JPH0661082A - Forming method of permanent magnet - Google Patents

Abstract

PURPOSE:To form a large permanent magnet which is magnetically uniform and mechanically excellent, by a method wherein the composition of an ingot satisfies a specified condition. CONSTITUTION:A plurality of ingots of an R-Fe-B-M base permanent magnet (R is a rare earth element whose main component is praseodymium or neodymium and M is an additive element) which have the same composition are put in a frame to be arranged. By performing hot processing, a plurality of the ingots are integrally unified in a body, and magnetic anisotropy is induced. Thereby a magnetically uniform permanent magnet is manufactured. As to the composition of the ingot, the following conditions are satisfied: a>0, b>0 and 2<=a+b<=11, where a=R(at.%)-11.76(at.%) and b=M(at.%). Hence a permanent magnet which is magnetically uniform and mechanically excellent can be formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a large permanent magnet from a plurality of ingots. More specifically, it is mainly composed of rare earth elements, iron and boron, and is magnetically uniform and has a high mechanical strength. The present invention relates to a method of manufacturing a permanent magnet.

[0002]

BACKGROUND OF THE INVENTION Permanent magnets have hitherto been used in various electric devices, but their applications have greatly expanded with the recent development of electronic technology.

Typical permanent magnets are alnico type,
Hard ferrite-based and samarium-cobalt-based alloys are known, but recently, rare earth elements-iron-boron-based alloys have been used as a permanent magnet having high magnetic properties without containing expensive samarium or cobalt. It has attracted attention and has been put to practical use in various applications.

Along with the increase in size and performance of industrial equipment, the permanent magnets used are also required to increase in size and performance.

As a method for producing a rare earth element-iron-boron permanent magnet, a rare earth element-iron-boron alloy is pressed while applying magnetism to magnetically anisotropically produce a permanent magnet. There is. However, in this method, there is a limit to the size of the magnet that can be obtained because the range of generation of the uniform magnetic field is limited, and the size is about 150 mm × 150 mm × 25 mm. Therefore, in order to manufacture a large magnet, a small magnet must be bonded with an adhesive such as an epoxy resin.

However, there are a number of problems with this method. Since the adhesive surface is magnetically neutral, it forms a magnetic valley, resulting in poor magnetic properties. Moreover, it is weak in bending strength and shear strength, and also weak in heat. The heat resistant temperature is about 200 ° C. In addition to that, mechanical precision is not obtained.

On the other hand, there is also a method in which a large ingot is made of a rare earth element-iron-boron system alloy and is anisotropically made by rolling to make a large permanent magnet.

In the method for producing such a large ingot, the cooling rate inside the cast ingot becomes small and the equiaxed crystal inside and the columnar crystal at the outer peripheral portion are macroscopically divided. Therefore, if it is left as it is, the magnetic characteristics after hot working will be high or low. Therefore, in order to obtain a magnet having uniform characteristics from the magnet, it is necessary to cut out the magnet, but this leads to a low yield and a high cost. In addition, since the high-characteristic portion is limited, it is not possible to make a high-performance and uniform large magnet.

Therefore, it is an object of the present invention to provide a method for producing a large permanent magnet which is magnetically uniform and mechanically excellent.

[0010]

In view of the above object, the R-F
As a result of earnest research on a method in which a plurality of ingots containing e-B as a main component and having the same composition are arranged side by side and subjected to hot working to integrate the plurality of ingots and cause magnetic anisotropy The present inventor has discovered that a large permanent magnet that is magnetically uniform and mechanically excellent can be produced by using an ingot whose composition is limited to a specific range. The present invention is based on the above findings.

That is, according to the method of the present invention, an R-Fe-BM system having the same composition (wherein R represents a rare earth element containing praseodymium or neodymium as a main component, and M represents an additive element) is permanent. A method for producing a magnetically uniform permanent magnet by placing a plurality of magnet ingots side by side and performing hot working to unify the plurality of ingots and magnetically anisotropy, R's a
Letting t.%-11.76 at.% be a and M at.% be b, the composition of the ingot should satisfy the following conditions: a> 0, b> 0, and 2 ≦ a + b ≦ 11. Characterize.

