JPH04214604A - Sintered magnet with excellent corrosion resistance using diffused Zn and its manufacturing method - Google Patents

Abstract

PURPOSE:To offer a permanent magnet, which is superior in magnetic characteristics and moreover, whose corrosion resistance is improved, and the manufacturing method of the magnet using an Nd-Fe-B sintered magnet. CONSTITUTION:An Nd-Fe-B sintered magnet is used. A molded material molded in the composition of the Nd-Fe-B sintered magnet is buried in a mixed material obtained by mixing Zn power, a Zn sintering inhibitor and a Zn diffusion reaction promotor and thereafter, this molded material is heat treated in a vacuum or an inert atmosphere. Thereby, a targeted permanent magnet is obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-magnetic-force sintered magnet in which the corrosion resistance of Nd-Fe-B magnets exhibiting excellent magnetic properties is further enhanced, and a method for manufacturing the same.

0002

2. Description of the Related Art Typical magnets currently used in industry include alnico magnets, hard ferrite magnets, and rare earth magnets, all of which have excellent magnetic properties.

[0003] Among these, rare earth magnets have attracted the attention of the public as magnets that will lead to the next generation, and have been used in an extremely wide range of fields, from various home appliances to large computer peripherals. It is used in

[0004] However, since rare earth magnets contain extremely reactive Nd or Fe in their metal structure, they easily react with not only moisture in the air but also hydrogen gas and nitrogen gas. As a result, oxides, hydrogen compounds, and even nitrogen compounds are likely to form on the surface of magnetic products, causing surface rust, and products with magnets attached to them may be shaken by vibrations, shocks, etc. As a result, the rust that occurs on the surface of these magnetic products easily exhibits phenomena such as peeling, falling, and scattering, which has a negative impact on other equipment and parts built into the surrounding area. It will be like that.

[0005] Furthermore, since the magnetic properties of sintered magnet products are significantly impaired by the rusting phenomenon, this rusting phenomenon is not treated as a fatal defect for sintered magnets where magnetic properties are important. Ta.

Therefore, there has been an urgent need to discover a method for improving the corrosion resistance of sintered magnets with excellent magnetic properties.

[0007] As a method for improving the corrosion resistance of magnets,
For permanent magnets containing rare earth elements, Fe, and B, A
By adding 0.05% to 20% by weight of l,
JP-A-64-72501 discloses a method of forming a rust-resistant intermetallic compound phase and surrounding a rust-prone magnetic phase with a rust-resistant intermetallic compound phase to improve the corrosion resistance of the magnetic material.
A method of coating the surface of a permanent magnet with an oxidation-resistant plating layer was also reported in JP-A-60-5440.
Reported as 6.

Furthermore, a method of forming and coating a corrosion-resistant thin film layer on the surface of a permanent magnet using means such as ion plating and sputtering was disclosed in Japanese Patent Laid-Open No. 61-1661.
17, and a method of providing an oxidation-resistant resin layer on the surface of a permanent magnet is disclosed in JP-A-60-63901.
has been reported.

However, for permanent magnets containing rare earth elements, Fe, and B, Al is added in an amount of 0.05% by weight to 20% by weight.
In the method of adding Al by weight%, in this case, by adding a large amount of Al, A
Since l is diffused, the magnetic properties of the magnet are deteriorated as a result, and the problem remains that the saturation magnetizing force of the permanent magnet is significantly reduced.

[0010] Furthermore, in the method of coating the surface of a permanent magnet with an oxidation-resistant plating layer, the magnet must be immersed in an aqueous solution in the manufacturing process. Elements and metals such as Fe easily oxidize to form oxides and hydroxides on the surface of the permanent magnet, but after that, corrosion-resistant materials such as Ni and Cr are applied to the top surface of these oxides and hydroxides. When a film is formed, the material and Ni or Cr
It is easy for defects such as swelling, cracking, and peeling to occur in the gaps with corrosion-resistant coatings such as metals, etc., and as a result, to this day, metals containing rare earth elements, Fe, and B still cannot provide sufficient corrosion resistance. Permanent magnets have not yet appeared.

On the other hand, in methods such as ion plating, sputtering, etc., in which a corrosion-resistant thin film layer is formed and coated on the surface of a permanent magnet, the thickness of the processed layer produced by these processing methods is , at most 20-3
Since it is only 0 μm, when using the product for a long time, it is impossible to avoid deterioration of the film properties, and there is a risk that the material will be exposed due to the occurrence of slight surface flaws. This has led to the problem that a local battery is formed between the thin film layer formed on the surface of the permanent magnet and the material, significantly accelerating the degree of corrosion.

