CA2151786C

CA2151786C - Formable composite panel

Info

Publication number: CA2151786C
Application number: CA002151786A
Authority: CA
Inventors: Corrado Bassi; Bernard Florey
Original assignee: Alcan Technology and Management Ltd
Current assignee: 3A Composites International AG
Priority date: 1994-07-13
Filing date: 1995-06-14
Publication date: 2004-12-21
Anticipated expiration: 2015-06-14
Also published as: CA2151786A1; EP0692371B1; CH687815A5; DE59509121D1; EP0692371A1

Abstract

Formable composite panel having a plurality of layers with at least one outer layer of an aluminium alloy and a core layer out of plastic. The core layer is 20 to 150 µm thick and each outer layer of aluminium alloy is 400 to 1600 µm thick and each layer of aluminium alloy is of a formable aluminium alloy of the type AA 1xxx (pure Al), AA 3xxx (AlMn), AA 5xxx (AlMg), AA 6xxx (AlMgSi), AA 7xxx (AlZnMg) or AlFeSi. Preferred composite panels feature a core e.g. of acrylic viscoelastic polymers and on both sides of the core outer layers of the above mentioned aluminium alloys.
The composite panels may for example find application as car body sheet in the production of the bodies of road bound vehicles such as private cars.

Description

Formable Com~~asite Panel The present invention relates to a formable composite panel having a plurality of layers with at least one outer layer of an aluminium alloy and a core layer out of plastic, and relates also to the manufacture of and use of the composite panels.
Known from EP 0 019 835 are formable metal-plastic-metal structural laminates and processes for manufacturing such laminates. The metal-plastic-metal structural laminates may e.g. concern such having a core of polymeric resin, clad on both sides with a metal skin which has a thickness e.g. of 0.05 to 0.5 mm. The choice of metal-plastic-metal laminate makes it possible to achieve good stretch formability without delamination. If aluminium or aluminium alloys are selected for the metal skin, then the thickness of that metal skin may amount to 150 to 300 um and the thickness of the intermediate polymeric resin between 450 and 900 lun . This results in a laminate of maximum thickness of 750 to 15001un . The described structural laminates exhibit relatively small sheet thicknesses and a thick layer of plastic. This is intended to provide laminates having good sound insulation properties.
Described in EP 0 184 549 is a thin formable composite panel having a plurality of layers, which is made up of at least one outer layer of an aluminium alloy with a flat stress-strain curve and a thermoplastic core layer of plastic. Described are outer layers of 0.05 to 1 mm thickness and core layers of 0.3 to 3 mm. The outer layers are e.g. of iron-bearing aluminium alloys. These composite panels refer to particular alloys and exhibit an exceptionally thick core layer.
The above mentioned composite panels are suitable for many purposes, but not e.g. for the production of equipment and automobiles. In these Helds, there is a greater demand for composite panels with high structural strength accompanied by sound and vibration absorbing characteristics. Such composite panels are required e.g. for the housings of machines and equipment and in particular in the bodywork of road bound vehicles such as lorries and private cars. Decisive from the practical standpoint are good formability by commonly known methods such as e.g, deep drawing, stretch drawing, or bending, and the easy use of conventional joining methods such as e.g. flanging, spot welding, clinching etc.
Sandwich-type laminates featuring thin-gauge sheets of two steel sheets and an intermediate viscoelastic layer have become known e.g. for the production of vehicle bodies and engines, housings and the like. The knowledge available up to now points to steel as being en excellent material for the outer layers of such thin-sheet sandwich panels, as a very good sound dampening effect can be achieved with steel combined with a viscoelastic intermediate Case 2032 layer. The degree of sound dampening achieved with such thin-sheet sandwich panels of steel combined with an intermediate layer is substantially greater than that using steel alone and very substantially greater than with aluminium. Because of its low density, aluminium would be an excellent material for the outer layers of composite panels as this would enable a considerable reduction in weight to be achieved.
The object of the present invention is to provide a composite panel which has optimum sound dampening properties, can be joined using the usual joining technologies such as e.g. spot welding, clinching or flanging, is easily deformed and can be worked into almost any shape required e.g. by deep-drawing, stretch-drawing or other forming methods, and which makes use of the advantages of aluminium such as corrosion resistance, low density etc.
That object is achieved by way of the invention in that the core layer is 20 to 150 um thick and each outer layer of aluminium alloy is 400 to 1600 um thick and each layer of aluminium alloy is of a formable aluminium alloy of the type AA lxxx (pure Al), AA 3xxx (AIMn), AA
Sxxx (AIMg), AA 6xxx (AIMgSi), AA 7xxx (AIZnMg) or AIFeSi.
Highly formable aluminium alloys are useful for the outer layers. The x in the alloy designations may be a number from 0 to 9 and can be taken from the register of aluminium alloys.
