JPH0321612B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a composite structural material, and more particularly to a composite structural material that is particularly suitable for applications where the maximum temperature during use reaches 600°C. In recent years, composite structural materials (hereinafter referred to as structural materials) made of metal and carbon fiber have been attracting attention in various fields. Among these, those using aluminum alloy as the metal are attracting attention in fields that require weight reduction because they have particularly excellent specific strength and specific rigidity. Such structures have conventionally been made using A201, an aluminum alloy with a very low silicon content, containing 0.1% by weight silicon, 4.7% by weight copper, 0.3% by weight magnesium and 0.6% by weight silver; An alloy in which the remainder is aluminum, and carbon fiber whose tensile modulus in the fiber axis direction (hereinafter referred to as elastic modulus) is about 28 tons/mm ² , which is relatively low among the so-called high-modulus types. There are things that can be combined. However, when such conventional structures are exposed to high temperatures of 200 to 600°C, the tensile strength (hereinafter referred to as strength) in the fiber axis direction of carbon fibers decreases to less than half of that before exposure, that is, before undergoing thermal history. The drawback was that it dropped to a low level. That is, the conventional structural materials described above have very low resistance to heat deterioration. It is generally said that the above-mentioned decrease in strength of structural materials occurs due to the reaction 4Al+3C→Al ₄ C ₃ at the interface between aluminum and carbon fibers. However, when such a reaction occurs, not only does the strength of the carbon fiber itself decrease, but also the carbon fiber and matrix bond excessively due to Al ₄ C ₃ generated at the interface between the carbon fiber and the matrix. I ended up
It makes the structural material brittle. Such structural materials have very low strength because if a minute crack occurs inside them due to stress, the crack will instantly propagate and break due to the strong interfacial adhesive force. Of course, the above reaction also occurs due to heating when manufacturing the structural material, that is, when compounding the aluminum alloy and carbon fiber. In fact, structural materials using what is generally called a high-strength type of carbon fiber, rather than a high-modulus type, have significantly lower strength than the theoretical strength, and there has already been a significant decrease in strength, which is thought to be due to the above reaction. It's happening. In this respect, when high-modulus carbon fibers are used, the decrease in strength is not so great, and a structural material having a strength extremely close to the theoretical strength may be obtained. However, as mentioned above, such structural materials also suffer a significant decrease in strength due to thermal history after manufacture. The purpose of the present invention is to solve the above-mentioned drawbacks of conventional structural materials using carbon fibers, and to provide a structure with excellent heat deterioration resistance, which has a strength extremely close to the theoretical strength, and has extremely little decrease in strength due to heat history after manufacturing. We provide materials. To achieve the above object, the present invention uses an aluminum alloy containing 1 to 22% by weight of silicon, and a carbon material having a tensile modulus of elasticity in the fiber axis direction of at least 30 tons/mm ² and not subjected to surface oxidation treatment. It is characterized by a composite structure material made of fibers. To explain the present invention in detail, in the present invention, an aluminum alloy containing silicon is used. As will be explained later, silicon prevents aluminum from reacting with specific carbon fibers, and prevents the carbon fibers from reacting with aluminum at their interfaces.
It acts to suppress the formation of a compound called Al ₄ C ₃ . However, if the content is less than 1% by weight, the above-mentioned suppressing effect can hardly be obtained. On the other hand, if the amount is too large, the alloy becomes brittle and cannot exhibit the strength required as a structural material, since silicon is an inherently brittle metal. Therefore, the upper limit needs to be 22% by weight so that no significant decrease in strength due to embrittlement occurs. Note that when the silicon content reaches around 13% by weight, silicon primary crystals precipitate in the alloy, which reduces the tensile strength and elongation of the alloy. Also, the toughness of the alloy is greater when the silicon content is less than 8% by weight. Therefore, the silicon content is 1-13% by weight
is preferable, and more preferably 1 to 8
Weight%. The alloy may also contain other elements in addition to silicon. For example, if titanium is contained in a range of 0.3% by weight or less, the crystal grains of the alloy will be made finer and the mechanical properties of the structural material will be further improved, so it is preferable. A similar effect can be achieved by using up to 2% nickel, up to 1% cobalt, or up to 0.5% by weight of nickel.
It can also be obtained with less than % by weight of chromium. Also,
Copper of 4% by weight or less also makes crystal grains finer as Al ₂ Cu. Furthermore, iron below 0.8% by weight is
When manganese is included, a granular ternary alloy called Fe-Mn-Al is created, further increasing the high temperature strength of the alloy. Also, 0.3 to 0.5% by weight of magnesium is preferred because it promotes age hardening of the alloy. The carbon fibers used in the present invention are pitch type, rayon type, and polyacrylonitrile (PAN).
