EP1727921B1 - Structural element for aircraft engineering exhibiting a variation of performance characteristics - Google Patents

Abstract

The invention relates to a method for producing a part made of aluminium alloy with structural hardening consisting a) in melting a semifinished extruded or forged rolled stock followed by water quenching, b) in optionally carrying out a controlled drawing with a permanent stretching which is equal to or greater than 5 % and c) in tempering. Said invention is characterised in that at least one tempering operation is carried out in a controlled thermal gradient linear furnace comprising at least two areas or groups of areas (Z<SUB>1</SUB>, Z<SUB>2</SUB>) at initial temperatures (T<SUB>1</SUB>, T<SUB>2</SUB>) in which the variation of each temperature T<SUB>1</SUB>, T<SUB>2</SUB>) around a specified temperature is equal or less than 5 °C through the length of said areas or the groups of areas, the difference between the specified temperatures of the initial temperatures T1 and T2 is equal or greater than 5 °C and said areas or the groups of areas are dividable by a transition area or group of areas (Z<SUB>1</SUB>,<SUB>2</SUB>) inside of which the initial temperature varies from T1 to T2 and a length which is parallel to the axis of the linear furnace of each at least two areas or the groups of areas Z<SUB>1</SUB> and Z<SUB>2</SUB> is equal to or greater than 1 meter.<SUP/>

Description

Technical field of the invention

The present invention relates to wrought products and structural elements, especially for aircraft construction, heat-treated aluminum alloy. It relates in particular to so-called long products, ie products having a length significantly greater than the other dimensions, typically at least twice as long as they are wide, and of a length typically of at least 5 meters. . These products can be rolled products (such as thin sheets, medium sheets, thick sheets), spun products (such as bars, profiles, tubes or wires), and forged products.

State of the art

Very large aircraft have unique construction problems. For example, the assembly of structural elements becomes increasingly critical, firstly as a cost factor (riveting is a very expensive process), secondly as a generator of discontinuities in the properties of assembled parts.
To minimize the assemblies, structural elements can be prepared by integral machining in thick plates; these structural elements can then integrate into a single piece (called monolithic) different functions such as the wing skin function and the stiffener function. It is also possible, and at the same time, to enlarge the dimension of the monolithic structural elements. This poses new manufacturing problems of these parts by rolling, spinning, forging or molding, because it is more difficult to ensure homogeneous properties in very large parts.

It was also mentioned to prepare monolithic pieces having a controlled variation of properties, which makes it possible in theory to better adapt the properties of the parts to the needs of the manufacturer. As such, the patent EP 0 630 986 (Pechiney Rhenalu ) discloses a method of manufacturing structurally hardened aluminum alloy sheets having a continuous variation of the use properties, wherein the final income is made in a specific structure furnace comprising a hot chamber and a cold room, connected by a heat pump. This process made it possible to obtain small pieces with a length of about one meter in alloy 7010, one end of which is in the T651 state and the other in the T7451 state, by an isochronous tempering treatment. This process has never been developed on an industrial scale because it is difficult to control in a manner compatible with the quality requirements of the field of aeronautical construction; these difficulties increase with the size of the parts, knowing that it is particularly for the very large parts that the designer would like to be able to integrate two or more functionalities by means of a continuous variation of the properties of use. Another problem with this method for the example described in the cited patent is that the optimal durations of the T651 and T7451 treatments are different. Yet another problem is that a 7010 product in the T7451 state is typically obtained by a two-stage income treatment, while the T651 state is obtained by a single-stage income treatment.

The problem addressed by the present invention is to develop a method for the manufacture of structural elements, in particular for aircraft construction, having a variation of the use properties, which allows the production of very long parts, and which is sufficiently controllable, stable and reproducible under the stringent quality assurance and process control conditions that are commonly required by the aviation industry.

Object of the invention

1. a) la mise en solution d'un demi-produit laminé, filé ou forgé, suivie d'une trempe,
2. b) éventuellement la traction contrôlée avec un allongement permanent d'au moins 0,5%,
3. c) le traitement de revenu,

caractérisé en ce qu'au moins une étape dudit traitement de revenu est effectuée dans un four à profil thermique contrôlé dans la longueur, ledit four comportant au moins deux zones ou groupes de zones Z₁, Z₂ avec des températures initiales T₁, T₂, dans lesquelles la variation de la température autour de la température de consigne de chacune des températures T₁ et T₂ ne dépasse pas ± 5°C (préférentiellement ± 4°C, et encore plus préférentiellement ± 3°C) sur la longueur desdites zones ou groupes de zones, la différence entre les températures de consigne des températures initiales T₁ et T₂ étant supérieure ou égale à 5°C (préférentiellement comprise entre 10°C et 80°C, plus préférentiellement entre 10°C et 50°C, et encore plus préférentiellement entre 20°C et 40°C), et lesdites zones ou groupes de zones pouvant être séparées par une zone ou groupe de zones Z_1,2 dit de transition à l'intérieur de laquelle ou duquel la température initiale varie de T₁ à T₂,
et caractérisé en ce que la longueur parallèle à l'axe du four de chacune desdites au moins deux zones ou groupes de zones Z₁ et Z₂ est d'au moins un mètre (et préférentiellement d'au moins deux mètres).A first object of the present invention is a method of manufacturing a structural hardening aluminum alloy part, comprising:

1. a) dissolving a semi-finished product rolled, spun or forged, followed by quenching,
2. b) optionally controlled traction with a permanent elongation of at least 0.5%,
3. (c) the income treatment,

characterized in that at least one step of said tempering treatment is carried out in a controlled temperature profile furnace in length, said furnace comprising at least two zones or groups of zones Z ₁ , Z ₂ with initial temperatures T ₁ , T ₂ , in which the variation of the temperature around the set temperature of each of the temperatures T ₁ and T ₂ does not exceed ± 5 ° C (preferably ± 4 ° C, and even more preferably ± 3 ° C) over the length said zones or groups of zones, the difference between the set temperatures of the initial temperatures T ₁ and T ₂ being greater than or equal to 5 ° C (preferably between 10 ° C and 80 ° C, more preferably between 10 ° C and 50 ° C). ° C, and even more preferably between 20 ° C and 40 ° C), and said zones or groups of zones can be separated by a zone or group of zones Z _1,2 said transition within which or which the temperatur e initial varies from T ₁ to T ₂ ,
and characterized in that the length parallel to the furnace axis of each of said at least two zones or groups of zones Z ₁ and Z ₂ is at least one meter (and preferably at least two meters).

