JPH0982510A - Re-t-m-b sintered magnet excellent in magnetic characteristic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a sintered magnet mass-producible and having an excellent magnetic characteristic by making the areas of crystal grains whose diameters are a specific value or more to the total area of the main-phase crystals of a magnet a specific value or more, the sum of the areas of crystal grains whose diameters are a specific value or less in a specific range, and magnetic characteristics Br, iHc specific values or more. SOLUTION: Ingots wherein RE-B-M-T are adjusted into various composition are manufactured, and they are finely ground into various average grain sizes after their coarse grinding. Two ingots having the same composition are ground into crystal grain diameters 4.3 and 5.2 microns, and they are mixed by a ratio of 50 to 50. The average grain size after the mixing is 4.7 microns, and the main-phase area ratio (%) after sintering is 50% or more for crystal grain diameters of 15 microns or more, and in a range of 2-5% for crystal grain diameters of 5 microns or less. Besides, its magnetic characteristics are in ranges Br>=12.8kG and iHc>=16kOe . By controlling the main-phase crystal grain diameter after sintering in this way, it becomes possible to obtain a high- performance magnet of high Br and iHc.

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 characteristics, which is 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 abundant in Fe as a main material, and are inexpensive.
Since d is resource-friendly and cheaper than Sm, Sm-Co
It has become the mainstream of rare earth magnets instead of permanent magnets. However, this magnet has a low Curie point (Nd ₂ Fe ₁₄
(B has a Curie point of 312 ° C.) and has a large reversible temperature coefficient of coercive force iHc. As a method of compensating for these drawbacks, part of Fe is replaced by Co to raise the Curie point, and part of Nd is Dy, Tb, Ho.
There is generally known a method of substituting a heavy rare earth element such as, for example, to increase the magnetocrystalline anisotropy constant to increase the coercive force iHc at room temperature so as to withstand use at a high temperature to some extent. However, the improvement of the Curie point due to the addition of Co leads to a decrease in iHc, and the addition of a large amount of a rare earth element such as Dy lowers the saturation magnetic flux density Br of the magnet, resulting in a high Br and a high iH.
It was difficult to realize the magnet of c.

As a method for improving Br, there is generally used a method of reducing RE and increasing T, or a method of bringing magnet alloy powder close to a single domain particle size (for example, 3 microns or less) to increase anisotropy during magnetic field molding. Target. However, if RE is reduced, i
Hc decreases monotonically. Also, if the alloy powder is pulverized to an average particle size of 3 microns or less, the powder is oxidized, resulting in iH
c is greatly reduced. To prevent oxidation, it is possible to keep the process up to sintering in an oxygen-free or low-oxygen atmosphere (for example, 1% or less), but very expensive equipment is required for mass-scale production. Since it also deteriorates the productivity, it causes a large increase in the cost of the product and is not practical. On the other hand, miniaturization and high performance of various electric and electronic devices are remarkable, and it has been desired to put into practical use magnets having high Br and high iHc as magnet materials used for these devices.

[0004]

An object of the present invention is to provide an inexpensive RE-T-M-B system sintered magnet having a high Br and a high iHc, which can be manufactured by a low cost and simple method which is rich in mass productivity.

[0005]

As a result of various investigations for high Br and high iHc, the inventors have found that controlling the crystal structure of the sintered body is extremely effective.
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 crystal grain areas having a grain size a of 15 microns or more is 50 of the total main phase area.
It has been found that a magnet having a high Br and a high iHc can be obtained by controlling the sum of the crystal grain areas where a is 5% or less and a is 5 μm or less to 2% or more and 5% or less of the total main phase area. Here, the crystal grain size a represents the number obtained by dividing the sum of the major axis and minor axis of the main phase crystal grains observed when the magnet is cut along a plane perpendicular to the anisotropic direction and the polished surface is etched, by 2. ,
The crystal grain area is calculated by a circle approximation having a as a diameter.

A magnet having a sintered body structure and high magnetic properties according to the present invention is realized by the following composition. That is, RE (a rare earth element containing Y, in which the sum of Nd, Pr and Dy is 90% by weight or more of the RE total) 29.5% or more and 32.5% or less,
B 0.8% or more and 1.5% or less, M (Al, Nb, Ga,
Mo, Ti, V, Ni, Cr, Mn, Ta, Zr, H
f, Cu, Sn, at least one kind or more, more preferably three kinds or more) 0.5% or more and 2.5% or less, the balance T (Fe, but a part thereof can be replaced by Co) and unavoidable impurities Is.

