JPH0680609B2 - Method for manufacturing permanent magnet having excellent oxidation resistance - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a Fe—BR permanent magnet having excellent acid resistance, and particularly to a chemical conversion treatment for improving the oxidation resistance of a Fe—BR permanent magnet. The present invention relates to a method for producing a Fe-BR permanent magnet having a pretreatment for a chemical conversion treatment that can be made relatively easy and can significantly improve oxidation resistance.

BACKGROUND ART The applicant has previously proposed a Fe-BR-based (R is at least one of rare earth elements including Y) permanent magnet as a new high-performance permanent magnet that does not contain expensive Sm or Co (Japanese Patent Application No. Sho. 57-1
No. 45072).

This permanent magnet is an excellent permanent magnet that uses Nd or Pr as a resource rich abundant light rare earth as R, and has an extremely high energy product of 25 MGOe or more with Fe as a main component.

However, Fe-BR having the above-mentioned excellent magnetic properties
The main component of the permanent magnet is a magnetic anisotropy sintered body.
Since it contains rare earth elements, especially Nd and iron, which easily oxidize in air and gradually produce stable oxides, the output of the magnetic circuit decreases due to the oxides formed on the magnet surface when incorporated into the magnetic circuit. And causes variations between magnetic circuits, and
There was a problem of contamination of peripheral devices due to the dropping of surface oxides.

Therefore, in order to improve the corrosion resistance of the Fe-BR permanent magnet, the applicant has previously performed a chemical conversion treatment on the surface of the magnet body, and a permanent magnet coated with a phosphate coating or a chromate coating, and the above-mentioned chemical conversion coating. A permanent magnet coated with an oxidation-resistant resin layer by a spray method, a dipping method, or an electrodeposition coating method on the coating film (JP-A-60-6).
3903, JP-A-60-63902, JP-A-60-63901).

However, since the permanent magnet coated with the chemical conversion coating does not sufficiently improve the corrosion resistance, when an oxidation resistant resin layer is formed on the surface of the chemical conversion coating, the adhesion with the resin layer is improved, but No improvement in corrosion resistance was obtained.

OBJECT OF THE INVENTION The present invention aims to improve the corrosion resistance of the chemical conversion coating provided on the Fe-BR sintered magnet body, facilitates the chemical conversion coating treatment industrially, and can significantly improve the oxidation resistance of Fe-BR. It aims at a method of manufacturing a permanent magnet.

Structure and effect of the present invention, the present invention is to improve the chemical conversion treatment method of phosphate or chromate applied to the Fe-BR system sintered magnet, in order to improve the improvement of the oxidation resistance, the chemical conversion treatment and its pretreatment, As a result of various studies, the following findings were obtained and the present invention was completed.

It was found that the oxidation resistance of the chemical conversion coating is remarkably improved by pre-treating the surface of the Fe-BR sintered magnet body by the oxalic acid treatment.

It is considered that this effect is due to the passivation of easily oxidizable R in the sintered magnet body, especially Nd by oxalic acid. However, the passivation treatment of Nd with an oxalic acid solution requires a long time and is not industrial, and as a result of further studies, the Fe-BR sintered magnet was It was found that Nd in the magnet body is passivated in a short time and the oxidation resistance is remarkably improved by treating with a phosphoric acid solution or an organic acid such as formic acid or tartaric acid.

That is, the present invention provides R (R is at least one of Nd, Pr, Dy, Ho, and Tb, or further La, Ce, Sm, Gd,
(At least one of Er, Eu, Tm, Yb, Lu, Y) 10 atom% to 30 atom%, B2 atom% to 28 atom%, Fe65 atom to 80 atom% as main components, and the main phase is square A method for producing a permanent magnet having excellent oxidation resistance, which comprises subjecting a surface of a sintered magnet body composed of a crystal phase to passivation treatment of R in the magnet body, and then performing a chemical conversion treatment.

