JP2000082610A - High electric resitivity rare earth permanent magnet and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an RTB magnet for suppressing the generation of excess currents such as an RTB magnet whose electric resistance is made two times higher or more than that of a conventional permanent magnet, or an RTB magnet having an inclined function whose electric resistivity is changed to the magnetizing direction of the permanent magnet, and a method for manufacturing this RTB magnet. SOLUTION: A rare earth oxide with a relatively small mean grain size is mixed and stirred in material powder for a normal high performance RTB magnet with a required mean grain size, and then this is molded and sintered so that a structure in which the rare earth oxide is contained in the crystal grain boundary of a magnet alloy structure can be obtained. Thus, electric resistivity which is two times higher or mote than that of a conventional RTB magnet can be obtained. For example, it is possible to obtain a laminated structure by using alloy powder containing the oxide only to the surface, to apply any insulating film to the surface in a following process for reducing excess currents, and to manufacture this RTB magnet in a normal magnet manufacturing process without adding any process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a high performance rare earth magnet (hereinafter, referred to as an RTB magnet) mainly composed of a rare earth (including Y), a transition metal and boron used for a motor or the like. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high electric resistivity rare earth permanent magnet in which, in addition to the inherent high performance characteristics of a system magnet, the electric resistivity is increased and the generation of eddy current when used in a motor or the like is reduced, and a method of manufacturing the same.

[0002]

2. Description of the Related Art In recent years, the trend toward smaller, lighter, more efficient and energy-saving motors and generators for electric equipment has been
A configuration using a B-based magnet has been adopted. For the same reason, it is also used in motors and generators of electric vehicles.

An RTB magnet is a metal magnet composed of an intermetallic compound containing a transition metal as a main component.
Since the electric resistance is essentially low, an eddy current is easily generated inside the magnet, which causes a decrease in magnetic properties and efficiency due to heat generated by the eddy current.

[0004] Therefore, in general, measures are taken to reduce eddy currents by processing the magnet into a final magnet shape, such as a core material of a motor, for example, a silicon steel plate, and then applying an insulating film on the magnet surface. Have been.

[0005]

However, since the conventional insulating film insulates only the magnet surface, the field of use, application,
There was a problem that could not cope with the usage conditions.

On the other hand, if the electrical resistivity is increased by changing the composition or the like of the RTB magnet itself, the magnetic properties are reduced. Therefore, a configuration or means for increasing the electrical resistivity by improving the RTB magnet itself has been proposed. I didn't.

For example, in the case of a magnet for a motor, it is expected that the generation of an eddy current can be suppressed if the electric resistivity is high only on the air gap side where the magnetic field acts. No proposal has been made regarding an RTB magnet having a rate-grading function.

According to the present invention, at least one rare earth element R selected from the rare earth elements containing Y and boron B
Containing transition metal and transition metal (50% of transition metal amount)
% Can be replaced by Co), in view of the problem with respect to the electrical resistivity of the RTB-based magnet composed of RTB-based magnets whose electrical resistance is more than twice as high as that of conventional permanent magnets, and in the direction of magnetization of the permanent magnets. It is an object of the present invention to provide an RTB-based magnet capable of suppressing generation of eddy current, such as an RTB-based magnet having a tilting function with changed electric resistivity, and a method of manufacturing the same.

[0009]

Means for Solving the Problems The inventors of the present invention conducted various studies on the crystal structure for the purpose of increasing the electrical resistivity of the RTB magnet itself, and as a result, obtained a normal high-performance RTB magnet having a required average particle size. A rare earth oxide having a relatively small average particle size is mixed and stirred with the raw material powder for use, and then molded and sintered to form a structure containing the rare earth oxide in the crystal grain boundaries of the magnet alloy structure. It has been found that an electrical resistivity twice or more that of a magnet can be obtained.

In addition, the inventor of the present invention prepared a molded body in which the content of the rare-earth oxide-containing RTB magnet was changed such that the content of the rare-earth oxide increased from the center of the magnet to the surface layer. Having an inclination function of increasing the electric resistance from the center of the magnet toward the surface by sintering R
A TB-based magnet can be obtained, and a high-resistivity RTB-based magnet raw material according to the present invention is placed on a normal RTB-based magnet raw material to form a molded body, which is sintered to obtain a surface layer of the magnet. It has been found that an optimum magnet for a motor having only a portion having a high electric resistivity can be obtained.

