High-strength metal-matrix composite and method for producing high-strength metal-matrix composite

Abstract

The present invention provides an aluminum alloy matrix composite that cannot be obtained with conventional production techniques, that has good workability while exhibiting high strength, and that makes it possible to suppress an increase in production costs, the composite having a high economically practical value. The present invention also provides a method for producing the composite. Specifically, there are provided: a high-strength metal matrix composite obtained by impregnating and filling a porous filled body or molded body (preform) with molten aluminum or a molten aluminum alloy, wherein the porous filled body or molded body (preform) is formed of a mixed powder obtained by adding at least one aluminum or aluminum alloy powder selected from the group consisting of an aluminum powder and an aluminum alloy powder each having an average particle size of 10 µm to 300 µm to at least one fine powder selected from the group consisting of a metal powder and a ceramic powder each having an average particle size of 0.3 µm to 8 µm, and the composite has a fine powder-filling rate of 10% by volume to 50% by volume and a flexural strength of 500 MPa to 800 MPa; and a method for producing the metal matrix composite.

Description

Technical Field

[0001] The present invention relates to a metal matrix composite obtained by forming a composite from a fine ceramic powder and / or a fine metal powder that functions as a reinforcing material and molten aluminum or a molten aluminum alloy as a matrix material. In detail, the present invention relates to a technique that provides: a high-strength metal matrix composite having high strength and excellent processability, wherein the high strength and excellent processability are realized by using a mixed powder obtained by adding an aluminum powder or an aluminum alloy powder (hereinafter, also referred to as "powder of an aluminum alloy or the like") having a larger particle size than the above-described fine powder to the above-described fine powder; and a method for producing the same.Background Art

[0002] In recent years, materials (so-called MMCs) in which aluminum or an aluminum alloy and a ceramic form a composite, CFRPs (Carbon Fiber Reinforced Plastics) in which a carbon fiber and a resin form a composite, CMCs (Ceramic Matrix Composites) in which a ceramic-molded body and a ceramic form a composite by CVD or the like, composites in which aluminum and another metal powder form a composite, and the like have been developed and put into practical use. Among these, the MMCs using aluminum or an aluminum alloy (hereinafter, representatively referred to as aluminum alloy or the like) as a matrix material and having properties of two types of different inorganic materials have been developed as described below and put into practical use because the weights of the materials can be reduced. For example, such MMCs have been widely used in the industrial world as mechanical parts, electronic substrates, apparatuses for producing semiconductors or liquid crystals, robot arms, gas turbine materials, power devices, and the like that possess desired properties such as light weight, high strength, high rigidity, and high heat resistance.

[0003] Patent Literature 1 discloses a composite-forming method including: curing a ceramic powder and an inorganic binder added to the ceramic powder to produce an intermediate molded body (preform); and infiltrating a molten aluminum alloy or the like into pores of the intermediate molded body (preform) with a high-pressure press. According to this high-pressure impregnation method using aluminum, an aluminum alloy matrix composite (MMC) in which the ceramic powder is uniformly distributed can be simply prepared by impregnating the characteristic intermediate molded body (preform) with the molten aluminum alloy or the like forcibly at a high pressure. The above-described production method is also applicable to an aluminum alloy matrix composite (MMC) using, as a material for forming a composite, a powder-filled body formed of a ceramic powder.

[0004] Patent Literature 2 discloses a method for forming a composite, wherein a particular intermediate molded body (preform) in which a Mg powder is added to a ceramic powder is placed in a nitrogen atmosphere, and an aluminum alloy is infiltrated into the intermediate molded body (preform) without pressurization. The principle of this method is that the wettability between the ceramic and the aluminum alloy or the like is improved in the Mg-and-nitrogen atmosphere to accelerate a so-called capillary phenomenon, and thereby the molten aluminum alloy or the like is infiltrated into voids of the preform. According to this production method, the ceramic-filling rate is increased to decrease the voids, thereby making it possible to increase the ceramic-filling rate, and as result, an aluminum alloy matrix composite (MMC) of a ceramic and an aluminum alloy or the like, having high physical property values of Young's modulus, thermal conductivity, coefficient of thermal expansion, and the like, can be produced. In addition, according to this production method, the aluminum alloy or the like can be infiltrated into the voids by using the preform while the shape of the preform by using the preform is kept, and therefore the MMC having a near-net shape close to a product shape can be produced.

[0005] In addition, the aluminum alloy matrix composite (MMC) can also be produced by the following casting method other than the above-described production method. In this method, first, a ceramic powder of silicon carbide, alumina, or the like is put into a molten aluminum alloy or the like, and the resulting mixture is stirred at a high speed to prepare a molten aluminum alloy or the like containing the ceramic powder, or a composite obtained by impregnating a mixed powder obtained by adding Mg to a ceramic powder with an aluminum alloy or the like in a nitrogen atmosphere without pressurization is melted and mixed uniformly to prepare a molten metal for casting. Subsequently, the molten metal prepared is cast in a conventionally used mold, such as a sand mold for casting, a metal mold, and a mold for lost wax casting, to produce a composite of the ceramic and the aluminum alloy.

[0006] Further, the aluminum alloy matrix composite (MMC) can also be produced by a production method making use of the following HIP (Hot Isostatic Pressing) method. Specifically, a so-called SupremEX method is known, in which a powdery molded body obtained by subjecting a ceramic powder to mechanical alloying coating with an aluminum alloy or the like is subjected to firing and subsequent high-pressure isostatic pressing by HIP to produce a complex of the ceramic powder and the aluminum alloy or the like. Moreover, as a method which is similar to this, a method is known, wherein: a molten aluminum alloy or the like in which a ceramic powder is mixed is sprayed and deposited to produce a deposit of a composite; and the deposit is subjected to HIP treatment to remove pores contained in this deposit, and thereby a composite is produced.Citation List Patent Literature

[0007] Patent Literature 1: Japanese Patent No. 6837685 Patent Literature 2: Japanese Patent No. 6984926 Summary of Invention Technical Problem

[0008] However, the present inventors have recognized that: there are problems as given below in the above-described conventional methods for producing an aluminum alloy matrix composite (MMC); and therefore, there is room for improving the aluminum alloy matrix composite into one having more excellent functionality in any of the methods.

