JPH06140218A - Shock-resistant rare-earth cobalt magnet and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a shock-resistant rare-earth cobalt magnet, whose shock resistance and mechanical strength are improved without reducing its magnetic characteristics, and a method of manufacturing the cobalt magnet. CONSTITUTION:A single-layer metal-plated layer 2 having a thickness, which exceeds 2mum and is 7mum or thinner, is formed on the surface of a magnet main body 1 consisting of a rare-earth cobalt sintered material, which is shown by the composition formula=R1Co5 or R2Co17 (where R is at least one of a metal of rare-earth metals of Sm, Pr, La, etc.).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an impact-resistant rare earth cobalt magnet and a method for producing the same, and more particularly to an impact-resistant rare earth cobalt magnet having improved impact resistance and mechanical strength without deteriorating magnetic properties and its production. Regarding the method.

[0002]

_2. Description of the Related Art Conventionally, RCo ₅ or R ₂ Co
Sintered magnets such as SmCo ₅ , Sm ₂ Co _{17 and the} like as sintered body magnets made of an intermetallic compound represented by ₁₇ (where R is at least one kind of rare earth metal such as Sm, Y, Ce, La and Pr). However, it has been put to practical use in a wide range of fields such as generators, electric motors, precision measuring instruments, home appliances, copying machines, medical devices, automobile parts, toys, and the like.

These magnets are usually manufactured through the following steps. For example, taking SmCo ₅ as an example,
After melting and casting the Sm raw material and the Co raw material, the obtained ingot is annealed, and then finely pulverized using a pulverizer such as a ball mill in a non-oxidizing atmosphere, and the obtained fine raw material powder is pressed in a magnetic field. It is manufactured by performing powder molding and sintering the obtained molded body in an inert gas atmosphere.

By the way, the rare earth metals such as Sm, Pr and La which compose the above rare earth cobalt magnet are naturally oxidized in the air to be converted into more stable oxides, and the magnetic characteristics are deteriorated with time. Had.

As a measure against the above, for example, Japanese Patent Publication No. 57-21
Japanese Patent No. 842 discloses a technique of forming a metal plating layer of Ni or the like having a thickness of 0.1 to 0.5 μm on the surface of a SmCo ₅ sintered body magnet, and the effect of blocking oxygen by this metal plating layer. As a result, deterioration of magnetic characteristics due to oxidation is prevented. On the other hand, in Japanese Unexamined Patent Publication No. 56-81908, a resin coating having a thickness of 10 to 50 μm or a thickness of 1 μm is provided for the purpose of preventing the above-mentioned oxidation and improving the strength of the sintered magnet.
2 μm thick Au on the surface of the electroless Ni plating layer of
A configuration for forming the plating layer in a multi-layer structure is described.

[0006]

However, in the SmCo ₅ magnet described in Japanese Patent Publication No. 57-21842, a metal plating layer having a thickness of 0.1 to 0.5 μm is formed. Although it has an excellent prevention effect, it has almost no effect of improving impact resistance and the like, and has a drawback that cracks and chips are likely to occur during use. In addition, JP-A-5
As disclosed in JP-A-6-81908, the thickness is 1 μm.
Even with a rare earth magnet in which a 2 μm Au plating layer is formed on the m electroless plating layer so as to have a multi-layer structure, the effect of improving impact resistance is small, and the plating process is performed twice and the first plating is performed. After that, it is necessary to add washing and drying steps, which increases the number of manufacturing steps and complicates them, resulting in a significant increase in manufacturing costs. In addition, peeling may occur at the joint between the Ni-plated layer and the Au-plated layer, resulting in insufficient impact resistance. Further, when the metal plating layer is formed in a multi-layer structure, a magnetic gap is likely to be formed at the interface between adjacent metal plating layers, and the magnetic characteristics such as the residual magnetic flux density are likely to deteriorate.

In recent years, devices such as various motors, sensors, precision measuring instruments, and watch parts used in industrial equipment, home electric appliances, automobile parts, etc., which use rare earth cobalt magnets, and miniaturization and heightening of parts themselves. Along with the functionalization, the magnetic properties as well as the impact resistance and mechanical strength properties required for the rare earth cobalt magnet itself have increased, and it is difficult to obtain satisfactory impact resistance and mechanical strength properties with conventional magnets. there were.

