Patent Application
20250236932
The present invention relates to an aluminum alloy, an aluminum strip made of the aluminum alloy, a method for producing the aluminum strip and a use of the aluminum strip.
Aluminum cans generally have a can body, a can end and usually a can tab, the materials of which are sometimes subject to different requirements for production or in the product, for example with regard to their formability, strength and the like.
When manufacturing aluminum cans, different aluminum alloys are therefore typically used for the can body on one side and the can end and the can tab on the other side. An AA3xxx aluminum alloy, usually AA 3104, is used for the can body and an AA5xxx aluminum alloy, usually AA 5182, is used for the can end and the can tab. These aluminum alloys for the can body and the can end or the can tab have been used unchanged in the aluminum beverage can sector for many years.
In order to improve the carbon footprint of aluminum products, a high use of scrap in their production is generally desirable. However, not all scrap has the same effect on the carbon footprint. The use of scrap generated during the production of aluminum products, so-called production scrap, only has a slightly positive, neutral or possibly even negative impact on the carbon footprint. In contrast, the carbon footprint of a product can be significantly improved by using scrap that is generated at the end of the life cycle of a product made from aluminum, so-called old scrap. In practice, old scrap is sometimes also referred to as post-consumer scrap or end-of-life scrap.
In the production of beverage cans, production scrap can arise, for example, during the production of aluminum strip (e.g. as trimming scrap) or during the production of can bodies, can ends or can tabs from the aluminum strip (e.g. as punching scrap). Old scrap from used aluminum beverage cans is referred to in practice as UBC scrap (UBC: Used Beverage Can).
Up to now, old scrap, such as UBC scrap, has mainly been used for new can body material of the AA 3xxx alloy group, as the alloy composition permits this.
On the other hand, due to the alloy specifications of the aluminum alloy AA 5182 used for can end strip or can tab strip, in particular the quite low tolerance limits for the alloying elements Si, Fe, Cu and Mn, it has proven difficult to use scrap other than that of the AA 5xxx alloy group for its production. As a result, only small amounts of aluminum scrap, and in particular only small amounts of old scrap, can be used in the production of aluminum can end strip or can tab strip, i.e. aluminum strip for the production of can ends or can tabs, respectively.
This applies in particular to UBC scrap, which, due to the mixture of different alloys contained therein, namely the alloy(s) of the can body and the alloy(s) of the can end, and the proportions of silicon, zinc or copper typically contained in the scrap as a result, currently make it impossible to use larger quantities of such scrap for the production of new can end or can tab strip, as otherwise the alloy specification of alloy AA 5182 cannot be met.
In the production of can end or can tab strip, it is therefore currently necessary to add high proportions of primary aluminum or clean, unalloyed scrap in order to comply with the specification limits for can end or can tab strip.
At the end of the 1990s, there were considerations to use only one alloy for can bodies, can ends and can tabs, as described in the article “Formability of recycled aluminum alloy 5017” by W. H. Sillekens et al., J Mat Proc Tech 65 (1997) 252. However, this idea has not proved successful in practice, so that the aluminum can manufacturers have stuck with the tried and tested alloy combination of AA3104 for the can body and AA5182 for the can end and can tab.
Against this background, the present invention is based on the object of improving the production of aluminum strip for can ends and can tabs in such a way that a greater use of scrap, in particular old scrap, is made possible.
According to the invention, this object is solved by an aluminum alloy having the following composition:
It was found that this aluminum alloy can be used to produce aluminum strips that meet the requirements, in particular the mechanical requirements, for aluminum end strip and/or aluminum tab strip and at the same time allow a higher use of old scrap due to the specified content limits for the individual alloying elements.
In particular, the alloy composition described allows greater use of UBC scrap. In this way, the cycle of aluminum beverage cans can be closed, so that in addition to the can bodies, also can ends and can tabs and thus all production components of the aluminum beverage can can be newly produced from old beverage cans. This increases the recyclability of aluminum beverage cans and significantly improves their carbon footprint.
Accordingly, the aforementioned object is further solved according to the invention by an aluminum strip for producing can ends and/or can tabs from the aforementioned aluminum alloy or an embodiment thereof.
