Aluminium alloy strip for adhesive connection

Abstract

The invention relates to a strip consisting of an aluminium alloy for providing adhesive connections. In addition, the invention relates to a method for producing a strip having a one or two-sided surface structure which consists of an aluminium alloy, at least provided in certain areas and prepared for an adhesive connection, and also relates to a corresponding adhesive connection. The object of providing an aluminium alloy strip optimised for adhesive connections, which has optimised surface properties for ageing-resistant adhesive connections, on the one hand, and which can be cost-effectively produced in a way which is reliable in terms of the process, on the other hand, is achieved for a strip consisting of an aluminium alloy for providing adhesive connections by the strip at least in areas having a surface structure prepared for adhesive connections, wherein the surface structure has depressions which were produced using an electrochemical graining process.

Claims

1. A method, comprising: utilizing a strip consisting of an aluminium alloy for providing adhesive connections in motor vehicles, wherein the strip at least in certain areas has a surface structure prepared for an adhesive connection, wherein the surface structure has depressions which were produced using an electrochemical graining process, wherein the surface structure which is at least provided in certain areas is provided on at least one or on both sides of the strip and has a reduced valley depth S.sub.vk of 1.0 m to 6.0 m.

2. The method according to claim 1, wherein the strip comprises an aluminium alloy of the type AA7xxx, type AA6xxx, type AA5xxx or of the type AA3xxx.

3. The method according to claim 1, wherein the strip is designed for producing sheets for motor vehicles.

4. The method according to claim 1, wherein the surface structure which is at least provided in certain areas is provided on at least one or on both sides of the strip and has a reduced valley depth S.sub.vk of 1.5 m to 4.0 m.

5. The method according to claim 1, wherein the strip is soft-annealed (state O) or is solution-annealed and quenched (state T4).

6. The method according to claim 1, wherein the strip or sheet has a passivation layer which is applied after the electrochemical graining.

7. The method according to claim 1, wherein the average roughness of the surface S.sub.a is 0.7 m to 1.5 m.

8. The method according to claim 3, further comprising producing one or more sheets by cutting the strip to size.

9. A method for producing a strip or a sheet having a one or two-sided surface structure which is prepared for an adhesive connection in motor vehicles, wherein a hot- and/or cold-rolled strip or sheet is subjected to electrochemical graining after the rolling, wherein homogenously distributed depressions are at least in certain areas introduced into the strip or sheet by the electrochemical graining and the strip or sheet comprises an aluminium alloy of the type AA7xxx, type AA6xxx, type AA5xxx or of the type AA3xxx, wherein depressions with a reduced valley depth Svk of 1.0 m to 6.0 m are at least in certain areas introduced into the strip or sheet surface by the electrochemical graining.

10. The method according to claim 9, wherein strip or sheet is subjected to a cleaning step before the electrochemical graining, in which the surface is cleaned by alkaline or acid pickling and a homogenous removal of material is carried out.

11. The method according to claim 9, wherein the electrochemical graining is carried out using HNO.sub.3 in a concentration of 2.5 to 20 g/l with a charge carrier input of at least 200 C/dm.sup.2.

12. The method according to claim 9, wherein after the electrochemical graining, a passivation of the surface is carried out.

13. The method according to claim 9, wherein a strip is electrochemically grained after soft annealing (state O) or after solution annealing and quenching (state T4).

14. The method according to claim 12, wherein the method steps are carried out in-line on a production line: uncoiling the strip from a coiler: cleaning and pickling the strip; at least in certain areas electrochemically graining the strip; and at least in certain areas applying a forming aid and/or a conversion layer or applying a protective oil.

15. An adhesive connection in a motor vehicle, between at least two join partners, wherein at least one join partner is a sheet according to claim 8 and the adhesive connection is provided in at least one area of the sheet which has a surface structure produced by electrochemical graining.

16. A strip or sheet consisting of an aluminium alloy for a utilizing according to the method of claim 1, wherein the strip or sheet consists of an aluminium alloy of the type AA7xxx, type AA6xxx, type AA5xxx or of the type AA3xxx, the strip or sheet at least in certain areas has a surface structure prepared for an adhesive connection, wherein the surface structure has depressions which were produced using an electrochemical graining process, the surface structure which is at least provided in certain areas is provided on at least one or on both sides of the strip and has a reduced valley depth S.sub.vk of 1.0 m to 6.0 m.

