EP0504077A1 - Strong, formable, isotropic aluminium alloys for deep drawing - Google Patents

Abstract

Al-based alloys intended for deep drawing and/or drawing and exhibiting high mechanical strength characteristics as well as good isotropy (low distortion wedge content) and good cold processability. The alloys according to the invention have the following compositions by weight (%): (I) (II) Fe </= 0.25 from 0.7 to 1.5 Si </= 0.25 </= 0.4 Mn from 0.8 to 1.6 </= 0.8 Mg from 0.7 to 2.5 from 1.5 to 3 Cu from 0 to 0.6 from 0 to 0.6 Cr from 0 to 0.35 from 0 to 0.35 Ti from 0 to 0.1 from 0 to 0.1 V from 0 to 0.1 from 0 to 0.1 Remainder Al and unavoidable remainder Al and unavoiable impurities: impurities Each </= 0.05% </= 0.05 Total </= 0.15% </= 0.15 They are particularly well-suited for the manufacture of drawn cans, particularly beverage cans, which are lighter and/or stronger with an increased saving of material, the manufacturing range being wholly comparable with that of the conventional alloys (3004/3104), with optional omission of the intermediate annealing operations.

Description

The invention relates to alloys based on A1 intended for stamping and / or drawing and having high mechanical characteristics of resistance as well as good isotropy (low rate of horns) and good cold formability.

It is known that the alloys usually used for the manufacture of drawn can bodies are alloys 3004 or 3104, according to the designations of the Aluminum Association.

The current evolution pushes to seek alloys at the same time more mechanically resistant, which allows correlatively to decrease the wall thicknesses for a given application, and more isotropic that is to say at low rate of horns during the stamping and / or drawing in order to improve the utilization rate of the alloy, while remaining sufficiently cold formable. However, for the conventional alloys mentioned above, the first and the last 2 properties are relatively contradictory.

Thus in patent US-A-4318755 alloys of this type are claimed but their mechanical characteristics in the hardened state remain relatively modest R: 280-300 Mpa, E 0.2: 250-280 Mpa and A%: 2- 4% to guarantee acceptable formability in drawing and drawing, while retaining good isotropy.

The alloys based on A1 according to the invention, which exhibit both high mechanical characteristics, good isotropy and good formability belong to two distinct families, one (I) derived from conventional 3004 alloys, the other (II) essentially containing additions of Fe and Mg.

They are distinguished from the prior art by two essential analytical characteristics, either a "classic" Mn content associated with a low iron content, or, on the contrary, a high Fe content associated with a low Mn content. In addition, a Cu content relatively high is preferred.

More specifically, the alloys according to the invention have the following weight compositions (%):

In the compositions (I), a Cu content greater than or equal to 0.20% or even 0.25% is preferable. Likewise, it is preferable to have an Fe content ≦ 0.20, or better still less than 0.15%.

In addition, it has been observed that, preferably, the contents of Mn, Fe and Mg must be limited, to avoid the rough precipitation of primary compounds, precipitates which are harmful and cause defects during the subsequent rolling and / or stamping-stretching; in this case, the relationship to be observed is as follows: $$\text{\% Mn + 0.9\% Fe + 0.3\% Mg ≦ 1.9}$$

Likewise, to obtain cold deformation rates, defined by: (initial thickness - final thickness) / initial thickness, greater than 50%, or even 60 or 65%, without intermediate annealing (s), while retaining a high isotropy, the following relationship should be observed for the compositions (I): $$\text{\% Mn -2.25\% Fe ≧ 0.50}$$

The analytical limitations are justified as follows:
As regards the compositions (I), for Fe ≧ 0.25 and / or Si ≧ 0.25, there appears in the micrographic structure of "white bands" after homogenization or reheating and hot rolling, zones in which the Mn content is low, thus promoting the anisotropy of the material.
The contents of Mn and Mg are limited below to obtain sufficient mechanical strength; however, beyond 1.6% Mn, there is appearance of primary intermetallic particles harmful with regard to formability during rolling or stamping and / or drawing operations, and for Mg ≧ 2 , 5%, there is an appearance of stretching defects, for example sticking to the die (also called a ring) and too great anisotropy.

