EP3088556B1 - Carbon fibre metal composite material - Google Patents

Description

The subject of the present invention is a carbon fiber-metal composite which is characterized by being produced by a casting process but has no adverse interfacial reactions between carbon fibers and metal.

Various methods of making fiber reinforced metals are known. Frequently, the dry fibers are infiltrated under pressure by means of a molten metal. Other methods provide fibers as short fibers in a molten metal and disperse there. Procedures in which the fibers are unwound from a supply roll and drawn into the melt, are known.

The US 3,970,136 A proposes a method in which fibers arranged in parallel in a mold are provided. The use of stacked or rolled fiber mats is also provided. These are then infiltrated with the liquid molten metal, the melt enclosing the fibers.

A disadvantage of this method is that the use of carbon fibers at the interface of the carbon fibers is expected to form metal carbides. This is detrimental to the strength of the bond between the fibers and the matrix metal.

Subject of the EP 0 634 494 A2 is a process to equip copper with a carbon fiber reinforcement. In this process, the carbon fiber reinforcement is encased in a resin matrix and then carbonized, even graphitized if necessary. Subsequently, further carbon is deposited in a CVI process to achieve a density of the carbon material varying in a given direction. Thereafter, the carbon is converted to SiC and then impregnated with the copper melt.

This procedure bypasses the problems of the US 3,970,136 A described procedure by the carbon is converted at least at the interface specifically in SiC and can form compounds to a much lesser extent with the matrix metal.

The references discussed so far deal with the bonding of fibers to a metal matrix. If an already fiber-reinforced plastic without degradation of the plastic matrix to be connected to metal, usually adhesive or the like are used.

The EP 0 938 969 B1 connects a fiber-reinforced plastic to a metal component by means of an adhesion promoter layer based on epoxy resin.

However, such adhesive bonds are unstable to a variety of substances, especially solvents. In addition, they are subject to aging, which after a certain time can lead to failure of the connection.

The EP 2 695 687 A1 describes a method to produce composite structures of a fiber composite material and a metallic material. In this method, the molded part made of fiber composite material is cast in a casting mold with metallic material. It is characteristic that the molding is provided before the casting process with an electrically insulating sheath, which prevents the direct contact between the fiber composite material and the molded part.

The DE 10 2010 050970 A1 describes a motor vehicle component in which a portion of a fiber-reinforced plastic semi-finished product is surrounded by a light metal casting. At least the portion of the fiber-reinforced plastic semifinished product, which is surrounded by the light metal casting, in this case has a thermally insulating layer.

The DE 10 2009 048709 A1 describes a composite component consisting of a metal, a fiber composite material and a connection zone, wherein the cohesive connection of the metal with the fiber composite material in the connection zone is formed by the casting with subsequent solidification of the metal.

The EP 0 416 432 A2 describes a method in which a layer of carbon fiber is applied to a metal layer. The metal layer was previously or post-formed (eg, rolled to obtain a shaft shank) to the desired shape, and the carbon fiber layer is then soaked with the matrix material and cured. Various process variants provide for the use of prepregs or carbon fiber braids. Bonding agents between the layers can also be used. This procedure is only suitable for a few technical tasks. In particular, the formability of the metal must be in the cold state, which is true only for thin metal layers.

It thus sets itself the task of proposing a carbon fiber reinforcement for metal components, which avoids in addition to a strong non-positive connection between the fiber reinforcement and metal, in particular undesirable interfacial reactions between metal and carbon fiber reinforcement.

According to the invention the object is achieved with an arrangement according to claim 1. Advantageous embodiments are disclosed in the dependent claims.

The solution according to the invention provides a carbon fiber reinforcement in a thermo-matrix matrix, preferably a phenolic resin matrix, a composite, which is completely or partially enclosed in metal. Resole resins and mixtures of phenolic and resole resins, as well as polymers from the group of carbosilanes, such as boron carbosilanes and boron carbosilazanes, are subsumed under the term "Thermodur" in addition to phenolic resins.

The intimate bond between carbon fiber reinforced matrix and metal is achieved by completely or at least partially surrounding the carbon fiber reinforced matrix (composite) with molten metal or metal in a semi-liquid, eg thixotropic, melt state. The at least partial cladding with the metal in the molten or partially liquid state leads to a contraction of the metal on cooling. Since this thermal contraction of the metal is much stronger than that of the carbon fiber reinforced matrix, it is stably enclosed. When cooling from the melting point of the metal to the ambient temperature (about 20 ° C), the occlusive effect resulting from the contraction due to the thermal shrinkage is maximized.

It will be appreciated by those skilled in the art that the carbon fiber reinforced matrix must be completely enclosed by metal, at least in a circumferential line, for the carbon fiber reinforced matrix to be securely encased and confined as the metal contracts.

As a result of this method of production, the metal penetrates in a flowable state into all naturally existing surface irregularities, thus producing a surface-fit connection in addition to the frictional connection. Since the thermo-polymers used here have comparatively high decomposition temperatures, only a slight deterioration of the matrix surface takes place, which manifests itself in increased roughness, which likewise contributes to a better connection of the metal with the carbon-fiber-reinforced matrix.

