JPH04214806A - Manufacture of rare earth anisotropic permanent magnet powder - Google Patents

Abstract

PURPOSE:To obtain permanent magnet powder having high coercive force and improve in anisotropy by subjecting a rare earth-Fe-B based alloy having a specified compsn. to hot plastic working in specified conditions and pulverizing it. CONSTITUTION:An alloy consisting fundamentally of rare earth elements (including Y), T (transition metal consisting essentially of Fe) and B and constituted of RxT(100-x-y-z)ByCuz is subjected to hydrogen absorption and dehydrogenation treatment to obtain magnet powder having <=10mum mean grain size. In the formula, 12<=x<=18, 4<=y<=10 and 0.05<z<=6 (atm%) are satisfied. This magnet powder is subjected to hot plastic working in the conditions of 600 to 900 deg.CX>=5/s strain rate and >=60% deforming rate and is then pulverized. In such a manner, the magnet powder for an anisotropic resin bond magnet having high coercive force and about >=60% orientating rate can be obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention uses rare earth elements (including Y, sometimes referred to as R hereinafter) and transition metals (essentially containing Fe, hereinafter sometimes referred to as T). The present invention also relates to a method for producing an anisotropic permanent magnet powder that has boron, particularly rare earth element-iron-boron, as a basic component and is used in bonded magnets.

It is well known that resin-bonded permanent magnets (composite magnets) can be obtained by mixing magnet powder and resin and then extrusion molding, compression molding, or injection molding. Rare earth bonded permanent magnets are attracting attention. The present invention relates to a manufacturing method for improving the characteristics of magnet powder used in such rare earth bonded permanent magnets.

[Prior Art] Conventional methods for producing R-T-B (typically Nd-Fe-B) alloy magnet powder include (a) mechanically crushing alloy ingots and permanent magnets; Yes (Unexamined Japanese Patent Publication No. 1983-
219904).

Furthermore, there is also a method (b) of pulverizing a ribbon obtained from a molten R-T-B alloy by a liquid quenching method (Japanese Patent Laid-Open No. 57
-210934, JP-A-59-64739).

The obtained powder is heat treated as necessary to improve the coercive force of the magnetic properties.

However, it has been known for a long time that if a bonded magnet is made from magnetic powder mechanically pulverized by the method (a), both residual magnetization and coercive force are reduced. As a method intended to overcome this drawback, (c) the R-T-B alloy is hydrogenated in a hydrogen atmosphere and then ground to obtain a powder with an average particle size of 10 μm to 500 μm, followed by heating at 600 to 1000 °C. A method of dehydrogenation using
No. 23903).

Furthermore, there is a method proposed in JP-A No. 1-132136, which involves (d) hydrogenating and dehydrogenating an ingot or powder of R-T-B alloy to obtain a recrystallized texture of fine crystals. We propose to obtain a powder with a high coercive force by obtaining the above-mentioned results, and, if necessary, to plastically process the ingot or powder having the above-mentioned recrystallized texture to produce a magnet powder having magnetic anisotropy.

[Problems to be Solved by the Invention] Although it is possible to manufacture permanent magnet powder whose basic components are rare earth elements, iron, and boron using the above-mentioned conventional techniques, these manufacturing methods have the following drawbacks. .

The magnetic powder obtained by the method (a) tends to deteriorate in characteristics due to distortion during pulverization and alteration of the powder surface that occurs during pulverization, and its magnetic characteristics are not necessarily sufficient. Furthermore, by heat-treating the magnet powder obtained by this method, the distortion of the magnet powder is relaxed, and an R-rich phase is formed around the main phase R2Fe14B phase, so the magnet powder has a
It exhibits a high coercive force of ~13 KOe, but when used as magnet powder for bonded magnets, the coercive force of the bonded magnet decreases as the molding pressure increases in the production of compression molded magnets.
At a molding pressure of 5 ton/cm2, the coercive force was less than 5 KOe, which had the disadvantage that it could not be put to practical use as a bonded magnet.

