WO2005052199A1

WO2005052199A1 - Method for producing a component provided with a metal matrix and a fibre or particle reinforcement

Info

Publication number: WO2005052199A1
Application number: PCT/EP2003/012352
Authority: WO
Inventors: Rainer Gadow; Marcus Speicher; Konstantin Von Niessen; Peter Unseld; Günther MESSMER; Klaus Siegert
Original assignee: Universität Stuttgart Center Of Competence For Casting & Thixoforging
Priority date: 2003-11-05
Filing date: 2003-11-05
Publication date: 2005-06-09
Also published as: AU2003282089A1; ATE402271T1; US20060021728A1; DE50310214D1; EP1685263B1; EP1685263A1

Abstract

The invention relates to a method for producing a component made of a composite material (MMC) comprising a metallic matrix forming material which is reinforced with incorporated fibres or particles consisting in producing a semifinished material (20) containing fibres (16) or particles and a metallic matrix material (24). Afterwards, a shaping is carried out by thixomoulding in a tool whose temperature is higher than a solidus temperature and lower than a liquidus temperature of said metallic matrix material.

Description

Process for the production of a component with a metallic matrix and reinforcement by fibers or particles

The invention relates to a method for producing a component from a composite material (MMC) with a metallic matrix material which is reinforced by embedded fibers or particles.

The invention further relates to such a composite material and the use of such a composite material. The need to save primary energy sources and reduce emissions makes the light metal material of increasing importance in automobile construction and in aerospace technology. The use of MMC materials (Metal Matrix Composites) or the incorporation of high-strength reinforcing fibers can increase the high-temperature strength and stiffness of these materials, which are insufficient for many applications. In addition, the manufacturing costs are to be reduced through short manufacturing cycles and the manufacture of components close to final dimensions ("net shape for ing").

In the prior art, the incorporation of fibrous reinforcement components leads to a significant increase in manufacturing costs. In addition, the inadequate resistance of the fiber types in question to the chemically aggressive metal melts in conventional manufacturing processes from the liquid phase prevents the optimal use of fiber strength. The conventional production routes from the liquid phase for MMC materials are mostly pressure infiltration processes in which the melt is pressed into the porous fiber preform by means of a piston to overcome the capillary resistance ("squeeze casting"). This pressure casting process can also be carried out under vacuum ("Vacural- Procedure "). In order to realize complex geometries and to reduce the mechanical load on this fiber-containing preform during the infiltration process, it can be immersed in the melt in an evacuated autoclave and then pressurized with gas pressure ("gas pressure process"). In addition, of course, there is of course basically the powder-metallurgical shaping route by sintering and subsequent pressing , possibly known by hot pressing or hot isostatic pressing (HIP). However, processes are very time-consuming and costly and do not allow net-shape impressions of complex component geometries. In addition, considerable residual porosities usually occur in the sintering process, which can adversely affect the properties.

In the production of fiber-reinforced light metals based on aluminum, melt metallurgical and liquid phase impregnations as well as die casting techniques are generally used. The long reaction and contact times of molten metallic phases with the reinforcing fibers and the molding tools or surfaces result in undesirable damage. For example, dissolution and precipitation processes as well as chemical interface reactions occur. This leads to difficulties due to sticking when separating from the mold, due to heat transfer-related microstructures with an overall very complex process control. This necessitates complex plant technology which works with comparatively long cycle times for the shaping. In all cases, liquid, chemically highly active light metal melts (usually aluminum) are used, so that additional protection of the fibers used is essential with a suitable protective layer. Particularly when aluminum is to be reinforced with carbon fibers, the formation of an aluminum carbide layer (Al ₃ C ₄ ) at the fiber-matrix interface is undesirable, since this carbide phase, due to its pronounced susceptibility to brittle fracture and its lack of corrosion resistance, causes the bond to fail prematurely. A fiber coating can basically be dispensed with if the light metal matrix is joined to the reinforcing component in the solid phase (“diffusion bonding”) laminates of fiber fabrics and metal sheets are processed using the hot press process. The economic viability of this process is, however, questioned by the very high cycle times. A summary of the common processes for the production of fiber-reinforced aluminum composite materials can be found in Talat Lecture 1402, Froyne, L., Verlinden, B., University of Leuven (Belgium), 1994, EAA European Aluminum Association.

It is therefore an object of the invention to enable the production of a composite material with a metallic matrix which is reinforced by embedded fibers or particles (MMC), in which the embedded fibers or particles are damaged as little as possible by a metal melt during the manufacturing process. The process is intended to enable the most cost-effective and energy-saving production of components that are shaped close to production (net-shape molding).

