JP2006286779A - Magnet and its production process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rare earth magnet exhibiting sufficient corrosion resistance and excellent heat resistance, and to provide its production process. <P>SOLUTION: The rare earth magnet 1 comprises a magnet element 3, and a protective layer 5 covering the surface of the magnet element 3. The protective layer 5 comprises a first layer 6 containing a rare earth element and covering the magnet element 3, a second layer 7 having a content of rare earth element lower than that of the first layer 6 and covering the first layer 6, and a metal salt layer 8 covering the second layer 7. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnet, in particular, a magnet having a protective layer formed on the surface, and a method for manufacturing the same.

  In recent years, so-called rare earth magnets (R-Fe-B magnets; R represents a rare earth element such as neodymium (Nd); the same applies hereinafter) exhibiting a high energy product of 25 MGOe or more are being actively developed as metal magnets. ing. As such a rare earth magnet, for example, Patent Document 1 discloses a magnet formed by sintering, and Patent Document 2 discloses a magnet formed by rapid quenching.

  Generally, a metal magnet has a low corrosion resistance because it contains a metal that is relatively easily oxidized. In particular, although the rare earth magnet described above shows a high energy product, it contains a rare earth element and iron that are very easily oxidized as main components, and therefore has a tendency to be particularly low in corrosion resistance among metal magnets.

In order to improve the corrosion resistance of such a magnet, it has been proposed to form a protective layer on the surface. Among these, Patent Document 3 proposes forming a protective layer by heating a rare earth magnet at 200 to 500 ° C. in an oxidizing atmosphere.
JP 59-46008 A JP-A-60-9852 JP-A-5-226129

  However, in Patent Document 3, it is proposed to form a protective layer at a specific temperature in an oxidizing atmosphere. However, such a method can sufficiently prevent corrosion of magnets, particularly rare earth magnets. In many cases, the resulting protective layer could not be satisfactorily formed. For this reason, it was still difficult for the obtained rare earth magnet to sufficiently prevent the occurrence of dusting and weight loss due to the corrosion resistance test.

  In recent years, the use of rare earth magnets as motor magnets in hybrid vehicles has been studied. In this case, the rare earth magnet is used around the engine and is exposed to a high temperature exceeding 150 ° C. However, the rare earth magnet described in Patent Document 3 tends to be subject to corrosion deterioration under such a high temperature environment, and there is still room for improvement in terms of heat resistance of the protective layer.

  Then, this invention is made | formed in view of such a situation, and it aims at providing the magnet which has sufficient heat resistance while having sufficient heat resistance, and its manufacturing method.

  In order to achieve the above object, the present inventors have conducted extensive research, and as a result, a plurality of layers having different compositions are formed on the surface of the metal magnet body, resulting in superior corrosion resistance and heat resistance as compared with the prior art. As a result, the present invention was completed.

  That is, the magnet of the present invention includes a metal magnet body and a protective layer formed on the surface of the metal magnet body. The protective layer includes an oxide layer covering the metal magnet body, and an oxide layer. And a metal salt layer covering the surface.

  As described above, the magnet of the present invention includes a metal salt layer as a protective layer in addition to the oxide layer covering the metal magnet body. For this reason, compared with the magnet which formed only one layer of the conventional oxide layer, it has more excellent heat resistance by covering with a metal salt layer. Here, when the metal salt layer is directly attached to the surface of the metal magnet element body, the adhesion to the element body is poor, and therefore, the metal salt layer is liable to be peeled off during use. On the other hand, in the magnet of the present invention, since the metal salt layer is provided on the metal magnet element body via the oxide layer, the adhesion of the metal salt layer to the element body is extremely good. As a result, the magnet of the present invention is also less susceptible to a decrease in corrosion resistance due to the peeling of the protective layer as described above.

  In addition, when the surface of the magnet is further coated or the like, the metal salt layer can also exhibit the property of improving the adhesion between the metal magnet body and the coating film. For this reason, the magnet of the present invention having a metal salt layer on the surface has excellent adhesion to the coating film, and extremely excellent corrosion resistance and heat resistance after coating.

  The magnet of the present invention includes a metal magnet element and a protective layer formed on the surface of the metal magnet element. The protective layer covers the metal magnet element and contains a rare earth element. It may be characterized by having a layer, a second layer covering the first layer and having a rare earth element content less than the first layer, and a metal salt layer covering the second layer.

  Thus, by having two layers between the metal magnet element body and the metal salt layer, the magnet has more excellent corrosion resistance and heat resistance. In particular, the second layer has a rare earth element content less than that of the first layer, and thus is less likely to be oxidized than the first layer, and includes the first and second layers in such a combination. The magnet can exhibit excellent corrosion resistance. In the second layer, “the rare earth element content is lower than that in the first layer” includes a case where the rare earth element is not substantially contained.

