JPS6026601A - Manufacture of magnetic manganese-aluminum-carbon alloy powder - Google Patents

Abstract

PURPOSE:To obtain magnetic alloy powder having improved magnetizability by removing the surface part of Mn-Al-C magnet alloy powder by etching. CONSTITUTION:The surface of Mn-Al-C magnet alloy powder whose principal phase is epsilon-phase as a high temp. phase, tau-phase as a ferromagnetic phase, epsilon'- phase as an intermediate phase or a phase of a mixture thereof is etched. For example, the surface of the alloy powder is chemically reacted with an etching soln. to remove the surface part, so the deposition of beta-phase is inhibited. The etching is carried out before or after heat treating the alloy powder at about 350-800 deg.C. By this method the magnetizability of the Mn-Al-C alloy powder having high coercive force can be improved. The resulting magnetic alloy powder can be used as a material for a sintered magnet, a magnetic tape, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing a manganese-aluminum-carbon (Mn-Al-C) based alloy magnetic powder with improved magnetic properties.

Structure of the conventional example and its problems Since it was discovered that the Mn-Al binary alloy has a ferromagnetic phase, much research and development has been carried out on magnetization. Al-C system, ie Mn65. O~74.0% by weight (hereinafter simply expressed as %), aluminum 25.0~34.0%, carbon 4.0% by weight.
A Mn-AI-C alloy magnet with excellent magnetic properties, which has a composition of 0% or less (but does not contain 0), has been developed (Japanese Patent No. 495674). This magnet was then subjected to warm plastic working to significantly improve its magnetic properties and has been put into practical use (Japanese Patent No. 996692).

On the other hand, in recent years, the use of powder sintered magnets and resin molded magnets, which can be freely formed into magnet shapes, has been increasing, and there is a demand for the development of high-performance powdered magnet paulownia materials. In line with these demands, Mn-
Research and development of magnetic powder is also being carried out in the Jl series.

However, a material that can be put to practical use in terms of magnetic properties and manufacturing cost has not yet been provided. Below is Mn-
Conventional examples and problems regarding 1711 series alloy magnetic powder will be described.

When Mn-Human β-based alloy magnetic powder is produced by mechanical pulverization, the coercive force (IHc) increases as the particle size of the powder becomes finer.
increases, but the magnetization (4πI)l residual magnetization (Br) tends to decrease rapidly. This tendency is remarkable when the particle size is 150 μm or less. This is reported to be due to a decrease in the regularity of the ferromagnetic phase due to mechanical crushing, the introduction of stacking faults, anti-phase boundaries, etc. For this reason, the particle size cannot be reduced, and 1
It has been reported that large grain sizes of 25 to 1507 (R, A, McCurri
e, J., Rickman, P-Dunk.
and D, G, Hawkridge, “Depend
ence of the permanent magnet
et properties of Mn 55A 14
50n par tlo les, I EEE T
r ans.

Magnetics Mag-14, No3, p
682-p 6845ept.

1978). However, it has not been put to practical use because (BH)m2LX is low.

Still 4π1. To increase Br, anisotropy M n -A
A method of pulverizing l-C alloy magnets has been proposed, but when the particle size becomes smaller than 100 mm, 4π1 decreases rapidly, and the optimum particle size is as large as 10 Q to 150 mm. In addition, since the alloy is crushed after warm extrusion processing, the manufacturing cost is high, and the process is dusty, so it has not been put to practical use.

On the other hand, according to Makino et al., it has been reported that by mechanically crushing a ferromagnetic phase Mn-Aβ alloy and subjecting this powder to a tempering treatment, 4πI and Br increase, but IHC decreases. (Journal of the Japan Institute of Metals, Vol. 28, 196)
4. P4.83-P489).

Characteristics after tempering at 350'C are Br=1620G
.

5Hc = 128 o Os, 4πi and Br were low, so it was not put into practical use.

As mentioned above, as a powder for magnets, the particle size is 100 to 150.
However, there are problems in terms of the magnetic properties of the powder and the manufacturing cost, and powder with a high particle size of 1) (c) less than 1001 has a low 4π■ and Br, so it is difficult to use powder molded magnets. There was a big problem that paulownia powder was not suitable for any practical use.

Purpose of the Invention The present invention provides magnetic properties of Mn-kl-C alloy magnetic powder,
In particular, the purpose is to increase the value of 4π engineering.

Structure of the Invention As a result of various experiments, the present inventors have found that when magnetic powder is heat-treated, a non-magnetic phase is precipitated on the surface of the powder, and that it is possible to improve the υ4π process by removing this surface phase. I found out.

The present invention is based on this, and M n -A
ε phase (close-packed hexagonal structure 2) of the high-temperature phase of I-C alloy magnets
Typical lattice constant 2L: 2.70A, c-4,40A)
2 ferromagnetic τ phase (CuAu type face-centered tetragonal 1 typical lattice constant &=3.91, c=3.e3X).

