JPH0712005B2 - High corrosion resistance rare earth permanent magnet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a highly corrosion-resistant rare earth permanent magnet, and particularly to a rare earth / iron / iron alloy having a uniform corrosion-resistant double layer on the surface of a fired magnet body.
The purpose is to provide a boron-based permanent magnet.

(Prior Art) Rare earth permanent magnets are widely used in the field of electric and electronic devices due to their excellent magnetic properties and economic efficiency, and in recent years, their performance has been increasingly required. Of these, Nd-based rare earth permanent magnets are cheaper in raw material cost because they contain more abundant Nd, which is the main element than Sm, compared to conventional Sm-based rare earth permanent magnets, and do not use large amounts of Co. Since it is an extremely excellent permanent magnet material whose characteristics far surpass those of Sm-based rare earth permanent magnets, the small magnetic circuit in which Sm-based rare earth magnets have been used up until now is not only replaced by this, but also hard in terms of cost. It is about to be widely applied to fields where ferrites or electromagnets were used. However, this material has the disadvantage that it easily oxidizes in humid air in a very short time. Oxidation not only produces oxides on the surface of the magnet, but also progresses from the surface along the grain boundaries along the grain boundaries, causing the phenomenon of so-called grain boundary corrosion. This is because there is an active Nd-rich phase. Corrosion of grain boundaries causes extremely large deterioration of magnetic properties, and if corrosion progresses during practical use, the performance of the device incorporating the magnet is deteriorated and the surroundings of the device are contaminated.

Various surface treatment methods have been proposed in order to overcome such drawbacks of Nd magnets, but none of them is perfect as a corrosion-resistant surface treatment. For example, in a resin coating film formed by spraying or electrodeposition coating, rust occurs due to the hygroscopicity of the resin, and vapor deposition methods such as vacuum deposition, ion sputtering, and ion plating are too costly, and the inner hole, There are disadvantages such as not being able to coat the groove.

(Structure of the Invention) As a result of intensive studies to eliminate the disadvantages and drawbacks of the related art, the present inventors have found that the magnetic characteristics are not deteriorated over a long period of time.
We have succeeded in obtaining a permanent magnet that can maintain the aesthetic appearance and have reached the present invention. That is, in the present invention, R (R is at least one kind of rare earth element including Y) is 5 to 40% by weight, and Fe is 50 to 90%.
% Of Co, 0.1 to 15% by weight of Co, 0.2 to 8% by weight of B, and 8% by weight or less of transition metal as main components. The main point is a corrosion resistant rare earth permanent magnet.

This will be described in detail below. In the present invention, R
As Y or as rare earth elements La, Ce, Pr, Nd, P
Examples include m, Sm, Gd, Tb, Dy, Ho, Er, Lu, Yb,
One or more of these are used, and among them, it is preferable to contain at least one of Ce, La, Nd, Pr, Dy and Tb.

Transition metals include Ni, Nb, Al, Ti, Zr, Cr, V, Mn, M
At least one selected from o, Si, Sn, Cu, Ca, Mg, Pb, Sb, Ga and Zn is used.

The present invention contains R5 to 40% by weight, Fe50 to 90% by weight, Co0.1 to 15% by weight, B0.2 to 8% by weight and transition metal of 8% by weight or less, in which C, O, P, S A Nd-based rare earth burned magnet body containing industrially unavoidable trace impurities is used, and a Cu layer and a Ni-P alloy double layer are provided on this surface. In this case, the electroplating method, The electroless plating method may be used, and a preferable method is to first deposit the Cu layer on the surface of the fired magnet body and then deposit the Ni—P alloy layer thereon by the electroless plating method.

The composition of the Cu electroless solution used in this case is at least one of copper sulfate, copper nitrate, and copper chloride as a metal salt.
It is preferable to contain 100 g / or less and 200 g / or less as a reducing agent of at least one compounding agent such as formalin, hydrazine and its derivatives, hydroquinone, sodium hypophosphite, formate and sucrose. In this electrolyte, as a complexing agent, at least one of Rossiel salt, EDTA, triethanolamine, gluconate, and salicylate is 180 g / or less, a pH adjuster, carbonate as a buffer, ammonia, and blue. 10 of at least one of soda
In addition to containing 0 g / or less accelerator, 10 g / or less as a stabilizer, sulfide, disulfide, chloride, fluoride, can each contain a surfactant, this aqueous solution is used in the range of pH 8-14, The bath temperature during plating is in the range of 10 to 60 ° C.