  Among them, the rare earth element content in the second layer is preferably half or less of the rare earth element content in the first layer, and the second layer is substantially free of rare earth elements. More preferred. By so doing, the second layer can exhibit even better corrosion resistance.

  The second layer preferably contains a transition element and oxygen. Since the second layer containing a transition element and oxygen and having a rare earth element content less than that of the first layer is more difficult to be oxidized, the magnet having such a second layer is more excellent. It will have corrosion resistance.

  Further, in the magnet of the present invention, the metal magnet body includes a rare earth element and a transition element other than the rare earth element, the first layer contains the rare earth element, the transition element, and oxygen, It is more preferable that the second layer contains the transition element and the oxygen and has a rare earth element content less than that of the first layer.

  By doing so, the first layer adjacent to the metal magnet element contains the same rare earth element as the metal magnet element, so that the adhesion to the element becomes good. Further, the second layer formed on the outside contains a transition element and oxygen, and is less likely to be oxidized because the content of rare earth elements is smaller than that of the first layer. For this reason, the magnet provided with these two layers has very little peeling of the protective layer, and further has excellent corrosion resistance.

  The rare earth element in the first layer, the transition element in the first layer, and the transition element in the second layer are more preferably elements derived from a metal magnet body. That is, the first and second layers are preferably formed by changing the magnet body by reaction or the like. In particular, the rare earth element in the first layer, the transition element in the first layer, and the transition element in the second layer are more preferably elements that constitute the main phase of the metal magnet body. With such a configuration, the adhesion of each layer is further improved, and each layer can be an extremely dense film. As a result, the corrosion resistance of the magnet is further improved.

  More specifically, the metal salt layer in the magnet of the present invention includes at least one element selected from the group consisting of Cr, Ce, Mo, W, Mn, Mg, Zn, Si, Zr, V, Ti, and Fe. And at least one element selected from the group consisting of P, O, C and S is preferable. The metal salt layer containing these elements has extremely excellent corrosion resistance and heat resistance.

  In particular, the metal salt layer is preferably a layer made of phosphate or sulfate because it has particularly excellent corrosion resistance and heat resistance.

  The present invention also provides a method for suitably producing the magnet of the present invention. That is, the magnet manufacturing method of the present invention is a magnet manufacturing method in which a protective layer is formed on the surface of a metal magnet body containing a rare earth element, and the metal magnet body is heat-treated to form a metal magnet body. A first step of covering a first layer containing a rare earth element, and a first step of covering the first layer and forming a second layer having a lower rare earth element content than the first layer, and a metal after the first step And a second step of forming a chemical conversion treatment layer on the surface of the second layer by chemical conversion treatment of the magnet base body. In the first step, the first layer and the second layer are formed on the surface of the metal magnet base body. It is characterized in that at least one of the oxidizing gas partial pressure, the processing temperature, and the processing time is adjusted so that the layer is formed.

  According to such a manufacturing method, on the surface of the metal magnet element body, the first and second layers obtained by altering the element body are satisfactorily formed, and the metal that is the chemical conversion treatment layer is formed by the chemical conversion treatment. A salt layer is formed well. And the magnet which has such a structure has extremely excellent corrosion resistance and heat resistance as described above.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the magnet which has sufficient corrosion resistance, and has the outstanding heat resistance, and its manufacturing method.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the following description, a rare earth magnet containing a rare earth element will be described as an example of the magnet.

  FIG. 1 is a schematic perspective view showing a rare earth magnet of the present embodiment, and FIG. 2 is a view schematically showing a cross-sectional structure taken along line II-II of the rare earth magnet shown in FIG. As shown in FIGS. 1 and 2, the rare earth magnet 1 includes a magnet body 3 (metal magnet body) and a protective layer 5 that covers the surface of the magnet body 3. The protective layer 5 includes a first layer 6, a second layer 7, and a third layer 8 in order from the magnet body 3 side. Hereinafter, each configuration of the rare earth magnet 1 will be described.

(Magnet body)
First, the magnet body 3 will be described. The magnet body 3 is a permanent magnet containing a rare earth element. Rare earth elements refer to scandium (Sc), yttrium (Y), and lanthanoid elements belonging to Group 3 of the long-period periodic table. Here, the lanthanoid elements include, for example, lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), Examples include dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

  Examples of the constituent material of the magnet body 3 include a material containing the rare earth element and a transition element other than the rare earth element in combination. In this case, the rare earth element is preferably at least one element selected from the group consisting of Nd, Sm, Dy, Pr, Ho, and Tb. These elements include La, Ce, Gd, Er, Eu, Tm, Yb, and More preferably, it further contains at least one element selected from the group consisting of Y.

