JPS634001A - Production of permanent magnet of sintered body - Google Patents

Abstract

PURPOSE:To increase the suitability of powder to orientation in a magnetic field during compression molding and to improve the characteristics of a magnet by rapidly cooling a molten magnetic alloy under prescribed conditions to form a fine wire, crushing the wire, molding the resulting powder under orientation in a specified direction in a magnetic field and sintering the molded body. CONSTITUTION:An alloy contg. prescribed components is melted. The molten alloy is solidified by rapid cooling at >=10<3> deg.C/sec cooling rate to form a fine wire and this wire is crushed to obtain fine columnar powder having >= 1.5 average aspect ratio. The powder is compression-molded in a magnetic field and the molded body is sintered and annealed.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for manufacturing a sintered permanent magnet, and in particular, by using fine columnar powder, such as a cylindrical powder, with good magnetic field orientation as a powder raw material. This is an attempt to further improve the magnetic properties.

(Prior Art) In recent years, there has been an increasing demand for smaller size, lighter weight, higher performance, and higher reliability for various electrical measuring instruments, communication devices, and even micro motors. For this reason, the permanent magnets used in the above-mentioned devices are (Bll
) There is a demand for materials with larger max.

Alloy permanent magnets such as rare earth magnets and alnico magnets are suitable for use in the above-mentioned applications, and these magnets have been developed as high coercive force magnets since their initial development and have continued to the present day.

By the way, although the above-mentioned alloy permanent magnets, especially rare earth permanent magnets, have excellent magnetic properties, they have difficulties in workability, so they are usually manufactured by a powder compacting and sintering method (for example, JP-A-59-1999 46008).

The manufacturing process for such a sintered magnet is shown in Figure 2. As shown in Figure 2, a molten alloy prepared to have a predetermined composition is first cast into an ingot, then pulverized by mechanical crushing, and then compressed. The product is formed by sequentially applying molding, sintering, and heat treatment. In particular, when adding directionality to the product magnet, it is important to carry out the compression molding process under the application of a magnetic field.

(Problems to be Solved by the Invention) As mentioned above, since powdering is generally done by mechanically crushing an ingot, the resulting powder has an extremely uneven shape. When producing a molded body using a pressure press, the powder bodies move or rotate due to the unevenness of the powder surface. It was not always possible to obtain a molded body with good orientation in which all the particles were aligned in the direction of application of the magnetic field.

Further, depending on the shape of the powder, the shape anisotropy becomes large, and the axis of easy magnetization of the powder is not necessarily oriented in the direction of application of the magnetic field.

Although good magnetic properties can be obtained by firing a compact with the above-mentioned orientation, in order to further improve the magnetic properties, it is important to improve the orientation of the powder.

This invention was developed in view of the above-mentioned current situation.
When manufacturing permanent magnets using the powder compaction-sintering method,
As a powder raw material, the surface unevenness is extremely small compared to conventional crushed ingot powder, and there is very little movement or rotation of the powder particles among themselves even during pressure pressing, so the orientation is not greatly disturbed even after pressure pressing and no magnetic field is applied. The purpose of the present invention is to propose a method for manufacturing a sintered permanent magnet that can further improve magnetic properties by using powder with so-called good magnetic field orientation that can maintain its orientation in the same direction.

(Means for solving the problem) As a result of intensive research to achieve the above object, the inventors have found that: i) Using a powder with a large vertical-to-width ratio, that is, a large aspect ratio, as a powder raw material, It is extremely effective to achieve the intended purpose by taking advantage of the shape anisotropy caused by the difference in the demagnetizing field coefficient of the powder, oriented it in a specific direction in a magnetic field, and compression molding it, followed by sintering and heat treatment. , ii)
Such a powder should not only have a large aspect ratio, but also have the property that its major axis is oriented in the direction of magnetic field application, and should have surface irregularities to the extent that the orientation will not be disturbed due to contact between the powder bodies during press processing. Although small size is required, it has been found that pulverized quenched fine wire is extremely suitable as such a powder.

This invention is based on the above knowledge.

That is, in this invention, a molten alloy prepared to have a predetermined composition is rapidly solidified into a thin wire at a cooling rate of 103° C./s or more, and then the thin wire is crushed to have an average aspect ratio of 1.
．． This is a method for manufacturing a sintered permanent magnet, which comprises forming a fine columnar powder of 5 or more, compressing the powder under the application of a magnetic field, sintering it, and then annealing it.

In this invention, suitable methods for producing the quenched fine wire include melt spinning, pulling, drawing, and melt extraction. This quenching method is used because rare earth magnets and alnico magnets are extremely brittle, so the normal ingot-rolling-drawing method cannot achieve thinning. This is because the desired aspect ratio cannot be obtained due to the unidirectional pulverization.

Here, the cooling rate during the production of rapidly quenched thin wire is 103'C/
If the cooling rate is less than s, there are disadvantages such as severe oxidation of some components and the failure to obtain desired magnetic properties, so the cooling rate needs to be 103° C./s or more.

