JP2518265B2 - Method for manufacturing RCo-lower 5 type sintered alloy magnet with excellent magnet characteristics - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a coercive force (hereinafter, iHc), a residual magnetic flux density (hereinafter, Br), and a maximum energy product (hereinafter, (BH) _max ). (Shown in)), it relates to a method for producing an RCo ₅ type sintered alloy magnet which has excellent magnet characteristics.

[Conventional technology]

Conventionally, RCo ₅ type sintered alloy magnets generally have superior magnetic characteristics compared to alnico magnets and ferrite magnets, so they are mainly used in various electric and electronic devices that need to be made smaller and lighter. Widely used for practical use.

Usually, this RCo ₅ type sintered alloy magnet (where R represents one or more of rare earth elements and Y) is used to produce RCo ₅ type alloy powder having an average particle size of about 3 to 5 μm in a magnetic field. By press forming into a green compact, which is then pressed from 1100 to 1200
Sintered at a predetermined temperature within the range of ℃, in the cooling process after sintering,
For example, cool up to 800 ℃ at a cooling rate of 60 ℃ / hr, then
It is manufactured by a basic process consisting of a quenching heat treatment by spraying gas. In this manufacturing process, (1) In the process of raising the temperature to the sintering temperature, for example, it is raised in vacuum up to 800 ° C. Heat, and then raise the temperature and sinter in a hydrogen atmosphere or Ar atmosphere, and in the case of Ar atmosphere, perform the above heat treatment as it is, while in a hydrogen atmosphere, after sintering, change this to Ar atmosphere (2) In the process of raising the temperature to the sintering temperature, e.g., raise the temperature to 200 ° C in a vacuum, then change to a hydrogen atmosphere and raise the temperature to just before the sintering temperature. A typical method is to perform the above heat treatment in an Ar atmosphere, and then perform the above heat treatment in the same Ar atmosphere.

[Problems to be solved by the invention]

However, in the sintering in Ar atmosphere in the above method (1), since crystal grains do not grow, a magnet having a high iHc can be obtained, but the densification is insufficient and the magnet density is low. High Br and (BH) _max could not be obtained, and the sintering in the hydrogen atmosphere in the above method (1) resulted in
On the contrary, since densification progresses during sintering and a magnet with high density is obtained, Br and (BH) _max are excellent, but grain growth is promoted by hydrogen in the atmosphere during sintering. Therefore, iHc is inevitably low, and in the above method (2), since the temperature is raised in a hydrogen atmosphere to a temperature close to the sintering temperature, in the green compact during sintering. It is unavoidable that hydrogen remains in the steel, and therefore, compared with the case of sintering in the hydrogen atmosphere of the above method (1), grain growth is inevitable, but grain growth is unavoidable, while firing in an Ar atmosphere. As a result, the densification of the magnet is insufficient, and therefore, at present, all of the above-mentioned magnet characteristics remain at an intermediate value between the values obtained by the above method (1). iH
It is impossible to produce an RCo ₅ sintered alloy magnet having excellent magnet characteristics of c, Br, and (BH) _max .

[Means for solving problems]

Therefore, from the above viewpoints of the present inventors, iH
As a result of conducting research to produce an RCo ₅ type sintered alloy magnet that has excellent magnet characteristics of c, Br, and (BH) _max , it was found that when burning the RCo ₅ type sintered alloy magnet, (A) First, the green compact is heated to room temperature to 200 ° C in a hydrogen atmosphere during the temperature rising process to the binding temperature.
When kept at a predetermined temperature within a range of, for a predetermined time, the green compact occludes hydrogen to form a hydride, and (b) 900 ° C. in a state where the hydrogen is occluded to form a hydride. When the hydrogen atmosphere is changed to an Ar atmosphere at the following predetermined temperature, hydrogen occluded in the green compact is released, but at the time of this hydrogen release, the crystal atoms existing in the raw material powder forming the green compact are released. The disordered arrangement disappears to form a regular arrangement, and the resulting regular arrangement of crystal atoms significantly improves the sinterability during sintering, so densification progresses, and the magnet after sintering has a high Br and (BH) _max , while sintering is performed in an Ar atmosphere, so as described above,
By performing conversion to Ar atmosphere at a relatively low temperature of 900 ° C or lower, complete dehydrogenation from the green compact is achieved, and grain growth during sintering is prevented. From this, we have found that iHc is also high.

The present invention has been made based on the above findings, in which a green compact formed from a raw material powder mainly composed of RCo ₅ type alloy powder is sintered at a predetermined temperature within a range of 1100 to 1200 ° C. RC
o When manufacturing a ₅ type sintered alloy magnet, in the process of raising the temperature to the sintering temperature, (a) first, the green compact is heated in a hydrogen atmosphere at room temperature to 20 ° C.
It is kept at a predetermined temperature in the range of 0 ° C. for a predetermined time to occlude hydrogen to make it a hydride, and (b) then, to prevent the growth of crystal grains at the time of sintering and to prevent the crystal atoms of the raw material powder In order to improve the sinterability by regularizing the arrangement disorder in the, the above hydrogen atmosphere was changed to Ar atmosphere at a predetermined temperature of 900 ° C or less, complete dehydrogenation was performed to eliminate residual hydrogen, and This method is characterized by a method for producing a RCo ₅ type sintered alloy magnet having excellent magnet characteristics by performing sintering at the above temperature in an Ar atmosphere.

Next, the reason why the manufacturing conditions are limited as described above in the method of the present invention will be described.

