WO2005098072A2

WO2005098072A2 - Structural element for aircraft engineering exhibiting a variation of performance characteristics

Info

Publication number: WO2005098072A2
Application number: PCT/FR2005/000681
Authority: WO
Inventors: Philippe Lequeu; David Dumont
Original assignee: Alcan Rhenalu
Priority date: 2004-03-23
Filing date: 2005-03-21
Publication date: 2005-10-20
Also published as: BRPI0507940B1; CN1930317A; EP1727921B1; CA2560672A1; BRPI0507940A; ES2307180T3; FR2868084A1; FR2868084B1; CN100507066C; WO2005098072A3; CA2560672C; DE602005006764D1; EP1727921A2; ATE395444T1

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 (Z1, Z2) at initial temperatures (T1, T2) in which the variation of each temperature T1, T2) 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 (Z1,2) 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 Z1 and Z2 is equal to or greater than 1 meter.

Description

STRUCTURAL ELEMENT FOR AERONAUTICAL CONSTRUCTION HAVING A VARIATION IN THE PROPERTIES OF USE

Technical field of the invention

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

State of the art

Very large aircraft present very specific construction problems. For example, the assembly of structural elements becomes more and more critical, on the one hand as a cost factor (riveting is a very expensive process), on the other hand as a generator of discontinuities in the properties of the assembled parts. To minimize the assemblies, structural elements can be prepared by integral machining in thick sheets; these structural elements can then integrate in a single piece (called monolithic) different functions such as the wing skin function and the stiffener function. It is also possible, and in parallel, to enlarge the dimension of the monolithic structural elements. This poses new problems in manufacturing these parts by rolling, spinning, forging or molding, since it is more difficult to guarantee homogeneous properties in very large parts. It has also been mentioned to prepare monolithic parts having a controlled variation in properties, which, in theory, makes it possible to better adapt the properties of the parts to the needs of the manufacturer. As such, patent EP 0 630 98-5 (Pechiney Rhenalu) describes a process for manufacturing sheets of al iminium alloy with structural hardening exhibiting a continuous variation in the properties of use, in which the final tempering is carried out in an oven of specific structure comprising a hot room and a cold room, connected by a heat pump. This process made it possible to obtain small parts with a length of about one meter of 7010 alloy, 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 posed by the field of aeronautical construction; these difficulties increase with the size of the pieces, knowing that it is particularly for very large pieces that the. designer would like to be able to integrate two or more functionalities through a continuous variation of the properties of use. Another problem posed by this method for the example described in the cited patent is that the optimal durations of. T651 and T7451 treatments are different. Yet another problem is that a product in 7010 in state T7451 is typically obtained by a two-stage income treatment, while the state T651 is obtained by a single-stage income treatment.

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

OBJECT OF THE INVENTION A first object of the present invention is a method of manufacturing an aluminum alloy part with structural hardening, comprising: a) dissolving a rolled, extruded or forged semi-finished product, followed by quenching, b) optionally controlled traction with a permanent elongation of at least 0.5%, c) tempering treatment, characterized in that at least one step of said tempering treatment is carried out in an oven with a thermally controlled profile in the length, said oven comprising at least two zones or groups of zones Zi, Z ₂ with initial temperatures Ti, T, in which the variation of the temperature around the set temperature of each of the temperatures T _\ and T ₂ does not exceed ± 5 ° C (preferably ± 4 ° C, and even more preferably ± 3 ° C) over the length of said zones or groups of zones, the difference between the set temperatures of the initial temperatures T 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, 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 to be transition within which or from which the initial temperature varies from Tι to T ₂ , and characterized in that the length parallel to the axis of the furnace of each of said at least two zones or groups of zones Z and Z ₂ is at least one meter (and preferably at least two meters).