• a) P₁ : K_IC(L-T) > 38 NPa√m et P₂ : R_m(L) > 580 MPa
  (et préférentiellement > 590 MPa, et encore plus préférentiellement > 600 MPa).
• b) P₁ : K_IC(L-T) > 40 MPa√m et P₂ : R_m(L) > 580 MPa
  (et préférentiellement > 590 MPa).
• c) P₁ : K_IC(L-T) > 41 MPa√m et P₂ : R_m(L) > 580 MPa
  (et préférentiellement > 590 MPa).
• d) P₁ : K_IC(L-T) > 42 MPa√m et P₂ : R_m(L) > 590 MPa.
• e) P₁ : K_IC(L-T) > 39 MPa√m et P₂ : R_m(L) > 580 MPa et P₂ : R_m(TL) > 550 MPa.
• f) P₁ : K_IC(L-T) > 39 MPa√m et P₂ : R_m(L) > 580 MPa et P₂ : R_p0,2(L) > 550 MPa,
• i) P₁ : K_IC(L-T) > 39 MPa√m et P₁ : R_m(L) > 530 MPa, et P₂ : R_m(L) > 580 MPa.
• j) P₁ : K_IC(L-T) > 40 NTa√m et P₁ : R_m(L) > 540 MPa, et P₂ : R_m(L) > 590 MPa.
• k) P₁ : K_{app(L-T)(CCT406)} > 125 MPa√m et P2 : R_m(L) > 590 MPa.

A second object of the present invention is a monolithic structural element according to claims of structural hardening aluminum alloy having a length L greater than the width B and the thickness E, in particular for aircraft construction,
said monolithic structure element being characterized in that at least two segments P ₁ and P ₂ located on a different length of said structural element have mechanical properties (measured at mid-thickness) selected from the group consisting of:

• a) P ₁ : K _{IC (LT)} > 38 NPa√m and P ₂ : R _m (L)> 580 MPa
  (and preferentially> 590 MPa, and even more preferentially> 600 MPa).
• b) P ₁ : K _{IC (LT)} > 40 MPa√m and P ₂ : R _m (L)> 580 MPa
  (and preferentially> 590 MPa).
• c) P ₁ : K _{IC (LT)} > 41 MPa√m and P ₂ : R _m (L)> 580 MPa
  (and preferentially> 590 MPa).
• d) P ₁ : K _{IC (LT)} > 42 MPa√m and P ₂ : R _m (L)> 590 MPa.
• e) P ₁ : K _{IC (LT)} > 39 MPa√m and P ₂ : R _m (L)> 580 MPa and P ₂ : R _m (TL)> 550 MPa.
• f) P ₁ : K _{IC (LT)} > 39 MPa√m and P ₂ : R _m (L)> 580 MPa and P ₂ : R _p0.2 (L)> 550 MPa,
• i) P ₁ : K _{IC (LT)} > 39 MPa√m and P ₁ : R _m (L)> 530 MPa, and P ₂ : R _m (L)> 580 MPa.
• j) P ₁ : K _{IC (LT)} > 40 NTa√m and P ₁ : R _m (L)> 540 MPa, and P ₂ : R _m (L)> 590 MPa.
• k) P ₁ : K _{app (LT) (CCT406)} > 125 MPa√m and P2: R _m (L)> 590 MPa.

Yet another object of the present invention is an aircraft comprising at least one wing which integrates at least one structural element according to the present invention, characterized in that the segment P ₁ is located close to the fuselage, and the segment P ₂ close to the geometric end of the wing, opposite the fuselage.

Description of figures

The figure 1 schematically shows the evolution of the static mechanical properties (curve 1), for example the tensile or compressive strength, and dynamic (curve 2), for example the damage tolerance, in the length of a panel of wing according to the invention.
The figure 2 shows the mechanical strength in a structural element with a length of 34 meters according to the invention.

Description of the invention a) Terminology

Unless stated otherwise, all the information relating to the chemical composition of the alloys is expressed in percent by weight. Therefore, in a mathematical expression, "0.4 Zn" means: 0.4 times the zinc content, expressed in mass percent; this applies mutatis mutandis to other chemical elements. The designation of the alloys follows the rules of The Aluminum Association, known to the skilled person. The metallurgical states are defined in the European standard EN 515. The chemical composition of standardized aluminum alloys is defined for example in the standard EN 573-3. Unless otherwise stated, the static mechanical characteristics, ie the breaking strength R _m , the yield _stress R _p0,2, and the elongation at break A, are determined by a tensile test according to EN 10002-1 standard, the location and direction of specimen collection being defined in EN 485-1. The tenacity K _IC was measured according to the ASTM E 399 standard. The curve R is determined according to ASTM standard 561. From the curve R, the critical stress intensity factor K _C is calculated, that is to say the intensity factor that causes the instability of the crack. The stress intensity factor K _{CO is} also calculated by assigning to the critical load the initial length of the crack at the beginning of the monotonic loading. These two values are calculated for a specimen of the desired shape. K _app denotes the K _CO corresponding to the test piece used to perform the R curve test. The resistance to exfoliating corrosion was determined according to the EXCO test described in the ASTM G34 standard.
Unless otherwise specified, the definitions of the standard European EN 12258-1 apply. The term "sheet metal" is used here for rolled products of any thickness.

