JP4770556B2 - magnet - Google Patents

Description

  The present invention relates to a magnet in which a coating layer is formed on a magnet body containing rare earth.

  Since rare earth magnets have high performance, they are widely used for motors and actuators of various devices. In particular, R-Fe-B rare earth magnets (where R is a Y element or a rare earth element) have high magnetic properties and a relatively inexpensive raw material is used, so the application range is widened. .

  However, since this rare earth magnet contains rare earth elements that are easily oxidized and iron as main components, the corrosion resistance is relatively low, and degradation of performance, variation, and the like are problems. Therefore, a method for improving the corrosion resistance by subjecting the magnet body to a surface treatment such as plating or vapor deposition has been proposed. In particular, Ni plating is widely used because it is inexpensive and relatively excellent in corrosion resistance.

  However, the Ni plating has good adhesion to the magnet body, but has a problem that the corrosion resistance is not sufficient in an environment where high reliability is required, and the scratch resistance is inferior. In addition, when the plating thickness is increased to improve the corrosion resistance, there is a problem in that the stress generated in the plating layer causes a crack at the magnet interface and induces peeling of the plating, and conversely, the corrosion resistance is inferior. . For this reason, a method is adopted in which Cu having good adhesion to the magnet body is directly plated on the magnet body, and Ni or Ni alloy is further plated thereon to improve the corrosion resistance ( For example, Patent Documents 1 and 2).

  For example, in Patent Document 1, a Cu layer and a Ni—P alloy layer are formed on an R—Fe—Co—B type rare earth magnet (where R is at least one kind of rare earth element including Y). In Patent Document 2, an R-T-B rare earth magnet (where R is at least one rare earth element including Y and T is Fe or Fe and Co), a Cu-Ni alloy layer, Is forming.

  By the way, when designing a magnetic circuit with a rare earth magnet and a coil, it is necessary to obtain a high magnetic flux in the magnetic circuit. For this purpose, the distance between the surface of the rare earth magnet and the coil, that is, the gap between the nonmagnetic portions is set. It needs to be small. However, in Patent Documents 1 and 2, since the plating layer formed on the surface of the rare earth magnet element is non-magnetic, the distance between the rare earth magnet and the coil is increased by the thickness of the plating layer. Become. As a result, there is a problem that the magnetic flux obtained in the magnetic circuit is reduced.

For this reason, for example, it is excellent in corrosion resistance and scratch resistance in order to be applied to applications that require high reliability and high performance such as a voice coil motor for driving a head of a hard disk drive, and furthermore it is possible to suppress a decrease in magnetic flux. There has been a need for rare earth magnets.
JP-A-1-42805 JP 2002-332592 A

  The present invention has been made in view of such a situation, and an object thereof is to provide a magnet that can obtain a high magnetic flux and is excellent in scratch resistance and corrosion resistance even when, for example, a coil and a magnetic circuit are formed. That is.

  As a result of intensive studies to achieve the above object, the present inventors formed a first coating layer containing a magnetic metal on the surface of a magnet containing a rare earth, and further formed a second coating layer containing a copper alloy. By forming, it is found that the adhesion between the magnet body and the coating layer can be maintained, a high magnetic flux can be obtained in the magnetic circuit, and further, a magnet having excellent scratch resistance and corrosion resistance can be obtained. The present invention has been completed.

That is, the magnet according to the present invention is
A magnet body containing a rare earth element;
A first coating layer formed on a surface of the magnet body;
A magnet having a second coating layer laminated on the first coating layer,
The first coating layer includes a magnetic metal;
The second coating layer includes a Cu alloy.

  When the first coating layer contains a magnetic metal, a high magnetic flux can be obtained in the magnetic circuit while maintaining adhesion with the magnet body. Furthermore, a magnet excellent in scratch resistance and corrosion resistance can be obtained by using the second coating layer as a Cu alloy. In addition, although it is preferable that the 1st coating layer formed in a magnet element body covers the whole magnet element body without a gap, it does not necessarily need to coat | cover the whole magnet element body. The same applies to the second coating layer.

  Preferably, the Cu alloy is an alloy of Cu and at least one metal selected from Ni, Sn, Zn and Fe. Since an alloy of Cu and the above metal has sufficient hardness, a magnet having excellent scratch resistance can be obtained by forming the second coating layer of an alloy of Cu and the above metal. Can do. Furthermore, since the alloy of Cu and said metal is excellent also in corrosion resistance, the said magnet can make both flaw resistance and corrosion resistance compatible.

  Preferably, the magnetic metal is Ni or Ni-P alloy. Among magnetic metals, Ni and Ni-P alloys have good adhesion to the magnet body and can be easily formed on the surface of the magnet body.

  Preferably, the thickness of the second coating layer is made thinner than the thickness of the first coating layer. By doing in this way, the effect which improves magnetic flux can be enlarged.

