JPS63107009A - Manufacture of permanent magnet - Google Patents

Abstract

PURPOSE:To obtain a rare earth-iron group permanent magnet having high performance at low cost by using a casting method as the process of a base and combining hot working. CONSTITUTION:An alloy mainly comprising a rare earth element, iron and boron is dissolved and cast, and hot-worked. Or the alloy consisting of said basic ingredients is dissolved and cast, hot-worked, and thermally treated. Or the alloy composed of said basic ingredients is dissolved and cast, hot-worked and thermally treated, hydrogen is occluded into said cast alloy and the alloy is crushed, and the powder of the crushed alloy is kneaded with an organic binder and pressure-molded. A temperature in said hot working is brought to a recrystallization temperature or more of 500-1100 deg.C, either of extrusion, rolling working or stamping working is employed as hot working, and the magnet alloy is oriented and treated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a permanent magnet whose basic components are rare earth elements, iron, and boron.

[Prior Art] Permanent magnets are one of the important electrical and electronic materials used in a wide range of fields, from various household appliances to peripheral terminal equipment for large computers.

With the recent demand for smaller and more efficient electrical products,
Permanent magnets are also required to have increasingly higher performance. Typical permanent magnets currently in use are alnico, hard ferrite, and rare earth-transition metal magnets. In particular, R-Co permanent magnets, which are rare earth-transition metal magnets, and R
Since -Fe-B permanent magnets provide high magnetic performance, much research and development has been carried out on them.

Conventionally, there are methods for manufacturing these R-Fe-B permanent magnets as shown in the following documents.

(1) A sintering method based on powder metallurgy.

(Reference 12 Reference 2) (2) A quenched thin strip manufacturing device used for manufacturing amorphous alloys produces quenched thin flakes with a thickness of about 30 μm, and the quenched thin flakes are made into magnets using a resin bonding method. Resin bonding method used. (Reference 31 Reference 4) (3) A method in which the rapidly cooled flakes used in the method (2) above are mechanically oriented by a two-step hot press method. (Reference 4
1 Reference 5) Here, Reference 1: Japanese Unexamined Patent Publication No. 1983-46008; Reference 2:
M, Sagawa, S, Fujilmura, N, T
ogava, tl.

YaIIlaioto and Y, Matsuura
;J, Appl, Phys, Vol, 55 (8B5Ma
roh 1984. p2083゜Reference 3: Unexamined Japanese Patent Publication No. 1983-
Publication No. 211549; Document 4: R, W, Lee: A
ppl, Phys, Lett, Vol, 4B(8)
.

15 April 1985. p790; Document 5: Japanese Unexamined Patent Publication No. 80-100402 Next, the above conventional method will be explained.

First, in the sintering method (1), an alloy ingot is produced by melting and casting, and then pulverized to obtain magnet powder with an appropriate particle size (several μm). 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 was sintered in argon at a temperature of around 1100°C for 1 hour.
It is then rapidly cooled to room temperature. After sintering, the coercive force is further improved by heat treatment at a temperature of around 600°C.

In the resin bonding method (2) using quenched flakes by the melt spinning method, first, a quenched ribbon of R-Fe-B alloy is produced at an optimal rotation speed of a quenched ribbon manufacturing apparatus. Obtained thickness 3
A ribbon-like thin strip of 0 μm is an aggregate of crystals with a diameter of 1000 Å or less, is brittle and easily broken, and since the crystal grains are distributed in the same direction, it is also magnetically isotropic. If this ribbon is crushed to a suitable particle size, kneaded with a resin, and press-molded, it is possible to fill the ribbon to about 85% by volume at a pressure of about 7 tons/C-.

In the manufacturing method (3), first, a ribbon-like quenched ribbon or piece of ribbon is heated in a vacuum or in an inert atmosphere for about 70 minutes.
Place in a graphite or other heat-resistant press mold preheated to 0°C. When the ribbon reaches the desired temperature - axial pressure is applied. Although the temperature and time are not specified, suitable conditions for producing sufficient plasticity include T-725±25°C and pressure of about P-1.4 ton/cd. At this stage, although the magnet is slightly oriented in the pressing direction, it is generally isotropic. The subsequent hot pressing is carried out in a mold with a large surface area. Most commonly, 700
Press at 0.7 ton/c for a few seconds. The sample then becomes 1/2 of its original thickness and is oriented parallel to the pressing direction, making the alloy anisotropic. A method using these steps is called a two-step hot press method. By this method, a dense and anisotropic R-Fe-B magnet is obtained.

