JP4766042B2 - Rare earth magnets - Google Patents

Description

  The present invention relates to a rare earth magnet.

Rare earth magnets are powerful permanent magnets containing rare earth elements and have a sufficiently strong magnetic force even if they are reduced in size, and thus have been widely used for industrial machines. However, heretofore, rare earth magnets have a problem that they are extremely rusted. Therefore, in order to improve the corrosion resistance of rare earth magnets, means for forming a protective layer by metal plating on the magnet surface has been studied. For example, a rare earth magnet (see Patent Document 1) coated with a copper layer, a nickel layer, and a zinc layer (or a tin layer) in order, or a rare earth magnet coated sequentially with a copper layer and a zinc layer (see Patent Document 2). Is disclosed.
JP-A-5-335123 JP 2002-332592 A

  However, further improvement in corrosion resistance is required for rare earth magnets for industrial machines. Then, an object of this invention is to provide the rare earth magnet which has the outstanding corrosion resistance.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have formed a protective layer made of a combination of specific metal layers on the surface of the magnet body, thereby providing a rare earth magnet having excellent corrosion resistance. Has been found to be possible, and the present invention has been completed.

  That is, the present invention comprises a magnet element containing a rare earth element and a protective layer formed on the surface of the magnet element, and the protective layer is at least one selected from the group consisting of copper, nickel and tin. A first layer that is a metal layer that contains zinc, a second layer that is a metal layer that contains zinc, and a third layer that is a metal layer that contains tin, the first layer, the second layer, and the third layer The layers are rare earth magnets provided in this order from the inside. By providing a protective layer comprising such a combination of specific metal layers, the rare earth magnet according to the present invention has excellent corrosion resistance.

  The second layer preferably further contains iron, nickel or tin in addition to zinc, and the third layer preferably further contains nickel in addition to tin. Thereby, the corrosion resistance of the rare earth magnet is further improved.

  According to the present invention, a rare earth magnet having excellent corrosion resistance can be provided. Furthermore, in the rare earth magnet according to the present invention, sufficient corrosion resistance can be obtained even if the protective layer is thin. Therefore, by reducing the protective layer, it is possible to suppress a decrease in magnetic force due to the formation of the protective layer. Therefore, according to the present invention, it is possible to provide a rare earth magnet having both sufficient corrosion resistance and magnetic force.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings as necessary. However, the present invention is not limited to the following embodiments. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios.

  FIG. 1 is a perspective view showing a rare earth magnet according to the present embodiment. FIG. 2 is an end view of the rare earth magnet of FIG. 1 taken along the line II-II. As shown in FIGS. 1 and 2, the rare earth magnet 100 according to the present embodiment includes a magnet body 10 and a protective layer 20 formed on the surface of the magnet body 10.

  The magnet body 10 is a permanent magnet containing a rare earth element, iron (Fe), and boron (B). The magnet body 10 preferably contains at least one rare earth element selected from the group consisting of Nd, Pr, Ho, and Tb. Thereby, the magnetic characteristics of the magnet body 10 are enhanced. Among them, it is preferable to contain Nd because particularly high magnetic properties can be obtained. Furthermore, the magnet body 10 may contain Dy as an additive in order to increase the coercive force (iHc).

  The content of the rare earth element is preferably 8 to 40 atomic% with respect to the total amount of atoms constituting the magnet body 10, and 18 to 65 mass% with respect to the total mass of the magnet body 10. Is preferred. If the content of the rare earth element is less than 8 atomic% or less than 18% by mass, the crystal system becomes a cubic crystal having the same structure as that of α-iron, so that it is difficult to obtain a sufficient coercive force. On the other hand, when the content ratio of the rare earth element exceeds 40 atomic% or 65 mass%, the rare-earth rich phase that is a nonmagnetic phase increases, so that a sufficient residual magnetic flux density (Br) tends to be hardly obtained.

  The content ratio of iron is preferably 42 to 90 atomic% with respect to the total amount of atoms constituting the magnet element body 10, and is preferably 28 to 85 mass% with respect to the total mass of the magnet element body 10. If the iron content is less than 42 atomic% or less than 28% by mass, sufficient coercive force tends to be difficult to obtain, and if it exceeds 90 atomic% or 85% by mass, sufficient residual magnetic flux density is obtained. It tends to be difficult.