17. The method according to claim 1, wherein the strip comprises an aluminium alloy of the type AA7020, AA7021, AA7108, AA6111, AA6060, AA6014, AA6016, AA6005C, AA6451, AA5454, AA5754, AA5182, AA5251, AIMg6, AA3104, or AA3103.

18. The method according to claim 3, wherein the sheets are for structural applications of motor vehicles.

19. The method according to claim 4, wherein the reduced valley depth S.sub.vk is from 2.2 m to 4.0 m.

20. The method according to claim 1, wherein the average roughness of the surface S.sub.a is 0.7 m to 1.3 m.

21. The method according to claim 1, the average roughness of the surface S.sub.a is 0.8 m to 1.2 m.

22. The method according to claim 9, wherein the strip or sheet comprises an aluminium alloy of the type AA7020, AA7021, AA7108, AA6111, AA6060, AA6014, AA6016, AA6005C, AA6451, AA5454, AA5754, AA5182, AA5251 AlMg6, AA3104, or AA3103.

23. The method according to claim 9, wherein the reduced valley depth S.sub.vk is from 1.5 m to 4.0 m.

24. The method according to claim 23, wherein the reduced valley depth S.sub.vk is from 2.2 m to 4.0 m.

25. The method according to claim 11, wherein the charge carrier input is at least 500 C/dm.sup.2.

26. The method of claim 12, wherein the passivation of the surface is carried out by applying a conversion layer.

27. The strip or sheet of claim 16, wherein the reduced valley depth S.sub.vk is from 1.5 m to 4.0 m.

28. The strip or sheet of claim 16, wherein the reduced valley depth S.sub.vk is from 2.2 m to 4.0 m.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is to be explained in more detail below by means of exemplary embodiments in conjunction with the figure. In the figure shows

(2) FIG. 1 schematically the determination of the parameters S.sub.k, S.sub.pk and S.sub.vk by means of an Abbott curve,

(3) FIG. 2 a microscopic photograph of an exemplary embodiment not according to the invention,

(4) FIG. 3 a microscopically enlarged photograph of an exemplary embodiment of a strip surface according to the invention,

(5) FIG. 4 in a schematic illustration an exemplary embodiment of a production line for carrying out the method according to the invention,

(6) FIG. 5 a schematic sectional view of an exemplary embodiment of a strip or sheet according to the invention,

(7) FIGS. 6a), b) schematically in a plan view and a perspective view the test arrangement for carrying out the shear tension tests on adhesive connections,

(8) FIGS. 7a) to e) different fracture patterns during the shear tension test in a schematic sectional view,

(9) FIG. 8 in a diagram results of shear tension tests for eight different exemplary embodiments before and after weathering and

(10) FIGS. 9a) to c) three schematic sectional views of exemplary embodiments of an adhesive connection according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(11) In FIG. 1, it is firstly illustrated how the parameter values for the core roughness depth S.sub.k, the reduced valley depth S.sub.vk and the reduced peak height S.sub.pk can be determined from an Abbott curve. The determination is carried out according to DIN-EN-ISO 25178 for a measurement area conforming to standards. Usually, optical measurement methods, for example confocal microscopy, are used in order to determine a height profile of a measurement area. From the height profile of the measurement area the area ratio of the profile can be determined which intersects an area parallel to the measurement area at the height c or runs above the area. If the height c of the intersecting plane is represented as a function of the area ratio of the intersecting plane to the whole area, the Abbott curve is obtained which shows the typical S-shaped course for rolled surfaces.

(12) In order to determine the core roughness depth S.sub.k, the reduced valley depth S.sub.vk or the reduced peak height S.sub.pk, a secant D having a 40% length is moved into the determined Abbott curve such that the value of the slope of the secant D is minimal. The core roughness depth S.sub.k of the surface results from the difference between the abscissa values of the intersection points of the secant D with the abscissa at 0% material ratio and at 100% material ratio. The reduced peak height S.sub.pk and the reduced valley depth S.sub.vk correspond to the height of a triangle which has an area equal to the peak area A1 or groove area A2 of the Abbott curve. The triangle of the peak area A1 has as the base area the value Smr1 which results from the intersection point of a parallel to the X axis with the Abbott curve, wherein the parallel to the X axis runs through the intersection point of the secant D with the abscissa at 0% material ratio. The triangle of the groove area or valley area A2 has as the base area the value 100%Smr2, wherein Smr2 results from the intersection point of a parallel to the X axis with the Abbott curve and the parallel to the X axis runs through the intersection point of the secant D with the abscissa at 100% material ratio.

