JPH07335468A - Manufacture of rare-earth magnet - Google Patents

Abstract

PURPOSE:To provide a high-performance Nd magnet, which has an intrinsic residual magnetization in a high density and moreover, has a full coercive force from the viewpoint of practical use, by the establishment of a new method of manufacturing the magnet. CONSTITUTION:In a method of manufacturing a rare-earth magnet consisting of a compositional formula, Rx(Fe1-aCoa)yBzTb (Here, the R is at least one kind of an element or the mixed element of two kinds or more of elements out of rare-earth elements containing Y, the T is one kind or more of a transition metal or transition metals out of transition metals and (x), (y), (z), the (a) and the (b) are respectively used on the conditions of 11<=x<=16, 70<=y<=85, 4<=z<=9, 0<=a<=0.2 and 0<=b<=4.), a sintering is conducted to the degree of vacuum of 85 to 95% in a vacuum and subsequently a sintering is conducted at the atmosphere pressure of 50 to 500 in an inert gas atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a rare earth permanent magnet, particularly an Nd based sintered magnet.

[0002]

2. Description of the Related Art Sintered rare earth magnets have recently been in high demand due to their high magnetic properties, although they are much more expensive than ferrites and the like. Among them, Nd magnets are becoming the mainstream of rare earth magnets because they have higher magnetic characteristics and are cheaper than Sm magnets. In order to improve the magnetic characteristics of the Nd-based magnet, it is sufficient to increase the remanent magnetization. However, since the Nd-based magnet has poor temperature characteristics of coercive force, it is possible to increase the remanent magnetization while maintaining as high a coercive force as possible. is necessary. In order to increase the remanent magnetization, it is sufficient to bring the density of the magnet close to the true density, but according to the usual sintering operation in vacuum or in an inert gas atmosphere from reduced pressure to atmospheric pressure, sintering is performed. If the temperature is raised or the sintering time is lengthened, the density of the magnet rises and approaches the true density, and the remanent magnetization rises.However, the sintered particles become enlarged and the coercive force decreases, so the density should be increased easily. As a result, the remanent magnetization of a practical Nd-based magnet was lower than that at the true density. As a method of bringing the density of the sintered body close to the true density without significantly reducing the coercive force, for example,
There is a method of increasing the density and residual magnetization by performing hot isostatic pressing at a pressure of 500 to 1300 atm (see Japanese Examined Patent Publication No. 4-45573), but this method uses a very high pressure, so the equipment However, there are problems to be improved, such as being very expensive, requiring careful handling of the device due to the high pressure, long processing time, and very poor production efficiency.

[0003]

The problems caused by the low density of the manufactured Nd type magnet are not only lower than the remanent magnetization originally possessed by the magnet, but also the generation of rust and the adhesion of the surface-treated coating. Performances other than magnetic properties such as defects and lack of mechanical strength will be adversely affected. The present invention solves these problems and establishes a new manufacturing method to provide a high-performance Nd-based magnet having a high density, original remanent magnetization, and practically sufficient coercive force. Is what you are trying to do.

[0004]

In order to solve such a problem, the present inventor diligently studied the manufacturing conditions of Nd-based magnets, especially the sintering conditions, and as a result, the ultrahigh pressure of 500 to 1300 atm as described above was obtained. Is a heat treatment furnace that can control the atmosphere from vacuum to 500 atm. 85 to 95% of true density in vacuum
Sintering to 50-50 in an inert gas atmosphere.
By sintering at 00 atm, it becomes possible to manufacture an Nd-based magnet having a high density, a high residual magnetization, and a practically sufficient coercive force, thus completing the present invention. The gist of the present invention is that the composition formula R _x (Fe _1-a Co _a ) _y B _z T _b (where R
Is at least one kind of rare earth element including Y or a mixed element of two or more kinds, and T is one or more kinds of transition metals, 11
≤x≤16, 70≤y≤85, 4≤z≤9, 0≤a≤0.2,0
In the method for producing a rare earth magnet of ≦ b ≦ 4), the sintering is performed to 85 to 95% of the true density in a vacuum, and then the sintering is performed at 50 to 500 atm in an inert gas atmosphere. There is a method of manufacturing a rare earth magnet.