If the sum of the crystal grain areas having a crystal grain size a of 15 microns or more is less than 50% of the total area of the main phase, the degree of orientation improvement due to the secondary recrystallization during sintering is insufficient, and Br ≧ 12. 8
Cannot get kG. When the sum of the crystal grain areas where a is 5 microns or less is less than 2% of the total area of the main phase, iHc decreases and 16
Cannot obtain more than kOe. The reason for this has not been fully clarified, but it is presumed that the number of buds of the reverse magnetic domain in the grain boundary of the main phase increases. If it exceeds 5%, the degree of orientation improvement due to secondary recrystallization at the time of sintering becomes insufficient, and Br decreases.
I can't get more than 8kG.

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 in the magnet manufacturing process is extremely suppressed (for example, 2500 ppm or less), the reduction of iHc can be prevented, but this is accompanied by a large cost increase, and therefore it is set to 29.5% or more. When RE exceeds 32.5%, iHc can easily maintain a high level, but Br is lowered, so the content is set to 32.5% or less. Also Nd, Pr and D
If the sum of y is less than 90% of the RE total, Br ≧ 1
Since 2.8 kG and iHc ≧ 16 kOe cannot be satisfied at the same time, it 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%, B
Since the decrease of r becomes large, it is made 0.8% or more and 1.5% or less.

The element M has a function as an element for suppressing iHc improvement or abnormal grain growth at the time of sintering, but if it is less than 0.5%, both functions are insufficient, and as a result, the area of the crystal grain having a grain size of 5 μm or less is obtained. Is less than 2% of the total area of the main phase crystal grains, iHc ≧ 16 kOe cannot be obtained. When M exceeds 2.5%, Br decreases and Br ≧ 12.8 kG cannot be obtained, so 0.5% or more and 2.5% or less.

As a simple method for controlling the crystal grain size of the RE ₂ T ₁₄ B main phase after sintering, the average grain size (FISCHER
It is possible to apply a method in which a plurality of fine powders having different SUB-SIEVE SIZERs) are prepared, and these are mixed, followed by molding in a magnetic field, sintering and heat treatment. In addition, a method of mixing finely divided alloys having a final magnet composition into a plurality of average particle sizes, and a plurality of alloys having different compositions are finely pulverized to have different average particle sizes and then mixed at a ratio of the final magnet composition. 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 slightly changes depending on the magnet composition, the average particle size of the RE ₂ T ₁₄ B crystal grains of the magnet main phase after sintering conforms to claim 1 of the present invention. Just set it. The key point is to have multiple average particle sizes.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below with reference to Examples. However, the present invention is not limited to the examples. (Examples) Ingots adjusted to various compositions shown in Table 1 were produced, and after coarse pulverization, various average particle sizes (F.
S. S. S. ). Any commonly used method may be used as a method for producing an ingot (for example, ordinary high-frequency melting or arc melting, die casting or quenching method) and a crushing method (for example, dry jet mill method or wet ball mill method). The obtained fine powders were mixed at the mixing ratio shown in Table 2, and the mixed powders were molded in a magnetic field and then sintered magnetized by a usual method. The magnetic properties of the obtained magnet and the crystal grain size a of the main phase observed when the magnet is cut along a plane perpendicular to the anisotropic direction and the polished surface is etched have a particle size of 5 μm or less and 15 μm or more. The ratio of the sum of the crystal grain areas to the total area of the main phase (main phase area ratio) is shown in Examples 1 to 5 in Table 3.

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

[0013]

[Table 1]

[0014]

[Table 2]

[0015]

[Table 3]

[0016]

[Table 4]

The contents of each example and comparative example will be described below. Example 1 is an ingot No. 1 having the same composition. 1
And No. 2 was crushed to 4.3 microns and 5.2 microns and mixed at a ratio of 50:50, and the average particle size after mixing was 4.7 microns. As shown in Table 3, the main phase area ratio conforms to claim 1, and the magnetic characteristics are also Br.
It satisfies ≧ 12.8 kG and iHc ≧ 16 kOe.
On the other hand, Comparative Example 1 is an ingot N having the composition of Example 1.
o. 12 (see Table 4) was crushed to an average particle size of 4.7 microns, but the main phase area ratio after sintering is different from that of Example 1, and the magnetic properties are also low. This difference is due to the fact that even if the average particle size of the fine powder is the same, the particle size distribution is different.

