Method of co-extrusion of metal products and die set for carrying out the method

Abstract

 The present invention relates to a method of co-extruding at least two metallic materials, a first and a second metallic material (1,4), into an extruded profile, wherein the first metallic material (1) forms an outer shell of the extruded profile and the second material (4) forms a core of the extruded profile, said core being bonded to the outer shell, and wherein the first and the second metallic material (1,4) are separated during at least part of the extrusion process.
The invention also relates to a die set for carrying out the method.

Description

Field of the Invention

[0001] The invention relates to a method of co-extruding at least two metallic materials, a first and a second metallic material, into an extruded profile, preferably a hollow-profile workpiece, wherein the first metallic material forms an outer shell of the extruded profile and the second metallic material forms a core or inner shell of the extruded profile, said core being bonded to the outer shell. Furthermore, the invention relates to an extrusion arrangement used in the method according to this invention.

Background to the invention

[0002] As will be appreciated herein below, except as otherwise indicated, alloy designations and temper designations refer to the Aluminum Association designations as published by the Aluminum Association in 2009.

[0003] Alloys having a poor corrosion resistance are often coated with alloys having a better corrosion resistance to obtain a good corrosion resistance of the final product. In addition, it is possible to use the good properties of alloys having a poor corrosion resistance, e.g. the high strength of a 7xxx alloy can be combined with the good corrosion resistance of a 6xxx alloy or pure aluminium. This also applies to hollow-profile workpieces. A problem in the extrusion of hollow-profile workpieces consisting of two materials is achieving a uniform layer thickness of each material. When co-extruding two alloys, there is the problem of an advance of the inner billet. Accordingly, the inner billet which forms the core material after the co-extrusion of the hollow-profile workpiece is thicker at the beginning of the hollow-profile workpiece than at the end of this workpiece. These effect leads to different material properties across the whole extruded workpiece which is not desired.

[0004] Furthermore, it is a problem to bond a metal foam, especially aluminum foam, to an aluminum hollow-profile workpiece. Commonly, the foamable material is brought into a finished aluminum tube. To foam the foamable material it is necessary to heat the aluminum tube. However, due to a irregular heat transfer between tube and foamable material, it is likely that the aluminum tube partially melts before the foamable material is completely foamed. Therefore, there is a need for a method which overcomes the above mentioned deficiencies.

[0005] Document EP 1 008 406 discloses a method for producing a hollow-profile workpiece of an aluminum alloy, the hollow space of which is filled with a foamable material, by co-extruding the two materials and subsequently foaming the semi-finished product.

[0006] Document WO 2008/107000 discloses a method for applying a metal plating material as a plating layer onto the surface of a profile made of an aluminum alloy as the base material. Thereto, a billet made of the base material and, in front of the billet, a disk comprising substantially the same cross section as the billet and made of the plating material is inserted into the container of an extruder press, and the billet made of the base material is pressed together with the prepositioned disk made of the plating material through the opining of a die, to give a plated profile. Although according to this method aluminum alloy profiles can be provided with a metal plating layer, the method lacks preciseness because the thickness of the coating layer cannot be adjusted exactly. Moreover, plating material, e.g. pure aluminum, is wasted because it is extruded at the beginning of the extrusion process.

[0007] Document DE 10 2007 038 923 discloses a method and a semi-finished product for joining workpieces. The method is characterized by arranging a semi-finished product which consists of an expandable starting material, in a joining area of the workpiece in such a manner that the semi-finished product encloses one of the workpieces. However, this document does not disclose the specific process steps for producing the joined workpiece.

[0008] Document DE 10 2007 006 156 discloses a method for producing a composite body which contains at least one component that is connected to an expandable body. The method comprises the following steps: connecting a pressed body, consisting of an expandable material, with the component, the pressed body and the component being brought into loose contact, shaping the component and/or the pressed body in such a manner that the component and the pressed body are form- and/or force-locked, and expanding the press body, consisting of an expandable material, by external heat supply. The method also relates to an intermediate for producing a composite body. However, in this method a pressed body of the foamable material is formed and then placed into a component having a hollow profile.