The intermediate l phase that appears at the intermediate stage of the ε phase to τ phase transformation process (MgCd type 819 structure 2 typical lattice constant lL: 4
．． 39X, b=2. -re Another feature is that etching is performed after heat treatment.

According to the present invention, it is possible to improve the magnetic properties of the Mn-1-C alloy magnetic powder, especially the 4π-magnetic properties.

DESCRIPTION OF EMBODIMENTS First, in order to study the improvement of 4π strength by heat treatment, the present inventors pulverized a Mn-kl-0 alloy magnet after melting, casting, and heat treatment, and when this powder was subjected to vacuum heat treatment. Experiments were conducted by varying the heat treatment temperature. As a result, there is no effect of heat treatment on magnetic properties at temperatures lower than 350°C.
Furthermore, heat treatment at a temperature higher than 8Q°C decomposed the ferromagnetic τ phase into the high-temperature ε phase and the nonmagnetic τ phase (A1Mn(r) phase), which had no effect on improving magnetic properties. It has been found that heat treatment of the powder at 350 to 800'C is effective in improving the properties.

Next, we investigated the effect of the particle size of the vacuum heat-treated powder on its magnetic properties. The results are shown in FIG.

As shown in the figure, the influence of powder particle size on magnetic properties is
Similar to the results reported so far, the particle size of the powder becomes smaller after pulverization and heat treatment, and 4π115K (H=
15KOe T measurement 1. ta value) decrease in ta.

In order to investigate the cause of this decrease in 4π115, the powder was examined by X-ray diffraction, and it was revealed that the non-magnetic β phase (β-Mn phase) was precipitated by heat treatment, and the amount of β phase was still small in the powder. It was found that the smaller the particle size, the larger the amount.

Based on the above results, the present inventors believe that the main reason why the 4π-factor decreases with grain size is the precipitation of the β phase, and have investigated various processing methods that do not cause the precipitation of the β phase. As a result, it has been found that precipitation of the β phase can be suppressed by etching the powder after heat treatment and heat treating the etched powder.

Etching here refers to a process in which the surface portion of the powder is chemically reacted with an etching solution to remove the surface portion. A specific example of this process will be described next. The etching solution and sample powder were placed in a beaker or the like, and the two were allowed to react. Then, operations such as stirring were performed to prevent selective etching of the powder. Next, this etched powder was washed with an organic solvent (acetone, ethyl alcohol, etc.), and then dried.

An etched version of the heat-treated powder is shown in FIG.

However, the characteristics of the powder after etching are indicated by the particle size after pulverization. As shown in the figure, the 4π115K of the powder after etching increases compared to that of the powder after heat treatment.
becomes less dependent on particle size. As is clear from FIG. 1, etching has little effect on tl(c).

From the above, this etching treatment can increase the 4π-factor of a powder with a high XHc of 150)l or less, and the present invention is of great industrial value.

The reason why a large amount of β phase precipitates when the powder is heat-treated is because there is inherent processing strain near the powder surface and there is still a lot of crystal disorder, so it is easy to transform into the non-magnetic stable β phase. It is thought that the amount of β phase increases because the surface area of the particles becomes very large when the powder becomes fine. and 4π
The increase in I and Br is thought to be due to the removal of the β phase on the surface by etching.

Next, FIG. 2 shows the results when the etched powder was subjected to vacuum heat treatment. As is clear from the figure, the precipitation of the β phase is suppressed and the 4π115K is improved. This is thought to be due to the fact that the β phase is less likely to precipitate as the part of the powder surface that receives processing strain is removed.

Although it is difficult to remove all the β phase with this method of heat treatment after etching, the amount is much smaller than the amount of β phase in the powder after heat treatment, and the magnetic properties can be improved.

In addition, this etching process is performed not only on the powder obtained by crushing the heat-treated alloy mainly containing the τ phase, but also on the
It is a very effective treatment method, as it has the same effects as above for powders mainly consisting of the ε phase and ε' phase, powders consisting of the above-mentioned mixed phases, and powders of extruded materials.

On the other hand, as an etching solution, He l, HNO3, N
When aOH and Keller's solution were used, there was an etching effect and the magnetic properties of the powder were improved.

It has been found that a treatment in which the powder is etched, heat treated, and then etched is also effective in improving the magnetic properties in the same manner as mentioned above.

A specific example of the hook will be described below.

Example 1 A heat-treated Mn-), l-C alloy magnet was pulverized using a jet mill. This powder was vacuum heat treated at 450°C for 30 minutes and then etched with He6. The magnetic properties after etching are 4π115FF-5950G with an average grain size of 2 ol.
+IHC=185008, which was about 20% improved in 4π engineering 15 compared to the powder after heat treatment.

