JPS63166975A - Production of permanent magnet having excellent oxidation resistance - Google Patents

Abstract

PURPOSE:To produce a permanent magnet having excellent oxidation resistance by subjecting the surface of a sintered magnetic body of a tetragonal phase consisting of specific ratios of rate earth elements, B and Fe to a shot blast treatment and oxalic acid treatment, and thereafter executing a chemical conversion treatment thereto. CONSTITUTION:The surface of the sintered magnetic body consisting essentially of 10-30atom% R (formed with at least one kind among Nd, Pr, Dy, Ho and Tb, and furthermore formed with at least one kind among La, Ce, Sm, Gd, Er, Eu, Tm, Yb, Lu and Y). 2-30atom% B and 42-90atom% Fe, and the main phase thereof consisting of a tetragonal phase is subjected to the shot blast treatment with Al2O3 powder, etc. Said magnetic body is immersed in a satd. soln. of oxalic acid at the temp. of about 20-120 deg.C for an hour to execute the oxalic acid soln. treatment, and thereafter the chemical conversion treatment is executed by zinc phosphate, manganese phosphate, etc., to form a coated film of said magnetic body. The chemical conversion treatment can be industrially executed and the permanent magnet having the excellent oxidation resistance can obtd., by the above-mentioned manner.

Description

[Detailed description of the invention] Industrial field of application The present invention relates to a method for manufacturing Fe-BR permanent magnets with excellent oxidation resistance, and in particular improves the oxidation resistance of Fe-BR permanent magnets. The present invention relates to a method for producing a Fe-BR permanent magnet having a chemical conversion pretreatment that facilitates chemical conversion treatment industrially and significantly improves oxidation resistance.

Background Art The applicant previously proposed a Fe-BR-based permanent magnet (R is at least one rare earth element including Y) as a new high-performance permanent magnet that does not contain expensive Sm or Co.
(Japanese Patent Application No. 145072/1982).

This permanent magnet uses resource-rich light rare earths such as Nd and Pr as R, and is made of 25M with Fe as the main component.
It is an excellent permanent magnet that exhibits an extremely high energy product exceeding GOe.

However, Fe-
Permanent magnets made of B-R magnetic anisotropic sintered bodies contain rare earth elements, especially Nd and iron, which tend to oxidize in the air and gradually form stable oxides, so they are difficult to use in magnetic circuits. Due to oxides generated on the magnet surface when incorporated,
This causes a decrease in the output of the magnetic circuit and variations between the magnetic circuits, and there is also the problem of contamination of peripheral equipment due to shedding of surface oxides.

Therefore, in order to improve the corrosion resistance of the above-mentioned Fe-B-R permanent magnet, the applicant first applied a chemical conversion treatment to the surface of the magnet body,
Permanent magnets with phosphate or chromate coatings,
and permanent magnets in which an oxidation-resistant resin layer is coated on the chemical conversion coating by spraying, dipping, or electrodeposition coating (JP-A-60-63903, JP-A-60-63902, JP-A-Sho 60-63902, 60-63901).

However, permanent magnets coated with the chemical conversion film do not have sufficient corrosion resistance, so when an oxidation-resistant resin layer is formed on the surface of the chemical conversion film, the adhesion with the resin layer is improved. However, a sufficient improvement in corrosion resistance could not be obtained.

Purpose of the Invention The present invention aims to improve the corrosion resistance of a chemical conversion coating provided on a Fe-B-R based sintered magnet body. B-
The purpose is a method for manufacturing R-based permanent magnets.

Structure and Effects of the Invention The present invention improves the chemical conversion treatment method using phosphate or chromate applied to Fe-B-R sintered magnets, and improves the chemical conversion treatment and its pretreatment in order to improve the oxidation resistance. As a result of various studies, the following findings were obtained and the present invention was completed.

It has been found that the corrosion resistance of the chemical conversion coating is significantly improved by treating the surface of the Fe-BR-based sintered magnet with oxalic acid as a pretreatment.

This effect is thought to be due to the passivation of easily oxidized R and Nd in the sintered magnet body by oxalic acid.

However, in the passivation treatment of Nd with oxalic acid solution,
As it takes a long time and is not industrially practical, after further study, we decided to perform shot blasting on the Fe-B-R sintered magnet body prior to the oxalic acid treatment to eliminate Nd in the magnet body. It has been found that passivation takes place in a short time and corrosion resistance is significantly improved.

