JPH0371601A - Manufacture of rare-earth magnet - Google Patents

Abstract

PURPOSE:To contrive improvement both in thermal stability and magnetic characteristics by a method wherein alloy powder having high coercive force is added to the main alloy powder containing a small quantity of Nd and also having high residual magnetic flux density, and the mixture is subjected to heat compression molding. CONSTITUTION:Alloy powder (X) consists of 8-13% R (rare-earth element including at least Nd or Pr except Dy) manufactured using a liquid quenching method, 4 to 8% B and the remaining part consisting of Fe and inevitable impurities, alloy powder (Y) consists of 13 to 20% R, 0.2 to 8% Dy, 4 to 8% B, 0.2 to 8% Cu, and the remaining part consisting of Fe and inevitable impurities. A mixture containing 5-50wt.% powder (X) and the balance of powder (Y) is subjected to hot compression. As a result, both high coercive force and high residual magnetic flux density can be obtained, and high thermal stability can also be obtained with a small added quantity of Dy.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention provides an RzFe+J compound (where R is Nd or P
The present invention relates to a method for producing a rare earth magnet having a main phase containing at least one rare earth element.

Magnets produced by the method of the present invention have a wide range of applications in various actuators such as small motors due to their potential for high performance and low cost.

[Conventional technology]

Rare earth element R and representative transition metal elements Fe and B at 2:1
By ultra-quenching a molten alloy containing a ratio close to 4:1 by a liquid quenching method such as a single roll method, a quenched ribbon with excellent magnetic properties can be obtained (U.S. Pat. No. 4,802).
931 specification, JP-A-5964739, JP-A-60-9852).

A flaky thin strip with a thickness of about 30 μm is obtained by liquid quenching by a so-called single roll method in which a molten Nd-Fe-B alloy is injected onto the surface of a rotating copper roll. It is known that depending on the degree of rapid cooling, the ribbon becomes amorphous or has a fine crystal grain structure with a crystal grain size of 0.01 to 0.5 marks.

This quenched ribbon exhibits high coercive force when its crystal grain size is around 0.05n.

By hot compression molding (hot pressing) a powder obtained by pulverizing a rapidly solidified ribbon of an Nd-Fe-B alloy, it is possible to form a molded bulk in a state close to the true density of the alloy.

This is described in U.S. Patent No. 4,792,367,
0-10.042 and the paper published by R.W. Lee IFot-pressed neodymium
-iron-boron magnets” (Appli
ed Physics Letters+ Vol.4
6°No, 8. pp 790-791. April
15.1985). Here, when hot forming is carried out under compressive stress, plastic flow occurs within the molded body, and the easy magnetization axis (C axis) tends to be slightly oriented parallel to the pressing direction due to the plastic flow. the result,
It is known from the prior art that a residual magnetic flux density of about 8 kG can be obtained in the pressurizing direction.

In order to put the above-mentioned hot compression molded magnet into practical use, a magnet with higher residual magnetic flux density is required in terms of characteristics.
A method is needed that allows mass production of such magnets at low cost.

JP-A-64-42554 discloses a technique for improving formability and plastic workability by mixing different types of powders with different Nd contents and hot-compressing the mixture. Zr is included as a component of the powder of
, Nb, Tf, V, If, Ta, , W as essential components. In such a component system, as shown in the example of the above-mentioned publication, the density of the molded body reaches the true density (7.5 g/cd) only when 50% of high Nd component powder is added.
It is close to.

[Problem to be solved by the invention]

When hot compression molding of R-Fe-B alloy powder is performed using a normal real press machine, it is common to heat the die by high-frequency induction to indirectly heat the powder in the die. This method is not suitable for mass production of magnets because it takes time to heat and cool the die.

Molding can be completed in a short time by heating in the hot pressure WITC type by heating by electrical current heating (current sintering). This heating method uses 100 to 1000 kg/c
In this method, a compressive stress of d is applied to the powder in the die, and an electric current is passed through the powder through a punch to directly heat the powder. According to this method, the density of the compact reaches the true density of the alloy in 1 to 4 mtn after the start of energization. This current sintering is suitable for mass production because the die and molded body can be cooled quickly after molding is completed.

