EP4015658A1 - Aluminium foil with improved barrier property - Google Patents

Abstract

The invention relates to an aluminum alloy foil with a thickness of not more than 12 μm, not more than 9 μm or less than 8 μm, the aluminum alloy foil being an AAlxxx or A8xxx aluminum alloy in the annealed condition. In addition, the invention relates to a method for producing an aluminum alloy foil and its use. The object of proposing an aluminum alloy foil with improved barrier properties, a method for its production and a use of the aluminum alloy foil according to the invention is achieved in that the aluminum alloy foil has a maximum number of pores with a pore size of 1 μm to 200 μm of a maximum of 12 per dm ² , has a maximum of 8 per dm ² or a maximum of 6 per dm ² . In addition, a method is specified as to how this aluminum alloy foil can be produced.

Description

The invention relates to an aluminum alloy foil with a thickness of at most 12 μm, at most 9 μm or less than 8 μm, the aluminum alloy foil having an AAlxxx or A8xxx aluminum alloy in the H2x or 0 material state. In addition, the invention relates to a method for producing an aluminum alloy foil and its use.

Aluminum alloy foils with the thicknesses mentioned are often used in food packaging, these being, for example, a component of multi-layer composite materials. The aluminum alloy foils contained in multi-layer composite materials are mainly used because of their good barrier properties. As a rule, the aluminum alloy foil has a very good barrier effect, for example for water vapour, oxygen, carbon dioxide and larger molecules such as aromas. This is achieved by the crystalline structure of the aluminum alloy foil, which essentially prevents the solubility and diffusion of larger atoms through the crystal structure. Material transport through the aluminum alloy foil is only possible at defects in an aluminum alloy foil, for example at pores or holes. Pores are the smallest openings in aluminum alloy foils that can be detected when light passes through the foil locally. According to DIN EN 546-4, pores in an aluminum alloy foil are randomly distributed holes with a maximum diameter of 200 µm. According to a definition in DIN EN 546-4, 200 µm or more are roller holes. It was previously known that the porosity of aluminum alloy foils increases with decreasing thickness. Pores can have a number of different causes. Inclusions or impurities in the molten metal, for example those from refractory materials or coarse cast phases (eg Al ₃ Fe) can fall out of the rolling stock during rolling and Leave rolling holes in the aluminum alloy foil. If the particles enclosed in the metal are particularly brittle, e.g. B. Al ₃ Fe phases, these can also shatter during rolling and the smallest fragments are rolled into the rolling stock. This then results in individual pores or pore streets in the rolled aluminum alloy foils, which impair the barrier properties of the aluminum alloy foil. In addition, it was discovered during investigations into the present invention that aluminum alloy foils can also have micropores with a size of significantly less than 20 μm, in particular with a size of 1 μm to 5 μm, which occur in very large numbers, locally limited in so-called “populations”. typically extending in the rolling direction of the aluminum alloy foil. The pores, referred to as micropores, can also adversely affect the barrier properties of the aluminum alloy foil.

A necessary process in the production of aluminum alloy foil for the manufacture of multilayer composite materials is the final annealing to degrease the rolled aluminum alloy foil. Rolling oil emulsions and rolling oils are used in the rolling of aluminum alloy strip and foil. Their residues must be removed from the foil after rolling so that the properties of the aluminum alloy foil that are important for processing into multi-layer materials, such as e.g. B. adhesive properties, wetting properties have a predetermined level. For this purpose, the foils are wound up into a coil or into a ready-made roll and annealed as a coil or roll. Essentially, the rolling media present on the aluminum alloy foil must be removed as completely as possible from the coil or roll by decomposition and evaporation. The temperature treatment puts the aluminum alloy foil either in the partially hard material condition H2x or in the soft-annealed material condition 0.

From the US patent application U.S. 2002/0043310 A1 is known, an AlFe aluminum alloy foil with a thickness of less than 12 microns by a final annealing at temperatures of 200°C to 300°C for at least 50 hours. In material state 0 with a thickness of less than 12 μm, the aluminum alloy foil has a porosity of less than 10 pores/dm ² according to DIN-EN 546-4. In the exemplary embodiment from the cited US patent application, the foils with a thickness of 6.6 μm are soft-annealed at 280° C. for 80 hours. Although the known aluminum alloy foils have a porosity according to DIN EN 546-4 of 6 pores/dm ² , the barrier properties of the aluminum alloy foil cannot be ensured as a result.

DIN EN 546-4 only records pores from a minimum size of 20 µm. Pores with a size of less than 20 µm are not covered by DIN EN 546-4. In practice, most pores are round or oval in shape with irregular edges. To determine the pore size, the area of the pore is determined in transmitted light under the microscope, imaging the exact outline with edges that are as sharp as possible, and an area-equivalent circular diameter is calculated from this. To measure the porosity according to DIN EN 546-4, the rolled foils are tested using a light box. The film sample is placed on the light box, with a double-rolled film the matt side faces the tester. According to DIN EN 546-4, the test takes place in a darkened room with a remaining maximum illuminance of 20 to 50 lux. A translucent glass plate is used as a light box, which is illuminated from below with the help of a light source that provides a uniform illuminance of 1000 to 1500 lux. According to a variant in DIN EN 546-4, the porosity can be measured in such a way that a 1 dm ² measurement area is selected from a larger film area, which has the highest porosity and thus represents the poorest measurement area on the film. The number of pores determined on this measuring surface according to DIN EN 546-4 was determined as a measure of the porosity. But even if the worst measuring surface of the film according to DIN EN 546-4 has a very low porosity, the barrier properties of the film could not always be ensured, since the occurrence of the discovered micropores with a size of less than 20 µm, or with sizes from 1 µm to 5 µm, is not covered by DIN EN 546-4.

Proceeding from this prior art, the present invention is therefore based on the object of proposing an aluminum alloy foil with improved barrier properties, a method for its production and a use according to the invention of the aluminum alloy foil.

The aforementioned object is achieved according to a first teaching of the present invention in that the aluminum alloy foil has a maximum number of pores with a pore size of 1 μm to 200 μm of a maximum of 12 per dm ² , a maximum of 8 per dm ² or a maximum of 6 per dm ² having.

It has been found that the pores not covered by DIN EN 546-4, namely pores with a pore size of less than 20 µm, can significantly influence the barrier properties of an aluminum alloy foil. Aluminum alloy foils according to the invention can be provided by considering even the smallest pores from 1 μm when limiting the maximum number of pores with a pore size of 1 μm to 200 μm to a maximum of 12 per dm ² or a maximum of 8 per dm ² or a maximum of 6 per dm ² which have significantly better barrier properties than the aluminum alloy foils produced according to DIN EN 546-4. The reason for this is that in the case of the aluminum alloy foils according to the invention, the influence of so-called micropores with a size of 1 μm to 20 μm on the barrier properties is also minimized. The aluminum alloy foils according to the invention are therefore particularly suitable for use as a barrier layer, for example in a multilayer composite material.

Pores with a size of 1 μm to 20 μm, in particular 1 μm to 5 μm, are present in conventional aluminum alloy foils in spatially limited, so-called "populations". In these populations, however, there are still a large number of micropores.