Preferred are outer layers of an age-hardenable aluminium alloy of the AIMgSi type, where the magnesium and the silicon content lie in an area of the ternary equilibrium phase diagram for AIMgSi alloys limited by the boundary points A = 1 % silicon/ 0.6 % magnesium B = 1.8 % / 0.6 % magnesium silicon C = 1.8 % / 0.2 % magnesium silicon D = 1.2 % / 0.2 % magnesium.
silicon Figure 1 shows the equilibrium phase diagram for such AIMgSi alloys and the corresponding composition limits that define the field in question. Figure 1 is the ternary phase diagram for the AIMgSi alloys i.e. the diagram showing the solubility limits in the solid state and has been taken from METALS HANDBOOK, 8th edition, Vol. 8, Metallography, Structures and Phase Diagrams, ASM, 1973, S. 397 and plotted on orthogonal axes.
Case 2032 The outer layers are in particular in the form of sheets, strips and thin strips of high mechanical strength, good formability and low Baring properties. In particular, e.g. in the case of the above mentioned AIMgSi alloys, the magnesium and silicon contents of the AIMgSi alloys may be selected such that, at the homogenisation and solution treatment temperature of 450°C to 550°C which is normal for this type of alloy, they exhibit a silicon-excess of at least 0.1 %, preferably at least 0.2 °Io which cannot be dissolved in the alpha matrix and is in a finely dispersed form in that matrix, the total silicon content being at most 1.8 % Si. The alloy out of which the outer layer is made, may also contain additions of at most 0.3 % chromium, manganese, zirconium and/or titanium.
'The alloy for the outer layers may be manufactured by continuous casting or strip casting, hot and cold rolling to the required sheets, coils and thin strips, the alloy preferably being cooled in the air after hot rolling. The cold rolled alloy may be solution treated for up to 2 hours, preferably 1 hour and in particular at most 30 minutes including heating up time. A highly preferred version is such that, in the course of cold rolling, the alloy is solution treated at a thickness of 1 to 5 times the final thickness, preferably at 1.3 to 4 times the end thickness, quenched, naturally age-hardened and cold rolled to final thickness in this condition.
Useful is a composite panel having a 20 to 150 dun thick core layer on both sides of which is a 400 to 1600 pm thick outer layer of aluminium alloy. Preferred are composite panels having a 25 to 50 Pm thick core layer. Preferred are composite panels having 400 to 1500 thick outer layers. The core layer of plastic may be a material that is soft under shear loading conditions e.g. an elastomer or a thermoplastic. Suitable thermoplastics are e.g.
polyolefins of the polyethylene type and polypropylenes, whereby, crystalline and amor phous or mixed forms rnay be employed. Further core layers of plastic may be of the polyurethane type or of the type containing acrylics, in particular acrylic viscoelastic polymers may be selected for this purpose. The thermoplastic polymers may for example also be a copolymer of polyethylene or polypropylene and an ethylene type unsaturated carboxylic acid. The preferred carboxylic acid is acrylic acid.
The core layer may exhibit a short-time elastic modules of 103 to 108 Pascal and a loss factor of GII/GI of 0.1 to 1 in the service temperature range. The service temperature may be e.g. from - 40°C to + 100°C and usefully from - 10°C
to + 40°C.
The plastic core layer may be for example a 25 to 150 Nm thick film or a 20 to 150 ~
thick laminate of films or a 20 to 150 um thick coating. The total thickness of coatings, however, is preferably 25 to 50 lun . A film or film laminate may exhibit for example a lower and upper adhesive layer and between these the film or film laminate.
The adhesive Case 2032 layer may be both an adhesive in the form of a coating or a layer, or may be an adhesive film. The adhesive may be employed in amounts of e.g. 0.1 to 15 g/m2, or an adhesive film may e.g. be 6 to 25 um thick. A film laminate may for example be made up of two or more monofilms of the same or of different plastics. The formable composite panel according to the present invention preferably feature a lower and an upper outer layer and between them the above mentioned core layers. Among the useful versions of composite panels are those with an upper and lower outer layer and with a core layer in the form of a plastic film that exhibits adhesive properties towards the metal layers. In another preferred version the core features a plastic film or a plastic film laminate which is joined on both sides to the outer layers. It is also possible to provide one or both outer layers with a layer of adhesive in liquid or pasty form or in the form of a dry coating, and to bring the coated side of the outer layer into contact with the non-coated side of an untreated outer layer or to bring both adhesive treated sides of the outer layers into contact with each other and to join these permanently to each other. The adhesive layer may be deposited e.g.
by brushing, spraying, wiping, rolling etc. either over the whole surface or only part thereof e.g. in the form of a pattern on the outer layer surfaces) in question. If desired, a solvent or dispersion agent may be removed under reduced pressure and/or under the influence of heat or simply by allowing to dry. The outer layers, may be joined permanently to each other under the influence of pressure and/or heat, this whether employing the aid of adhesives, films, or adhesives and films.
