JP2012094766A - Rare earth magnet, method of producing rare earth magnet and rotary machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rare earth magnet having excellent corrosion resistance.SOLUTION: A rare earth magnet 100 comprises an R-T-B based magnet element 10 containing a light rare earth element R, a transition metal element T and boron B, and a protective layer 20 covering the surface of the magnet element 10. The protective layer 20 contains R, T and Al, and the magnet element 10 and the protective layer 20 each contain Fe as T. Content of Rin the protective layer 20 is 31-40 atom% for the total amount of R, T and Al in the protective layer 20, content of T in the protective layer 20 is 35-64 atom% for the total amount of R, T and Al in the protective layer 20, and content of Al in the protective layer 20 is 5-25 atom% for the total amount of R, T and Al in the protective layer 20.

Description

  The present invention relates to a rare earth magnet, a method for producing a rare earth magnet, and a rotating machine.

  R-T-B rare earth magnets containing a rare earth element R, a transition metal element T such as iron (Fe) or cobalt (Co), and boron B have excellent magnetic properties (see, for example, Patent Documents 1 to 4). . However, rare earth magnets tend to have low corrosion resistance because they contain rare earth elements that are easily oxidized as the main component. Therefore, in order to improve the corrosion resistance of the rare earth magnet, a protective layer made of resin, plating or the like is often provided on the surface of the magnet body.

JP 2001-196215 A JP-A-62-192566 JP 2002-25812 A International Publication No. 2006/112403 Pamphlet

  However, even a rare earth magnet having a protective layer formed on the surface does not always have complete corrosion resistance. This is because, in a high temperature and high humidity environment, the water vapor permeates the protective layer and reaches the magnet body, thereby causing corrosion of the magnet body.

  The present invention has been made in view of such problems of the prior art, and an object thereof is to provide a rare earth magnet excellent in corrosion resistance and a method for producing the rare earth magnet. Moreover, an object of this invention is to provide the rotary machine which can maintain the outstanding performance over a long period of time.

The present invention comprises an R _L -T-B magnet body containing a light rare earth element R _L , a transition metal element T and boron B, and a protective layer covering the surface of the magnet body, , R _L , T and aluminum (Al), the magnet body and the protective layer each contain Fe as T, and the content of _{RL in} the protective layer is equal to the total amount of _RL , T and Al in the protective layer. On the other hand, it is 31 to 40 atomic%, and the content of T in the protective layer is 35 to 64 atomic% with respect to the total amount of R _L , T and Al in the protective layer, and the content of Al in the protective layer Provides a rare earth magnet with 5 to 25 atomic% based on the total amount of R _L , T and Al in the protective layer.

  According to the present invention, the corrosion resistance of the rare earth magnet is improved.

  The rotating machine of the present invention includes the rare earth magnet of the present invention. A rotating machine including a rare earth magnet having excellent corrosion resistance can maintain excellent performance for a long period of time even when used in a harsh environment.

The method for producing a rare earth magnet according to the present invention includes a step of attaching Al to the surface of an R _L -T-B system magnet body containing a light rare earth element R _L , a transition metal element T, and boron B; Heating the magnet body made at 540 to 630 ° C., and the magnet body contains Fe as T. This makes it possible to obtain the rare earth magnet of the present invention provided with a protective layer containing R _L , T and Al as described above in a predetermined content. The state of the magnet body is not necessarily the same before and after heating with Al deposited. This is because in the heating process, a protective layer is formed by a reaction between Al adhered to the magnet body and the surface portion of the magnet body.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the rare earth magnet excellent in corrosion resistance, and the manufacturing method of a rare earth magnet. Moreover, according to this invention, it becomes possible to provide the rotary machine which can maintain the outstanding performance over a long period of time.