This object is achieved by a method for producing a component from a composite material (MMC) with a metallic matrix material, which is reinforced by embedded fibers or particles, comprising the following steps:

Manufacture of a semi-finished product in which the fibers or particles and the metallic matrix material are contained and

Thixoforming of the semi-finished product in a tool at a temperature above the solidus temperature and below the liquidus temperature of the metallic matrix material. The Thixou molding process is basically known in the prior art for forming special alloys, in particular aluminum-based or copper-based, with which a two-phase or multi-phase region is used within a specially selected temperature range above the solidus line and below the liquidus line, in which a liquid phase share is present. With this hot forming in the partially solidified state, a pronounced solidification interval of the alloy to be formed is required, ie a temperature range in which both solid and liquid phase components are present side by side (cf. FIG. 1). In this temperature range, the application of pressure in a tool enables a near-net-shape forming to be achieved (thixotropy = shear rate-removing behavior). Ideally one is; Suitable alloy with thixoidal forming has a globolithic structure that forms a solid phase skeleton and thus ensures good handling of the heated semi-finished product when it is inserted into a press mold. This solid phase skeleton breaks open under shear loads and thus reduces the yield stress, so that only short flow distances result in the tool and a near-net-shape deformation can be achieved.

By using the Thixou molding, which is generally known for light metal alloys, for the production of composite materials that are reinforced by embedded fibers or particles, significantly improved properties can be achieved.

A first advantage is that the temperature is significantly lower than the use of melt processes or melt infiltration processes and the significantly shortened molding exercise time. In this way, it is possible to dispense with the coating of the embedded fibers or particles, since the embedded fibers are hardly damaged by the only short melting process at a relatively low temperature.

Compared to squeeze casting, significantly shorter infiltration paths of the melt can be achieved through an alternating layer structure of the semi-finished product. As a result of the shortened process times and the relatively short contact of the required tool with the melt, the tool life is significantly improved, which leads to considerable cost savings compared to squeeze casting, for example. Fast process times in the millisecond range can be achieved compared to several seconds in squeeze casting and several hours in diffusion bonding. Furthermore, the shape in a temperature range below the squeeze casting (about 100 K lower) achieves an appropriate amount of energy savings. The reduced proportion of liquid phase during shaping enables a shortening of the solidification time in the tool and thus a reduction in the cycle time. Due to a suitable preconditioning of the matrix material, the entire melting shop (melting furnace, alloy furnace, degassing, alloy control, casting furnace) can be dispensed with. Furthermore, due to the modified tool concept, there is significantly less recycle material that has to be melted down again before being reintroduced into the production process.

Due to the lack of air pockets in thixoforming, especially in thixo forging, it is also possible to use the To increase the strength of the matrix material by means of a suitable heat treatment, in particular by solution annealing and aging.

With thixo forging, it is also possible to join the component with other components.

In the context of this application, the term “semifinished product” is understood to mean the preform, which is subsequently formed into a component by thixoui-molding within the tool.

This semifinished product can be a prepreg which consists of a single or preferably a plurality of laminate layers, or a preform which is produced from a granulate on the basis of a pressing process. In the context of this application, semi-finished products are therefore always understood to be the generic term, which includes a prepreg and other preforms prepared in some other way, which are manufactured within the tool by thixoforming to form the component.

According to a first method variant, a prepreg is produced by laminating layers of fiber composites and matrix material in the form of sheets.

In this particularly simple method variant, layers of fiber composites are preferably joined alternately with the suitable sheets by lamination in order to provide the desired shape of the semi-finished product. As a result of the thixoforming, the provision of the matrix material is sufficient: ials in the form of sheets, sufficiently short flow paths and yet to ensure uniform wetting of the enclosed fibers or particles.

In an advantageous development of this process variant, the sheets are provided in the form of cold-rolled sheets. This results in a fine-grained recrystallization with a globular structure due to the dislocation density induced by the cold rolling process, which has a favorable effect on the resulting properties of the component.

According to a further method variant of the invention, a fiber composite is coated with a metallic matrix material.

With such a procedure, improved homogeneity can be achieved compared to the use of individual layers made of fiber composites and matrix material.

In an expedient development of this embodiment, several coated fiber composites are laminated to form a prepreg.

In this way, a near-net-shape geometry can be approximated and targeted, directional property characteristics can be achieved.

According to a first process variant, the fiber composite can be coated with the metallic matrix material by a screen printing process.

Another method variant for coating a fiber composite with the metallic matrix material consists in an application by means of electrostatic charging. Another method variant for coating a fiber composite with metallic matrix material generally consists of an electrophoretic deposition (EPD) from an aqueous suspension with the support of an electric field.

Here, the fiber structure to be coated is switched to be electrically conductive as an electrode, and the charge-bearing metal powder particles are driven by the electric field onto the fiber or fabric surface as a uniform layer. Such a procedure is particularly suitable for fiber composites that are inherently electrically conductive, such as C fibers. However, other fibers that are not readily electrically conductive can also be processed if suitable intermediate layers are used.