The Thermodur prevents the direct contact between carbon fiber reinforcement and metal, whereby no or only a small amount of metal carbide formation can take place.

In a preferred embodiment, the composite has a structuring on the surfaces in contact with the metal. These may preferably be corrugations or other elevations or depressions which are suitable for improving the positive connection in the metal.

As illustrated, it is desirable to use a thermodur with a high decomposition temperature. These phenolic resins are characterized by a particularly high carbon content. The carbon yield when carbonizing the thermo-type used is therefore preferably more than 50%, particularly preferably more than 70% and very particularly preferably more than 85%.

The thermo polymers are known substances from the prior art or combinations of such known thermo polymers.

For the fiber reinforcement is in principle any type of carbon fiber suitable, which can also be used in fiber-reinforced components with thermo-matrix matrix. Both Carbon fibers may be unidirectional, predominantly parallel fiber bundles, rovings, scrims or braids. Other textile forms and felt-like clusters are preferred.

In a first preferred embodiment, all carbon fibers consist of one and the same type of fiber with identical diameters. Further preferred embodiments provide several different carbon fiber types with different stiffnesses, different diameters or otherwise varying properties with each other.

The fiber volume contents of the composite are preferably above 20%, particularly preferably above 50% and very particularly preferably above 65%, but always below 100%.

Particularly preferred are carbon fibers, which are designed as individual fibers and coated with a thermo mod. Even a few carbon fibers can thus be combined into a thin fiber bundle and wrapped together with Thermodur. The flexibility of the carbon fibers or fiber bundles remains particularly preferred. In a further preferred embodiment, these coated carbon fibers or carbon fiber bundles are arranged as a collar, which is optionally fanned in the metal interior and thus achieves a particularly good penetration of the metal to be reinforced.

Further preferred are elongate carbon fiber strands having substantially unidirectional fibers parallel to the longitudinal axis of the strands in a thermo-matrix matrix, the resulting composite having a circular, oval, triangular, rectangular, or otherwise polygonal cross-section. Also band-shaped embodiments are preferred in which the composite has a pronounced rectangular cross-section with a large longitudinal extent.

In a further preferred embodiment, the composite is present as a hollow profile or in some other way cavities and undercuts having geometry. Here is a particular advantage seen as composite geometries can be processed, the known approaches are not accessible and the carbon-metal composite of the invention can have almost any composite reinforcing body and is not limited to simple carbon fiber strands or unidirectional forms.

The skilled person is aware that when using rod-shaped composite carbon fibers can end at the end face lying in the metal and are thus directly accessible to the metal. This is to be regarded as uncritical, since the lateral surface located in the metal applies the holding force and therefore metal carbide formations on the face are not critical. Preferred embodiments also cover the face with thermo-matrix matrix.

In principle, any metal or any metal alloy can be used as metal in the arrangement according to the invention. This is limited only by the fact that during production the penetrating melt should not reach the carbon fibers. Partial or complete carbonation of the matrix material of the composite is permitted. However, it is particularly preferable for this carbonization to take place only superficially.

Aluminum, magnesium or their alloys are particularly preferably used. Further preferred are copper, zinc, but also iron or steel or another metal or other metallic alloy having a melting temperature above 250 ° C. The carbon fiber-metal composite material may be formed as a structural element and / or as a functional or load introduction element. Depending on the application, the metal can be arranged at the ends of the composite or else centrally or between the ends. It is also possible to completely cover the composite with metal. The carbon fiber-metal composite material can have a plurality of composite inserts in different shapes. In addition to rod-shaped and flat (eg textile) or three-dimensional shapes are possible.

In a preferred embodiment, the composite has a metallic or ceramic coating of the composite at the interface between composite surface and metal. This is advantageous for achieving a material bond between metal and composite or for preventing a chemical attack of the metal on the matrix material or the carbon fibers of the composite. The application of these layers is carried out by methods of the prior art. Preferred are chemical or physical vapor depositions. Other known methods are suitable here.

To produce the arrangement according to the invention, the composite is preferably coated under pressure, by means of injection molding or casting, at least partially with the liquid metal. The fastest possible cooling is carried out (preferably a few seconds from casting to solidification, more preferably 1 to 2 seconds). The fiber volume content in the metal-compound composite is preferably at least 20%, more preferably at least 50%, but always less than 100%.

The composite can also be wrapped in different places with different metals. Thus, for example, at different ends of a composite strand connection or load introduction elements may be arranged, which consist of different metals.

