JPH09320825A - Manufacture of rare earth magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an Nd magnet which can realize a high orientation, by solving such a problem that good magnetic characteristics corresponding to the composition of the magnet cannot be obtained because of incomplete orientation at the time of molding magnet powder is a magnetic field to manufacture an Nd magnet. SOLUTION: In the method for manufacturing a rare earth made of composition alloy expressed by an expression of Rx (Fe1-a Coa )y Bz Tb (where R is not smaller than one and not larger than 10 types selected from rare earth elements including Y, T is not smaller than one and not larger than 10 types selected from a group of transition metals, 11<=x<=16, 70<=y<=85, 4<=z<=9, 0<=a<=0.2, and 0<=b<=4); the alloy containing crystalline grains having an average grain diameter of not smaller than 50μm and not larger than 10mm is hydro-crushed.

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. The Nd-based sintered magnet is manufactured by using the powder metallurgy method and undergoes the following steps. That is, an alloy is prepared by melting so as to have a predetermined composition, and the alloy is pulverized to obtain a fine powder having a size of 1 to 20 μm.
Nd-based sintered magnets are manufactured by performing molding in a magnetic field in order to give anisotropy by aligning the crystal orientation of the obtained fine powders in one direction and subjecting the obtained compacts to sintering and heat treatment. To be done. In order to improve the magnetic characteristics of the Nd-based magnet, its composition may be brought closer to that of the 2-14-1 intermetallic compound phase, which is the main phase of the Nd-based magnet, but the closer it is, the more Nd-based it becomes. Since the coercive force, which is important for the magnetic properties of the system magnet, is reduced and the tolerance for oxidation is lost, it is necessary to take measures to suppress oxidation, such as performing all the steps in a non-oxidizing atmosphere. There are drawbacks such as increased cost. On the other hand, when trying to obtain the highest possible magnetic properties by maximizing the magnetic properties of the alloy, how completely the crystal orientation can be aligned in one direction in the magnetic field of the fine powder, That is, how high the degree of orientation can be made is important. However, in a commonly used molding method using a mold, the degree of orientation is only about 90%, which is a problem to be solved in manufacturing a higher performance Nd-based magnet.

[0003]

[Problems to be solved by the invention] Nd by molding in a magnetic field
When manufacturing a system magnet, there is an adverse effect that the magnetic properties according to the composition of the magnet cannot be obtained because the orientation degree at the time of molding is not perfect. The present invention intends to solve the problems associated with the production of such Nd-based sintered magnets and to provide a method for producing an Nd-based magnet that achieves a high degree of orientation.

[0004]