It is a perspective view of the rare earth magnet concerning one embodiment of the present invention. It is the II-II sectional view taken on the line of the rare earth magnet shown in FIG. It is a composition diagram which shows the composition ratio of 3 components of light rare earth elements _RL , transition metal element T, and Al contained in the protective layer with which the rare earth magnet based on this invention is equipped. 2 is a scanning electron microscope (SEM) photograph of a cut surface of the rare earth magnet of Example 1. FIG. It is explanatory drawing which shows the internal structure of the rotary machine which concerns on one Embodiment of this invention.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiments. In the drawings, the same elements are denoted by the same reference numerals.

(Rare earth magnet)
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 that covers the surface of the magnet body 10. The protective layer 20 does not necessarily have to completely cover the surface of the magnet body 10, but preferably covers the surface completely. By completely covering the surface, the corrosion resistance of the rare earth magnet 100 can be further improved.

The magnet body 10 is an R _L -T-B system rare earth magnet including a light rare earth element R _L , a transition metal element T, and boron B. Magnet body 10 is as _{R L,} it is selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm) and europium (Eu) Including at least one. In particular, _RL preferably includes at least one of Nd and Pr. Thereby, the residual magnetic flux density and the coercive force of the rare earth magnet 100 are remarkably improved.

The magnet body 10 may further contain a rare earth element other than the above _RL . That is, the magnet body 10 includes scandium (Sc), yttrium (Y), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium ( It may further contain at least one selected from the group consisting of Yb) and lutetium (Lu). In particular, the magnet body 10 preferably contains Dy or Tb. At this time, it is more preferable that the magnet body 10 contains Dy or Tb at a ratio of 8 wt% or less with respect to the entire magnet body 10 because the coercive force of the rare earth magnet 100 is further improved. The unit “wt%” used in the present embodiment is almost synonymous with “mass%”.

The magnet body 10 includes at least Fe as T. The magnet body 10 preferably contains Co as T. Thereby, the residual magnetic flux density and the coercive force of the rare earth magnet 100 are remarkably improved. The magnet body 10 is made of copper (Cu), nickel (Ni), manganese (Mn), niobium (Nb) from the viewpoints of further improving the coercive force of the rare earth magnet 100, improving productivity, and reducing costs. Other transition metal elements such as zirconium (Zr), titanium (Ti), tungsten (W), molybdenum (Mo), and vanadium (V) may be included. In this specification, T is a transition metal element obtained by removing all the rare earth elements (light rare earth elements _RL and other rare earth elements) described above from elements belonging to Group 3 to Group 11 elements of the periodic table. Shall mean.

The content ratio of _{RL in} the magnet body 10 is preferably 8 to 40% by weight and more preferably 15 to 35% by weight with respect to the entire magnet body 10. When the content ratio of _RL is less than 8% by weight, it tends to be difficult to obtain the rare earth magnet 100 having a high coercive force. On the other hand, when the content ratio of _RL exceeds 40% by weight, the residual magnetic flux density of the rare earth magnet 100 tends to decrease.

  The content ratio of T in the magnet body 10 is preferably 42 to 90% by weight and more preferably 60 to 80% by weight with respect to the entire magnet body 10. If the T content is less than 42% by weight, the residual magnetic flux density of the rare earth magnet 100 tends to decrease, and if it exceeds 90% by weight, the coercive force of the rare earth magnet 100 tends to decrease.

  The ratio of Fe contained in the magnet body 10 is preferably 80 atomic% or more, more preferably 90 atomic% or more, and still more preferably 95 atomic%, with respect to the entire T contained in the magnet body 10. It is less than 100 atomic%. As a result, the rare earth magnet 100 having low manufacturing cost and excellent magnetic characteristics can be obtained. In order to realize desired magnetic characteristics, it is preferable that the magnet body 10 contains Co as Fe and Co as T.

  The content ratio of B in the magnet body 10 is preferably 0.5 to 5% by weight with respect to the entire magnet body 10. If the B content is less than 0.5% by weight, the coercive force of the rare earth magnet 100 tends to decrease. On the other hand, if the B content exceeds 5% by weight, the residual magnetic flux density of the rare earth magnet 100 tends to decrease.