(13) The measurement profile can be characterised by these parameters. It can be determined whether it is a plateau-like height profile with depressions or, for example, the peaks in the height profile of the measurement area predominate. In the former case, the value for S.sub.vk increases and in the latter case the value for S.sub.pk increases.

(14) From the optical measurement of the surfaces, the valley density of the texture n.sub.clm can also be determined as a further parameter of the surface via the maximum number of closed void volumes n.sub.clm, i.e. depressions or valleys dependent on the measurement height c in percent per mm.sup.2. This gives the number of closed void areas per unit area (1/mm.sup.2) at a given measurement height c (%). The maximum n.sub.clm is determined from n.sub.cl (c). The greater n.sub.clm is, the finer the surface structure is.

(15) Furthermore, the closed void volume Vvcl can also be determined by the optical measurement by integration of the closed void areas A.sub.vcl (c) via the measurement height c. The closed void volume is also a characteristic surface feature of the strips and sheets according to the invention.

(16) The measurement of the roughness of the surface, as already mentioned, is carried out optically, since in this way scanning can be performed considerably faster compared to a tactile measurement. The optical measurement is carried out, for example, via interferometry or confocal microscopy, as was carried out in the case of the present measurement data. According to EN ISO 25178-2, the measurement areas are also determined with regard to their size. The measurement data was determined via quadratic measurement areas with a side length of 2 mm in each case.

(17) In FIG. 2, firstly a view of a conventional strip surface magnified 250 times is depicted, in order to show the differences between the conventional strips roughened for example with EDT structured rolls and the strips structured according to the invention. In contrast, FIG. 3 shows an exemplary embodiment of a strip surface according to the invention which was produced using an electrochemical graining process and has likewise been magnified 250 times. It can be clearly identified that for one thing the structures in the case of the electrochemical graining are finer and consist of depressions in a plateau-like surface. Unlike in the conventional embossing by rolling depicted in FIG. 2, in the case of the electrochemical graining according to the invention no peaks are introduced into the material, but rather the rolled surface, here a mill finish surface, is only altered or modulated by the introduction of depressions. It is at the present time assumed that the depressions which form during electrochemical graining can provide more lubricants for the forming process due to the larger closed void volumes and therefore improved forming properties are obtained. It was also recognised that the higher valley depth S.sub.vk can evidently also provide lubricants in the case of great surface stress during the forming and hence improves the forming behaviour.

(18) In FIG. 4, a first exemplary embodiment of a method is depicted by means of a schematic diagram of a production line for producing a strip B according to the invention. In the illustrated exemplary embodiment, the strip B which preferably at least partly consists of an aluminium alloy of the type AA7xxx, type AA6xxx or type AA5xxx or type AA3xxx, in particular AA7020, AA7021, AA7108, AA6111, AA6060, AA6014, AA6016, AA6106, AA6005C, AA6451, AA5454, AA5754, AA5182, AA5251, AA3104, AA3103 or AlMg6 is uncoiled via a coiler 1. The thickness of the strip is preferably at least 0.8 mm, but at most 4 mm, and preferably between 1.0 mm and 1.5 mm, for use in the automotive industry for example. In principle, the thickness, for example in the case of strips for the production of beverage cans, can also be 0.1 mm to 0.5 mm. In the case of these thin strips, the improved forming behaviour is also noticeable with the production of beverage cans which requires maximum deformation degrees.

(19) According to the present exemplary embodiment, the strip uncoiled with the coiler 1 preferably has the state soft annealed 0 if it is an aluminium alloy of the type AA55xxx or preferably the state solution annealed and quenched T4 in the case of an aluminium alloy of the type AA6xxx. Hence, the strip is already available in a state in which it can be particularly well formed. However, it is also conceivable to carry out the heat treatment after the surface processing or the introduction of depressions and process the surface of hard rolled strips.

