JPH069168B2 - High corrosion resistance rare earth permanent magnet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a highly corrosion-resistant rare earth permanent magnet, and particularly to a rare earth / iron / iron alloy having a uniform corrosion-resistant alloy layer on the surface of a sintered magnet body.
The purpose is to provide a boron-based permanent magnet.

(Prior Art) Rare earth permanent magnets are widely used in the fields of electric and electronic devices due to their excellent magnetic properties and economic efficiency, and in recent years, higher performance has been demanded. Of these, Nd-based rare earth permanent magnets are cheaper in raw material cost because Nd, which is a main element, is more abundant than Sm and does not use a large amount of Co, as compared with conventional Sm-based rare earth permanent magnets. Since it is an extremely excellent permanent magnet material whose characteristics far surpass those of Sm-based rare earth permanent magnets, it not only replaces the small magnetic circuit in which Sm-based rare earth magnets have been used in the past, but also hard ferrite in terms of cost. Or it is about to be widely applied to the fields where electromagnets were used. However, this material has the disadvantage that it easily oxidizes in humid air in a very short time. This oxidation not only produces oxides on the surface of the magnet, but also progresses from the surface along the grain boundaries along the crystal grain boundaries, causing the phenomenon of so-called grain boundary corrosion. This is because there is an active Nd-rich phase. Corrosion of grain boundaries causes extremely large deterioration of magnetic properties, and if corrosion progresses during practical use, the performance of the device incorporating the magnet is deteriorated and the surroundings of the device are contaminated.

Various surface treatment methods have been proposed in order to overcome such drawbacks of Nd magnets, but none of them is perfect as a corrosion-resistant surface treatment. For example, in a resin coating film formed by spraying or electrodeposition coating, rust occurs due to the hygroscopicity of the resin, and vapor deposition methods such as vacuum deposition, ion sputtering, and ion plating are too costly, and the inner hole, There are disadvantages such as not being able to coat the groove.

(Structure of the Invention) As a result of intensive studies to eliminate the disadvantages and drawbacks of the related art, the present inventors have found that the magnetic characteristics are not deteriorated for a long time.
We have succeeded in obtaining a permanent magnet that can maintain the aesthetic appearance and have reached the present invention. That is, in the present invention, R (R is at least one of rare earth elements including Y) 5 to 40 wt%, Fe5
0 to 90% by weight, B 0.2 to 8% by weight and additional element M
(M is Ni, Nb, Al, Ti, Zr, Cr, V, M
n, Mo, Si, Sn, Cu and Zn (at least one selected from Zn) 8% by weight or less
The gist is a highly corrosion-resistant rare earth permanent magnet having an i-P alloy layer.

This will be described in detail below. In the present invention, R
Is Y or La, Ce, Pr as a rare earth element,
Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, L
u, Yb, etc. are exemplified, but among them, Ce, L
It preferably contains at least one of a, Nd, Pr, Dy and Tb.

In the present invention, R5 to 40% by weight, Fe50 to 90% by weight, B
0.2 to 8% by weight and additional element M (M is Ni, Nd, A
l, Ti, Zr, Cr, V, Mn, Mo, Si, Sn,
At least one kind of Cu and Zn) 8% by weight or less is used, and an Nd-based rare earth sintered magnet body containing industrially unavoidable trace impurities such as C, O, P, and S is used. An Ni-P alloy layer is provided on this surface. In this case, an electroplating method or an electroless plating method may be used, and a preferable method is an electroless plating method on the surface of the sintered magnet body.
It is preferable to deposit an i-P alloy layer.

As the electroless electrolytic solution used in this case, nickel chloride, nickel sulfate as a metal salt, containing at least one kind of nickel hypophosphite 100 g / or less, sodium hypophosphite as a reducing agent 100 g / or less, As a pH adjuster, at least one selected from basic compounds such as sodium hydroxide and ammonium hydroxide, inorganic acids and organic salts is used.
Those containing 0 g / g or less are preferable. In this electrolytic solution, 150 g or less of at least one of an oxycarboxylic acid such as sodium citrate and sodium acetate, an inorganic acid or organic salt such as boric acid and carbonic acid, or a sodium salt of an inorganic acid is used as a complexing agent as a buffering agent. As sodium citrate, sodium acetate, ammonium hydroxide, ethylene glycol, as well as organic acids (acetic acid, glycolic acid, citric acid,
Alkali salt of tartaric acid, etc., thioglycolic acid, ammonia, triethanolamine, ethylenediamine, glycine, pyridine, 100 g / at least one accelerator, and as a stabilizer, 10 g / s or less of sulfide, chloride,
Fluoride and surfactant can be contained respectively,
This aqueous solution is used in the pH range of 3 to 13, and the bath temperature for plating is in the range of 20 to 100 ° C.

The method of immersing the magnet body in the plating solution may be either a barrel method or a hooking jig method, and is appropriately selected depending on the size and shape of the sintered magnet body.

