JPH07312321A - Manufacture of rare-earth permanent magnet - Google Patents

Abstract

PURPOSE:To obtain a rare-earth permanent magnet in which an ideal Nd-Fe-B- based magnet texture is realzed and which obtains a high magnetic characteristic by a method wherein a phase which is generated in an R-rich-phase formation alloy is controlled. CONSTITUTION:In the method of manufacturing a rare-earth permanent magnet, a powder of an alloy 2 in which an area ratio occupied by one kind or more kinds out of R<2>T<2>2, R<2>T<2>3 and R<2>2T<2>7 (where R<2> represents one kind or more kinds of rare-earth elements and T<2> represents one kind or more kinds of transition metals) is at 90% or higher is added to and mixed with a powder of an alloy 1 which is composed mainly of an R<1>2T14B intermetallic compound (where R<1> represents one kind or more kinds of rare-earth elements including Y and T represents one kind or more kinds of transition metals), and this mixture is crushed fine so as to be formed into a shape and sintered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a rare earth permanent magnet having excellent magnetic properties.

[0002]

2. Description of the Related Art Among rare earth permanent magnets, Nd-Fe-B magnets are excellent in magnetic properties, and the demand for Nd-Fe-B magnets is high year by year because they are abundant in resources and relatively inexpensive. It is increasing. However, since the Nd ₂ Fe ₁₄ B compound has a low Curie point of 312 ° C., it is common to replace the part of Fe with Co to improve the heat resistance, but it causes a decrease in coercive force. Various attempts have been made to add them. Moreover, coercive force can be increased by adding Dy, but it is known that the residual magnetic flux density is lowered.

Generally, when an Nd-Fe-B magnet is produced by powder metallurgy, the steps of producing an alloy ingot, coarse pulverization, fine pulverization, molding, sintering and heat treatment are performed. One of the manufacturing method, the metal powder consisting mainly of R ¹ ₂ T ₁₄ B compound, an alloy for forming the R-rich phase (hereinafter, referred to as R-rich phase forming alloy) mixing powders, method of sintering (Hereinafter, referred to as a blend method) has been proposed. Ideal Nd
The structure of the -Fe-B magnet is such that the R-rich phase is thin and uniformly surrounds Nd ₂ Fe ₁₄ B, which is a smooth-shaped matrix phase. In the blending method, it is considered that the R-rich phase is uniformly dispersed between the main phases and becomes a liquid phase at the time of sintering to assist the sintering, so that high magnetic properties can be obtained.

[0004]

However, when the R-rich phase forming alloy is composed of multiple phases, grains having a greatly different composition are generated during pulverization, and a uniform grain boundary phase is not generated after sintering. . Further, since the R-rich phase contains a large amount of rare earths, it is easily oxidized in the manufacturing process, resulting in deterioration of magnetic properties. Therefore, the present invention aims to realize an ideal Nd-Fe-B system magnet structure and obtain high magnetic characteristics by controlling the phases generated in the R-rich phase forming alloy.

[0005]

In order to solve the above problems, the present invention has investigated the constituent components of the R-rich phase forming alloy and the constituent phases thereof. The present invention, R ¹ ₂ T ₁₄ B intermetallic compound (R ¹ is a rare earth of one or two or more, including Y, T is one or two or more transition transfer metal) alloy 1 powder mainly comprising, R ² T ² ₂ , R ² T ² ₃ , R ² ₂ T
² ₇ (R ² is one or two of Dy or Pr, T ² is one or two or more transition metals) added alloy 2 powder inside one or more of the occupied area ratio of not less than 90% The method for producing a rare earth permanent magnet is to finely pulverize, mold, and sinter after mixing.