  A part of iron may be substituted with cobalt (Co). Thereby, it tends to be possible to improve the temperature characteristics without impairing the magnetic characteristics. In this case, the content ratio of iron and cobalt after substitution is preferably such that Co / (Fe + Co) is 0.5 or less on an atomic basis. If the cobalt content is higher than this, sufficient magnetic properties tend to be difficult to obtain.

  The content ratio of boron is preferably 2 to 28 atomic% with respect to the total amount of atoms constituting the magnet body 10, and 0.3 to 6 mass% with respect to the total mass of the magnet body 10. Is preferred. If the boron content is less than 2 atomic% or less than 0.3% by mass, the crystal structure becomes rhombohedral (trigonal), so that sufficient holding power tends to be difficult to obtain, and 28 atomic% or If it exceeds 6 mass%, the boron-rich phase, which is a nonmagnetic phase, increases, so that it is difficult to obtain a sufficient residual magnetic flux density.

  A part of boron may be substituted with at least one element selected from the group consisting of carbon (C), phosphorus (P), sulfur (S), and copper (Cu). Thereby, the productivity of the rare earth magnet 100 is improved, and the production cost tends to be reduced. In this case, the content ratio of C, P, S and / or Cu is preferably 4 atomic% or less with respect to the total amount of atoms constituting the magnet body 10. When the content is greater than 4 atomic%, sufficient magnetic properties tend to be difficult to obtain.

  Further, from the viewpoint of improving coercive force, improving productivity, and reducing cost, the magnet body 10 is made of 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), It may contain at least one element selected from the group consisting of silicon (Si), gallium (Ga), copper (Cu), and hafnium (Hf). In this case, the content ratio of the element is preferably 10 atomic% or less with respect to the total amount of atoms constituting the magnet body 10. If the content exceeds 10 atomic%, sufficient magnetic properties tend to be difficult to obtain.

  Further, in the magnet body 10, oxygen (O), nitrogen (N), carbon (C), calcium (Ca), and the like as unavoidable impurities are included in the amount of all atoms constituting the magnet body 10. It is often contained in a range of 3 atomic% or less.

The magnet body 10 is manufactured, for example, by the procedure shown in the following (1) to (5).
(1) A desired composition containing the above-described elements is cast by a powder metallurgy method to obtain an ingot.
(2) The obtained ingot is coarsely pulverized to a particle size of about 10 to 100 μm using a stamp mill or the like, and then finely pulverized to a particle size of about 0.5 to 5 μm using a ball mill or the like. Get.
(3) The obtained fine powder is press-molded in a magnetic field to obtain a molded body. At this time, the magnetic field strength is preferably 10 kOe or more, and the molding pressure is preferably about 1 to 5 ton / cm ² .
(4) The obtained molded body was fired at 1000 to 1200 ° C. for about 0.5 to 5 hours in an inert gas atmosphere such as Ar gas, quenched, and then heat treated at 500 to 900 ° C. for 1 to 5 hours. (Aging process) is performed.
(6) The obtained sintered body is processed into a rectangular parallelepiped shape to obtain the magnet body 10. The magnet body 10 has a rectangular parallelepiped shape of 20 × 20 × 2 (mm), for example.

  A protective layer 20 is formed on the surface of the magnet body 10. The protective layer 20 is formed so as to cover the entire surface of the magnet body 10. The protective layer 20 includes a first layer 22, a second layer 24, and a third layer 26 that are provided in order from the inside.

  The first layer 22 is a metal layer containing at least one selected from the group consisting of copper, nickel and tin. For example, the first layer 22 is a metal plating film made of copper, nickel, or tin, or a metal plating film made of a copper alloy, nickel alloy, or tin alloy. Here, the “alloy” means a material containing 0.5% to 50% by mass, more preferably 5% to 40% by mass of another metal element (in the case of a copper alloy, a metal element other than copper). means. Further, in this specification, the “metal plating film consisting of” means that the metal plating film does not completely contain other elements but may contain impurities such as C, S, P, and Si. means. The thickness of the first layer 22 is 2 μm to 10 μm.

  The second layer 24 is a metal layer containing zinc. For example, the second layer 24 is a metal plating film made of a zinc alloy. Here, the “zinc alloy” means that containing 0.5 to 80% by mass, more preferably 0.7 to 77% by mass of a metal element other than zinc. Preferred zinc alloys include zinc-iron alloys (ZnFe), zinc-nickel alloys (ZnNi), and zinc-tin alloys (ZnSn). The second layer 24 may be a metal plating film made only of zinc, but is more preferably a metal plating film made of a zinc alloy as described above because an effect of improving corrosion resistance can be obtained. The thickness of the second layer 24 is 2 μm to 10 μm.