[0009] If co-extrusion is to be carried out via regular extrusion arrangements, several problems occur. First of all, the thickness of the materials is not consistent over the length of the extruded hollow-profile workpiece. This means that at the beginning of the hollow-profile workpiece the core material is thicker than at the end the workpiece. Moreover, during extrusion, the two materials are mixed in the burr by turbulences in the die set.

[0010] It is an object of the present invention to provide a method for producing an extruded profile via co-extrusion of at least two metallic materials, wherein the layer thickness of the core material remains substantially constant from the beginning of the extruded hollow profile to the end of the hollow profile. It is another object of the invention to provide a method wherein the bonding between a metal foam and an extruded hollow-profile workpiece is improved.

Summary of the invention

[0011] The invention provides a method of co-extruding at least two metallic materials, a first and a second metallic material, into an extruded profile, wherein the first metallic material forms an outer shell of the extruded profile and the second metallic material forms a core or inner shell of the extruded profile, said core being bonded to the outer shell, and wherein the first and the second metallic material are separated during at least part of the extrusion process. Moreover, the present invention relates to an extrusion arrangement and a die set used in the method of the present invention.

Detailed description of the invention

[0012] The expression "part of the extrusion process" means that it is not mandatory for the method of the present invention that the first metallic material and the second metallic material are separated throughout the whole extrusion process. Preferably, they will be separated for example by walls or any other separation device during the last part of the extrusion process, i.e. while the billets are pressed through the die set. In an embodiment the two materials will be separated over a length of e.g. 10 to 60% in relation to the length of the die set. Preferably, the first and second metallic material will be separated only until just before the extrusion die, e.g. until about 10 - 120 mm, preferably until about 25 to 105 mm before the die.

[0013] The first metallic material and the second metallic material which are to be extruded according to the method of the present invention form an outer billet of the first metallic material and an inner billet of the second metallic material, which may be put together to form together an extrusion (final) billet. In particular, in the (final) billet which is extruded according to the method of the present invention, the inner billet of the second material is surrounded by the outer billet of the first material.

[0014] The extruded profile is preferably a hollow profile (e.g. tube) with e.g. an approximately circular, oval or angular, in particular rectangular cross-section which may have rounded corners. However, the method of the invention may also be used for producing solid profiles, e.g. coated rods, wherein the profiles will preferably have a circular, oval, angular and in particular rectangular cross-section and which may have rounded corners.

[0015] In the method of the present invention the separation of the two metallic materials during the extrusion process can be achieved by providing different compartments and inlets for the first and second metallic material in a die set which is part of an extrusion arrangement. For example, the first and second billet are inserted into different inlets of the die set, the inlets in turn being separated by walls.

[0016] Moreover, this die set can have additional brakes in the compartment of the first and/or the second metallic material whereby the metal flow of each metallic material is regulated. In an embodiment of the present invention the brakes are located only just before the extrusion die, e.g. until about 10 to 100 mm, preferably until about 19 to 70 mm before the die entry. With such an extrusion arrangement it is possible to achieve a substantial flow of the inner and outer billet of each metallic material and, therefore, the inner billet does not longer show an advance.

[0017] The separating device, the brakes and the extrusion arrangement are all made of the same material, preferably tool steel as known in the art.

[0018] Preferably, dependent on the alloys which are used as the first and the second metallic material the shape of the brake is designed. In the present invention the brake is preferably located in the compartment of the second metallic material forming the core of the extruded profile and is suspended on radial spiders or bridges of the die set. The separating device may also be held by radial spiders or bridges. For example, four bridges spand by 90° may form a spider in each case.

[0019] In the method of the present invention, the first metallic material and/or the second metallic material can be an aluminium alloy, a magnesium alloy or a lithium containing aluminium alloy. In an embodiment of the present invention, the first metallic material is a 7xxx alloy and the second metallic material is a 6xxx alloy or a 1xxx-series alloy.

