JPH0613211A - Permanent magnet having excellent corrosion resistance and manufacture thereof - Google Patents

Abstract

PURPOSE:To prevent the deterioration in the ceramic characteristics due to cutting or polishing step thereby enabling the permanent magnet having excellent corrosion resistance to be manufactured by a method wherein an A(chromate processed film is formed on the surface of a sintered permanent magnet body mainly comprising Fe-B-R base with principal phase comprising tetragonal phase. CONSTITUTION:The permanent magnet is mainly composed of 10-30 atomic % of R (R(rare earth element) at least one kind out of Nd, Pr, Dy, Ho, Tb furthermore at least one kind out of La, Ce, Sm, Gd, Er, Eu, Tm, Yb, Lu, Y, 2-28 atomic % of B, 65-80 atomic % of Fe. Next, the surface of sintered permanent magnet body with the principal phase thereof comprising tetragonal phase is coated with Al thin film to be chromate-processed later. Through these procedures, an Fe-B-R base permanent magnet with the surface thereof stably coated with Al chromate film having excellent corrosion resistance capable of preventing the deterioration in the magnetic characteristics due to polishing step and oxide layer can be manufactured at low cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to F which is excellent in corrosion resistance.
According to the e-B-R permanent magnet and the manufacturing method thereof, by providing a chromate treatment film of Al on the ground surface of the sintered permanent magnet, the deterioration of the magnet characteristics due to the grinding processing is prevented, Further, the present invention relates to a Fe—B—R permanent magnet having excellent corrosion resistance in which the adhesion of the corrosion resistant coating on the magnet surface is improved, and a method for producing the same.

[0002]

2. Description of the Prior Art Typical representative permanent magnet materials at present are alnico, hard ferrite and rare earth cobalt magnets. Since this rare earth cobalt magnet has remarkably excellent magnetic characteristics, it is used for various purposes. However, Sm and Co as main components are both resource-deficient and expensive, and stable for a long term in the future. Then, it is difficult to supply a large amount. Therefore, there has been a strong demand for a permanent magnet that is excellent in magnetic properties, inexpensive, rich in resources, and composed of composition elements that can be stably supplied in the future.

The applicant of the present invention has previously proposed the Fe--BR system (R) as a new high-performance permanent magnet containing no expensive Sm or Co.
Proposed a permanent magnet containing at least one of rare earth elements including Y (Japanese Patent Laid-Open Nos. 59-46008 and 59-59).
64733, JP-A-59-89401, JP-A-59.
-132104). This permanent magnet uses light rare earths such as Nd and Pr, which are rich in resources, as R, and B,
25MGOe or more with Fe as the main component, 45M at maximum
Shows an extremely high energy product that reaches even more than GOe,
It is an excellent permanent magnet.

In recent years, Fe-BR type permanent magnets have attracted more and more attention as the performance and size of magnetic circuits have increased. In order to manufacture a permanent magnet for such an application, in order to remove irregularities and distortion on the surface of the sintered magnet body that has been molded and sintered, or to remove the surface oxide layer, and further to incorporate it in a magnetic circuit, It is necessary to cut or grind the entire surface or a required surface, and an outer peripheral blade cutting machine, an inner peripheral blade cutting machine, a surface grinding machine, a centerless grinder, a lapping machine, etc. are used for the processing.

However, when the Fe-BR permanent magnet is cut or ground, the Fe-BR permanent magnet is apt to oxidize in the air as a main component, and a rare earth element which immediately forms a stable oxide. Since the element and iron are contained, there is a problem that an oxide layer is generated due to heat generation or contact between the atmosphere and the processed surface, resulting in deterioration of magnetic characteristics.

Further, when a permanent magnet made of a Fe—BR magnetic anisotropy sintered body is incorporated in a magnetic circuit, the oxide produced on the surface of the magnet causes a reduction in output of the magnetic circuit and an increase in the magnetic circuit. However, there was a problem that the peripheral equipment was contaminated due to the loss of the surface oxide.