With such a method, metal particles are preferably used which have a grain size with a diameter between 10 n and 100 μm, preferably with sizes between 100 nm and 10 μm. The use of surface active liquid or dissolved auxiliaries enables targeted charge distributions of the solid particles in the suspension to be set, which allow concentration and field strength-dependent mass transport for layer separation. In this way, the properties of the component subsequently produced from this can be varied within wide limits and adapted to the respective requirements.

According to a further variant of the invention, a fiber composite is coated with the metallic matrix material by thermal spraying. Basically, atmospheric plasma spraying (APS), arc wire spraying, wire flame spraying or high-speed flame spraying are possible. However, the thermal spraying is preferably carried out by electric arc wire spraying or powder plasma spraying, in particular by atmospheric plasma spraying.

Fiber composites with _. are provided with thermally sprayed metal layers, offer the advantage of a finer-grained structure compared to the use of alternating layers of sheet metal and fiber composites. While the grain sizes of thixotropically formable Al-Si sheets are in the range of 2 to 20 μm, the dimensions of the individual phases in the thermally sprayed AlSi layer structure are in the submicrometer range due to the high cooling rate when applying layers. This enables improved impregnability of the metallic phase into the fiber structure during thixotropic forming.

The volume ratio of matrix material to fibers in thermal spraying is preferably set between 0.3 and 8.0, in particular between 0.8 and 3.0.

In all process variants of the invention, it is ensured that when the semi-finished product is produced from sizes for the metallic matrix and the embedded reinforcement layers, the temperature is only raised to a low temperature. Even in the case of coating by thermal spraying, a suitable process control can ensure that the semi-finished product is heated to a temperature of at most 300 ° C for only a few seconds. In this case, this time period can be a maximum of five seconds or a maximum of two seconds or even be limited below. These measures ensure according to the invention that the fiber composites are not degraded or chemically attacked even during the manufacture of the semi-finished products.

For this purpose, the fiber composite is preferably cooled during thermal spraying, in particular using liquid carbon dioxide.

Through targeted cooling measures, even a brief heating of the fiber composite during the coating to temperatures that are significantly lower than 300 ° C and preferably in the range of about 100 to 200 ° C maximum can be avoided.

According to a preferred development of the invention, the fiber composite is held under tension during thermal spraying on a carrier device.

In this way, differences can be compensated for, which are due to the considerably greater thermal expansion of the metallic matrix material compared to the embedded fibers. In particular, composite materials can be produced in this way in which embedded long fibers are stressed under tensile stress without the matrix itself being previously undesirably stressed.

For the purpose of coating on an industrial scale, the carrier device can promote the fiber composite in Allow continuously or in cyclical operation in a coating level for thermal spray coating.

For this purpose, the fiber composite can be guided over a winding device.

Furthermore, when using such a winding device, it is possible to first coat the fiber composite on a first side and then to coat it on the opposite side.

According to a preferred development of the invention, a spraying distance of 50 to 200 mm is maintained between the surface of the fiber composite and the nozzle outlet during coating by plasma spraying, while a spraying distance of 80 to 300 mm is maintained when coating by electric arc spraying.

Using such process parameters, particularly favorable coatings of fiber composites can be achieved, with which on the one hand a uniform coating is achieved and on the other hand an excessive thermal load on the fiber composites is avoided.

According to a further process variant of the invention, a mixture of the matrix material and short fibers is granulated or pelletized.

Here, fibers with a length of between 0.5 and 20 mm, preferably between 2 and 6 mm, are preferably used. The volume ratio of matrix material to fibers is preferably between 0.3 and 5, preferably between 1 and 2.

According to a further process variant, a mixture of the matrix material and of powdery particles is granulated or pelletized.

The production of granules or pellets using short fibers or powdery particles can advantageously be used to produce special graded layers or, for example, to produce bearing materials.

According to a first process variant, the granulated or pelletized mixtures can be processed into a semi-finished product by cold pressing. If the matrix material used is sufficiently ductile, this cold pressing process can be carried out without the addition of binders. However, if there is a lack of ductility, suitable pressing aids, e.g. Paraffin added.

According to a further process variant, the mixture produced by granulating or pelletizing is applied to a fiber composite by means of a suitable coating process. Thermal spraying, a screen printing process or another previously mentioned process can in turn be used for this purpose.

In order to enable targeted improvements in the strength of the components produced according to the invention, at least one layer with a fiber composite made of long fibers is preferably used for the manufacture. used a prepreg. In this context, long fibers are understood to mean a fiber length of at least 1 mm or an aspect ratio (ratio of length to diameter) of the fiber of at least 50, preferably of at least 100, particularly preferably of at least 150.

