Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
  • C22F1/057—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys with copper as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/12—Alloys based on aluminium with copper as the next major constituent
  • C22C21/16—Alloys based on aluminium with copper as the next major constituent with magnesium

Definitions

• the invention relates to a method for manufacturing highly deformed parts, intended for mechanical construction and in particular for aeronautical construction, using AlCuMg aluminum alloy sheets of type 2024 according to the nomenclature of the Aluminum Association.
• the 2024 alloy is widely used in aircraft construction and its composition registered with the Aluminum Association is as follows (% by weight): If ⁇ 0.5 Fe ⁇ 0.5 Cu: 3.8 - 4.9 Mn: 0.3 - 0.9 Mg: 1.2 - 1.8 Zn ⁇ 0.25 Cr ⁇ 0.10 Ti ⁇ 0 , 15 Certain parts, produced in particular by stretching-forming (the English term "stretch-forming" is often used), stamping, flow-forming, folding or rolling, require, in addition to the properties usually required for aeronautical construction, such as high resistance mechanical, toughness, resistance to propagation of cracks, etc., sheets having good formability.
• Patent EP 0473122 describes a process for manufacturing sheets of alloy of composition (% by weight): Cu: 4 - 4.5 Mg: 1.2 - 1.5 Mn: 0.4 - 0.6 Fe ⁇ 0.12 Si ⁇ 0.05, including intermediate annealing at a temperature> 488 ° C. He teaches that these sheets have toughness and resistance to improved crack propagation compared to conventional 2024.
• Patent application EP 0731185 describes sheets of modified 2024 alloy, subsequently registered with the Aluminum Association under the designation 2024A, having a reduced level of residual stresses and improved toughness for heavy sheets, and improved elongation for thin sheets.
• This application limits the content of Mn to 0.55% and that of Fe to 0.25%, with the relation: 0 ⁇ Mn - 2 Fe ⁇ 0.2 (the contents Mn and Fe being expressed in%).
• Patent application WO 96/29440 describes a process for manufacturing a product in aluminum alloy type 2024, comprising hot rolling, annealing, cold rolling, dissolving, quenching and cold deformation minimum, which can be traction, straightening or leveling, a process intended to improve formability.
• the application recommends a preferential composition of the alloy: Cu: 4.0 - 4.4, Mg: 1.25 - 1.5, Mn: 0.35 - 0.5, Si ⁇ 0.12, Fe ⁇ 0.08, Ti ⁇ 0.06.
• the intermediate annealing between hot rolling and cold rolling is presented as favorable to mechanical strength and toughness. This step additional and unusual process has drawbacks economic. Nor does it solve the problem posed by the market, namely supply sheets having characteristics such as their shaping either simplified.
• aeronautical manufacturers seek to minimize the number of steps for forming sheets, and to use sheets that can be produced inexpensively using short transformation ranges, that is to say say including as few individual steps as possible.
• the current practice of aeronautical manufacturers consists in supplying hot or cold rolled sheets according to the required thickness, in the raw state of manufacture (state "F” according to standard EN 515) or annealed ("O” state) or matured quenched state ("T3" or "T4" state), subject them to a heat treatment in solution followed by quenching, then to shape them and subjecting them to natural or artificial aging, so as to obtain the required mechanical characteristics.
• the sheets are in a state characterized by good formability, but this state is unstable (state "W"), and the shaping must take place on fresh quenching, c that is to say within a short time after quenching, of the order of a few tens of minutes to a few hours. If this is not possible for production management reasons, the sheet must be stored in a cold room at a sufficiently low temperature and for a sufficiently short period so as to avoid natural maturation.
• this heat treatment for dissolving requires large ovens, which makes the operation inconvenient, even compared to the same operation performed on flat sheet metal.
• the possible need for a cold room adds to the costs and disadvantages of the state of the art. For highly deformed parts, this operation may need to be repeated, if the material does not have, in the metallurgical state in which it is found, sufficient formability allowing the desired shape to be achieved in a single operation.
