JPH0815122B2 - Rare earth magnet having excellent corrosion resistance and method for manufacturing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a Fe-BR rare earth permanent magnet having high magnet characteristics, and by its specific composition and simple surface treatment,
TECHNICAL FIELD The present invention relates to a rare earth / boron / iron-based permanent magnet in which the corrosion resistance of a permanent magnet material is remarkably improved, and a manufacturing method thereof.

BACKGROUND ART The present inventor has previously used Bd, Fe as a main component by using a resource-rich light rare earth centering on Nd and Pr, does not contain expensive Sm and Co, and is a conventional rare earth cobalt magnet. Fe-BR permanent magnets have been proposed as new high-performance permanent magnets that greatly exceed the maximum characteristics (Japanese Patent Laid-Open Nos. 59-46008 and 59-89401).

The Curie point of the magnet alloy is generally 300 ° C to 370 ° C.
However, by substituting a part of Fe with Co, an Fe-BR permanent magnet having a higher Curie point can be obtained (Japanese Patent Laid-Open No. 2000-242242).
59-64733, JP-A-59-132104), and further has a Curie point equal to or higher than that of the Fe-BR rare earth permanent magnet containing Co and a higher (BH) max, and its temperature characteristics, in particular, i
In order to improve Hc, at least one of heavy rare earth elements such as Dy and Tb is contained in a part of R of the Fe-BR rare earth permanent magnet containing Co centering on light rare earth elements such as Nd and Pr as rare earth elements (R).
Due to the inclusion of seeds, it is extremely high (25MGOe or more) (B
We proposed a Co-containing Fe-BR rare earth permanent magnet with further improved iHc while retaining H) max (JP-A-60-340).
No. 05).

However, Fe-B having the above excellent magnetic properties
-The permanent magnet made of R type magnetic anisotropy sintered body contains iron as a main component, which is a rare earth element and iron which easily oxidize in air to form a stable oxide. The oxides generated on the surface of the magnet cause a decrease in the output of the magnetic circuit and a variation between the magnetic circuits, and there is a problem that the peripheral devices are contaminated due to the dropping of the surface oxide.

Therefore, in order to improve the corrosion resistance of the above Fe-BR permanent magnet, the applicant has proposed a permanent magnet whose surface is coated with a corrosion-resistant metal plating layer by electroless plating or electrolytic plating (Japanese Patent Application Laid-Open No. 58-162350). No.), and a permanent magnet whose surface is coated with a corrosion-resistant resin layer by spraying or dipping (Japanese Patent Application No. 58-171907).

However, in the former plating method, since the permanent magnet body is a sintered body and is porous, the acidic solution or alkaline solution in the plating pretreatment remains in this hole, and there is a risk of corrosion over time, Further, since the magnet body has poor chemical resistance, the magnet surface is corroded during plating, resulting in poor adhesion and corrosion resistance.

In addition, since the latter method of resin coating has directionality, it takes a great deal of time and effort to form a uniform resin coating on the entire surface of the object to be processed, especially for a deformed magnet body with a complicated shape. It is difficult to apply a coating of uniform thickness, and
In the dipping method, the thickness of the resin coating becomes non-uniform, and the product dimensional accuracy is poor.

Furthermore, as a Fe-BR permanent magnet that eliminates the drawbacks of the above plating and spraying methods or dipping methods and has stable corrosion resistance over a long period of time, a corrosion-resistant vapor-phase plating layer made of various metals or alloys was provided on the surface thereof. Proposed permanent magnets (Japanese Patent Application No. 59-278489, Japanese Patent Application No. 60-7949, Japanese Patent Application No. 60-7)
No. 950, Japanese Patent Application No. 60-7951). This vapor-phase plating suppresses the oxidation of the surface of the magnet body, does not deteriorate the magnetic characteristics, and does not use or leave corrosive chemicals, so that it has an advantage of being stable for a long period of time. However, although it is extremely effective in improving the corrosion resistance, there is a problem that the processing apparatus and the productivity thereof are low and the processing requires a large cost.

OBJECT OF THE INVENTION The present invention aims to improve the corrosion resistance of Fe-BR permanent magnets. To improve the corrosion resistance, the composition is specified, and a simple surface treatment is performed to exhibit excellent corrosion resistance.
It aims at Fe-BR permanent magnets and their manufacturing methods.

