Aluminum alloy matrix composite material, method for manufacturing aluminum alloy matrix composite material

Abstract

The present invention provides an aluminum alloy matrix composite material that is easily impregnated with aluminum alloy and has good mechanical properties, as well as a method for manufacturing the aluminum alloy matrix composite material. [Solution] Primary ceramic particles are obtained by crushing the ceramic raw material with a jet mill (S1). The volume average diameter of the primary ceramic particles is adjusted to 0.1 to 10 μm. Next, an organic binder and an inorganic binder are added to an aqueous slurry using the primary ceramic particles to obtain a slurry. The obtained slurry is granulated using a known spray-drying method to obtain secondary ceramic particles (pseudoparticles). Next, a preform is formed using the obtained ceramic particles (S2). Next, molten aluminum alloy is pressure-impregnated into the obtained preform (S3). By doing so, an aluminum alloy matrix composite material can be obtained.

Description

[Technical Field]

[0001] This invention relates to a metal matrix composite material in which an aluminum alloy is used as the matrix material and reinforcing particles are dispersed, and to a method for producing the same. [Background technology]

[0002] Conventionally, metal matrix composites (MMCs) have been proposed, and some have been put into practical use, in which molten aluminum alloy is pressure-impregnated into an intermediate molded body (preform) solidified with ceramic powder filler or binder, and ceramic is used as a reinforcing phase. In this method, the molten metal penetrates into the voids in the preform under pressure, reducing residual pores, and the metallic structure becomes uniform due to rapid cooling, making it easy to obtain MMCs with high strength and low strength variation.

[0003] As a method for producing such metal matrix composite materials, for example, a method has been proposed in which aluminum borate powder with a central particle size of about 30 to 50 μm is filled into a porous container, and molten aluminum alloy is poured and pressurized in a mold to impregnate it (Patent Document 1).

[0004] Furthermore, a method has been proposed in which a slurry consisting of aluminum borate powder and a binder is molded and dried to obtain a preform, and then high-pressure impregnated with molten aluminum alloy to obtain MMC (Patent Document 2). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2019-099850 [Patent Document 2] Japanese Patent Publication No. 2020-196932 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] While lightweight and highly rigid MMC (Magnetic Metallic Compound) is in high demand for applications in rotating components and other applications, there is a need for further improvements in durability (tensile, bending, and fatigue). The inventors investigated the point of failure and found that the concave areas on the aluminum alloy side, opposite the pointed protrusions on the preform surface, become the starting points for stress concentration / crack propagation under tensile, bending, and cyclic loading. In contrast, while reducing particle size decreases the number of pointed protrusions, it creates a manufacturing challenge as the pore size becomes smaller, making impregnation difficult.

[0007] This invention has been made in view of the above problems, and aims to provide an aluminum alloy matrix composite material that is easily impregnated with an aluminum alloy and has good mechanical properties, as well as a method for manufacturing an aluminum alloy matrix composite material. [Means for solving the problem]

[0008] To achieve the aforementioned objective, the first invention impregnates a preform consisting of reinforcing particles with an aluminum alloy, and the circularity of the reinforcing particles, obtained from the projected area A and circumference P based on image analysis, is 4πA / P 2 In the distribution based on the number of elements, the circularity of C10 is 0.80 or higher. 1.0 or less Furthermore, the circularity of the C50 is 0.93 or higher. 1.0 or less An aluminum alloy matrix composite material characterized by the following:

[0009] In the volume-based particle size distribution of the reinforced particles, it is desirable that D10 is 10 μm or larger and D90 is 90 μm or smaller.

[0010] It is desirable that the volume fraction Vf of the reinforcing particles relative to the total volume of the aluminum alloy and the reinforcing particles is 32% or more and 46% or less.

[0011] Regarding the circularity distribution of the reinforced particles, it is desirable that (C90-C10) / C50 be 0.20 or less.

[0012] The reinforcing particles preferably contain at least one of the following: alumina, mullite, cordierite, silicon nitride, magnesium borate, aluminum borate, silicon carbide, spinel, metallic silicon, carbon, or graphite.

