EP4144461A1

EP4144461A1 - Method for producing high metal powder content aluminum composite body, method for preparing preform, and high metal powder content aluminum composite body

Info

Publication number: EP4144461A1
Application number: EP22792730.8A
Authority: EP
Inventors: Mutsuo Hayashi; Shuhei KATSUMATA; Shogo Ochiai
Original assignee: Advance Composite Corp
Current assignee: Advance Composite Corp
Priority date: 2021-07-14
Filing date: 2022-04-13
Publication date: 2023-03-08
Also published as: CN115812011A; JP7037848B1; JP2023012613A; WO2023286407A1

Abstract

The present invention provides a technique of obtaining a high metal powder content aluminum composite body, in which the numbers of cracks and defects are small and a metal content ratio is high, by impregnating a preform with an Al alloy or the like at a high pressure or by causing an Al alloy or the like to infiltrate without pressurization into a preform. This technique can be provided by establishing a preparation technique of obtaining a uniform preform of a metal powder in which the filling rate of the metal powder can be increased and there are no defects in the inside thereof. The present invention provides a method for producing a high metal powder content aluminum composite body, wherein: in a preform preparation step, two or more materials each having a different particle size are selected from metal powder materials having a particle size of 1 to 200 µm; a molded product obtained from a material obtained by adding and mixing an organic/inorganic binder to these metal raw materials is calcined at a temperature of 300°C or higher to obtain a preform having a metal raw material content ratio of 55 v% or more; and the obtained preform is impregnated with a molten metal of an aluminum alloy or the like at a high pressure, or a molten metal of an aluminum alloy or the like is caused to infiltrate without pressurization into the obtained preform. The present invention also provides a composite body obtained by these production methods, and a method for preparing the preform.

Description

Technical Field

The present invention relates to a method for producing a high metal powder content aluminum composite body, a method for preparing a preform, and a high metal powder content aluminum composite body. In more detail, the present invention relates to a novel technique capable of providing a high metal powder content aluminum composite body in which a preform that has a high volume filling rate and is formed from a metal powder is favorably impregnated with metal aluminum or an aluminum alloy (hereinafter, also referred to as Al alloy or the like) and capable of bringing about a dramatic improvement in productivity and product quality of the composite.

Background Art

In recent years, materials obtained by forming a composite from a metal and an aluminum alloy or the like have been attracting attention as materials that are light-weight and exhibit high strength, high Young's modulus, high thermal conductivity, and low thermal expansion, for example, as electronic materials such as a heat sink, a heat dissipating spreader, and electronic parts package products or as semiconductor apparatus members such as an XY slider and a vacuum chuck. Each of these materials is a kind of so-called MMCs (Metal Matrix Composites). In the past, MMCs have been generally obtained by forming a composite from a metal matrix and a ceramic powder, but in recent years, composites formed from a metal powder and an Al alloy or the like have been attracting attention. For example, a composite of silicon that exhibits high Young's modulus and low expansion and an Al alloy or the like, and forming a composite from a titanium or iron powder exhibiting high strength and an Al alloy or the like have been proposed. In addition, as described below, a composite body of a metal powder and an Al alloy or the like has been attracting attention also because it is excellent in processability.
For example, a silicon metal has a small coefficient of thermal expansion and therefore is used as an electronic component or a semiconductor component, but has weak points such that it is very brittle and besides, a complicated, large-sized component cannot be produced. For this reason, silicon-aluminum composite bodies formed with an Al alloy or the like are being developed. From the reason described above, first of all, a composite body formed together with aluminum, in which a silicon powder is contained as much as possible is desired, and on top of that, a composite body having a small coefficient of thermal expansion and a large Young's modulus while keeping processability is desired. Specifically, when a silicon-aluminum composite body containing, for example, 70 v% or more, desirably approximately 80 v%, of a silicon component can be produced, it is expected that applications to heat sinks and electronic component packages equipped with an electronic component having a small coefficient of thermal expansion will spread dramatically.
A titanium metal is used as various types of mechanical parts as a metal that has a small coefficient of thermal expansion and is light-weight and highly rigid. However, the titanium metal has high hardness and is a material that is difficult to process, and therefore the use application is limited in this regard. Accordingly, when the processability can be improved by forming a composite from the titanium metal and an aluminum metal, the application range can be enlarged further, and therefore development of a titanium-aluminum composite body has been desired and is proceeding.
Here, methods exemplified below are general methods for producing a composite body of a metal powder and an Al alloy or the like.

(Method for Casting High Content Silicon Aluminum Alloy)

This method is a method in which a silicon-containing aluminum alloy (also referred to as silicon-aluminum alloy) powder that contains a silicon component and is commonly called silumin is melted to cast the molten silicon-containing aluminum alloy powder in a sand mold or a metal mold. However, in this method, when the silicon component increases, the flowability of the alloy is lowered and casting cannot be performed, and therefore the content of the silicon component is generally approximately 20 v% at the maximum. Accordingly, it is difficult to produce a high content silicon aluminum composite body that has been desired in the above-described casting method and has a high metal component content ratio.

(Spray Forming Method)

This method is a method for producing a silicon-aluminum composite body, wherein a burette of a powder-deposited body obtained by melting silicon and aluminum at a high temperature and spraying a resultant molten product is prepared and the burette is subjected to hot extrusion, and is called a "spray forming method." In the spray forming method, a composite raw material powder in which the ratio between silicon and aluminum is arbitrarily changed by melting the metals at a high temperature can be prepared. Therefore, it is theoretically possible to produce a high content silicon aluminum composite body having a high metal component content ratio. However, to produce a composite having a silicon content ratio of 50 v% or more, the materials need to be melted at 1000°C or higher. In addition, silicon is first deposited in a spraying/cooling process, so that a uniform composite body cannot be obtained, and therefore only silicon-aluminum composite bodies in which a silicon component is up to approximately 50 v% have been made into a product, and a silicon-aluminum composite body having a higher silicon component content ratio has not been able to be produced yet. In addition, voids are generated in a coagulation/deposition process in which the burette of the powder-deposited body is prepared by subjecting the molten product to spraying, and therefore to make a product, it is necessary that the obtained burette is made into a semi-molten state and thereafter subjected to high-pressure extrusion or subjected to an HIP treatment to squash the voids. In this regard, the "spray forming method" has an industrially serious problem that production costs increase significantly and this method is inferior in economic efficiency.

(Method for Causing Aluminum to Infiltrate without Pressurization into Silicon Powder Filled Body)

Patent Literature 1 proposes a silicon-aluminum composite metal obtained by causing a molten Al alloy or the like to infiltrate without pressurization into a filled or molded body in which the filling rate of a silicon powder is 50 to 70% by volume at a temperature of 700°C to 1000°C in a nitrogen atmosphere containing magnesium vapor. Patent Literature 1 discloses that the infiltration of the molten Al alloy or the like into the filled body can be made faster by allowing the magnesium vapor to be contained in the nitrogen atmosphere. In addition, Examples of Patent Literature 1 describe: use of a filled body obtained by filling, in a container, a mixture obtained by adding and mixing 2 parts by mass of a magnesium powder into 100 parts by mass of a silicon powder having an average particle size of 5 µm; and the filling rate of the silicon being 50% by volume. With regard to the above-described Examples, Examples of Patent Literature 1 describe changing the silicon powder to one having an average particle size of 1 to 100 µm as necessary.
As described above, Patent Literature 1 discloses adding a magnesium powder to a single type of a silicon powder, filling a resultant mixture in a container, and causing a molten Al alloy or the like to infiltrate into the filled body in a nitrogen atmosphere at ordinary pressure (without pressurization), thereby preparing a composite metal. However, according to studies conducted by the present inventors, there is a risk that a simple filled body of a silicon powder is non-uniform or pores remain inside a simple body of a silicon powder. When such a filled body is impregnated with a molten metal of aluminum without pressurization, there is a problem that a crack or defect occurs or a filled body in which the silicon powder is sufficiently filled in a uniform state is not obtained. Therefore, a uniform metal powder-aluminum composite body in which the content ratio of a metal component is high and which is required for a product cannot be produced by a pressureless infiltration process using the filled body described above.
In addition, Patent Literature 2 describes causing a molten metal such as molten aluminum to infiltrate without pressurization into a molded body or calcined body of a metal powder, obtained by adding PVA (polyvinyl alcohol) as a binder to the metal body such as a silicon powder, to infiltrate. Examples of Patent Literature 2 describe: impregnating a molded body obtained by performing press molding using a material obtained by adding PVA as a binder to a silicon powder having an average particle size of 20 µm with a molten Al alloy at ordinary pressure in a furnace set to a nitrogen atmosphere where magnesium is present, thereby obtaining a composite metal; using two types of metal powders; mixing a ceramic powder to the metal powders; and the like. However, the technique described in Patent Literature 2 is not a technique that intends to make the molded body or calcined body of the metal powders into one in which the metal content ratio is high, as can be understood from the fact that the ceramic powder is mixed with the metal powders. Here, the metal powders are counterparts of forming a composite by causing the molten metals to infiltrate without pressurization.
According to studies conducted by the present inventors, when, for example, a filled body in which a silicon powder is filled at a high content ratio is impregnated with an Al alloy or the like at a high pressure, or when, for example, an Al alloy or the like is caused to infiltrate without pressurization into a filled body in which a silicon powder is filled at a high filling rate, stress occurs in a contact surface between the filled body and the Al alloy or the like in the impregnation process, so that when the filled body is impregnated with the molten metal of the Al alloy or the like, a crack or the like may occur to a metal powder molded body in some cases, or a capillary phenomenon is inhibited due to a crack to cause a defect that the filled body is unimpregnated in some cases. Facing this, any of the above-described conventional techniques is neither one in which studies on how to obtain a high content metal powder-aluminum composite body in which the numbers of cracks and the like and the number of defects are extremely small and the metal content ratio is high nor one that provides such a composite body. For example, as in the above-described conventional techniques, when an aluminum metal is caused to infiltrate without pressurization into a silicon powder filled body or a molded body obtained by only performing press molding, the stress also occurs in a contact surface between the silicon powder filled body and the Al alloy or the like, so that when the silicon powder filled body or the molded body is impregnated with the molten metal of the Al alloy or the like, a crack or the like may occur in some cases or a defect that the filled body or the molded body is unimpregnated may occur in some cases.
Here, the merit obtained by impregnating the filled body or the molded body with the molten metal of the Al alloy or the like without pressurization, which is performed in the above-described conventional techniques, is that the inside of a molded body (preform) obtained by subjecting a metal powder to press molding or the like is impregnated with a molten metal of an Al alloy or the like calmly due to a capillary phenomenon with the shape of the molded body kept as it is, thereby making it possible to produce a metal powder-aluminum composite body having a shape close to a product shape after impregnation. That is, when a composite body having a shape close to a product shape can be obtained after a molded body is impregnated with a molten metal, machining that is usually necessary thereafter can be reduced, and therefore there is a merit of reducing the production costs.
This means that in the case where the molten metal of the Al alloy or the like is caused to infiltrate without pressurization, when a strong molded body (preform) in which a crack or a defect does not occur can be obtained, the product value and cost merit become dramatically great. In addition, when the content of the metal powder material such as silicon in a resultant metal powder-aluminum composite body can be increased, a metal powder-aluminum composite body which exhibits lower expansion and a higher Young's modulus can be obtained. For example, when a method for producing a silicon powder-aluminum composite body containing more than 50 v% of silicon can be established, the use application of the composite body becomes especially greater.
Under the above-described circumstances, production of a preform by method for temporarily sintering a powder, wherein a molded body of a metal powder having a fine particle size is sintered at a temperature slightly lower than the melting temperature of the metal has been widely performed. However, according to studies conducted by the present inventors, since the molded body (preform) is produced by sintering in this method, there is a risk that: the molded body is contracted during sintering, so that the preform is deformed or voids in the preform are turned into closed pores shut off from the outside; therefore favorable impregnation is not performed in the subsequent impregnation step with an Al alloy or the like; and as a result a non-uniform metal powder-aluminum composite body is produced.

