JP2625767B2 - Rare earth magnet surface treatment method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a surface treatment method for a rare earth magnet used for a motor or the like.

(Prior Art) In recent years, permanent magnets used for electric devices, motors, etc.
Magnetic properties such as coercive force and maximum energy product have become extremely high performance.

Rare earth magnets are well known as a representative of the permanent magnets, but these rare earth magnets have poor corrosion resistance, and
Nd-Fe-B-based magnets, both sintered magnets and plastic magnets, are used by applying a coating layer on the magnet surface.

As a conventional magnet surface coating method, an organic resin coating method by electrodeposition coating or spraying and a plating method are known. With these surface treatment methods, the corrosion resistance of the surface of the rare earth magnet is improved.

(Problems to be solved by the invention) However, in such a conventional surface treatment method for a rare earth magnet, specifically, in the case of an organic resin coating method, the film thickness of the organic resin is required to be 10 μm or more. In addition, there is a problem that the film thickness accuracy is poor and the coating operation is complicated.

In the case of the plating method, since the plating solution easily penetrates into the pores inside the magnet, there is a problem that the plating solution remaining in the pores generates rust from inside the magnet.

Furthermore, when a magnet is subjected to, for example, a zinc phosphate coating treatment by a chemical conversion coating method known as a surface treatment method for steel materials, a phosphoric acid acid solution is merely immersed in the magnet surface, and the magnet is formed from the acid solution. There is a problem that the film is not sufficiently formed on the magnet surface when it is taken out.

The present invention has been made in order to solve such a problem, and by dipping a rare earth magnet in an alkaline aqueous solution of a predetermined chemical component containing a rare earth element, a high corrosion resistance with high adhesion to the magnet surface with a simple operation. The purpose is to form a coating.

(Means for Solving the Problems) For that purpose, the method for treating the surface of a rare earth magnet according to the present invention comprises at least one or more elements of Al, K, Na and Si, and at least one or more of rare earth elements. Characterized in that the rare earth magnet is wetted with an alkaline aqueous solution containing the element described above, and then the rare earth magnet is dried to form a corrosion resistant film on the surface of the rare earth magnet.

In this case, as a coating method, it is desirable to immerse the rare earth magnet in an alkaline aqueous solution from the viewpoint of workability, but spray coating may be used. Further, when the rare earth magnet is immersed in an alkaline aqueous solution in a vacuum state, the effect of impregnating the pores inside the magnet with the solution is enhanced, and the corrosion resistance is further improved. This is presumably because the rare earth element penetrates the pores inside the magnet and forms a dense compound in the magnet surface layer.

(Effects of the Invention) According to the present invention, a coating with high adhesion can be formed on the surface of a rare-earth magnet by a very simple operation of immersing the rare-earth magnet in an alkaline aqueous solution, so that the corrosion resistance of the magnet is further improved. This has the effect.

(Example) An example of the present invention will be described.

The rare earth magnet used in the embodiment of the present invention is: Nd (32 wt%)-Fe-B (1 wt%) sintered magnet: Nd (30 wt%)-Fe-B (0.7 wt%) plastic magnet. In this case, the resin used as the plastic material of the Nd-Fe-B plastic magnet was an epoxy resin (content 2%), and this plastic magnet was formed by press molding. The magnets and were both disk-shaped, having a diameter of 10 mm and a height of 5 mm.

The chemical solution in which the magnets were immersed was A: Al 6.0 wt% K 2.0 wt% Na 2.0 wt% Si 1.0 wt% An alkaline aqueous solution containing a rare earth element 0.2 wt% (PH = 11.7, specific gravity 1.04
1), B: Two kinds of alkaline aqueous solutions containing 6.0% by weight of Al, 2.0% by weight of K, 2.0% by weight of Na, and 1.0% by weight of Si (pH = 11.7, specific gravity 1.041) were used. Here, the rare earth element is Y, La, Ce, Pr, Lu or the like.

