JPH04134802A - Manufacture of permanent magnet - Google Patents

Abstract

PURPOSE:To obtain a high-performance permanent magnet by horizontally installing a cast metal mold having a bottom face higher in cooling power than the side face of the metal mold at the time of casting and by pouring a molten alloy into the metal mold. CONSTITUTION:A cast metal mold having a bottom face made higher in cooling power than the side face of the metal mold is installed horizontally and a molten alloy is poured into the metal mold. According to such casting, the air gap between the mold and ingot in the bottom face is sharply reduced by the effect of gravity and the substantial cooling power is improved so that columnar crystals can be seen to expand sharply. When a hot working process and heat treatment process are applied to a cast ingot obtained in this manner, it is possible to obtain a high-performance permanent magnet.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial IIJ Field] The present invention relates to a method for manufacturing a permanent magnet whose basic components are rare earth elements, transition metals, and boron.

[Prior Art] Conventionally, rare earth-transition metal-boron based permanent magnets have been reported using the following four methods.

(1) Magnet made by sintering method based on powder metallurgy method.

(Reference Document 1) (2) A magnet in which a quenched thin strip with a thickness of about 30 μm is made using a quenched ribbon production device used to produce an amorphous alloy, and the thin pieces are bonded with a resin. (Reference Document 2) (3) A magnet obtained by mechanically aligning the same flakes used in method (2) using a two-step hot press method. (Reference Document 3) (4) A magnet obtained by subjecting a cast ingot to mechanical orientation through one-step hot working and further heat treatment.

(Reference 4) Reference 1. Japanese Unexamined Patent Publication No. 59-46008, Publication No. 59-211549, 3. Unexamined Japanese Patent Application 1986-10
Publication No. 0402/14. JP-A-63-151905 Next, the above conventional method will be explained.

First, in the sintering method (1), an alloy ingot is produced by melting and casting, and then pulverized to obtain magnet powder with an appropriate particle size (several μm). Magnetic powder is kneaded with a binder, which is a molding aid, and press-molded in a magnetic field to complete a molded product. The compact was sintered in argon at a temperature of around 110°C for 1 hour.
It is then rapidly cooled to room temperature. After sintering, the coercive force is improved by heat treatment at a temperature of around 600°C.

(2) In the resin bonding method using quenched flakes by melt spinning, first, a quenched ribbon of R-TM-B alloy is produced at an optimal rotation speed of a quenched ribbon manufacturing apparatus. Obtained thickness 3
A ribbon-like thin strip of 0 μm is an aggregate of crystals with a diameter of 100 OA° or less, is brittle and easily broken, and since the crystal grains are distributed isotropically, it is also magnetically isotropic. This ribbon is pulverized to an appropriate particle size, kneaded with resin, and press-molded.

In the manufacturing method (3), the ribbon-like quenched ribbon or flake in (2) is heated in a vacuum or in an inert atmosphere.
A dense and anisotropic R-TM,-B magnet is obtained by a method called a stepwise hot pressing method.

In this pressing process, uniaxial pressure is applied, the axis of easy magnetization is oriented parallel to the pressing direction, and the alloy becomes anisotropic.

In addition, the crystal grains of the ribbon-like ribbon produced by the initial melt spinning method are made smaller than the grain size at which they exhibit the maximum coercive force, to avoid coarsening of the crystal grains during the subsequent hot pressing. Allow the particles to grow to the optimum particle size.

The manufacturing method (4) is as follows: An alloy ingot produced by melting and spinning in the same manner as in (1) is hot-processed in a vacuum or in an inert gas atmosphere to obtain anisotropy.
Moreover, an R-TM-B magnet having good magnetic properties upon heat treatment is obtained.

In this method, the anisotropy direction is in the processing direction, as in (3), but the difference is that only one step of hot working is required and the crystal grains are also made smaller by the working.

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

In the sintering method (1), it is essential to turn the alloy into powder, but R-T M-B permanent magnets are very active against oxygen, so it is necessary to go through the process of turning the alloy into powder. The surface area increases, oxidation becomes more intense, and the oxygen temperature in the sintered body inevitably rises. Also, shaping aids, such as zinc stearate, must be used when compacting the powder. Although this is removed beforehand during the sintering process, it remains in the form of carbon within the magnet for several moments. This carbon is undesirable because it deteriorates the magnetic performance of the R-TM-B permanent magnet.