Furthermore, the aforementioned object is solved according to the invention by using the aforementioned alloy or an embodiment thereof or the aforementioned aluminum strip or an embodiment thereof for producing can ends and/or can tabs.
In addition, the aforementioned object is solved according to the invention by a method for producing the aluminum strip described above, comprising the following steps:
The melt is provided at least partly by melting aluminum scrap, in particular old scrap, preferably at least partly by melting UBC scrap.
The melt is preferably cast into an ingot in a discontinuous casting process, in particular die casting, or in a semi-continuous casting process, in particular DC casting.
The ingot can then be sawn or milled.
The ingot is preferably homogenized for a period of at least 0.5 hours at a holding temperature of 450-550° C., preferably 490-550° C. Homogenization can be carried out in particular in a pusher-type or crucible furnace. Homogenization is preferably carried out for a period of less than 12 hours.
Hot rolling is preferably carried out to a hot strip thickness in the range of 2-4 mm. Hot rolling can be carried out on a reversing hot rolling stand, for example, possibly followed by a multi-stand finishing train.
Cold rolling can be carried out with or without intermediate annealing.
The strip is preferably trimmed after cold rolling.
The Si content of the aluminum alloy is in the range of 0.03-0.6 wt %. A Si content above 0.6 wt % has a negative effect on strength and formability. A Si content below 0.03 wt % would limit the use of scrap too much.
Further preferably, the aluminum alloy has a Si content of above 0.20 wt %, preferably a Si content in the range 0.21-0.6 wt %, more preferably in the range 0.25-0.6 wt %. It was found that a Si content in these ranges enables a larger proportion of old scrap, as old scrap can have a fairly high Si content. At the same time, it was recognized that even with a Si content in these ranges, advantageous properties of the aluminium strip can still be achieved, which enable it to be used for the production of can ends and/or can tabs.
An increased Si content can lead to an increased formation of Mg2Si phases. The Mg content bound in these phases is then no longer available to increase the strength of the aluminum strip. It has been recognized that this can be compensated for without increasing the Mg content by increasing the thickness of the aluminium strip or sheet, particularly for the production of can ends. Additionally or alternatively, increasing the thickness can also compensate for a reduction in the Mg content, for example. Simulations have shown that even an increase in sheet thickness from 0.206 mm to 0.210 mm, for example, i.e. by approx. 2%, results in an increase in strength of approx. 4%.
Accordingly, the aluminum strip or aluminum sheet preferably has a thickness of at least 0.210 mm, more preferably at least 0.220 mm, particularly preferably if the Si content is above 0.20 wt %, for example in the range 0.21-0.6 wt % or 0.25-0.6 wt %, and/or if the Mg content is in the range 3.0-4.0 wt %.
In one embodiment, the Si content is preferably limited to a maximum of 0.35 wt %. Si contents of up to 0.35 wt % still allow the use of quite high proportions of old scrap to produce the alloy. At the same time, limiting the Si content to a maximum of 0.35 wt % leads to improved formability of the aluminum strips or aluminum sheets produced from the aluminum alloy and to higher strength, as less strength-enhancing Mg is bound in Mg2Si phases with a lower Si content.
The Fe content of the aluminum alloy is in the range of 0.15-0.8 wt %, more preferably in the range of 0.16-0.8 wt %, in particular 0.20-0.8 wt %. An Fe content above 0.8 wt % has a negative effect on formability. An Fe content below 0.15 wt % would limit the use of scrap too much.
Further preferably, the aluminum alloy has an Fe content of above 0.35 wt %, preferably an Fe content in the range 0.36-0.8 wt %, more preferably in the range 0.4-0.8 wt %. It was found that an Fe content in these ranges enables a greater proportion of old scrap, as old scrap can have a fairly high Fe content. At the same time, it was recognized that even with an Fe content in these ranges, advantageous properties of the aluminium strip can still be achieved, which enable it to be used for the production of can ends and/or can tabs.
