JP2564868B2 - Permanent magnet manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a permanent magnet, and more specifically,
Nd-Fe-B with excellent magnetic properties such as residual magnetic flux density (Br), coercive force (iHc) and maximum energy product ((BH) max)
System for producing anisotropic permanent magnets.

(Prior Art) A 2Nd-Fe-B based sintered magnet is generally manufactured as follows. First, a conventional melt quenching method is applied to an Nd-Fe-B alloy having a predetermined composition to prepare an amorphous ribbon or flake having the composition of the alloy. Next, the thin strips or flakes are crushed to obtain powder having a predetermined particle size, and then heat treatment is applied to this to promote crystallization and impart high iHc.

Then, the obtained magnetic powder is filled in a predetermined mold and subjected to cold pressing or hot pressing to compression-mold a molded body. In the case of hot pressing, the temperature is usually 700-800 ° C. At this time, the magnetic powder, which generally has shape anisotropy, is oriented so that its c-axis direction is orthogonal to the pressing direction, so that the formed body is given magnetic anisotropy.
The greater the degree of orientation at this time, the greater the magnetic anisotropy of the finally obtained magnet.

The obtained molded body is then 700 to 800 ° C in vacuum.
After subjecting to plastic deformation at a temperature of 1 to process into a predetermined shape, this is cooled to a temperature around 100 ° C to obtain a product. However, in some cases, the product is immediately cooled after hot pressing.

(Problems to be Solved by the Invention) However, in the above-mentioned method, since the applied temperature at the time of hot pressing or plastic deformation treatment is 700 to 800 ° C., the crystal grains of the Nd—Fe—B alloy are in this process. The problem that should be most avoided for permanent magnets is that the iHc of the obtained magnets decreases due to the coarsening of particles.

In order to suppress the occurrence of such problems, Nd-Fe-B
It is known to further mix Ga as a system alloy composition. When the above-mentioned manufacturing method is applied to this Ga-blended Nd-Fe-B-based alloy, iHc of the magnet is increased, but on the other hand, Br is lowered and eventually (BH) max is lowered. However, since Ga is expensive in the first place, there is a problem that the total cost must be increased.

The present inventor has conducted extensive studies in order to prevent the deterioration of the magnetic properties after hot pressing or after plastic deformation treatment, and inspected each unit step of the above-mentioned manufacturing method. The fact that the cooling rate in the cooling process is extremely important for improving the characteristics of the magnet was found and the method of the present invention was developed.

That is, the present invention has excellent magnetic properties only by cooling control for a molded body after hot pressing or plastic deformation treatment without adding other components such as Ga, iH
It is intended to provide a method for manufacturing a permanent magnet having a high c.

(Means for Solving Problems) In order to achieve the above-mentioned object, the method for producing a permanent magnet of the present invention has a structure in which an alloy powder containing Nd, Fe, and B as a main component is added to 600- It is characterized in that after hot pressing or plastic deformation treatment is performed in a temperature range of 800 ° C to obtain a molded body, the molded body is rapidly cooled at a cooling rate of 5 ° C / min or more.

The alloy powder to which the method of the present invention is applied is not particularly limited as long as it is known as a raw material magnetic powder for Nd-Fe-B system permanent magnets.

This Nd-Fe-B system magnetic powder can be easily obtained by crushing thin strips or flakes of Nd-Fe-B system alloy having a predetermined composition prepared by a melt quenching method.

In the method of the present invention, first, the Nd-Fe-B magnetic powder is subjected to hot pressing or plastic deformation treatment to form a magnetic compact. At this time, the surrounding atmosphere needs to be maintained in a vacuum state. If the vacuum is not maintained, there is a situation in which the density does not increase during hot pressing and the coercive force also decreases. It is inconvenient. A suitable vacuum degree is a high vacuum degree of 1 × 10 ⁻³ Torr or more.

The temperature at this time is set in the range of 600 to 800 ° C. If the processing temperature is less than 600 ° C, it is difficult to shape the magnetic powder in the hot press, and
Plastic deformation does not occur during plastic deformation. Conversely 800
When the treatment is carried out at a temperature higher than ° C, the crystal grains of the Nd-Fe-B system alloy of the magnetic powder become coarse and the iHc thereof is lowered in both hot pressing and plastic deformation treatment, which is inconvenient. It is preferably 650 to 750 ° C.

The pressure during hot pressing is preferably 0.3 to ² tonf / cm ² , and in the plastic deformation treatment, 0.1 to 2 tof.
It is preferably nf / cm ² .

After the hot pressing or the plastic deformation treatment described above, the obtained molded body is rapidly cooled at a cooling rate of 5 ° C / min. Usually, it is preferable to blow Ar gas at room temperature onto the treated compact to cool it. At this time, the cooling rate of the molded body can be adjusted by adjusting the amount of Ar gas sprayed.