The term "machining" includes any material removal process such as turning, milling, drilling, reaming, tapping, EDM, grinding, polishing, chemical machining.
The term "spun product" also includes products that have been drawn after spinning, for example by cold drawing through a die. It also includes drawn products.
The term "structural element" refers to an element used in mechanical engineering for which the static and / or dynamic mechanical characteristics are of particular importance for the performance and integrity of the structure, and for which a calculation of the structure is usually prescribed or performed. It is typically a mechanical part whose failure is likely to endanger the safety of said construction, its users, its users or others.

For an aircraft, these structural elements include the elements that make up the fuselage (such as fuselage skin (fuselage skin in English), stiffeners or stringers, bulkheads, fuselage (circumferential frames), wings (such as wing skin), stiffeners (stiffeners), ribs (ribs) and spars) and empennage including horizontal stabilizers and vertical stabilizers horizontal or vertical stabilizers, as well as floor beams, seat tracks and doors.

The term "monolithic structural element" refers to a structural element which has been obtained from a single piece of semi-finished product, rolled, forged or molded, without assembly, such as riveting, welding, gluing, with another room.

b) Detailed description of the invention

According to the invention, the problem is solved by a method in which in an oven which preferably has an internal length greater than the length of the workpiece, the temperature is kept substantially constant over at least two furnace zones of a furnace. length of at least one meter. Such a temperature profile can be obtained by subdividing the oven along its length into several thermal zones.

The invention is applicable to all long metal products, that is to say having a dimension (called length) significantly larger than the other two (width, thickness). The length is the largest dimension of the product. Typically, in the context of the present invention, the length is at least twice as large as the other two dimensions. In particularly advantageous embodiments, it is five or even ten times larger than the other two dimensions. It usually coincides with the long direction of manufacture (rolling or spinning direction); in some cases, it may be different. The products according to the invention may be rolled products (such as sheets or plates), spun products (such as bars, tubes or profiles), forged products; these products can be raw or machined.

The term "extreme property segments" of a product is understood to mean the two segments showing the greatest difference in properties. Depending on the embodiments chosen, these segments may be close to the two "geometric ends" (or "geometrical ends") of the product, or elsewhere: the present invention also makes it possible to manufacture parts in which at least one of the two segments showing the greatest difference in properties are closer to the geometric medium than to the geometrical end of the part.

Here the term "zone" of an oven means the smallest thermal unit over the length of the oven characterized by a substantially constant temperature, that is to say by a temperature variation parallel to the axis of the oven which is low. compared to the temperature difference that characterizes the temperature profile of the oven over its entire length. Such an oven zone is characterized by heating and control means which make it possible to maintain the temperature at a substantially constant value within said zone. Within such an area, the variation of the temperature around the set temperature must not exceed ± 5 ° C, and preferably does not exceed. ± 4 ° C. In a preferred embodiment, this difference does not exceed ± 3 ° C. For some products, the difference should not exceed ± 2 ° C. In other directions of the oven, the temperature should be as constant as possible. In any case, the variation of the temperature around the set temperature inside a zone must be lower than the temperature difference between the hottest oven zone and the coldest oven zone. .

Several contiguous zones can form a "zone group", that is, a thermal unit within which the temperature is substantially constant, or follows a controlled thermal profile. For example, in a furnace comprising 9 furnace zones (numbered from 1 to 9), two groups of thermal zones can be formed, each comprising three furnace zones (having the successive numbers 1, 2, 3, 7, 8 and 9), separated by a central zone group comprising a controlled thermal profile and obtained via three oven zones (bearing the successive numbers 4, 5 and 6). As the term "zone group" is used in the context of this patent, a group of zones may have only one oven zone.

According to the findings of the applicant, the minimum temperature difference that leads to differences in industrially exploitable properties between two segments with extreme properties of the product according to the invention is five degrees. A difference of at least ten degrees is preferred. The difference in temperature can be much greater, up to 80 ° C, or even up to 100 ° C, or even more, but this can cause problems of temperature control and its profile parallel to the axis of the oven, and this especially in the case of relatively small parts. If one wants to obtain returned states, the difference in temperature will not exceed typically fifty degrees. A temperature difference greater than fifty degrees can advantageously be used to manufacture a part of which one of the segments with extreme properties is in a state close to a state T3 or T4. For alloys of Al-Zn-Cu-Mg type (series 7xxx), a relatively small temperature difference (for example between ten and about thirty degrees) makes it possible to obtain exploitable effects for parts that can be used in aeronautical construction, while for alloys of the Al-Cu type (2xxx series), a greater temperature difference is advantageously used, for example between fifty and one hundred degrees, or even more.

The Applicant has found that it is not only the temperature difference between two segments with extreme properties that counts, but also the temperature control between the segments with extreme properties. Therefore, an oven having a plurality of contiguous furnace zones is used in the present invention. By plurality is meant at least two, and preferably at least three furnace zones. A partition between two contiguous zones, as proposed in the patent EP 0 630 986 , is neither necessary nor useful. It does not allow to exercise sufficient control over the temperature between two zones. Similarly, the use of a heat pump that connects the cold room to the hot room, as proposed in EP 0 630 986 , makes the thermal profile inside the oven too unstable. In the context of the present invention, a good control of the thermal profile inside the furnace is essential to be able to manufacture structural elements in a manner compatible with the requirements of quality assurance of aeronautical products.

