Aluminum composite material and method for the production thereof

Abstract

The invention relates to an aluminum composite material, comprising an aluminum metal phase 1 and an aluminum oxide phase 2, the aluminum metal phase 1 comprising aluminum and / or an aluminum alloy, and the aluminum oxide phase 2 comprising aluminum oxide particles 21 comprising Al2O3, and the aluminum oxide particles 21 forming a support structure. The invention further relates to a method for the production of such an aluminum composite material.

Description

[0001] Aluminium composite material and process for its production

[0002] The invention relates to an aluminum composite material with advantageous mechanical properties and high electrical conductivity and a method for its production.

[0003] Aluminum materials made of aluminum and aluminum alloys as well as with various additives are known from the state of the art.

[0004] In particular, it is known to cast aluminum into aluminum blocks and then draw wires from them, for example, or press profiles, such as extruded profiles. Pure aluminum is very soft and therefore must be alloyed with other materials, such as silicon, manganese, or magnesium, to achieve the generally desired mechanical properties. The disadvantages of this approach are the high cost of some alloying elements, the limited availability of some of the alloying elements, and the cost and technical complexity of producing such alloys.

[0005] The object of the invention is to provide an aluminum-based material with advantageous mechanical and electrical properties that can be produced cost-effectively and without the need for hard-to-find alloying elements.

[0006] The problem is solved with respect to the aluminum composite material by the features listed in claim 1 and with respect to the method for producing an aluminum composite material by the features listed in claim 7. Preferred developments arise from the respective subclaims.

[0007] The aluminum composite material according to the invention is formed in particular by an aluminum metallic phase and an aluminum oxide phase. The interaction of these two phases is crucial for the advantageous properties of the aluminum composite material according to the invention.

[0008] The aluminum metallic phase is preferably formed by aluminum without the addition of alloying elements. It is preferably 99.5% aluminum, hereinafter also referred to as pure aluminum. Such pure aluminum is the commercially available base material for aluminum alloys.

[0009] For the purposes of the present invention, the aluminum metallic phase is also understood to mean an aluminum with a higher proportion of accompanying elements or an aluminum alloy with alloying elements such as silicon, magnesium, manganese, copper and zinc.

[0010] For the sake of simplicity, pure aluminum, aluminum with a higher proportion of accompanying elements, and aluminum alloy are collectively referred to as aluminum below, unless expressly stated otherwise.

[0011] The aluminum composite material according to the invention is characterized in particular by an aluminum oxide phase.

[0012] According to the invention, the aluminum oxide phase is formed by aluminum oxide particles. These are, in particular, particles with a predominant proportion of Al2O3.

[0013] The aluminum oxide particles are not distributed homogeneously throughout the volume of the aluminum composite material, but rather exhibit regions of higher concentration, thus forming a support structure. A support structure is defined as linear or, preferably, planar zones in which a higher concentration of aluminum oxide particles is present than in other zones. The aluminum oxide particles are highly rigid and embedded in the aluminum metal lattice. Their size, typically in the micrometer range, creates higher-strength bodies in the surrounding metal lattice that counteract deformation and thus increase the strength of the aluminum grain-posite material compared to aluminum without an aluminum oxide phase. This is further supported by the relative proximity of the aluminum oxide particles to one another in the regions of higher concentration.As a result, the aluminum oxide particles are embedded as macroscopic, high-strength bodies in the aluminum, which thus forms a matrix material. The aluminum oxide particles therefore do not form closed regions. Rather, the metallic lattice of the aluminum penetrates the spaces between the aluminum particles without the lattice defects necessary for strength. The increase in strength is therefore advantageously not primarily due to solid solution strengthening, but primarily due to the mechanical properties of the aluminum oxide particles in their mutual support.

[0014] Although aluminum oxide has very low electrical conductivity, the aluminum composite material according to the invention provides a material with a particular advantage that is only slightly reduced in conductivity compared to pure aluminum. It has been found that both by leaving zones with a low concentration of aluminum oxide particles and by embedding the aluminum oxide particles in the metal lattice of the aluminum in the region of the support structures, the metal lattice structure is only insignificantly impaired. Thus, the aluminum composite material exhibits very high conductivity while simultaneously exhibiting high strength, something unattainable in aluminum alloys of comparable strength. The aluminum composite material is therefore particularly advantageous for the production of conductor wires.Conductor wires produced in this way are particularly suitable for use in the automotive or aviation sectors, as they offer not only advantageous electrical and mechanical properties but also low weight. Their use is particularly advantageous in the field of electromobility. Another advantage of the aluminum composite material is its high chemical and thermal stability. Even at temperatures exceeding 300 degrees Celsius, its strength is essentially maintained.

