crushing and sintering, and a yoke-integrated magnet is obtained by hot working the sheath or capsule using a material such as a yoke. Can be manufactured, and the steps of cutting and polishing are greatly reduced. As a result, the production process of permanent magnets can be greatly reduced,
This has the effect of increasing the productivity of permanent magnets.

[Brief description of the drawings]

FIG. 1 is a schematic view of a sheath used in the present invention. FIG. 2 is a schematic view of a yoke-integrated magnet for VCM manufactured according to the present invention. FIG. 3 is a schematic cross-sectional view of a sheath / mold used in the present invention. FIG. 4 is a schematic view of a motor yoke-integrated magnet manufactured according to the present invention. DESCRIPTION OF SYMBOLS 1 ... Cast ingot 2 ... Sheath 3 ... Mold 10 ... Magnet 11 ... Magnet 20 ... Yoke 21 ... Yoke

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-54-3292 (JP, A) JP-A-54-125497 (JP, A) JP-A-62-264609 (JP, A)

Claims (2)

(57) [Claims] 1. A method for producing a permanent magnet comprising a rare earth element (including Y), a transition metal and boron as basic components, at least a first step of melting and casting an alloy composed of the basic components; In a state where the cast ingot obtained in the first step is covered with a soft magnetic material or a material to be used in combination with a magnet,
A second step of performing hot working at a temperature of not less than 100 ° C. to form the cast ingot into a desired magnet shape and magnetically anisotropy; and a third step of performing a heat treatment at a temperature of not less than 250 ° C. A method for producing a permanent magnet, comprising: 2. A method for producing a permanent magnet comprising a rare earth element (including Y), a transition metal and boron as basic components, wherein at least an alloy comprising the basic components is melted and joined to a soft magnetic material or a magnet. Casting into a mold composed of the materials used
And hot working the cast ingot obtained in the first step together with the mold at a temperature of 500 ° C. or more to form the cast ingot into a desired magnet shape and to make it magnetically anisotropic. A method for manufacturing a permanent magnet, comprising: a second step; and a third step of performing a heat treatment at a temperature of 250 ° C. or higher.