The present invention has been made in order to solve the above problems, and is an impact resistant rare earth cobalt magnet having improved impact resistance and mechanical strength without deteriorating the original magnetic characteristics of the magnet and a method for producing the same. The purpose is to provide.

[0009]

In order to achieve the above object, the impact resistant rare earth cobalt magnet according to the present invention has a composition formula R
₁ Co ₅ or R ₂ Co ₁₇ (where R is Sm, Pr, La
2 μm on the surface of the magnet body composed of a rare earth cobalt sintered body represented by at least one kind of rare earth metal such as
And a single-layer metal plating layer having a thickness of 7 μm or less is formed.

In addition, the surface roughness of the magnet body has a maximum height (Rma
x) It is preferable to set 2 to 10 μm as a standard.

Further, the first method of manufacturing the impact resistant rare earth cobalt magnet according to the present invention is the composition formula R ₁ Co ₅ or R
₂ Co ₁₇ (where R is at least one of rare earth metals such as Sm, Pr, La, etc.) is used to polish the surface of the magnet body made of a rare earth cobalt sintered body to obtain the maximum surface roughness ( Rmax) is set to 2 to 10 μm, and then a single-layer metal plating layer having a thickness of more than 2 μm and 7 μm or less is formed on the surface of the magnet body.

A second method of manufacturing the impact resistant rare earth cobalt magnet according to the present invention is the composition formula R ₁ Co ₅ or R ₂
By polishing the surface of the magnet body made of a rare earth cobalt sintered body represented by Co ₁₇ (where R is at least one kind of rare earth metal such as Sm, Pr, La), the surface roughness is maximized (Rmax ) It is characterized by forming a single-layer metal plating layer having a thickness of more than 2 μm and not more than 7 μm on the surface of the magnet body after the standard exceeds 10 μm.

A third method of manufacturing the impact resistant rare earth cobalt magnet according to the present invention is the composition formula R ₁ Co ₅ or R ₂
The thickness of the magnet body made of a rare earth cobalt sintered body represented by Co ₁₇ (where R is at least one of rare earth metals such as Sm, Pr, and La) is not subjected to surface roughness adjustment treatment such as polishing. Is directly formed with a single-layer metal plating layer of 2 μm or more and 7 μm or less.

The single-layer metal plating layer is formed to improve the impact resistance and mechanical strength of the rare earth magnet. As the metal constituting the single-layer metal plating layer, Ni,
Ni-P, Ni-S, Cu, Ni-Co alloy, Al, C
A simple metal or alloy such as r, Sn, Ag, Zn, zinc chromate, Au is used, and N, Ni-P is particularly preferable for improving impact resistance and mechanical strength.

As a method for forming the single-layer metal plating layer, electroless plating may be carried out while applying a rotational force to the magnet body in the plating tank, or an ion plating method or an electrolytic plating method may be used. In the case of the electroless plating method, the number of pinholes is small even when the rare earth cobalt magnet is plated, and a plating layer having a uniform thickness can be formed on each part of the surface of the magnet body. Further, in the case of the electrolytic plating method, the uniformity of the film thickness is inferior to that in the case of the electroless plating method, but the plating layer having a predetermined thickness can be formed in a relatively short time.

Generally, there are various coating methods such as a thermal spraying method as well as a plating method as a means for coating a metal layer on a sintered body. However, rare earths having excellent impact resistance, mechanical strength and high adhesion strength are available. If you want to produce a cobalt magnet industrially cheaply,
The plating method is excellent and therefore the coating means of the present invention is limited to the plating method only.

The thickness of the single-layer metal plating layer has a great influence on the impact resistance and mechanical strength of the magnet, and is set to more than 2 μm and 7 μm or less in the present invention.
When the thickness of the single-layer metal plating layer is 2 μm or less, the effect of improving impact resistance and strength is small. On the other hand, when the thickness exceeds 7 μm, the magnetic characteristics are deteriorated and the plating treatment is performed. This is because the time increases rapidly and the manufacturing cost of the magnet also increases rapidly. Therefore, the thickness of the single-layer metal plating layer is set to more than 2 μm and 7 μm or less, and more preferably set to more than 3 μm and 5 μm or less. That is, the impact resistance and mechanical strength required depending on the application of the rare earth cobalt magnet are slightly different, but in the case of a relatively small rare earth cobalt magnet that is generally applied to motors, sensors, measuring instruments, etc. From the viewpoint of shortening the time required for the process, the thickness exceeds 3 μm and 5 μm
It is more preferable that the amount is less than 1.