The challenges in current sintering are as follows. Although it is possible to mold R-Fe-B powder in a short time by electrical sintering, the temperature of the molded product reaches 800 to 900"C when sintering is completed. Therefore, the crystal grains that make up the powder are The thermal stability of the molded magnet decreases.

According to the experiments of the present inventors, Fe-14at$Nd-6
Differences appeared in the thermal stability of molded magnets when a rapidly cooled powder of atXB (hereinafter referred to as Nd H4Fea.B) having an M1 precept was compression molded using an electric sintering machine and a normal hot press machine. Irreversible demagnetization rate (ΔΦ1rr
) was as follows for each magnet.

Hot blur, magnet: ΔΦ1rr = -7.4% (iHc = 16.5 koe
) Current-carrying sintered magnet: ΔΦ1rr = -12.4% (iHc = 16.7 ko
e) Here, hot pressing is performed at 600°C under a pressure of 2000 kg/effl, and electrical sintering is performed at 400°C.
) A current of 477 A/C4 was applied under a pressure of cg/c111.

In the case of energization sintering, the temperature rose rapidly with the start of energization and reached 810° C. after about 3 w1n, at which point sintering was completed. As mentioned above, the thermal stability of energized sintered magnets is poor, and it is necessary to improve this in order to put the magnets into practical use.

Addition of Dy is often used to improve the thermal stability of R-Fe-B magnets. It is known that the coercive force of sintered magnets is significantly improved by the addition of Dy (M, Sag
aiva et al., IEEE Trans, Mag, Vol.
, Mag-20°No, 5. pp1584-1589
(1984)). It is known that the irreversible demagnetization rate of the magnet decreases due to the effect of increasing the coercive force (M, To
kunaga et al., IEEE Trans, Mag.

Vol, Mag-22, No, 5. pp904-90
9 (1986)). Nd- prepared by liquid quenching
It is known that the coercive force of Fe-B-based quenched ribbons can be improved by substituting a portion of Nd with DV (J, J, Croat et al., J, Hepp), Phys,
Si o1.55. No, 6. pp207B-2087(1
984)).

In all of the above-mentioned known documents, the amount of Dy added is relatively large, ranging from 10 to 20% expressed as a Nd substitution rate.

It is expected that by adding Dy, the thermal stability of the hot compression molded magnet of the quenched ribbon can be improved. on the other hand,
As seen in the above-mentioned report by J. J. Croat et al., the addition of Dy causes a significant decrease in the residual magnetic flux density (Br). According to experiments conducted by the present inventors, quenched ribbon ((Ndo, qDVo, +) + h
FeteB6) hot compression molded magnet has a Br of 7.0 k
G and iHc are 21.4 kOe, which is practically necessary and r=8.0 to 8.5 kG cannot be secured. Also, 1
Substitution of Dy up to 0% (addition of 1.6 at% in the entire magnet) also causes an increase in the cost of the magnet because the Dy element is expensive.

An object of the present invention is to provide a method for producing a hot compression molded magnet that exhibits high thermal stability in a component system in which the amount of ayO added is smaller than conventional ones.

[Means to solve the problem]

The method for producing a rare earth magnet of the present invention includes an atomic percentage of R of 9% or more and 14% or less (R is a rare earth element excluding Dy containing at least one of Nd or Pr), 0.105% or more and 2% or less. oy, B of 4% or more and 8% or less, 0.0
In a method for producing a rare earth magnet consisting of 5% or more and 2% or less Cu, and the balance being Fe and unavoidable impurities,
R14% of 8% or more and less than 13% produced by liquid quenching method
Alloy powder (X) consisting of 8% or less B, and the balance Fe and unavoidable impurities, and 13% or more and 20% R10, 2% or more and 8% or less, also produced by the liquid quenching method. An alloy powder (Y) consisting of Dy, 4% or more and 8% or less B, 0.2% or more and 8% or less Cu, and the balance consisting of Fe and unavoidable impurities is mixed to form the alloy powder (Y). After obtaining a mixture having a volume percentage of 5% or more and 50% or less, the mixture is hot compression molded. Here, it is possible to replace up to 20% of Fel with Co. Rare earth magnets can be manufactured with high productivity by heating in hot compression molding by electrical heating.