It is understood that the layer sequence can be varied in a suitable manner when laminating prepregs. in order to influence the properties of the component to be produced in a targeted manner. In this way, fiber composites made of long fibers coated with matrix material can be laminated together in a suitable manner. At the same time, layers of matrix material in the form of sheets or foils can be inserted. Intermediate layers of granules or pellets can also be inserted. Finally, it is also conceivable to combine coated fiber composites with preforms which are produced from mixtures of matrix material and short fibers or particles produced by pelletizing or granulating.

According to a further advantageous development of the invention, a prepreg produced by lamination is provided with an outer layer made of matrix material.

In this way it can be achieved that the surface of the component produced is largely free of embedded fibers or particles.

The fiber composites can be used in a wide variety of forms to ensure certain properties of the component produced. For example, fiber composites can be used as scrims made of unidirectional long fibers (UD). se ("un oven") or woven fiber composites in the form of 2D fiber composites, 3D fiber composites, in the form of knitted fabrics or knitted fabrics.

In this case, the semi-finished product can also be produced from graded layers in order to achieve a targeted influencing of properties at particularly stressed points on the component or in preferred directions of stress. In this way, the ratio of matrix material to fibers can be specifically changed over the component cross-section.

This is particularly advantageous in order to be able to produce components which are particularly thermally or mechanically particularly stressed locally, such as pistons or the like.

Basically, all materials that allow thixotropic forming are suitable as matrix materials.

Aluminum alloys or copper alloys are preferably used for this purpose, in particular alloys which consist of the main components aluminum, magnesium and copper or which consist of the main components copper and tin or zinc.

In this context, alloys are preferred as the matrix material which consist of alloys of the type AlMg4.5Mn0.4 (AA 5182), of the type AlMgSil (EN AW-6082), of the type AlSi7Mg (EN AW-356, EN-AW-357), type AlSi3 (AA 208, AA 296), type A1SÜ2 (AA 336, AA 384), type CuZn40A12 or type CuSnl3, 5A10, 3. When using copper alloys, the wear-reducing effect of reinforcing asters is in the foreground. These materials can be used in particular to produce advantageous bearing materials, for which purpose a combination with carbon fibers or articles in a modification close to graphite is suitable, since emergency running properties can be achieved in this way.

According to a further process variant, the metallic matrix material itself is reinforced by embedded particles, which are preferably designed as oxide ceramics, as carbides, as nitrides, as metals or alloys or as tribologically active substances.

According to the invention, fibers consisting of carbon, silicon carbide, aluminum oxide, mullite are used for fiber reinforcement of the MMC. Modifications of these fibers with nitrogen, titanium, boron, carbon or silicon and their compounds are also conceivable.

Although in principle no coating of the fibers used is necessary as a result of the shortened process times and the lower process temperatures, according to a further process variant fibers coated on their surface can also be used, in particular fibers provided with diffusion barrier or protective layers or fibers provided with adhesion promoter layers.

In this way, the properties of the component to be manufactured can be adapted to the respective requirements to an even greater extent. For example, by using Adhesion promoters improve the interfacial adhesion between embedded fibers and the metallic matrix phase. At the same time, fibers can be embedded that are less compatible with the matrix phase used.

Silicon carbide, silicon nitride, titanium carbide, titanium nitride, carbon or mixed phases or compounds thereof are particularly suitable for coating the fibers.

According to the invention, fibers with a diameter between 0.5 and 150 μm, particularly preferably between 5 and 20 μm, are preferably used.

As already mentioned, the fibers can be used both as long fibers or continuous fibers and in the form of short fibers (“chopped fibers”).

As already mentioned, in the thixoforming according to the invention, depending on the matrix material used, the semifinished product is heated to a specific temperature interval within which the matrix material has a defined liquid phase fraction.

If, for example, the alloy AlSi7Mg is used, the semi-finished product is heated to a temperature between 574 and 584 ° C for thixoforming, with a liquid phase fraction between 43 and 51 percent by volume. If, for example, the alloy AlMgSil is used, the thixoforming is heated to a temperature between 635 ° C and 645 ° C, with a liquid phase fraction between approximately 15 and 35%. provides. When using the alloy CuZn40Al2, heating takes place to a temperature range between 871 ° C and 875 ° C, resulting in a liquid phase fraction between approximately 20 and 40%.

The Thixoumformung preferably done as thixoforging within a suitable tool (die) at a controlled ram speed and ^Pres' skraft. The impact speed and pressing force are adapted to the specific process. Ram speeds of up to 800 mm / s are possible. The speed of impact of the upper part of the tool on the workpiece is preferably set between 10 mm / s and 300 mm / s depending on the fiber-matrix ratio used, the component complexity and the component volume.

To prevent premature solidification of the metallic material, the tool is preferably heated to temperatures between 100 ° C and 400 ° C.

Particularly by increasing the ram speed after touchdown, particularly rapid infiltration can be achieved, namely in the range of significantly less than a second under high pressure. This results in a short contact time between the metallic melt and the fiber material, which leads to a reduced chemical attack of the melt on the fibers and thus leads to improved properties of the component produced.

