WO2002018089A1 - Method for joining foamed metallic materials - Google Patents

Abstract

The invention relates to a method for joining foamed metallic materials (1, 2). According to said method, a rotating stud is moved in the joining area (7) between the two foamed materials (1, 2) in a friction fit, in such a way that the two objects (1, 2) in the joining area (7) are heated and plasticized as a result of the friction and the pressure that is exerted on the foamed materials (1, 2) by the friction stud (6). As a result, the two foamed materials (1, 2) are welded together in the joining area (7).

Description

 Process for joining metallic foam materials

The present invention relates to a method for connecting metallic foam materials to other metallic materials. Such methods are required in metalworking, especially when using the new metallic foam materials.

Metallic foam materials, also called cellular metallic materials, especially made of aluminum, have met with great interest with the invention of a new powder metallurgical manufacturing process, which is published, for example, in DE 40 11 836.0, and are currently being introduced into industrial production. They consist of three-dimensional arrangements of gas-filled cells or pores made of metallic material. Such metallic foam materials are not only processed into sheets. processed, but also used for example in sandwich structures, with a central core layer made of metallic foam between two layers of conventional metal sheets and the like is arranged. Such sandwich structures, preferably made of aluminum, are produced by gluing or roll-cladding conventional sheets onto the core layer. Such sandwich structures are used in particular in the vehicle industry. Metallic foams or the associated not yet foamed semi-finished product and process for their production are further disclosed in DE AS 1 933 321 and PCT / WO90 / 00115. Metallic foams used in the present invention and their production are described in particular in J. Banhart "Production Methods for Metallic Foams" in "Metal Foams / Fraunhofer USA Symposium, Stanton, Delaware, 7-8 October 1997, Verlag Metall Innovation Technologie MIT 1998, p 3 to 9. As far as metallic foams are referred to in this context, metallic foams of this type are meant. A further illustration of such metallic foams can be found in Automobiltechnische Zeitschrift, ATZ / MTZ special edition "Materials in Auto obilbau 1998, Pages 66 to 69.

The increasing use of metallic foams in the industrial field makes it necessary to provide joining methods with which semi-finished products made of metallic foam or foamed objects can be further processed, in particular joined together. To date, only adhesive methods have been available for this purpose, the bonding of aluminum components not being a satisfactory solution, since only overlapping connections and no butt connections are possible. Furthermore, the Temperature resistance of the entire component is determined by the adhesive. The welding processes tested so far, such as MIG (metal inert gas welding) or WIG (tungsten inert gas welding) and the like, do not offer a satisfactory solution, since the foam-like structure of the semi-finished products to be joined does not enable a reproducible weld connection with these processes , Such unsuccessful welding processes are described, for example, in Schweissen & Schneid, 1998, pages 786 to 787. There it was shown that these new materials pose various foam-specific problems. The laser-assisted joining of the cellular material leads to a breakdown of the foam structure, which can only be compensated for by massive feeding of wire-shaped welding consumables.

In general, as also described there, there is a risk during welding that the material which has not yet been foamed has already outgassed due to the heating above the melting point, as is also done for foaming, so that the welded material no longer foams in the vicinity of the welding line shows. In the case of materials which have already been foamed, it is expected that the entire foam structure will collapse as a result of the melting of the material during welding, so that a mechanically stable connection is not possible.

It is therefore an object of the present invention to provide a method by which a material connection between metallic foam materials in the non-foamed or foamed state with other metallic materials is made possible, or composites of such materials whose cellular structure is not substantially destroyed or impossible. was made and which nevertheless have a stable, mechanically resilient connection.

This object is achieved by the method according to claim 1 and the composite according to claim 8. Advantageous further developments of the method and the combination are given in the respective dependent claims.

According to the invention, the above object is achieved by a method in which the metallic foam material is connected to the further metallic object by means of the friction-stir welding method. Such a method is known for example from EP 0 615 418 B1 for materials such as metals, alloys or thermoplastics. This method is surprisingly suitable for connecting and joining metallic foam materials. This contributes to the fact that the connection formation during friction stir welding takes place in a solid state and thus the known difficulties in welding aluminum can be avoided.