[0007] Therefore, the applicant has previously proposed the above Fe-B-
In order to improve the corrosion resistance of the R-based permanent magnet, a permanent magnet whose surface is coated with a corrosion-resistant metal plating layer by electroless plating or electrolytic plating (Japanese Patent Application No. 58-162350).
No.) and a permanent magnet whose surface is coated with a corrosion-resistant resin layer by a spraying method or a dipping method (Japanese Patent Application No. 58).
No. 171907). However, in the former plating method, since the permanent magnet body is a sintered body and is porous, an acidic solution or an alkaline solution remains in this hole during the plating pretreatment,
There is a risk of rusting over time, and the magnet body has poor chemical resistance, so the magnet surface is corroded during plating, resulting in poor adhesion and corrosion resistance.

Further, since the latter method of resin coating has directionality, it takes a lot of steps and labor to form a uniform resin coating on the entire surface of the object to be processed, and in particular, the deformed magnet having a complicated shape. It is difficult to apply a coating having a uniform thickness to the body, and the resin coating thickness becomes non-uniform by the dipping method, resulting in a problem of poor product dimensional accuracy.

Therefore, as a method for improving the corrosion resistance of the Fe-BR permanent magnet, the inventors have performed grid blasting with a hard powder having a specific particle size and hardness on the surface of the sintered magnet, Using the thin film formation technology, Al on the magnet surface
A permanent magnet coated with a thin film layer (Japanese Patent Application No. 60-110793).
No.) was proposed.

[0010]

As a result, Fe-B
Although the -R permanent magnet has significantly increased corrosion resistance, the Al thin film is formed by depositing Al particles evaporated by a vapor deposition method or the like on the surface of the magnet body, resulting in insufficient density, and thus, in long-term use, The Al thin film peels off locally,
There is a problem that cracks may occur in the thin film layer and local rust may be generated.

The present invention improves the deterioration of the magnetic properties associated with the cutting or grinding of the sintered magnet body in a new permanent magnet containing rare earths, boron and iron as the main components, and further, corrosive chemicals. An object of the present invention is to provide a permanent magnet on which a corrosion-resistant thin film layer having excellent adhesion and corrosion resistance is applied without using or contacting the above, and a method for producing the same.

[0012]

The present invention is based on R (R is N
At least one of d, Pr, Dy, Ho, Tb, or further, La, Ce, Sm, Gd, Er, Eu, T
consisting of at least one of m, Yb, Lu and Y) 1
0 atom% to 30 atom%, B2 atom% to 28 atom%, Fe
A permanent magnet having excellent corrosion resistance, which comprises a sintered permanent magnet body containing 65 atom% to 80 atom% as a main component and a tetragonal phase as a main phase, and having an aluminum chromate-treated coating on the surface thereof. .

The present invention also provides R (R is Nd, Pr,
At least one of Dy, Ho, Tb or further La, Ce, Sm, Gd, Er, Eu, Tm, Y
b), Lu, Y) (at least one of b, Lu, Y) 10 atomic% to 30 atomic%, B2 atomic% to 28 atomic%, Fe 65 atomic% to 80 atomic% as main components, and a main phase composed of a tetragonal phase. A method for producing a permanent magnet having excellent corrosion resistance, which comprises depositing an Al thin film layer on the surface of a bonded permanent magnet body and then performing chromate treatment.

Further, the present invention is based on R (R is Nd, P
At least one of r, Dy, Ho, Tb or further La, Ce, Sm, Gd, Er, Eu, Tm, Y
b), Lu, Y) (at least one of b, Lu, Y) 10 atomic% to 30 atomic%, B2 atomic% to 28 atomic%, Fe 65 atomic% to 80 atomic% as main components, and a main phase composed of a tetragonal phase. A method for producing a permanent magnet having excellent corrosion resistance, which comprises depositing an Al thin film layer on the surface of a bonded permanent magnet body, performing shot peening, and then performing chromate treatment.