According to the present invention, the maximum number of pores per dm ² with a pore size of 1 μm to 200 μm is determined by dividing the aluminum alloy foil across the entire foil width into 5 to 6 dm ² large measuring areas with an edge length of 100 mm to 320 mm across to the rolling direction of the aluminum alloy foil, so that there are at least 3, preferably at least 5 measuring areas over the entire width of the aluminum alloy foil. The number of pores with a pore size of 1 µm to 200 µm is then determined in each measuring area and the maximum number of pores per dm ² is determined from the measuring area with the highest number of pores per measuring area by dividing it by the selected size of the measuring area and integer number of pores rounded. The maximum number of pores is measured after the final annealing in the material state H2x or 0, for example on coils or ready-made rolls. In this context, ready-made means that the aluminum alloy foil has already been cut to size, at least in width, for later use.

With the parameter of the maximum number of pores per dm ² according to the present invention, micropores are also detected, which locally accumulate with a size of 1 μm to 20 μm, can occur in so-called populations. As already mentioned, these populations often extend in the direction of rolling of the aluminum alloy foil and are only found locally in certain areas of the aluminum alloy foil. When determining the maximum number of pores per dm ² according to the present invention, however, these populations of micropores are reliably recorded since the entire width of the film is taken into account. The aluminum alloy foil according to the invention with a maximum number of pores of at most 12, at most 8 or preferably at most 6 per dm ² is therefore almost free of micropores and thus provides particularly good barrier properties.

The number of pores is measured in a completely darkened room with a residual illuminance of less than 0.25 lux. The surface of the aluminum alloy foil to be measured is placed on a transparent glass surface and fixed with a frame whose inner dimensions correspond to the measuring surface. Below the glass plate is a light source that illuminates the measuring surface as evenly as possible. The foil is fixed over the frame in such a way that the measuring surface is fixed on the aluminum alloy foil and essentially no residual light from the light source is emitted past the foil. The edges of the foil must be completely darkened. A planar light source with at least 15,000 lux illuminance can be used as a light source with a glass plate, for example.

In the darkened room, the measurement area is photographed with a digital camera centered over the measurement area, using an exposure time of 30 s with an ISO value of 800 or more in order to record the passage of light through the smallest pores with a size of 1 µm to 20 µm be able. The distance of the camera should be selected so that the measuring area is completely covered. However, the distance should be as small as possible. The number of pores with a size of 1 µm to 200 µm of the photographed measuring surface of the aluminum alloy foil is then evaluated digitally using image analysis software.

As already described, this test method can also be used to measure micropores with a pore size of 1 µm and more. The result showed that pores with a pore size below 20 μm, in particular below 5 μm, can significantly impair the barrier properties of the aluminum alloy foil. The reason for this is seen in the locally limited, population-like occurrence of the micropores with a high pore density. A large number of micropores can therefore be present in narrowly defined areas of the aluminum alloy foil, which locally greatly reduce the barrier properties of the aluminum alloy foil. The aluminum alloy foils according to the invention with a maximum number of pores per dm ² of at most However, 12, a maximum of 8 or a maximum of 6 pores with a pore size of 1 μm to 200 μm have particularly good barrier properties, since these have no areas with a high micropore density.

It has been found that in order to provide the aluminum alloy foil according to the invention, precautions must be taken in the entire production chain of the aluminum alloy foil in order to keep the number of pores with a pore size of 1 μm to 200 μm low. Thus, during the production of the aluminum alloy for the aluminum alloy foil, the melt can already be filtered before and/or during the casting of the rolling ingot and can pass through appropriate filters in order to keep non-metallic inclusions out of the alloy. Ideally, the purification of the melt should begin in the furnace. As a result, some of the contamination is removed early, before casting, and costs are saved. In the furnace, purification of the melt can take place by gas flushing with Ar, N ₂ , by salt treatments and by standing. These measures are often combined for effective melt cleaning. This usually removes carbides, oxides and alkaline metals. The impurities are transported to the melt surface with the help of gas bubbles and absorbed by the dross. After a standing period, the accumulated impurities are scraped off. When casting, in-line cleaning processes such as deaerators and filters can be used on the way from the furnace to the molds. The degassers work with a scavenging gas, for example the Ar, N ₂ scavenging gases mentioned above. On the one hand, they serve to reduce the hydrogen content in the melt. On the other hand, the flushing gases also have additional filter/flotation effects that can remove particle-like inclusions or, for example, oxide skins. The flushing gases are usually introduced via rotors in order to generate fine gas bubbles and thus further improve the degassing and filtering effect. The degassers can be equipped with more than one treatment chamber, so that several degassers can be connected in series in one unit. At the exit of these degassers with multiple treatment chambers, a chamber for standing out the Melt may be provided in the remaining bubbles and inclusions can migrate to the strip surface and be discharged from the melt.

Filters that use various filter mechanisms can be used to further purify the melt. Foam ceramic filters, for example CFF foam ceramic plate filters, deep-bed filters are used as filters. For example, a casting plant with a furnace for 70 t between furnace and casting plant with an in-line degasser of the SIR filter type and a degasser from the company HYCAST for a throughput of 50 t/h as well as a downstream CFF foam ceramic plate filter with a pore size finer than 40 ppi ("pores per inch"). The CFF foam ceramic filter plate is used as a disposable filter and replaced after each pour. Alternatively, a deep bed filter, also known as a bulk bed filter, can be used. The filter medium consists of alternating beds of balls and broken balls made of tabular alumina with a diameter of up to approx. 20mm, for example, which are layered in a filter box of approx. 2 x 3m.

In DC casting, homogenization of the cast rolling ingot at the temperatures and durations specified for the specific alloy types also leads to a reduction in coarse cast phases in the rolling ingot, for example coarse Al ₃ Fe cast phases, and thus to the avoidance of correspondingly brittle particles in the very thinly rolled ones aluminum alloy foils.

In the continuous strip casting process (CC casting), for example using a twin roll caster (TRC), the molten metal is fed to water-cooled rolls, for example, where it solidifies. The solidified strip is then immediately rolled further. The melt goes through the same cleaning steps in the furnace as in the case of DC casting. This removes non-material phases such as carbides and oxides. In contrast to DC casting, the strips produced in CC casting tend to form so-called central segregations, which are either in the form of coarse intermetallic phases, eg AlFe phases in the case of AlFeSi alloys, or in the form of accumulations of other alloying elements are present. The composition of the precipitates depends on the composition of the alloy and the chosen parameters of the casting process. The composition of the AlFeSi alloy influences, for example, the width of the temperature interval at which the melt solidifies, which is also called the solidification interval. The wider the solidification interval, the greater the tendency for central segregation to form. In order to counteract the formation of segregations, the casting speed is reduced, for example, with a simultaneous increase in the cooling capacity. The casting speed in the TRC process, for example, varies between 1000 and 2500mm/min. The cooling capacity is influenced by the outer diameter of the rollers. The larger the outer diameter, the higher the cooling capacity. For an AA8xxx alloy with a solidification interval of 30K, for example, a casting speed of 1000 to a maximum of 1500mm/min can be selected with a roll diameter of approx. 600mm. For purer aluminum alloys, such as type AA1050 or AA1070, on the other hand, a higher casting speed of 2000 to 2500mm/min with a roll diameter of approx. 900mm is advantageous in order to counteract central segregation.