[0009] In the above-described high-pressure impregnation method in which impregnation is performed with a molten aluminum alloy or the like at a high pressure, the percentage by volume of the powder-filled body itself or the powder itself of the preform is determined by the properties of the powder, and therefore a product having a volume percentage of higher than 50% by volume can only be produced. In the high-pressure impregnation method, the pores in the powder-filled body or preform are impregnated with the molten aluminum alloy or the like, and therefore it is difficult to decrease the volume of the metal powder and the ceramic powder and increase the amount of the aluminum alloy or the like. For this reason, it is difficult to produce a composite having good processability and a large impregnation amount of an aluminum alloy or the like by a high-pressure impregnation method. In other words, a composite having a volume percentage of a ceramic powder and a metal powder of 50% or lower and good processability cannot be produced by a method of impregnating pores with a molten aluminum alloy or the like at a high pressure. In addition, a metal powder of about 10 µm or larger and a ceramic powder of about 10 µm or larger are usually used as a reinforcing material or the like to be used for forming a composite, which increases the load to working tools, and therefore there is a problem that an aluminum alloy matrix composite (MMC) obtained by the above-described high-pressure impregnation method is inferior in processability.

[0010] In addition, also in the above-described method for forming a composite by infiltrating a molten aluminum alloy or the like into voids of a preform without pressurization, a powder is molded into a preform, and voids of the preform are impregnated with the molten aluminum alloy or the like, but a preform with more than 50% by volume of voids, in other words, an aluminum alloy matrix composite having a powder-filling rate of 50% by volume or lower, cannot be produced.

[0011] Further, also in the above-described casting method, there are problems as described below. First, in the casting method, as the content of the ceramic powder in the aluminum alloy or the like is higher, the fluidity of the molten metal is deteriorated, and therefore the upper limit of the volume content of the ceramic is generally considered to be about 30% by volume. On the other hand, the particle size of the ceramic powder which is used for the casting method, such as a SiC powder, needs to be large as large as 15 µm or larger in order to retain castability. For this reason, the resulting aluminum alloy matrix composite has low processability although the volume percentage of SiC is low as low as 30% or lower and can only be processed with a diamond tool, which makes the aluminum alloy matrix composite inferior in processability. Furthermore, as another problem, the molten metal is likely to entrap air during casting, and therefore a composite without a defect is considered to be hard to obtain.

[0012] Furthermore, in the above-described production method making use of the HIP method, there are major practical problems as follows: a metal powder is used as the metal raw material for the main component, so that the surfaces of the metal powder are likely to be oxidized in the production process, which makes it difficult to achieve the strength required for the composite; and on top of that, the HIP treatment, which is a complicated process, is necessary, which increases costs.

[0013] Accordingly, an object of the present invention is to provide new techniques on an aluminum alloy matrix composite that cannot be obtained with conventional production techniques, that has good workability while having high strength, and that makes it possible to suppress an increase in production costs, the composite being useful in terms of industrial utility and having a high practical value; and a method for producing the composite.Solution to Problem

[0014] The above-described objects are achieved by the present invention described below. Specifically, the present invention provides a high-strength metal matrix composite described below. In the present invention, "average particle size" is a particle size at an integrated value of 50% (median diameter) in the particle size distribution determined by a laser diffraction / scattering method. [1] A high-strength metal matrix composite obtained by impregnating and filling a porous filled body or molded body (preform) with molten aluminum or a molten aluminum alloy, wherein the porous filled body or molded body (preform) is formed of a mixed powder obtained by adding at least one aluminum or aluminum alloy powder selected from the group consisting of an aluminum powder and an aluminum alloy powder each having an average particle size of 10 µm or larger and 300 µm or smaller to at least one fine powder selected from the group consisting of a metal powder and a ceramic powder each having an average particle size of 0.3 µm or larger and 8 µm or smaller, and the composite has a fine powder-filling rate of 10% by volume or more and 50% by volume or less and a flexural strength of 500 MPa or higher and 800 MPa or lower. Preferred embodiments of the high-strength metal matrix composite include the following. [2] The high-strength metal matrix composite according to [1], wherein the metal powder which is the fine powder in the mixed powder is any one selected from the group consisting of a silicon powder, an iron powder, a stainless steel powder, a copper powder, and a titanium powder, the ceramic powder which is the fine powder in the mixed powder is any one selected from the group consisting of an alumina powder, a silica powder, an aluminum borate powder, a silicon carbide powder, a silicon nitride powder, and an aluminum nitride powder, and the blending ratio of the fine powder to the aluminum or aluminum alloy powder in the mixed powder is 10:90 to 90:10. [3] The high-strength metal matrix composite according to [1] or [2], wherein at least one binder selected from the group consisting of a silica-based binder and alumina-based organic / inorganic binder within a range of 0.5% or more and 10% or less on a mass basis is externally added to the mixed powder. The present invention provides, as other embodiments, methods for producing a high-strength metal matrix composite, described below. [4] A method for producing a high-strength metal matrix composite, the method including: providing a porous filled body or molded body (preform) using a mixed powder obtained by adding at least one aluminum or aluminum alloy powder selected from the group consisting of an aluminum powder and an aluminum alloy powder each having an average particle size of 10 µm or larger and 300 µm or smaller to at least one fine powder selected from the group consisting of a metal powder and a ceramic powder each having an average particle size of 0.3 µm or larger and 8 µm or smaller; and impregnating and filling the resulting filled body or molded body (preform) with molten aluminum or a molten aluminum alloy at a high pressure as high as a pressure of 20 MPa or higher and 200 MPa or lower to form a composite, thereby providing a metal matrix composite having a fine powder-filling rate of 10% by volume or more and 50% by volume or less and a flexural strength of 500 MPa or higher and 800 MPa or lower. [5] A method for producing a high-strength metal matrix composite, the method including: providing a porous filled body or molded body (preform) using a Mg powder-containing mixed powder obtained in such a way that a mixed powder is obtained by adding at least one aluminum or aluminum alloy powder selected from the group consisting of an aluminum powder and an aluminum alloy powder each having an average particle size of 10 µm or larger and 300 µm or smaller to at least one fine powder selected from the group consisting of a metal powder and a ceramic powder each having an average particle size of 0.3 µm or larger and 8 µm or smaller, and further a magnesium powder within a range of 0.5 parts by mass or more and 10 parts by mass or less is added to 100 parts by mass of the mixed powder; and impregnating and filling the resulting filled body or molded body (preform) with molten aluminum or a molten aluminum alloy without pressurization to form a composite, thereby providing a metal matrix composite having a fine powder-filling rate of 10% by volume or more and 50% by volume or less and a flexural strength of 500 MPa or higher and 800 MPa or lower. Preferred embodiments of the method for producing a high-strength metal matrix composite according to [4] or [5] include the following. [6] The method for producing a high-strength metal matrix composite according to [4] or [5], wherein the metal powder which is the fine powder in the mixed powder is any one selected from the group consisting of a silicon powder, an iron powder, a stainless steel powder, a copper powder, and a titanium powder, the ceramic powder which is the fine powder in the mixed powder is any one selected from the group consisting of an alumina powder, a silica powder, an aluminum borate powder, a silicon carbide powder, a silicon nitride powder, and an aluminum nitride powder, and the blending ratio of the fine powder to the aluminum or aluminum alloy powder in the mixed powder is 10:90 to 90:10. [7] The method for producing a high-strength metal matrix composite according to any one of [4] to [6], wherein at least one binder selected from the group consisting of a silica-based binder and an alumina-based organic / inorganic binder within a range of 0.5% or more and 10% or less on a mass basis is externally added to the mixed powder. Advantageous Effects of Invention