The arrangement according to the invention is preferably used as a lightweight component for further weight reduction. It can be used in particular in vehicle construction, in the aircraft industry or other industries where high rigidity and strength can be combined with low weight. The arrangement according to the invention advantageously provides powerful carbon-fiber-reinforced metal components to a large number of application areas.

characters

• Fig. 1 schematically shows an inventive arrangement. The carbon fiber reinforced phenol resin rod 2 is disposed in a metal cylinder 1. The carbon fiber reinforced phenolic resin rod (composite) 2 has unidirectional carbon fibers 4 arranged in a phenolic resin matrix 3.
• Fig. 2 schematically shows an inventive arrangement in which 2 metal elements 1 are arranged at both ends of the carbon fiber reinforced phenolic resin rod. The opposite hatching indicates different metals.
• Fig. 3 schematically shows the arrangement of a bundle of carbon fibers 4, which are individually coated with phenolic resin 3. The bundle fans inside the metal 1 to achieve a better distribution in the metal and thus a better stop.
• Fig. 4 schematically shows an arrangement according to the invention, in which the carbon fiber-reinforced phenolic resin rod 2 is completely enclosed by metal 1.
• Fig. 5 schematically shows an arrangement in which a plurality of reinforcements made of carbon fiber reinforced phenolic resin rods 2 are arranged in a metal body 1.
• Fig. 6 schematically shows in the upper figure a section (BB) by an inventive arrangement along the longitudinal axis of the carbon-fiber-metal composite. This has a circular cross-section. As a reinforcement, the carbon fiber-metal composite contains a hollow, tubular carbon fiber-reinforced phenolic resin rod 2. For clarity, a section perpendicular to the longitudinal axis along the line AA is shown in the lower figure. The carbon fibers 4 extend unidirectionally in the interior of the composite 2, parallel to the longitudinal axis of the carbon fiber-metal composite.

embodiment

The following embodiment shows one way of carrying out the invention without limiting it to the embodiment shown.

The carbon fiber-metal composite is present as a rod-shaped component with a circular cross-section. In this case, a Phenolhatzstab with a diameter of 6 mm and a length of 350 mm at one end with a distance to this end of 20 mm over a length of 150 mm with an aluminum alloy is surrounded. The jacket thickness of this aluminum layer is 4.5 mm. As aluminum alloy AISi10 was used. The phenolic resin rod is a commercial phenolic resin having a carbonation carbon yield of 55%. The fiber volume content in the composite rod is 60% of unidirectionally arranged carbon fibers.

The carbon fiber-metal composite material was produced by means of pressureless gravity casting in a graphite / copper casting mold. The casting temperature was 670 ° C.

LIST OF REFERENCE NUMBERS

1

metal

2

carbon fiber reinforced phenolic resin rod

3

phenolic resin

4

Carbon fiber reinforcement

Claims (12)

1. Carbon fibre-metal composite material comprising at least one carbon fibre-reinforced Thermodur composite which is at least partially enclosed by a metal in the solid physical state, Thermodur comprising compounds from the group consisting of phenolic resins, resol resins, mixtures of phenolic resins and resol resins, and polymers from the group of carbosilanes, and the metal being taken from the group consisting of aluminum, magnesium, copper, zinc, iron or steel or the alloys thereof, characterised in that

   a. the carbon fibre-reinforced Thermodur composite is contained in the metal in a non-positive manner due to different thermal expansion coefficients when the metal is cooled from the melting point to the ambient temperature, and

   b. the metal penetrates into the naturally existing surface irregularities of the Thermodur composite and said composite is thus held in a positive manner,

   c. the Thermodur prevents direct contact between the carbon fibre reinforcement and the metal, and

   d. the metal is connected to the carbon fibre-reinforced matrix.
2. Carbon fibre-metal composite material according to any of the preceding claims, characterised in that the metal is copper, zinc, steel or another metal or another metal alloy having a melting temperature above 250°C.
3. Carbon fibre-metal composite material according to either of the preceding claims, characterised in that the carbon fibre-reinforced Thermodur composite is present in a rod-like shape, having a round, triangular, rectangular or polygonal cross section, as a hollow profile, or having three-dimensional geometry having an undercut shape in the composite material.
4. Carbon fibre-metal composite material according to any of the preceding claims, characterised in that the composite on the surfaces in contact with the metal is structured, preferably has corrugations or other elevations and depressions.
5. Carbon fibre-metal composite material according to any of the preceding claims, characterised in that the carbon fibre-reinforced Thermodur composite is present as a flat or three-dimensional composite.
6. Carbon fibre-metal composite material according to any of the preceding claims, characterised in that the carbon fibre-reinforced Thermodur composite is present as a collar of individual carbon fibres which are surrounded by Thermodur.
7. Carbon fibre-metal composite material according to claim 6, characterised in that the collar is fanned out inside the metal.
8. Carbon fibre-metal composite material according to any of the preceding claims, characterised in that the fibre volume content in the carbon fibre-reinforced Thermodur composite is at least 20%.
9. Carbon fibre-metal composite material according to any of the preceding claims, characterised in that the Thermodur reaches a carbon yield of more than 50% during carbonisation.
10. Carbon fibre-metal composite material according to any of the preceding claims, characterised in that the fibre volume content in the carbon fibre-metal composite material reaches at least 20%.
11. Carbon fibre-metal composite material according to any of the preceding claims, characterised in that the interface of the Thermodur is carbonised to the metal.
12. Carbon fibre-metal composite material according to any of the preceding claims, characterised in that the Thermodur is carbonised, but the liquid metal has not reached the carbon fibres of the carbon fibre-metal composite material.

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