EP1184474B1 - Process for making aluminium-iron alloy foil - Google Patents

Description

Field of the invention

The invention relates to a method of manufacturing very thin strips of thickness less than or equal to 12 microns, of aluminum-iron type alloy. Such strips are used in particular for the manufacture of multilayer complexes comprising a layer of paper or cardboard, an aluminum alloy layer and a polymer layer, which can be used for the manufacture of aseptic, flexible or rigid food packaging of the type bricks.

State of the art

The desirable properties of use for very thin aluminum alloy strips are good mechanical strength, sufficient elongation, very few holes per unit area and good resistance to tearing and bending. The absence of holes is essentially related to the grain size, which must, in any case, be less than the final thickness.

Furthermore, in terms of the industrial production of the product, it is important that the chosen alloy can flow and roll easily, that it is not too expensive to develop, especially that it does not require a content in silicon too low, and that finally the transformation range of the product is not too complicated, in particular that it avoids too many heat treatments.

• Si < 0,4 Fe : 1,2 - 2 Cu < 0,30 Mn : 0,3 - 1 Mg < 0,10 Zn < 0,10

The alloys usually used for this application are alloys of the type 1100 or 1200 containing less than 1% by weight for the sum of silicon and iron contents. It is also known to use, to improve the mechanical strength, alloys with higher iron and manganese addition, such as alloys 8006 and 8015, registered at the Aluminum Association respectively in 1978 and 1988. The registered composition of 8006 is (% by weight):

• If <0.4 Fe: 1.2 - 2 Cu <0.30 Mn: 0.3 - 1 Mg <0.10 Zn <0.10

• Si < 0,30 Fe : 0,8 - 1,4 Cu < 0,10 Mn : 0,10 - 0,40 Mg < 0,10 Zn < 0,10

The registered composition of 8015 is:

• If <0.30 Fe: 0.8 - 1.4 Cu <0.10 Mn: 0.10 - 0.40 Mg <0.10 Zn <0.10

A major disadvantage of high iron alloys is the difficulty of recycling manufacturing scrap for other applications; indeed, the manufacture of very thin strips is a delicate operation that leads to an important upgrade by generating a lot of rejects. One way of avoiding this disadvantage is to use, for the production of blanks, a continuous casting machine, for example a continuous casting between rolls, which makes it possible to directly recycle the scrap and scrap production in the feed furnace. the machine. This advantage is in addition to the intrinsic advantages of continuous casting, especially the low investment cost.

• Si < 0,2 Fe : 1,35 - 1,6 Cu :0,1 - 0,4 Mn : 0,3 - 0,6 B : 0,01 - 0,02

élaborée par coulée continue entre cylindres à une épaisseur comprise entre 4,8 et 10 mm, recuit à plus de 450°C et laminage à froid. Dans le cas où l'épaisseur finale de la bande est inférieure à 9 µm, le brevet préconise un recuit intermédiaire supplémentaire.US Patent 5,380,379, filed in 1993 in the name of Alcoa Aluminio Do Nordeste, discloses an aluminum strip of composition (% by weight):

• If <0.2 Fe: 1.35 - 1.6 Cu: 0.1 - 0.4 Mn: 0.3 - 0.6 B: 0.01 - 0.02

produced by continuous casting between rolls to a thickness of between 4.8 and 10 mm, annealed at over 450 ° C and cold rolling. In the case where the final thickness of the strip is less than 9 μm, the patent recommends an additional intermediate annealing.

• Si < 0,4 Fe: 1,2 - 2,0 Mn : 0,2 - 1,0 Mg et/ou Cu: 0,1 - 0,5 Zn < 0,1

avec une taille moyenne de grain inférieure à 5 µm après recuit final. Le métal peut être coulé par coulée semi-continue conventionnelle, ou par coulée continue entre cylindres ou entre courroies.The patent EP 0750685 (Alcan International), filed in 1994, relates to a thin sheet of thickness between 5 and 40 microns, of composition (% by weight):

• If <0.4 Fe: 1.2 - 2.0 Mn: 0.2 - 1.0 Mg and / or Cu: 0.1 - 0.5 Zn <0.1

with an average grain size of less than 5 μm after final annealing. The metal can be cast by conventional semi-continuous casting, or by continuous casting between rolls or between belts.