Structure and effect of the present invention The present invention is to study various Fe-BR permanent magnets compositionally for the purpose of Fe-BR permanent magnets exhibiting excellent corrosion resistance. As a result, Nd, Dy as rare earth elements (R) And the inclusion of a specific amount of B, Co, Al, C, or Ti or Nb, improves the corrosion resistance that cannot be obtained in the past without degrading the magnetic properties of the permanent magnet material. It is characterized in that the effect is obtained and, as a simple surface treatment, electrodeposition coating is applied to further improve the corrosion resistance.

That is, the present invention is Nd 11at% ~ 15at%, Dy0.2at% ~ 3.0at%, and the total amount of Nd and Dy is 12at% ~ 17at%, B5at% ~ 8at%, Co0.5at% ~ 13at%, Al 0.5 to 4 at%, C 1000ppm or less, balance Fe and unavoidable impurities, the main phase is a tetragonal structure on the surface of the magnet body, has a corrosion-resistant resin layer of uniform thickness by electrodeposition coating A Fe-BR rare earth magnet having excellent corrosion resistance and a method for producing the same.

The rare earth permanent magnet material according to the present invention has (BH) max25M
Has magnetic properties of GOe or higher and iHc of 10 kOe or higher.

Further, in addition to the above composition, one kind of Ti or Nb is added.
By containing 1 at% to 1.0 at%, the magnet characteristics of the permanent magnet, particularly the squareness of the demagnetization curve, can be improved, and (BH) max can be improved.

The grain boundary phase in the Fe-BR permanent magnet alloy is an R-rich phase containing almost no B and containing a few% of Fe, most of which is a rare earth element, when Co and Al are not contained in the alloy. Since it is composed of the R ₁ + _ε Fe ₄ B ₄ phase containing a large amount of B and B, the reason why the corrosion resistance of the Fe-BR permanent magnet is deteriorated is that the R-rich mainly composed of chemically active rare earth element is used. This is probably due to the existence of phases.

In the case of the Fe-BR permanent magnet alloy according to the present invention, Co and Al contained in the grain boundary phase enter the R-rich phase to become a multiphase, and by adjusting the amounts of Co and Al,
It is considered that it contributes greatly to the corrosion resistance of the grain boundary phase without deteriorating the magnetic properties.

In this invention, the electrodeposition coating method for forming the corrosion resistant resin layer on the surface of the magnet body is as follows: the permanent magnet body is immersed in an aqueous paint, and the permanent magnet body is used as an anode or a cathode, and a direct current is applied between the permanent magnet body and the counter electrode. It is an electrodeposition coating method in which an electric current is supplied, the entire permanent magnet body is electrically coated, and a corrosion-resistant resin layer is formed on the surface. Anion electrodeposition coating method or magnet to be treated with the magnet body to be treated as an anode A cation electrodeposition coating method using a body as a cathode can be adopted.

The resin used for the above-mentioned anion electrodeposition coating is a polycarboxylic acid resin having a drying oil, polyester, polybutadiene, epoxy ester, polyacrylic acid ester, etc. as the nucleus, and is usually a base such as an organic amine or caustic potash. It is neutralized and converted to an aqueous solution or dispersed in water to become negatively charged.

The resin used for the cationic electrodeposition coating is mainly a polyamino resin having an epoxy resin, an acrylic resin or the like as a nucleus, and is usually neutralized with an organic acid and then made into an aqueous solution or water dispersion to form a positive resin. In this invention, by the permanent magnet surface electrodeposition coating,
The thickness of the corrosion-resistant resin layer is 5 μm to 30 μm.

Further, for the purpose of rust prevention and coating film reinforcement improvement, the above resin may contain a rust preventive pigment such as zinc oxide, zinc chromate, strontium chromate, and red lead, or benzotriazole may be added. It may be contained.

In the present invention, the amount of the above pigment contained in the resin may be 80% or less with respect to the resin amount, and the amount of benzotriazole may be 5% or less with respect to the resin amount.

Before applying the resin layer by the electrodeposition coating method, the surface of the permanent magnet body may be subjected to an undercoating treatment, and the undercoating film may be a phosphate coating such as zinc phosphate, manganese phosphate or the like, or chromium. An acid salt coating is preferable, and the thickness of the chemical conversion coating of the base treatment is preferably 5 μm or less in view of corrosion resistance, strength and cost.

Reasons for limiting components In this invention, if Nd is less than 11 at%, the Nd-rich phase necessary for obtaining a high coercive force is insufficient, and α-iron with a small coercive force appears, resulting in a sharp decrease in magnet characteristics. If it exceeds 15 at%, the coercive force slightly increases, but
(BH) max decreases with the decrease of B and the decrease of Br, so it should be 11at% to 15at%.