(20) According to the exemplary embodiment, the uncoiled aluminium alloy strip B is conveyed to an optional trimming process for trimming the side edges 2. Subsequently, likewise optionally, the strip passes through a straightening device 3, in order to remove deformations from the strip. In the device 4, the strip is subjected to an optional cleaning and an optional pickling step or an electrolytic degreasing. Mineral acids, but also bases, for example based on sodium hydroxide solution, come into consideration as the pickle here. The response of the strip to electrochemical graining can hereby be improved. The step 4 of pickling is also optional. After an optional rinsing, in step 5 the aluminium strip is subjected to an electrochemical graining process, in which depressions are introduced into the surface. During electrochemical graining, current flows at a certain current density through the strip surface, which by choosing a suitable electrolyte causes depressions to be introduced into the strip surface and aluminium to be removed at the corresponding places. Preferably, the electrochemical graining is carried out in such a way that a valley depth S.sub.vk of 1.0 m-6.0 m, preferably. 1.5 m-4.0 m, particularly preferably 2.2 m-4.0 m, is obtained. It has been shown that with these specific values the forming behaviour of the aluminium alloy strip is very good in a subsequent forming process. In addition, it was shown that the ageing resistance of adhesive connections could also be increased with this surface treatment.

(21) Preferably, the electrochemical graining is carried out using HNO.sub.3 (nitric acid) in a concentration of 2.5-20 g/l, preferably with 2.5 to 15 g/l, with alternating current at a frequency of 50 Hz. The charge carrier input is preferably at least 200 C/dm.sup.2, preferentially at least 500 C/dm.sup.2, in order to achieve a sufficient area coverage with electrochemically introduced depressions. At least 1 A/dm.sup.2, preferably up to 100 A/dm.sup.2 and more, are used as peak current densities for this purpose. The choice of the current densities and of the concentration of the electrolyte is dependent on the production rate and can be adapted accordingly. In particular, the reactivity and hence the production rate can also be influenced via the temperature of the electrolyte. Preferably the electrolyte can have a temperature of at most 75 C. With nitric acid as the electrolyte, a preferred operating range is between room temperature and about 40 C., at most 50 C. In addition to nitric acid, hydrochloric acid is also suitable as the electrolyte.

(22) Preferably, the electrochemical graining of the surface of the strip B in step 5 is carried out on both sides. However, it is also conceivable for a corresponding surface structure to be introduced on just one side. After electrochemical graining, a rinsing step has proved to be particularly beneficial. Subsequently, according to the exemplary embodiment illustrated in FIG. 5, in production step 6 the aluminium alloy strip surface can be passivated, for example by applying a conversion layer. This processing step is also optional.

(23) Preferably, drying is carried out in step 7 before in the optional step 8, according to the illustrated exemplary embodiment, either a protective oil or a layer comprising a forming aid is applied to the strip, preferably on both sides. The forming aid is preferably a lubricant, in particular a meltable dry-film lubricant, for example a hot melt. A meltable dry-film lubricant as a protective layer and lubricant can make it easier to handle the aluminium alloy strips or sheets according to the invention and, at the same time, further improve the forming properties. Lanolin, for example, can also be used as a dry-film lubricant which consists of renewable raw materials.

(24) As an alternative to coiling the strip B with the coiler 11, the strip can also be cut up into sheets by means of the strip cutter 10. A visual inspection of the strip for defects is provided in step 9, so that surface defects can be identified early.

(25) As has already been stated, the exemplary embodiment from FIG. 4 shows several optional production steps which are carried out inline directly one after the other on the same production line. The exemplary embodiment from FIG. 4 is therefore a particularly economic variant of the method according to the invention. However, it is also possible to just combine the uncoiling of a strip according to step 1 and the electrochemical graining according to step 5 with a coiling or cutting up into sheet blanks. In principle, electrochemical graining of sheet blanks is also conceivable.

(26) An exemplary embodiment of a strip B according to the invention is now illustrated in a schematic sectional view in FIG. 5 which has depressions 12 introduced into the surface on both sides and additionally has an applied layer of a meltable dry-film lubricant 13. A corresponding strip B has maximum forming properties and can also be stored without difficulty, since the surface is protected. Corresponding strips B, even with a surface grained on one side, can also be used as outer skin parts of a motor vehicle, since the surface has maximum protection from the forming process or considerably supports the forming. Due to the surface protection, sheets produced from a strip B have very good handleability in the forming process and exhibit a very good adhesion to adhesives which, in addition, is particularly resistant to ageing.