  The magnet body 10 is made of aluminum (Al), gallium (Ga), zinc (Zn), silicon (Si), and bismuth from the viewpoint of improving the coercive force of the rare earth magnet 100, improving productivity, and reducing the cost. Other elements such as (Bi) may be further included.

  The magnet body 10 may include at least one element selected from oxygen (O), nitrogen (N), carbon (C), calcium (Ca), and the like as an unavoidable impurity.

The protective layer 20 that covers the surface of the magnet body 10 contains light rare earth elements R _L , transition metal elements T, and Al as main components. The protective layer 20 includes at least one element selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, and Eu as _RL . In particular, the light rare earth element _RL preferably includes at least one of Nd and Pr. Incidentally, R _L contained in the protective layer 20, or at least one or a R _L contained in the magnet body 10 is coincident. In particular, it is preferable that all types of _RL contained in the protective layer 20 and the magnet body 10 are the same.

The protective layer 20 contains at least Fe as T. The protective layer 20 preferably contains Co as T. By including Co, the corrosion resistance of the rare earth magnet 100 tends to be further improved. Furthermore, the protective layer 20 may contain elements other than R _L , T, and Al. Examples of such elements include O, B, and C.

The composition ratio of the three components R _L , T, and Al in the protective layer 20 is included in the region E in the composition diagram of FIG. That is, the content of R _L , T and Al in the protective layer 20 is such that _RL is 31 to 40 atom% and T is 35 to 64 atoms with respect to the total amount of R _L , T and Al in the protective layer 20. %, And Al is 5 to 25 atomic%. Preferably, R _L is 35 to 38 atomic%. Preferably, T is 40 to 50 atomic%. Preferably, Al is 8 to 22 atomic%. When the protective layer 20 includes the three components R _L , T, and Al in such a composition, the corrosion resistance (particularly, corrosion resistance under high temperature, high humidity, and high pressure conditions) of the rare earth magnet 100 is significantly improved. When the content of _{RL in} the protective layer 20 is too large, the protective layer 20 tends to occlude hydrogen generated by the corrosion reaction. When the content of _RL in the protective layer 20 is too small, the adhesion strength of the protective layer 20 tends to be low. When there is too much content of T in the protective layer 20, the coating property of the protective layer 20 tends to deteriorate. If the T content in the protective layer 20 is too small, the protective layer 20 itself tends to be oxidized. When there is too much content of Al in the protective layer 20, the surface roughness of the protective layer 20 tends to become rough. When the Al content in the protective layer 20 is too small, the sacrificial anticorrosive effect of the protective layer 20 tends to be insufficient.

The total content of the three components R _L , T and Al in the protective layer 20 is preferably 50 to 100 atomic% with respect to the entire protective layer 20. Thereby, the corrosion resistance of the rare earth magnet 100 can be sufficiently improved. Moreover, it is more preferable that it is 80-100 atomic%. Thereby, the corrosion resistance of the rare earth magnet 100 can be further improved sufficiently.

  The thickness D of the protective layer 20 should just be 0.01-30 micrometers, and it is preferable that it is 0.1-15 micrometers. When the thickness D is within the above range, the corrosion resistance and magnet characteristics of the rare earth magnet 100 are likely to be good.

FIG. 4 is an electron micrograph showing an enlarged cross section of the rare earth magnet 100. The interface between the magnet body 10 and the protective layer 20 has a difference in composition between the magnet body 10 and the protective layer 20, and can be determined visually from, for example, an electron micrograph. The interface between the magnet body 10 and the protective layer 20 can be determined by the difference in the content of _RL or Al in the magnet body 10 (main phase) and the protective layer 20. That is, the content of _RL or Al can be determined based on this because the protective layer 20 is higher than the magnet body 10 (main phase). Furthermore, the interface between the magnet body 10 and the protective layer 20 can be determined by the difference in the T content. That is, the content of T can be determined based on this because the magnet body 10 (main phase) is higher than the protective layer 20.