Cu is kept below 0.6% to meet food standards (decree of August 27, 1987), but is preferably held above 0.20% or even 0.25% to obtain the high characteristics mechanical properties required when firing the coverings. Above 0.35% Cr, appearance of coarse primary intermetallic compounds detrimental to formability by damaging effect. The upper limits in Ti and V are justified for the same reason.

A preferred composition contains from 1.2 to 1.6% Mn, from 0.8 to 1.2% Mg, from 0.2 to 0.6% Cu, and up to 0.25% Cr.

With regard to the compositions (II), it is preferable that the content of Mn is kept below 0.40%, and preferably 0.35%. Likewise, it is preferable that the Fe is held above 1.05% or better 1.10%.

• . au-dessous de Fe = 0,7 %, on observe des problèmes d'anisotropie élevées (cornes importantes à 45°) et des défauts de collage lors de l'étirage.
• . au-dessus de 1,5% Fe, il y a apparition de phases primaires grossières et endommagement au cours du laminage et des opérations d'emboutissage et/ou d'étirage.

Au-dessus de Mn = 0,8 %, il y a apparition de particules grossières néfastes au laminage ou à l'emboutissage- étirage par endommagement.
Si Mg est inférieur à 1,5 %, les caractéristiques mécaniques sont insuffisantes.
Si Mg est supérieur à 3 %, l'anisotropie est trop forte et on observe des défauts de type collage à l'étirage.
Le Cu est maintenu en-dessous de 0,6 % pour respecter les normes d'alimentarité.
Au-dessus de Cr = 0,35 %, il y a apparition de précipités primaires néfastes à la formabilité (endommagement). Les teneurs en Cr et V sont limitées supérieurement pour cette même raison.These two measures can still be preferably combined. The analytical limitations of the compositions (II) are justified as follows:

• . below Fe = 0.7%, there are high anisotropy problems (large horns at 45 °) and bonding defects during drawing.
• . above 1.5% Fe, coarse primary phases appear and damage occurs during rolling and drawing and / or drawing operations.

Above Mn = 0.8%, there is the appearance of coarse particles which are harmful to rolling or drawing-drawing by damage.
If Mg is less than 1.5%, the mechanical characteristics are insufficient.
If Mg is greater than 3%, the anisotropy is too strong and there are defects of the bonding type when drawn.
Cu is kept below 0.6% to meet food standards.
Above Cr = 0.35%, there is the appearance of primary precipitates detrimental to formability (damage). The contents of Cr and V are limited above for this same reason.

A preferred composition contains 1.1 to 1.4% Fe, 1.6 to 2.5% Mg and up to 0.25% Cr.

The use of the alloys according to the invention is entirely analogous to that of the alloys 3004 and 3104, as will appear in detail in the examples, except as regards the need for intermediate annealing for the alloys (I).

• coulée, généralement par coulée semi-continue en lingots ou coulée directe en bandes
• homogénéisation ou réchauffage
• laminage à chaud jusqu'à une épaisseur intermédiaire
• laminage à froid avec ou sans recuits intermédiaires

ce qui fournit des ébauches adaptées aux opérations d'emboutissage et d'étirage.The manufacturing range therefore essentially comprises the following operations:

• casting, generally by semi-continuous ingot ingots or direct strip casting
• homogenization or reheating
• hot rolling to an intermediate thickness
• cold rolling with or without intermediate annealing

which provides blanks suitable for stamping and drawing operations.

It should be noted that the products retain good isotropy even if the rates of cold deformation exceed 50%, or even 60 or 65% without intermediate annealing (s).

The essential differences between the conventional 3004 alloys and the alloys (I) according to the invention lie in limited Fe and / or Si contents, which lead to micrographic structures on hot-rolled products (generally sheets or strips of thickness greater than 3 mm) completely different.

The classic 3004 alloy is characterized by the existence of a structure comprising, in addition to the coarse primary intermetallic precipitates situated in the interdendritic zones and the intragranular secondary precipitates, fine "white bands", free of precipitates, in the interdendritic zones. On the contrary, the alloys according to the invention have similar microstructures, but in the total absence of "white bands".