It should be noted that the crystal grains of the ribbon produced by the initial melt spinning method are made smaller than the grain size at which the ribbon exhibits its maximum coercive force, so that coarsening of the crystal grains may occur during subsequent hot pressing. to obtain the optimum particle size.

However, in this method, at high temperatures, for example, 800° C. or higher, the crystal grains become significantly coarsened, resulting in an extremely low coercive force iHc, and the magnet cannot be used as a practical permanent magnet.

[Problems to be Solved by the Invention] Although R-Fe-B magnets can be manufactured using the above-mentioned conventional techniques, these manufacturing methods have the following drawbacks.

In the sintering method (1), it is essential to turn the alloy into powder, but since R-Fe-B alloys are very active against oxygen, oxidation becomes even more intense when they are turned into powder. The oxygen concentration in the body inevitably increases. Also, when compacting the powder, compacting aids, such as zinc stearate, must be used, which are removed beforehand during the sintering process, but some carbon forms remain inside the magnet. So it remains. This carbon is undesirable because it significantly reduces the magnetic performance of R-Fe-B.

The molded body after press molding with the addition of a molding aid is called a green body. It is very fragile and difficult to handle. Therefore, a major drawback is that it takes a considerable amount of effort to arrange them neatly in the sintering furnace.

Because of these drawbacks, generally speaking, R-Fe-B
Manufacturing sintered magnets of this type not only requires expensive equipment, but also has poor production efficiency, resulting in high magnet manufacturing costs. Therefore, R-Fe, which has relatively low raw material cost,
-It is hard to say that this is a method that can take advantage of the advantages of B-based magnets.

Next, methods (2) and (3) use a vacuum melt spinning device, which currently has very low productivity and is expensive.

The method (2) is isotropic in principle, resulting in a low energy product, and the squareness of the hysteresis loop is also poor, which is disadvantageous in terms of temperature characteristics and usage.

Method (3) is a unique method that uses a hot press in two stages, but it cannot be denied that it is extremely inefficient when considering actual mass production.

Furthermore, in this method, at high temperatures, for example, 800° C. or higher, the crystal grains become significantly coarsened, resulting in an extremely low coercive force iHc, making it impossible to produce a practical permanent magnet.

The present invention solves the above-mentioned drawbacks of the prior art, and its purpose is to create a high-performance, low-cost rare earth-iron permanent magnet by using a casting method as a base process and also using hot working. The purpose of this invention is to provide a method for manufacturing the same.

[Means for Solving the Problems] The first method of manufacturing a permanent magnet of the present invention is a method of manufacturing a magnet whose basic components are rare earth elements, iron, and boron.
A method for producing a permanent magnet, comprising at least the steps of melting and casting an alloy made of the basic components, and hot working after casting, and the second method is a method for producing a permanent magnet that is similar to the casting method of the first method. A method for producing a permanent magnet, characterized in that a step of heat treatment is added subsequent to the step of post-hot working, and the third method is a method for manufacturing a permanent magnet, which is characterized in that a step of heat treatment is added after the step of hot working after casting in the first method. This method of manufacturing a permanent magnet is characterized by comprising a step of absorbing hydrogen into a cast alloy after heat treatment and pulverizing it, and then kneading the pulverized alloy powder with a machine binder and press-molding it.

[Function] As mentioned above, the sintering method and the rapid cooling method, which are methods for producing rare earth-iron magnets, each have major drawbacks such as difficulty in powder control through pulverization and poor productivity.

In order to improve these drawbacks, the present inventors undertook research on magnetization in the bulk state, and first developed an anisotropic process by hot working in the composition range of a magnet whose basic components are rare earth elements, iron, and boron. The inventors have discovered that it is possible to obtain a resin-bonded magnet by heat-treating the cast ingot, pulverizing it by hydrogen pulverization, and cross-curing it with an organic binder.

The anisotropy caused by hot working in this method is described in the above-mentioned document 4.
Only one step is required, instead of two steps as in the quenching method shown in Figure 2, and the process can be carried out in bulk, resulting in extremely high productivity. Furthermore, since there is no need to crush the cast ingot, the sintering method does not require any strict atmosphere control, and equipment costs are greatly reduced.

Furthermore, resin-bonded magnets do not have the problem of being isotropic in principle like magnets produced by the quenching method, and an anisotropic resin-bonded magnet can be obtained, achieving the high performance of R-Fe-B magnets. , it is possible to take advantage of the feature of low cost.

Research on magnetization in the bulk state (Reference 6) shows that Nd
Fe Co V B Toi 1B
, 2 50.7 22.8 1.3 9.2 The argon gas spraying with the composition was a test using a small sample sucked up by dissolution in the atmosphere, and this is thought to be due to the rapid cooling effect of small sample collection. .