  The composition of each element of the magnet body 10 and the protective layer 20 is measured by, for example, an electron probe microanalyzer (EPMA), laser ablation inductively coupled plasma mass spectrometry (Laser Absorption Inductively Coupled Plasma Mass Spectrometry). LA-ICP-MS), X-ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES), or Energy Dispersive X-ray Spectroscopy Using a known composition analysis method Door can be.

  Furthermore, the rare earth magnet 100 may further include another layer for protecting the rare earth magnet 100 on the surface of the protective layer 20 described above. Examples of such a layer include a resin layer and a plating layer.

  The dimensions of the rare earth magnet 100 are not particularly limited, but the vertical length is 1 to 200 mm, the horizontal length is 1 to 200 mm, and the height is about 1 to 30 mm. In addition, the shape of the rare earth magnet 100 is not limited to the rectangular parallelepiped shown in FIGS. 1 and 2, and may be a ring shape or a disk shape.

(Rare earth magnet manufacturing method)
The method of manufacturing a rare earth magnet according to the present embodiment includes an adhesion step of attaching Al to the surface of an R _L -T-B magnet body including a light rare earth element R _L , a transition metal element T, and boron B; And a heating step of heating the magnet body to which sapphire is attached at 540 to 630 ° C.

In the attaching step, first, an R _L -T-B system magnet body is prepared. This magnet body contains Fe as T. This magnet body can be manufactured as follows, for example.

A raw material alloy is cast to obtain an ingot. As the raw material alloy, an alloy containing R _L , Fe and B may be used. The raw material alloy may further contain an element such as T other than Fe, for example, Co, Cu, Ni, Mn, Nb, Zr, Ti, W, Mo, and V, if necessary. Furthermore, the raw material alloy may contain rare earth elements other than _RL , for example, elements such as Sc, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, if necessary. Furthermore, elements such as Al, Ga, Zn, Si and Bi may be included as necessary. What is necessary is just to adjust the chemical composition of an ingot according to the chemical composition of the main phase of the magnet body to obtain finally.

  The ingot is roughly pulverized by a disk mill or the like to obtain an alloy powder having a particle size of about 10 to 100 μm. The alloy powder is pulverized by a jet mill or the like to obtain an alloy powder having a particle size of about 0.5 to 5 μm. The alloy powder is pressure-molded in a magnetic field. The strength of the magnetic field applied to the alloy powder during molding is preferably 800 kA / m or more. The pressure applied to the alloy powder during molding is preferably about 10 to 500 MPa. As the molding method, either a uniaxial pressing method or an isotropic pressing method such as CIP may be used. The obtained molded body is fired to form a sintered body. The baking temperature should just be about 1000-1200 degreeC. The firing time may be about 0.1 to 100 hours. Firing may be performed a plurality of times. Firing is preferably performed in a vacuum or in an inert gas atmosphere such as Ar gas.

  It is preferable to apply an aging treatment to the sintered body. In the aging treatment, the sintered body may be heated at about 450 to 950 ° C. In the aging treatment, the sintered body may be heated for about 0.1 to 100 hours. The aging treatment may be performed in an inert gas atmosphere. Such an aging treatment further improves the coercivity of the rare earth magnet. The aging treatment may be performed by multi-stage heating. For example, in an aging treatment comprising two stages of heating, the sintered body may be heated at a temperature of 700 ° C. or higher and lower than the firing temperature for 0.1 to 50 hours in the first stage. What is necessary is just to heat a sintered compact at 450-700 degreeC for 0.1 to 100 hours at the 2nd step.

  The sintered body (magnet body) obtained by the above treatment may be processed into a desired shape as necessary. Examples of the processing method include shape processing such as cutting and grinding, and chamfering processing such as barrel polishing.