The magnitude of the surface roughness of the magnet body before the formation of the single-layer metal plating layer is a factor that greatly affects the impact resistance of the magnet itself and the adhesion strength of the single-layer metal plating layer. If the surface roughness is large, the adhesion strength tends to increase, but a defective portion that becomes a starting point of cracking is likely to be formed, which causes a decrease in impact resistance. In the present invention, it is desirable to set the maximum height (Rmax) to 2 to 10 μm in order to satisfy both properties of impact resistance and adhesion strength at the same time. Further, when the surface roughness is finished to be less than 2 μmRmax, highly accurate polishing such as polishing and lapping is required, and there is a problem that the processing time and the processing cost increase sharply. On the other hand, when the surface roughness exceeds 10 μmRmax, a recess that causes cracking may be formed, and the impact resistance and mechanical strength of the magnet may decrease.
Grinding with a general-purpose resin bond grindstone is sufficient to adjust the surface roughness within the range of 2 to 10 μmRmax, and the processing cost is low.

It is also possible to form a single-layer metal plating layer having a thickness of more than 2 μm and not more than 7 μm after performing polishing processing having a surface roughness of more than 10 μm Rmax. Normal,
The surface roughness (Rmax) of the as-sintered magnet body surface is 1
Even if it is measured to be about 0 μm, it varies remarkably depending on the measurement portion, and a large groove (recess) of about several tens μm to 100 μm exists depending on the portion. Even when the polishing process has a surface roughness of more than 10 μmRmax, these large grooves (recesses) can be removed, so that the impact resistance and the mechanical strength are improved as compared with the case where the polishing process is not performed. Examples of this polishing process include lapping and polishing using a resin bond grindstone having a coarse abrasive grain size.

However, it is also possible to directly form a single-layer metal plating layer having a thickness of more than 2 μm and not more than 7 μm on the surface of the as-sintered magnet body without performing the above-mentioned polishing process. Also in this case, the impact resistance and the mechanical strength are improved and the number of manufacturing steps is reduced as compared with the single-layer metal plating having a thickness of 2 μm or less. In this case, it is desirable to remove burrs generated in the as-sintered magnet body or powder adhered to the magnet body by barrel treatment, blast treatment or the like.

[0021]

According to the impact resistant rare earth cobalt magnet and the manufacturing method having the above-described structure, since the single-layer metal plating layer having a thickness of more than 2 μm and not more than 7 μm is formed on the surface of the hard and brittle magnet body, the magnetic characteristics are improved. The impact resistance and mechanical strength of the magnet can be significantly improved without damaging it, and the durability and operation reliability of the device using the rare earth cobalt magnet can be significantly improved.

Further, since the metal plating layer is formed as a single layer, the plating process is simplified once as compared with the conventional metal plating layer having a multilayer structure, and the manufacturing cost is significantly reduced. There is no peeling of each plating layer, which tends to occur in the case of a multi-layer structure. Furthermore, since no magnetic gap is formed between the plating layers, there is little risk that the magnetic characteristics will deteriorate.

Further, the surface roughness of the magnet body before the formation of the single-layer metal plating layer is polished to 2 to 10 μmRmax.
Or 10 μmRmax or more, the adhesion strength between the magnet body and the single-layer metal plating layer is increased, and the defects that cause the occurrence of cracks are reduced, so that the impact resistance and mechanical strength of the magnet are further improved. be able to.

When the polishing process is not performed, the number of manufacturing steps can be reduced, and the rare earth cobalt magnet for the above purpose can be easily manufactured.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described more specifically with reference to the accompanying drawings.