[0020] In an embodiment of the present invention the second metallic material is a foam pre-form (not yet a foam), which consists of an alloy having a lower melting temperature than the first metallic material, and further comprising foaming agents such as hydrides, hydroxides, and carbonates. After the co-extrusion, the extruded profile can be heated to a temperature above that at which the core material melts and expands into a foam core due to the decomposition of the foaming agents.

[0021] A suitable foaming agent is e.g. a metal hydride, wherein the metal is selected from the group consisting of Ti, Fe, Co, Al, Cu, Mg, W, Mn, Cr, Be, or an alloy thereof. During heating of these hydrides, the hydrides will decompose and generate the required hydrogen gas. The hydrogen will lead to the formation of bubbles of the molten foamable metal, e.g. an aluminium alloy. A preferred foaming agent is in the form of titanium hydride (TiH2) powder, and can be added in a quantity of from 0.02 to 8 weight percent to an aluminium alloy.

[0022] Moreover, the present invention relates to a die set for co-extruding at least two metallic materials, a first and a second metallic material, which comprises a separating device for separating the first metallic material and the second metallic material.

[0023] The separating device can comprise different compartments and inlets for the first and the second metallic material. Moreover, the separating device can function as a brake.

[0024] Furthermore, it is possible to position a brake in the compartment of the first and/or second metallic material. Such a brake may have the form of a baffle positioned to slow down the flow of the metallic material in the extrusion direction. Preferably, the brake will be positioned in the compartment of the second metallic material forming the core of the extruded profile. The brake may extend even closer to the die than the separating device. Alternatively, it may be closer to the inlet than the separating device. The form, position and thickness of the brake will determine the amount of slow-down of the flow of the respective metallic material.

[0025] In a further aspect, the present invention relates to the use of the (inventive) extrusion arrangement in the method disclosed in the present application.

[0026] Other objects, advantages and novel features of the present invention will become apparent from the detailed description of the drawings.

Fig. 1

is a schematic, longitudinal sectional view of an extrusion arrangement according to the state of the art;

Fig. 2

is a schematic, longitudinal sectional view of an extrusion arrangement according to an embodiment of the invention, showing the separating device between the inner and outer billet material located in the die set;

Fig. 3

is a schematic, longitudinal sectional view of an extrusion arrangement according to an embodiment of the invention, showing the separating device between the inner and outer billet material and brakes in the compartment of the inner billet material, wherein the separating device as well as the brakes are located in the die set;

Fig. 4

is a longitudinal sectional view of a die set according to an embodiment of the invention;

Fig. 5

is a cross sectional view of the die set of Fig. 4.

[0027] Fig. 1 is a schematic, longitudinal sectional view of an extrusion arrangement according to the state of the art for manufacturing a hollow-profile workpiece made of two metallic materials 1, 4. The extrusion arrangement comprises a container 2, which comprises a cavity 12 for receiving billets of the metallic materials 1, 4, wherein the first metallic material 1 forms the outer billet and the second metallic material 4 forms the inner billet. A ram (stem) 3 is guided in the cavity 12 and can perform a longitudinal movement along the arrow 7 in order to push the metallic materials 1, 4 through the die set 16. The die set 16 comprises the die 10 and the die holder 6. The die 10 is preferably ring-shaped in order to produce a hollow profile 11 having an outer shell of the first metallic material 1 and an inner layer/core of the second metallic material 4.

[0028] In the die set 16, the metallic materials 1, 4 are guided around a mandrel 5 positioned along the longitudinal axis of the die set/extrusion arrangement.

[0029] For manufacturing an extruded profile, the metallic materials inserted into the cavity 12 of the container 2 are pressed by the ram 3 around the mandrel 5 through the die 10, whereby an extruded hollow profile 11 is created whose cross-section depends on the shape of the die 10.