(27) Finally, sheets were produced with the different surface topographies both from an aluminium alloy of the type AA5xxx and of the type AA6xxx and were measured in relation to their surface parameters using a confocal microscope. The strips of the aluminium alloy of the type AA5xxx were in the 0 state and the strips of the aluminium alloy of the type AA6xxx were in the T4 state. An aluminium alloy of the type AA 5182 was used as the AA5xxx type. The aluminium alloy of the AA6xxx alloy corresponded to an aluminium alloy of the type AA6005C. The tests V1 to V4 were produced using an identical aluminium alloy of the type AA6005C and the tests V5 to V8 using an identical aluminium alloy of the type AA5182, in order to exclude influences of different compositions within the alloy types.

(28) As Table 1 shows, the surface topographies of the comparison examples V1, V2, V3 and V6 were produced using conventional methods in the last rolling step by rolling with a roll with a mill finish surface or by embossing by rolling these strips having a mill-finish surface using an EDT textured roll.

(29) The strips produced in this way were used for the tests V3, V4, V7 and V8. In the case of the exemplary embodiments V3, V4, V7 and V8 according to the invention, both the strips with surfaces embossed using EDT rolls and the strips with mill finish surfaces were additionally electrochemically grained using the method according to the invention.

(30) TABLE-US-00001 TABLE 1 Electrochemical Strip No. Alloy Surface graining thickness V1 Comparison 6005C Mill finish No 1.15 mm V2 Comparison 6005C EDT No 1.10 mm V3 Invention 6005C Mill finish Yes 1.15 mm V4 Invention 6005C EDT Yes 1.10 mm V5 Comparison 5182 Mill finish No 1.15 mm V6 Comparison 5182 EDT No 1.10 mm V7 Invention 5182 Mill finish Yes 1.15 mm V8 Invention 5182 EDT Yes 1.10 mm

(31) In the tests V1 to V4, a hot- and cold-rolled strip consisting of an alloy of the type AA6005C was used. The final thickness of the strip after the conventional rolling process with a mill finish surface was 1.15 mm, the tests V1 and V3. A strip likewise having a mill finish surface was produced from an aluminium alloy of the type AA 5182 and used for the tests V5 and V7.

(32) The tests V2, V6 were textured conventionally by using EDT rolls. As can be understood from Table 1, the EDT textured surfaces were subjected to electrochemical graining and were evaluated as tests V4 and V8. The same was carried out for the strips with mill finish surfaces of both aluminium alloys. The electrochemically grained sheets were evaluated as tests V3 and V7. With the electrochemical graining, depending on the alloy, a HNO.sub.3 concentration of 4 g/l with a charge carrier input of 500 C/dm.sup.2 was used in the tests V3 and V4 and a HNO.sub.3 concentration of 5 g/l with a charge carrier input of 900 C/dm.sup.2 was used for V7 and V8. The electrolyte temperature was between 30 C. and 40 C. with all variants.

(33) When the surfaces of the test sheets were optically measured it was, according to expectations, apparent that the sheets of the tests V2, V6 produced by means of EDT textured rolls had distinctly larger values with regard to the arithmetical mean deviation of the roughness profile S.sub.a and the reduced peak height S.sub.pk than the strips of tests V1 and V5 which had the mill finish surfaces. In contrast, the electrochemically grained exemplary embodiments V3, V4, V7 and V8 exhibited an average roughness S.sub.a which was approximately at the level of the EDT surface texture of tests V2 and V6. The measured values are specified in Table 2.

(34) However, in contrast to the conventional texture, with electrochemical graining the value for the reduced valley depth S.sub.vk increases by more than a factor of 4, and here by a factor of at least 5. The differences in the textures can be read clearly here.

(35) The closed void volume V.sub.vcl, which represents the volume for providing lubricant in lubricant pockets, is larger in the case of the strips V2 and V6 with 362 and 477 mm.sup.3/m.sup.2 respectively compared to the mill finish variants V1 and V5 with 151 mm.sup.3/m.sup.2 and 87 mm.sup.3/m.sup.2 respectively.

(36) The electrochemically grained exemplary embodiments V3, V4 and V7 and V8 according to the invention, on the other hand, show a closed void volume V.sub.vcl of at least 500 mm.sup.3/m.sup.2. The closed void volume, which is important for absorbing lubricant, can be increased by distinctly more than 10% in the case of the strips according to the invention which have passed through an electrochemical graining step.