[0015] The present invention makes it possible to provide a metal matrix composite product that cannot be obtained by the conventional production techniques, the metal matrix composite having a high practical value, wherein: the volume percentage of a reinforcing material composed of a metal powder and / or a ceramic powder is 50% by volume or lower; the strength is high as high as a flexural strength of 500 MPa or higher; and the processability is good. Further, the present invention provides a method for producing a metal matrix composite, the method making it possible to produce the metal matrix composite having excellent properties as described above by a simple method and being extremely useful also in terms of practicality in that an increase in production costs is suppressed.Brief Description of Drawings

[0016] [Figure 1] Figure 1 is a schematic diagram for describing a method of producing a high-strength metal matrix composite of the present invention without pressurization.Description of Embodiments

[0017] Hereinafter, preferred embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

[0018] As described above, as methods for producing a composite of: a reinforcing material composed of a metal powder and / or a ceramic powder; and a matrix material such as an aluminum alloy or the like, the methods of impregnating a filled body or molded body (preform) of the reinforcing material with the molten aluminum alloy or the like by high-pressure impregnation or non-pressurization infiltration have been employed so far. However, according to studies conducted by the present inventors, when, for example, a preform having the metal powder- and / or ceramic powder-filling rate of 50% by volume or less is prepared by the above-described production methods, the particle-filling rate is low, and therefore it is difficult to retain the shape of the preform, which makes it difficult to prepare a preform that can withstand the high-pressure impregnation method or the non-pressurization infiltration method. In other words, it is difficult to make a porous preform having more than 50% by volume of voids by the conventional techniques, and therefore a metal matrix composite containing higher than 50% by volume of a matrix material such as an aluminum alloy or the like cannot be produced by high-pressure impregnation or non-pressurization infiltration. Description above is made giving a molded body (preform) as an example, but even a filled body obtained by packing a raw material powder in a metal box or the like to perform vibration molding or the like without active molding by pressing unlike the molded body (preform) also generally has a volume percentage of 50% or higher, and therefore there is a problem that the processability of the composite is deteriorated, which is the same as in the composite using the molded body (preform). Hereinafter, the filled body or molded body (preform) of a metal powder and / or a ceramic powder is also referred to as a "preform or the like."

[0019] Facing the difficulty of preparing a preform or the like formed of a metal powder and / or a ceramic powder and having a filling ratio of 50% by volume or less in the above-described conventional techniques, the present inventors have conducted diligent studies to find that the problems can be solved by forming the preform or the like in the manner as described below. Specifically, by forming, in the manner as described below, the preform or the like, which forms a metal matrix composite, which is to be impregnated and filled with a molten aluminum alloy or the like, and which is formed of the metal powder and / or the ceramic powder, the problems can be solved. First, to achieve the above-described object, it is effective to use a fine material having an average particle size of 0.3 µm or larger and 8 µm or smaller as the metal powder and / or the ceramic powder to be used for forming the preform or the like. Second, the present inventors have found that by using a mixed powder obtained by adding a powder of an aluminum alloy or the like having an average particle size of 10 µm or larger and 300 µm or smaller to the above-described fine metal powder and / or fine ceramic powder to prepare the preform or the like formed of the mixed powder, the above-described problems can be solved. As described above, the "average particle size" specified in the present invention refers to a particle size at an integrated value of 50% in the particle size distribution determined by a laser diffraction / scattering method, that is, a so-called 50% median size.

[0020] Specifically, the present inventors have found that the amount of the aluminum alloy or the like in the metal matrix composite being higher than 50% by volume can be achieved when the preform or the like is prepared with a particular mixed material obtained by adding a powder of an aluminum alloy or the like to the above-described fine metal powder and / or fine ceramic powder (hereinafter, also referred to as "fine metal powder and / or the like"), and the resulting preform or the like is impregnated with a molten aluminum or the like. Here, the particle size of the powder of an aluminum alloy or the like is larger than that of the fine metal powder and / or the fine ceramic powder. Thus, the present inventors have completed the present invention. In other words, the amount of the aluminum alloy or the like in the metal matrix composite of the present invention is the sum total of the amount derived from the powder of an aluminum alloy or the like preliminarily added to the material for forming the preform or the like and the amount of the molten aluminum alloy or the like which is melted to impregnate the preform or the like. The metal matrix composite of the present invention formed in the manner as described above is a novel metal matrix composite containing the aluminum alloy or the like in an amount of higher than 50% by volume in the metal matrix composite, which has never been obtained so far.