Citation List

Patent Literature

Patent Literature 1: Japanese Patent Laid-Open No. 2005-036253
Patent Literature 2: Japanese Patent Laid-Open No. 2004-052011

Summary of Invention

Technical Problem

Accordingly, an object of the present invention is: to establish a technique of preparing a strong molded body (preform) of a metal powder represented by a powder of, for example, silicon, a silicon-aluminum alloy, iron, titanium, copper, nickel, or ferrosilicon, and preparing a uniform preform in which the filling rate of a metal powder can be increased according to the target performance and the number of defects in the inside is extremely small; and to provide an excellent technique making it possible to obtain a high metal powder content aluminum composite body in which the occurrence of cracks and defects is extremely rare and the metal content ratio is high in any of the case where the obtained preform is impregnated with an Al alloy or the like at a high pressure and an Al alloy or the like is caused to infiltrate without pressurization into the obtained preform.

Solution to Problem

The above-described object is achieved by a technique of producing a high metal powder content aluminum composite body having a high metal content ratio. That is, the present invention provides the following method for producing a high metal powder content aluminum composite body.
As the first invention, the present invention provides the following production method for obtaining a high metal powder content aluminum composite body by impregnation with an Al alloy or the like at a high pressure.

[1] A method for producing a high metal powder content aluminum composite body, the method comprising: a preform preparation step for obtaining a metal powder molded body (preform) having a high metal content ratio; and an aluminum or aluminum alloy impregnation step of impregnating the obtained preform with molten aluminum or a molten aluminum alloy, or causing molten aluminum or a molten aluminum alloy to infiltrate into the obtained preform, wherein
- in the preform preparation step, two or more metal powder materials each having a different average particle size are selected from metal powder materials each having an average particle size of 1 µm or larger and 200 µm or smaller to use the two or more metal powder materials as metal raw materials for the preform, molding is performed using a mixture obtained by adding and mixing an organic/inorganic binder into the metal raw materials, and a resultant molded product is calcined at a temperature of 300°C or higher and 800°C or lower, thereby obtaining a metal powder molded body having a content ratio (volume content ratio) of the metal raw materials of 55 v% or more, and
- in the aluminum or aluminum alloy impregnation step, the metal powder molded body obtained in the preform preparation step is impregnated with a molten metal of the aluminum or the aluminum alloy at a high pressure of 10 MPa to 200 MPa.

Particularly, the organic/inorganic binder is preferably at least any one selected from the group consisting of a silicone resin, a Si alkoxide, and an Al alkoxide, which are in a liquid form or in a state of having been made into a liquid form.
As the second invention, the present invention provides the following production method for obtaining a high metal powder content aluminum composite body by pressureless infiltration of an Al alloy or the like.
A method for producing a high metal powder content aluminum composite body, the method comprising: a preform preparation step for obtaining a metal powder molded body (preform) having a high metal content ratio; and an aluminum or aluminum alloy impregnation step of impregnating the obtained preform with molten aluminum or a molten aluminum alloy, or causing molten aluminum or a molten aluminum alloy to infiltrate into the obtained preform, wherein

in the preform preparation step, two or more metal powder materials each having a different average particle size are selected from metal powder materials having an average particle size of 1 µm or larger and 200 µm or smaller (excluding powder materials of a Mg powder, an AlMg powder, a ZnMg powder, a ZnAl powder, and a Mg₂Si powder) to use the two or more metal powder materials as metal raw materials for the preform, molding is performed using a mixture obtained by adding one or more powders selected from the group consisting of a Mg powder, an AlMg powder, a ZnMg powder, a ZnAl powder, and a Mg₂Si powder in an amount within a range of 0.2 to 5 parts by mass based on 100 parts by mass of the metal raw materials, and further adding and mixing an organic/inorganic, and a resultant molded product is calcined at a temperature of 500°C or lower, thereby obtaining a metal powder molded body having a content ratio (volume content ratio) of the metal raw materials of 55 v% or more, and
in the aluminum or aluminum alloy impregnation step, aluminum or an aluminum alloy is caused to infiltrate without pressurization in a nitrogen atmosphere into the metal powder molded body obtained in the preform preparation step.

Particularly, the organic/inorganic binder is preferably at least any one selected from the group consisting of a silicone resin, a Si alkoxide, and an Al alkoxide, which are in a liquid form or in a state of having been made into a liquid form.
Preferred embodiments of the above-described method for producing a high metal powder content aluminum composite body of the present invention include the following.

[3] The method for producing a high metal powder content aluminum composite body according to [1] or [2], wherein the metal powder is selected from a silicon powder or a silicon-based alloy powder containing silicon, a titanium powder, an iron powder or an iron-based alloy powder containing iron, and a nickel powder or a nickel-based alloy powder containing nickel.
[4] The method for producing a high metal content aluminum composite body according to any one of [1] to [3], wherein the high metal content aluminum composite body has a volume metal powder content ratio of 55 v% or more and 85 v% or less.
[5] The method for producing a high metal powder content aluminum composite body according to any one of [1] to [4], wherein the two or more metal powders each having a different average particle size comprise at least: a metal powder A having an average particle size of 10 µm or smaller; and a metal powder B having an average particle size of 40 µm or larger, and comprise at least 3% of the metal powder A and 50% or more of the metal powder B in a total amount of the metal powders on a mass basis.
[6] The method for producing a high metal powder content aluminum composite body according to any one of [1] to [5], wherein the organic/inorganic binder is at least any one selected from the group consisting of a Si alkoxide and an Al alkoxide.

Moreover, the present invention provides, as another embodiment, the following method for preparing a preform which is suitably used in the method for producing a high metal powder content aluminum composite body of the first invention.
A preform preparation method for obtaining a metal powder molded body (preform) which is used in obtaining a high metal powder content aluminum composite body metal by impregnating the preform with molten aluminum or a molten aluminum alloy at a high pressure and has a high metal powder content ratio, wherein
two or more metal powder materials each having a different average particle size, the metal powder materials containing at least a metal powder A having an average particle size of 10 µm or smaller, a metal powder B having an average particle size of 40 µm or larger and containing at least 3% of the metal powder A and 50% or more of the metal powder B in the total amount of the metal powders on a mass basis, are selected from metal powder materials having an average particle size of 1 µm or larger and 200 µm or smaller to use the two or more metal powder materials as metal raw materials for the preform, molding is performed using a mixture obtained by adding and mixing an organic/inorganic binder being into the metal raw materials, and a resultant molded product is calcined at a temperature of 300°C or higher and 800°C or lower, thereby obtaining a metal powder molded body having a content ratio (volume content ratio) of the metal raw materials of 55 v% or more.
Particularly, the organic/inorganic binder is preferably at least any one selected from the group consisting of a silicone resin, a Si alkoxide, and an Al alkoxide, which are in a liquid form or in a state of having been made into a liquid form.
Further, the present invention provides, as another embodiment, the following method for preparing a preform which is suitably used in the method for producing a high metal powder content aluminum composite body of the second invention.
A preform preparation method for obtaining a metal powder molded body (preform) which is used in obtaining a high metal powder content aluminum composite body metal by causing molten aluminum or a molten aluminum alloy to infiltrate without pressurization into the preform and has a high metal powder content ratio, wherein
two or more metal powder materials each having a different average particle size, the metal powder materials containing at least a metal powder A having an average particle size of 10 µm or smaller, a metal powder B having an average particle size of 40 µm or larger and containing at least 3% of the metal powder A and 50% or more of the metal powder B in a total amount of the metal powders on a mass basis, are selected from metal powder materials having an average particle size of 1 µm or larger and 200 µm or smaller (excluding powder materials of a Mg powder, an AlMg powder, a ZnMg powder, a ZnAl powder, and a Mg₂Si powder) to use the two or more metal powder materials as metal raw materials for the preform, molding is performed using a mixture obtained by adding one or more powders selected from the group consisting of a Mg powder, an AlMg powder, a ZnMg powder, a ZnAl powder, and a Mg₂Si powder in an amount within a range of 0.2 to 5 parts by mass based on 100 parts by mass of the metal raw materials, and further adding and mixing an organic/inorganic binder, and a resultant molded product is calcined at a temperature of 500°C or lower, thereby obtaining a metal powder molded body having a content ratio (volume content ratio) of the metal raw materials of 55 v% or more.
Particularly, the organic/inorganic binder is preferably at least any one selected from the group consisting of a silicone resin, a Si alkoxide, and an Al alkoxide, which are in a liquid form or in a state of having been made into a liquid form.
Furthermore, the present invention provides, as other embodiments, the following high metal powder content aluminum composite bodies.

[9] A high metal powder content aluminum composite body having an extremely small number of internal defects such as blowholes, wherein the high metal powder content aluminum composite body is obtained by the method for producing a high metal powder content aluminum composite body according to any one of [1] and [3] to [6], in which high-pressure impregnation is utilized.
[10] A high metal powder content aluminum composite body having a near-net shape close to a product shape, wherein the high metal powder content aluminum composite body is obtained by the method for producing a high metal powder content aluminum composite body according to any one of [2] to [6], in which pressureless infiltration is utilized.