That is, this invention provides R (R is Nd, Pr, Dy
, Ho, and at least one of Tb, or further,
La, Ce, Sm, Gd, Er, Eu, T
(consisting of at least one of m, Yb, Lu, and Y) 10% to 30 at%, B2 at% to 28 at%, Fe42 at% to 90 at%, and the main phase is a tetragonal phase. This method of manufacturing a permanent magnet with excellent oxidation resistance is characterized in that the surface of a sintered magnet body is shot blasted, treated with oxalic acid, and then subjected to chemical conversion treatment.

Further, to describe this invention in detail, an amorphous powder consisting of at least one type of powder having an average particle size of 20 μm to 35% m and a Mohs hardness of 5 or more is applied to the surface of the sintered magnet having the above composition and crystalline phase under pressure. 1.0kg/
cm2~6.0kg/cm2 of pressurized gas and 0.
After applying shot blast for 5 to 60 minutes,
After treating with an oxalic acid solution by a spray method, dipping method, or steam treatment method to promote passivation of easily oxidized components R1, especially Nd, in the Fe-B-R sintered magnet body, chemical conversion treatment is performed. Furthermore, if necessary, in order to improve oxidation resistance, a resin film or a metal plating film is formed by a spray method, a dipping method, etc. in a subsequent step.

Preferred Embodiments of the Invention In the present invention, the following configuration is preferable as the shot blast treatment method in the first stage of the passivation treatment for R1, particularly Nd, in the sintered magnet body.

In this invention, the amorphous hard powder with a Mohs hardness of 5 or more used for shot blasting includes Al2O2-based powder,
There are silicon carbide-based, ZrO□-based, boron carbide-based, garnet-based powders, etc., and Ae203 No. 203, which has high hardness, is preferred.

If the Mohs hardness of the above-mentioned amorphous hard powder is less than 5, the grinding force is too small and the grinding process takes a long time, which is not preferable.

In addition, the average particle size of the amorphous hard powder is 201 trn to 35 trn.
The reason for setting 0 prn is that if it is less than 20 pm, the grinding force is too small and it takes a long time to grind, and if it exceeds 350 machining, the surface roughness of the sintered magnet surface becomes too rough and the amount of grinding is insufficient. This is because it becomes uniform, which is not preferable.

In addition, the injection conditions for the amorphous hard powder were set at a pressure of 1.0 k.
If it is less than g/cm2, the grinding process will take a long time, and
If the pressure exceeds 6.0 kg/cm2, the amount of grinding on the surface of the magnet body becomes uneven, and there is a concern that the surface roughness may deteriorate.

Furthermore, if the spraying time is less than 0.5 minutes, the amount of grinding will be small and non-uniform, and if it exceeds 60 minutes, the amount of grinding on the magnet surface will increase, which is undesirable as the surface roughness will deteriorate.

In addition, air or an inert gas such as Ar or N2 gas can be used as the pressurized fluid for injecting the hard powder, but in order to prevent oxidation of the magnet body, an inert gas is preferable. In such cases, dehumidified air is preferable.

In addition, as the second stage treatment method using oxalic acid solution,
There are immersion methods, spray methods, steam treatment methods, etc., but the immersion method is preferable from the point of view of work efficiency and quality stabilization, and the immersion conditions include a solution concentration of oxalic acid diluted solution, and a solution temperature of 20°C to 1.
The temperature is preferably 20°C, particularly 60°C to 80''C, and the immersion time is preferably within 1 hour, particularly 1 minute to 15 minutes.

In addition, as the chemical conversion coating according to the present invention, a phosphate coating made of zinc phosphate, manganese phosphate, etc. is preferable, and as for the thickness of the chemical conversion coating, in the case of a phosphate coating, oxidation resistance, strength,
From the viewpoint of cost, the thickness is preferably 10 pm or less, and in the case of a chromate film, 5 μm or less.

Furthermore, in order to improve corrosion resistance, an oxidation-resistant resin may be deposited on the chemical conversion coating by dipping, spraying, etc., or Ni, Cu, Zn may be coated by electroless plating or electrolytic plating. An oxidation-resistant metal or alloy plating such as oxidation-resistant metal or alloy plating, or a composite plating layer thereof may be applied.

In this invention, as the resin to be deposited on the chemical conversion film by dipping or spraying, epoxy resins, urethane resins, phenol resins, fluororesins, furan resins, polysiloxane resins, etc., and composite resins thereof are preferable.

Reason for limiting the composition of the permanent magnet The rare earth element R used in the permanent magnet of this invention has a composition of 8
Although Nd and Pr account for atomic% to 30 atomic%.