[0012]

The method of the present invention for producing a permanent magnet will be described in detail below. FIG. 1 is a flow chart showing a manufacturing process of a permanent magnet using the method of the present invention.

First, the raw materials are mixed in step (a). In this type of permanent magnet, the phase exhibiting magnetic properties (main phase) is R ₂ Fe ₁₄ B. Here, R represents a rare earth element containing praseodymium or neodymium as a main component. However, in addition to R ₂ Fe ₁₄ B as the main phase, it is easier to form the liquid phase portion in the hot working by having a phase whose composition is slightly changed, and to easily form solid particles that are the ferromagnetic main phase. Since the magnet can be rotated and oriented, the strength of the finally obtained magnet is improved.

Specifically, R at.%-11.76 at.% Is a, and M at.% Is b, and the raw materials are mixed so that the composition of the ingot satisfies the following three conditions. (A) a> 0 (I) b> 0 (U) 2 ≦ a + b ≦ 11

When the composition is R ₂ Fe ₁₄ B, at.% Of R is
= 11.76 at.%. Since the at.% Of R> 11.76 at.% Is transformed by modifying the formula under the condition of (a), the condition of (a) is said to be larger than when the at.% Of R is the composition of R ₂ Fe ₁₄ B. It means that. Specifically, the condition is satisfied by adding a rare earth element such as Dy or Tb.

The expression under the condition (ii) indicates that an element (additive element M) other than R, Fe, and B is present. As such additional elements, Co, Cu, N
There are transition metal elements such as b and V, and elements of Group 3B of the periodic table such as Al and Ga.

The formula under the condition (u) represents the range in which the phases other than R ₂ Fe ₁₄ B exist in at.%. (A +
If b) is less than 2 at.%, the phase of intermetallic compound R ₂ Fe ₁₄ B will increase in the ingot and the liquid phase other than that will decrease in the hot working described later. The liquid phase diffusion does not proceed sufficiently and the 4-point bending strength of the obtained magnet is lower than 20 kgf / mm ² . On the other hand, when (a + b) exceeds at. 11%, the amount of intermetallic compound R ₂ Fe ₁₄ B in the ingot is small in the hot working described later, and liquid phase diffusion proceeds, but other than the intermetallic compound. Since there are many phases, the strength of the obtained magnet is low, and the 4-point bending strength is lower than 20 kgf / mm ² .

If the three conditions of (a), (i), and (u) are satisfied, the four-point bending strength of the finally obtained magnet will be 20.
More than kgf / mm ² .

After the raw material mixture is obtained, as a step (b), this is heated and melt-mixed. This melt mixing must be performed in an inert gas atmosphere for the purpose of preventing oxidation. Specifically, the raw material mixture is placed in a crucible such as Al ₂ O ₃ , vacuumed once, and then an inert gas such as high-purity argon gas is introduced to heat and melt.

In the present invention, the heat-melted raw material mixture is used for casting to produce an ingot. Here, the finally obtained magnet has excellent magnetic properties,
The conditions for achieving excellent mechanical strength are (1) the cross-sectional area of the ingot pouring surface, (2) the volume fraction of columnar crystals in the ingot, (3) the average cooling rate after ingot casting, The volume of the ingot (4) and the average particle diameter of the main phase particles in the ingot (5) are preferably as follows. However, it is not necessary to satisfy all the conditions in (1) to (5), and when one condition is prioritized, the ranges in other conditions may change with a certain width.

(1) Ingot pouring surface cross-sectional area When the raw material mixture is heated and melted into a uniform state,
As (c), the melt is poured into a mold. As a mold,
It is preferable to use a material made of Cu-Be, pure Cu, stainless steel or the like. In order for the obtained magnet to have characteristics of 25 MGOe or more, casting is performed with the cross-sectional area of the pouring surface being 20 cm ² or less. It is particularly preferably 0.5 to 16 cm ² . here,
The cross-sectional area of the pouring surface in the mold is defined by the cross-sectional area of the pouring surface (A) = V / h, where V is the volume of the casting ingot and h is the average height of the casting ingot. . At this time, the cross section of the cast ingot is preferably a rectangle whose shortest side is in the range of 0.4 to 4 cm.