For this purpose, it is necessary to be able to control, and preferable to adjust, the temperature in each oven zone. In an advantageous embodiment of the present invention, the furnace comprises at least three furnace zones with a unit length of at least one meter. For example, to manufacture structural elements of a length of about thirty-four meters, the inventors use a furnace with a total length of thirty-six meters with thirty oven zones of substantially identical length, adjustable independently of each other. Advantageously, these thirty furnace zones are grouped so as to form a reduced number of groups of thermal zones, for example three to five.

The method according to the invention comprises the preparation of a corrected piece of aluminum alloy with a hardening, a dissolution, quenching, possibly traction with a permanent elongation of at least 0.5%, a treatment of income in a controlled thermal profile oven. Said tempering treatment in a thermal profile furnace may comprise, for at least one of the groups of thermal zones that make up the controlled thermal profile, one or more, typically two or three, temperature stages, or a more or less continuous ramp of no net temperature. Optionally, the tempering treatment in the controlled thermal profile oven is preceded or followed by another step of treatment of income in a homogeneous oven (which can be the same oven, adjusted so as to obtain a uniform temperature in all its zones , or another oven). Such a final homogenous furnace income is particularly useful when aiming to obtain a state suitable for an income shaping operation; in this case, the homogeneous final income allows the formation of income. In addition, a room may incur an income in the controlled thermal gradient oven, then at least one shaping or machining operation, and then a treatment step in a homogeneous oven.

• a) P₁ : K_IC(L-T) > 38 MPa√m et P₂ : R_m(L) > 580 MPa
  (et préférentiellement > 590 MPa, et encore plus préférentiellement > 600 MPa).
• b) P₁ : K_IC(L-T) > 40 MPa√m et P₂ : R_m(L) > 580 MPa
  (et préférentiellement > 590 MPa).
• c) P₁ : K_IC(L-T) > 41 MPa√m et P₂ : R_m(L) > 580 MPa
  (et préférentiellement > 590 MPa).
• d) P₁ : K_IC(L-T) > 42 MPa√m et P₂ : R_m(L) > 590 MPa.
• e) P₁ : K_IC(L-T) > 39 MPa√m et P₂ : R_m(L) > 580 MPa et P₂ : R_m(TL) > 550 MPa.
• f) P₁ : K_IC(L-T)> 39 MPa√m et P₂ : R_m(L) > 580 MPa et P₂ : R_p0,2(L) > 550 MPa,
• i) P₁ : K_IC(L-T) > 39 NPa√m et P₁ : R_m(L) > 530 MPa, et P₂ : R_m(L) > 580 MPa.
• j) P₁ : K_IC(L-T) > 40 MPa√m et P₁ : R_m(L) > 540 MPa, et P₂ : R_m(L) > 590 MPa.
• k) P₁ : K_{app(L-T)(CCT406)} > 125 MPa√m et P2 : R_m(L) > 590 MPa.

The invention makes it possible to produce a structurally hardened aluminum alloy monolithic structure element having a length L greater than the width B and the thickness E, in particular for aircraft construction, said element having a monolithic structure being characterized in that at least two segments P ₁ and P ₂ located on a different length of said structural element have physical properties (measured at mid-thickness) selected from the group consisting of:

• a) P ₁ : K _{IC (LT)} > 38 MPa√m and P ₂ : R _m (L)> 580 MPa
  (and preferentially> 590 MPa, and even more preferentially> 600 MPa).
• b) P ₁ : K _{IC (LT)} > 40 MPa√m and P ₂ : R _m (L)> 580 MPa
  (and preferentially> 590 MPa).
• c) P ₁ : K _{IC (LT)} > 41 MPa√m and P ₂ : R _m (L)> 580 MPa
  (and preferentially> 590 MPa).
• d) P ₁ : K _{IC (LT)} > 42 MPa√m and P ₂ : R _m (L)> 590 MPa.
• e) P ₁ : K _{IC (LT)} > 39 MPa√m and P ₂ : R _m (L)> 580 MPa and P ₂ : R _m (TL)> 550 MPa.
• f) P ₁ : K _{IC (LT)} > 39 MPa√m and P ₂ : R _m (L)> 580 MPa and P ₂ : R _p0.2 (L)> 550 MPa,
• i) P ₁ : K _{IC (LT)} > 39 NPa√m and P ₁ : R _m (L)> 530 MPa, and P ₂ : R _m (L)> 580 MPa.
• j) P ₁ : K _{IC (LT)} > 40 MPa√m and P ₁ : R _m (L)> 540 MPa, and P ₂ : R _m (L)> 590 MPa.
• k) P ₁ : K _{app (LT) (CCT406)} > 125 MPa√m and P2: R _m (L)> 590 MPa.

1. a) R_p0.2, mesuré dans le sens L ou dans le sens LT, présente un écart R_p0.2(P2) - R_p0._2(P1) d'au moins 50 MPa et préférentiellement au moins > 75 MPa, et / ou
2. b) R_p0.2, mesuré dans le sens TC, présente un écart R_p0.2(P2) - R_p0.2(P1) d'au moins 30 MPa et préférentiellement d'au moins 50 MPa, et / ou
3. c) K_IC, mesuré dans le sens L-T, présente un écart K_IC(P1) - K_IC(P2) d'au moins 5 MPa√m et préférentiellement d'au moins 7 MPa√m, et / ou
4. d) K_app, mesuré dans le sens L-T, présente un écart K_app(P1) - K_app(P2) d'au moins 10 MPa√m et préférentiellement d'au moins 15 MPa√m.