In one embodiment, the Fe content is preferably limited to a maximum of 0.5 wt %. Fe contents of up to 0.5 wt % still allow the use of quite high proportions of old scrap to produce the alloy. At the same time, limiting the Fe content to a maximum of 0.5 wt % leads to improved formability of the aluminum strips or aluminum sheets produced from the aluminum alloy.
The Cu content of the aluminum alloy is in the range of 0.02-0.25 wt % A Cu content above 0.25 wt % would result in excessive strength, which would impair the workability of the aluminum strip. In addition, a Cu content above 0.25 wt % causes an increased tendency to certain forms of corrosion. The lower Cu limit of 0.02 wt % improves the ageing resistance of the aluminum strip and the products made from it. In addition, the tendency towards intergranular corrosion (IC corrosion) is reduced in this way.
Further preferably, the aluminum alloy has a Cu content of above 0.15 wt %, preferably a Cu content in the range 0.16-0.25 wt %, more preferably in the range 0.20-0.25 wt %. It was found that a Cu content in these ranges enables a greater proportion of old scrap, as old scrap can have a fairly high Cu content. At the same time, it was recognized that even with a Cu content in these ranges, advantageous properties of the aluminium strip can still be achieved, which enable it to be used for the production of can ends and/or can tabs.
The Mn content of the aluminum alloy is in the range of 0.20-1.4 wt %. Manganese leads to the formation of dispersoids, which increase the strength of the aluminum strip. Furthermore, additions of Mn favor the forming of Fe-containing casting phases and thus improve the formability. Below a Mn content of 0.20 wt %, these positive effects are only insufficiently achieved. A Mn content above 1.4 wt %, on the other hand, leads to a deterioration in formability.
Further preferably, the aluminum alloy has a Mn content of above 0.50 wt %, preferably a Mn content in the range 0.51-1.4 wt %, more preferably in the range 0.6-1.4 wt %. It was found that a Mn content in these ranges enables a larger proportion of old scrap, as old scrap can have a fairly high Mn content. At the same time, it was recognized that even with a Mn content in these ranges, advantageous properties of the aluminium strip can still be achieved, which enable it to be used for the production of can ends and/or can tabs.
In one embodiment, the Mn content is preferably limited to a maximum of 0.8 wt %. Mn contents of up to 0.8 wt % still allow the use of quite high proportions of old scrap to produce the alloy. At the same time, limiting the Mn content to a maximum of 0.8 wt % leads to improved formability of the aluminum strips or aluminum sheets produced from the aluminum alloy.
In one embodiment, the composition of the aluminum alloy, for one or two alloying elements from the group Si, Fe, Cu, Mn, fulfills the respective associated specification from specifications a1) to d1):
and, for the remaining alloying elements from the group Si, Fe, Cu, Mn the corresponding specification from the specifications a2) to d2):
For example, the composition of the aluminum alloy can meet the associated specifications a1) and d1) for Si and Mn and the associated specifications b2) and c2) for Fe and Cu.
In this way, an aluminum alloy is provided that better meets the requirements, in particular the mechanical requirements, for aluminum end strip and/or aluminum tab strip and at the same time enables a higher use of old scrap due to the specified content limits for certain alloying elements.
The Mg content of the aluminum alloy is in the range of 3.0-5.0 wt %. The addition of magnesium increases the strength and internal pressure stability of the can ends made from the aluminum strip. In order to achieve good strength and internal pressure stability of the aluminum strip, the aluminum alloy preferably has a Mg content of at least 3.5 wt %, more preferably at least 3.6 wt %, even more preferably at least 4.0 wt %.
The Cr content of the aluminum alloy is max. 0.1 wt %. Preferably, the aluminum alloy has a Cr content of at least 0.01 wt %, as a Cr content below 0.01 wt % would limit the use of scrap too much.
The Zn content of the aluminum alloy is max. 0.25 wt %. Preferably, the aluminum alloy has a Zn content of at least 0.01 wt %, as a Zn content below 0.01 wt % would limit the use of scrap too much.
The Ti content of the aluminum alloy is max. 0.10 wt %. Preferably, the aluminum alloy has a Ti content of at least 0.001 wt %, as a Ti content below 0.001 wt % would limit the use of scrap too much.