It is a so-called graphitized carbon fiber, which consists of a carbon fiber having a modulus of elasticity of at least 30 tons/mm ² .
The carbon fibers, as mentioned above, react very little with aluminum when at least 1% by weight silicon is present in the alloy. This is considered to be due to the following reasons. That is, the carbon fiber has a structural unit consisting of an elongated ribbon-like polycyclic aromatic molecular fragment condensed with benzene rings and oriented in the fiber axis direction. These ribbon-like fragments have an extremely high degree of condensation of benzene rings and can be considered as the ultimate aromatic compound, but some of them stack up to form graphite crystal regions, and they also branch out. It forms a fine fibrillar structure. In other words, the surface of carbon fiber is covered with carbon atoms in the network plane of graphite crystals, but carbon fibers with an elastic modulus of at least 30 tons/mm ² have an extremely high degree of orientation of the ribbon-like fragments. , the arrangement of carbon atoms in the network plane on the surface is orderly, and the number of peripheral carbon atoms is small. In other words, it is that much more inert. However, even such carbon fibers react when heated to high temperatures while in contact with aluminum, producing a compound called Al ₄ C ₃ at the interface. This is thought to be because when heated to high temperatures, it becomes a driving force and disturbs the arrangement of carbon atoms in the network plane.
When at least 1% by weight of silicon is present in the aluminum, almost no formation of the above compounds is observed. In other words, silicon in the alloy is
It is thought that this prevents the arrangement of carbon atoms in the plane of the network from becoming disordered, thereby suppressing the reaction between aluminum and carbon fibers. When the carbon fiber in the present invention as described above is analyzed by laser Raman spectroscopy,
A band with a wave number of around ₁₅₈₅ cm ^-1 (hereinafter referred to as A
This may be because the A ₁ g symmetric vibration (forbidden transition) of the graphite structure becomes an allowed transition due to structural disorder at the crystal edge, or it may be due to differences in the chemical structure around the benzene ring. The intensity ratio with the band near the wave number 1355 cm ^-1 (hereinafter referred to as B band), that is, the peak height of B band/peak height of A band (hereinafter referred to as B/A ratio) is 0.7 or less, It is preferably 0.6 or less, more preferably 0.5 or less.
The smaller the B/A ratio is, the more graphitized the carbon fiber is. In other words, the elastic modulus is high. Here, laser Raman spectroscopy is
Information about the molecular structure of a material is obtained by using the Raman effect, a phenomenon in which when laser light is directed at a material and is scattered, light whose wavelength has changed by an amount specific to that material is mixed into the scattered light. This is what you get. In the present invention, the above analysis is carried out using a laser Raman spectrophotometer JRS-
Using 400D, attach one or several carbon fiber strands to the holder, and irradiate the carbon fiber with light from a CR-3 argon laser (wavelength 5145〓, output 200mW) manufactured by Coherent, Inc., USA, in a nitrogen atmosphere. After condensing the Raman scattered light, we separated it using a double grating, received the spectrum with a photomultiplier tube R268 manufactured by Hamamatsu Television Co., Ltd., recorded it on a chart, and read the B/A ratio from the chart. I'm waddling along. Furthermore, the above-mentioned carbon fibers have not been subjected to surface oxidation treatment. That is, in structural materials such as the present invention, in order to improve adhesion at the interface with metal, carbon fibers are generally subjected to surface oxidation treatment such as electrolytic oxidation treatment to disturb the arrangement of carbon atoms in the plane of the network. In addition to increasing the active surface area, the surface is made to have irregularities. However, in the present invention, carbon fibers that have not been subjected to such surface oxidation treatment are used. Figure 1 shows the surface of conventionally commonly used carbon fibers subjected to surface oxidation treatment, and
The figures are scanning electron micrographs (50,000x magnification) showing the surfaces of carbon fibers used in the present invention that have not been subjected to surface oxidation treatment.
