Corrosion-resisting permanent magnet and method for producing the same

An object of the present invention is to provide an Fe--B--R permanent magnet that exhibits stabilized high magnetic properties, wear resistance, electrical insulating performance, and corrosion resistance and shows minimized deterioration from the initial magnetic properties when exposed for an extended time to atmospheric conditions of a temperature of 80.degree. C. and relative humidity of 90%, by providing a coating film having outstanding adhesion with the Fe--B--R permanent magnet and improved wear resistance and corrosion resistance. After cleaning the surface of the permanent magnet body by ion sputtering or the like, an Al or Ti coating film is formed on the surface of that magnet body by a vapor film-forming method such as ion plating, and then an aluminum oxide coating film is formed by a vapor film-forming method such as ion plating while introducing either simple O.sub.2 gas or a rare gas containing O.sub.2. When that is done, the adhesiveness with the coating film is sharply improved and outstanding corrosion resistance properties are realized. Thus, an Fe--B--R permanent magnet is obtained which exhibits stabilized magnetic properties due to the anticorrosive, wear-resistant, and electrically insulating properties of the anticorrosive metallic coating film applied.

TECHNICAL FIELD
 This invention relates to an Fe--B--R permanent magnet provided with an
 anticorrosive coating film, exhibiting high magnetic characteristics and
 adhesion, outstanding corrosion resistance, acid resistance, alkaline
 resistance, wear resistance, and electrical insulating properties, and
 relates more particularly to an anticorrosive permanent magnet, and
 fabrication method therefor, wherewith an Fe--B--R permanent magnet having
 extremely stable magnetic properties and high corrosion resistivity which
 shows little deterioration from its initial magnetic properties even when
 exposed for an extended time to an atmosphere of 80.degree. C. temperature
 and 90% relative humidity is obtained by providing an aluminum oxide
 coating layer to a specific thickness on the magnet surface, with an Al or
 Ti coating layer interposed therebetween.
 BACKGROUND ART
 Fe--B--R permanent magnets containing B and Fe as their main components and
 no high-cost Sm or Co which are obtained by using light rare earth
 elements such as Nd and Pr which are plentiful resources have already been
 proposed as new high-performance permanent magnets that greatly exceed the
 maximum performance of conventional rare earth cobalt magnets (Japanese
 Patent Laid-open No. S59-46008/1984 and Japanese Patent Laid-open No.
 S59-89401/1984.)
 The magnet alloys noted above have a Curie temperature ranging generally
 from 300.degree. C. to 370.degree. C. By replacing some of the Fe with Co,
 however, an Fe--B--R permanent magnet is obtained having a higher Curie
 temperature (Japanese Patent Laid-open No. S59-64733/1984, Japanese Patent
 Laid-open No. S59-132104/1984).
 Also proposed is a Co-containing Fe--B--R permanent magnet that exhibits a
 Curie temperature that is at least as high as the Co-containing Fe--B--R
 permanent magnet noted above, and a higher (BH)max, wherein, in order to
 enhance the temperature characteristics, and especially to improve the
 iHc, at least one heavy rare earth element such as Dy or Tb is contained
 as the rare earth element (R) in some of the R in the Co-containing
 Fe--B--R permanent magnet wherein the R primarily consists of light rare
 earth elements as Nd and Pr, whereby, while maintaining an extremely high
 (BH)max of 25 MGOe or greater, iHc is raised higher (Japanese Patent
 Laid-open No. S60-34005/1985).
 There are problems, however, in that the permanent magnets noted above,
 which are made from Fe--B--R magnetic anisotropic sintered bodies
 exhibiting outstanding magnetic properties, have a peculiar composition
 and structure, wherein the primary components are iron and rare earth
 elements that readily oxidize in air, wherefore, when they are built into
 magnetic circuits, due to oxides that are produced on the surface of the
 magnets, magnetic circuit output decline and variation between magnetic
 circuits are induced, and peripheral equipment is contaminated by the
 separation of the oxides from the magnet surfaces.
