JP2001203104A - METHOD OF MANUFACTURING RARE-EARTH-Fe-N PERMANENT MAGNET - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method by which a rare-earth-Fe-N permanent magnet is obtained securing sufficient coercive force even when the magnet is made by using rough powder, and accordingly, the manufacturability of which is improved sharply and the performance of which is stabilized over a long period. SOLUTION: After a metal coating film composed at least of one kind selected from among Sn, Zn, Pb, In, Al, and Mg is formed on the surface of alloy powder which contains a rare-earth metal (R), Fe, and N as main constituents and has particle diameters of 20-150 μm and the main phase of which is composed of a compound having a ThMn12 type crystal structure and heat-treated at a temperature of 100-600 deg.C, the alloy powder is molded by adding a metal or organic binder, as necessary. Alternatively, after molding, the molded body is impregnated with the metal or organic binder.

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-iron-nitrogen permanent magnet, and more particularly to a permanent magnet having improved productivity and long-term stability in performance by using coarse powder. It relates to a manufacturing method.

[0002]

2. Description of the Related Art In recent years, with the miniaturization of various electronic devices, high-performance Nd-Fe-B permanent magnets have been widely used. However, since this magnet has a low Curie point of 310 ° C, its temperature characteristics are poor, and it has been difficult to use it at 150 ° C or higher.

[0003] On the other hand, nitrogen invades an alloy of a rare earth metal and iron.
By entering, for example, Th_TwoZn₁₇Type crystal structure
Sm-Fe-NH-based alloys having a main phase of
With improved magnetic properties and Curie point of about 470 ℃
Have been. Also, ThMn ₁₂Type of crystal structure compound
The Nd-Fe-Ti-N alloy used as the main phase has similar magnetism.
Have been reported.

[0004]

However, the above rare earth-iron-nitrogen alloy cannot obtain the coercive force required for a permanent magnet unless it is finely ground to a particle size of several μm. However, there has been a problem that the moldability is deteriorated and high-pressure molding is required, and a reduction in the mold life is inevitable. Further, this kind of alloy powder is easily oxidized under high temperature and high humidity, and the use of fine powder promotes the oxidation, so that it is difficult to obtain a permanent magnet having stable performance over a long period of time. Was.

The present invention has been made in view of the above-mentioned conventional problems, and a sufficient coercive force can be ensured even when coarse powder is used, so that rare earth elements greatly contribute to improvement in manufacturability and long-term stability of performance. An object of the present invention is to provide a method for producing an iron-nitrogen permanent magnet.

[0006]

In order to solve the above-mentioned problems, a method of manufacturing a rare earth magnet according to the present invention comprises a rare earth metal (R), Fe and N as main components and ThMn ₁₂
Average particle size 20-150μm with compound of main type crystal structure as main phase
Sn, Zn, Pb, In, Al, M
g) to form a metal film consisting of at least one of
It is characterized in that the heat treatment is performed in a temperature range of 100 to 600 ° C., and then the molding is performed.

In the present invention, the rare earth-iron-nitrogen based alloy is an N-type alloy containing a compound having a ThMn ₁₂ type crystal structure as a main phase.
d (Fe, M) ₁₂ Nx composition and Pr (Fe, M) ₁₂ Nx
The composition is exemplified as a representative (where M indicates a transition element). In this case, the content of N is selected from several to several tens of atomic%. In these alloys, the saturation magnetic flux density, the magnetocrystalline anisotropy and the Curie point are greatly improved by the inclusion of nitrogen, and are excellent as permanent magnet materials. In these alloys, a part of iron can be replaced by another transition metal such as Co or Ti, or two or more rare earth metals can be used as a rare earth metal. Co is particularly effective in increasing the Curie point and improving corrosion resistance. Good magnetic properties can also be obtained by replacing part of the above N with C.