(37) The valley density of the structure with values of the variants V3, V4, V7 and V8 according to the invention of more than 80 per mm.sup.2, preferably between 100 and 150, is greater by distinctly more than 25% than in the case of conventionally EDT textured strip surfaces of the comparison tests V2 and V6.

(38) The improvement in the forming behaviour is attributed to the different topography of the exemplary embodiments according to the invention which is characterised by the different values of the reduced valley depth S.sub.vk, of the closed void volume V.sub.vcl, and of the valley density of the surface. In addition, the adhesion of the adhesive is also improved by the electrochemical graining, both in the unweathered original state and after climatic and/or corrosive stress.

(39) As a result, a formed sheet, for example an inside door panel or an outer skin panel of a motor vehicle, can hence also be provided which goes through high degrees of deformation until it is made into the final shape.

(40) Thus, by means of the method according to the invention and by means of the strip or sheet according to the invention, an even wider area of application can be made available for aluminium alloys in the field of motor vehicles, since the greater deformation degrees allow further application possibilities. Due to the fact that, at the same time, the adhesive connections often used in these areas of the motor vehicle are improved with regard to their ageing resistance, new applications can also be made possible in the motor vehicle having regard to the adhesive connections.

(41) TABLE-US-00002 TABLE 2 S.sub.a S.sub.pk S.sub.k S.sub.vk n.sub.clm V.sub.vcl No. Alloy m m m m Ssk 1/mm.sup.2 mm.sup.3/m.sup.2 V1 Cmp. 6005C 0.38 1.21 0.98 0.57 2.72 75 151 V2 Cmp. 6005C 0.83 1.56 2.79 0.40 0.79 66 362 V3 Inv. 6005C 0.93 0.47 1.33 3.34 1.32 123 555 V4 Inv. 6005C 1.13 1.50 3.21 2.08 0.18 94 566 V5 Cmp. 5182 0.37 0.51 1.21 0.37 0.32 56 87 V6 Cmp. 5182 1.13 2.66 2.54 0.34 1.35 67 477 V7 Inv. 5182 0.93 0.55 1.84 3.13 2.15 135 605 V8 Inv. 5182 1.19 2.42 2.87 2.03 0.56 83 542 V13 Cmp. AA1xxx 0.3 0.2 0.9 0.44 0.85 200 to <360 (Lithographic to to to to to 0.32 240 sheet after 0.6 0.55 1.5 1.1 EC graining)

(42) Since electrochemical graining is also used in the production of printing plate supports, several electrochemically grained lithographic sheets of the alloy A1xxx were measured and the measurement results were summarised as test V13. Although lithographic sheets are electrochemically roughened, the roughening serves another purpose. Also, no forming is carried out on lithographic strips or sheets, but rather, after the electrochemical roughening they are coated with a light-sensitive layer. The roughening is intended to enable a print result to be produced that is as uniform as possible. Hence, in the sense of the present invention, lithographic sheets and strips are neither provided nor prepared for forming or for adhesive bonding. They differ fundamentally in their structure.

(43) The surfaces optimised according to the invention for providing adhesive connections show clear differences in the topography to lithographic sheets, as the summarised measurement results of various measured lithographic sheets, shown in comparison example V13, show. Lithographic, heets usually have not only distinctly lower average roughness values S.sub.a, but also possess a distinctly lower reduced valley depth S.sub.vk. The average valley density n.sub.clm, on the other hand, lies slightly above the surfaces of the sheets V3, V4, V7 and V8 according to the invention which are electrochemically grained and are optimised for the forming process.

(44) FIGS. 6a) and 6b) schematically show the carrying out of shear tension tests of adhesive connections between two samples, in which FIG. 6a) shows the arrangement of the samples 14 and 15 in a plan view. The samples 14 and 15 are cut out of a strip or sheet. The cut edges are deburred. The dimensions of the samples are 100 mm in the length and 25 mm in the width. A clamping area 14a and 15a is provided at a distance of approximately 50 mm from an approximately 10 to 14 mm large overlapping area 16 of the two samples 14 and 15. The overlapping area is provided for the adhesive connection between the samples 14, 15. Depending on the testing machine, the clamping area 14a and 15a can be provided with a punch hole. The samples are designed corresponding to the norm DIN EN 1465, wherein the overlapping area is not 12.5 mm, but can as described vary between 10 and 14 mm. DIN EN 1465 describes the measurement of shear tension strengths of high-strength overlapping adhesive connections.