[0021] The above-described high-strength metal matrix composite of the present invention is a composite obtained by impregnating and filling a porous preform or the like with a "molten aluminum alloy or the like," wherein the porous preform or the like is formed of a mixed powder containing a "powder of an aluminum alloy or the like," and therefore part or the whole of the "powder of an aluminum alloy or the like" may be melted to change the form of the composite. For this reason, it can be said that in the high-strength metal matrix composite of the present invention as the product invention, there exist some parts not directly specified by the structure or properties. However, with regard to this point, there are circumstances that it is impossible or substantially not practical to directly specify the microscopic dissolution states of such a metal powder forming the porous preform or the like, which are different individually, by the structure or properties of the product, because the extent of dissolution and the state of the dissolution of each metal powder forming the porous preform or the like is variously changed as a matter of course, and such changes are caused by impregnating and filling complicated pores of the porous preform or the like, which forms the high-strength metal matrix composite of the present invention, with the molten aluminum alloy or the like. It is clear that there exist such circumstances, and therefore, with regard to the high-strength metal matrix composite of the present invention, which is the product invention, the product is specified by the method for producing the composite, which provides "a composite obtained by impregnating and filling a porous filled body or molded body (preform) with molten aluminum or a molten aluminum alloy, wherein the porous filled body or molded body (preform) is formed of a mixed powder containing an aluminum or aluminum alloy powder."

[0022] In the method for producing a metal matrix composite of the present invention, a powder of an aluminum alloy or the like having a larger size than the fine metal powder or fine ceramic powder is added to the raw material to prepare a porous preform or the like as described above, which is different from the conventional methods for preparing a preform or the like consisting of a metal powder or a ceramic powder, furthermore, voids of the preform or the like are impregnated with a molten aluminum alloy or the like, and thereby the volume percentage of the aluminum alloy or the like being higher than 50% is realized, so that a metal matrix composite having excellent processability and high strength can be produced.

[0023] Specifically, the metal matrix composite of the present invention, which is composed of the above-described combination, is a metal matrix composite having high strength, as high as a flexural strength of 500 MPa or higher, for example, 550 MPa or higher, and further, 700 MPa or higher. Furthermore, surprisingly enough, although the metal matrix composite of the present invention has high flexural strength as described above, it has good processability, and it is ascertained that processing with a cemented carbide tool is possible, which is not realized for the conventional composites. The flexural strength is a value measured according to JIS R1601. Specifically, the flexural strength is a value measured, according to JIS R1601, by the three-point flexural test preparing a specimen having a specified size. The measurement is performed at 25°C (room temperature).

[0024] According to the method for producing a metal matrix composite of the present invention, the ratio of the fine metal powder and / or the like to the powder of an aluminum alloy or the like, which are materials for forming the preform or the like, can be changed freely, and therefore the ratio of the fine metal powder and / or the like to the aluminum alloy or the like in the final metal matrix composite can also be designed freely. Furthermore, in the production method of the present invention, the particle size of the fine metal powder and / or the like, which is determined within the range specified in the present invention according to the material quality of the fine metal powder and / or the like which is used as the material for forming the preform or the like can be freely designed, and therefore a metal matrix composite having desired properties can be obtained. For example, according to studies conducted by the present inventors, the smaller the average particle size of the fine metal powder and / or the like, the higher the strength of the final metal matrix composite. Hereinafter, details on the metal matrix composite and method for producing a metal matrix composite of the present invention will be described. First, the method for producing a metal matrix composite of the present invention will be described.[Method for Producing Metal Matrix Composite of Present Invention]

[0025] As described above, the production method of the present invention is a totally new production method that makes it possible to make the percentage by volume of the aluminum alloy or the like in the finally obtained metal matrix composite higher than 50% by preliminarily adding the powder of an aluminum alloy or the like to the material for forming the preform or the like. In other words, the present invention makes it possible to realize an effective influence on the physical property values of the finally obtained metal matrix composite, the influence brought about by the average particle size of the fine metal powder and / or the like which is used as a raw material, and such an effective influence can be realized by obtaining the metal matrix complex according to the following procedure, which is different from the conventional methods for producing a metal matrix composite using a preform or the like consisting of a metal powder or a ceramic powder.(1) Fine Metal Powder or Fine Ceramic Powder

[0026] In the method for producing a metal matrix composite of the present invention, at least one fine powder selected from the group consisting of a metal powder and a ceramic powder each having an average particle size of 0.3 µm or larger and 8 µm or smaller is used as the material for forming a porous filled body or molded body (preform). The metal powder is not particularly limited, and examples thereof include at least one selected from the group consisting of a silicon powder, an iron powder, a stainless steel powder, a copper powder, a titanium powder, and the like. Examples of the ceramic powder include one selected from the group consisting of an alumina powder, a silica powder, an aluminum borate powder, a silicon carbide powder, a silicon nitride powder, an aluminum nitride powder, and the like. In the present invention, even if any of the materials is used, a fine particle having an average particle size within the range specified in the present invention needs to be used as the metal powder or the ceramic powder. Specifically, a metal powder or a ceramic powder each having an average particle size within a range of 0.3 µm or larger and 8 µm or smaller is used. The reason that the average particle size of the metal powder or the ceramic powder is set to 8 µm or smaller is because when a material having an average particle size larger than that, the interface between the metal powder or the ceramic powder and the aluminum alloy or the like is too large after the impregnation with the molten aluminum alloy or the like, so that the strength of a metal matrix composite as the final product is deteriorated. On the other hand, the reason that the average particle size is set to 0.3 µm or larger is because the strength of a resulting metal matrix composite is not changed so much even when the average particle size is made smaller than that, and when the powder is too fine, it is likely to aggregate, so that there is a risk that uniform dispersion of the reinforcing material in the preform or the like formed from the mixed powder is impaired.(2) Aluminum Powder or Aluminum Alloy Powder

[0027] The method for producing a metal matrix composite of the present invention is characterized in that a mixed powder obtained by adding an aluminum powder or an aluminum alloy powder each having an average particle size of 10 µm or larger and 300 µm or smaller to the above-described fine metal powder and / or the like is used for forming the porous filled body or molded body (preform). According to studies conducted by the present inventors, when a metal matrix composite is formed as just described above, thereby the percentage by volume of the fine metal powder and / or the like that functions as a reinforcing material can be controlled into a desired percentage by volume in the metal matrix composite of the present invention. Specifically, by adding the powder of an aluminum alloy or the like to the material for forming the porous preform or the like, the whole amount of the aluminum alloy or the like in the metal matrix composite as the final product can be controlled, wherein the whole amount of the aluminum alloy or the like includes the amount of the molten aluminum alloy or the like with which voids of the porous preform or the like is impregnated in the next step. As just described above, according to the present invention, by changing the ratio of at least one fine powder selected from the group consisting of a metal powder and a ceramic powder to the aluminum alloy or the like in the metal matrix composite as the final product, desired physical property values can be obtained.

