CH643001A5 - ALUMINUM ALLOY AND METHOD FOR PRODUCING A TAPE AND LID TAPE. - Google Patents

Description

The invention relates to an aluminum alloy with magnesium and manganese as essential alloy components and a method for producing a strip made of an aluminum alloy that is suitable for the production of deep-drawn and stretched can bodies and lids.

Aluminum food and beverage containers have been manufactured with great success since around 1960. The term “container” is understood here to mean all products made of aluminum sheet which are shaped to hold a filling material, such as cans for carbonated drinks, vacuum cans, dishes and container parts such as completely removable lids and tear-off ring lids. The term “can” refers to a fully closed container that is resistant to internal and external pressure, such as vacuum and beverage cans.

Originally, only the can lids were made of aluminum and referred to as “soft lids”. These lids had no features of an easy to open can closure and were made from the alloy AA 5086. The introduction of the lids with the properties of an easy-open can closure, such as the “ring pull” lids, required the use of more deformable alloys such as AA 5182.5082 and 5052. The most commonly used alloys 5082 and 5182 have a high magnesium content (4.0 to 5.0% Mg) and are therefore relatively hard compared to the alloys used in can bodies. Alloy 5052 was primarily used for multi-stage deep-drawn, non-pressurized containers because it does not have sufficient strength for most can applications.

Shortly after the introduction of the aluminum can lids, the aluminum can bodies were also introduced. Aluminum can bodies were initially made as parts of three-part cans, as is known from the traditional “tin cans”. Three-part cans consist of two ends and a cylindrically shaped and seamed can body. In the case of beverage cans, the newly developed two-part can has gradually replaced the three-part can. Two-part cans consist of a lid and a seamless can body with an integral base. Can bodies of two-part cans are formed in several stages by deep drawing and drawing.

US Pat. No. 3,402,591 describes a device for producing deep-drawn and ironed cans. During deep drawing and stretching, the can body is formed from a circular piece of sheet metal, which is drawn into a bowl in a first step. The sidewall is then lengthened and thinned by running the cup through a series of draw rings with decreasing holes. The pull rings result in an ironing effect, through which the side wall is drawn in length, the side wall is thinner than the bottom. The alloy AA 3004 is most often used to produce can bodies from two-part cans, since it has sufficiently good deformation, strength and tool wear properties for the deep-drawing and ironing process. These properties are a function of the alloy's low magnesium (0.3 to 1.8%) and manganese (1.0 to 1.5%) content.

The disadvantage of the currently used alloy A A 3004 is that it is used to achieve the desired s

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End properties require long-term annealing or homogenization at high temperature. Conventional billet annealing is one of the biggest cost factors in sheet metal production. In addition, the casting speed for alloy 3004 is relatively low and if improperly cast, it shows a tendency to form coarse primary segregations.

Other alloys have previously been considered for use in can bodies, such as alloy AA 3004. This alloy probably meets all the requirements for deformability during deep drawing and drawing, but was dropped again because of its low strength with economical material thicknesses.

The above-described conventional alloys for can lids and can bodies differ significantly in their compositions, as can be seen from Table I. The numerical values given are percentages by weight, as incidentally throughout the present description. Unless range information is available, the weight percentages given in Table I represent maximum values. The designation AA and the associated numerical information refer to the classification system of the Aluminum Association.

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At the moment, great efforts are being made to conserve energy and raw material sources as well as to eliminate the waste and waste problems that affect the beverage industry in particular. This is to be made possible by the establishment of a total recycling program in the aluminum can industry, which consists of io (1) the collection and return of used, empty aluminum beverage cans, and

(2) the reuse of aluminum from used cans to make new cans.

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In the finished can, the lid and can body are practically inseparable, so that an economical recycling system requires the use of the entire can. As a result, the composition of the melt of recycled cans differs considerably from the compositions of conventional alloys for lids and can bodies. The following are alloys and strips for manufacturing

