CA2475700A1 - Thin strips made of aluminium-iron alloy - Google Patents

Abstract

The invention relates to aluminium alloy strips which are 30 - 150 µm thick, the composition of the alloy being as follows (in wt. %): Si < 0.4 Fe: 1.5 1.9 Mn: 0.04 0.15 other elements; < 0,05 each and 0.15 in total, the rest being aluminium. Said strips are used, in particular, for the manufacture of trays and dishes for the distribution of foodstuffs and fast food.

Description

Aluminum-iron alloy thin strips Field of the invention The invention relates to thin strips, typically of thickness between and 150 ~ .m, aluminum-iron type alloy, suitable for stamping, for particularly in packaging, and more particularly in the manufacture of trays and lo thin dishes for food distribution and fast food.
State of the art Al-Fe alloys of the 8000 series according to the nomenclature of Aluminum Association are widely used for making sheets or strips thin intended for packaging. They can be made either conventional by casting a plate, hot rolling, then cold rolling, with one or several intermediate anneals and most often a final anneal, either by cast continuous, for example between two rolls, and cold rolling, and possibly a or more annealed.
The continuous casting of strips allows, for a moderate investment cost, to obtain in a fairly wide range of alloys strips which do not require no subsequent hot rolling. In recent years, significant progress has been made.
been made by manufacturers of casting machines to reduce the thickness of the strip casting which can go down in some cases to around 1 mm, which decreases therefore the cold rolling to be carried out.
The use of continuous casting, insofar as the conditions of solidification are different from the usual process, leads to a different microstructure.
So, Alcan patent US 3,989,548, published in 1976, describes (Example 9) alloys 3o of aluminum containing at least one of the elements Fe, Mn, Ni or Si cast in strips by continuous casting between cylinders to a thickness of 7 mm. The structure of the casting strip has sticks of fragile intermetallic compounds of diameter between 0.1 and 1.5 gym, that a cold rolling with a reduction

2 at least 60% breaks into fine particles of size less than 3 ~ ,. The bands obtained have a good compromise between mechanical strength and formability.
US patent 5,380,379 of Alcoa Aluminio de Nordeste relates to the manufacture, by continuous casting between cylinders of very thin sheets of alloys containing 1.35 1.6% iron, 0.3-0.6% manganese, 0.1-0.4% copper and less 0.2% silicon. The silicon content is limited by the appearance of phases intermetallic AIFeSi or AIMnSi type, while the presence of copper East necessary to give the product sufficient mechanical resistance.
1 o Patent application WO 98/52707 by the applicant describes a method of manufacture of aluminum alloy strips containing (by weight) one at less elements Fe (from 0.15 to 1.5%) or Mn (from 0.35 to 1.9%) with Fe + Mn <2.5%, and possibly containing Si (<0.8%), Mg (<0.2%), Cu (<0.2%) by casting continuous between cooled and shrunk cylinders to a thickness between 1 and 5 mm, followed by cold rolling. The bands obtained have both limit greater elasticity than that of the strips produced by the conventional process, and a good formability.
The manufacture of trays and thin dishes for prepared foods requires tapes having good mechanical strength, good formability, in 2o particularly for deep enough stampings, and good isotropy of mechanical characteristics, especially for circular products. A
alloy frequently used for this application is the alloy 8021B, the composition registered with the Aluminum Association is as follows (% by weight) Si Fe Cu Mn Mg Cr Zn Ti <0.40l, l-1.7 <0.05 <0.03 <0.01 <0.03 <0.05 <0.05 ace The invention aims to improve the compromise between mechanical strength, the formability and isotropy of mechanical properties compared to this alloy of reference.
3o Object of the invention WO 03/06900

3 PCT / FR03 / 00452 The subject of the invention is strips of thick aluminum alloy range between 30 and 150 ~, m, alloy composition (% by weight) If <0.4 Fe: 1.5 - 1.9 Mn: 0.04 - 0.15 other elements; <0.05 each and 0.15 in total, aluminum remainder.
The invention also relates to a method of manufacturing strips of alloy of this composition by continuous casting between cylinders of a thick strip between 2 and 10 mm, possibly the homogenization of this strip Between 420 and 550 ° C, cold rolling of this strip to the thickness final with possibly an intermediate annealing of 1 to 4 h between 300 and 350 ° C, and an annealing final lo at a temperature between 200 and 430 ° C with a duration of at least minus 30 h.
The invention also relates to the use of these strips for dishes and trays for food products.
Description of the invention The alloy used for the sheets and strips according to the invention is characterized by one iron content between 1.5 and 1.9%, higher than that used habitually for alloy 8021B intended for the manufacture of dishes and trays.
The advantage of higher iron content lies in improving strength mechanical ; this 2o effect is even more marked when the strips are obtained by casting keep on going between cylinders. The iron content must remain below 1.9% to avoid getting too close to the AIFe eutectic content, and therefore seeing of the coarse primary phases AIFe.
The other characteristic is a manganese content between 0.04 and 0.15%.
This addition has a favorable effect on the mechanical strength, while now a high level of elongation, the trade-off between these properties usually antagonists being markedly improved when producing the strips by casting keep on going. Beyond 0.15% manganese, it plays its role more clearly anti recrystallizing, which may affect the efficiency of the final annealing, necessary for obtaining a good isotropy of the mechanical characteristics.
The manufacture of sheets and strips according to the invention is preferably done by cast continuous of a strip of thickness between 2 and 10 mm between two cylinder cooled and shrunk (“twin-roll casting”). The casting strip can be homogenized,