The composition of the Ni-P electroless solution contains at least one of nickel chloride, nickel sulfate, and nickel hypophosphite as a metal salt in an amount of 100 g / or less, and sodium hypophosphite as a reducing agent in an amount of 100 g / or less, Sodium hydroxide as a pH adjuster, basic compounds such as ammonium hydroxide,
It is preferable that at least one kind of inorganic acid and organic acid is contained in an amount of 150 g / or less. In this electrolytic solution, at least one kind of an oxycarboxylic acid such as sodium citrate and sodium acetate as a buffering agent, or an inorganic acid such as boric acid and carbonic acid is 150 g or less, sodium citrate and sodium acetate as a complexing agent, Ammonium hydroxide, ethylene glycol, alkaline salts of organic acids (acetic acid, glycolic acid, citric acid, tartaric acid, etc.), thioglycolic acid, ammonia, triethanolamine, ethylenediamine,
In addition to 100 g / at least one of glycine and pyridine, accelerators and stabilizers of 10 g / s or less of sulfides and chlorides,
Fluoride and surfactant can be contained respectively,
This aqueous solution is used in the pH range of 3 to 13, and the bath temperature during plating is 2
It is in the range of 0 to 100 ° C.

The method of immersing the sintered magnet body in the plating solution may be either the barrel method or the hooking jig method, and is appropriately selected depending on the size and shape of the fired magnet body.

The Cu layer formed on the surface of the fired magnet body by the above method and the double layer consisting of the Ni-P alloy on it exhibit extremely excellent corrosion resistance, and the Cu layer or the Ni-P alloy layer is formed on the surface of the fired magnet body. Corrosion resistance is excellent as compared with the case of coating alone. The reason for this is that the pinhole existing in the electroless Cu plating film is interrupted by newly coating the Ni-P alloy thereon, and the pinhole is covered with the Ni-P alloy coating, and the pin in the Ni-P coating is also interrupted. This is because the hole has corrosion resistance due to the presence of the Cu layer in the base. In this way, there are very few pinholes that reach the substrate from the film surface, and high corrosion resistance is guaranteed.

Furthermore, the following corrosion protection mechanism is established from the relationship of the ionization tendency of both layers. Ni-, which has a greater ionization tendency than the Cu film
P coating is present on Cu coating. Therefore, corrosion is base Ni-P
It progresses as the film dissolves anodically,
The Cu coating is cathodically protected. At the same time, the groundwork is protected. In other words, the Ni-P coating has the same anticorrosion mechanism as zinc plating on the iron substrate, which sacrifices corrosion and protects the substrate.

For the above reasons, the burned magnet alloy having the double layer of the CU layer and the Ni-P alloy layer has extremely excellent corrosion resistance. The Ni-P alloy layer formed on the Cu layer contains Ni and P as main components. And P is Ni
It is composed of a supersaturated solid solution in an amorphous phase or a fine mixed phase of nickel and a nickel phosphide phase such as Ni ₃ P. The P content in this layer is preferably 1 to 14% by weight. An electroless plating film containing only Ni cannot be used because it has many pinholes or has poor adhesion to the lower layer, resulting in poor corrosiveness. Also, the Ni-B or Ni-N alloy coating cannot provide sufficient corrosion resistance because it has many pinholes and poor adhesion.

The thickness of the Cu layer is appropriately 1 to 10 μm, preferably 2 to 5 μm, and the thickness of the Ni—P alloy layer is 1 to 30 μm, preferably 5 to 15 μm. That is, the thickness of the double layer is
10 to 20 μm is suitable, and 30 μm or more is not practical because the time and amount of chemicals required for plating are large and it is too expensive. Also, if it is a uniform double layer, it can be practically used even if it is 10 μm or less. This double layer can be improved in corrosion resistance, adhesion and wear resistance by heat treatment after plating. The temperature range is 100 to 500 ° C. and the time is 10 minutes to several hours.

Next, the reasons for limiting the constituent components of the permanent magnet containing R-Fe-Co-B as an essential element according to the present invention will be described. When the amount of R contained as the main component in the permanent magnet used in the present invention is 5% by weight or less, a high coercive force cannot be obtained because the amount of α iron deposited is too large. The amount of non-magnetic phase contained is too much, the residual magnetic flux density is lowered, and the magnet characteristics cannot be obtained. Therefore, the amount of R as a main component is 5 to 40% by weight.

When B is 0.2% by weight or less, coercive force cannot be obtained, and when it is 8% by weight or more, the nonmagnetic phase containing B is too much and the residual magnetic flux density is lowered, so that magnet characteristics cannot be obtained. Therefore, the amount of B is
It is 0.2 to 8% by weight.