  Preferably, the magnet body includes R (wherein R is one or more selected from rare earth elements including Y element), TM (where TM is a transition element mainly composed of Fe), and B. R-TM-B rare earth magnet.

  By using the R-TM-B rare earth magnet as the magnet body, it is possible to obtain a rare earth magnet having excellent magnetic properties such as magnetic flux in a magnetic circuit and excellent corrosion resistance and scratch resistance.

Hereinafter, the present invention will be described based on embodiments shown in the drawings. put it here,
FIG. 1 is a schematic cross-sectional view of a rare earth magnet according to an embodiment of the present invention.
FIG. 2 is a graph showing only the second quadrant of the magnetic history curve graph showing the relationship between the magnetic field and the magnetic flux density.
Magnet 2

As shown in FIG. 1, in this embodiment, the magnet 2 includes a first covering layer 6 having a thickness T <b> 1 on the surface of the magnet body 4, and a first covering layer 6 on the surface of the first covering layer 6. Two covering layers 8 are formed with a thickness T2.
Magnet element 4

  The magnet body 4 is not particularly limited as long as it is a magnet containing rare earth, but preferably R (where R is one or more of rare earth elements including Y), TM (where TM is mainly composed of Fe). And an R-TM-B rare earth magnet containing B.

  R includes at least one of Nd, Pr, Dy, Ho, and Tb, or one or more of La, Sm, Ce, Gd, Er, Eu, Pm, Tm, Yb, Lu, and Y. Those are preferred.

  In addition, when using 2 or more types of elements as R, mixtures, such as a misch metal, can also be used as a raw material.

  The content of R is preferably 5.5 to 30 atomic%. If the content of R is too small, the crystal structure of the magnet becomes a cubic structure having the same structure as α-Fe, so that a high coercive force (iHc) cannot be obtained. The residual magnetic flux density (Br) is decreased.

  When R is Nd, the corrosion resistance can be improved by substituting part of Nd with Pr. At the same time, the hydrogen occlusion property is also lowered, so that even when hydrogen gas is generated during the plating process, embrittlement of the magnet body due to hydrogen occlusion can be suppressed. In this case, the Pr substitution amount is preferably 1 to 50 atomic% of Nd.

  The TM content is preferably 42 to 90 atomic%. If the TM content is too low, Br decreases, and if it is too high, iHc decreases.

  Note that by replacing part of Fe with Co, the temperature characteristics can be improved without deteriorating the magnetic characteristics. In this case, if the Co substitution amount exceeds 50 atomic% of Fe, the magnetic properties deteriorate, so the Co substitution amount is preferably 50 atomic% or less.

  The content of B is preferably 2 to 28 atomic%. If the B content is too small, the coercive force (iHc) is insufficient because the crystal structure of the magnet has a rhombohedral structure. If the B content is too large, the B-rich nonmagnetic phase increases, resulting in a residual magnetic flux density ( Br) decreases.

  In addition, by replacing a part of B with one or more of C, P, S, and Cu, productivity can be improved and cost can be reduced. In this case, the amount of substitution is preferably 4 atomic% or less. In addition, Al, Ti, V, Cr, Mn, Bi, Nb, Ta, Mo, W, Sb, Ge, Sn, Zr, Ni, Si are used to improve coercive force, improve productivity, and reduce costs. , Hf or the like may be added. In this case, the total amount added is preferably 10 atomic% or less.

  In addition to R, Fe and B, as an inevitable impurity, Ni, Si, Al, Cu, Ca and the like may be contained in 3 atomic% or less of the whole.

The magnet body 4 in the present embodiment has a main phase with a substantially tetragonal crystal structure. The particle size of the main phase is preferably about 1 to 100 μm. And it usually contains 1-50% nonmagnetic phase by volume ratio. The magnet body 4 may be a sintered magnet or a bonded magnet (resin-bonded magnet).
First covering layer 6

  The 1st coating layer 6 will not be specifically limited if it is a magnetic metal (an alloy is also included), and should just have adhesiveness with the magnet element | base_body 4. FIG. Ni or Ni-P alloy is preferable. Ni and Ni-P alloy have good adhesion to the magnet body 4 and can be easily formed on the surface of the magnet body 4 by electrolytic plating or electroless plating. The first covering layer 6 formed on the magnet element body 4 preferably covers the entire magnet element body 4 without a gap, but does not necessarily need to cover the entire magnet element body 4.