 Thereupon, a permanent magnet has been proposed (in Japanese Patent
 Publication No. H3-74012/1991) wherein the surface of the magnet body is
 coated with an anticorrosive metal plating layer, by either an
 electrolytic or non-electrolytic plating method, in order to improve the
 anticorrosion performance of the Fe--B--R magnets noted above.
 With these plating methods, however, the permanent magnet body is a porous
 sintered body, wherefore, in a pre-plating process, acidic solution or
 alkaline solution remains in the pores, giving rise to fears of
 degradation over time and corrosion, and the chemical resistance of the
 magnet body deteriorates, wherefore the magnet surface is corroded during
 plating so that adhesion and anticorrosion performance are impaired.
 Even when the anticorrosive plating layer is provided, in anticorrosion
 tests in which samples are exposed to a temperature of 60.degree. C. and
 relative humidity of 90% for 100 hours, the magnetic characteristics
 proved to be very unstable, exhibiting 10% or greater degradation from the
 initial magnetic characteristics.
 For this reason, it has been proposed (in Japanese Patent Publication No.
 H5-15043/1993) that, in order to improve the anticorrosion performance of
 Fe--B--R permanent magnets, an ion plating method, ion sputtering method,
 or vapor deposition method or the like be used to coat the surfaces of the
 magnets noted above with Al, Ti, or Al.sub.2 O.sub.3, and the
 anticorrosion performance thereby improved.
 However, the Al.sub.2 O.sub.3 coating film has a coefficient of thermal
 expansion and ductility that differ from those of the Fe--B--R magnet
 bodies, wherefore adhesion is poor and, although the adhesion of the Al
 and Ti coatings is good, they are highly reactive, so that localized
 rusting occurs due to the external environment, and their anti-wear
 performance is also poor.
 A method has also been proposed (Japanese Patent Publication No.
 H6-66173/1994) wherein, in order to improve the anticorrosion performance
 of the Al layer, the surface is subjected to a chromate treatment after
 the Al coating film, but the chromate treatment is problematic because it
 involves the use of 6-valence chromium which is environmentally toxic, and
 because treatment of the waste liquid is complex.
 SUMMARY OF THE INVENTION
 An object of the present invention is to improve antiwear and anticorrosive
 performance by providing a coating film having excellent adhesion with an
 Fe--B--R permanent magnet substrate, and in particular to provide an
 Fe--B--R permanent magnet that exhibits stabilized high magnetic
 properties, wear resistance, electrical insulating performance, and
 corrosion resistance, with minimized deterioration from the initial
 magnetic properties when exposed for an extended time to atmospheric
 conditions of a temperature of 80.degree. C. and relative humidity of 90%.
 In order to provide an Fe--B--R permanent magnet exhibiting outstanding
 stable magnetic characteristics, the inventors conducted various
 investigations on methods of forming aluminum oxide coating films on
 permanent magnet surfaces, as an anticorrosive metallic coating film which
 exhibits outstanding adhesion with the magnet substrate, corrosion
 resistance, anti-wear, and electrical insulating properties even when
 exposed for an extended time to atmospheric conditions of a temperature of
 80.degree. C. and relative humidity of 90%.
 As a result of their assiduous investigations, the inventors discovered
 that the object noted above can be attained by employing an ion plating
 method, ion sputtering method or the like, or vapor-phase film-forming
 method to form a coating film of Al or Ti of a prescribed film thickness,
 after cleaning the surface of the magnet body by ion sputtering or the
 like, and thereafter forming an aluminum oxide coating film of a
 prescribed film thickness using a vapor film-forming method while
 introducing a gas containing O.sub.2 under specific conditions.
 More specifically, the inventors perfected the present invention,
 discovering that the oxide material present on the magnet surface is
 reduced, either wholly or partially, by a reaction with Al or Ti at the
 interface with the Al or Ti, and that, by generating an aluminum oxide
 coating film on the Al or Ti coating film, AlO.sub.x (where 0&lt;x&lt;1) is
 generated at the interface between the Al and the aluminum oxide, or, in
 the case of Ti, a (Ti--Al)O.sub.x (where 0&lt;x&lt;1) is generated at the
 interface with the aluminum oxide, whereupon the adhesiveness between the
 Al or Ti coating layer and the aluminum oxide can be sharply improved.