0012

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and provide a sintered magnet with excellent corrosion resistance, as well as a method for manufacturing the same.

[0013]

[Means for Solving the Problems] As a result of intensive research, the present inventors have found that in order to solve the above problems, a method containing 3 to 45% by weight of Nd and 0.2 to 8% by weight of B is used. , the balance is Fe and unavoidable impurities, and Zn is diffused in a range of 1 to 100 μm from the surface layer of the sintered body, and the balance is Fe and unavoidable impurities. After molding a raw material powder having a composition containing 45% by weight of B, 0.2 to 8% by weight of B, and the remainder being Fe and unavoidable impurities, Zn powder and a Zn sintering inhibitor, The above-mentioned molded body is embedded in a mixture obtained by mixing with a reaction accelerator, and further, in a vacuum or an inert atmosphere,
This provides a method of heat treatment at 100°C.

In this case, as the Zn sintering inhibitor, A
It has a composition of l2 O3, TiO, NdO, etc., and has a composition of 100 to
A 300 mesh powder is utilized.

[0015] As the reaction accelerator, halogen compounds such as lithium fluoride and lithium fluoride are used.

[0016] It is preferable that the Zn powder used for the Zn diffusion treatment has a mesh size of about 10 to 300 mesh.

[0017]

[Function] In the present invention, the Nd content is specified as 3 to 45% by weight in the composition of the permanent magnet, because if the Nd content is less than 3% by weight, the magnetic properties of the magnet, especially the holding force, are maintained high. If the addition amount exceeds 45% by weight, the non-magnetic phase rich in Nd composition will increase, and the residual magnetic flux density of the permanent magnet will decrease, making it possible to obtain a good permanent magnet. This is because it becomes difficult to do so.

Further, the amount of B added is specified as 0.2 to 8% by weight, but in this case, if the B content is less than 0.2% by weight, a high coercive force cannot be obtained; This is because if the content exceeds 8% by weight, a large amount of non-magnetic phase rich in B content will precipitate, resulting in a decrease in the residual magnetic flux density of the magnet.

In the present invention, a Zn diffusion layer with a thickness of 1 to 100 μm is formed under the surface of the magnet. This improves the corrosion resistance of the magnet by forming a Zn diffusion layer under the surface of the magnet. It is meant to further enhance sexuality.

In this case, the Zn diffusion layer is 1 to 100 μm thick.
The reason for this stipulation is that if the thickness of the Zn diffusion layer is less than 1 μm, it will not be effective in improving corrosion resistance, and on the other hand, if the thickness of the Zn diffusion layer exceeds 100 μm, it will not be effective in improving corrosion resistance. This is because as the magnetic field reaches saturation, a phenomenon of deterioration of the magnetic properties begins to be observed.

On the other hand, in the present invention, a Zn sintering inhibitor and a reaction accelerator are used in the Zn diffusion treatment, but this is because, without the use of a Zn sintering inhibitor, Zn
This is to generate a large amount of Zn vapor during the diffusion process, to enable the diffusion process at a relatively low temperature, and to contribute to shortening the Zn diffusion process time.

[0022]

[Example] Example 1 An ingot having a composition of 15% by weight Nd, 8% by weight B, and 77% by weight Fe was melted in an Ar atmosphere using a high-frequency melting furnace. was coarsely ground using a disk mill, and then finely ground using a ball mill to obtain a fine powder with an average particle size of 2.5 μm.

[0023] This fine powder was filled into a mold and oriented in a magnetic field of 15 KOe, and at the same time, 20 tons of powder was applied in a direction parallel to the magnetic field.
A green compact was produced by molding at a pressure of /cm2.

[0024] This green compact was mixed with 30 parts of Zn powder and Al2
After embedding it in a mixed powder consisting of 69.5 parts of O3 powder and 0.5 parts of LiF, the compact was subjected to a sintering treatment of heating in an Ar atmosphere at 1100°C for 1 hour, and then
A sintered magnet was manufactured by performing heat treatment for 30 minutes in an Ar atmosphere at 00°C.

After embedding this sintered magnet in epoxy resin and etching it with nitric alcohol, the thickness of the Zn diffusion layer diffused from the surface of the sintered magnet was measured using an optical microscope, and separately, As a result of analysis using an X-ray microanalyzer at an accelerating voltage of 10 KV and a sample current of 1 x 10-7 A, the relationship between the Zn diffusion concentration and the distance from the surface was as shown in Table 1. 10μm
It was found that Zn was 67% by weight at this point, and 5% by weight at 90 μm from the sample surface, and that Zn was diffused up to 100 μm from the sample surface.

