JP3253006B2 - RE-T-M-B sintered magnet with excellent magnetic properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare earth iron boron-based sintered permanent magnet having excellent magnetic properties and used as a material for various electric and electronic devices.

[0002]

2. Description of the Related Art Nd-Fe-B magnets have high magnetic properties, are rich in Fe as a main material and are inexpensive.
Since d is resource-friendly and cheaper than Sm, Sm-Co
Rare earth magnets have become the mainstream for permanent magnets. However, this magnet has a low Curie point (Nd ₂ Fe ₁₄
B has a Curie point of 312 ° C.) and a large reversible temperature coefficient of coercive force iHc. As a method for compensating for these disadvantages, a part of Fe is replaced with Co to raise the Curie point, and a part of Nd is replaced with Dy, Tb, Ho.
It is generally known that the material can be used at a certain high temperature by replacing it with a heavy rare earth element such as the above to increase the crystal magnetic anisotropy constant and increase the coercive force iHc at room temperature. However, an increase in the Curie point due to the addition of Co causes a decrease in iHc, and the addition of a large amount of heavy rare earth elements such as Dy lowers the saturation magnetic flux density Br of the magnet, resulting in a high Br and high iHc.
It was difficult to realize magnet c.

[0003] As a method of improving Br, a method of reducing RE and increasing T, and a method of increasing the anisotropy at the time of magnetic field molding by bringing the magnet alloy powder close to a single magnetic domain particle diameter (for example, 3 microns or less) are common. It is a target. However, when RE is reduced, i
Hc decreases monotonically. Also, when the alloy powder is pulverized to an average particle size of 3 μm or less, the powder is oxidized, resulting in iH
c is greatly reduced. Oxidation can be prevented by keeping the process up to sintering in an oxygen-free or low-oxygen atmosphere (for example, 1% or less). However, mass production scale requires very expensive equipment and production. As a result, the cost of the product is greatly increased, which is not practical. On the other hand, the miniaturization and high performance of various electric and electronic devices are remarkable, and the practical use of a high Br and high iHc magnet as a magnet material used for these devices has been desired.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide an inexpensive RE-T-MB-based sintered magnet having high Br and high iHc which can be mass-produced and manufactured by an inexpensive and simple method.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted various studies to increase the Br and iHc, and have found that it is extremely effective to control the crystal structure of the sintered body.
Although the magnet is mainly Seiritsu' from 3-phase RE-rich phase and B-rich phase present in RE ₂ T ₁₄ B phase and the grain boundary is a magnet main phase, the main phase RE ₂ T ₁₄ B crystal The sum of the area of crystal grains having a particle diameter a of 15 microns or more is 50 of the total area of the main phase.
It has been found that a magnet having a high Br and a high iHc can be obtained by controlling the sum of crystal grain areas where a is 5% or less and a is 5% or less to 1% to 10% of the total area of the main phase. Here, the crystal grain size a represents a number obtained by dividing the sum of the major axis and the minor axis of the main phase crystal grains, which is observed when the magnet is cut at a plane perpendicular to the anisotropic direction and the polished surface is etched, by two. The crystal grain area is calculated by a circle approximation having a as a diameter.

The sintered body structure of the present invention and the magnet having high magnetic properties are realized by the following composition. That is, RE (Y is a rare earth element containing Y, and the sum of Nd, Pr and Dy is 90% by weight.
29.5% or more and 32.5% or less (weight% or less the same), B 0.8% or more and 1.5% or less, M (Al, Nb,
Ga, Mo, Ti, V, Ni, Cr, Mn, Ta, Z
at least one of r, Hf, Cu, Sn) 0.5%
2.5% or less, the balance is made up of the balance T (Fe but part of it can be replaced by Co) and unavoidable impurities.

If the sum of the areas of the crystal grains having a crystal grain size a of 15 μm or more is less than 50% of the total area of the main phase, grain growth during sintering is insufficient, and Br ≧ 12 kG is obtained. I can't. If the sum of the crystal grain areas where a is 25 microns or more is 50% or more of the total area of the main phase, the grain growth during sintering is excessive, iHc decreases, and 15 kOe or more cannot be obtained. . When the sum of the crystal grain areas where a is 5 μm or less is less than 1% of the total area of the main phase, iHc decreases, and
5 KOe or more cannot be obtained. This is presumed to be due to the small amount of fine particles contributing to the improvement of iHc. If it exceeds 10%, the grain growth during sintering is insufficient, so that Br ≧
12 kG cannot be obtained.

