EP1644545B1 - Thin strips or foils of al-fe-si alloy - Google Patents

Description

Field of the invention

The invention relates to thin sheets or strips with a thickness of less than 200 μm, and preferably 50 μm, made of aluminum alloy with iron and silicon, substantially free of manganese, and a method of manufacturing such leaves or strips. These strips can be obtained by semi-continuous casting of conventional plates or by continuous casting, for example the continuous casting between belts ("twin-belt casting") or between cylinders ("twin-roll casting").

State of the art

• Si : 0,30 - 1,1 Fe : 0,40 - 1,0 Cu < 0,10 Mn < 0,10

L'absence de manganèse permet d'obtenir plus facilement la recristallisation au recuit final, mais la résistance à la rupture R_m reste insuffisante pour les épaisseurs inférieures à 100 µm.
Il est donc nécessaire de développer de nouveaux alliages et/ou d'optimiser les gammes de transformation pour répondre à la demande du marché.The market trend for thin aluminum alloy sheets leads to a constant reduction of the thicknesses used for a given application, while requiring high mechanical characteristics and good formability.
Very thin alloys of manganese, such as for example alloy 8111 of composition (% by weight) recorded at the Aluminum Association, are often used for thin sheets:

• Si: 0.30 - 1.1 Fe: 0.40 - 1.0 Cu <0.10 Mn <0.10

The absence of manganese makes it easier to obtain recrystallization at the final annealing, but the breaking strength R _m remains insufficient for thicknesses less than 100 μm.
It is therefore necessary to develop new alloys and / or optimize the transformation ranges to meet market demand.

• Si < 0,40 Fe : 1,2 - 2,0 Cu < 0,30 Mn: 0,30-1,0 Mg < 0,10

L'ajout de manganèse a en effet pour résultat de durcir le matériau. Dans le cas du brevet US 6,517,646 de la demanderesse, les caractéristiques mécaniques obtenues avec un alliage de composition : Si = 0,23%, Fe = 1.26%, Cu = 0.017%, Mn = 0.37%, Mg = 0.0032%, Ti = 0.008%, en combinaison avec une gamme de transformation favorable, conduit à une valeur de R_m de 103 MPa pour une épaisseur de 6.6µm.To increase the mechanical strength, it is usual to add manganese, as for example in alloy 8006, whose composition recorded in the Aluminum Association is as follows (% by weight):

• If <0.40 Fe: 1.2 - 2.0 Cu <0.30 Mn: 0.30-1.0 Mg <0.10

The addition of manganese has the effect of hardening the material. In the case of US Pat. No. 6,517,646 of the Applicant, the mechanical characteristics obtained with an alloy of composition: Si = 0.23%, Fe = 1.26%, Cu = 0.017%, Mn = 0.37%, Mg = 0.0032%, Ti = 0.008%, in combination with a favorable transformation range, leads to a value of R _m of 103 MPa for a thickness of 6.6 μm.

The mechanical characteristics can also be improved by the addition of manganese in small quantities in iron-loaded 8000 series alloys. The patent application WO 02/64848 (Alcan International) describes the continuous casting of thin strips of AlFeSi alloy containing from 1.2 to 1.7% Fe and from 0.35 to 0.8% Si. high mechanical strength by adding to the alloy from 0.07 to 0.20% manganese. This addition of manganese is recognized as necessary to obtain a small grain size after the final annealing.

Manganese thus appears as an element allowing to increase the mechanical characteristics of alloys 8000. However, manganese in solid solution or in the form of fine precipitates can block or delay the recrystallization during the final annealing. It is therefore necessary to precisely control the precipitation of the phases containing manganese during each step of the range, which is often difficult. Any drift in the transformation range has significant consequences on the effectiveness of the final annealing. It is therefore very interesting to develop an alloy that does not contain manganese, but nevertheless has high mechanical characteristics.

US Pat. Nos. 5,503,689 (Reynolds Metals) discloses a process for manufacturing a thin alloy strip containing from 0.30 to 1.1% Si and from 0.40 to 1.0% Fe, less than 0.25% Cu. and less than 0.1% Mn, by continuous casting and cold rolling without intermediate annealing. The preferred levels of iron and silicon are between 0.6 and 0.75%.
US Patent 5,725,695 (Reynolds Metals) discloses for the same compositional range a range with intermediate annealing between 400 and 440 ° C (750 - 825 ° F) and final recrystallization annealing at 288 ° C (550 ° F). The ratio of Si / Fe contents is equal to or greater than 1. In the examples, the maximum ultimate tensile strength obtained is 90 MPa (13.13 ksi), the maximum yield strength is 39.1 MPa (5.68 ksi), and the elongation is 11.37% for thicknesses of 46μm (0.00185 '). These mechanical characteristics are still low for some applications.