Examples 1 to 7 A raw material mixture consisting of 23.1% by weight of Sm and the balance Co so as to be Sm ₂ Co ₁₇ was melted in a high frequency melting furnace to prepare an ingot. After annealing for 5 hours at a temperature of 1050 ° C. in a heating furnace in an Ar gas atmosphere and coarse crushing with a hammer crusher, the coarse powder obtained is further crushed and mixed in an alumina ceramic pot for about 20 hours to obtain an average particle size of 3 Adjusted to ˜5 μm powder. Next, the obtained Sm ₂ Co ₁₇ powder was subjected to magnetic field molding under a molding pressure of 2 t / cm ² and an applied magnetic field of 12000 Oersted, and the obtained molded body was heated at a temperature of 1100 ° C. to 1200 ° C. in an argon gas atmosphere.
After 60 minutes of sintering, solution treatment and aging treatment were performed to produce a large number of Sm ₂ Co ₁₇ magnet main bodies having a diameter of 9.5 mm and a thickness of 1.5 mm.

Next, the surface of the obtained Sm ₂ Co ₁₇ magnet main body was ground using a resin bond grindstone, and as shown in Table 1, the surface roughness was 4 to 10 μm Rmax (for Examples 1 to 6). ) Was adjusted. A magnet main body for Example 7 was prepared as a sample that was not subjected to grinding.

Next, as shown in Table 1, the thickness of each sample subjected to the above-mentioned grinding (for Examples 1 to 6) and the sample not subjected to grinding (for Example 7) was measured by electroless plating. A single-layer Ni plating layer having a thickness of 2.5 to 7 μm is formed, and FIG.
Sm according to Examples 1 to 7 in which a uniform single-layer Ni plating layer 2 is formed on the entire surface of the Sm ₂ Co ₁₇ magnet body 1 as shown in FIG.
₂ Co ₁₇ magnet 3 was manufactured.

[0029] without performing grinding to the magnet body 1 prepared in Comparative Example 1 Example 7, also was Sm ₂ Co ₁₇ magnet as in Comparative Example 1 without performing Ni plating.

COMPARATIVE EXAMPLE 2 A single-layer Ni plating layer having a thickness of 1.5 μm was directly formed on the magnet body 1 prepared in Example 7 without grinding by electroless plating, and Sm according to Comparative Example 2 was used. _{A 2} Co ₁₇ magnet was prepared.

Comparative Example 3 The surface of the magnet body prepared in Example 7 was ground to have a surface roughness of 4 μmRmax, and an Sm ₂ Co ₁₇ magnet according to Comparative Example 3 was formed without forming a Ni plating layer.

Comparative Example 4 A 1 μm-thick Ni plating layer was directly formed on the surface of the magnet body 1 prepared in Example 7 by an electroless plating method without polishing the surface, and further on the Ni plating layer surface. Thickness 2
A Sm ₂ Co ₁₇ magnet according to Comparative Example 4 having a multi-layer structure was prepared by forming a gold (Au) plating layer having a thickness of μm.

An impact test was carried out in order to evaluate the impact resistance of the Sm ₂ Co ₁₇ magnets of Examples 1 to 7 and Comparative Examples 1 to 4 thus prepared.

The impact test was carried out using an impact test device 4 as shown in FIG. That is, the impact test device 4
Is a steel base 5 having a thickness of 30 mm, a pillar 6 standing on the steel base 5, and slidably mounted on the pillar 6.
And a holding metal fitting 8 for detachably holding a steel ball 7 weighing 5.47 g. Then, in the impact test, one sample (Sm ₂ Co ₁₇ magnet) 3 was placed on the steel base 5 and the 1
The steel ball 7 is naturally dropped once from a predetermined drop height (H) with respect to each sample 3 and a shock is applied to the sample 3, and the ratio of the number of samples with cracks or chips to the total number of samples is damaged. The impact resistance for each type of each sample was evaluated.

The measurement results are shown in Table 1 below.