Table I

alloy

silicon

iron

copper

manganese

Magnesium chrome

zinc

titanium

Others individually

Total

A A 3003 A A 3004 AA 5182 AA 5082 AA 5052 AA 5042

0.6 0.30. 0.20 0.20

0.7 0.70 0.35 0.35

0.45 Si + Fe 0.20 0.35

0.05-0.2

0.25

0.15

0.15

0.10

0.15

1.0-1.5

1.0-1.5

0.20-0.50

0.15

0.10

0.20-0.50

0.8-1.3 4.0-5.0 4.0-5.0 2.2-2.8 3.0-4.0

0.10 0.15

0.15-0.35 0.10

0.10 0.25 0.25 0.25 0.10 0.25

0.10 0.10

0.10

0.05 0.05 0.05 0.05 0.05 0.05

0.15 0.15 0.15 0.15 0.15 0.15

of can bodies referred to as can alloys or strips and alloys and strips for the production of lids as cover alloys or strips. If the original alloy compositions are to be obtained again from the melt of recycled cans, considerable amounts of primary or pure aluminum must be added in order to obtain a conventional can alloy; Correspondingly larger amounts of primary aluminum must be added to restore a conventional cover alloy.

It would therefore be advantageous to use an aluminum alloy of the same composition for the lid and can body, so that it would no longer be necessary to adjust the alloy composition when these cans were remelted. This advantage was developed by Setzer et al. recognized and described in US Pat. No. 3,787,248, in which it is proposed to produce both the lid and the can body from an alloy of the type AA 3004, the deformability required for the lid being achieved by a heat treatment. The by Setzer et al. The proposed method involves holding at high temperature after cold rolling. In addition, those of Setzer et al. proposed alloy compositions result in a composition of the melt that would differ significantly from a melt from conventional, two-part cans with different can and cover alloy.

The invention has for its object to provide an aluminum alloy and a method for producing a strip suitable for the production of deep-drawn and ironed can bodies and lids, which reuse used aluminum cans and can parts by melting them and adjusting the melt to the desired composition enable economical way.

40 According to the invention, the object is achieved in that the alloy

The remainder essentially contains aluminum in this way, the total content of magnesium and manganese being between 2.0 and 3.3% and the weight ratio of magnesium to manganese being between 1.4: 1 and 4.4: 1.

a) a melt from the aluminum alloy according to the invention at a temperature of 700 to 750 ° C.

60 bars is shed

b) the ingot is homogenized at a temperature of 550 to 600 ° C for 4 to 6 h,

c) the homogenized ingot is rolled hot into a strip, and f> s d) the hot-rolled strip is cold-rolled to its final thickness with a thickness reduction of at least 40%.

The melt of the method according to the invention can be characterized. The method according to the invention is characterized in that

1.3 to 2.5% magnesium 0.4 to 1.0% manganese, 45 0.1 to 0.9% iron, 0.1 to 1.0% silicon, 0.05 to 0.4% copper,

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be composed of at least 40% aluminum scrap metal.

The alloy according to the invention and the method and its advantages which can be achieved in particular when reusing aluminum scrap metal are explained in more detail below and illustrated by means of graphic representations.

It shows:

1 shows a flow chart to illustrate the method according to the invention as part of a recycling system

2 shows a graphical representation of the work hardening of the alloy according to the invention and two comparison alloys as a function of the cold working

3 shows a graphic representation of the changes in the mechanical properties of the alloy according to the invention and of a comparative alloy during thermal treatment.

The processes of melting different types of scrap, adapting the melt to a desired composition, pouring the melt, producing strip material and manufacturing containers contain, according to FIG. 1, a closed cycle system in which the scrap produced by the manufacturing process is recycled and again is provided as raw material for the process. The scrap used in the present invention includes scrap from the production of tape material (tape scrap), scrap from the manufacture of cans (can scrap) and consumer scrap.

Consumer scrap is understood to mean products made from aluminum alloys, in particular cans, which have been printed, coated or otherwise contaminated and then sold and used.

The present invention has been particularly adapted for the use of aluminum can scrap. Cans are preferably recovered in a clean form, free of dirt, plastic parts, glass and other contaminants. The can bodies of conventional cans are inseparably connected to the lids. During the recovery of scrap cans, the entire cans are therefore crushed, flattened, clenched or otherwise brought into a compact form. The cans are then crushed in conventional grinders, hammer mills, counter-rotating knives, etc. to preferably loosely occurring pieces of about 2.5 to 4 cm in diameter. The dismembered aluminum scrap is freed from iron and steel parts by means of magnetic separation processes and paper and other light-weight substances by centrifugal separators. The cleaned scrap is then introduced into a paint incinerator. A suitable paint incinerator is a kiln in which the scrap is transported through a rotating tunnel in the presence of hot air. Another possibility is a paint incinerator, in which the shredded scrap is embedded in a basket from 15 to 25 cm deep made of stainless steel. Hot air is blown through the basket to burn organic substances such as plastic coatings on food containers and beverage cans as well as painted or printed labels containing pigments such as titanium (IV) oxide.