It is also possible to carry out the thixoforming under a protective gas atmosphere in order to reduce the formation of oxide. According to a first method variant, the semi-finished product is pre-compressed in a mold for thixoforming. The mold used later for thixoforming is preferably used as the shape.

The pre-compressed semifinished product can now be preheated outside the tool, which can be done inductively, in a forced-air oven with a protective gas atmosphere, with infrared emitters or with lasers, is then inserted into the tool in the preheated state and then thixotropically formed, especially thixo-forged.

The preferred matrix materials allow the semifinished product to be heated up to the temperature necessary for thixotropic forming, while the semifinished product is still sufficiently strong, which allows the semifinished product to be handled for insertion into the mold, which can be done automatically, for example. The semi-finished product loses its shear strength only when the thixo forging is subsequently applied via the stamp, so that the material is formed in the shortest possible time.

According to a process variant, the semi-finished products are heated within the tool to a temperature above the solidus line, but below the liquidus line of the matrix material. The layered material can be brought into contact with the tool wall by applying a low pressure. This improves the heat transfer and thus reduces the heating-up time. Immediately afterwards, the thixotropic forming is preferably carried out by forging. In both process variants, the thixotropically formed component is preferably cooled in a controlled manner within the tool in order to achieve a directional solidification of the metallic matrix.

Composite materials produced in this way can preferably be used according to the invention as high-strength structural components with high-specific rigidity or with a high specific modulus of elasticity, which are shaped close to production (net-shaped). In addition, there is an advantageous use as bearing materials.

It goes without saying that the features of the invention mentioned above and those yet to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own without departing from the scope of the invention.

Further features and advantages of the invention result from the following description of preferred exemplary embodiments with reference to the drawing. Show it:

1 shows a phase diagram Al-Si with selected areas for a thixotropic deformation for the wrought alloy AlMgSil and the cast alloy AlSi7Mg;

2 shows a prepreg, which consists of a layer composite of alternating layers of fiber layers and sheets (foils);

3 shows a prepreg consisting of a sequence of fiber composites coated with metallic matrix material; 4 shows a globolithic structure of an Al-Si alloy;

5 shows a cross section through an Al-Si composite material infiltrated with a metal matrix with embedded C fibers after a Thixo separation process

Fig. 6 is a. Schematic representation of a winding system for thermal ^' spray coating of fiber fabrics on an industrial scale.

1 shows a phase diagram of the preferred eutectic system Al-Si (with magnesium additives). The fixed part in the dark hatched area is α (AI). The wrought alloy AlMgSil and the cast alloy AlSi7Mg are entered as alloys suitable for thixotropic forming. For a thixotropic forming, a narrow temperature range is required, which for the wrought alloy AlMgSil lies between the solid line and the liquid line and is characterized in Fig. 1 by the rectangular temperature range, which lies between 635 and 645 ° C. In this area there is a liquid share (L) of 15 to 35%. For the thixotropic forming of the cast alloy AlSi7Mg, on the other hand, there is a temperature range that is immediately above the eutectical and is again indicated by a rectangle. This temperature window is between 574 ° C and 584 ° C. This results in a liquid portion (L) of approximately 43 to 51%.

Such relationships for the thixotropic forming of light metal alloys are known in principle (cf. Siegert, K .; Messmer, G .; Baur, J .; Wolf, A.: "Thixosch ieden von Aluminiumteile", in: Conference volume on the 7th Saxon specialist Forming technology, Chemnitz, 2000; Baur. J., Messmer, G.:

"Automated Thixoforging Unit, in: Proceeedings to the 7th Int.

Conf. on Semi-Solid-Processing of Alloys and Composites, Tsukuba, Japan, September 24-28, 2002).

The thixoforming of such light metal materials was developed in particular for the production of molded components which have a shape close to the production line. In the '' temperature range at which the thixoforming takes place, the semi-finished product in question is still of sufficient strength, which enables the semi-finished product to be handled (also called “bolts” in thixo forging). The alloys in question ideally have a globolithic structure which Forms solid phase skeleton and thus ensures the easy handling of the heated semi-finished product when inserting it into the tool (the press mold) (see Fig. 4). This solid phase skeleton breaks open under shear stress and thus reduces the yield stress, so that long flow distances in the tool and a near-net-shape forming can be guaranteed.

According to the invention, MMCs are now produced with a metallic matrix material which is reinforced by embedded fibers or particles by preparing a semi-finished product in which the fibers or particles are contained under a metallic matrix tool and the semi-finished product by thixoforming in a tool at a temperature above the solidus temperature and below the liquidus temperature of the metallic matrix tool is formed.

A loose combination of fibers on the one hand and metallic matrix material on the other is sufficient to to produce a high-quality, practically non-porous composite material in the thixoforming process with only a short forming time.

Basically, three process lines are possible.

