JP2002020822A - Metal matrix composite material and its production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal matrix composite material in which new TaC particles different from the conventional ones are dispersed as a crystal particle refining agent and to provide its production method. SOLUTION: This metal matrix composite material has a cast structure in which TaC particles are dispersed into a metal matrix material composed of Al or an Al alloy, and in which the crystal particles are refined compared with the case of the cast structure composed of only the same metal matrix material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a metal-based composite material in which particles are dispersed in a metal substrate, and a method for producing the same.

[0002]

2. Description of the Related Art In order to reduce the fuel consumption and enhance the performance of automobiles, it is necessary to reduce the weight. Research and development for replacing iron-based parts with aluminum-based parts are being pursued. At this time, since the strength of the aluminum-based material is lower than that of the iron-based material, it is necessary to increase the strength. However, in general, the ductility of a material is reduced with an increase in strength, so that plastic working into a predetermined component shape becomes difficult, and there are only a limited number of objects that can replace a high-strength aluminum-based component with an iron-based component.

Therefore, in order to expand the range of objects that can be replaced with aluminum-based parts, it is important to improve ductility by making crystal grains finer. Conventionally, as a means for increasing the strength of an aluminum-based casting material, a dispersion strengthening method in which TiC particles or the like as a reinforcing material is dispersed in a base material of aluminum or an aluminum alloy is known (for example, see Japanese Unexamined Patent Publication No.
3-83239, Japanese Patent No. 2734891).

On the other hand, as a means for refining the crystal grains of an aluminum-based casting material, TiC particles and Al ₃ Ti particles are added as a crystal grain refining agent to a molten metal at the time of casting (see, for example, Japanese Patent Application Laid-Open No. 10-204555). As described above, TiC particles and the like act as a reinforcing material and at the same time act as a crystal grain refining agent, and thus are extremely useful as a means for simultaneously improving strength and ductility.

Here, the particles must be sufficiently fine in order to act as a reinforcing material and a grain refiner. However, it is difficult to directly incorporate the fine particles in the form of powder into the molten metal of the base metal. Therefore, in any of the above prior arts, first, a molded body in which fine particles are generated and dispersed by in-situ generation (in-situ generation) in a base metal is formed, and this molded body is separated into another base metal. By charging the molten metal in the molten metal, the base metal of the molded body is dissolved, and at the same time, fine particles are dispersed in the molten metal and solidified to obtain a final dispersion-reinforced composite material.

[0006] As described above, since it is premised that fine particles are generated by in-situ generation, the chemical composition of the fine particles exhibiting a strengthening action and a crystal grain refining action is necessarily limited. Conventionally, various types of dispersed particles as a reinforcing material have been known. Among them, the practically effective dispersed particles known as a crystal grain refining agent are the above-described TiC particles and Al _3.
It has been desired to develop still other particles which are only Ti particles and are effective as a crystal grain refiner.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a metal matrix composite material in which novel particles different from the conventional one are dispersed as a crystal grain refining agent, and a method for producing the same.

[0008]

In order to achieve the above object, the metal matrix composite of the present invention has a cast structure in which TaC particles are dispersed in a metal substrate made of Al or an Al alloy. It is characterized in that the crystal grains are finer than in a cast structure composed of only the metal substrate. The method for producing a metal-based composite material according to the present invention includes a step of forming a powder compact of Al or Al alloy powder, a Ta powder, and a C powder, and forming a first compact of Al or Al alloy on the compact. Impregnating the molten metal, heat-treating the impregnated compact to generate TaC particles in the compact in situ,
The formed body containing the generated TaC particles is made of Al or Al
A step of charging the alloy into a second molten metal to disperse the TaC particles in the molded body in the second molten metal, and a step of solidifying the second molten metal. I do.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventor has investigated the crystal grain refining effect of a metal matrix composite material in which various particles generated by in-situ generation have been dispersed, and as a result, has found that TiC particles, Al ₃ Ti In addition to the particles, the present inventors have newly found that TaC particles have a remarkable crystal grain refining action, and completed the present invention.

[0010]

EXAMPLES The heterogeneous solidification nuclei, which are the main factors in the refinement of crystal grains, have not yet been sufficiently elucidated, and it is not possible to estimate what particles will be solidification nuclei. Therefore, the present inventor
Fine particles of various carbides, borides, oxides, and nitrides by in-situ generation (hereinafter abbreviated as "in-situ particles")
Was prepared, and the effect of crystal grain refinement was examined on an aluminum-based composite material in which this was dispersed.

FIG. 1 shows steps (1) to (4) for producing an aluminum-based composite material. In the step (1), a green compact was produced using the raw material powders shown in the figure according to the type of in-situ particles to be generated. Step (2)
In the above, the molded body was immersed in a 750 ° C. molten aluminum for 30 seconds to impregnate the gap with the molten aluminum (implemented only for carbides and borides).