[0030] Fig. 2 is a schematic, longitudinal sectional view of an extrusion arrangement according to an embodiment of the invention for manufacturing a hollow-profile workpiece made of two metals 1, 4. The extrusion arrangement comprises a container 2 having a hollow space or cavity 12 for receiving billets of the metallic materials 1, 4, a ram 3 which is guided in the container 2 and presses the metallic materials 1, 4 through the die 10, and a separating device 8 for separating the two metallic materials 1, 4, i.e. the inner billet of the first metallic material 4 and the outer billet of the second metallic material 1, in the die set 16.

[0031] For manufacturing an extruded profile, the metallic materials in the cavity 12 are pressed by ram 3 around the mandrel 5 through the die 10 of the die set 16, whereby an extruded hollow profile 11 is created whose cross-section depends on the shape of the die 10. The separating device 8 may e.g. be the separating wall between two compartments in the die set 16, i.e. one compartment for the outer billet and one compartment for the inner billet. As shown in Figures 2 and 3, the separating device 8 is located in the die set 16 distanced from the die 10 and the mandrel 5.

[0032] In extrusion direction downstream of the separating device 8, the two metals 1 and 4 begin to be pressed together before flowing through the die 10. In this area 14, metals 1 and 4 are bonded together to form a weld-like bond. Therefore, this area 14 is designated welding chamber.

[0033] Fig. 3 is a schematic, longitudinal sectional view of an extrusion arrangement according to another embodiment of the invention for manufacturing a hollow-profile workpiece 11 made of two metals 1, 4. The assembly is the same as described in Fig. 2 and further contains brakes 9 in the die set 16, positioned in the second metallic material 4 to regulate the flow of this material. Apart from this difference, the extrusion arrangement functions as the extrusion arrangement described in Fig. 2.

[0034] Fig. 4 is a longitudinal sectional view of a die set according to an embodiment of the present invention for manufacturing a hollow-profile workpiece made of two metals 1, 4 along the line A-A in Fig. 5. In this figure, the section through the first metallic material 1 is shown dashed, whereas sections through the second metallic material are shown dotted. The figure also shows the hollow profile 11, the cavity 12 extending through the die holders 6, and the die ring 7 holding the die 10, through which a hollow profile 11 is extruded. The figure additionally shows a separation device 8 between outer billet material 1 and inner billet material 4 and a brake 9 located in the compartment of the inner billet material. In the portion between the downstream end of the separating device 8 and the die 10, the first and the second metallic materials 1, 4 are bonded together in the welding chamber 14.

[0035] When manufacturing an extruded profile, the metallic materials are pressed through the die 10. The die 10 forms the outer contour of the extruded profile while the mandrel 5 forms the inner contour of the extruded profile.

[0036] Fig. 5 is a cross sectional view of the extrusion arrangement of Fig. 4. This figure shows four inlets 13 for the billet of the first metallic material and four inlets 15 for the billet of second metallic material. Each inlet 13 is separated from each inlet 15 by a wall 8, which forms the separating device. In this case the brake 9 is approximately rectangular with rounded corners. Moreover, this figure shows the spider or bridge 17 of the die set. The mandrel 5 is surrounded by the hollow profile 11 having a rectangular shape with rounded corners.

Examples

Example 1

[0037] A 6063 alloy was co-extruded with a foam pre-form of a foamable material according to the method of the present invention wherein the 6063 alloy forms the shell of the extruded profile.

[0038] The tensile properties of the hollow-profile workpiece were measured by the yield strength Rp 0.2 and the tensile strength Rm. The hollow-profile workpiece shows a yield strength of 169 ± 1 MPa and a tensile strength of 226 ± 1 MPa and an elongation A of 13.5 ± 0.5%. The standard requirements for a 6063 alloy with temper T6 are a yield strength of 160 MPa and a tensile strength of 215 MPa and an elongation of 10%. By using the method of the present invention these standard requirements were fulfilled, although a softer layer was used as the inner billet.

[0039] The tensile properties were tested with three samples, one from the beginning, one from the middle, and one from the end of the hollow-profile workpiece. The results are shown in Table 1.