[0028] As the powder of an aluminum alloy or the like which is used for forming the porous preform or the like that forms the metal matrix composite of the present invention and that characterizes the present invention, a powder having an average particle size of 10 µm or larger and 300 µm or smaller is used. When the powder has an average particle size of smaller than 10 µm, it is likely to aggregate, and it is difficult to uniformly mix the powder with the fine metal powder and / or the like to be used together with the powder. On the other hand, when the powder has an average particle size of larger than 300 µm, the powder of the aluminum alloy or the like is too large in size, and therefore there is a risk that the uniformity with the fine metal powder and / or the like to be used together for the mixed powder is impaired, which deteriorates the strength of the preform or the like. As will be described below, by adding the powder of an aluminum alloy or the like having the above-described particular average particle size to the mixed powder for forming the porous preform or the like, it is made possible to control the percentage by volume of the metal powder and / or the ceramic powder that functions as a reinforcing material in the metal matrix composite as the final product.

[0029] For example, the percentage by volume of the powders of the molded body (preform) prepared from the mixed powder of a ceramic powder and / or a metal powder and the powder of an aluminum alloy or the like in the present invention is different depending on the particle sizes and mixing ratios of the powders used, but the molded body (preform) generally has a volume percentage of 50 to 60% by volume as a whole and contains 40 to 60% by volume of voids. Accordingly, the percentage by volume of the metal powder and the like can be controlled by the molten aluminum alloy or the like with which voids of the porous preform or the like is impregnated and the powder of an aluminum alloy or the like that characterizes the present invention and that is to be added to the molded body or the like. In other words, when the addition amount of the powder of the aluminum alloy or the like is increased, the percentage by volume of the fine aluminum powder and / or the like in the metal matrix composite as the final product can be decreased. As a result, according to the present invention, a product of a good metal matrix composite having a percentage by volume of 50% or lower can be produced, which cannot be achieved by only using the metal powder and / or the ceramic powder. The powder of an aluminum alloy or the like that characterizes the present invention may be used changing the addition amount in order to achieve the finally desired percentage by volume of the metal powder and / or the ceramic powder. The addition amount is not particularly limited. In outline, the total percentage by volume of the metal powder and / or the ceramic powder and the powder of an aluminum alloy or the like is 50 to 70%, and therefore the total amount of the aluminum alloy or the like can be controlled by changing, as necessary, the ratio of the powder of an aluminum alloy or the like to be added and taking into account the amount of the molten aluminum alloy or the like with which voids of the porous body is impregnated.

[0030] Examples of the fine metal powder for forming the metal matrix composite of the present invention include a silicon powder, an iron powder, a stainless steel powder, a copper powder, and a titanium powder. Examples of the fine ceramic powder for forming the metal matrix composite of the present invention include an alumina powder, a silica powder, an aluminum borate powder, a silicon carbide powder, a silicon nitride powder, and aluminum nitride powder. In the present invention, one, or two or more powders selected from the metal powders and ceramic powders as given above can be used.

[0031] The metal matrix composite of the present invention is preferably a metal matrix composite obtained by impregnating and filling the porous preform or the like with a molten aluminum alloy by pressurization or without pressurization, wherein the porous preform or the like is formed of the mixed powder of the above-described metal powder and / or ceramic powder and powder of an aluminum alloy or the like, and the mixed powder is obtained by blending the fine metal powder and / or the like and the powder of an aluminum alloy or the like in the ratio as described below. Specifically, the blending ratio of the fine metal powder and / or the like to the powder of an aluminum alloy or the like in the mixed powder is preferably 10:90 to 90:10. It is not preferable that the ratio of the fine metal powder and / or the like to the powder of an aluminum alloy or the like is less than 10:90 because the ratio of the fine metal powder and / or the like that functions as a reinforcing material in a metal matrix composite as the final product is too small, so that it may happen that the desired effect of improving the strength cannot be obtained. On the other hand, it is not preferable that the ratio of the fine metal powder and / or the like to the powder of an aluminum alloy or the like is more than 90:10 because the ratio of the fine metal powder and / or the like that forms the metal matrix composite is too large, so that the processability of a metal matrix composite as the final product is deteriorated.

[0032] In the metal matrix composite of the present invention, the fine metal powder and / or the like having an average particle size of 0.3 µm or larger and 8 µm or smaller is used in order to improve the strength of the composite, but on the other hand, when such a fine powder is used, aggregation due to static electricity is likely to occur, and therefore the mixed powder obtained by adding the powder of an aluminum alloy or the like having a relatively large average particle size of 10 µm to 300 µm to the fine metal powder and / or the like is used. Such composition also gives a secondary effect of suppressing the aggregation of the metal powder and / or the ceramic powder as a reinforcing material and can finally realize a good metal matrix composite formed of uniformly dispersed metal powder and / or ceramic powder and aluminum alloy or the like. In addition, in the case where a molded body or the like is impregnated with a molten aluminum alloy or the like by a non-pressurization infiltration method, when a metal powder and / or a ceramic powder each having an average particle size of 1 µm or smaller is used for preparation of a porous preform or the like in the conventional techniques, there is a problem that pores are too small, which makes it difficult to impregnate the porous preform or the like with the molten metal. However, according to the technique of the present invention, the problem can be solved due to the following effect. Specifically, with respect to the metal matrix composite of the present invention, the addition of the powder of an aluminum alloy or the like having an average particle size of 10 µm or larger and 300 µm or smaller for preparation of the porous preform or the like makes pores larger, which makes it easier to impregnate the porous preform or the like with the molten aluminum alloy or the like even when the above-described non-pressurization infiltration method is applied.(3) Preparation of Mixed Powder