• the only possible shaping is rolling.
• the rolled sheet is then dissolved and quenched, and a second shaping is carried out either on fresh quenching, or after storage in a cold room. In all other cases, the sheet is directly dissolved and quenched before shaping.
• a first shaping operation is carried out from this state, and a second shaping after dissolution and quenching.
• This variant is used when the target formatting is too great to be able to be carried out in a single operation from a state W, but can however be carried out in two passes from the state O. In this state, the sheet metal is certainly less formable, but state O is easier to use than state W, which is unstable, and requires additional heat treatment.
• the manufacture of the sheet in the O state involves a final annealing of the raw rolling sheet, and therefore an additional manufacturing step, which is contrary to the aim of simplification aimed by the present invention.
• an additional manufacturing step which is contrary to the aim of simplification aimed by the present invention.
• a sheet in the W state which generally has the best formability
• the object of the invention is therefore to simplify the process for manufacturing formed parts, and in particular parts which are strongly deformed by one or more methods such as stretch-forming, stamping, flow-forming or folding, by association of an optimized chemical composition and specific manufacturing processes, making it possible to avoid solution as much as possible on formed sheet. It goes without saying that any new process for manufacturing highly deformed parts must result in parts having mechanical and working characteristics at least as good as existing products. Another object of the invention is to obtain parts whose damage tolerance properties do not degrade after deformation.
• the alloy has a copper content of between 3.9 and 4.3% (and again preferably between 3.9 and 4.2%), a magnesium content between 1.2 and 1.4% (and more preferably between 1.25 and 1.35%), a manganese content between 0.3 and 0.45% an iron content ⁇ 0.10%, a silicon content ⁇ 0.10% (and preferably ⁇ 0.08%), a content of titanium, chromium and zirconium ⁇ 0.07% (preferably ⁇ 0.05%).
• the method according to the invention makes it possible to use plated sheets, for example example of sheets coated with an alloy plating more resistant to corrosion, as is usually the case for aircraft fuselage cladding sheets.
• a first characteristic of the invention consists in using an alloy modified compared to the traditional 2024.
• the first modification consists in reducing the Si and Fe contents respectively below 0.25 and 0.20%, and preferably below 0.10%.
• the Mn content is also reduced below 0.5% and preferably below 0.45%.
• the Cu content is also slightly reduced and kept below 4.5%, and preferably below 4.3%, or even 4.2%.
• the Mg content is also slightly reduced, and kept below 1.5%, preferably between 1.2 and 1.4%, or even between 1.25 and 1.35%.
• the alloy is cast in plates, which are optionally homogenized at a temperature between 460 and 510 ° C (preferably between 470 and 500 ° C) for 2 to 12 h (preferably 3 to 6 h).
• the plates are scalped.
• Hot rolling takes place with an inlet temperature of between 430 and 470 ° C, and preferably between 440 and 460 ° C.
• the outlet temperature of the strips is preferably carried out at a temperature higher than the usual temperature,> 300 ° C., and preferably> 310 ° C., in particular in the case where part of the shaping is carried out before dissolving .
• the strips are wound. At this stage, they have an elongation of more than 13.5%, and more often than 15% in the L and TL directions. They can optionally be cold rolled if the required thickness is not accessible by hot rolling.
• the strips are then cut into sheets.
• a first variant of the invention consists in carrying out the shaping, by stretching-forming, stamping, flow-forming or folding, directly in this state F without annealing or other prior treatment.
• the partially formed sheet is then dissolved at a temperature between 480 and 500 ° C for a period between 5 min and 1 h, then quenched, generally with cold water.
• the shaping is done in two or more passes.