• Si: 0,2 - 0,5 Fe: 0,4 - 0,8 Cu: 0,1 - 0,3 Mn : 0,05 - 0,3

contenant au moins 2% en poids de dispersoïdes et au moins 0,1% de cuivre et/ou de manganèse en solution solide. L'alliage est coulé en continu et on procède à un recuit intermédiaire au cours du laminage à froid.The application WO 98/45492 (Alcan International) describes a recyclable thin sheet, intended in particular for household applications, of composition:

• If: 0.2 - 0.5 Fe: 0.4 - 0.8 Cu: 0.1 - 0.3 Mn: 0.05 - 0.3

containing at least 2% by weight of dispersoids and at least 0,1% of copper and / or manganese in solid solution. The alloy is cast continuously and intermediate annealing is carried out during cold rolling.

Object of the invention

The object of the invention is to provide a method for manufacturing alloy strips of aluminum-iron type with a thickness of less than or equal to 12 μm, and preferably less than 9 μm, using a continuous casting between rolls, and leading to strips having both a good mechanical strength and a high resistance to tearing and bending under technical and economic conditions compatible with a large industrial production.

• l'élaboration d'un alliage de composition (% en poids) :
  • Si : 0,15 - 0,40 Fe : 1,10-1,70 Mg < 0,02 Mn : 0,30 - 0,50
  
  autres éléments < 0,05 chacun et < 0,15 au total, reste aluminium,
• la coulée continue entre cylindres d'une bande de cet alliage d'épaisseur comprise entre 2 et 10 mm,
• l'homogénéisation de cette bande à une température comprise entre 450 et 620°C d'une durée comprise entre 8 et 40 h,
• le laminage à froid de cette bande
• le recuit intermédiaire de la bande laminée à froid à une température comprise entre 200 et 400°C, et d'une durée comprise entre 8 et 15 h,
• le laminage à froid de la bande recuite jusqu'à l'épaisseur finale inférieure ou égale à 12 µm,
• le recuit final de la bande à une température comprise entre 200 et 300°C, d'une durée d'au moins 50 h.

The subject of the invention is a method for manufacturing aluminum alloy strips with a thickness of less than or equal to 12 μm, and preferably <9 μm, comprising:

• the elaboration of a composition alloy (% by weight):
  • Si: 0.15 - 0.40 Fe: 1.10-1.70 Mg <0.02 Mn: 0.30 - 0.50
  
  other elements <0.05 each and <0.15 in total, remaining aluminum,
• continuous casting between rolls of a strip of this alloy with a thickness of between 2 and 10 mm,
• homogenizing this strip at a temperature of between 450 and 620 ° C. for a duration of between 8 and 40 hours,
• the cold rolling of this band
• intermediate annealing of the cold-rolled strip at a temperature between 200 and 400 ° C and a duration of between 8 and 15 hours,
• the cold rolling of the annealed strip up to the final thickness less than or equal to 12 μm,
• the final annealing of the strip at a temperature between 200 and 300 ° C, with a duration of at least 50 hours.

Description of the invention

The process according to the invention combines a particular composition inside the AA composition of the 8006 and a manufacturing range, leading to advantageous use properties for the manufacture of food packaging complexes, avoiding penalizing constraints on the industrial plan.

The composition of the alloy has a silicon content of between 0.15 and 0.40%, which does not require the use of a pure base and therefore does not need to be particularly controlled, unlike the teaching of US Patent 5,380,379 which recommends a silicon content of less than 0.2% to avoid the formation of AlFeSi and AlMnSi intermetallics. The iron content, between 1.1 and 1.7%, and preferably <1.4%, is in the low range of 8006, and is in that of 8015. The manganese content, between 0 , 3 and 0.5%, is also in the low range of 8006. The magnesium and copper contents are kept at low levels.