  Since the first coating layer 6 has magnetism, a magnetic pole is induced on the surface of the first coating layer 6 by the magnetic field from the magnet body 4. As a result, the magnetic flux in the magnetic circuit can be improved. In addition, when the alloy which comprises the 2nd coating layer 8 mentioned later is made into the 1st coating layer 6, adhesiveness with the magnet element | base_body 4 cannot be obtained, and also the 2nd coating layer 8 is made into Since the alloy which comprises is nonmagnetic, the effect which improves the magnetic flux in a magnetic circuit cannot be acquired. Further, when the second coating layer 8 is the outermost surface, the corrosion resistance is higher when the second coating layer 8 is made of a Cu alloy than when the second coating layer 8 is made of a magnetic metal. Therefore, it is preferable to form the first coating layer 6 on the surface of the magnet body 4 with the first coating layer 6 as a base layer, and further form the second coating layer 8 on the surface of the first coating layer 6.

  When the magnetic metal constituting the first coating layer 6 is a Ni—P alloy, the P content in the Ni—P alloy is preferably 10 atomic% or less, more preferably in order to have magnetism. 7 atomic% or less.

The thickness of the 1st coating layer 6 becomes like this. Preferably it is 1-30 micrometers, More preferably, it is 3-20 micrometers. If the thickness of the first coating layer 6 is too thin, pinholes are generated and sufficient adhesion to the magnet body 4 tends to be difficult to obtain. On the other hand, if the thickness of the first coating layer 6 is too thick, the manufacturing cost in the process of forming the first coating layer 6 tends to increase. There is a tendency for cracks to be generated at the interface, and to induce peeling of the first coating layer 6.
Second coating layer 8

  The second coating layer 8 includes a Cu alloy and serves to protect the magnet element body 4. By including the Cu alloy in the second coating layer, the magnet according to the present embodiment can achieve both scratch resistance and corrosion resistance. Since Cu alone is soft, the performance of protecting the magnet body 4 is low and the scratch resistance is inferior, but by forming an alloy with other metals, the hardness can be increased and the scratch resistance can be improved. Can do. At the same time, the corrosion resistance is improved. An alloy of Cu and at least one metal selected from Ni, Sn, Zn, and Fe is preferable. By making the metal that forms an alloy with Cu the above metal, the hardness of the alloy can be further increased, so that the scratch resistance is remarkably improved while maintaining the corrosion resistance. The second covering layer 8 preferably covers the entire magnet body 4 and the entire first covering layer 6 without any gap, but it is not always necessary to cover the entire magnet body 4 and the entire first covering layer 6. .

  Each composition of the Cu—Ni alloy, Cu—Sn alloy, Cu—Zn alloy and Cu—Fe alloy constituting the second coating layer 8 is not particularly limited, but in order to ensure sufficient scratch resistance and corrosion resistance, The Cu content in the above alloy is preferably as follows. In the Cu—Ni alloy, the Cu content is preferably 10 to 90 atomic%, and more preferably 10 to 80 atomic%. In the Cu—Sn alloy, the Cu content is preferably 10 to 90 atomic%, more preferably 20 to 80 atomic%. In the Cu—Zn alloy, the Cu content is preferably 10 to 90 atomic%, more preferably 10 to 70 atomic%. In the Cu—Fe alloy, the Cu content is preferably 10 to 90 atomic%, and more preferably 30 to 90 atomic%.

The thickness of the 2nd coating layer 8 becomes like this. Preferably, it is 0.5-25 micrometers, More preferably, it is 2-15 micrometers. If the thickness of the second coating layer 8 is too thin, scratch resistance and corrosion resistance tend to be reduced. On the other hand, if the thickness of the second coating layer 8 is too thick, the gap between the surface of the first coating layer 6 and the surface of the magnet 2 increases, and the effect of improving the magnetic flux in the magnetic circuit tends to decrease, The manufacturing cost in the process of forming the second coating layer 8 tends to increase. Further, preferably, the thickness of the second coating layer 8 is thinner than the thickness of the first coating layer 6. By doing in this way, the effect which improves the magnetic flux in a magnetic circuit can be enlarged.
Magnet manufacturing method

  Next, a method for manufacturing the magnet 2 according to this embodiment will be described.

  (1) First, the magnet body 4 is manufactured. It is preferable to use a powder metallurgy method for manufacturing the magnet body 4. Manufacture of the magnet body 4 by powder metallurgy is performed as follows.

  First, an alloy having a desired composition is produced using various alloy manufacturing processes such as a casting method and a strip casting method. Next, the obtained alloy is coarsely pulverized to a particle size of about 10 to 100 μm using a coarse pulverizer such as a jaw crusher, brown mill, or stamp mill, and then finely pulverized by a jet mill, attritor, ball mill, or the like. Finely pulverize to a particle size of about 0.5-5 μm. The obtained powder is then preferably shaped in a magnetic field. The obtained molded body is sintered and rapidly cooled. The atmosphere during sintering is preferably an inert gas such as Ar gas. Thereafter, heat treatment (aging treatment) is preferably performed in an inert gas atmosphere.