(45) As has already been explained, the adhesives are usually prepared on the delivered surfaces of the aluminium alloy strip provided, for example, with, a protective oil, a conversion layer or another organic coating, so that no further surface treatments have to be carried out before applying the adhesive.

(46) The adhesive is now applied in the overlapping area 16 of one of the samples 14, 15. In order to ensure that there is a uniform thickness in the adhesive connection, particularly when testing structural adhesives, glass beads, for example having a diameter of 0.3 mm, are arranged in the adhesive mass, so that the glass beads provide a firm joint thickness for the adhesive connection for each sample. The adhesion itself is carried out using positioning devices, in which the samples 14, 15 can be precisely positioned, so that the overlap adhesion in the overlapping area 16 is not exposed to any torsional moments during the tension test. These positioning devices ensure that the samples can only be adhesively connected precisely aligned with one another. Such positioning devices can also hold a plurality of samples, so that a plurality of adhesively connected samples can be hardened at the same time. The positioning devices used are not illustrated here.

(47) After applying the adhesive and positioning the two samples together, the excess adhesive is removed on all face sides of the sample using a spatula. Then, the adhesively connected samples 14, 15 are hardened. Hardening can, for example, take place in two stages, wherein, the specifications of the adhesive used must, of course, be observed. In the present exemplary embodiments, the samples were used using the adhesive Betamate 1630 from the Dow Chemical Company. The hardening of this epoxide-based adhesive takes place in two stages. In the first stage, the samples were heated to 125 C. for 12 minutes. After cooling to room temperature, these samples were then heated again to 175 C. for 15 minutes. The unaged samples were then after 24 hours or so measured in relation to the tensile lap-shear strength of the adhesive connection. The samples provided for artificial ageing were aged for 500 hours in a salt spray test according to DIN EN ISO 9227 and subsequently examined in relation to their tensile lap-shear strength.

(48) FIG. 6b) shows in a perspective, schematic view the two samples 14 and 15 which are joined together by an adhesive connection or adhesive joint 17. Since the tensile lap-shear strength is dependent on the overlap surface of the adhesive connection 17, the surfaces of the adhesive connection were in each case measured after each shear tension test. The maximum forces F to be exerted until the adhesive connection breaks were measured in order to determine the tensile lap-shear strength. With the respective sample the tensile lap-shear strength then results by dividing by the corresponding areas of the respective adhesive surface.

(49) As has already been mentioned, an aim in using adhesive connections, for example in automotive engineering, is to utilise the cohesion forces of the adhesive. For this purpose, the adhesion bond between the adhesive and the sheet must be greater than the cohesion forces of the adhesive. FIGS. 7a) to 7e) show the different fracture patterns of the samples which can be divided into undesirable fracture patterns of FIGS. 7a) and 7b) and into the desirable fracture patterns 7c), 7d) and 7e). In the case of the undesirable fracture patterns of FIGS. 7a) and 7b), the force of adhesion to the surface of the sheet is insufficient, so that the adhesive 18, for example, becomes fully detached from the sample 15. In this case, the cohesion forces of the adhesive used are not fully utilised. The same also applies when the adhesive becomes detached from one of the samples 14 or 15 in one or more partial areas 18a, 18b. The undesirable fracture patterns of the adhesive connections illustrated in FIGS. 7a) and 7b) could not be observed in the samples according to the invention.

(50) In contrast, FIGS. 7c), 7d) and 7e) show fracture patterns in which the adhesive 18 has remained on the respective side of the sample over the full surface and the fracture seam runs fully through the mass of the adhesive. In this case, the cohesion forces of the adhesive have been utilised to the maximum and an adhesive connection providing the maximum strength of the adhesive is made available.

(51) Corresponding samples were produced from the above described aluminium alloy strips consisting of the alloys AA6005C or AA5182, which were produced either conventionally or according to the invention, and the tensile lap-shear strength was determined. Five samples were produced for each test material V1 to V8 and subjected to a shear tension test in each case. Subsequently, the average values of the measured tensile lap-shear strengths were determined for the respective tests V1 to V8 and illustrated in a diagram in FIG. 8. The hatched column in each case represents the measurement of the tensile strength in the original state, i.e. unaged. The black column, on the other hand, in each case shows the tensile lap-shear strength after an ageing test of 500 hours according to DIN EN ISO 9227.