  As transition elements other than rare earth elements, iron (Fe), cobalt (Co), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), nickel (Ni), copper (Cu) At least one element selected from the group consisting of zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta) and tungsten (W) is preferable, and Fe and / or Co are more preferable. preferable.

  More specifically, examples of the constituent material of the magnet body 3 include R-TM-B and R-Co materials. In the former constituent material, R is preferably a rare earth element mainly composed of Nd. In addition, examples of TM include transition elements such as Fe and Co. Further, in the latter constituent material, R is preferably a rare earth element mainly composed of Sm.

  As the constituent material of the magnet element body 3, an R—Fe—B based constituent material is particularly preferable. Such a material has a main phase of a substantially tetragonal crystal structure, and a rare earth-rich phase having a high mixing ratio of rare earth elements in the grain boundary portion of the main phase and a mixing of boron atoms. It has a high proportion of boron-rich phase. These rare earth-rich phase and boron-rich phase are nonmagnetic phases that do not have magnetism, and such a nonmagnetic phase is usually contained in an amount of 0.5 to 50% by volume in the magnet constituting material. Moreover, the particle size of the main phase is usually about 1 to 100 μm.

  In such R—Fe—B-based constituent materials, the rare earth element content is preferably 8 to 40 atomic%. When the rare earth element content is less than 8 atomic%, the crystal structure of the main phase becomes almost the same as that of α-iron, and the coercive force (iHc) tends to decrease. On the other hand, if it exceeds 40 atomic%, a rare earth-rich phase is excessively formed, and the residual magnetic flux density (Br) tends to be small.

  The content of Fe is preferably 42 to 90 atomic%. When the Fe content is less than 42 atomic%, the residual magnetic flux density decreases, and when it exceeds 90 atomic%, the coercive force tends to decrease. Furthermore, the B content is preferably 2 to 28 atomic%. If the B content is less than 2 atomic%, a rhombohedral structure is likely to be formed, and this tends to reduce the holding force. If it exceeds 28 atomic%, a boron-rich phase is excessively formed. Therefore, the residual magnetic flux density tends to be small.

  In the constituent materials described above, a part of Fe in the R—Fe—B system may be substituted with Co. Thus, if a part of Fe is replaced by Co, the temperature characteristics can be improved without deteriorating the magnetic characteristics. In this case, it is desirable that the amount of substitution of Co not be larger than the content of Fe. When the Co content exceeds the Fe content, the magnetic properties of the magnet body 3 tend to deteriorate.

  A part of B in the constituent material may be substituted with an element such as carbon (C), phosphorus (P), sulfur (S) or copper (Cu). By replacing a part of B in this way, the magnet body can be easily manufactured and the manufacturing cost can be reduced. At this time, the substitution amount of these elements is desirably an amount that does not substantially affect the magnetic properties, and is preferably 4 atomic% or less with respect to the total amount of constituent atoms.

  Further, from the viewpoint of improving the holding power and reducing the manufacturing cost, in addition to the above-described structure, aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), bismuth (Bi ), Niobium (Nb), tantalum (Ta), molybdenum (Mo), tungsten (W), antimony (Sb), germanium (Ge), tin (Sn), zirconium (Zr), nickel (Ni), silicon (Si) ), Gallium (Ga), copper (Cu), hafnium (Hf), or other elements may be added. These addition amounts are also preferably in a range that does not affect the magnetic properties, and specifically, they are 10 atomic% or less with respect to the total amount of constituent atoms. In addition, oxygen (O), nitrogen (N), carbon (C), calcium (Ca), and the like are conceivable as other components that are inevitably mixed. It may be contained in an amount of.

The magnet body 3 having such a configuration can be manufactured by powder metallurgy. In this method, first, an alloy having a desired composition is produced by a known alloy production process such as a casting method or a strip casting method. Next, this alloy was pulverized to a particle size of 10 to 100 μm using a coarse pulverizer such as a jaw crusher, a brown mill, or a stamp mill, and then further pulverized by a fine pulverizer such as a jet mill or an attritor. The particle size is 5 to 5 μm. The powder thus obtained is preferably molded at a pressure of 0.5 to ⁵ t / cm ² in a magnetic field having a magnetic field strength of 600 kA / m or more.

  Thereafter, the obtained compact is preferably sintered in an inert gas atmosphere or under vacuum at 1000 to 1200 ° C. for 0.5 to 10 hours and then rapidly cooled. Furthermore, this sintered body is subjected to heat treatment at 500 to 900 ° C. for 1 to 5 hours in an inert gas atmosphere or vacuum, and if necessary, the sintered body is processed into a desired shape (practical shape). A magnet body 3 is obtained.

  The thus obtained magnet body 3 is preferably further subjected to acid cleaning. That is, it is preferable that the surface of the magnet body 3 is subjected to acid cleaning in the previous stage of heat treatment to be described later.