[For production] The details of the present invention will be explained below.

The magnetic properties of the Nd-Fe-B quenched ribbon produced by the liquid quenching method vary greatly depending on the Nd and Dy contents. That is, the amount of Ndo is higher than that of the NdzFe+J compound.
It is known that as the ratio (11.8%) increases, the coercive force (ILLC) increases, but the residual magnetic flux density (Br) decreases. Furthermore, addition of a small amount of ay significantly increases iHc. Furthermore, the present inventors have found that the combined addition of Dy and Cu increases iHc more than when only oy is added. Examples of the magnetic properties of various alloy ribbons are shown below.

Fe-12X Nd-6X B: iHc = 9.
9kOe, Br = 7.0kGFe-15X Nd
-6χB: iHc = 19.1 kOe, Br =
5.9kGFe-14,4χNd-1,6X Dy-
6X B: iHc =25.6kOe.

Br = 5.3kG Fe-14,4χNd-1,6X Dy-5X B4.
5χCu: iHe >26 kOe, Br = 5
．． 2kG These values are the measurement results of a bonded magnet (density 6.0 g/CTII) in which the alloy ribbon is crushed to 1501 Im or less and the resulting powder is solidified with resin.

The manufacturing method of the present invention involves adding high ice alloy powder (additional powder) to alloy powder with high Br and low Nd content (main powder), and hot compression molding after mixing. Features. The present inventors have newly discovered a phenomenon in which the thermal stability of hot compression molded magnets is significantly improved by adding a powder containing a combination of oy and Cu. Details are shown in Example 1, but for example, Fe-12XNd-4,92
Main powder of Co-6χB and Fe14.4χNd-1,6χ
In a high-density magnet that is made by mixing Dy-52B-1,5χCu additive powder at a ratio of 4:1 and increasing the density to more than 95% of the true density by hot compression molding using electrical heating, Pc The irreversible demagnetization rate at =2 is -4 at 180″C
, 2% (irreversible demagnetization rate: after magnetization at room temperature (30 °C), the magnet is heated to a predetermined temperature (for example, 180 °C),
rate of decrease in magnetic flux when returned to room temperature). Example 2.3
Such high thermal stability is due to Dy
This cannot be obtained without the combined addition of Cu and Cu.

In the present invention, the effect is sufficiently exhibited when an additive powder containing a combination of Dy and Cu is used and the amount of the additive powder is 5 to 50%. Therefore, the residual magnetic flux density of the shaped magnet is almost determined by the low NdO main powder, and the B
A high value of r-8 to 8.5 kG is maintained.

The rare earth magnet of the present invention has two types of alloy powders X having different compositions.
and Y are mixed and solidified by hot compression. As the rare earth element R, Nd is most preferable, but
It is also possible to replace part or all of Nd with Pr. Here, R1 of the powder X is limited to 8% or more and less than 13%, centering around 11.8%, which is the composition ratio of the R2Fe+J phase, to impart a high residual magnetic flux density to the powder X. The amount of R is 8%
When it is less than 1, the coercive force of powder X is extremely reduced and cannot be put to practical use. Furthermore, when the amount of R is 13% or more, the residual magnetic flux density decreases. High coercive force powder Y is added to powder X having such a composition range. The properties of powder Y include an R-rich phase (a ternary Nd-Fe-B system with a melting point of about 700°C) that melts and oozes during hot compression. It is necessary to bring it out. An appropriate mechanism is that this oozing R-rich melt wets the surface of the powder χ and increases the coercive force of the powder X. For these reasons, the amount of R in powder Y is limited to 13% or more and 20% or less. When the amount of R exceeds 20%, the residual magnetic flux density of the powder Y decreases significantly, and the characteristics of the high-density magnet obtained by mixing the powders X and Y deteriorate.