When Fe is less than 50% by weight, the residual magnetic flux density is low and the magnetic properties cannot be obtained, and when it is more than 90% by weight, the amount of α iron precipitated is too large to obtain a high coercive force. Therefore, the amount of Fe is 50 to 90% by weight.

Co is effective in improving the temperature change of the residual magnetic flux density, and if the addition amount of Co is less than 0.1% by weight, a sufficient effect cannot be obtained, while if it exceeds 15% by weight, the coercive force decreases. The amount is 0.1 to 15% by weight, preferably 0.5 to 10% by weight.

The transition metal that can replace the essential element is added to improve the magnetic properties or to reduce the cost, and the amount thereof is 8% by weight alone or in a total of two or more kinds.
It is the following. However, any of these elements should be avoided because if added in excess of the above amounts, the magnetic properties will deteriorate.
The permanent magnet of the present invention is a burned anisotropic permanent magnet obtained by anisotropy of crystalline alloy powder in a magnetic field press, and then fired, and its magnetic property is 20 MGOe or more at the maximum energy product.
It is up to MGOe, and 20 MGOe or less is a defective product and it is not suitable for surface treatment.

Next, examples according to the present invention will be described.

Example 1 By high frequency melting in an Ar atmosphere, the weight ratio was 32Nd-1.2B-5.
An ingot having a composition of 9.8Fe-7Co was prepared.

This ingot was roughly crushed with a jaw crusher and then finely crushed with a jet mill using N ₂ gas to obtain fine powder having an average particle size of 3.5 μm.

Next, this fine powder was filled in a mold to which a magnetic field of 10000 Oe was applied, and molded at a pressure of 0.8 t / cm ² . Then in vacuum 1100
It was burned at ℃ for 2 hours and further aged at 550 ° C for 1 hour to obtain a permanent magnet. 30 mm outer diameter from the obtained permanent magnet,
A cylindrical test piece having an inner diameter of 10 mm and a height of 2 mm was cut out. The anisotropic direction is the height direction.

These test pieces 1, 2, 3 and 4 were solvent washed with trichlorethylene, and then immersed in a mixed alkaline aqueous solution of sodium hydroxide 30g /, sodium carbonate 20g /, sodium orthosilicate 50g / for 10 minutes to degrease with alkali. After washing, wash with water and add 30 ml of sulfuric acid 25 ml / and hydrofluoric acid 25 ml / in mixed acid.
It was pickled for 2 seconds and then washed with water. 3 g of this in an aqueous solution containing 14 g of Cu sulfate, 45.5 g of Rossiel salt, 53 g of formalin, 10 g of sodium hydroxide, and 4.2 g of sodium carbonate.
Immerse the test pieces 1 and 2 at 0 ° C for 10 minutes and the test pieces 3 and 4 for 60 minutes by Cu
The layers were each coated to a thickness of 1.5 μm. Then, wash with water, and test pieces 1, 2, 3 and 4 at 90 ° C in an aqueous solution containing 30 g of Ni chloride / 10 g of sodium hypophosphite / 50 g of sodium hydroxyacetate for 4 minutes, 20 minutes, 20 minutes and 40 minutes, respectively. It was smashed for a minute and coated with a Ni-P alloy layer to a thickness of 1,5,5,10 µm. After plating, the plate was washed with water and heat-treated at 150 ° C for 30 minutes.

After each test piece was kept in a test tank at 60 ° C. and 95% relative humidity for 600 hours, the appearance was observed to evaluate the corrosion resistance. The magnetic properties before and after the corrosion resistance test were also measured.

For comparison with the examples, the same corrosion resistance test was performed on a test piece A of the same size, which was not subjected to surface treatment after cutting, and a test piece B of the same size, in which only the Ni—P alloy layer was electrolessly deposited.
The results are shown in Table 1.

As is clear from Table 1, the Cu layer and Ni according to the present invention
It can be seen that the rare earth permanent magnet having the double layer of the P layer exhibits excellent corrosion resistance in terms of appearance and magnetic characteristics.

Claims (1)

[Claims] 1. R (R is at least one of rare earth elements including Y) 5 to 40% by weight, Fe 50 to 90% by weight, Co 0.1 to 15% by weight, B 0.2 to 8% by weight and transition metal 8% by weight % Of the main component is a highly corrosion-resistant rare earth permanent magnet having a double layer consisting of a Cu layer and a Ni-P layer on the surface of a burned body.