[0013] It is desirable that the aluminum alloy matrix composite material has a tensile strength of 300 MPa or more and a bending strength of 500 MPa or more.

[0014] The density of the aforementioned aluminum alloy matrix composite material is 2.9 g / cm³. 3 More than 3.1g / cm 3 The following is preferable:

[0015] According to the first invention, the reinforcing particles that form the preform are formed by granulating primary particles. That is, the reinforcing particles are formed by integrating a large number of finer primary particles, and the preform is obtained by integrating the resulting (secondary) reinforcing particles. Therefore, the formation of pointed protrusions on the surface of the reinforcing particles that form the preform is suppressed, and stable mechanical properties can be obtained. In addition, since the diameter of the reinforcing particles can be adjusted during the granulation of the primary particles, the pore size of the preform does not become excessively small, and the impregnation process of aluminum alloy is facilitated.

[0016] In particular, if the particle size distribution of the reinforcing particles is based on volume, and D10 is 10 μm or more and D90 is 90 μm or less, then both mechanical properties and manufacturability can be efficiently achieved.

[0017] Furthermore, if the volume fraction Vf of the reinforcing particles relative to the total volume of the aluminum alloy and reinforcing particles is between 32% and 46%, then both mechanical properties and manufacturability can be efficiently achieved.

[0018] Furthermore, regarding the circularity distribution of the reinforcing particles, if (C90-C10) / C50 is 0.20 or less, the influence of pointed protrusions can be minimized.

[0019] As the reinforcing particles, by containing at least one of alumina, mullite, cordierite, silicon nitride, magnesium borate, aluminum borate, silicon carbide, spinel, metallic silicon, carbon, or graphite, a good aluminum alloy-based composite material can be obtained.

[0020] Moreover, if the tensile strength of the aluminum alloy-based composite material is 300 MPa or more and the bending strength is 500 MPa or more, a material with sufficient strength can be obtained.

[0021] Moreover, the density of the aluminum alloy-based composite material is 2.9 g / cm 3 or more and 3.1 g / cm 3 or less, which is desirable because it does not have excessive voids.

[0022] The second invention is a method for manufacturing an aluminum alloy-based composite material according to the first invention, comprising a step of pulverizing a reinforcing particle raw material to adjust the volume average diameter of primary particles to 0.1 to 10 μm, a step of using the primary particles to form a slurry containing water and a binder, spray-drying and granulating to obtain secondary particles, and forming a preform of the secondary particles, and a step of pressure-impregnating the preform with molten aluminum alloy.

[0023] According to the second invention, since the reinforcing particle raw material is pulverized once and the obtained primary particles are granulated to obtain secondary particles, the formation of pointed convex portions on the surface of the secondary particles can be suppressed without making the secondary particles overly fine. Therefore, when aluminum is impregnated using a preform made of secondary particles, the formation of sites that become fracture initiation points can be suppressed, and excellent mechanical properties can be obtained.

Effects of the Invention

[0024] According to the present invention, impregnation of the aluminum alloy is easy, and an aluminum alloy-based composite material having good mechanical properties and a method for manufacturing an aluminum alloy-based composite material can be provided.

Brief Description of the Drawings

[0025] [Figure 1] A diagram illustrating the manufacturing process of aluminum alloy matrix composite materials. [Figure 2] SEM image of granulated ceramic particles. [Figure 3] SEM image of granulated ceramic particles. [Figure 4] SEM image of ungranulated ceramic particles. [Figure 5] SEM image of ungranulated ceramic particles. [Figure 6] Optical microscope image of a composite material using granulated ceramic particles. [Figure 7] Optical microscope image of a composite material using non-granulated ceramic particles. [Figure 8] A figure showing the evaluation results of bending strength. [Figure 9] A diagram showing the evaluation results of tensile strength. [Figure 10] A figure showing the results of density evaluation. [Modes for carrying out the invention]

[0026] Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is a diagram showing the manufacturing process of an aluminum alloy matrix composite material according to this embodiment.

[0027] (primary particles) First, the reinforcing particle material is crushed in a jet mill to obtain primary particles (S1). In this embodiment, the reinforcing particle material is a ceramic material, and an example of obtaining primary ceramic particles is described, but other materials such as metallic silicon, carbon, and graphite can also be used.

