JP7021774B2 - Method for manufacturing Mn-Al-C magnet - Google Patents

Description

The present invention relates to a method for manufacturing an Mn—Al—C magnet.

In the present specification, those represented by element symbols such as Mn, Al, and C represent elements as chemical components, and are represented as "-quality raw materials" such as manganese raw materials, aluminum raw materials, and carbon raw materials. The thing shall represent the actual raw material which may contain unavoidable impurities.

The Mn-Al-C magnet is a permanent magnet containing Mn, Al, and C as main components, does not need to contain a rare earth element in order to develop spontaneous magnetization, and can exhibit a larger maximum energy product than a ferrite magnet. It has such characteristics.

As disclosed in Patent Document 1, the Mn—Al—C magnet is manufactured from a manganese raw material, an aluminum raw material, and a carbon raw material. Specifically, Patent Document 1 describes an alloying step of solidifying a molten metal obtained by melting a manganese raw material, an aluminum raw material, and a carbonaceous raw material to obtain an alloy, and a heat treatment step of heat-treating the obtained alloy. The manufacturing method to have is disclosed.

Further, as disclosed in Patent Document 2, a Mn—Al—C magnet is obtained by sintering an atomized alloy powder containing an alloy of Mn and Al as a main component together with a powder of a carbonaceous raw material. The method is also known.

Japanese Unexamined Patent Publication No. 10-270224 Special Fair 2-17921 Bulletin Japanese Unexamined Patent Publication No. 2015-63725 Japanese Unexamined Patent Publication No. 2017-157738

The reason why the above-mentioned alloying step and heat treatment step are required in the manufacturing method of Patent Document 1 is that a ferromagnetic phase cannot be produced without going through these steps. In other words, since the ferromagnetic phase is a quasi-stable phase, conventionally, a method is adopted in which a stable paramagnetic high-temperature phase is once generated in the alloying process, and the high-temperature phase is transformed into a ferromagnetic phase in the heat treatment process. I needed it.

Also in the production method of Patent Document 2, a step of alloying Mn and Al is required in advance in order to obtain an atomized alloy powder at a stage before sintering.

As described above, conventionally, it has not been possible to directly generate a ferromagnetic phase from a manganese raw material, an aluminum raw material, and a carbonaceous raw material in one step. For this reason, it takes time and effort to manufacture the Mn—Al—C based magnet, and a technique capable of manufacturing the Mn—Al—C based magnet more easily has been desired.

Further, as disclosed in Patent Document 1, the above-mentioned alloy can be used as a material for a bonded magnet having enhanced magnetic anisotropy. That is, an anisotropic bonded magnet can be obtained by crushing the above-mentioned alloy and solidifying the obtained crushed product with a resin while increasing the degree of crystal orientation by an external magnetic field. However, since alloys are hard and tenacious, they require a large amount of energy to be crushed. Therefore, a material that can be easily pulverized has been desired.

An object of the present invention is to provide a method for manufacturing a Mn-Al-C-based magnet, which can obtain a Mn-Al-C-based magnet more easily than before.

The method for manufacturing a Mn—Al—C magnet according to the present invention is as follows.
It is a raw material powder composed of a manganese raw material powder, an aluminum raw material powder, and a carbonaceous raw material powder, and the mol ratio of Mn content / Al content is 50/50 or more, 60. By molding the raw material powder having a C content of / 40 or less and 1.5 mol% or more of the total content of Mn and Al in the raw material powder of 100 mol% or more . The molding process with the molded body and
A sintering step of heating the molded product at a temperature of less than 1275 K for 10 hours or more to form a sintered body.
A slow cooling step in which the sintered body is cooled to room temperature at a temperature lowering rate of 80 K / hr or less,
Have.

After the slow cooling step,
A crushing step of crushing the sintered body to make a crushed product,
A remolding step of remolding the pulverized product and in the process of remolding, by orienting the easily magnetized axis of the particles constituting the pulverized product, a remolded body obtained by magnetically differentiating the crushed product is obtained.
The magnetizing step of magnetizing the remolded body and
May further have.