The magnetic powder obtained by method (b) has isotropic magnetic properties, so the maximum energy product is low, but
It shows a high coercive force of about 8 to 15 KOe when used as a powder for bonded magnets.

However, since it requires a magnetizing field of 35 KOe or more, its practical use is limited. Furthermore, anisotropic magnet powder can be obtained by the die-abset method, which is a development of this method, but this method has the disadvantage of poor productivity.

The magnet powder obtained by the method (c) is substantially isotropic, and when the inventor conducted an experiment using the method (c), no anisotropy was obtained.

The magnet powder with the recrystallized texture obtained by the method (d) is
The main phase R2Fe14B phase in the powder is fine, (a)
Although the decrease in coercive force due to pulverization is small, the magnet powder obtained by the texture formation method by recrystallization has small anisotropy. The present inventor conducted a detailed study on the hot plastic working disclosed in (d) as a means to increase the degree of anisotropy, and confirmed that anisotropy could not be obtained.

Therefore, the present inventors found that even when magnetic powder is mechanically pulverized and bonded magnetized (compression molded), the coercive force is high;
In order to obtain anisotropic magnet powder with an orientation rate of 60% or more, we investigated the manufacturing method, including the composition of the magnet and hot plastic working conditions.

[Means for solving the problem] As a result, using the R-T-B-Cu system as the alloy composition,
The microcrystalline powder obtained by subjecting this alloy to hydrogen absorption and dehydrogenation treatment is subjected to hot plastic working with a deformation rate of 60% or more.
By applying at a strain rate of 5/s or more at 00 to 900°C,
The inventors discovered that the decrease in coercive force during the manufacturing process of bonded magnets was small, leading to the present invention. That is, the present invention clearly defines the composition of the magnet powder and the hot composition processing conditions. The alloy plastically worked by this method is
Even if the powder is further pulverized to about 5 μm, a powder with a coercive force of 8 KOe or more and an orientation rate of 60% or more can be obtained.

That is, the present invention provides rare earth elements (including Y) and T.
(transition metal whose essential element is Fe) and boron (B), and the composition is as follows: RxT (100-x-y-
z) ByCuz12≦x≦18, 4≦y≦10, 0.05<z≦6 (at%) By subjecting an alloy to hydrogen absorption and dehydrogenation treatment to obtain magnet powder with an average crystal grain size of 10 μm or less, This magnet powder is heated at a temperature of 600 to 900°C, a strain rate of 5/s or more, and a deformation rate of 60%.
It is characterized by performing hot plastic working under the above processing conditions, and then pulverizing.

The present invention will be described below with regard to Nd-Fe-B-Cu alloys.

In the alloy of the present invention, the Nd content (x) is 12 to 18a
t%. Ndrich when x is less than 12at%
The phase becomes insufficient and the magnetism decreases.

Also, when x exceeds 18 at%, Br decreases, so x
=12 to 18 at%. Further, the B content (y) is 4 to 10 at%. When y is less than 4 at%, α-Fe, Nd2F, which is a magnetically soft phase
The e17 phase precipitates, deteriorating the magnetic properties, and if it exceeds 10 at%, not only does the deformation resistance during hot working increase, but also the refinement of crystal grains is inhibited.
%. Is T the total amount of Fe?
Alternatively, it is composed of Fe and preferably 20 at% or less of Co.

As the composition of the present invention, it is essential to add Cu as an additive element to the Nd-Fe-B alloy.

Regardless of the crystal grain size at the time of casting, Cu makes the structure of the alloy subjected to hydrogen absorption and dehydrogenation treatment fine and uniform. The final grain size no longer depends on the grain size at the time of casting. Further, Cu improves orientation during hot working. However, the effect of Cu addition is recognized from around 0.05at%, but when the amount of Cu added is 6%
In the above case, since Cu is a nonmagnetic element, the residual magnetization Br decreases and the magnetic properties deteriorate. Therefore, the amount of Cu added needs to be 6 at% or less, especially 1
~3 at% is preferable. In addition, as other additive elements, C is added to improve the magnetic properties of Nd-Fe-B alloys.
o, Ga, Nb, Ti, V, Cr, Mo, Mn, Bi,
Al, Si, Zr, etc. may be added.