A second object of the present invention is a monolithic structural element of aluminum alloy with structural hardening having a length L greater than the width B and the thickness E, in particular for aeronautical construction, said monolithic structural element being characterized in that at least two segments Pi and P ₂ located on a different length of said structural element have mechanical properties (measured at mid-thickness) selected from the group formed by: a) Pi: KI _C (-T)> 38 MPaVm and P ₂ : R _m (L)> 580 MPa (and preferably> 590 MPa, and even more preferably> 600 MPa). b) P,: KIC LT)> 40 MPa m and P ₂ : R _m (L)> 580 MPa (and preferably> 590 MPa). c) P _t : K _{IC (} LT)> 41 MPa m and P ₂ : R _m (L)> 580 MPa (and preferably> 590 MPa). d) Pi: K _{IC (} LT)> 42 MPa m and P ₂ : R _m (L)> 590 MPa. e) Pi: K _IC (L- _T )> 39 MPaVm and P ₂ : R _m (L)> 580 MPa and P ₂ : R _m (TL)> 550 MPa. f) Pi: K _{IC (L} - _T )> 39 MPaVm and P ₂ : R _m (L)> 580 MPa and P ₂ : R _p0 , 2 (L)> 550 MPa, i) Pi: K _IC (LT) > 39 MPa m and Pi: R _m (L)> 530 MPa, and P ₂ : R _m (L)> 580 MPa. j) Pi: K _IC (LT)> 40 MPaVm and P! : R _m (L)> 540 MPa, and P ₂ : R _m (L)> 590 MPa. k) PI: K _ap p (L-τ) (ccτ406)> 125 MPaVm and P2: R _m (L)> 590 MPa.

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

Description of the figures

Figure 1 shows schematically the evolution of static mechanical properties (curve 1), for example tensile or compressive strength, and dynamic (curve 2), for example damage tolerance, in the length of a wing panel according to the invention. 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 otherwise stated, all the indications relating to the chemical composition of the alloys are expressed in percent by mass. Consequently, in a mathematical expression, "0.4 Zn" means: 0.4 times the zinc content, expressed in percent by mass; this applies mutatis mutandis to other chemical elements. The designation of alloys follows the rules of The Aluminum Association, known from the skilled person. The metallurgical states are defined in European standard EN 515. The chemical composition of standardized aluminum alloys is defined for example in standard EN 573-3. Unless otherwise stated, the static mechanical characteristics, that is to say the tensile strength R _m , the elastic limit R _p o, _2> and the elongation at break A, are determined by a tensile test according to standard EN 10002-1, the place and direction of specimen collection being defined in standard EN 485-1. The tenacity Kic was measured according to standard ASTM E 399. The curve R is determined according to standard ASTM 561. From the curve R, the critical stress intensity factor Kc is calculated, ie the factor of intensity which causes the instability of the crack. One also calculates the stress intensity factor Kco _> by assigning to the critical load the initial length of the crack, at the beginning of the monotonous loading. These two values are calculated for a test piece of desired shape. K _app designates the Kco corresponding to the test piece which was used to perform the R curve test. The resistance to exfoliating corrosion was determined according to the EXCO test described in standard ASTM G34. Unless otherwise stated, the definitions of European standard 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 which 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 construction 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 generally prescribed or performed. It is typically a mechanical part, the failure of which is likely to endanger the safety of said construction, of its users, of its users or of others. For an aircraft, these structural elements include in particular the elements that make up the fuselage (such as the fuselage skin), the stiffeners or bulkheads, bulkheads, fuselage (circumferential frames), the wings (such as the wing skin), the stiffeners (stringers or stiffeners), the ribs (ribs) and spars (spars)) and the empennage composed in particular of horizontal and vertical stabilizers (horizontal or vertical stabilizers), as well as the floor profiles (floor beams), the seat rails (seat tracks) and the doors.

The term "monolithic structural element" refers to a structural element which has been obtained from a single piece of rolled, spun, forged or molded semi-finished product, without assembly, such as riveting, welding, bonding, 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 part to be treated, the temperature is kept substantially constant over at least two oven zones of a length of at least one meter. Such a temperature profile can be obtained by dividing 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). 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 manufacturing direction (rolling or spinning direction); in some cases it may be different. The products according to the invention can be laminated products (such as sheets or heavy plates), extruded products (such as bars, tubes or profiles), forged products; these products can be raw or manufactured.

The term “segments with extreme properties” of a product is understood here to mean the two segments showing the greatest difference in properties. Depending on the embodiments chosen, these segments may be located close to the two “geometric ends” (or “geometric 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 strongest difference in properties is closer to the geometric center than to the geometric end of the part.

The term "zone" of an oven is understood here to mean the smallest thermal unit over the length of the oven characterized by a substantially constant temperature, that is to say by a variation in temperature parallel to the axis of the oven which is small 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 inside said zone. Within such an area, the temperature variation 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 certain products, the difference must not exceed ± 2 ° C. In the other directions of the oven, the temperature should be as constant as possible. In any case, the temperature variation around the set temperature inside a zone must be less than the temperature difference between the hottest oven zone and the coldest oven zone. .