Advantageous Effects of Invention

According to the present invention, the following can be realized in preparation of a molded body (preform) of a metal powder, represented by powders of, for example, silicon, a silicon-aluminum alloy, iron, titanium, copper, nickel, and ferrosilicon: that is, the volume filling rate of the metal powder can be increased to 55 v% or more according to the target performance; and a resultant preform is made uniform such that the number of defects is extremely small inside thereof. As a result, according to the present invention, even when the preform is impregnated with an Al alloy or the like at a high pressure, or even when an Al alloy or the like is caused to infiltrate without pressurization into the preform, there is provided an excellent method for producing a high metal powder content aluminum composite body, by which a high-quality high metal powder content aluminum composite body in which occurrence of cracks and defects is reduced and a volume metal content ratio is high can be obtained. In addition, according to the present invention, providing a high-quality high metal powder content aluminum composite body in which the number of internal defects such as blowholes is extremely small is realized. These composite bodies can be utilized as a vacuum component in, for example, semiconductor/liquid crystal production apparatuses, electron microscopes, and packages for optical communication. Further, according to the present invention, a high metal powder content aluminum composite body having a near-net shape close to a product shape can also be produced, and therefore machining steps to be necessary thereafter and costs for the steps can be reduced, and further, the size of the composite body can be increased, and therefore use as a large-sized structural component such as a robot arm, shape measurement apparatus frame, or an XY table is expected.

Brief Description of Drawings

[Figure 1(A)] Figure 1(A) is a schematic diagram for explaining a procedure of a pressurized infiltration process which is utilized in a method for producing a high metal powder content aluminum composite body of the first invention of the present invention and in which a molten metal of an Al alloy or the like is pressurized and caused to infiltrate into a preform. Figure 1(A) is a schematic diagram showing a situation of pouring a molten metal of an Al alloy or the like 2 in a frame mold/metal mold 3 of a press machine for high-pressure impregnation loaded with a preform 1.
[Figure 1(B)] Figure 1(B) is a schematic diagram for explaining a state where a press punch has been installed at an opening of the frame mold/metal mold 3 in a state where the preform 1 and the molten metal of the Al alloy or the like 2 are loaded as a result of the operation in Figure 1 (A).
[Figure 1(C)] Figure 1(C) is a schematic diagram showing a situation of impregnating the preform 1 with the molten metal of the Al alloy or the like 2 by applying a load (high pressure) to the molten metal in the frame mold/metal mold 3 in the state of Figure 1 (B).
[Figure 2(A)] Figure 2(A) is a schematic diagram for explaining a situation in which a molten metal of an Al alloy or the like infiltrates into a preform due to a capillary phenomenon by a pressureless infiltration process, which is performed in a method for producing a high metal powder content aluminum composite body of the second invention of the present invention, to impregnate the preform with the molten metal of the Al alloy or the like. Figure 2(A) is a schematic diagram showing a disposed state of the preform 1 and the Al alloy or the like 2, which are loaded in a container 5 made of carbon.
[Figure 2(B)] Figure 2(B) is a schematic diagram showing a situation in which the Al alloy or the like 2 in the container 5 made of carbon becomes a molten metal and the molten metal infiltrates without pressurization into infiltration channels 4 supporting the preform 1.
[Figure 2(C)] Figure 2(C) is a schematic diagram showing a situation in which the molten metal of the Al alloy or the like 2 infiltrates without pressurization into the preform 1 in the container 5 made of carbon through the infiltration channels 4 supporting the preform 1.
[Figure 2(D)] Figure 2(D) is a schematic diagram showing a situation after the molten metal of the Al alloy or the like 2 infiltrates without pressurization into the whole of the preform 1 in the container 5 made of carbon.

Description of Embodiments

Hereinafter, the present invention will be described giving preferred embodiments. The present invention is not limited to these embodiments.

[Preparation of Metal Powder Molded Body (Preform)]

In view of the above-described conventional techniques, the present inventors have conducted diligent studies on a method for producing a uniform high metal powder content aluminum composite body in which the volume metal content ratio is high, the number of defects in the inside is small, and the utilization of which for various use applications can be expected. As a result, the present inventors have reached a conclusion that it is important to establish a method by which a metal powder molded body (preform) having a high volume metal content ratio and a small number of voids in the inside thereof can be simply prepared. Then, first of all, the present inventors have found that to obtain a metal preform having a small number of voids, which cause the defects of a composite to be finally obtained, it is effective to use a material obtained by mixing two, or three or more metal powders each having a different average particle size instead of using a group of metal powders having the same particle size as a material. That is, the present inventors have found that when the preform is formed in this way, particles having a small average particle size are present between particles having a large average particle size, and as a result, the effects of the present invention are obtained. In the present invention, two or more metal powders each having a different average particle size are selected, and a mixture obtained by mixing these is used as a metal raw material for a preform.

(Metal Powder Materials)

In the present invention, as the metal powder materials for preparing a preform, materials having an average particle size within a range of 1 µm or larger and 200 µm or smaller are used. The metal powders having an average particle size within a range of preferably 3 µm or larger and 180 µm or smaller, more preferably 3 µm or larger and 100 µm or smaller, are used. The preform that constitutes the present invention needs to be prepared using a mixture obtained by selecting two or more metal powders each having a different average particle size among the metal powders having an average particle size within such ranges and mixing the selected metal powders. When only the materials having an average particle size of less than 1 µm are used, particles are excessively fine and the number of surface oxidation phases of the metal powders is large, so that there is risk that the performance as metal powders is lowered. On the other hand, it is not preferable that the metal powders to be used are only the metal powders having an average particle size of larger than 200 µm because the particle size is excessively large and the performance of filling the particles for performing press molding, CIP molding, sedimentation molding, and the like is lowered.
In the present invention, when the two or more metal powder materials each having a different average particle size for preparing a preform are selected, it is preferable to use a mixture obtained by combining a metal powder having a large particle size and a metal having a small particle size. For example, the mixture is preferably prepared in such a way as to contain at least a metal powder A having an average particle size of 10 µm or smaller and a metal powder B having an average particle size of 40 µm or larger and to contain at least 3% of the metal powder A and 50% or more of the metal powder B in the total amount of the metal powders on a mass basis.
For example, when silicon powders each having a different particle size, 45 µm and 5 µm, are press-molded respectively, the volume filling rate (v%: Vf) is 47% and 52%, respectively. According to studies conducted by the present inventors, when the silicon powders having an average particle size of 45 µm and 5 µm respectively are mixed in a ratio of 70:30 on a mass basis and press molding or the like is performed using the resultant mixture, thereby a molded body in which Vf = 73% can be finally obtained. Similarly, when silicon powders having an average particle size of 70 µm, 25 µm, and 5 µm respectively are mixed in a ratio of 70:25:5 on a mass basis and press molding or the like is performed using the resultant mixture, thereby a silicon molded body in which Vf = 78 v% (volume%) can be obtained.
With regard to a metal powder such as a silicon powder, the filling rate is changed depending on the average particle size, particle shape, particle size distribution, and the like of the metal powder, and therefore as a method for obtaining a desired high volume filling rate (v%), there is also a method, for example, in which a metal powder is put into a container or the like made of carbon to apply vibration with considerable care so as to increase the filling rate as much as possible to make a filled product in which the metal powder is filled so as to reduce voids as much as possible. However, according to studies conducted by the present inventors, it is not easy to obtain a filled product having a metal powder raw material content ratio of 55 v% or more by this method of utilizing vibration, or even if such a filled product is obtained, a crack occurs or a streak-like defect occurs in the case where the filled product is thereafter impregnated with a molten metal of an Al alloy or the like at a high pressure, so that it has been found that a high-quality high metal powder content aluminum composite body cannot be obtained.
The present inventors have conducted diligent studies from the above-described knowledge and have found the following. When a mixed powder blended using two or more metal powder materials each having a different average particle size is molded adopting a molding method such as press molding, CIP molding, or a sedimentation method in such a way that the metal powders are filled without gaps as much as possible, thereby it is made possible to prepare a strong preform that has a higher filling rate, as high as a metal raw material content ratio of 55 v% or more, and that can be bearable when impregnated with a molten metal of an Al alloy or the like at a high pressure. Further, the present inventors have found that in order to enhance the strength of the preform more, it is effective to add and mixed an organic/inorganic binder into the mixture of the metal powders, formed in the manner as described above, and to calcine a molded product composed of the resultant mixture at a temperature of 300°C or higher and 800°C or lower. Details on these points will be described later.
Further, the present inventors have conducted diligent studies on preparation of a preform that enables infiltration of an Al alloy or the like without pressurization and that has a metal powder raw material content ratio of 55 v% or more. As a result, it has been found that it is effective to use a mixture obtained by adding 0.2 to 5 parts by mass of one or more powders selected from compounds such as a metal Mg powder, a magnesium-based alloy including an Al-Mg-based alloy powder, a Zn-Mg-based alloy powder, and the like, and a Zn-Al-based alloy powder, and a Mg₂Si powder having a high magnesium content (these are also referred to as Mg component-containing metal powder and/or the like, or these are sometimes described as Mg component) to 100 parts of the metal powder materials on a mass basis. Then, the present inventors have found that by using a preform obtained by adding a unique organic/inorganic binder to the mixture and calcining a molded product formed from the mixture of these at a temperature of 500°C or lower, a molten metal of an Al alloy or the like can be caused to infiltrate without pressurization in a favorable state and a high-quality high metal powder content aluminum composite body is obtained. That is, for example, from the Mg component having been allowed to be present in a preform, Mg₃N₂ is generated in a nitrogen atmosphere in performing pressureless infiltration, which will be described later, and in addition, the Mg component reduces a metal oxide on the metal powder surface into a metal through a thermit reaction of Mg, thereby improving the wettability between the metal powders and the molten metal of the Al alloy or the like. It is considered that the infiltration of the molten metal of the Al alloy or the like without pressurization into the prepared preform in a favorable state can be realized by these functions of the Mg component that constitutes the present invention.
It is preferable to use powders each having an average particle size of 0.5 µm or larger and 150 µm or smaller as the Mg component-containing metal powder and/or the like given above. The powders each having an average particle size of larger than 150 µm are not preferable because the powders are excessively coarse and cannot be mixed uniformly with the above-described metal powder materials in some cases. Further, when the particle size is coarse, the surface area of the Mg component is small, and therefore the amount of Mg₃N₂ which is generated after Mg contained in the preform reacts with nitrogen in the atmosphere and undergoes nitriding is small. Here, when the amount of Mg₃N₂ which is generated is small, the infiltration speed of the Al alloy or the like into the preform is slow, and thus this case is not preferable. On the other hand, when the Mg component is finer, the surface area is larger, so that the Mg component is easily oxidized by oxygen in the air into MgO, making the amount of Mg smaller, and thus this case is not preferable. Therefore, it is desirable to use the Mg component-containing metal powder and/or the like having an average particle size of 0.5 µm or larger. In addition, when the average particle size is larger than 150 µm, the surface area as a whole is small, so that the amount of Mg₃N₂ which is generated is small as described above, and thus this case is not preferable.
With regard to the amount of the Mg component-containing metal powder and/or the like which is added and mixed, the Mg component-containing metal powder and/or the like is used within a range of 0.2 to 5 parts by mass in terms of Mg based on 100 parts by mass of the metal powders on a mass basis. More preferably, the Mg component-containing metal powder and/or the like is used within a range of 0.5 to 5 parts by mass. When the amount of the Mg component-containing metal powder and/or the like is small, as small as less than 0.2 parts by mass, the amount of Mg₃N₂ which is generated is small and the infiltration speed of the molten metal of the Al alloy or the like is not promoted sufficiently, and thus this case is not preferable. On the other hand, when the amount of the Mg component-containing metal powder and/or the like is more than 5 parts by mass, the amount of the Mg component in the preform prepared from these raw materials is locally large in terms of the distribution state, so that there is a risk that the amount of the Al alloy or the like which infiltrates is nonuniform due to this, and thus this case is not preferable. When the Mg-based alloy or the Mg-containing compound given above is used, the mixing amount may be determined in terms of Mg contained in these.
The metal powder which is used in the present invention is not particularly limited, and examples thereof include metal powders represented by a silicon power, a silicon-aluminum alloy powder, a ferrosilicon alloy powder, an iron or iron-based powder, a titanium powder, a nickel or nickel-based powder, and the like. As described above, in order to impregnate a preform with a molten metal of an Al alloy or the like in a favorable state without pressurization, it is preferable to allow the Mg component to be present in the preform. Therefore, in the mixture in preparing a preform which is used for pressureless infiltration, one or more Mg component-containing metal powder and/or the like need to be added in an amount within a range of 0.2 to 5 parts by mass in addition to the above described metal powder, and further a molded product is calcined at a temperature of 500°C or lower. Therefore, in preparing a preform which is used for pressureless infiltration, any of the Mg component-containing metal powder and/or the like needs to be not used as the two or more metal powder materials each having a different average particle size.
In contrast, when a preform is for use for high-pressure impregnation, there is no problem to use the Mg component-containing metal powder and/or the like as the two or more metal powder materials each having a different average particle size in preparing the preform. Note that in this case, the preform is prepared by calcining a molded product obtained by molding the mixture at a temperature of 300°C or higher and 800°C or lower, and therefore when calcining is performed at a temperature higher than 500°C, for example, Mg in the Mg component-containing metal powder and/or the like is oxidized to change into MgO, so that the Mg component that is important in pressureless infiltration is not present in the preform. In addition, at a temperature higher than 800°C, the metal powder is oxidized and the characteristics inherent in the metal are impaired.