Alloy 1 and alloy 2 used in the present invention are prepared by weighing each element into a predetermined composition and then melting it by means such as arc melting or high frequency melting. Alloy 1 is liable to produce soft magnetic α-iron, so 900 ° C to 12 ° C in a non-oxygen atmosphere
Heat treatment is performed at a temperature of 00 ° C. for 5 hours or more. After that, both alloy 1 and alloy 2 occlude hydrogen to embrittle and then 700 μm
The material is coarsely pulverized into the following particle sizes to obtain raw material coarse powder. At this time, alloy 2
Since it is easily oxidized, it is desirable to perform coarse pulverization in a non-oxygen atmosphere. The raw material coarse powder is finely pulverized to about 1 to 20 μm by means of a jet mill, a ball mill or the like. This fine powder is molded by a press or the like in a magnetic field of 10 to 25 kOe, and then sintered at 950 to 1200 ° C. in a non-oxygen atmosphere. The sintered body after sintering is 700 in a non-oxygen atmosphere.
After performing the primary heat treatment at ˜1000 ° C., the primary heat treatment is performed at 400 to 700 ° C. in a non-oxygen atmosphere to obtain the target magnet.

[0007]

The present invention provides a powder of an intermetallic compound having a composition of R ¹ ₂ T ₁₄ B intermetallic compound (R ¹ is ^one or more rare earth elements including Y, T: on a transition metal), and R ² T ² ₂ , R ² T ² ₃ , R ² ₂ T ² ₇ (R ²
Is one or two of Dy or Pr, and one or more of T ² is one or more of the transition metals), and the alloy 2 powder having an area ratio of 90% or more is added and mixed,
By finely pulverizing, molding and sintering, a rare earth permanent magnet having excellent magnetic properties can be obtained.

This is due to the following reasons. By setting the area ratio of one or more of R ² T ² ₂ , R ² T ² ₃ , and R ² ₂ T ² ₇ in Alloy 2 to 90% or more, a single phase or a mixed phase of phases close to each other Since it is possible to obtain the alloy 2 powder which is, powder having a small composition deviation can be obtained at the time of pulverization. Further, since the phases have similar grindability, a powder having a relatively uniform particle size is obtained after fine grinding. When alloy 2 powder with small composition deviation and uniform particle size is mixed with alloy 1 powder and then sintered, the R-rich alloy 2 powder is uniformly dissolved around alloy 1 powder which is the main phase forming alloy, Liquid phase sintering can be effectively advanced, and a uniform grain boundary phase can be formed after sintering. This uniform grain boundary phase effectively reduces the magnetic interaction between the main phases and contributes to the improvement of magnetic characteristics, and mainly to the expression of coercive force. Alloy 2 is preferably a single phase, but even if it is a mixed phase, R ² T ² ₂ , R ² T ² ₃ , R ² ₂ T ² ₇ have a large difference in the ratio of R ² and T ^2. Since it does not occur, a large deviation does not occur during pulverization, and a uniform grain boundary phase can be generated after sintering.

In the present invention, R ² T ² ₂ , R ² T ² ₃ , R ² ₂ T ² ₇ (R ² T ^{2 2}
Is an alloy 2 in which one or more of rare earth elements including Y, and one or more of T ² are one or more of transition metals) have an area ratio of 90% or more, 40 ≦ R ₂
It can be obtained by using an R ² -T ² alloy containing ≦ 80 wt%. The main phase that can form in R ² -T ² alloys is R ² ₂ T ²
_17, R ² T ² ₂ , R ² T ² ₃ , R ² ₂ T ² ₇ , R ² ₁ T ² ₅ and R ² eutectic. However, if the amount of R ² contained in the R-rich phase forming alloy 2 is less than 40 wt%, there is a problem in the sinterability of the magnet, and a large amount of soft magnetic R ² ₂ T ² ₁₇ is present, resulting in a magnetism. The characteristics deteriorate. The amount of R ² is R eutectic generates exceeds 80 wt%, the oxidation is easily accelerated, also R ¹ ₂ T ₁₄ B phase in the magnet after sintering is reduced, the magnetic characteristics are deteriorated.

