JP2720040B2 - Sintered permanent magnet material and its manufacturing method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare earth sintered permanent magnet containing Fe-BR as a basic system and containing Co, and a method of manufacturing the same. The present invention relates to a permanent magnet, a sintered permanent magnet material having a wide optimum range of heat treatment conditions, and extremely excellent manufacturability, and a method for producing the same.

BACKGROUND ART The present applicant has previously described Nd and Pr that do not require expensive Sm or Co.
A new high-performance magnet that uses B and Fe as main components, and greatly exceeds the highest characteristics of conventional rare-earth cobalt magnets, using Fe-BR-based permanent magnets. It was proposed (Japanese Patent Publication No. 61-34242).

Further, in these magnet materials, a permanent magnet was proposed in which part of Fe was replaced with Co to increase the Curie temperature and improve the temperature characteristics of the magnet (Japanese Patent Application Laid-Open No. 59-64733).

Furthermore, in order to obtain a stable coercive force in the harsh environment required for today's permanent magnets, that is, when used in a high temperature atmosphere or when exposed to a demagnetizing field due to armature reaction when incorporated in a motor etc. Additional element M (= Nb,
(Cr, Mo, W, Al, etc.) (JP-A-59-64733)
And Japanese Patent Application Laid-Open No. Sho 58-132104) and those in which a part of the above-mentioned Nd and Pr are substituted with heavy rare earth elements such as Tb and Dy to obtain a higher coercive force (Japanese Patent Application Laid-Open No. 58-141850). Permanent magnet with improved coercive force by performing
No. 04, JP-A-59-218704).

In each of the above permanent magnets, Fe-Co-BR containing Co is used.
Although system magnets improve the temperature characteristics and corrosion resistance of magnets,
In order to obtain a high coercive force, the optimum temperature range of the heat treatment condition is narrow, and it is difficult to maintain the temperature range. This has the effect of reducing the coercive force and the demagnetization curve squareness.

Further, in order to obtain a high coercive force, the additive element M and heavy rare earth element must be used in a large amount. Although the coercive force increases, the residual magnetic flux density Br decreases by that amount, and a high energy product is obtained. There was no problem.

SUMMARY OF THE INVENTION The present invention provides a Fe-Co-BR-based permanent magnet material containing Co, which exhibits high magnetic properties of the order of 40MGOe, and has high coercive force and excellent squareness. And a manufacturing method for obtaining the permanent magnet with good productivity.

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention has conducted various studies on the composition of a permanent magnet material, and found that Fe-Co-BR
Fe-Co-BR- containing a small amount of Cu based on the system
By molding a Cu-based alloy powder of a certain composition range, sintering it, and heat-treating it at a specific temperature, there is no decrease in magnet properties, especially residual magnetic flux density, and the coercive force and demagnetization curve angle The inventors have found that a permanent magnet material with significantly improved moldability can be obtained, and have completed the present invention.

Atomic ratio of Nd and Pr is 12-17at% (However, part of Nd and Pr can be replaced with heavy rare earth elements such as Dy and Tb at 0.2at% -3.0at%), B5-14at%, Co20at% or less A sintered permanent magnet material comprising 0.02 to 0.5 at% of Cu, the balance being Fe and unavoidable impurities; and forming an alloy powder having an average particle size of 0.5 μm to 10 μm having the above-mentioned composition. A method for producing a sintered permanent magnet material, comprising: sintering at 900 to 1200 ° C in an oxidizing or reducing atmosphere; and performing heat treatment at a temperature of 430 to 600 ° C after sintering.

Effect of the Invention The Fe-Co-BR-Cu permanent magnet is a compound magnet based on the Fe-BR system, and has an X-ray analysis pattern of crystallinity completely different from conventional amorphous thin films and super-quenched ribbons. And the main phase is a tetragonal crystal structure.