For the alloys obtained by continuous casting, it is often necessary to carry out a heat treatment at high temperature in order to reduce the harmfulness of the segregations, by resorbing the clusters of precipitation and by homogenizing the structure in the thickness. The effect of a homogenization at 600 ° C is described for the alloy 8011 (composition: 0.71% Fe, 0.77% Si, 0.038% Cu, 0.006% Mn, 98.45% Al) obtained by casting between rolls in the article by Y. Birol "Centerline Segregation in Twin-Roll Cast AA8011 Alloy" Aluminum, 74, 1998, pp. 318-321. A modification of the precipitated phases and a reduction in heterogeneities are obtained. The reduction of the central segregation makes it possible later to limit the porosity of the very thin leaves, and to improve their formability.

It is interesting for economic reasons to limit the temperature of heat treatment. For an alloy 8111 of composition: 0.7% Fe, 0.7% Si, Mn <0.02, Zn <0.02, Cu <0.02, a beginning of phase transformation is observed and a total recrystallization from 460 ° C, although annealing at 550-580 ° C is required to achieve a more complete transformation (see M. Slamova et al., "Response of AA8006 and AA8111 Strip-Cast Rolled Alloys to High Temperature Annealing", ICAA-6, 1998) . Homogenization at low temperature is therefore possible for alloys without manganese.

Moreover, in the subsequent conversion to homogenization, up to small thicknesses, it is usual to introduce an intermediate annealing step, in order to soften the metal. For manganese alloys, control of the intermediate annealing generally requires high temperature heat treatment (above 400 ° C) to obtain recrystallization.

For type 8000 alloys without manganese, it is conceivable to perform a heat treatment at a lower temperature than for type 8006 alloys.

The patent application WO 99/23269 (Nippon Light Metal and Alcan International) describes a process applicable to AlFeSi alloys containing from 0.2 to 1% Si and from 0.3 to 1.2% Fe, with a Si / Fe ratio. between 0.4 and 1.2, wherein the intermediate annealing is carried out in two stages, the first between 350 and 450 ° C, the second between 200 and 330 ° C. The purpose of this method is to reduce the surface defects of the sheet. Mechanical characteristics are not mentioned.

The object of the invention is to obtain thin sheets or strips of AlFeSi alloy without the addition of manganese, having a high mechanical strength, while maintaining a good formability, with an industrial manufacturing range that is as economical as possible.

Object of the invention

• Si : 1,0 - 1,5 Fe : 1,0 - 1,5 Cu < 0,2 Mn < 0,1 autres éléments < 0,05

chacun et < 0,15 au total, reste Al, avec de préférence la condition Si/Fe ≥ 0,95, présentant à l'état recuit une résistance à la rupture R_m > 110 MPa pour les épaisseurs > 9 µm, et > 100 MPa pour les épaisseurs de 6 à 9 µm. La feuille mince a, de préférence, une limite d'élasticité R_0.2 (mesurée sur éprouvettes cisaillées) > 70 MPa. L'allongement à la rupture est supérieur aux valeurs suivantes en fonction de l'épaisseur de la feuille : Epaisseur (µm) A (%) supérieur à et de préférence à 6-9 3 4 9 - 15 5 7 15-25 10 15 25-50 18 25 50-200 20 25 L'alliage a, de préférence, une teneur en silicium comprise entre 1,1 et 1,3% et une teneur en fer comprise entre 1,0 et 1,2%.The subject of the invention is a thin sheet with a thickness of between 6 and 200 μm, and preferably between 6 and 50 μm, of alloy composition (% by weight):

• Si: 1.0 - 1.5 Fe: 1.0 - 1.5 Cu <0.2 Mn <0.1 other elements <0.05

each and <0.15 in total, remains Al, preferably with the Si / Fe condition ≥ 0.95, having in the annealed state a breaking strength R _m > 110 MPa for thicknesses> 9 μm, and> 100 MPa for thicknesses from 6 to 9 μm. The thin sheet preferably has a yield strength R _0.2 (measured on sheared specimens)> 70 MPa. The elongation at break is greater than the following values depending on the thickness of the sheet: Thickness (μm) A (%) greater than and preferably to 6-9 3 4 9 - 15 5 7 15-25 10 15 25-50 18 25 50-200 20 25 The alloy preferably has a silicon content of between 1.1 and 1.3% and an iron content of between 1.0 and 1.2%.