In order to solve the above problems, the inventors of the present invention have carried out a magnetic field forming step in which the metallographic structure of the Nd-based magnet alloy produced through the melting step and the crushing method are post-steps. As a result of careful investigation focusing on the metallographic structure and pulverization method, it was found that the crystal grain shape in the alloy after melting was 50 μm or more with an average grain size of 10 mm or more.
It was found that the Nd-based magnets produced by forming in the magnetic field using the following alloys obtained by hydrogenation crushing have an improved degree of orientation, and as a result, Nd-based magnets having high magnetic properties are obtained.
It has become possible to manufacture a system magnet, and the present invention has been completed. The gist of the present invention is that the composition formula R _x (Fe _1-a Co _a ) _y B _z T _b
(Here, R is 1 or more and 10 or less of rare earth elements including Y, T is 1 or more and 10 or less of transition metals, x, y, z
Is atomic%, 11 ≦ x ≦ 16, 70 ≦ y ≦ 85, 4 ≦ z ≦ 9,
a and b are atomic ratios, 0 ≦ a ≦ 0.2 and 0 ≦ b ≦ 4)
The method for producing a rare earth magnet according to claim 1, wherein the alloy having crystal grains in the alloy having an average particle size of 50 μm or more and 10 mm or less is hydro-pulverized.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION 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 Co _a ) _y B _z T _b , where R is a rare earth element, Y containing La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb,
One or more selected from Dy, Ho, Er, Tm, Yb and Lu
10 or less rare earth elements, T is a transition element, Al, S
i, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Sn,
1 or more and 10 or less selected from Hf, Ta and W, atomic% x is 11 ≦ x ≦ 16, y is 70 ≦ y ≦ 85, z is 4 ≦
z ≦ 9, the atomic ratio a is 0 ≦ a ≦ 0.2, and b is 0 ≦ b ≦ 4. In this composition, when the amount x of R is 11 or less, α-Fe is precipitated and the coercive force is remarkably decreased, which is not preferable, and when it is 16 or more, the residual magnetization is low, which is not preferable. The amount z of B is not preferable because the coercivity is significantly reduced by precipitation of Nd ₂ Fe ₁₇ phase is 4 or less, Nd Fe ₄ amount of B ₄ phase increases residual magnetization to decrease at least 9 is a non-magnetic phase Not good for a represents the ratio of Fe and Co, and the residual magnetization can be increased by substituting Fe for Co. However, if the amount of a is 0.2 or more, the coercive force is remarkably reduced, which is not preferable. Additive element T
Is used to increase the coercive force, but when b is 4 or more, 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 magnets are usually manufactured through melting, coarse pulverization, fine pulverization, molding, sintering, and aging steps, but the shape of crystal grains in the alloy after melting is 50 μm or more and 10 mm or less in average particle size. The alloy may be hydrogenated into coarse powder, finely pulverized, and then molded in a magnetic field. First, the raw metal is weighed so as to have the above composition. Melting is performed in a high frequency melting furnace in a vacuum or in an inert atmosphere, and then casting is performed to produce an alloy having a predetermined composition. Next, the crystal grains of the alloy should have a mean particle size of 50 μm or more and 10 mm or less at a temperature of 900 ℃ to 1200 ℃ 0.1 ~
Heat treatment for 100 hours. The alloy thus produced having an average crystal grain size of 50 μm or more and 10 mm or less is hydrogenated into coarse powder, and then finely pulverized by a jet mill. Next, the obtained fine powder with an average particle size of 1 to 20 μm is placed in a magnetic field of about 15 kOe.
Molded at a pressure of 0.2 to ² Ton / cm ² and a density of 3 to 5 g / cc
To obtain a molded body of. The molded body obtained as described above,
Sinter in a vacuum at 1000 ℃ to 1150 ℃ or in an inert gas below atmospheric pressure for 0.1 to 10 hours, cool it down to 400 ℃ to 10 ℃.
Aging treatment is performed at 00 ° C for 0.1 to 10 hours to obtain an Nd-based magnet.

If the heat treatment temperature of the alloy is lower than 900 ° C., it takes a very long time to grow the average grain size of the crystal grains in the alloy to 50 μm, which is not preferable.
If the temperature exceeds 00 ° C, the alloy may melt due to the high temperature, which is not preferable. If the heat treatment time of the alloy is less than 0.1 hours, the average grain size of the crystal grains in the alloy is 50
It is not preferable because it is difficult to grow to μm, and productivity is unfavorable even after 100 hours because productivity is poor. The heat treatment may be performed by selecting the conditions in the above range, and more preferably in the temperature range of 1050 ° C to 1150 ° C for 2 to 20 hours. If the average grain size of the crystal grains is less than 50 μm, the crystal growth is insufficient, and the pulverization rate from the crystal grain boundaries that occurs in the hydrogenation in the next step will decrease. Further, the reason why the particle size is set to 10 mm or less is that the hydrogenation and pulverization effect does not change even if the particle size is in this range, but it takes a very long time for crystal growth and the productivity is poor. The coarse pulverization by hydrogenation is performed at a hydrogen gas pressure of 0.001 MPa to 5 MPa. When the hydrogen gas pressure is less than 0.001 MPa, the hydrogen storage rate is extremely slow and the productivity is very poor, which is not preferable. Further, even if the hydrogen gas pressure exceeds 5 MPa, the hydrogen absorption rate does not almost increase, and the vicinity of the alloy surface becomes excessive hydrogen concentration and becomes amorphous, which adversely deteriorates the magnetic characteristics, which is not preferable. Nd as above
By producing a system magnet, the degree of orientation of the fine powder during molding in a magnetic field is improved, and as a result, the magnetic characteristics of the Nd system magnet can be improved.