 The present invention is an anticorrosive permanent magnet, and fabrication
 method therefor, wherewith, after cleaning the surface of an Fe--B--R
 permanent magnet, the main phase whereof is a tetragonal lattice phase, a
 coating film of Al or Ti is formed by a vapor film-forming method on the
 surface of the magnet body to a film thickness of 0.06 .mu.m to 30 .mu.m,
 after which a coating film layer of aluminum oxide that is mainly
 amorphous is formed to a film thickness of 0.1 to 10 .mu.m by a vapor
 film-forming method in an atmosphere that is either simple O.sub.2 or a
 rare gas such as Ar or He containing 10% or more of O.sub.2 gas.
 BEST MODE FOR CARRYING OUT THE INVENTION
 In the present invention, such so-called vapor film formation methods as
 ion plating, ion sputtering, and vapor deposition can be used as
 appropriate for the method of forming the Al coating film, Ti coating
 film, and aluminum oxide coating film on the surface of the Fe--B--R
 permanent magnet body. However, the ion plating method and reaction ion
 plating method are preferable in the interest of coating film fineness,
 uniformity, and coating film formation speed, etc.
 It is also desirable that the temperature of the permanent magnet that
 constitutes the substrate during reaction coating film formation be
 200.degree. C. to 500.degree. C. At temperatures below 200.degree. C. the
 reaction adhesion with the substrate magnet is inadequate, while at
 temperatures exceeding 500.degree. C. the temperature difference with room
 temperature (25.degree. C.) becomes larger, whereupon cracks develop in
 the coating film during the subsequent cooling process, and the coating
 film peels away from some parts of the substrate. Hence the temperature
 should be set at 200.degree. C. to 500.degree. C.
 In the present invention, the aluminum oxide coating film layer obtained is
 a compound formed from aluminum and oxygen, the structure is primarily
 amorphous, whereupon, depending on the reaction conditions, the layer
 obtained will either be completely amorphous or crystalline material will
 be present in some places. In the structure that is primarily amorphous,
 no clear grain boundaries exist, and localized electrochemical reactions
 that cause corrosion do not readily occur, wherefore the anticorrosive
 property is superior as compared to crystalline Al.sub.2 O.sub.3 coating
 films.
 An example of a method of fabricating the anticorrosive magnet of the
 present invention wherein an aluminum oxide coating film layer is provided
 with an intervening Al or Ti coating film layer on the surface of an
 Fe--B--R permanent magnet is now described in detail.
 First, using an arc ion plating apparatus, a vacuum vessel is evacuated to
 produce a vacuum of 1.times.10.sup.-4 Pa or lower. Then the surface of the
 Fe--B--R magnet body is cleaned by Ar-ion surface sputtering with an Ar
 gas pressure of 10 Pa at -500V.
 Next, using an Ar gas pressure of 0.2 Pa and bias voltage of -50 V, the
 target Al or Ti is vaporized and an Al or Ti coating film layer is formed
 to a film thickness of 0.06 .mu.m to 30 .mu.m on the surface of the magnet
 body with an arcion plating method. The ion plating method provides a fast
 film formation speed, and is the preferred method for forming an Al or Ti
 coating film of 5 .mu.m or greater.
 Following that, an aluminum oxide coating film layer is formed to a
 prescribed film thickness on the Al or Ti coating film under conditions of
 O.sub.2 gas pressure of 0.8 Pa and bias voltage of -80 V, maintaining the
 substrate temperature at 250.degree. C.
 In the present invention, the reason for limiting the thickness of the Al
 or Ti coating film on the surface of the Fe--B--R permanent magnet to 0.06
 to 30 .mu.m is that, at thicknesses below 0.06 .mu.m it is difficult to
 make the Al or Ti adhere evenly to the surface of the magnet body, and the
 effectiveness of the lower film is inadequate, whereas when 30 .mu.m is
 exceeded there is no problem with effectiveness but the cost of the
 underlying film rises and becomes impractical. Hence the Al or Ti coating
 film thickness is made 0.06 to 30 .mu.m.