In step (3), each of the impregnated compacts is heated at a rate of 5 ° C./min and maintained at a temperature of 800 to 1500.
A heat treatment was performed in an Ar atmosphere at ℃ to generate in-situ particles. The structure after the reaction was observed by X-ray diffraction and scanning electron microscope (SEM) to identify the generated phase. The volume ratio of the in-situ particles was set to 25 vol% in each of the molded bodies.

Table 1 shows the types and particle sizes of the in-situ particles,
The types and particle sizes of the raw material powders and the reaction generation process are shown together.

[0014]

[Table 1] The particle size of the generated in-situ particles was 0.2 to 2 μm. This particle size is much finer than the minimum particle size of the dispersed particles obtained by adding the particle powder to the molten metal without in-situ generation, which is about 10 μm. Also, in general,
In-situ particles are affected by the particle size and shape of the raw material powder,
Carbides (TiC, TaC, HfC, ZrC) and borides (ZrB ₂ , TiB ₂ ) produced much finer particles than the raw material powder. On the other hand, the particle diameters of AlN and Al ₂ O ₃ were almost equal to those of the raw material powder. This difference is shown in Table 1.
In contrast to the former, the final compound is generated indirectly via the formation of transition compounds, whereas the latter is generated directly from the raw material powder, as shown in the figure. I have.

Finally, in step (4), the in-sit
The compact containing the u particles was added to a molten Al-4.5% Cu alloy at 750 ° C and stirred for 5 minutes. As a result, Al of the compact was dissolved in the molten alloy, and in-situ particles in the compact were dispersed in the molten alloy. Thereafter, it was cast into a JIS No. 4 boat at a melt temperature of 750 ° C., taken out after solidification, and an aluminum-based composite material was obtained. The dispersion amount of each compound particle in the aluminum-based composite material was 1 vol%.

Table 2 shows the results of measuring the average crystal grain size of the above-mentioned aluminum-based composite material in the case where no particles were added (in the table, "Al" is shown in the column of "in-situ particles"). Shown in comparison with.

[0017]

[Table 2] As shown in the table, the conventional TiC particles, the Ta of the present invention
With the addition of the C particles, the crystal grains were remarkably refined (indicated by “○” in the same table). In contrast, TiB ₂ particles, Zr
C particles, HfC particles, (displayed in the table "△") less the effect of refining the ZrB ₂ particles, further Al ₂ O ₃ particles,
AlN particles hardly exhibited a refining effect (indicated by "x" in the table).

In particular, the TaC particles of the present invention are made of a conventional TiC
It can be seen that there is a crystal grain refining effect exactly equivalent to that of the particles. That is, while the crystal grain size of Al with no particles added was 3 mm, the crystal grain size was 0.1 mm by addition of either the TaC particles of the present invention or the conventional TiC particles.
The size is remarkably reduced to 05 mm. Table 2 shows the substrate Al
The crystal structure and lattice constant of the and in-situ particles are also shown.

The TaC of the present invention has the same face-centered cubic crystal structure as the substrate Al, similarly to the conventional TiC.
The deviation of the lattice constant from 1 is 6.6% for the conventional TiC and 9.7% for the TaC of the present invention, all of which have lattice constants close to those of the base material Al. This result suggests that when the particles to be dispersed have the same crystal structure as the base metal and have a lattice constant close to that of the base metal, a crystal grain refinement effect can be obtained.

Further, from the results in Table 2, it can be estimated that the range of the shift of the lattice constant for obtaining the crystal grain refining action is generally within 10% for the same face-centered cubic crystal structure as the base material Al. .

[0021]

According to the present invention, there is provided a metal matrix composite material in which a novel TaC particle different from the conventional one is dispersed as a crystal grain refiner, and a method for producing the same.

[Brief description of the drawings]

FIG. 1 is a process chart showing a method for producing an Al-based composite material of the present invention.

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Claims (2)

[Claims] 1. It has a casting structure in which TaC particles are dispersed in a metal substrate made of Al or an Al alloy, and has a crystal grain finer than a casting structure made of only the metal substrate. Characteristic metal matrix composite material. 2. The method for producing a metal-based composite material according to claim 1, wherein a step of forming a green compact of an Al or Al alloy powder, a Ta powder, and a C powder is performed. A step of impregnating a first molten metal of Al or an Al alloy, a step of heat-treating the impregnated compact to generate TaC particles in the compact in situ, and a step of forming the compact including the generated TaC particles in the compact. Al or Al
A step of charging the alloy into a second molten metal to disperse the TaC particles in the molded body in the second molten metal, and a step of solidifying the second molten metal. Of producing a metal matrix composite material.