It is preferred that the process be conducted in such a way that the elongation at break A _(L) is greater than 9%, and preferably> 10%, in the P ₁ and P ₂ segments. This is advantageous especially when the parts must undergo formatting operations after income. Likewise, it is preferable for A (L) to be greater than 9% outside these P ₁ and P ₂ segments. Semi-finished products characterized in that they have two segments P ₁ and P ₂ in which (measured at mid-thickness) can be obtained

1. a) R _p0.2 , measured in direction L or in direction LT, has a deviation R _{p0.2 (P2)} - R _p0 . _{2 (P1)} of at least 50 MPa and preferably at least> 75 MPa, and / or
2. b) R _p0.2 , measured in the TC direction, has a deviation R _{p0.2 (P2)} -R _{p0.2 (P1)} of at least 30 MPa and preferably at least 50 MPa, and / or
3. c) K _IC , measured in the LT direction, has a difference K _{IC (P1)} -K _{IC (P2)} of at least 5 MPa√m and preferably at least 7 MPa√m, and / or
4. d) K _app , measured in the LT direction, has a K _{app (P1)} - K _{app (P2) difference} of at least 10 MPa√m and preferably at least 15 MPa√m.

The process according to the invention can be used to form semi-finished products of any structurally hardened alloy, such as 2xxx, 4xxx, 6xxx and 7xxx series aluminum alloys, as well as 8xxx series hardening alloys. containing lithium.

The method according to the invention can, in the case of Al-Zn-Cu-Mg alloys (series 7xxx), be used to have one of the segments with extreme properties in a state close to T6, and another segment with properties extremes close to T74 or T73.
In alloys of the 2xxx series, the 6xxx series as well as in the 8xxx series alloys which contain lithium, the method according to the invention can be used to obtain on one of the segments with extreme properties a state close to T3 or T4, and on the other segment with extreme properties a state close to T6 or T8.

In an advantageous embodiment of the invention, the alloy comprises between 6 and 15% of zinc, between 1 and 3% of copper and between 1.5 and 3.5% of magnesium. In other advantageous embodiments, the zinc content is at least 7%, and is preferably between 8 and 13%, and even more preferably between 8.5 and 11%. The copper content is advantageously between 1.3 and 2.1%, and the magnesium content between 1.8 and 2.7%. These alloys, including 7449, 7349 and 7056, make it possible to obtain both a very high mechanical strength (for example in the T651 or T7951 state) and a very high toughness (for example in the T76 state, T7651 or T74, or in the T7451, T73 or T7351 state), while maintaining in the two states corresponding to the two extreme property segments of the product, as well as in the intermediate zones, a compromise between acceptable strength and toughness and resistance to exfoliating corrosion (EXCO test) maintained at a good level (EA).

• Une première étape homogène à une température comprise entre 115°C et 125°C pour une durée comprise entre 2 et 12 heures,
• une deuxième étape pendant laquelle un segment ou une extrémité géométrique est traité à une température comprise entre 115°C et 125°C, alors qu'un autre segment ou l'autre extrémité est traité à une température comprise entre 150°C et 160°C, les deux pour une durée comprise entre 8 et 24 heures.

Ce revenu convient notamment aux produits en alliage 7xxx, et notamment en alliage 7349, 7449 ou 7056.In an advantageous embodiment of the present invention, it is carried out on a sheet metal, a profiled or a piece of forging put in solution, tempered and tractionned, a revenue in two steps:

• A first homogeneous step at a temperature of between 115 ° C. and 125 ° C. for a duration of between 2 and 12 hours,
• a second step during which a segment or a geometric end is treated at a temperature between 115 ° C and 125 ° C, while another segment or the other end is treated at a temperature between 150 ° C and 160 ° C, both for a period of between 8 and 24 hours.

This income is particularly suitable for 7xxx alloy products, including 7349, 7449 or 7056 alloys.

In another advantageous embodiment of the present invention, a product made of 2xxx alloy (such as 2024 or 2023) on one segment or a geometrical end (P ₁ ) is tempered at about 120 ° C, and on another segment or the other geometric end (P ₂ ) a peak income of mechanical strength (T851 state) at about 190 ° C. In a variant of this embodiment, the segment or geometric end that is not worn at the peak of mechanical strength (ie P ₁ ) is tempered at about 100 ° C (or 80 ° C); it is an under-income state.

In another advantageous embodiment, on a 7xxx alloy product (such as 7349, 7449 or 7056), on a segment or a geometrical end, an income at peak strength (state T651) at about 120 ° C. is carried out. and on another segment or the other geometric end an overflow (state T7651, T7451 or T7351) in two stages at 120 ° C and 150 ° C - 165 ° C.

In yet another advantageous embodiment, a 6xxx alloy product (such as 6056 or 6156) is made on a segment or a geometrical end. returned to the peak of mechanical strength (T651 state) at about 190 ° C, and on another segment or the other end geometric over-income (T7851 state) in two stages.

The metal parts obtained by the process according to the invention can be used as a structural element in the aeronautical construction. These structural elements can be bi-functional or multi-functional, that is to say, bring together in a single piece of monolithic different functionalities that the methods according to the prior art could only bring together the assembly of different parts. These structural elements may also allow a simpler and lighter construction and manufacture of aircraft, particularly aircraft of very large cargo or passenger capacity.

A specific advantage of the process according to the invention is that in each segment with extreme properties, the optimal properties targeted in a well-controlled length of the product are obtained. The designer of the aircraft knows exactly how long the product will have the optimal properties recommended and guaranteed. In a particularly preferred embodiment, the method according to the invention is used to manufacture structural elements which do not have a continuous variation of properties over their entire length, but which have at least two zones in which the mechanical properties ( or some of them) are constant over a certain length of the product. In an advantageous embodiment of the invention, this zone has a length of at least one meter, and preferably at least two meters. Such a product, as well as its use as a structural element in an aircraft wing, is schematically shown on the figure 1 .