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

According to the Applicant's observations, the minimum temperature difference which 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 temperature difference can be much larger, up to 80 ° C, even up to 100 ° C, or even more, but this can cause problems with temperature control and its profile parallel to the axis of the oven, especially in the case of relatively small parts. If one wants to obtain returned states, the temperature difference will typically not exceed fifty degrees. A temperature difference greater than fifty degrees can advantageously be used to manufacture a part in which one of the segments with extreme properties is in a state close to a T3 or T4 state. For alloys of the Al-Zn-Cu-Mg type (7xxx series), a relatively small temperature difference (for example between ten and about thirty degrees) makes it possible to obtain exploitable effects for parts usable in aeronautical construction, while for Al-Cu type alloys (2xxx series), a larger 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 control of the temperature between the segments with extreme properties. This is why an oven is used in the present invention comprising a plurality of contiguous oven zones. By plurality is meant at least two, and preferably at least three oven zones. A partition between two contiguous zones, as proposed in patent EP 0 630 986, is neither necessary nor useful. It does not allow sufficient control over the temperature between two zones. Similarly, the use of a heat pump which 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, good control of the thermal profile inside the oven is essential in order to be able to manufacture structural elements in a manner compatible with the quality assurance requirements of aeronautical products.

For this purpose, it is necessary to be able to control, and preferably to be able to adjust, the temperature in each oven zone. In an advantageous embodiment of the present invention, the oven comprises at least three oven zones with a unit length of at least one meter. By way of example, to manufacture structural elements with a length of around thirty-four meters, the inventors use an oven with a total length of thirty-six meters with thirty oven zones of substantially identical length, adjustable independently of each other. Advantageously, these thirty oven 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 production of a wrought piece of aluminum alloy with structural hardening, dissolution, quenching, possibly traction with a permanent elongation of at least 0.5%, a tempering treatment in an oven with controlled thermal profile. Said tempering treatment in a thermal profile furnace may comprise, for at least one of the groups of thermal zones which make up the controlled thermal profile, one or more, typically two or three, temperature stages, or a more or less continuous ramp of temperature without net plateau. Optionally, the tempering treatment in the oven with controlled thermal profile is preceded or followed by another step of tempering treatment in a homogeneous oven (which can be the same oven, adjusted so as to obtain a homogeneous temperature in all its zones , or another oven). Such a final income in a homogeneous furnace is particularly useful when the aim is to obtain a state suitable for an income forming operation; the homogeneous final income in this case allows income training. Furthermore, a part can undergo tempering in the oven with controlled thermal gradient, then at least one shaping or machining operation, and then a tempering treatment step in a homogeneous oven.

The invention makes it possible to produce a monolithic structural element of aluminum alloy with structural hardening having a length L greater than the width B and the thickness E, in particular for aeronautical construction, said monolithic structural element being characterized in that '' at least two segments Pi and P ₂ located on a different length of said structural element have physical properties (measured at mid-thickness) selected from the group formed by: a) Pi: K _IC (LT)> 38 MPa m and P ₂ : R _m (L)> 580 MPa (and preferably> 590 MPa, and even more preferably> 600 MPa). b) Pi: K _IC LT)> 40 MPaVm and P ₂ : R _m (L)> 580 MPa (and preferably> 590 MPa). c) Pi: K _IC (L- _T) > 41 MPaVm and P ₂ : R _m (L)> 580 MPa (and preferably> 590 MPa). d) Pi: K _IC ( _L - _T )> 42 MPaVm and P ₂ : R _m (L)> 590 MPa. e) Pi: K _{IC (} LT ₎ > 39 MPaVm and P ₂ : R _m (L)> 580 MPa and P ₂ : R _m (TL)> 550 MPa. f) Pi: KI _C (LT)> 39 MPaVm and P ₂ : R _m (L)> 580 MPa and P ₂ : R _p0 , ₂ (L)> 550 MPa, i) Pi: K _IC ( _L - _T ) > 39 MPaVm and P _t : R _m (L)> 530 MPa, and P ₂ : R _m (L)> 580 MPa. j) Pi: K _{IC (L} -τ)> 40 MPaVm and P! : R _m (L)> 540 MPa, and P ₂ : R _m (L)> 590 MPa. k) PI: K _ap p (L-τ) (ccτ406)> 125 MPaVm and P2: R _m (L)> 590 MPa.