The molded body after press molding with the addition of a molding aid is called a green body. This is very fragile and difficult to handle. Therefore, another major drawback is that it takes a considerable amount of effort to arrange them neatly in a sintering furnace.

Furthermore, in order to obtain an anisotropic magnet, press molding must be performed in a magnetic field, which requires large equipment such as a magnetic field power source and a coil.

Because of the above drawbacks, - In other words, manufacturing R-TMB sintered magnets not only requires expensive equipment, but also reduces production efficiency and increases the cost of manufacturing the magnets. Put it away. Therefore, R-T M-B, which uses relatively cheap raw materials,
It is difficult to say that the advantages of magnets can be fully utilized.

Next, methods (2) and (3) use a vacuum melt spinning device, which currently has very low productivity and is 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 it is disadvantageous in terms of temperature characteristics and usage.

Although method (3) yields an anisotropic magnet, since hot pressing is used in two stages, it cannot be denied that it will be extremely inefficient when considering mass production.

In addition, 1. In this method, at high temperatures, for example, 800° C. or higher, the crystal grains become significantly coarsened, resulting in an extremely low coercive force, making it impossible to produce a practical permanent magnet.

Method (4) does not involve a powder process and requires only one step of hot pressing, which simplifies the manufacturing process the most, but the problem is that it is slightly inferior to methods (1) and (3) in terms of performance. was there.

The present invention is intended to solve the performance disadvantage (4) in particular of the above-mentioned conventional techniques, and its purpose is to provide a high-performance, low-cost R-TM-B permanent magnet. It's there.

[Means for Solving the Problems] The present invention involves the production of a permanent magnet, which includes a step of hot working and a heat treatment step after casting an alloy whose basic components are a rare earth element (including Y), a transition metal, and boron. In the method,
At the time of the casting, an ingot is cast by placing a casting mold horizontally in which the cooling capacity of the bottom surface is larger than that of the side surfaces and pouring the alloy into the casting mold.

[Function] The present inventors evaluated a number of R-Fe-B based cast alloys and found that a high coercive force can be obtained by applying appropriate heat treatment to the Pr-Fe-B based alloy, and further, Based on this alloy, we studied mechanical orientation treatment using hot pressing and the effect of additive elements on improving magnetic properties, and found a method for manufacturing high-performance permanent magnets.

However, when casting an alloy ingot using a conventional casting mold, an air gap occurs between the alloy ingot and the mold, which reduces the actual cooling capacity and prevents the formation of a columnar crystal structure. . Therefore, in the present invention, by horizontally installing a casting mold in which the cooling capacity of the bottom surface is larger than that of the sides, and pouring the molten alloy into it, the crystal growth from the side surfaces is suppressed, and the columnar crystals are removed from the bottom of the ingot. An ingot developed in the vertical direction was obtained. According to this casting method, the air gap between the mold and the ingot at the bottom was significantly reduced due to the effect of gravity, and the substantial cooling capacity was improved, resulting in a significant elongation of the columnar crystals. A high-performance permanent magnet can be obtained by subjecting the thus obtained cast ingot to a hot working step and a heat treatment step.

Examples will be described below.

[Example] Fig. 1 shows a manufacturing process diagram in the present invention. FIG. 2 shows a schematic diagram of the casting mold used in the present invention and the resulting ingot. Further, FIG. 3 shows a schematic diagram of a conventional casting mold and an obtained ingot as a comparative example.