The furnace temperature is preferably selected so that the temperature of the scrap reaches the pyrolysis temperature of the organic coating materials. The temperature must be high enough, usually around 480 to 540 ° C, so that all organic coating materials pyrolyze but the metal scrap is not oxidized.

The scrap used in the present invention includes aluminum alloy material such as tape scrap, can scrap, and consumer scrap, which has been refurbished as described above. A large part of the consumer scrap consists of aluminum cans, which usually contain 25 percent by weight can lid made of the alloy AA 5182 and 75 percent by weight can body made of the alloy AA 3004. The compositions of these alloys and the composition obtained when these alloys were remelted are described in Table II below.

Strip scrap contains waste from the cast strip and from the cutting operations carried out in a rolling mill, such as trimming the rolled strip. The initial melt composition obtained from typical tape scrap consists of about 88% A A 3004 alloy and 12% AA 5042 alloy. AA 5042,

another high magnesium alloy used in the manufacture of lids is described in Table III below.

The scrap used in the present invention may also include scrap that is produced in the manufacture of containers and container parts, such as can lids and bodies. Can scrap is generated, for example, when rejects are formed due to tip formation. The scrap used in the present invention can also contain other aluminum materials containing elements with a mixed crystal hardness effect and, of course, also strip, can and consumer scrap made from the alloy according to the invention.

The scrap to be recycled is melted in an oven such as is known, for example, from US Pat. No. 969,253. The initial melt naturally changes its composition according to the compositions and the amounts of the various types of scrap loaded in the furnace. In the process according to the invention, the melt is adjusted in such a way that the composition comes to lie within the following values:

Magnesium 1.3 to 2.5% preferably 1.6 to 2.0%

Manganese 0.4 to 1.0% preferably 0.6 to 0.8%

Iron 0.1 to 0.9% preferably 0.3 to 0.7%

Silicon 0.1 to 1.0%, preferably 0.15 to 0.40%

Copper 0.05 to 0.4%

The values listed above represent the broad ranges and the preferred ranges of the composition of the alloy according to the invention. The composition of the present alloy can vary within the ranges specified, but the ranges themselves are critical, in particular those of the main alloying elements magnesium and manganese. Magnesium and manganese together have a mixed crystal hardness effect in the present alloy due to their presence in solid solution. It is therefore essential that the concentrations of these elements are within the specified ranges, that the ratio of magnesium to manganese has a value between 1.4: 1 and 4.4: 1 and the total content of magnesium and manganese between 2.0 and is 3.3%. Further trace elements, which are to be expected as impurities in the recycling process, are permissible up to a certain limit in the present alloy composition, for example chromium up to 0.1%, zinc up to 0.25% titanium up to 0.2%, and others individually up to 0.05% together up to 0.2%.

Copper and iron are present in the present composition due to their inevitable presence in consumer scrap. The presence of copper in

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a content between 0.05 and 0.4% brings an improvement in terms of low tip formation and additionally brings about an increase in strength in the present alloy.

In order to achieve the specified ranges or the preferred ranges for the composition of the present alloy, it may be necessary to adjust the melt. This can be done by adding magnesium or manganese, or - to dilute excess alloy elements - by adding unalloyed aluminum to the melt.

The total energy required to produce unalloyed primary aluminum from its ore is about twenty times higher than the amount of energy required to smelt aluminum scrap. As a result, considerable amounts of energy and costs can be saved if the amount of primary aluminum required to produce a desired alloy is kept as low as possible. If there is an excess of magnesium, the magnesium content in the melt can also be reduced by rinsing the molten alloy with chlorine, the insoluble magnesium chloride which forms being removed with the slag. However, because of the loss of magnesium from the melt and the danger and the environment when working with chlorine, this process is not absolutely desirable.

The melt can also be adjusted by adding lower-alloy aluminum, in which the alloy elements for diluting excess elements are present in the appropriate ratio.