In the present invention, the method of obtaining the above alloy powder is optional. For example, a method of obtaining a mother alloy powder with a rare earth metal and iron (and other metals as desired) and injecting N into the powder is used. Can be. In this case, as a method for obtaining the mother alloy powder, a raw material in which a rare earth metal and Fe are mixed at a predetermined ratio is subjected to high frequency melting, and the molten alloy is poured into a mold to form an alloy ingot, which is then homogenized at a high temperature. After performing the method, a method of forming a desired powder using a jaw crusher, a stamp mill, a ball mill, or the like, or a quenching method of directly quenching a molten alloy directly to obtain a powder can be used. The entry of N into the mother alloy powder can be performed by bringing the mother alloy powder into contact with a nitriding gas such as nitrogen, ammonia, or a mixed gas of nitrogen and hydrogen at a high temperature. In this case, the nitriding temperature is
If the temperature is lower than 200 ° C., the penetration of N is insufficient, and if the temperature exceeds 600 ° C., the compound phase is easily decomposed. Therefore, it is desirable to select the range of 200 to 600 ° C. Further, by performing this nitriding treatment under a high pressure of several tens of atmospheres, nitrogen can be efficiently introduced into the mother alloy powder. Further, after the nitriding treatment, it is possible to carry out pulverization again to adjust the powder particle size.

In the present invention, the particle size of the alloy powder is 20 μm.
If it is less than m, it is not preferable for mass production because high pressure molding is required when forming a bonded magnet, and it is easy to oxidize during the manufacturing process. On the other hand, if the particle size exceeds 150 μm, N does not penetrate sufficiently. This was in the range of 20 to 150 μm.

In the present invention, as described above, Sn, Zn, Pb, In, A, which are low melting point metals, are formed on the surface of the alloy powder.
It is characterized by forming a film composed of at least one of l and Mg. The reason for selecting these low melting metals is that these metals not only function as binders for bonded magnets but also are subjected to heat treatment described later. This is because it has a function of increasing the coercive force by partially reacting with the alloy powder. As a method for forming a metal film on the surface of the alloy powder, a plating method or a mechanical bonding method can be used. As a plating method, a chemical method using chemicals, or vapor deposition,
There are physical methods such as sputtering, and on the other hand, as a mechanical bonding treatment method, there is a method in which a strong mechanical force is applied by a vibrating mill.

In the present invention, the heat treatment is performed by heating in an inert gas atmosphere or in a vacuum. This heat treatment improves the magnetic properties, especially the coercive force, presumably because the soft magnetic iron component contained in the alloy powder in a small amount reacts with the coating metal and disappears. If the heating temperature of this heat treatment is less than 100 ° C, the above-mentioned improvement is not observed.If it exceeds 600 ° C, the compound tends to be decomposed and the magnetic properties tend to be reduced. did.

In the molding of the heat-treated powder, the low-melting metal film fixes the powder to each other by pressurization.
A hard molded body can be obtained by pressure molding of Ton / cm ² . In this case, a powder having the same kind of metal binder as the coating metal is added to the powder by several weight%, and the powder is subjected to pressure molding, whereby a molded article having more excellent strength can be obtained. Furthermore, a molded article having excellent strength can also be obtained by impregnating the molded article with an organic substance such as an epoxy resin or a varnish after molding without adding a binder. For this molding, various methods such as compression, injection, and extrusion can be used.

[0013]

In the above-described method for producing a rare earth-iron-nitrogen permanent magnet, the formation of a low-melting metal film on the alloy powder and the subsequent heat treatment increase the magnetic properties, especially the coercive force, and the coarse powder Can be used.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

