JPS6236365B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing rare earth permanent magnets made of intermetallic compounds of rare earth metals and transition metals, typified by samarium-cobalt permanent magnets, by powder metallurgy.

Initially, attempts were made to manufacture rare earth cobalt magnets by a casting method, but high magnetic properties could not be obtained. After that, the magnetic properties of rare earth permanent magnets improved dramatically after they began to be manufactured using powder metallurgy.

To briefly explain the manufacturing method using the powder metallurgy method, first, raw material powder containing each component in a predetermined amount is melted in an inert atmosphere to obtain an alloy ingot. After pulverizing this alloy, it is subjected to magnetic field orientation and processing to obtain a molded body of a desired shape. After sintering this compact, heat treatment such as solution treatment and aging treatment is performed to obtain a permanent magnet material.

Here, the pulverization is carried out in two stages: coarse pulverization and fine pulverization, and the final powder is 1 to 10 μm in size. Magnetic field orientation and pressure molding are usually performed at the same time when a mold is used, and the magnetic field strength required for orientation is 8 to 20 KOe, and the pressing force is 0.3 to 20 KOe.
It is estimated to be ^around 10ton/cm2.

The sintered body density of rare earth cobalt magnet is the theoretical value.
8.6g/cm ³ , 8.3-8.4 for industrially produced ones
g/ ^cm3 . Keep the molding density as close to this value as possible,
By minimizing shrinkage due to sintering,
A sintered body with more accurate dimensions can be obtained, and loss of expensive metal due to processing can be reduced. However, since the frictional force of powder is large,
In order to increase the molding density, the pressing force must be extremely increased, and if the pressing force is increased, the degree of orientation deteriorates, making it impossible to obtain high magnetic properties. In addition, due to the large frictional force of the powder, when the molded product is taken out of the mold,
It also has the disadvantage of being prone to cracking, chipping, cracking, etc., resulting in poor yield.

In order to solve these drawbacks, paraffin was mixed into the molding powder, but since alloys of rare earth metals and transition metals are extremely reactive, the paraffin evaporates during the sintering process. This causes a reaction between the magnet and the alloy, which actually worsens the magnetic properties. For this reason, lubricants for reducing the frictional force of powder are generally not used.

In view of the above, the present inventor conducted various studies on lubricants that reduce the frictional force of magnet alloy powder without adversely affecting magnetic properties, and as a result, discovered that oleic acid is suitable for this purpose.

The present invention was made based on this discovery.According to the present invention, it is possible to reduce the frictional force of the compacted powder, thereby increasing the compaction density and degree of orientation without increasing the pressing force or the orientation magnetic field. Moreover, it does not adversely affect the magnetic properties, and therefore the magnetic properties as a whole can be improved.

That is, the present invention is characterized in that, in a method for producing a rare earth permanent magnet using a powder sintering method, oleic acid is mixed in an amount of 1 wt % or less during pressure molding of alloy powder in a magnetic field.

Hereinafter, the present invention will be described in detail with reference to examples.

Sm26.0wt%, Fe15.5wt%, Cu9.0wt%,
The raw material was adjusted to contain 1.6 wt% Zr, 0.1 wt% Ti, and the balance Co, and was heated and melted in an argon atmosphere to obtain an alloy ingot. This alloy was coarsely ground and then finely ground in a ball mill. The obtained alloy powder was mixed with 0 to 1.0 wt% of oleic acid using isopropyl alcohol as a solvent. This was press-molded in a magnetic field of 10 KOe or more with a pressure of 1.5 ton/cm ² in a direction perpendicular to the magnetic field. This molded product was sintered at 1210°C for 1 hour in an argon atmosphere, and then solution treated at 1180°C for 1 hour. This sintered body was heated to 800℃ for 1
After time aging treatment, cooling rate of 100℃/hour
Cooled to 300°C.

The magnetic properties of the magnet material thus obtained were measured.
Of these, the residual flux density B _r and the maximum energy product (BH) _nax are shown in the figure. The density of the compact after pressure molding is also shown. From the figure, the amount of oleic acid is
B _r has a peak at 0.2 to 0.5 wt%, while (BH) _nax has a peak at 0.05 wt% of oleic acid, and decreases above that, and when it exceeds 1 wt%, it becomes worse than when it is not added. I know it's going to get worse. It is also shown that the molded density increases rapidly with the addition of a small amount of oleic acid, and that the rate of increase decreases at 0.05 wt% or more.

From the above results, it can be seen that by adding 1.0 wt% or less of oleic acid to the molding alloy powder, both the molding density and magnetic properties can be improved.

Although the above examples concerned _the production of samarium cobalt magnets represented by Sm ₂ (Cu Fe _Zr Ti Co) _{17 ,} similar olefin The effect of acid addition was observed.

[Brief explanation of the drawing]

The figure is a graph showing changes in maximum energy product (BH) _nax , residual magnetic flux density B _r , and molding density with respect to the amount of oleic acid mixed in an example of the present invention.

Claims (1)

[Claims] 1. In a method for manufacturing a rare earth permanent magnet by a powder metallurgy method in which alloy powder whose main components are rare earth metals (including yttrium) and transition metals is pressure-formed in a magnetic field and sintered, the alloy powder before pressure-forming in a magnetic field is used. A method for producing a rare earth permanent magnet, which comprises adding 1.0 wt% or less of oleic acid to improve the magnetic field orientation of the alloy powder.