At least one of Dy, Ho, Tb, or in addition, La, Ce, Sm, Gd, Er, E
Preferably, it contains at least one of u, Tm, Yb, Lu, and Y.

Also, normally one type of R is sufficient, but in practice two types are sufficient.
Obtain a mixture of seeds or higher (Mitushmetal, Jijim, etc.)
It can be used for reasons such as convenience as described in 2.

Note that this R does not have to be a pure rare earth element, and may contain impurities that are unavoidable in production within an industrially available range.

R is an essential element in the above-mentioned permanent magnet, and 8
If it is less than 30 atomic %, the crystal structure becomes a cubic structure that is the same as α-iron, so high magnetic properties, especially high coercive force, cannot be obtained, and if it exceeds 30 atomic %, R-rich nonmagnetic phase increases. , the residual magnetic flux density (Br) decreases, making it impossible to obtain a permanent magnet with excellent characteristics. Therefore, the rare earth element is in the range of 8 atomic % to 30 atomic %.

B is an essential element in the permanent magnet according to the present invention. If it is less than 2 at %, the rhombohedral structure becomes the main phase and high coercive force (iHc) cannot be obtained, and if it exceeds 28 at %, B-rich The number of non-magnetic phases increases, and the residual magnetic flux density (Br
) decreases, making it impossible to obtain an excellent permanent magnet. Therefore, B is in the range of 2 atomic % to 28 atomic %.

Fe is an essential element in the above-mentioned permanent magnet, and 4
If it is less than 2 atomic %, the residual magnetic flux density (Br) decreases, and 90
If it exceeds atomic%, high coercivity cannot be obtained, so Fe
The content is 42 atomic % to 90 atomic %.

Further, in the permanent magnet of the present invention, a part of Fe is replaced with Co.
Substitution with Co can improve the temperature characteristics without impairing the magnetic properties of the resulting magnet, but if the amount of Co substitution exceeds 20% of Fe, the magnetic properties will deteriorate, so it is preferable. do not have. When the amount of Co substitution is 5 at % to 15 at % in total of Fe and Co, (Br) increases compared to the case where no substitution is made, which is preferable in order to obtain a high magnetic flux density.

In addition, the permanent magnet of the present invention can tolerate the presence of unavoidable impurities in industrial production in addition to R, B, and Fe; P, 2
．． By replacing at least one of S at 5 atomic % or less and Cu at 3.5 atomic % or less, with a total amount of 4.0 atomic % or less, it is possible to improve the manufacturability and lower the price of permanent magnets. .

Furthermore, at least one of the following additional elements is R-B-
It can be added to Fe-based permanent magnets because it is effective in modifying the coercive force and squareness of the demagnetization curve, improving manufacturability, and reducing costs.

9.5 atom% or less of AI, 4.5 atom% or less of Ti, 9
．． 5 at% or less V, 8.5 at% or less Cr, 8.0
Mn below 5.0 atom %, Bi below 5.0 atom %, Nb below 9.5 atom %, Ta below 9.5 atom %, Mo below 9.5 atom %, W below 9.5 atom % , 2.5 atom% or less sb, 7 atom% or less Ge, 3.5 atom% or less Sn, 5.5 atom% or less Zr, 9.0 atom% or less N
i, 9.0 at% or less Si, 1.1 at% or less Zn
, 5.5 atomic % or less of Hf.However, if two or more types are contained, the maximum content shall be atomic % or less of the one having the maximum value among the added elements. This makes it possible to increase the coercive force of the permanent magnet.

It is essential that the main phase of the crystalline phase is a tetragonal one in order to produce a sintered permanent magnet having superior magnetic properties than a fine and uniform alloy powder.

Further, the permanent magnet of this invention has an average crystal grain size of 1 to 80p.
It is characterized by having a main phase of a compound having a tetragonal crystal structure in the range of m, and containing a nonmagnetic phase (excluding oxide phase) of 1% to 50% by volume.

The permanent magnet according to the present invention has a coercive force iHc≧1koe,
The residual magnetic flux density Br>4kG is shown, and the maximum energy product (BH)max is (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 5
In the case where 0% or more is occupied by light rare earth metals mainly consisting of Nd and Pr, R12 atomic % to 20 atomic %, B44 atomic % to 2
When the main component is 4 at% Fe and 74 at% to 80 at% Fe, it exhibits excellent magnetic properties of (BH)max 35MGOe or more, and especially when the light rare earth metal is Nd, the maximum value is 45MGOe. reach more than that.

