JP4091349B2 - Method for improving weather resistance of rare earth magnet alloys - Google Patents

Description

【００３９】
【発明の効果】
以上説明したように，本発明によると，めっきや樹脂被膜などの保護被膜を設けなくても，簡単な処理で希土類磁石合金の耐候性を向上させることができ，このため，安価にして耐候性の優れた希土類磁石合金を提供できる。また，本発明の処理を行うと磁着品同士から磁着品を切り出す抵抗が小さくなり，磁着品の部品への装着操作の負荷を低減できる。
【図面の簡単な説明】
【図１】耐候性試験後の希土類磁石合金の表面状態を示す写真である。
【図２】他の耐候性試験後の希土類磁石合金の表面状態を示す写真である。
【図３】他の耐候性試験後の希土類磁石合金の表面状態を示す写真である。
【図４】本発明に従う希土類磁石合金の磁気特性を比較例と対比して示した図である。
【図５】本発明に従う希土類磁石合金の磁着物同士の切り出し性試験における最大荷重（切り出し力）を比較例と対比して示した図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rare earth magnet alloy having excellent weather resistance.
[0002]
[Prior art]
An Sm-Co magnet is known as a rare earth magnet excellent in oxidation resistance and heat resistance. However, this magnet is expensive. As a cheaper rare earth magnet, an R—Fe— (Co) —B rare earth sintered magnet alloy is known. R represents one or more rare earth elements, and (Co) represents that it may contain Co. The surface of this magnet is generally easy to oxidize. For this reason, the magnet surface is used after an oxidation-resistant film is applied by a plating method, a sputtering method, a vapor deposition method, an organic film method or the like.
[0003]
As a rare earth magnet that is cheaper and has improved oxidation resistance and heat resistance, for example, there is an R—Fe— (Co) —B—C based rare earth sintered magnet alloy proposed in Japanese Patent No. 2789364. This material contains C (carbon) as an essential component of the alloy element, and is excellent while maintaining a high maximum energy product (BHmax) due to the presence of a nonmagnetic phase having a high C concentration around the magnetic crystal grains. It is explained that the oxidation resistance is obtained.
[0004]
[Problems to be solved by the invention]
When an oxidation-resistant film is formed on the surface of an R—Fe— (Co) —B rare earth sintered magnet alloy, a strong and homogeneous protective film layer of several tens μm or more is formed on the outer surface of the alloy. Therefore, the operation must be complicated and consist of many processes, which inevitably involve problems such as peeling of the coating, dimensional accuracy of the magnet product, and cost increase.
[0005]
In the case of R-Fe- (Co) -BC rare earth sintered magnet alloy, it has better oxidation resistance and weather resistance than the former. However, if the surface condition is uneven, corrosion will occur in corrosive environments. Easy to progress.
[0006]
Therefore, an object of the present invention is to provide a conventional R—Fe—B or R—Fe—B—C rare earth magnet alloy (R represents at least one rare earth element, and Fe is partially substituted by Co. The weather resistance may be improved.
[0007]
[Means for Solving the Problems]
According to the present invention, an R—Fe—B or R—Fe—B—C rare earth magnet alloy (R represents at least one rare earth element, and Fe may be partially substituted with Co. Is provided with a solution containing a fatty acid salt compound on the surface of the rare earth magnet alloy. Furthermore, according to the present invention, the first step of contacting the surface of the R—Fe— (Co) —B— (C) rare earth magnet alloy with the acidic solution and the organic layer contacting with the solution containing the fatty acid salt compound. There is provided a method for improving the weather resistance of a rare earth magnet alloy comprising a second step of carrying out a system coating treatment.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The magnet alloy targeted by the present invention is an R—Fe— (Co) —B— (C) based rare earth magnet alloy [(Co) may contain cobalt, and (C) contains carbon. This is mainly about rare earth magnet alloys mainly composed of so-called R ₂ Fe ₁₄ B compounds containing rare earth elements R, B and Fe as essential constituent elements. This means that a part of Fe is substituted with Co, and further contains C and other elements.
[0009]
The component composition of a typical rare earth magnet alloy targeted by the present invention is as follows:
C: 15 at.% Or less (including 0 at.%)
B: 0.5 to 15 at.%,
Co: 40 at.% Or less (including 0 at.%),
R: 8-20 at.%,
Where R represents at least one rare earth element,
Remainder: It can be expressed by Fe and unavoidable impurities, including those containing 5 at.% Or less of other alloy elements that improve various functions.