• Si : 1,0 - 1,5 Fe : 1,0 - 1,5 Cu < 0,2 Mn < 0,1 autres éléments < 0,05 chacun et < 0,15 au total, reste Al, avec de préférence la condition Si/Fe ≥ 0,95,

comportant la préparation d'une première bande soit par coulée semi-continue verticale d'une plaque et laminage à chaud, soit par coulée continue éventuellement suivie d'un laminage à chaud, le laminage à froid de cette première bande jusqu'à l'épaisseur finale avec éventuellement un recuit intermédiaire de 2 à 20 h à une température comprise entre 250 et 350°C, et de préférence entre 280 et 340°C, et un recuit final à une température comprise entre 200 et 370°C.The subject of the invention is also a process for producing thin strips with a thickness of less than 200 μm in Al-Fe-Si alloy of composition (% by weight):

• If: 1.0 - 1.5 Fe: 1.0 - 1.5 Cu <0.2 Mn <0.1 other elements <0.05 each and <0.15 in total, remain Al, preferably with condition Si / Fe ≥ 0.95,

involving the preparation of a first web either by vertical semi-continuous casting of a plate and hot rolling, or by continuous casting possibly followed by hot rolling, cold rolling of this first web to final thickness with optionally an intermediate annealing of 2 to 20 hours at a temperature between 250 and 350 ° C, and preferably between 280 and 340 ° C, and a final annealing at a temperature between 200 and 370 ° C.

Description of the invention

The thin sheets or strips according to the invention are manufactured from 8000 AlSiFe alloys substantially free of manganese, with a content typically less than 0.1%. The iron and silicon contents are significantly higher than those of alloys 8011 and 8111, which are the AlSiFe alloys for the most commonly used manganese-free thin sheets. A preferred composition domain is an alloy containing 1.1 to 1.3% silicon and 1.0 to 1.2% iron.

The alloys according to the invention should preferably have a composition such that the Si / Fe ratio of the respective silicon and iron contents is ≥ 0.95. They have, in the annealed state (state O), an unusual mechanical strength for alloys of this composition, with a breaking strength R _m > 110 MPa, or even 115 MPa, for thicknesses> 9 μm and> 100 MPa for thicknesses from 6 to 9 μm, and a yield strength of 0.2% R _0.2 > 70 MPa. This high mechanical strength is not obtained at the expense of formability, since, with respect to alloys 8011 or 8111, the elongations are at least the same, and the burst pressures are increased.

These high mechanical properties are obtained both for strips produced from plates obtained by vertical semi-continuous casting conventional and hot-rolled, only for bands from continuous casting, or between belts ("belt casting") or between rolls ("roll casting"). Continuous casting between belts is also followed by hot rolling.

In the case of continuous casting between rolls, the hot-rolled or untreated tapes are optionally subjected to a low-temperature homogenization (between 450 and 500 ° C) to reduce the central segregation which may be a source of a reduction in the formability at final thickness. This low-temperature heat treatment is sufficient to reduce the possible central segregations in these alloys without manganese. The strips are then cold rolled, either to the final thickness, or to an intermediate thickness of between 0.5 and 5 mm, to which they are subjected to an intermediate annealing. Unlike alloys containing manganese, it is possible to carry out this intermediate annealing at a relatively low temperature, between 250 and 350 ° C, and preferably between 280 and 340 ° C, for a duration greater than 2 hours. Such a temperature range, although described in the literature, especially in the patent application WO 02/064848 mentioned above, is below the usual range which is above 400 ° C.

The Applicant has found that the application to an AlFeSi alloy, more particularly to a composition such as Si / Fe ≥ 0.95, of low temperature heat treatments, possibly with the suppression of the intermediate annealing when it is technically possible, leads to a significantly improved mechanical strength, at least 15% compared to the usual intermediate annealing. This superior mechanical strength is obtained while improving the formability measured by burst pressure or dome height according to ISO 2758.

The final annealing is carried out at a temperature of between 200 and 370 ° C. for a duration of between 1 and 72 hours. The annealing times are conditioned by the quality of the degreasing of the sheet. After final annealing, a fine grain structure with an average grain size, measured by scanning electron microscope image analysis, of less than 3 μm is obtained.

The conjunction of a homogenization at low temperature or a lack of homogenization and an intermediate annealing at low temperature or completely suppressed, in addition to its economic advantage, is favorable to obtaining a fine size of grains. The grain size is reduced by about 30% compared with heat treatments at higher temperatures, which leads to an increase in the mechanical characteristics R _0.2 and R _m , which for thin thicknesses are related to the number of grain boundaries. This gain is not at the expense of elongation, as increasing the number of grains in the thickness also limits the risk of damage located in one or two single grains of the thickness of the sheet.

The thin sheets according to the invention are particularly suitable for applications requiring both a good mechanical strength and a high formability, such as for example the manufacture of multilayer complexes, in particular for the lids of fresh product packaging, overcap caps or of household aluminum.