From these photographs, it can be seen that carbon fibers subjected to surface oxidation treatment have many minute irregularities and have a roughened surface compared to those without surface oxidation treatment. Conventionally, when the surface is roughened, the response creates a state in which the metal seems to be anchored (called an anchor effect), and this, combined with the large active surface area, It was thought that this would improve the adhesion at the interface and increase the strength of the structural material. As shown in Figure 2, when the surface of a carbon fiber that has not been subjected to surface oxidation treatment is analyzed by ESCA (X-ray photoelectron spectroscopy), carbon atoms forming a graphite structure appear at 1202 eV. It is characterized by a peak half width of 1.2 to 1.5 eV in the C _1S spectrum, which represents the energy level of the 1S orbit. In other words, when surface oxidation treatment is applied to carbon fibers, the arrangement state of carbon atoms in the network plane is disturbed as described above, and reaction with aluminum becomes more likely to occur. In other words, this indicates that the above-mentioned disturbance is extremely small up to a depth of several tens of meters. Here, ESCA irradiates the surface of a sample with soft X-rays and measures the kinetic energy of electrons ejected by the photoelectric effect. , let Ke be the kinetic energy of the ejected electron,
From the law of conservation of energy, the formula hν=Be+Ke holds true, where hν is determined by the X-ray source used,
Since Ke can be determined through measurement, it is possible to determine Be, that is, the binding energy of the electron. In a substance, there are molecular orbital atoms that participate in chemical bonds at shallow depths, and atomic orbital atoms unique to the constituent atoms at deep depths.
The ESCA spectrum directly represents the pattern of these orbitals, and the oxidation number and bonding state of an element can be determined from the chemical shift at a unique position. In the present invention, the above analysis is performed using an X-ray photoelectron spectrometer ES-200 manufactured by Kokusai _Electric Co., Ltd.
mA), the temperature was 40°C, and the vacuum was 10 ^-8 Torr. The above carbon fibers may be present in the structural material in the form of continuous fibers or short fibers. It may also exist in the form of a fabric or mat. The array may be a unidirectional array or a random array. In addition, for example, in the case of cylindrical or cylindrical structural materials, carbon fibers formed by filament winding arrangement, woven fabric, matte, or unidirectionally aligned sheets into a sushi-wound shape can be used as structural materials. The arrangement may be such that it has an angle of ±α with respect to the axial direction. For example, if the above angle is ±(10-30) degrees, preferably ±(15
A filament winding array with a winding angle of ~25) degrees is useful as a piston pin for internal combustion engines such as automobiles. The structural material of the present invention can be manufactured by various methods. For example, carbon fibers are coated with aluminum alloy by thermal spraying or ion plating, and the coated materials are collected and hot-pressed at a temperature slightly lower than the melting point of the aluminum alloy; carbon fibers and aluminum alloy powder are mixed and hot-pressed; Improving the wettability of carbon fibers with aluminum alloy using methods such as powder metallurgy, diffusion bonding, and chemical vapor deposition, in which carbon fibers and aluminum alloy foil are alternately layered and heated and pressed. The so-called molten metal infiltration method involves coating a thin film of a material such as titanium boride, and passing it through a molten aluminum alloy to impregnate the fibers between the fibers to obtain a composite wire.
After filling a mold with carbon fibers, a molten aluminum alloy is injected into the mold, and high pressure is applied to impregnate the aluminum alloy between the fibers, which is the so-called high-pressure casting method. The structural material of the present invention has excellent heat deterioration resistance,
Since there is almost no decrease in strength even when used at high temperatures or subjected to thermal cycles, it is particularly suitable for applications where the temperature during use is 200 to 600°C. For example, fan blades such as jet engine compressors, various parts of rockets and artificial satellites, brake linings of automobiles, pistons of internal combustion engines, piston pins, connecting rods, push rods, rocker arms, crank pins, automobile transmissions, etc. Shift forks, apex seals for rotary engines, vanes for compressors, other bearings, current collector sliders for railway vehicles, electric brushes,
Suitable for applications such as electrical contacts. Next, the present invention will be explained in more detail using Examples. Example 1 A polyacrylonitrile (PAN) polymer copolymerized with 1.2 mol% of acrylic acid was wet-spun using dimethyl sulfoxide (DMSO) as a solvent and water as a coagulant to obtain 1.0 denier (single yarn denier),
Acrylic fibers with 6000 filaments were obtained. Next, the above acrylic fibers were placed in an oxidizing atmosphere.
It was fired at 240°C for about 2 hours to make it flame resistant, and then heat treated in a nitrogen atmosphere under the firing conditions shown in Table 1.
A total of four types of carbon fibers from 1A to 4A were obtained. However, for No. 2A carbon fiber, after manufacturing, the carbon fiber was used as an anode and passed through a 10% by weight sodium hydroxide aqueous solution while passing a direct current through an energizing roller, giving it an energy of 150 coulombs/g. The surface was subjected to electrolytic oxidation treatment. Next, for each of the carbon fibers No. 1A to 4A, the strength and elastic modulus were measured by the method specified in 5.3.2 of JIS R7601 using Shimadzu Corporation's tensile tester IS-5000, and laser Raman spectroscopy. The B/A ratio by analytical method and the half width by ESCA were measured. The measurement results are shown in Table 1. On the other hand, a mixture of a solution of 1 part by weight of polymethyl methacrylate (PMMA) dissolved in 6 parts by weight of ethanol and an aluminum alloy powder containing 8% by weight of silicon with an average particle size of approximately 35 μm was prepared, and in the above solution, The mixture has a content of 30% by weight
to obtain a suspension. Next, while stirring the suspension, pour No.