[0010]
This rare earth magnet alloy is generally formed into a sintered magnet through a series of processes of melting, casting, crushing, molding and sintering, and a cut product having a predetermined shape is obtained by cutting the sintered magnet alloy. Cutting is performed using a wire saw or the like, but since the surface of the cut product cut by the machine is rough, surface grinding using a polishing machine or the like is usually performed.
[0011]
In the past, attempts have been made to prevent rusting by forming inorganic oxidation-resistant protective coatings such as plating and vapor deposition or organic protective coatings on cut and surface-ground products. It is intended to provide weather resistance directly to the exposed surface of the magnet alloy without forming a film.
[0012]
The method for improving the weather resistance of a rare earth magnet alloy according to the present invention is a simple method of contacting with a solution containing a fatty acid salt compound. Prior to that, it is desirable to perform an acid treatment (pickling with a weak acid) in which the exposed surface of the magnet is brought into contact with an acidic solution. For pickling, it is preferable to use an acidic aqueous solution having a pH of 3 to 6 containing boron, and typically an aqueous boric acid solution having a pH of 3 to 6 is preferably used. Although it is possible to adjust the pH to 3 to 6 with boric acid alone, it is also possible to adjust the pH with a mineral acid such as sulfuric acid after dissolving boric acid or other boron compounds. Boron compounds other than boric acid include borax and sodium peroxoborate, but boric acid is easy to handle.
[0013]
Next, the fatty acid salt compound is coated, but usable fatty acid salt compounds include saturated fatty acids represented by C _n H _{2n + 1} COOH, such as enalenic acid, caprylic acid, pelargonic acid, capric acid, undecyl acid, Examples thereof include alkali salt compounds such as lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, and behenic acid. Also, unsaturated fatty acids represented by C _n H _2n-5 COOH, C _n H _2n-3 COOH, C _n H _2n-1 COOH, such as acrylic acid, crotonic acid, isocrotonic acid, undecylic acid, oleic acid, elaidin Examples include alkali salts such as acid, celetic acid, brassic acid, erucic acid, sorbic acid, linoleic acid, linolenic acid, and arachidonic acid. Among these, an alkali salt compound of an unsaturated fatty acid is preferable, and for example, oleate such as sodium oleate is easy to handle.
[0014]
It was found that the weather resistance can be improved by pickling a rare earth magnet alloy with a weakly acidic aqueous solution containing boron (typically boric acid aqueous solution). The reason is not clear, but elemental analysis of the surface before and after pickling with an electron probe microanalyzer (EPMA) confirmed that the rare earth elements on the magnet surface were concentrated. , Fe (including Co) is relatively reduced on the treated surface, and the remaining rare earth element appears on the surface, which is covered with a very thin oxide film, so that the surfaces of the magnetic crystal grains and the grain boundaries are unaffected. It may be dynamic. It is presumed that boron is also involved as an oxide in the formation of this passive film.
[0015]
In this pickling treatment, a cut product obtained by cutting a sintered product, or a surface-ground product in some cases, may be immersed in the pickling solution, stirred if necessary, then washed and dried. Good. For stirring, it is convenient to immerse the cut or ground product in the barrel, immerse it in pickling solution, and rotate the barrel. The concentration of the pickling solution depends on the type and form of the rare earth magnet alloy to be treated, but it is convenient to use a boric acid aqueous solution having a pH of 3 to 6, preferably a pH of 4 to 6. The treatment temperature is not particularly limited, and any temperature from 0 to 100 ° C. can be adopted, but it is appropriate to carry out at room temperature.
[0016]
Next, a coating treatment with a fatty acid salt compound is performed, and this treatment may be performed by immersing the fatty acid salt compound in a solution of water or an organic solvent, washing with water as necessary, and drying. The concentration of the fatty acid salt compound in the solution depends on the type and form of the rare earth magnet alloy to be treated, but a solution in which about 0.01 to 0.1 wt% of the compound is dissolved may be used. The treatment temperature is not particularly limited, and any temperature from 0 to 100 ° C. can be adopted, but it is desirable to carry out at a temperature of 30 to 50 ° C.
[0017]
After pickling with a weakly acidic solution containing boron, coating with a fatty acid salt compound improves the weather resistance and improves the adhesion between the magnet and the adherend compared to the case where the pickling is not performed. It has been confirmed that the surface wettability is improved. The reason for this is not clear, but the passivating film described above is formed by the pickling, and at the same time the magnet surface becomes moderately rough, so that the adhesion between the fatty acid salt compound and the magnet is good. Thus, it is assumed that the protective film made of the fatty acid salt compound is uniformly and firmly formed on the magnet surface.