According to the method for producing a Mn—Al—C magnet according to the present invention, a ferromagnetic phase is generated inside by sintering a molded product at a temperature of less than 1275 K for 10 hours or more. You can get a body.

That is, it is not necessary to separate the step of forming the high temperature phase and the step of phase transitioning the high temperature phase to the ferromagnetic phase as in the conventional case, and the ferromagnetic phase can be obtained through one sintering step. Therefore, the Mn—Al—C magnet can be obtained more easily than before.

The flowchart which shows the manufacturing method of the Mn-Al-C system magnet. The graph which shows the heating temperature in a sintering process and a slow cooling process. A photograph showing the appearance of a Mn—Al—C-based magnetic sintered body. A photograph showing the appearance of a molded product before sintering. The graph which shows the X-ray diffraction pattern of the Mn—Al—C based magnetic sintered body. The graph which shows the magnetization when the magnetic field of 1.5T is applied to the Mn-Al-C-based magnetic sintered body.

A method for manufacturing a Mn—Al—C magnet according to an embodiment of the present invention will be described with reference to the flowchart shown in FIG.

(A) Mixing Step First, a manganese raw material powder, an aluminum raw material powder, and a carbonaceous raw material powder are mixed to obtain a raw material powder (step S1). As the manganese raw material, one containing Mn as a main component, for example, metallic manganese can be used. As the aluminum raw material, a material containing Al as a main component can be used. As the carbonaceous raw material, one containing C as a main component, for example, graphite, amorphous carbon or the like can be used. As used herein, the term "main component" means that the purity is 95 wt% or more, preferably 98 wt% or more.

The particle size of the raw material powder is preferably less than 1 mm, more preferably less than 75 μm, from the viewpoint of accelerating the reaction in the sintering step (step S3) described later. In the present specification, the particle size of the particles is less than d, which means that the particles pass through the sieve of the opening d specified in JIS-Z8801.

Further, the content of C in the raw material powder is preferably 1.5 mol% or more, preferably 2 mol% or more, based on the total content of Mn and Al in the raw material powder of 100 mol%. More preferred. The higher the content of C in the raw material powder, the greater the residual magnetization that can be imparted to the sintered body or remolded body described later.

The mol ratio of Mn content / Al content in the raw material powder is 50/50 or more and 60/40 or less from the viewpoint of minimizing the excess or deficiency of Mn and Al in the generation of the ferromagnetic phase. It is preferably 52/48 or more, and more preferably 58/42 or less.

(B) Molding Step Next, the above-mentioned raw material powder is molded to form a molded product (step S2). As a method for forming the raw material powder, a method involving pressure, for example, a mold forming method in which the raw material powder is filled in a mold and pressed is typical. However, it is not limited to this. A laminated molding method may be used in which raw material powder is sprayed and molded while being laminated. At the time of molding, a binder that enhances the shape retention of the obtained molded product may be used.

(C) Sintering step and slow cooling step Next, the obtained molded product is heated at a temperature lower than the melting point of the alloy of Mn and Al for 10 hours or more, and then slowly cooled (steps S3 and S4). ). In the process of sintering by this heating, a reaction occurs in which Mn and Al form the τ phase, which is a ferromagnetic phase having a face-centered tetragonal structure. C mainly plays a role of stabilizing the τ phase.

The melting point of the alloy of Mn and Al is approximately 1345K to 1595K. In the present embodiment, the temperature below the melting point of the alloy of Mn and Al specifically means a temperature of less than 1275K.

The heating temperature is preferably 1175 K or less, and more preferably 1075 K or less. Those skilled in the art will understand that there is naturally a lower limit for the heating temperature in order to cause sintering. In order to ensure the formation of the τ phase, the lower limit of the heating temperature is preferably a value to which liquid phase sintering can occur.

If the heating time is less than 10 hours, it is difficult to sufficiently generate the τ phase. In order to make the formation of the τ phase more reliable, the heating time is preferably 12 hours or more, and more preferably 20 hours or more. The heating time refers to the time excluding the temperature rise period until the temperature of the molded product is raised to a temperature at which sintering can occur.