 In particular, the thickness of the Al or Ti coating layer is selected
 according to the surface roughness of the magnet body. When that surface
 roughness is 0.1 .mu.m or less, the coating layer thickness should be made
 0.06 .mu.m or greater. When that surface roughness is 0.1 to 1.2 .mu.m,
 the coating layer thickness should be made 0.1 .mu.m or greater.
 In the present invention, the reason for limiting the thickness of the
 aluminum oxide coating layer to 0.1 to 10 .mu.m is that, at thicknesses of
 less than 0.1 .mu.m, adequate corrosion resistance is not obtained,
 whereas at thicknesses greater than 10 .mu.m, while there is no problem
 with effectiveness, the manufacturing costs rise to undesirable levels.
 In the present invention, the interface between the Al or Ti coating layer
 and the aluminum oxide coating layer is a laminar coating layer having an
 interposing reaction coating layer. In order to obtain adequate corrosion
 resistance, a configuration may be adopted wherein the thickness of the Al
 or Ti coating layer is made 5 .mu.m to 30 .mu.m, for example, and the
 aluminum oxide coating layer is made thin, or, alternatively, the Al or Ti
 coating film layer is made thin, on the order of 0.06 .mu.m to 5 .mu.m,
 and the thickness of the aluminum oxide coating film layer is made
 thicker, on the order of 0.5 .mu.m to 10 .mu.m.
 However, in order to obtain outstanding wear resistance and electrical
 insulating properties, in view of the fact that these properties arise
 from the aluminum oxide coating film layer, the thickness of the aluminum
 oxide coating film layer should be made 0.5 .mu.m to 10 .mu.m.
 In the present invention, the gas atmosphere containing O.sub.2 in the
 vapor film-forming method is limited to either simple O.sub.2 or to a rare
 gas (i.e. an element in the O group in the periodic table) containing 10%
 or more of O.sub.2 gas. When this is less than 10%, too much time is
 required for forming the aluminum oxide coating film, wherefore that is
 undesirable. For industrial reasons, either a simple O.sub.2 gas or an Ar
 gas atmosphere containing O.sub.2 gas is generally to be preferred.
 In the present invention, the rare earth element R used in the permanent
 magnet described in the foregoing accounts for 10 atomic % to 30 atomic %
 of the composition, but it is desirable that this contain either at least
 one element from among Nd, Pr, Dy, Ho, and Th, or, in addition thereto, at
 least one element from among La, Ce, Sm, Gd, Er, Eu, Tm, Yb, Lu, and Y.
 Ordinarily, it is sufficient to have one of the R elements, but in
 practice, it is possible to use a mixture of two or more elements (misch
 metal, didymium, etc.) for reason of ease of procurement. This R need not
 be a pure rare earth element either; there is no problem with it
 containing impurities as may be unavoidable in manufacture, with a range
 as can be procured industrially.
 R is a mandatory element in the permanent magnets noted above. At lower
 than 10 atomic %, the crystalline structure becomes a cubic crystal system
 having the same structure as .alpha.-iron, wherefore high magnetic
 characteristics, especially high coercive force, are not obtained. When 30
 atomic % is exceeded, the R-rich nonmagnetic phase increases and residual
 magnetic flux density (Br) declines, wherefore a permanent magnet
 exhibiting outstanding characteristics is not obtained. Thus the range of
 10.about.30 atomic % for R is desirable.
 B is a mandatory element in the permanent magnets noted above. At lower
 than 2 atomic %, a rhombohedral structure becomes the main phase, and high
 coercive force (iHc) is not obtained. When 28 atomic % is exceeded, the
 B-rich nonmagnetic phase increases and residual magnetic flux density (Br)
 declines, so that outstanding permanent magnets are not obtained. Thus the
 range of 2.about.28 atomic % is desirable for B.
