DE4204120C1 - Carbon@ or graphite fibre-aluminium composite mfr. - by passing fibre bundle into electrolysis chamber for aluminium@ (alloy coating) and placing fibres in aluminium@ (alloy) melt to form composite - Google Patents

Abstract

Carbon or graphite fibre- Al composite is mfd. from fibres which are first coated with Al (alloy) by passing them as a bundle into an electrolysis chamber, where they are sepd. by injection of N2 gas. The fibres are then put in an Al (alloy) melt to form the composite. The coating alloy pref. has a higher m.pt. than the alloy of the composite. ADVANTAGE - Formation of inhomogeneous mixts. bewteen the fibre coating and the matrix melt is avoide

Description

The invention relates to a method for manufacturing a carbon or graphite fiber-aluminum composite, in the carbon or graphite fibers with a metal coating provided and then with an aluminum or an alumini Alloy melt processed into the composite material will.

Composites made from non-metallic fibers and a metal or alloy composite material, for example a metal matrix, in which the fibers are embedded are better than purely metallic materials mechanical material properties, especially a height modulus of elasticity and higher tensile strength.

In the manufacture of such composite materials a melt is inserted into a fiber preform in the usual way brought and cooled. The problem arises that the Melt and the fibers badly wet each other and that in addition, the melt and the fibers are chemically involved react differently, so that the reaction product becomes brittle and the Overall network is weakened. If in particular coating tion-free carbon fibers for the production of an aluminum ver are used, then it comes to the direct Contact of the uncoated carbon fibers with the aluminum for the formation of aluminum carbide, which is brittle and because its acicular crystal form contains crack initiation nuclei.

In order for such a process, in the untreated Carbon or graphite fibers with the aluminum or alumi nium alloy melt processed to the composite material be to increase the mechanical strength caused by the Formation of aluminum carbide is weakened, it is from the DE-OS 31 30 140 known, the untreated fibers with a Metal matrix, for example a matrix made of aluminum or to process an aluminum alloy, the certain Ele elements such as potassium, cesium, rubidium, francium, strontium, Barium, radium, bismuth or indium can be added.  

The carbon fibers can be processed before processing can also be provided with a metal coating. For this purpose it is, for example, from US Pat. No. 4,341,823, the US PS 40 72 516, US-PS 38 94 863 and US-PS 38 94 677 known in the manufacture of an aluminum matrix composite the carbon or graphite fibers before embedding into the aluminum matrix with a tantalum, nickel, copper, Titanium boride, titanium carbide or silicon carbide coating too Mistake.

When using sheathed in this way Fibers join in processing to composite who coated the fibers with aluminum in this way Come in contact, inhomogeneous mixtures between the jacket and the matrix material and in particular alloy formations as well as in some cases very brittle intermetallic ver bonds that reflect the properties of the overall network affect. In addition, the specific weight increases of the overall network because of compared to aluminum and to the carbon fibers relatively heavy coating material lien.

The object underlying the invention is therefore in the procedure of the type mentioned above to design that the appearance of inhomogeneous mixtures between the material of the fiber covering and the aluminum or the aluminum alloy melt during processing to the composite is avoided.

According to the invention, this object is achieved by that the metal coating electrolytically made of aluminum or an aluminum alloy is formed.

Particularly preferred developments and refinements gene of the inventive method are the subject of Claims 2 to 5.

The following is based on the associated drawing particularly preferred embodiment of the invention described in more detail.

The single figure shows a device schematically to carry out the method according to the invention.

With the device shown in the drawing, fiber bundles 1 are coated electrolytically with aluminum, which he follows by means of a known electrolyte, which consists of triethylene aluminum, potassium fluoride and toluene. The electrolyte is used in the absence of air at about 100 ° C. This requires a system in which the actual electrolysis is carried out free of oxygen and water. At the same time, the fiber bundle 1 must be separated into the individual fibers during the electrolysis so that a largely uniform coating of all individual fibers is possible.

The carbon fibers are spooled as a fiber bundle 1 from supply spools and drawn off and pulled through a synchronously working transport device with several transport rollers 2 , 6 , 12 synchronously through the entire device, the fiber bundle being initially relaxed by turning back the front rollers at the beginning and between the individual transport rollers 2 , to which it is pressed, can sag loosely as required.

After the fiber bundle 1 has been pulled off, it is dried in a drying device 3 and rolled over transport 12 through a washing bath 4 . The fiber bundle 1 is then conveyed through an airtight airlock 5 filled with toluene. This lock 5 prevents the ingress of air and moisture into the closed electrolysis device. The lock 5 is made of metal and at the same time serves for the electrical contacting of the fiber bundle 1 , which passes through the electro lysis chamber 8 as the cathode.

There is no electrical connection between the airlock 5 and the electrolysis chamber 8 , which is made of stainless steel or glass. The actual electrolysis chamber 8 is designed in the form of a vertical tubular reactor through which the fiber bundle 1 is guided from bottom to top. The fiber bundle 1 is separated into the individual fibers by nitrogen, which is introduced into the electrolysis chamber 8 from below via an inlet 7 .

