JP2720039B2 - Rare earth magnet material with excellent corrosion resistance - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Fe-BR-based rare earth permanent magnet having high magnet properties, and a rare earth, boron, and iron having significantly improved corrosion resistance of a permanent magnet material by a specific composition. Related to permanent magnets.

Background Art Applicants have previously made B and Fe the main components using resource-rich light rare earths such as Nd and Pr without the need for expensive Sm or Co. As a new high-performance permanent magnet which greatly exceeds the characteristics, an Fe-BR based permanent magnet has been proposed (Japanese Patent Publication No. 61-34242, Japanese Patent Application Laid-Open No. 59-8).
No. 9401).

The Curie point of the magnet alloy is generally between 300 ° C and 370 ° C.
However, by substituting a part of Fe with Co, an Fe-BR based permanent magnet having a higher Curie point can be obtained (Japanese Patent Application Laid-Open Nos. 59-64733 and 59-132104). Further, it has a Curie point equal to or higher than that of each of the above Fe-BR based rare earth permanent magnets and a higher (BH) max, and as a rare earth element (R) for improving its temperature characteristics, particularly iHc. By containing at least one kind of heavy rare earth elements such as Dy and Tb in a part of R of the Fe-BR based rare earth permanent magnet centering on light rare earth elements such as Nd and Pr, it is extremely high at least 25MGOe ( Proposal of a Fe-BR-based rare earth permanent magnet with further improved iHc while retaining BH) max (Japanese Patent Laid-Open No. 60-3230)
No. 6, JP-A-60-34005).

However, Fe-
Since the permanent magnet made of a BR-based magnetic anisotropic sintered body contains a large amount of a rare earth element and iron which are easily oxidized in moisture-containing air to gradually produce a stable oxide,
Oxide generated on the magnet surface when used in a magnetic circuit for a long time causes the output of the magnetic circuit to decrease and causes variations between the magnetic circuits, and also causes the problem of contamination of peripheral devices due to the loss of the surface oxide. was there.

In order to improve the moisture resistance of the above-mentioned Fe-BR permanent magnet, the applicant has proposed a permanent magnet having a magnet body surface coated with a corrosion-resistant metal plating layer by an electroless plating method or an electrolytic plating method (Japanese Patent Application No. 58-162350) and a permanent magnet having a corrosion-resistant resin layer coated on the surface of a magnet body by spraying or dipping (Japanese Patent Application No. 58-171907).

Furthermore, we have proposed permanent magnets in which a corrosion-resistant vapor-phase plating layer made of various metals or alloys is provided on the surface of Fe-BR-based permanent magnets (Japanese Patent Application Nos. 59-278489, 60-7949, and 7974). 60
No. 7950, Japanese Patent Application No. 60-7951).

However, although the corrosion-resistant vapor-deposited plating layer is extremely effective in improving corrosion resistance, there is a problem that its processing equipment and productivity are low and a large cost is required for processing.

Object of the Invention The present invention aims to improve the corrosion resistance of Fe-BR based permanent magnet materials, and demonstrates excellent corrosion resistance by specifying its composition without special surface treatment for improving corrosion resistance. The purpose of the present invention is to provide an Fe-BR based permanent magnet.

SUMMARY OF THE INVENTION The present invention aims to provide Fe-BR-based permanent magnets exhibiting excellent corrosion resistance without performing a surface treatment for improving corrosion resistance. As a result of the study, it has not been possible to obtain the conventional magnet without deteriorating the magnet properties of the permanent magnet material by specifying Nd, Pr, and Dy as the rare earth elements (R) and containing the specified amounts of B and Cr. It has been found that the effect of improving corrosion resistance can be obtained.

That is, according to the present invention, the total of Nd and Pr is 11 at% to 15 at%, Dy 0.2 at% to 3.0 at%, and the total amount of Nd and Pr and Dy is 12 at% to 17 at%, and B5 at% to 14 at Corrosion resistance characterized in that it contains 0.2 at% to 2.0 at% of Cr, or further contains 0.5 at% to 20 at% of Co, and the balance consists of Fe and unavoidable impurities, and the main phase has a tetragonal structure. It is an excellent rare earth magnet material.

Structure and Effect of the Invention The rare earth permanent magnet material, having the above composition, has a (BH) max of 25 MGOe or more, has an iHc of 10 kOe or more, has an atmosphere of 125 ° C. and a relative humidity of 85%, and has a pressure of 2 atm. PCCT test (Pressure Cooker test) and 80 ℃,
In a long-term retention test in an atmosphere with a relative humidity of 95%,
Compared with conventional Fe-BR-based permanent magnets that have been subjected to an aluminum base treatment and then subjected to chromate treatment, they exhibit significantly better corrosion resistance.

The microstructure of the Fe-BR based sintered permanent magnet material is as follows:
The main phase is a R ₂ Fe ₁₄ B compound having a tetragonal structure, and the grain boundary phase contains almost no nonmagnetic B at room temperature, contains a few% of Fe, and an R-rich phase consisting mostly of rare earth elements, and It is composed of the R ₁ + εFe ₄ B ₄ phase containing a large amount of B.