[0018]
As for the magnetic characteristics when the treatment according to the present invention is performed, the weather resistance is improved, so that the deterioration of the magnetic characteristics is reduced accordingly. Moreover, even if the process according to the present invention is performed, the maximum energy product does not decrease.
[0019]
Thus, according to the present invention, the surface of the R—Fe— (Co) —B— (C) rare earth magnet alloy is brought into contact with the acid solution and the solution containing the fatty acid salt compound is brought into contact with the surface. A method for improving the weather resistance of a rare earth magnet alloy comprising the second step of performing an organic coating treatment is provided, in which case the acidic solution is an acidic solution containing boron and has a pH of 3 to 6, and the fatty acid salt compound is an unsaturated fatty acid compound. , For example, sodium oleate. According to the present invention, there is also provided an R—Fe— (Co) —B— (C) -based rare earth magnet alloy having a surface coated with an organic coating comprising a fatty acid salt compound and excellent in weather resistance. This is X / Y> 0.5, where X is the atomic ratio of R / (Fe + Co + B) on the magnet surface and Y is the atomic ratio of R / (Fe + Co + B) on the entire magnet. This indicates that the rare earth magnet alloy surface of the treated product according to the present invention has a higher concentration of rare earth elements than the untreated product.
[0020]
Hereinafter, representative examples of the present invention will be given, and the effects thereof will be shown in comparison with comparative examples (untreated products).
[0021]
【Example】
[Example 1]
Using 99.9% pure electrolytic iron as a raw material, a ferroboron alloy with a boron content of 19.3%, neodymium metal with a purity of 98.5% (containing other rare earth metals as impurities), and a composition ratio of 18Nd-76Fe-6B. After being melted in a vacuum in a high frequency induction furnace, it was cast into a water-cooled copper mold to obtain an alloy lump. This was crushed with a jaw crusher, further pulverized to 100 mesh using a stamp mill in argon gas, and then pulverized to an average particle size of 5 μm using a vibration mill.
[0022]
The obtained alloy fine powder was formed in a magnetic field of 10 kOe at a pressure of 1 ton / cm ² , and the formed body was subjected to a sintering treatment in which it was held at 1100 ° C. for 1 hour in an argon gas atmosphere. Was rapidly cooled to obtain a sintered body. The obtained sintered body was cut, and a large number of 5 mm × 5 mm × 1 mm square test pieces were cut out and used as test pieces.
[0023]
After adding 99% pure boric acid to pure water at a rate of 12.5 g / L, dilute sulfuric acid was added to prepare a boric acid aqueous solution with pH 4.5. 3000 cc of this boric acid aqueous solution and 700 test pieces were loaded into a barrel, and the barrel was rotated at a rotational speed of 5 times / min while maintaining the boric acid aqueous solution at a pH of 4.4 to 4.6 at a temperature of 40 ° C. Then, the test piece was pulled up, washed with water, and naturally dried at room temperature.
[0024]
This boric acid-treated test piece is immersed in a sodium oleate aqueous solution (concentration 0.01 wt.%) Heated to 40 ° C for 1 minute, air-dried at room temperature, placed in pure water for 5 minutes, and excess sodium oleate. Was removed and dried. The magnet body thus obtained was subjected to a weather resistance evaluation test. For comparison, an “untreated product” (not treated with boric acid or oleate) as cut from the sintered body was also subjected to the same test. The results of these tests are shown in the photograph of FIG. The weather resistance evaluation test was conducted under the following conditions.
[0025]
[Weather resistance evaluation test]: Place the test piece on glass wool in the constant temperature and humidity chamber (model KCH-1000) manufactured by Tokyo Rika Kogyo Co. After that, the appearance was evaluated.
Condensation conditions: Water droplets were formed on the surface by inserting the test piece directly into an 80 ° C 90% RH atmosphere, and after 20 hours exposure, the appearance was visually evaluated.
Non-condensing conditions: After setting the specimens at room temperature, they were exposed to an atmosphere of 80 ° C and 90% RH for 300 hours, and then the specimens were taken out and visually evaluated.
[0026]
As evaluation criteria, the following four-step evaluation was performed.
Rank A: Less than 2% rust generation area relative to the entire surface area Rank B: 2% or more and less than 5% rust generation area relative to the entire surface rank C: Rust against the entire surface area Generation area of 5% or more and less than 40% Rank D: Rust generation area is 40% or more with respect to the entire surface area.