  The third layer 26 is a metal layer containing tin. For example, the third layer 26 is a metal plating film made of a tin alloy. Here, the “tin alloy” means a metal element other than tin containing 0.5% by mass to 50% by mass, more preferably 5% by mass to 40% by mass. A preferable tin alloy is a tin-nickel alloy (SnNi). The third layer 26 may be a metal plating film made only of tin, but is preferably a metal plating film made of a tin alloy as described above because an effect of improving corrosion resistance can be obtained. The thickness of the third layer 26 is 0.2 μm to 5 μm.

  Since the first layer 22, the second layer 24, and the third layer 26 as described above are sequentially provided on the surface of the magnet body 10 from the inside, the rare earth magnet 100 has excellent corrosion resistance. The protective layer 20 may include a further metal layer in addition to the first layer 22, the second layer 24, and the third layer 26. The further metal layer may be the same as or different from the first layer 22, the second layer 24, and the third layer 26, and between the magnet body 10 and the first layer 22, the first layer 22 and the second layer. It may be provided between the layer 24, between the second layer 24 and the third layer 26, or outside the third layer 26.

The protective layer 20 is formed on the surface of the magnet body 10 by the procedure shown in the following (1) to (3), for example.
(1) The pre-treated magnet body 10 is immersed in a plating bath containing at least one metal ion selected from the group consisting of copper, nickel, and tin, and subjected to electroplating treatment. A plating film (first layer 22) is formed on the surface of the film.
(2) By washing the magnet obtained by the above procedure and having the first layer 22 formed on the surface of the magnet body 10 with water and then immersing it in a plating bath containing zinc ions, and performing electroplating treatment. Then, a plating film (second layer 24) is formed on the surface of the first layer 22.
(3) The magnet obtained by the above procedure and having the first layer 22 and the second layer 24 formed on the magnet body 10 is washed with water and then immersed in a plating bath containing tin ions to perform electroplating treatment. By doing so, a plating film (third layer 26) is formed on the surface of the second layer 24.
In this way, the protective layer 20 including the first layer 22, the second layer 24, and the third layer 26 is formed on the surface of the magnet body 10.

  The rare earth magnet 100 is obtained by forming the protective layer 20 according to the above procedure on the surface of the magnet body 10 manufactured by the above procedure.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

(Manufacture example 1) Magnet body The ingot which consists of the following compositions containing rare earth elements was produced by the powder metallurgy method.
Composition Fe (iron): 68.6% by mass
Nd (neodymium): 27.4% by mass
Dy (Dysprosium): 3% by mass
B (boron): 1% by mass

  The obtained ingot was coarsely pulverized by a stamp mill and then finely pulverized by a ball mill to obtain a fine powder having the above composition. The fine powder was filled in a mold and press-molded in a magnetic field. The obtained molded body was fired at 1100 ° C. for 1 hour, then rapidly cooled, and subjected to an aging treatment in an Ar gas atmosphere at 600 ° C. for 2 hours. The obtained sintered body was processed into a 20 × 20 × 2 (mm) rectangular parallelepiped shape, and further chamfered by barrel polishing to obtain a magnet body.

Example 1 Cu / Zn / Sn
Pretreatment The following processes (1) to (6) were sequentially performed on the magnet body obtained in Production Example 1.
(1) Alkali degreasing treatment (2) Washing with water (3) Acid washing treatment with nitric acid solution (4) Washing with water (5) Smut removal treatment with ultrasonic washing (6) Washing with water In this way, a pretreated magnet body is obtained. It was.

Plating treatment A first plating bath having the following composition and conditions was prepared.
Composition Potassium pyrophosphate: 200 g / L
Copper pyrophosphate trihydrate: 10 g / L
Potassium citrate: 60 g / L
28% ammonia water: 1 mL / L
Condition pH: 10.5
Temperature: 40 ° C

The pretreated magnet body was immersed in the first plating bath and subjected to electroplating. The electroplating process was performed by barrel plating at a current density of 0.2 A / dm ² until a 5 μm-thick plating film (hereinafter referred to as “first layer”) was formed on the surface of the magnet body. In this way, a magnet (hereinafter referred to as “magnet 1”) having the first layer formed on the surface of the magnet body was obtained. Next, the magnet 1 was washed with water.