After foil rolling, degreasing takes place through an annealing process to provide the material condition H2x and O. Here it was recognized that the degreasing process by annealing the rolled aluminum alloy foil can have a major impact on the presence of pores with a pore size of 1 µm to 20 µm. Surprisingly, by reducing the annealing temperature to a maximum of 245° C. with a simultaneous extension of the annealing time and taking into account a special cooling phase of a maximum of 3 h at 100° C., the formation of micropores could be significantly reduced.

According to a further embodiment of the invention, the aluminum alloy foil according to the invention is characterized in that the aluminum alloy foil has an oxide layer thickness of 3 to 6 nm measured along the entire width of the Having aluminum alloy foil, the oxide layer thickness of the aluminum alloy foil being at most 30% greater at the edge region of the aluminum alloy foil than in the middle of the aluminum alloy foil. Not only is the thickness of the oxide layer particularly thin at 3 to 6 nm, it is homogeneous over the width of the aluminum alloy foil and only shows a slight increase towards the edge areas. The reason for this advantageous property of the aluminum alloy foil according to the invention is seen in the specific degreasing annealing with the subsequent cooling process. This achieves more uniform surface properties for use in a multi-layer composite. For example, the adhesive properties of the foil are kept particularly constant across the entire width due to the even distribution of the oxide layer thickness. The layer thickness of the aluminum oxide layer can be measured, for example, by ATR (attenuated total reflection) infrared spectroscopy. With this measuring method, the oxide layer thickness can be recorded over the entire thickness with a resolution in the sub-nanometer range.

According to a further configuration of the aluminum alloy foil, the oxide layer thickness is a maximum of 5 nm both on the matt side and on the shiny side of the aluminum alloy foil. The reduced thickness of the oxide layer due to the production route leads to better adhesion properties of the surface of the aluminum alloy foil and thus to a good suitability of the aluminum alloy foil for a multilayer composite material, for example for packaging, for example as part of a flat bag packaging.

• 0,05 % ≤ Si ≤ 0,30 %,
• 0,7 ≤ Fe ≤ 1,3 %,
• Cu ≤ 0,05 %,
• Mn ≤ 0,05 %,
• Mg ≤ 0,05 %,
• Cr ≤ 0,05 %,
• Zn ≤ 0,10 %,
• Ti ≤ 0,025 %,

Rest Al und unvermeidbare Verunreinigungen einzeln 0,05 Gew.-%, in Summe maximal 0,15 Gew.-%, kann eine höherfeste und gleichzeitig kostengünstige Aluminiumlegierungsfolie bereitgestellt werden.According to a next embodiment, the aluminum alloy foil has an aluminum alloy with the following alloy components in % by weight:

• 0.05% ≤ Si ≤ 0.30%,
• 0.7 ≤ Fe ≤ 1.3%,
• Cu ≤ 0.05%,
• Mn ≤ 0.05%,
• Mg ≤ 0.05%,
• Cr ≤ 0.05%,
• Zn ≤ 0.10%,
• Ti ≤ 0.025%,

Residual Al and unavoidable impurities individually 0.05% by weight, in total not more than 0.15% by weight, a higher-strength and at the same time cost-effective aluminum alloy foil can be provided.

Despite the low content of the alloy components, the properties in AlFeSi alloys are decisively influenced by the elements in solution and by the binary AlFe and ternary AlFeSi phases. When the cast solidifies, an Al mixed crystal that is oversaturated with Si and Fe is formed. Due to the low solubility, Fe is precipitated as an intermetallic compound Al3Fe and is deposited at the grain boundaries of the Al solid solution. This binary phase is stable and hardly changes during the subsequent thermomechanical treatment. Only in the rolling process under the influence of the rolling forces are AlFe phases broken down. The equilibrium solubility of Fe in aluminum is low and is max. 400ppm (655°C). The maximum solubility of Si is much higher and is 1.65 wt% (577°C). Strength and elongation are positively influenced by adding Si. Silicon forms AlFeSi dispersoids and thus contributes to an increase in strength due to particle hardening and an increase in elongation. The Si atoms in solution in the Al matrix contribute to solid solution hardening. The siliceous AlFeSi precipitates also provide nucleation centers for recrystallization and therefore improve the recrystallization properties of the aluminum alloy foil. With increasing Si content, however, the solubility of iron decreases and thus also the strength contribution of Fe through mixed crystal hardening, so that the Si content is preferably limited to a maximum of 0.30% by weight. In order not to deteriorate the strength, the Si content is preferably at least 0.05% by weight.

Iron in solution also leads to an increase in strength, with a simultaneous fine grain size and an increase in the thermal stability of the aluminum alloy foil, so that it preferably contains at least 0.7% by weight of iron. Fe contents below 0.7% by weight reduce the amount of iron in solution and the phase density becomes low, so that the strength of the aluminum alloy foil is reduced. However, iron has a rather low solubility in the aluminum matrix and forms AlFe intermetallic phases when solidifying from the cast. These precipitates are coarse and tend to be detrimental to the mechanical properties. Therefore, the iron content is limited to 1.3% by weight.

Due to the high solubility of Cu, Mn, Mg or Cr in the aluminum matrix, these elements mostly remain in solution at the specified upper limits of a maximum of 0.05% by weight and contribute to the strength of the aluminum alloy foil. Excessive weight percentages of Cu, Mn, Mg or Cr can be used to further increase strength. However, they also lead to an unwanted increase in the necessary rolling force in the foil rolling process. Zinc also increases the strength, but also has positive effects on the refinement of the grain structure, so that a maximum of 0.10% by weight is preferably permitted.

Titanium acts as a grain refiner and leads to a slight increase in strength and recrystallization temperature. In order to achieve good casting properties with a fine grain structure but at the same time good recrystallizability of the aluminum alloy foil, the aluminum alloy foil contains a maximum of 0.025% by weight of titanium.

• 0,8 % ≤ Fe ≤ 1,15 %,
• Cu ≤ 0,05 %,
• 0,01 % ≤ Mn ≤ 0,04 %, bevorzugt 0,015 % ≤ Mn ≤ 0,035 %, besonders bevorzugt 0,018
• % ≤ Mn ≤ 0,025 %,
• Mg ≤ 0,01 %, bevorzugt Mg ≤ 0,005 %, besonders bevorzugt Mg ≤ 0,0035 %,
• Cr ≤ 0,02 %,
• Zn ≤ 0,07 % und/oder
• 0,005 % ≤ Ti ≤ 0,025 %.

According to a preferred variant, the aluminum alloy of the aluminum alloy foil has at least one of the following restrictions on the alloying components in % by weight:

• 0.8% ≤ Fe ≤ 1.15%,
• Cu ≤ 0.05%,
• 0.01%≦Mn≦0.04%, preferably 0.015%≦Mn≦0.035%, particularly preferably 0.018
• % ≤ Mn ≤ 0.025%,
• Mg ≤ 0.01%, preferably Mg ≤ 0.005%, particularly preferably Mg ≤ 0.0035%,
• Cr ≤ 0.02%,
• Zn ≤ 0.07% and/or
• 0.005% ≤ Ti ≤ 0.025%.