(Example 1) The composition of the alloy used in this example is 17 atomic % Pr, 76.5 atomic % Fe, 5 atomic % B, and 1.5 atomic % Cu. Ingots were produced from this alloy by the casting method shown in FIG. 2 (specified as type A) and by normal casting as shown in FIG. 3 (specified as type B). As a result of microstructural observation of a cross section in the ingot thickness direction for each ingot, it was found that ingots of type B have an ingot structure containing a uniform crystal region in the center of the thickness direction when the thickness is 30 mm or more. Formation of such equicrystals is undesirable because it deteriorates magnetic properties. Furthermore, from this result, it can be determined that in the B type ingot, the length of the columnar crystals that develop from the poet on one side is 15 mm or less. In the A-type ingot according to the present invention, columnar crystals developed from the bottom surface of the pyramid having a large cooling capacity, and the maximum length thereof reached about 40 mm. On the other hand, almost no crystal growth was observed from the sides of the mold with reduced cooling capacity.
An ingot with elongated columnar crystals solidified in one direction was obtained. Equicrystalline regions may be formed at the top of the ingot, but unlike 8-type ingots, the columnar crystalline regions are separated from the bottom and the equicrystalline regions from the top, making it easy to separate both regions by cutting. I can do it. Efficient use of the ingot can be realized by remelting the cut ingot in the equicrystalline region. Such a type A ingot was produced, and its upper crystal region was cut to cut out a 35 mm ingot billet consisting only of columnar crystals. In addition, a type B 35 mm thick ingot having the same composition was produced. A sample piece was cut out from each ingot and annealed for 1000'024 hours in an argon atmosphere.
Further, heat treatment was performed at 475° C. for 2 hours in an argon atmosphere, and the resulting magnetic performance was measured. The results are shown in Table 1.

As shown in Table 1 and Table 2, it is clear that the type A ingot made by the casting method of the present invention has superior magnetic performance after heat treatment compared to the type 8 ingot made by conventional casting. It became a thing.

(Example 2) Sample pieces were cut out from each ingot similar to that of Example 1, and hot pressed at 1000°C in an argon atmosphere. During pressing, an iron ring was attached to the ingot sample piece and pressed. After pressing, the same two-stage heat treatment as in Example 2 was performed. The magnetic performance obtained as a result is
Table.

From the above, it can be seen that the magnetic performance after hot pressing is also A.
It became clear that the seed ingot showed higher performance.

(Example 3) Ingots similar to those in Example 1 were encapsulated in a metal sheath and hot rolled at 950°C with a workability of 75%. After hot rolling, heat treatment was performed at 950°C for 6 hours,
Further, heat treatment was performed at 475°C for 2 hours. The magnetic performance results obtained are shown in Table 3.

As shown in Table 3 and Table 5 above, it has been revealed that the type A ingot produced by the casting method of the present invention can obtain good values in magnetic performance after hot rolling.

(Example 4) For each alloy having the composition shown in Table 4 below, sample pieces were cut out from two types of ingots, A type and B type similar to those in Example 1 above, and heated in the same manner as in Example 3 above. Table 5 shows the magnetic performance obtained as a result of the interpressure and heat treatment.

From the results shown in Table 6 and above, it is clear that in any composition, the type A ingot obtained by the casting method according to the present invention has superior magnetic performance.

[Effects of the Invention] As described above, according to the present invention, the casting method in which the cooling capacity of the bottom surface is larger than that of the side surfaces is installed horizontally and the alloy is poured into the casting mold, which is essential for improving magnetic properties. This makes it possible to elongate columnar crystals, improve the magnetic properties that were a drawback of conventional casting methods, and achieve performance equivalent to or better than sintered magnets. Therefore, the advantages of the casting method, such as shortening the manufacturing process, are further promoted.

[Brief explanation of drawings]

Figure 1 is a manufacturing process diagram of the R-Fe-B magnet of the present invention, Figure 2 is a schematic cross-sectional view of a mold and ingot in the casting method of the present invention, and Figure 3 is a diagram of the mold and ingot in the ordinary casting method. FIG. 2 is a schematic cross-sectional view of an ingot. 201.301..., -Cu casting mold alloy ingot/ceramic plate

Claims (1)

[Claims] In a permanent magnet manufacturing method that includes a hot working process and a heat treatment process after casting an alloy whose basic components are rare earth elements (including Y), transition metals, and boron, the cooling ability of the bottom surface is A method for manufacturing a permanent magnet, which is characterized by casting an ingot by placing a casting mold horizontally, which is larger than the side surface, and pouring alloy into the mold.