Another specific advantage of the method according to the invention is the precise control of the properties in the transition segment P _1,2 between two groups of segments P ₁ and P ₂ (there may be two or more, depending on the number of groups of thermal zones), P ₁ and P ₂ being segments with extreme properties. Indeed, the designer of the aircraft does not need, in the transition segment, maximum properties for one or other of the properties (or groups of properties) to be optimized, for example the breaking strength. in the long direction R _{m (L)} and the toughness K _{IC (LT)} . But it does require a certain compromise between these properties or groups of properties, because in this transition segment, the structural element plays a structural role and must meet precise specifications.

• des panneaux de voilure (en anglais : upper (top) or lower (bottom) wing (skin) panels) ;
• des raidisseurs de voilure (en anglais : upper or lower wing stringers)
• des longerons de voilure (en anglais : wing spars) ;
• des lissesde fuselage (en anglais : fuselage stiffeners) ;
• des panneaux de jonction (en anglais : butt straps), notamment pour des panneaux de voilure (upper and lower wing butt straps) ;
• des panneaux de fuselage (en anglais : fuselage panels).

The structural elements according to the invention are in particular:

• wing panels (in English: upper (top) or lower (bottom) wing (skin) panels);
• wing stiffeners (in English: upper or lower wing stringers)
• wing spars (in English: wing spars);
• fuselage beams (in English: fuselage stiffeners);
• butt straps, especially for upper and lower wing butt straps;
• fuselage panels (in English: fuselage panels).

The method according to the invention makes it possible to heat-treat long structural parts or elements. Most often, their section perpendicular to the length is substantially constant along their length, but it may be otherwise. Similarly, the parts can be straight or not; for example, slightly curved forged structural elements can be processed. The method could be used also for processing molded parts, but long molded parts are very rare and difficult to manufacture. In a preferred embodiment, the length of the piece is at least 5 meters or better still at least 7 meters, but a length of at least 15 meters or even at least 25 meters is preferred to take full advantage of possibilities to create several functionalized segments distributed over the length of the room. Structural elements with at least two segments P ₁ and P _{2 have thus been produced} in which the length F _P1 and F _P2 (expressed as a percentage of the total length of the workpiece L) of the at least two segments P ₁ and P ₂ is such that F _P1 > 25% and F _P2 > 25% and preferably F _P1 > 30% and F _P2 > 30%. In other embodiments, F _P1 > 35% and F _P2 > 30%, or F _P1 > 40% and F _P2 > 30%.

Structural elements according to the invention can be advantageously used in aeronautical construction. By way of example, it is possible to construct a large-capacity airplane comprising at least one wing comprising at least one structural element according to the invention, characterized in that the segment P ₁ is located close to the fuselage, and the segment P ₂ close to the geometrical end of the wing (see figure 1 ). In an advantageous embodiment, said wing panels have a length of at least 15 meters, and preferably at least 25 meters. As described in the example below, the inventors made wing panels more than 30 meters long.

Said parts and structural elements may be monolithic. The method according to the invention also makes it possible to heat-treat parts or structural elements that are not monolithic but assembled from at least two rolled or forged pieces or semi-finished products (preferably in hardening aluminum alloys). structural), for example by welding, riveting or gluing. It is also conceivable that in such an assembly, one or more of the parts are made from a base material that is not an aluminum alloy.

In this embodiment, it is possible for example to first manufacture an assembly between at least one sheet of structural hardening aluminum alloy and at least one structural hardening aluminum alloy section by riveting, welding or gluing, said assembly being subsequently treated by the process according to the invention. In an advantageous embodiment of this variant of the method according to the invention, the sheets and profiles are in the T351 state, and the assembly is performed by laser welding (Laser Beam Welding, LBW), friction welding (Friction Stir Welding, FSW) or Electron Beam Welding (EBW). The Applicant has found that it may be preferable to treat such a welded assembly after welding by the method according to the invention, instead of treating the semi-finished products (sheets and profiles) intended to constitute said assembly before welding, because an improvement in the mechanical strength and the corrosion resistance of the welded joint is obtained. This effect is significant when the welded joint is spread over a large length of the structural element (for example substantially parallel to the long direction of the product).

The invention will be better understood with the aid of the following example, which however does not have a limiting character.

Example:

A sheet 36 meters long, 2.5 meters wide and 30 mm thick was manufactured by hot rolling a rolling plate.
The composition of the alloy was:
Zn 9.1%, Mg 1.89%, Cu 1.57%, Fe 0.06%, Si 0.03%, Ti 0.03%, Zr 0.11%,
other items <0.01 each.
The rolling plate was homogenized for 14 hours at 475 ° C. The inlet temperature to the hot mill was 428 ° C, the outlet temperature of the hot rolled sheet was 401 ° C. The sheet was put into solution, quenched and quenched under the following conditions: hold for 6 hours at 471 ° C, quench in water at a temperature between about 15 and 16 ° C, then controlled pull with permanent elongation about 2.5% The sheet was trimmed to give a sheet of 34 meters long. It was positioned in length in an oven consisting of 30 zones with a unit length of 1200 mm. For all tempering temperatures, the variation around the setpoint did not exceed ± 3 ° C.

The treatment of income consisted of a first step of homogeneous treatment at 120 ° C for 6 hours ("first step"), immediately followed by a second step during which a geometric end of 18 meters (called Z ₁ , corresponding to 15 furnace zones) was treated for 15 hours at 155 ° C ("second stage", preceded by an adjustment period of about 1 hour), while the other geometric end of 10.8 meters (called Z ₂ , corresponding to 9 furnace zones) was maintained for 16 hours at 120 ° C. The transition zone between these two ends corresponded to 7.2 meters (called Z _1.2 , corresponding to 6 furnace zones).