• the freshly soaked piece (less than an hour) can immediately undergo a new shaping, or it is transferred to a cold room at a temperature below 10 ° C and preferably below 0 ° C, and shaped at leaving the cold room.
• Sheets can be used plated on one or two sides, which is the most common case for aircraft fuselage panels, plated with an alloy of the 1000 series, for example alloys 1050, 1100, 1200, 1135 , 1145, 1170, 1175, 1180, 1185, 1188, 1199, 1230, 1235, 1250, 1285, 1350 or 1435.
• the distributed elongation is the difference in elongation between the start and the end of the plastic deformation range, i.e. the deformation range permanent before necking, of the deformation curve.
• a cold rolled strip according to the invention has an LDH value greater than 42 mm and preferably greater at 44 mm, while a hot rolled strip has an LDH value greater than 73 and preferably greater than 75 mm.
• the preferred composition gives better formability than the traditional composition.
• the mechanical characteristics of the intermediate product do not matter in this situation, provided that the finished product at the end of the whole process has at least mechanical characteristics as high as the product resulting from the process according to the prior art.
• the two products In the T42 state, as defined by the draft standard prEN 4211 of July 1995, for a thickness of 6 mm and with an identical manufacturing range, the two products have equivalent mechanical properties.
• the LDH value and the level of the CLF curves are lower for a sheet cold worked only for a sheet which has undergone only hot rolling; this effect is known.
• the plaintiff was surprised to find that for a given process (hot rolling or hot rolling followed by cold rolling) and for comparable thickness, the LDH value, which is one of the relevant parameters for measure formability, increases significantly when the chemical composition is located within a preferred domain: Cu 3.9 - 4.3 and preferably 3.9 - 4.2, Mg 1.2 - 1.4 and preferably 1.25 - 1.35, Mn 0.30 - 0.45, Si ⁇ 0.10 and preferably ⁇ 0.08, Fe ⁇ 0.10.
• the Applicant has found that the formability is further improved when certain elements of addition and impurities are strictly controlled, as follows: Zn ⁇ 0.20%, Cr ⁇ 0.07% and preferably ⁇ 0.05%, Zr ⁇ 0.07% and preferably ⁇ 0.05%, Ti 0.07% and preferably ⁇ 0.05%.
• the advantage of the method according to the invention compared to the prior art is therefore to be able to carry out deeper shaping in the W state, or even to eliminate an intermediate solution for very deep shaping. It was thus possible to manufacture parts in a single pass, while according to the prior art, two passes were necessary to achieve them.
• Examples 3s, 3t, 3u, 3v, 3w, 3x correspond to the present invention.
• Examples 3e, 3f, 3g, 3h, 3i, 3j, 3k, 3L, 3m, 3n, 3p, 3q, 3r correspond to the prior art.
• Examples 3a, 3b, 3c, 3d correspond to Examples 2h, 2f, 2L and 2m from Example 2; they appear here for comparison to represent a 2024 state W according to the prior art.
• the method according to the invention does not lead, after shaping by stretching, to a significant reduction in the damage tolerance properties, unlike the method according to the prior art. It is even observed that the method according to the invention improves the tolerance for damage in a stretched state, that is to say the state in which the part is in the finished state.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Heat Treatment Of Sheet Steel (AREA)
• Shaping Metal By Deep-Drawing, Or The Like (AREA)
• Metal Rolling (AREA)

Applications Claiming Priority (2)

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Cited By (16)

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Citations (5)

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• 1999
  • 1999-04-12 FR FR9904685A patent/FR2792001B1/fr not_active Expired - Lifetime
• 2000
  • 2000-04-06 GB GB0008506A patent/GB2352453A/en not_active Withdrawn
  • 2000-04-07 BR BR0001563-6A patent/BR0001563A/pt not_active IP Right Cessation
  • 2000-04-10 DE DE60020188T patent/DE60020188T2/de not_active Expired - Lifetime
  • 2000-04-10 DE DE0001045043T patent/DE00420071T1/de active Pending
  • 2000-04-10 EP EP00420071A patent/EP1045043B1/de not_active Expired - Lifetime
  • 2000-04-12 JP JP2000110617A patent/JP2000328211A/ja active Pending
• 2003
  • 2003-03-07 US US10/382,519 patent/US20030140990A1/en not_active Abandoned

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