JPH04143221A - Production of permanent magnet - Google Patents

Abstract

PURPOSE:To uniformize and refine the structure of grain boundary phase and to obtain a magnet improved in uniform properties by performing heat treatment under specific conditions in a method for producing an R-Fe-B type permanent magnet by applying hot working to a cast ingot of alloy and making it anisotropic. CONSTITUTION:An alloy containing R (one or more elements among rare earths including Y), Fe, and B as essential components is melted and cast, and the resulting cast ingot is hot-worked at >=500 deg.C. This alloy is heat-treated at 750-1100 deg.C, held, as a second-stage heat treatment, at 250-750 deg.C, and cooled from the temp. right above the eutectic point of the alloy to the temp. right above the Curie temp. at >=5 deg.C/min cooling rate. The heat treatment temp. in the first stage is regulated to >=750 deg.C for the purpose of the early diffusion of primary- crystal Fe, and the grain of an R2Fe14B phase is rapidly grown and coercive force is lost when the above temp. is >=1100 deg.C. The heat treatment temp. in the second stage is regulated to a temp. not higher than the vicinity of the melting point (750 deg.C) of the R-enriched phase in the grain boundaries, and it takes time too much to attain this heat treatment when the temp. is below 250 deg.C. The range of temp. specifying the cooling rate is limited to the above range in order to prevent the occurrence of cracks, etc., and further, the structure of the grain boundary phase is coarsened when the cooling rate is lower than 5 deg.C/min, and, as a result, the properties of the magnet are deteriorated.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a method for producing a permanent magnet having magnetic anisotropy due to mechanical orientation, in particular R (where R is at least one rare earth element including Y). )+Fe+B as the basic raw material components.

[Prior Art] Permanent magnets are one of the important electrical and electronic materials used in a wide range of fields, from various household electrical appliances to peripheral terminal equipment for large computers. With the demand for smaller size and higher efficiency, permanent magnets are also required to have increasingly higher performance.

A permanent magnet is a material that generates a magnetic field without supplying electrical energy from the outside, and one that has a large coercive force and a high residual magnetic flux density is suitable.

Typical permanent magnets currently in use are alnico cast magnets, ferrite magnets, and rare earth-transition metal magnets, especially rare earth-transition metal magnets.
Co-based permanent magnets and R-Fe-B-based permanent magnets have been extensively researched and developed as permanent magnets with extremely high coercive force and energy product.

Conventionally, there are the following methods for manufacturing these R-Fe-B-based high-performance anisotropic permanent magnets.

(1) First, see Japanese Patent Application Laid-Open No. 59-46008 and )1.
sagaWa.

S, Fujimura, N, Togawa, H, Yam.
amoto and Y, Matsu-ura;-J,
Appl, Phys, Vol, 55(8), 15 M
Arch E984, P20A3, etc. are magnetically anisotropic sintered with an atomic percentage of 8 to 30% R (however, R is at least one rare earth element including Y), 2 to 28% B, and the balance Fe. It is disclosed that a permanent magnet is produced by sintering based on powder metallurgy.

In this sintering method, an alloy ingot is produced by melting and casting, and then pulverized to obtain magnetic powder with an appropriate particle size (several μm).

The magnetic powder is kneaded with a binder, which is a molding aid, and press-molded in a magnetic field to complete a molded product. The compact is sintered in argon at a temperature of around 1100° C. for 1 hour and then rapidly cooled to room temperature.

After sintering, the permanent magnet is heat-treated at a temperature of around 600°C to further improve its coercive force.

Regarding the heat treatment of this sintered magnet, Japanese Patent Application Laid-Open No. 61-2
The effects of multi-stage heat treatment are disclosed in Japanese Patent Laid-Open No. 17540, Japanese Patent Application Laid-open No. 165305/1983, and the like.

(2) JP-A-59-211549, R, W, Le
e; Appl.

Phys, Lett, Vol, 46(8), 15 Ap
ril 1985. P790 discloses an R-Fe-B magnet in which fine pieces of melt-spinned alloy ribbon with a very fine crystalline magnetic phase are bonded together with a resin.

This permanent magnet is manufactured by making a quenched thin piece with a thickness of about 30 μm using a quenched ribbon manufacturing apparatus used for manufacturing an amorphous alloy, and then kneading the thin piece with a resin and press-molding it.

(3) JP-A-60-100402, R, W, Le
e; Appl.