While the operation of the present invention has been focused on bringing the composition thereof closer to that of the 2-14-1 intermetallic compound which is a ferromagnetic material, as a means for improving the magnetic properties, the prior art has been focused on. Then, focusing on trying to extract 100% of the magnetic properties of the composition, the effect of the average crystal grain size in the alloy on the magnetic properties was clarified. Usually N
When manufacturing d-based magnets, the magnet alloy has an average grain size of about 5μ.
It is crushed to a size of about m. When this fine powder is a single crystal, it is considered that the fine powder can be aligned in parallel with the crystal orientation in the magnetic field even in the subsequent magnetic field formation. When there is a fine powder that has grain boundaries, that is, when it is a polycrystal, the fine powder is aligned in the most stable direction in the magnetic field, and the direction is the direction of the magnetic field and the crystal. It is considered that this is a factor that reduces the degree of orientation because the directions are not aligned in parallel. For these reasons, the average grain size in the alloy is preferably larger than that of the fine powder obtained by pulverization. Further, when pulverization by hydrogenation is performed, the alloy is characterized by being preferentially pulverized at the grain boundaries. This is because lattice defects, rare earth elements, impurities, etc. are concentrated in the crystal grain boundaries that have been subjected to heat treatment to enlarge the crystal grains in the alloy,
It is considered that hydrogen is caused by diffusion along the grain boundaries of the alloy. Due to these phenomena, it is considered that there is no or very few particles that include grain boundaries in the fine powder that has undergone the pulverization process with hydrogen, using an alloy that includes large-grown crystal particles. It is considered that the degree of orientation is increased.

[0009]

EXAMPLES Hereinafter, embodiments of the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. (Example 1) Composition formula Nd _12.7 Dy _2.2 Fe _74.6 Co ₄ B ₆ A
An alloy of _0.5 was melted in an induction heating high-frequency melting furnace in a raw material metal having a purity of 99.9% by weight or more, and cast to prepare an alloy. Next, heat treatment is performed at a temperature of 1080 ° C. for 20 hours so that the crystal grains of the alloy have an average particle diameter of 50 μm or more and 10 mm or less, and then cooled. The average crystal grain size of the alloy thus produced was 95 μm. The alloy was roughly pulverized by hydrogenation in an atmosphere of 0.07 MPa hydrogen having a purity of 99.99% by volume, 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 0.9 Ton / cm ² in order to align the directions, to obtain a compact.
This molded body was sintered in vacuum at 1060 ° C. for 90 minutes and then cooled to obtain a sintered body. The sintered body thus obtained was subsequently subjected to an aging treatment at 600 ° C. for 120 minutes in an inert gas atmosphere to obtain a Nd-based sintered permanent magnet, and the magnetic properties were measured and shown in Table 1.

(Example 2) An average crystal grain size of 150 μm having the same composition as in Example 1 obtained by heat treatment at 1120 ° C. for 40 hours
This alloy was treated in the same manner as in Example 1 except that the alloy was roughly pulverized by hydrogenation in an atmosphere of 0.25 MPa of hydrogen having a purity of 99.99% by volume to obtain a Nd-based sintered permanent magnet. The magnetic properties were measured and are also shown in Table 1.

(Comparative Example 1) The alloy of Example 1 has a purity of 99.99.
A Nd-based sintered permanent magnet was obtained in the same manner as in Example 1 except that coarse pulverization was carried out by hydrogenation in an atmosphere of 0.0007 MPa of hydrogen in volume%. The magnetic properties were measured and are also shown in Table 1.

(Comparative Example 2) The alloy of Example 2 has a purity of 99.99.
A Nd-based sintered permanent magnet was obtained in the same manner as in Example 2 except that coarse pulverization was carried out by hydrogenation in an atmosphere of 5.2% by volume hydrogen. The magnetic properties were measured and are also shown in Table 1.

(Calculation of degree of orientation) The degree of orientation was calculated using the following formula based on the results of the magnetic characteristics obtained in the examples and comparative examples. F = (Br × (ρt / ρr) ^2/3 / Is) × 100 F: orientation degree (%), Br: remanent magnetization of sample (k
G), ρt: true density (g / cc), ρr: sample density (g / c)
c), Is: Saturation magnetic flux density (kG) of the sample. The results are shown in Table 1. As is clear from Table 1, according to the method of the present invention, the degree of orientation can be improved, the residual magnetization can be increased, and as a result, the energy product can be increased.

[0014]

[Table 1]

[0015]

According to the manufacturing method of the present invention, a high-performance rare earth sintered magnet having a high degree of orientation can be provided, and its utility value is extremely high in industry.

Claims (1)

[Claims] 1. A composition formula R _x (Fe _1-a Co _a ) _y B _z T _b (wherein R is one or more and 10 or less of rare earth elements containing Y, and T is one of transition metals). 10 to 10 species, x, y, z are atomic%
And 11 ≦ x ≦ 16, 70 ≦ y ≦ 85, 4 ≦ z ≦ 9, and a and b are atomic ratios of 0 ≦ a ≦ 0.2 and 0 ≦ b ≦ 4. A method for producing a rare earth magnet, characterized in that an alloy having an average grain size of 50 μm or more and 10 mm or less is hydro-pulverized.