EP1971698B1

EP1971698B1 - Method for the production of a composite material or a precursor product for the production of a composite material

Info

Publication number: EP1971698B1
Application number: EP06828864.6A
Authority: EP
Inventors: Andreas Lohmüller; Mark Hartmann; Robert F. Singer
Original assignee: Neue Materialien Fuerth GmbH
Current assignee: Neue Materialien Fuerth GmbH
Priority date: 2005-11-03
Filing date: 2006-10-26
Publication date: 2013-06-05
Anticipated expiration: 2026-10-26
Also published as: US20080264594A1; DE102005052470B3; WO2007051557A3; WO2007051557A2; EP1971698A2

Description

The invention relates to a method for the production of a composite material or a precursor product for the production of a precursor product for the production of a composite material.
Metallic composite materials are generally known according to the prior art. In this connection these are particularly composite materials for which a reinforcement phase is included in a metallic matrix phase. Depending on the demands on the composite material the reinforcement phase can be made of particles, in particular non-metallic particles, or of fibers. According to the prior art it is furthermore known how to produce molded parts made of composite materials by means of a casting method. For this the melted metal is mixed in a container with the reinforcement phase by means of a stirrer and then transferred to a casting device. According to the prior art the problem occurs that the reinforcement phase is not distributed homogeneously in the metallic matrix phase. This can be caused by the formation of agglomerates of the particles forming the reinforcement phase. Regardless of this the reinforcement phase can sink or swim in the molten mass due to differences in density. The thus caused inhomogeneities lead to poor mechanical properties for the product produced from the molten mass.
EP 0 409 966 A1 discloses a method for the production of a composite material for which metallic material is fed to an extruder device. The metallic material can be an alloy with a discontinuous phase.
WO 00/49192 describes a method for the production of a metal-matrix composite material. In this connection the matrix-metal is plasticized in a processing unit comprising an extruder, and a reinforcement component is fed to the extruder by means of a side-feeder device. The mixture of plasticized matrix-metal and reinforcement component is homogenized in the extruder.
US 6,360,576 B1 discloses a method for the production of a composite material having a metallic matrix phase and a reinforcement phase with the following steps:

Feeding a solid preform into a first portion of an extruder;
transporting the preform by punch to heating means, where it is heated until it is becomes thixotropic;
feeding reinforcement particles into a second portion of the extruder thereby producing a mixture; and
cooling mixture below the solidus temperature of the metallic matrix phase during transport of the mixture through the die.

