JPH0422008B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Field This invention relates to a permanent magnet whose main components are R (R is at least one rare earth element including Y), B, and Fe, and the surface of the R-Fe-B permanent magnet is acid-resistant. This invention relates to rare earth/iron/boron based permanent magnets coated with a chemical conversion film to improve oxidation resistance. BACKGROUND ART Permanent magnetic materials are one of the extremely important electrical and electronic materials used in a wide range of fields, from various household appliances to peripheral terminal equipment for large computers. The miniaturization of electrical and electronic equipment in recent years,
With the demand for higher efficiency, permanent magnet materials are required to have increasingly higher performance. Current typical permanent magnet materials are alnico, hard ferrite and rare earth cobalt magnets. As the cobalt raw material situation has become unstable in recent years, the demand for alnico magnets containing 20 to 30 wt% cobalt has decreased, and inexpensive hard ferrite, whose main component is iron oxide, has become the mainstream magnet material. Summer. On the other hand, rare earth cobalt magnets contain cobalt from 50 to
It is very expensive because it contains 60wt% and uses Sm, which is not included in rare earth ores.
Compared to other magnets, the magnetic properties are much higher,
It has come to be used mainly for small, high value-added magnetic circuits. Therefore, the present inventor first developed R-
We proposed a permanent magnet of Fe-B system (R is at least one rare earth element including Y) (patent application 1983-
No. 145072). In this R-Fe-B permanent magnet, R is Nd or
Using resource-rich light rare earths, mainly Pr,
It is an excellent permanent magnet that has Fe as its main component and exhibits an extremely high energy product of over 25 MGOe. Problems to be Solved by the Invention However, the R-Fe-B permanent magnets having the above-mentioned excellent magnetic properties contain rare earth elements and iron, which tend to oxidize in the air and gradually form oxides. When an R-Fe-B permanent magnet is incorporated into a magnetic circuit, oxides generated on the magnet surface cause a decrease in the output of the magnetic circuit and variations between the magnetic circuits, and the surface oxide may fall off. There was a problem of contamination of peripheral equipment due to The object of the present invention is to provide a new permanent magnet based on rare earth elements, iron, and boron, which has improved oxidation resistance. Means for Solving the Problems This invention comprises R (where R is at least one rare earth element including Y) 8 at% to 30 at%, B2 at% to 28 at%, Fe42 at% to 90 at% R, characterized in that the surface of the permanent magnet body is composed of as a main component and the main phase is a tetragonal phase, and is coated with an oxidation-resistant chemical conversion film.
-Fe-B permanent magnet. Effect This invention forms a strong and stable oxidation-resistant chemical conversion coating on the surface of an R-Fe-B permanent magnet in order to suppress oxides generated on the surface. The oxidation-resistant chemical conversion coating in this invention is preferably a phosphate coating such as zinc phosphate or manganese phosphate, or a chromate coating, and the surface of these chemical conversion coatings may be further coated with a paint or resin layer. In the case of a phosphate coating, the thickness of the chemical conversion coating of this invention is 3 μm or more in terms of oxidation resistance, strength, and cost.
10 μm, preferably 2 μm to 5 μm in the case of a chromate coating. This invention mainly uses resource-rich light rare earths such as Nd and Pr as R, and Fe, B, R,
By using as the main component, it is possible to obtain an excellent R-Fe-B permanent magnet at a low cost, which has an extremely high energy product of 25 MGOe or more, high residual magnetic flux density, high coercive force, and high oxidation resistance. can. Reasons for limiting the composition The reasons for limiting the composition of the permanent magnet according to the present invention will be explained below. The rare earth element R used in the permanent magnet of this invention is
It is a rare earth element that includes yttrium Y, light rare earth elements, and heavy rare earth elements, and at least one of these elements, preferably a light rare earth element such as Nd or Pr, or a mixture with Nd, Pr, etc. is used. That is, R includes neodymium (Nd), praseodymium (Pr), lanthanum (La), cerium (Ce), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), and eurobium (Eu). , samarium (Sm), cadrinium (Gd), thulium (Tm), ytterbium (Yb), lutetium (Lu), and ythtrium (Y). In addition, it is usually sufficient to have one type of R, but in practice, a mixture of two or more types (Mitsushimetal, didymium, etc.) can be used for reasons such as convenience of availability, Sm, Y, La, Ce, Gd etc. are other R, especially
It can be used as a mixture with Nd, Pr, etc. Note that this R may not be a pure rare earth element,
It may contain impurities that are unavoidable during production within an industrially available range. R is an essential element in new R-Fe-B permanent magnets, and if it is less than 8 atomic %, the crystal structure becomes cubic, which is the same structure as α-iron, resulting in high magnetic properties, especially high coercive force. If it exceeds 30 atomic %, the R-rich nonmagnetic phase increases and the residual magnetic flux density Br decreases, making it impossible to obtain a permanent magnet with excellent characteristics. Therefore, R should be in the range of 8 atomic % to 30 atomic %. B is an essential element in the new R-Fe-B permanent magnet, and if it is less than 2 atom%, it will form a rhombohedral structure and high coercive force (iHc) cannot be obtained;