Table II shows the compositions of the alloys AA 3004 and 5182 and the stoichiometric melt composition which results from the melting of typical consumer scrap from cans of the alloys mentioned:

Table II

Alloy (typical primary factor (%)

Composition)

3004 5182 melt 3004 5182 present

alloy

magnesium

0.9

4.5

1.5

40 -

manganese

1.0

0.25

0.8

70 18

iron

0.45

0.25

0.4

39 3

silicon

0.2

0.12

0.2

33 -

titanium

0.04

0.05

0.04

_

copper

0.18

0.08

0.1

27 -

In the number of 1.5% magnesium in the column titled "melt", a magnesium loss of 0.3% due to the magnesium oxidation during melting is taken into account. The numerical values in the table labeled "Primary Factor" represent the amount of primary or pure aluminum that has to be added in order to reduce each element to the nominal composition of AA 3004.5182 or the present alloy. The nominal composition of the present alloy as used in the description and examples is as follows:

Magnesium 1.8%

Manganese 0.7%

Iron 0.45%

Silicon 0.25%

Copper 0.2%

Titanium 0.05%

Since the contents given for the elements in alloys AA 3004 and 5182 are maximum values except for manganese and magnesium, the largest primary factor specified is decisive for each alloy.

s Table II shows that an amount of pure aluminum corresponding to 40% of the melt weight must be added if the content of magnesium in the melt is to be reduced to the typical 0.9% of AA 3004. Similarly, an amount of pure aluminum corresponding to 70% of the melt weight must be added if the manganese content in the melt is to be reduced to the typical 0.25% of AA 5182. On the other hand, only 18% pure aluminum is necessary in order to reduce the manganese content in the melt to the nominal value of the alloy of the process according to the invention.

Table III shows the same ratios with respect to tape scrap with 88% AA 3004 and 12% AA 5042.

Table III

Alloy (typical primary factor (%)

Composition)

3004 5042 melt 3004 5042 present

alloy

0.9

3.5

1.21

26 -

-

1.0

0.25

0.91

73

23

0.45

0.25

0.43

42

5

0.2

0.12

0.19

37

-

0.04

0.05

0.04

-

-

0.18

0.08

0.17

53

_

According to Table III, 26% primary aluminum 35 would be necessary to reduce the magnesium content of the melt to the typical AA 3004 value of 0.9%. Likewise, 73% primary aluminum would be necessary to bring the manganese content of the melt to the value of 0.25% of the 5042 composition. On the other hand, only 23% of primary 40 aluminum would be necessary to reduce the manganese content of the melt to the nominal content of the present alloy.

Tables II and III show that less than 25% of unalloyed aluminum would be required in the composition of the present alloy to prepare the melt. A smaller amount of primary aluminum is therefore required than for processing any other known container alloy.

The tables also show that the type of scrap in the melt thus affects the amount of primary metal required to achieve a desired melt composition. Depending on the type of scrap fed into the melting system, the present alloy composition can also be achieved by using 55 100% scrap. A typical can manufacturing plant, for example, requires 83% can tape (AA 3004) and 17% lid tape (5042). Of the 27.6% scrap that accumulates as waste in the can production and has to be melted down again, 24.9% is for can scrap and 2.7% 60 for lid scrap. Scrap from the can manufacturing plant and consumer scrap in the form of returned, used cans can be added to the melt. Assuming a melt loss of 5% based on the can manufacturing scrap and 8% based on 65 of the cans returned by the consumer, returning all the cans produced on such a system requires the addition of only 7.2% primary aluminum to the melt in order for the present alloy to combine -

magnesium

manganese

iron

silicon

titanium

copper

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Settlement is achieved. This amount can be further reduced by using other scrap alloys in the melt, including using scrap from the present alloy.

Until now, when using known alloy compositions, it was not possible to reduce the amount of primary aluminum required to achieve a usable melt composition from consumer scrap to less than 40% of the scrap weight in the melting furnace. The present invention allows the present alloy composition to be formed from at least 40% scrap over a wide range of proportions of tape scrap, can scrap, and consumer scrap.

The present alloy has numerous advantages, which are based on the fact that the alloy composition is achieved starting from the melt. As already mentioned, a first advantage is the fact that the present alloy can easily be obtained from the recycling of currently existing aluminum scrap. Another advantage can be seen in the fact that the present alloy has a wide tolerance range for silicon, iron, copper and other elements, which are regarded as undesirable contamination in conventional alloys, but which are inevitably present in consumer scrap. For example, a relatively high concentration of titanium may be present, which is particularly important from the recycling point of view, since a large part of consumer scrap contains titanium oxide, which is reduced during melting and dissolves in the molten alloy. A wide tolerance range for titanium is also important because the titanium content in the melt increases when scrap is smelted in successive cycles. The expected concentration in the range between 0.15 and 0.20% may also be present in the present alloy.