The present invention will be described in detail below. The composition formula of the rare earth permanent magnet alloy to which the present invention is applied is R _x (Fe _1-a C
o _a ) _y B _z T _b , where R includes Y, La, C
e, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb
And one or more rare earth elements selected from Lu and T is Al, Si, Ti, V, Cr, Mn, N
It is one or more kinds of transition metal elements selected from i, Cu, Zn, Ga, Zr, Nb, Mo, Sn, Hf, Ta and W. Atomic ratio x is 11 ≦ x ≦ 16, y is 70 ≦ y ≦ 85, z is 4 ≦ z ≦
9, a is 0 ≦ a ≦ 0.2, and b is 0 ≦ b ≦ 4. In this composition, if the amount X of R is less than 11, it is not preferable because α-Fe is precipitated and the coercive force is remarkably reduced, and if it exceeds 16 the remanent magnetization becomes low, which is not preferable. Amount of B z
Is less than 4, it is not preferable because the coercive force is remarkably reduced by precipitation of the Nd ₂ Fe ₁₇ phase, and if it exceeds 9, the amount of the nonmagnetic phase Nd Fe ₄ B ₄ phase is increased and the residual magnetization is decreased, which is not preferable. . a represents the ratio of Fe and Co, and
Although the residual magnetization can be increased by substituting Fe for Co, if the amount of a exceeds 0.2, the coercive force is significantly reduced, which is not preferable. The transition metal element T, which is an additional element, is used to increase the coercive force,
If b exceeds 4, the effect of increasing the coercive force is weakened and the remanent magnetization is significantly reduced, which is not preferable.

Next, the manufacturing method of the present invention will be described. Nd-based magnets are generally sintered in vacuum or in an inert gas atmosphere from reduced pressure to atmospheric pressure, but the density of Nd-based magnets is increased without decreasing the coercive force. In order to increase the remanence, the sintering should be performed in vacuum to 85 to 95% of the true density and then continuously in two different atmospheres such as 50 to 500 atm in an inert gas atmosphere. Then, it was found that the sintering is very effective. First, the raw material metal is melt-cast in a high-frequency melting furnace in a vacuum or in an inert gas atmosphere so as to have the above composition. Next, the produced alloy is coarsely pulverized by a jaw crusher, a brown mill or the like, and then finely pulverized by a jet mill or the like. The powder having an average particle size of 1 to 20 μm obtained here was molded in a magnetic field of about 15 kOe at a pressure of 1 to ² Ton / cm ² and a density of 3 to 5
A g / cc molded body is obtained.

The compact thus obtained is subjected to sintering under the specific conditions, which is the greatest feature of the present invention. Ie 900
Sinter in a vacuum of ~ 1150 ℃ for 0.05-10 hours, increase the density of the magnet to 85-95% of the true density without open pores in the magnet, and then add an inert gas of 50-500%.
Introduce to atmospheric pressure and sinter at a temperature of 800 ℃ to 1100 ℃ for 0.1 to 5 hours. Here, the purpose of sintering in vacuum is to eliminate the magnet open pores. At temperatures below 900 ° C, the magnet density can be increased to 85 to 95% of the true density even after 10 hours or more of sintering. However, it is not preferable because the open pores do not disappear, and when sintering is performed at a temperature higher than 1150 ° C., sintered particles grow abnormally even for 0.05 hours, resulting in a rapid decrease in coercive force, which is not preferable. Also
If it is less than 0.05 hours, it is difficult to control the sintering reaction closely to keep the density within a predetermined range, which is not preferable.
If the time is exceeded, productivity will be significantly impaired, which is not preferable.

In the latter half of sintering when introducing an inert gas up to 50 atm to 500 atm, if the pressure is less than 50 atm, it takes time for the density to rise and the grain growth is accompanied with the decrease of coercive force. Even if the pressure exceeds the atmospheric pressure, the effect of increasing the density is not the same as the case where the pressure is less than 500 atmospheric pressure, since the size of the device is increased. If the temperature is lower than 800 ° C, the rate of increase in density is slow and the productivity is remarkably hindered, and if it is higher than 1100 ° C, the density and the sintered particles are rapidly enlarged and the coercive force is significantly decreased, which is not preferable. Further, if the sintering time is less than 0.1 hours, the effect of accelerating the densification is small due to the pressure of the inert gas, which is not preferable, and if it exceeds 5 hours, the coercive force and the productivity are reduced due to the grain growth, so that 0.1 to 5 is required. Good time The magnet manufactured in this way had a higher density and a higher remanent magnetization than the magnet manufactured by ordinary sintering. Further, the coercive force is reduced to about 200 G, which is very small and has a practically sufficient coercive force, and the treatment of the present invention is very effective in improving the energy product of the magnet with almost no decrease in coercive force. Met.