The magnetic properties of this permanent magnet material are based on R ₂ Fe ₁₄
It is dominated by the B tetragonal magnetic compound, which accounts for a significant part of the volume fraction.

In the case of the Fe-BR-based permanent magnet alloy according to the present invention,
The contained Cr mainly substitutes for a part of Fe in the R ₂ Fe ₁₄ B tetragonal magnetic compound forming the main phase, without greatly deteriorating magnet properties, greatly contributing to the corrosion resistance of the main phase. It is considered something.

Further, when Co is added to the above composition, Co substitutes for iron to enter the tetragonal main phase, further increasing the effect of improving moisture resistance, and at the same time, part of Co also exists at the crystal grain boundaries and its corrosion resistance And good results are also shown in the PCT test.

Further, in the permanent magnet of the present invention, C is contained as an impurity in the raw material used and as an impurity in the manufacturing process due to the use of a binder, a lubricant and the like of the raw material powder, but has a great influence on the corrosion resistance of the permanent magnet. If the conventional content exceeds 1000 ppm, the corrosion resistance sharply decreases and a practical permanent magnet cannot be obtained.However, in the present invention containing Cr, even if C remains at about 1000 ppm to 4000 ppm, A permanent magnet material having excellent corrosion resistance can be obtained.

In the present invention, when the total amount of Nd and Pr is less than 11 at%, the R (Nd, Pr) -rich phase required for obtaining a high coercive force is insufficient, and the α- When iron appears and the magnetic properties decrease rapidly, and when it exceeds 15 at%, the coercive force slightly increases, but the Br decreases and (BH) max decreases with the decrease of Br, 11at% to 15at%,
The preferred amount of Nd + Pr is in the range of 12 at% to 14 at%.

In the present permanent magnet, Nd and Pr have almost the same function as elements and can contain either one alone. However, when Nd is added due to the nature of the raw material, usually about several% of Pr is added. Whether to be contained and whether to actively add Pr may be appropriately selected according to the raw material.

If Dy is less than 0.2 at%, there is no effect of increasing iHc and (BH) max, and if it exceeds 3.0 at%, it is effective in improving iHc, but Dy is resource-efficient and expensive, Further, since Br is unfavorably reduced, the content is limited to 0.2 at% to 3.0 at%. The preferred range is from 0.2 at% to 2.0 at%.

Further, when the total amount of Nd + Pr and Dy, that is, the total amount of rare earth elements is less than 12 at%, Fe precipitates in the metal compound of the main phase and iHc decreases rapidly. When it exceeds 17 at%, iHc becomes
10 kOe or more, but the residual magnetic flux density Br decreases (B
H) Since the required Br is not obtained more than max25MGOe, which is not preferable, the total amount of Nd + Pr and Dy is limited to 12 at% to 17 at%.
Further, the preferable total amount is 12.2 at% to 15 at%.

If B is less than 5 at%, iHc is not more than 10 kOe because it is not preferable. If it exceeds 14 at%, iHc increases, but Br decreases, and (BH) max 20 MGOe or more cannot be obtained. % To 14 at%.

Cr is effective for increasing iHc and improving moisture resistance. In particular, when Co is contained, it also has the effect of improving iHc, which decreases with an increase in the amount of Co added. iH
The effect of increasing c and improving corrosion resistance is small, and 2.0 at
%, It is effective to improve iHc, but Br, (B
H) Since max decreases rapidly, the content is limited to 0.2 at% to 2.0 at%. A more preferable content is 0.5 at% to 1.5 at%.

Co is effective for raising the Curie point, corrosion resistance of products and oxidation resistance of raw material powder, and increasing saturation magnetization Is.
%, The effect of increasing the Curie point and improving corrosion resistance is small. If it exceeds 20 at%, Co is condensed and collected in the grain boundaries at a high concentration, and ferromagnetic R (Nd. D
y) The content of 0.5 at% to 20 at% is set so that the -Co compound precipitates and the magnetization reversal of the present system magnet is easily performed to reduce iHc. Considering only the corrosion resistance, the addition of Co shows a remarkable effect even with a small amount, and the preferable range of Co is 1 at% to 8 at%, and more preferably 2 at% to 6 at%.

In the rare earth permanent magnet alloy according to the present invention, the balance after containing the element is Fe and inevitable impurities, and the impurities are inevitably mixed in P, S, and
Cu, Mn, Ni and the like are acceptable.

Further, the content of O ₂ is preferably 8000 ppm or less, more preferably 6000 ppm or less.

In the present invention, the total of Nd and Pr is 12 at% to 14 at%, Dy 0.2 at% to 2.0 at%, and the total amount of Nd and Dy is 12.2 at% to 15 at%, B 5 at% to 8 at%, Cr 0.2 at % To 2.0 at%, or further 0.5 to 20 at% of Co, with the balance being Fe
Permanent magnets consisting of unavoidable impurities and having a main phase of a tetragonal structure, when a magnetic field is applied at right angles to the pressing direction during pressing,
(BH) has excellent magnet properties of max 30 MGOe or more and iHc 13 kOe or more, and has extremely high corrosion resistance.