The area ratio occupied by R ² T ² ₂ , R ² T ² ₃ and R ² ₂ T ² ₇ is 90.
% For the alloy 2 having a content of at least%, considering the anisotropic magnetic field, saturation magnetization and cost of the R ₂ T ₁₄ B compound after sintering.
Dy and / or Pr are preferred. Dy and / or Pr
Not only remains in the R-rich phase during sintering, but also the main phase R
₂ T ₁₄ B Diffuses into crystal grains to improve magnetic properties. Dy is effective in improving the coercive force, and when added to Alloy 2, the coercive force can be effectively improved by being present in the R ₂ T ₁₄ B crystal grains with a distribution after sintering. Further, by adding Pr together with Co into the alloy 2, it is possible to prevent a decrease in coercive force due to the addition of Co.
Co is desirable as T ² . Alloy 2 contains a large amount of rare earth elements and is therefore susceptible to oxidative deterioration. However, when the alloy 2 is an intermetallic compound containing Co, it becomes electrochemically noble, and it is possible to significantly prevent oxidation in the manufacturing process. Further, during sintering, Co diffuses into the main phase and the Curie point can be improved.

The alloy 1 which is the main phase in the present invention is preferably a substantially single phase, which is, for example, 27 wt% ≦ R ≦ 30.
It can be obtained by setting wt%, 1.05 wt% ≤ B ≤ 1.20 wt%, T: bal. If the amount of R is less than 27 wt%, the amount of α-Fe crystallized by the peritectic reaction increases, and if it exceeds 30 wt%, a large amount of fine R-rich phase remains, and the oxidation becomes severe during the subsequent pulverization process. Therefore, it is desirable that 27 wt% ≤ R ≤ 30 wt%.

If the amount of B is less than 1.05 wt%, the crystallized α-Fe will not disappear unless the homogenization treatment is carried out for a long time, and the R ¹ ₂ T ₁₇ phase, which is a soft magnetic phase, will precipitate, and It becomes a factor that deteriorates the characteristics. When it exceeds 1.20 wt%, a B-rich phase (RT ₄ B ₄ ) is generated, and R is consumed for this generation, so R becomes deficient,
α-iron tends to precipitate, and it cannot be reduced even by heat treatment, which causes a decrease in magnetic properties. Therefore, 1.05
It is desirable that the range is wt% ≤ B ≤ 1.20 wt%.

In the present invention, the area ratio of each phase was determined by using a scanning electron microscope. Specifically, a 400 × structure photograph was obtained, 100 points were extracted from the structure photograph at 5 mm intervals, and the ratio of each phase on the point was defined as the area ratio.

[0014]

【Example】

(Example 1) 25.0Nd-3.0Dy-70.9Fe-1.1B in a weight ratio by high frequency melting using Nd, Dy, B and electrolytic iron with a purity of 95% or more.
Alloy 1 consisting of 44.0Co-56.0Dy in alloy 2 (Dy ₂ Co ₇ single phase), alloy 40.0Co-60.0Dy 3 (DyC
o ₂ : 94% balance Dy eutectic), 30.0Co-70.0Dy alloy 4 (Dy
Co ₂ : 78% balance Dy eutectic), 20Co-25Fe-55Dy alloy 5
(Dy ₂ (Co, Fe) ₁₇ : 12%, Dy (Co, Fe) ₃ : 70%, Dy (Co, Fe) ₂ : 18%)
Prepared.

