JPH0478699B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing RCo ₅ -based magnets, typified by SmCo ₅ .

[Prior art]

Methods for manufacturing rare earth magnets made of intermetallic compounds of R (yttrium and at least one of rare earth metals) and Co can be roughly divided into three methods: sintering, casting, and using a binder. (Japanese Patent Application Laid-Open No. 60-48884).

[Problems with conventional technology]

By the way, among the methods that use a binder, there is one that uses a polymer resin as the binder (called a polymer composite magnet).
The former has the advantage of being strong and easy to mold into complex shapes, but has poor magnetic properties compared to magnets made by sintering or casting. There is a drawback. Furthermore, the latter method has the disadvantage that mass production efficiency is low, and the resulting magnet not only has poor magnetic properties but also low heat resistance (Japanese Patent Application Laid-Open No. 60-214505).

On the other hand, magnets manufactured using the sintering method are susceptible to cracking, chipping, and slipping during pressure molding. Moreover, since there is shrinkage deformation due to sintering, the final shape of the product cannot be obtained during molding, and therefore processing of the sintered body is required, resulting in poor product yield.

Therefore, it is an object of the present invention to produce RCo _5- based magnets that can obtain the final shape of the product during molding and have much higher magnetic properties and improved mechanical strength than the previously mentioned conventional binder-based polymer composite magnets. An object of the present invention is to provide a manufacturing method.

[Means for solving problems]

In the present invention, powdered low-melting point metal M (M is one or two of Al and Zn) is mixed with RCo ₅ magnet alloy powder in a volume ratio of 5 to 30%, and the mixture is heated in vacuum or in an inert gas atmosphere. It is characterized by hot press forming at a temperature of more than 500°C and less than 750°C.

Here, if the mixing amount of the low melting point metal M is less than 5%, it will be insufficient to fill the voids between the powders, resulting in low mechanical strength after molding, and if it exceeds 30%, non-magnetic phase will occur. becomes too large, making it impossible to improve the magnetic properties. Therefore, the mixing amount of M is 5 to 30%.

Further, the reason why the hot pressurization was performed in a vacuum or in an inert gas atmosphere is because if the hot pressurization is performed in the air, the characteristics of the magnet after molding will be significantly deteriorated due to oxidation of the magnetic powder.

In addition, if the temperature during hot pressing is 500℃ or less,
This is not preferable because the coercive force is significantly reduced. This is considered to be because RCo ₅ was decomposed into an R ₂ Co ₇ phase and an R ₂ Co ₁₇ phase, according to the observation of the magnet structure and the analysis results of X-ray diffraction.

On the other hand, if the temperature during hot pressurization exceeds 750° C., the residual magnetization Br decreases, and as a result, the maximum energy product (BH) _nax decreases, which is not preferable. This is considered to be because, according to observation of the magnet structure, a reaction layer is generated at the interface between the magnet particle phase and the low melting point metal phase, that is, the volume fraction of the magnet particle phase is reduced. If the temperature exceeds 750℃,
Since the density improvement effect is saturated, this is also unfavorable from the point of view of energy consumption in the manufacturing process.

Note that pressing may be carried out not only by ordinary hot pressing but also by hot isostatic pressing, and a pressing force of at least 5 kg/cm ² is preferable in order to make the compact compact.

Examples of the present invention will be described below.

Example 1 Sm was 36.5wt% and Co was 63.5wt%.
An ingot was produced by melting by high frequency heating in an argon atmosphere.

After holding this ingot at 1100℃ for 2 hours,
After cooling to 800°C at 2°C/min, it was rapidly cooled to room temperature. The ingots subjected to the above heat treatment were ground in a ball mill so that the average particle size was 7 μm.

This magnet powder was mixed with 5 to 30 vol% of powdered Zn to obtain a molding powder. This molding powder was packed into a mold and pressure molded under vacuum at a temperature of 600° C. and a pressure of 1000 Kg/cm ² for 15 minutes while applying a magnetic field of 20 kOe.

FIG. 1 shows the transverse rupture strength of the molded product molded by the above method.

At a mixing amount of 5 to 20 vol%, the transverse rupture strength is proportional to the mixing amount, but even if the amount exceeds 20 vol%,
There is no significant change in transverse rupture strength, and it becomes saturated at 30vol%.

Furthermore, FIG. 2 shows the change in magnetic properties with respect to the amount of Zn mixed. The magnetic properties deteriorate as the amount of Zn added increases, and when Zn is added at 35%, the properties become almost the same as those of conventional polymer composite magnets. Therefore, the amount of Zn added is
It is necessary to keep it below 35%.

Example 2 As in Example 1, 5 was added to the SmCo ₅ alloy magnet powder.
〜500℃ of molding powder mixed with 30vol% Zn powder
Hot pressure molding was carried out at a temperature range of ~700°C and a pressure of 1000 Kg/cm ² .

In order to obtain a molded article having the theoretical density at a constant molding temperature, the lower the molding temperature, the more binder phase is required. Therefore, Fig. 3 shows the relationship between the molding temperature and the minimum amount of Zn mixed to obtain the theoretical density. As the molding temperature increases, the amount of Zn mixed can be reduced.

In the example, only Zn was used as the binder, but
This effect is also expected for pure metals and alloys of Al, which is another low melting point metal.

〔Effect of the invention〕

Although the present invention has been explained in detail above, RCo ₅
By mixing alloy powder obtained by pulverizing a magnetic alloy with appropriate heat treatment and low melting point metals such as Zn and Al, and hot-pressing it, it has the same strong toughness as a polymer composite magnet, but has a high yield. significantly improve, and
Compared to polymer composite magnets, much higher magnetic properties can be obtained, making it very useful industrially.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between the amount of Zn powder mixed with SmCo ₅ alloy powder and refractive force in Example 1, and Figure 2 is a graph showing the relationship between the amount of Zn powder mixed with SmCo ₅ alloy powder and refractor strength in Example 1. Figure 3, a diagram showing the relationship between magnetic properties, is a diagram showing the relationship between the temperature during hot pressing in Example 2 and the minimum amount of Zn required to obtain a compact with the theoretical density. .

Claims (1)

[Claims] 1 RCo ₅ (R is at least one of yttrium and rare earth metal) based magnet alloy powder is mixed with powdered low melting point metal M (M is one or two of Al and Zn) at a volume ratio of 5 to 30%, A method for producing a rare earth magnet, characterized by hot press forming at a temperature of more than 500°C and less than 750°C in a vacuum or an inert gas atmosphere.