As explained in the section above, the proportions by weight of Si and Fe are selected in such a way that an optimal Fe solution state can be set with an optimal AlFe, AlFeSi phase density and thus the optimal strength characteristics in the manufacturing process adapted to the foil product requirements. Above a preferred Fe content of 0.8% by weight, the strength and thermal stability of the aluminum alloy foil increase again. In addition, the coarsening of the grain structure is counteracted. Exceeding 1.15 wt% Fe results in higher density of AlFe intermetallic cast phases and hence reduction in elongation and deterioration in porosity.

The manganese content of the aluminum alloy in % by weight is preferably 0.01%≦Mn≦0.04%, preferably 0.015%≦Mn≦0.035%, particularly preferably 0.018%≦Mn≦0.025%. If the Mn content is less than 0.01% by weight, the strength and thermal stability of the aluminum alloy foil decrease. With manganese contents of more than 400ppm, on the other hand, the rolling force during foil rolling increases and thus also the process costs. A good compromise between strength increase and process costs is therefore achieved with contents of 0.0150% by weight to 0.035% by weight, preferably at 0.018% by weight to 0.025% by weight.

The element Mg is characterized by very good diffusion in the Al matrix and therefore tends to accumulate on the foil surface. Therefore, the Mg content is limited to a maximum of 0.01% by weight, preferably a maximum of 0.005% by weight, particularly preferably a maximum of 0.0035% by weight. Compliance with these values ensures that Mg accumulations on the film surface do not contribute to the undesirable formation of magnesium oxide or magnesium hydroxide products Temperature influence in the customer process comes, which has adverse effects on the adhesion of coatings.

In order to reduce the rolling forces during foil rolling, the Zn content is preferably limited to a maximum of 0.07% by weight.

Cr and Ti are only contained in small amounts in the aluminum alloy. The Cr content is limited to a maximum of 0.02% by weight. Cr is easily soluble in the aluminum matrix and, even at low concentrations, leads to a significant increase in the rolling force during foil rolling. Ti is limited to a maximum proportion by weight of 250 ppm, with the consideration of a minimum content of at least 50 ppm Ti leading to better castability with good mechanical properties at the same time. This means that, on the one hand, the additional costs due to the unnecessarily high addition of alloying elements are avoided and, on the other hand, the foil yield stress and thus also the rolling forces do not exceed the limits provided for in the foil rolling process.

According to a further embodiment of the aluminum alloy foil according to the invention, this has a yield strength Rp0.2 measured transversely, longitudinally or diagonally to the rolling direction of at least 55 MPa, preferably at least 58 MPa, in the material state O. In connection with the reduced maximum number of pores per dm ² , the aluminum alloy foil according to the invention is very good for processing into multilayer composite materials.

The aluminum alloy foil according to the invention also shows an improvement with regard to the C-coating of the aluminum alloy foil, ie the amount of carbon from the rolling media which still remains on the aluminum alloy foil after final annealing. According to a further configuration of the aluminum alloy foil, the C occupancy in the center of the aluminum alloy foil is 20% less than in the edge areas of the aluminum alloy foil. Usually here are the differences about the Bandwidth between the edge and center areas of the aluminum alloy foil is significantly larger. The aluminum alloy foil according to the invention also has more uniform properties, for example adhesion properties, due to the more homogeneous C coating over the foil width.

To determine the C-coating of the aluminum alloy foil, 5 cm wide foil strips in the gram range are cut lengthwise from the annealed foil coil or from the annealed foil roll, wound up, weighed exactly and burned at 600°C in a quartz tube in a stream of oxygen. The resulting CO ₂ from the rolling oil and its residues is measured coulometrically or quantitatively using IR spectroscopy. The area of the sample is calculated from the weight of the sample, the density and the film thickness. The C allocation is given in mg/m ² film. The samples are taken from at least the center and edges of the annealed aluminum alloy foil. For example, a total of 5, 7, 9 or more strips can be taken symmetrically about the center of the annealed aluminum alloy foil, taking into account the edges, to determine the distribution of C coverage across the width of the aluminum alloy foil.

According to a further embodiment of the aluminum alloy foil according to the invention, this has a tensile strength measured transversely, longitudinally and/or diagonally to the rolling direction in the factory condition H2x or O of at least 80 MPa. To achieve a low maximum number of pores, the aluminum alloy foil with the aforementioned composition is subjected to the specific manufacturing steps mentioned, which increase the tensile strength Rm to more than 80 MPa even in the H2x material condition, but especially in the O material condition. The higher tensile strength allows, for example, an increase in web tension when processing the aluminum alloy foil and thus faster processing of the aluminum alloy foil, for example when producing a multilayer composite material.

This also applies to the next embodiment of the aluminum alloy foil according to the invention, according to which the elongation at break A _{100 mm} of the aluminum alloy foil measured diagonally to the rolling direction is at least 6.2%, preferably at least 6.5%. Surprisingly, the elongation at break value diagonally to the rolling direction remains almost constant despite the increase in tensile strength values and yield point values and only falls very slightly in relation to a standard film. Improved elongation at break values A _100mm are also advantageous for the processing of the aluminum alloy foil, especially in the production of aluminum composite materials with multi-layer systems and the manufacture of packaging, especially in deepening, folding, folding and sealing, as this reduces the risk of the aluminum alloy foil tearing during processing .

• Herstellen eines Aluminiumlegierungsbands für das Kaltwalzen durch Gießen eines Walzbarrens aus einer Aluminiumlegierung aus einer AAlxxx oder AA8xxx Aluminiumlegierung, wobei die Aluminiumlegierungsschmelze vor und/oder während des Gießens des Walzbarrens gefiltert wird, Homogenisieren des gegossenen Walzbarrens und Warmwalzen des Walzbarrens zu einem Warmband oder kontinuierliches Gießen eines Gießbandes aus einer Schmelze aus einer gefilterten Aluminiumlegierung vom Typ AA8xxx oder AAlxxx mit einem anschließenden, optionalen Warmwalzen des Gießbands,
• Kaltwalzen des Aluminiumlegierungsbands auf eine erste Zwischendicke,
• Rekristallisationsglühen des kaltgewalzten Aluminiumlegierungsbands bei dieser Zwischendicke,
• Kaltwalzen des Aluminiumlegierungsbands auf eine zweite Zwischendicke,
• Doppeln des Aluminiumlegierungsbands und Durchführen einer Zwischenglühung,
• Folienwalzen des gedoppelten Aluminiumlegierungsbands auf Enddicke der gedoppelten Folie,
• Separieren und Aufwickeln der Lagen bei einer Enddicke der einzelnen Lagen von maximal 12, maximal 9 µm oder weniger als 8 µm, wobei optional eine Konfektionierung der Aluminiumlegierungsfolie in mehrere Rollen erfolgt und
• Durchführen einer Endglühung des Coils oder der konfektionierten Rollen für mindestens 150h bei 200 bis 245 °C, vorzugsweise maximal 240 °C oder maximal 235 °C Ofenlufttemperatur mit einer abschließenden Kühlphase für mindestens 3h bei 100 °C Ofenlufttemperatur.