[0028] Furthermore, in this embodiment, aluminum borate is described as an example of the ceramic raw material, but any at least one selected from alumina, mullite, cordierite, silicon nitride, magnesium borate, aluminum borate, silicon carbide, spinel, etc. is acceptable. Among these, the present invention is particularly effective for aluminum borate, silicon carbide, and spinel, which tend to form pointed protrusions in their particles when crushed.

[0029] The volume-average diameter of the primary ceramic particles is preferably 0.1 to 10 μm. The volume-average diameter of the primary ceramic particles is set to approximately 1 / 10 to 1 / 1000 of the volume-average diameter of the secondary ceramic particles, as described later. The volume-average diameter of the primary ceramic particles can be adjusted by optimizing the grinding conditions or by sieving the resulting particles.

[0030] (Secondary ceramic particles) Next, an organic binder (e.g., polyvinyl alcohol) and an inorganic binder (e.g., colloidal silica, colloidal alumina) are added to the primary ceramic particles in an aqueous slurry to obtain a slurry. The type and amount of binder used are selected as appropriate.

[0031] Using the obtained slurry, primary ceramic particles are granulated using a known spray-drying method to obtain secondary ceramic particles (pseudoparticles). The spray-drying method is a technique that involves spraying a liquid raw material (slurry) into hot air to instantly evaporate the water and obtain dry particles. For example, it can be manufactured under conditions of a disc diameter of φ65 mm, a rotation speed of 10,000 to 25,000 rpm, an inlet temperature of 80°C to 350°C, an outlet temperature of 50°C to 250°C, and a differential pressure of -0.2 to -0.3 kPa. However, the conditions for the spray-drying method are not limited to those above, and the conditions can be appropriately set according to the equipment, the secondary ceramic particles, and the size of the secondary ceramic particles.

[0032] In this way, secondary ceramic particles (hereinafter, these reinforced particles may simply be referred to as ceramic particles) can be obtained using the primary ceramic particles obtained by grinding. The volume-average diameter of the granulated ceramic particles is preferably 10 to 120 μm.

[0033] The volume-average diameter of ceramics can be analyzed using known laser diffraction methods or dynamic image analysis. When evaluating by image analysis, first, the particles are dispersed (dried powder dispersed in air, suspension placed on a slide / filter). Next, images are acquired for each large number of particles (several thousand to tens of thousands). The illumination conditions, such as dark-field / bright-field and transmission / reflection, are set appropriately to ensure that the particle contours are clear. For each obtained particle, the contour can be acquired automatically or manually, and the area on the image (projected area), circumference, maximum diameter, major axis, minor axis, etc., can be calculated. In this way, the equivalent circular diameter of the particle can be obtained based on the information obtained. The volume-average diameter mentioned above is calculated as the average value of the measured equivalent circular diameters of the particles.

[0034] Furthermore, in the volume-based particle size distribution of the ceramic particles, it is desirable that D10 be 10 μm or larger and D90 be 90 μm or smaller. In addition, in the volume-based particle size distribution of the ceramic particles, it is desirable that D50 be 20 μm or larger and 80 μm or smaller. Here, Dx is the quantile of the volume distribution obtained by arranging the particle diameters of each ceramic particle in order from the smallest diameter (the particle diameter of the particle that accounts for x% of the total volume when accumulated from the smallest particle diameter).

[0035] If the ceramic particles are too fine, the pore size (the gap between particles) in the preform becomes too small, making it difficult to impregnate them with molten aluminum alloy. On the other hand, if the ceramic particles are too large, the dispersion of the ceramic particles in the aluminum alloy matrix composite becomes insufficient, which can actually degrade the mechanical properties.

[0036] The circularity of the obtained ceramic particles is measured. First, the cross-section of the ceramic particles embedded in resin and mirror-polished is observed, and the 4πA / P ratio is obtained from the projected area A and circumference P of each particle based on 2D image analysis of the observed cross-section. 2 This is defined as the circularity of the ceramic particles. In this case, it is desirable that the circularity of C10 is 0.80 or higher and the circularity of C50 is 0.93 or higher in the number-based distribution of circularity. Here, Cx is the quantile of the number distribution arranged in descending order of circularity (the circularity of the particles that represent x% of the total number of particles, accumulated from the particle with the smallest circularity). The total number of particles used for measurement is preferably 2,000 or more. When the circularity is small (i.e., the surface irregularities of the particles are large), there are many (large) pointed protrusions, which is a factor in the deterioration of the mechanical properties of the aluminum alloy matrix composite material.