  The magnet body thus obtained may be appropriately subjected to pretreatment in order to remove surface irregularities and impurities attached to the surface. The pretreatment may be performed on the sintered body (magnet body) or may be performed on the processed magnet body. Examples of the pretreatment include acid cleaning (etching) using an acid solution, cleaning using an alkaline solution, and shot blasting. Among these, acid cleaning is preferable. According to the acid cleaning, it becomes easy to obtain a magnet body having a smooth surface by dissolving and removing irregularities and impurities on the surface of the magnet body, and the protective layer described later can be efficiently formed.

  The acid used in the acid cleaning is preferably nitric acid, which is an oxidizing acid that generates little hydrogen. The concentration of nitric acid in the treatment liquid is preferably 1 N or less, particularly preferably 0.5 N or less. The amount of dissolution of the surface of the magnet body by such acid cleaning is preferably 5 μm or more, preferably 10 to 15 μm in average thickness from the surface. By doing so, the altered layer and the oxide layer due to the processing of the surface of the magnet body can be almost completely removed, and the formation of a protective layer described later can be performed efficiently.

  In addition, after removing the treatment liquid used for the acid cleaning by washing with water after the above acid cleaning, the magnet body is subjected to ultrasonic waves in order to completely remove a small amount of undissolved substances and residual acid components remaining on the surface. It is preferable to carry out ultrasonic cleaning using This ultrasonic cleaning can be performed, for example, in pure water or an alkaline solution with very little chlorine ions that generate rust on the surface of the magnet body. After the ultrasonic cleaning, water cleaning may be performed as necessary.

  Next, Al alone, an Al alloy, or an Al compound is adhered to the surface of the magnet body. Examples of the Al adhesion method include a method in which a coating liquid in which particles (Al powder or the like) made of Al are dispersed is uniformly applied to the entire surface of the magnet body. The particle size of the Al particles is preferably 50 μm or less. When the particle size of the Al particles is too large, there is a problem that it is difficult to form a protective layer due to a reaction with the magnet body. Moreover, it is preferable to make the coating liquid contain a resin binder. By containing the resin binder, the adhesion strength of the particles increases and it becomes difficult to drop off from the surface. Note that Al may be attached to the surface of the magnet body by a technique such as plating or vapor phase. The amount of Al deposited on the surface can be, for example, 0.001 to 5% by weight, preferably 0.01 to 1% by weight, based on the entire magnet body.

  In the heating step, the magnet body with Al attached to the surface is heated at 540-630 ° C. Thereby, the protective layer 20 is formed on the surface of the magnet body. The protective layer 20 is a liquid phase formed by heating, and Al diffuses into the grain boundary phase component (R-rich phase) that has oozed out in the vicinity of the surface of the magnet body. We believe that it is formed by reacting with. When the heating temperature is too high, since the melting point of Al is about 660 ° C., the components of the magnet body may diffuse excessively in the molten Al. As a result, it becomes difficult to form a protective layer having the desired composition, and the corrosion resistance and magnetic properties of the rare earth magnet are deteriorated. If the heating temperature is too low, the grain boundary phase component oozes out to the surface of the magnet body and the diffusion of Al becomes insufficient, and it becomes difficult to form a protective layer, thereby deteriorating the corrosion resistance of the rare earth magnet. Note that the R-rich phase is a phase in which the element having the highest concentration (ratio of the number of atoms) among the elements constituting the phase is R.

  The heating time of the magnet body with Al deposited on the surface is preferably 10 to 600 minutes. When the heating time is too short, there is a tendency that a sufficient protective layer is hardly formed as compared with the case where the heating time is within the above numerical range. When the heating time is too long, Al tends to thermally diffuse not only to the surface of the magnet element body but also to the deep part of the magnet element body as compared with the case where the heating time is within the above numerical range. However, it is possible to obtain the rare earth magnet of the present embodiment even when the heating time is outside the above numerical range.