[0009]

The major difference between the present invention and the prior art is the continuous sintering process and the pressure range of the inert gas.
In Japanese Examined Patent Publication No. 4-45573, high density is achieved by heating again after sintering and cooling and performing hot isostatic pressing using a pressure as high as 500 to 1300 atm. In the present invention, the same effect is obtained at a pressure of 1/3 or less. This difference is concentrated on the difference between continuous treatment or once cooling and retreatment. In the present invention, since the treatment is continuous, the liquid phase generated during the first sintering is the latter half of the inert gas. It exists even during densification processing by pressure, and acts to promote densification, while in Japanese Patent Publication No. 4-45573.
In No. 1, the liquid phase changes to various intermetallic compounds after being cooled once after the primary sintering, so the amount and quality of the liquid phase in the hot isostatic pressing process, which is secondary sintering, is Since it is different from the liquid phase in binding, densification does not easily proceed 500
It is speculated that a high pressure of ~ 1300 atm may be required.

[0010]

[Examples] The following will describe specific embodiments of the present invention with reference to Examples, but the present invention is not limited thereto. (Example 1, Comparative Examples 1 to 3) The composition is Nd 13.4-Dy 0.6.
-Fe 74.5-Co 5-B 6-Al 0.5 (atomic%) alloy was melted in the induction heating high frequency melting furnace in the Ar heating atmosphere to melt each raw material metal with a purity of 99.9% by weight or more, and was cast into an ingot. It was made. This alloy was coarsely crushed using a jaw crusher and a brown mill in an Ar atmosphere, and then fine powder having an average particle size of 5 μm was obtained by a jet mill using nitrogen gas. This fine powder was pressure-molded in a magnetic field of about 15 kOe in a direction perpendicular to the magnetic field at a pressure of about ² Ton / cm ² in order to make the orientation uniform, to obtain a molded body. This compact was sintered as a first-stage sintering at 1060 ° C in vacuum for 10 minutes, and then as a second-stage sintering at 1060 ° C for 30 minutes in an atmosphere where the Ar pressure was set to three levels of 30, 200, and 600 atm. Sintering was performed. In order to confirm the density in the first-stage sintering, the density of the magnet was 7.1 g / cc, which was 7.1 g / cc when the molded body was only sintered in vacuum at 1060 ° C for 10 minutes in the same manner as above. It was 93%. The sintered body obtained in this way was
Comparative example 1 (30 atm) after aging treatment at 00 ℃ for 2 hours
Example 1 (200 atm) and Comparative Example 2 (600 atm) were used to measure the magnet characteristics, which are shown in Table 1. Separately, a molded article of the same composition obtained as described above was sintered in vacuum at 1100 ° C. for 1 hour and then subjected to the aging treatment as Comparative Example 3, and the results are also shown in Table 1. did. As is clear from Table 1, according to the method of the present invention, the density and the residual magnetization can be efficiently increased at a relatively low pressure with almost no decrease in the coercive force, and as a result, the energy product can be increased. I was able to. Further, the magnet obtained by the method of the present invention,
There were few cracks and chips, and the strength was increased.

(Example 2, Comparative Example 4) Composition formula Nd 13.6-
Dy 0.4 -Fe 74 -Co 2-B 6 -Ga 0.5 -Mo 0.5
Magnets were produced under the same processing conditions as in Example 1 and Comparative Example 3 except that the alloy (atom%) was used as the magnet raw material. It was also written in 1.

[0012]

[Table 1]

[0013]

By the manufacturing method of the present invention, it is possible to provide a high-performance rare earth sintered magnet having an increased magnet density and residual magnetization without reducing the coercive force of the magnet, and its industrial utility value is extremely high. .

Claims (1)

[Claims] 1. A composition formula R _x (Fe _1-a Co _a ) _y B _z T _b (wherein R is at least one element of rare earth elements including Y or a mixed element of two or more elements, and T is a transition element). One or more of metals, 11 ≦ x ≦ 16, 70 ≦ y ≦ 85, 4 ≦ z ≦ 9, 0 ≦ a ≦
0.2, 0 ≤ b ≤ 4) In the method for producing a rare earth magnet, the sintering should be performed to 85 to 95% of the true density in vacuum, and then to 50 to 500 atm in an inert gas atmosphere. And a method for manufacturing a rare earth magnet.