JPH0411703A - Manufacture of rare earth magnet - Google Patents

Abstract

PURPOSE:To eliminate need of magnetic field orientation to easily obtain a highly characteristic magnet by hot-rolling ultra-rapidly cooled Nd-Fe-B powder to be anisotropic and also orientating the anisotropic powder to be hot- compression-molded. CONSTITUTION:When an R2TM14B1 tetragonal compound {where R is a rare earth element containing at least one of Nd and Pr, and TM=Fe1-xCOx (0<=x<=0.4)} is used as a main phase to manufacture a rare earth magnet by molding anisotropic rare earth magnetic powder wherein a diameter of a crystal particle of the tetragonal compound is 1mum or below, the following steps are taken. That is, when a shape of the powder is flat while the thickness is (t) and the maximum length is (d), such powder wherein 0.1mm<=(t)<=2mm and 2<=(d)/(t)<=40 is laminate-orientated and hot-compression-molded. In addition 5 atomic percentage or below of Co is contained in this powder. The hot- compression-molding is performed with a pressure applied and heated with power supplied.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing an anisotropic rare earth magnet whose main phase is an RJe+aB+ compound (where R is a rare earth element containing at least one of Nd or Pr). It is. The magnets produced by the manufacturing method of the present invention have the potential to be high-performance and low-cost, so they can be used as magnet parts for various actuators such as small motors, and for magnetic resonance imaging diagnostic equipment (nR).
It is expected that it will be widely used as giant magnet parts such as I).

[Conventional technology]

Rare earth element R and representative transition metal element Fe! :B and 2
: By ultra-quenching a molten alloy containing a ratio close to 14:1 using a liquid phase or cold method such as a single roll method, a cold ribbon with excellent magnetic properties can be obtained (US Pat. No. 4,802,931). No. specification, JP-A-59-64739
(Japanese Patent Application Laid-Open No. 60-9852). This quenched ribbon is almost magnetically isotropic.

By hot compression molding (hot pressing) the powder obtained by crushing the quenched ribbon of the Nd-Fe-B alloy described above, it is possible to form a molded bulk in a state close to the true density of the alloy. This is based on U.S. Pat.
ium-ironboron magnets J (
Applied Physics Letters, V
ol.

46, No, 8. pp 790-791. ^pril
15.1985). It is known from the prior art that a value of about 8 kG can be obtained as the residual magnetic flux density of the above-mentioned hot compression molded body.

In order to obtain higher residual magnetic flux density, it is necessary to impart anisotropy to the magnet. R, W, and Lee mentioned above have proposed an anisotropy method using plastic deformation. This method uses Nd-Fe-
After increasing the density of a compression molded body of B-series alloy powder to a density close to the true density of the alloy by hot pressing, the molded body is plastically deformed by die-upsetting again. . It has been reported that a residual magnetic flux density of 8 to 13 kG can be obtained depending on the degree of upsetting or the alloy composition (for example, Y, N
ozawa et al., J. Appl.

Phys., Vol. 64. No, 10. pp52
85-5289. November 15, 1988).

This method of obtaining an anisotropic magnet by applying plastic deformation to a molded body has the disadvantage that the manufacturing process is long and that it is difficult to produce a finished magnet shape, such as cracks occurring on the surface during plastic deformation.

The present applicant has previously developed a method for producing R-Fe-B optically anisotropic powder for forming anisotropic magnets using the above-mentioned isotropic elephant, cold ribbon (or powder obtained by crushing it). ) was proposed to be packed in a metal container and hot-rolled together with the container (Japanese Patent Application No. 202675). By using this method of orienting and molding anisotropic powder, it is possible to easily obtain an anisotropic magnet of any product shape.

Conventionally, the method for molding the above-mentioned anisotropic powder has been to add a resin such as epoxy to the anisotropic powder and compression mold it in a magnetic field (for example, see J.

Eshelman et al., J. Appl, phys.
, Vol. 64. No, L.O.

pp 5293-5295. November 15
．． 1988). The residual magnetic flux density of the resin-bonded magnet obtained using this method is 8 to 9 kG, which is not a sufficiently satisfactory characteristic as a practical magnet.

[Problem to be solved by the invention]

In order to manufacture rare earth magnets at low cost, there is a method that is mass-producible and can omit cutting or polishing after forming, the so-called near-net shave (Near-Net-5).
hape) molding method is preferred.

The present invention aims to provide a method for obtaining a magnet with high magnetic properties from Nd-Fe-B optically anisotropic powder.

[Means to solve the problem] The gist of the present invention is as follows.