Table 1

sample	Yield strength [MPa]	Tensile strength [MPa]	Elongation [%]
Workpiece, beginning	170	225	13.9
Workpiece, middle	169	227	13.0
Workpiece, end	168	227	12.9

[0040] Table 1 shows that the tensile properties over the whole hollow-profile workpiece show very low variations in yield strength and tensile strength.

Example 2

[0041] A 6063 alloy was co-extruded with a 7020 alloy, wherein the 6063 formed the inner billet and the 7020 the outer billet. The materials were co-extruded to form a tube-like hollow profile.

[0042] The thickness of the inner layer was stable over the length of the workpiece, namely maximally 4.18 mm at the beginning of the workpiece and only marginally thinner, namely maximally 3.85 mm at the end of the workpiece.

[0043] The alloys of inner and outer layer were well-bonded together with no pores between the layer, although a few scattered oxides were visible at the interface between the layers.

[0044] The mechanical properties were much higher than the specification for 6063 alloys, as can be seen in table 2. Please note that around 50% of the wall thickness of the profile was formed by the 6063 alloy. In this light, the tensile strength values are very good.

[0045] It is also notable that, again, the differences in mechanical properties between the beginning and the end of the profile are almost within measurement error.

[0046] Thus, the two alloys could well be co-extruded together. The bonding between the alloys is very good, and the properties are constant over the length of the extrusion workpiece.

Table 2

Alloy	Yield strength Rp0,2 [MPa]	Tensile strength Rm [MPa]	Rm/Rp0,2 [%]	Elongation [%]
EN 755-2 6063 T6	170	215		8
EN 755-2 7020 T6	290	350		10
Workpiece 7020/6063 beginning	265 ± 6	314 ± 7	84	14.2 ± 0.2
Workpiece 7020/6063, end	270 ± 7	316 ± 14	85	13.8 ± 0.3

Claims

1. Method of co-extruding at least two metallic materials, a first and a second metallic material (1, 4), into an extruded profile, wherein the first metallic material (1) forms an outer shell of the extruded profile and the second metallic material (4) forms a core of the extruded profile, said core being bonded to the outer shell, and wherein the first and the second metallic material (1, 4) are separated during at least part of the extrusion process.

2. Method according to claim 1, wherein the first and the second metallic material (1, 4) are separated during the extrusion process by using different compartments and inlets in a die set.

3. Method according to claim 1 or 2, wherein during the extrusion process a flow of the first and/or the second metallic material is regulated by a brake (9) which is located in the respective compartment of the metallic material in the die set.

4. Method according to any one of the preceding claims, wherein the first and/or the second metallic material (1, 4) is an aluminium alloy or a magnesium alloy.

5. Method according to any one of the preceding claims, wherein the first and/or the second metallic material (1, 4) is an aluminium lithium alloy.

6. Method according to any one of the preceding claims, wherein the second metallic material (4) is a foam pre-form of a foamable material.

7. Method according to any one of the preceding claims wherein during the extrusion process the outer shell of the first metallic material (1) and the core of the second metallic material (4) are bonded by welding.

8. Method according to claim 6 or 7, wherein after the co-extrusion the extruded profile is heated to a temperature above the temperature at which the core of the second metallic material melts to expand the second metallic material (4) into a foam.

9. A die set for co-extruding at least two metallic materials, a first and a second metallic material (1, 4), into an extruded profile, wherein the first metallic material (1) forms an outer shell of the extruded profile and the second metallic material forms a core of the extruded profile, comprising a separating device (8) for separating the first metallic material (1) and the second metallic material (4).

10. The die set of claim 9, wherein the separating device (8) comprises different compartments and inlets for the first and the second metallic material (1, 4).

11. The die set according to claim 9 or 10, wherein the separation device (8) functions as a brake.

12. The die set according to claim 10 or 11, wherein in the compartment of the first and/or second metallic material comprises a brake (9).

13. Use of the die set according to claims 9 to 12 in the method according to any one of claims 1 to 8.

Drawing