[0033] The above-described mixed powder composed of: a fine metal powder and / or the like; and a powder of an aluminum alloy or the like having an average particle size of 10 µm to 300 µm is easily obtained through uniform mixing using a commonly used mixer. In the present invention, the porous preform or the like is obtained using the particular mixed powder prepared. When the fine powder as described above is used, the filling rate is low, and therefore in obtaining the molded body (preform) by, for example, a press molding method, a CIP method, or a sedimentation method, a binder may be used as necessary together with the mixed powder. As the binder, inorganic binders, such as ethyl silicate, silicone, and water glass, and inorganic binders, alumina-based inorganic binders, such as aluminum alkoxides, and organic / inorganic binders can be suitably used. As for the use amount of the binder, the binder is preferably added to the mixed powder within a range of 0.5% or more and 10% or less on a mass basis. To further enhance the moldability of the molded body (preform), an organic binder, such as, for example, PVA and PVB, may be further added in addition to the inorganic binder as given above.(4) Preparation of Preform or the Like

[0034] The preform or the like prepared using the mixed powder having a composition as described above may be fired at a temperature of, for example, about 200°C to about 700°C, so that the subsequent operation could be easily performed. When the metal powder is used as a reinforcing material, the firing temperature is desirably set at 700°C or lower so that the metal powder will not be oxidized. In addition, when a Mg powder is added to the mixed powder for the purpose of impregnation with the molten aluminum alloy or the like using a non-pressurization infiltration method, the firing temperature is desirably set to 500°C or lower so that Mg would not be depleted by oxidation during firing.(5) High-Pressure Impregnation with Molten Aluminum Alloy or the Like

[0035] In the method for producing a high-strength metal matrix composite of the present invention, the metal matrix composite can be obtained by well impregnating and filling the porous preform or the like obtained in the manner as described above with the molten aluminum alloy or the like irrespective of using the method of either the high-pressure impregnation or the non-pressurization infiltration. When a high-pressure impregnation method is used, the preform or the like is impregnated with a molten aluminum alloy or the like whose temperature is, for example, about 700°C to about 800°C at a pressure of, for example, about 20 MPa to about 200 MPa. A pressure of lower than 20 MPa is not preferable because the pressure is too low, so that there may be concern over insufficient impregnation. On the other hand, even when the pressure is higher than 200 MPa, the impregnation is feasible, but a pressure of 200 MPa or lower is enough taking energy cost and life of a pressure vessel into consideration.(6) Infiltration of Molten Aluminum Alloy or the like without Pressurization

[0036] When the preform or the like is impregnated with the molten aluminum alloy or the like by a non-pressurization infiltration method, a so-called Lanxide process, a mixed powder obtained by adding 0.5 to 10 parts by mass of a Mg powder to 100 parts by mass of the total amount of the fine metal powder and / or the like and the powder of the aluminum alloy or the like needs to be used. When the molten aluminum alloy or the like is infiltrated without pressurization in, for example, a nitrogen atmosphere at 700°C to 900°C to impregnate the porous preform or the like obtained using the above-described mixed powder, thereby a good metal matrix composite can be obtained.Examples

[0037] Hereinafter, the present invention will be described in more detail giving Examples of the present invention and Comparative Examples. Note that the present invention is not limited to the Examples.[Example 1]

[0038] In a pot made of plastic, 1,200 g of a SiC powder having an average particle size of 5 µm and 800 g of an A6061 aluminum alloy powder having an average particle size of 25 µm were placed, and the resulting mixture was mixed putting alumina balls thereto for 2 hours. To this mixture, 100 g of a hydrolyzed ethyl silicate solution was added in order that 40 g of SiO 2 might be contained, and the resulting mixture was mixed for 30 minutes. This mixture was placed in a mold having an internal size of 200 mm × 200 mm to perform press molding at a pressure of 45 t. Further, the mixture was subjected to firing at 500°C for 2 hours to prepare a molded body (preform) containing the SiC powder and the aluminum alloy powder. The resulting molded body was placed in a metal mold, a molten A6061 aluminum alloy melted at 750°C was poured therein to impregnate the preform at a pressure of 100 MPa, and thus a composite was cast.

[0039] The composite obtained by the above-described method was an aluminum alloy matrix composite formed of 30% by volume of the SiC fine powder and 70% by volume of the balance. A specimen for measurement having a specified size was cut out from the resulting composite, and the flexural strength of the composite was measured using the specimen at room temperature in accordance with JIS R1601. Also in other examples, the flexural strength was measured by the same method. The measurement result was that the flexural strength was 740 MPa, which indicated that the obtained composite had significantly high strength. In addition, the obtained composite had good processability and was confirmed to be processable with a cemented carbide tool.[Example 2]

[0040] To 1,200 g of the SiC powder having an average particle size of 5 µm and 800 g of the A6061 aluminum alloy powder having an average particle size of 25 µm, which were the same as those used in Example 1, 40 g of a Mg powder having an average particle size of 50 µm was added, and the resulting mixture was mixed for 2 hours in the same manner as in Example 1. To this mixture, a solution obtained by dissolving a silicone resin (trade name: KR-220L, manufactured by Shin-Etsu Chemical Co., Ltd.) in isopropyl alcohol was added in an amount so as to give a silicone resin concentration of 30 g% in terms of SiO 2 , and the resulting mixture was mixed for 30 minutes. This mixture was subjected to press molding and firing by the same operation as in Example 1 to prepare a molded body (preform). A preform having a size of 100 mm × 100 mm × 30 mm was cut out from this molded body. Then, as shown in Figure 1, the preform 1 was impregnated and filled with a molten A6061 aluminum alloy 2 without pressurization to form a composite, and thus an aluminum alloy matrix composite was prepared. Specifically, as shown in Figure 1, the preform 1 and the A6061 aluminum alloy 2 were placed in a container 4 made of carbon; this container was placed in a furnace in a nitrogen atmosphere; the temperature was increased at a rate of 100°C / hour and then kept at 780°C for 2 hours; and thereafter the composite was taken out. Reference numeral 3 in Figure 1 shows an infiltration path of the same material as the preform 1. The composite taken out was processed for measurement, and the physical property values were measured by the same method as in Example 1.