(2) Volume fraction of columnar crystals in ingot The volume fraction of columnar crystals in the ingot is 40% or more. If the volume fraction of columnar crystals is less than 40%, the volume fraction of equiaxed crystals will increase, and there will be a magnetic difference in height inside the magnet obtained after hot working. Can't get The volume fraction of columnar crystals is 40 to 10
Magnet obtained if the 0% (BH) _{ma x} is equal to or greater than 25 MGOe. In order to adjust the volume fraction to the above range, the temperature of the mold is set to 200 ° C. or lower in the step (c). Mold temperature is 20
Above 0 ° C, the volume fraction of columnar crystals formed in the ingot becomes less than 40%.

(3) Rapid cooling is performed as an average cooling rate step (d) after ingot casting . The rapid cooling can be performed by bringing the cooling medium into contact with the side surface of the mold. By this quenching, fine crystal nuclei (which become the nuclei of columnar crystals formed in the material in the heat treatment described later) consisting of the ferromagnetic main phase are formed in the material. Average cooling rate is 5 ℃ /
It is preferably not less than sec, especially 5 to 200 ° C./sec. If it is less than 5 ° C / sec, the obtained magnet cannot have characteristics of 25MGOe or more. Further, at 200 ° C./sec, the upper limit value of 35 MGOe is reached, so it is not preferable in terms of cost to set the cooling rate higher than that. The average cooling rate can be calculated by measuring the cooling curve with a thermocouple.

(4) Volume of Ingot Once the ingot is obtained by the step (d), it is released from the mold (step
(e)) and machine to the required size (cross-sectional area: 0.2 to 20 cm ² ) by mechanical cutting and polishing. Volume of each cast ingot and 0.1 cm ³ or more, particularly preferably in the 0.1 ~1000cm ^3. If you use an ingot of this size,
The finally obtained magnet will have characteristics of 25 MGOe or more. On the other hand, when an ingot larger than 1000 cm ³ is used, the volume fraction of equiaxed crystals increases when cast. It should be noted that each ingot does not necessarily have to have the same volume as long as it has a volume within the above-mentioned range, and the volume may be slightly different depending on the position. If necessary, degreasing is performed using acetone or the like. From process (a) to process
By repeating (e), the required number of ingots are manufactured in consideration of the size of the finally obtained magnet.

[0025] (5) a heat treatment for a plurality of ingots obtained in an average particle size above the main phase particles in the ingot (step (f)
)I do. By this heat treatment, α-Fe in the ingot
Disappears and the main phase (R ₂ Fe ₁₄ B), which is a ferromagnetic phase, crystallizes out. The heat treatment must be performed in a vacuum of 5.0 × 10 ^-4 Torr or less or in an inert gas. The average particle size of the main phase particles in the ingot is 15 μm or less, and particularly preferably 1 to 15 μm. According to the research conducted by the present inventors, if the average particle size is within the above range, the finally obtained permanent magnet (BH)
_{The max} is 25 MGOe or more, and the 4-point bending strength is 20 kgf / mm ² or more. In order to obtain such a magnet, the heat treatment time is preferably about 1 to 10 hours, and the heat treatment temperature is preferably 600 to 1100 ° C. In addition, the particle diameter in the present invention is measured by a direct intersection method.

After the heat treatment, a plurality of ingots produced by the above method are lined up and put in a frame (step (g)). Each ingot preferably has the same composition, but each element in the composition is 0.1 at. There may be a difference of about%.
It is preferable to use a frame made of a metal material such as a mild steel material (S35C) that is easily compositionally deformed. The thickness of the frame is preferably 1 to 4 mm. If the thickness is less than 1 mm, it tends to be damaged during deformation, while if it exceeds 4 mm, it becomes difficult to deform.

