Patent Application
20240209480
The present invention relates 5xxx series alloy aluminium sheet and their method of making, particularly useful for can making industry.
As a recognized efficient and environment friendly solution for beverage packaging, the aluminium beverage can is very popular.
In order to minimize CO2 emissions, can makers are acting to reduce the weight of can body and can end, and try to increase the recycled content of their solutions. It is worth highlighting that using 1 ton of scraps instead of 1 ton of primary metal reduces the CO2 emissions by 10 tons.
Regarding the can end, also called lid, can-makers have progressively reduced the can end diameters from 68.3 mm to 54 mm, and then 50.8 mm, using optimized designs. The combination of smaller diameter and new can end design has enabled the down-gauging from 223 m to about 203 m and an associated significant weight reduction.
However, the can end light-weighting has met a “plateau” during last years and now it is more and more difficult to down-gauge to less than 200 am.
The alloy used to manufacture can ends is typically alloy AA5182. Because of its high mechanical properties, AA5182 requires a high level of purity (e.g. Fe, Si) to obtain the necessary forming properties. Such high level of purity in AA5182 limits its recycled content and implies that the elaboration of AA5182 can end relies on primary aluminium. The more the primary aluminium is used, the more CO2 emissions are important.
It is also preferable to have the possibility to recycle the can end and the can body together as the metal quantity is larger in the can body than in the can end. For this reason, specific can end and can body alloys have been developed.
Patent application WO2013/103957 A2 discloses an aluminium alloy and recycling method in which the recycled used beverage containers form an alloy composition useful with relatively minor compositional adjustments for body stock.
Patent application WO2014/107188 A1 discloses an aluminium alloy and recycling method in which the recycled used beverage containers form an alloy composition useful with relatively minor or no compositional adjustments for body, end and tab stock, apart from magnesium levels.
Patent application WO2015/200570 A2 discloses 3xxx aluminium alloys useful in fabricating can ends and tabs used for opening cans, particularly AA3104 and AA3204 aluminium alloys.
Patent application WO2016/002226 A1 discloses an aluminium alloy sheet for a beverage can body, comprising by mass, 0.20-0.45% of Si, 0.35-0.60% of Fe, 0.1-0.3% of Cu, 0.5-1.5% of Mn, 0.8-1.5% of Mg, 0.1% or less of Ti, and 0.05% or less of B, with the remainder made up by Al and unavoidable impurities.
U.S. Pat. No. 5,746,847 A discloses an aluminium alloy for can ends, comprising in weight percentage: 3.0-4.0% Mg, 0.5-1.0% Mn, 0.2-0.6% Cu, 0.05-0.4% Fe and inevitable impurities.
Patent application JP H11 269594 A discloses an aluminium alloy for can ends, comprising in weight percentage: 0.6-1.2% Mn, 0.5-3.2% Mg, 0.2-0.5 Si, 0.3-0.5% Cu, 0.3-0.6% Fe, remainder aluminium and inevitable impurities.
Patent application US 2018/274072 A1 discloses several compositions of recycling alloys, for example adapted for producing beverage cans.
There is a need in the can making industry for an improved aluminium sheet product to make can end which combines careful balance between different criteria: strength, formability and high recyclability.
A first object of the invention is an aluminium sheet made of a 5xxx series aluminium sheet comprising in wt. %:
Another object of the invention is a method for producing a 5xxx series aluminium sheet according to the invention comprising the successive steps of:
Still another object of the invention is a can end obtained from a sheet according to the invention.
Still another object of the invention is a beverage can obtained from a can end according to the invention and a can body made of a AA3xxx alloy.
All aluminium alloys referred to in the following are designated using the rules and designations defined by the Aluminium Association in Registration Record Series that is published regularly, unless mentioned otherwise.
Metallurgical tempers referred to in the following are designated using the European standard EN-515 (April 2017).
All the alloy compositions are provided in weight % (wt. %). The expression “7.9 Mn” means that the manganese content, expressed as a percentage by weight, is multiplied by 7.9.
The tensile tests were performed according to ISO/DIS 6892-1 (July 2014).
The inventors have found improved 5xxx aluminium alloy sheets which combine careful balance between different criteria: strength, formability and high recyclability.