Dy and Cu are added as components of powder Y. Here, Cu is concentrated in the R-rich phase and lowers the melting point of the R-rich phase by about 200°C. This facilitates oozing of the R-rich melt during hot pressing. D
A part of y is taken into the R-rich melt and reaches near the surface of powder X by oozing out, contributing to increasing the coercive force of powder It is thought to provide stability. Therefore, Cu is, so to speak, a promoter of Dy diffusion, and both elements diffuse together, and the surface of the powder
-X interface).

Add as a component of powder Y. y is 0.2% or more and 8%
Limited to: The reason is that when rh is less than 0.2%, the amount of Dy incorporated into the R-rich melt is small, and when rh is more than 8%, the residual magnetic flux density of the powder Y is significantly reduced. Cu is added as a component of powder Y in a range of 0.2% or more and 8% or less. If the amount of Cu added is less than 0.2%, it does not contribute to improving the thermal stability of the shaped magnet, and if it exceeds 8%, the reduction in the residual magnetic flux density of the powder Y cannot be ignored.

The volume percentage of Y in the mixture of powders X and Y is limited to 5% or more and 50% or less. The reason is as follows. If the volume percentage of Y in the additive powder is less than 5%, a sufficiently high coercive force and excellent thermal stability cannot be obtained. Furthermore, if the volume percentage of Y exceeds 50%, the high residual magnetic flux density of the powder X cannot be fully utilized. The average R of the magnet obtained under such a mixing ratio (where R is Nd
The atomic percentage of rare earth elements (excluding Dy and containing at least one type of Pr) is limited to 9% or more and 14% or less. The reason for this is that if R is less than 9%, a sufficiently high coercive force cannot be obtained, and if R exceeds 14%, a high residual magnetic flux density cannot be obtained. The average amount of y in the magnet is limited to 0.05% or more and 2% or less for the same reason as the limitation on the composition of R. A more preferable oyO composition range is 0.1% or more and 1% or less, which is a range that can ensure both high Br and high thermal stability.

The average amount of CuO is limited to 0.05% or more and 2% or less. A more preferable composition range of Cu is 0.1% or more and 1% or less for the same reason as in the case of ay.

When the amount of B is less than 4% in atomic percentage, an RzFe+= phase appears, and when it exceeds 8%, a B-rich phase appears.

Either phase inhibits densification of the powder by hot compression.

Therefore, the amount of B in the quenched ribbons and their solidified magnets according to the present invention is uniformly limited to 4% or more and 8% or less.

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 magnet according to the present invention, up to 20% of the FeO amount can be replaced with Co without impairing the magnetic properties.

Next, details of the manufacturing method of the present invention will be described.

The ultra-quenched alloy powder having the above-mentioned limiting 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. In the case of a single roll method, the thickness is 20 to 30-1, the width is 1.5 to 2 marks, and the length is 1.
Flake-like ribbons of 0 to 20 mm are obtained. The magnetic properties of a ribbon quenched by the single roll method vary depending on the degree of quenching, which is controlled by the rotational speed of the roll. Under optimal quenching conditions, a ribbon consisting of fine grains with a size of 0.01-0.1 tm is obtained, and the ribbon exhibits excellent magnetic properties. On the other hand, under superquenching conditions, a nearly amorphous ribbon is obtained, but the ribbon is crystallized by heat treatment and exhibits high magnetic properties. Either ribbon can be crushed and subjected to hot compression molding magnets. The particle size of the powder is preferably around 100,77111. In the present invention, it is necessary to mix two types of alloy powders in an appropriate ratio, which can be easily done using, for example, a V-type mixer.

The hot compression of the present invention can be carried out by hot pressing, HIP, current sintering, etc., but it is most preferable to use a method using a current sintering machine that can perform current heating because it can be carried out with high mass productivity.