In the present invention, Al is formed on the surface of the sintered magnet body.
For depositing the layer, a thin film forming method such as vacuum deposition, sputtering, or ion plating can be appropriately selected and used. The thickness of the thin film layer is 30 μ in consideration of peeling of the thin film layer, deterioration of mechanical strength, and securing of corrosion resistance.
The thickness is preferably m or less, and most preferably 5 μm to 25
The layer thickness is μm. Further, the thickness of the chromate film deposited on the Al thin film layer is preferably 1 μm to 5 μm, and the appearance is preferably finished from a bright iridescent color to a golden brown yellow brown.

In the present invention, grit blasting in which a hard powder having a required shape is jetted together with a pressurized gas onto the surface of the sintered magnet body before the Al thin film layer is adhered is performed by the black skin or oxidation of the sintered magnet body. This is an effective treatment because the surface layer such as the layer and the work strain layer can be removed to clean the surface and improve the corrosion resistance of the Al thin film layer deposited in the subsequent step.

As the hard powder used for this grit blast, there are Al ₂ O ₃ based powders having a Mohs hardness of 5 or more, silicon carbide based powders, ZrO ₂ based powders, boron carbide based powders, garnet based powders, etc., which have high hardness. Al ₂ O ₃ based powder is preferred. If the Mohs hardness of the above-mentioned amorphous hard powder is less than 5, the grinding force is too small, and it takes a long time for the grinding treatment, which is not preferable. When the average particle size of the irregular hard powder is less than 20 μm, the grinding force is too small and it takes a long time to grind.
If it exceeds 50 μm, the surface roughness of the surface of the sintered magnet body becomes too rough and the grinding amount becomes non-uniform, so 20 μm to 350 μm.
m is preferred.

Further, as the injection condition of the irregular hard powder,
If the pressure is less than 1.0 kg / cm ^2, it takes a long time for the grinding treatment, and if the pressure exceeds 6.0 kg / cm ² , the amount of grinding on the surface of the magnet body becomes non-uniform, and the surface roughness may be deteriorated. . Further, if the injection time is less than 0.5 minutes, the amount of grinding is small and non-uniform, and if it exceeds 60 minutes, the amount of grinding on the surface of the magnet body is large and the surface roughness deteriorates, which is not preferable. Further, as the pressurized fluid for jetting the hard powder, air or an inert gas such as Ar or N ₂ gas can be used.
An inert gas is preferable for preventing oxidation of the magnet body,
When air is used, dehumidified air is desirable.

In the present invention, as the shot peening powder, a spherical hard powder having a Mohs hardness of 3 or more can be used, and steel balls, glass beads or the like can be used, and the hardness must be equal to or higher than the hardness of the Al thin film layer deposited. Good luck
Glass beads are preferred. If the Mohs hardness of the spherical powder for peening is less than 3, it is less than the hardness of the Al thin film layer and the peening effect cannot be obtained, which is not preferable. When the average particle size of the spherical powder for peening is less than 30 μm, the pressing force against the Al thin film layer is small and the treatment takes a long time, and when it exceeds 3000 μm, the surface roughness of the sintered magnet body surface becomes too rough. 3 because the finished surface is not uniform
0 μm to 3000 μm is preferable. A more preferable average particle size is 40 μm to 2000 μm.

As for the conditions for spraying the spherical powder, if the pressure is less than 1.0 kg / cm ² , the pressing force against the Al thin film layer is small and the treatment requires a long time, and the pressure is 5.0 kg / cm ^2.
If it exceeds cm ² , the pressing force on the Al thin film layer becomes non-uniform, and the surface roughness is deteriorated. Furthermore, if the jetting time is less than 1 minute, the entire surface cannot be uniformly treated, and the upper limit of the jetting time is determined by the amount of peening treatment and the treatment conditions, but if it exceeds 60 minutes, the surface roughness deteriorates. Is not preferable.