  Nitric acid is preferably used as the acid used in the acid cleaning. When plating a general steel material, non-oxidizing acids such as hydrochloric acid and sulfuric acid are often used. However, when the magnet body 3 contains a rare earth element like the magnet body 3 in the present embodiment, hydrogen generated by the acid is removed from the magnet body 3 by performing treatment using these acids. Occluded on the surface, the occlusion site becomes brittle and a large amount of powdery undissolved material is generated. Since this powdery undissolved material causes surface roughness, defects, and poor adhesion after the surface treatment, it is preferable not to include the above-described non-oxidizing acid in the acid cleaning solution. Therefore, it is preferable to use nitric acid, which is an oxidizing acid that generates little hydrogen.

  The amount of dissolution of the surface of the magnet body 3 by such acid cleaning is preferably 5 μm or more, preferably 10 to 15 μm in average thickness from the surface. By completely removing the altered layer or oxide layer by processing the surface of the magnet body 3, a desired oxide film can be formed with higher accuracy by heat treatment described later.

  The concentration of nitric acid in the treatment solution used for the acid cleaning is preferably 1 N or less, particularly preferably 0.5 N or less. If the nitric acid concentration is too high, the dissolution rate of the magnet body 3 is extremely fast, and it becomes difficult to control the amount of dissolution. In particular, large-scale processing such as barrel processing has a large variation, making it difficult to maintain the dimensional accuracy of the product. Tend. Moreover, when the nitric acid concentration is too low, the dissolved amount tends to be insufficient. For this reason, the nitric acid concentration is preferably 1 N or less, and particularly preferably 0.5 to 0.05 N. The amount of Fe dissolved at the end of the treatment is about 1 to 10 g / l.

  In order to completely remove a small amount of undissolved substances and residual acid components from the surface of the magnet body 3 that has been subjected to acid cleaning, it is preferable to perform cleaning using ultrasonic waves. This ultrasonic cleaning is preferably performed in pure water with very few chlorine ions that generate rust on the surface of the magnet body 3. Moreover, you may perform the same water washing before and after the said ultrasonic cleaning, and in each process of acid cleaning as needed.

(Protective layer)
Next, the protective layer 5 will be described. As described above, the protective layer 5 has a three-layer structure including the first layer 6, the second layer 7, and the third layer 8 in order from the magnet body 3 side.

  The first layer 6 is a layer containing a rare earth element, and the second layer 7 is a layer having a rare earth element content lower than that of the first layer. The first layer 6 and the second layer 7 contain an element derived from the magnet body 3 and oxygen. More specifically, it contains the elements constituting the main phase described above and oxygen in the magnet body 3.

  Here, the element derived from the magnet body 3 is a constituent material of the magnet body 3, particularly a material constituting the main phase of the magnet body 3, and includes at least a rare earth element and a transition element other than the rare earth element, Furthermore, B, Bi, Si, Al, etc. may be included. The first layer 6 and the second layer 7 are not separately attached on the magnet element body 3 by coating or the like, but the element elements of the magnet element body 3 react to cause the magnet element body 3 to react. It is a layer formed on the surface by changing. An example of such a reaction is an oxidation reaction. Therefore, the first and second layers 6 and 7 do not contain a new metal element that does not constitute a magnet body, but may contain a non-metal element such as oxygen or nitrogen.

  The first layer 6 contains a rare earth element derived from the magnet body 3 and oxygen, and more specifically, preferably contains oxygen, a rare earth element, and a transition element other than the rare earth element. For example, when the constituent material of the magnet body 3 is an R—Fe—B type material, the transition element mainly contains Fe, and may contain Co or the like depending on the composition of the constituent material.

  The second layer 7 contains an element derived from the magnet body 3 and oxygen, but has a rare earth element content lower than that of the first layer. For example, when the constituent material of the magnet body 3 is an R—Fe—B type material, the transition element mainly contains Fe, and may contain Co or the like depending on the composition of the constituent material. From the viewpoint of obtaining further excellent corrosion resistance by the second layer 7, the content of the rare earth element in the second layer 7 is preferably not more than half of the content of the rare earth element in the first layer 6. More preferably, the second layer 7 is a layer that does not substantially contain a rare earth element. That is, the second layer 7 is particularly preferably a layer containing oxygen and a transition element other than the rare earth element contained in the magnet body 3.

  The content of each constituent material of the first layer 6 and the second layer 7 is EPMA (X-ray microanalyzer method), XPS (X-ray photoelectron spectroscopy), AES (Auger electron spectroscopy) or EDS (energy dispersion). This can be confirmed using a known composition analysis method such as X-ray fluorescence X-ray spectroscopy. Here, as a mode in which the second layer 7 is “substantially free of rare earth elements”, a mode in which rare earth elements are not detected by the above-described composition analysis method can be considered. That is, in this case, in the second layer 7, the rare earth element content is about the detection limit or less by the composition analysis method.