A second plating bath having the following composition and conditions was prepared.
Composition: Zinc oxide: 20 g / L
Sodium hydroxide: 150 g / L
Condition pH: 12.5
Temperature: 30 ° C

  The magnet 1 washed with water is immersed in the second plating bath, and an electroplating process similar to the above is performed to form a plating film (hereinafter referred to as “second layer”) having a thickness of 8 μm on the surface of the first layer. I went until. Thus, a magnet (hereinafter referred to as “magnet 2”) in which the first layer and the second layer were formed on the magnet body was obtained. Next, the magnet 2 was washed with water.

A third plating bath having the following composition and conditions was prepared.
Composition Potassium stannate: 100 g / L
Potassium hydroxide: 10g / L
Condition pH: 11.0
Temperature: 60 ° C

  The water-washed magnet 2 is immersed in the third plating bath, and a plating film (hereinafter referred to as “third layer”) having a thickness of 2 μm is formed on the surface of the second layer by electroplating similar to the above. I went until. In this way, a rare earth magnet was obtained in which a protective layer composed of the first layer, the second layer, and the third layer was formed on the magnet body. The obtained rare earth magnet was pure, washed, and dried as a sample. As a result of observing the sample by EPMA (Electron Probe Microanalysis), it was confirmed that the first layer was composed of uniform Cu, the second layer was composed of uniform Zn, and the third layer was composed of uniform Sn.

Corrosion Resistance Evaluation The obtained sample was subjected to a salt spray test (SST) in which 35 ° C. salt water (50 g / L) was sprayed for a predetermined time based on JIS (JIS Z 2371). The appearance change of the sample before and after the test was visually observed. The observation results are shown in Table 1. In Table 1, “A”, “B”, and “C” mean the following states. “White rust” is an oxidation product of Zn, and “red rust” is caused by corrosion of the magnet body.
A: No change in appearance B: White rust C: Red rust

Further, the residual magnetic flux density Br and the coercive force iHc of the sample before and after the test were measured with a vibrating sample magnetometer (VSM). Based on the obtained measurement value, the maximum energy product (BH) max in the sample before and after the test was calculated. Furthermore, the decrease rate of (BH) max before and after the test was calculated by the following formula. The results are shown in Table 1. In addition, it is evaluated that the corrosion resistance of a sample is so favorable that this fall rate is small.
(Formula) Reduction rate (%) = (Before test (BH) max−After test (BH) max) / Before test (BH) max

(Example 2) Cu / ZnFe / Sn
A sample was obtained in the same manner as in Example 1 except that the second plating bath had the following composition and conditions.
Composition: Zinc oxide: 20 g / L
Ferrous sulfate hexahydrate: 2g / L
Sodium hydroxide: 120 g / L
Condition pH: 12.0
Temperature: 35 ° C

  As a result of observing the obtained sample with EPMA, it was confirmed that the first layer was composed of uniform Cu, the second layer was composed of a ZnFe alloy having a uniform composition, and the third layer was composed of uniform Sn. The Zn content in the ZnFe alloy was 99.2% by mass. The same corrosion resistance evaluation as that of Example 1 was performed on this sample. The results are shown in Table 1.

Example 3 Cu / ZnNi / Sn
A sample was obtained in the same manner as in Example 1 except that the second plating bath had the following composition and conditions.
Composition: Zinc chloride: 100 g / L
Nickel chloride hexahydrate: 140 g / L
Ammonium chloride: 200 g / L
28% aqueous ammonia: 10 mL / L
Condition pH: 5.5
Temperature: 35 ° C

  As a result of observing the obtained sample with EPMA, it was confirmed that the first layer was composed of uniform Cu, the second layer was composed of a ZnNi alloy having a uniform composition, and the third layer was composed of uniform Sn. The Zn content in the ZnNi alloy was 86% by mass. The same corrosion resistance evaluation as that of Example 1 was performed on this sample. The results are shown in Table 1.

(Example 4) Ni / ZnNi / Sn
A sample was obtained in the same manner as in Example 3 except that the first plating bath had the following composition and conditions.
Composition Nickel sulfate hexahydrate: 300 g / L
Nickel chloride hexahydrate: 45 g / L
Boric acid: 35 g / L
Condition pH: 4.0
Temperature: 45 ° C

  As a result of observing the obtained sample with EPMA, it was confirmed that the first layer was made of uniform Ni, the second layer was made of a ZnNi alloy having a uniform composition, and the third layer was made of uniform Sn. The Zn content in the ZnNi alloy was 86% by mass. The same corrosion resistance evaluation as that of Example 1 was performed on this sample. The results are shown in Table 1.