(Organic/Inorganic Binder)

Since a preform is impregnated with a molten metal of an Al alloy or the like at a high pressure, or a molten metal of an Al alloy or the like is caused to infiltrate without pressurization into a preform, the preform which is used needs strength to bear stress caused by the impregnation with the molten metal of the Al alloy or the like or the infiltration of the molten metal of the Al alloy or the like. In the first invention of the present invention, impregnation with a molten metal of an Al alloy or the like at a high pressure is required, and specifically, impregnation with a molten Al alloy or the like is performed at several tens of MPa, and therefore a preform which is used in this case in particular needs higher strength that is bearable to such high pressure. In addition, even when a molten Al alloy or the like is caused to infiltrate by means of pressureless infiltration into the preform of the second invention of the present invention, stress occurs on a surface of the molten metal of the Al alloy or the like which is in contact with the preform. According to studies conducted by the present inventors, when a molten metal of an Al alloy or the like is caused to infiltrate at a high pressure or without pressurization into a filled phase of a metal powder filled simply by a method of vibration or the like, a crack or a defect may occur in some cases. Therefore, when impregnation with a molten metal of an Al alloy or the like is performed or infiltration of a molten metal of an Al alloy or the like is performed by any of the methods, it is desirable to prepare a preform and impregnate the preform with an Al alloy or the like.
In order to prepare a preform having high strength from a ceramic powder or the like and obtain a composite body of ceramic-Al alloy or the like, a preform usually needs to be prepared by adding and mixing an inorganic binder such as colloidal silica into ceramic to perform molding and to calcine a resultant molded body at a temperature of approximately 1000°C or higher. However, the composite body of the present invention is a composite body of a metal powder and an Al alloy or the like, and therefore the above-described conventional techniques cannot be utilized. That is, when a molded body obtained by adding and mixing an inorganic binder into a metal powder is calcined at a temperature of 1000°C for the purpose of obtaining a preform having high strength, the metal powder is oxidized and the performance as a metal is impaired, and therefore the conventional methods cannot be adopted. In contrast, in the present invention, by obtaining a molded body by adding and mixing an organic/inorganic binder into the metal powders as specified in the present invention, a strong preform containing a metal powder at a high content ratio can be prepared by calcining at a low temperature region of 300°C to 800°C, and as a result, remarkable effects of the present invention are obtained.
To meet the above-described demand, the present inventors have diligently proceeded with the development and, as a result, have found that it is effective to use the above-described mixture obtained by adding and mixing an organic/inorganic binder into two or more metal powder materials each having a different average particle size as means for obtaining a stronger preform. The particulars will be described below.
To make a preform strong, it is desirable to fill the metal powders to be dense as much as possible with the above-described press, CIP, sedimentation method, or the like and mold the metal powders applying pressure, and to add a binder to the metal mixed powders which are raw materials. As a binder which is used for molding ceramic or the like, an organic substance represented by polyvinyl alcohol (PVA) or polyvinyl butyral (PVB) is generally used. However, when a preform prepared using these organic binders is impregnated with a molten Al alloy or the like at a high pressure or when a molten Al alloy or the like is caused to infiltrate without pressurization into a preform prepared using these organic binders, a gas is generated, and therefore there is a risk that the impregnation with the Al alloy or the like is inhibited. In order to prevent this problem, the organic substance which is a gas generation source has to be calcined and removed by calcining the preform in advance. This means that the organic binder such as PVA or PVB cannot function as a binder for making the preform after calcining strong and cannot be used. On the other hand, it is conceivable that an inorganic binder such as colloidal silica or colloidal alumina is added to the metal powder materials to mold a resultant mixture by press, CIP, or the like, and then calcining is performed to make the preform strong. Then, to obtain a preform which exhibits strength due to these inorganic binders, the preform needs to be calcined at 1000°C or higher. However, when calcining is performed at this temperature, the metal powders which are main raw materials are oxidized and a function as metals is inhibited. Accordingly, general inorganic binders such colloidal silica and colloidal alumina cannot be used.
Facing those described above, the present inventors have conducted diligent studies, and as a result, have found that by performing molding using a mixture obtained by adding and mixing an organic/inorganic binder into two or more metal powder materials, and calcining a resultant molded product at a particular temperature according to the method of impregnation with a molten Al alloy or the like, thereby preparing a preform, a strong preform in which impregnation with a molten metal of an Al alloy or the like with pressurization or without pressurization can be realized in a favorable state can be obtained.
As the organic/inorganic binder which is used in the present invention, a silicone resin, a silicon organic derivative such as a Si alkoxide having a chemical structure of Si-O-R (R: organic substance), or an aluminum organic derivative such as an aluminum alkoxide having a chemical structure of Al-O-R (R: organic substance) can be used. According to studies conducted by the present inventors, first of all, by using a mixture of metal powders, in which an organic/inorganic compound given above is added as a binder, a strong molded product can be prepared at normal temperature. Then, according to studies conducted by the present inventors, it has been found that by thereafter calcining the obtained molded product at a temperature of 300°C or higher and 800°C or lower, which is 800°C or lower where the metal powders are not oxidized, to prepare a preform, a strong metal powder molded body (preform) is obtained after calcining although the organic substance in the molded product is calcined and removed. With regard to the reason that such an effect is obtained, the present inventors consider as follows. First of all, the organic/inorganic compound given above, when added to the metal powders and molded, exhibits strength at normal temperature as a so-called glue agent similarly to a general organic binder. When heating is further performed at 300°C or higher, an organic substance in the organic/inorganic compound is combusted and removed, but an inorganic substance in the structure of the organic/inorganic compound functions as an inorganic binder and therefore makes a preform to be obtained after calcining strong. That is, by performing calcining at a temperature of 300°C or higher, the organic substance in the molded product is removed, and the inorganic substance functions as an inorganic binder, and as a result, a metal powder molded body having a metal raw material content ratio (volume content ratio) of 55 v% or more can be obtained. The effect that is obtained by using the organic/inorganic binder is more specifically described below.
As described above, a general inorganic binder such as colloidal silica or colloidal alumina cannot contribute to exhibition of the strength of a preform unless it is calcined at a temperature of 1000°C or higher. On the other hand, when the organic/inorganic binder which is used in the present invention is calcined, an organic substance is calcined and removed at a calcining temperature of 300°C or higher, and a SiO2 component, an Al2O3 component, and the like, which are left after calcining, bond to metal powders while being amorphous as it is. Therefore, the preform even after being calcined at a low temperature of, for example, approximately 300°C exhibits strength. In addition, according to studies conducted by the present inventors, even when calcining is performed at a high temperature of 800°C or lower, the metal powders are not oxidized, and therefore a sufficiently strong preform can be produced. Further, in the organic/inorganic binder given above, the organic substance is decomposed and removed at a temperature of 300°C, and therefore the organic/inorganic binder also has an advantage in that there is no generation of an organic gas due to an organic substance during impregnation with a molten metal of an Al alloy or the like. The reason that the above-described effect is obtained is considered to be as follows. That is, for example, a Si alkoxide that is the organic/inorganic binder which is used in the present invention has a molecular structure of Si-O-R (R: organic substance), and therefore the organic substance is more unlikely to be carbonized and left and is more likely to be combusted and removed even at a temperature of 300°C to 800°C than in general organic binders, so that the Si alkoxide functions as an inorganic binder of SiO₂ in the molded body after calcining, and as a result, it is considered that the obtained preform exhibits the strength. Furthermore, the inorganic/organic binder which needs to be used in the present invention can be used with an organic solvent such as ethanol, IPA, or toluene, and therefor also has an advantage in that deterioration due to the reaction between the metal powders and water is suppressed.
As described above, in any of the cases of the first invention and second invention of the present invention, the organic substance is decomposed and removed at a relatively low temperature and a strong preform is obtained. As will be described later, this is an important factor for impregnating the obtained preform with a molten metal of an Al alloy or the like in a favorable state at a high pressure or without pressurization. Specifically, in the case of the high-pressure impregnation which is performed in the first invention of the present invention, the preform is preheated at a temperature of 800°C or lower, and thereafter, the preform is impregnated with a molten metal of an Al alloy or the like having a temperature of 700°C to 800°C at a high pressure. The preform that constitutes the present invention can exhibit sufficient strength even to a molten metal having such a high temperature. Further, in the present invention in which a unique preform is used, there is no gas which is generated from the inside of the preform and which is difficult to remove, and therefore even the inside of the preform can be impregnated with a molten metal of an Al alloy or the like.
On the other hand, in the case of the pressureless infiltration which is performed in the second invention of the present invention, the preform prepared in the manner as described below is used. As described above, in the second invention, the Mg component-containing metal powder and/or the like is contained in the preform in such a way that a predetermined amount is mixed in the preform. When the Mg component-containing metal powder and/or the like is, for example, a metal Mg powder or a Mg-containing alloy powder, it is oxidized into MgO at higher than 500°C, and therefore the preform needs to be calcined at a temperature of 500°C or lower. In addition, according to studies conducted by the present inventors, by adding a desired amount of the above-described organic/inorganic binder in addition to calcining a preform at a low temperature of 500°C or lower in obtaining a molded product by mixing the metal powder materials, the Mg component-containing metal powder and/or the like is not oxidized when the molded product is calcined, and a strong preform that does not collapse when a molten metal of an Al alloy or the like is caused to infiltrate without pressurization can be produced.
The organic/inorganic binder which is used in the present invention, when being in a solid form, is preferably added after being dissolved into an organic solvent such as ethanol or IPA. In addition, the organic/inorganic binder, when being in a liquid form, can be added as it is or after being diluted with an organic solvent such as ethanol or IPA. An appropriate amount of the organic solvent such as ethanol or IPA may be added and mixed in such a way as to easily mix the metal powder raw materials and the organic/inorganic binder. The organic/inorganic binder which is used in the present invention is preferably added and mixed within a range such that the addition amount of the organic/inorganic binder falls within a range of, for example, approximately 0.3 to approximately 5.0 parts by mass based on 100 parts by mass of the metal powder raw materials in terms of SiO₂ or Al₂O₃. When the addition amount is smaller than the above-described range, the addition amount is excessively small and therefore desired strength of the preform may not be sufficiently obtained in some cases. When the addition amount is larger than the above-described range, the aluminum composite body that is finally obtained has a large amount of an inorganic substance such as SiO₂ or Al₂O₃, and there is concern that a high metal powder content aluminum composite body that is an object of the present invention and has a high metal content ratio is not obtained, so that the performance of a product is lowered and thus this case is not preferable.

