FR2503738A1 - PROCESS FOR MANUFACTURING SHEETS OF HYPOEUTECTIC ALUMINUM IRON ALLOYS - Google Patents

Abstract

1. A process for the production of sheets of hypoeutectic aluminium-iron alloy by the addition of a fining agent to the metal bath, semicontinuous casting in an ingot mould or continuous casting between cylinders, cold rolling and annealing at from 380 degrees C to 430 degrees C, characterised in that the fining agent is added in an amount such that it generates a cast structure wherein the grains are of a maximum size of less than 100 mu m and the spacing between dendrite arms is from 8 to 30 mu m, and that the rolling operation is performed using a thickness reduction ratio of from 98 to 99.8% so as to develop a final semirecrystallised structure after annealing.

Description

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  PROCESS FOR PRODUCING DALUMINIMS-IRON ALLIAOES SHEETS

hypoeutectic

  The present invention relates to a process for producing sheets of hypoeutectic aluminum-iron alloys, intended more particularly for the production of light dishes, flexible tubes, stoppers and

  all applications requiring the said sheet of

  mechanical processes that promote stamping, bending and rigidity

ity.

  Here we mean by hypoeutectic aluminum-iron alloys, those which

hold less than 1.7% iron.

  Such alloys are known in particular from French Patent No. 1,438,096, which protects a product suitable for the production of metal sheets with a thickness of less than 76 am, characterized in that it contains from 0.6 to 1.2% of iron, the rest being aluminum. Such a sheet is obtained by conventional semi-continuous casting followed

  cold rolling and has inherent mechanical characteristics

  interesting, namely a tensile breaking strength of

  the order of 80 MPa and an elongation of 7%.

  Another French patent, No. 2,291,285, also claims a process for manufacturing alloy sheets containing between 1.1 and

  2, 5% iron. This process uses the use of

  HUNTER type linders, rolling and final annealing. However, his teaching is rather focused on compositions close to 1.7% of iron, that is to say eutectics, which lead to

  homogeneous solid phases, consisting of fine particles of

  metallics scattered throughout the material.

  The applicant has oriented its research towards alloys of

  quite apart from eutectic and containing at most 1.3%

  of iron. Those skilled in the art know that, under these conditions, solidification

  cation begins with the appearance of so-called primary aluminum crystals.

  in the form of dentrites and ends with a deposition of

  layer of AlnFe intermetallics separating the grains from

  other. This leads to a heterogeneous structure quite different

  of the homogeneous structure obtained in the case of a composition

  tectique. s DaIhns the field of these hypoeutectic aluminum-iron alloys, the

  French patent no. 1 438 096 shows, by means of curves, the variations

  mechanical characteristics, such as

  tensile rupture and elongation, depending on the reduction rate

  the thickness of the metal during rolling. This rate, also called hardening rate, corresponding to the formula

  : - .. --1t00 in which E'represente the thickness before laininag & -

and the final thickness.

  These curves show that hypoeutectic AlnFe has a characteristic

  This property makes it clear that, as the patent teaches, "the alloy adapts better to the manufacturing operations of the alloys of the conventional alloys 1100 and 5005.

  thin sheets and makes the product obtained superior for use in

  packaging, for which improved mechanical strength is

  that would be ineffective if it were accompanied by an appreciable loss of elongation. "It is, in fact, principally the search for an optimum compromise between these two characteristics which guides the art of ho sheets for packaging and it is in this perspective that the applicant has sought and found a way to improve the compromise, and thus confer the product obtained

  qualities favoring stamping, folding and stiffness.

  This means consists of a process to develop in the sheet

  metallic a final structure called "semi recrystallized".

  It is known, in fact, that during cold rolling, in particular, the metal hardens or better cures, that is to say that it gradually loses

  any capacity for plastic elongation while acquiring a resistance

  more important. It can then be heated to a temperature close to

  sine 400 C and proceed to a so-called recrystallization annealing, -3-

  operation during which the mechanical characteristics change.

  significantly reduce and focus on decreasing the breaking load and increasing elongation. Admittedly, the elongation is considerably improved, but most often the resistance has become insufficient. This is why the plaintiff thought that by limiting this

  recrystallization, it was possible to create an inter-

  which would simultaneously develop the benefits of good

  resistance of the hardened state and the proper elongation of the state

  recrystallised thus concretizing the achievement of the desired compromise.

  To achieve this, she has developed a process in which the metal bath is treated by refining, it flows semi-continuously in a

  ingot mold or continuously between rolls, it is cold rolled and

  baked between 3800C and 430'C, this process being characterized in that -

  the refining agent is added in such a quantity that it generates a casting structure in which the grains have a maximum dimension of less than 1 μm and the spacing between the dendrite arms is between 8 and 30 μm and in that the rolling is performs according to a reduction rate

  thickness between 98 and 99.8%.

  Thus, the method according to the invention consists in implementing the conventional steps in metallurgy, refining of the alloy in the liquid state, casting, rolling, final annealing. We can note,

  however, whether the method applies indifferently to a

  semi-continuous casting by means of ingot molds or type 3C rolling mills, provided that the refining and work hardening parameters are adapted to the type of casting so as to lead to

to the same final structure.

  The process is first characterized by the addition of a refining agent

  as it generates a casting structure in which the

  grains have a maximum dimension less than 100 im.

  In a conventional manner, particles of about 200 μm are obtained during casting. But, experience has shown that with such a size, the alloy has a too heterogeneous behavior during rolling and that shear bands are created favorable to the development of a total recrystallization, which goes to against obtaining a semi-recrystallized structure. However, looking for a grain size that is too small is not

  interesting because it leads to a too

  form and regularity of the eutectic and results in a product that recreates

not tallifying.