As a further example, the alloy can have a relatively high proportion of silicon from sand or dirt contained in the scrap. The present alloy permits this content and also has the advantage that heat treatment is possible with silicon contents above 0.45% and with the element ranges listed above. Heat treatment refers to the process of heating an alloy to a temperature high enough to solubilize the soluble alloy elements or components (Mg2Si), typically 510 to 610 ° C. The alloy is then quenched to obtain these elements in supersaturated, solid solution. The alloy is then aged either at room temperature or at elevated temperature, during which time precipitates are formed which cause the alloy to harden. The curing can take place at temperatures which are customary when baking polymer coatings of aluminum containers and are described below. This permits the use of manufacturing processes which produce sheets of lower strength than would otherwise be required for sheets in the hard-rolled condition.

After the alloy is set to the desired composition in the furnace, the melt is treated to remove dissolved hydrogen and non-metallic inclusions that would affect the casting of the alloy and the quality of the sheet produced. For this purpose, a gas mixture of chlorine and an inert gas such as nitrogen or argon is passed through at least one carbon inlet tube, which is located at the bottom of the furnace and permits gas purging of the melt. The gas mixture is bubbled through the molten alloy for about 20 to 40 minutes with the slag that forms floating to the surface of the melt and skimmed off therefrom by any suitable method. The low magnesium content of the alloy according to the invention leads to less slag and a lower magnesium erosion than the alloys AA 5082, 5182 and other conventional cover alloys. The skimmed alloy is then freed of non-metallic inclusions by means of a filter bed made of refractory material such as aluminum oxide. For further degassing of the alloy, a gas mixture as described above is passed through the melt in countercurrent.

The molten alloy of the present composition can then be cast into ingots using known continuous casting techniques. When pouring into the mold, the temperature of the molten metal for the present alloy is 700 to 750 ° C.

The alloy according to the invention can be cast in a given mold for rolled ingots at a speed of more than 110 kg / min, while in comparison the alloy AA 3004 can be cast at a maximum speed of 110 kg / min. The present alloy can be cast faster because of its smaller grain size, the smaller dendrite arm distances and the smaller primary excretions of (FeMn) Alò. These properties also cause fewer cracks during casting, which leads to a reduction in the amount of scrap from the ingots.

The cast ingots are then milled to remove the irregularities in the composition of the rolling surfaces. It has been shown that bars made from the present alloy have to be milled less than bars made from AA 3004, which corresponds to a smaller amount of scrap. Ingots made from the alloy according to the invention have to be milled off on each side by about 12 mm, which means about 25% less than with ingots made from AA 3004 alloy.

The milled mill bars are homogenized at a temperature of 550 to 600 ° C, preferably at 570 ° C, for 4 to 6 hours. This homogenization time refers to the holding time at a given temperature, excluding heating and cooling times. In comparison, an AA 3004 bar requires a homogenization of 4 to 6 hours at 565 to 610 ° C. The lower homogenization temperature in the alloy according to the invention is possible because of the smaller manganese and greater magnesium content compared to the alloy AA 3004.

The homogenization temperature is chosen to be below the imbalance solidus temperature of the alloy, i.e. below the lowest temperature at which any phases or components present begin to melt. The atomic mobility at the homogenization temperature compensates for the increases that occur during casting and reduces the grain boundary concentration of the alloy elements. In addition, certain solid-state reactions occur in alloys which contain the elements manganese, iron and silicon, in which part of the phase (FeMn) ale changes into the a-phase Al (FeSiMn). The present alloy has a stronger a-transformation at a given temperature than the alloy AA 3004, which results in less tool wear during the deep-drawing and ironing process in the can production. The present alloy is processed such that an a-transformation of at least 25% is achieved, usually 30 to 50% or more. a-transformation can occur during homogenization annealing, during that described below

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high temperatures and hot rolling with sharp decreases, or during annealing at elevated temperatures.