Document 6: Hiroaki Miho et al. (Japanese Society of Metals, 1985 Autumn Lecture, Lecture number (544)) In this composition, Nd2F, which is the main phase in normal casting,
The 614B phase becomes coarse and good magnetic properties cannot be obtained by a little plastic working.

The optimal composition of conventional R-Fe-B magnets was R15Fe77B8 as shown in Document 2.

This composition has a Roll, 7
B2.4 5.9 Shifting to the B-rich side. This is explained from the point that in order to obtain a coercive force, not only the main phase but also non-magnetic phases such as an R-rich phase and a B-rich phase are required.

However, in the composition according to the present invention, on the contrary, the peak value of the coercive force exists where the B content shifts to the side where there is less B. In this composition range, the coercive force is drastically reduced in the case of the sintering method, so it has not been much of a problem so far. However, although high coercive force cannot be obtained by ordinary casting methods, high coercive force can be obtained by hot working.

These points can be considered as follows. First of all, whether a sintering method or a casting method is used, the coercive force mechanism itself is ntJ.
It follows the creatiorl model. This is because the initial magnetization curves of both exhibit a steep rise like S m Co 5. The coercive force of this type of magnet is basically based on a single domain model.

That is, in this case, R2Fe having large magnetocrystalline anisotropy
If the 14B compound is too large, it will have domain walls within the grains, so reversal of magnetization will easily occur due to movement of the domain walls, and the coercive force will be small.

On the other hand, when the particles become smaller to a certain size or less, the particles no longer have domain walls, and the reversal of magnetization proceeds only by rotation, so the coercive force increases.

That is, in order to obtain an appropriate coercive force, it is necessary that the RF e 14B phase has an appropriate particle size. The appropriate particle size is around 10 μm, and in the case of sintered type,
The particle size can be adapted by adjusting the powder particle size before sintering.

However, when the casting method and hot working method are combined, R2
The crystal size of the F814B compound is first determined at the stage of solidification from the molten metal, but since the crystals are made finer by hot working, the final crystal size of the magnet depends on the hot working processing conditions. It can be adjusted by selecting , and a sufficient coercive force can be created.

Next, regarding resin bonding, resin bonded magnets can certainly be created using the quenching method described in Document 4.

However, the powder created by the rapid cooling method has a diameter of 1000 Å.
Since the following polycrystals are gathered in the same direction, it is magnetically isotropic, and it is not possible to create an anisotropic magnet.
-The characteristics of low cost and high performance of the B series cannot be utilized. In the case of a water-based material, if pulverization is performed using hydrogen pulverization with small mechanical strain, the holding force can be maintained considerably and resin bonding can be performed. The biggest advantage of this method is that, unlike Document 4, it is possible to create an anisotropic magnet.

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

Rare earth elements include Y, La, Ce, and Pr.

Nd, Sm, Eu, Gd, Tb, Dy, t(o, Er,
Tm, Yb, and Lu are listed as candidates, and one or more of these may be used in combination. The highest magnetic performance is obtained with Pr.

Therefore, Pr, Pr-Nd alloy, Ce-Pr-
Nd alloy or the like is used. Also, a small amount of additive elements, such as heavy rare earth elements DY, Tb, etc., and AI.

Mo, Si, etc. are effective in improving coercive force.

The main phase of the R-Fe-B magnet is R2Fe14B. Therefore, if R is less than 8 atoms and 96 atoms, the above compound is no longer formed and a cubic crystal structure having the same structure as α-iron is formed, so that high magnetic properties cannot be obtained. On the other hand, if R exceeds 30 atomic %, the nonmagnetic R-rich phase increases and the magnetic properties deteriorate significantly. Therefore, the appropriate range of R is 8 to 30 atomic %. However, in order to form a cast magnet, preferably R8 to 25 atomic % is appropriate.

B is an essential element for forming the R2Fe14B phase, and if it is less than 2 atomic %, it becomes a rhombohedral R-Fe system, so a high coercive force cannot be expected. Moreover, when it exceeds 28 at %, the amount of B-rich nonmagnetic phase increases, and the residual magnetic flux density decreases significantly. However, as a cast magnet, B88 atoms or less are preferable, and if it is larger than that, a fine R2F e 14B phase cannot be obtained unless special cooling is performed, and the coercive force is small.

Co is an element that is effective in increasing the Curie point of water-based magnets, and basically replaces Fe sites to create R2F 81
4B, but this compound has a small crystal anisotropy magnetic field, and as the amount of this compound increases, the coercive force of the magnet as a whole decreases. Therefore, IK can be considered as a permanent magnet.
In order to provide a coercive force of Oe or more, the content is preferably within 50 atomic %.