[0026] Table 2 shows the results of a 1000-hour durability corrosion test conducted on the above sintered magnet using a constant temperature and humidity test chamber set at a temperature of 600°C and a humidity of 90%. As described above, by implementing the present invention,
It was confirmed that the corrosion resistance of the Nd-Fe-B magnet was sufficiently improved and that its magnetic properties were not impaired even by the presence of the Zn diffusion layer.

Example 2 When an ingot with a composition of 41% by weight of Nd, 5% by weight of B, and 54% by weight of Fe was processed in the same manner as in Example 1, its corrosion resistance was sufficiently improved and also
It was confirmed that its magnetic properties were not impaired.

Example 3 When an ingot with a composition of 39% by weight Nd, 2% by weight B, and 59% by weight Fe was processed in the same manner as in Example 1, its corrosion resistance was sufficiently improved and also
It was confirmed that its magnetic properties were not impaired.

Example 4 When an ingot with a composition of 35% by weight Nd, 5% by weight B, and 60% by weight Fe was processed in the same manner as in Example 1, its corrosion resistance was sufficiently improved and also
It was confirmed that its magnetic properties were not impaired.

Example 5 When an ingot with a composition of 33% by weight of Nd, 4% by weight of B, and 63% by weight of Fe was processed in the same manner as in Example 1, its corrosion resistance was sufficiently improved and also
It was confirmed that its magnetic properties were not impaired.

Example 6 When an ingot with a composition of 40% by weight Nd, 3% by weight B, and 57% by weight Fe was processed in the same manner as in Example 1, its corrosion resistance was sufficiently improved and also
It was confirmed that its magnetic properties were not impaired.

Example 7 A molded body treated in the same manner as in Example 1 except that an ingot having a composition of 40% by weight of Nd, 3% by weight of B, and 57% by weight of Fe was produced. After manufacturing multiple pieces using the same method as in 1, the Zn diffusion treatment time for each molded body was set to 3 hours, the surface of the sintered magnet was ground, and each Zn
After adjusting the thickness of the diffusion region as shown in Table 3, a corrosion resistance test similar to that in Example 1 was conducted, and the results shown in Table 3 were obtained.
It was found that it exhibited almost good corrosion resistance.

Comparative Example 1 After melting an ingot having a composition of 35% by weight of Nd, 5% by weight of B, and 60% by weight of Fe, a molded body produced in the same manner as in Example 1 was prepared using Al2. The magnet was embedded in O3 powder (the difference with Example 1 is that it does not contain Zn powder) and made into a sintered magnet in the same manner as in Example 1, and its characteristics were the same as in Example 1. When measured using the method, there was no change in the magnetic properties compared to Example 1, but
Rust was confirmed to occur over the entire surface of the sample.

Comparative Example 2 When an ingot having a composition of 15% by weight of Nd, 8% by weight of B, and 77% by weight of Fe was processed in the same manner as in Comparative Example 1, except for melting 2, the results were as follows: In comparison, its corrosion resistance was significantly impaired, and rust was observed over the entire surface of the product.

As described above, in the case of the present invention, Nd
It has become possible to easily obtain a sintered magnet with sufficiently improved corrosion resistance without impairing the magnetic properties of the -Fe-B sintered magnet.

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

[Table 3]

[0039]

[Effects of the Invention] According to the present invention, it is possible to sufficiently improve the corrosion resistance of Nd-Fe-B sintered magnets without impairing their excellent magnetic properties. There is a great contribution to be made to an industry that uses a large amount of .

Claims (2)

[Claims] Claim 1: 3 to 45% by weight of Nd and 0.2% of B
~8% by weight, with the remainder being Fe and unavoidable impurities, the sintered body having a composition of 1~8% by weight from the surface layer of the sintered body.
A sintered magnet with Zn diffused and excellent in corrosion resistance, characterized in that Zn is diffused in a range of 100 μm. Claim 2: 3 to 45% by weight of Nd and 0.2% of B
After molding raw material powder with a composition containing ~8% by weight and the balance being Fe and unavoidable impurities, Zn powder and
The molded body is embedded in a mixture obtained by mixing the sintering inhibitor of n and a reaction accelerator, and further heated at 600 to 1100°C in a vacuum or inert atmosphere. A method for producing a sintered magnet with excellent corrosion resistance in which Zn is diffused.