(52) The two alloy groups of the tests V1 to V4, an aluminium alloy of the type AA6xxx and the test group of the tests V5 to V8, an aluminium alloy of the type Aa5xxx show different adhesive properties. The tests V5 to V8 with samples consisting of an aluminium alloy AA5182 exhibit tensile lap-shear strengths which are below those of the aluminium alloy AA6005C. It is assumed that the increased magnesium content of the samples adversely affects the development of an adhesive connection. After baking the adhesive, the samples V1 to V4 have the state T6 which is typical for the AA6xxx aluminium alloys.

(53) The variants V3, V4 according to the invention show, for example, a distinct increase with respect to the tensile lap-shear strength of the adhesive connection compared to the non-electrochemically grained surfaces of the tests V1 and V2. In particular, it can also be noticed that after ageing the tensile lap-shear strength of the electrochemically grained variants V3, V4, V7 and V8 is higher compared to the untreated variants V1, V2, V5 and V6. For example, the tensile lap-shear strength does not fall below 15 MPa after a weathering process in the case of the electrochemically grained exemplary embodiments.

(54) The individual measurement results can be read in Table 3. The tensile lap-shear strength Pmax is also shown in addition to the maximum tensile force Fmax measured by the tension shear test arrangement. As has already been explained, Pmax results by the division of the measured value by the measured surface of the adhesive connection between the samples. The average value, which is shown in Table 3, was then determined from the respectively determined values for Pmax of the individual tension tests. The fracture path is additionally specified by s in millimetres. The fracture path corresponds to the distance by which the sample has stretched up to fracture. The values Fmax, Pmax and s just mentioned are additionally illustrated after weathering of the samples for 500 hours in the cold salt spray test (NSS) according to DIN EN ISO 9227. Additionally, the relative reduction in the tensile lap-shear strength Pmax is also shown.

(55) It has also been shown that the exemplary embodiments according to the invention have considerably lower reductions in the tensile lap-shear strengths in their respective alloy areas and surface areas in a weathering process. Thus, for example, the comparison example V1 has a reduction in the tensile lap-shear strength of 25.5%, while the exemplary embodiment according to the invention with an identical original surface before the electrochemical graining only has a reduction in the tensile lap-shear strength of 8.9% after weathering. Correspondingly, the pairings comparison example V2 can be compared with the exemplary embodiment V4 and V5 with V7 and V6 with V8. As a result, the reduction in the tensile lap-shear strength of the adhesive connection due to ageing can be improved by the aluminium alloy strip according to the invention by more than 20%.

(56) In FIG. 9, three typical adhesive connections, as used for example in motor vehicles, are schematically shown. In addition to the full-surface connecting joint shown in FIG. 9a), for example of a profile 19 with a flat sheet 20 for providing a hollow profile, crimped adhesive connections between two sheets 21 and 22, as shown in FIGS. 9b) and 9c), are often also used as adhesive connections in automotive engineering. Here, the adhesive 18 at the same time serves as a sealant. Bonnets, parts of the door sill and attached parts in the area of the boot, amongst other things, are bonded with such adhesive connections. The possible uses of the adhesive connections in connection with aluminium alloy sheets can be expanded even further by the aluminium alloy strips according to the invention, since the strips according to the invention can provide adhesive connections which are particularly resistant to ageing.

(57) TABLE-US-00003 TABLE 3 Original state 500 h NSS Fmax Pmax s Fmax pmax s pmax Sample No. N MPa mm N Mpa mm % V1 Comparison 5814 20.8 1.4 4049 15.5 0.5 25.5 V2 Comparison 5754 19.0 1.8 3143 14.0 0.4 26.3 V3 Invention 5979 21.1 1.7 5620 19.2 1.3 8.9 V4 Invention 5784 22.3 1.6 4662 18.8 0.6 15.5 V5 Comparison 5136 18.5 1.6 4146 14.6 0.9 20.8 V6 Comparison 4859 16.8 1.5 3949 14.6 0.8 13.3 V7 Invention 5087 18.8 1.7 4184 15.8 0.9 16.1 V8 Invention 5274 17.1 2.0 4469 15.7 1.3 8.1

(58) All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

(59) The use of the terms a and an and the and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms comprising, having, including, and containing are to be construed as open-ended terms (i.e., meaning including, but not limited to,) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., such as) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

(60) Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.