Next, the reasons for limiting the composition will be described. R
If E is less than 29.5%, good iHc cannot be obtained. If the oxidation of the magnet alloy powder and the molded body generated during the magnet manufacturing process is extremely suppressed (for example, 2500 ppm or less), the decrease in iHc can be prevented, but this involves a large cost increase, so that it is set to 29.5% or more. If RE exceeds 32.5%, iHc can easily maintain a high level, but Br decreases, so it is set to 32.5% or less. Nd, Pr and D
When the sum of y is less than 90% of the total RE, Br ≧ 12
Since kG and iHc ≧ 15 kOe cannot be simultaneously satisfied, the content is set to 90% or more. If the B content is less than 0.8%, good iHc cannot be obtained, and if it exceeds 1.5%, the reduction of Br becomes large, so the content is made 0.8% or more and 1.5% or less.

The M element has a function as an element for improving iHc or suppressing abnormal grain growth during sintering, but if it is less than 0.5%, both functions are insufficient, and as a result, the area of crystal grains having a grain size of 5 μm or less is consequently reduced. Is less than 1% of the total area of the main phase crystal grains, iHc ≧ 15 kOe cannot be obtained. If M exceeds 2.5%, Br decreases and Br ≧ 12 kG cannot be obtained.

As a simple method for controlling the crystal grain size of the main phase of RE ₂ T ₁₄ B after sintering, an average grain size (FISCHER
A method in which a plurality of fine powders having different SUB-SIEVE SIZER) are prepared, mixed, then molded in a magnetic field, sintered, and heat-treated can be applied. Also, a method of mixing the alloy having the final magnet composition into fine powders having a plurality of average particle sizes, and a method of mixing a plurality of alloys having different compositions into different average particle diameters at a ratio of the final magnet composition after being pulverized to different average particle sizes. Either method of performing the same processing after the magnetic field shaping may be used. Further, since the optimum value of the average particle size of the fine powder is slightly changed depending on the magnet composition, the average particle size of the magnet main phase RE ₂ T ₁₄ B after sintering is adjusted so as to conform to claim 1 of the present invention. Just set it. The key point is to have multiple average particle sizes.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments. However, the present invention is not limited only to the embodiments. (Examples) Ingots adjusted to various compositions shown in Table 1 were prepared, and after coarse pulverization, various average particle sizes (F.
S. S. S. ). Regarding the ingot production method (for example, ordinary high frequency melting or arc melting, mold casting or quenching method, etc.) and the pulverization method (for example, dry jet mill method or wet ball mill method), any generally used method may be used. The obtained fine powder was mixed at a mixing ratio shown in Table 2, and the mixed powder was molded in a magnetic field and then converted into a sintered magnet by an ordinary method. The magnetic properties of the obtained magnet and the main phase crystal grain size a observed when the magnet was cut along a plane perpendicular to the anisotropic direction and the polished surface was etched were 5 μm or less and 15 to 2 μm.
The ratio of the sum of the crystal grain areas having 5 microns to the total area of the main phase (main phase area ratio) is shown in Examples 1 to 5 of Table 3.

Comparative Examples Ingots adjusted to various compositions shown in Table 4 were prepared, coarsely pulverized, and then finely pulverized to various average particle sizes shown in the same table. The following method was performed exactly as in the case of the example. The mixing ratio of the fine powder is shown in Table 5, and the magnetic properties and the area ratio of the main phase are shown in Comparative Examples 1 to 4 in Table 3.

[0013]

[Table 1]

[0014]

[Table 2]

[0015]

[Table 3]

[0016]

[Table 4]

The contents of each of the examples and comparative examples will be described below. Example 1 shows ingot No. 1 having the same composition. 1
And No. 2 was crushed to 4.3 microns and 5.2 microns, and then mixed at a ratio of 50:50. The average particle size after mixing was 4.7 microns. As shown in Table 3, the area ratio of the main phase is in accordance with claim 1, and the magnetic properties are also Br.
≧ 12KG, iHc ≧ 15kOe. On the other hand, Comparative Example 1 is an ingot N having the composition of Example 1.
o. 12 (see Table 4) was pulverized to an average particle size of 4.7 microns, but the area ratio of the main phase after sintering was different from that of Example 1 and the magnetic properties were low. This difference is due to the difference in particle size distribution even though the average particle size of the fine powder is the same. FIG. 1 shows a photograph of the crystal structure of Example 1, and FIG. 2 shows a photograph of the crystal structure of Comparative Example 1.