Various embodiments of the aluminum alloy, the aluminum strip, the method and the use are described below, with the individual embodiments each applying independently of one another both to the aluminum alloy and the aluminum strip and also to the method and the use. Furthermore, the individual embodiments can be combined with one another as desired.
In one embodiment, the aluminum alloy has a Si content of more than 0.20 wt % and/or an Fe content of more than 0.35 wt % and/or a Cu content of more than 0.15 wt % and/or an Mn content of more than 0.5 wt %. With these content ranges, it is possible to use a larger proportion of old scrap to provide the aluminum alloy. It was recognized that even with these alloying element limits, advantageous properties of the aluminium strip can still be achieved, which enable it to be used for the production of can ends and/or can tabs.
In one embodiment, the aluminum strip has an old scrap recyclate content, in particular a UBC scrap recyclate content, of at least 5 wt %, preferably at least 20 wt %, further preferably at least 30 wt %, more preferably at least 35 wt %, in particular at least 40 wt %. In a corresponding embodiment of the method, the melt is provided in a proportion of at least 5 wt %, preferably at least 20 wt %, more preferably at least 30 wt %, more preferably at least 35 wt %, in particular at least 40 wt %, by melting old scrap, in particular UBC scrap. The aluminum alloy described allows a higher use of old scrap than the alloy specification AA 5182 previously used for can end strip or can tab strip. In particular, UBC scrap or other scrap available on the market can be used for the aluminum alloy strip in this way. The use of at least 5 wt %, preferably at least 20 wt %, more preferably at least 30 wt %, particularly preferably at least 35 wt %, especially at least 40 wt %, of recycled scrap, especially recycled UBC scrap, can significantly improve the carbon footprint in the production of aluminum cans.
In one embodiment, the aluminum strip has a coating, in particular a stove enamel coating. In a corresponding embodiment of the method, this further comprises the following step:
In preparation for painting, the cold strip can be degreased, for example. The strip can also be treated with an adhesion promoter to prepare the surface for painting.
For stoving, preferably after an optional degreasing step, a liquid lacquer can be applied to one or both sides of the aluminum strip, which is then stoved in a stoving step. The lacquer can be a polymer-based lacquer, for example an epoxy-based lacquer. The paint is preferably stoved in an oven, for example a continuous oven, at a temperature of preferably 180-320° C. PMT (peak metal temperature). The heating of the aluminum strip during the stoving step can cause a change in the condition of the aluminum strip. In particular, the aluminum strip can have a condition H48 according to EN 546-2 after stove enameling. In a corresponding embodiment, the aluminum strip has a condition H48 according to EN 546-2.
Coated, in particular stove-enameled, strip is preferably used for the production of can ends or can tabs. In this way, there is no need for a painting process after punching out and forming into can ends or can tabs. Can end strip or can tab strip can also be distinguished from aluminum strip intended for other purposes by the existing lacquer coating.
In one embodiment, the aluminum strip has a thickness in the range of 0.20-0.24 mm. In a corresponding embodiment of the method, cold rolling takes place up to a final thickness of the cold strip in the range of 0.20-0.24 mm. A strip thickness in this range is particularly suitable for the production of can ends and can tabs.
In one embodiment, the aluminum strip has a yield strength Rp0.2 in the range 250-400 MPa. A yield strength in this range can be achieved in particular by the described alloy composition in combination with the described production method. An aluminum strip with such strength properties meets the mechanical requirements for the manufacture of can ends and can tabs.
In one embodiment, the aluminum strip has a tensile strength Rm in the range 300-450 MPa. A tensile strength in this range can be achieved in particular by the described alloy composition in combination with the described production method. An aluminum strip with such strength properties meets the mechanical requirements for the production of can ends and can tabs.
The yield strength Rp0.2 and the tensile strength Rm are each to be determined by tensile testing in accordance with DIN EN ISO 6892-1:2020-06
Further advantages and features of the aluminum alloy, the aluminum strip, the method and the use are shown in the following description of embodiments, with reference being made to the attached drawing.