The alloy is cast using a machine for continuous casting of strips between two cooled rolls, such as for example the Jumbo 3C ™ from the company Pechiney Rhenalu. The casting is at a thickness of between 2 and 10 mm, at a casting speed of between 0.5 and 3 m / min. It is possible to recycle all scrap and scrap in the machine's feed oven. The cast strip is then homogenized at a temperature between 450 and 620 ° C for a period of between 8 and 40 h, then cooled slowly.

Cold rough rolling is then carried out to a thickness of between 0.8 and 0.3 mm, followed by intermediate annealing at a temperature of between 200 and 400 ° C., so as to obtain a fine structure. and preferably between 302 ° C and 370 ° C to obtain a recrystallized structure, with a grain size not exceeding 30 microns, and preferably 15 microns. The strip is then cold rolled to the final thickness according to the usual technique, then subjected to a final degreasing annealing at a temperature between 200 and 300 ° C, for a period of at least 50 h., Dependent in particular the width of the band.

The strips according to the invention have a tensile strength greater than 100 MPa, a yield strength greater than 80 MPa, an elongation at break greater than 3% and a porosity according to EN 546-4 of less than 10 holes per dm. ² . They also have improved tear and bend resistance compared to conventional casting tapes.

It may be noted that a strip of less than 12 μm is obtained with quite satisfactory use properties having only one intermediate annealing, whereas, for the same thickness range, US Pat. No. 5,380,379 recommends a first intermediate annealing between 200 and 250 ° C, at a thickness of between 0.31 and 0.38 mm, then a second annealing intermediate between 200 and 300 ° C, at a thickness between 20 and 45 microns.

These performances are obtained thanks to a precise control of the recrystallization by means of the size, the morphology and the distribution of the intermetallic particles. A homogeneous distribution of particles of sufficiently large size and maximum desaturation of the solid manganese solution lead to a recrystallization with fine and homogeneous grains, which contributes to the good mechanical properties, in particular the resistance to tearing and folding, as well as the low porosity of the product.

The strips obtained by the process according to the invention are particularly suitable for the manufacture of multilayer complexes, for example paper or cardboard-aluminum-polymer complexes intended for the manufacture of aseptic food packaging of the brick type. They can also be used naked, lacquered or varnished for various types of packaging.

Examples Example 1

An alloy of composition was prepared: Si = 0.23% Fe = 1.26% Cu = 0.017% Mn = 0.37% Mg = 0.0032% Ti = 0.008%

The alloy was cast in width 1500 mm, at the thickness of 8 mm and at a speed of 0.96 m / min on a casting machine between two cooled cylinders Jumbo 3C ™ brand from the company Pechiney Rhenalu. The cast strip was homogenized for 12 hours at a temperature of 600 ° C. The strip was then cold rolled to a thickness of 0.5 mm, and then subjected to a 12 hour coil intermediate anneal at 350 ° C, for the metal to recrystallize fine grain. It was then re-rolled to the final thickness of 6.60 μm and then subjected to a final degreasing annealing for about 80 hours at 280 ° C.

The tensile strength R _m , the conventional yield stress at 0.2% elongation R _0.2 (in MPa) and the elongation at break A (in%), were measured by comparing them with properties of strips of the same thickness in 1200 alloy cast in traditional semi-continuous casting. The results are shown in Table 1. Table 1 Invention 1200 R _m (Mpa) 103 73 R _0.2 (Mpa) 86 50 AT (%) 3.2 2.7

The porosity of the strip was also measured by the number of holes at dm ² according to the EN 546-4 standard. This porosity is 6 holes in dm ² , compared to an average value of 13 holes dm ² for the alloy 1200 in conventional casting.