Phys, Lett, Vol, 46(8), 15 Ap
ril 1985. p? In step 90, the quenched flakes used in the method (2) above are subjected to a method called a two-step hot pressing method in a vacuum or an inert atmosphere to obtain a dense and anisotropic R-Fe-B magnet. is disclosed.

(4) Japanese Patent Application Laid-Open No. 62-276803 states that R (where R is at least one rare earth element including Y) 8 to
30 atom%, B2 to 28 atom%, Co50 atom% or less,
After melting and casting an alloy consisting of 115 at. A rare earth-iron permanent magnet is disclosed in which the cast alloy is made magnetically anisotropic by orienting its axis in a specific direction.

[Problems to be Solved by the Invention] The conventional methods for manufacturing R-Fe-B permanent magnets described in (1) to (4) above have the following drawbacks.

The manufacturing method for permanent magnets in (1) requires that the alloy be made into powder, but since R-Fe-B alloys are highly active against oxygen, making them into powder will cause additional oxidation. This results in a barrel-like appearance, and the oxygen temperature in the sintered body inevitably increases.

Also, when compacting the powder, a compacting aid such as zinc stearate must be used, which is removed beforehand during the sintering process. This carbon remains in the form of carbon, which is undesirable because it significantly reduces the magnetic performance of the R-Fe-B magnet.

The molded body after press molding with the addition of a molding aid is called a green body, which is extremely brittle and difficult to handle.

Therefore, a major drawback is that it takes a considerable amount of time to arrange them neatly in the sintering furnace.

Because of these drawbacks, generally speaking, R-Fe-B
Not only does the production of sintered magnets of this type require expensive equipment, but the production method has poor production efficiency, resulting in an increase in the production cost of the magnets. Therefore, it is not possible to take advantage of the advantages of R-Fe-B magnets, which have relatively low raw material costs.

Next, the permanent magnet manufacturing methods (2) and (3) use a vacuum melt spinning device, but this device currently has very poor productivity and is expensive.

The permanent magnet (2) is isotropic in principle, so it has a low energy product, and the squareness of the hysteresis loop is also poor.
It is disadvantageous both in terms of temperature characteristics and in terms of use.

The method (3) for manufacturing permanent magnets is a unique method of using hot press in two stages, but it cannot be denied that it is inefficient when considering actual mass production.

Furthermore, in this method, crystals -
The coarsening of the grains is significant, and the coercive force iHc is thereby extremely reduced, so that it cannot be used as a practical permanent magnet.

The method (4) for manufacturing permanent magnets does not involve a powder process and only requires one step of hot pressing, so it is the manufacturing method that can simplify the manufacturing process and reduce mass production costs the most.
There was a problem that the magnetic properties were slightly lower than those of the sintering method. In particular, in order to avoid the occurrence of cracks and chips during cooling after heat treatment, the cooling rate must be suppressed, resulting in problems such as deterioration of magnetic properties and deterioration of productivity.

The present invention solves the above-mentioned drawbacks of the prior art, particularly (4) the problem of the performance drawback and cracking of permanent magnets,
The purpose is to provide a high-performance, low-cost method of manufacturing permanent magnets.

[Means for Solving the Problems] The method for manufacturing a permanent magnet of the present invention uses R (where R is at least one rare earth element including Y).

Fe7E is used as the basic raw material component, the alloy as the basic component is melted and cast, then the cast ingot is hot worked at a temperature of 500°C or higher, and then the first heat treatment is performed at 750 to 1100°C. After that, as a second heat treatment, the temperature is maintained at 250 to 750°C, and then the magnetic alloy is cooled at a cooling rate of 5°C/min or more from a temperature just above the eutectic point to a temperature just above the Curie temperature. It is characterized by

The coercive force of the crystal grains of a magnetic alloy largely depends on the nature of the grain boundary phase with which the crystal grains are in contact. The grain boundary phase has a eutectic structure, but if the structure is coarse, the grain boundary phase becomes non-uniform, which causes the distribution of coercive force to become uneven within the same magnet, and the magnet's worsen performance. In the present invention, the structure of the grain boundary phase is made uniform and fine by cooling the temperature range from just above the eutectic point of the grain boundary phase to just above the Curie temperature at a cooling rate of 5°C/min or more. It was discovered that a uniform coercive force distribution could be obtained and the performance of the magnet would be improved. It has also been found that cracks and chips caused by cooling after heat treatment can be avoided by using the method of the present invention if the weight of the ingot is within 10 kg.