  (2) Next, the surface of the obtained magnet body 4 is subjected to alkaline degreasing treatment, and then subjected to chemical etching with an acid to clean the surface of the magnet body 4. By performing this treatment, there is an advantage that the surface of the magnet body 4 can be removed and the first coating layer 6 can be formed reliably. Nitric acid is preferably used as the acid used in the chemical etching. In addition, in order to remove the burr | flash etc. on the surface of the magnet body 4 before alkali degreasing, barrel polishing may be performed.

  After the above acid cleaning treatment is performed, black foreign matter (smut) remains on the surface of the magnet body 4, and it is preferable to remove them by ultrasonic cleaning. Moreover, it is preferable to use a gluconic acid solution for ultrasonic cleaning. Moreover, you may perform the same water washing before and behind the ultrasonic cleaning, and in each process of the said pre-processing as needed.

  (3) Next, the 1st coating layer 6 and the 2nd coating layer 8 are formed in the surface of the magnet body 4 in which the pre-processing mentioned above was performed. The method for forming the first coating layer 6 and the second coating layer 8 is not particularly limited, and may be a method using a gas phase reaction such as vacuum deposition, ion sputtering, or ion plating. For this reason, it is preferable to form by wet plating. In the present embodiment, it is preferable to appropriately select barrel plating or electroless plating in accordance with the composition of the metal or alloy constituting the first coating layer 6 and the second coating layer 8. Specifically, first, the magnet body 4 is immersed in a first plating bath prepared under predetermined conditions, and the first coating layer 6 is formed on the surface of the magnet body 4.

  The 1st plating bath used for forming the 1st coating layer 6 is not specifically limited, What is necessary is just to select suitably according to the metal which comprises a 1st coating layer. For example, when Ni is formed as the first coating layer 6, a Ni watt bath may be used. Moreover, when forming a Ni-P alloy as the 1st coating layer 6, you may perform electroless plating using the 1st plating bath containing nickel sulfate, sodium hypophosphite, etc. Further, the first plating bath may contain a brightener and the like.

  The pH and bath temperature of the first plating bath are not particularly limited, and may be appropriately determined according to the composition of the first plating bath. However, if the pH is too low, rare earth elements such as Nd tend to be dissolved from the magnet body 4 and a desired shape cannot be obtained or the magnetic properties tend to be reduced. If the pH is too high, Fe Is melted from the magnet body 4 and a desired shape cannot be obtained or the magnetic properties tend to be deteriorated. Moreover, when process temperature is too low, there exists a tendency for reaction in a process liquid to be scarce and processability to fall. On the other hand, if the treatment temperature is too high, spots or the like may occur and the aesthetic appearance may be impaired.

  The treatment time in the first plating bath is not particularly limited, and may be appropriately determined according to the desired layer thickness. However, if the treatment time is too short, the treatment liquid does not sufficiently contact the surface of the magnet body 4 and the reaction becomes insufficient, and there is a tendency that the uniform first coating layer 6 cannot be formed. On the other hand, if the treatment time is too long, the thickness of the first coating layer 6 exceeds 30 μm, and the manufacturing cost tends to increase.

  (4) Next, the surface of the first coating layer 6 is subjected to an alkaline degreasing treatment, and then the surface is sufficiently washed with pure water. By performing this treatment, there is an advantage that dirt (organic matter such as a brightening agent) attached to the surface of the first coating layer 6 can be removed and the second coating layer 8 can be formed reliably.

  (5) Next, wet plating is performed on the surface of the first coating layer 6 using the second plating bath to form the second coating layer 8. Specifically, the magnet body 4 on which the first coating layer 6 is formed is immersed in a second plating bath prepared under predetermined conditions to form the second coating layer 8 on the surface of the first coating layer 6. .

  The 2nd plating bath used for forming the 2nd coating layer 8 is not specifically limited, What is necessary is just to select suitably according to the metal which comprises the 2nd coating layer 8. FIG. For example, when a Cu—Sn alloy is formed as the second coating layer 8, a first plating bath containing copper pyrophosphate, stannous pyrophosphate, or the like may be used. Further, when a Cu—Zn alloy is formed as the second coating layer 8, a second plating bath containing cuprous cyanide, zinc cyanide, or the like may be used. Further, the second plating bath may contain a brightener and the like.

  The pH and bath temperature of the second plating bath are not particularly limited, and may be appropriately determined according to the composition of the second plating bath. However, when the pH of the second plating bath is too high, the hydroxide tends to eutect and there is a tendency that sufficient hardness cannot be obtained. On the other hand, if the pH of the second plating bath is too low, the plating bath tends to become unstable. Moreover, when process temperature is too low, there exists a tendency for reaction in a process liquid to be scarce and processability to fall. On the other hand, if the treatment temperature is too high, spots or the like may occur and the aesthetic appearance may be impaired.