[0036]

[Table 1]

As is clear from the results shown in Table 1, in the Sm ₂ Co ₁₇ magnets according to Examples 1 to 7 in which the single-layer Ni plating layer having a thickness of 2.5 to 7 μm was formed on the surface of the magnet body, the drop height was increased. It was confirmed that when the thickness (H) was up to 150 mm, almost no cracking or chipping occurred and excellent impact resistance was exhibited.
In particular, Example 1 in which the roughness of the surface of the magnet main body was ground to 4 to 5 μm Rmax prior to forming the single-layer Ni plating layer
In the Sm ₂ Co ₁₇ magnets according to Nos. 4 and 6, the adhesion strength between the single-layer Ni plating layer and the magnet body is increased, and the microdefects that cause the occurrence of cracks are reduced. It has been proved that it has extremely low impact resistance up to the range of 300 mm and has excellent impact resistance. Further, in the magnet according to Example 7 in which the single-layer Ni plating layer was directly formed on the rough surface (15 μm Rmax) without performing the grinding process, the impact resistance was relatively decreased as compared with the above Example, The value was higher than that of the comparative example.

On the other hand, it was found that the magnet according to Comparative Example 1 in which the grinding process was not carried out and the Ni plating layer was not formed was 70% broken at a drop height (H) of 50 mm and was not practical. The other comparative examples also showed similar values.

[0039]

As described above, in the impact resistant rare earth cobalt magnet and the method for producing the same according to the present invention, a single metal plating layer having a thickness of more than 2 μm and not more than 7 μm is formed on the surface of a hard and brittle magnet body. Therefore, the impact resistance and mechanical strength of the magnet can be significantly improved without impairing the magnetic characteristics, and the durability and operation reliability of the device using the rare earth cobalt magnet can be significantly improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a rare earth cobalt magnet according to the present invention.

FIG. 2 is a front view showing the configuration of an impact test device,

[Explanation of symbols]

1 Magnet Main Body 2 Single Layer Ni Plating Layer (Single Layer Metal Plating Layer) 3 Sm ₂ Co ₁₇ Magnet (Rare Earth Cobalt Magnet) 4 Impact Test Equipment 5 Steel Base 6 Support 7 Steel Ball 8 Holding Metal

Claims (7)

[Claims] 1. A surface of a magnet body made of a rare earth cobalt sintered body represented by a composition formula R ₁ Co ₅ or R ₂ Co ₁₇ (where R is at least one kind of rare earth metal such as Sm, Pr, La) A shock-resistant rare earth cobalt magnet having a single-layer metal plating layer having a thickness of more than 2 μm and not more than 7 μm. 2. The impact resistant rare earth cobalt magnet according to claim 1, wherein the single metal plating layer is made of nickel (Ni). 3. The surface roughness of the magnet body has a maximum height (Rmax).
2) The impact resistant rare earth cobalt magnet according to claim 1, wherein the standard is 2 to 10 μm. 4. The impact resistant rare earth cobalt magnet according to claim 1, wherein the thickness of the single-layer metal plating layer is more than 3 μm and 5 μm or less. 5. The surface of a magnet body made of a rare earth cobalt sintered body represented by a composition formula R ₁ Co ₅ or R ₂ Co ₁₇ (where R is at least one kind of rare earth metal such as Sm, Pr, La) is polished. By processing, the surface roughness is set to 2 to 10 μm based on the maximum height (Rmax), and then a single-layer metal plating layer having a thickness of more than 2 μm and 7 μm or less is formed on the surface of the magnet body. Method for manufacturing impact resistant rare earth cobalt magnet. 6. A surface of a magnet body made of a rare earth cobalt sintered body represented by a composition formula R ₁ Co ₅ or R ₂ Co ₁₇ (where R is at least one kind of rare earth metal such as Sm, Pr, La) is polished. The surface roughness is processed to the maximum height (Rmax
) A method for producing an impact resistant rare earth cobalt magnet, which comprises forming a single-layer metal plating layer having a thickness of more than 2 μm and not more than 7 μm on the surface of the magnet body after the standard exceeds 10 μm. 7. A surface of a magnet body made of a rare earth cobalt sintered body represented by a composition formula R ₁ Co ₅ or R ₂ Co ₁₇ (where R is at least one kind of rare earth metal such as Sm, Pr, La) is polished. A method for producing an impact resistant rare earth cobalt magnet, which comprises directly forming a single-layer metal plating layer having a thickness of more than 2 μm and not more than 7 μm without performing a surface roughness adjusting treatment such as working.