[0037] Furthermore, it is desirable that the circularity distribution of ceramic particles, Cd = (C90 - C10) / C50, be 0.20 or less. Cd is an index representing the variation in circularity; the smaller the value, the smaller the variation in particle circularity. Therefore, a larger Cd value contributes to the variation in the quality of the aluminum alloy matrix composite material.

[0038] (Preform) Next, a preform is formed using the obtained ceramic particles (S2). Conventional methods can be applied to form the ceramic particle preform, such as the sedimentation method or the pressing method. In the sedimentation method, the ceramic particles are sedimented and dried to form the preform. In the pressing method, the ceramic particles and binder mixture are pressed in a mold and dried to form the preform. In either case, the porosity of the preform can be adjusted by applying vibration pressure during the formation process. Furthermore, the strength required for the next process can be obtained by calcining the preform at a temperature of 800°C or higher.

[0039] In this embodiment, it is desirable that the porosity of the preform be between 20% and 68%. By doing so, the volume fraction Vf of the ceramic particles relative to the total volume of the aluminum alloy and ceramic particles after impregnation with the aluminum alloy can be set to between 32% and 80%. By appropriately adjusting the volume fraction of the aluminum alloy and ceramic particles as described above, good mechanical properties can be obtained.

[0040] (Aluminum alloy matrix composite material) Next, the obtained preform is pressure-impregnated with molten aluminum alloy (S3). This completes the process to obtain an aluminum alloy matrix composite material. The pressure impregnation method can be any known method (gas pressure impregnation, high-pressure casting, die casting, etc.). For example, molten aluminum alloy is poured into a mold or high-pressure container, and pressure of approximately 50-120 MPa is applied to pressure-impregnate the preform. The method is not limited to gas pressure impregnation, high-pressure casting, or die casting; squeeze impregnation, press-in casting, semi-solid formation, stirring casting, low-pressure casting, low-pressure impregnation, etc., may also be used. It is desirable to confirm that the residual porosity of the aluminum alloy after solidification is 5.0 volume% or less. Residual porosity can be confirmed, for example, by the apparent density described later. The composition of the aluminum alloy is not particularly limited, as long as impregnation into the preform is possible.

[0041] Furthermore, whether or not the material was manufactured using the above method can be determined by observing the fine particles obtained by destroying the resulting aluminum alloy matrix composite material with an electron microscope. This allows for the determination of whether or not the ceramic particles forming the preform are granulated primary ceramic particles. In particular, aluminum borate, silicon carbide, and spinel tend to form angular shapes rather than circular (spherical) shapes when simply crushed, so it is possible to determine whether or not they are granulated primary ceramic particles even in the preform state. Similarly, after destroying the resulting aluminum alloy matrix composite material, the diameter of the ceramic particles can be accurately measured by observing the fine particles with an electron microscope and performing image analysis. [Examples]

[0042] (Ceramic particles) (Examples) Primary ceramic particles with a volume-average diameter of 1 to 10 μm were produced by pulverizing aluminum borate using a jet mill. A slurry (solid content 21.08% by mass) containing water, polyvinyl alcohol (0.5% by mass), and colloidal silica (10.02% by mass) was prepared using the obtained primary ceramic particles. Ceramic particles A were produced using the obtained slurry by spray drying. The diameter of ceramic particles A was set so that the D50 was approximately 50 μm.

[0043] (Comparison product) Ceramic particles B were directly produced by pulverizing aluminum borate using a jet mill. The diameter of ceramic particles B was set so that D50 was approximately 50 μm.