1A carbon fiber is passed through at a speed of approximately 30cm/min.
After the suspension was impregnated between the fibers, the fibers were dried at about 60° C. and wound onto a bobbin. Exactly the same thing, No.
Carbon fibers of 2A to 4A were also tested. Next, No. 1A carbon fiber was pulled out from the above bobbin, cut into lengths of 90 mm, lined up in one direction, placed in a mold, and then heated and pressurized at approximately 560°C and approximately 300 kg/cm ² in a vacuum. (hot pressing) to obtain a structural material with a carbon fiber content of approximately 50% by volume. Carbon fiber structural members No. 2A to 4A were obtained in exactly the same manner. Next, from each of the above structural materials, a test piece having the dimensions and shape shown in Fig. 3 with the fiber direction as the longitudinal direction was cut out, and using the above tensile tester, the test piece was tested at a tensile speed.
A tensile test was conducted under the condition of 0.5 mm/min. on the other hand,
The theoretical strength of each test piece was calculated, and the ratio of the measured strength to the theoretical strength, that is, the measured strength/theoretical strength, was determined. The results are shown in Table 1. Note that the theoretical strength was calculated using the following formula. σ=σ _f・V _f +σ _n (1−V _f ) Where, σ: Theoretical strength of the test piece σ _f : Strength of carbon fiber V _f : Volume content of carbon fiber σ _n : Aluminum alloy at the time of carbon fiber breakage Next, the four types of test pieces described above were heat treated at 550° C. for 8 hours in a vacuum, and then the ratio between the measured strength and the theoretical strength was determined in the same manner as above. The results are shown in Table 1.

[Table] From Table 1 above, if carbon fiber with an elastic modulus of 23 tons/mm ² is used, even if the surface oxidation treatment is not performed and the silicon content is within the range of the present invention, , only about 1/5 of the theoretical strength was obtained, and that strength was further reduced to 1/5 by heat treatment.
You can see that it drops to about 6. Also,
Comparing No. 2A and No. 3A, the only difference between the two is the presence or absence of surface oxidation treatment, but the heat deterioration resistance of the latter is much higher than that of the former. This tendency is even more pronounced in the case of No. 4A carbon fiber having an elastic modulus of 40 tons/mm ² . Example 2 Using the carbon fiber No. 3A above, the same method as in Example 1 was carried out, but as shown in Table 2,
A total of seven types of test pieces 1B to 7B were made using aluminum alloy powders with different silicon contents, and the same test as in Example 1 was conducted on each test piece to determine the ratio between the measured strength and the theoretical strength. The results are shown in Table 2.

[Table] From Table 2, even if carbon fiber with an elastic modulus of 30 tons/mm ² and without surface oxidation treatment is used, the silicon content is within the range of 1 to 22% by weight. It can be seen that without it, a structural material with excellent heat deterioration resistance cannot be obtained. This is the same even when No. 4A carbon fiber having an elastic modulus of 40 tons/mm ² is used. FIG. 4 is a micrograph (500x magnification) showing a cross section of the No. 4B test piece in the fiber axis direction after heat treatment. Looking at this photo, the outline of the carbon fiber is extremely clear, but the photo of No. 2B test piece, taken in exactly the same way (Fig. 5, magnification: 500
When looking at the image (magnified), it can be seen that the above outline is extremely unclear, indicating that a reaction between aluminum and carbon fibers has occurred.

[Brief explanation of the drawing]

Figure 1 is a scanning electron micrograph showing the surface of carbon fiber that has been subjected to oxidation treatment, Figure 2 is a scanning electron microscope photograph showing the surface of carbon fiber that has not been subjected to oxidation treatment, and Figure 3 is a test piece. A schematic perspective view showing
FIG. 4 is a microphotograph showing a cross section of a structural material according to the present invention, and FIG. 5 is a microphotograph showing a cross section of a conventional structural material.

Claims (1)

[Claims] 1. It is characterized by being made of a composite of an aluminum alloy containing 1 to 22% by weight of silicon and carbon fibers having a tensile modulus of elasticity in the fiber axis direction of at least 30 tons/mm ² and not subjected to surface oxidation treatment. Composite structural materials.