 Fe is a mandatory element in the permanent magnets noted above. Below 65
 atomic %, the residual magnetic flux density (Br) declines. When 80 atomic
 % is exceeded, high coercive force is not obtained. Thus a range of
 65.about.80 atomic % is desirable for Fe. By replacing some of the Fe with
 Co, the temperature characteristics can be improved without impairing the
 magnetic characteristics of the magnets obtained. When the amount of Co
 replacement exceeds 20% of the Fe, on the other hand, the magnetic
 characteristics deteriorate, so that is undesirable. When the amount of Co
 replacement is 5 to 15 atomic % of the total quantity of Fe and Co, Br
 increases as compared to when there is no substitution, and high magnetic
 flux density is realized, which is desirable.
 In addition to the R, B, and Fe elements, the presence of such impurities
 as is unavoidable in the course of industrial production is allowable. By
 substituting at least one element out of C, P, S, and Cu for some of the
 B, namely C at 4.0 wt % or less, P at 2.0 wt % or less, S at 2.0 wt % or
 less, and/or Cu at 2.0 wt % or less, for example, such that the total
 amount of the substitution is 2.0 wt % or less, it is possible to improve
 permanent magnet productivity and reduce costs.
 It is also possible to add at least one element out of Al, Ti, V, Cr. Mn,
 Bi, Nb, Ta, Mo, W, Sb, Ge, Sn, Zr, Ni, Si, Zn, and Hf, to the Fe--B--R
 permanent magnet material in order to improve the coercive force, the
 rectangularity of the demagnetization curve or manufacturing perfomance,
 or to reduce costs. As to the upper limit of the quantity of such
 additives, Br must be at least 9 kG or greater in order to get (BH)max of
 the magnetic material above 20 MGOe, so it should be within a range
 wherein this condition can be satisfied.
 Furthermore, the Fe--B--R permanent magnets are characterized in that the
 main phase is made a compound having a tetragonal crystalline structure
 wherein the mean crystal grain diameter is within a range of 1.about.30
 .mu.m, containing a non-magnetic phase (excluding oxide phase) within a
 volume ratio of 1.about.50%. Such Fe--B--R permanent magnets exhibit
 coercive force iHc.gtoreq.1 kOe, residual magnetic flux density Br&gt;4 kG,
 and maximum energy product (BH)max.gtoreq.10 MGOe, with a maximum value of
 25 MGOe or higher.

EMBODIMENTS
 Embodiment 1
 A commonly known cast ingot was crushed and finely pulverized, and then
 subjected to molding, sintering, heat treatment, and surface treatment to
 yield magnet body test pieces having the composition 17Nd-1Pr-75Fe-7B,
 measuring 23.times.10.times.6 mm. The magnetic properties thereof are
 noted in Table 1. Pieces having two types of surface roughness were
 obtained by surface polishing. The surface roughness is noted in Table 2.
 A vacuum vessel was evacuated to produce a vacuum of 1.times.10.sup.-4 Pa
 or below, surface sputtering was conducted for 35 minutes in an Ar gas
 pressure of 10 pa, at -400 V, and the surface of the magnet body was
 cleaned. Then, maintaining the substrate magnet temperature at 280.degree.
 C., under the conditions noted in Table 2, and using a target of metallic
 Al, arc ion plating was performed to form Al coating film layers of
 thickness 0.2 .mu.m and 2.0 .mu.m on the magnet body surfaces.
 Then, with the substrate magnet temperature at 320.degree. C., the bias
 voltage at -85 V, the arc current at 88 A, and an O.sub.2 gas pressure of
 0.7 Pa, arc ion plating was conducted for 3.5 hours to form an aluminum
 oxide coating film layer of thickness 5 .mu.m on the surface of the Al
 coating film.
 Subsequently, tests were conducted wherein the permanent magnets having
 aluminum oxide coating film layers obtained by radiation cooling were
 allowed to stand for 1000 hours under conditions of 80.degree. C.
 temperature and 90% relative humidity. After this test, the magnetic
 properties and the deterioration therein were measured. The results are
 given in Table 3. The aluminum oxide coating films obtained were also
 subjected to structural analysis using x-ray diffraction, as a result of
 which the structure was found to be amorphous.