If the value exceeds Br, the amount of B-rich nonmagnetic phase increases and the residual magnetic flux density Br decreases, making it impossible to obtain an excellent permanent magnet. Therefore, B should be in the range of 2 atomic % to 28 atomic %. Fe is an essential element in new R-Fe-B permanent magnets, and if it is less than 42 at%, the residual magnetic flux density
If Br decreases and exceeds 90 atomic %, high coercive force cannot be obtained, so Fe is contained in a range of 42 atomic % to 90 atomic %. In addition, in the alloy for permanent magnets according to the present invention, replacing a part of Fe with Co can improve the temperature characteristics without impairing the magnetic properties of the obtained magnet, but the amount of Co substitution is If it exceeds 50%, the magnetic properties will deteriorate, which is not preferable. Further, the permanent magnet according to the present invention has R, B,
In addition to Fe, the presence of unavoidable impurities due to industrial production is acceptable, but a portion of Fe or B may be replaced with 4.0 at% or less C, 3.5 at% or less P, 2.5 at% or less S, and 3.5 at% At least one of the following Cu,
By substituting a total amount of 4.0 at% or less,
It is possible to improve the manufacturability and lower the cost of permanent magnets. In addition, at least one of the following additional elements is
It is added to R-Fe-B permanent magnets because it is effective in improving coercive force, etc., improving manufacturability, and reducing costs. However, addition to improve coercive force causes a decrease in residual magnetic flux density Br, so it is desirable to add in a range that is equal to or higher than the residual magnetic flux density of conventional hard ferrite magnets. Al less than 9.5 atom%, Ti less than 4.5 atom%, V less than 9.5 atom%, Cr less than 8.5 atom%, Mn less than 8.0 atom%, Bi less than 5 atom%, Nb less than 12.5 atom%, 10.5 Ta less than 9.5 atom%, Mo less than 9.5 atom%, W less than 9.5 atom%, Sb less than 2.5 atom%, Ge less than 7 atom%, Sn less than 3.5 atom%, Zr less than 5.5 atom%, 5.5 atom % or less of Hf; however, if two or more types are contained, the maximum content is less than or equal to the atomic percentage of the element having the maximum value among the added elements.
It becomes possible to increase the coercive force of permanent magnets. In the R-Fe-B permanent magnet of this invention,
It is essential that the main crystal phase be tetragonal, which is effective in obtaining a fine and uniform alloy powder and producing a sintered permanent magnet with excellent magnetic properties. In addition, in the case of a sintered magnet, the alloy for permanent magnets of the present invention has a compound having a tetragonal crystal structure as the main phase, and the non-magnetic phase (oxide (excluding phases). In addition, the R-Fe-B permanent magnet of the present invention can be press-molded in a magnetic field to obtain a magnetically anisotropic magnet, and press-molded in a no-magnetic field to obtain a magnetically isotropic magnet. Obtainable. Permanent Magnet Characteristics The R-Fe-B permanent magnet according to the present invention exhibits a coercive force iHc≧1kOe, a residual magnetic flux density Br>4kG,
The maximum energy product (BH)max is equal to or higher than that of hard ferrite, and in the most preferable composition range, (BH)max≧10MGOe, and the maximum value is
Reach over 25MGOe. In addition, in the composition of the permanent magnet according to the present invention, when the main component of R is 50% or more of light rare earth metals, R12 atomic% to 20 atomic%, B4 atomic% to 24 atomic%, Fe65 atomic% to 82 atomic%. At. Examples Examples according to the present invention will be shown below to clarify its effects. As a starting material, electrolytic iron with a purity of 99.9%, B19.4
%, the balance is Fe and Al5.3%, Si0.7%,
Feroboron alloy consisting of impurities such as C0.03%,
Nd with a purity of 99.7% or higher was used, and after being high-frequency melted, it was cast into a water-cooled copper mold. Thereafter, the ingot was coarsely ground with a stamp mill to a throughput of 35 meshes, and then ground with a ball mill for 3 hours to obtain a fine powder with a particle size of 3 to 10 μm. This fine powder was inserted into a mold, oriented in a magnetic field of 10 kOe, and molded under a pressure of 1.5 t/cm ² . The obtained compact was sintered at 1100°C for 1 hour in Ar, then allowed to cool, and then sintered in Ar for 600°C.
A permanent magnet according to the present invention was produced by subjecting it to an aging treatment at ℃ for 2 hours. The composition at this time is 14Nd−7.5B−78.5Fe
It was hot. Test pieces with dimensions of 15 mm x 10 mm x 6 mm were cut out from the obtained permanent magnet, and as shown in Table 1, each test piece was degreased, pickled, and then treated with phosphate under the following conditions (1) (2).
and lead chromate treatment (3). The coating thickness, magnetic properties, oxidation resistance, and adhesive strength of each test piece after the chemical conversion coating treatment were measured. The measurement results are shown in Table 1.