[0015] Another advantage is the very simple manufacturing process, for which reference is made to the description of the manufacturing process according to the invention. In particular, it is advantageous that no expensive and sometimes very limited alloying elements are required for production.

[0016] In a first advantageous development, the aluminum composite material is characterized in that the support structure is designed as surface zones which surround spatial zones as walls, wherein the surface zones have a higher mass fraction of aluminum oxide particles than the spatial zones.

[0017] The surface zones can be designed in the manner of walls, similar to a three-dimensional honeycomb structure. The surfaces preferably surround regions in which no or only small amounts of aluminum oxide particles are embedded in the aluminum. For the purposes of this development, surface zones and spatial zones differ by definition in that the surface zones have a higher mass fraction of aluminum oxide particles than the spatial zones. Preferably, the mass fraction in the surface zones is at least ten times the mass fraction in the spatial zones.

[0018] According to an advantageous development, the aluminum composite material is characterized in that the aluminum oxide phase has a mass fraction of 0.1% to 3%. The mass specification according to this development refers to the total mass without differentiation according to zones of higher and lower concentration, such as surface zones and spatial zones.

[0019] It was found that with such a mass fraction, on the one hand, a significant increase in elongation at break and strength can be achieved, and on the other hand, the electrical conductivity is only slightly reduced compared to aluminum or pure aluminum.

[0020] For example, a wire with a diameter of approximately 1 mm produced with the aluminum composite material according to the invention achieved an elongation at break of 15.4% and a tensile strength of 151 Pa. Aluminum with a purity of 99.7% was used as the starting material.

[0021] As a comparison value, a wire of this diameter, also based on aluminum with a purity of 99.7%, according to EN AW-1070A in a material temper H18, has a typical elongation at break of 3% and a typical tensile strength of 125 Pa.

[0022] According to a further advantageous development, the aluminum composite material is characterized in that the aluminum oxide phase has a mass fraction of 10% to 90% in the surface zones and a mass fraction of less than 1% in the spatial zones.

[0023] Advantageously, by varying the concentration of the aluminum oxide particles in the ranges specified in this development, a low mass fraction relative to the total mass can be achieved and at the same time high strength and high electrical conductivity can be provided.

[0024] According to a further advantageous development, the aluminum composite material is characterized in that the spatial zones have a spatial diagonal extension of 10 to 500 micrometers.

[0025] The space diagonal extension is to be understood as the designation for the largest diameter of the space zones in order to describe their size. It has been found that space zones of this size particularly advantageously support the high electrical conductivity without significantly reducing the increase in strength achieved by means of the support structures. In a special development, the aluminum composite material is anisotropic. For this purpose, it is particularly characterized in that the average extension of the space zones in a longitudinal axis is more than 1.5 times the average extension of the space zones in a plane transverse to the longitudinal axis. The longitudinal axis describes the axis of the aluminum composite material in which there is greater strength than in any other axis. This is achieved in that the space zones and the surrounding surface zones have a greater longitudinal extension than transverse extension.The arrangement of the support structures thus also has a greater longitudinal extension than transverse extension. This means that, for example, a conductor wire has a particularly high tensile strength in its longitudinal direction, which corresponds to the longitudinal axis, but is also easy to bend and exhibits only a low tendency to fracture when bent.

[0026] A further aspect of the invention relates to a method for producing such an aluminum composite material.

[0027] Such a process for producing an aluminum composite material comprises the following process steps: a) producing an aluminum shot, comprising an aluminum metal body and an aluminum oxide shell, by spraying, blowing, stirring, or pouring an aluminum melt in an oxygen-containing atmosphere; b) compression molding the aluminum shot, while fragmenting the aluminum oxide shell into aluminum oxide particles, creating a material bond between the aluminum metal bodies and embedding the aluminum oxide particles to form the aluminum composite material. The description of the aluminum composite material according to the invention applies correspondingly to the process according to the invention, taking into account the following aspects.

[0028] In process step a), aluminum shot is produced. Aluminum shot and its production are known per se from the prior art, so that aluminum shot is inexpensive and commercially available. For the purposes of the present process, aluminum shot refers to granular bodies with a size of preferably 0.3 to 3 mm, hereinafter also referred to as shot bodies. They comprise an aluminum metal body enclosed by an aluminum oxide shell. The aluminum metal body provides the aluminum metallic phase for the aluminum composite material to be produced. The aluminum oxide particles of the aluminum oxide phase of the aluminum composite material to be produced are formed from the aluminum oxide shell.