[0041] The composite obtained in Example 2, as well as the composite obtained in Example 1, was also an aluminum alloy matrix composite composed of 30% by volume of the SiC fine powder and 70% by volume of the aluminum alloy. The flexural strength measured by the same method as in Example 1 was 650 MPa, which indicated that the obtained composite was a high-strength composite. In addition, the obtained composite had good processability and was processable with a cemented carbide tool.[Example 3]

[0042] To 800 g of a SiC powder having an average particle size of 3 µm and 1,200 g of an A1050 aluminum alloy powder having an average particle size of 30 µm, 100 g of a hydrolyzed ethyl silicate solution was blended and mixed in order that 40 g of SiO 2 might be contained, and further a preform containing the SiC powder and the aluminum alloy powder was prepared in the same manner as in Example 1. Then, the resulting preform was impregnated with molten A1050 aluminum alloy at a high pressure by the same operation as in Example 1 to obtain a composite of the present example.

[0043] The physical property values of the composite obtained above were measured to find that the composite was an aluminum alloy matrix composite composed of 20% by volume of the SiC fine powder and 80% by volume of the balance. The flexural strength measured by the same method as in Example 1 was 700 MPa, which indicated that the obtained composite was a significantly high-strength composite. In addition, the obtained composite had good processability and was processable with a cemented carbide tool.[Example 4]

[0044] Mixed were 1,200 g of a metal silicon powder having an average particle size of 5 µm and 200 g of the A6061 aluminum alloy powder having an average particle size of 25 µm in the same manner as in Example 1; 100 g of a hydrolyzed ethyl silicate solution was added thereto in order that 40 g of SiO 2 might be contained; and the resulting mixture was mixed for 30 minutes. A molded body (preform) was prepared using the resulting mixture by the same operation as in Example 1. Then, the resulting preform was impregnated with molten A6061 aluminum alloy at a high pressure by the same operation as in Example 1 to obtain a composite.

[0045] The physical property values of the composite obtained above were measured to find that the composite was an aluminum alloy matrix composite composed of 25% by volume of the silicon powder and 75% by volume of aluminum alloy powder. The flexural strength measured by the same method as in Example 1 was 580 MPa, which indicated that the obtained composite had high strength. In addition, the obtained composite had good processability and was processable with a cemented carbide tool.[Comparative Example 1]

[0046] To 2,000 g of a SiC powder having an average particle size of 14 µm, which is larger than the average particle size specified in the present invention, 100 g of a hydrolyzed ethyl silicate solution was added in order that 40 g of SiO 2 might be contained to prepare a preform using the mixed material in the same manner as in Example 1. Then, the resulting preform was impregnated with the molten aluminum alloy which was the same as used in Example 1 to prepare a composite. Comparative Example 1 is different from the present invention in that: the average particle size of the SiC powder is larger than that specified in the present invention; and the aluminum powder and / or the like is not used in the raw material mixture.

[0047] The physical property values of the composite obtained above were measured to find that the obtained composite was a composite composed of 55% by volume of SiC and 45% by volume of the aluminum alloy. The flexural strength measured by the same method as in Example 1 was 320 MPa which was about the same as those of general aluminum alloys, and therefore the composite was confirmed not to be a high-strength composite. In addition, the obtained composite had inferior processability and was not processable with a cemented carbide tool, and therefore the composite was processed with a diamond end mill.[Comparative Example 2]

[0048] A composite of the present example was prepared by the same operation as in Example 1 except that a mixture of 1,200 g of a SiC powder having an average particle size of 14 µm, which is larger than the average particle size specified in the present invention, and 800 g of an A6061 aluminum alloy powder having an average particle size of 25 µm was used. The physical property values of the obtained composite were measured to find that the obtained composite was a composite composed of 28% by volume of SiC and 72% by volume of the aluminum alloy. The flexural strength measured by the same method as in Example 1 was 330 MPa which was about the same as those of general aluminum alloys, and therefore the obtained composite was not a high-strength composite. In addition, the obtained composite had inferior processability and was not processable with a cemented carbide tool, and therefore the composite needed to be processed with a diamond end mill.[Comparative Example 3]

[0049] A molded body (preform) was prepared by the same operation as in Example 1 except that a mixture of 1,200 g of a SiC powder having an average particle size of 22 µm, which is larger than the average particle size specified in the present invention, and 800 g of an A6061 aluminum alloy powder having an average particle size of 25 µm was used. Then, the molded body (preform) obtained above was impregnated with molten A6061 aluminum alloy by the same operation as in Example 1 to obtain a composite of the present example.

[0050] The physical property values of the obtained composite were measured to find that the obtained composite was an aluminum alloy matrix composite composed of 31% by volume of the SiC powder and 69% by volume of the balance. In addition, the flexural strength measured by the same method as in Example 1 was 410 MPa, which was lower than those of the composites of Examples 1 to 4 and was about the same as those of general aluminum alloys, and therefore the obtained composite was not a high-strength composite. In addition, the obtained composite had inferior processability and was only processable with a diamond tool.[Comparative Example 4]

[0051] A molded body (preform) was prepared using 1,200 g of a metal silicon powder having an average particle size of 45 µm, which is larger than the average particle size specified in the present invention, and 800 g of an A6061 aluminum alloy powder having an average particle size of 25 µm by the same operation as in Example 1, and the preform was impregnated with A6061 aluminum alloy by the same operation as in Example 1 to obtain a composite.

[0052] The physical property values of the obtained composite were measured to find that the obtained composite was a composite composed of 29% by volume of the metal silicon powder having an average particle size of 45 µm and 71% by volume of A6061 aluminum alloy. In addition, the flexural strength measured by the same method as in Example 1 was 270 MPa, which indicated that the obtained composite was a low-strength composite.[Comparative Example 5]

[0053] A commercially available ingot of a composite composed of 30% by volume of a SiC powder / 70% by volume of aluminum, DURALCAN manufactured by Rio Tinto Alcan Inc., a Canadian company, was used, and the ingot was melted at 730°C and casted in a sand mold to produce a composite of 200 mm × 200 mm × 50 mm (thickness). A specimen for measurement was cut out from this in the same manner as in Example 1 to measure the flexural strength by the same method as in Example 1. As a result, the composite obtained above had low strength as low as a flexural strength of 380 MPa and inferior processability, and therefore the composite was only processable with a diamond tool.[Evaluation Results]