  The treatment time in the second plating bath is not particularly limited, and may be appropriately determined according to the desired layer thickness. However, if the treatment time is too short, the treatment liquid does not sufficiently contact the surface of the first coating layer 6, and there is a tendency that the reaction becomes insufficient and the uniform second coating layer 8 cannot be formed. On the other hand, if the treatment time is too long, the thickness of the second coating layer 8 exceeds 25 μm, and the manufacturing cost tends to increase.

  (6) The magnet body 4 on which the second coating layer 8 is formed by being immersed in the second plating bath is washed with pure water and dried. At this time, drying is usually carried out at 80 to 150 ° C. to remove moisture on the surface, but it is also preferable to immerse in alcohol and air dry for simplification of the process.

  (7) By passing through the above process, the magnet 2 which concerns on this embodiment shown in FIG. 1 is manufactured.

  The present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the present invention.

  For example, in the above-described embodiment, the first coating layer is directly formed on the surface of the magnet body, and the second coating layer is directly formed on the surface of the first coating layer, but it is not necessarily formed directly. It is not necessary and may be formed indirectly. That is, another coating layer may be formed between the magnet body and the first coating layer, or another coating layer is formed between the first coating layer and the second coating layer. May be. Alternatively, another coating layer may be formed on the surface of the second coating layer.

Hereinafter, although this invention is demonstrated based on a more detailed Example, this invention is not limited to these Examples.
Example 1

  An ingot having a composition of 27.4Nd-3Dy-1B-68.6Fe (numbers are weight ratios) prepared by powder metallurgy was pulverized by a stamp mill and a ball mill to obtain an alloy fine powder having the above composition. The obtained alloy fine powder was press-molded in a magnetic field to obtain a compact. This molded body was sintered under the conditions of holding temperature: 1100 ° C. and holding time: 1 hour, and subjected to aging treatment under the conditions of Ar gas atmosphere, holding temperature: 600 ° C., holding time: 2 hours, and sintered body Got. The obtained sintered body was processed into a size of 20 × 10 × 1 (mm), and further chamfered by barrel polishing to obtain a magnet body. In addition, the composition by the atomic ratio of this magnet body was 12.4Nd-1.2Dy-6.1B-80.3Fe.

  Next, the sample of the magnet body is subjected to an alkaline degreasing treatment, an acid washing treatment with a nitric acid solution, and an ultrasonic washing treatment with a gluconic acid solution, and the first coating layer is formed by an electroless plating method or a barrel plating method described below. And the 2nd coating layer was formed.

  First, the composition of the first plating bath for forming the first coating layer is as follows: nickel sulfate: 0.075 mol / l, sodium hypophosphite: 0.14 mol / l, sodium citrate: 0.1 mol / l, Ammonium chloride: 0.6 mol / l. The first plating bath was adjusted to pH: 9.5 and bath temperature: 45 ° C. The magnet body obtained above was immersed in this plating bath, and electroless plating was performed until the thickness T1 of the first coating layer became 7 μm.

  Next, the magnet body on which the first coating layer was formed was subjected to the above alkaline degreasing treatment and ultrasonic cleaning treatment, and then a second coating layer was further formed. The composition of the second plating bath for forming the second coating layer is as follows: nickel sulfate: 0.095 mol / l, copper sulfate: 0.005 mol / l, sodium hypophosphite: 0.2 mol / l, sodium citrate : 0.2 mol / l. This second plating bath was prepared at pH 10.0 (adjusted with sodium hydroxide) and bath temperature 80 ° C. The magnet body obtained above was immersed in this plating bath, and electroless plating was performed until the thickness T2 of the second coating layer became 3 μm.

  The magnet on which the first coating layer and the second coating layer were formed was washed with pure water and further dried to obtain a rare earth magnet sample. As a result of observing EPMA (electron probe microanalysis) for the obtained rare earth magnet sample, the Ni-P alloy having a uniform composition in the first coating layer and the Cu-Ni-P alloy having a uniform composition in the second coating layer It was confirmed that Further, the P content in the Ni—P alloy was 6 atomic%, the Cu content in the Cu—Ni—P alloy was 15 atomic%, and the P content was 5 atomic%.

About said rare earth magnet sample, the characteristic evaluation was performed about the adhesiveness and corrosion resistance of a magnet element | base_body and a 1st coating layer with the method shown below.
Adhesion test

About the magnet in which the 1st coating layer and the 2nd coating layer were formed, the adhesiveness of a magnet element | base_body and a 1st coating layer was evaluated by the cross-cut tape method (JIS K5400). That is, a grid pattern (100 locations) with an interval of 1 mm is made in a 1 cm square region of the magnet surface on which the first layer coating and the second coating layer are formed. On top of that, one tape was applied, and when the tape was peeled off, the adhesion was evaluated by the number of locations where the first coating layer did not peel from the magnet body. (Adhesiveness between magnet body and first coating layer) = (location where the first coating layer was not peeled) / 100. For example, when the number of places where the first coating layer is peeled is one in 100 places, the above-mentioned adhesion is 99/100. Adhesiveness made 100/100 favorable. The results are shown in Table 1.
Corrosion resistance test