[0044] Figures 2 and 3 are SEM images of ceramic particle A, obtained by granulating primary ceramic particles formed by pulverizing aluminum borate, while Figures 4 and 5 are SEM images of ceramic particle B, obtained directly by pulverizing aluminum borate. Both ceramic particles A and B shown in Figures 3 and 5 had a diameter of approximately 40-50 μm. As shown in Figure 5, the surface of ceramic particle B, obtained by pulverizing the ceramic raw material, had large irregularities, including pointed protrusions due to crystal interfaces. In contrast, as shown in Figure 3, ceramic particle A, obtained by first pulverizing the ceramic raw material to approximately 0.1-10 μm to form primary particles and then granulating the primary particles, was approximately circular (spherical) and had small surface irregularities.

[0045] Furthermore, the particle size and circularity of the obtained ceramic particles A and B were evaluated. Particle size was measured using a Malvern Panalytical particle image analyzer with a 5x objective lens and a spray pressure of 0.1 MPa. The results are shown in Table 1.

[0046] [Table 1]

[0047] In both the example (ceramic particle A) and the comparative example (ceramic particle B), the volume-average diameter D50 was approximately 50 μm. Although ceramic particle A had a slightly smaller D50, its volume-average diameter was larger. Ceramic particle B showed greater particle size variation, suggesting the presence of many fine particles. Ceramic particle A had a volume-average diameter of 10-120 μm, satisfying the conditions of D10 being 10 μm or more, D90 being 90 μm or less, and D50 being 30-50 μm.

[0048] Furthermore, regarding circularity, in the distribution based on the number of particles, the circularity of ceramic particle A at C10 was 0.80 or higher, and the circularity of C50 was 0.93 or higher. On the other hand, the circularity of ceramic particle B at C10 was less than 0.80, and the circularity of C50 was less than 0.93. In other words, the circularity of ceramic particle A was higher than that of ceramic particle B, and was closer to circular.

[0049] Furthermore, the (C90-C10) / C50 value was 0.20 or less for ceramic particle A, but exceeded 0.20 for ceramic particle B. This means that ceramic particle A had little variation in circularity and a uniform shape, while ceramic particle B contained a mixture of nearly circular particles and particles with large irregularities. Thus, according to the example, it was found that the resulting ceramic particle A had a shape close to circular (spherical) and had little variation in shape.

[0050] (Aluminum alloy matrix composite material) (Examples) Using the ceramic particles A obtained as described above, a preform was formed by the sedimentation method. During this process, the porosity was adjusted to 20-68% by vibration and pressure. After drying, the preform was placed in a mold and pressure-impregnated with molten aluminum at 100 MPa.

[0051] (Comparative example) A preform was formed using ceramic particles B by sedimentation, following the same procedure as in the examples. During this process, the porosity was adjusted to 20-68% by vibration and pressure. After drying, the preform was placed in a mold, and molten aluminum was pressure-impregnated at 100 MPa, followed by cooling and solidification to obtain an aluminum alloy matrix composite material.

[0052] Figure 6 is an optical microscope image (100x magnification) of an aluminum alloy matrix composite material using ceramic particles A. The roughly circular ceramic particles A were dispersed almost uniformly in the aluminum. On the other hand, Figure 7 is an optical microscope image (100x magnification) of an aluminum alloy matrix composite material using ceramic particles A. Corners were formed on the ceramic particles.

[0053] In both the examples and comparative examples, the bending strength, tensile strength, and apparent density of the aluminum alloy matrix composite material were measured. Each evaluation was performed using six test specimens.

[0054] Figure 8 shows the evaluation results for the bending strength of the examples and comparative examples. In the examples, all test specimens had a bending strength of 500 MPa or higher (and even 550 MPa or higher). In contrast, in the comparative examples, all test specimens had a bending strength of less than 450 MPa. Thus, even when using the same aluminum alloy, the examples were all able to satisfy a bending strength of 500 MPa or higher, while the comparative examples all showed lower bending strengths.

[0055] Figure 9 shows the evaluation results for tensile strength of the examples and comparative examples. In the examples, all test specimens had a tensile strength of 300 MPa or higher. In contrast, in the comparative examples, all test specimens had a tensile strength of less than 300 MPa. Thus, even when using the same aluminum alloy, the examples were all able to satisfy a tensile strength of 300 MPa or higher, while the comparative examples all showed lower tensile strength results.