That is, the present invention provides RZTM14BI tetragonal compound (
However, R has a main phase of a rare earth element containing at least one of Nd or Pr, TM=Fe+-, Co, (0≦x≦0.4), and the crystal grain size of the RzTM+J+tetragonal compound is 1irm or less. In a method for manufacturing a rare earth magnet formed by molding a certain anisotropic rare earth magnet powder, the shape of the powder is flat, the thickness of the powder is t, and the maximum length is d.
In the case where It's a method.

By the above manufacturing method, an anisotropic magnet having a high residual magnetic flux density and a maximum energy product can be obtained. In order to improve the coercive force of this anisotropic magnet, it is effective to contain 5% or less of Cu in terms of atomic percentage.

Moreover, by performing the above-mentioned hot compression molding by electrically heating under pressure, the clay W [stone] of the present invention can be manufactured at high speed.

(Function) The Nd-FeB ribbon produced by the single-roll liquid quenching process is flake-like, and its typical dimensions are 20 to 20 mm thick.
30tm, width l~2InI11, length 10~30III
II+.

The ribbon is composed of fine RZTMI48+ crystal grains (approximately 0.1irr
n), and is almost magnetically isotropic. An anisotropic powder can be obtained by a method of enclosing this band or its crushed pieces in a metal container and hot rolling (pack rolling). In the hot rolling process, thin strips are piled up in the thickness direction and joined together, and the aggregate of the thin strips is further subjected to plastic deformation. As a result, the ribbon becomes magnetically anisotropic. One rolled powder (anisotropic powder) consists of many anisotropic ribbons.

The shape of the anisotropic powder is thin and flat in the thickness direction, and the easy magnetization axis (
C axis) is oriented toward the thickness direction of the powder (Fig. 1 (
a): Quenched ribbon, Figure 1(b): Anisotropic powder).

Here, the NdzFe+J+ crystal grains grow during hot rolling and become larger than about 0.1 urrr when cold, but do not exceed 1 rm.

When the above-mentioned anisotropic powder is loaded into the cavity of the die, since the powder is flat in shape, the powder is piled up in the thickness direction, and a highly oriented state (stacked orientation) is achieved. By applying pressure to the powder in this state, raising the temperature, and hot compression molding, it is possible to obtain an anisotropic magnet that has high magnetic properties in the direction of pressure (Figure 1 (C): Anisotropic magnet) . The density of the magnet obtained by this method is almost the true density of the alloy (7,
5 g/cd), the magnet exhibits a high residual flux density (and thus a high maximum energy product).

The characteristics of the magnet obtained by the present invention are determined by the degree of lamination orientation of the anisotropic flat powder. In order to obtain a residual magnetic flux density of 1 okG or more, the flatness d of the flat powder must be
/t (t: thickness of flat powder, d: maximum length of flat powder)
must be 2 or more (Figure 2). When the flatness exceeds 40, the powder becomes large and densification by hot compression molding becomes difficult. Therefore, d/t of the present invention is limited to 2 or more and 40 or less. The thickness t of the above-mentioned flat powder can be adjusted by the thickness in the rolling direction of the filling powder before rolling in hot rolling and the final rolling rate. The lower limit of the thickness t of the flat powder of the present invention is 0.1 mm. This is because when the thickness is less than 0.1 mm, it becomes difficult to recover the rolled powder from the metal container after rolling. The upper limit of the thickness of the flat powder of the present invention is 2 mm. because,
This is because if t exceeds 2 mm, densification by hot compression molding becomes difficult.

The details of the present invention will be described below.

Desirable component ranges of the magnet related to the rare earth magnet manufacturing method of the present invention are as follows. Although the composition of the rare earth element R is not particularly limited, it is desirable that at least 60% of the total R be Nd and/or Pr in order to obtain a magnet with high characteristics. The gist of the present invention is lamination orientation and hot compression molding of powder made anisotropic by hot rolling. In order to obtain an anisotropic powder with high properties by hot rolling, the amount of R needs to be 12% or more and 20% or less in atomic percentage. R
If the amount of R is less than 12%, sufficient anisotropy will not be achieved and R
If the amount exceeds 20%, the decrease in residual magnetic flux density cannot be ignored. In order to improve the coercive force, it is effective to set a portion of the R to oy within a range not exceeding 20% of the total R amount. If the proportion of Dy in R exceeds 20%, the decrease in residual magnetic flux density cannot be ignored.

In the rare earth magnet manufactured by the manufacturing method of the present invention, it is effective to add 5% or less of Cu in atomic percentage to improve the coercive force. Here, if the amount of Cu added exceeds 5%, since Cu is a nonmagnetic element, the decrease in residual magnetic flux density becomes so large that it cannot be ignored.