  The third layer 8 is formed so as to cover the second layer 7 and is a layer mainly composed of a metal salt (metal salt layer). Unlike the first layer 6 and the second layer 7, the third layer 8 is not a layer formed by the reaction of the magnet body 3, but is newly added on the surface of the magnet body 3. It is the layer provided in. Therefore, the third layer 8 does not include an element derived from the magnet body 3. The thickness of the third layer 8 is preferably about 0.01 to 10 μm.

  The third layer 8 composed of this metal salt is particularly a chemical conversion treatment layer formed by subjecting the magnet body 3 formed with the first layer 6 and the second layer 7 to chemical conversion treatment. preferable. Such a chemical conversion treatment layer has, for example, a shape in which a large number of small plate crystals made of a metal salt are attached so as to cover the second layer 7.

  The metal salt constituting the third layer 8 includes at least one metal element selected from the group consisting of Cr, Ce, Mo, W, Mn, Mg, Zn, Si, Zr, V, Ti, and Fe. And those containing these elements and at least one element selected from the group consisting of P, O, C and S are preferred. Specifically, phosphates or sulfates of the above metal elements are preferable, and phosphates are particularly preferable.

  Among these, as the metal salt, at least one element selected from the group consisting of Mo, Ce, Mg, Zr, Mn and W, and at least one element selected from the group consisting of P, O, C and S, In particular, a phosphate or sulfate of the metal element is more preferable, and a phosphate is particularly preferable.

  Examples of the method for forming the protective layer 5 composed of the above layers include the following methods. That is, in a preferable manufacturing method of the protective layer 5, first, the magnet body 3 is heat-treated to form the first layer 6 and the second layer 7 (first step), and then the first layer 6 and The magnet body 3 on which the second layer 7 is formed is subjected to chemical conversion treatment to form a third layer 8 (metal salt layer) containing a metal salt on the surface of the second layer 7 (second step). .

  The first layer 6 and the second layer 7 can be formed by heat-treating (heating) the magnet body 3 in an oxidizing atmosphere containing an oxidizing gas in the first step. In the heat treatment of the first step, among the oxidizing gas partial pressure, the treatment temperature, and the treatment time so that both the first layer 6 and the second layer 7 are formed on the surface of the magnet body 3. Adjust at least one of the following conditions. In the heat treatment, it is more preferable to adjust all three conditions of the oxidizing gas partial pressure, the treatment temperature, and the treatment time.

  Here, the oxidizing atmosphere is not particularly limited as long as it contains an oxidizing gas. For example, the atmosphere, oxygen atmosphere (preferably oxygen partial pressure adjustment atmosphere), water vapor atmosphere (preferably water vapor partial pressure adjustment atmosphere) ) And the like. Examples of the oxidizing gas include oxygen and water vapor. Among these, for example, the water vapor atmosphere is an atmosphere having a water vapor partial pressure of 10 hPa or more, and an inert gas may coexist with the water vapor in the atmosphere. Such inert gas includes nitrogen. By making the oxidizing atmosphere a water vapor atmosphere, the protective layer tends to be formed more easily.

  When adjusting the above conditions, first, the magnet body 3 is heat-treated while appropriately changing the oxidizing gas partial pressure, the processing temperature, and the processing time, and the structure of the surface layer portion of the magnet body 3 and the oxidizing properties are changed. A correlation with at least one of the gas partial pressure, the processing temperature, and the processing time is obtained. Next, based on the correlation, during the heat treatment, the oxidizing gas partial pressure, the treatment temperature, and the treatment are performed so that both the first layer 6 and the second layer 7 are formed on the surface of the magnet body 3. Adjust at least one condition of time.

  In order to form the 1st layer 6 and the 2nd layer 7 by heat processing, it is preferable to adjust processing temperature in the range of 300-550 degreeC, and it is more preferable to adjust in the range of 350-500 degreeC. . When the processing temperature exceeds the upper limit, corrosion of the magnet body 3 tends to occur. On the other hand, when it is less than the lower limit, the first and second layers 6 and 7 tend to be hardly formed.

  Moreover, it is preferable to adjust processing time in the range of 1 minute-24 hours, and it is more preferable to adjust in the range of 5 minutes-10 hours. When the processing time exceeds the upper limit, the magnetic characteristics tend to deteriorate. On the other hand, when it is less than the lower limit, the first and second layers 6 and 7 tend to be hardly formed.