The object of the invention is to eliminate the disadvantages according to the prior art. In particular a method is to be specified for the production of a starting product which makes possible the production of a composite material with improved homogeneity.
This object is solved with the features of claim 1. Advantageous embodiments of the invention result from the features of claims 2 to 15.
According to the invention the method defined in claim 1 is provided
The suggested method provides a relatively simple and inexpensive way to produce a composite material or a precursor product for the production of a composite material in which the reinforcement phase is homogeneously distributed. Segregation processes are avoided by using an extruder device as suggested by the invention. In accordance with the purpose of the present invention the term "extruder device" is understood to be a device with which the metallic matrix phase and the reinforcement particles are mixed intensively, in particular using the effects of shearing force, and in this connection the mixture which is forming is transported in the direction of an outlet opening or a die.
Such extruder devices are also called "compounders." Use of such an extruder device surprisingly enables the production of a homogeneous mixture from a granulate with grains having an average grain size in the range of 1 µm to 10 mm which forms the metallic matrix phase and a reinforcement phase which is, for example, formed from particles with an average grain diameter of less than 100 µm or short fibers with a thickness of 5 to 10 µm. The production of a homogenous mixture starting with materials with such different average grain diameters has not been possible up to now according to the prior art.
The composite material which can be produced with the method is present in solid form. In this connection these can particularly be conventional profiles which can be produced by means of extrusion. The profiles can be rods, hollow profiles and similar for example. Furthermore the method according to the invention can also be used to produce precursor products for the production of a composite material. Such precursor products can be either solid or fluid. A solid precursor product can be a granulate in particular which can be produced by breaking up previously produced rods. While still in fluid form the precursor product can however also be fed after passing through the outlet opening of the extruder device directly to a further device for the production of molded parts.
According to the method of the invention it is provided that the reinforcement particles and the at least partially melted metallic matrix phase are mixed. In this connection it can happen that the reinforcement particles are brought into contact with the metallic matrix phase before or during the partial melting of same. It is advantageous, however, when the metallic matrix phase is at least partially melted before being brought into contact with the reinforcement phase. A "partial melting" of the metallic matrix phase is done by heating same to a temperature above the solidus temperature and below the liquidus temperature. In this connection the metallic matrix phase can first be heated to a temperature above the liquidus temperature and then cooled to the range between liquidus and solidus temperature. However, it is also possible to only heat the metallic matrix phase to a temperature above the solidus temperature and below the liquidus temperature. By cooling the mixture to a temperature below the solidus temperature of the metallic matrix phase before or during passing through the die, it is advantageously possible to break up the solidified mixture into a granulate. However, it is also possible to cut the solidified mixture into rod-shaped semi-finished products, wires, bars or rods with a predetermined length.
According to an advantageous embodiment it is provided that the metallic matrix phase and/or the reinforcement particles are fed to the extruder device in an atmosphere of inert gas. This makes it relatively easy to avoid an undesired reaction with oxygen and/or nitrogen.
According to a further embodiment it is provided that the metallic matrix phase is fed in the form of solid metal particles. The metal particles are advantageously made of magnesium, zinc or aluminum or an alloy predominantly containing one of the preceding metals.
Although the feeding of the metallic matrix phase in the form of solid metal particles is preferred, it is also possible to feed the metallic matrix phase to the extruder device in a melted or partially melted state.
The reinforcement particles can be produced from a metallic and/or a non-metallic, inorganic material. In case metallic materials are used, materials which have a low solubility during the metallic matrix phase are selected. Such non-metallic materials include in particular ceramic materials, for example aluminum oxide or SiC, or other suitable reinforcement phases.
The reinforcement particles can be in the form of fibers and/or particles. In this connection the fibers advantageously have a thickness in the range of 3 to 20 µm. Furthermore they can have a length in the range of 5 µm to 10 mm.
The particles advantageously have an average diameter of 10 nm to 100 µm. The method according to the invention enables the production of a homogeneous starting product even when the average diameter of the metal particles and the reinforcement particles significantly differ from one another.
According to a further advantageous embodiment it is provided that the metal particles are only partially melted while being transported in the direction of the die in the second portion of the extruder device. The partially melting of the metal particles is done by setting a temperature which is in the 2-phase area between the solidus and the liquidus temperature. In this range the matrix phase is only partially fluid, i.e. it consists of a mixture of solid phase and molten mass. Reinforcement particles introduced therein are distributed particularly homogeneously. In particular the crystals already located in the molten mass prevent segregation by gravitational sinking and/or the creation of agglomerates. This enables a particularly homogeneous mixture with the reinforcement particles.
According to a further embodiment the mixture which is leaving the die in a fluid state is fed to a casting device. The casting device can be a device for performing a gravitational casting method, a pressure casting method, an injection casting method or a thixomolding method. Energy can be saved with the suggested method. Regardless of this, this can be used to accelerate a method for the production of a molded part.
According to a further advantageous embodiment a contact time between the at least partially melted metallic matrix phase and the reinforcement phase is less than 20 minutes, preferably less than 15 minutes. Due to this extremely short contact time undesired reactions between the metallic molten mass and the reinforcement phase and/or the formation of undesired metastable phases can be avoided. A composite material produced from the starting product according to the invention exhibits improved properties.
The extruder device can have at least one, preferably two, worm shafts for the transport. In particular, a double worm shaft extruder device which has two parallel arranged, advantageously partially intermeshing worm shafts has been shown to be particularly suitable for performing the method according to the invention. An outstanding homogeneity of the produced mixture can be achieved therewith.
The homogeneity can still be increased even more according to a further embodiment by means of equipping the extruder device with at least one mixing device. These can be intermeshing, gear wheel-like devices on the worm shafts of the double worm shaft extruder device.
According to a further provision the use of the precursor product according to the invention is provided for the production of a molded part produced by a casting method. The casting method can be a gravitational casting method, a pressure casting method, an injection casting method and similar. It has been shown to be particularly advantageous to use the starting product for the so-called "thixomolding method". Thixomolding methods are known for example from EP 0 409 966 B1 .
Hereinafter, an example of an embodiment of the invention will be explained in more detail with reference to the drawings. The figures are listed below:

Fig. 1: a picture of the texture of a first composite material,
Fig. 2: a picture of the texture of a second composite material (prior art) and
Fig. 3: a schematic sectional view of an extruder device.