  In addition, it is preferable to quench rapidly the magnet body heated up in said heating process with the cooling rate of 30 degree-C / min or more. Thereby, it becomes easy to form a protective layer. The cooling rate is more preferably 50 ° C./min or more.

  Moreover, it is preferable to perform the aging treatment similar to the case of the sintered body described above on the rare earth magnet. The coercive force of the rare earth magnet is further improved by the aging treatment. The aging treatment temperature is preferably not higher than the heating temperature required for thermal diffusion of Al. It is preferable to rapidly cool the rare earth magnet heated in the aging treatment at a cooling rate of 30 ° C./min or more. Thereby, the magnetic characteristics of the rare earth magnet are easily improved. The cooling rate is more preferably 50 ° C./min or more.

  After heat-treating the magnet body with Al attached to the surface, unreacted Al or the like remaining on the surface of the rare earth magnet may be removed by washing or blasting.

  The rare earth magnet 100 including the magnet body 10 and the protective layer 20 covering the magnet body 10 can be obtained by the manufacturing method described above. Since the rare earth magnet 100 includes the protective layer 20, it has excellent corrosion resistance. Such a rare earth magnet 100 can maintain excellent magnetic properties over a long period of time even when used in an environment where a corrosive substance exists. The rare earth magnet 100 of this embodiment having such characteristics is suitably used as a permanent magnet for a rotating machine that is required to have excellent corrosion resistance, for example.

(Rotating machine)
FIG. 5 is an explanatory diagram showing the internal structure of the rotating machine (permanent magnet rotating machine) of the present embodiment. The rotating machine 200 of this embodiment is a permanent magnet synchronous rotating machine (SPM rotating machine), and includes a cylindrical rotor 50 and a stator 30 disposed inside the rotor 50. The rotor 50 is provided with a plurality of rare earth magnets 100 so that N poles and S poles are alternated along the inner circumferential surface of the cylindrical core 52 and the cylindrical core 52. The stator 30 has a plurality of coils 32 provided along the inner peripheral surface. The coil 32 and the rare earth magnet 100 are arranged to face each other.

  The rotating machine 200 includes the rare earth magnet 100 according to the above embodiment in the rotor 50. Since the rare earth magnet 100 is excellent in corrosion resistance, it is possible to sufficiently suppress a decrease in magnetic characteristics over time. Therefore, the rotating machine 200 can maintain excellent performance for a long time. The rotating machine 200 can be manufactured by a normal method using normal rotating machine parts for parts other than the rare earth magnet 100.

  The rotating machine 200 may be an electric motor (motor) that converts electric energy into mechanical energy by the interaction between the field by the electromagnet generated by energizing the coil 32 and the field by the rare earth magnet 100. The rotating machine 200 may be a generator that converts mechanical energy into electrical energy by electromagnetic induction interaction between the field by the rare earth magnet 100 and the coil 32.

  Examples of the rotating machine 200 that functions as an electric motor (motor) include a permanent magnet DC motor, a linear synchronous motor, a permanent magnet synchronous motor (SPM motor, IPM motor), and a reciprocating motor. Examples of the motor that functions as a reciprocating motor include a voice coil motor and a vibration motor. Examples of the rotating machine 200 that functions as a generator include a permanent magnet synchronous generator, a permanent magnet commutator generator, and a permanent magnet AC generator. The rotating machine described above is used in automobiles, industrial machines, household appliances, and the like.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail with reference to an Example and a comparative example, this invention is not limited to these Examples.

Example 1
According to the powder metallurgy method, the composition is 22.5 wt% Nd-5.2 wt% Pr-2.7 wt% Dy-0.5 wt% Co-0.3 wt% Al-0.07 wt% Cu-1 An ingot with 0.0 wt% B-balance Fe was prepared. The coarse powder obtained by coarsely pulverizing the ingot was pulverized by a jet mill in an inert gas to obtain a fine powder having an average particle diameter of about 3.5 μm. The fine powder was filled into a mold and pressure molded in a magnetic field to obtain a molded body. After the molded body was fired in vacuum, an aging treatment was performed to obtain a sintered body. The sintered body was cut out and processed to produce a magnet body having dimensions of 13 mm × 8 mm × 2 mm.