After homogenization, the ingot is cooled to a hot rolling start temperature of 450 to 510 ° C and 5 subjected to a first hot rolling pass. The bar does not necessarily require slow cooling, but can be cooled in calm air at room temperature. The starting temperature for hot rolling, which is not critical, is significantly lower than that used for the 10 A A 5182 alloy (480 to 525 ° C). During the first hot rolling passes, the ingot of, for example, thickness after the 47.6 cm over milling is rolled into a plate of typically about 19 mm, i.e. with a thickness reduction of about 96%. These first hot-rolling passes should take place with a reduction in thickness of about 40 to 96% and serve to bring the alloy into a suitable format for further hot-rolling. These first hot rolling passes are usually carried out on a reversing mill. 20th

After these first hot rolling passes, the hot rolling plate is immediately rolled on a multi-stand hot rolling mill with a thickness reduction of 70 to 96%, preferably about 85%, from 19 mm to 3.0 mm. Lubricants are used during hot rolling to prevent the hot rolling plate from sticking to the work rolls and to cool the rolls. The hot-rolled strip, which is now cold rolled, is later rolled to its final thickness by suitable cold rolling. The present alloy is considerably softer than alloy AA 5182, requires less energy in hot and cold working and is less susceptible to edge cracks. The hot rolled strip is coiled at a final temperature of preferably 300 ° C. The final temperature can also be lower, depending on the performance of the hot rolling mill used.

The coiled strip is then annealed before the subsequent cold rolling. This annealing is advantageously carried out at 315 to 400 ° C, preferably at about 345 ° C, for 2 to 4 hours. In hot rolling mills 40 which allow a sufficiently high final temperature to avoid cold forming (i.e. around 315 ° C), the annealing of the coiled strip can be omitted. Annealing is defined as heat treatment above the recrystallization temperature of the alloy and serves to break down 4S of preferred grain orientations, which result from hot working below the recrystallization temperature.

The annealing can also be carried out as a brief intermediate annealing of the strip in a continuous strip furnace between the cold rolling passes. For this purpose, the strip is annealed for 3 to 90 seconds, preferably 3 to 30 seconds, at a temperature between 350 and 500 ° C. This brief intermediate annealing leads to improved tip formation behavior and to better elongation values in the strip used for the manufacture of can bodies.

After hot rolling and the required annealing, the strip is cold-worked to its final thickness by cold rolling.

Cold work hardening means the increase in strength of a 60 alloy depending on the amount of cold forming that is exerted on the metal. Compared to conventional can lidding material, the alloy of the present invention exhibits a lower strain hardening rate, as shown in FIG. 2. This means that 65 fewer stitches are necessary to achieve the final thickness or the same number of stitches can be carried out at higher speed or with a wider range.

The present alloy also leads to less unevenness and less edge cracks compared to conventional cover alloys. Moreover, the strain hardening rate of the present alloy is quite comparable to that of the conventional can body alloy AA 3004, which shows that sufficient strength can be achieved for can band without excessive cold deformation.

The following stitch program for cold rolling has proven to be advantageous in the production of canned strip for deep-drawn and stretched can bodies:

After the annealing and subsequent cooling to less than 200 ° C, usually to room temperature, the coiled strip is changed from 3.0 mm to 0.34 mm - i.e. by 89% - cold rolled, preferably in one pass through at least one multi-stand tandem rolling mill. Another possibility is to cold roll the strip in several passes with the sequence 3.0 mm-> 1.30 mm-> 0.66 mm- »0.34 mm on a single-stand rolling mill. Annealing between cold rolling passes is referred to as intermediate annealing and, if necessary, is carried out as described above. Intermediate annealing may prove necessary if there are cracks between two passes or to change the cold rolling properties of the finished strip. If a single-stand rolling mill is used, the intermediate annealing is preferably carried out before the last pass. When performing an intermediate anneal, the final pass is preferably 40 to 60%. Such an intermediate annealing before the last cold rolling pass has an advantageous effect on the decrease in tip formation during deep drawing and drawing. In order to achieve the required cold forming in accordance with the strain hardening rate shown in FIG. 2, a combination of single and multi-stand rolling mills can also be used.

The tape is finished by trimming and cutting to the desired width. The sheet produced in this way has a 0.2% yield strength of 250 to 310 MPa, preferably 270 to 290 MPa, a tensile strength of 260 to 320 MPa, preferably 270 to 300 MPa, and an elongation at break (ASTM) of 1 to 8%, preferably 2 to 3%.

