JPH04196107A - Manufacture of permanent magnet - Google Patents

Abstract

PURPOSE:To form a permanent magnet, which is high in magnetic characteristics and has a good economical efficiency, by a method wherein when an alloy containing specified elements and the like as its basic components is cast, an alloy ingot is formed while the surface of molten alloy is pressed. CONSTITUTION:When an alloy containing one kind of rare earth elements containing Y, one kind of transition metal elements and boron as its basic components is cast, an alloy ingot is cast while a pressure is applied to the surface of molten alloy in a casting mold. By this pressing, the generation of air gaps in the ingot and the casting mold, which is caused by solidification and shrinkage, is inhibited, the heat transfer of the ingot and the casting mold is improved, an ingot of a fine columunar crystal structure is formed and when this ingot is subjected to hot processing and heat treatment, a permanent magnet, which is high in magnetic characteristics and has no gas defect, is formed at a good economical efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application 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, the following four methods have been reported for rare earth-transition metal-boron based permanent magnets: (1) magnets using a sintering method based on powder metallurgy;

(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 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. 3. Japanese Unexamined Patent Publication No. 59-46008 and Publication No. 59-211549/No. Tokukai Showa 6
0-100402 Publication 7/4, JP-A-63-1
No. 51905 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, and is brittle and easily broken. Since the crystal grains are distributed in the same direction, 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 of (4) is to obtain anisotropy by hot working an alloy ingot produced by melting and casting in the same manner as in (1) in a vacuum or in an inert gas atmosphere,
and has good magnetic properties for heat treatment.
B. Obtains a magnet.

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 it is possible to manufacture R-TM-B permanent magnets by using the above-mentioned conventional techniques, these manufacturing methods have drawbacks such as blowing.

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 in advance during the sintering process, several tenths of it remains in the magnet in the form of carbon. This carbon is undesirable because it deteriorates the magnetic performance of the RT M-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 time and effort to neatly line up the materials in the 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, - For boat fishing, manufacturing R-TM-B sintered magnets not only requires expensive equipment, but also reduces production efficiency and increases the manufacturing cost of magnets. turn into. Therefore, R-TM-B, which uses relatively cheap raw materials,
It is difficult to say that the advantages of magnets can be fully utilized.

Furthermore, methods (2) and (3) use vacuum melt spinning equipment, 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 bisteresis 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, 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 following two conventional techniques, and its purpose is to provide a high-performance and low-cost R-TM-B permanent magnet. It is in a place where we provide.

[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 a holon. In the method,
The method is characterized in that during the above casting, the alloy ingot is cast while applying pressure to the surface of the molten alloy in the 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 through hot working and the effect of additive elements on improving magnetic properties, and found a method for manufacturing high-performance permanent magnets. However, in the above method, if ordinary gold is poured into the mold during casting, an air gap will occur between the mold and the ingot, and the heat transfer from the ingot to the mold will rapidly decrease, resulting in the formation of columnar crystals. This impedes development and causes coarsening of grain size. Such factors lead to a decrease in magnetic performance obtained through hot working and heat treatment steps.

Therefore, the inventors of the present invention solved the problem of air gap between the ingot and the mold due to solidification by solidifying the alloy ingot by applying pressure to the surface of the molten alloy in the mold during casting to make the alloy ingot 1%. The heat transfer was suppressed to improve heat transfer, and an ingot consisting of a fine columnar crystal structure was obtained. 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. In addition, such an ingot solidified under pressure has fewer gas defects than a normal ingot, so an ingot with excellent mechanical strength and a very clean surface can be obtained.

Examples will be described below.

[Example] FIG. 1 shows a manufacturing process diagram in the present invention.

FIG. 2 shows an overview of the casting method according to the present invention and a schematic diagram of the obtained ingot. On the surface of the molten metal poured into the mold,
The desired ingot is obtained by solidifying while applying a pressure of 50 MPa using a preheated ceramic punch. Further, FIG. 3 shows an outline of a conventional casting method and a schematic diagram of 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 made using this alloy according to the present invention by the casting method shown in Figure 1 (specified as type A) and ingots made by conventional casting (specified as type B) were cut out from each ingot. The density was measured.

Furthermore, the average grain size of the ingot structure obtained as a result of the structure observation was measured. Furthermore, the occurrence of internal defects in the ingot (gas defects, shrinkage cavities) was investigated. The results are shown in Table 1.

Table 1 As shown, the ingot A according to the present invention had a fine grain size and a good ingot structure. In addition, there are fewer defects inside the ingot, which results in a higher density. This indicates that good ingots can be obtained by employing the casting method according to the present invention.

(Example 2) A sample piece was cut out from each ingot similar to Example 1, and after annealing at 1000°C for 24 hours in an argon atmosphere, it was further annealed at 475°C in an argon atmosphere.
After heat treatment for C2 hours, the resulting magnetic performance was measured. The results are shown in Table 2.

Table 2 As shown in Table 2, it has become clear that the ingot according to the present invention has superior magnetic performance after heat treatment compared to the normal ingot.

(Example 3) 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. After pressing, the same two-stage heat treatment as in Example 2 was performed. The magnetic performance obtained as a result is shown in Table 3.

From the above in Table 3, it can be seen that the magnetic performance after hot pressing is
It has become clear that the ingot according to the present invention exhibits higher magnetic performance.

(Example 4) 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, and further heat treatment was performed at 475°C for 2 hours. The magnetic performance results obtained are shown in Table 4. Further, a three-point bending test was conducted on each sample after rolling to measure the bending strength.

The results are also shown in Table 4.

As shown in Table 4 and above, the ingot according to the present invention can obtain good values in magnetic performance after hot rolling, and products with excellent mechanical properties can also be obtained.

(Example 5) For each alloy having the composition shown in Table 5 below, two types of ingots were cast by the casting method according to the present invention (Type A) and the normal casting method (Type B) in the same manner as in the above Examples. . Each of these ingots was subjected to the same hot pressing process and heat treatment process as in Example 3, and the magnetic performance obtained as a result is shown in Table 6.

From the results shown in Tables 5 and 6, it was found that in any composition, the ingot produced by the casting method of the present invention had better magnetic performance.

[Effects of the Invention] As described above, according to the present invention, by casting an alloy ingot by applying pressure to the surface of the molten alloy in the mold during casting, it is possible to improve the magnetic properties, which was a drawback of the conventional casting method. It is possible to 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 the drawing]

Fig. 1 is a manufacturing process diagram of the R-Fe-B magnet of the present invention, Fig. 2 is an outline of the casting method of the invention and a schematic diagram of the obtained ingot, and Fig. 3 is an outline of the ordinary casting method and the obtained ingot. FIG. 201.301... Casting mold 202.302... Molten alloy 203.303... Alloy ingot 204... Ceramic punch or more Applicant: Seiko Epson Co., Ltd. Agent Patent attorney Kizobe Suzuki and others 1 given name

Claims (1)

[Claims] In a permanent magnet manufacturing method that includes a step of hot working and a heat treatment step after casting an alloy whose basic components are rare earth elements (including Y), transition metals, and boron, the molten alloy in the mold is A method for producing a permanent magnet, which comprises casting an alloy ingot while applying pressure to the surface.