In addition, in this invention, as a permanent magnet that shows extremely high corrosion resistance in a corrosion resistance test where it is left in an environment of 60°C and a relative temperature of 90% for a long time, Ndllat% ~ 15 at%, Dy 0.2 at% ~ 3
．． Oat%, and the total amount of Nd and Dy is 12at% to 17
at%, B 5at% to 8at%, CoO,5
at%~13at%, AeO, 5at%~4at%, C
It is preferable that the Fe content is 1000 ppm or less, with the remainder consisting of Fe and unavoidable impurities.

Examples Example 1 As a starting material, electrolytic iron with a purity of 99.9%, B19.4
% and the remainder is Fe and impurities such as AI, Si, C, etc., N with a purity of 99.7% or more
d, Dy, Co, and AI, which were radio-frequency melted and then cast into water-cooled copper molds.

The ingot was then coarsely ground and then finely ground to obtain a fine powder with an average particle size of 3 pm.

This fine powder was inserted into a mold, oriented in a magnetic field of 10 KOe, and molded at a pressure of 1.5 t/cm 2 .

The obtained compact was sintered at 1060°C for 1 hour in Ar, then allowed to cool, and further sintered in Ar at 580°C for 2 hours.
A permanent magnet according to the present invention was produced by subjecting it to a time aging treatment.

The component composition at this time is 13.5Nd 7.5B-6
The remainder was Co-2A1-1.5Dy-Fe.

4mm x 8mm x 10m from the obtained permanent magnet
A test piece was cut into a size of m, and after degreasing the test piece, amorphous hard A6203 powder with an average particle size of 65 U was heated under a pressure of 2.0 k.
Shot blasting was performed for 10 minutes with pressurized N2 gas at g/cm2.

Further, oxalic acid solution treatment and phosphate treatment as chemical conversion treatment were performed under the following conditions.

Next, each sample was subjected to an oxidation resistance test, a salt spray test, and a measurement of magnetic properties. The results are shown in Table 1.

Conditions for oxalic acid solution Concentration/A oxalic acid aqueous solution Temperature: 80°C Immersion time: 10 min. The test piece was evaluated based on the time until rusting and the state of rusting when the test piece was left in an atmosphere of 80° C. and 90% humidity.

In addition, the salt spray test was evaluated based on the rust generated by immersion in a 5% NaCe solution at a liquid temperature of 35°C.

For comparison, a test piece with the same components as the example of this invention was subjected to chemical conversion treatment without shot blasting and passivation treatment with an oxalic acid solution. A salt water spray test was conducted under the same conditions as above, using a trowel in November in an atmosphere of 80° C. and 90% humidity, to measure the rusting state and magnetic properties. The results are shown in Table 1.

Table 1 Example 2 A test piece obtained in the same composition as in Example 1 and in the same manufacturing process f'1- was subjected to the same shot blasting, oxalic acid treatment, and zinc phosphate treatment as in Example 1. .

After that, the test piece was coated with polysiloxane resin MS-170.
0 (manufactured by Collicone), dried at room temperature for 3 hours, and then baked at 150°C for 15 minutes to prepare a test piece with resin coated on the surface, the same as in Example 1. Next, an oxidation resistance test, a salt spray test, and magnetic properties were measured. The results are shown in Table 2.

For comparison, a test piece obtained under the same composition and manufacturing conditions as above was directly subjected to the same chemical conversion treatment and resin dipping method as above, without shot blasting or passivation treatment such as oxalic acid solution treatment. Magnetic properties, oxidation resistance test, salt spray test, and adhesive strength were measured in the same manner as described above for the test piece with resin adhered to the surface. The results are shown in Table 2.

Table 2 April 6, 1988 Patent Application No. 313974 2, Name of the invention Method for manufacturing a permanent magnet with excellent oxidation resistance 3, Relationship with the person making the amendment Case Applicant 4, Agent 5. Date of amendment order March 31, 1985
Day 6, as shown in the title of the invention, scope of claims, and detailed description of the invention column 7 of the specification to be amended, and the content of the amendment as shown in the attached sheet.

Claims (1)

[Claims] (1) R (R is at least one of Nd, Pr, Dy, Ho, Tb, or in addition, La, Ce, Sm, Gd
, Er, Eu, Tm, Yb, Lu, Y) 10% to 30 atomic%, B2 atomic% to 28 atomic%, Fe42 atomic% to 90 atomic%, and the main phase is A method for producing a permanent magnet with excellent oxidation resistance, characterized in that the surface of a sintered magnet having a tetragonal phase is shot blasted, treated with oxalic acid, and then subjected to chemical conversion treatment.