According to a second teaching of the present invention, the above-mentioned object is achieved by a method for producing an aluminum alloy foil in that the method comprises the following steps:

• Manufacture of an aluminum alloy strip for cold rolling by casting an aluminum alloy slab from an AAlxxx or AA8xxx aluminum alloy, the aluminum alloy melt being filtered before and/or during the casting of the slab, homogenizing the cast slab and hot rolling the slab into a hot strip or continuously casting a cast strip from a melt of a filtered aluminum alloy of the type AA8xxx or AAlxxx with a subsequent, optional hot rolling of the cast strip,
• cold rolling the aluminum alloy strip to a first intermediate gauge,
• recrystallization annealing of the cold-rolled aluminum alloy strip at this intermediate gauge,
• cold rolling the aluminum alloy strip to a second intermediate gauge,
• doubling the aluminum alloy strip and performing an intermediate anneal,
• Foil rolling of doubled aluminum alloy strip to final thickness of doubled foil,
• Separating and winding up the layers with a final thickness of the individual layers of a maximum of 12, a maximum of 9 µm or less than 8 µm, with the aluminum alloy foil optionally being made up into several rolls and
• Carrying out a final annealing of the coil or the ready-made rolls for at least 150 h at 200 to 245 °C, preferably at most 240 °C or at most 235 °C furnace air temperature with a final cooling phase for at least 3 h at 100 °C furnace air temperature.

It has been found that by combining the above process features, starting with casting an ingot or casting a cast strip from a filtered aluminum alloy of an AAlxxx or A8xxx aluminum alloy, to performing the degreasing anneal in the form of a final anneal for at least 150 hours at 200 up to 245 °C furnace air temperature with a final cooling phase for at least 7 hours at 100 °C furnace air temperature, particularly advantageous properties of the aluminum alloy foil in the material state H2x or O can be achieved. In addition to advantageous properties in relation to the oxide layer thickness of the aluminum alloy foil and its C-coverage with carbon, the maximum number of pores per dm ² with a pore size of 1 µm to 200 µm of the aluminum alloy foil could be significantly reduced and thus the barrier properties of the aluminum alloy foil produced were process-reliable be stabilized. It has been found that if the claimed temperature window is observed during the annealing process and the cooling phase, significantly fewer or no micropores with a size of less than 5 μm can be found in the aluminum alloy foil. Lower temperatures of, for example, a maximum of 240° C. or a maximum of 235° C. showed an even lower maximum number of pores per dm ² . The cooling phase of at least 3 hours, preferably 7 hours at 100°C brings about a "gentle" cooling of the roll already in the oven, so that all layers in the film roll reach the temperature of approx. 100°C. The long holding time of at least 3 hours, preferably at least 7 hours, causes the temperature gradient within the roller before the roller exits the oven is as small as possible. This avoids distortion of the film layers during the final cooling in air. In addition, the foil surface is chemically activated after the completion of the annealing at 200°C up to a maximum of 245°C. The controlled cooling to 100 °C prevents strong oxidation of the film surface with moist air and thus prevents the formation of undesirable oxidation products on the film surface, which can lead to layers of the film roll sticking together, for example. As a result, improved unwinding properties of the aluminum alloy foil can be secured.

In the case of strip casting, the casting speed must be matched to the solidification interval. The casting speed, for example when using a twin-roll casting process, varies between 1000 and 2500mm/min. The cooling capacity is affected by the outside diameter of the rollers, with a larger outside diameter providing greater cooling capacity. For an AA8xxx alloy with a solidification interval of 30K, for example, a casting speed of 1000 to a maximum of 1500mm/min can be selected with a roll diameter of approx. 600mm. For purer AA1050 or AA1070 alloys, on the other hand, a higher casting speed of 2000 to 2500mm/min with a roll diameter of 900mm, for example, is selected. In this way, the formation of central segregations can be avoided. At the same time, this also significantly reduces the formation of pores in the aluminum alloy foil.

• 0,05 % ≤ Si ≤ 0,30 %,
• 0,7 % ≤ Fe ≤ 1,3 %,
• Cu ≤ 0,05 %,
• Mn ≤ 0,05 %,
• Mg ≤ 0,05 %,
• Cr ≤ 0,05 %,
• Zn: ≤ 0,10 %,
• Ti: ≤ 0,025 %,

Rest Al und unvermeidbare Verunreinigungen einzeln 0,05 Gew.-%, in Summe maximal 0,15 Gew.-%, und wird

• das Rekristallisationsglühen des kaltgewalzten Bands bei Ofenlufttemperatur von 450 °C bis 550 °C für mindestens 5h und
• die Zwischenglühung nach dem Doppeln des Bands bei einer Ofenlufttemperatur von 240 °C bis 320 °C für 0,5h durchgeführt, kann eine Aluminiumlegierungsfolie mit einer Dicke von beispielsweise 6,3 µm mit Streckgrenzwerten R_p0,2 gemessen quer, längs oder diagonal zu Walzrichtung von mindestens 55 MPa, vorzugsweise mindestens 58 MPa im Werkstoffzustand O hergestellt werden. Die erhöhten Streckgrenzwerte verbessern das Handling der weichgeglühten Aluminiumlegierungsfolie bei der Weiterverarbeitung der Aluminiumlegierungsfolie, zum Beispiel zu einem mehrschichtigen Verbundmaterial. In Bezug auf die Wirkungen der einzelnen Legierungsbestandteile wird auf die Ausführungen zur Aluminiumlegierungsfolie verwiesen.

According to a further embodiment of the method according to the invention, the aluminum alloy has the following alloy components in % by weight:

• 0.05% ≤ Si ≤ 0.30%,
• 0.7% ≤ Fe ≤ 1.3%,
• Cu ≤ 0.05%,
• Mn ≤ 0.05%,
• Mg ≤ 0.05%,
• Cr ≤ 0.05%,
• Zn: ≤ 0.10%,
• Ti: ≤ 0.025%,

Rest Al and unavoidable impurities individually 0.05% by weight, in total not more than 0.15% by weight, and is

• the recrystallization annealing of the cold-rolled strip at a furnace air temperature of 450 °C to 550 °C for at least 5 h and
• If the intermediate annealing is carried out after the strip has been doubled at a furnace air temperature of 240 °C to 320 °C for 0.5 h, an aluminum alloy foil with a thickness of 6.3 µm, for example, can be measured with yield strength values R _p0.2 transversely, longitudinally or diagonally to the rolling direction of at least 55 MPa, preferably at least 58 MPa in the O material state. The increased yield strength values improve the handling of the annealed aluminum alloy foil during further processing of the aluminum alloy foil, for example into a multi-layer composite material. With regard to the effects of the individual alloy components, reference is made to the statements on aluminum alloy foil.

