JPS6354054B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for manufacturing a linear composite material, and more particularly, to a method for manufacturing a linear composite material using carbon fiber as a reinforcing fiber and aluminum or an aluminum alloy as a matrix. BACKGROUND OF THE INVENTION In recent years, composite materials that use carbon fiber as a reinforcing fiber and metal as a matrix have been attracting attention in various fields. Among these, those using aluminum or aluminum alloy as a matrix have relatively excellent specific strength and specific rigidity, and are therefore attracting particular interest in fields that require weight reduction. There are various methods for manufacturing the above-mentioned composite materials, one of which is cutting a linear composite material of carbon fiber and aluminum or its alloy into desired lengths, collecting them together and hot pressing them,
There is a way to roll press. In that case, it is necessary to prepare the linear composite material prior to hot pressing or roll pressing. In this specification, unless otherwise specified, a linear composite material that is a so-called molding material will be referred to as a linear composite material, and a composite material obtained by hot pressing or roll pressing the linear composite material will be referred to as a linear composite material. For convenience, we will simply call it a composite material to distinguish between the two. Now, there are various methods of manufacturing such linear composite materials, one of which is the
As described in Publication No. 59-12733 and others,
The carbon fiber multifilament is subjected to a chemical vapor deposition process to coat each filament with a substance that wets well with molten aluminum or aluminum alloy, and then the coated carbon fiber multifilament is immersed in the molten metal to deposit the molten metal between the filaments. There is a method in which the molten metal is impregnated with water and then pulled out to solidify the molten metal.
This method is very suitable for manufacturing linear composite materials because the process is continuous. However, when measuring the tensile strength in the fiber axis direction of a linear composite material obtained by such a method, it is sometimes found to be extremely low. The reason for this is thought to be that carbon fibers and aluminum react to form a large amount of brittle aluminum carbide at the interface between carbon fibers and matrix aluminum or aluminum alloy. In other words, aluminum carbide is easily hydrolyzed even at room temperature, so if it is produced in large quantities, the linear composite material becomes extremely chemically unstable. Since the strength of the carbon fiber itself also decreases, it is estimated that these factors act synergistically to bring about a significant decrease in strength. However, the formation of aluminum carbide can be prevented to some extent by increasing the coating thickness of the so-called wettable substance considerably. However, forming thick coatings by chemical vapor deposition significantly lengthens the manufacturing time and increases manufacturing costs. Furthermore, the method described in Japanese Patent Publication No. 59-12733 involves coating with titanium boride or a mixture of titanium boride and titanium carbide; Since it is formed by simultaneously reducing a mixture with a boron compound on the surface of carbon fibers, it is not only very difficult to control the ratio of the amount of titanium boride and titanium carbide produced, but also because titanium carbide is not produced. There is a problem in that the carbon on the surface of the carbon fiber is consumed and the strength of the carbon fiber is greatly reduced. On the other hand, JP-A-59-1652 describes that carbon fibers should be coated with titanium boride, and JP-A-52-28433 describes that they should be coated with titanium. However, there is still the problem that the strength of carbon fibers is reduced due to the production of titanium carbide, and that carbon fibers are difficult to wet with molten metal. Problems to be Solved by the Invention The inventor of the present invention has discovered that in the conventional method described above, when a specific carbon fiber and a specific coating material are used and impregnation with molten metal is performed under specific conditions,
It has been discovered that it is possible to obtain a linear composite material that generates almost no aluminum carbide and has extremely high tensile strength in the fiber axis direction. That is, an object of the present invention is to provide a method for manufacturing a linear composite material having high tensile strength in the fiber axis direction, using carbon fiber as a reinforcing fiber and aluminum or an alloy thereof as a matrix. Means for Solving the Problems This invention to achieve the above object uses a carbon fiber multifilament having a tensile modulus of elasticity in the fiber axis direction of 38 tons/mm ² or more and not subjected to surface oxidation treatment. Each filament is coated first with boron and then with titanium through a chemical vapor deposition process, after which the coated carbon fiber multifilament is immersed in molten aluminum or aluminum alloy and the molten metal is impregnated between the filaments. When the molten metal-impregnated carbon fiber multifilament is pulled up from the molten metal and the molten metal is solidified, the molten metal impregnation is performed at a temperature of T.