When the amount of B is less than 2% in atomic percentage, R, Fe, 7
A large amount of B-rich phase appears, and when it exceeds 10%, a large amount of B-rich phase appears. Both phases inhibit the anisotropy of the powder due to hot rolling. Therefore, the amount of B is 1 at 2% or more.
A range of 0% or less is desirable.

In order to raise the Curie temperature of the alloy and reduce the temperature change in magnetic flux density at the operating temperature, a portion of Fe may be replaced with Co. Also in the case of the present invention, Co accounts for 40% or less of the total transition metal elements (TM) (i.e.,
TM-Fe+-xCox (0≦x≦0.4))
, :: and are possible. When the amount of Co substitution exceeds 40%, the coercive force decreases.

The quenched powder of the above components is most stably obtained by the usual single-roll method, but it can also be obtained by other twin-roll methods or gas atomization methods.

Anisotropy in quenched powder is achieved by subjecting the powder to plastic deformation. The method previously proposed by the applicant (Patent Application Hei 1m
M202675) is a method (back rolling) in which a metal container is filled with rapidly cooled powder and the powder is hot rolled together with the container (back rolling), and an anisotropic powder with high properties can be obtained in the most rational manner. In the present invention, the inside of the container is evacuated or replaced with an inert atmosphere such as argon gas to prevent oxidation of the powder due to heating. Rolling at a temperature of 500-900″C,
It is preferably carried out at an optimum temperature of 600-800°C. The reason is that when the rolling temperature is lower than 500'C, plastic deformation is difficult to occur, and when it exceeds 900°C, the crystal grains become coarse and the coercive force decreases. In order to obtain high properties as an anisotropic powder, it is necessary to perform rolling at a rolling rate of 40% or more expressed as the thickness reduction rate of the rapidly solidified powder.

After hot rolling, the rolled material is usually broken and recovered as fragments with cracks. Anisotropic powder is obtained by crushing the rolled material. The flatness of the powder is defined by the ratio d/t of the thickness t of the rolled material and the pulverized particle size d (maximum length of the powder), and can be adjusted by changing the rolling rate and the pulverized particle size. For pulverization, a pulverizer such as a brown mill or a bottle mill can be used.

The anisotropic powder is molded by hot compression molding.

If the anisotropic powder has a high degree of flatness, the laminated orientation, which is the core of the present invention, can be achieved naturally by simply loading the powder into the cavity of a die. It is effective to apply vibration to the die to further promote stacking orientation.

Hot compression molding is carried out at a temperature range of 500-900°C and under a pressure of 0.1-5 ton/c+fl. This is easily done in a conventional hot press using high frequency induction heating. Also, in order to increase productivity,
The powder is rapidly heated by current heating under pressure using an electric current sintering machine, and the desired hot compression molding can be completed in a short time (1 to 5 minutes).

Electrical heating increases productivity because it is rapid.

[Example] Example 1 Fe-14%Nd-5%B-1%Cu(N
d+4Fea.

B5Cu+) was melted by high-frequency induction heating, and the molten metal was injected onto the surface of a rotating copper roll through a quartz nozzle with a 1 mm diameter hole. The surface speed of the roll at this time was 25 m/sec, which is the optimum rapid cooling condition for obtaining fine crystal grains. The thickness of the obtained ribbon is 20~
30mm, width 1~2wn, length 10~30 plates.

This ribbon was pulverized to 355 nm or less.

After the powder obtained by the above procedure was inserted into an iron vibrator, the pressure inside the vibrator was reduced to 10-10-'torr and the vibrator was sealed. This was hot-rolled at a temperature of 700°C, resulting in a reduction in the thickness of the ribbon of 82%. The average thickness t of the produced rolled materials is 0.24 mm and 0.98++on. The magnetic properties of the rolled material in the thickness direction are (BH)may =
It is 35MGOe. These rolled materials were crushed to a particle size of 0 to 0.611n (average particle size d = 0.3 mm).
, 0.7-1.0 m (d = 0.85 m++) , 1
．． Anisotropic powders were produced in four sizes: 0 to 4.0 mm (d = 2-.5 an), and 4.0 to 5.7 mm (d = 4.9 mm). Here, the flatness of the powder is expressed as d/t.

The prepared powder was hot compression molded using an electric current sintering machine. In this experiment, the powder was loaded into the cavity of a ceramic die, and the powder was heated by applying a current of 100 OA while applying a pressure of 400 kg/ci to the powder. Here, the cavity is a cavity with a diameter of 20IIfi.