More specifically, the present invention will be described in detail. A sintered magnet body having the above composition and crystal phase is treated with a phosphoric acid solution or an organic acid solution for a short time by a spray method, a dipping method, or the above treatment method, and then an oxalic acid solution. In the same manner as above, after treatment by a spray method, a dipping method, or a steam treatment method to promote the passivation of the easily oxidizable component R, particularly Nd, in the Fe-BR sintered magnet body,
A chemical conversion treatment is performed, and in order to further improve oxidation resistance, a resin film or a metal plating film is formed in a subsequent step by an electrodeposition coating method, a spray method, a dipping method, or the like. It is a thing.

Preferred Embodiments of the Invention In the present invention, as a treatment method with a phosphoric acid, formic acid, or oxalic acid solution in the first step of the passivation treatment of R in the sintered magnet body, particularly Nd, a dipping method, a spray method, a steam treatment is used. However, the immersion method is preferable from the viewpoints of work efficiency and quality stabilization. As the immersion conditions, the solution concentration is 100 wt% to 10 wt%, the solution temperature is 5 ° C to 25 ° C, and the immersion time is 30 seconds or less. preferable.

In addition, as the treatment method with the oxalic acid solution in the second stage,
Although there are dipping method, spraying method, steam treatment method, etc., the dipping method is preferable in terms of work efficiency and quality stabilization. As dipping conditions, the solution concentration is oxalic acid saturated solution, solution temperature 20 ° C to 120 ° C.
C., especially 60.degree. C. to 80.degree. C., is preferred, and the immersion time is preferably within 1 hour, particularly 1 minute to 15 minutes.

The chemical conversion treatment film according to the present invention is preferably a phosphate film such as zinc phosphate and manganese phosphate, and the chemical conversion film thickness is 10 μm or less in terms of oxidation resistance, strength and cost in the case of a phosphate film. 5μ for acid salt coating
m or less is preferable.

Further, in order to improve the corrosion resistance, on the chemical conversion treatment film, by dipping method, spray method, electrodeposition coating method, by applying an oxidation resistant resin, or by electroless plating or electrolytic plating method, Ni , Cu, Zn or other oxidation resistant metal or alloy plating, or a composite plating layer of these may be deposited.

In the present invention, the resin to be deposited on the chemical conversion coating by the dipping method or the spray method is preferably an epoxy resin, a urethane resin, a fluorine resin, a furan resin, a polysiloxane resin, or the like, and a resin to be deposited by the electrodeposition coating method. as,
Epoxy resin and acrylic resin are preferred.

Reasons for Limiting Components of Permanent Magnet The rare earth element R used in the permanent magnet material of the present invention occupies 8 atom% to 30 atom% of the composition, but Nd, Pr, Dy, Ho, Tb
At least one of the above, or further, La, Ce, Sm,
Those containing at least one of Gd, Er, Eu, Tm, Yb, Lu and Y are preferable.

Also, one type of R is usually sufficient, but it is practically 2
A mixture of one or more kinds (Misch metal, didymium, etc.) can be used for any reason such as availability.

It should be noted that this R does not have to be a pure rare earth element, and may contain an impurity that is unavoidable in manufacturing within the industrially available range.

R is an essential element in the above-mentioned permanent magnet,
If it is less than 30% by atom, the crystal structure will be a cubic structure having the same structure as q-iron, so that high magnetic properties, especially high coercive force, cannot be obtained. However, the residual magnetic flux density (Br) decreases, and a permanent magnet with excellent characteristics cannot be obtained. Therefore, the rare earth element is 10 atomic%
The range is up to 30 atom%.

B is an essential element in the permanent magnet according to the present invention. If it is less than 2 atomic%, the rhombohedral structure becomes the main phase and a high coercive force (iHc) cannot be obtained.
An excellent permanent magnet cannot be obtained because the rich nonmagnetic phase increases and the residual magnetic flux density (Br) decreases. Therefore,
B is in the range of 2 atomic% to 28 atomic%.

Fe is an essential element in the above-mentioned permanent magnet, and the residual magnetic flux density (Br) decreases if it is less than 6 atomic%, and a high coercive force cannot be obtained if it exceeds 80 atomic%.
The content is up to 80 atom%.