 Embodiment 2
 Magnet body test pieces having the same composition as in the first
 embodiment were obtained in two types of surface roughness by surface
 polishing under the same conditions as in the first embodiment. After
 surface cleaning under the same conditions as in the first embodiment, arc
 ion plating was implemented, using metallic Ti as the target, under the
 same conditions as noted in Table 2, maintaining the substrate magnet
 temperature at 250.degree. C., to form Ti coating film layers of 0.2 .mu.m
 and 2.0 .mu.m thickness on the magnet body surfaces.
 An aluminum oxide coating film layer was then formed to a thickness of 5
 .mu.m under the same conditions as in the first embodiment and, after
 testing by being allowed to stand for 1000 hours under conditions of
 80.degree. C. temperature and 90% relative humidity, the magnetic
 properties and deterioration therein were measured. The results are noted
 in Table 3. The aluminum oxide coating films obtained were also subjected
 to structural analysis using x-ray diffraction, as a result of which the
 structure was found to be amorphous with crystalline material present in
 some places.
 Embodiment 3
 A magnetic body test piece having the same composition as in the first
 embodiment (with surface roughness of 0.5 .mu.m) was surface-cleaned under
 the same conditions as in the first embodiment. Then Al wire used as the
 coating material was heated and vaporized under an Ar gas pressure of 1 Pa
 with a voltage of 1.5 kV and ionized in an ion plating process for 15
 minutes to form an Al coating film layer of 15 .mu.m thickness.
 Next, an aluminum oxide coating film layer having a film thickness of 0.5
 .mu.m was formed on the Al coating film surface by arc ion plating for 20
 minutes with a substrate magnet temperature of 320.degree. C., bias
 voltage of -85 V, and O.sub.2 gas pressure of 0.7 Pa. As a result of
 structural analysis using x-ray diffraction the aluminum oxide coating
 film was found to be amorphous.
 After the arc ion plating noted above, the permanent magnets having
 aluminum oxide coating film layers obtained by cooling were allowed to
 stand for 1000 hours under conditions of 80.degree. C. temperature and 90%
 relative humidity. After this test, the magnetic properties and the
 deterioration therein were measured. The results are given in Table 3.
 Comparison 1
 A magnetic body test piece having the same composition as in the first
 embodiment (with surface roughness of 0.5 .mu.m) was surface-cleaned under
 the same conditions as in the first embodiment. Then an aluminum oxide
 coating film layer of 7 .mu.m thickness was formed on the magnet body
 under the same reaction conditions as in the first embodiment. After the
 test piece was allowed to stand for 1000 hours under the same conditions
 of 80.degree. C. temperature and 90% relative humidity as in the first
 embodiment, the post-test magnetic properties and deterioration therein
 were measured. The results are noted in Table 3.
 Comparison 2
 A magnetic body test piece having the same composition as in the first
 embodiment (with surface roughness of 0.5 .mu.m) was surface-cleaned under
 the same conditions as in the third embodiment. Then an aluminum oxide
 coating film layer of 17 .mu.m thickness was formed on the magnet body
 under the same reaction conditions for 17 minutes as in the third
 embodiment. After the test piece was allowed to stand for 1000 hours under
 the same conditions of 80.degree. C. temperature and 90% relative humidity
 as in the first embodiment, the post-test magnetic properties and
 deterioration therein were measured. The results are noted in Table 3.
 As indicated in Table 3, with the magnets of the comparison examples
 wherewith only an aluminum oxide coating film layer is provided on the
 surface of the Fe--B--R permanent magnets having the same magnetic
 properties, the deterioration in magnetic properties after corrosion tests
 wherein the test pieces were allowed to stand for 1000 hours under
 conditions of 80.degree. C. temperature and 90% relative humidity was
 large and rusting also occurred. In contrast therewith, it is evident that
 the Fe--B--R permanent magnets of the present invention wherein the
 aluminum oxide coating film layer is provided with an Al or Ti coating
 film layer interposed between the aluminum oxide coating film and the
 magnet surface exhibited no rusting and the magnetic properties hardly
 changed at all.