The composite panels according to the present invention may find application in a form featuring two outer layers of the same or different thickness. When outer layers of different thickness are employed, the thickness of the second outer layer may be up to 4 times the thickness of the first outer layer. An outer layer of 1.1 to 3 times the thickness of the first layer is preferred. Different thicknesses of outer layers result in panels of higher bend strength than monolithic panels of the same overall thickness. If the application calls for low weight, then the thickness of one of the outer layers should be as small as possible.
Preferred are composite panels comprising a core with an outer layer on both sides of the core, where one outer layer is thicker than the other outer layer, and the outer layers are of an alloy of elevated strength belonging to the AA 6XXX, AA 7XXX or AA SXXX
series of alloys having a manganese content greater than 3%. Such composite panels exhibit a high degree of stiffness, especially the thicker outer layer is on the outside of a shaped part. Also preferred are composite panels having a core layer and two outer layers, where one of the outer layers is of a soft aluminium alloy from the alloy series AIMn, AIMg with a magnesium content of less than 3%, or AIFeSi. Such composite panels Case 2032 exhibit good formability and an excellent appearance after coating, especially when the outer layer is of a soft alloy.
Composite panels according to the invention having two outer layers may feature outer layers of the same or different alloys.
One or both outer layers may be provided with a roughening pattern on one or both sides.
Especially for the purposes of adhesive joining a surface with a roughening pattern offers a higher specific surface area.
The texturing of the surface with a roughening pattern is usefully done by means of work rolls exhibiting an appropriate roughening pattern which is transferred to the surface of the outer layers in an embossing roll pass with small reduction in thickness.
As in all embossing processes, the topography of the work roll and therefore that of the embossed surface are complementary to one another i.e. peaks or raised parts on the roll surface become valleys or recesses in the surface of the component and vice versa.
In the case of aluminium or aluminium alloy sheets the transfer of the roughening pattern of the work rolls to the sheet is preferably performed during the last cold roll pass with a reduction of 3 to 5%.
Suitable roughening patterns for performing the process according to the invention can be achieved by embossing the surface with a texture from work rolls, the surface of which has been roughened by the following processes.
1. Spark erosion processes (EDT - electrical discharge texturing). In EDT
processes the roll is turned past a row of electrodes accompanied by axial oscillation, whereby the surface is textured to a predetermined depth. The discharge of electrical energy between the roll surface and the electrodes through a dielectric fluid between electrodes and roll surface, causes small craters to form on the roll surface.
The rough-ess of the roll can be selected in a known manner by means of a series of machine para-meters. The roughness pattern is a statistical distribution of peaks and valleys. The EDT process enables average roughness values Ra of 1 to 6 jlm to be selected.
Average value and peak number are to a large extent related to one another.
Suitable for the process according to the invention is a surface texture of low roughness and high peak number.
Case 2032 2. Shot blast methods (SBT - shot blast texturing) . In the case of SBT the sharp edged shot is fed to a centrifugal wheel which propels the shot onto the roll. On striking the surface of the roll the individual particles of shot lose their kinetic energy and in the process plastically deform the surface of the roll. The roughness of the roll may be regulated by the choice of shot particulate size, the speed of rotation of the centrifugal wheel and other machine parameters. Average roughness values Ra of 1.5 to 6 lun may be achieved this way. Here too, the roughness pattern corresponds to a statistical distribution of peaks and valleys.
3. Lasertex methods. In this process a laser beam is focused onto the roll surface by means of a lens and interrupted by means of a chopper wheel. In the process, the roll is rotated and displaced along its axis of rotation. The roll material is melted locally at the point of focus of the beam.. The desired roughness is achieved via the speed of rotation of the roll, the power of the laser and the point of focus of the laser beam.
The rough-ness pattern has the appearance of a uniform distribution of craters on the roll surface.
4. Electron beam processes. (EBG - electron beam graying). In the EBG process a rotat-ing roll is led, under vacuum, past a stationary electron beam generator. On striking the roll, the high energy electrons release their energy in the form of heat. If the temperature is sufficiently high, the volume of material struck is melted and partially evaporated. The roughness pattern appearing on the roll is comparable with that produced by the lasertex method. The crater depth of the can be adjusted at will and . depends on the duration of impingement of the beam. The crater diameters depend on the focusing of the electron beam.
5. Isomill process. In the Isomill process the roll surface is engraved in the circumferential direction and in the transverse direction to produce a roughness pattern that is essen-dally quadratic in form.