Reasons for limiting composition The rare earth element R used in the permanent magnet of the present invention has a composition of 1
Occupies 0 atom% to 30 atom%, but Nd, Pr, Dy,
At least one of Ho and Tb, or L
a, Ce, Sm, Gd, Er, Eu, Tm, Yb, L
Those containing at least one of u and Y are preferable. Further, although one of R is usually sufficient, a mixture of two or more kinds (Misch metal, didymium, etc.) can be practically used for the convenience of availability. In addition, this R
Does not have to be a pure rare earth element, and may contain impurities that are unavoidable in production within a range that is industrially available. R is an essential element in the novel permanent magnet, and if it is less than 10 atomic%, the crystal structure becomes a cubic crystal structure having the same structure as α iron, so that high magnetic properties, particularly high coercive force cannot be obtained. If it exceeds 30 atomic%, the amount of R-rich nonmagnetic phase increases, the residual magnetic flux density (Br) decreases, and a permanent magnet having excellent characteristics cannot be obtained. Therefore, R is 10 atomic%
The range is -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, and if it exceeds 28 atomic%, B rich. Since the non-magnetic phase is increased and the residual magnetic flux density (Br) is reduced, an excellent permanent magnet cannot be obtained. Therefore, B is in the range of 2 at% to 28 at%.

Fe is an essential element in the novel permanent magnet of the above system, and if the content is less than 65 atomic%, the residual magnetic flux density (B
Since r) decreases and a high coercive force cannot be obtained when it exceeds 80 atomic%, Fe is contained in an amount of 65 atomic% to 80 atomic%.

In the permanent magnet according to the present invention,
By substituting a part of Fe with Co, the temperature characteristics can be improved without impairing the magnetic characteristics of the obtained magnet. However, when the Co substitution amount exceeds 20% of Fe, the magnetic characteristics are reversed. Is deteriorated, which is not preferable. The substitution amount of Co is Fe
When the total amount of Co and Co is 5 atom% to 15 atom%, (B
Since r) increases as compared with the case where no substitution is made, it is preferable to obtain a high magnetic flux density.

The permanent magnet according to the present invention has R,
In addition to B and Fe, the presence of impurities that are unavoidable in industrial production can be tolerated, but a part of B is 4.0 atomic% or less of C and 3.5.
P of atomic% or less, S of 2.5 atomic% or less, 3.5 atomic%
Improving the manufacturability of the permanent magnet by substituting at least one of the following Cu with a total amount of 4.0 atomic% or less,
The price can be reduced.

Further, at least one of the following additional elements is effective for improving the coercive force and squareness of the demagnetization curve of the RB-Fe based permanent magnet, improving the manufacturability, and lowering the cost. Therefore, it can be added. 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 M
n, 5.0 atomic% or less Bi, 9.5 atomic% or less N
b, Ta of 9.5 atomic% or less, M of 9.5 atomic% or less
o, W of 9.5 atomic% or less, Sb of 2.5 atomic% or less,
Ge of 7 atomic% or less, Sn of 3.5 atomic% or less, 5.5
At least one of Zr of atomic% or less, Ni of 9.0 atomic% or less, Si of 9.0 atomic% or less, Zn of 1.1 atomic% or less, and Hf of 5.5 atomic% or less is added and contained. However, in the case where two or more kinds are contained, the maximum content can be made high by increasing the coercive force of the permanent magnet by containing at most atomic% of the additive element having the maximum value.

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 fine and uniform alloy powder. Further, the permanent magnet of the present invention has a compound having a tetragonal crystal structure having an average crystal grain size in the range of 1 to 80 μm as a main phase and a nonmagnetic phase (oxide phase) of 1% to 50% by volume. Except) is included.

Further, the permanent magnet of the present invention can be magnetically anisotropic magnet obtained by press molding in a magnetic field, and can be magnetically isotropic magnet by press molding in a non-magnetic field. You can

[0029]

According to the present invention, the surface of the Fe-BR permanent magnet is coated with a chromate treatment film of Al to improve the deterioration of the magnetic properties due to oxidation and cutting work. The following specific powder is injected together with a pressurized gas to densify the Al thin film layer, improve the adhesion between the material and the surface thin film layer, and further improve the corrosion resistance of the material.