[0056] Figure 10 shows the evaluation results for the density of the examples and comparative examples. In the examples, all test specimens had a density of 2.90 g / cm³. 3The above was the case. In contrast, in the comparative examples, the density of all test pieces was less than 2.85 g / cm 3 3. It is considered that, even when the same aluminum alloy is used, the density of the comparative examples is low because the residual porosity has increased.

[0057] When the residual porosity of the examples was confirmed, it was 5.0 volume% or less. The residual porosity can be obtained by the Archimedes method or image analysis (pore area ratio). By reducing the unevenness on the surface of the ceramic particles that make up the preform, the tortuosity of the pore network in the preform can be reduced. Therefore, it is presumed that the entrainment of bubbles during the impregnation of the molten aluminum is reduced and the residual porosity is decreased. In the case of this example, when the density exceeded 3.1 g / cm 3 3, the volume ratio of the aluminum alloy would decrease, which was not desirable.

[0058] In all of the aluminum alloy-based composite materials of the examples, the volume fraction Vf of the ceramic particles with respect to the total volume of the aluminum alloy and the ceramic particles was in the range of 32% or more and 80% or less.

[0059] As described above, according to the present embodiment, by using ceramic particles obtained by granulating primary ceramic particles as a raw material for the ceramic preform constituting the aluminum alloy-based composite material, high mechanical properties can be obtained.

[0060] In addition, in order to reduce the surface unevenness of the ceramic particles, it is not necessary to use overly fine particles, so it is possible to suppress the pore diameter of the preform from becoming too small when the preform is formed. Therefore, the impregnation of the molten aluminum alloy is easy.

[0061] Although embodiments of the present invention have been described above with reference to the attached drawings, the technical scope of the present invention is not limited to the embodiments described above. It is clear to those skilled in the art that various modifications or alterations can be conceived within the scope of the technical idea described in the claims, and these will naturally also fall within the technical scope of the present invention.

Claims

1. A metal matrix composite material in which an aluminum alloy is impregnated into a preform consisting of reinforcing particles, The reinforcing particles are formed by granulating primary particles, The circularity of the aforementioned reinforced particle, obtained from the projected area A and circumference P based on image analysis, is 4πA / P. ２ An aluminum alloy matrix composite material characterized in that, in the distribution based on the number of elements, the circularity of C10 is 0.80 or more and 1.0 or less, and the circularity of C50 is 0.93 or more and 1.0 or less.

2. The aluminum alloy matrix composite material according to claim 1, characterized in that, in the volume-based particle size distribution of the reinforcing particles, D10 is 10 μm or more and D90 is 90 μm or less.

3. The aluminum alloy matrix composite material according to claim 1, characterized in that the volume fraction Vf of the reinforcing particles relative to the total volume of the aluminum alloy and the reinforcing particles is 32% or more and 80% or less.

4. The aluminum alloy matrix composite material according to claim 1, characterized in that the circularity distribution of the reinforcing particles is such that (C90-C10) / C50 is 0.20 or less.

5. The aluminum alloy matrix composite material according to claim 1, characterized in that the reinforcing particles contain at least one of alumina, mullite, cordierite, silicon nitride, magnesium borate, aluminum borate, silicon carbide, spinel, metallic silicon, carbon, or graphite.

6. The aluminum alloy matrix composite material according to claim 1, characterized in that it has a tensile strength of 300 MPa or more and a bending strength of 500 MPa or more.

7. The density of the aforementioned aluminum alloy matrix composite material is 2.9 g / cm³. ３ 3.1g / cm or more ３ The aluminum alloy matrix composite material according to claim 1, characterized in that it is as follows.

8. A method for producing an aluminum alloy matrix composite material according to any one of claims 1 to 7, A process of crushing the reinforced particle raw material to adjust the volume average diameter of the primary particles to 0.1 to 10 μm, A process of using primary particles, forming a slurry containing water and a binder, spray-drying it to obtain secondary particles, and forming a preform of the secondary particles, The process involves pressure-impregnating the preform with molten aluminum alloy, A method for manufacturing an aluminum alloy matrix composite material, characterized by comprising the following:

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