Further, the inventor of the present invention has found that, in the RTB-based magnet containing the rare earth oxide, the electric resistance can be increased in proportion to the amount of the oxide, and the oxidation of alumina, magnesia, calcia or the like can be substituted for the rare earth oxide. The present invention has been found to be able to contain ceramics and can be used, for example, in a rotor of a permanent magnet type high-speed generator having a problem that eddy current is generated in proportion to the peripheral speed, and completed the present invention.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Rare earth elements (including Y) R
Accounts for 10 to 30 atomic% of the composition, but Nd,
At least one of Pr, Dy, Ho, and Tb, or La, Ce, Sm, Gd, Er, Eu, T
Those containing at least one of m, Yb, Lu, and Y are preferable. Also, usually one of R is sufficient,
Practically, a mixture of two or more kinds (mish metal, sidinium, etc.) can be used for reasons such as convenience in obtaining. Note that R may not be a pure rare earth element, and may contain impurities that are unavoidable in production within the industrially available range.

R is an essential element in the above-mentioned system magnet powder, and if it is less than 10 atomic%, the crystal structure has the same cubic structure as that of α-iron, so that high magnetic properties, especially high coercive force, cannot be obtained. , More than 30 atomic%, the R-rich nonmagnetic phase increases, the residual magnetic flux density (Br) decreases, and a permanent magnet having excellent characteristics cannot be obtained. Therefore, R is desirably in the range of 10 at% to 30 at%.

Boron B is an essential element in the above-mentioned system magnet powder. If it is less than 2 atomic%, a rhombohedral structure becomes the main phase, and a high coercive force (iHc) cannot be obtained. Since the number of non-magnetic phases increases and the residual magnetic flux density (Br) decreases, an excellent permanent magnet cannot be obtained. Therefore, B is desirably in the range of 2 to 28 atomic%.

A transition metal, particularly Fe, is an essential element in the above-mentioned system magnet powder. When the content is less than 65 at%, the residual magnetic flux density (Br) decreases, and when it exceeds 80 at%, a high coercive force cannot be obtained. Fe is desirably contained at 65 to 80 atomic%. Replacing part of Fe with Co can improve the temperature characteristics without impairing the magnetic characteristics of the obtained magnet. However, when the amount of Co exceeds 20% of Fe, the magnetic characteristics are conversely increased. It is not preferable because it deteriorates.
When the substitution amount of Co is 5 atomic% to 15 atomic% in the total amount of Fe and Co, (Br) increases as compared with the case where the substitution is not performed, so that it is preferable to obtain a high magnetic flux density.

In addition to the above-mentioned main components, the presence of unavoidable impurities in industrial production can be tolerated. For example, C, P, S, Cu, etc., and Al, Ti, V, Cr, Mn, Bi, N
b, Ta, Mo, W, Sb, Ge, Ga, Sn, Zr,
At least one of Ni, Si, Zn, and Hf may be added to the magnet powder because it is effective for improving the coercive force and the squareness of the demagnetization curve, improving the productivity, and reducing the price. it can. In particular, it is also effective to add Co, Al, Si, Mo, Ta, W as a small amount of additional element in order to enhance the magnetic characteristics, or to replace a part of B with C in order to improve the corrosion resistance.

The raw material for the magnet is prepared by dissolving a required R-Fe-B-based alloy and pulverizing it after casting, a melt-pulverization method, a direct reduction diffusion method of obtaining powder directly by Ca reduction, a required R-Fe-B
Quenching alloy method of obtaining a ribbon foil using a dissolving jet caster and crushing and annealing it, gas atomizing method of melting a required R-Fe-B alloy, pulverizing it with a gas atomizer and heat-treating it, required metal After mechanically pulverizing, pulverizing by mechanical alloying and heat treatment, and a method of decomposing and recrystallizing a required R-Fe-B alloy by heating it in hydrogen (HDDR
And isotropic and anisotropic powders obtained by various production methods such as

In the method of manufacturing an RTB magnet according to the present invention, a normal powder sintering method is used in which a rare earth oxide powder is mixed and stirred with an R-Fe-B magnet alloy powder, and then molded and sintered. Rare earth element R, transition metal T, boron B
As the oxide to be mixed with the alloy powder containing as a main component, one or more rare earth oxides or ceramic oxides such as alumina, magnesia, and calcia are used.