The inclusion of a very small amount of Cu, which is a feature of the present invention, relaxes the heat treatment conditions for the Fe-Co-BR-based permanent magnet material containing Co, and does not lower the residual magnetic flux density. It is possible to obtain a magnetic force and an excellent squareness of a demagnetization curve, and as a result, a high maximum energy product of 25 MGOe or more can be obtained.

In the present invention, Cu is a conventional Fe-B-
Rigorous heat treatment conditions required in the R system, ie,
The narrow optimum temperature range and fast cooling rate conditions are relaxed, and a wide optimum temperature and a free cooling rate can be selected. These are extremely effective for heat treatment of large magnets and for cracking of magnets during cooling after heat treatment.

Reasons for limiting the permanent magnet composition Rare earth element R needs to be added in an amount of 12 at% or more in order to make the coercive force of the permanent magnet 12 kOe or more and the maximum energy product 25 MGOe or more. In addition, since (BH) max decreases with the decrease in Br, the total of Nd and Pr must be 12 at% to 17 at%, and a more preferable range is 12.5 at% to 15 at%.

In the present permanent magnet, Nd and Pr have almost the same function as elements and can contain either one alone. However, when Nd is added for convenience of the raw material, about several% is always required.
Whether or not Pr is contained and Pr is positively added may be appropriately selected according to the raw material.

Some of Nd and Pr are replaced by heavy rare earth elements such as Dy and Tb.
A higher coercive force can be obtained by substituting 0.2 at% to 3.0 at%.

Furthermore, of the impurities contained in the rare earth elements, La, Ce
And the like may be contained in a small amount, for example, 5 at% or less of all rare earth elements.

In the present permanent magnet material, Co is effective for improving oxidation resistance even in a small amount of, for example, about 1 at%, and is effective for increasing Tc.
Is obtained.

The amount of Co is added to make the iHc of the permanent magnet 12 kOe or more, but the content is made 20 at% or less in consideration of the Tc improvement effect and cost. As the Co component, an R-Co alloy or the like can be added. The preferred range of the Co amount is 1 to 8 at%.

B is 5 at to make the coercive force of the permanent magnet 10 kOe or more.
% Or more is required, and iHc increases with the addition. However, in order to set (BH) max to 20MGOe or more, it is necessary to set it to 14at% or less.

In the present invention, Cu makes it possible to relax the heat treatment conditions in the Fe-Co-BR-based permanent magnet without reducing other magnetic properties, that is, the residual magnetic flux density B and the maximum energy product (BH) max at all. Yes, as a result, the coercive force is increased, the squareness of the demagnetization curve is improved, and (BH) max can be improved.

As shown in FIG. 1 showing changes in the amount of Cu and the obtained magnetic properties,
Cu greatly improves the magnetic properties of Fe-BR-based magnets containing Co even with a very small addition.

In the present invention, the amount of Cu needs to be added at least 0.01 at% in order to improve the magnetic properties. However, if it exceeds 0.5 at%, the sintered density decreases, so the upper limit is 0.5 at%. A preferred range is from 0.03 at% to 0.3 at%. More preferably, it is 0.05 at% to 0.2 at% from the viewpoint of (BH) max.

Cu used in the present invention may be a mixture with iron or ferroboron used as a raw material.

Furthermore, the presence of small amounts of C, S, P, Ca, Mg, O, Al, and Si contained in the raw materials used or mixed in the production process does not impair the effects of the present invention.

Manufacturing Method First, an alloy powder having a Fe-Co-BR-Cu composition as a starting material is obtained.

After normal alloy melting, for example, casting, such as alloy ingot obtained by cooling under conditions that do not become amorphous state, may be pulverized and classified into alloy powder by blending, etc., or Fe,
An alloy powder obtained by a reduction method from a rare earth oxide by using a reducing agent such as Ca together with Co, FeB powder or the like can be used.

The average particle size of the alloy powder is 0.
If it is less than 5 μm, the powder is oxidized remarkably during pulverization or in the subsequent manufacturing process, and the density after sintering does not increase, resulting in low magnet properties. Average particle size
The range is 0.5 to 10 μm. In order to obtain excellent magnet properties, the average particle size is most preferably from 1.0 to 5 μm.