EXAMPLE 1 A samarium having a purity of 99.9% and an electrolytic iron are blended in a predetermined ratio, and are melted by high frequency to obtain a compound having a Th ₂ Zn ₁₇ type crystal structure having magnetic properties similar to those of a ThMn ₁₂ type crystal structure. An alloy ingot having a composition of Sm ₂ Fe ₁₇ and having a main phase of was produced. This was homogenized at 1200 ° C. for 12 hours in an Ar gas atmosphere, and various mother alloy powders having an average particle size of 3 to 200 μm were obtained by a stamp mill and a ball mill. Next, this master alloy powder was placed in a 5 atm N gas atmosphere at 450 ° C. for 2 hours.
Nitrogen powder (alloy powder) by holding N for 36 hours and allowing N to enter
I got Subsequently, these nitrided powders were immersed in a zinc chemical plating bath using a catalyst to form a zinc film on the surfaces of the powders. The amount of zinc deposited on the nitrided powder determined by the gravimetric method was 1.8 μm in average on the film thickness. Next, this metal-coated powder was charged into an electric furnace, and the
Heat treatment was performed at 6 ° C. for 6 hours. Thereafter, the obtained powder is supplied to a molding die, and 5 T
A compact sample (magnet sample) was produced by compression molding at a pressure of on / cm ² , and these were subjected to a test for measuring magnetic properties using a BH tracer, and the crystal structure was confirmed by X-ray diffraction. .

FIG. 1 shows the effect of the average powder particle size of the nitrided powder on the maximum magnetic energy product BHmax, coercive force iHc and residual magnetic flux density Br of the compact sample.
From FIG. 1, the maximum magnetic energy product BHmax and the coercive force iH
c is a peak at an average powder particle size of about 25 μm,
It has a high value in the range of 20 to 150 μm. on the other hand,
The coercive force iHc increases as the nitride powder particle diameter decreases according to the single domain particle theory. Therefore, in order to obtain good magnetic properties under practical molding pressure in this example, it was found that the average powder particle size needs to be in the range of 20 to 150 μm. In addition, as a result of X-ray diffraction,
It was confirmed that each of the nitrided powders used here had a desired main phase having a desired Th ₂ Zn ₁₇ type crystal structure.

Example 2 An alloy ingot having a composition of Sm ₂ Fe ₁₇ was produced using samarium and electrolytic iron as raw materials in the same manner as in Example 1, and was homogenized. A mother alloy powder was obtained. Next, this mother alloy powder was placed in a 5 atm N gas atmosphere for 450 minutes.
The temperature was kept at 12 ° C. for 12 hours to obtain a nitrided powder. Then, a vapor deposition method, which is one of physical plating methods, was adopted for the nitrided powder, and the powder was set on a rotating small plate of a vacuum vapor deposition machine, and a vacuum degree of 1
Each of Zn, Sn, Pb, In, Al, and Mg was deposited by resistance heating under × 10 ^-5 torr. The production conditions were adjusted so that the amount of the metal deposited was 1.5 to 2 μm as the coating film thickness. Next, these metal-coated powders were charged into an electric furnace and heat-treated at 100 to 700 ° C. for 1 hour. Thereafter, molding was performed in the same manner as in Example 1 to obtain magnet samples 1 to 7. The same magnetic property measurement test as in Example 1 was performed. For comparison, a sample 8 on which Cu was vapor-deposited and a sample 9 on which no metal was vapor-deposited were obtained, and these were subjected to the same measurement test. Table 1 shows the results.

[0018]

[Table 1]

As is clear from Table 1, the samples 1 to 7 according to the present invention using the powder on which the low-melting point metal film was formed,
In each case, a high residual magnetic flux density Br and a coercive force iHc are obtained. On the other hand, the sample 8 on which Cu was deposited had a coercive force.
Sample 9 in which no improvement in iHc was observed and in which no vapor deposition was performed has a remarkably small coercive force iHc. Therefore, it has been clarified that the low melting point metals specified in the present invention are necessary for obtaining excellent magnetic properties. In addition, it was confirmed that there was no problem even when the vapor deposition method was applied to the formation of the metal film on the nitrided powder.

Example 3 The nitrided powder produced in Example 2 was charged into a stainless steel ball mill container lined with zinc, the inside of the container was replaced with N gas, and the dry operation was performed for 24 hours. A zinc film was mechanically formed on the powder surface. Next, this metal-coated powder was placed in a vacuum furnace and heat-treated at 100 to 700 ° C. for 1 hour in N gas. Thereafter, the magnetic properties of a molded sample obtained by molding in the same procedure as in Example 1 were measured.