℃, and the immersion time of the multifilament of coated carbon fiber is t minutes, the method is characterized by a method for manufacturing a linear composite material carried out within a range that satisfies the following formula: 0.03T+0.6t≦22t<3. To explain this invention in more detail, in this invention, preferably polyacrylonitrile fiber (PAN fiber) is used as the reinforcing carbon fiber.
As the raw material fiber (precursor), so-called graphitized carbon fiber having a tensile modulus in the fiber axis direction (hereinafter referred to as tensile modulus) of 38 tons/mm ² or more is used. When such carbon fibers are impregnated with molten aluminum or aluminum alloy under specific conditions, they react extremely little with aluminum and hardly produce aluminum carbide. That is, the carbon fiber has a structural unit consisting of an elongated ribbon-shaped 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 seen as the ultimate aromatic compound. Several of them stack up to form graphite crystal regions, and they also branch out to form fine particles. It forms a fibrillar structure. In other words, the surface is covered with carbon atoms in the network plane of the graphite crystal, but those with a tensile modulus of 38 tons/mm ² or more have an extremely high degree of orientation of the ribbon-like fragments, and the surface The arrangement of carbon atoms in the network plane is orderly and the number of peripheral carbon atoms is small. In other words, it is considered to be more inert, and therefore the reaction with aluminum is suppressed. When carbon fibers such as those mentioned above are analyzed using laser Raman spectroscopy, it is found that a band ( ^hereinafter referred to as _A This may be because the A ₁ g symmetrical vibration (forbidden transition) of the graphite structure shifts to an allowed transition due to structural disorder at the crystal edge, or it may be due to a difference in the chemical structure around the benzene ring. It is said that 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 It is characterized by being less than 0.5. Laser Raman spectroscopy refers to the Raman effect of laser light, that is, when a material is irradiated with laser light and scattered, light whose wavelength has changed by an amount specific to that material is emitted among the scattered light. This phenomenon is used to obtain information about the molecular structure of a substance. Therefore, in this invention, such analysis is carried out using a laser Raman spectrophotometer JRS-400D manufactured by JEOL Ltd., with one or several carbon fiber multifilaments attached to its holder, and placed in a nitrogen atmosphere. Apply light from an argon laser (wavelength: 5145 Å), collect the Raman scattered light, separate it using a double grating, receive the spectrum with a photomultiplier tube, record it on a chart, and read the B/A ratio. I'm going by this. Now, as mentioned above, the carbon fiber needs to have a tensile modulus of 38 tons/mm ² or more, but at the same time, it needs to be free from surface oxidation treatment. That is, regardless of whether it is linear or not, in general, in composite materials such as the one of the present invention, carbon fibers are subjected to surface oxidation treatment such as electrolytic oxidation treatment in order to improve adhesion at the interface with the matrix. It is common to have an uneven surface. Therefore, when the surface has irregularities, a state generally called an anchor effect, as if the matrix is anchored to the irregularities, is created, and it is thought that the adhesion at the interface is improved. However, the present invention uses carbon fibers that have not been subjected to such surface oxidation treatment and have relatively smooth surfaces. In this invention, the carbon fibers described above are used in the form of a multifilament, that is, a continuous fiber bundle. Although it is possible to use it in monofilament, i.e. single fiber form, it is economically
Almost no profit. Next, regarding the so-called matrix, aluminum or an aluminum alloy is used in this invention. Examples of aluminum alloys include aluminum-silicon alloy, aluminum-copper alloy, aluminum-magnesium alloy, and aluminum-silicon alloy.
Silicon-magnesium alloy, aluminum-copper
Zinc alloy, aluminum-manganese alloy, etc. can be used. In this invention, first, using chemical vapor deposition, each filament that makes up the multifilament, that is, each carbon fiber, is coated with boron as a so-called base, and then the boron coating is applied. A titanium coating is formed thereon, independent of the boron coating. Here, the boron coating suppresses the formation of titanium carbide, which was a drawback of the conventional method mentioned above, and prevents deterioration of the carbon fiber.