In Example 2, the ingot No. was made higher in RE than the final composition of the magnet, and M element was added. No. 3 was pulverized to 4.3 microns, and M element-free ingot No. No. 4 was ground to 5.2 microns and they were mixed at a ratio of 40:60.
By increasing the amount of the M element having the effect of improving the coercive force and suppressing the growth of crystal grains, the M after mixing was increased to 1.2%, and the iHc was further improved as compared with the first embodiment. On the other hand, in Comparative Example 2, as in Example 2, RE was higher than the final composition and M
Ingot No. to which the element was added. 13 and the ingot No. 14, 4.3 microns each,
It was pulverized to 4.5 microns and mixed at 40:60. As is clear from Table 3, the magnetic properties are high for iHc but Br
Has not reached 12KG. It has a grain size of 15-25
This is because the main phase area ratio of microns is as low as 41.9%.
The ingot No. of the main phase area ratio is low. 13 and No. 1
This is because secondary recrystallization during sintering did not proceed sufficiently because the particle diameters of the fine powders of No. 4 were almost the same.

Example 3 shows an ingot N having the same composition.
o. 5 and No. 5 6 were pulverized to 4.0 microns and 5.6 microns, respectively, and then mixed at a ratio of 35:65, and the average particle size after mixing was 5.0 microns. Table 3
As shown in the above, the area ratio of the main phase conforms to claim 1. As compared with Example 1, the addition amount of the M element was slightly reduced, so that Br was slightly higher and iHc was slightly lower, but all exceeded the specified values. Comparative Example 3 was the same as Example 3 except that the addition amount of M element was further reduced to 0.4% from Example 3, but as shown in Table 3, the main particles having a crystal grain size of 5 μm or less were used. The phase area ratio becomes 0.2%,
As a result, iHc is as low as 14 kOe. This is due to the fact that the amount of M element was too small to sufficiently suppress the grain growth.

Embodiment 4 shows the ingot No. 7, 8 (Table 1) were pulverized to an average particle size of 3.9 microns and 5.7 microns, respectively, and then mixed at a ratio of 30:70, and the average particle size after mixing was 5.2 microns. As shown in Table 3, the main phase area ratio is consistent with claim 1. Example 1
The magnetic properties Br and iHc are higher than those of Example 1 by reducing the amount of the rare earth element, slightly increasing the average particle diameter after mixing, and slightly increasing the addition amount of the crystal grain growth suppressing element M. Is shown. Comparative Example 4 was prepared for ingot No. 1 containing 2.8% of M element. 17 and ingot N
o. 18 were mixed to a ratio of 30:70 after pulverization to 4.0 μm and 5.6 μm, respectively, and the average particle size after mixing was 5.1 μm. That is, although the amount of the M element after mixing is higher than the 1.3% of Example 4 to 2.8%, it is almost the same as that of Example 4;
The iHc is very high at 18.6 kOe as shown in FIG.
r is a low value of 11.75 kG. This is because grain growth suppression during sintering was too effective due to the large amount of M element, and sufficient secondary recrystallization did not occur.

Example 5 shows an ingot N having the same composition.
o. 9, 10, and 11 are 3.7, 4.5, and 5.9, respectively.
After pulverization to a micron, the mixture was mixed at a ratio of 20:20:60, and the average particle size after the mixing was 5.9 μm. As shown in Table 3, both the area ratio of the main phase and the magnetic properties are consistent with the first aspect.

[0022]

[Table 5]

[0023]

The RE-T-M-B based sintered magnet of the present invention has a high Br and iHc which is unprecedented by controlling the crystal grain size of the main phase after sintering. It is a magnet that can sufficiently respond to miniaturization and high functionality of various electric and electronic devices.

[Brief description of the drawings]

FIG. 1 is a micrograph of the crystal structure of Example 1.

FIG. 2 is a micrograph of the crystal structure of Comparative Example 1.

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) H01F 1/032-1/08 C22C 33/02 C22C 38/00 303

Claims (2)

(57) [Claims] 1. The sum of the areas of crystal grains having a crystal grain size of 15 to 25 microns is 50% or more of the total area of the magnet main phase crystals.
The sum of the areas of crystal grains having a crystal grain size of 5 μm or less is 1% or more and 10% or less, and the magnetic properties thereof are Br ≧ 12 kG,
An RE-T-MB-based sintered magnet having excellent magnetic properties, wherein iHc ≧ 15 kOe. 2. A rare earth element containing RE (Y, Nd, P
The sum of r and Dy is 90% by weight or more) 29.5% or more 3
2.5% or less (same as weight% or less), B 0.8% or more and 1.5% or less, M (Al, Nb, Ga, Mo, Ti,
V, Ni, Cr, Mn, Ta, Zr, Hf, Cu, Sn
2. The sintering according to claim 1, wherein the sintering is made up of at least one of 0.5% or more and 2.5% or less, the balance T (Fe but part of which can be replaced by Co) and unavoidable impurities. magnet.