From the results shown in FIG. 1 and Table 1, it was observed that the untreated product was ranked D in both the 20-hour condensation condition and the 300-hour non-condensation condition. It can be seen that rusting hardly occurred even under non-condensing conditions for 300 hours.
[0028]
[Example 2]
Carbon black with a purity of 99.5% was added to the same raw materials as in Example 1, and the alloy composition was weighed and blended to be 18Nd-2Dy-67Fe-9Co-1.9B-2.1C. Then, stearic acid with a purity of 90% is added to the powder so as to be 18Nd-2Dy-65Fe-9Co-1.9B-4.1C depending on the amount of C contained therein, and then using a vibration mill. It grind | pulverized to the average particle diameter of 5 micrometers. Thereafter, Example 1 was repeated to obtain a treated product with boric acid and sodium oleate. In addition to the same weather resistance evaluation as in Example 1, the obtained processed product was further subjected to magnetic properties, measurement of the cutting force between magnetized materials, and analysis of the abundance of transition metals and rare earth elements on the magnet surface under the following conditions. went. For comparison, the same test was performed on “untreated products” (not treated with boric acid and oleate) as cut from the sintered body.
[0029]
[Magnetic properties]: Coercive force (iHc) and maximum energy product (BHmax) were measured using a vibrating sample magnetometer (VSM-5-19) manufactured by Toei Kogyo Co., Ltd.
[Cutability between magnetized materials]: After magnetizing at 6450A with a φ30 coil with a capacitor removable magnet (MSD-200-3500P) manufactured by Hitech Co., Ltd., and then mounted on a push-pull tester manufactured by Imada Manufacturing Co., Ltd. The load applied when the magnetized test pieces were pushed out one by one from the upper part of the plastic jig was measured, and the evaluation was made for the cut-out property when the magnetized objects were separated from each other with the maximum load and attached to the part.
[Magnet composition analysis]: Nd, Dy, and Co in the magnet body are quantified using a high-frequency induction plasma emission spectrometer (IRIS / AP) manufactured by Japan Jarrel Ash Co., and B is quantified by Seiko Electronics Industry Co., Ltd. Inductively coupled plasma emission spectrometer (SPS-1200A) is used, C is analyzed using Horiba Metal Carbon Analyzer (EMIA-1110) manufactured by Horiba, Ltd., and Fe is quantified by Hiranuma Automatic manufactured by Hiranuma Sangyo Co., Ltd. A titration apparatus (COMTIME-980) was used.
[Magnetic surface composition analysis]: Rare earth elements and other elements on the surface of the magnet body can be quantified using an electron beam probe microanalyzer (JED-2100) manufactured by JEOL Ltd. at an accelerating voltage of 15 kV. The average of these values was used as the quantitative analysis value of the element on the magnet surface.
[0030]
Among these tests, the weather resistance evaluation test results are shown in FIG. 2 (under 20-hour dew condensation conditions) and FIG. 3 (under 300-hour non-condensation conditions), and the evaluation results are also shown in Table 1. 2A shows the untreated product, and FIG. 2B shows the treated product of Example 2 (boric acid + oleate treatment), and FIG. 3A shows the untreated product. ) Is the treated product of Example 2 (boric acid + oleate treatment).
[0031]
From the results shown in FIGS. 2 to 3 and Table 1, rusting of rank C was observed in the untreated product of this example under the 20-hour condensation condition and the 300-hour non-condensing condition. It turns out that it did not rust.
[0032]
FIG. 4 shows the measured magnetic properties, where the horizontal axis represents the coercive force (kOe) and the vertical axis represents the maximum energy product (MGOe). It is plotted against the thing. As is clear from FIG. 4, even if the treatment is performed in this example, neither the coercive force nor the maximum energy product is significantly different from that of the untreated product.
[0033]
FIG. 5 shows the cutting force (the above-mentioned maximum load) between the magnetized materials in comparison with the untreated product and the treated product of this example. In this example, the cutting force decreases, It can be seen that the cutting resistance for separating the magnetic deposits is low. This means that the load is reduced when the magnet bodies of this example are incorporated into the apparatus one by one.
[0034]
Furthermore, according to the magnet surface composition analysis of the treated product of Example 2,
R = 7.67at.%,
Fe = 40.3at.%,
Co = 4.7 at.%,
B = 0.85at.%
Met. From this, the atomic ratio X of R / (Fe + Co + B) on the magnet surface is calculated to be 0.167.
On the other hand, the composition of the whole magnet of Example 2 is determined by ICP.