Further, the heating is performed in an atmosphere of an inert gas, an atmosphere of reduced pressure, preferably in a vacuum, from the viewpoint of preventing oxidation of the obtained unmagnetized sintered body. As the inert gas, for example, argon gas, nitrogen gas, carbon dioxide gas, carbon monoxide gas and the like can be used.

Slow cooling of the sintered body is performed by cooling to room temperature at a temperature lowering rate of 80 K / hr or less. Here, the normal temperature refers to a temperature of 278.15K to 308.15K in accordance with the provisions of JISZ8703. Also in this slow cooling step, the formation of the τ phase, specifically, the phase transformation from the ε phase to the τ phase occurs.

By setting the temperature lowering rate to 80 K / hr or less, the formation of the τ phase can be made more reliable. The temperature lowering rate is preferably 75 K / hr or less, and more preferably 70 K / hr or less.

Similarly to sintering, slow cooling is also performed in an atmosphere of an inert gas, an atmosphere of reduced pressure, preferably in a vacuum, from the viewpoint of preventing oxidation of the sintered body.

The volume of the sintered body (hereinafter referred to as Mn—Al—C-based magnetic sintered body) obtained through the sintering step and the slow cooling step is larger than that of the original molded body before sintering. is doing. This volume expansion also increases the porosity. The porosity of the Mn—Al—C based magnetic sintered body is, for example, 15% or more.

As described above, the τ phase, which is a ferromagnetic phase, is generated inside the Mn—Al—C-based magnetic sintered body. However, since the direction in which the τ-phase crystal grains are easily magnetized is random inside the Mn—Al—C magnetic sintered body, the Mn—Al—C magnetic sintered body is an isotropic magnet. ..

As described above, the Mn—Al—C-based magnetic sintered body according to the present embodiment is composed of a sintered body containing Mn, Al, and C as main components and having a porosity of 15% or more, and has magnetic properties inside. It contains an τ phase in an anisotropic manner. The total amount of Mn, Al, and C in the Mn—Al—C magnetic sintered body accounts for 95 wt% or more, preferably 98 wt% or more of the magnetized sintered body.

The Mn—Al—C magnetic sintered body itself can be magnetized and used as an isotropic magnet, or can be used as a material for obtaining an anisotropic magnet. Therefore, in the following, a method for obtaining an anisotropic magnet by using a Mn—Al—C-based magnetic sintered body will be subsequently described.

(D) Crushing Step First, the Mn—Al—C-based magnetic sintered body is crushed to form a crushed product (step S5). The particle size of the pulverized product is not particularly limited, but it is preferable to decompose the Mn—Al—C-based magnetic sintered body to the magnetic domain level as much as possible. From such a viewpoint, the particle size of the pulverized product is preferably, for example, 45 μm or less, and more preferably 20 μm or less. As described above, since the Mn—Al—C-based magnetic sintered body has a porous structure having a porosity of 15% or more, it can be easily pulverized as compared with conventional alloys.

After the Mn—Al—C magnetic sintered body is crushed to obtain a pulverized product, particles that do not contain the ferromagnetic phase are removed from the pulverized product by magnetic force selection to obtain a ferromagnetic phase in the pulverized product. It is preferable to increase the abundance ratio of the particles containing.

(E) Remolding step Next, the obtained pulverized product was remolded, and in the remolding process, the easily magnetized axes of the particles constituting the pulverized product were oriented to be magnetically differentiated. A remolded body is obtained (step S6).

Specifically, the crushed product is kneaded with a binder to obtain a kneaded product, and the kneaded product is formed while the binder is uncured and an external magnetic field is applied. In the process of molding, the magnetic anisotropy is enhanced by orienting the easy magnetization direction of the particles constituting the pulverized product in the direction of the external magnetic field.

After molding the kneaded product, the binder is cured. As the binder, for example, a resin such as a thermosetting resin such as an epoxy resin or a thermoplastic resin such as a nylon resin can be used.

(F) Magnetization Step Next, the regenerated body is magnetized by applying a magnetic field to the remolded body (step S7). This completes the remolded body which is an anisotropic magnet as the Mn—Al—C based magnet according to the present embodiment.