[0029] To produce aluminum shot, liquid aluminum is first prepared and then sprayed, blown, atomized, stirred, or shaken to form shot. The aluminum shot can have various shapes and different size fractions. The shapes and size fractions of the shot influence the properties of the aluminum composite material to be produced and can be determined during the production of the aluminum shot and, if necessary, by grading curves. Blowing or atomizing produces more needle-like geometries, while stirring and shaking produce more spherical geometries of the shot.

[0030] Process step a) is further characterized in particular by the fact that the powder formation takes place in an oxygen-containing atmosphere. The aluminum reacts with the oxygen on the hot surface, particularly to form Al2O3. This produces the aluminum oxide shell of the powder bodies of the aluminum powder according to the invention. In particular, the oxygen content of the oxygen-containing atmosphere to be provided allows the conversion rate of aluminum to aluminum oxide and thus the thickness of the aluminum oxide shell, as well as the resulting mass fraction of the aluminum oxide particles in the aluminum composite material to be produced, to be advantageously and easily adjusted, allowing its properties to be influenced in a targeted manner.

[0031] An aluminum oxide shell within the meaning of the present invention also includes other compounds or substances contained in the shell in addition to Al2O3. This can be due, for example, to impurities. In advantageous refinements, however, targeted admixtures can also be made in the oxygen-containing atmosphere.

[0032] In process step b), the aluminum grit obtained in process step a) is transformed into the aluminum composite material by means of pressure forming.

[0033] As a result of the forces acting on the aluminum shot during pressure forming, the shot particles are pressed against each other and deformed. While the aluminum metal body forms plastically due to its good flowability, the aluminum oxide shell is broken up and shattered due to the low ductility of the aluminum oxide, with the resulting fragments of the aluminum oxide shell forming the aluminum oxide particles. The aluminum oxide particles are irregularly shaped and also warp due to the movements during pressure forming. Thus, the aluminum oxide particles do not form a closed plane between the adjacent aluminum metal bodies of the shot particles; rather, there are points of penetration where the aluminum of the aluminum metal bodies of adjacent aluminum metal bodies directly encounters one another and forms a lattice structure, creating a material cohesion.As a result, the aluminum oxide particles are enclosed by the aluminum of the aluminum metal bodies. In the zones of the former aluminum oxide shells, there is a higher concentration and thus a higher mass fraction of aluminum oxide particles than in the zones that originated from the aluminum metal bodies. The greater the degree of deformation and the flow of the material during pressure forming, the more the shapes of the zones with a high concentration of aluminum oxide particles deviate from the shapes of the aluminum oxide shells of the granulated bodies prior to pressure forming. In addition, the aluminum oxide particles are more widely distributed in the aluminum than in the matrix material.

[0034] Pressure forming, as defined in this process step, refers to all processes that fall under the generic term of pressure forming, such as, in particular, press-forging, drop forging, and rolling. Pressure forming particularly preferably takes the form of extrusion, impact extrusion, and tapering.

[0035] The process particularly advantageously produces an aluminum composite material, the properties of which are described in the description of the aluminum composite material in claims 1 to 6. Another particular advantage of the process is its simplicity. Surprisingly, a process has been found that can be provided by a minor modification and a combination of existing processes.

[0036] In an advantageous further development, the method for producing an aluminum composite material is characterized in that after the method step a), a method step a1) is carried out, that in the method step a1) a tempering of the aluminum shot to a temperature of 200 to 500 degrees Celsius is carried out and that the method step b) is carried out with the aluminum shot tempered according to the method step a1).

[0037] Tempering advantageously supports the pressure forming process in this step, reducing the required force and improving the bonding between the aluminum metal bodies for the formation of the aluminum metallic phase. Tempering is particularly preferably carried out at 300 to 400 degrees Celsius.

[0038] In an advantageous further development, the method for producing an aluminum composite material is characterized in that in process step b) the pressure forming is carried out by means of extrusion.

[0039] The invention is illustrated by way of example with reference to

[0040] Fig. 1 Micrograph at 300x magnification

[0041] Fig. 2 Schematic sectional view with aluminum oxide particles in surface zones explained in more detail.

[0042] Identical reference symbols in the various figures refer to identical features or components. These reference symbols are used in the description even if they are not shown in the respective figure.