Example 2 Mn-A71 after heat treatment! The -C alloy magnet was pulverized using a jet mill. This powder was etched with Keller's solution and then vacuum heat treated at 500'C for 30 minutes. When powders with a particle size of 20 to 46 μm were examined by X-ray diffraction, the amount of β phase was smaller than that of powders heat-treated without etching. The magnetic properties of the 20-46μ powder after etching and heat treatment are 4π 15K”6500G, Hc=16
000 s, the 4πh5 process was 12% better than the powder after heat treatment without etching.

Example 3 The powder after etching and heat treatment of Example 2 was further keratinized.
Etched with liquid. Magnetic properties after this etching
π115=5700G, which is further increased from the characteristics of Example 2. X-ray diffraction of the powder revealed that there was almost no β phase.

Example 4 An alloy having a composition of 70.0% Mn, 29.5% Ad, and 5% G O was produced by melting and casting. This alloy is 1
Solution treatment was performed at 100°C for about 1 hour and quenched in water to produce a high temperature phase (ε phase) alloy. This alloy was ground using a jet mill. When this powder was analyzed by X-ray diffraction, it was found that the ε phase was the main component. This powder was heat treated in a vacuum at 500°C and then etched with HGl.

The characteristics of powder with an average particle size of 20μ after etching treatment are 4π
Engineering 15K ==55ooc, Engineering H6=165000
4πI]'5K was about 16% higher than that of the powder after heat treatment.

Example 5 A warm extruded anisotropic Mn-Al-C alloy magnet was pulverized using a jet mill. This powder was heat treated in the air at 50Q°C and then etched with Keller's solution. The magnetic properties of powder with an average particle size of 20/l after etching are 4π11
5: 6400Cr + zHc = 32QQ Os, 4π115K was improved by about 17% compared to before etching.

Example 6 A warm extruded anisotropic Mn-Al-C alloy magnet was ground to 100 μm or less using a jet mill, and then crushed to about 2 μm in a mortar.
Time crushed. This powdered wood was heat treated at 600°C and then etched with HNO3. After this etching, the powder is
As a result of line diffraction, there were almost no β-phase peaks. 4
The value of π115 was improved by about 10% compared to before etching.

Example 7 The ε-phase alloy of Example 4 was tempered at 400°C to produce a mixed τ-phase and ε'-phase alloy. This alloy was pulverized by a jet mill and vacuum heat treated at 500°C.

Next, this powder was etched with Keller's solution.

Characteristics of powder with an average particle size of 20 after etching treatment d, 4
π engineering 15=5900G, engineering Hc-160ooe, which was about 18% improved in 4πII 5 compared to the powder after heat treatment.

Example 8 A heat-treated Mn-Al-C alloy magnet was pulverized using a jet mill. This powder was subjected to vacuum heat treatment at 600°C for 30 minutes and then etched with HGl. The magnetic properties after etching are 4π work 15 with an average grain size of 150/L = 660
0G2. Ho=75oOe, and the 4π engineering I5 was improved by about 9% compared to the powder after heat treatment.

Effects of the Invention The present invention improves the magnetic properties of Mn-Al alloy powder, which could not be put to practical use in the past, and in particular makes it possible to improve the 4π strength of powder with a particle size of 150μ or less, which has a high coercive force. , 4π engineering, and IHC have excellent magnetic properties.
This product provides an n-41 magnetic powder, which is very promising as a magnetic powder for sintered magnets and resin-molded magnets, and as a magnetic powder for magnetic tapes.

-Also, even if the surface of the powder is oxidized by heat treatment in the air rather than in a vacuum, reducing atmosphere, or inert gas, the oxide film can be removed by etching the powder. , the heat treatment process becomes simpler.

[Brief explanation of drawings]

Figure 1 shows the particle size dependence of IHC on 4π115 after pulverization, after pulverization/vacuum heat treatment, and after pulverization/vacuum heat treatment/etching, and Figure 2 shows X-rays after vacuum heat treatment, vacuum heat treatment, and etching. β/τ peak ratio and 4π115 due to diffraction
It is a figure showing K. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Zukotsu Ritsaiso (Me L)

Claims (3)

[Claims] (1) Etching an alloy powder mainly consisting of the high-temperature ε phase, the ferromagnetic τ phase, the intermediate ε' phase, or a mixed phase of the above phases in a manganese-aluminum-carbon magnet alloy. A method for producing a characteristic manganese-aluminum-carbon alloy magnetic powder. (2) Etching the powder at 350-800°
The method for producing a manganese-aluminum-carbon alloy magnetic powder according to claim 1, which is carried out after heat treatment in the range of C. (3) Etching the powder at 350-800°
The method for producing a manganese-aluminum-carbon-based alloy magnetic powder according to claim 1, which is carried out before heat treatment in the range of C.