Under the above pressure, when the measured temperature of the sample reaches approximately 800°C, the density of the powder is 7.5g/2, which is close to the true density of the alloy.
reached cnl. The time required from the start of heating to the end of sintering was 3 to 4 minutes. After performing pulse magnetization of 60 kOe in the pressing direction of the obtained compact, the magnetic properties were measured using a self-recording magnetometer.

Figure 2 shows the magnetic properties of the compact in the pressing direction, and the flatness d of the powder.
/t. The larger d/t is, the better the characteristics are obtained, and when d/t is 5 or more, the maximum energy product (
BH) max = 30 MGOe high characteristics can be obtained. Here, since the property of the rolled material itself used in this example is (BH)IIlax = 35MGOe, it can be seen that a sufficiently high lamination orientation is achieved.

Figure 3 shows d/t, = 10.4 in t = 0.24 dishes.
A photograph of the cross-sectional structure of the hot compression molded product in the case of is shown. The photo shows that the anisotropic powder is layered in the direction of pressure.

Example 2 An experiment was conducted to examine the formability and magnetic properties of laminated and oriented rolled powder. The composition of the alloy used was Nd, Fe,.

B6 and Nd,,Fe,. There are two types of compositions of B5Cu1. According to the manufacturing method described in Example 1, the rolling reduction was 82%.
Anisotropic powder was prepared. The shape of the powder has an average thickness of t=0
．． It is 63 mm and has an average flatness d/t = 4.0.

A trapezoidal magnet for a voice coil motor (thickness: 6 mm, trapezoidal surface area: 7C111) was selected as the shape of the molded body, and the molding was performed by hot compression molding using electrical heating.

The shape of the molded magnet was determined by the cavity of the die used and the shape of the punch, and the dimensional accuracy of the magnet was sufficiently satisfactory.

The demagnetization curves in the pressing direction of the molded bodies with the above two types of compositions are
The magnetic properties obtained therefrom are shown in Table 1.

A highly square demagnetization curve was obtained, (BH)
Even as wax, high properties of 30 MGOe or more were obtained.

The coercive force iHc was significantly increased by the addition of Cu.

Table 1 C Effects of the Invention] The method for producing rare earth magnets according to the present invention includes Choei, cold Nd-
It consists of hot rolling Fe-B powder to make it anisotropic, and orienting the anisotropic powder and hot compression molding. Here, since the anisotropic powder produced by hot rolling has a flat shape, the powder is laminated and oriented in the process of filling the powder into a die for hot compression molding. As a result, the shaped magnet exhibits high magnetic properties. In the method described above, it is not necessary to manipulate the magnetic field orientation of anisotropic powder, which is usually performed, and a magnet with high characteristics can be obtained very easily.

Furthermore, since the magnet is manufactured by hot compression molding, the shape after molding is close to the shape of the final product. Therefore, post-processing such as polishing for dimensioning is not required. Therefore, it is advantageous in terms of cost compared to normal pressureless sintered magnets that require post-processing.

[Brief explanation of drawings]

Figure 1 is a diagram illustrating an anisotropic magnet produced by laminated orientation, in which (a) is a quenched ribbon made by ultra-quenching, and (b) is an anisotropic powder made by hot rolling the ribbon. , (C) is an anisotropic magnet made by laminating and orienting the anisotropic powder and hot compression molding. FIG. 2 is a diagram showing the magnetic properties of the molded magnet with respect to the flatness d/t of the anisotropic powder. FIG. 3 is a metal structure photograph taken with an optical microscope, showing how flat powder is laminated in a molded magnet. FIG. 4 is a diagram showing demagnetization curves of molded magnets with and without Cu addition. (C) Figure 8 θ2rnM

Claims (3)

[Claims] (1) R_2TM_1_4B_1 tetragonal compound (R is a rare earth element containing at least one of Nd or Pr,
TM=Fe_1_−_xCo_x (0≦x≦0.4))
A method for producing a rare earth magnet by molding an anisotropic rare earth magnet powder having a main phase of R_2TM_1_4B_1 tetragonal compound with a crystal grain size of 1 μm or less, wherein the shape of the powder is flat, When the thickness of the powder is t and the maximum length is d, t is 0.1 mm or more and 2 mm.
A method for producing a rare earth magnet, characterized in that powders having a d/t of 2 or more and 40 or less are laminated and oriented and hot compression molded. (2) The method for producing a rare earth magnet according to claim 1, characterized in that it contains 5% or less of Cu in atomic percentage. (3) The method for producing a rare earth magnet according to claims 1 and 2, wherein the hot compression molding is carried out by electrical heating under pressure.