(Example 5) Cu / ZnSn / Sn
A sample was obtained in the same manner as in Example 1 except that the second plating bath had the following composition and conditions.
Composition Tin pyrophosphate: 20 g / L
Zinc pyrophosphate: 40 g / L
Potassium pyrophosphate: 250 g / L
Gelatin: 1g / L
Condition pH: 9.0
Temperature: 60 ° C

  As a result of observing the obtained sample with EPMA, it was confirmed that the first layer was composed of uniform Cu, the second layer was composed of a ZnSn alloy having a uniform composition, and the third layer was composed of uniform Sn. The Zn content in the ZnSn alloy was 25% by mass. The same corrosion resistance evaluation as that of Example 1 was performed on this sample. The results are shown in Table 1.

(Example 6) Ni / Zn / Sn
A sample was obtained in the same manner as in Example 1 except that the first plating bath had the same composition and conditions as those of the first plating bath in Example 4. As a result of observing the obtained sample with EPMA, it was confirmed that the first layer was composed of uniform Ni, the second layer was composed of uniform Zn, and the third layer was composed of uniform Sn. The same corrosion resistance evaluation as that of Example 1 was performed on this sample. The results are shown in Table 1.

(Example 7) Sn / Zn / Sn
A sample was obtained in the same manner as in Example 1 except that the first plating bath had the following composition and conditions.
Composition Stannic chloride dihydrate: 35 g / L
Potassium pyrophosphate: 150 g / L
Condition pH: 9.0
Temperature: 40 ° C

  As a result of observing the obtained sample with EPMA, it was confirmed that the first layer was composed of uniform Sn, the second layer was composed of uniform Zn, and the third layer was composed of uniform Sn. The same corrosion resistance evaluation as that of Example 1 was performed on this sample. The results are shown in Table 1.

(Example 8) Cu / Zn / SnNi
A sample was obtained in the same manner as in Example 1 except that the third plating bath had the following composition and conditions.
Composition Nickel chloride hexahydrate: 30 g / L
Stannic chloride dihydrate: 30 g / L
Potassium pyrophosphate: 200 g / L
Glycine: 20 g / L
28% ammonia water: 5 mL / L
Condition pH: 8.0
Temperature: 50 ° C

  As a result of observing the obtained sample with EPMA, it was confirmed that the first layer was composed of uniform Cu, the second layer was composed of uniform Zn, and the third layer was composed of a SnNi alloy having a uniform composition. The Sn content in the SnNi alloy was 25% by mass. The same corrosion resistance evaluation as that of Example 1 was performed on this sample. The results are shown in Table 1.

(Example 9) Ni / Zn / SnNi
A sample was obtained in the same manner as in Example 8, except that the first plating bath had the same composition and conditions as those of the first plating bath in Example 4. As a result of observing the obtained sample with EPMA, it was confirmed that the first layer was made of uniform Ni, the second layer was made of uniform Zn, and the third layer was made of SnNi alloy having a uniform composition. The Sn content in the SnNi alloy was 25% by mass. The same corrosion resistance evaluation as that of Example 1 was performed on this sample. The results are shown in Table 1.

(Comparative Example 1) Cu / Ni / Sn
The second plating bath has the same composition and conditions as the first plating bath of Example 4, except that the thickness of the first layer is 10 μm, the thickness of the second layer is 5 μm, and the thickness of the third layer is 5 μm. A sample was obtained in the same manner as in Example 1. As a result of observing the obtained sample with EPMA, it was confirmed that the first layer was composed of uniform Cu, the second layer was composed of uniform Ni, and the third layer was composed of uniform Sn. The same corrosion resistance evaluation as that of Example 1 was performed on this sample. The results are shown in Table 1.

Comparative Example 2 Cu / Ni / Zn
A sample was obtained in the same manner as in Comparative Example 1 except that the third plating bath had the same composition and conditions as those of the second plating bath in Example 1. As a result of observing the obtained sample with EPMA, it was confirmed that the first layer was made of uniform Cu, the second layer was made of uniform Ni, and the third layer was made of uniform Zn. The same corrosion resistance evaluation as that of Example 1 was performed on this sample. The results are shown in Table 1.

(Comparative Example 3) Cu / Ni
A sample was obtained in the same manner as in Comparative Example 1 except that the third layer was not formed. As a result of observing the obtained sample with EPMA, it was confirmed that the first layer was made of uniform Cu and the second layer was made of uniform Ni. The same corrosion resistance evaluation as that of Example 1 was performed on this sample. The results are shown in Table 1.