• 0,8 % ≤ Fe ≤ 1,15 %,
• Cu ≤ 0,05 %,
• 0,01 % ≤ Mn ≤ 0,04 %, bevorzugt 0,015 % ≤ Mn ≤ 0,035 %, besonders bevorzugt 0,018
• % ≤ Mn ≤ 0,025 %,
• Mg ≤ 0,01 %, bevorzugt Mg ≤ 0,005 %, besonders bevorzugt Mg ≤ 0,0035 %,
• Cr ≤ 0,02 %,
• Zn ≤ 0,07 % und/oder
• 0,005 % ≤ Ti ≤ 0,025 %.

According to a further embodiment of the method, the aluminum alloy has at least one of the following restrictions on the alloy components in % by weight:

• 0.8% ≤ Fe ≤ 1.15%,
• Cu ≤ 0.05%,
• 0.01%≦Mn≦0.04%, preferably 0.015%≦Mn≦0.035%, particularly preferably 0.018
• % ≤ Mn ≤ 0.025%,
• Mg ≤ 0.01%, preferably Mg ≤ 0.005%, particularly preferably Mg ≤ 0.0035%,
• Cr ≤ 0.02%,
• Zn ≤ 0.07% and/or
• 0.005% ≤ Ti ≤ 0.025%.

With regard to the technical effects of the preferred limitations of the aluminum alloy components, reference is made to the statements relating to the invention Aluminum alloy foil pointed out. In the process for producing the aluminum alloy foil, the focus is not only on the mechanical properties, but also on the rolling forces and the lowest possible maximum number of pores per dm ² .

All specified mechanical parameters such as tensile strength R _m , yield point R _p0.2 or elongation at break A _100mm are measured in accordance with DIN EN 546-2. The elongation at break values are exclusively A _100mm values.

In addition to casting a filtered aluminum alloy foil alloy, it is advantageous according to a further embodiment to carry out the homogenization of the rolling ingot at 420° C. to 600° C. for at least 7 hours. During homogenization, the already cold cast ingot is brought to a temperature close to the melting point in order to reduce or eliminate microsegregations that have occurred during the solidification of the ingot. During the homogenization, unstable phases are also dissolved and converted into stable phases. After preheating before homogenization, fine phases in the form of dispersoids are separated when the ingot cools again. The homogenization thus leads to the establishment of a homogeneous structure with the lowest possible proportion of microsegregation and a precipitation structure that is favorable for rollability and the properties of the end product.

It has also been found that it is advantageous if, according to a further embodiment, the rolling slab is hot-rolled during hot-rolling to a final hot-rolling thickness of 2 mm to 4 mm and the final hot-rolled strip temperature after the hot-rolled strip has been coiled is between 300° C. and 350° C. This ensures that the hot strip is statically recrystallized after coiling, thus enabling maximum rolling degrees in the first cold rolling. This in turn has a positive effect on the recrystallization during the first intermediate annealing, since the recrystallization energy is reduced due to the high hardening caused by cold rolling with high reduction ratios.

Because, according to a further embodiment of the method, the final annealing is carried out for at least 150 hours at a temperature of 200° C. to 225° C., additional positive properties can be achieved. In particular, the occurrence of micropores in the order of less than 20 µm, in particular micropores with a size of 1 µm to 5 µm, is even more limited by reducing the upper limit temperature to 225 °C and thus the barrier properties of the aluminum alloy foil for the application in multi-layer composite materials, for example in the area of composite packaging, ensured by the production process.

Finally, the use of the aluminum alloy foil according to the invention or the aluminum alloy foil produced with the method according to the invention in multi-layer composite materials which are used above all in the field of packaging is particularly advantageous. In addition, aluminum alloy foils can also be used advantageously for packaging that is to be folded, creased, scored, deep-drawn or stretch-drawn, since the very good barrier properties of the aluminum alloy foil ensure better protection for the products packaged with it.

Cardboard packaging, in particular sterilizable cardboard packaging, comprising a multi-layer composite material with an aluminum layer benefit from the very good barrier properties of the aluminum alloy foil according to the invention.

Fig.1a

eine REM-Aufnahme einer Walzpore einer Folie, welche mit der DIN EN 546-4 erfasst werden,

Fig.1b

eine REM-Aufnahme eines Schliffs einer mit Mikroporen belasteten Pakets von Aluminiumlegierungsfolien,

Fig.2

eine schematische Schnittansicht einer Vorrichtung zur Messung der maximalen Anzahl an Poren pro 1 dm² über die Folienbreite,

Fig. 3

eine schematische Draufsicht auf die Messflächen zur Bestimmung der maximalen Anzahl an Poren pro dm² und

Fig. 4a),b), c)

digitale Fotografien von erfindungsgemäßen und nicht erfindungsgemäßen Folienmuster

The invention is to be explained in more detail below using exemplary embodiments in conjunction with the drawing. In the drawing shows:

Fig.1a

an SEM image of a rolled pore of a foil, which is recorded with DIN EN 546-4,

Fig.1b

an SEM image of a section of a package of aluminum alloy foils loaded with micropores,

Fig.2

a schematic sectional view of a device for measuring the maximum number of pores per 1 dm ² across the film width,

3

a schematic plan view of the measurement areas for determining the maximum number of pores per dm ² and

Fig. 4a),b),c)

digital photographs of film samples according to the invention and not according to the invention

In FIG. The previously known DIN EN 546-4 covers corresponding pores in aluminum alloy foils, since according to this standard pores with a size of 20 µm and up to 200 µm must be taken into account.

Figure 1b shows, on the other hand, an SEM micrograph of a micrograph of a film package that was contaminated with micropores and was prepared using a Cross Section Polisher (CSP). The middle film shows an approximately 1 μm indentation and a micropore channel. Microvoids are believed to be three-dimensional structures that create a not always straight line connection from one side of the film to the other side of the film.

It is easy to imagine that a large number of micropores with a size well below 20 μm, for example 1 to 5 μm, can also lead to the barrier effect of the aluminum alloy foil being negatively affected. For this reason, aluminum alloy foils which, according to DIN EN 546-6, have a low number of pores per dm ² do not necessarily also have a very good one barrier effect. This applies to all aluminum alloy types mentioned here, i.e. to alloys of type AAlxxx or AA8xxx.

The aluminum alloy foils according to the invention made from the aforementioned aluminum alloy types AA8xxx and AAlxxx with a maximum thickness of 12 μm, maximum 9 μm or less than 8 μm, however, have a maximum number of pores with a pore size of 1 μm to 200 μm in the H2x or O material state a maximum of 12 per dm ² , a maximum of 8 or a maximum of 6 per dm ² . Pores are also taken into account that have a size of 1 µm to 20 µm, which are not taken into account according to DIN EN 546-6. Because the aluminum alloy foils according to the invention have a particularly low maximum number of pores with a pore size of 1 μm to 200 μm and thus also the smallest pores starting at 1 μm pore size, improved barrier properties of the aluminum alloy foil can be made available.

In figure 2 a schematic sectional view of a device for measuring the maximum number of pores per dm ² over the entire film width is now shown. Can be seen in figure 2 the aluminum alloy foil 1, a light source 2, for example an overhead projector, and a still camera 3 which is to photograph the measurement surface 3A for evaluation. The device must be positioned in a darkened room so that no stray light affects the measurement. The residual illuminance in the darkened room is preferably less than 0.25 lux. The aluminum alloy foil 1 is fixed in the measuring area by a frame 5, which completely surrounds the measuring area, so that the aluminum alloy foil 1 is positioned as evenly as possible in the measuring area 3A.