The outer layers may, if desired, be anodised, be treated with another process that thick-ens the oxide layer, or they may be decoratively anodised. Also, the surfaces of the outer layers may be provided with conversion layers e.g. a chromate or phosphate conversion layer. Likewise, especially the visible surfaces of the composite panels may be altered structurally and/or chemically i.e. by coating, chromating, phosphadng and provided with other layers that change the attractiveness of the material or improve the surface. The composite panels according to the present invention may be manufactured in the form of Case 2032 ,._ -7- _ panels or in strip form, and the strips may be rolled or coiled and then uncoiled and cut to size according to the requirements of its use.
The present invention relates also to a process for manufacturing the composite panel according to the invention, whereby a first outer layer, is for example uncoiled from a spool and one of the surfaces is covered completely with an adhesive film as the core layer. As a rule the adhesive film contains a protective layer in order to prevent the adhesive film from adhering to itself and to the alignment and pressure rolls.
The adhesive side of the film is brought into contact with the surface of the outer layer and joined permanently to it by means of rolls applying pressure to it. Following that, the protective film is pulled off the adhesive film. A second outer layer is uncoiled from a second spool and brought onto the adhesive layer; under the influence of pressure and/or heat, for example by passing between rollers or rolls or in a strip press or the like, the second outer layer is joined permanently to the outer layer and adhesive film laminate to give a three layer laminate. This composite may again be coiled up or be cut to size immediately.
In another manufacturing process the composite panels according to the invention may be produced as follows. A first outer layer is e.g. uncoiled or unrolled. An adhesive in liquid to pasty form is applied, covering one of the surfaces of the first outer layer, for example by spraying, brushing or wiping or the like, and any solvent present removed under reduced pressure and/or elevated temperature. The adhesive forms the core layer. The second outer layer, likewise e.g. uncoiled strip, is unrolled and preheated and then the first outer layer with the coating of adhesive and the preheated second outer layer presented to each other such that the adhesive lies between the two outer layers. The outer layers are joined together permanently by means of rollers or rolls or in a strip press, for example under pressure and/or temperature, if necessary cooled and coiled again or cut directly to size. In this process the second layer may be prepared e.g. in such a way that the outer layer is previously covered with an adhesive as core layer in liquid to pasty form, any solvent present removed under reduced pressure and/or heat and, if desired, also a protective film laid over the adhesive, and the strip coiled up again. If now such a coiled strip is employed, one adhesive layer may be brought into contact with the other adhesive layer, whereby a more intimate join is achieved between the adhesive layers than would be possible between the adhesive layer and metal. The layers of adhesive form the actual core layer in the final composite.
Figure 2 shows a cross-section anywhere in a formable panel according to the invention, comprising for example of the two outer layers 1 and 3 and the core layer 2.
Case 2032 The present invention relates also to shaped parts containing the formable panel according to the present invention. Shaped parts may be for example body parts of road bound vehicles, housings, parts of housings for machines and equipment, covers and cladding for machines, equipment and buildings. Car body parts may be for example car bonnets, boot lids, doors, wings, inner wings, parts separating passenger cabin and engine space, interior cladding of doors, roofs, bumpers or also chassis parts such as longitudinal and transverse beams or longitudinal and transverse stiffening elements. Housings and parts of housings for machines and equipment may be for example cylinder head covers or oil sumps on internal combustion engines, cladding for electromotors and the like; these may also be cladding parts for household equipment such as refrigerators, washing machines, dish washers, clothes washers, vertical and horizontal deep-freeze boxes etc.
Covers, dividing walls, walls, floors, roofs etc., or shaped parts on buildings etc., may likewise be included.
Parts that may be subject to vibration e.g. also housings or covers on building machines or testing equipment may also be manufactured out of the composite panels.
The composite panels may also be provided on one or both sides with cladding or decorative layers such as e.g. paint or other coating layers, or also layers of plastic or textiles or other textile-like material. For example, for the interior cladding of vehicles, such as vehicle doors, the composite panels may be clad with leather, leather-like or textile material.
The composite panels according to the present invention are fonmable into almost any shape e.g. by means of deep-drawing, stretch-drawing or by combinations of both such methods. Further, the composite panels can be joined by conventional joining methods.
The composite panels according to the invention can be joined and so made into larger parts e.g. by means of resistance welding, stud welding, laser welding, spot welding, adhesive bonding, bolting, folding, flanging or clamping.