In a first process line, shown schematically in FIG. 2. is a generally designated by the numeral 10. semifinished product is produced by laminating of alternating ^'sheet metal and fiber fabric layers. A fiber composite 12 consists, for example, of carbon fibers which are arranged in the form of a fabric. To produce the semi-finished product 10, fiber composite layers 12 are alternately laminated with thin sheets 14 made of the matrix material, for example AlSi7Mg. Depending on the desired volume ratio between fibers and matrix material, the thicknesses d _{x of} the fiber composites 12 and d _{2 of} the sheets 14 are adjusted. The semifinished product 10 is expediently enclosed by an outer layer 18 made of matrix material, in order to ensure that during the subsequent thixoforming, if possible, no fibers reach the surface of the component. Such a semifinished product or prepreg is placed in a suitable die mold and shaped therein by thixo forging in the suitable temperature range using a ram.

In this case, precompacting can first take place inside the tool while it is still cold, and then the semifinished product 10 can be preheated outside the die shape to the temperature necessary for thixoforming. This can be done by quickly heating the pre-compressed semi-finished product inductively or alternatively in a forced-air oven with a protective gas atmosphere or with high-performance infrared radiators or using a laser. Then a quick transfer takes place into the suitably preheated die mold (100 to 400 ° C). This process can be done manually, semi or fully automatically. The Thixo forging process is then carried out. For this purpose, the plunger hits the surface of the semi-finished product with a plunger speed of up to 800 mm / s, which is adapted to the process. The speed of impact of the ram on the semi-finished product is preferably set between 10 mm / s and 300 mm / s depending on the fiber-matrix ratio, the component complexity and the component volume. In order to prevent premature solidification of the metallic matrix material, the plunger is also appropriately preheated.

Alternatively, the semi-finished product can also be heated within the die. The layered semi-finished product can be brought into contact with the tool wall by a low pressure, which improves the heat transfer and reduces the heating-up time. Immediately afterwards the thixotropic forming is carried out by thixo forging.

When using sheets (foils), cold-rolled sheets are preferably used, since the high dislocation density during subsequent reheating in the course of thixoforming results in fine-grained recrystallization with a globular structure.

A second process variant for the production of a semi-finished product consists in the coating of individual fiber composites, which are then laminated to form a prepreg by superimposing them and are expediently in turn surrounded by an outer sheet metal layer or film layer made of matrix material. This method variant is explained in more detail below with reference to FIGS. 3 and 6.

A third alternative to the production of the semi-finished product consists in the production of a mixture of short fibers or powdery reinforcement particles with metallic matrix powders. This is followed by shaping by dry pressing or further processing, in turn by application to a fiber composite using a coating process.

In the second process variant, application by electrostatic charging, application by screen printing or electrophoretic deposition (EPD) onto the fiber structure is generally suitable for coating the fiber composite.

An electrically conductive or electrically conductive fiber structure is switched as an electrode by means of EPD, and the charge-carrying metal powder particles are deposited on the fiber or fabric surface as a uniform layer, driven by an electric field. The metal particles have a grain size with diameters between 10 nm and 100 μm, preferably with sizes between 100 nm and 10 μm. The use of surface-active liquid or dissolved auxiliaries enables a targeted charge distribution of the solid particles in the suspension to be set, which permits concentration and field strength-dependent material transport for layer deposition.

A particularly preferred coating method is coating by thermal spraying. Here, special electric arc wire spraying and powder plasma spraying, preferably atmospheric plasma spraying (APS) in the foreground.

During the thermal spray coating of the fibers, a temperature rise of the fiber composite is largely avoided by targeted cooling measures, so that temperatures of at most 100 ° C. can generally be maintained and damage to the fibers is thus excluded. For this purpose, cooling can be carried out locally using coolant injectors and other suitable devices, preferably using compressed air and possibly liquid carbon dioxide (C0 ₂ ).

Furthermore, in this variant of the method, it is preferred to stretch long or continuous fibers or fiber composites made therefrom (laid, woven or knitted) onto a suitable carrier device 30 (cf. FIG. 6) and to apply one or more layers of matrix metal by thermal means Apply syringes. With a winding system 30 according to FIG. 6, the fiber composite material can be unwound continuously or intermittently from a roll 34, which contains fiber composite layers to be coated, in a coating plane (left curved surface in FIG. 6) and then again after the coating on a roll 32 wind up. With a suitable dimensioning and coating thickness, a coating can first be carried out on a first upper side and then a coating on the opposite surface. A particular advantage lies in the targeted prestressing of the fabrics in the coating plane, which can also be designed to be adjustable in order to ensure an equal, permanent prestressing. Thereby, thermally and convectively generated tensions in the fiber structure are mechanically compensated. A 5-axis robot-based movement system can be used for coating, which moves an arc or plasma torch in such a way that NC-controlled movement sequences with the aim of uniform coating can be called up from previously saved programs and can be reproduced and realized in a process-stable manner , Spray distances of 50 to 200 mm between the nozzle outlet and the fiber surface are preferably used between 100 and 140 mm for APS and between 120 and 160 mm for electric arc spraying.