In Example 2, ingot No. No. 1 having an RE higher than that of the final magnet composition and an element M added thereto was used. 3 was crushed to 4.3 microns and RE was made lower than the final magnet composition. 4 was ground to 5.2 microns and they were mixed in a ratio of 40:60.
By increasing the addition amount of M element having the effect of improving coercive force and suppressing crystal grain growth, M after mixing was increased to 1.2%, and iHc was further improved as compared with Example 1. On the other hand, in Comparative Example 2, as in Example 2, RE was set higher than the final composition, and M
Ingot No. with element added No. 13 and RE having a low RE. 14 was crushed to 4.3 micron and 4.5 micron, respectively, and mixed at 40:60. As is clear from Table 3, the magnetic characteristics are high in iHc, but Br does not reach 12.8 KG. This is because the area ratio of the main phase having a crystal grain size of 15 microns or more is as low as 41.9%.
The ingot No. has a low main phase area ratio. 13 and No. 1
This is because secondary recrystallization at the time of sintering did not proceed sufficiently because the fine powder particle size of 4 was almost the same.

Example 3 is an ingot N having the same composition.
o. 5 and No. 6 was pulverized to 4.0 micron and 5.6 micron respectively and then mixed in a ratio of 35:65, and the average particle size after mixing was 5.0 micron. Table 3
The main phase area ratio conforms to claim 1, as shown in FIG. Compared with Example 1, Br was slightly higher and iHc was slightly lower by slightly reducing the amount of addition of the M element, but both exceeded the specified values. Comparative Example 3 is the same as Example 3 except that the amount of M element added is further reduced from that of Example 3 to 0.4%, but as shown in Table 3, the crystal grain size of 5 μm or less is mainly used. Phase area ratio becomes 0.9%,
As a result, iHc is as low as 12.3 KOe. This is because the M element was too small and the grain growth was not sufficiently suppressed.

In the fourth embodiment, the ingot No. Nos. 7 and 8 (Table 1) were pulverized to have an average particle size of 3.9 microns and 5.7 microns and 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 and the magnetic properties conform to claim 1. The magnetic properties Br and iHc thereof are further increased as compared with those of Example 1 by reducing the amount of rare earth element, slightly increasing the average particle size after mixing, and increasing the addition amount of the crystal grain growth suppressing element M as compared with Example 1. It shows a high value. Comparative Example 4 is an ingot No. 3 containing 2.8% of M element. 17 and ingot No. 18 to 4.0 microns and 5.
It was crushed to 6 microns and mixed at a ratio of 30:70, and the average particle size after mixing was 5.1 microns. That is, it is almost the same as in Example 4 except that the amount of M element after mixing is as high as 2.8% as compared with 1.3% in Example 4, but as shown in Table 3, iHc was 18. Although it is very high at 6 kOe, Br is as low as 12.6 kG. This is because the large amount of M element suppresses the grain growth at the time of sintering, resulting in insufficient secondary recrystallization.

Example 5 is an ingot N having the same composition.
o. 9, 10, 11 for 3.7, 4.5, 5.9 respectively
The mixture was pulverized to micron and mixed at a ratio of 20:20:60, and the average particle size after mixing was 5.2 microns. As shown in Table 3, both the main phase area ratio and the magnetic characteristics meet claim 1.

[0022]

[Table 5]

[0023]

EFFECTS OF THE INVENTION The RE-T-M-B system sintered magnet of the present invention controls the grain size of the main phase after sintering to achieve a high Br and a high iHc which have never been achieved in the past. It is a magnet, and can sufficiently meet the demand for miniaturization and high functionality of various electric and electronic devices.

Claims (2)

[Claims] 1. The total area of crystal grains with a grain size of 15 microns or more is 50% or more and the sum of area of crystal grains with a grain size of 5 microns or less is 2% with respect to the total area of the main phase crystals of the magnet. 5% or less, and the magnetic characteristics are Br ≧ 12.8 kG,
A RE-T-M-B system sintered magnet excellent in magnetic characteristics, characterized in that iHc ≧ 16 kOe. 2. RE (Y is a rare earth element containing 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 below by weight%), 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
0.5% or more and 2.5% or less, the balance T (Fe, but a part thereof can be replaced by Co), and unavoidable impurities. magnet.