(Method for Preparing Molded Product)

In the present invention, two or more metal powder materials each having a different average particle size are selected and used as the metal raw materials for a preform; molding is performed using a mixture obtained by adding and mixing the organic/inorganic binder as given above into the metal raw materials to obtain a molded product; and the resultant molded product is calcined at a particular temperature, thereby preparing a preform having high strength. Specifically, the molded product is obtained by molding a metal powder mixture obtained by mixing the organic/inorganic binder as described above with two or more metal powder materials each having a different average particle size.
The molding method for the molded product is not particularly limited, and examples thereof include the following methods. That is, examples thereof include a method for obtaining a molded body by drying the metal powder mixture to perform dry molding such as press molding or CIP, and a method for obtaining a molded body by making the metal powder mixture into a slurry form using an organic solvent to perform vibration sedimentation molding or slip molding with a gypsum mold. When making the metal powder mixture into a slurry form, it is preferable to prepare a slurry with an organic solvent to reduce the use amount of water. This is because when the amount of water is large, there is a risk that the metal powder reacts with water and the metal powder change into a hydroxide or the like and is deteriorated. For example, in the case where the metal powder is a silicon powder, the reaction described below progresses and there is a risk that silicon is deteriorated.

Si + 4H₂O → Si(OH)₄ + 2H₂
In addition, also in the case where the metal powder is a titanium powder, the reaction described below progresses and there is a risk that titanium is deteriorated. That is, titanium changes into an oxide through a reaction Ti + 2H₂O →TiO₂ + 2H₂. Another metal powder also reacts with water to change into an oxide, and therefore basically, it is not preferable to use water. To suppress this problem, an organic solvent such as an alcohol is used, or a mixed solvent of water and a hydrophilic organic solvent such as an alcohol is used. In this case, it is also preferable to reduce the water content in the mixed solvent in order to suppress the reaction. According to studies conducted by the present inventors, when the water content is 30 parts by mass or less based on 100 parts by mass of the organic solvent, the reaction as described above does not occur.
When the molded product is obtained by drying the metal powder mixture and then performing dry molding such as press molding or CIP, the problem as described above does not occur. By utilizing press molding that is used for general purposes as a method for obtaining a molded product of a powder material, a molded product that is desired in the present invention can easily be obtained. In addition, by utilizing CIP molding, the density of a resultant molded body can be made uniform, and therefore it is also preferable to obtain the molded product utilizing CIP molding. For example, it is also a preferred method to perform pre-molding by means of press molding and then perform CIP molding.

(Calcining Molded Product)

In the present invention, the molded product obtained in the manner as described above is calcined to obtain a metal powder molded body (preform) having a high metal content ratio. On that occasion, when the preform is impregnated with a molten metal of an Al alloy or the like at a high pressure of 10 MPa to 200 MPa, calcining is performed at a temperature of 300°C or higher and 800°C or lower. In addition, when a molten metal of an Al alloy or the like is caused to infiltrate without pressurization into the preform, calcining is performed at a temperature of 500°C or lower, for example, at a temperature of 300°C or higher and 500°C or lower. First of all, by calcining the molded product at the above-described temperature, an organic substance derived from the organic/inorganic binder contained in the molded product is removed. If the organic substance is left in the molded product, a gas is generated by the contact of the high-temperature molten metal of the Al alloy or the like and the organic substance when the Al alloy or the like is caused to infiltrate into the molded product, so that the infiltration of the Al alloy or the like may be inhibited in some cases, and therefore the organic substance needs to be removed by calcining.
Further, by preparing a preform by calcining the molded product at the above-described temperature, sufficient strength can be imparted when the preform is impregnated with the molten Al alloy or the like under any of the conditions at a high pressure or without pressurization, and this is an original object of the present invention. In addition, as described above, when a high metal powder content aluminum composite body having a near-net shape close to a product shape can be produced by the present invention, processing costs can be significantly reduced and therefore the high metal powder content aluminum composite body is very useful. To achieve this object, it is necessary to make the preform into one having strength that enables machining before the preform is impregnated with a molten Al alloy or the like, and therefore it is important to prepare the preform by calcining the molded product in order to realize this object.
The temperature condition in obtaining a metal powder molded body (preform) having a high metal content ratio is different depending on whether to perform high-pressure impregnation or pressureless infiltration as a method in impregnating the preform with a molten Al alloy or the like in the subsequent step. When a preform to be provided for the high-pressure impregnation is obtained, the impregnation with the molten metal of the Al alloy or the like is performed at a relatively high pressure of approximately 10 MPa to approximately 100 MPa, and therefore the preform to be used needs to have strength that is bearable to this impregnation. However, according to studies conducted by the present inventors, when the calcining temperature is excessively high, the metal powder which is a raw material for the preform is oxidized, and therefore calcining needs to be performed at a temperature of 800°C or lower in order to suppress the oxidation. In addition, to sufficiently remove an organic substance derived from the organic/inorganic binder or the like added to the metal powder, calcining needs to be performed at a temperature of 300°C or higher. According to studies conducted by the present inventors, when a preform to be provided for the high-pressure impregnation is obtained, it is preferable to perform calcining at a temperature higher than 500°C and 800°C or lower. Calcining is more preferably performed at a temperature of 700°C or higher and 800°C or lower.
According to studies conducted by the present inventors, when a preform to be provided for the pressureless infiltration is obtained, stress occurs at a part of the preform where the molten metal of the Al alloy or the like is in contact in the pressureless infiltration, and therefore the preform having strength that is bearable to this stress is necessary. Therefore, by performing calcining in the same manner as in obtaining the preform to be provided for the high-pressure impregnation, an organic substance in the molded product is removed and the strength of a resultant preform is improved. However, as described above, in the case of the pressureless infiltration, the preform to be provided for the infiltration needs to be in a state in which the above-described Mg component-containing metal powder and/or the like such as a Mg metal powder is added in order to cause the molten metal of the Al alloy or the like without pressurization in a favorable state. On the other hand, for example, when the temperature becomes more than 500°C, the Mg metal powder reacts with oxygen in the air to change into MgO, and therefore the Mg component necessary for the pressureless infiltration is deficient. Thus, the calcining needs to be performed at a calcining temperature of 500°C or lower. According to studies conducted by the present inventors, when a preform is provided for the pressureless infiltration, by calcining at a temperature of 300°C or higher and 450°C or lower, an organic substance can be sufficiently calcined and removed, and a preform having a high metal content ratio can be made into strong one having strength that is bearable to the pressureless infiltration.

[Preparation of High Metal Powder Content Aluminum Composite Body]

Next, the aluminum alloy or the like impregnation step, which is performed in obtaining a high-metal powder content aluminum composite body of the present invention, will be described. In the step, a preform which is obtained in the manner as described above, which has a high metal content ratio, and which is excellent in strength is impregnated with a molten Al alloy or the like, or a molten Al alloy or the like is caused to infiltrate into a preform which is obtained in the manner as described above, which has a high metal content ratio, and which is excellent in strength. Hereinafter, the method according to the high-pressure impregnation and the method according to the pressureless infiltration will be described respectively.