In the drawings
The can body 4 on the one hand and the can end 6 and the can tab 8 on the other hand are typically made from different aluminum alloys. Accordingly, aluminum strips made of different alloys are required to manufacture the aluminum beverage can, namely can body stock, from which blanks are punched out and formed into can bodies by stretch drawing, and can end stock or can tab stock, from which the can ends and can tabs are punched out.
In the state of the art, can body strip made of AA 3104 and can end strip or can tab strip made of AA 5182 are typically used
Since the can body 4, the can end 6 and the can tab 8 of the aluminum beverage can 2 are firmly connected to each other and are not separated from each other when the aluminum beverage can 2 is scrapped at the end of its life cycle, UBC scrap contains a mixture of different aluminum alloys, in particular a mixture of AA 3104 and AA 5182.
Due to the narrow tolerance limits of the AA 5182 alloy specification for certain alloying elements, in particular for Si, Fe, Cu and Mn, no significant proportion of UBC scrap or other old scrap available on the scrap market can currently be used for the production of can end strips and can tab strips. The production of strips from AA 5182 therefore currently requires a high use of primary aluminum and essentially unmixed production scrap, which has a negative impact on the carbon footprint.
In the first step 110, an aluminum melt 114 having the following target composition is provided in a melting furnace 112:
The aluminum melt 114 is provided by melting old scrap 115, production scrap 116, primary aluminum 117 and additives 118. For example, UBC scrap or other market-available scrap with a suitable composition can be used as old scrap 115. The aforementioned target composition of the molten aluminum 114 allows a significant use of old scrap to provide the molten aluminum 114. Preferably, the amount of old scrap is at least 5 wt %, preferably at least 30 wt % of the molten aluminum 114.
In the second step 120, the molten aluminum 114 is DC cast into an ingot 122. The ingot 122 can then be milled (not shown).
In the third step 130, the ingot is homogenized, in particular in a pusher-type or crucible furnace 132, for example for a period of at least 0.5 hours at a holding temperature of 450-550° C.
In the fourth step 140, the ingot is hot-rolled to form a hot strip 142, for example in a reversing hot rolling mill 144.
In the fifth step 150, the hot strip 142 is cold rolled to form a cold strip 152. The cold rolling is carried out in particular in several passes, either in single passes or in two or more tandem cold rolling stands 154 arranged one behind the other. Optionally, the cold rolling can be interrupted for one or more recrystallizing intermediate annealing steps 155, in which the strip, wound up into a coil, is annealed in a chamber furnace 156, for example for a period of 0.5-4 hours at a holding temperature of 300-450° C. After the last cold rolling pass, the cold strip 152 preferably has a thickness of 0.20-0.24 mm. After cold rolling, the cold strip for example can be trimmed (not shown) to remove the irregular edges of the cold strip and to adjust the width of the cold strip.
In the optional sixth step 160, the cold strip is subjected to a degreasing treatment in order to prepare the strip surface for subsequent painting in the seventh step 170. For the degreasing treatment, the belt 152 can, for example, be passed through or exposed to a degreasing solution 162, for example an alkaline or acidic degreasing solution.
In the optional seventh step 170, the belt 152 is painted. In particular, the painting can take the form of stove enameling. For this purpose, the aluminum strip can be coated on one or both sides with a liquid lacquer 174 by means of a lacquer application device 172 and then passed through a stoving oven 176, which is preferably designed as a continuous oven.
After the last step, the finished aluminum strip 182 is wound into a coil 184 and can be supplied to a manufacturer of aluminum cans as can end strip and/or can tab strip. According to the provision of the aluminum melt 114, the aluminum strip 182 has a recycled scrap content of at least 5 wt %, preferably at least 30 wt %.
The use of the aluminum strip 182 produced in this way for the production of can ends and/or can tabs of aluminum cans, as shown for example in
| Number | Date | Country | Kind |
|---|---|---|---|
| 21203179.3 | Oct 2021 | EP | regional |
This application is the United States national phase of International Patent Application No. PCT/EP2022/078897 filed Oct. 18, 2022, and claims priority to European Patent Application No. 21203179.3 filed Oct. 18, 2021, the disclosures of which are hereby incorporated by reference in their entireties.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/078897 | 10/18/2022 | WO |