The Mg content is from 2.50 wt. % to 4.00 wt. %, preferably from 2.50 wt. % to 3.85 wt. %, more preferably from 3.10 wt. % to 3.85 wt. % and even more preferably from 3.10 wt. % to 3.65 wt. %.
Mg is the main alloying element of the alloy and it contributes to strength improvement. When the Mg content is under 2.50 wt. %, strength improvement may be insufficient. On the other hand, a content exceeding 4.00 wt. % may result in a lower formability. Minimum Mg content of 3.00 wt. % or 3.05 wt. % or 3.10 wt. % or 3.15 wt. % or 3.20 wt. % or 3.25 wt. % or 3.30 wt. % or 3.35 wt. % or 3.40 wt. % may be advantageous. Maximum Mg content of 3.85 wt. % or 3.80 wt. % or 3.75 wt. % or 3.70 wt. % or 3.65 wt. % or 3.60 wt. % may be advantageous.
Mn is also an effective element for strength improvement, crystal grain refining and structure stabilization. The Mn content is from 0.70 wt. % to 1.20 wt. %, preferably from 0.80 wt. % to 1.15 wt. % and more preferably from 0.90 wt. % to 1.10 wt. %, and even more preferably from 0.92 wt. % to 0.98 wt. %.
When the Mn content is under 0.70 wt. %, the aforementioned effect is insufficient. On the other hand, a Mn content exceeding 1.20 wt. % may not only cause a saturation of the above effect but also cause the generation of multiple intermetallic compounds that could have an adverse effect on formability. Moreover, the Mn content of the invention ensures in an embodiment to maximize the addition of recycled scrap, and more particularly UBC (Used Beverage Can) scrap during the casting step. Minimum Mn content of 0.76 wt. % or 0.78 wt. % or 0.80 wt. % or 0.85 wt. % or 0.90 wt. % or 0.91 wt. % or 0.92 wt. % or 0.93 wt. % may be advantageous. Maximum Mn content of 1.15 wt. % or 1.10 wt. % or 1.05 wt. % or 1.00 wt. % or 0.98 wt. % or 0.96 wt. % may be advantageous.
The control of Fe and Si is critical to reach the desired properties of the sheets of the invention, in particular the balance between formability and recyclability. The Fe content is from 0.25 wt. % to 0.55 wt. % and preferably from 0.30 wt. % to 0.40 wt. %.
A Fe content under 0.25 wt. % may not produce a sufficient effect while a Fe content above 0.55 wt. % may result in difficulties of forming, related to formation of large Al6MnFe primary phases. Minimum Fe content of 0.28 wt. % or 0.30 wt. % or 0.31 wt. % may be advantageous. Maximum Fe content of 0.45 wt. % or 0.40 wt. % or 0.38 wt. % may be advantageous.
The Mn and Mg contents are preferably related to the Fe content. Preferably, for a Fe content of at least 0.50 wt. %, the sum Mg+7.9 Mn is at most 11.4 wt. %, preferably at most 10.7 wt. % and more preferably at most 10.1 wt. %, for a Fe content of at least 0.44 wt. % (and less than 0.50 wt. %), the sum Mg+7.9 Mn is at most 12.1 wt. %, preferably at most 11.4 wt. % and more preferably at most 10.8 wt. %, for a Fe content of at least 0.40 wt. % (and less than 0.44 wt. %), the sum Mg+7.9 Mn is at most 12.5 wt. %, preferably at most 11.8 wt. % and more preferably at most 11.2 wt. %, for a Fe content of at least 0.35 wt. % (and less than 0.40 wt. %), the sum Mg+7.9 Mn is at most 12.8 wt. %, preferably at most 12.1 wt. % and more preferably at most 11.5 wt. %, for a Fe content of at least 0.30 wt. % (and less than 0.35 wt. %), the sum Mg+7.9 Mn is at most 13.1 wt. %, preferably at most 12.4 wt. % and more preferably at most 11.8 wt. %, for a Fe content of at least 0.25 wt. % (and less than 0.30 wt. %), the sum Mg+7.9 Mn is at most 13.5 wt. % preferably at most 12.8 wt. % and more preferably at most 12.2 wt. %. In a preferred embodiment the Fe content is from 0.30 wt. % to 0.40 wt. % and the sum Mg+7.9 Mn is from 8.0 wt. % to 12.5 wt. %, preferably from 9.4 wt. % to 11.8 wt. % and more preferably from 10.2 wt. % to 11.2 wt. %. The claimed Fe, Mn and Mg contents ensure in particular to maximize the addition of recycled scrap, and more particularly UBC scrap during the casting step.