  That is why, one refines so as to have grains of sizes between 10 and 50 a. This refining can be obtained by means of any agent generally used in the metallurgy of aluminum and, in particular, boron and titanium products, such as

for example, V'AT5B.

  With the same aim of avoiding this homogeneity of structure, it is obvious

  for those skilled in the art, to use alloy compositions away as much as possible from the eutectic zone, but keeping

  nevertheless enough iron to benefit from the particular properties

  of this element and, in particular, its action as a blocking agent for recrystallization. Thus, a content between

  1.1 and 1.3% iron is preferred.

  Still with the same concern for heterogeneous structure search, it is avoided to cast the alloy in a cylinder machine type HUNTER because the rate of solidification is too great and leads to dendrites too fine less than 5 pm. On the other hand, the machine 3C proves to be particularly interesting in the process of the invention since it gives rise to the formation of dendrites still sufficiently large so that we can clearly distinguish on the structure the

areas with and without eutectic.

  The method is also characterized in that the cold rolling applied directly to the casting structure is carried out according to

  a thickness reduction ratio of between 98 and 99.8%.

  It is obvious, by cold rolling, a rolling done at a

  temperature below the recrystallization temperature.

  This choice results from the fact that, when this level is too low, of s of the order of 96% for example, hardening is insufficient and, consequently, the metal will recrystallize easily and completely during the annealing. On the contrary, if the work hardening is too high, branches of dendrites have become so fine that recrystallization

  can not occur and the structure evolves only by restoration.

  Between these two rates of hardening, a limited number of regions can

  recrystallize and form isolated recrystallized grains in a restored material and these grains can not grow and

  invade the entire structure due to the presence of the particles

  tectiques. These rates were chosen so as to subsequently form

  a semi-recrystallized structure in which the recrystallic volume

  is between 10% and 30% of the total volume, the most

compatible with the purpose.

  Finally, the process also comprises an annealing between 380 and 430 ° C. after rolling at a rate that is not temperature-proof and of a duration such that the desired semi-recrystallized structure is developed and which is then composed of recrystallized grains of smaller diameter.

  at 30 pim and usually between 5 and 15 lm, isolated in one

  trice restored with sub-grains of 1- to 2 pm.

  The semi-recrystallized structure thus obtained seems to be essential

  dispersion in the distribution of distances between the intermetallic particles allowing both recrystallisation

  when this distance is frande and the blocking of recrystallisa-

  when this distance is small.

  The small volume occupied by the recrystallized grains seems to be

  because it gives the alloy a significant improvement in ductility, whereas the structure of the sub grains makes it possible to conserve

high elastic limit.

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  This combination gives the alloy sheet an advantageous compromise

  between its characteristics, particularly favorable for subsequent processing operations such as stamping

for example.

  The invention also relates to the alloy sheet obtained by the

  process having a thickness of between 50 and 250 M, a composition

  such that: Fe: 2.1 - 1.3% Si <0.7% Mh <0.1 t Ti <0.1% Cu <0.2% characterized by a structure in which 10 to 30% of the volume is

  in the recrystallized state in the form of grains greater than S pm and

  than 30 M, and the rest is in the restored state so as to obtain

  an advantageous compromise between tensile breaking load

  and elongation, and being for the first mechanical characteristic

  between 120 and 140 Pa, and for the second, above 17 t.

  The invention can be illustrated by means of the following examples which show the results of mechanical characteristics obtained with

  sheets of 100 μm in thickness, prepared according to the process

than.

EXAMPLE 1

An alloy of composition:

  Fe: 1.3% - Si: 0.3% - Cu: 0.1% - l 0.015% -

  Ti: 0.03%, was refined using a parent alloy of AT5B at a ratio of

  of 3 kg per ton of alloy, then continuously cast with a

  bottomless pitcher in the form of a plate whose section is

  38 x 7 cm with a speed of 8 cm / minute.

  The structure of the cast product was composed of primary aluminum grains having a maximum dimension of less than 150 pmn separated by

  each other by eutectic zones of AlnFe.

  The plate was cold rolled at a rate of reduction of

  99.8% to give a 100-mm thick sheet

  which was annealed at 420 C for 30 hours.

  The final structure of this sheet had 30% of its volume in the recrystallized state and its mechanical characteristics were as follows: Breaking load .......... 120 MPa Elongation ...... ....... 20% compromise of values particularly favorable to the development of

dishes obtained by stamping.

EXAMPLE 2

An alloy of composition

  Fe: 1.15 e - Si 0.3% - Ti: 0.03% - -Cu: 0.002% -

  Mn: 0.020%, was refined using a parent alloy of ATSB at a ratio

  of 2 kg per tonne of alloy and then cast continuously by means of a

  chilled cylinder type 3C in the form of a sheet of thick

  0.8 cm with a speed of 100 cm / minute.

  The structure of the cast product contained primary aluminum grains

  mayor of dimensions between 30 and 80 im separated any of

  others by eutectic zones of AlnFe.

  The sheet has been cold rolled following a thickness reduction rate

  99% so as to form a sheet of thickness 80 mt which was

annealed at 400 ° C for 30 hours.

  The sheet had a final structure recrystallized to 20% and its mechanical characteristics were as follows: Breaking load .... 130 MPa Elongation .... 23%

  characteristics that made it possible to use this sheet in

  stamped dishes, with a virtually zero scrap rate.

  The present invention finds its application in the aluminum industry whenever it is desired to obtain sheets with a thickness of between 50 and 150 μm having a pair of optimum values in terms of

  regarding tensile breaking load and elongation.

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