The corrosion-resistant alloy layer formed on the surface of the sintered magnet body according to the present invention contains Ni and P as main components, and an amorphous phase in which P is supersaturated in Ni to form a solid solution, or nickel and Ni ₃ P and the like are phosphized. It is composed of a fine mixed phase with a nickel phase, and the proportion of P in this layer is preferably 1 to 14% by weight.

If there are many pinholes in the electroless plating film containing only Ni,
Alternatively, it cannot be used because of poor adhesion to the substrate and poor corrosion resistance. Further, the Ni-B or Ni-N alloy coating also has insufficient pinholes and poor adhesion, so that sufficient corrosion resistance cannot be obtained.

The thickness of the alloy layer is 1 to 30 μm, preferably 5 to 20 μm
m is appropriate, and if it is 30 μm or more, it is not practical because the time required for plating and the amount of chemicals are large and it is too expensive. Also, if the alloy layer is uniform, it can be practically used even at about 1 μm.

By subjecting the alloy layer according to the present invention to heat treatment after plating, it is possible to improve corrosion resistance, adhesion and wear resistance.
The temperature range is 100 to 500 ° C., and the time is 10 minutes to several hours.

Next, the reasons for limiting the constituent components of the permanent magnet containing R-Fe-B as an essential element according to the present invention will be described. When the amount of R contained as the main component in the permanent magnet used in the present invention is 5% by weight or less, a high coercive force cannot be obtained because the amount of α iron precipitated is too large. The amount of non-magnetic phase contained is too much, the residual magnetic flux density is lowered, and the magnet characteristics cannot be obtained. Therefore, the amount of R as the main component is 5 to 40% by weight.

If B is 0.2% by weight or less, coercive force cannot be obtained, and if it is 8% by weight or more, the nonmagnetic phase containing B is too much and the residual magnetic flux density is lowered, so that magnet characteristics cannot be obtained. The amount of B is
It is 0.2 to 8% by weight.

When Fe is 50% by weight or less, the residual magnetic flux density is low and the magnetic properties cannot be obtained, and when it is 90% by weight or more, the amount of α iron deposited is too large to obtain a high coercive force. Therefore, the amount of Fe is 50-9
It is to be 0% by weight.

The additional element M capable of substituting the essential element can be added to improve the magnetic characteristics or reduce the cost. The amount of the additional element M can be used alone or in two types because it improves the temperature change of the magnetic characteristics. The total of the above is 8% by weight or less. However, any of these elements should be avoided because if added in excess of the above amounts, the magnetic properties will deteriorate.

The permanent magnet of the present invention is a sintered anisotropic permanent magnet obtained by anisotroping crystalline alloy powder in a magnetic field press and then sintering, and its magnetic property has a maximum energy product of 20 MGOe or more and 50 MGOe or more. Up to 20 MGOe or less, the characteristics are poor, and it is not suitable for surface treatment.

Next, examples according to the present invention will be described.

Example 1 32 Nd-1 by weight ratio by high frequency melting in an Ar atmosphere.
An ingot having a composition of 2B-66.8Fe was prepared.

This ingot was roughly crushed with a jaw crusher and further finely crushed with a jet mill using N ₂ gas to obtain fine powder having an average particle size of 3.5 μm.

Next, this fine powder was filled in a mold to which a magnetic field of 10,000 Oe was applied, and molded at a pressure of 0.8 / cm ² . Then, it was sintered in vacuum at 1100 ° C. for 2 hours and further subjected to aging treatment at 550 ° C. for 1 hour to obtain a permanent magnet. From the obtained permanent magnet, a cylindrical test piece having an outer diameter of 30 mm, an inner diameter of 10 mm and a height of 2 mm was cut out. The anisotropic direction is the height direction.

After washing this test piece with trichlorethylene, NaO
The sample was immersed in an aqueous solution of H 50 g / 40 ° C. for 15 minutes for alkaline degreasing, followed by washing with water, followed by pickling for 45 seconds in a mixed acid of sulfuric acid 50 ml / and hydrofluoric acid 25 ml /, and then washing with water. This was placed in an aqueous solution containing nickel sulfate 21 g /, sodium hypophosphite 25 g /, sodium citrate 20 g /, and lead sulfide 0.1 g / at 90 ° C. for 3 minutes and 12 minutes,
It was immersed for 25 minutes and 40 minutes to coat the Ni-P alloy layer with a thickness of 1, 5, 10, and 15 μm, respectively. After plating,
It was washed with water and heat-treated at 150 ° C. for 30 minutes.

After each test piece was kept in a test tank at 60 ° C. and 95% humidity for 600 hours, the appearance was observed and the corrosion resistance was evaluated. The magnetic properties before and after the corrosion resistance test were also measured.

For comparison with the examples, the same corrosion resistance test was performed on the test piece A of the same size which was not subjected to the surface treatment after cutting and the test piece B of the same size in which Ni was electrolessly deposited. The results are shown in Table 1.