The corrosion resistance was evaluated by a salt spray test (JIS C0023). The salt water concentration was 5% NaCl and the test temperature was 35 ° C. The surface condition of the sample after being held for 96 hours under the above conditions was visually observed, and bulging due to rust and peeling of the coating layer was observed. A sample in which no rust or blister was observed was designated as “◯”, and a sample in which rust or blister was observed was designated as “x”. Also, 20 samples each before test and 2 samples after test are magnetized at 2T, and the magnetic flux at a position 0.5 mm from the sample surface is measured using a 7-turn search coil and a flux meter. The average value was calculated. From the measured value of the magnetic flux of the sample before the test and the measured value of the magnetic flux of the sample after the test, the decrease rate of the magnetic flux before and after the test was calculated. The decrease rate was 3% or less. The results are shown in Table 1.
Example 2

Magnet body in the same manner as in Example 1 except that the first plating bath for forming the first coating layer and the second plating bath for forming the second coating layer have the following compositions and conditions. The first coating layer and the second coating layer were formed by barrel plating.
First plating bath nickel sulfate: 1.15 mol / l,
Nickel chloride: 0.2 mol / l,
Boric acid: 0.55 mol / l,
pH: 4.0,
Bath temperature: 45 ° C.
Second plating bath nickel sulfate: 0.25 mol / l,
Copper sulfate: 0.01 mol / l,
Glycine: 0.8 mol / l,
pH: 7.0 (adjusted with sodium hydroxide),
Bath temperature: 60 ° C.
It was confirmed by EPMA observation that the obtained sample was made of Ni having a uniform first coating layer and a Cu—Ni alloy having a uniform composition in the second coating layer. Moreover, Cu content in a Cu-Ni alloy was 70 atomic%. Furthermore, the same evaluation as Example 1 was performed about the obtained sample. The results are shown in Table 1.
Example 3

The first plating bath for forming the first coating layer is the same as the first plating bath of Example 2, and the second plating bath for forming the second coating layer has the following composition and conditions. Produced a magnet body in the same manner as in Example 1, and formed the first coating layer and the second coating layer by barrel plating.
Copper pyrophosphate: 0.15 mol / l,
Stannous pyrophosphate: 0.2 mol / l,
Sodium pyrophosphate: 0.6 mol / l,
Ammonium oxalate: 0.15 mol / l,
pH: 9.0 (adjusted with sodium hydroxide),
Bath temperature: 60 ° C.
It was confirmed by EPMA observation that the obtained sample was made of Ni having a uniform first coating layer and a Cu—Sn alloy having a uniform composition in the second coating layer. Moreover, Cu content in a Cu-Sn alloy was 55 atomic%. Furthermore, the same evaluation as Example 1 was performed about the obtained sample. The results are shown in Table 1.
Example 4

The first plating bath for forming the first coating layer is the same as the first plating bath of Example 2, and the second plating bath for forming the second coating layer has the following composition and conditions. Produced a magnet body in the same manner as in Example 1, and formed the first coating layer and the second coating layer by barrel plating.
Cuprous cyanide: 0.2 mol / l,
Zinc cyanide: 0.7 mol / l,
Sodium cyanide: 1.2 mol / l,
pH: 13.0 (adjusted with sodium hydroxide),
Bath temperature: 35 ° C.
It was confirmed by EPMA observation that the obtained sample was made of Ni having a uniform first coating layer and a Cu—Zn alloy having a uniform composition in the second coating layer. Moreover, Cu content in a Cu-Zn alloy was 25 atomic%. Furthermore, the same evaluation as Example 1 was performed about the obtained sample. The results are shown in Table 1.
Example 5

The first plating bath for forming the first coating layer is the same as the first plating bath of Example 2, and the second plating bath for forming the second coating layer has the following composition and conditions. Produced a magnet body in the same manner as in Example 1, and formed the first coating layer and the second coating layer by barrel plating.
Cuprous cyanide: 0.13 mol / l,
Ferrocyan iron: 0.10 mol / l,
Rochelle salt: 0.06 mol / l,
pH: 11.5 (adjusted with potassium hydroxide),
Bath temperature: 60 ° C.
It was confirmed by EPMA observation that the obtained sample was made of Ni having a uniform first coating layer and a Cu—Fe alloy having a uniform composition in the second coating layer. Moreover, Cu content in a Cu-Fe alloy was 85 atomic%. Furthermore, the same evaluation as Example 1 was performed about the obtained sample. The results are shown in Table 1.
Comparative Example 1