The preferred composition range of the permanent magnet in the present invention will be explained below.

Rare earths include Y, La, Ce+Pr,
Nd.

Sm, Eu, Gd, Tb, Dy,
Candidates include Ho, Er, Tm, Yb, and Lu, and one or more of these may be used in combination. The highest magnetic performance is obtained with Br, so Pr, Pr-Nd alloy, Ce-Pr-N are practically used.
d alloy etc. are used. Small amounts of heavy rare earth elements, e.g. DV
, Tb, etc. are effective in improving coercive force.

The main phase of the R-Fe-B magnet is R2FezB. Therefore, when R is less than 8w%, the above-mentioned compound is no longer formed and high magnetic properties cannot be obtained.On the other hand, when R exceeds 30 atomic%, the nonmagnetic R-rich phase increases and the magnetic properties are significantly deteriorated. Therefore, the appropriate range of R is 8 to 30 atomic %. However, for high residual magnetic flux density, preferably R8
~25W% is appropriate.

B- is an essential element for forming the R2Fe+4B phase, and if it is less than 2 atom%, it becomes a rhombohedral R-Fe system, so high coercive force cannot be expected, and if it exceeds 28 atom%, B-
The amount of non-magnetic phase rich in ions increases, and the residual magnetic flux density decreases significantly. However, in order to obtain a high coercive force, it is preferable to use B88 atoms or less, and if it is more than that, fine R2Fe+
It is difficult to obtain the 4B phase and the coercive force is small.

CO is an effective element for increasing the cu1↓- point of the present magnet, but since it reduces the coercive force, it is preferably 50 atomic % or less.

Elements such as Cu, Ag, Au, Pd, and Ga that exist together with the R-rich phase and lower the melting point of the phase have the effect of increasing coercive force. However, since these elements are non-magnetic elements, increasing the amount will reduce the residual magnetic flux density, so it is preferably 6 at % or less.

The temperature during hot working is desirably higher than the recrystallization temperature, preferably 500°C in the R-Fe-B alloy of the present invention.
That's all.

The heat treatment temperature is preferably 250°C or higher in order to clean grain boundaries and diffuse primary Fe, and R2Fe+J
If the B phase exceeds 1100°C, grains will grow rapidly and lose coercive force, so a temperature lower than this is preferred.

In addition, when performing heat treatment in two or more stages, the temperature in the first stage is preferably 750°C or higher so that primary Fe crystals can diffuse quickly, and the temperature in the second stage is preferably around the melting point of the R-rich phase at the grain boundaries or below. That is, the temperature is preferably 750°C or lower, and the temperature higher than 250°C is preferable because it takes too much time for the effect of heat treatment to occur.

The reason for the temperature range that determines the cooling rate is that in order to make the grain boundary phase into a fine and uniform eutectic structure, it is best to start at a temperature just above the eutectic point, and to cool around the Curie temperature of the main phase at a fast cooling rate. In this case, defects such as cracks will occur due to the strain that occurs as the main phase passes the Curie temperature. Therefore, the temperature range for cooling at a cooling rate of 5°C/min or more is from the temperature just above the eutectic point of the magnetic alloy to the Curie temperature. A range up to just above temperature is desirable.

Regarding the cooling rate, if it is slower than 5°C for 1 minute, the grain boundary phase group -
The weave becomes coarse, which is unfavorable for improving the performance of the magnet. Therefore, it is desirable that the speed be 5° C./min or more.

Next, examples of the present invention will be described.

[Example] [Example 1] A process diagram of the manufacturing method according to the present invention is shown in FIG.

According to this process, using an induction heating furnace in an argon atmosphere, P r +vF e va, 5Bsc u +, b
An alloy with the following composition was melted and cast. 7 At this time, rare earth, iron, and copper raw materials with a purity of 99.9% were used, and boron was ferroboron.

The cast ingot thus obtained was placed in an iron capsule, degassed, and sealed. To this, processing degree 3 at 950℃
0% hot rolling was performed in air four times to give a final working degree of 76%.

Further, during this hot working, the axis of easy magnetization of the crystal was oriented parallel to the direction in which the alloy was pressed.

After that, heat treatment was performed at 1000°C for 24 hours,
Next, after holding at 475℃ for 2 hours, 475℃~3
The temperature range of OO=C- was cooled at various cooling rates.
The cooling rate from 300°C was about 3°C for 1 minute.