The light source 2 illuminates the aluminum alloy foil 1 through a transparent glass plate, which is figure 2 is not shown. However, the expansion of the light source 2 indicates that the aluminum alloy foil 1 should be illuminated as homogeneously as possible from below. Of the The distance of the camera 3 depends on the size of the measuring area to be recorded and the lens used. A lens with the smallest possible focal length should be selected so that the minimum distance can be selected in order to scan the measuring surface with the best possible resolution.

The light source 2 is completely darkened with the aluminum alloy foil and the frame 5, so that only light that has penetrated the aluminum alloy foil 1 through pores within the measurement area 3A can reach the camera. The aluminum alloy foil 1 is divided along the entire width 4 into preferably at least three or at least five measuring areas and the entire width of the foil is thus covered by the measurement. Since the aluminum alloy foils are often cut to a certain width in so-called rolls after foil rolling and then annealed, the width 4 of the aluminum alloy foil 1 means the width of the foil roll or, without finishing, the entire width of the foil coil. The division into different measuring areas 3A, preferably at least five measuring areas 3A along the entire width of the aluminum alloy foil, also enables the detection of locally occurring populations of pores with sizes of 1 μm to 20 μm. These pores are not taken into account in the known porosity measurement according to DIN EN 546-4.

The following test setup was used for the foils measured below: An overhead projector from Andreas + Kern with a 36 V and 400 W optical halogen lamp with a luminous flux of up to 6000 lumens served as the light source. The film to be examined was placed on the projector and fixed using a metal frame of a defined size so that the film lay flat on the projector and was sealed at the side. The camera used was a Sony Alpha 6000 with 6000 × 4000 pixels with a Minolta MD Rokkor 50 mm f1.4 lens. An aperture of 2 with an ISO value of 800 was used for the photographs with an exposure time of 30 seconds. The distance from the camera sensor to the foil was 700 mm. The software was used for image analysis Image analyzer used. The measurement areas 3A were how figure 4 shows arranged side by side without gaps across the width 4 perpendicular to the longitudinal direction 7 of the aluminum alloy foil 1, so that the entire width of the aluminum alloy foil 1 is measured. The size of the measuring area was 183 mm x 276 mm and thus 5.0508 dm ² . From the measurement area with the highest number of pores, the number of pores with a size of 1 µm to 200 µm was then determined by software and normalized to 1 dm ² by comparing the measured number of pores in the worst measurement area with the total area of the measurement area in dm ² was divided. The result was rounded to a whole number. With this measuring method, the smallest pores that occur locally and have a size of less than 20 µm, in particular 5 µm to 1 µm, can be recorded and counted.

As an example A, an aluminum alloy having an alloy composition according to Table 1 was cast into a rolling ingot. The aluminum alloy melt was treated with flushing gases before and/or during the casting of the rolling ingot and filtered through degassers and a deep-bed filter. As already explained above, this filtration serves to avoid non-metallic impurities from the melt in the subsequent rolling ingot. The rolling ingot was then subjected to homogenization, which was carried out for the present aluminum alloy in the temperature range of 420-600° C. for at least 5 hours in order to redissolve as many casting phases as possible.

The rolling ingot was then hot-rolled during hot-rolling to a final hot-rolling thickness of 2 mm to 4 mm and coiled to form a hot-rolled strip with a final hot-rolled temperature between 300° C. and 350° C. The hot strip was cold-rolled in several cold-rolling passes to an intermediate thickness of, for example, 0.60 mm to a maximum of 0.80 mm. Subsequently, recrystallization annealing was performed at a furnace air temperature of 450°C to 550°C for at least 5 hours. The aluminum strip recrystallized in this way was subjected to further cold-rolling steps to a second intermediate thickness of between 11 μm and 20 μm subjected and doubled for foil rolling. After doubling, an intermediate anneal took place for half an hour at an oven air temperature of 240°C to 320°C. Subsequently, foil rolling of the doubled tape was carried out.

After separating the film layers, the coils were optionally packaged in rolls. The aluminum alloy foil had a final thickness of at most 12 µm, at most 9 µm or less than 8 µm. In the exemplary embodiment, an aluminum alloy foil thickness of 6.3 μm was achieved. After the optional packaging, i. H. After cutting the film to roll width and winding the rolls, final annealing of the rolls was carried out at 200°C to 245°C oven air temperature for at least 150 hours with a cooling phase of at least 3 hours at 100°C oven air temperature. Unlike the exemplary embodiment A according to the invention, the comparative example B was annealed at a temperature of 330° C. for 50 hours and then cooled to room temperature.

Table 2 shows the mechanical characteristics of the aluminum alloy foil according to DIN EN 546-2 of the two variants A and B. It was found that the aluminum alloy A according to the invention surprisingly had similarly high elongation at break values A _{100 mm} measured diagonally to the rolling direction at higher yield point values R _p0.2 and tensile strength values R _m as the variant B annealed at high temperature. The comparison variant B, on the other hand, showed significantly lower values Yield strength values R _p0.2 and lower tensile strength values R _m .

The measurement of the oxide layer thickness distribution across the width of the aluminum alloy foil also showed that variant A according to the invention has a more homogeneous distribution of the oxide layer thickness across the roll width than variant B, which is not according to the invention.

The production variants A and B were now examined in relation to the maximum number of pores per dm ² according to the present invention. At the same time other aluminum alloy foils were produced from alloy 1 and finally annealed using different processes. The measurements with the in figure 2 The device described showed that oven air temperatures of up to 245 °C for 150 hours with a cooling phase at 100 °C oven air temperature for 7 hours did not greatly affect the maximum number of pores per dm ² . It could be measured as a maximum number of pores 10 per dm ² .

From a temperature of 260 °C for 100 hours or 280 °C for 100 hours, and in particular at 330 °C oven air temperature for 50 hours without a cooling phase, the values for the maximum number of pores with a size of 1 µm to 200 µm increased significantly on. This also illustrates the in Figure 4a ) shown photo of an aluminum alloy foil not according to the invention annealed according to variant B. In comparison to the variants annealed according to the invention 4b) and 4c ) a large number of very small pores can be seen, which have a size of less than 20 µm. The aluminum alloy foils in Figure 4b ) and c) were annealed at 245 °C or 220 °C furnace air temperature for 150 h with a cooling phase at 100 °C furnace air temperature for 7 h. As in the 4b) and 4c ) can be seen, the aluminum alloy foils according to the invention showed no populations of micropores and thus a significantly improved barrier property. Tab. 1 Alloy composition in % by weight, remainder Al, legs si feet Cu Mn mg Cr Zn Ti no 1 req 0.074 0.88 0.002 0.019 0.002 0.0007 0.005 0.005 0.004 Var. final annealing Rp0.2 rm A _100mm [%] [h] @ [°C] [MPa] [MPa] l q i.e L Q i.e D A 150 @ 220 + 7 @ 100 61 60 59 84 82 80 6.7 B 50 @ 330 43 42 41 74 69 70 7.4 Var. Oxide layer thickness shiny side [nm] Oxide layer thickness matt side [nm] edge center edge Increase edge vs. center edge center edge Increase Edge vs Center A 4.0 3.6 4.0 11% 3.2 2.7 3.2 18.5% B 5.5 2.9 5.5 89% 4.5 2.3 4.6 97.8% Var Final annealing [h] @ [°C] maximum number of pores per dm ² [pores/dm ² ] A req 150 @ 220 + 7 @ 100 6 B See. 50 @ 330 673 C req 150 @ 245 + 7 @ 100 10 E See. 100 @ 260 31 f See. 100 @ 280 380