The Si content is from 0.20 wt. % to 0.50 wt. % and preferably from 0.22 wt. % to 0.35 wt. % and more preferably from 0.23 wt. % to 0.30 wt. %. Excessive addition of Si may generate more Mg2Si phases that could have an adverse effect on formability. Minimum Si content of 0.21 wt. % or 0.22 wt. % or 0.23 wt. % or 0.24 wt. % may be advantageous. Maximum Si content of 0.40 wt. % or 0.35 wt. % or 0.30 wt. % or 0.28 wt. % may be advantageous.
The Cu content is from 0.10 wt. % to 0.25 wt. % and preferably from 0.10 wt. % to 0.20 wt. %, more preferably from 0.12 wt. % to 0.20 wt. %. Minimum Cu content of 0.11 wt. % or 0.12 wt. % or 0.13 wt. % or 0.14 wt. % may be advantageous as Cu in solid solution may be beneficial for strength and/or formability. Maximum Cu content of 0.25 wt. % or 0.20 wt. % or 0.18 wt. % may be advantageous as formation of Cu containing phases may have an adverse effect on formability. In an embodiment the Cu content is from 0.14 wt. % to 0.18 wt. %.
The Cr content is up to 0.10 wt. %, preferably up to 0.05 wt. %. In an embodiment, some Cr may be added for strength improvement, crystal grain refining and structure stabilization with a content from 0.01 wt. % to 0.05 wt. %, preferably from 0.01 wt. % to 0.03 wt. %.
Zn may be added up to 0.25 wt. % and preferably up to 0.20 wt. % or up to 0.15 wt. % without departing from the advantages of the invention. In an embodiment, Zn is among the unavoidable impurities.
Grain refiners comprising Ti are typically added with a total Ti content of up to 0.10 wt. % and preferably from 0.005 wt. % to 0.05 wt. % and even more preferably from 0.01 wt. % to 0.03 wt. %. In an embodiment, the Ti content is from 150 ppm to 250 ppm.
The rest is aluminium and unavoidable impurities up to 0.05 wt. % each and up to 0.15 wt. % in total.
According to the invention, an ingot is prepared by casting, typically by Direct-Chill casting or continuous casting, using 5xxx series aluminium alloys of the invention. Preferably the casting step comprises melting recycled scrap into liquid metal.
As used herein, the term recycled scrap (e.g., recycled stock) can refer to a collection of recycled metal comprising mainly aluminium, preferably at least 60% or 70% or 80% or 90% aluminium. Recycled scrap can include materials recycled from any suitable source, such as from a metal production facility (e.g., metal casting facility), from a metalworking facility (e.g., production facility that uses metal product to create consumable products), or from post-consumer sources (e.g., regional recycling facilities). Certain aspects of the present disclosure can be well-suited for recycled scrap from sources other than a metal production facility, since such recycled scrap likely contains a mixture of alloys or is mixed with other impurities or elements (e.g., such as paints or coatings). Recycled scrap can refer to recycled sheet aluminium products (e.g., aluminium pots and pans, cars inner and outer products), recycled cast aluminium products (e.g., aluminium grills and wheel rims), UBC scrap (e.g., beverage cans), aluminium wire, extruded materials and other aluminium materials.
Preferably recycled scrap metal includes used beverage can (UBC) scrap which is collected metal from used beverage cans and similar products that can be recycled for use in further metal products. Aluminium UBC scrap is often a mixture of various aluminium alloys (e.g., from different alloys used for can bodies and can ends) and can often include foreign substances, such as rainwater, drink remainders, organic matter (e.g., paints and laminated films), and other materials. UBC scrap can be shredded and decoated or delacquered prior to being melted for use as liquid metal stock in casting a new metal product of the invention. Because of the impurities and unbalanced alloying elements present in the liquid UBC metal, it can be necessary to either treat the liquid UBC metal to remove undesirable elements or combine the liquid UBC metal with sufficient amounts of new, primary aluminium prior to casting. Similarly, recycled scrap from other sources can have relatively high amounts of impurities and/or unbalanced alloying elements.