Next, in the step (h), hot working is performed on the plurality of ingots arranged side by side in the frame to make them magnetically anisotropic and diffusion bonded. This hot working is preferably carried out under the following conditions: (a) working temperature, (b) strain rate, (c) working rate, and (d) average working pressure. However, it is not necessary to satisfy all the conditions in (a) to (d), and when one condition is prioritized, the ranges under the other conditions may change with a certain width. When a pressure is applied to the ingot in one direction under these conditions, the ingot easily plastically deforms. During this plastic deformation, the solid phase, which is the main phase, diffuses, and if there are cracks on the dividing surface of the ingot or the ingot, the crack interfaces are joined. As a result, magnetic anisotropy is achieved in a completely bonded state without magnetic drop at the bonded interface.

(B) Working temperature Hot working is preferably carried out within a temperature range of 800 to 1140 ° C. Α-Fe precipitates at temperatures higher than 1140 ° C,
The (BH) _max of the resulting magnet is below 25 MGOe. Also, if hot working is performed at a temperature lower than 800 ° C, the mechanical strength is reduced. Specifically, the 4-point bending strength is 20 kgf / mm ² or less.

(B) Strain rate The strain rate in hot working is preferably 0.0001 to ¹ sec ^-1 . In order for the finally obtained magnet to obtain a coercive force of 10 kOe or more, the strain rate must be 0.0001 sec ^-1 or more. To obtain a 4-point bending strength of 20 kgf / mm ² or more, the strain rate must be It must be less than 1 sec ^-1 . Distortion speed is 1 sec ^-1
If it exceeds, diffusion of each component element does not proceed sufficiently,
This is because a uniform member cannot be obtained and sufficient strength cannot be obtained. Here, as shown schematically in FIG. 2, the strain rate is ΔL = L−L ′ when the object (ingot) having the height L is pressed in one direction to have the height L ′. Speed (S) = (ΔL / L) / time required for processing (se
c), the dimension is [sec ^-1 ].
Is. Therefore, for example, the strain rate S when an object having a height of 40 mm is processed to a height of 10 mm in 20 minutes is S = (30/40) /20×60=6.25×10 ⁻⁴ / sec.

(C) Working Rate The working rate in hot working is preferably 30% or more. If the processing rate is lower than 30%, the anisotropy under plastic deformation does not proceed sufficiently, so the residual magnetic flux density, which is a guide for the anisotropy, does not improve, and the (BH) _max value is
This is because it is not possible to obtain the characteristics of 25 MGOe or more. If the processing rate is 10% or less, the diffusion under plastic deformation does not proceed sufficiently, resulting in a significant decrease in strength and 20 kgf / mm
You cannot get more than ² strengths. Here, as shown schematically in FIG. 2, the processing rate is ΔL = L−L ′ when the object (ingot) having the height L is pressed in one direction to have the height L ′. The rate (P) = (ΔL / L) × 100.

(D) Average working pressure The average working pressure in hot working is 5 to 50,000 kg.
/ cm ² is preferable. When hot working is performed at an average working pressure outside that range, the (BH) _{max of the} resulting magnet
The value cannot get the characteristic more than 25MGOe.

The hot working is performed in a vacuum of 2 × 10 ^-3 Torr or less or in an inert gas such as argon gas in order to prevent the material from being oxidized.

After this hot working, the obtained magnet material is cooled at a cooling rate of 2 ° C./sec (step (i)) to obtain a desired permanent magnet member. In addition, in order to use it for various purposes, the permanent magnet member is machined into a predetermined shape (process
(j)) It is necessary to cut out.

As described above, the magnet member according to the present invention can be used as a large magnet in which all parts are magnetically uniform.

Example 1 As a starting material, electrolytic iron having a purity of 99.9% or more, purity 99.0%
Using the above praseodymium, crystal boron having a purity of 99.0% or more, pure copper having a purity of 99.5% or more, and gallium having a purity of 99.5% or more, the composition is Pr ₁₉ Fe ₇₄ B ₅ Cu _1.5 Ga _0.5 , and the total amount is 140 g. And mixed. In this case, a =
19-11.76 = 7.24, b = 1.5 + 0.5 = 2, and (a +
b) = 9.24, a> 0, b> 0, and 2 ≦ (a
+ B) ≦ 11 was satisfied.

The above mixture was placed in an alumina crucible, the atmosphere was once set to a vacuum of 2 × 10 ^-4 Torr or less, and then high frequency heating was performed under an argon gas pressure of 26 cmHg. 1500 ° C
And held for 5 minutes to obtain a melt.