The following stitch program for cold rolling has proven to be advantageous in the production of lid tape with sufficient strength and flexibility for the manufacture of can lids:

Hot rolled strip of 3.0 mm thickness is cold rolled in one pass through a multi-stand tandem mill with a reduction from 91% to 0.26 mm. The reduction should be between 60 and 95%. Another possibility is to cold roll the tape in 4 passes with the sequence 3.0 mm - 1.30 mm - 0.66 mm - 0.34 mm - * 0.26 mm on a single-stand rolling mill. An intermediate annealing is not necessary. The sheet is finished by trimming and cutting to the desired width. The stitch program of cold rolling for flat strip leads to the following mechanical properties in the rolled state: 0.2% yield strength from 310 to 370 MPa, preferably 320 to 360 MPa; Tensile strength of 320 to 380 MPa, preferably 340 to 350 MPa; and elongation at break (ASTM) of 1 to 5%, preferably 1 to 3%.

The above-described process steps for can and lid band are designed for the production of corresponding work-hardened sheet, based on the consideration that can band has a minimum 0.2% yield strength of 240 MPa and lid band in the hard state a minimum 0.2% Should have a yield strength of 300 MPa.

The method steps described can of course be modified to change the state

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received, such as soft annealed, work hardened and partially annealed, work hardened and stabilized, solution annealed, aged and softened. If the present alloy is produced in such conditions, it can also be used for the production of closures and containers such as sardine cans, meat preserve cans, containers for ready meals, oil cans, film cans and other containers and closures for both edible and non-edible filling goods. These containers can of course also be produced by methods other than those described below, such as by deep drawing in one or more steps or by hollow stamping.

The can band produced by the above-described processes is formed into one-piece, deep-drawn can bodies. For this purpose, blanks are cut from the sheet, which are drawn through a die through a stamp and thus formed into cups. The edge of a cup shaped in this way preferably lies in a circular plane. The amount by which the edge deviates from this level is referred to as the tip formation. With a first deep drawing of 32 to 40%, the present alloy leads to an up to 50% lower tip formation at 45 ° to the rolling direction than AA 3004 can band. As can be seen from Table V above, with the present alloy, values for tip formation of 2% and less can be achieved with ease. The percentage for deep drawing is calculated by subtracting the diameter of the bowl from the diameter of the round blank and dividing it by the diameter of the round blank. The deep-drawn cups are then drawn further and ironed in a deep-drawing and ironing process, where the bowl is pressed through a series of drawing rings with circular bores of decreasing radii. The pull rings result in an ironing effect, by means of which the side wall of the can is lengthened by reducing the wall thickness. In this way, can bodies can be produced whose side wall is thinner than the bottom. If the metal to be deformed is too soft, it can stick to the work surfaces of the ironing rings and thus interfere with the deep-drawing and ironing process, which leads to material defects and interruptions in the manufacturing process. The present alloy shows this effect to a lesser extent than conventional can band alloys and consequently also leads to less tool wear.

When manufacturing can lids, the lid tape is leveled, cleaned, provided with a conversion layer and - if desired - primed. The cover tape is then coated in the manner described below. The coated cover tape is then fed to a press, where the covers are preformed as deep-drawn and flanged shells. The shell is then fed to a conversion press to form an easy-to-open lid, where the lid is scored and an integral rivet is formed. A tear ring can be produced in a corresponding press in a separate work step and fed to the conversion press for riveting with the cover. However, the tear ring can also be produced in the conversion press from a separate band and the tear rings and the covers can be formed and connected in the same conversion press. Tear rings are often made of a different alloy than the can lid. The formability of the present alloy also allows

Manufacture of tear rings. A further description of the manufacture of cans, lids and tear-open rings can be found in US Pat. No. 3,787,248 (Setzer et al.) And in US Pat. No. 3,888,199.

Usually both the lid band and the deep-drawn and stretched can bodies are covered with a polymer layer in order to avoid direct contact between the container and the filling material. A typical coating consists of an epoxy or vinyl polymer, which is applied as a powder emulsion or by means of a solvent and then baked into a resistant protective layer. The coating is baked at an elevated temperature - usually for about 5 to 20 seconds at 175 to 220 ° C. This heat treatment softens most aluminum alloys. 3 shows the mechanical values of the present alloys and alloy AA 5082 with a degree of cold deformation of 85% after a softening time of 4 minutes. The curves are similar for all tested softening times. The tensile strength of the present alloy drops from 340 MPa to 330 MPa at a temperature of 190 ° C., while the tensile strength of coated A A 5082 cover tape falls from 400 MPa to 370 MPa. For the 0.2% yield strengths, the heat treatment means a drop between 29 and 33 MPa for the present alloy and between 30 and 35 MPa for the alloy AA 5082. In another test, the drop in strength after a heat treatment of 8 minutes at 190 ° C. was determined for alloy 5182 and for the present alloy. The 0.2% yield strength showed a drop from 340 to 305 MPa for the present alloy and a drop from 360 to 290 MPa for the AA 5182 alloy.