Such a quenching treatment is preferably continued until the temperature of the molded body reaches about 300 ° C. The reason for this has not been clarified, but this treatment increases iHc of the molded body and also causes magnetic anisotropy. The degree will improve.

In any case, when the cooling rate is lower than 5 ° C./min, the values of Br, iHc, (BH) max of the obtained molded body are all small, which is inconvenient.

In this way, the permanent magnet of the present invention can be obtained, but by further subjecting this to a heat treatment at a temperature of 600 ° C. or lower, it is possible to remove the strain accumulated in the compact during the rapid cooling treatment,
It is preferable because iHc can be further increased. 500-60
A temperature of 0 ° C. is preferred.

In the present invention, the molded body itself obtained by the above-mentioned method can be used as a permanent magnet, but it is once pulverized into a powder and mixed with a resin matrix such as an epoxy resin for a plastic magnet. It can also be used as magnetic powder.

(Examples of the invention) Examples 1 to 7 Nd: 32% by weight, B: 0.6% by weight, Al: 0.1% by weight, Si: 0.1% by weight, the balance Fe alloy alloy melt composition (single roll method) ) Was applied to form a ribbon. When this ribbon was measured by an X-ray diffraction method, about 80% thereof was amorphous.

Then, the thin strip was crushed and classified using a sieve specified in JIS Z8801, and the powder under 60 mesh was collected.

This powder was filled in a mold, heated in a vacuum of 1 × 10 ⁻³ Torr to 700 ° C. for 4 minutes, and press-molded at 1 tonf / cm ² .

After maintaining the press molding for 3 minutes, the pressure was released, the molded body was taken out of the mold, and Ar gas was blown onto the molded body to rapidly cool the molded body. The cooling rate of the molded body up to 50 ° C. was measured with a thermocouple.

The magnetic properties of the obtained molded body were measured, and the relationship with the cooling rate is shown in Table 1.

Next, the molded body of Example 2 was heat-treated under the conditions shown, and the magnetic characteristics of the obtained magnet were measured. The results are shown in Table 2.

As is clear from Table 2, when the heat treatment temperature exceeds 600 ° C, the magnetic properties of the magnet deteriorate.

Examples 8 to 10 Nd: 30% by weight, B: 0.8% by weight, Ga: 0.2% by weight, Co: 2% by weight, the alloy having a composition of Fe as the balance was subjected to the melt quenching method (single roll method). It was a thin strip. When this ribbon was measured by an X-ray diffraction method, about 90% thereof was amorphous.

Then, the thin strip was crushed with Ar in an atmosphere and classified using a sieve specified in JIS Z8801 to collect powder under 60 mesh.
This powder was cold pressed to obtain a green compact having a density of 5.8 g / cm ² .

The green compact was housed in a SUS304 container, subjected to vacuum deaeration, and then the lid was welded to seal the green compact in the container. Then, it was put into a furnace at 700 ° C. After 30 minutes, the temperature of the container was raised to 700 ° C. Immediately after heating to 700 ° C., the container was hot-pressed until its thickness became 1/5, and the green compact inside was subjected to plastic deformation treatment.

Then, the molded container was put into the furnace again and cooled at the indicated cooling rate. After cooling to room temperature, the molded body was taken out from the container and crushed to obtain powder under 60 mesh.

After mixing 97.5% by weight of each magnetic powder obtained, 2 parts by weight of epoxy resin, and 0.5 parts by weight of zinc stearate as a lubricant, and magnetizing by pulse magnetization, the whole was 20 KO
A plastic magnet was obtained by compression molding in a magnetic field of e at a pressure of 7 tong / cm ² .

The relationship between the magnetic characteristics of the obtained magnet and the cooling rate
Shown in the table.

(Effects of the Invention) As is apparent from the above description, the method for producing a permanent magnet of the present invention has a structure in which an alloy powder containing Nd, Fe, and B as the main components has a temperature of 600 to 800 ° C. in a vacuum. After hot pressing or plastic deformation treatment in the temperature range to form a molded body, the molded body was cooled rapidly at a cooling rate of 5 ° C / min or more. Therefore, magnetic properties such as Br, iHc, (BH) max, etc. Any of these can provide an excellent Nd-Fe-B-based permanent magnet, and its industrial value is extremely large.

Claims (2)

(57) [Claims] 1. An alloy powder containing Nd, Fe, B as a main component is hot-pressed or plastically deformed in a temperature range of 600 to 800 ° C. in a vacuum to form a molded body, and then the molded body is subjected to 5 ℃
A method for manufacturing a permanent magnet, which comprises rapidly cooling at a cooling rate of not less than / min. 2. The method for producing a permanent magnet according to claim 1, further comprising a heat treatment at a temperature of 600 ° C. or lower after the quenching treatment.