Moreover, the adhesion between the titanium coating formed thereon and the carbon fibers is improved. In addition, titanium coating is
Improves the wettability of carbon fiber and creates a bond between filaments.
To facilitate and uniformly impregnate the molten aluminum or aluminum alloy in the impregnation step described below. That is, the improvement in wettability is due to the titanium coating. The thickness of the boron coating or titanium coating may be about 100 to 1000 Å. The boron or titanium coating by chemical vapor deposition is preferably applied as follows. That is, while flowing a mixed vapor consisting of boron trichloride, boron tribromide, or boron trifluoride, zinc, and argon into a reaction tube, a carbon fiber multifilament is passed through the reaction tube, and 0.5 Expose for ~5 minutes. Then, the boron compound is reduced by zinc to zinc chloride, zinc boride, or zinc fluoride, and each filament constituting the multifilament is coated with boron. The reaction temperature is about 650 to 750°C. Alternatively, the boron compound may be reduced with hydrogen using a vapor mixture of boron trichloride or boron tribromide and hydrogen. The reaction temperature in this case is
The temperature is about 900-1300℃. On the other hand, the titanium coating is also applied in the same manner as the boron coating. That is, a mixed vapor of titanium tetrachloride, zinc, and argon is used to reduce titanium tetrachloride with zinc. It may be reduced with hydrogen. In this invention, next, a titanium-coated carbon fiber multifilament is passed through a molten metal of aluminum or its alloy, and the molten metal is impregnated between the filaments. The temperature of the molten metal at this time is kept at or above the solidification start temperature of aluminum or aluminum alloy, but is preferably as low as possible so as not to significantly deteriorate the carbon fibers. However, in terms of easy temperature control,
It is preferable to set the temperature at least 5°C higher than the solidification start point temperature. Therefore, this impregnation step satisfies the following equation, where the temperature of the molten metal is T°C and the immersion time of the titanium-coated carbon fiber multifilament is t minutes, 0.03T+0.6t≦22...t<3... It needs to be done within a range. That is, as shown in the Examples described below, if these formulas are not satisfied at the same time, a linear composite material with high tensile strength in the fiber axis direction (hereinafter referred to as tensile strength) cannot be obtained. Next, the present invention will be explained in more detail based on examples. Example 1 Carbon fibers with a tensile modulus of about 40 tons/mm ² , a tensile strength of about 280 Kg/mm ² , and a B/A ratio of about 0.4, without surface oxidation treatment, were made into a multifilament ( Number of filaments: 3000), boron trichloride 6.3% by weight, zinc 6.6% by weight, argon 87.1%
Each filament was coated with boron by applying a vapor mixture of about 680°C for about 1 minute. The thickness of the boron coating was approximately 100 Å. Next, a steam mixture at about 680°C consisting of 3.2% by weight of titanium tetrachloride, 2.5% by weight of zinc, and 94.3% by weight of argon was applied to the multifilament of boron-coated carbon fiber for about 1 minute, so that a thick layer was formed on the boron coating. A titanium coating of approximately 100 Å was applied. Next, the multifilament of titanium-coated carbon fiber is passed through a molten aluminum alloy (JIS A6061) whose solidification starting point temperature is approximately 658°C, and pulled up to solidify the molten metal, so that the volume content of carbon fiber is approximately 50°C. % linear composite material was obtained. At this time, the temperature of the molten metal and the immersion time of the titanium-coated carbon fiber multifilament were varied to obtain a total of eight types of linear composite materials. Next, for the above eight types of linear composite materials, the tensile strength and the weight of carbon consumed in the production of aluminum carbide relative to the weight of carbon fiber were determined. The measurement results are shown in the table. The tensile strength was measured using a universal testing machine IM500 manufactured by Shimadzu Corporation. Further, the carbon consumption was calculated by utilizing the fact that aluminum and aluminum carbide are hydrolyzed to generate hydrogen and methane as described below, and by quantifying the amount of methane using a gas chromatograph. Al ₄ C ₃ +12H ₂ O →3CH ₄ +4Al(OH) ₃ Al+3H ₂ O →3/2・H ₂ +Al(OH) ₃

[Table] From the above table, the linear composite materials No. 1 to 5 that satisfy all the conditions stipulated by this invention are the linear composite materials No. 6 that satisfy the above formula but do not satisfy the formula.