Case 2032

Claims

1. A formable composite panel consisting of a plurality of layers with at least one outer layer consisting of an aluminium alloy and a plastic core layer, characterized in that the core layer is 20 to 150 µm thick, each outer layer is 400 to 1600 µm thick and each outer layer is made of an age-hardenable aluminium alloy of the AlMgSi-type, the magnesium and silicon content being situated in a field of the ternary phase diagram for AlMgSi alloys having the corner points A = 1 % silicon/0.6% magnesium B = 1.8% silicon/0.6% magnesium C = 1.8% silicon/0.2% magnesium D = 1.2% silicon/0.2% magnesium.

2. A composite panel according to claim 1, characterized in that the composite panel has a core layer having a thickness of 20 to 150 µm and respective outer layers on either side of the core layer having a thickness of 400 to 1600 µm.

3. A composite panel according to claim 2, wherein said outer layers each have a thickness of 400 to 1500 µm.

4. A composite panel according to claim 1, 2 or 3, characterized in that the core layer has a thickness of 25 to 50 µm.

5. A composite panel according to claim 1, 2, 3 or 4, characterized in that the core layer has a modulus of elasticity of 10 3 to 10 8 Pascals and a loss factor GII/GI
of 0.1 to 1.

6. A composite panel according to claim 1, 2, 3, 4 or 5, characterized in that the core layer is an acrylic-containing polymer.

7. A composite panel according to claim 6, wherein said core layer is an acrylic-containing visco-elastic polymer.

8. A composite panel according to claim 1, 2, 3, 4 or 5, characterized in that the core layer is a visco-elastic polymer layer.

9. A composite panel according to claim 2, characterized in that the outer layers have different thicknesses and the thickness of one outer layer is up to 4 times the thickness of the other outer layer.

10. A composite panel according to claim 9, wherein one outer layer has a thickness of 1.1 to 3 times the thickness of the other outer layer.

11. A composite panel according to any one of claims 1 to 10, characterized in that at least one of the surfaces of at least one outer layer is provided with a roughness pattern.

12. A composite panel according to any one of claims 1 to 5, characterized in that the core layer is a lacquer, a film, a film composite or a combination of lacquer with a film or a film composite.

13. A process for the production of a composite panel according to claim 1, characterized in that a first outer layer is covered in an adhesive film, a second outer layer is applied to the adhesive film and the layers are joined permanently together by the application of at least one of pressure and heat, said core layer being formed with said adhesive film.

14. A process for the production of a composite panel according to claim 1, characterized in that a first outer layer is covered in an adhesive layer in liquid to pasty form, any solvents present are removed by at least one of negative pressure and heat, a second outer layer is subjected to the influence of heat and applied to the adhesive layer in the warm state by the application of at least one of heat and pressure and the layers are thus joined permanently together, said core layer being formed with said adhesive layer.

15. A process according to claim 14, characterized in that the second layer is covered in an adhesive in liquid to pasty form, any solvent present is removed by at least one of negative pressure and heat, the second layer with the adhesive layer is subjected to the influence of heat in another step and applied to the adhesive layer of the first outer layer in the warm state by the further application of at least one of heat and pressure, the adhesive layers bearing against one another and the layers thus being joined permanently together.

16. A shaped part containing a formable composite panel according to any one of claims 1 to 12.

17. A shaped part, body part of a land vehicle, housing, housing part of a machine and equipment, cover and casing for machine, equipment or building containing a formable composite panel according to any one of claims 1 to 12.