The characteristic of current sintering is that sintering can be completed in a short time (1 to 4 m1n) at a high temperature close to 800 to 900'C and a relatively low pressure. Based on the manufacturing method of the present invention
A magnet with a composite addition of Dy and Cu exhibits high thermal stability even when molded at the above-mentioned high temperature.

〔Example〕

Example 1 Fe-12zNd-4,9%Co-6XB in atomic percentage
(Nd+z(Fee, qaCoo, 06) 112
B6) alloy powder X with the composition Fe-14,4χNd1,
6XDV-52B-1, 5% Cu ((Ndo, gD
yo, +) + bFet7.5BsCu L s)
An alloy powder Y having the composition was prepared. To produce these powders, an alloy having the above composition was first melted by high-frequency induction heating, and the molten metal was injected onto the surface of a rotating copper roll from a quartz nozzle having a hole with a diameter of 1 mm. The surface speed of the O-ru at this time was 25 m/sec, which is the optimum rapid cooling condition for obtaining fine crystal grains. The thickness of the obtained thin strip is 20~30-1, the width is about 1.5 mm, and the length is 10~20.
[+1111.

This ribbon was ground to 150 mm or less to obtain powders X and Y for press molding. Add 3w of epoxy resin to each powder
t% was added, and a bonded magnet was produced by compression molding. The magnetic properties of the bonded magnet (density 6.0g/afl) are 60
The results measured using a self-recording magnetometer after performing pulse magnetization of kOe are shown below.

Powder X: 1Hc=10.6kOe, Br=7.
0kG.

(88) max=11.0MGOe Powder Y: iHc>26kOe, Br=5.2k
G.

(BH)max=6.2MGOe Powders X and Y were mixed in various proportions, and the mixed powder was hot compression molded using an electric current sintering machine. In this experiment, the powder was loaded into the cavity of a carbon die, and a pressure of 400 kg/C11l was applied to the powder.
The powder was heated by applying a current of 00A. Here, the cavity has a cylindrical shape with a diameter of 20 m+n. Although it varied depending on the mixing ratio of the mixed powder, under the above pressure, the density of the mixed powder reached 7.6 g/c+d, which is close to the true density of alloy powder X, when the measured temperature of the sample reached 800 to 900°C. Reached. The time required from the start of heating to the end of sintering was 3-4
It was min.

Figure 1 shows the magnetic properties of the hot compression molded magnet in the pressing direction when the volume percentage of powder Y in the mixed powder is different, and 140
'C and 180''C. The magnetic properties were measured with a self-recording magnetometer after pulse magnetization at 60 kOe. The irreversible demagnetization rate is the balance coefficient Pc (=-B/ II) was obtained by measuring the amount of change in magnetic flux due to heating of the cylindrical sample in 2.As can be seen from Figure 1, powder Y to which Dy and Cu were added in combination was compared to the main powder X. By adding 10 to 20%, the coercive force iHc is significantly improved.With the above addition range of powder Y, a high residual magnetic flux density Br of 8.2 to 8.4 kG is ensured.Also, due to the increase in iHe, Correspondingly, the absolute value of the irreversible demagnetization rate becomes smaller. When the amount of powder Y added is 20%, the irreversible demagnetization rate at 140°C and 180"C is -1.7% and -4.2%, respectively. be.

Example 2 Electrical sintering of mixed powder was performed while changing the type of added powder Y. The main powder X described in Example 1 was used, and the experimental conditions were the same as those detailed in Example 1. Table 1 shows the composition of the added powder, the amount added, and the average composition of the mixed powder consisting of powders X and Y. What is described as Nd-based is a single Fe-
This is a component system of a magnet obtained by solidifying powder having a composition of 14XNd-62:B.

Nd + Cu system, Nd f Dy system, and Nd +
Dy f Cu type refers to Cu and /
Alternatively, it is a magnet component system consisting of an additive powder containing Dy and the above-mentioned main powder.