The present inventor investigated the relationship between strain rate, coercive force of pulverized powder (45 μm or less), and orientation rate at a processing temperature of 750° C. regarding Nd-Fe-B-Cu alloys. As a result, the coercive force showed a tendency to improve as the strain rate increased, and by setting the strain rate to 5/s or more, preferably 10/s or more, the coercive force (iHc) of the powder became 10 KOe or more. , there was almost no change in the orientation rate. Furthermore, the strain rate is 20/s
The relationship between the rolling temperature and the coercive force (iHc) and orientation rate of the pulverized powder (45 μm or less) was investigated in the case of . As a result, it was found that as the processing temperature increases, the coercive force of the powder decreases, but the orientation rate and maximum energy product tend to improve. The deformation rate is 60% or more in all cases.

Therefore, it has been found that setting the strain rate to 5/s or more has a favorable effect on both the maximum energy product and the processing rate. In addition, we similarly investigated the effects of strain rate and magnetic properties on the Nd-Fe-B system without Cu addition, but found that there was almost no effect (see Comparative Examples 1 and 2 in Table 1 below).
.

The reason why the initial average crystal grain size of Nd-Fe-B-Cu platinum (before hot plastic working) was specified to be 10 μm or less is that recrystallization occurs during subsequent hot working and the crystal grain size becomes too coarse. This is to prevent this. When the average crystal grain size becomes 10 μm or more due to recrystallization, the coercive force decreases due to pulverization in the subsequent process. In order to prevent a decrease in coercive force after pulverization, assuming the hot working conditions of the present invention, the initial average grain size should be 10μ.
Must be less than m.

In order to obtain the above-mentioned plastic alloy powder with an average crystal grain size of 10 μm or less, it is necessary to perform hydrogenation/dehydrogenation treatment. The processing conditions include crushing a Nd-Fe-B-Cu alloy ingot to about 1 to 3 mm and heating it to 700 to 800°C in an atmosphere of 1 atm of hydrogen gas, so that hydrogen is sufficiently absorbed into the powder. , then 0.3Torr
It is preferable to heat and maintain the temperature at 600 to 850° C. again in a vacuum as described below.

Examples of hot plastic working methods include hot forging, hot rolling, and hot pressing, but hot rolling is preferable from the viewpoint of productivity and condition control.

In addition, in actual plastic working, the average grain size obtained was 10
After sufficiently filling a steel sheath with pulverized particles having a size of 1 to 3 mm (μm or less), the sheath is vacuum-sealed, heated, and then subjected to hot plastic working.

As a result of these studies, in the R-Fe-B alloy containing Cu, by setting the hot working temperature to 600 to 900°C, preferably 700 to 800°C, and setting the strain rate to 5/s or more, It was found that an anisotropic bonded magnet with good properties could be manufactured.

As indicators of properties, (a) the coercive force (iHc) of the powder pulverized to about 45 μm is 8 KOe or more (the coercive force of the powder itself), (b) the orientation rate is 60% or more, (c) The coercive force (BHc) of the bonded magnet is 5
It must be KOe or higher.

Here, the orientation rate is σr(‖)/{σr(‖)+σr(⊥)
}×100.

However, σr(‖) is the measured value of σr in the direction parallel to the magnetic field when the powder is oriented in a magnetic field, and σr(⊥) is the measured value of σr in the direction perpendicular to the magnetic field.

[Function] As shown in Table 1 of Examples, the magnet powder of the present invention consists of microcrystals with an average crystal grain size of 10 μm or less. The reason why this powder develops anisotropy is that the microcrystals are hydrogenated and
It is thought that it was obtained by recrystallization during dehydrogenation treatment. However, when microcrystals are simply recrystallized by heat treatment, as in the method of prior art (d), the preferential direction of recrystallization growth is not necessarily aligned in one direction. Therefore, in the present invention, the anisotropy is improved by applying processing strain energy to recrystallize. but,
If all the recrystallized grains have grown to 10 μm or more, the coercive force of the powder will significantly decrease due to pulverization and it will not become a magnet.
In the present invention, the average crystal grain size is set to 10 μm or less.