The alloys according to the invention are therefore characterized by a very homogeneous distribution of the primary and secondary precipitates in a matrix based on A1 from the ingot stage.

FIGS. 1, 2 and 3 are micrographs at magnification X400 respectively of the conventional alloy 3004 (example 0) and of the alloys of examples 1 (or 3) and 2, according to the invention, in the raw state of rolling to hot.

Figure 4 is a schematic profile of the distribution of precipitates (volume fraction in%) as a function of the distance (in µm) counted from an interdendritic zone on a cross section of a dendrite having about 95 µm wide for a conventional 3004 alloy (thick line) and an alloy according to the invention (thin line).

où H α = (H + H_180-α + H_180+α + H_360-α )/4 H étant la hauteur de l'embouti cylindrique dans une direction faisant un angle α avec la direction de laminage et $\overline{\text{H}}$

la hauteur moyenne de l'embouti cylindrique définie par

n étant le nombre d'extréma = 2 x nombre de cornes - voir norme NFA 50-301, juin 1976 -The invention will be better understood using the following examples, compared with an alloy 3004 taken as a reference.
In these examples, the material obtained is characterized by its mechanical tensile characteristics (transverse direction), by the horn index S 45/90 as defined below, and the values of LDR and LIR also defined below.
The rate of horns: S α / β = $$\frac{\overline{\text{H}}\text{α -}\overline{\text{H}}\text{β}}{\overline{\text{H}}}$$

where H α = (H + H _180-α + H _{180 + α} + H _360-α ) / 4 H being the height of the cylindrical stamp in a direction making an angle α with the rolling direction and $\overline{\text{H}}$

the average height of the cylindrical stamp defined by

n being the number of extrema = 2 x number of horns - see standard NFA 50-301, June 1976 -

The LDR (limiting drawing ratio) is the value of the ratio: 0̸ maxi blank / 0̸ punch without appearance of rupture under determined stamping conditions: lubrication, pressure of blank holder, geometry of the punch (rounded), sheet thickness (blank), etc.
The LIR (limiting ironing ratio) in% is the nominal value of the ratio
LIR = 100 (eo - ef) / eo
allowing the stretching on a punch of a cylinder without the appearance of defects under determined conditions of tool geometry (die / punch), lubrication, initial thickness, number of passes, (generally 3), etc. .., e _o being the initial thickness of the wall and e _f being the final thickness.

The following examples (1 to 5) illustrate the invention with respect to the alloy 3004 taken as a reference (example 0). Examples 1 to 3 relate to the compositions (I) and Examples 4 and 5 to the compositions (II).

The alloys, the chemical composition of which is given in Table I, were cast in trays of 1100 x 300 x 2650 mm³, homogenized or reheated, scalped, hot rolled up to 3mm thick and cold up to 0.3mm thick, with or without intermediate annealing under the conditions detailed in Table 2 (state H 1x).
A simulation of the firing of the varnishes was carried out by maintaining for 10 minutes at 204 ° C. (state H 28).

The results obtained are reported in Table 3.

• que l'exemple 1 présente des caractéristiques mécaniques élevées et une faible anisotropie avec une formabilité comparable à celle du 3004.
• que l'exemple 2 présente des caractéristiques mécaniques très élevées associées à une bonne formabilité, l'isotropie étant notablement plus forte que celle du 3004
• que l'exemple 3 présente une isotropie particulièrement élevée, les caractéristiques de résistance mécanique et de formabilité étant équivalentes à celle de 3004
• que les exemples 4 et 5 présentent des caractéristiques mécaniques particulièrement élevées avec une isotropie au moins égale et une formabilité comparable à celle du 3004.

It can be observed :

• that Example 1 has high mechanical characteristics and low anisotropy with a formability comparable to that of 3004.
• that example 2 has very high mechanical characteristics associated with good formability, the isotropy being notably stronger than that of 3004
• that Example 3 has a particularly high isotropy, the mechanical strength and formability characteristics being equivalent to that of 3004
• that Examples 4 and 5 have particularly high mechanical characteristics with an isotropy at least equal and a formability comparable to that of 3004.