Surprisingly, friction stir welding does not lead to the fact that the not yet foamed metallic foam material outgasses, although it is plasticized along the weld seam. This makes it possible to foam up such connected foam materials later and to obtain the desired structure. In the same way, friction stir welding does not destroy the foam-like structure of the metallic foam material in the already foamed state, so that a firm connection seam between the metallic, foamed foam material and other metallic materials is possible. The friction stir welding according to the invention is carried out by means of a friction bolt, the bolt being rotated between the two semi-finished products in such a way that the semi-finished products are heated by the friction and the pressure is plasticized and the material transport caused by the rotation leads to a welding of the plasticized materials , The friction body suitable for friction stir welding is guided linearly or in a curve such that it touches the side surfaces of the objects firmly clamped on the opposite side and is thermally activated by friction. This thermal activation consequently places the surfaces in a bondable state. At the same time, a pressure is generated by the friction body in the area of the binding zone, through which the edge areas are plasticized and material is transported to the opposite side as described. The quality of the weld seam is determined by the shape and the material of the friction pin as well as by its positioning, speed, feed speed and feed movement. The clamping technology for the semi-finished products is also of major importance for the quality of the weld. The process is therefore preferably carried out with the raw material not yet foamed, and the material is foamed only after welding. The raw material that has not yet been foamed can be clamped in a simple manner for the friction-stir welding.

Compared to all other welding processes, friction stir welding is particularly suitable for the connection of metallic foam materials. Because of the design of the friction pin, only the connection areas that are at a certain point in time of the frictional movement are activated exposed to the bolts. The connection itself then takes place in the solid state, damage to the welded connection as a result of outgassing processes is thereby largely excluded. In contrast to conventional welding processes, no welding consumables are required and connections of different types are also possible.

The following are some examples of the method and composites of the invention ^'are given.

Show it:

• Figure 1 is a schematic diagram of the friction stir welding with metallic foam materials;

Figure 2 shows an example of the welding of two sheets of metallic foam material not yet foamed;

FIG. 3 shows an example of the welding of two sandwich structures with a core layer made of foam material that has not yet been foamed;

FIG. 4 shows a break test on a material according to FIG. 3; and

Figure 5 shows an example of the welding of a conventional metal sheet with a metallic foam material.

Figure 1 shows a schematic diagram for the friction-stir welding of metallic foam materials. The reference numerals 1 and 2 denote a first and a second workpiece, which are to be welded together along a welding zone 7. The welding is carried out by means of a tool 4, which has a tool shoulder 5 and a pin 6 which projects therefrom between the workpieces 1 and 2. The pin 6, which can be unprofiled or profiled, rotates at high speed and thus heats the material it is contacted in the welding zone 7.

The entire arrangement is applied to a solid base 3 and the pin or bolt 6 is pressed into the material of the workpieces 1 and 2 via the tool shoulder 5.

In Figure 1, the welding zone or welding path 7 can be seen, which has already been traversed by the pin 6 and the tool shoulder 5. With the reference characters 8, 8 'and a is the area in which the original structure was obtained in the workpieces 1 and 2. The reference numerals 9, 9 'and b denote a zone which is already influenced by the heat generated by the bolt 6. Reference number 10 denotes a thermomechanically influenced structure which is plastically deformed with some areas of recrystallization. Numeral 11 denotes a dynamically recrystallized area (nugget).

Here, as in the following figures, a corresponding element is denoted by corresponding reference numerals. Figure 2 shows an example of the welding of aluminum foam AlSi7 (aluminum alloy, made from a powder mixture with the composition 92.5% Al, 7% Si and 0.5% TiH as blowing agent). Both sheets 1 and 2 consist of ω ω ro t- ¹ Cn o Cπ o Cn Cn

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they consist of conventional metal, while only the intermediate layer 1c or 2c has been foamed.

FIG. 4 shows the result of a tensile test on a friction-stir-welded, non-foamed semi-finished product made of AlSi7.

Here again it can be seen that the two sandwich-like semi-finished products, as also shown in FIG. 3a, are connected to one another by a welding track 7. Obviously, the weld seam 7 has such a high mechanical stability that the break occurs due to the tension with a break line 40 adjacent to the weld path. This also proves the high stability that can be generated by friction stir welding with metallic foam material in the non-foamed state.

FIG. 5 shows a further example of welding a workpiece 1 made of aluminum foam material in a still unfoamed state with a conventional sheet 2 made of an aluminum-magnesium alloy with 3% magnesium. The welding path 7 can again be seen in FIG. 5A.

Figure 5B shows the same material in expanded state, but now viewed from the rear, so that the aluminum foam material 1 on the right side ^• and the conventional aluminum-magnesium sheet 2 can be seen on the left. It can be seen immediately that the weld path 7 has produced an excellent connection between these two different materials. In summary, for the first time and completely surprisingly, the present invention offers the possibility of connecting metallic foam materials to one another by a welding process without preventing or destroying the typical structures of the metal foam. This is not possible with other welding processes.

Claims

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