The first plating bath for forming the first coating layer is the same as the second plating bath of Example 1, except that the thickness T1 of the first coating layer is 10 μm and the second coating layer is not formed. A magnet body was manufactured in the same manner as in Example 1, and the first coating layer was formed by electroless plating. In the obtained sample, it was confirmed by EPMA observation that the first coating layer was made of a Cu—Ni—P alloy having a uniform composition. Further, the Cu content in the Cu—Ni—P alloy was 15 atomic%, and the P content was 5 atomic%. Furthermore, the same evaluation as Example 1 was performed about the obtained sample. The results are shown in Table 1.
Comparative Example 2

The first plating bath for forming the first coating layer is the same as the second plating bath of Example 2, except that the thickness T1 of the first coating layer is 10 μm and the second coating layer is not formed. A magnet body was manufactured in the same manner as in Example 1, and the first coating layer was formed by barrel plating. In the obtained sample, it was confirmed by EPMA observation that the first coating layer was made of a Cu—Ni alloy having a uniform composition. Moreover, Cu content in a Cu-Ni alloy was 70 atomic%. Furthermore, the same evaluation as Example 1 was performed about the obtained sample. The results are shown in Table 1.
Comparative Example 3

The first plating bath for forming the first coating layer is the same as the second plating bath of Example 3, except that the thickness T1 of the first coating layer is 10 μm and the second coating layer is not formed. A magnet body was manufactured in the same manner as in Example 1, and the first coating layer was formed by barrel plating. In the obtained sample, it was confirmed by EPMA observation that the first coating layer was made of a Cu—Sn alloy having a uniform composition. Moreover, Cu content in a Cu-Sn alloy was 55 atomic%. Furthermore, the same evaluation as Example 1 was performed about the obtained sample. The results are shown in Table 1.
Comparative Example 4

The first plating bath for forming the first coating layer is the same as the second plating bath of Example 4, except that the thickness T1 of the first coating layer is 10 μm and the second coating layer is not formed. A magnet body was manufactured in the same manner as in Example 1, and the first coating layer was formed by barrel plating. In the obtained sample, it was confirmed by EPMA observation that the first coating layer was made of a Cu—Zn alloy having a uniform composition. Moreover, Cu content in a Cu-Zn alloy was 25 atomic%. Furthermore, the same evaluation as Example 1 was performed about the obtained sample. The results are shown in Table 1.
Comparative Example 5

The first plating bath for forming the first coating layer is the same as the second plating bath of Example 5, except that the thickness T1 of the first coating layer is 10 μm and the second coating layer is not formed. A magnet body was manufactured in the same manner as in Example 1, and the first coating layer was formed by barrel plating. In the obtained sample, it was confirmed by EPMA observation that the first coating layer was made of a Cu—Fe alloy having a uniform composition. Moreover, Cu content in a Cu-Fe alloy was 85 atomic%. Furthermore, the same evaluation as Example 1 was performed about the obtained sample. The results are shown in Table 1.
Comparative Example 6

The first plating bath for forming the first coating layer has the following composition and conditions, and the second plating bath for forming the second coating layer is the same as the second plating bath of Example 2. Produced a magnet body in the same manner as in Example 1, and formed the first coating layer and the second coating layer by barrel plating.
Cuprous cyanide: 0.28 mol / l,
Sodium cyanide: 0.7 mol / l,
Sodium carbonate: 0.28 mol / l,
Sodium hydroxide: 0.25 mol / l
pH: 12.5
Bath temperature: 45 ° C.
It was confirmed by observation of EPMA that the obtained sample was made of Cu having a uniform first coating layer and a Cu—Ni alloy having a uniform composition in the second coating layer. Moreover, Cu content in a Cu-Ni alloy was 70 atomic%. Furthermore, the same evaluation as Example 1 was performed about the obtained sample. The results are shown in Table 1.
Comparative Example 7

  The first plating bath for forming the first coating layer is the same as the first plating bath of Example 2, except that the thickness T1 of the first coating layer is 10 μm and the second coating layer is not formed. A magnet body was manufactured in the same manner as in Example 1, and the first coating layer was formed by barrel plating. In the obtained sample, it was confirmed by EPMA observation that the first coating layer was made of uniform Ni. Furthermore, the same evaluation as Example 1 was performed about the obtained sample. The results are shown in Table 1.

  From Table 1, the following can be confirmed. In the samples of Examples 1 to 5, good results were obtained for both adhesion and corrosion resistance. Moreover, since the 1st coating layer is comprised with the magnetic metal, it can confirm that a high magnetic flux can be obtained and the change rate of the magnetic flux before and behind a corrosion resistance test is almost zero.