It can be seen that the tensile strength is significantly higher than that of No. 8. That is, in Nos. 6 to 8, the amount of carbon consumed, that is, the amount of aluminum carbide produced was very large, and this is thought to be the reason for the decrease in tensile strength. For comparison, when manufacturing the No. 1 linear composite material that showed the highest tensile strength, the immersion time in the molten metal was set to 3 minutes, and the tensile strength of the resulting linear composite material was approximately 95 kg/ mm ² and decreased significantly. In addition, in manufacturing the No. 1 linear composite material, carbon fibers are treated with surface oxidation treatment, although their tensile modulus and tensile strength are about 40 tons/mm ² and 280 kg/mm ² , respectively. Applied (B/A ratio: approx.
0.6), the tensile strength of the obtained linear composite material was only about 78 Kg/mm ² . Carbon consumption increased to approximately 0.3% by weight. Furthermore, for comparison, in manufacturing the No. 1 linear composite material, carbon fibers with a tensile modulus of approximately 32
ton/mm ² , tensile strength of approximately 360 Kg/mm ² , and is not subjected to surface oxidation treatment (B/A ratio: approximately
0.8), the tensile strength of the obtained linear composite material was about 80Kg/ ^mm2 , and the carbon consumption was about 0.3
It was in weight%. Furthermore, although no surface treatment was applied, the tensile modulus of elasticity was approximately 24 tons/mm ² and the tensile strength was approximately 360 Kg/mm ² , and the tensile strength of the resulting linear composite material was only slightly Approximately 30Kg/mm ²
Moreover, carbon consumption increased significantly to about 2% by weight. Example 2 In Example 1 above, the molten metal was changed to a molten aluminum-silicon alloy (JIS AC4C) whose solidification starting point temperature was approximately 615°C (temperature: approximately 630°C),
Two types of linear composite materials were obtained according to the method of the invention, with soaking times of 1 minute and 2.5 minutes. Example 1 for these two types of linear composite materials
When a similar test was conducted, the tensile strength was approximately 152 Kg/mm ² (carbon consumption 0.002% by weight) when the immersion time was 1 minute, and the tensile strength was approximately 140 kg/mm 2 when the immersion time was 2.5 minutes.
Kg/mm ² (carbon consumption 0.006% by weight), all showed high values. Example 3 In Example 2 above, when manufacturing a product with a soaking time of 2.5 minutes, the tensile modulus was approximately 46 tons/
When using carbon fiber (number of filaments: 6000, B/A ratio: approximately 0.3), which has a tensile strength of approximately 240 Kg/mm ² and has not been subjected to surface oxidation treatment, it has a tensile ^strength of approximately 130 Kg/mm A linear composite material with a high tensile strength of ² was obtained. The carbon consumption in this linear composite material was approximately 0.001% by weight. For comparison, we changed the carbon fiber to one that had undergone surface oxidation treatment (B/A ratio: approximately 0.6), although the tensile modulus and tensile strength remained the same.
The tensile strength decreased significantly to approximately 60Kg/mm ² . Also,
Carbon consumption increased to approximately 0.3% by weight. Comparative Example 1 Using the same carbon fiber as in Example 1, it was heated for 1 minute in a mixed vapor at 680°C containing 1.2% by weight of boron trichloride, 5.1% by weight of titanium tetrachloride, and the remainder being argon gas. processing, each filament has a thickness
A 300 Å titanium boride coating was formed. Next, in the same manner as in Example 1, five types of linear composite materials having an aluminum alloy as a matrix were manufactured and evaluated in the same manner as in Example 1. Table 2 shows the evaluation results.
Shown below.

