JP2617113B2 - Rare earth permanent magnet excellent in corrosion resistance and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a permanent magnet alloy containing R, Fe, B as a main component,
Particularly, the present invention relates to a rare earth permanent magnet alloy having excellent corrosion resistance and a method for producing the same.

[Prior Art] An R-Fe-B permanent magnet alloy is obtained by crushing an ingot having a predetermined composition and sintering it by a powder metallurgy method. And this alloy is a conventional rare earth magnet, Sm-Co
It has higher magnetic properties than the system magnet.

However, since the R-Fe-B-based magnet alloy contains an Nd-Fe solid solution phase which is extremely easily oxidized in this metal structure, when incorporated in a device such as a magnetic circuit, even under ordinary environmental conditions. Deterioration of characteristics due to oxidation of the magnet and variation thereof are larger than those of the Sm-Co magnet. Further, scattering of the oxide generated from the magnet also affects the peripheral portion.

Attempts to improve the corrosion resistance by plating the magnet thus obtained are found in JP-A-49-86896, JP-A-60-63901, etc., which occur during the manufacture of the magnet. It is difficult to prevent oxidation.

On the other hand, when electrolytic plating is conventionally performed in an alkaline aqueous solution plating bath, Nd-Fe
The solid solution phase corrodes and dissolves out, so a clean plating film with good adhesion cannot be obtained, rust is generated from that part during use, and there is a problem that a plating film with excellent corrosion resistance cannot be obtained. ing.

The present invention is to solve the problems described in the preceding paragraph, and the technical problem is to prevent oxidation of the Nd-Fe solid solution phase during electrolytic plating and to form a plating film with good adhesion on the magnet surface. Another object of the present invention is to provide a rare earth permanent magnet alloy having excellent corrosion resistance and a method for producing the same.

[Means for Solving the Problems] According to the present invention, 0.1% of R-Fe-B (R represents a rare earth element containing yttrium) is added to the surface of a sintered magnet alloy.
μm or more, having a good adhesion electrolytic plating layer having a thickness of at least μm, and the electrolytic plating layer gradually decreases in the R-Fe solid solution phase from the interface with the sintered magnet alloy toward the surface of the electrolytic plating layer. Thus, a rare earth permanent magnet excellent in corrosion resistance is obtained.

According to the present invention, a rare-earth permanent magnet in which an electrolytic plating layer is electrodeposited with an alkaline bath containing a metal salt on the surface of an R-Fe-B (R represents a rare earth element containing yttrium) -based sintered magnet alloy. In the production method, the alkaline bath comprises:
A method for producing a rare-earth permanent magnet excellent in corrosion resistance characterized by containing 5.0 ppm or less of dissolved oxygen is obtained.

Here, in the method for producing a rare earth permanent magnet excellent in corrosion resistance according to the present invention, it is desirable that the sintered magnet alloy be used as a cathode and immersed in the alkaline bath while energizing.

That is, when electrolytic plating is performed in an aqueous plating bath in which a metal salt is dissolved, particularly in an alkaline plating bath, in the case of a Nd-Fe-B magnet alloy, Nd-Fe which is extremely easily oxidized in the metallographic structure.
The solid solution phase corrodes selectively. On the surface, a hole is formed in a portion where the Nd-Fe solid solution phase is corroded and melted out, and a plated film with good adhesion cannot be obtained. Oxidation proceeds from that portion even under ordinary environmental conditions. The tendency is more remarkable as the current density during electrolytic plating is higher.

Examining this in various ways revealed that the amount of dissolved oxygen in the aqueous solution had a significant effect. Normally, the dissolved oxygen contained in the aqueous solution is large (saturation value: 20 ppm /), and if oxygen is dissolved in the aqueous solution, the Nd-Fe solid solution phase is corroded by the reduction of oxygen during electrolytic plating.

Thus, when electrolytic plating is performed in an aqueous solution containing a large amount of dissolved oxygen, it is difficult to obtain a plating film having excellent corrosion resistance.

Therefore, in the present invention, the aqueous solution to be used is previously bubbled with an inert gas such as N ₂ gas or Ar gas to remove dissolved oxygen as much as possible, and the amount is 5.0 ppm / or less.
It has been found that it is necessary to desirably control the concentration to 1.0 ppm / or less.

When electrolytic plating is performed using an aqueous solution from which dissolved oxygen has been removed, the Nd-Fe solid solution phase does not selectively corrode, and a plating film with good adhesion is obtained, and the effect of removing dissolved oxygen is remarkable. Was seen.

The metal for the alkaline bath electroplating may be any metal as long as it is less oxidizable than the rare earth metal contained in the magnet. Alternatively, a potassium bath or a pyrophosphoric acid bath for tin-nickel alloy plating may be used.

The pH of these alkaline electrolytic plating baths is 8 to 12, and the bath temperature is
The plating film is formed under the conditions of 20 to 50 ° C. and the current density of 0.5 to 10 A / dm ² . In particular, Cu plating is used as a base for Ni plating because the plating film surface is oxidized even in the air.

If the thickness of the plating film is less than 0.1 (μm), the plating is not sufficiently performed, so that oxidation on the magnet surface progresses.
Above (μm), the non-magnetic portion contained per unit volume of the magnet increases, and the magnetic performance of the magnet deteriorates.

When performing electroplating, usually, a sample is immersed in a plating solution and then a voltage is applied to perform electroplating. However, if the Nd-Fe-B magnet specimen is immersed in an alkaline plating bath and left as it is, the Nd-Fe solid solution phase melts out and corrodes. When immersion in the solution and electroplating, a clean plating film having good adhesion is formed.