Fig. 1 shows a reflected light microscopic view of a composite material produced by means of the method according to the invention. A magnesium alloy has been used as the starting material for the metallic phase, which contains 9 % in weight aluminum and 1% in weight zinc (AZ91). Particles produced from SiC with an average grain size of 5 to 15 µm, preferably approximately 10 µm, have been used for the reinforcement phase. The portion of the reinforcement phase has been 10 % by volume.
The metallic matrix phase has been heated to a temperature in the range between the solidus and the liquidus temperature to produce the composite material. The reinforcement phase has been added to the partially fluid molten mass. Due to the crystals, magnesium mixed crystals in this case, contained in the partially fluid molten mass, segregation or formation of agglomerates does not occur between the reinforcement phase. The particles of the reinforcement phase are kept uniformly distributed in the volume, wherein segregations are prevented by the primary crystals located between the reinforcement phase.
Fig. 2 (prior art) shows the same alloy, wherein the metallic matrix phase has been heated here however to a temperature above the liquidus temperature and then the reinforcement phase has been added. It can be observed here that the reinforcement phase is not as uniformly distributed as with the method using a partially fluid metal molten mass. This is attributed to the circumstance that, due to the lack of the magnesium primary phase, the reinforcement phase has more freedom of movement in the molten mass and therefore there a formation of segregations and/or agglomerates has a higher probability.
For the extruder device shown in Fig. 3 a worm shaft which can be driven with a drive 3 is housed in a cylinder 1. According to an advantageous embodiment two worm shafts 2 can also be provided in the cylinder 1. A die which is advantageously provided with a cooler is designated with the reference numeral 4. A first feeder device 5 is provided for feeding metal granulate in a first portion of the cylinder 1 located in the vicinity of the drive 3. The first feeder device comprises a suction conveyor 6, a first feeding hopper 7 set downstream, a first dosing worm shaft 8 and a first feeding shaft 9 which is provided with a first connection 10 for feeding inert gas. The inert gas can be argon for example.
A second feeder device 11 for feeding reinforcement phase is provided in a second portion of the cylinder 1 which is located in the vicinity of the die 4, downstream to the first portion. The second feeder device 11 comprises a second feeding hopper 12, a second dosing worm shaft 13 set downstream, a second feeding shaft 14 with a second connection 15 for feeding inert gas. Reference numeral 16 designates a fixed strand leaving the die 4 and reference numeral 17 designates strip heaters which surround the cylinder 1.
The device is operated as follows to perform the method according to the invention:
For example magnesium granulate having grains with an average diameter of 4 mm is drawn in by the suction conveyor 6 and is fed to the cylinder 1 in the first portion via the first feeding hopper 7 as well as the first dosing worm shaft 8 via the feeding shaft 9 under an atmosphere of inert gas. The magnesium granulate is transported with the worm shaft 2 in the direction of the die 4. In this connection it is heated to a temperature above the solidus temperature with the strip heaters 17. The magnesium granulate is at least partially melted in the region of the second portion. In the second portion reinforcement particles are added in turn under an atmosphere of inert gas via the second feeding hopper 12, the second dosing worm shaft 13 and the second feeding shaft 14. In this connection this can be short fibers with a thickness of 5 to 10 µm which are several centimeters in length. In the second portion the reinforcement phase is mixed intensively with the partially melted magnesium by means of the rotation of the worm shaft 2 and then enters the die 4. There the mixture is cooled and leaves the die in the form of the strand 16. The strand 16 can then be broken up into granules. The produced granulate is used as the starting product for the production of composite materials. In particular it can be processed further with the thixomolding method.
According to a variant of the suggested method, it is also possible to feed the mixture while still in its fluid state when it leaves the die 4, for example, directly to a casting device set downstream, in particular a thixomolding device or a pressure casting device.

List of Reference Numerals

1	Cylinder
2	Worm shaft
3	Drive
4	Die
5	First feeder device
6	Suction conveyor
7	First feeding hopper
8	First dosing worm shaft
9	First feeding shaft
10	First connection
11	Second feeder device
12	Second feeding hopper
13	Second dosing worm shaft
14	Second feeding shaft
15	Second connection
16	Strand
17	Strip heaters

Claims

Method for the production of a composite material having a metallic matrix phase and a reinforcement phase or of a precursor product for the production of a composite material with the following steps:
Providing an extruder device having at least one worm shaft (2) for transport and a die (4),

Feeding the metallic matrix phase in a first portion of the extruder device,

Transport of the metallic matrix phase in the direction of the die (4) by means of rotation of the worm shaft (2),

At least partially melting the metallic matrix phase,

Feeding reinforcement particles forming the reinforcement phase in the region of a second portion of the extruder device,

Producing a mixture created from the reinforcement particles and the at least partially melted metallic matrix phase by means of the rotation of the worm shaft and further transport of the mixture through the die (4) by means of rotation of the worm shaft, wherein the mixture is cooled to a temperature below the solidus temperature of the metallic matrix phase before or during passing through the die (4).
Method according to claim 1, wherein the metallic matrix phase and/or the reinforcement particles are fed to the extruder device under an atmosphere of inert gas.
Method according to one of the preceding claims, wherein the metallic matrix phase is fed in the form of solid metal particles.
Method according to claim 3, wherein the metal particles are formed from magnesium, zinc or aluminum or an alloy predominantly containing one of the preceding metals.
Method according to one of claims 3 or 4, wherein the metal particles form a granulate with grains having an average diameter in the range of 1, µm to 10 mm.
Method according to one of the preceding claims, wherein the reinforcement particles are produced from a metallic and/or non-metallic, inorganic material.
Method according to one of the preceding claims, wherein the reinforcement particles are present in the form of fibers and/or particles.
Method according to claim 7, wherein the fibers have a thickness in the range of 3 to 20 µm.
Method according to one of claims 7 or 8, wherein the fibers have a length in the range of 5 µm to 10 mm.
Method according to one of the preceding claims, wherein the particles have an average diameter in the range of 10 nm to 100 µm.
Method according to one of the preceding claims, wherein the metal particles are at least partially melted in the second portion of the extruder device during the transport in the direction of the die (4).
Method according to one of the preceding claims, wherein the solidified mixture is broken up into granules.
Method according to one of the preceding claims, wherein a contact time between the at least partially melted metallic matrix phase and the reinforcement phase is less than 20 minutes, preferably less than 15 minutes.
Method according to one of the preceding claims, wherein the extruder device has two partially intermeshing worm shafts for the transport.
Method according to one of the preceding claims, wherein the extruder device has at least one mixing equipment.