Examples Example 1

In order to show the influence of the composition of the alloy, two 6.1 mm thick strips of alloy A according to the invention and B of type 8111, of composition, were manufactured in continuous casting between rolls. (% by weight) shown in Table 1: Table 1 All. Yes Fe Cu mn mg Cr Ti B AT 1.17 1.11 0,001 0,003 0.0004 0.0007 0.006 0.0005 B 0.7 0.7 0,001 0,003 0.0005 0,001 0,007 0.0005 The strips were cold rolled to a thickness of 2 mm and then subjected to a 5 hour intermediate anneal at 320 ° C. The strips were then cold rolled in several passes until the final thickness of 38 microns. They were then subjected to a final annealing of 40 h at 270 ° C.

The mechanical characteristics were measured in each case: tensile strength R _m (in MPa), conventional yield strength at 0.2% R _0.2 and elongation A (in%) according to standard NF-EN 546- 2, as well as the air burst pressure Pe (in kPa) measured according to the ISO 2758 standard and the dome height Hd (in mm). The results are shown in Table 2: Table 2 Alloy R _m (MPa) R _0.2 (MPa) AT (%) Pe (kPa) Hd AT 123 76 30 394 9.2 B 104 54 15.8 284 6.6 It is found that, unlike alloy B type 811 1, the breaking strength of the alloy strip A is much greater than 110 MPa, and the yield strength greater than 70 MPa. In addition, burst pressure and elongation are also higher, so that this alloy is both strong and formable.

Example 2

An alloy strip A of Example 1 with a thickness of 6.1 mm was cast in continuous casting between rolls. The strip was then cold rolled to a thickness of 2 mm. Part of the strip was subjected to a usual intermediate anneal for such a 5 hour alloy at 500 ° C. The other part of the strip has undergone an intermediate anneal according to the invention for 5 hours at 320 ° C. The two parts of the strip were then cold rolled in several passes until the final thickness of 10.5 microns. They were then subjected to a final annealing of 40 h at 270 ° C.

The same properties as in Example 1 were measured, the values of which are given in Table 3: Table 3 Annealing inter R _m (MPa) R _0.2 (MPa) AT (%) Pe (kPa) Hd (mm) 470 ° C 99 63 7.3 71 5.1 320 ° C 117 84 8.1 92 5.7 It is found that the lowering of the intermediate annealing temperature leads to both an increase in the mechanical strength, the elongation, the bursting strength and the formability.
The average grain size, measured by SEM image analysis, is 3.6 μm for annealing at 470 ° C, and 2.3 μm for annealing at 320 ° C. The increase in the mechanical characteristics for the low temperature annealing is therefore related to a reduction in the grain size obtained after final annealing.

Claims (10)

1. Foil or thin strip with a thickness between 6 and 200 µm, and preferably between 6 and 50 µm, made of an alloy with a composition (% by weight):

   Si: 1.0-1.5 Fe: 1.0-1.5 Cu < 0.2 Mn < 0.1, other elements < 0.05 each and < 0.15 in total, the remainder Al, having in the annealed state a breaking strength R_m> 110 MPa for thicknesses > 9µm, and > 100 MPa for thicknesses from 6 to 9 µm.
2. Foil or thin strip according to claim 1, characterized in that it has in the annealed state a breaking strength R_m> 115 MPa for thicknesses > 9µm.
3. Foil or thin strip according to either of claims 1 or 2, characterized in that it has in the annealed state an elastic limit R_0.2 > 70 MPa.
4. Foil or thin strip according to one of claims 1 to 3, characterized in that it has an elongation at break A, as a function of thickness: Thickness (µm) A (%) greater than and preferably greater than 6-9 3 4 9-15 5 7 15-25 10 15 25-50 18 25 50-200 20 25
5. Foil or thin strip according to one of claims 1 to 4, characterized in that the alloy has a composition such that Si/Fe ≥ 0.95.
6. Foil or thin strip according to one of claims 1 to 5, characterized in that the alloy has a silicon content of between 1.1 and 1.3% and an iron content between 1.0 and 1.2%.
7. Method for producing thin strips with a thickness less than 200 µm made of an Al-Fe-Si alloy with a composition (% by weight):

   Si: 1.0-1.5 Fe: 1.0-1.5 Cu < 0.2 Mn < 0.1, other elements < 0.05 each and < 0.15 in total, the remainder Al, comprising the preparation of a first strip either by the semi-continuous vertical casting of a sheet and hot rolling, or by continuous casting optionally followed by hot rolling, cold rolling this first sheet to the final thickness with optionally intermediate annealing at a temperature between 250 and 350°C, and preferably between 280 and 340°C, and a final annealing at a temperature between 200 and 370°C.
8. Method according to claim 7, characterized in that the alloy has a composition such that Si/Fe ≥ 0.95.
9. Method according to either of claims 7 or 8, characterized in that before cold rolling, the first strip is subjected to homogenisation at a temperature between 450 and 500°C.
10. Method according to one of claims 7 to 9, characterized in that the strip is prepared by continuous casting between cylinders.