Example 2 By high frequency melting in an Ar atmosphere, the weight ratio is 33 Nd-1.
An ingot having a composition of 0B-65Fe-0.5Al-0.5Nb was prepared.

The ingot was roughly crushed with a jaw crusher and further finely crushed with a jet mill using N ₂ gas to obtain fine powder having an average particle diameter of 3 μm.

Next, this fine powder was filled in a mold to which a magnetic field of 10,000 Oe was applied, and molded at a pressure of 1.2 t / cm ² . Then, it was sintered in vacuum at 1100 ° C. for 2 hours and further subjected to aging treatment at 550 ° C. for 1 hour to obtain a permanent magnet. A cylindrical test piece having an outer diameter of 30 mm, an inner diameter of 6 mm and a height of 15 mm was cut out from the obtained permanent magnet. The anisotropic direction is the height direction.

After washing the test pieces 5, 6, 7 and 8 with trichlorethylene, 1 g of an aqueous solution of NaOH 50 g / 40 ° C. was used.
Immerse for 5 minutes, degrease with alkali, then wash with water, 50 ml of sulfuric acid
It was pickled for 30 seconds in a mixed acid of / and hydrofluoric acid 25 ml /, and then washed with water. 25g / of nickel sulfate
Sodium hypophosphite 23 g /, lactic acid 10 g /, sodium citrate 10 g /, propionic acid 3 g /,
3 minutes at 90 ℃ in an aqueous solution containing 0.1 g of lead chloride, 12
It was immersed for 25 minutes, 40 minutes, and 25 minutes to coat the Ni—P alloy layer with a thickness of 1, 5, 10, and 15 μm, respectively. After plating, the plate was washed with water and heat-treated at 150 ° C. for 30 minutes.

After each test piece was kept in a test tank at 60 ° C. and 95% humidity for 600 hours, the appearance was observed and the corrosion resistance was evaluated. The magnetic properties before and after the corrosion resistance test were also measured.

For comparison with the example, the same corrosion resistance test was performed on a test piece C of the same size that was not subjected to surface treatment after cutting and a test piece D of the same size in which Ni was electrolessly deposited. The results are shown in Table 2.

Example 3 20 Nd-5 by weight ratio by high frequency melting in Ar atmosphere.
Pr-3Ce-3La-2Tb-64Fe-0.5Ti-
An ingot having a composition of 0.5Cu-0.5Zn was prepared.

This ingot was coarsely crushed with a jaw crusher, and was further pulverized with a jet sill by N ₂ gas to obtain fine pulverization having an average particle diameter of 3.3 μm.

Next, the fine powder was filled in a mold to which a magnetic field of 10,000 Oe was applied, and molded at a pressure of 1.2 t / cm ² . Among them, it was sintered in vacuum at 1090 ° C. for 2 hours and further subjected to aging treatment at 550 ° C. for 1 hour to obtain a permanent magnet.

A test piece with an outer diameter of 30φ × inner diameter of 10φ × 1.0 mmt was cut out from the obtained magnet. The anisotropic direction is 1 mmt.

The test pieces 9, 10 and 11 were washed with trichloroethylene at 20 g / sodium and then immersed in a mixed alkaline aqueous solution containing 20 g / sodium hydroxide, 20 g / sodium carbonate and 50 g / sodium orthosilicate for 15 minutes for alkali degreasing. After washing with water, oxalic acid 20ml /
The mixture was pickled for 30 seconds in a mixed acid of hydrogen peroxide 10 ml / and sulfuric acid 10 ml /, and then washed with water. 12g in an aqueous solution containing nickel sulfate 25g /, sodium hypophosphite 20g /, sodium citrate 60g /, ammonium chloride 20g /, boric acid 35g / at 90 ° C.
Min, 25 min, 40 min, dip the Ni-P alloy layer to 5
Coated to a thickness of μm, 10 μm, 15 μm. After plating, the plate was washed with water and heat-treated at 150 ° C. for 30 minutes.

These test pieces were placed in a test tank at 60 ° C and 95% humidity at 60%.
After holding for 0 hour, the corrosion resistance was evaluated by observing the appearance.

The magnetic properties before and after the corrosion resistance test were measured. For comparison with the examples, the same corrosion resistance test was performed on a test piece E of the same size that was not subjected to surface treatment after cutting and a test piece F of the same size on which Ni—N was electrolessly deposited. The results are shown in Table 3.

Claims (1)

[Claims] 1. R (R is at least one of rare earth elements including Y) 5 to 40% by weight, Fe 50 to 90% by weight, B0.2
~ 8 wt% and additional element M (M is Ni, Nb, Al,
Ti, Zr, Cr, V, Mn, Mo, Si, Sn, Cu
And at least one selected from Zn) 8 wt% or less and a highly corrosion-resistant rare earth permanent magnet having a Ni-P alloy layer on the surface of the sintered magnet body.