 TABLE 1
 Magnetic properties before corrosion resistance tests
 After aging treatment After surface treatment
 Br iHc (BH)max Br iHc (BH)max
 (kG) (kOe) (MGOe) (kG) (kOe) (MGOe)
 Embodiment 1 1 11.5 16.8 30.7 11.4 16.7 30.6
 2 11.4 16.8 30.6 11.4 16.6 30.6
 Embodiment 2 1 11.5 16.8 30.6 11.4 16.6 30.5
 2 11.5 16.8 30.7 11.4 16.7 30.6
 Embodiment 3 11.5 16.8 30.7 11.4 16.6 30.6
 Comparison 1 11.5 16.8 30.7 11.3 16.6 30.5
 Comparison 2 11.5 16.8 30.7 11.4 16.6 30.5
 TABLE 2
 Magnetic Arc ion plating conditions
 surface Gas Bias Coating
 Surface roughness pressure voltage Time thickness
 Embodiment finishing (.mu.m) (Pa) (V) (min) (.mu.m)
 1 1 Grinding 0.06 0.2 -50 10 0.2
 to a mirror
 finish
 2 Grinding 0.5 0.2 -50 100 2.0
 2 1 Grinding 0.06 0.2 -60 13 0.2
 to a mirror
 finish
 2 Grinding 0.5 0.2 -60 130 2.0
 TABLE 3
 Magnetic properties before corrosion-resistance tests Surface
 state
 After Corrosion resistance Percent deterioration in after
 corrosion
 tests (1000 Hrs) magnetic properties (%) resistance
 test
 Br iHc (BH)max Br iHc (BH)max (State of
 (kG) (kOe) (MGOe) (kG) (kOe) (MGOe) deterioration)
 Embodi- 1 11.4 16.5 30.0 &lt;1 1.8 2.3 No change
 ment 1 2 11.3 16.4 29.9 &lt;1 2.4 2.3
 Embodi- 1 11.4 16.4 29.8 &lt;1 2.4 2.6 No change
 ment 2 2 11.4 16.4 29.8 &lt;1 2.4 2.9
 Embodi- 11.4 16.3 29.8 &lt;1 3.0 2.9 No change
 ment 3
 Compari- 10.5 15.6 27.5 8.7 7.2 10.4 Coating
 son 1 peeling
 Compari- 10.4 15.3 27.3 9.6 8.9 11.1 Local rusting
 son 2
 Percentage deterioration in magnetic properties=(Magnetic properties of
 finished starting materials)-(Magnetic properties after moisture
 resistance test)/(Magnetic properties of finished starting
 materials).times.1000
 INDUSTRIAL APPLICABILITY
 In Fe--B--R permanent magnets according to the present invention, an
 aluminum oxide coating film layer is provided on the magnet surface with
 an Al or Ti coating film. As indicated in the embodiments, there was
 almost no deterioration in magnetic properties after being subjected to
 severe corrosion tests, particularly after being allowed to stand for 1000
 hours under conditions of 80.degree. C. temperature and 90% relative
 humidity. Hence the Fe--B--R permanent magnets according to the present
 invention are ideal for the high-performance, low-cost permanent magnets
 now most in demand.
 In the fabrication method according to the present invention, after
 cleaning the surface of the Fe--B--R permanent magnet body by ion
 sputtering or the like, an Al or Ti coating film is formed on the surface
 of that magnet body by a vapor film-forming method such as ion plating,
 and then an aluminum oxide coating film is formed by a vapor film-forming
 method such as ion plating while introducing a rare gas containing O.sub.2
 . By forming the Al or Ti coating film on the magnet body surface, oxides
 on the surface of the magnet body are either partially or entirely
 reduced, and outstanding adhesiveness is exhibited between the magnet body
 surface and the Al or Ti coating film. By laminating the aluminum oxide
 coating film on the Al or Ti coating film, the adhesiveness of that
 coating film is sharply improved, outstanding corrosion resistance is
 exhibited, and the adhesiveness with the underlying layer becomes
 excellent even when allowed to stand for an extended time under
 atmospheric conditions of 80.degree. C. temperature and 90% relative
 humidity. Due to the anticorrosive, wear-resistant, and electrically
 insulating properties of the anticorrosive metallic coating film applied,
 Fe--B--R permanent magnets are obtained which exhibit stable magnetic
 properties.