R = 14.71 at.%,
Fe = 70.07 at.%,
Co = 8.76 at.%,
B = 1.99at.%
Met. From this, the atomic ratio Y of R / (Fe + Co + B) of the whole magnet is calculated as 0.182. Therefore, the ratio of X / Y is 0.918, exceeding 0.5.
[0035]
In contrast, according to the magnet surface composition analysis of the untreated product of this example,
R = 5.37 at.%,
Fe = 55.3 at.%,
Co = 6.07 at.%,
B = 0.31at.%
Met. From this, the atomic ratio X of R / (Fe + Co + B) on the magnet surface is calculated to be 0.087.
On the other hand, the atomic ratio Y of R / (Fe + Co + B) of the whole magnet is calculated as 0.182 from the analysis result by ICP as described above. Therefore, the X / Y ratio of the untreated product is 0.478, which is less than 0.5.
[0036]
Thus, it can be seen that the ratio of the rare earth element is relatively increased on the surface of the magnet treated in this example.
[0037]
Example 3
Example 1 was repeated except that no boric acid treatment was performed. That is, the test piece as cut out from the sintered body was directly treated with sodium oleate under the same conditions as in Example 2 without performing pickling with boric acid. About the obtained processed goods, the weather resistance, the magnetic characteristic, the cut-out property between magnetic deposits, and wettability were evaluated similarly to Example 2, and those results were written together in Table 1 and FIGS. In FIG. 2 and FIG. 3, the processed product of this example is indicated by (C). From the results of Table 1 and FIGS. 2 to 3, it can be seen that the treated product of this example does not reach that of Example 2, but exhibits substantially the same sufficient weather resistance. Further, from the results of FIG. 4 and FIG. 5, it can be seen that the present example has substantially the same magnetic characteristics and cut-out property as those of the second embodiment.
[0038]
[Table 1]

[0039]
【The invention's effect】
As described above, according to the present invention, the weather resistance of the rare earth magnet alloy can be improved by a simple process without providing a protective coating such as plating or a resin coating. Excellent rare earth magnet alloy can be provided. Further, when the processing of the present invention is performed, the resistance for cutting out the magnetized products from the magnetized products is reduced, and the load of the operation of mounting the magnetized products on the parts can be reduced.
[Brief description of the drawings]
FIG. 1 is a photograph showing a surface state of a rare earth magnet alloy after a weather resistance test.
FIG. 2 is a photograph showing the surface state of a rare earth magnet alloy after another weather resistance test.
FIG. 3 is a photograph showing the surface state of a rare earth magnet alloy after another weather resistance test.
FIG. 4 is a diagram showing magnetic characteristics of a rare earth magnet alloy according to the present invention in comparison with a comparative example.
FIG. 5 is a diagram showing a maximum load (cutting force) in a cut-out test between magnetic deposits of rare earth magnet alloys according to the present invention in comparison with a comparative example.

Claims (6)

  R—Fe—B based rare earth magnet alloy (R represents at least one rare earth element, and Fe may be partially substituted with Co). A method for improving the weather resistance of a rare earth magnet alloy comprising a first stage for contacting with a solution and a second stage for performing an organic coating treatment for contacting with a solution containing a fatty acid salt compound.   R—Fe—B—C-based rare earth magnet alloy (R represents at least one rare earth element, and Fe may be partially substituted with Co), and has a pH of 3 to 6 containing boron. A method for improving the weather resistance of a rare earth magnet alloy comprising a first step of contacting with an acidic solution of the second step and a second step of performing an organic coating treatment in contact with a solution containing a fatty acid salt compound.   R—Fe—B based rare earth magnet alloy (R represents at least one rare earth element, and Fe may be partially substituted with Co). A method for improving the weather resistance of a rare earth magnet alloy comprising a first step of contacting with a solution and then drying, and a second step of performing an organic coating treatment that is contacted with a solution containing a fatty acid salt compound and then dried.   R—Fe—B—C-based rare earth magnet alloy (R represents at least one rare earth element, and Fe may be partially substituted with Co), and has a pH of 3 to 6 containing boron. A method for improving the weather resistance of a rare earth magnet alloy comprising: a first step of contacting with an acidic solution of the above and then drying; and a second step of contacting with a solution containing a fatty acid salt compound and then drying.   The method for improving the weather resistance of a rare earth magnet alloy according to any one of claims 1 to 4, wherein the fatty acid salt compound is an unsaturated fatty acid compound.   The method for improving the weather resistance of a rare earth magnet alloy according to any one of claims 1 to 4, wherein the fatty acid salt compound is sodium oleate.

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