FIG. 2 shows the effect of the heat treatment temperature on the coercive force iHc of the compact sample. From the figure, the coercive force iHc peaks around 400 to 500 ° C,
It became clear that the temperature range of 600 ° C. was an excellent value of 2000 Oe or more. In addition, it was confirmed that there was no problem even if a mechanical bonding method was applied to the formation of the metal film on the nitrided powder.

[0022] Example 4 99.9% pure samarium, cobalt, and electrolytic iron were blended at a predetermined ratio, and high frequency melting, Th ₂ Zn ₁₇ type crystal with magnetic properties similar to the compounds of ThMn ₁₂ type crystal structure Sm ₂ (Fe _0.8 Co _0.2 ) ₁₇ whose main phase is a compound having a structure
An alloy ingot of the composition was produced. This was homogenized in an Ar gas atmosphere at 1150 ° C for 12 hours, then quenched,
A master alloy powder having an average particle size of 50 μm and 3 μm was obtained by a stamp mill and a ball mill. Next, this mother alloy powder was charged into an electric furnace, and was held at 500 ° C. for 8 hours in N gas at 5 atm to infiltrate N. Subsequently, these nitride powders were removed in the same manner as in Example 1. It was immersed in a chemical zinc plating bath using a catalyst to form a 0.7 μm zinc film on the powder surface. Next, these metal-coated powders were placed in an electric furnace and heat-treated at 450 ° C. for 8 hours or 2 hours in an argon gas atmosphere. Thereafter, 3% by weight of an epoxy resin was mixed with the obtained powder, and 4 to 10 Ton / cm ² while applying a magnetic field of 15 KOe.
Compression molding at a pressure of 150 ° C., and a curing treatment at 150 ° C. to produce a molded body sample, which is subjected to a measurement test of the maximum energy product BH max and the molded body density, and to know the long-term stability, The above-mentioned nitrided powder was kept in a thermostat at 125 ° C. for 500 hours, and the weight change of the powder was measured.

FIG. 3 shows the maximum energy product B of the compact sample.
It is a view of the influence of the average powder particle size and the molding pressure on Hmax and the compact density. As shown in the figure, the molded body sample using the coarse powder having an average particle diameter of 50 μm has excellent magnetic properties with a maximum energy product (BHmax) of 10 MGOe or more at a molding pressure of 4 Ton / cm ² or more, and has a relatively low pressure. It has been clarified that it is possible to increase the density also in the above.

FIG. 4 shows the effect of the holding time on the weight increase rate. From the figure, it is apparent that the coarse powder having an average particle size of 50 μm has a significantly smaller weight increase rate due to oxidation than the fine powder having an average particle size of 3 μm, and is suitable for manufacturing a magnet having excellent long-term stability. is there.

Example 5 The nitrided powder of 50 μm used in Example 4 was immersed in a Sn plating bath using a nickel catalyst to form an approximately 0.4 μm Sn film on the surface of the powder. Subsequently, this metal-coated powder was charged into an electric furnace, and was placed in an argon gas at 300 ° C. for 30 minutes.
Heat treatment for a minute. Next, 10% by weight of S was added to this powder.
n powder was mixed and compression molded at a pressure of 7 Ton / cm ² in an applied magnetic field of 15 KOe to produce a molded sample. The sample density obtained was 6.5 g / cm ³ , and the magnetic properties were:
BHmax = 13.7MGOe, Br = 8647G, iHc = 7655
An excellent value of 0e was obtained.

Example 6 Neodymium, electrolytic iron, cobalt, and ferro-titanium having a purity of 99% or more were blended at a predetermined ratio, melted by high frequency, and
NdFe ₈ Co ₃ having a main phase of a compound having an hMn ₁₂ type crystal structure
An alloy ingot having a Ti composition was manufactured and homogenized by holding it at 1100 ° C. for 24 hours in an argon gas atmosphere. Then, the alloy ingot was pulverized by a stamp mill and a ball mill to obtain a particle size of 3 to 180 μm. A mother alloy powder was obtained. Next, this mother alloy powder was placed in a 5 atm N gas atmosphere for 350 minutes.
° C., for 1 to 24 hours, to infiltrate N to obtain nitrided powder,
Subsequently, this was immersed in a zinc electroplating bath using a catalyst to form a zinc film of about 0.7 μm on the surface of the powder. Thereafter, these metal-coated powders were charged into an electric furnace, and were placed in an argon gas atmosphere. Heat treatment was performed at 350 ° C. for 8 hours. Next, 3% by weight of a phenol resin was added to and mixed with the obtained powder,
Compression molding at a pressure of 5 Ton / cm ² in a magnetic field of 15 KOe
A cured product sample was manufactured by performing a curing process at 150 ° C. The magnetic properties of the obtained sample were measured with a BH tracer.