The reason why the average aspect ratio of the powder is limited to a range of 1.5 or more is as follows.

In other words, in this invention, a rapidly quenched thin wire is used as the powder material, but it does not have a strong magnetic anisotropy constant in the quenched state, so if the aspect ratio is less than 1.5, even if the magnetic field is Even if the magnetic field is applied, the long axis direction of the powder is not sufficiently oriented in the direction of the applied magnetic field. In this regard, when the aspect ratio is 1.5 or more, the demagnetizing field coefficient in the long axis direction of the powder becomes small, so that the long axis direction of the powder becomes well aligned with the direction of applying the magnetic field.

Note that the diameter of the quenched fine wire is, for example, 15 mm for rare earth magnets.
It is preferable to set it to about 0 μm or less. This is because if the diameter is larger than 150 μm, not only will the wire be severely oxidized and become more brittle, but also the wire will be crushed not only in the longitudinal direction of the wire but also in the direction perpendicular to the diameter direction. The reason for this is that the frequency of oxidation increases, making it difficult to obtain the desired aspect ratio, and increasing the possibility that the surface of the powder will become rough.

The powder thus obtained is compression molded while being subjected to orientation treatment in a magnetic field, and then sintered and heat treated according to conventional methods to produce a product.

Here, the magnitude of the applied magnetic field during compression molding is 1 kO.
It is preferable that it be more than e.

Sintering is preferably performed at 900 to 1300°C for 1 to 100 minutes, and further at 900°C or less for 1 to 100 minutes.
Excellent magnetic properties are developed by applying heat treatment for approximately 0 minutes or more.

FIG. 1 is a block diagram showing the manufacturing process of a sintered permanent magnet according to the present invention.

(Function) In this invention, the quenched fine wire crushed powder is used as the powder raw material because: (1) a powder having a large aspect ratio can be obtained; (2) the major axis direction is easily aligned with the direction of applying the magnetic field; (3) The powder surface has small irregularities, and the powder particles hardly move or rotate during press processing.

Note that the method for manufacturing sintered magnets according to the present invention applies not only to rare earth magnets and alnico magnets, but also to Fe-Cr-C magnets.

The present invention can be applied to any alloy-based magnet such as Mn-A ji-based, Mn-A ji-based, or Mn-B1-based.

(Example) Example 1 Using the direct thin wire manufacturing apparatus shown in FIG.
A molten alloy having a composition of +5FetsB+o was directly injected into the atmosphere and rapidly solidified (cooling rate: 105° C.) to produce a rapidly solidified thin wire with a diameter of about 5 μm. In the figure, number 1 is a high-frequency melting coil, 2 is a molten alloy, 3 is a glass tube, 4 is a rotating drum, and 5 is a motor.

The m-line was then crushed and divided into powders having various average aspect ratios shown in Table 1.

Then, for each powder of each aspect ratio, 5
It is compression molded into a predetermined shape at a pressure of 5 ton/rcm under the application of a magnetic field of kOe, and then heated at 1200°C in vacuum.
and then annealed at 650°C for 60 minutes.

Table 1 also shows the results of investigating the magnetic properties of each of the sintered magnets obtained.

Table 1 also shows the results of investigating the magnetic properties of products obtained by subjecting crushed ingot powder to raw materials and subjecting them to similar treatments according to the conventional method.

Table 1 As is clear from the table, all magnetic products obtained according to the present invention using quenched fine wire crushed powder with an average aspect ratio of 1.5 or more as a powder raw material have significantly higher magnetic properties than conventional products. It was showing.

Example 2 A quenched fine wire with a diameter of 8 μm was produced in the same manner as in Example 1 above from a molten alloy having a composition of Sm3sCObs in wt%.

After pulverization, the powders were separated into powders having various average aspect ratios shown in Table 2, and then subjected to compression molding, sintering, and annealing under the same conditions as in Example 1.

The results of investigating the magnetic properties of each of the sintered magnets thus obtained are also listed in Table 2 in comparison with the conventional example.

Table 2 (Effects of the Invention) Thus, according to the present invention, when manufacturing a sintered permanent magnet, the magnetic field orientation during compression molding can be made much higher than in the past, and the magnetic properties can be improved. A sintered permanent magnet can be obtained.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the manufacturing process of the conventional powder compaction-sintering method, Figure 2 is a block diagram showing the manufacturing process of a sintered permanent magnet according to the present invention, and Figure 3 is a block diagram showing the manufacturing process of a sintered permanent magnet according to the present invention. FIG. 2 is a schematic diagram of a thin wire manufacturing device.

Claims (1)

[Claims] 1. Heat the molten alloy prepared to a predetermined composition at 10^3°C.
After rapidly solidifying into fine wires at a cooling rate of /s or more, the fine wires are crushed into fine columnar powder with an average aspect ratio of 1.5 or more, and then such powders are compression-molded under the application of a magnetic field. A method for manufacturing a sintered permanent magnet, characterized by performing sintering and then annealing.