  When the oxidizing atmosphere is a steam atmosphere, first, the magnet body 3 is heat-treated while appropriately changing the steam partial pressure, the processing temperature, and the processing time, and the structure of the surface layer portion of the magnet body 3 and the steam A correlation with at least one of the partial pressure, the processing temperature, and the processing time is obtained. Next, based on the correlation, at least one of the water vapor partial pressure, the processing temperature, and the processing time in the heat treatment so that both the first layer 6 and the second layer 7 are formed on the surface of the magnet body 3. Adjust one condition. At this time, it is preferable to adjust processing temperature and processing time within the above-mentioned range. Moreover, it is preferable to adjust water vapor partial pressure in the range of 10-2000 hPa.

  The total film thickness of the first layer 6 and the second layer 7 is preferably 0.1 to 20 μm, and more preferably 0.1 to 5 μm. If the total film thickness is to be less than 0.1 μm, both the first layer 6 and the second layer 7 tend to be hardly formed. On the other hand, it is difficult to form the first layer 6 and the second layer 7 so that the total film thickness exceeds 20 μm. The film thickness of the second layer 7 is preferably 20 nm or more. When this film thickness is less than 20 nm, the effect of suppressing the corrosion of the first layer 6 becomes insufficient, and the corrosion resistance of the rare earth magnet 1 tends to be lowered.

  As described above, the third layer 8 can be suitably formed by subjecting the surface of the magnet body 3 on which the first and second layers 6 and 7 are formed to chemical conversion. In the chemical conversion treatment, first, the surface of the magnet body 3 after the first and second layers 6 and 7 are formed is cleaned using an alkaline degreasing agent or the like. Next, the magnet element body 3 is subjected to a chemical conversion treatment by, for example, immersing the magnet element body 3 in a chemical conversion treatment solution, thereby forming a third layer 8 made of a chemical conversion treatment layer on the surface of the second layer 7.

  Examples of the chemical conversion treatment liquid used for the chemical conversion treatment include an aqueous solution containing the metal and acid ions constituting the metal salt in the third layer 8 described above. For example, when forming the metal salt layer which consists of the metal phosphate mentioned above as the 3rd layer 8, the chemical conversion liquid containing a metal raw material, phosphoric acid, and an oxidizing agent can be used.

  More specifically, when the third layer 8 made of molybdenum phosphate is formed, the chemical conversion treatment liquid contains molybdate or molybdic acid such as sodium molybdate as a metal raw material, and this is converted to phosphoric acid and oxidation. A combination with an agent can be applied. When the third layer 8 made of cerium phosphate is formed, the chemical conversion treatment liquid includes a cerium salt such as cerium nitrate as a metal raw material, and a combination thereof with phosphoric acid and an oxidizing agent. it can. Examples of the oxidizing agent contained in the chemical conversion treatment liquid include sodium nitrite, sodium nitrate, potassium permanganate, sodium chromate, hydrogen peroxide, and the like.

  The temperature of the chemical conversion treatment liquid in the chemical conversion treatment is not particularly limited, but the chemical conversion treatment liquid is heated to room temperature or higher from the viewpoint of promoting the reaction between the magnet body 3 and the chemical conversion treatment liquid to form the chemical conversion treatment layer in a short time. It is preferable to use it, for example, it is preferable to set it as 30-100 degreeC. Moreover, the time (chemical conversion treatment time) for immersing the magnet body 3 in the chemical conversion treatment liquid is not particularly limited, but is preferably 1 to 60 minutes, and more preferably 2 to 30 minutes. If the chemical conversion treatment time is less than 1 minute, the formation state of the chemical conversion treatment layer tends to be non-uniform, and if it exceeds 60 minutes, the chemical conversion treatment layer becomes too thick and the denseness decreases, resulting in a rare earth magnet to be obtained. Corrosion resistance, etc. may deteriorate.

  Then, after the chemical conversion treatment, the surface of the obtained rare earth magnet 1 is washed with water to sufficiently remove the chemical conversion treatment liquid remaining on the surface, and then the rare earth magnet 1 is heated and dried sufficiently. It is preferable. If the drying is insufficient, the rare earth magnet 1 may be corroded by moisture adhering to the surface. However, the heating temperature at the time of drying is preferably set to a temperature that does not deteriorate the characteristics of the rare earth magnet 1.

  For example, when the chemical conversion treatment as described above is performed on a substrate containing a metal element, the chemical conversion treatment usually proceeds by dissolution of the metal element in the substrate, whereby a stable chemical conversion treatment layer is formed. It is formed. However, when the chemical conversion treatment layer is directly formed on the surface of the magnet body such as the R-TM-B system, the rare earth-rich phase in the magnet body as described above is selectively dissolved. There was a tendency that a chemical conversion treatment layer could not be formed sufficiently. However, in the above-described embodiment, since the chemical conversion treatment is performed after the first and second layers 6 and 7 are formed on the surface of the magnet body 3 containing the rare earth element, such a rare earth-rich material is formed. The selective dissolution of the phase is very difficult to occur. For this reason, in the present embodiment, a metal salt layer (third layer 8) that is a stable chemical conversion treatment layer is formed on the outermost layer of the rare earth magnet 1.