(Method for Impregnating Preform with Al Alloy or the Like at High Pressure)

Conceptual diagrams of the high-pressure impregnation are schematically shown in Figures 1(A) to (C). As shown in Figure 1(A), a preform 1 having a high metal content ratio is charged in a frame mold/metal mold 3 of a press machine, the frame mold/metal mold 3 preheated by heating to 300°C to 800°C. The reason that the preform 1 is charged in a state of being preheated is as follows: that is, in the case where the preform 1 is impregnated with a molten metal of an Al alloy or the like 2 at a high pressure, when the temperature of the preform 1 is low, it can happen that the Al alloy or the like 2 is cooled and solidified in the middle of the high-pressure impregnation and the inside of the preform 1 is not impregnated, and therefore this has to be prevented. It is preferable to warm (pre-heat) the frame mold/metal mold 3 to 200 to 400°C with a burner or the like lest the Al alloy or the like 2 be cooled and solidified similarly in the middle of the impregnation.
The Al alloy or the like 2 melted at 600°C to 800°C is poured into the frame mold/metal mold 3 charged with the preform 1 in the manner as described above, and is pressed by applying a load with an upper punch as shown in Figures 1(B) and (C) to isotropic impregnate the preform 1 with the molten metal of the Al alloy or the like 2. The impregnation is performed at a press pressure of 10 MPa to 200 MPa. When the pressure is lower than 10 MPa, the pressure is excessively low, and therefore the preform 1 may not be impregnated with the molten metal of the Al alloy or the like 2 in some cases, and thus this case is not preferable. The impregnation may be performed at a higher pressure of higher than 200 MPa, but in the case where the press pressure in the above-described range is obtained, the press pressure is sufficient as the performance of an apparatus for obtaining a composite body of the present invention. An impregnated body obtained using the press in the manner as described above is cooled, and aluminum surrounding the preform is removed, and thereby a high metal powder content aluminum composite body that is an object of the present invention is made.

(Pressureless Infiltration Method of Causing Al Alloy or The Like into Preform)

Stepwise conceptual diagrams of the pressureless infiltration are schematically shown in Figures 2(A) to (D). First of all, a preform 1 containing the Mg component-containing metal powders and/or the like, such as a Mg metal powder, and having a high metal content ratio is disposed in a manner as described below, and is charged in an electric furnace (not shown) in which a nitrogen atmosphere can be secured. Small pieces of preferably the same material as the material of the preform 1 are disposed as infiltration channels 4 under the preform 1. In addition, the solid Al alloy or the like 2 to be provided for the infiltration is disposed in the vicinity of the preform 1 so as not to be in contact with the preform 1. The preform 1 and the Al alloy or the like 2 are charged in the electric furnace in a state of being placed in a container 5 made of carbon as shown in Figure 2(A) so as not to react with a member inside the electric furnace.
After the preform 1 and the solid Al alloy or the like 2 are disposed and charged in the electric furnace in the manner as described above, the temperature is increased gradually and is kept at 700 to 900°C for 2 to 5 hours while the nitrogen atmosphere inside the electric furnace is retained. During this time, the molten Al alloy or the like 2 infiltrates without pressurization into the preform 1 through the infiltration channels 4, as shown in the schematic diagrams of Figures 2(B) to (D) in a stepwise manner, and thus a high metal powder content aluminum composite body is obtained.
Hereinafter, description will be given taking, as an example, a case where the Mg component-containing metal powder and/or the like is a Mg powder. The principle of obtaining the above-described excellent high metal powder content aluminum composite body by the pressureless infiltration is considered to be as follows. It is considered that this is because Mg and nitrogen react to generate Mg₃N₂ and the Mg₃N₂ is deposited in the preform, and thereby the wettability with the Al alloy or the like is improved, or Mg undergoes a thermit reaction to reduce an oxide on the surface of the metal powder forming the preform, and thereby the wettability between the metal powder and the Al alloy or the like is improved. As described above, in the conventional techniques, a molded product obtained by performing press molding or the like is used for pressureless infiltration without calcining the molded product, and in addition, when an Al alloy or the like is caused to infiltrate without pressurization, a method in which a molded product not containing a Mg powder is used, and this molded product is placed in a nitrogen atmosphere containing magnesium vapor to cause the Al metal to infiltrate is performed. However, according to studies conducted by the present inventors, in this method, the Mg vapor and nitrogen in the atmosphere react to generate Mg₃N₂ on the surface of a preform, and the Al alloy or the like infiltrates in this state, and therefore it takes a long time to impregnate the whole preform with aluminum. In addition, Mg₃N₂ is not uniformly generated on the surface of the preform, and therefore the Al alloy or the like nonuniformly infiltrates, so that the whole preform may not be uniformly impregnated in some cases.
According to the technique of the present invention, the Mg powder can be uniformly mixed into the preform, and therefore Mg₃N₂ is generated over the whole preform, and this is different from the above-described case of the conventional techniques. Thus, the impregnation speed with the Al alloy or the like is dramatically increased, and the whole preform can be uniformly impregnated. In addition, when the pressureless infiltration is utilized, the Al alloy or the like can be caused to infiltrate keeping the shape of the preform as it is, and therefore there is a major merit of enabling reduction of secondary processing in that a high metal powder content aluminum composite body having a near-net shape close to a product shape can be produced.

Examples

Hereinafter, further specific examples of the above-described embodiment will be described giving Examples and Comparative Examples, but the present invention is not limited to the following Examples. In the description below, w% is on a mass basis, and v% is on a volume basis. The average particle size as used herein is a value measured with a laser diffraction particle size distribution analyzer.

[Example 1] (Utilization of High-pressure Impregnation Method)

First of all, a metal powder molded body (preform) having a high metal content ratio was prepared according to the procedure described below. In the present Example, in order to prepare the preform, three types of silicon powders each having a different average particle size were combined according to the composition descried below, and a resultant mixture was stirred and mixed for use. Specifically, a mixture of three types of silicon powders each having a different average particle size in an amount of 2700 g in total, the mixture obtained by blending 1820 g of a silicon powder having an average particle size of 45 µm, 780 g of a silicon powder having an average particle size of 25 µm, and 100 g of a silicon powder having an average particle size of 5 µm, was used. To this mixture, 130 g of ethyl silicate being an organic/inorganic binder and containing 40 w% of silicon in terms of SiO₂ was added, and further, a resultant mixture was stirred and mixed for 15 minutes with a stirrer to obtain a mixed powder to be used in the present Example.
The whole amount of the mixed powder obtained above was put into a press metal mold having inner dimensions of 200 mm × 200 mm × 150 mm (depth) and was press-molded under a total pressure of 300 kg/cm² corresponding to a total load of 120 t. Then, the resultant press-molded article was put into an electric furnace, the temperature was increased to 700°C at a temperature increasing rate of 50°C/hr, the press-molded article was retained at this temperature for 3 hours and was then cooled to room temperature to prepare a preform made of a silicon metal. The weight and external dimensions of this preform were measured to calculate the bulk density and it was found that the preform is a silicon preform having a volume filling rate (Vf) of 77%.
The preform obtained above was preheated to 500°C in an electric furnace, and the preheated preform was charged in the frame mold/metal mold of a high-pressure impregnation press machine for performing high-pressure impregnation, wherein the frame mold/metal mold had dimensions of 300 mmΦ × 250 mm depth and was heated to 250°C with a burner. An aluminum alloy (AC4C) melted at 750°C was put into this frame mold/metal mold up to approximately 20 mm from the upper part of the metal mold, and a press punch was pressed into the frame mold/metal mold from above, and the preform and the molten aluminum alloy were retained at a pressure of 100 MPa for 10 minutes to impregnate the above-obtained preform with the molten aluminum at a high pressure (see Figures 1(A) to (C)).
After cooling, aluminum surrounding the preform was removed by processing to take out a product part of the silicon-aluminum composite body. The product part was found to be a silicon-aluminum composite body in which the preform was uniformly impregnated with aluminum without a small pore (blowhole) and crack. The bulk specific gravity was calculated from the weight measurement and the external dimension measurement and it was found that the silicon-aluminum composite body is a silicon-aluminum composite body containing 78 v% of silicon and 22 v% of the aluminum alloy.

[Example 2](Utilization of Pressureless Infiltration Process)

A metal powder molded body (preform) having a high metal content ratio to be used in the present Example was prepared according to the following procedure. To 2700 g in total of three types of the silicon powders each having a different average particle size, which were weighed so as to make the same composition as used in Example 1, 50 g of a Mg powder having an average particle size of 80 µm was added. Further, 130 g of ethyl silicate was added to this mixture in the same manner as in Example 1, and a resultant mixture was mixed with a stirrer for 10 minutes.
The whole amount of the mixed powder obtained above was put into a press metal mold having inner dimensions of 200 mm × 200 mm × 150 mm (depth) and was press-molded under a total pressure of 150 kg/cm² corresponding to a total load of 60 t. The resultant press-molded article was taken out of the metal mold and was put into an electric furnace set to an ordinary air atmosphere, the temperature was increased to 450°C at a temperature increasing rate of 50°C/hr, the press-molded article was retained at this temperature for 3 hours and then cooled to prepare a preform. The bulk density was calculated in the same manner as in Example to find the volume filling rate (Vf) was 73%.
The preform obtained above was disposed in the container 5 made of carbon as shown in the "pressureless infiltration principle diagram" schematically shown in Figures 2(A) to (D). Specifically, four infiltration channels 4 prepared from the same materials as the materials for the preform 1 obtained above and having a size of 30 mm × 30 mm × 30 mm were placed under the preform 1 in a state of being in contact with the bottom of the container, and further, 2500 g of a solid aluminum alloy (AC4C) 2 was disposed beside the preform 1. Then, the whole container 5 made of carbon, in which the preform 1 and the like were disposed as described above, was placed in a nitrogen atmosphere, and the temperature was increased at 50°C/hr, and the container 5 was retained at 800°C for 5 hours and was then cooled.
After cooling, the infiltration channels 4 were removed, and the surface and inside of the preform 6 after the impregnation were processed and observed, and it was ascertained that a resultant product was a silicon-aluminum composite body with the preform completely impregnated with aluminum. From the bulk specific gravity calculated from the measured values of the weight and external shape of the obtained silicon-aluminum composite body, it was found that the composite body is a silicon-aluminum composite body containing 73 v% of silicon and 26 v% of the aluminum alloy and not having a pore and a crack.

[Example 3] (Utilization of High-pressure Impregnation Method)

A metal powder molded body (preform) having a high metal content ratio to be used in the present Example was prepared according to the following procedure. A mixture of three types of silicon powders each having a different average particle size in an amount of 2700 g in total, obtained by blending 1820 g of a silicon powder having an average particle size of 80 µm, 780 g of a silicon powder having an average particle size of 25 µm, and 100 g of a silicon powder having an average particle size of 3 µm, was used. To this mixture, 180 g of an isopropyl alcohol solution obtained by dissolving a silicone resin (trade name: KR-220L, manufactured by Shin-Etsu Chemical Co., Ltd.) such that the concentration was 30 w% was added and stirred with a stirrer for 15 minutes, and the whole amount of a resultant mixture was charged in a press metal mold in the same manner as in Example 1 and press-molded under the same conditions as in Example 1. Then, a resultant press-molded article was put into an electric furnace, the temperature was increased to 750°C at a temperature increasing rate of 70°C/hr, and calcining was performed at this temperature to obtain a preform having a volume filling rate of 78 v%. Note that the volume filling rate was obtained in the same manner as in Example 1.
The preform obtained above was impregnated with a molten aluminum alloy using a high-pressure impregnation press machine according to the same conditions and procedure as in Example 1. After cooling, surrounding aluminum was removed by processing, a product part was taken out, and the weight and external shape of the product part were measured to calculate the bulk specific gravity. As a result, it was ascertained that a resultant composite body was a silicon-aluminum composite body containing 78 v% of silicon and 22 v% of the aluminum alloy without a pore (blowhole) and a crack.