Al exhibits the effect of increasing holding power. (Reference 7: Zhan
g Maocai et al.: Proceedlngsofth
e 8th International Works
hop on Rare-Farth Magnets
, 1985. Although this document 7 shows the effect on sintered magnets, the same effect also exists on cast magnets. However, since AI is a non-magnetic element, increasing the amount added will lower the residual magnetic flux density, and if it exceeds 15 at %, the residual magnetic flux density will be lower than that of hard ferrite, so it cannot fulfill its purpose as a rare earth magnet. . Therefore A
The amount of I added is preferably 15 atomic % or less.

Further, in the present invention, hot working is a concept with respect to cold working, and refers to plastic working at a high temperature in which most of the working strain caused by plastic working is removed during processing.

Therefore, during hot working, crystal grain refinement due to recrystallization and subsequent growth of crystal grains also occur, and it is clear that these phenomena are also included in hot working.

The temperature during hot working is desirably higher than the recrystallization temperature, and in the R-Fe-B alloy of the present invention, preferably 500
℃ or higher.

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.

First, as shown in FIG. 1, an alloy having a desired composition is melted in an induction furnace and cast into a mold.

Next, various types of hot working were performed to impart anisotropy to the magnet.

As various hot workings, Fig. 2 shows an explanatory diagram of extrusion processing, Fig. 3 shows an explanatory diagram of rolling processing, and Fig. 4 shows an explanatory diagram of stamping processing.

In the figure, 1: hydraulic press, 2: die, 3: magnet alloy, 4: direction of magnetized molten metal, 5: roll, 6: stamp, 7;
The board is shown.

In this example, the hot processing includes ■extrusion processing,
Either rolling or stamping was performed at 1000°C to orient the magnetic alloy.

Regarding the extrusion process (2), we devised a way to apply force from the die 2 side so that the force was applied in the same direction.

For the rolling process (2) and the stamping process (2), roll 5. Adjusted the speed of Stamp 6.

In either method, the axis of easy magnetization of the crystal is oriented parallel to the direction in which the alloy is pressed, as shown by the arrow, in the high temperature range (500 to 1100°C).

After melting and casting an alloy whose basic components are rare earth elements, iron, and boron, the present inventors conducted extensive plastic working experiments and obtained the following experimental results.

(1) Cracks occur in alloy ingots of most compositions when plastically worked at low temperatures between room temperature and 200°C and at high strain rates.

Coercive force IHc when magnetically measured using a small piece that is not broken
increases in proportion to the processing rate, but crystal orientation hardly occurs, so the residual magnetic flux density Br hardly increases. For this reason, in plastic working within this range, the maximum energy product (BH), ax, hardly increases.

(2) On the other hand, when plastic working is performed at a high temperature exceeding 1 ion° C., no cracking occurs even at a high strain rate, the workability becomes good, and good crystal orientation occurs. However, the coercive force 111c decreases.

(3) When hot working between 500 and 1100°C, the strain rate can be increased, the residual magnetic flux density Br and the coercive force iHc increase, and the maximum energy product (Bl) also increases. Above all, the plastic working temperature A temperature of 800 to 1050°C is preferable.

(4) Even when an ingot made of the alloy composition of the present invention is heated to near its melting point, coarsening of crystal grains occurs only slightly.

(5) The relationship between processing rate, average C-axis and orientation is as follows: When processing rate is 20%, C-axis orientation rate is 60-70%, when processing rate is 40%, C-axis orientation rate is 65-75%, and when processing rate is 40%, C-axis orientation rate is 65-75%. C-axis orientation rate is 75-85% at 60%, C-axis orientation rate is 85-959 at 80% processing rate.
6. At a processing rate of 90%, the C-axis orientation rate is 85-98%.

An alloy having the composition shown in Table 1 was melted and a magnet was produced by the method shown in FIG. However, the hot working method used is also listed in Table 1. In addition, all annealing heat treatment after hot processing is 100%
The test was carried out at 0°C for 24 hours.

In Table 1, hot working is performed at a processing temperature of 500 to 110.
Testing was carried out under various combinations of conditions at 0° C. and strain rates of 10 −4 to 1/sec, of which 1000° C. is shown as a representative example. Also, the optimum conditions for annealing, ie, temperature and time, vary depending on the composition of the alloy and the hot plastic working conditions. Depending on the composition, a temperature of 500 to 800°C is suitable, and a temperature of 800 to 1000°C is suitable depending on hot working conditions.