Example 2

Tear resistance tests were carried out for sheets cut in 1200 alloy strips from conventional casting and with a thickness of 6.3, 6.6 and 9 μm, and in strips of the same thickness according to the invention. . The tests were carried out using the Elmendorf method according to EN 21974 (ISO 1974). The test consists of determining the force required to propagate a tear on a specimen. A first test without a predefined slot gives an indicator of the resistance to initiation and propagation of a crack, and a second with a predefined slot makes it possible to quantify the resistance to propagation alone. The force selected in the list in paragraph 1 of Annex A of the standard is 4 N for the initiated tear, and 32 N for the unbound tear. Each specimen consists of an 8-sheet sandwich whose rolling direction coincides with the direction of crack propagation. The results (average of several tests) relating to the average force required for tearing F1 (with crack initiation) and F2 (without crack initiation) are shown in Table 2. Table 2 Alloy Thickness (μm) F1 (mN) F2 (mN) 1200 6.3 52 236 1200 6.6 53 224 1200 9 45 280 Invention 6.3 78 435 Invention 6.6 56 440 Invention 9 94 560

It is found that the sheets according to the invention have a higher tear resistance than those produced by conventional casting.

Example 3

Folding resistance measurements were made according to ISO 5626, using the Lhomargy apparatus. The folding bias is achieved by a reciprocating motion of a slot located between 4 cylinders which control the bending angle. The tape attachment and tensioning force have been slightly modified to account for the difference between aluminum and paper. The distance between the jaws was lengthened to 35 mm (instead of 28.5 mm) and the counterweight system adjusted to give voltages of 0.4 N, 1.7 N and 3 N (instead of 9.81 N and 8 N). The samples used have dimensions 170 mm x 15 mm (instead of 100 x 15 mm), the rolling direction being aligned with the folding blade, that is to say perpendicular to the direction of the tension force. . The tests were carried out on alloy strips 1200 of thickness 6.6 and 9 μm, from conventional casting, and strips according to the invention of the same thicknesses.

The number of failure cycles C was measured for different types of stresses (tension and stress). The results (average of several trials) are shown in Table 3. Table 3 Alloy / ep. Voltage (N) Constraint (MPa) VS 1200 6.6 μm 0.4 4 170 1.7 17 45 3 30 26 8 80 5 Invention 6.6 μm 0.4 4 184 1.7 17 50 3 30 29 8 80 8 1200 9 μm 0.4 3 209 1.7 13 47 3 22 27 Invention 9 μm 0.4 3 184 1.7 13 45 3 22 33

It is found that the belts according to the invention, although more mechanically resistant, have a rather better bending strength than the alloy 1200 in conventional casting for the thickness 6.6 μm, and approximately equivalent for the thickness 9. .mu.m.

Claims (6)

1. Process for producing strips of aluminium alloy with a thickness less than or equal to 12 µm, comprising :

   - preparing an alloy with a composition (% by weight) of :

   Si: 0.15-0.40 Fe: 1.10-1.70 Mg: <0.02 Mn: 0.30-0.50,

   
   other elements < 0.05 each and < 0.15 in total, the remainder being aluminium,

   - continuous casting between cylinders of a strip of this alloy with a thickness of between 2 and 10 mm,

   - homogenisation of this strip at a temperature between 450 and 620 °C for a period of 8 to 40 h,

   - cold-rolling this strip,

   - intermediate annealing of this cold-rolled strip at a temperature between 200 and 400°C, for a period of between 8 and 15 h,

   - cold-rolling the annealed strip to a final thickness less than or equal to 12 µm,

   - final annealing of the strip at a temperature between 200 and 300°C, for a period of at least 50 h.
2. Process according to claim 1, characterized in that the thickness of the strip is less than 9 µm.
3. Process according to claim 1 or 2, characterized in that the iron content of the alloy is less than 1.40%.
4. Process according to one of claims 1 to 3, characterized in that there is a single intermediate annealing step, that is to say there is not another between the two cold-rolling steps.
5. Aluminium alloy strip with a thickness less than or equal to 12 µm, produced by a process according to one of claims 1 to 4, characterized in that it has a breaking strength R_m > 100 MPa, an elastic limit R_0.2 > 80 MPa, an elongation at break A > 3% and a porosity according to EN standard 546-4 < 10 holes/dm².
6. Use of strips according to claim 5 for producing aseptic food packages of the brick type.