According to the present invention, when electrolytic plating is performed in an alkaline bath using an aqueous solution from which dissolved oxygen has been removed, a plating film having good adhesion is formed on the magnet surface, excellent in corrosion resistance, and poor in magnet properties. It became possible to obtain a magnet that was not very useful in practical use.

 Hereinafter, examples thereof will be described.

[Example] Example 1 33 Wt% Nd-1.0 Wt% BF obtained by powder metallurgy
The sintered body having the composition of ebal was processed into a size of 1 × 7 × 10 (mm) to obtain a sample. In a copper pyrophosphate plating bath (strike bath) shown in Table 1, a Cu plate was used on the anode side, and a Nd-Fe-B sintered sample was used on the cathode side. Cu plating was performed in the range of 2.02.0 A / dm ² for 30 minutes. At this time, the aqueous solution used for dissolving the metal salt was previously bubbled with N ₂ gas for 3 hours to remove dissolved oxygen as much as possible, and the dissolved oxygen amount was 1.0 ppm /.

Table 2 shows the thickness and appearance of the plating layer measured for each sample in which the electrolytic density was changed.

As shown in Table 2, as the current density increased, the plating layer became thicker. In particular, a very clean metallic plating with a metallic luster was obtained at a current density of 0.75 to 1.0 A / dm ² .

At this time, a micrograph of the interface between the substrate (Nd-Fe-B) and the Cu plating was shown in SEM photograph 1 of FIG. FIG. 1 shows that the adhesion to the substrate is very good, and a Cu plating with good adhesion is obtained.

Next, Table 3 shows the results of qualitatively confirming the effects of applying an external force (friction, bending, impact, etc.) to the specimen as an adhesion test.

Further, the surface of the Nd-Fe-B magnet was subjected to electrolytic Ni plating after Cu underplating. Table 4 shows the results obtained when these test pieces were subjected to a corrosion resistance test for 1000 hours under the conditions of constant temperature and humidity of 60 ° C. × 95%.

Table 5 shows the dissolved oxygen content and the plating surface condition.

It can be seen that the test piece according to the present invention is extremely excellent in corrosion resistance without causing defects such as red rust, peeling, and blistering.

Example 2 As shown in Table 6, in a tin plating bath (sodium bath) using an aqueous solution from which dissolved oxygen was removed, Sn was added to the anode side.
Plate, and Nd-Fe-B sintered samples were placed in the cathode side, resulting in a bath temperature of 60 ° C., it was subjected to 10 minutes electroplating at a current density of 1.0A / dm ^2, 5.0 .mu.m tin plating layer Was done.

The adhesion between the substrate and the tin plating was very good, and no defects such as blistering and peeling were found in the adhesion test.

When a corrosion resistance test was conducted for 1000 hours under the conditions of constant temperature and humidity of 60 ° C. × 95%, no change such as red rust, blistering and peeling was observed.

Example 3 As shown in Table 7, a tin-nickel alloy plating bath (pyrophosphate bath, Sn70-Ni
30 bath), 70Wt% Sn-30Wt% Ni alloy plate on the anode side,
And Nd-Fe-B sintered samples were placed in the cathode side, at a bath temperature of 50 ° C., was subjected to 10 minutes electroplating at a current density of 1.0A / dm ^2, 4.0 .mu.m tin - nickel plating layer is obtained Was done.

The adhesion between the base material of the alloy plate and the tin plating layer was very good, and no defects such as blistering and peeling were found in the adhesion test.

Further, when a corrosion resistance test was conducted for 1000 hours under the condition of constant temperature and humidity of 60 ° C. × 95%, no change such as red rust, blistering and peeling was observed, and it was found that the corrosion resistance was very excellent.

[Effects of the Invention] As described in detail above, according to the present invention, when an electrolytic plating is performed in an alkaline bath by using an aqueous solution from which the amount of dissolved oxygen has been removed as much as possible, the R-Fe-B magnet alloy A plated film with good adhesion is formed on the surface, and a rare-earth permanent magnet with extremely excellent corrosion resistance can be obtained.

[Brief description of the drawings]

FIG. 1 is an SEM photograph showing the metal structure of the fracture surface near the boundary when the Nd—Fe—B magnet surface is plated with Cu. Fig. 2 is an SEM showing the metallographic structure of the plating surface by the conventional method
It is a photograph.

Claims (3)

(57) [Claims] A sintered magnet alloy based on R-Fe-B (R represents a rare earth element containing yttrium) having an electrolytic plating layer having a thickness of 0.1 μm or more and having good adhesion, A rare earth permanent magnet excellent in corrosion resistance, characterized in that the plating layer has an R-Fe solid solution phase gradually decreasing from an interface with the sintered magnet alloy toward the surface of the electrolytic plating layer. 2. A method for producing a rare earth permanent magnet, wherein an electrolytic plating layer is electrodeposited from an alkaline bath on the surface of an R—Fe—B (R represents a rare earth element containing yttrium) based sintered alloy, A method for producing a rare earth permanent magnet excellent in corrosion resistance, characterized in that the bath contains dissolved oxygen of 5.0 ppm or less. 3. The method for producing a rare-earth permanent magnet having excellent corrosion resistance according to claim 2, wherein said sintered magnet alloy is immersed in said alkaline bath while being energized with a cathode.