As shown in FIG. 3, such layers 22 of fiber composites, which are coated on both sides with matrix metal 24, are laminated together to form a prepreg and are preferably enclosed in turn by a sheet or foil 18 made of matrix metal in order to produce a semi-finished product 20. The coating thickness d ₃ can be controlled in a suitable manner in the previous coating process. For this purpose, single or multiple layers can be applied and the layer thickness can, of course, be influenced by the speed at which the vehicle is driven over or the length of stay and the other spray parameters. If larger layers of matrix metal are desired, individual metal sheets or foils can also be interposed.

In the third process variant by granulation or pelleting, mixtures of matrix metal powders and short fibers or reinforcing particle powders are produced. This granu- Gelled or pelleted mixtures can then be compacted into a green body by cold pressing, which is then used as a semi-finished product. If the matrix metal has sufficient ductility, cold pressing can be carried out without pressing aids. If the ductility of the metal matrix material is lower, suitable binder additives (e.g. paraffin) that easily volatilize during later heating are added ...

A further process variant consists in applying the mixtures produced by granulating or pelleting to a fiber composite by means of a suitable coating process, which in turn can be carried out, for example, by thermal spraying.

As already mentioned at the beginning, graded layers can be used to produce special component properties that are adapted to specific local thermal or mechanical stresses, for which purpose the entire spectrum can be used in the processing of fiber composites.

The particularly favorable distribution which results from an infiltration process by thixo forging with such a composite material can be seen from FIG. 5.

Claims

claims

1. A method for producing a component from a composite material (MMC) with a metallic matrix material which is reinforced by embedded fibers or particles, comprising the following steps: producing a semi-finished product (10; 20) in which the fibers; (16) or particles and the metallic 'matrix material (14; 24) are contained and thixoforming of the semi-finished product (10; 20) in a mold at a temperature above the solidus temperature and below the liquidust temperature of the metallic matrix material (14; 24).

2. The method according to claim 1, wherein a prepreg is produced by laminating layers of fiber composites (12) and matrix material in the form of sheets (14).

3. The method of claim 2, are used in the cold-rolled sheets (14).

4. The method according to claim 1, wherein a fiber composite (22) with metallic matrix material (24) is coated.

5. The method according to claim 4, in which a plurality of coated fiber composites are laminated to form a prepreg (20).

6. The method according to claim 4 or 5, in which a fiber composite is coated by a screen printing method with the metallic matrix material.

7. The method according to claim 4 or 5, in which a fiber composite is coated by electrostatic charging with the metallic matrix material.

8. The method according to claim 4 or 5, in which a fiber composite is coated by electrophoretic deposition from an aqueous suspension with the support of an electric field with the ^' metallic matrix material.

9. The method according to claim 4 or 5, in which a fiber composite is coated with the metallic matrix material by thermal spraying, preferably by atmospheric plasma spraying (APS), wire flame spraying or by electric arc spraying.

10. The method according to any one of the preceding claims, wherein the volume ratio of matrix material to fibers between 0.3 and 8.0, preferably between 0.8 and 3.0 is set.

11. The method according to any one of the preceding claims, in which the fiber composite is heated to a temperature of at most 300 ° C for a period of at most 5 seconds, preferably of at most 2 seconds, during the production of the semi-finished product.

12. The method according to claim 11, wherein the fiber composite is cooled during the thermal spraying, preferably using compressed air, liquid carbon dioxide or nitrogen.

13. The method according to any one of claims 9 to 12, wherein the fiber composite is held under tension during the thermal spraying on a carrier device (30).

14. The method according to claim 13, in which the fiber composite is conveyed continuously or intermittently into a coating plane for thermal spray coating by the carrier device (30).

15. The method according to claim 14, wherein the fiber composite is guided over a winding device (32, 34).

16. The method according to claim 14 or 15, wherein the fiber composite is first coated on a first side and then coated on the opposite side.

17. The method according to any one of claims 9 to 15, wherein between the surface of the fiber composite and the nozzle outlet, a spraying distance of 50 to 200 mm is maintained during plasma spraying and a spraying distance of 80 to 300 mm is maintained during electric arc spraying.

18. The method according to any one of the preceding claims, in which a mixture of the matrix material and short fibers is granulated or pelletized.

19. The method according to claim 18, in which fibers with a length between 0.5 and 20 mm, preferably between 2 and 6 mm, are used.

20. The method according to claim 18 or 19, wherein a volume ratio of matrix material to fibers between 0.3 and 5, preferably between 1 and 2 is used.

21. The method according to any one of claims 1 to 17, in which a mixture of the matrix material and powdery particles is granulated or pelletized.