The preferable Nd amount is in the range of 12 at% to 14 at%.

In the present invention, a part of Nd can be replaced with Pr in a range that does not impair magnetic properties and corrosion resistance, and a commercially available product.
As the Nd material, a part of didymium containing Nb, Pr, and Ce can be used.

When Dy is less than 0.2 at%, there is no effect of increasing iHc and (BH) max, and when it exceeds 3.0 at%, it is effective in improving iHc, but Dy is scarce in resources and permanent magnet cost is low. However, it is not preferable because it causes the increase of 0.1 to 3.0 at%. The preferred range is 0.2 at% to 2.0 at%.

Further, when the total amount of Nd and Dy, that is, the total amount of rare earth elements is less than 12 at%, Fe is precipitated in the metal compound of the main phase, iHc sharply decreases, and when it exceeds 17 at%, iHc is
Although it becomes as large as 10 KOe or more, the residual magnetic flux density Br decreases, and Br required for (BH) max25MGOe or more cannot be obtained, which is not preferable. Therefore, the total amount of Nd and Dy is limited to 12 at% to 17 at%. Further, the preferable total amount of Nd and Dy is 12.5 at% to 15 at%.

If B is less than 5 at%, iHc is 10 kOe or less, which is not preferable, and if it exceeds 8 at%, iHc increases, but Br decreases and (BH) max25MGOe or more cannot be obtained. % ~ 8at%
Limited to

Co is effective for increasing the Curie point, weather resistance of the product and oxidation resistance of the raw material powder, and increasing Is, but if it is less than 0.5 at%, the effect of increasing the Curie point and improving the weather resistance is small, 13 at. %, Co is condensed in the grain boundary in a high concentration, and the ferromagnetic R (Nd-Dy) -Co containing 30 at% or more of Co is contained.
The compound precipitates and easily reverses the magnetization of the present system magnet to lower iHc, so the content is set at 0.5 at% to 13 at%. The preferable range of Co is 1 at% to 10 at%.

Al is effective in increasing iHc and improving weather resistance, and in particular, has an effect of improving iHc that decreases with an increase in the amount of Co added, but if it is less than 0.5 at%, iHc increases and weather resistance improves. Is less effective, and when it exceeds 4 at%, it is effective in improving iHc, but since Br and (BH) max decrease sharply, it is limited to 0.5 at% to 4 at%. The preferred content of Al is 0.
It is 5 at% to 2 at%.

Ti or Nb has an effect of compensating for the decrease of Br and (BH) max due to the addition of Al, but when Ti or Nb is less than 0.1 at%,
If the content exceeds 1.0 at%, it will combine with B in the magnet alloy to form Ti or Nb borides, which will reduce the B required for the magnet alloy and reduce iHc. at
% To 1.0 at%.

A more preferable range is 0.2 at% to 0.7 at%.

C has a great influence on the corrosion resistance of the permanent magnet, and when the content exceeds 1000 ppm, the corrosion resistance sharply decreases and a practical permanent magnet cannot be obtained. Therefore, the content of 1000 ppm or less is desirable, and preferably 800 ppm or less. Yes, more preferably 500 ppm
The contents are as follows.

In the rare earth permanent magnet alloy according to the present invention, the balance after containing the elements is Fe and inevitable impurities, and the impurities are Si, P, which are inevitably mixed in industrial production,
S, Cu, Mn, Ni, etc. are allowed.

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

In this invention, Nd12at% ~ 14at%, Dy0.2at% ~ 2.0at%, and the total amount of Nd and Dy is 12.5at% ~ 15at%, B5at% ~
Permanent magnets containing 8at%, Co1at% -10at%, Al0.5at% -2at%, C500ppm or less, the balance Fe and unavoidable impurities, and the main phase of which has a tetragonal structure are (BH) max30M when applying a magnetic field in the perpendicular direction
It has excellent magnet characteristics of GOe or higher and iHc13kOe or higher, and has extremely high corrosion resistance.

Further, the permanent magnet material according to the present invention has a crystal grain size of 1
Compound having a tetragonal crystal structure in the range of μm to 100 μm R ₂ (Fe · Co) ₁₄ B type as a main phase, R-rich phase containing Co without Al and R containing Al and Co The amount of Co contained in the R-rich phase of the multilayer composed of the rich phase is 5 to 30 at%, Al
When the grain boundary phase structure contains less than 5 at%, the corrosion resistance is the best.

The present invention contains a specific amount of Nd, Dy and a total amount of Nd, Dy and a specific amount of B, Co, Al, and C, and has extremely excellent corrosion resistance together with high magnet characteristics.