In the present invention, the rare earth oxides and other oxides can be used alone or as a mixture. Since the oxide can increase the electric resistance in proportion to its content, the resistance can be increased by a small amount. However, in practice, it is desirable that the oxide contains 0.5% by weight or more. 1.5% or more is desirable for applications that require an increase in In the case of a permanent magnet type high speed generator for special use, mixing of 2% or more oxide is effective.

In the present invention, the average particle size of the oxide rare earth oxide and ceramic is preferably 0.05 to 4 μm. If the average particle size is less than 0.05 μm, it reacts with the main phase in the sintering step to form the oxide boundary phase. If it is not formed, and if it exceeds 4 μm, the sintering density does not increase and desired magnetic properties cannot be obtained. A particularly preferred range is from 0.1 to 2 μm.

The average particle size of the RTB magnet alloy powder is 2 μm.
If it is less than m, oxidation in the pulverization, pressing and sintering steps is remarkable, and the sintering density does not increase.
If it exceeds μm, a sufficient sintering density cannot be obtained in the sintering step and the magnetic properties deteriorate, so that the average particle size is preferably 2 to 8 μm. A more preferred range is 3 to 6 μm.

In the present invention, the sintered magnet of the present invention containing the above-mentioned oxide has a sintering temperature lower than that of the conventional rare-earth magnet in order to suppress the reaction with the mixed oxide and obtain desired magnetic properties. It is necessary to sinter at a slightly lower sintering temperature. If the normal sintering temperature of only the conventional R, T, B ternary main component alloy is, for example, 1120 ° C., 1090 ° C.
Sintering in the vicinity is optimal.

In the present invention, since the sintering density is set low to contain the oxide, the magnetic characteristics are RTB.
Although it is slightly lower than the case where only the base magnet alloy is used, the maximum energy product is practically (BH) max = 25 to 38MGO
E-levels can be manufactured.

The electric resistivity of the RTB magnet according to the present invention can be set to a desired value by appropriately selecting the compounding amount of the oxide, the mixing method, the sintering temperature, and the like. It is desirable that only an ordinary RTB magnet alloy containing no oxide or the like has an electric resistivity of 1.3 times or more, and more preferably 2 times or more of the electric resistivity. 40,000 rpm for special applications
The above ultra-high-speed generator and electric motor require three times or more.

In the RTB magnet according to the present invention, it is also effective to form a concentration gradient of the contained oxide, that is, a gradient composition, in order to take advantage of the characteristic of having a high electric resistivity. That is, several kinds of alloy powders having different compositional concentrations of oxides to be added are prepared, and each powder is filled in a mold in a layered manner in a magnetization direction (NS direction) at the time of press molding of the powder, so that a sintered magnet is obtained. Can have a gradient function structure in which the oxide composition changes, for example, the magnetization direction changes, and the electrical resistivity increases toward the surface layer side.

In the present invention, the electric resistivity is increased by using an alloy powder having a large particle size or an alloy powder having a composition containing a large amount of rare earth or boron, and the electric resistivity is increased by using an alloy powder having a different particle size and / or composition. Means for changing
It is possible to cope with various uses by using together with a means for changing the concentration of the contained oxide.

By using alloy powders having different oxide composition concentrations, the obtained magnets have different densities after sintering, or the electric resistivity at the corresponding portions is changed depending on the oxide composition ratio. Alternatively, a permanent magnet with a functionally graded structure can be created. Only the surface layer or a required portion has an increased electric resistivity, or a layer having a high electric resistivity and a normal low layer are alternately laminated.
The configuration and the like can be appropriately selected. In high-speed generators and high-speed permanent magnet type synchronous machines, the thickness of the inclined layer is usually 1 to 15 m.
m, preferably 2 to 10 mm.

For example, the layer having a high electric resistivity or the inclined layer may be usually provided only on the gap side of the magnetic circuit where the eddy current is generated, that is, on the side facing the gap between the rotor and the stator in terms of the motor. Depending on the structure of the motor, a structure formed on both sides of the magnet is also effective.

[0029]

EXAMPLES Example 1 27.5 wt% Nd-3.5 wt% Dy-1.2 wt%
B-0.2wt% Si-0.4wt% Al-0.6wt
% W-balFe alloy is prepared by vacuum melting,
To a powder crushed to 2.9 μm by ball mill crushing,
2.8 wt% of Nd ₂ O ₃ oxide was mixed with a rocking mixer, and the obtained powder was press-molded, sintered at 1040 ° C. × 3 hr in a high-purity argon atmosphere, and 580
A heat treatment was performed at 3 ° C. × 3 hours to prepare a sintered magnet.