Etching was performed by degreasing the surface of the magnet body and then immersing it in a 2% HNO ₃ aqueous solution for 2 minutes, followed by ultrasonic water washing. A coating solution in which Al powder having an average particle size of 17 μm was dispersed was prepared. The coating solution was applied to the surface of the magnet body after etching by dip coating to form a coating film on the entire surface of the magnet body. This coating film was dried at 120 ° C. for 20 minutes. The total amount of Al contained in the coating film formed on the surface of the magnet body was adjusted to 0.12% by weight with respect to the entire magnet body.

  The magnet body having a coating film was heated at 600 ° C. for 60 minutes in an Ar atmosphere, and then rapidly cooled at 50 ° C./minute to diffuse Al in the coating film into the magnet body. The magnet body after heating was aged at 550 ° C. for 1 hour in an Ar atmosphere, and then rapidly cooled at 50 ° C./min. The rare-earth magnet of Example 1 was produced by removing unreacted Al powder remaining on the surface of the magnet body after the aging treatment by ultrasonic cleaning.

(Examples 2 to 12)
In Examples 2 to 12, the total amount of Al contained in the coating film formed on the surface of the magnet body was adjusted to the value (application amount) shown in Table 1 with respect to the entire magnet body. In Examples 2 to 12, a magnet body having a coating film was heated at a temperature (diffusion temperature) shown in Table 1 in an Ar atmosphere. Moreover, in Examples 2-12, the time (diffusion time) which heats the magnet body which has a coating film was adjusted to the time shown in Table 1. In Example 6, after heating the magnet body having a coating film, no aging treatment was performed. Except for the above, the rare earth magnets of Examples 2 to 12 were produced in the same manner as in Example 1.

(Comparative Example 1)
A rare earth magnet of Comparative Example 1 was produced in the same manner as in Example 1 except that the steps after the etching of the surface of the magnet body were not performed. That is, the rare earth magnet of Comparative Example 1 was produced without using Al powder.

(Comparative Example 2)
In Comparative Example 2, the diffusion temperature was 510 ° C. In Comparative Example 2, the aging treatment was not performed after heating the magnet body having the coating film. Except for these matters, a rare earth magnet of Comparative Example 2 was produced in the same manner as in Example 1.

(Comparative Example 3)
A rare earth magnet of Comparative Example 3 was produced in the same manner as in Example 1 except that the diffusion temperature was changed to 680 ° C.

(Comparative Example 4)
By forming a film (protective layer) having a composition of Nd50 atomic% -Al50 atomic% on the entire surface of the magnet body produced by the same method as in Example 1 by using the sputtering method, A rare earth magnet was produced. In Comparative Example 4, the thickness of the coating was 5 μm. The composition of the coating was confirmed by EPMA.

(Comparative Example 5)
By forming a film (protective layer) having a composition of Nd 30 atomic% -Fe 70 atomic% on the entire surface of the magnet body manufactured by the same method as in Example 1 by using the sputtering method, A rare earth magnet was produced. In Comparative Example 5, the thickness of the coating was 5 μm. The composition of the coating was confirmed by EPMA.

(Comparative Example 6)
By forming a coating (protective layer) having a composition of Nd30 atomic% -Fe35 atomic% -Al35 atomic% on the entire surface of the magnet body produced by the same method as in Example 1, using the sputtering method, A rare earth magnet of Comparative Example 6 was produced. In Comparative Example 6, the thickness of the coating was 5 μm. The composition of the coating was confirmed by EPMA.