  On the other hand, the sample of Comparative Examples 1-5 comprises the 1st coating layer by the alloy of the 2nd coating layer of the sample of Examples 1-5, and has not formed the 2nd coating layer. As a result, it is confirmed that the adhesion between the first coating layer and the magnet body is inferior, and further, in the corrosion resistance test, swelling occurs after 24 hours and the corrosion resistance is also inferior. Moreover, since the 1st coating layer is comprised with the nonmagnetic metal, the value of the magnetic flux before a corrosion resistance test is smaller than the sample of Examples 1-5. Furthermore, in the corrosion resistance test, since swelling has occurred, it can be confirmed that the magnetic flux after the test cannot be measured.

  In addition, the sample of Comparative Example 6 in which the first coating layer is Cu and the second coating layer is Cu-Ni has good adhesion to the magnet body and corrosion resistance because the first coating layer is made of Cu. Is about the same as the samples of Examples 1-5. However, since the 1st coating layer is comprised with the nonmagnetic metal, it can confirm that the value of magnetic flux is lower than the sample of Examples 1-5.

  The sample of Comparative Example 7 in which the first coating layer was made Ni and the second coating layer was not formed has good adhesion to the magnet body, but in the corrosion resistance test, it rusted after 48 hours, resulting in corrosion resistance. The result is inferior. Moreover, since the 1st coating layer is comprised with the magnetic metal, the magnetic flux comparable as the sample of Examples 1-5 is obtained before the corrosion resistance test. However, since corrosion occurs in the corrosion resistance test, it can be confirmed that the rate of decrease in magnetic flux before and after the test is increased.

  The reason why the samples of Examples 1 to 5 can obtain a higher magnetic flux than the samples of Comparative Examples 1 to 6 can be described as follows, for example.

  In general, when a magnetic circuit such as a voice coil motor is designed using a rare earth magnet and a coil, a certain distance is designed so that the rare earth magnet and the coil do not contact each other. Here, in the samples of Examples 1 to 5, since the first coating layer is made of a magnetic metal, a magnetic pole is induced on the surface of the first coating layer by the magnetic field from the magnet body. As a result, since the magnetic pole exists on the surface of the first coating layer, the distance between the surface on which the magnetic pole exists and the coil is smaller than when the first coating layer is not made of a magnetic metal. Since the permeance is proportional to the distance between the surface where the magnetic pole exists and the coil, that is, the reciprocal of the gap of the nonmagnetic portion, the permeance Pc of the samples of Comparative Examples 1 to 6 is Pc1, and the samples of Examples 1 to 5 are used. If the permeance Pc is Pc2, the permeance Pc2 of the sample of the example is larger than the permeance Pc1 of the sample of the comparative example.

  Here, the graph which showed only the 2nd quadrant of the graph of the magnetic history curve which shows the relationship between a magnetic field and magnetic flux density is made into FIG. When a straight line (permeance line) passing through the origin with the permeance values (Pc1 and Pc2) as an inclination is drawn, the intersection of the permeance line and the demagnetization curve indicates the magnetic flux density Bd1 corresponding to Pc1 and Pc2 in the above magnetic circuit. And Bd2. In general, the larger the permeance Pc, the larger the magnetic flux density Bd. Therefore, the magnetic flux density Bd2 of the sample of the example is larger than the magnetic flux density Bd1 of the sample of the comparative example. Therefore, the magnetic flux of the sample of the example is also larger than the magnetic flux of the sample of the comparative example.

FIG. 1 is a schematic cross-sectional view of a rare earth magnet according to an embodiment of the present invention. FIG. 2 is a graph showing only the second quadrant of the magnetic history curve graph showing the relationship between the magnetic field and the magnetic flux density.

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 ... Rare earth magnet 4 ... Magnet base body 6 ... 1st coating layer 8 ... 2nd coating layer

Claims (4)

A magnet body containing a rare earth element;
A first coating layer formed on a surface of the magnet body;
A magnet having a second coating layer laminated on the first coating layer,
Wherein the first coating layer made of a magnetic metal,
The second coating layer is made of one Cu alloy selected from a Cu-Ni alloy, a Cu-Sn alloy, a Cu-Zn alloy, and a Cu-Fe alloy,
Cu content of the Cu-Ni alloy is 10 to 80 atomic%,
Cu content of the Cu-Sn alloy is 10 to 90 atomic%,
Cu content of the Cu-Zn alloy is 10-70 atomic%,
Cu content of the Cu-Fe alloy is 30 to 90 atomic%,
A magnet , wherein the thickness of the second coating layer is thinner than the thickness of the first coating layer . The magnet according to claim 1, wherein the magnetic metal is Ni or a Ni—P alloy. The magnet body is R-TM containing R (wherein R is one or more selected from rare earth elements including Y element), TM (where TM is a transition element mainly composed of Fe) and B. magnet according to claim 1 or 2 is -B based rare earth magnet.   The magnet according to any one of claims 1 to 3, wherein the thickness of the second coating layer is 0.5 to 3 µm.

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