The pulverization can be performed by either a wet method or a dry method, but is preferably performed by a dry method. In order to prevent the powder from being oxidized, it is necessary to perform the pulverization in an atmosphere of an inert gas such as nitrogen or argon. Dry milling methods include disc mills,
There are jet mills and the like.

Next, the alloy powder is molded, and the molding method can be performed in the same manner as a normal powder metallurgy method, and pressure molding is preferable.
In order to make the alloy anisotropic, for example, the alloy powder is pressed at a pressure of 0.5 to 3.0 ton / cm ^{2 in} a magnetic field of 5 kOe or more.

The sintering of the molded body may be performed at a predetermined temperature of 900 to 1200 ° C. in a normal reducing or non-oxidizing atmosphere.

For example, this compact is not placed in a vacuum of 10 ^-2 Torr or less,
Sintering is carried out in an atmosphere of an inert gas or a reducing gas having a purity of 1 to 76 Torr and a purity of 99% or more at a temperature of 900 to 1200 ° C. for 0.5 to 4 hours.

The sintering is performed by adjusting conditions such as temperature and time so as to obtain a predetermined crystal grain size and sintering density.

The density of the sintered body is preferably 95% or more of the theoretical density (ratio) in terms of magnetic characteristics. For example, at a sintering temperature of 1040 to 1160 ° C, the density of the sintered body is 7.
2 g / cm ³ or more are obtained, which corresponds to more than 95% of the theoretical density. Furthermore, in sintering at 1060 to 1100 ° C, the theoretical density ratio is 99
%, Which is particularly preferred.

After sintering, the cooling rate to room temperature is
In the case of the Fe-Co-BR magnet, the cooling rate after sintering was required to be 100 ° C / min or more in order to prevent variations in magnetic properties.

However, in the present invention containing Cu, as shown in the examples, it is sufficient if the temperature is extremely slow cooling, for example, 3 ° C./min or more. Under such slow cooling conditions, the aforementioned 430-600
C. can be retained for a sufficiently long time, and the same effect as that of the present invention can be obtained by slow cooling after sintering without cooling to near room temperature once.

The aging treatment is performed in a temperature range of 430 ° C to 600 ° C in a vacuum, an inert gas, or a reducing gas atmosphere for about 5 minutes.
Perform for 40 hours.

Slow cooling after aging treatment also required a high cooling rate of 200 ° C./min or more in order to prevent a decrease in coercive force in the conventional case containing no Cu.

However, in the present invention, cooling can be performed at a cooling rate in a wide range of 3 to 200 ° C./min, and deformation and cracking of a magnet can be prevented, and the heat treatment furnace is extremely advantageous in terms of preventing damage.

In addition, as an aging treatment for the sintered magnet,
A two-stage or more multi-stage aging treatment in which the temperature is maintained at 0 to 900 ° C. for 5 minutes to 10 hours and then heat treatment is performed at a predetermined temperature is also effective.

In order to further increase the coercive force and improve the oxidation resistance of magnets and powders, Ti, V, Nb, Cr, M
o, W, Al, Zr, Hf, Zn, Ca, and Si may be contained.

EXAMPLES Example 1 Electrolytic iron and copper having a purity of 99.9% by weight as starting materials and a purity of 99.7%
Ferroboron containing more than wt% Co and 19wt% B, purity
Using Nd of 97 wt% or more, a composition alloy of Fe-4Co-14.5Nd-7B-xCu (x = 0.01 to 0.4 at%) in atomic ratio was melted in a vacuum and an argon atmosphere to obtain an ingot. .

After that, this ingot is coarsely crushed with a jaw crusher,
Further, finely pulverized by a jet mill with N ₂ gas flow, finely pulverized powder having an average particle size of 3.5 μm was charged into a mold of a press device, and
It was oriented in a magnetic field of 0 kOe and formed at a pressure of 1.5 ton / cm ^{2 in} a direction perpendicular to the magnetic field.