[0054] Table 1 shows conditions for preparing the composites of Examples and Comparative Examples and results of evaluations of the obtained composites. Regarding the evaluation of processability, a composite processable with a cemented carbide tool was rated as "good," and a composite not processable with a cemented carbide tool and only processable with a diamond tool was rated as "poor." In Comparative Example 5, a commercially available composite (commercially available product) of a SiC powder and aluminum metal was used. In Example 2, the preform was impregnated with the molten aluminum alloy without pressurization. In all the examples other than Example 2, the preform was impregnated and filled with the molten aluminum alloy at a high pressure of 100 MPa. Table 1: Conditions for preparing composites of Examples and Comparative Examples and results of evaluations of obtained compositesMetal powder particle size (µm)Aluminum powder particle size (µm)BinderAl or Al alloyFine powder: Al alloyFlexural strength (MPa)ProcessabilityExample 1SiC (5µm)A6061 alloy (25µm)Hydrolyzed ethyl silicate solutionA606130:70740GoodExample 2SiC (5µm)A6061 alloy (25µm) Mg(50µm)Silicone resinA606130:70650GoodExample 3SiC (3µm)A1050 alloy (30µm)Hydrolyzed ethyl silicate solutionA105020:80700GoodExample 4Metal silicon (5µm)A6061 alloy (25µm)Hydrolyzed ethyl silicate solutionA606125:75580GoodComparative Example 1SiC (14µm)Not blendedHydrolyzed ethyl silicate solutionA606155:45320PoorComparative Example 2SiC (14µm)A6061 alloy (25µm)Hydrolyzed ethyl silicate solutionA606128:72330PoorComparative Example 3SiC (22µm)A6061 alloy (25µm)Hydrolyzed ethyl silicate solutionA606131:69410PoorComparative Example 4Metal silicon (45µm)A6061 alloy (25µm)Hydrolyzed ethyl silicate solutionA606129:71270PoorComparative Example 5SiC (25µm)Not blendedNot usedAl30:70380Poor Reference Signs List

[0055] 1Preform 2Aluminum alloy or the like 3Infiltration path made of the same material as preform 4Container made of carbon

Claims

1. A high-strength metal matrix composite obtained by impregnating and filling a porous filled body or molded body (preform) with molten aluminum or a molten aluminum alloy, wherein the porous filled body or molded body (preform) is formed of a mixed powder obtained by adding at least one aluminum or aluminum alloy powder selected from the group consisting of an aluminum powder and an aluminum alloy powder each having an average particle size of 10 µm or larger and 300 µm or smaller to at least one fine powder selected from the group consisting of a metal powder and a ceramic powder each having an average particle size of 0.3 µm or larger and 8 µm or smaller, and the composite has a fine powder-filling rate of 10% by volume or more and 50% by volume or less and a flexural strength of 500 MPa or higher and 800 MPa or lower.

2. The high-strength metal matrix composite according to claim 1, wherein the metal powder which is the fine powder in the mixed powder is any one selected from the group consisting of a silicon powder, an iron powder, a stainless steel powder, a copper powder, and a titanium powder, the ceramic powder which is the fine powder in the mixed powder is any one selected from the group consisting of an alumina powder, a silica powder, an aluminum borate powder, a silicon carbide powder, a silicon nitride powder, and an aluminum nitride powder, and the blending ratio of the fine powder to the aluminum or aluminum alloy powder in the mixed powder is 10:90 to 90:10.

3. The high-strength metal matrix composite according to claim 1 or 2, wherein at least one binder selected from the group consisting of a silica-based binder and alumina-based organic / inorganic binder within a range of 0.5% or more and 10% or less on a mass basis is externally added to the mixed powder.

4. A method for producing a high-strength metal matrix composite, the method comprising: providing a porous filled body or molded body (preform) using a mixed powder obtained by adding at least one aluminum or aluminum alloy powder selected from the group consisting of an aluminum powder and an aluminum alloy powder each having an average particle size of 10 µm or larger and 300 µm or smaller to at least one fine powder selected from the group consisting of a metal powder and a ceramic powder each having an average particle size of 0.3 µm or larger and 8 µm or smaller; and impregnating and filling the resulting filled body or molded body (preform) with molten aluminum or a molten aluminum alloy at a high pressure as high as a pressure of 20 MPa or higher and 200 MPa or lower to form a composite, thereby providing a metal matrix composite having a fine powder-filling rate of 10% by volume or more and 50% by volume or less and a flexural strength of 500 MPa or higher and 800 MPa or lower.

5. A method for producing a high-strength metal matrix composite, the method comprising: providing a porous filled body or molded body (preform) using a Mg powder-containing mixed powder obtained in such a way that a mixed powder is obtained by adding at least one aluminum or aluminum alloy powder selected from the group consisting of an aluminum powder and an aluminum alloy powder each having an average particle size of 10 µm or larger and 300 µm or smaller to at least one fine powder selected from the group consisting of a metal powder and a ceramic powder each having an average particle size of 0.3 µm or larger and 8 µm or smaller, and further a magnesium powder within a range of 0.5 parts by mass or more and 10 parts by mass or less is added to 100 parts by mass of the mixed powder; and impregnating and filling the resulting filled body or molded body (preform) with molten aluminum or a molten aluminum alloy without pressurization to form a composite, thereby providing a metal matrix composite having a fine powder-filling rate of 10% by volume or more and 50% by volume or less and a flexural strength of 500 MPa or higher and 800 MPa or lower.

6. The method for producing a high-strength metal matrix composite according to claim 4 or 5, wherein the metal powder which is the fine powder in the mixed powder is any one selected from the group consisting of a silicon powder, an iron powder, a stainless steel powder, a copper powder, and a titanium powder, the ceramic powder which is the fine powder in the mixed powder is any one selected from the group consisting of an alumina powder, a silica powder, an aluminum borate powder, a silicon carbide powder, a silicon nitride powder, and an aluminum nitride powder, and the blending ratio of the fine powder to the aluminum or aluminum alloy powder in the mixed powder is 10:90 to 90:10.

7. The method for producing a high-strength metal matrix composite according to claim 4 or 5, wherein at least one binder selected from the group consisting of a silica-based binder and an alumina-based organic / inorganic binder within a range of 0.5% or more and 10% or less on a mass basis is externally added to the mixed powder.

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