Next, the obtained melt was kept at 1400 ° C.,
This was poured into a pure copper mold shown in FIG. At this time,
The cross-sectional area of the pouring surface was 2.89 cm ² (1.7 cm × 1.7 cm). Immediately after this casting, the side surface of the mold was rapidly cooled at an average cooling rate of 20 ° C / sec. There was that time. Then, it was left to cool and the ingot (16.5 mm × 16.5 mm × 43 mm) was taken out from the mold.

The obtained ingot was degreased and washed with acetone, and then machined and polished to 16 mm × 16 mm × 40.
The size is mm. When the macrostructure of the cross section of the ingot was visually observed, it was confirmed that columnar crystals were developed in the entire area. The volume fraction of columnar crystals was 100%. In the same manner, three ingots were produced to make a total of four ingots.

Next, these ingots were treated with 1 × 10 ^-4 Torr.
Heat treatment was performed in the following vacuum. In this heat treatment, (1) the temperature was raised from room temperature to 850 ° C over 30 minutes, (2) the temperature was maintained at 850 ° C for 8 hours, and then (3) cooled down to 500 ° C over 1 hour.
The average particle size of the main phase particles of the obtained ingot was 9 μm.

As shown in FIG. 4, four ingots each have a size of 3 mm.
It was inserted into the frame 2 made of thick mild steel material (S35C).

Next, the ingot inserted into the frame is set to 2 × 10.
Under a vacuum of ^-3 Torr or less, and at a temperature of 1090 ° C, pressure was applied in the direction of the arrow in Fig. 2 with an average processing pressure of 500 kg / cm ² . At this time, the ingot was compressed from a height of 40 mm to a height of 10 mm over 20 minutes. That is, the processing rate of the height of the ingot was 75%, and the strain rate was 6.25 × 10 ⁻⁴ / sec.

After cooling, the resulting magnet member was 16 mm × 10 mm ×
It was cut into a size of 64 mm, and the magnetic properties and mechanical strength were measured by the following methods.

Measuring Method (1) Measurement of Magnetic Properties As shown in FIG. 5, the magnet member was divided into three parts in the longitudinal direction and eight parts in the lateral direction to obtain 24 samples a1 to h3.
The size of each sample was 4 mm x 4 mm x 8 mm. The residual magnetic flux density B _r , the coercive force _i H _c , and the maximum energy product (BH) _max at 22 ° C. were measured for each sample using a measuring device (VSM) manufactured by Toei Industry Co., Ltd. (BH) _max average,
And the standard deviation was calculated.

(2) Measurement of Mechanical Strength A total of 10 samples of 3 mm × 4 mm × 36 mm were cut out from the above-mentioned magnet member in the longitudinal direction, and 4 samples were obtained for each sample.
A point bending test was conducted. With respect to the test results, a 4-point bending strength average value and a 4-point bending strength standard deviation were calculated.

The measurement results of the magnetic properties of this sample are shown in Table 1.
Table 2 shows the results of calculating the average value and standard deviation of the measured values of magnetic properties and mechanical strength.

Table 1 Part of residual magnetic flux density coercive force maximum energy product in magnet B _r ⁽¹⁾ _i H _c ⁽²⁾ (BH) _max ⁽³⁾ a1 12.8 11.2 34.2 a2 12.8 12.0 35.0 a3 12.7 11.3 34.9 b1 12.5 11.4 31.4 b2 12.6 11.7 33.0 b3 12.6 11.5 33.0 c1 12.4 11.5 32.0 c2 12.4 11.8 31.0 c3 12.3 11.6 31.4 d1 12.1 11.5 31.1 d2 12.2 11.9 30.4 d3 12.1 11.7 31.4 e1 12.2 11.5 31.2 31.2 11.5 30.2 10.9 30.2 12.3 12.2 30.4 f3 12.3 11.7 31.4 g1 12.5 11.4 32.0 g2 12.4 12.7 33.0 g3 12.7 11.7 32.0 h1 12.6 11.9 34.0 h2 12.8 12.4 34.9 h3 12.8 12.0 34.0

Table 1 Note (1): The unit is kG. Note (2): The unit is kOe. Note (3): The unit is MGOe.