The introduction of nitrogen is preferably carried out so that a nitrogen bubble rises, the electro lysis chamber 8 is preferably formed so that the nitrogen bubble occupies the entire cross section. By introducing nitrogen, fiber bundles consisting of up to 36,000 individual fibers with a thickness of approximately 0.008 mm can be isolated and evenly coated with an aluminum layer whose thickness is in the µm range.

The electrolysis takes place at temperatures between 80 ° and 105 ° C and at current densities between 0.5 and 2.5 A / dm ² . The residence time of the fiber bundle 1 in the electrolysis chamber 8 is between 1 and 60 minutes, depending on the desired layer thickness. An aluminum alloy serves as the anode material.

The diameter of the tubular electrolysis chamber 8 should be as small as possible regardless of its dimensioning with regard to the thickness of the rising nitrogen bubble because of the high specific resistance of the electrolyte, the anode 9 being attached to the inner wall of the electrolysis chamber 8 . The diameter of the electrolysis chamber 8 should continue to be so large that the individual fibers of the fiber bundle do not come into direct contact with the anode 9 .

The aluminum layer formed on the carbon fibers is equally opaque and of the same thickness and chemically purely. The coating is on all fibers within the Fiber bundle largely evenly, the individual coated carbon fibers lead freely movable against each other ben, so that in the subsequent processing, for example the Embedding in an aluminum matrix by infiltration with liquid aluminum, the aluminum freely between the individual coated carbon fibers can get.

After completion of the electrolysis process, in which an aluminum layer grows on the fibers of the fiber bundle 1 at a speed of 1 μm / min, the fiber bundle 1 is transported via transport rollers 6 , which simultaneously represent contact points, into an airtight washer 10 , the latter of which Washing solution is supplied via an inlet 11 . The coated fiber bundle 1 is washed several times with hot and cold toluene in order to remove electrolyte residues. The toluene used for washing is cleaned again in a connected facility, the electrolyte residues are collected separately.

After the last washing process, the fiber bundle 1 is conveyed out of the system by an outlet airlock, which corresponds to the function and structure of the inlet airlock 5 and if it is filled with toluene.

After being transported through a drying stage, this becomes Post-treated fiber bundles. This thermal after Treatment is similar to that of a previous surgery pretreatment at temperatures between 400 ° and 650 ° C in the absence of oxygen.

To achieve a smoothing of the fiber bundle, you can the fiber bundle during transport through the drying stage by another with isopropanol or a comparable one Wash bath filled with washing solution. In this bathroom ultrasonic cleaning may also be carried out, to remove loose fiber parts and deposits.

The carbon coated in this way with aluminum or graphite fibers are then covered with aluminum or an aluminum alloy to the desired composite processed. In particular, the fibers are made into one Aluminum or an aluminum alloy existing matrix embedded around a carbon or graphite fiber aluminum Manufacture matrix composite.

When inserting the aluminum matrix into the preform with aluminum coated fibers it should be ensured that then when the melt introduced is too hot and not is cooled sufficiently quickly, the aluminum layer on the fibers melt down to the surface of the fibers, so that carbide formation occurs again.

To avoid this, there is the option of a To use melt that is not too hot and so fast introduced and cooled that the aluminum layer on the fibers only melt on the surface. To do this, the Aluminum layer on the fibers sufficiently strong and if possible be evenly thick, with the preform temperature below the Aluminum melting temperature should be.  

The infiltration process can continue as quickly be carried out that due to the good wetting of the Fibers have little time for carbide formation.

Another way to melt the over avoid the fibers and thus carbide formation, consists of adding an aluminum alloy to the matrix use a lower melting temperature than that Has aluminum alloy that is used for fiber coating becomes.

In addition to the production of a coal fa ser- or graphite fiber-aluminum matrix composite material, where the with aluminum or an aluminum alloy coated fibers in a matrix of aluminum or one Aluminum alloy can be embedded using coated carbon or graphite fibers also macro scopic aluminum composite materials, for example made of changing fiber and aluminum or aluminum alloy layers are formed, likewise the formation inhomogeneous mixtures between the material of the fiber trains and the material of the aluminum layers can be avoided nen.

Claims (5)

1. A method for producing a carbon or graphite fiber-aluminum composite material, in which carbon or graphite fibers are provided with a metal coating and then processed with an aluminum or an aluminum alloy melt to the composite material, characterized in that the metal coating is electrolytic is formed from aluminum or an aluminum alloy. 2. The method according to claim 1, characterized in that that when applying the fiber coating a coal or Gra phit fiber bundle from bottom to top by a vertical Electrolysis chamber is guided and the fibers of the fiber bund dels are isolated in that at the lower part of the Electrolysis chamber nitrogen is introduced. 3. The method according to claim 2, characterized in that that a nitrogen rising in the electrolysis chamber bubble is formed. 4. The method according to claim 3, characterized in that the nitrogen bubble the full horizontal cross section the electrolysis chamber occupies. 5. The method according to any one of the preceding claims, characterized in that for the fiber coating an aluminum nium alloy is used, whose melting temperature is higher than the melting temperature of the aluminum alloy, with which processes the fibers into a composite.