Further, in the permanent magnet of the present invention, substituting a part of Fe with Co can improve the temperature characteristics without impairing the magnetic characteristics of the obtained magnet. Co substitution amount is
If it exceeds 20% of Fe, the magnetic properties are deteriorated, which is not preferable. The substitution amount of Co is 5 atom% in the total amount of Fe and Co.
In the case of 15 atom%, (Br) is increased as compared with the case of not substituting, so that it is preferable to obtain a high magnetic flux density.

Further, the permanent magnet material of the present invention can tolerate the presence of impurities unavoidable in industrial production in addition to R, B and Fe, but part of B is 4.0 atomic% or less of C and 3.5 atomic% or less of P. , 2.5 atom%
At least one of the following S and Cu of 3.5 atomic% or less,
By substituting the total amount by 4.0 atom% or less, it is possible to improve the manufacturability of the permanent magnet and reduce the cost.

In addition, at least one of the following additional elements is added to the RB-Fe based permanent magnet because it is effective in improving the coercive force and squareness of the demagnetization curve, improving the manufacturability, and lowering the cost. be able to.

9.5 atomic% or less Al, 4.5 atomic% or less Ti, 9.5 atomic% or less V, 8.5 atomic% or less Cr, 8.0 atomic% or less Mn, 5.0 atomic% or less Bi, 9.5 atomic% or less Nb, 9.5 Ta less than atomic%, Mo less than 9.5 atomic%, W less than 9.5 atomic%, Sb less than 2.5 atomic%, Ge less than 7 atomic%, Sn less than 3.5 atomic%, Zr less than 5.5 atomic%, 9.0 atomic % Or less Ni, 9.0 atom% or less Si, 1.1 atom% or less Zn, and 5.5 atom% or less Hf at least one kind is added, but when two or more kinds are contained, the maximum content is By containing at most atomic% of the additive element having the maximum value,
It is possible to increase the coercive force of the permanent magnet.

The fact that the main phase of the crystal phase is a tetragonal crystal is indispensable for producing a sintered permanent magnet having excellent magnetic properties from a fine and uniform alloy powder.

The permanent magnet of the present invention has an average crystal grain size of 1 to 80 μm.
The compound having a tetragonal crystal structure in the range of 1) as the main phase and containing 1% to 50% by volume of the nonmagnetic phase (excluding the oxide phase) is characterized.

The permanent magnet according to the present invention exhibits a coercive force iHc ≧ 1 kOe and a residual magnetic flux density Br> 4 kG, and has a maximum energy product (BH) max.
Indicates (BH) max ≧ 10MGOe, and the maximum value reaches 25MGOe or more.

Further, the main component of R of the permanent magnet according to the present invention is 50
% Of light rare earth metal mainly composed of Nd and Pr, R12 atom% to 20 atom%, B4 atom% to 24 atom%, Fe74
(BH) max35M when the main component is from atomic% to 80 atomic%
It shows excellent magnetic properties over GOe, and its maximum value reaches over 45MGOe especially when the light rare earth metal is Nd.

Further, in this invention, in a corrosion resistance test of leaving it in an environment of 60 ° C and a relative temperature of 90% for a long time, as a permanent magnet showing extremely high corrosion resistance, Nd11at% ~ 15at%, Dy0.2at% coarse 3.0at%, and Nd and The total amount of Dy is 12at% to 17at%, B5at% to 8at%, Co0.5at
% To 13 at%, Al 0.5 at% to 4 at%, C 1000 ppm or less, and the balance Fe and inevitable impurities are preferable.

Examples Example 1 As a starting material, electrolytic iron having a purity of 99.9%, a ferroboron alloy containing B19.4% and the balance being Fe and impurities such as Al, Si, and C, Nd, Dy, Co having a purity of 99.7% or more. , Using Al,
These were high-frequency melted and then cast in a water-cooled copper mold.

Then, the ingot was roughly crushed and then finely crushed to obtain a fine powder having an average particle size of 3 μm.

Insert this fine powder into the mold, orient in a magnetic field of 10KOe,
It was molded at a pressure of 1.5 t / cm ² .

The obtained molded body is sintered at 1100 ° C. for 1 hour in Ar, then allowed to cool, and then subjected to aging treatment at 580 ° C. for 2 hours in Ar to produce a permanent magnet according to the present invention. did.