As described above, according to the present embodiment, a ferromagnetic phase is generated inside by sintering the molded body at a temperature lower than the melting point of the alloy of Mn and Al for 10 hours or more. A Mn—Al—C based magnetic sintered body can be obtained. That is, the ferromagnetic phase can be obtained through one sintering step by heating at a lower temperature than before and for a longer time than before. It is not necessary to separate the step of forming the ε phase and the step of changing the phase of the ε phase to the τ phase as in the conventional case. Therefore, a remolded body as a Mn—Al—C magnet can be obtained more easily than before.

Further, since the Mn—Al—C-based magnetic sintered body according to the present embodiment has a porosity of 15% or more, it is easier to pulverize than a conventional alloy. Therefore, it is easier than ever to manufacture an anisotropic magnet accompanied by pulverization. From the viewpoint of facilitating pulverization, the porosity of the Mn—Al—C-based magnetic sintered body is preferably 20% or more, and more preferably 25% or more. Those skilled in the art will understand that the porosity can be adjusted by the particle size of the raw material powder, the molding pressure when forming the molded body, the heating temperature when obtaining the sintered body, the heating time, and the like.

It is composed of a powder having a particle size of less than 75 μm made of a manganese raw material having a purity of 99.9 wt%, a powder having a particle size of less than 75 μm made of an aluminum material having a purity of 99.99 wt%, and a carbonaceous material having a purity of 99.99 wt%. Powders having a particle size of less than 75 μm were weighed and mixed to obtain four kinds of raw material powders according to Examples 1-4, which had different contents of Mn, Al, and C.

The mol ratio of Mn, Al, and C in the raw material powder according to Example 1 is Mn: Al: C = 55: 45: 0.5. The mol ratio of Mn, Al, and C in the raw material powder according to Example 2 is Mn: Al: C = 55: 45: 1.0. The mol ratio of Mn, Al, and C in the raw material powder according to Example 3 is Mn: Al: C = 55: 45: 1.5. The mol ratio of Mn, Al, and C in the raw material powder according to Example 4 is Mn: Al: C = 55: 45: 2.0.

Further, as a comparative example, the same powders as the manganese raw material powder and the aluminum raw material powder according to Examples 1-4 were used to obtain raw material powders containing no carbonaceous raw material. The mol ratio of Mn, Al, and C in the raw material powder according to the comparative example is Mn: Al: C = 55: 45: 0.

Next, each of the raw material powders according to Examples 1-4 and Comparative Examples described above was filled in a mold and pressure-molded at 15 MPa to obtain a columnar molded body. Then, each of the molded bodies was sintered in an atmosphere of argon gas in a heating furnace, and then slowly cooled.

FIG. 2 shows the temperature pattern in the heating furnace. In the sintering step, each molded product was heated from 293K at room temperature to 1073K, which is a temperature below the melting point of the alloy of Mn and Al, at a heating rate of 300K / hr, and then 1073K was heated for 48 hours. Retained. In this way, each molded product was made into a sintered body by heating for 48 hours.

In the slow cooling process, each sintered body was cooled to room temperature at a temperature lowering rate of 65 K / hr. The slow cooling was performed for 12 hours.

As described above, the sintered bodies according to Examples 1-4 and Comparative Examples were obtained. FIG. 3A shows the appearance of the sintered body according to the third embodiment. Further, FIG. 3B shows the appearance of the molded product before sintering according to the third embodiment.

As can be seen from the comparison between FIGS. 3A and 3B, volume expansion was observed by sintering. The volume of the sintered body shown in FIG. 3A was about three times the volume of the molded body shown in FIG. 3B. It is presumed that the reason for the expansion of the volume in this way is that the C atom entered the Mn—Al system crystal in the process of sintering and slow cooling. Porosity also increases with volume expansion. The porosity of the sintered body shown in FIG. 3A was about 25%.

Next, the crystal phases contained in each of the sintered bodies according to Examples 1-4 and Comparative Examples were identified using an X-ray diffractometer.

FIG. 4 shows the X-ray diffraction pattern of each sintered body. The horizontal axis represents the angle 2θ in units of “degrees”, and the vertical axis represents the intensity of the diffracted beam in relative scales. Further, in FIG. 4, the content ratio X of C at the stage of the raw material powder is added to each sintered body. The value of X represents an external amount with respect to the total content of Mn and Al of 100 mol%.

