JP3168484B2 - Method for manufacturing rare earth-iron-nitrogen permanent magnet - Google Patents

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.

On the other hand, by injecting nitrogen into an alloy of a rare earth metal and iron, an Sm-Fe-NH alloy having, for example, a compound having a crystal structure of the Th ₂ Zn ₁₇ type as a main phase, has an excellent magnetic property. It is reported to have properties and a Curie point of about 470 ° C. Also, with Nd -Fe -Ti -N based alloys similar magnetism as the main phase of the compound of Th Mn ₁₂ type crystal structures it has 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 Th ₂ Zn.
Average particle size 20-150μ with compound of ₁₇ type crystal structure as main phase
m, a metal film made of at least one of Al, Al-Mg, and Sn-Pb is formed on the surface of the alloy powder of
It is characterized in that the heat treatment is performed in a temperature range of 00 ° C., and then the molding is performed.

The rare earth-iron-nitrogen based alloy in the present invention is mainly composed of a compound having a Th ₂ Zn ₁₇ type crystal structure.
The composition of Sm ₂ Fe ₁₇ Nx is mentioned as a representative . 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. 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 only unfavorable from the viewpoint of mass production because high pressure molding is required when forming a bonded magnet, and it is easy to be oxidized in the manufacturing process. This was in the range of 20 to 150 μm.

In the present invention, as described above, a metal (alloy) film made of at least one of Al, Al-Mg and Sn-Pb, which is a low melting metal, is formed on the surface of the alloy powder. The choice of these low melting metals was
This is because these metals not only function as a binder for the bonded magnet, but also have a function of increasing the coercive force by partially reacting with the alloy powder by a heat treatment described later. 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, there is a chemical method using a chemical, or a physical method such as vapor deposition or sputtering. On the other hand, as a mechanical bonding method, there is a method of applying a strong mechanical force to a vibration 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 were mixed at a predetermined ratio, and were melted by high frequency to produce an alloy ingot of a composition of Sm ₂ Fe ₁₇ having a compound having a Th ₂ Zn ₁₇ type crystal structure as a main phase. did. 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 mother alloy powder was kept at 450 ° C. for 2 to 36 hours in N gas at 5 atm to allow N to penetrate to obtain a nitrided powder (alloy powder). Subsequently, these nitrided powders were immersed in a zinc chemical plating bath using a catalyst to form a zinc coating as a low melting point metal 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, the metal-coated powder was placed in an electric furnace and heat-treated at 420 ° C. for 6 hours in an argon gas atmosphere. afterwards,
The obtained powder is supplied to a molding die, and compression-molded at a pressure of 5 Ton / cm ² while applying a magnetic field of 15 KOe to produce a molded sample (magnet sample). And a crystal structure was confirmed by an X-ray diffraction method.

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 nitride powders used herein had a desired main phase of the Th ₂ Zn ₁₇ type crystal structure.

Example 2 An alloy ingot having a composition of Sm ₂ Fe ₁₇ was prepared using samarium and electrolytic iron as raw materials in the same manner as in Example 1, and after homogenization, pulverized to obtain an average powder particle size of 25 μm. 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. Thereafter, 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
Zn, Sn, Pb, In, Al, Al- under × 10 ^-5 torr
Each of Mg and Sn-Pb was deposited by resistance heating. The production conditions were adjusted so that the amount of the deposited metal 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 deposited and a sample 9 on which no metal deposition was performed were obtained, and these were subjected to the same measurement test. Table 1 shows the results.

[0018]

[Table 1]

[0019] As is apparent from Table 1, Samples 1 to 7 using the powder to form a low-melting-point metal film are both and obtain a high residual magnetic flux density Br and coercive force iHc, the present invention
In regulations boss was a low melting point metals Al, Al-Mg, Sn- Pb Nitsu
Magnetic properties comparable to those of Zn, Sn, etc.
I have. On the other hand, the sample 8 on which Cu was deposited has a coercive force i
Sample 9 in which little improvement in Hc was observed and in which no vapor deposition was performed has a remarkably small coercive force iHc. Therefore , it became clear that low melting point metals are necessary to obtain 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, and the inside of the container was replaced with N gas. 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.

EXAMPLE 4 Sm ₂ (Fe _0.8 Co _0.2 containing 99.9% pure samarium, cobalt, and electrolytic iron in a predetermined ratio, and subjecting them to high frequency dissolution and containing a compound having a Th ₂ Zn ₁₇ type crystal structure as a main phase. An alloy ingot of ₁₇ compositions was produced. This at 1150 ° C for 12 hours,
After homogenizing treatment in an Ar gas atmosphere, the mixture is quenched, and the average particle size is 50 μm and 3 μm by a stamp mill and a ball mill.
A μm mother alloy powder was obtained. 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, compression-molded at a pressure of 4 to 10 Ton / cm ² while applying a magnetic field of 15 KOe, and cured at 150 ° C. to obtain a molded sample. It was subjected to a measurement test of the maximum energy product BHmax and the density of the compact, and the nitrided powder was held in a thermostat at 125 ° C. for 500 hours in order to know the long-term stability. The change in weight 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 same procedure as in Example 1 was carried out except that the nitride powder having a particle size of 25 μm was used.
Immersed molded product sample in epoxy resin with a viscosity of 150 CPS
Immersion, hold for 1 hour under reduced pressure of about 10 Torr,
Impregnated with epoxy resin and cured at 120 ° C for 2 hours
Was. The magnetic properties of the obtained sample are the same as those without impregnation
The maximum magnetic energy product BHmax was 12 MGOe
However, the compressive strength of the sample is 1.8 times higher than that without impregnation.
Hits 60 kgf / mm ^2, and the greater the improvement in strength of the molded body
It was found to contribute.

[0026]

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.

Continuation of the front page (56) References JP-A-4-359405 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01F 1/06 B22F 1/02 B22F 3/02

Claims (3)

(57) [Claims] 1. An alloy powder comprising a rare earth metal (R), Fe and N as main components and a compound having a Th ₂ Zn ₁₇ type crystal structure as a main phase and having an average particle diameter of 20 to 150 μm, Al, Al
A rare earth-iron-nitrogen permanent magnet, which is formed by forming a metal film made of at least one of Mg, Sn-Pb , heat-treating the metal film at a temperature in the range of 100 to 600 ° C., and then forming. Production method. 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.