[Example 4] (Utilization of Pressureless Infiltration Process)

A metal powder molded body (preform) having a high metal content ratio to be used in the present Example was prepared according to the following procedure. Machining was performed with a milling cutter on a preform containing a Mg powder and having a shape of 200 mm × 200 mm × 40 mm, which was prepared according to the same procedure as in Example 2. Specifically, a preform having a rib structure wherein four cavities having dimensions of 75 mm × 75 mm × 25 mm (depth) were uniformly disposed on the above-obtained preform was obtained. The obtained preform was a strong preform having machinable strength.
Pressureless infiltration of an aluminum alloy (AC4C) was performed in the same manner as in Example 2 using the preform obtained above from the infiltration channels disposed under the preform in the container made of carbon. Then, the infiltration channels were removed to measure the bulk specific gravity in the same manner as in Example 2, and as a result, it was ascertained that a silicon-aluminum composite body containing 73 v% of silicon and 27 v% of the aluminum alloy without a pore and a crack was obtained. In addition, the silicon-aluminum composite body was able to be produced with a near-net shape keeping the shape of the preform as it was without bleed out of the aluminum alloy inside the cavities.

[Example 5] (Utilization of High-pressure Impregnation Method)

A metal powder molded body (preform) having a high metal content ratio to be used in the present Example was prepared according to the following procedure. To 1400 g of an iron powder having an average particle size of 80 µm and 600 g of an iron powder having an average particle size of 10 µm, 80 g of ethyl silicate containing 40 v% of silicon in terms of SiO₂ was added, and a resultant mixture was stirred and mixed for 15 minutes. This mixed powder was placed in a press metal mold having internal dimensions of 200 mm × 200 mm × 150 mm (depth) and was press-molded under a total pressure of 150 kg/cm² corresponding to a total load of 60 t. Then, the press-molded article was put into an electric furnace, the temperature was increased to 700°C at a temperature increasing rate of 50°C/hr, and the press-molded article was retained at this temperature and was then cooled to room temperature to prepare a preform made of an iron metal. The weight and external dimensions of the obtained preform were measured to calculate the bulk density and it was found that the preform is an iron powder preform having a volume filling rate (Vf) of 73%.
The preform obtained above was preheated to 500°C in an electric furnace, and the preheated preform was charged in a frame mold/metal mold of a high-pressure impregnation press machine in order to perform high-pressure impregnation, wherein the frame mold/metal mold had dimensions of 300 mmΦ × 250 mm depth and was heated to 250°C with a burner. An aluminum alloy (AC4C) melted at 750°C was put into this frame mold/metal mold up to approximately 20 mm from the upper part of this frame mold/metal mold, and a press punch was pressed into the frame mold/metal mold from above, and the preform and the molten aluminum alloy were retained at a pressure of 100 MPa for 10 minutes to perform high-pressure impregnation.
After cooling, surrounding aluminum was removed by processing to take out a product part of the iron-aluminum alloy composite body (hereinafter, also referred to as iron-aluminum composite body). The product part was found to be an iron-aluminum composite body in which the preform made of an iron powder was uniformly impregnated with aluminum without a small pore (blowhole) and crack. The bulk specific gravity was calculated from the weight measurement and the external dimension measurement and it was found that the iron-aluminum composite body is an iron-aluminum composite body containing 73 v% of iron and 27 v% of the aluminum alloy.

[Comparative Example 1] (Utilization of High-pressure Impregnation Method without Using Binder)

A silicon mixed powder having the same composition and weight as in Example 1 was put into an iron box having dimensions of 200 mm × 200 mm × 100 mm without adding a binder, such as a silicone resin or ethyl silicate, the whole box was mounted on a vibrator to apply vibration for 20 minutes, and thus the silicon mixed powder was filled in the box. Then, high-pressure impregnation with aluminum was performed in the same manner as in Example 1 together with the whole of this box, and after cooling, a composite body was cut out.
When the processed surface of the cut-out composite body was observed, a large number of streak-like aluminum defects were seen. It is considered that this is because cracks occurred in the metal powder filled body in the middle of the high-pressure impregnation and the aluminum alloy penetrated into these cracks. A part where the cracks were not present was cut out to calculate the bulk specific gravity, and as a result, it was found that the filling rate of silicon was 62 v% and was lower when compared to that of the preform prepared in Example 1. The above-described results show that by only filling the particles of the silicon powder as they are, the filling rate of silicon is low and the strength of the silicon filled phase is not sufficient, and the filled phase broke in the middle of the high-pressure impregnation with molten aluminum and defects in which aluminum penetrated occurred.

[Comparative Example 2] (Preparation of Preform by Press Molding without Using Binder)

Press molding was performed according to the same procedure as in Example 1 using a silicon mixed powder having the same composition and weight as in Example 1 without adding ethyl silicate. However, a resultant molded body had insufficient strength and collapsed during taking out of the metal mold, and therefore a preform usable for production of a composite body was not able to be prepared. From the above-described result, it was found that addition of a binder into a powder material is essential when press molding is performed using a silicon mixed powder material.

[Comparative Example 3] (Preparation of Preform by Sedimentation Molding without Using Binder)

A slurry was prepared using a silicon mixed powder having the same composition and weight as in Example 3 without adding a binder, such as a silicone resin or ethyl silicate, and sedimentation molding was performed using the slurry. A molded body obtained after drying had insufficient strength and was vulnerable one such that it collapsed immediately after it was touched by hand. In addition, when a part of the molded body was heated by increasing the temperature to 700°C in the same manner as in Example 1, it was found that it had hardly strength and was vulnerable such that it collapsed quickly, so that, as a matter of course, it was not one that can be used in high-pressure impregnation and pressureless infiltration.

[Comparative Example 4] (Preparation of Preform by Press Molding and Calcination Using Binder of Organic Substance)

A silicon mixed powder having the same composition and weight as in Example 1 and an ethanol solution containing 20 w% of polyvinyl butyral (hereinafter, abbreviated as PVB) in terms of solid content were used, the ethanol solution was added to the silicon mixed powder such that the proportion of PVB was 2 w%, and then a molded body was prepared by press molding by the same operation as in Example 1. The obtained molded body, when calcined at 750°C, became vulnerable to such an extent that it collapsed when it was touched. It is considered that this is because PVB functions as a binder for the silicon mixed powder at normal temperature but was lost as a result of calcination. From the above-described result, it was ascertained that a binder of an organic substance can be used for retaining the shape of a press-molded article but cannot keep the strength of a preform in calcining in the subsequent step.

[Comparative Example 5] (Preparation of Preform by Calcination at 850°C Using Organic/Inorganic Binder)

Press molding was performed by the same method as in Example 1 using the same amount of the silicon mixed powder, wherein the silicon mixed powder was obtained in such a way that to a mixture of three types of the silicon powders each having a different average particle size used in Example 1, the same amount of ethyl silicate being an organic/inorganic binder was added, and a resultant mixture was stirred and mixed. A resultant press-molded article was put into an electric furnace, the temperature was increased to 850°C at a temperature increasing rate of 50°C/hr, the press-molded article was calcined by being retained at this temperature for 3 hours to perform calcining and was then cooled to room temperature, and thus a silicon preform was prepared.
The surface of a calcined body obtained above was observed to find that silicon was oxidized to change into SiO₂ and discolored into a whitish color. In addition, silicon changed into SiO₂ and the volume increased, and therefore stress occurred at the surface to generate fine cracks, so that a preform without a defect was not able to be obtained.

[Comparative Example 6] (Preparation of Preform by Calcination at 570°C Using Mg Powder and Organic/Inorganic Binder, Utilization of Pressureless Infiltration Process)

Press article was obtained by performing press molding in the same manner as in Example 2 using a mixture which is the same as used in Example 2, wherein the mixture was obtained in such a way that to three types of the silicon powders each having a different average particle size, a Mg powder having an average particle size of 80 µm was added, further, ethyl silicate was added thereto, and a resultant mixture was mixed with a stirrer. Then, the press-molded article obtained above was degreased by calcining at 570°C for 3 hours to prepare a preform (calcined body).
Pressureless infiltration of a molten metal of an aluminum alloy into the preform (calcined body) obtained above was attempted by the same method as in Example 2. However, the aluminum alloy did not infiltrate into the preform (calcined body) without pressurization. It is considered that the reason is because Mg added to the inside of the press article was oxidized to change into MgO by calcining at 570°C and therefore was not able to contribute to the pressureless infiltration.

[Comparative Examples 7 to 9] (Preparation of Preform Using Each of Silicon Powders Having Respective Average Particle Sizes Singly)

Press molding was performed and a preform was prepared by calcining a press-molded article according to the same procedure as in Example 1 except that 2700 g of each of the silicon powders having an average particle size of 45 µm, 25 µm, and 5 µm respectively, which were used for the mixture of the silicon powders in Example 1, was used singly. Then, the volume filling rate (Vf) was calculated in the same manner as in Example 1 for the preform obtained using each of the silicon powders singly, the silicon powders having an average particle size of 45 µm, 25 µm, and 5 µm respectively. As a result, the preform obtained by using the 45 µm silicon powder had a filling rate of 50 v%, the preform obtained by using the 25 µm silicon powder had a filling rate of 52 v%, and the preform obtained by using the 5 µm silicon powder had a filling rate of 53 v%. As just described above, it was ascertained that in any of the preforms obtained by using each of the silicon powders having respective average particle sizes singly, the filling rate was lower than in the cases of the preforms of Examples, and it was found that the metal powders, such as silicon, each having a different average particle size need to be mixed and used in order to prepare a preform having a high content ratio.

The conditions for producing the preforms, the impregnation methods with the Al alloy or the like, the characteristics of the obtained high metal powder content aluminum composite bodies, etc. in Examples and Comparative Examples are shown together in Table 1.