The permanent magnet according to the present invention has a coercive force iHc.
≧ 1 kOe, residual magnetic flux density Br> 4 kG, and the maximum energy product (BH) max is (BH) max ≧ 10.
It shows MGOe, and the maximum value reaches 25 MGOe or more.
The main component of R of the permanent magnet according to the present invention is 5
When the light rare earth metal mainly composed of Nd and Pr occupies 0% or more, R12 atom% to 20 atom%, B4 atom% to 2
When 4 atomic% and Fe 74 atomic% to 80 atomic% are the main components, (BH) max shows excellent magnetic characteristics of 35 MGOe or more, and particularly when the light rare earth metal is Nd, the maximum value is 45 MGOe or more. Reach

[0031]

[Example] As a starting material, electrolytic iron having a purity of 99.9%,
A ferroboron alloy and Nd having a purity of 99.7% or more were used. After blending these, high frequency melting was performed and then casting was performed in a water-cooled copper mold to obtain an ingot having a composition of 16.0Nd 7.0B77.0Fe. Then, this ingot was roughly pulverized by a stamp mill and then finely pulverized by a ball mill to obtain a fine powder having an average particle size of 2.8 μm.

This fine powder was inserted into a mold, oriented in a magnetic field of 15 kOe, and perpendicular to the magnetic field, 1.2 ton / c.
Molded at a pressure of m ² . The obtained molded body is 1100
25m long by sintering at 1 ℃ for 1 hour in Ar atmosphere
A sintered body of m × width 40 mm × thickness 30 mm was obtained. Furthermore, 800 ° C. in Ar, 1 hour and 630 ° C., 1.5
A two-step aging treatment of time was applied.

The above-mentioned permanent magnet body was cut out into a size of 5 mm in length × 10 mm in width × 3 mm in thickness at a rotational speed of 2400 rpm and a feed rate of 5 mm / min using diamond # 200 as a grindstone in the atmosphere. Furthermore, this cut sample,
An amorphous Al ₂ O ₃ hard powder having an average particle diameter of 50 μm and a Mohs hardness of 9 was used, and grit blasting was performed under the conditions of a pressure of 2.5 kg / cm ² and a pressurized gas of N ₂ gas for 20 minutes. The surface layer of the magnet body was removed.

Next, the above sample was placed in a vacuum vessel having a degree of vacuum of 5 × 10 ^-5 Torr, and Ar gas was fed thereinto to obtain 1 × 10 5.
After discharging in Ar gas of ^-2 Torr at a voltage of 500 V for 15 minutes, an Al plate having a purity of 99.99% was continuously used as a coating material, which was heated and evaporated A
1 was ionized, and these ionized particles were attracted to an electric field and adhered to the test piece constituting the cathode to form an Al thin film. The thickness of the thin film formed on the surface of the test piece was 15 μm. The ion plating condition is a voltage of 1.5.
It was kV for 10 minutes.

1% of the above test piece was placed in a 2% Alodine # 1200 (trade name, manufactured by Nippon Paint Co., Ltd.) solution kept at 30 ° C.
After dipping for a minute, a chromate film was applied in golden color on the surface of the Al thin film layer to obtain a test piece (Invention 1).

For the magnet body sample coated with the Al thin film layer, spherical glass bead powder having an average particle size of 120 μm and a Mohs hardness of 6 was used, with a pressure of 1.5 kg / cm ² , and a pressurized gas of N ₂ gas. After subjecting to shot peening under the condition of spraying for 5 minutes, the test piece is dipped in a 2% Alodine # 1200 (trade name, manufactured by Nippon Paint Co., Ltd.) solution kept at 30 ° C. for 1 minute to form an Al thin film layer after peening. A test piece was obtained by depositing a chromate coating on the surface in a golden color (Invention 2).

These test pieces were subjected to a corrosion resistance test and a thin film adhesion strength test after the corrosion resistance test. In addition, the magnetic properties before and after the corrosion resistance test were measured. The test results and measurement results are shown in Table 1.