• Segment P₁ : comprise entre 18,2 et 19,5 MS/m.
• Segment P₂ : comprise entre 22,5 et 23,5 MS/m
• Segment P_1,2 : comprise entre 18,2 et 23,6 MS/m

After this second step, the electrical conductivity of the sheet was measured in different places:

• Segment P ₁ : between 18.2 and 19.5 MS / m.
• P ₂ segment: between 22.5 and 23.5 MS / m
• Segment P _1.2 : between 18.2 and 23.6 MS / m

Then, the sheet was subjected to a third step of income, namely a homogeneous income consisting of a rise in temperature at 148 ° C for 1:30, followed by maintenance at 150 ° C for 15h hours. This third step was intended to simulate an income shaping operation or income after shaping the structural element.

The sheet has been cut and characterized. Table 1 summarizes the static mechanical characteristics obtained by a tensile test. These are averages obtained from measurements made at mid-thickness and at different locations spread across the width of the sheet. There was no significant variation in properties in the width of the sheet. It should be noted that for R _p0.2 in the L and TL directions, the values were also measured by a compression test; they are shown in Table 1 in parentheses. Table 1 Position [mm] in the length of a 34 m panel L sense (long) TL direction TC sense (Through-long) (Through-short) R _m R _p0,2 AT R _m R _p0,2 AT R _m R _p0,2 AT [MPa] [MPa] [%] [MPa] [MPa] [%] [MPa] [MPa] [%] 0 (P ₁ ) 561 517 13.5 550 506 12.5 550 495 8.5 (509) (519) 13600 (P ₁ ) 565 522 13.5 553 511 12.5 548 502 8.5 (513) (528) 16000 (P ₁ ) 556 509 13.5 547 501 12.5 540 500 8.5 (500) (514) 18400 (P _1.2 ) 566 523 13.5 559 519 12.5 546 498 7.5 (527) (538) 20800 (P _1.2 ) 612 587 12.0 598 575 11.5 590 545 7.0 (573) (593) 25600 (P ₂ ) 621 598 12.5 607 585 11.5 595 554 6.5 (590) (605) 34000 (P ₂ ) 624 602 12.1 608 586 11.5 599 558 6.1 (594) (607)

The K _IC and K _app toughness results (the latter obtained with a CT127 type specimen and with a CCT406 type specimen) are shown in Table 2. Table 2 Position [mm] in the length of a 34 m panel K _IC (LT) K _IC (TL) K _app (LT) I _app (LT) [MPa m] [MPa m] (CT127) (CCT406) [MPa m] [MPa m] 0 (P ₁ ) 43.8 36.1 106 132 13600 (P ₁ ) 45.8 38.1 108 - 16000 (P ₁ ) 46.7 37.3 99 - 18400 (P _1.2 ) 43, 0 34.2 102 - 20800 (P _1.2 ) 39.4 32.9 88 - 25600 (P ₂ ) 36.1 34.9 89 34000 (P ₂ ) 34.9 29.1 94 110

Such a sheet of 34 meters length can be used as a wing panel for cargo or passenger planes of very large capacity. For this use, the geometric end X of the sheet (corresponds to high K _IC toughness, the static mechanical resistance being lower) is positioned on the fuselage side, and the geometric end Z of the sheet (corresponds to a high static mechanical resistance , toughness K _IC being lower) corresponds to the geometrical end of the wing.

The set-point, sheet and air temperatures in the furnace zones for the second tempering stage are shown in Table 3. The temperature profile is shown during the tempering step at 120 ° C. and 155 ° C. ° C in the stationary thermal state. The temperature of the sheet was measured using forty thermocouples; the values given in Table 3 were measured at mid-width. Table 3 Oven area Set temperature [° C] Sheet temperature [° C] Air temperature [° C] 1 120 3 120 120.5 6 120 120.8 120.8 9 120 124.4 124.3 10 123 125.9 126.7 11 129 129.9 129.7 14 147 147.7 148.3 16 155 157.2 156.6 17 155 156.8 156.6 18 155 155.3 154.9 22 155 155.1 154.8 30 155

Claims (27)

1. Process for manufacturing an aluminium alloy part with structural hardening, comprising:

   a) solution heat treatment of a semi-finished rolled, extruded or forged product, followed by quenching,

   b) possibly controlled tension with permanent elongation of at least 0.5%,

   c) annealing treatment,

   characterised in that at least one step of the said annealing treatment is conducted in a furnace with a controlled temperature profile comprising at least two zones or groups of zones Z₁, Z₂ with initial temperatures T₁ and T₂ in which the temperature variation around the set temperature for each of the temperatures T₁ and T₂ does not exceed ± 5°C within the length of the said zones or groups of zones, the difference between the set values of the initial temperatures T₁ and T₂ being greater than or equal to. 5°C, and the said zones or groups of zones possibly being separated by a zone or a group of zones Z_1,2. called the transition group, within which the initial temperature varies from T₁ to T₂,
   and characterised in that the length parallel to the axis of the furnace of each of the said at least two zones or groups of zones Z₁ and Z₂ is at least one meter.
2. Process according to claim 1, wherein the temperature variation around the set temperature for each of the temperatures T₁ and T₂ does not exceed ± 4°C and even better ± 3°C within the length of the said at least two zones or groups of zones Z₁ and 2₂.
3. Process according to either claim 1 or 2, wherein the difference between the set temperatures T₁ and T₂ is between 10°C and 80°C, and preferably between 10°C and 50°C and even more preferably between 20 and 40 °C.
4. Process according to any one of claims 1 to 3, wherein the temperature in at least one of the zones or groups of zones Z₁ or Z₂ varies as a function of time according to at least two temperature plateaux, or according to a temperature ramp with no plateau.
5. Process according to any one of claims 1 to 4, wherein the said annealing treatment in a furnace with controlled temperature profile is followed by at least one forming or machining operation and an annealing treatment step in a homogeneous furnace.
6. Process according to any one of claims 1 to 5, wherein the said annealing treatment in a furnace with a controlled temperature profile is preceded by an annealing treatment step in a homogeneous furnace.
7. Process according to any one of claims 1 to 6, wherein the length of the part is at least 5 meters and preferably at least 7 meters, more preferably at least 15 meters and even more preferably at least 25 meters.
8. Process according to any one of claims 1 to 7, wherein the said aluminium alloy part with structural hardening is monolithic.
9. Process according to any one of claims 1 to 7, wherein said aluminium alloy part with structural hardening is assembled starting from at least two aluminium alloy parts with structural hardening.
10. Process according to claim 9, wherein assembly is made by riveting, bonding, laser beam welding, friction stir welding or electron beam welding.
11. Process according to any one of claims 1 to 10, wherein said annealing treatment comprises a first homogeneous step at a temperature between 115°C and 125°C for a duration of between 2 and 12 hours, a second step during which one end is treated at a temperature between 115°C and 125°C, while the other end is treated at a temperature between 150°C and 160°C, both for a duration of between 8 and 24 hours.
12. Monolithic structural member made of an aluminium alloy with structural hardening with a length L greater than its width B and thickness E, particularly for aeronautical construction,
    the said monolithic structural member being characterised in that at least two segments P₁ and P₂ of at least one meter located on a different length of the said structural member have physical properties (measured at mid-thickness) selected from the group formed of:

    a) P₁: K_IC(L-T) > 38 MPa√m and P₂: R_m(L) > 580 MPa
    (and preferably > 590 MPa and even better > 600 MPa

    b) P₁: K_IC(L-T) > 40 MPa√m and P₂: R_m(L) > 580 MPa
    (and preferably > 590 MPa)

    c) P₁: K_IC(L-T) > 41 MPa√m and P₂: R_m(L) > 580 MPa
    (and preferably > 590 MPa)

    d) P₁: K_IC(L-T) > 42 MPa√m and P₂: R_m(L) > 590 MPa

    e) P₁: K_IC(L-T) > 39 MPa√m and P₂: R_m(L) > 580 MPa
    and P₂: R_m(TL) > 550 MPa

    f) P₁: K_IC(L-T) > 39 MPa√m and P₂: R_m(L) > 580 MPa
    and P₂: R_p0.2(L) > 550 MPa

    i) P₁: K_IC(L-T) > 39 MPa√m and P₁: R_m(L) > 530 MPa, and P₂: Rm(L) > 580 MPa

    j) P₁: K_IC(L-T) > 40 MPa√m and P₁: R_m(L) > 540 MPa, and P₂: Rm(L) > 590 MPa

    k) P_{1 :} K_{app(L-T) (CCT406)} > 125 MPa√m and P2 _: R_m(L) > 590 MPa.
13. Structural member according to claim 12, wherein A_(L) > 9% (and preferably > 10%) in segments P₁ and P₂.
14. Structural member according to claim 13, characterised in that A_(L) > 9% outside segments P₁ and P₂.
15. Structural member according to claim 12, wherein the length F_P1 and F_P2 (expressed as a percent of the length L) of the said at least two segments P₁ and P₂ is such that F_P1 > 25% and F_P2 > 25% and preferably F_P1 > 30% and F_P2 > 30%.
16. Structural member according to claim 15, wherein F_P1 > 35% and F_P2 > 30%.
17. Structural member according to claim 16, wherein F_P1 > 40% and F_P2 > 30%.
18. Structural member according to one of claims 12 to 17, wherein the said alloy comprises between 6. and 15% of zinc, between 1 and 3% of copper and between 1.5 and 3.5% of magnesium.
19. Structural member according to claim 18, wherein the zinc content is higher than 7%.
20. Structural member according to claim 18, wherein the zinc content is between 8 and 13%, and preferentially between 8,5 and 11%.
21. Structural member according to claim 20, wherein the copper content is between 1.3 and 2.1%.
22. Structural member according to claim 21, wherein the magnesium content is between 1.8 and 2.7%.
23. Structural member according to any one of claims 12 to 22, wherein the length of the part is at least 7 meters, and preferably at least 15 meters, and even more preferably at least 25 meters.
24. Monolithic structural member according to claim 12, made of an aluminium alloy with structural hardening with a length L greater than its width B and thickness E, particularly for aeronautical construction,
    wherein said monolithic structural member is made of an Al-Cu type alloy and wherein it comprises at least two segments P₁ and P₂ located on a different length of the said structural member wherein one is in a T8 temper and the other is in an under-aged temper.
25. Monolithic structural member according to claim 12, made of an aluminium alloy with structural hardening with a length L greater than its width B and thickness E, particularly for aeronautical construction,
    said monolithic structural member being characterised in that it comprises two segments P₁ and P₂ wherein:

    a) R_p0.2, determined in the L direction or in the LT direction, has a difference p_0.2(P2) - R_p0.2(P1) of at least 50 MPa and preferably of at least > 75 MPa, and / or

    b) R_p0.2 determined in the ST direction, has a difference R_p0.2(P2) - R_p0.2(P1) of at least 30 MPa and preferably at least 50 MPa, and / or

    c) K_IC, measured in the L-T direction, has a difference K_IC(P1) - K_IC(P2) of at least 5 MPa√m and preferably of at least 7 MPa√m, and / or

    d) K_app, measured in the L-T direction, has a difference K_app(P1) - K_app(P2) of at least 10 Mpa√m and preferably of at least 15 MPa√m.
26. Use of a structural member according to any one of claims 12 to 25 for making an aircraft wing panel, wing stringers, wing spars, fuselage stiffeners, fuselage panels or butt straps.
27. Aircraft comprising at least one wing panel made from a structural member according to any one of claims 12 to 25, characterised in that segment P₁ is located close to the fuselage, and segment P₂ is close to the geometric tip of the wing.

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