(Comparative Example 4) Cu / Zn
A sample was obtained in the same manner as in Comparative Example 3 except that the second plating bath had the same composition and conditions as those of the second plating bath of Example 1 and the thickness of the second layer was 10 μm. As a result of observing the obtained sample with EPMA, it was confirmed that the first layer was made of uniform Cu and the second layer was made of uniform Zn. The same corrosion resistance evaluation as that of Example 1 was performed on this sample. The results are shown in Table 1.

  Table 2 summarizes the metal types and thicknesses of the three-layer plating films constituting the protective layer for the samples obtained in Examples 1 to 9 and Comparative Examples 1 to 4.

  As shown in Table 1, in Comparative Examples 1 to 4, red rust due to corrosion of the magnet body was observed 48 hours to 336 hours after the start of the salt spray test (SST), and the (BH) max reduction rate was 3 On the other hand, in Examples 1 to 9, no red rust was observed at all after 672 hours, and the (BH) max reduction rate was less than 0.4%. From this, it became clear that the rare earth magnets according to the present invention obtained in Examples 1 to 9 have better corrosion resistance than the rare earth magnets obtained in Comparative Examples 1 to 4.

  In Example 1, red rust was observed after 1500 hours from the start of SST, and the (BH) max decrease rate was 3.8%, whereas in Examples 2, 3 and 5, 1500 hours had elapsed. No red rust was observed at all, and the (BH) max reduction rate was 0.3% or less. Therefore, the rare earth magnets obtained in Examples 2, 3 and 5 in which the second layer is made of a zinc alloy is more preferable than the rare earth magnet obtained in Example 1 in which the second layer is made only of zinc. It was revealed that it has excellent corrosion resistance.

  In Examples 1 and 7, red rust was observed after 1000 hours to 1500 hours from the start of SST, and the (BH) max reduction rate was 3.8% or more, whereas in Examples 8 and 9, Even after 1500 hours, no red rust was observed, and the (BH) max reduction rate was 0.2% or less. From this, the rare earth magnets obtained in Examples 8 and 9 in which the third layer is made of a tin alloy are more preferable than the rare earth magnets obtained in Examples 1 and 7 in which the third layer is made only of tin. It was revealed that it has excellent corrosion resistance.

  Furthermore, as shown in Table 2, in Examples 1 to 9, the total thickness of the protective layer is 15 μm, whereas in Comparative Examples 1, 2, and 4, the total thickness of the protective layer is 20 μm. That is, although the rare earth magnets obtained in Comparative Examples 1, 2, and 4 were provided with a thicker protective layer than the rare earth magnets obtained in Examples 1-9, in Examples 1-9 It was shown that the obtained rare earth magnets have better corrosion resistance than the rare earth magnets obtained in Comparative Examples 1, 2, and 4. From this, it is clear that the rare earth magnet according to the present invention can have sufficient corrosion resistance even when the protective layer is thin by having a protective layer made of a combination of specific metal layers. became.

  Since the rare earth magnet according to the present invention has excellent corrosion resistance, it is suitably used as a magnet for industrial machinery. In particular, since it has sufficient corrosion resistance even when the protective layer is made thin, it can be suitably used as a magnet for electric and electronic equipment as a miniaturizable rare earth magnet having both sufficient magnetic force and corrosion resistance.

It is a perspective view which shows the rare earth magnet which concerns on this embodiment. It is an end view which shows the rare earth magnet which concerns on this embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Magnet body, 20 ... Protective layer, 22 ... 1st layer, 24 ... 2nd layer, 26 ... 3rd layer, 100 ... Rare earth magnet.

Claims (3)

A magnet body containing a rare earth element;
A protective layer formed on the surface of the magnet body,
A first layer, wherein the protective layer is a metal layer containing at least one selected from the group consisting of copper, nickel and tin;
A second layer that is a metal layer containing zinc;
A third layer that is a metal layer made of a tin -nickel alloy containing 0.5 mass% to 50 mass% of nickel ,
The rare earth magnet in which the first layer, the second layer, and the third layer are provided in this order from the inside.   The rare earth magnet according to claim 1, wherein the second layer further contains iron, nickel, or tin.   The rare earth magnet according to claim 1 or 2, wherein the second layer is a metal layer made of a zinc-iron alloy or a zinc-tin alloy containing 0.5% by mass to 80% by mass of a metal element other than zinc.

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