For comparison, the as-cut test piece (Comparative Example 3) and the test piece were subjected to grit blasting under the same conditions as in the present invention, solvent-degreased with trichlene for 3 minutes, and 5% NaOH was added. After alkali degreasing at 60 ° C. for 3 minutes at room temperature, pickling with 2% HCl at room temperature for 10 seconds, current density 4 A / dm ² in a watt bath, bath temperature 60 ° C., conditions for 20 minutes, Electro nickel plating is applied to the surface 20
A comparative test piece (Comparative Example 4) having a nickel plating layer having a thickness of μm was obtained. Furthermore, after depositing the Al thin film layer, a comparative test piece (Comparative Example 5) not subjected to shot peening treatment was obtained.

These comparative test pieces were subjected to the same tests and measurements as in Example 1 above, and the results are also shown in Table 1. For the corrosion resistance test, the test piece was tested at a temperature of 70 ° C and a temperature of 90%
Evaluation was made based on the appearance condition of the test piece and adhesion strength when left for 500 hours in the atmosphere of humidity, and the magnetic characteristics before and after the corrosion resistance test. Further, the test piece 1 of the present invention was examined for the time until rusting under the above conditions. Further, the adhesion strength test was evaluated by breaking the test pieces of the present inventions 1 and 2 and the comparative examples 4 and 5 after the corrosion resistance test and observing the fracture surface.

[0040]

[Table 1]

[0041]

As is clear from Table 1 of the examples, the method according to the present invention in which an Al thin film layer is deposited on the surface of a sintered permanent magnet body, and then shot peening is performed to perform chromate treatment, It can be seen that the deterioration of magnetic properties due to processing or grinding is improved and a permanent magnet excellent in corrosion resistance is obtained, and the effect is remarkable. The production method of the present invention uses, as R, a light rare earth which is abundant in resources centered on Nd and Pr, and contains 25 MGOe containing B and Fe as main components.
As mentioned above, it shows an extremely high energy product reaching a maximum of 45 MGOe or more, a high residual magnetic flux density, and a high coercive force.
Al, which is an excellent permanent magnet, which prevents deterioration of magnetic properties due to grinding and oxidation, and has excellent corrosion resistance.
Fe-BR with stable chromate coating on the surface
A system permanent magnet can be obtained at low cost.

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location H01F 41/02 G 8019-5E // H01F 1/08 B

Claims (3)

[Claims] 1. R (R is Nd, Pr, Dy, Ho, Tb
At least one of them, or further, La, Ce, S
m, Gd, Er, Eu, Tm, Yb, Lu, Y) 10 atom% to 30 atom%, B2
Corrosion resistance characterized by having a chromate-treated coating of Al on the surface of a sintered permanent magnet body containing atomic% to 28 atomic% and Fe 65 atomic% to 80 atomic% as main components and having a tetragonal phase as a main phase. Excellent permanent magnet. 2. R (R is Nd, Pr, Dy, Ho, Tb
At least one of them, or further, La, Ce, S
m, Gd, Er, Eu, Tm, Yb, Lu, Y) 10 atom% to 30 atom%, B2
After the Al thin film layer is deposited on the surface of the sintered permanent magnet body containing atomic% to 28 atomic% and Fe 65 atomic% to 80 atomic% as the main components and the main phase of which is a tetragonal phase, chromate treatment is performed. A method for producing a permanent magnet having excellent corrosion resistance, which is characterized in that it is applied. 3. R (R is Nd, Pr, Dy, Ho, Tb
At least one of them, or further, La, Ce, S
m, Gd, Er, Eu, Tm, Yb, Lu, Y) 10 atom% to 30 atom%, B2
After the Al thin film layer is deposited on the surface of the sintered permanent magnet body whose main phase is a tetragonal phase with atomic% to 28 atomic% and Fe 65 atomic% to 80 atomic% as the main components, and shot peening is further performed. , A method for producing a permanent magnet having excellent corrosion resistance, which is characterized by performing a chromate treatment.