These numerical values show that the stoving temperatures and stoving times customary for aluminum containers weaken conventional lid band to a greater extent than lid band made from the present alloy. As a result, the present alloy can be rolled to a lower strength than other alloys and still have sufficient strength in the end product. The elongation curves indicate that the elongation of the present alloy increases more in comparison with alloy AA 5082 for a given stoving process and thus the present alloy also has a greater increase in formability compared to other alloys for a given stoving process.

The use of the alloy and the method according to the invention brings, among other things, the following advantages in the production of the strip material and in the manufacture of can parts from this strip material:

(1) lower energy requirements for hot and cold rolling operations and improved behavior during thermal treatment compared to conventional cover alloys;

(2) improved handling in a rolling mill as a result of a number of fabrication steps that are identical for the can and lid tape;

(3) improved handling with regard to alloy preparation and casting processes as a result of the uniform alloy composition for can and lid tape; and

(4) the subsequent manufacture of all parts of a can from strip material of the same alloy composition.

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3 sheets of drawings

Claims (10)

643001 1.3 to 2.5% magnesium, 0.4 to 1.0% manganese, 0.1 to 0.9% iron, 0.1 to 1.0% silicon, 0.05 to 0.4% copper, The remainder essentially contains aluminum, the total content of magnesium and manganese being between 2.0 and 3.3% and the weight ratio of magnesium to manganese being between 1.4: 1 and 4.4: 1. 1. Aluminum alloy, with magnesium and manganese as essential alloy components, for the production of a tape suitable for the production of deep-drawn and ironed can bodies and lids, characterized in that they 2. Aluminum alloy according to claim 1, characterized in that it contains 1.6 to 2.0% magnesium, 0.6 to 0.8% manganese, 0.3 to 0.7% iron and 0.15 to 0.40% Contains silicon. 2nd PATENT CLAIMS 3. Aluminum alloy according to one of claims 1 to 3, characterized in that it contains 0.04 to 0.15% titanium. 4. A process for the production of a strip made of an aluminum alloy suitable for the production of deep-drawn and stretched can bodies and lids according to one of claims 1 to 3, characterized in that a) the melt is cast into an ingot at a temperature of 700 to 750 ° C , b) the ingot is homogenized at a temperature of 550 to 600 ° C for 4 to 6 h, c) the homogenized ingot is rolled hot into a strip, and d) the hot-rolled strip is cold rolled to a final thickness with a thickness reduction of at least 40%. 5. The method according to claim 4, characterized in that the starting temperature for hot rolling is between 450 and 510 ° C. 6. The method according to any one of claims 4 or 5, characterized in that the hot rolling of the billet in several passes to a plate and then takes place continuously with a decrease in thickness of 70 to 96%. 7. The method according to any one of claims 4 to 6, characterized in that the hot-rolled strip is annealed before the cold rolling at a temperature of 315 to 400 ° C for 2 to 4 h. 8. The method according to any one of claims 4 to 7, characterized in that for the production of a strip suitable for the production of deep-drawn and ironed can bodies, the cold rolling to final thickness is carried out in such a way that a) the hot-rolled strip is cold-rolled to an intermediate thickness in a first pass series , b) the strip, which has been cold-rolled to an intermediate thickness, is subjected to a brief intermediate annealing at a temperature between 350 and 500 ° C. for 3 to 90 seconds, preferably 3 to 30 seconds, and c) the strip, which has been briefly annealed, to final thickness with a thickness reduction of 40 to 60 % is cold rolled. 9. The method according to any one of claims 4 to 7, characterized in that for the production of a strip suitable for the production of lids, the cold rolling to final thickness takes place with a thickness reduction of 60 to 95%. 10. The method according to any one of claims 4 to 9, characterized in that the melt is made of at least 40% aluminum scrap metal.