The permanent magnet material according to the present invention has a crystal grain size of 1
The compound R ₂ (Fe.Cr) ₁₄ B type having a tetragonal crystal structure in the range of μm to 50 μm is used as a main phase and exhibits excellent corrosion resistance.

Furthermore, when Co is added, the compound R ₂ (Fe, Co, Cr) ₁₄ B
In the case of a grain boundary phase structure containing Co as the main phase and containing Co, the corrosion resistance is the best.

In the present invention, Nb, Ti, V, Nb, Mo, W, Al,
Even if Zr, Hf, Zn, Ca, and Si are contained, the effect of the present invention is not impaired.

EXAMPLES Example 1 As starting materials, electrolytic iron having a purity of 99.9%, ferroboron alloy, Nd, Dy, Co, and ferrochrome were used, and in atomic ratio, Nd _14.5 Dy _0.5 Fe _78-xy Co _x B ₇ Cr _y , ( x = 0, y =
0) (x = 0, y = 2) (x = 6, y = 2)
High frequency melting was performed and then cast into a water-cooled copper mold to obtain ingots of various compositions. The ingot contains very little Pr, but is shown here together with Nd.

Thereafter, the ingot was roughly pulverized with a stamp mill and further finely pulverized with a jet mill to obtain a finely pulverized powder having an average particle size of 3.5 μm.

This finely pulverized powder was charged into a mold of a press machine, oriented in a magnetic field of 12 kOe, and molded at a pressure of 1.5 t / cm ^{2 in} a direction perpendicular to the magnetic field. ~ 1120 ° C, 2 hours, A
After sintering under the conditions in the atmosphere, and after allowing to cool,
Aging treatment at 550 ° C for 1 hour in an atmosphere, 20mm x 10mm
X8mm permanent magnet material was obtained.

Table 1 shows the results of measuring the magnet properties of the obtained permanent magnet material.

In addition, a change in weight per unit surface area due to corrosion over time after standing in a constant temperature and constant humidity atmosphere at 80 ° C. and a relative humidity of 95% was measured. The results are shown in FIG.

It can be seen that the Cr-containing permanent magnet material according to the present invention exerts remarkable effects on corrosion resistance and moisture resistance.

Further, after the sample was mirror-polished, the microstructure was observed using an electron probe microanalyzer (EPMA). As a result, most of the added Cr is present in the crystals forming the main phase, and they are R ₂ (FeCr) ₁₄ B or R ₂ (Fe
As a tetragonal compound of (CoCr) ₁₄ B, it was found that it contributed to the improvement of corrosion resistance.

Example 2 In the same production method as in Example 1, the atomic ratio of Nd _13.5 Pr _0.5 Dy _0.5 Fe _78.5-xy Co _x B ₇ Cr _y , (x
= 0, y = 0) (x = 0, y = 2) (x = 6, y = 2).

Paraffin 115F was added to and mixed with the finely pulverized ka in the production process, and the residual C amount of the sintered body was adjusted to be 300 ppm to 4200 ppm.

The change in the coercive force iHc with the increase in the amount of C was measured and is shown in FIG.

In a constant temperature and humidity atmosphere of 80 ° C and 95% relative humidity, 240
The change in weight per unit surface area due to corrosion after standing for a period of time was measured, and the results are shown in FIG.

In the case of the permanent magnet material according to the present invention containing Cr, it can be seen that the adverse effect of C, which lowers the corrosion resistance and the coercive force, can be reduced.

[Brief description of the drawings]

FIG. 1 is a graph showing a change in weight of a permanent magnet material in a constant temperature and constant humidity atmosphere over time. FIG. 2 is a graph showing a change in coercive force iHc with an increase in the amount of carbon. FIG. 3 is a graph showing a change in weight of the permanent magnet material in a constant temperature and humidity atmosphere by increasing the amount of C.

Claims (2)

(57) [Claims] 1. The total amount of Nd and Pr is 11 at% to 15 at%, Dy 0.2 at% to 3.0 at%, and the total amount of Nd and Pr and Dy is 12 at% to 17 at%, and B5 at% to 14 at% A rare earth magnet material having excellent corrosion resistance, comprising 0.2 at% to 2.0 at% of Cr, the balance being Fe and unavoidable impurities, and a main phase having a tetragonal structure. 2. The total amount of Nd and Pr is 11 at% to 15 at%, Dy 0.2 at% to 3.0 at%, and the total amount of Nd, Pr and Dy is 12 at% to 17 at%, and B5 at% to 14 at% A rare earth magnet material with excellent corrosion resistance, characterized by containing 0.5 at% to 20 at% of Co, 0.2 at% to 2.0 at% of Cr, the balance being Fe and unavoidable impurities, and a main phase having a tetragonal structure. .