11 for alloy 1 which is the main phase forming alloy
After homogenizing at 00 ℃ × 20H, coarsely pulverize to 500
Alloy 1 powder having a size of μm or less was used. The alloys 2, 3, and 4, which are R-rich phase forming alloys, were melted and cooled, and then coarsely pulverized to obtain an alloy 2 powder of 500 μm or less. Alloy 1 powder 8
Alloy 2 powder was mixed at a ratio of 12.5 wt% to 7.54 wt%,
This was finely pulverized with a jet mill using N ₂ as a pulverizing medium so as to have an average particle size of 2 to 5 μm. The obtained finely pulverized powder was subjected to transverse magnetic field molding at a molding pressure of ² ton / cm ² in a magnetic field of 10 kOe. The obtained molded body was sintered in vacuum at 1100 ° C. × 2 Hr. The sintered body was subjected to a first heat treatment at 900 ° C x 2H in an Ar atmosphere and then a second heat treatment at 600 ° C x 1H. Magnet alloys obtained from alloy 1 and alloy 2, alloy 3 and alloy 4 in this manner are designated as A, B, C and D, respectively.

For comparison, an alloy having the same composition as A was produced by a conventional single method, and the same crushing, sintering and aging treatment as described above was performed. This magnet alloy is E
And Table 1 shows the results of measuring the magnetic properties of A to E.

In Table 1, when A and E having the same final composition are compared, the residual magnetic flux density Br, the coercive force iHc, and the maximum energy product (BH) m are all superior to A. Further, comparing A, B, C and D, if the area ratio occupied by R ² T ² ₂ , R ² T ² ₃ , R ² ₂ T ² ₇ in the constituent phase of Alloy 2 is 90% or more, it is high. It can be seen that magnetic characteristics can be obtained.

[0018]

[Table 1]

Example 2 Alloy 2 which is an R-rich phase forming alloy having the composition shown in Table 2 was prepared and coarsely pulverized to 500 μm or less to prepare an alloy 2 powder, and the oxygen content was measured. Also,
Alloy 1 powder of 27.1Nd-1.1B-71.8Fe (wt%) was prepared in the same manner as in Example 1. Alloy 1 was prepared in the same manner as in Example 1.
The powder and Alloy 2 powder were added and mixed, and then finely pulverized, molded, sintered and heat-treated to prepare a rare earth permanent magnet, and the magnetic characteristics and the Curie temperature were measured. The results are shown in Table 2.

From Table 2, it can be seen that the addition of Co to alloy 2 can reduce the amount of oxygen and improve the magnetic characteristics. Further, it can be seen that the addition of Co raises the Curie temperature and improves the heat resistance.

Example 3 Alloy 2 which was an R-rich phase forming alloy having the composition shown in Table 3 was prepared and coarsely pulverized to 500 μm or less to prepare an alloy 2 powder, and the oxygen content was measured. Also,
Alloy 1 powder of 27.1Nd-1.1B-71.8Fe (wt%) was prepared in the same manner as in Example 1. Alloy 1 was prepared in the same manner as in Example 1.
The powder and Alloy 2 powder were added and mixed, and then finely pulverized, molded, sintered and heat-treated to prepare a rare earth permanent magnet, and the magnetic characteristics and the Curie temperature were measured. The results are shown in Table 3.

From Table 3, it is possible to reduce the amount of oxygen by adding Co to alloy 2 and improve the magnetic characteristics.
Moreover, it can be seen that the Curie temperature rises and the heat resistance is improved.

[0023]

[Table 2]

[0024]

[Table 3]

[0025]

The rare earth permanent magnet obtained by the present invention has excellent magnetic properties and heat resistance, and can be used in various fields.

Claims (3)

[Claims] 1. An alloy 1 powder mainly composed of R ¹ ₂ T ₁₄ B intermetallic compound (R ¹ is ^one or more rare earth elements including Y, T is one or more transition metals), R ² T ² ₂ , R ² T ² ₃ ,
R ² ₂ T ² ₇ (R ² is one or more rare earth elements including Y,
T ² is one or more kinds of transition metals), and one or more kinds of alloy 2 powder having an area ratio of 90% or more is added, mixed, pulverized, molded and sintered. A method for manufacturing a rare earth permanent magnet. 2. The method for producing a rare earth permanent magnet according to claim 1, wherein T ² is Co. 3. R ¹ is Dy and / or Pr.
Alternatively, the method for producing a rare earth permanent magnet according to the item 2.