  The rare earth magnet 1 and the method for manufacturing the same according to the preferred embodiment have been described above. In the rare earth magnet 1 having such a configuration, first, the first layer 6 and the second layer 7 are magnet bodies. 3 is formed by the change of the surface, it has a dense structure and excellent adhesion to the magnet body 3. For this reason, the influence of the outside air on the magnet body 3 can be satisfactorily reduced. Further, the third layer 8 which is the outermost protective layer is a stable layer made of a metal salt layer separately provided on the surface of the magnet body 3 (second layer 7). It can exhibit excellent heat resistance that is difficult to obtain with the layer derived from No. 3.

  Conventionally, as the protective layer, a single oxide layer obtained by oxidizing the surface of the magnet body or a resin layer formed by coating or the like on the surface of the magnet body is known. It is difficult to obtain sufficient corrosion resistance with the oxide layer alone, and it is difficult to obtain sufficient heat resistance (specifically, heat resistance that can withstand temperatures exceeding about 120 ° C.) with the resin layer alone. It was. On the other hand, since the rare earth magnet 1 of the present embodiment includes the protective layer 5 having the above-described configuration, it has not only excellent corrosion resistance but also a high temperature of about 200 ° C. required for applications such as a hybrid car motor. It has heat resistance that can withstand.

  In addition, the magnet of this invention is not limited to the thing of embodiment mentioned above, You may change the structure suitably. That is, in the above-described embodiment, the rare earth magnet containing the rare earth element is exemplified as the magnet. However, the present invention is not limited to this, and the present invention can also be applied to a metal magnet not containing the rare earth element.

  Further, the magnet of the present invention does not necessarily have the first and second layers as described above between the magnet body and the metal salt layer. It may have only. Such an oxide layer preferably includes oxygen and an element derived from a magnet body, and a rare earth magnet more preferably includes an element constituting the main phase of the magnet body.

EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to these Examples.
[Manufacture of rare earth magnets]

Example 1
An ingot having a composition of 13.2Nd-1.5Dy-77.6Fe-1.6Co-6.1B (the number represents an atomic percentage) was prepared by powder metallurgy, and this was coarsely pulverized. Thereafter, jet milling with an inert gas was performed to obtain a fine powder having an average particle size of about 3.5 μm. The obtained fine powder was filled in a mold and molded in a magnetic field. Next, after sintering in vacuum, heat treatment was performed to obtain a sintered body. The obtained sintered body was cut into a size of 35 mm × 19 mm × 6.5 mm and processed to obtain a magnet body processed into a practical shape.

Next, the obtained magnet body was immersed in a 2% HNO ₃ aqueous solution for 2 minutes and then subjected to ultrasonic water washing. Then, the magnet body subjected to the acid cleaning (acid treatment) was heat-treated at 450 ° C. for 8 minutes in an oxygen-nitrogen mixed atmosphere having an oxygen partial pressure of 70 hPa (oxygen concentration 7%).

  Then, the magnet body after the heat treatment is immersed for 10 minutes in a chemical conversion treatment solution at 70 ° C. containing 0.1 M sodium molybdate, 1.0 M phosphoric acid and 0.05 M sodium nitrite. A chemical conversion treatment was performed to form a chemical conversion treatment layer on the surface.

  The obtained rare earth magnet was thinned using a focused ion beam processing apparatus, and the film structure near the surface was observed with a transmission electron microscope (JEM-3010 made by JEOL). On the surface of the magnet body, It was confirmed that two layers, a layer having an average film thickness of 2.5 μm and a layer having an average film thickness of 80 nm, were formed in this order from the magnet body side between the magnet body and the chemical conversion treatment layer. As a result of analyzing elements contained in these two layers using EDS (Voyager III manufactured by Noraan Instruments), Nd, Fe, O are detected as main components from the layer on the magnet body side, and the chemical conversion treatment layer Fe and O were detected from the side layer, and Nd was not detected.

(Example 2)
First, in the same manner as in Example 1, after producing a magnet body, acid cleaning was performed. Next, heat treatment was performed at 450 ° C. for 8 minutes in an oxygen-nitrogen mixed atmosphere with an oxygen partial pressure of 70 hPa (oxygen concentration 7%). Here, the film structure in the vicinity of the surface of the magnet body after the heat treatment was analyzed by depth direction analysis by Auger electron spectroscopy. For Auger electron spectroscopy, SAM680 manufactured by ULVAC-PHI was used. As a result, a layer containing Fe and O and not detecting Nd is formed at a depth of 80 nm from the surface, and a layer containing Nd, Fe and O is formed 2.5 μm below this layer. It was confirmed.