Described herein are recycled scrap contents of the products according to the invention. For example, the alloy according to the invention can allow suitable cast products to be produced from a modified liquid metal containing more than about 50 wt. %, about 60 wt. %, about 70 wt. %, about 80 wt. %, about 85 wt. %, about 90 wt. %, about 91 wt. %, about 92 wt. %, about 93 wt. %, about 94 wt. %, about 95 wt. %, about 96 wt. %, about 97 wt. %, about 98 wt. %, or about 99 wt. % recycled scrap. In other words, the cast products described herein can include less than about 50 wt. %, about 40 wt. %, about 30 wt. %, about 20 wt. %, about 15 wt. %, about 10 wt. %, about 9 wt. %, about 8 wt. %, about 7 wt. %, about 6 wt. %, about 5 wt. %, about 4 wt. %, about 3 wt. %, about 2 wt. %, or about 1 wt. % primary aluminium and optional hardeners (master alloys containing for example Al+Cu, Al+Si, Al+Mn, Al+Fe, etc. or pure metals for example Cu, Mg, Zn, etc.). Certain aspects of the present disclosure relate to metal products made using a modified liquid metal that is mostly recycled scrap. Preferably, the recycled scrap includes recycled aluminium scrap, such as UBC scrap. UBC scrap, for example, generally contains a mixture of metal from various alloys, such as metal from can bodies (e.g., 3104, 3004, or other 3xxx aluminium alloy) and can ends (e.g., 5182 or other 5xxx aluminium alloy). Due to the content of Mg and Mn, the composition of the alloy of the invention is particularly well suited to recycle UBC scrap. Preferably the recycled scrap melted in the method of the invention contains more than about 50 wt. %, about 60 wt. %, about 70 wt. %, about 80 wt. %, about 90 wt. %, about 91 wt. %, about 92 wt. %, about 93 wt. %, about 94 wt. %, about 95 wt. %, about 96 wt. %, about 97 wt. %, about 98 wt. %, or about 99 wt. % UBC scrap. Adding primary aluminium reduces the amount of recycled content and raises the costs and greenhouse effect gas emissions, as primary aluminium is more expensive to produce and generates more greenhouse effect gas emissions than recycled scrap. Therefore, a trade-off is often made between processing the recycled scrap and adding primary aluminium. Using the alloy of the invention described herein, recycled scrap can be used with little or no purification and little or no addition of primary aluminium and optional hardeners.
The ingot thickness is preferably at least 250 mm, or at least 350 mm and preferentially a very thick gauge ingot with a thickness of at least 400 mm, or even at least 500 mm or 600 mm in order to improve the productivity of the process. Preferably the ingot is from 1000 to 2000 mm in width and 2000 to 8000 mm in length. Preferably the ingot is scalped.
The ingot is then pre-heated, typically at a temperature from 440° C. to 550° C., and hot rolled in order to obtain a sheet having a thickness of typically from 2 to 12 mm. Preferably, the sheet is hot rolled in two successive steps, for example with a first hot rolling step on a reversible rolling mill, also known as roughing mill, up to a thickness of typically from 12 to 40 mm and a second hot rolling step on a tandem mill, also known as finishing mill, up to a thickness of typically from 2 to 12 mm. A tandem mill is a rolling mill in which several cages supporting rolling mill rolls, typically 2, 3, 4 or 5 act successively (“in tandem”). According to the invention rough hot rolling on the reversible mill is done with a rough hot rolling entry temperature of more than 440° C. and preferably more than 460° C. The first step on a reversible mill can be carried out on one or even two reversible mills placed successively.
In the second hot rolling step the final temperature which is the hot rolling exit temperature should be at least 300° C., and preferably at least 330° C. so that preferably the hot rolled sheet obtained after finish hot rolling exhibits a volume fraction of recrystallized grains of at least 50% and preferably at least 80%.