FIG. 5 shows the effect of the average powder particle size of the nitrided powder on the maximum magnetic energy product BHmax, coercive force iHc and residual magnetic flux density Br of the compact sample.
From FIG. 5, the maximum magnetic energy product BHmax and the coercive force iH
c is a peak at an average powder particle size of about 25 μm as in Example 1, but has a high value in the range of 20 to 150 μm, and the coercive force iHc is the nitride powder particle size according to the single domain particle theory. Are increasing as the value of is smaller.

Example 7 A sample of a molded article manufactured by using the nitrided powder having a particle size of 25 μm in Example 1 was immersed in an epoxy resin having a viscosity of 150 CPS, and held at a reduced pressure of about 10 Torr for 1 hour to obtain a molded article. It was impregnated with an epoxy resin and cured at 120 ° C. for 2 hours. The magnetic properties of the obtained sample were the same as those without impregnation, and the maximum magnetic energy product BHmax was 12 MGOe, but the compressive strength of the sample was 60 kgf / mm ² , which is 1.8 times that of the sample without impregnation. It was found that it greatly contributed to strength improvement.

[0029]

As described above in detail, according to the method for manufacturing a rare earth-iron-nitrogen permanent magnet according to the present invention,
Magnets with excellent magnetic properties can be manufactured even with coarse powder having an average powder particle size of 20 to 150 μm, and the use of this coarse powder eliminates the need for molding under high pressure, extending the life of the mold. The performance is greatly improved. Further, by using the coarse powder, the oxidation of the powder is suppressed in the production process, and the performance of the obtained magnet is stabilized for a long time.

[Brief description of the drawings]

FIG. 1 is a graph showing the influence of the average powder particle size of an alloy powder on the magnetic properties of a rare earth-iron-nitrogen magnet sample obtained by the method of the present invention.

FIG. 2 is a graph showing the influence of a heat treatment temperature on the magnetic properties of a magnet body sample obtained by the method of the present invention.

FIG. 3 is a graph showing the influence of the average powder particle size and the molding pressure on the magnetic properties and density of the magnet body sample obtained by the method of the present invention.

FIG. 4 is a graph showing the influence of the average powder particle size and the retention time on the increase in oxidized weight of the powder used in the present invention.

FIG. 5 is a graph showing the influence of the average powder particle size of the alloy powder on the magnetic properties of the rare earth-iron-cobalt-nitrogen-based magnet sample obtained by the method of the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // C21D 6/00 H01F 1/04 A (72) Inventor Shunki Suzuki 1743 Asana, Asaba-cho, Iwata-gun, Shizuoka Prefecture Address 1 Inside the Minebea Hamamatsu Factory

Claims (3)

[Claims] 1. An alloy powder comprising a rare earth metal (R), Fe and N as main components and a compound having a ThMn ₁₂ type crystal structure as a main phase and having an average particle diameter of 20 to 150 μm, is coated with Sn, Zn.
, Pb, In, Al, Mg, a rare earth-iron-nitrogen-based permanent metal film formed by subjecting the metal film to a heat treatment in a temperature range of 100 to 600 ° C. Manufacturing method of magnet. 2. The method for producing a rare earth-iron-nitrogen permanent magnet according to claim 1, wherein after the heat treatment is performed, a metal binder or an organic binder is added to carry out molding. 3. The method for producing a rare earth-iron-nitrogen permanent magnet according to claim 1, wherein the molded body is impregnated with an organic binder after the molding.