[Table] From the above table, although the carbon consumption of Comparative Example 1 is almost the same as that of Example 1, the tensile strength is significantly decreased. The reason for this is that in Comparative Example 1, titanium carbide is generated in the coating process, and the carbon on the surface of the carbon fiber is consumed, resulting in a decrease in the strength of the carbon fiber. Comparative Example 2 The same carbon fiber as in Example 1 was heated at 1050°C for 1 minute in titanium tetrachloride vapor in which hydrogen was bubbled at 100 c.c. per minute as a carrier gas and methane gas at 15 c.c. per minute. The filaments were treated to form a 1000 Å thick titanium carbide coating on each filament. Next, in the same manner as in Example 1, five types of linear composite materials having an aluminum alloy as a matrix were manufactured and evaluated in the same manner as in Example 1. Table 3 shows the evaluation results.
Shown below.

[Table] As is clear from the above table, when coating titanium carbide, the coated carbon fiber is immersed in molten metal at 700°C for 30 minutes.
Linear composites are only obtained if soaked for minutes. Moreover, even in that case, the tensile strength is only 58 Kg/mm ² . This is because not only does the above-described strength deterioration of the carbon fiber occur in the coating process, but also sufficient wettability cannot be obtained with titanium carbide coating. Comparative Example 3 The same carbon fiber as in Example 1 was used, and titanium tetrachloride was 3.2% by weight, zinc was 2.5% by weight,
Each filament was treated with a 1000 Å thick titanium coating by treatment in a mixed vapor at 680° C. with the remainder being argon gas for 1 minute. Next, in the same manner as in Example 1, five types of linear composite materials having an aluminum alloy as a matrix were manufactured and evaluated in the same manner as in Example 1. Table 4 shows the evaluation results.
Shown below.

[Table] From the above table, it can be seen that although a linear composite material is obtained when the immersion time in the molten metal is 1 minute, the tensile strength is considerably lower than that of Example 1.
This is because the strength of the carbon fiber is reduced due to the formation of titanium carbide during the coating process. Further, when the immersion time reaches 2 minutes, a linear composite material can no longer be obtained. This is presumed to be because the coated titanium dissolves into the molten metal as the immersion time increases. Comparative Example 4 The same carbon fiber as in Example 1 was used, and boron trichloride was 6.3% by weight, zinc was 6.6% by weight,
Each filament was treated with a 100 Å thick boron coating by treatment in a mixed vapor at 680° C. with the remainder being argon gas for 1 minute. Next, the coated carbon fibers were immersed in a molten aluminum alloy and pulled up in the same manner as in Example 1, but the carbon fibers were not wetted by the molten metal and no linear composite material was obtained. Effects of the Invention The method of the present invention uses carbon that has extremely little reaction with aluminum, is difficult to generate aluminum carbide, has a tensile modulus of elasticity in the fiber axis direction of 38 tons/mm ² or more, and has not been subjected to surface oxidation treatment. In addition to using fibers, we form a boron coating as a so-called base that suppresses the formation of titanium carbide and prevents deterioration of carbon fibers, and also improves the adhesion between the titanium coating formed on it and the carbon fibers. The impregnation of a carbon fiber multifilament with a molten metal onto which titanium as a wetting substance is coated is given by the formula 0.03T+0.6t≦22 t<3, where the temperature of the molten metal is T°C and the immersion time in the molten metal is t minutes. Since this is carried out under conditions that satisfy the above conditions, it is possible to obtain a linear composite material with extremely high tensile strength, as shown in the examples.

Claims (1)

[Claims] 1. A carbon fiber multifilament having a tensile modulus of elasticity in the fiber axis direction of 38 tons/mm ² or more and not subjected to surface oxidation treatment is passed through a chemical vapor deposition process, and each filament is After first coating with boron and then coating with titanium, the coated carbon fiber multifilament is immersed in molten aluminum or aluminum alloy to impregnate between the filaments, and the molten metal-impregnated carbon fiber multifilament is When the molten metal is pulled up from the molten metal and solidified, the molten metal impregnation is performed using the formula: 0.03T+0.6t≦22 t< 3. A method for producing a linear composite material, characterized in that the method is carried out within a range that satisfies the following.