[0048]

Table 2 Note (1): The unit is MGOe. Note (2): The unit is kgf / mm ² .

As it is apparent from Table 2, the permanent magnet according to Example 1 shows a high magnetic properties in the average value of (BH) _max, exhibited uniform magnetic properties in standard deviation (BH) _max. In addition, sufficient strength was exhibited even in the mean value and standard deviation of the four-point bending strength.

Examples 2 to 6 As starting materials, electrolytic iron with a purity of 99.9% or more, purity 99.0%
The above praseodymium, crystal boron having a purity of 99.0% or more, pure copper having a purity of 99.5% or more, and gallium having a purity of 99.5% or more are used, and a> 0 and b> 0 are satisfied in the composition, and (a + b) is 2 to 11 Changed. (A + b)
= 2 is the second embodiment, (a + b) = 4 is the third embodiment,
When (a + b) = 6, it was designated as Example 4, when (a + b) = 10.5 was designated as Example 5, and when (a + b) = 11, it was designated as Example 6. Under the above conditions, they were weighed and mixed so that the total amount became 140 g.

Using the above mixture, a magnet was obtained in the same manner as in Example 1. The 4-point bending strength of the obtained magnet was measured in the same manner as in Example 1. FIG. 6 shows the relationship between the value of (a + b) and the four-point bending strength in Examples 2 to 6.

Comparative Examples 1 and 2 As starting materials, electrolytic iron having a purity of 99.9% or more, purity 99.0%
Using the above praseodymium, crystal boron having a purity of 99.0% or more, pure copper having a purity of 99.5% or more, and gallium having a purity of 99.5% or more, the composition satisfies a> 0 and b> 0, and (a + b) = 0.5. Comparative Example 1, (a +
b) = 13 was set as Comparative Example 2. Under the above conditions, they were weighed and mixed so that the total amount became 140 g.

Using the above mixture, a magnet was obtained in the same manner as in Example 1. The 4-point bending strength of the obtained magnet was measured in the same manner as in Example 1. FIG. 6 shows the relationship between the value of (a + b) and the 4-point bending strength in Comparative Examples 1 and 2.

As is apparent from FIG. 6, in order to make the 4-point bending strength of the obtained magnet 20 kgf / mm ² or more, (a + b)
The range of at.% must be 2-11 at.%.

[0056]

As described in detail above, according to the method of the present invention, at the joining interface between adjacent cast ingots,
Liquid phase diffusion of solid particles, which is the main phase, occurs, so that the plurality of ingots are well joined. This makes it possible to produce a permanent magnet that is magnetically uniform and mechanically excellent.

According to the method of the present invention, a large-sized and highly-permanent permanent magnet, which has been impossible in the past, can be produced. Therefore, the permanent magnet according to the present invention can be widely used industrially.

[Brief description of drawings]

FIG. 1 is a flowchart showing a process of producing a permanent magnet.

FIG. 2 is a schematic view showing a state in which an ingot is pressure-formed in one direction in hot working.

FIG. 3 is a diagram showing a mold for casting an ingot in an example.

FIG. 4 is a diagram showing a state in which an ingot has entered a frame.

FIG. 5 is a diagram showing boundary lines of samples a1 to h3 in the obtained magnet.

FIG. 6 shows (a) in Examples 2 to 6 and Comparative Examples 1 and 2.
It is a graph which shows the change of 4-point bending strength with the change of the value of + b).

[Explanation of symbols]

 1 press mold 2 frame

Claims (1)

[Claims] 1. A plurality of R-Fe-B-M-based (wherein R is a rare earth element containing praseodymium or neodymium as a main component and M is an additive element) permanent magnets are arranged side by side and heat-treated. A method for producing a magnetically uniform permanent magnet by integrating a plurality of the ingots with each other and magnetically anisotropy by performing hot working, wherein R at.%-11.76 at.% Is a and M at.% Is b, the composition of the ingot satisfies the following conditions: a> 0, b> 0, and 2 ≦ a + b ≦ 11.