The above magnets were immersed in the chemical conversion solutions A and B. Specifically, as shown in FIG. 2 (A), the container 7 containing the magnet 10 as a sample is evacuated by the vacuum pump 8, then the valve 9 is opened, and as shown in FIG. 2 (B). Next, the alkaline aqueous solution in the container 11 is moved to the container 7 via the passage 12, and the magnet 10 is immersed in the alkaline aqueous solution. The temperature of the alkaline aqueous solution is 70 ° C and the immersion time is 2
Minutes. Thereafter, the magnets were removed from the chemical solutions of A and B, drained and dried. Drying temperature is 130
° C and the drying time was 3 minutes.

As a result, the thicknesses of the films formed on the magnet surfaces were 2.1 μm, respectively.

A corrosion resistance test was performed on each of the magnets on which a film was formed. The corrosion resistance test was performed at a temperature of 60 ° C. and a relative humidity of 95% based on the presence or absence of rust. The results of the rust generation test were as shown in Table 1.

As is clear from Table 1, in Comparative Example 2 in which the magnet was not immersed in the chemical conversion solution, rust was generated, and the amount of rust was higher as the test time was longer. there were. In Comparative Example 1 in which the magnet was immersed in the chemical conversion liquid B, the rust generation rate was lower than that of the comparative example in which the magnet was not immersed in the chemical conversion liquid, but the value was still considerable. On the other hand, when the magnet was immersed in the chemical conversion solution A as in the case of the present invention, no rust was generated in a relatively short time. Also, the rust generation rate was quite low even for long test times. As in the present invention, the occurrence of rust hardly occurred because the chemical conversion solution contains a rare earth element that is a contained element of the rare earth magnet,
It is considered that the rare earth element in the chemical conversion solution was strongly bonded to the rare earth element in the magnet, and a film having high adhesion was formed on the magnet surface.

Next, for the Nd-Fe-B plastic magnet, an adhesion test of the coating on the magnet surface was performed. The adhesion test was performed as an adhesion test. That is, as shown in FIG. 1, a coating layer 2 is formed on the surface of a rare earth magnet 1 and an iron piece 4 is bonded to the coating layer 2 with an adhesive layer 4 interposed therebetween. The chucks 5 and 6 were respectively engaged with each other, and a tensile force was applied in the direction of the arrow shown in the figure. The adhesive area of the adhesive layer 3 was 0.2 cm ² , the iron piece 4 was steel type SS41, and the adhesive was a two-component epoxy resin.

The results of the adhesion test were as shown in Table 2.

In Comparative Example 3 in which the magnet was immersed in the chemical solution B containing no rare earth element, the magnet was peeled off at the interface between the magnet and the adhesive layer, that is, the coating layer, and the adhesive strength at that time was 12 kg.
/ cm ² , a low value. On the other hand, when the magnet is immersed in the chemical conversion solution A containing a rare earth element as in the present invention, the magnet peels off at the interface between the iron piece and the adhesive layer without peeling off at the coating layer, and has an adhesive strength of 29 kg. / cm ² was a high value.

The amount of the rare earth element contained in the alkaline aqueous solution of the present invention is desirably in the range of 0.001 to 1 wt% in the solution. This is because if the content is less than 0.001 wt%, a film having a sufficient thickness cannot be formed on the magnet surface, and if it exceeds 1 wt%, the surface treatment cost becomes high.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a schematic configuration of a tensile test apparatus when an adhesion test is performed, and FIGS. 2 (A) and 2 (B).
FIG. 3 is a view showing an operation process for immersing a magnet in a chemical conversion solution. 1 ... Rare earth magnet, 2 ... Coating layer, 3 ... Adhesive layer, 4 ... Iron piece, 5, 6 ... Chuck.

Claims (1)

(57) [Claims] At least one of Al, K, Na and Si
At least one of more than one element and rare earth element
A rare earth magnet surface treatment method comprising: wetting a rare earth magnet in an alkaline aqueous solution containing at least one kind of element; drying the rare earth magnet; and forming a corrosion-resistant coating on the rare earth magnet surface.