Table 2 shows the composition of Pr Pe B 5Nd3
oPe55B and Ce3NdxoPrt4Fe5o
Taking CO17Zr2B14 as a representative example, the relationship between plastic working temperature and workability ◆1110" C-axis orientation rate is shown. The working rate is targeted at 80%, and Δ marks indicate cracks occurred during plastic working. , x marks indicate those that could not be plastically processed.

The plastic working temperature ranges from 500 to 1,100°C, and among them, 800 to 1,050°C is excellent.

When both magnetic properties and productivity are evaluated together, it is 900-1
050°C is optimal. The strain rate can be increased as the temperature increases and as the boron content of rare earth elements decreases.

The strain rate in this experiment was in the range of 10-' to 1/sec.

Among them, a strain rate of 1 O-3 to 10"/sec was better. At around 1000°C, it is recommended to set the strain rate to 1 to 102/sec. Especially in extrusion molding, the processing stress is mainly compressive stress. It turned out that this is possible because the tensile stress is small.

Furthermore, as the C-axis orientation rate increases, both the residual magnetic flux density B' and the coercive force 1c increase, and (Bit) and ax rapidly increase.

Table 3 shows the results. The residual magnetic flux density of the sample without hot working is shown as reference data.

From Table 3, it can be seen that the residual magnetic flux density increased and magnetic anisotropy was achieved by all hot working methods such as extrusion, rolling, and stamping. Among these, the extrusion method is superior.

[Example 2] Here, an example using a normal casting method will be described.

First, an alloy having the composition shown in Table 4 was melted in an induction furnace, cast in an iron mold, and after hot working, annealing heat treatment was performed at 1000° C. for 24 hours to magnetically harden the ingot.

At this time, the average grain size after annealing was about 15 μm.

If this step is used to cut and grind the material, it will become an anisotropic magnet.

For resin-bonded type magnets, 18-8 at room temperature.
After repeatedly absorbing hydrogen in a hydrogen gas atmosphere of about 10 atm in a stainless steel container and dehydrogenating it at 10'' tor, and pulverizing it, 4% epoxy resin was kneaded and mixed in a magnetic field of 10 KOe. Transverse magnetic field forming was performed.

The above results are shown in Table 5.

Table 1 Table 3 Table 4 Table 5 [Effects of the Invention] As described above, according to the method for producing a permanent magnet of the present invention, after casting rare earth elements, etc., the temperature is 500 to 1100 °C,
By hot working at a processing rate of 50% or more and a small strain rate, the following effects are achieved.

(1) The C-axis orientation ratio can be increased, and the residual magnetic flux density B
It was possible to significantly improve r.

(2) Also, by making the crystal grains finer, the coercive force IH
It was possible to significantly increase c.

(3) The synergistic effect of (1) and (2) made it possible to significantly increase the maximum energy product (B11).

ax (4) Compared to conventional sintering methods, processing man-hours and production equipment investment can be significantly reduced.

(5) Compared to the conventional melt spinning method, it was possible to produce magnets with high performance and at low cost.

[Brief explanation of the drawing]

Fig. 1 is a manufacturing process diagram of the R-Fe-B magnet of the present invention, Fig. 2 is an explanatory diagram of the orientation treatment of the magnet alloy by hot extrusion,
FIG. 3 is an explanatory diagram of orientation treatment of magnetic alloy by hot rolling,
FIG. 4 is an explanatory diagram of orientation processing of a magnetic alloy by hot stamping. In the figure, 1: hydraulic press, 2: die (mold), 3: magnet alloy, 4: direction of magnetized molten metal, 5: roll, 6: stamp, 7: substrate. Note that the reference numerals in the drawings indicate the same or equivalent parts.

Claims (3)

[Claims] (1) A method for manufacturing a magnet whose basic components are rare earth elements, iron, and boron, characterized by comprising at least the steps of melting and casting an alloy made of the basic components, and hot working after casting. A method of manufacturing permanent magnets. (2) A method for manufacturing a magnet whose basic components are rare earth elements, iron, and boron, including at least the steps of melting and casting an alloy made of the basic components, hot working after casting, and then heat treatment. A method for producing a permanent magnet characterized by: (3) A method for manufacturing a magnet whose basic components are rare earth elements, iron, and boron, which includes at least a step of melting and casting an alloy made of the basic components, a step of hot working after casting, and a step of hot working the cast alloy after heat treatment. 1. A method for producing a permanent magnet, comprising the steps of pulverizing the alloy by absorbing hydrogen therein, and then kneading the pulverized alloy powder with an organic binder and press-molding the powder.