In addition, when crystal refinement and recrystallization are caused only by hot working without using hydrogen absorption and dehydrogenation treatment together with hot working, the crystal grain size is uniform, as shown in Table 1 Comparative Example. 10μ to
Microcrystals smaller than m cannot be obtained. For this reason, when a sample obtained only by hot working is crushed to a size of 45 μm or less, the coercive force decreases due to the crushing, probably because there are many coarse crystals, and good characteristics as a bonded magnet cannot be obtained.

Cu forms a main phase (
It plays an important role in improving the orientation of the Nd2Fe14B phase).

It is estimated that Cu mainly exists in the Nd-rich phase and helps improve the orientation of the main phase.

Nd2Fe14B crystal has a property that during processing, the direction of processing pressure tends to be the same as the direction of easy magnetization.

As mentioned above, by controlling the recrystallization growth by determining the manufacturing conditions such as composition and hot processing conditions, and controlling the directionality, the coercive force does not decrease even when powdered (45 μm or less) and A powder with good anisotropic orientation can be obtained.

Hereinafter, the present invention will be explained in detail with reference to Examples.

〔Example〕

The alloy composition was melted in a vacuum high-frequency melting furnace to obtain an alloy ingot having the composition shown in Table 1. The ingot was subjected to homogenization treatment at 1100° C. for 8 hours in a vacuum. Thereafter, in an argon atmosphere, the alloy was coarsely crushed to 1 to 3 mm using a jaw crusher and kept in a vacuum for 3 hours in a hydrogen treatment furnace. Set the hydrogen treatment furnace to a hydrogen atmosphere of 1 atm, and
The mixture was heated to 00° C. to sufficiently absorb hydrogen and cooled in the furnace.

Next, the inside of the hydrogen treatment furnace was set to a vacuum of 10-3 Torr, and
The mixture was heated to 00°C and dehydrogenated.

Approximately 50% of the hydrogen-treated magnet powder is placed in a carbon steel sheath.
0 g was packed sufficiently tightly, kept in vacuum at 300°C for 1 hour, and then sealed.

Hot rolling was repeatedly carried out under the following conditions.

Processing temperature: 700°C Strain rate: 10-30/s Total deformation rate: 80% After cooling, the magnet powder taken out from the sheath is in a state where the grains are fused together due to the hot rolling, so it is stamped in an argon gas atmosphere. Grind with a mill to 45μm
The following powder was obtained. Table 1 shows the results of measuring the magnetic properties of the powder using VSM.

Table 1 also shows examples with different manufacturing conditions as comparative examples.

In addition, 2% by weight of epoxy resin was mixed with the magnet powder shown in Table 1, compression molded at a pressure of 6 ton/cm2 in a magnetic field of 15 KOe, and the resin was cured to create a bonded magnet. Table 2 shows the magnetic properties of the bonded magnet.

[Effects of the Invention] According to the present invention, it is possible to obtain high-performance rare earth-iron-boron-based, especially Nd-Fe-B-based, anisotropic resin-bonded magnet powder for anisotropic resin bonded magnets without the need for particularly expensive equipment. be able to.

Patent applicant: Showa Denko Co., Ltd. Intermetallics Co., Ltd. Agent: Patent attorney Takuo Murai

Claims (1)

[Claims] Claim 1: The basic components are rare earth elements (including Y), T (transition metal with Fe as an essential element), and boron (B), and the composition is as follows: RxT (100-x-y-z) ByCuz12≦x≦1
8, 4≦y≦10, 0.05<z≦6 (at%) Magnet powder with an average crystal grain size of 10 μm or less is obtained by hydrogen absorption and dehydrogenation treatment, and this magnet powder is heated at a temperature of 600 μm. ~900℃, strain rate 5/s or more, deformation rate 60%
A method for producing rare earth anisotropic permanent magnet powder, which is characterized by hot plastic processing under the above processing conditions and then pulverization.