The invention finds a main application in the manufacture of stretched cans, particularly of drink cans, lighter and / or more resistant with an increased saving of material, with a manufacturing range entirely similar to that of conventional alloys (3004 -3104), with a simplification of the manufacturing range by avoiding intermediate annealing.

Claims (17)

Alloy based on A1 intended for stamping and / or drawing, characterized in that it contains (by weight%)
Fe ≦ 0.25 - Si ≦ 0.25 - Mn from 0.8 to 1.6 - Mg from 0.7 to 2.5 - Cu from 0.20 to 0.6 - Cr from 0 to 0.35 - Ti from 0 to 0.1 - V from 0 to 0.1 - other elements: each ≦ 0.05, total ≦ 0.15, remains A1 Alloy according to claim 1, characterized in that the Fe content is less than 0.20%. Alloy according to claim 1 characterized in that the Fe content is less than 0.15%. Alloy according to one of claims 1 or 3, characterized in that the Cu content is greater than 0.25%. Alloy according to one of Claims 1 to 4, characterized in that% Mn + 0.9% Fe + 0.3 Mg ≦ 1.9 Alloy according to one of claims 1 to 5, characterized in that it contains from 1.2 to 1.6% Mn, from 0.8 to 1.2% Mg, from 0.2 to 0.6% Cu and up to 0.25% Cr. Alloy according to one of Claims 1 to 6, characterized in that% Mn - 2.25% Fe ≧ 0.50. Alloy according to one of claims 1 to 7, characterized in that in the homogenized state or in the hot rolled state, its structure consists of a matrix based on A1 containing primary and secondary precipitates regularly distributed , in the absence of "white stripes". Process for obtaining a laminated strip of A1 alloy comprising the casting of an alloy containing (by weight%):
Fe ≦ 0.25 - Si ≦ 0.25 - Mn from 0.8 to 1.6 - Mg from 0.7 to 25 - Cu from 0 to 0.6 - Cr from 0 to 0.35 - Ti from 0 to 0.1 - V from 0 to 0.1 other elements = each ≦ 0.05 - total ≦ 0.15, rest: A1
homogenization or reheating, hot rolling, cold rolling, without intermediate annealing (s), characterized in that
% Mn - 2.25% Fe ≧ 0.50
and in that the rate of cold deformation is greater than 50%. Alloy based on A1 intended for stamping and / or drawing, characterized in that it contains (by weight%)
Fe from 0.7 to 1.5 - Si ≦ 0.4 - Mn ≦ 0.8 - Mg from 1.5 to 3 - Cu from 0 to 0.6 - Cr from 0 to 0.35 - Ti from 0 to 0.1 - V from 0 to 0, 1 - other elements - each ≦ 0.05, total ≦ 0.15, remains A1. Alloy according to claim 10 obtained according to the conventional semi-continuous casting or continuous strip casting methods, characterized in that there is the relation:
% Mn + 0.9% Fe + 0.3% Mg ≦ 1.9 Alloy according to one of claims 10 or 11 characterized in that% Mn ≦ 0.40. Alloy according to claim 12 characterized in that% Mn ≦ 0.35. Alloy according to one of Claims 10 to 13, characterized in that% Fe ≧ 1.05. Alloy according to Claim 14, characterized in that% Fe ≧ 1.10. Alloy according to one of Claims 9 to 15, characterized in that it contains 1.1 to 1.4% Fe, 1.6 to 2.5% Mg and up to 0.25% Cr. Process for obtaining a laminated strip of alloy of A1 comprising the casting of an alloy containing (by weight%) from 0.7 to 1.5 Fe; up to 0.4 Si; 1.5 to 3 Mg; up to 0.6 Cu; up to 0.35 Cr; up to 0.1 Ti; up to 0.1 V; impurities: up to 0.05 each and 0.15 or total, homogenization or reheating, hot rolling, cold rolling without intermediate annealing, characterized in that the rate of cold deformation is greater than 50%.

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