Table 1 : Production conditions and characteristics of resultant composite in Examples and Comparative Examples

	Mixed powder particle size: amount	Molding method	Binder	Preform calcining temperature and filling rate	Impregnation method with Al alloy	Characteristics of composite body
Example 1	45:1820g	Press 120t	Ethyl silicate	700°C	AC4C	Si=78%, Al=22%
	25: 780g			3hr	750°C	Without pore and crack
	5: 100g			Vf=77%	100Mpa	Silicon-aluminum composite body
Example 2	45:1820g	Press 60t	Ethyl silicate	450°C	AC4A	Si=73%, Al=26%
	25: 780g			3hr	800°C	Without pore and crack
	5: 100g			Vf=73%	5hr	Silicon-aluminum composite body
	80:Mg50g			Vf=73%	5hr	Silicon-aluminum composite body
Example 3	80:1820g	Press 120t	Isopropyl alcohol solution of silicone resin	750°C	AC4C	Si=78%, Al=22%
	25: 780g			3hr	750°C	Without pore and crack
	3: 100g			Vf=78%	100Mpa	Silicon-aluminum composite body
Example 4	45:1820g	Press 60t	Ethyl silicate	450°C	AC4A	Si=73%, Al=27%
	25: 780g			3hr	800°C	Without pore and crack
	5: 100g			Rib structure by Machining	5hr	Silicon-aluminum composite body
	80:Mg50g			Rib structure by Machining	5hr	Silicon-aluminum composite body
Example 5	Using iron powder	Press 60t	Ethyl silicate	700°C	AC4C	Fe=73%, Al=27%
	80:1400g			3hr	750°C	Without pore and crack
	10: 600g			3hr	100Mpa	Iron-aluminum composite body
Comparative Example 1	45:1820g	Vibration filling	Not used	Not fired	AC4C	Si=62%
	25: 780g				750°C	Cracks occur
	5: 100g				100Mpa	Streak-like Al defects
Comparative Example 2	45:1820g	Press 120t	Not used	Preparation impossible	Impossible	Production impossible
	25: 780g
	5: 100g
Comparative Example 3	80:1820g	Sedimentation molding	Not used	Molded body vulnerable and unusable	Impossible	Production impossible
	25: 780g
	3: 100g
Comparative Example 4	45:1820g	Press 120t	2% of 20%PVB ethanol solution added	Calcined at 750°C Vulnerable and collapsed	Impossible	Production impossible
	25: 780g				Impossible
	5: 100g
Comparative Example 5	45:1820g	Press 120t	Ethyl silicate	850°C	Preform is defective product	Production impossible
	25: 780g			3hr
	5: 100g			Whitish discoloration Fine cracks
Comparative Example 6	45:1820g	Press 60t	Ethyl silicate	570°C	AC4A	Al alloy does not infiltrate
	25: 780g			570°C	800°C
	5: 100g			3hr	5hr
	80:Mg50g			3hr	5hr
Comparative Example 7	45:2700g	Press 120t	Ethyl silicate	700°C,3hr	Not produced
Comparative Example 7	45:2700g	Press 120t	Ethyl silicate	Vt=50%	Not produced
Comparative Example 8	25:2700g	Press 120t	Ethyl silicate	700°C,3hr	Not produced
Comparative Example 8	25:2700g	Press 120t	Ethyl silicate	Vf=52%	Not produced
Comparative Example 9	5:2700g	Press 120t	Ethyl silicate	700°C,3hr	Not produced
Comparative Example 9	5:2700g	Press 120t	Ethyl silicate	Vf=53%	Not produced

Reference Signs List

1: Preform
2: Al alloy or the like
3: Frame mold/metal mold
4: Infiltration channel
5: Container made of carbon
6: Preform after impregnation

Claims

A method for producing a high metal powder content aluminum composite body, the method comprising:
a preform preparation step for obtaining a metal powder molded body (preform) having a high metal content ratio; and

an aluminum or aluminum alloy impregnation step of impregnating the obtained preform with molten aluminum or a molten aluminum alloy, or causing molten aluminum or a molten aluminum alloy to infiltrate into the obtained preform, wherein

in the preform preparation step, two or more metal powder materials each having a different average particle size are selected from metal powder materials each having an average particle size of 1 µm or larger and 200 µm or smaller to use the two or more metal powder materials as metal raw materials for the preform, molding is performed using a mixture obtained by adding and mixing an organic/inorganic binder being at least any one selected from the group consisting of a silicone resin, a Si alkoxide, and an Al alkoxide, which are in a liquid form or in a state of having been made into a liquid form, into the metal raw materials, and a resultant molded product is calcined at a temperature of 300°C or higher and 800°C or lower, and thereby an organic substance in the molded product is removed and an inorganic substance functions as an inorganic binder to obtain a metal powder molded body having a content ratio (volume content ratio) of the metal raw materials of 55 v% or more, and

in the aluminum or aluminum alloy impregnation step, the metal powder molded body obtained in the preform preparation step is impregnated with a molten metal of the aluminum or the aluminum alloy at a high pressure of 10 MPa to 200 MPa.
A method for producing a high metal powder content aluminum composite body, the method comprising:
a preform preparation step for obtaining a metal powder molded body (preform) having a high metal content ratio; and

an aluminum or aluminum alloy impregnation step of impregnating the obtained preform with molten aluminum or a molten aluminum alloy, or causing molten aluminum or a molten aluminum alloy to infiltrate into the obtained preform, wherein

in the preform preparation step, two or more metal powder materials each having a different average particle size are selected from metal powder materials having an average particle size of 1 µm or larger and 200 µm or smaller (excluding powder materials of a Mg powder, an AlMg powder, a ZnMg powder, a ZnAl powder, and a Mg₂Si powder) to use the two or more metal powder materials as metal raw materials for the preform, molding is performed using a mixture obtained by adding one or more powders selected from the group consisting of a Mg powder, an AlMg powder, a ZnMg powder, a ZnAl powder, and a Mg₂Si powder in an amount within a range of 0.2 to 5 parts by mass based on 100 parts by mass of the metal raw materials, and further adding and mixing an organic/inorganic binder being at least any one selected from the group consisting of a silicone resin, a Si alkoxide, and an Al alkoxide, which are in a liquid form or in a state of having been made into a liquid form, and a resultant molded product is calcined at a temperature of 300°C or higher and 500°C or lower, and thereby an organic substance in the molded product is removed and an inorganic substance functions as an inorganic binder to obtain a metal powder molded body having a content ratio (volume content ratio) of the metal raw materials of 55 v% or more, and

in the aluminum or aluminum alloy impregnation step, aluminum or an aluminum alloy is caused to infiltrate without pressurization in a nitrogen atmosphere into the metal powder molded body obtained in the preform preparation step.
The method for producing a high metal powder content aluminum composite body according to claim 1 or 2, wherein the metal powder is one, or two or more selected from a silicon powder or a silicon-based alloy powder containing silicon, a titanium powder, an iron powder or an iron-based alloy powder containing iron, and a nickel powder or a nickel-based alloy powder containing nickel.
The method for producing a high metal powder content aluminum composite body according to any one of claims 1 to 3, wherein the content ratio (volume content ratio) is 55 v% or more and 85 v% or less.
The method for producing a high metal powder content aluminum composite body according to any one of claims 1 to 4, wherein the two or more metal powders each having a different average particle size comprise at least: a metal powder A having an average particle size of 10 µm or smaller; and a metal powder B having an average particle size of 40 µm or larger, and comprise at least 3% of the metal powder A and 50% or more of the metal powder B in a total amount of the metal powders on a mass basis.
The method for producing a high metal powder content aluminum composite body according to any one of claims 1 to 5, wherein the organic/inorganic binder is at least any one selected from the group consisting of a Si alkoxide and an Al alkoxide.
A preform preparation method for obtaining a metal powder molded body (preform) which is used in obtaining a high metal powder content aluminum composite body metal by impregnating the preform with molten aluminum or a molten aluminum alloy at a high pressure and has a high metal powder content ratio, wherein
two or more metal powder materials each having a different average particle size, the metal powder materials containing at least a metal powder A having an average particle size of 10 µm or smaller, a metal powder B having an average particle size of 40 µm or larger and containing at least 3% of the metal powder A and 50% or more of the metal powder B in the total amount of the metal powders on a mass basis, are selected from metal powder materials having an average particle size of 1 µm or larger and 200 µm or smaller to use the two or more metal powder materials as metal raw materials for the preform, molding is performed using a mixture obtained by adding and mixing an organic/inorganic binder being at least any one selected from the group consisting of a silicone resin, a Si alkoxide, and an Al alkoxide, which are in a liquid form or in a state of having been made into a liquid form, into the metal raw materials, and a resultant molded product is calcined at a temperature of 300°C or higher and 800°C or lower, thereby obtaining a metal powder molded body having a content ratio (volume content ratio) of the metal raw materials of 55 v% or more.
A preform preparation method for obtaining a metal powder molded body (preform) which is used in obtaining a high metal powder content aluminum composite body metal by causing molten aluminum or a molten aluminum alloy to infiltrate without pressurization in a nitrogen atmosphere into the preform and has a high metal powder content ratio, wherein
two or more metal powder materials each having a different average particle size, the metal powder materials containing at least a metal powder A having an average particle size of 10 µm or smaller, a metal powder B having an average particle size of 40 µm or larger and containing at least 3% of the metal powder A and 50% or more of the metal powder B in a total amount of the metal powders on a mass basis, are selected from metal powder materials having an average particle size of 1 µm or larger and 200 µm or smaller (excluding powder materials of a Mg powder, an AlMg powder, a ZnMg powder, a ZnAl powder, and a Mg₂Si powder) to use the two or more metal powder materials as metal raw materials for the preform, molding is performed using a mixture obtained by adding one or more powders selected from the group consisting of a Mg powder, an AlMg powder, a ZnMg powder, a ZnAl powder, and a Mg₂Si powder in an amount within a range of 0.2 to 5 parts by mass based on 100 parts by mass of the metal raw materials, and further adding and mixing an organic/inorganic binder being at least any one selected from the group consisting of a silicone resin, a Si alkoxide, and an Al alkoxide, which are in a liquid form or in a state of having been made into a liquid form, and a resultant molded product is calcined at a temperature of 300°C or higher and 500°C or lower, thereby obtaining a metal powder molded body having a content ratio (volume content ratio) of the metal raw materials of 55 v% or more.
A high metal powder content aluminum composite body having an extremely small number of internal defects such as blowholes, wherein the high metal powder content aluminum composite body is obtained by the method for producing a high metal powder content aluminum composite body according to any one of claim 1 and claims 3 to 6, in which high-pressure impregnation is utilized.
A high metal powder content aluminum composite body having a near-net shape close to a product shape, wherein the high metal powder content aluminum composite body is obtained by the method for producing a high metal powder content aluminum composite body according to any one of claims 2 to 6, in which pressureless infiltration is utilized in a nitrogen atmosphere.