Cold rolling is realized directly after the hot rolling step to further reduce the thickness of the aluminium sheets. With the method of the invention annealing after hot rolling or during cold rolling is optional, because this step seems not necessary to obtain sufficient strength, formability, surface quality and corrosion resistance. Preferably no annealing after hot rolling or during cold rolling is carried out. The sheet directly obtained after cold rolling is referred to as the cold rolled sheet. The cold rolled sheet thickness is typically from 0.15 to 0.30 mm and preferably from 0.18 to 0.23 mm.
In an embodiment, the cold rolling reduction is at least 80%, or at least 85%.
Preferably the cold rolled sheet is coated. In one coating process, the cold rolled sheet is cleaned and chemically treated, optionally dried in an oven, optionally primed, coated, and thermally (oven) cured to form a coated sheet. In another coating process, the cold rolled sheet is cleaned and chemically treated, coated with a suitable (e.g., food-grade) electron beam (“EB”) and/or ultraviolet (“UV”) curable coating composition, and EB or UV cured to form a coated sheet.
Preferably the coating is a BPA-Free or BPA-NI (Bisphenol-A Free or Bisphenol-A Non-Intent) coating or a laminate.
The products of the invention after simulation of baking of coating at 205° C. for 20 min have preferably a Tensile Yield Strength (TYS) in the Long Transverse (LT) direction, from 320 MPa to 380 MPa and preferably from 320 MPa to 360 MPa.
Formability is the capacity of a sheet to be formed under a specific shape. Formability is in particular linked to the tensile yield strength (TYS or Rp0.2): as the TYS increases, the formability generally decreases. According to a preferred embodiment, the TYS of the sheet according to the present invention is less than or equal to 380 MPa, preferably less than or equal to 360 MPa in H48 temper or after a heat treatment at 205° C. for 20 minutes simulating the baking of coating and giving mechanical properties similar to the mechanical properties in H48 temper. According to another preferred embodiment, the TYS of the sheet according to the present invention is more than or equal to 320 MPa in H48 temper or after a heat treatment at 205° C. for 20 minutes simulating the baking of coating. This minimal TYS allows to obtain sufficient strength and to resist to internal pressure.
Preferably the products of the invention are in a H4X metallurgical temper as defined by European standards EN 515 (April 2017) and EN 541 (May 2007).
According to these standards, the H4X metallurgical temper describes strain-hardened and lacquered or painted products. Thus H4X is the temper of materials obtained after work hardening and coating, during which a certain level of restoration may happen. A preferred temper is the H48 temper which is assigned to the hardest H4X tempers normally produced. The H48 mechanical properties may be obtained from the cold rolled sheet in H18 or H19 temper after simulation of baking of coating at 205° C. for 20 min.
In particular, the H48 metallurgical temper guarantees shaping of the metal to fabricate can ends for beverage cans. Preferably, the 5xxx series aluminium sheet according to the present invention is coated and is preferably in a H48 temper.
The invention also concerns a can end obtained from a sheet according to the invention and a beverage can obtained from a can end according to the invention and a can body made of a AA3xxx alloy.
The use of the 5xxx series aluminium sheets according to the invention for making can ends is advantageous. In particular, the use of can ends according to the invention in combination with can bodies made of a AA3xxx alloy, preferably an alloy selected from AA3002, AA3102, AA3003, AA3103, AA3103A, AA3103B, AA3203, AA3403, AA3004, AA3004A, AA3104, AA3204, AA3304, AA3005, AA3005A, AA3105, AA3105A, AA3105B, AA3007, AA3107, AA3207, AA3207A, AA3307, AA3009, AA3010, AA3110, AA3011, AA3012, AA3012A, AA3013, AA3014, AA3015, AA3016, AA3017, AA3019, AA3020, AA3021, AA3025, AA3026, AA3030, AA3130, and AA3065, most preferably selected from AA3004, AA3004A and AA3104 is advantageous because this beverage can is easy to recycle.
In this example several ingots with an alloy having the composition disclosed in Table 1 were cast by DC-casting technology.
Alloys D, E and F are not according to the present invention because they comprise too much Cu (more than 0.25 wt. % Cu).
The TYS in the LT direction in the H48 temper was evaluated from a computer software. The results are provided in Table 2.
| Number | Date | Country | Kind |
|---|---|---|---|
| FR2104673 | May 2021 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/060502 | 4/21/2022 | WO |