The magnetic properties of these magnets are shown in Table 1, as well as the demagnetization curves! ! I (4πX-H curve) is shown in FIG. 2, and the coercive force distribution curve is shown in FIG. 3.

Table 1 All magnetic properties are B- at the maximum applied magnetic field of 25 kOe.
It was measured using an H tracer.

As shown in FIGS. 2 and 3, it can be seen that under conditions where the cooling rate after heat treatment is faster, the coercive force is more uniform and the squareness of the demagnetization curve is also improved.

For this reason, as shown in Table 1, although there is no large difference in coercive force depending on the cooling rate, there is a difference in maximum energy product.

In addition, no cracks or chips occurred due to cooling after heat treatment at any cooling rate.

[Example 2] Similarly to Example 1, an alloy having the composition shown in Table 2 was melted and cast using an induction heating furnace in an argon atmosphere according to the manufacturing process shown in FIG. The raw materials used at this time were also of similar purity.

The cast ingot thus obtained was placed in an iron capsule, degassed, and sealed. This was then hot-rolled in air for 4 baths at 1000°C, resulting in a final working degree of 75.
%.

After this, after holding at 1000°C for 24 hours, air cooling to room temperature, then holding at T2 shown in Table 2 for 2 hours, cooling under the following conditions, cutting and polishing. The magnetic properties were measured.

Condition 1: Air cooling after taking out from the heat treatment furnace. The cooling rate at this time is approximately 25° C./min in the temperature range from T2 to the Curie temperature of each alloy.

In the temperature range below the Curie temperature, controlled air cooling was performed at a cooling rate of 3°C/min.

Condition 2: After maintaining the temperature at T2, controlled air cooling (approximately 2.2°C/, e) was performed so that the temperature decreased linearly from T2 to the Curie temperature of each alloy in 90 minutes, and then the cooling rate was Controlled air cooling was performed at a rate of 3°C/min.

The magnetic properties of these magnets are shown in Table 3.

From the examples above in Table 1, it is clear that a permanent magnet whose basic raw material components are R (where R is at least one rare earth element including Y) + Fe and B can be hot worked at 500°C or higher. If it is, it becomes anisotropic and exhibits a high coercive force by heat treatment at 250 to 750°C, the highest (BH)max exceeds 308 GOe, and after heat treatment, the Curie It is clear that by cooling to just above the temperature at a cooling rate of 5°C/min or more, the magnetic properties are significantly improved and a magnet without cracks or chips can be obtained.

[Effects of the Invention As described above, the method for manufacturing a permanent magnet of the present invention has the following effects.

(1) The c-axis orientation rate can be increased, and the residual magnetic flux density B
It was possible to significantly increase r, and by making the crystal grains finer, it was possible to increase coercive force iHc, and the maximum energy product (BH) max was able to be significantly improved.

(2) The manufacturing process is simple and the cost is low.

(3) Compared to conventional sintering methods, processing man-hours and production investment can be significantly reduced.

(4) Compared to the conventional method of producing magnets using melt spinning, it is possible to produce magnets with high performance but at low cost.

(5) Compared to the conventional method of manufacturing magnets using hot working methods, the magnetic properties, particularly the squareness of the demagnetization curve, can be improved.

(6) Compared to conventional magnet manufacturing methods using hot working methods, magnets can be manufactured without cracks or chips caused by cooling after heat treatment.

[Brief explanation of the drawing]

FIG. 1 is a manufacturing process diagram of the R-Fe-B magnet of the present invention. The 27th graph shows the demagnetization curves of magnets with compositions of Pr+7Fe7s, 5BsCu+, and s. 1... Cooling rate 20°C/min 2... Cooling rate 3°C/min Figure 3 shows P r 17F ete, 5Bsc u +,
3 is a graph showing a distribution curve of coercive force in a magnet having an s composition. 1. Cooling rate of 20°C/min Application for cooling rate of 3°C/min or more - Seiko Epson Corporation

Claims (1)

[Claims] (1) R (where R is at least one rare earth element including Y), Fe, and B are used as the basic raw material components, and the alloy containing the basic components is melted and cast, and then the cast ingot is
Hot working at a temperature of 00℃ or higher, then 750~110℃
After performing the first heat treatment at a temperature of 0°C, as the second heat treatment, after holding at a temperature of 250 to 750°C, the range is from a temperature just above the eutectic point of the magnetic alloy to a temperature just above the Curie temperature. A method for producing a permanent magnet, characterized by cooling at a cooling rate of 5° C./min or more.