Examples Example 1 As starting materials, electrolytic iron having a purity of 99.9%, ferroboron alloy, and Nd, Dy, Co, Al, Ti, and Nb having a purity of 99.7% or more were used, and after mixing these, high-frequency melting was performed, followed by water-cooled copper. It was cast in a mold to obtain ingots having various compositions shown in Table 1.

Then, this ingot was roughly pulverized with a stamp mill and then finely pulverized with a ball mill to obtain finely pulverized powder having an average particle size of 3 μm.

This finely pulverized powder was charged into a die of a press machine, oriented in a magnetic field of 12 kOe, and molded in a direction perpendicular to the magnetic field at a pressure of 1.5 t / cm ² to obtain a molded body at 1060 ° C. ~ 1120 ℃, 2 hours, A
Sintered under the conditions of r, and allowed to cool, then A
In a r atmosphere, a two-stage aging treatment was performed at 800 ° C for 1 hour and then at 580 ° C for 2 hours to obtain a permanent magnet.

20 mm outer diameter × 10 mm inner diameter × 8 mm thickness from the obtained permanent magnet
A test piece was cut into a size.

As cationic electrodeposition paint, epoxy-based Svia CED,
Using S-20 (manufactured by Shinto Paint Co., Ltd.), the test piece previously degreased and dried with trichlene was used as the cathode, and the SUS316 material plate was used as the anode. Electrodeposition was performed at a temperature of 28 ° C, a voltage of 150V for 3 minutes. It was painted.

Then, after washing with water and air-drying, it was kept at 180 ° C. for 30 minutes to prepare a permanent magnet body sample piece according to the present invention having a resin layer coated on the surface of 20 to 24 μm. The test piece was subjected to a corrosion resistance test and a resin layer adhesion strength test after the corrosion resistance test.

The magnetic properties before and after the corrosion resistance test were measured, and the corrosion resistance test results and the magnetic property measurement results are shown in Table 2.

For comparison, a test piece prepared from a comparative Fe-BR type permanent magnet whose composition is shown in Table 1 was subjected to electrodeposition coating under the same conditions as above to perform a corrosion resistance test.

Corrosion resistance test conditions are 60 ° C and 90% relative humidity.
For 1000 hours, the adhesion strength test was performed by pulling the squares at intervals of 1 mm with an adhesive tape to evaluate the peeling state of the resin layer based on the number of non-peeling cells / total number of cells. It is shown in Table 2.

As is clear from Table 2, the permanent magnet material according to the present invention has remarkably excellent corrosion resistance that cannot be imagined from the conventional Fe-BR based permanent magnet material.

Claims (3)

[Claims] 1. Nd11 at% to 15 at%, Dy0.2 at% to 3.0 at%,
And the total amount of Nd and Dy is 12at% to 17at%, and B5at% to 8a.
t%, Co0.5at% ~ 13at%, Al0.5at% ~ 4at%, C1000ppm
A rare earth magnet excellent in corrosion resistance, comprising the following: a balance of Fe and unavoidable impurities, and a main phase having a tetragonal crystal structure, and a corrosion resistant resin layer formed by electrodeposition coating on the surface of the magnet. 2. Nd11 at% to 15 at%, Dy0.2 at% to 3.0 at%,
And the total amount of Nd and Dy is 12at% to 17at%, and B5at% to 8a.
t%, Co0.5at% ~ 13at%, Al0.5at% ~ 4at%, C1000ppm
Below, one kind of Ti or Nb containing 0.1at% ~ 1.0at%,
A rare earth magnet having excellent corrosion resistance, characterized in that it has a corrosion resistant resin layer formed by electrodeposition coating on the surface of a magnet body composed of the balance Fe and unavoidable impurities and having a tetragonal structure as a main phase. 3. Nd11 at% to 15 at%, Dy0.2 at% to 3.0 at%,
And the total amount of Nd and Dy is 12at% to 17at%, and B5at% to 8a.
t%, Co0.5at% ~ 13at%, Al0.5at% ~ 4at%, C1000ppm
A magnet body containing the following, which consists of the balance Fe and unavoidable impurities, and whose main phase has a tetragonal crystal structure, is immersed in a water-based paint, and the permanent magnet body is used as an anode or a cathode, and the permanent magnet body and the counter electrode are A method for producing a rare earth magnet having excellent corrosion resistance, characterized in that a direct current is supplied to the magnet and the entire magnet body is electrically coated to form a corrosion resistant resin layer on the surface.