As a comparative example, 27.5 wt% Nd-3.
5 wt% Dy-1.2 wt% B-0.2 wt% Si-
An alloy having a composition of 0.4 wt% Al-0.6 wt% W-balFe is prepared by vacuum melting, and a 2.9 μm pulverized powder is prepared by ball mill pulverization, and is press-molded to 1100 ° C. in a high-purity argon atmosphere. × 3hr sintered and 580
A heat treatment was performed at 3 ° C. × 3 hours to prepare a sintered magnet.

The sintered magnets of Example 1 and Comparative Example were measured for electrical resistance and magnetic properties using a (BH) tracer by a four-terminal method, and the measurement results are shown in Table 1. As shown in Example 1, it can be seen that the sintered magnet of the present invention has a slightly reduced magnetic property but a significantly increased electrical resistivity.

Example 2 27.5 wt% Nd-3.5 wt% Dy-1.2 wt%
B-0.2wt% Si-0.4wt% Al-0.6wt
% Of W-balFe, and two kinds of RTB-based alloy powders, an oxide-added alloy powder obtained by mixing this alloy powder with Nd ₂ O ₃ oxide of 3.5 wt%. The alloy powder layer is a 6 mm thick base layer, and each side is 1 m each.
A plate-shaped compact having a three-layer structure in which an oxide-added alloy powder layer having a thickness of m is arranged is formed, and is formed in a high-purity argon atmosphere at 1080 m.
And sintered at 580 ° C. for 3 hours to prepare a sintered magnet.

In the same manner as in Example 1, the sintered magnet was measured for electric resistance and magnetic properties by a (BH) tracer by a four-terminal method, and the measurement results are shown in Table 1. As shown in Example 1, it can be seen that the sintered magnet of the present invention showed a slight decrease in magnetic properties but a large increase in electric resistivity.

[0034]

[Table 1]

[0035]

According to the RTB magnet of the present invention, the electrical resistivity of the magnet itself is remarkably increased while the high magnetic properties of the rare-earth magnet are maintained at an appropriate level, and the RTB magnet is suitable for high-speed generators, high-speed permanent magnet type synchronous machines, and the like. The electric resistivity can be made to have a gradient in the electric resistivity in a required portion such as the whole magnet or a surface layer, and further in the direction of easy magnetization, which has the effect of reducing the generation of eddy current.

In general, measures are taken to reduce the eddy current by applying an insulating film on the surface in a post-process, such as a core material of a motor, for example, a silicon steel plate. There is no additional process such as insulation treatment, so it can be manufactured in the usual magnet manufacturing process.In addition, the electric resistance of the magnet itself is increased, and depending on the application, the inclination function is further added, so that the field of use, application, use There is an advantage that various additional functions can be realized depending on conditions.

Claims (7)

[Claims] 1. An RTB-based magnet alloy structure mainly composed of a rare earth element (including Y), a transition metal and boron, wherein at least one kind of rare earth oxide or at least one kind of ceramic is contained in a crystal grain boundary. Electric resistivity rare earth permanent magnet. 2. The high electric resistivity rare earth permanent magnet according to claim 1, wherein the amount of the rare earth oxide or the amount of the ceramic contained in the magnetizing direction increases and the electric resistance increases in the same direction. 3. A required portion of an RTB-based magnet alloy containing a rare earth element (including Y), a transition metal and boron as main components,
A high electric resistivity rare earth permanent magnet having a high electric resistance magnet layer containing a rare earth oxide at a crystal grain boundary of a B-based magnet alloy structure. 4. The permanent magnet of claim 3, wherein the magnet layer having a high electric resistance is provided on a surface layer of the RTB magnet. 5. The high electric resistivity rare earth permanent magnet according to claim 1, wherein the rare earth oxide or the ceramic further contains 0.5% by weight or more in total. 6. An RTB-based magnet alloy powder containing a rare earth element (including Y), a transition metal and boron as main components and having an average particle size of 2 to 8 μm, and at least one of an average particle size of 0.05 to 4 μm. Rare earth oxide powder or at least 1
A method for producing a high electric resistivity rare earth magnet in which various ceramic powders are mixed and stirred, then molded and sintered. 7. The method according to claim 6, wherein a rare earth oxide or a ceramic is added in a total amount of 0.5% by weight or more.