(A) Hydrogen atmosphere holding temperature in the temperature rising process Hydrogen absorption of the green compact from the hydrogen atmosphere occurs at room temperature,
If the temperature exceeds 200 ° C, the hydrogen absorption rate of the green compact decreases rapidly, that is, even if the green compact is kept at a temperature of over 200 ° C in a hydrogen atmosphere, sufficient hydrogen absorption cannot be achieved. Therefore, the temperature is determined to be room temperature to 200 ° C, preferably room temperature to 100 ° C. Although the holding time is not limited, it is usually necessary to hold it for 30 minutes or longer.

(B) Atmosphere switching temperature in the temperature raising process The switching of the hydrogen atmosphere or the Ar atmosphere in the temperature raising process completely releases the hydrogen absorbed by the green compact while the temperature is raised to the sintering temperature, and To improve the sintering temperature and prevent grain growth. Therefore, when the conversion temperature becomes higher than 900 ° C, the sintering temperature is reached before the release of hydrogen can be completed, and the residual hydrogen Since the sintering takes place in the presence of the above, grain growth occurs, and a high iHc
Therefore, the switching temperature is set to 900 ° C or lower, preferably 400 ° C or lower.

(C) Sintering temperature If the temperature is less than 1100 ° C, sufficient sintering cannot be performed, densification is insufficient, and desired Br and (BH) _max cannot be obtained. The temperature is 1200 ℃
If it exceeds, the grain growth will occur and the iHc will be lowered, so the temperature was set to 1100 to 1200 ℃.

〔Example〕

Next, the method of the present invention will be specifically described by way of Examples.

First, using a high frequency furnace, in an Ar atmosphere, in a weight ratio,
RC with a composition consisting of Sm: 28.5%, Pr: 7.0%, Co: balance
o Prepare a molten ₅ type alloy, cast it, and then use a stamp mill.
Grinding in Ar atmosphere, then grinding in Daiflon using an attritor mill to produce a raw material powder with an average particle size of about 4 μm, and then the raw material powder was oriented in a magnetic field of 12 KOE. Then, it is compressed in a direction parallel to the orientation direction with a pressure of ² ton / cm ² to form a green compact oriented in a thickness direction of diameter: 11 mmφ × thickness: 10 mm. according heating curve of figure, a hydrogen atmosphere maintained temperature T _1, the T ₂ from the hydrogen atmosphere switching temperature to the Ar atmosphere, the T ₁ and T ₂
At various temperatures shown in Table ₁ , and the holding time of T ₁ was also changed as shown in Table 1,
In Ar atmosphere, heated to a sintering temperature of 1120 ° C at a heating rate of 480 ° C / hr, and then in Ar atmosphere After holding at the sintering temperature for 1 hour, the method of the present invention 1 to 15 is carried out by cooling to 800 ° C. at a cooling rate of 60 ° C./hr and quenching from 800 ° C. by blowing Ar gas. Then
An RCo ₅ type sintered alloy was produced.

Also, for the purpose of comparison, according to the heating curve shown in FIG. 2 as well, the temperature is raised to 800 ° C. in a vacuum, and thereafter the sintering is completed in an Ar atmosphere (conventional method 1).
Or, except that the hydrogen atmosphere (conventional method 2) is used,
Conventional methods 1 and 2 were performed under the same conditions as the method of the present invention, and
An RCo ₅ type sintered alloy magnet was manufactured.

Further, for the purpose of comparison, as shown in Table ₁ , the hydrogen atmosphere holding temperature T ₁ or the atmosphere switching temperature T _{2 in the} temperature rising process is out of the range of the present invention, and Comparative methods 1 to 10 are performed. An RCo ₅ type sintered alloy magnet was manufactured.

Next, the densities of the various RCo ₅ type sintered alloy magnets obtained as a result were measured and the magnet characteristics were measured.
The results of these measurements are shown in Table 1.

〔The invention's effect〕

From the results shown in Table 1, all of the RCo ₅ type sintered alloy magnets manufactured by the methods 1 to 15 of the present invention have high density and have any of iHc, Br, and (BH) _max . While the RCo ₅ type sintered alloy magnets manufactured by the conventional methods 1 and 2 and the comparative methods 1 to 10 have at least one of the above magnetic characteristics, Is clearly inferior.

As described above, according to the method of the present invention, iHc, Br, and (B
It is possible to manufacture RCo ₅ type sintered alloy magnets with excellent H) _max magnet characteristics.

[Brief description of drawings]

FIG. 1 is a heating curve diagram showing the method of the present invention, and FIG. 2 is a heating curve diagram showing the conventional method.

Claims (1)

(57) [Claims] 1. A green compact formed from a raw material powder mainly composed of RCo ₅ type alloy powder (where R is one or more kinds of rare earth elements and Y) is heated to 1100 to 1200 ° C. in an Ar atmosphere.
When manufacturing an RCo ₅ type sintered alloy magnet by sintering at a predetermined temperature within the range of (1), (a) first, the green compact is heated in a hydrogen atmosphere at room temperature. ~ 20
It is kept at a predetermined temperature within the range of 0 ° C for a predetermined period of time to occlude hydrogen to make it a hydride, and (b) then, to prevent the growth of crystal grains at the time of sintering and to prevent the crystal atoms of the raw material powder In order to improve the sinterability by regularizing the arrangement disorder in, the hydrogen atmosphere is changed to an Ar atmosphere at a predetermined temperature of 900 ° C. or less, and complete dehydrogenation is performed to eliminate residual hydrogen, Of RCo ₅ type sintered alloy magnet with excellent magnet characteristics.