[SEM observation]
The rare earth magnets of each Example and Comparative Example were cut and the cut surface was polished with a cross section polisher. When the polished surface was observed with an SEM, it was confirmed that a protective layer was formed on the entire surface of the R _L -T-B magnet body in each of the rare earth magnets of Examples and Comparative Examples 3 to 6. . In Comparative Examples 1 and 2, no protective layer was formed. In FIG. 4, the SEM photograph of the cut surface of the rare earth magnet of Example 1 is shown. In addition, the continuous line described in FIG. 4 shows the interface of a magnet body and a protective layer. The average thickness D of the protective layer provided in the rare earth magnets of each Example and Comparative Example 3 was measured using SEM. Table 2 shows the average thickness D of each protective layer.

[Composition analysis]
The rare earth magnets of each Example and Comparative Example were cut, and the elemental composition in the magnet body and the protective layer was confirmed by EPMA. As an EPMA apparatus, JXA-8800 manufactured by JEOL was used. It was confirmed that the magnet bodies of all Examples and Comparative Examples contained Nd, Pr, Dy, Co, Al, Cu, B, and Fe as in the ingot. Table 2 shows the elemental composition of the protective layer of each Example and Comparative Example 3. The numerical values set forth in the _"R L -T-Al ratio" column in Table 2, _R L contained in the protective layer, a content of each T and Al, _R L, T and Al contained in the protective layer Is the ratio to the total amount (100 atomic%). _RL is the total value of the contents of Nd and Pr. T is the total content of Co and Fe. In FIG. 3, the composition diagram which plotted the composition of each protective layer of all the Examples and Comparative Examples 3-6 is shown. Value of each side of the composition diagram is, R _L contained in the protective _layer, a content of each T and Al, the ratio to the total amount of R _L, T and Al contained in the protective layer: is (a unit atomic%) . In FIG. 3, the compositions corresponding to Examples 1 to 12 were plotted with “◯”, and the compositions corresponding to Comparative Examples 3 to 6 were plotted with “Δ”.

[Evaluation of corrosion resistance]
The corrosion resistance of each of the rare earth magnets of Examples 1 to 12 and Comparative Examples 1 to 6 was evaluated by a pressure cooker test (PCT). In PCT, the amount of decrease in the weight of each rare earth magnet was measured after 300 hours from the installation of each rare earth magnet in an environment of 2 atm, temperature of 120 ° C., and humidity of 100% RH. Table 3 summarizes the weight loss (unit: mg / cm ² ) per unit surface area of each rare earth magnet.

  It was confirmed that the amount of weight reduction of the rare earth magnets in each example was significantly smaller than in each comparative example. That is, it was confirmed that the rare earth magnets of each example were remarkably superior in corrosion resistance compared to the comparative examples.

  DESCRIPTION OF SYMBOLS 10 ... Magnet body, 20 ... Protective layer, 30 ... Stator, 32 ... Coil, 50 ... Rotor, 52 ... Core, 100 ... Rare earth magnet, 200 ... Rotating machine, D: thickness of the protective layer.

Claims (3)

An R _L -T-B based magnet element containing a light rare earth element R _L , a transition metal element T and boron B, and a protective layer covering the surface of the magnet element,
The protective layer includes R _L , T and Al;
The magnet body and the protective layer each include Fe as T,
The content of R _{L in} the protective layer is 31 to 40 atomic% with respect to the total amount of R _L , T and Al in the protective layer,
The content of T in the protective layer is 35 to 64 atomic% with respect to the total amount of R _L , T and Al in the protective layer,
The content of Al in the protective layer is 5 to 25 atomic% with respect to the total amount of R _L , T and Al in the protective layer.
Rare earth magnet.   A rotating machine comprising the rare earth magnet according to claim 1. A step of attaching Al to the surface of an R _L -T-B system magnet body containing a light rare earth element R _L , a transition metal element T and boron B;
Heating the magnet body to which Al is adhered at 540 to 630 ° C., and
The magnet body includes Fe as T;
A method for producing a rare earth magnet.