[0043] Fig. 1 shows a microscopic image of a micrograph of the aluminum composite material obtained by the process at 300x magnification. The inhomogeneous distribution of the aluminum oxide particles 21 can be seen. Furthermore, the anisotropic formation in this exemplary embodiment is evident. The distribution of the aluminum oxide particles 21 has a significantly larger extension along a longitudinal axis 5, which runs between the top left and bottom right.

[0044] Fig. 2 shows a schematic sectional view of an embodiment in which a high concentration of aluminum oxide particles 21 is present in surface zones 4, adjacent to the spatial zones 3, which resulted from the aluminum metal bodies of the aluminum shot bodies in process step b). The section runs horizontally to the surface zones 4. The surface zones 4 are partially connected to one another and thus spatially enclose the spatial zones 3. Furthermore, the arrows, using the example of a spatial zone 3 in the center of the figure, show that the extension here along the longitudinal axis 5 is considerably greater than in a transverse plane 6 to the longitudinal axis 6.

[0045] In an embodiment of the manufacturing process according to the invention (not illustrated by figures), the aluminum shot was produced in process step a) based on pure aluminum with a purity of 99.7%. The aluminum shot was produced in an air atmosphere, so that the aluminum oxide shell was formed by contact with atmospheric oxygen at a natural oxygen concentration. The aluminum shot thus produced in process step a) has a grain size of 75 to 125 micrometers.

[0046] Furthermore, in process step b), the aluminum shot from process step a) was compression-formed using an extrusion press. A core diameter of 50 mm was selected, and a 1.0 mm wire was produced at a pressing force of 2.2 MN, with a die with a diameter of 1.0 mm and a temperature of 330 degrees Celsius. Compression-forming shattered the aluminum oxide shell of the aluminum shot into aluminum particles, creating the aluminum composite material. The resulting wire achieved an elongation at break of 15.4% and a tensile strength of 151 Pa.

[0047] In an alternative embodiment of process step b), a compression molding process was also carried out with a core diameter of 50 mm using a 0.8 mm die and a slightly higher temperature of 360 degrees Celsius, with a pressing force of 1.7 MN. This resulted in a 0.8 mm wire. Reference symbols used

[0048] 1 aluminum metallic phase

[0049] 2 aluminum oxide phase

[0050] 21 aluminum oxide particles

[0051] 3 room zones

[0052] 4 area zones

[0053] 5 Longitudinal axis

[0054] 6 transverse plane

Claims

Patent claims 1. An aluminum composite material comprising an aluminum metallic phase 1 and an aluminum oxide phase 2, wherein the aluminum metallic phase 1 comprises aluminum and / or an aluminum alloy, wherein the aluminum oxide phase 2 comprises aluminum oxide particles 21 comprising AI2O3, wherein the aluminum oxide particles 21 form a support structure.

2. Aluminium composite material according to claim 1, characterized in that the support structure is designed as surface zones 4 which surround spatial zones 3 as walls, wherein the surface zones 4 have a higher mass fraction of aluminium oxide particles 21 than the spatial zones 3.

3. Aluminium composite material according to one of the preceding claims, characterized in that the aluminium oxide phase 2 has a mass fraction of 0.1% to 3%.

4. Aluminium composite material according to one of the preceding claims, characterized in that the aluminium oxide phase 2 has a mass fraction of 10% to 90% in the surface zones and a mass fraction of less than 1% in the spatial zones 4.

5. Aluminium composite material according to one of the preceding claims, characterized in that that the spatial zones 2 have a spatial diagonal extension of 10 to 500 micrometers. Aluminum composite material according to one of the preceding claims, characterized in that the aluminum composite material is anisotropic, and that the average extension of the spatial zones 3 in a longitudinal axis 5 is more than 1.5 times the average extension of the spatial zones 3 in a transverse plane 6 to the longitudinal axis 5.A method for producing an aluminum composite material, comprising the following process steps: a) producing an aluminum shot, comprising an aluminum metal body and an aluminum oxide shell, by spraying, blowing, stirring, or pouring an aluminum melt in an oxygen-containing atmosphere; b) compression-molding the aluminum shot, with the aluminum oxide shell shattering, to form aluminum oxide particles, creating a material bond between the aluminum metal bodies and embedding the aluminum oxide particles, to form the aluminum composite material. A method for producing an aluminum composite material according to claim 7, characterized in that a process step a1) is carried out after process step a). that in process step a1), the aluminum shot is tempered to a temperature of 200 to 500 degrees Celsius; that process step b) is carried out with the aluminum shot tempered according to process step a1). A method for producing an aluminum composite material according to one of claims 7 or 8, characterized in that in process step b), the compression molding is carried out by extrusion.

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