The component composition at this time is 14Nd-7.5B-6Co-2Al-2.0Dy.
-Fe balance.

A test piece having a size of 4 mm × 8 mm × 10 mm was cut out from the obtained permanent magnet, and after degreasing the test piece, a phosphoric acid solution treatment, an oxalic acid solution treatment, and a phosphate treatment were performed under the following conditions.

Then, an oxidation resistance test, a salt spray test, and measurement of magnet characteristics of each sample were performed. The results are shown in Table 1.

Phosphoric acid solution treatment condition Concentration 10% Solution temperature 10 ° C Immersion time 10 seconds Oxalic acid solution treatment condition Concentration / supersaturated oxalic acid solution Solution temperature 80 ° C Immersion time 5 minutes Phosphate treatment condition Zinc 12g / l Phosphate root 100g / l Melt temperature 60 C. Holding time 3 minutes The oxidation resistance test was evaluated by the time until rusting and the rusting condition when the above test piece was left in an atmosphere at a temperature of 80 ° C. and a humidity of 90%.

Further, the salt spray test was evaluated by the rusting condition generated by immersion in a 5% NaCl solution at a liquid temperature of 35 ° C.

For comparison, a test piece having the same composition as that of the example of the present invention was subjected to the chemical conversion treatment without subjecting it to passivation treatment with a phosphoric acid solution and an oxalic acid solution. A rusting condition and a magnetic property were measured by conducting a salt spray test under the same conditions as above in an atmosphere of 80 ° C. and a humidity of 90%. The results are shown in Table 1.

Example 2 A test piece obtained under the same composition and under the same manufacturing conditions as in Example 1 was treated with phosphoric acid solution, oxalic acid solution and zinc phosphate under the same conditions as in Example 1.

Furthermore, as a cationic electrodeposition paint, epoxy-based PTU-50
(Manufactured by Nippon Paint) at a temperature of 26 ° C and a voltage of 210V,
After forming a resin thickness of 25 μm to 35 μm, as a baking condition
A test piece obtained by curing at 180 ° C. for 30 minutes was prepared as in Example 1.
Similarly, the oxidation resistance test, the salt spray test, and the measurement of the magnet characteristics were performed. The results are shown in Table 2.

For comparison, the same test pieces as above were subjected to a chemical conversion treatment under the same conditions as above directly without performing passivation treatment with a phosphoric acid solution or an oxalic acid solution, and a test piece obtained by electrodeposition coating. An oxidation resistance test, a salt spray test, and measurement of magnet characteristics were performed, and the results are shown in Table 2.

Example 3 The test piece obtained under the same composition and the same manufacturing conditions as in Example 1 was subjected to the same phosphoric acid solution treatment, oxalic acid treatment and zinc phosphate treatment as in Example 1.

Then, the test piece is dipped in polysiloxane resin MS-1700 (made by Silicone Co., Ltd.), dried at room temperature for 3 hours, and then baked at 150 ° C. for 15 minutes to deposit the resin on the surface. The prepared test piece was prepared, and the oxidation resistance test, the salt spray test and the magnet characteristics were measured in the same manner as in Example 1. The results are shown in Table 3.

For comparison, the test pieces obtained under the same composition and the same production conditions as above were directly subjected to the same chemical conversion treatment and resin dipping method as described above without the passivation treatment of the phosphoric acid solution treatment and the oxalic acid solution treatment. For the test piece whose surface is coated with resin,
The magnet characteristics, the oxidation resistance test, and the salt spray test were measured in the same manner as described above. The results are shown in Table 3.

Claims (1)

[Claims] 1. R (R is at least one of Nd, Pr, Dy, Ho and Tb, or further La, Ce, Sm, Gd, Er, Eu, T
m, Yb, Lu, and Y) consisting of at least 1) 10 atom% to 30 atom%, B2 atom% to 28 atom%, Fe65 atom% to 80 atom% as main components, and main phase from tetragonal phase A method for producing a permanent magnet having excellent oxidation resistance, comprising the step of passivating R in the magnet body and then chemical conversion treatment on the surface of the sintered magnet body.