22. The method according to any one of claims 18 to 21, wherein the granulated or pelletized mixture is processed into a semi-finished product by cold pressing.

23. The method according to any one of claims 18 to 21, wherein the mixture is applied to a fiber composite by a coating process.

24. The method according to any one of the preceding claims, wherein at least one layer with a fiber composite of long fibers of a length of at least one millimeter or of long fibers with an aspect ratio (ratio of length to diameter) of at least 50, preferably at least 100, particularly preferably of at least 150, is used to make a prepreg.

25. The method according to any one of the preceding claims, in which a sequence of layers (12, 14; 22) is laminated to form a prepreg (10; 20), the fiber composites (12) made of long fibers (16), fiber composites coated with matrix material (22 ), Matrix material (14) or mixtures of matrix material and short fibers or particles.

26. The method according to claim 25, wherein the prepreg (10; 20) is provided with an outer layer (18) made of matrix material.

27. The method according to any one of claims 24 to 26, wherein a scrim of unidirectional long fibers (UD), a spunbonded fabric or a woven fiber composite (2D, 3O _r knitted fabric) is used as fiber composite .- *

28. The method according to any one of the preceding claims, wherein the semi-finished product is made of graded layers.

29. The method according to any one of the preceding claims, in which an aluminum alloy or a copper alloy is used as the matrix material, in particular an alloy consisting of the main components aluminum, magnesium and silicon or of the main components copper and tin or zinc.

30. The method as claimed in claim 29, in which an alloy is used as the matrix material, which alloy is selected from the group which is formed by alloys of the type AlMg4.5MnO, 4, AlMgSil, AlSi7Mg, AlSi3, A1SÜ2, CuZn40Al2 and CuSnl3.5A10, third

31. The method according to any one of the preceding claims, in which the metallic matrix material is reinforced by embedded particles, which are preferably formed as oxide ceramics, carbides, nitrides, metals or alloys or tribologically active materials.

32. The method according to any one of the preceding claims, in which fibers are used which consist of carbon, silicon carbide, aluminum oxide, mullite or contain modifications of these fibers with nitrogen, titanium, boron, carbon or silicon or their compounds.

33. The method according to any one of the preceding claims, are employed in the coated fibers on its surface ^■ ,, in particular with diffusion barrier layers and protective layers or primer layers provided fibers.

34. The method according to claim 33, in which fibers coated with silicon carbide, silicon nitride, titanium carbide, titanium nitride, carbon or mixed phases or compounds thereof are used.

35. The method according to any one of the preceding claims, are used in the fibers with a diameter between 0.5 and 150 microns, preferably between 5 and 20 microns.

36. The method according to any one of the preceding claims, in which the semi-finished product, depending on the matrix material used for thixoforming, is heated to a specific temperature interval within which the matrix material has a defined liquid phase fraction, preferably from 10 to 60%, in particular from 35 to 45% ,

37. The method according to claim 36, in which the semi-finished product is heated to a temperature between 574 and 584 ° C. when using the AlSi7Mg alloy for thixoforming, and to a temperature between see 635 and 645 ° C is heated, and when using the alloy CuZn40A12 is heated to a temperature between 871 and 875 ° C.

38. The method of claim 36 or 37, wherein the semi-finished product is thixo-forged using a press.

39.- '.Method according to claim 38, in which the tool is tempered.

40. The method according to any one of the preceding claims, wherein the semi-finished product is pre-compressed in a mold.

41. The method according to any one of the preceding claims, wherein the tool is preheated, preferably to a temperature between 100 and 400 ° C.

42. The method of claim 40, or 41, wherein the pre-compressed semifinished product is preheated outside the tool, preferably inductively, in a forced air oven, with infrared radiators or lasers, then is introduced into the tool in a preheated state and is thixotropically formed.

43. The method as claimed in one of claims 1 to 41, in which the semi-finished product is heated in the tool to a temperature above the solidus line but below the liquidus line of the matrix material and is subsequently thixotropically formed in the tool.

44. The method according to any one of the preceding claims, wherein the semi-finished product by a plunger of the tool with a defined path-time profile, preferably at a speed of 80 to 600 mm / s in the thixotropic state of the matrix material is formed and compressed.

45. The method according to any one of claims 36 to 44, in which the thixoforming and / or heating to the temperature for thixoforming is carried out under protective gas, in particular under forming gas (mixture of nitrogen and hydrogen).

46. The method according to any one of the preceding claims, wherein the component is cooled to below the solidus temperature after the thixotropic forming within the tool.

47. Composite material with a thixotropically shaped metallic matrix material which is reinforced by embedded fibers or particles, in particular produced by a method according to one of the preceding claims.

48. Use of the composite material according to claim 47 as near net shape ("near net shaped") high-strength structural components with high specific strength, with high specific elastic modulus or as bearing materials.