In each of the diffraction patterns of Example 2 with X = 1.0, Example 3 with X = 1.5, and Example 4 with X = 2.0, 2θ is about 41 degrees and about 47 degrees. At the position, a peak indicating the existence of the τ phase, which is a ferromagnetic phase, appears. From this, it was confirmed that the τ phase was generated in the sintering step and the slow cooling step.

On the other hand, in the diffraction patterns of Example 1 in which X = 0.5 and Comparative Example in which X = 0.0, a peak indicating the presence of the τ phase was not clearly observed.

Further, in both the diffraction patterns of Examples 1-4 and Comparative Examples, a peak indicating the presence of the β phase is observed. However, the β phase is a paramagnetic phase. In addition, the peak indicating the presence of the ε phase was not clearly observed in any of the diffraction patterns.

Next, for each of the sintered bodies according to Examples 1-4 and Comparative Examples, the magnetization that could be maintained when an external magnetic field having a magnetic flux density of 1.5 T was applied was measured by a vibration sample magnetometer.

FIG. 5 shows the measurement result of the magnetization. The vertical axis represents the magnetization per unit mass. The horizontal axis represents the C content ratio X at the stage of the raw material powder for each sintered body. That is, the graph of FIG. 5 shows the dependence of the residual magnetization on the amount of C added.

As the amount of C added increases, the magnetization tends to increase. In the Mn—Al system crystal, since the ferromagnetic phase is only the τ phase, the increase in magnetization indicates the increase in the τ phase. In particular, when the addition ratio of C is X = 1.5 mol% or more, the residual magnetization is dramatically increased.

From this, the C content in the sintered body is preferably 1.5 mol% or more, more preferably 2.0 mol% or more, in terms of the total content of Mn and Al in the sintered body, which is 100 mol% or more. It can be said that it is preferable.

In addition, the sintered body according to Example 1 in which the addition ratio of C was X = 0.5 mol% was also found to retain the magnetization. From this, it can be said that the sintered body according to Example 1 did not clearly show the peak of the τ phase in the X-ray diffraction pattern of FIG. 4, but the τ phase was certainly generated. No residual magnetization was observed in the comparative example in which the addition ratio of C was X = 0 mol%.

Although the embodiments and examples of the present invention have been described above, the present invention is not limited thereto. The above embodiments and Examples 1-4 are for explaining the present invention, and do not limit the scope of the present invention. The scope of the invention is indicated by the claims. Various modifications made within the claims and equivalents are considered to be within the scope of the invention.

For example, in addition to the above method, it is possible to remold by pressing a Mn—Al—C-based magnetic sintered body before pulverization.

Further, by hot plastic working the Mn—Al—C magnetic sintered body as in the prior art, an anisotropic magnet can be manufactured.

Further, according to Patent Document 3 and Patent Document 4, by applying a magnetic field to the sintered body in the sintering step (step S3) and the slow cooling step (step S4), the synthesis of the τ phase can be promoted and the crystal orientation can be promoted. The τ phase can be generated.

Claims (2)

It is a raw material powder composed of a manganese raw material powder, an aluminum raw material powder, and a carbonaceous raw material powder, and the mol ratio of Mn content / Al content is 50/50 or more, 60. By molding the raw material powder having a C content of / 40 or less and 1.5 mol% or more of the total content of Mn and Al in the raw material powder of 100 mol% or more . The molding process with the molded body and
A sintering step of heating the molded product at a temperature of less than 1275 K for 10 hours or more to form a sintered body.
A slow cooling step in which the sintered body is cooled to room temperature at a temperature lowering rate of 80 K / hr or less,
A method for manufacturing a Mn—Al—C magnet. After the slow cooling step,
A crushing step of crushing the sintered body to make a crushed product,
A remolding step of remolding the pulverized product and in the process of remolding, by orienting the easily magnetized axis of the particles constituting the pulverized product, a remolded body obtained by magnetically differentiating the crushed product is obtained.
The magnetizing step of magnetizing the remolded body and
The method for producing a Mn—Al—C magnet according to claim 1 , further comprising.

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