Claims (15)

1. Aluminum alloy foil with a thickness of not more than 12 µm, not more than 9 µm or less than 8 µm, where the aluminum alloy foil has an AAlxxx or AA8xxx aluminum alloy in the material temper H2x or O,
characterized in that
the aluminum alloy foil has a maximum number of pores with a pore size of 1 µm to 200 µm of at most 12 per dm ² , at most 8 per dm ² or at most 6 per dm ² . 2. Aluminum alloy foil according to claim 1,
characterized in that
the aluminum alloy foil has an oxide layer thickness of 3 to 6 nm measured along the entire width of the aluminum alloy foil, the oxide layer thickness of the aluminum alloy foil at the edge area of the aluminum alloy foil being a maximum of 30% greater than in the middle of the aluminum alloy foil. 3. Aluminum alloy foil according to one of claims 1 or 2,
characterized in that
the oxide layer thickness is a maximum of 5 nm on both the matt and the bright side of the aluminum alloy foil. 4. Aluminum alloy foil according to any one of claims 1 to 3,
characterized in that
the aluminum alloy foil has an aluminum alloy with the following alloy components in % by weight: 0.05% ≤ Si ≤ 0.30%, Fe: 0.7 ≤ Fe ≤ 1.3%, Cu ≤ 0.05%, Mn ≤ 0.05%, Mg ≤ 0.05%, Cr ≤ 0.05%, Zn ≤ 0.10%, Ti ≤ 0.025%, Residual Al and unavoidable impurities individually not more than 0.05% by weight, in total not more than 0.15% by weight. 5. Aluminum alloy foil according to claim 4,
characterized in that
the aluminum alloy of the aluminum alloy foil has at least one of the further restrictions on the alloying components in % by weight: 0.05% ≤ Si ≤ 0.30%, 0.8 ≤ Fe ≤ 1.15%, Cu ≤ 0.05%, 0.01%≦Mn≦0.04%, preferably 0.015%≦Mn≦0.035%, particularly preferred 0.018% ≤ Mn ≤ 0.025%, Mg ≤ 0.01%, preferably Mg ≤ 0.005%, particularly preferably Mg ≤ 0.0035%, Cr ≤ 0.02%, Zn ≤ 0.07% and/or 0.005% ≤ Ti ≤ 0.025%. 6. Aluminum alloy foil according to claim 4 or 5,
characterized in that
the aluminum alloy foil in the material state O has a yield point Rp0.2 measured transversely, longitudinally or diagonally to the rolling direction of at least 55 MPa, preferably at least 58 MPa. 7. Aluminum alloy foil according to one of claims 3 or 4,
characterized in that
the aluminum alloy foil has a tensile strength Rm measured in the transverse, longitudinal and/or diagonal direction to the rolling direction in the H2x or O temper of at least 80 MPa. 8. aluminum alloy foil according to any one of claims 3 to 5,
characterized in that
the elongation at break A of the aluminum alloy foil, measured diagonally to the rolling direction, is at least 6.2%, preferably at least 6.5%. 8. The method for producing an aluminum alloy foil according to claims 1 to 7, the method comprising the following steps: - producing an aluminum alloy strip for cold rolling by casting an aluminum alloy slab from an AAlxxx or AA8xxx aluminum alloy, filtering the aluminum alloy melt before and/or during the casting of the slab, homogenizing the cast slab and hot rolling the slab into a hot strip or
continuous casting of a cast strip from a melt of a filtered aluminum alloy of the type AA8xxx or AAlxxx with a subsequent, optional hot rolling of the cast strip, - cold rolling the aluminum alloy strip to a first intermediate gauge, - recrystallization annealing of the cold-rolled aluminum alloy strip at this intermediate gauge, - cold rolling the aluminum alloy strip to a second intermediate gauge, - doubling the aluminum alloy strip and performing an intermediate anneal, - foil rolling of doubled aluminum alloy strip to final thickness of doubled foil, - Separation and winding of the layers at a final thickness of the individual layers of a maximum of 12, a maximum of 9 µm or less than 8 µm, with the aluminum alloy foil optionally being made up into several rolls and - Carrying out a final annealing of the coils or the ready-made rolls for at least 150 hours at a furnace air temperature of 200 to 245 °C with a final cooling phase for at least 3 hours, preferably at least 7 hours at a furnace air temperature of 100 °C. 9. The method according to claim 8,
characterized in that
the aluminum alloy has the following alloy components in % by weight: 0.05% ≤ Si ≤ 0.30%, 0.7 ≤ Fe ≤ 1.3%, Cu ≤ 0.05%, Mn ≤ 0.05%, Mg ≤ 0.05%, Cr ≤ 0.05%, Zn: ≤ 0.10%, Ti: ≤ 0.025%, remainder Al and unavoidable impurities individually 0.05% by weight, in total not more than 0.15% by weight, and - the recrystallization annealing of the cold-rolled strip at a furnace air temperature of 450 °C to 550 °C for at least 5 h and - the intermediate annealing after the doubling of the strip is carried out at a furnace air temperature of 240 °C to 320 °C for 0.5 h. 10. The method according to claim 9,
characterized in that
the aluminum alloy foil has at least one of the following alloying component weight percent limitations: 0.05% ≤ Si ≤ 0.30%, 0.8% ≤ Fe ≤ 1.15%, Cu ≤ 0.05%, 0.01%≦Mn≦0.04%, preferably 0.015%≦Mn≦0.035%, particularly preferred 0.018% ≤ Mn ≤ 0.025%, Mg ≤ 0.01%, preferably Mg ≤ 0.005%, particularly preferably Mg ≤ 0.0035%, Cr ≤ 0.02%, Zn ≤ 0.07% and/or 0.005% ≤ Ti ≤ 0.025%. 11. The method according to claim 9 or 10,
characterized in that
the homogenization of the rolling ingot is carried out at 420 to 600 °C for at least 7 h. 12. The method according to any one of claims 9 to 11,
characterized in that
the rolling slab is hot-rolled to a final hot-rolling thickness of 2 mm to 4 mm during hot-rolling and the final hot-rolled strip temperature is between 300 °C and 350 °C. 13. The method according to any one of claims 8 to 12,
characterized in that
the final annealing is carried out for at least 150 hours at 200 °C to 225 °C. 14. Use of an aluminum alloy foil according to any one of claims 1 to 8, in the multi-layer composite material, in particular packaging with barrier requirements for the aluminum foil.

Images