【table】

【table】

[Table] In the oxidation resistance test, the above specimen was heated at 60°C and 90°C.
The test piece was evaluated based on the oxidation weight increase when the test piece was left in an atmosphere with a humidity of 30% for 3 days. In the adhesive strength test, the above test piece after chemical conversion treatment was adhered to a holding plate using an adhesive called Araldite AW-106 (trade name), and then a shearing force was applied to the test piece using an Amsler tester to determine the adhesion per unit area. The strength was measured. For comparison, test specimens with the same components as those used in the examples of the present invention were subjected to oxidation tests in the same atmosphere at 60°C and 90% humidity as described above, without being subjected to chemical conversion treatment.
Each sample was evaluated based on oxidation weight gain and oxide film thickness (maximum oxide film thickness value due to oxidation) when left for 1 day, 2 days, and 3 days, and the results are shown in Table 2.

【table】

[Table] Effects of the invention As is clear from the examples, an oxide film was formed on the surface of the magnet alloy in the comparative untreated sample during the short-term oxidation test, and oxidation progressed inside as time progressed. As a result, it was confirmed that the magnetic properties had deteriorated. In addition, the increase in the oxide film due to oxidation of the comparative example magnet incorporated in the magnetic circuit is caused by
becomes narrower and narrower, and eventually the sky 〓 becomes 0,
This will cause a decrease in the output of the magnetic circuit and even cause difficulty in operation. On the other hand, since the R-Fe-B permanent magnet according to the present invention has a strong and stable oxidation-resistant chemical coating, it is clear that it has excellent oxidation resistance as shown in Table 1. . Therefore, when the R-Fe-B permanent magnet having the oxidation-resistant chemical conversion film according to the present invention is incorporated into a magnetic circuit, it is extremely effective in stabilizing output characteristics and improving reliability.

Claims (1)

[Claims] 1 R (wherein R is at least one rare earth element including Y) 8 to 30 atom%, B2 to 28 atom%, and Fe42 to 90 atom% as main components , A permanent magnet characterized in that the surface of a permanent magnet body whose main phase is a tetragonal phase is coated with an oxidation-resistant chemical conversion film.