4 especially in the case where one wishes to favor the elongation rather than the resistance mechanical. This homogenization must be done at a temperature not too high, between 420 and 550 ° C, to avoid degrading the resistance too much mechanical. If the elongation requirements are less stringent, homogenization is not essential.
The strip is then cold rolled with the number of passes required until the final thickness between 30 and 150 ~, m. This cold rolling can do with or without intermediate annealing. When intermediate annealing is necessary, he must be relatively short, around 1 to 4 hours, and be done at a temperature not too much 1o high, typically between 300 and 350 ° C, to avoid magnification grain. But it is possible, when not looking for very high values for elongation, to avoid both homogenization and annealing intermediate, which makes the manufacturing range particularly simple.
The laminated strip is then annealed at a temperature between 200 and 400 ° C, at least 30 hours long, so as to obtain a structure recrystallized. This annealing can be carried out in one or more temperature stages, for example a first level between 200 and 300 ° C, and a second between 300 and 400 ° C. We cut then the sheet metal strip if necessary.
An improvement in the tensile strength Rm and the limit 2o of elasticity Ro, 2 of the order of 5% relative to the conventional 8021B alloy, with a elongation of the same order and a smaller difference between the values of Rm and from R0.2 measured in the rolling direction (long direction) and in the perpendicular direction (meaning through). These properties are particularly suitable for the manufacture of dishes and trays.
Examples Example 1 3o On a 3C ~ casting machine from the company Pechiney Rhenalu, we poured of the 7 mm thick strips in two alloys A (8021B classic) and B according to the invention, the compositions of which are given in Table 1 Table 1 Alloy Fe Si Mn Cu Ti A 1.25 0.22 0.02 0.005 0.007 B 1.55 0.18 0.085 0.007 0.009 These strips were cold rolled without intermediate annealing until thickness

5 final of 58 ~, m in 9 passes with successive stops at 4.7 mm, 2.7 mm, 1.5 mm, 0.9 mm, 0.6 mm, 0.41 mm, 0.21 mm, 0.12 mm and 0.08 mm. They then underwent a annealing from 20 h at 260 ° C, then 65 h at 340 ° C.
The tensile strength Rm (in MPa) was then measured on the 2 bands, the limit of elasticity Ro, 2 (in MPa) and the elongation at break A (in%), in the long sense and lo in the cross direction. The results are shown in Table 2 Table 2 Alloy Rm direction Ro, 2 A direction Rm direction Ro, 2 directionA direction L meaning LTTT
The A 138 121 20.5 136 123 21 B 149 130 22.5 145 131 22.5 We note that Rm and Ro, 2 are higher for B, that the elongations are also and that the difference between the L direction and T direction results is reduced.
Example 2 2o Two coils of alloys C of type 8021B and I) were cast according to the invention, the composition is indicated in table 3 Table 3 Alloy Fe Si Mn Cu Ti C 1.17 0.12 0.005 0.008 0.010 D ~ 1.63 ~ 0.04 ~ 0.09 ~ 0.007 0.006

6 The transformation guide is identical to that of Example 1, except that one added an intermediate annealing of 2 h at 340 ° C to the thickness 0.6 mm.
The static mechanical characteristics in the L and T directions are indicated in board 4:
Alloy Rm (L) Ro, 2 A (L) Rm (T) Ro, 2 A (T) (L) (T) D 143 127 24 146 129 23.5 The comparison of the results between alloys C and D leads to the same remarks than the previous example. In addition, we note that, although the alloy D is a little more loaded with iron, the introduction into the range of an intermediate annealing leads lo compared to alloy B of Example 1, a slight drop in Rm and Ro, 2, and one slight increase in elongation.
Example 3 Two coils of alloys E (8021B) and F (according to the invention) were cast, the compositions are indicated in table 5 Table 5 Alloy Fe Si Mn Cu Ti E 1.21 0.08 0.007 0.005 0.007 F 1.72 0.06 0.12 0.009 0.007 The manufacturing range is identical to that of Example 2, with an additional homogenization of the casting strip from 10 h at 520 ° C. The characteristics static mechanical in L and T directions are shown in Table 6

7 Table 6 Alloy Rm (L) Rp, 2 A (L) Rm (T) Rp, 2 A (T) (L) (T) F 134 121 25 132 114 24.5 The comparison of alloys E and F leads to the same remarks as to the two previous examples. In addition, the introduction of homogenization leads for alloy F, compared with alloy D of Example 2, to a slight drop in Rm and Rp, 2, and a slight improvement in elongation. Thus, the introduction into the range homogenization and / or intermediate annealing depends on the compromise sought between mechanical strength and formability.
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Claims (3)

Claims 1. Using aluminum alloy strips with thickness between 30 and 150 µm, and alloy composition (% by weight) If < 0.4 Fe: 1.5 -1.9 Mn: 0.04 - 0.15 other elements: < 0.05 each and 0.15 in total, rest aluminium, for the manufacture of dishes and trays for food, 2. Process for the manufacture of dishes and trays for food comprising:
has. The preparation of an aluminum alloy composition (% by weight) If < 0.4 Fe: 1.5 - 1.9 Mn: 0.04 - 0.15 other elements: < 0.05 each and 0.15 in total, rest aluminum, b. Continuous casting between rolls of a strip of thickness comprised between 2 and 10 mm, vs. Possibly the homogenization of this band between 420 and 550°C, d. The cold rolling of this strip to the final thickness between 30 and 150 µm, possibly with an intermediate annealing of 1 to 4 hours between 300 and 350°C, e. A final anneal at a temperature between 200 and 430°C of a duration of at least 30 hours.
f. Final shaping to obtain dishes or trays. 3. Method according to claim 2, characterized in that the final annealing is done in 2 levels, the first between 200 and 300°C, the second between 300 and 430°C.