The obtained molded body is sintered at 1060 to 1100 ° C. for 2 hours in an Ar atmosphere, and further heat-treated at 500 to 600 ° C. in an Ar atmosphere.
It was cooled at a rate of about 30 ° C./min.

The coercive force, maximum energy product, and sintered density of the obtained various permanent magnets were measured, and the relationship with the change in the amount of Cu added is shown in FIG. The figure plots the highest values obtained for each composition.

In addition, in the same manner, the case of not containing Cu produced by the same method as in the example of the present invention and the case of a comparative example to which Al added, which is known to increase the coercive force with a small amount of addition, were compared. Example The coercive force and the maximum energy product of a permanent magnet were measured, and the relationship with the change in the amount of Al added is shown in FIG.

As is clear from FIG. 1, when Al of the comparative example was added, the coercive force increased with an increase in the amount of Al added. However, when the coercive force was sufficiently increased, the maximum energy product was conversely increased. Is declining.

On the other hand, in the case of adding Cu according to the present invention, it can be seen that the coercive force and the maximum energy product are remarkably increased by adding a very small amount of Cu.

Example 2 Using the sample of the present invention containing 0.1 at% of Cu obtained in Example 1 and a comparative sample containing no Cu at all, after sintering, at various temperatures of 430 to 620 ° C. for 1 hour. FIG. 2 shows the change in coercive force of each magnet as a function of the heat treatment temperature when cooled at a rate of 80 ° C./min after the heat treatment.

In the case of the comparative example, in order to obtain a high coercive force, the optimal heat treatment temperature range can be obtained only in an extremely narrow range, whereas in the case of the magnet according to the present invention containing Cu, a high coercive force can be obtained in a wide temperature range. You can see that it is obtained.

Example 3 The same manufacturing method as in Example 1 was used to obtain Fe-2Co-1 at an atomic ratio.
A sample of the present invention containing 0.1 at% Cu in 3.5Nd-1.5Dy-7B and a sample containing no Cu as a comparative example were produced.

At the time of production, after sintering,
After the heat treatment for a time, the cooling rate after the heat treatment is variously changed, and the coercive force of each of the obtained permanent magnets is measured. The relationship between the heat treatment temperature, the cooling rate and the coercive force is shown in FIG. FIG. 4 shows the case of the comparative example. The numbers in the figure indicate the coercive force iHc (kOe).

As is clear from FIGS. 3 and 4, conventionally, in order to obtain a high coercive force, the cooling rate after the heat treatment must be maintained within a required range.

In contrast, in the case of the present invention containing Cu, any cooling rate may be used, from extremely slow cooling to rapid cooling, and a permanent magnet having an extremely high coercive force can be obtained without being affected by manufacturing conditions. I understand.

[Brief description of the drawings]

FIG. 1 is a graph showing changes in coercive force, maximum energy product, and density of a permanent magnet with respect to changes in the amount of Cu (Al) added. FIG. 2 is a graph showing the relationship between the heat treatment temperature and the coercive force iHc. FIGS. 3 and 4 are graphs showing the relationship between the heat treatment temperature, the cooling rate, and the coercive force. FIG. 3 shows the case of the present invention, and FIG. 4 shows the case of the comparative example.

Claims (2)

(57) [Claims] (1) The total of Nd and Pr is 12 to 17 at% in atomic ratio (however,
Part of Nd and Pr are heavy rare earth elements such as Dy and Tb.
A sintered permanent magnet material comprising: B5-14at%, Co20at% or less, Cu0.02-0.5at%, balance Fe and inevitable impurities. 2. The atomic ratio of Nd and Pr is 12 to 17 at% (however,
Part of Nd and Pr are heavy rare earth elements such as Dy and Tb.
can be replaced by at%), B5-14at%, Co20at% or less, Cu0.02-0.5at%, alloy powder consisting of balance Fe and inevitable impurities, sintering at 900-1200 ℃, 430 after sintering A method for producing a sintered permanent magnet material, comprising heat-treating at a temperature of up to 600 ° C.