Figure 2 shows the demagnetization lIh of the current-carrying sintered magnets of each component system.
Show the line. The residual magnetic flux density does not change much depending on the component system and is 8.2 to 8.4 kG, but the coercive force is Nd
y f It is the largest in the Cu system. In Figure 3, Pc=2
The measurement results of the irreversible demagnetization rate are shown below. The absolute value of irreversible demagnetization rate is Nd system, Nd f Cu system, Nd +DV
It can be seen that the size decreases in the order of Nd+DyfCu series. Here, it has been confirmed that the magnetic properties and irreversible demagnetization rate do not change much depending on the presence or absence of addition of 5% or less Co.

Example 3 Current-applied sintered magnets of mixed powders consisting of various main powders X and additive powders Y were produced, and the values of magnetic properties and irreversible demagnetization rates were compared. The volume percentage of the added powder (addition N) was 20% except for the - example, and the other experimental conditions were the same as those detailed in Example 1. Electrically sintered magnets of mixed powders consisting of various main powders and additive powders shown in Table 2 were prepared,
These magnets were designated as No. 1, 2.3.4.5.6.

Table 3 shows the magnetic properties of each magnet (iHc, Brs (BH
)max) and the irreversible demagnetization rate (ΔΦ1rr) at 180°C under the conditions of PC-2.

3 As seen from Tables 2 and 3, coercive force (iHc)
Even if they are almost the same, the Nd-Pe-83 element system or Nd
-Fe-B-Dy Compared to the four-element system, Nd-Fe-B
The absolute value of the irreversible demagnetization rate (ΔΦ1rr) of the -Dy-Cu five-element system is small and has excellent thermal stability. Also, as seen from the results for magnet No. 6, Pr can be used instead of Nd.

〔Effect of the invention〕

The magnetic properties of the Nd-Fe-B magnet obtained by the present invention are comparable to the properties of Sm-Go sintered magnet formed by vertical magnetic field forming,
The poor thermal stability, which was a weak point of water-based magnets, has been greatly improved. In the case of the present invention, the rare earth raw material is mainly N, which is inexpensive.
Since d is used, it is possible to provide a low-cost magnet. Furthermore, the shape of the magnet obtained according to the present invention can be precisely determined according to the shape of the cavity of the die used for hot compression molding, and therefore post-processing such as polishing is not required. This allows Nd-
It can also be advantageous in terms of cost compared to PeB magnets.

[Brief explanation of drawings]

Figure 1 shows the magnetic properties and irreversible demagnetization rate of an energized sintered magnet with respect to the volume percentage of Fe-Nd-Dy-B4:u-based powder (the average atomic percentage of Dy and Cu calculated from it). Figure 2 shows the demagnetization curves of the energized sintered magnets of each component system, and Figure 3 shows the irreversible demagnetization rate of the magnets of each component system.
n-terminus 1% 4' (%) average Dy atomic hundred molecules (
'/,) Average CU atomic capacity (〃) H(Se0e) 4π1(/2σ)

Claims (3)

[Claims] (1) R in an atomic percentage of 9% or more and 14% or less (R is a rare earth element excluding Dy containing at least one of Nd or Pr), 0.05% or more and 2% or less of Dy, 4%
More than 8% B, 0.05% or more and less than 2% Cu
, and the balance is Fe and unavoidable impurities.
Alloy powder consisting of less than 13% R, 4% or more and 8% or less B, and the balance being Fe and unavoidable impurities (
X) and 20 with 13% or more produced by the same liquid quenching method.
% or less, Dy of 0.2% or more and 8% or less, B of 4% or more and 8% or less, Cu of 0.2% or more and 8% or less, and the balance consisting of Fe and inevitable impurities. Powder (
Y) and the alloy powder (Y) has a volume percentage of 5.
% or more and 50% or less, and then hot compression molding the mixture. (2) The method for producing a rare earth magnet according to claim 1, characterized in that up to 20% of the amount of Fe is replaced with Co. (3) The method for manufacturing a rare earth magnet according to claims 1 and 2, wherein the heating in the hot compression molding is performed by electrical heating.