  Thereafter, the magnet body after the heat treatment is immersed in a chemical conversion solution at 80 ° C. containing 0.1 M cerium nitrate, 1.0 M phosphoric acid and 0.05 M sodium nitrite for 10 minutes to form a chemical with respect to the magnet body. The treatment was performed to form a chemical conversion treatment layer on the surface.

(Comparative Example 1)
A magnet body was formed in the same manner as in Example 1, acid washed, and then heat treated to obtain a rare earth magnet. When the obtained rare earth magnet was observed with a transmission electron microscope in the same manner as in Example 1, a layer having an average film thickness of 5 μm was formed on the surface of the magnet body between the magnet body and the oxide layer. In addition, it was confirmed that two layers of an average film thickness of 80 nm were formed in order from the magnet body side. As a result of analyzing the elements contained in these two layers using EDS, Nd, Fe, O are detected as main components from the layer on the magnet body side, and Fe, from the layer on the oxide layer side. O was detected and Nd was not detected.
[Characteristic evaluation]

(Salt spray test)
In accordance with JIS K5600-7-1, a salt spray test in which 5% salt water was sprayed at 35 ° C. for 96 hours was performed on the rare earth magnets of Examples 1 and 2 and Comparative Example 1. As a result, rust was not generated in the rare earth magnets of Examples 1 and 2, whereas rust was generated in the rare earth magnet of Comparative Example 1.

(Heat resistance test)
An immersion test was conducted in which the rare earth magnets of Examples 1 and 2 and Comparative Example 1 were immersed in ATF (Automission Transfer Field) manufactured by Nippon Oil Corporation under the conditions of 200 ° C. and 1000 hours. As a result, the rare earth magnets of Examples 1 and 2 all had a magnetic flux deterioration after immersion of 0.2% or less, whereas the rare earth magnet of Comparative Example 1 was 5.3%.

  From the results of the above salt water spray test and heat resistance test, it was confirmed that the rare earth magnets of Examples 1 and 2 were excellent in both corrosion resistance and heat resistance characteristics.

It is a model perspective view which shows the rare earth magnet of this embodiment. It is a figure which shows typically the cross-sectional structure which follows the II-II line | wire of the rare earth magnet shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Rare earth magnet, 3 ... Magnet base body, 5 ... Protective layer, 6 ... 1st layer, 7 ... 2nd layer, 8 ... Metal salt layer.

Claims (10)

A metal magnet body, and a protective layer formed on the surface of the metal magnet body,
The said protective layer has an oxide layer which covers the said metal magnet base, and a metal salt layer which covers the said oxide layer, The magnet characterized by the above-mentioned. A metal magnet body, and a protective layer formed on the surface of the metal magnet body,
The protective layer includes a first layer that covers the metal magnet body and contains a rare earth element; a second layer that covers the first layer and has a rare earth element content less than the first layer; And a metal salt layer covering the second layer.   3. The magnet according to claim 2, wherein a content of the rare earth element in the second layer is not more than half of a content of the rare earth element in the first layer.   The magnet according to claim 2 or 3, wherein the second layer contains a transition element and oxygen. The metal magnet body includes a rare earth element and a transition element other than the rare earth element,
The first layer contains the rare earth element, the transition element and oxygen,
5. The second layer according to claim 2, wherein the second layer contains the transition element and oxygen, and the content of the rare earth element is smaller than that of the first layer. Magnet.   The rare earth element in the first layer, the transition element in the first layer, and the transition element in the second layer are elements derived from the metal magnet body. 5. The magnet according to 5.   The rare earth element in the first layer, the transition element in the first layer, and the transition element in the second layer are elements constituting the main phase of the metal magnet body. The magnet according to claim 5.   The metal salt layer is composed of at least one element selected from the group consisting of Cr, Ce, Mo, W, Mn, Mg, Zn, Si, Zr, V, Ti, and Fe, and P, O, C, and S. The magnet according to claim 1, comprising at least one element selected from the group.   The magnet according to claim 1, wherein the metal salt layer is a layer made of phosphate or sulfate. A method of manufacturing a magnet for forming a protective layer on the surface of a metal magnet body containing a rare earth element,
The metal magnet body is heat-treated to cover the metal magnet body and to contain a rare earth element, and to cover the first layer and to contain less rare earth element than the first layer. A first step of forming a second layer;
And a second step of forming a metal salt layer containing a metal salt on the surface of the second layer by subjecting the metal magnet body after the first step to chemical conversion treatment,
In the first step, at least one of an oxidizing gas partial pressure, a processing temperature, and a processing time so that the first layer and the second layer are formed on the surface of the metal magnet body. A method for producing a magnet, characterized in that heat treatment is performed under adjusted conditions.

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