It is preferred that the process is carried out in such a way that the elongation at break A (D is greater than 9%, and preferably> 10%, in the segments Pj and P _2. This is advantageous in particular when the parts have to undergo shaping operations after tempering. Similarly, it is preferable that A (L) is greater than 9% outside these segments Pj and P _2. We can obtain semi-finished products characterized in that they have two segments? _\ and P ₂ in which (measured at mid-thickness) a) Rpo.2, measured in the L direction or in the LT direction, has a deviation R _p o. _{2 (} p ₂₎ - Rpo. ₂ ( _P i ₎ of at least 50 MPa and preferably at least> 75 MPa, and / or b) R o. ₂ . measured in the direction TC, has a deviation R _p0 . ₂ (p ₂ ) - R _p0 . ₂ (pi) of at least 30 MPa and preferably of at least 50 MPa, and / or c) Kic, measured in the direction LT, has a difference Kιc (pi) - Kιc ( _P2 ) of at least 5 MPaVm and preferably at least 7 MPaVm, and / or d) K _app , measured in the LT direction, has a difference K _app (p ₁₎ - K _app (p ₂₎ of at least 10 MPaVm and preferably at least minus 15 MPaVm.

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

The method according to the invention can, in the case of alloys of the Al-Zn-Cu-Mg type (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 state T74 or T73.

In the alloys of the 2xxx series, of the 6xxx series as well as in the alloys of the 8xxx series 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 resistance (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 state T7451, T73 or T7351), while maintaining in the two states corresponding to the two segments with extreme properties of the product, as well as in the intermediate zones, a compromise between acceptable mechanical strength and toughness and resistance to exfoliating corrosion (EXCO test) maintained at a good level (EA).

In an advantageous embodiment of the present invention, an annealing is carried out in two stages on a sheet, a section or a forged piece dissolved, quenched and drawn.

A first homogeneous step at a temperature between 115 ° C and 125 ° C for a period 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, and in particular alloy

7349, 7449 or 7056.

In another advantageous embodiment of the present invention, a 2xxx alloy product (such as 2024 or 2023) is carried out on a segment or a geometric end (P an income at approximately 120 ° C., and on another segment or the other geometric end (P) returns to the peak of mechanical resistance (state T851) at approximately 190 ° C. In a variant of this embodiment, the segment or the geometric end which is not brought to the peak of mechanical resistance (ie t?) undergoes an income at around 100 ° C (or 80 ° C); it is an under-income state.

In another advantageous embodiment, a 7xxx alloy product (such as 7349, 7449 or 7056) is applied to a segment or a geometric end with tempering at the peak of mechanical resistance (state T651) at approximately 120 ° C., and on another segment or the other geometric end an over-income (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 carried out on a segment or a geometric end with a returned to the peak of mechanical resistance (state T651) at around 190 ° C, and on another segment or the other geometric end an over-income (state T7851) in two stages.

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

A specific advantage of the process according to the invention is that in each segment with extreme properties, the optimum properties targeted are obtained in a well-controlled length of the product. The designer of the aircraft therefore 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 shown diagrammatically in FIG. 1. Another specific advantage of the method according to the invention is the precise control of the properties in the transition segment P _lι2 between two groups of segments Pi and P ₂ (there may be two or more, depending on the number of groups of thermal zones), Pi and P ₂ may be 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 sense R _m (L) and the toughness KIQL-T). But it nevertheless requires 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.

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); - junction panels (in English: butt straps), in particular for wing panels (upper and lower wing butt straps); - fuselage panels (in English: iuselage panels).

The method according to the invention makes it possible to heat treat long parts or structural elements. Most often, their cross section perpendicular to the length is substantially constant over their length, but it can be otherwise. Likewise, the pieces can be straight or not; one can for example treat slightly curved forged structural elements. The process could also be used to process 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 at least 7 meters, but we prefer a length of at least 15 meters, or even at least 25 meters, to take full advantage of the possibilities of creating several functionalized segments distributed over the length of the part. Structural elements have thus been produced with at least two segments Pi and P ₂ in which the length Fpi and Fp ₂ (expressed in percent of the total length of the part L) of said at least two segments Pj and P ₂ is such that Fpi> 25% and Fp ₂ > 25% and preferably Fpi> 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 used advantageously in aeronautical construction. By way of example, it is possible to construct a large capacity aircraft comprising at least one wing comprising at least one structural element according to the invention, characterized in that the segment Pi is located close to the fuselage, and the segment P ₂ close from 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 have produced wing panels of more than 30 meters in length.

Said parts and structural elements can be monolithic. The method according to the invention also makes it possible to heat treat parts or structural elements which are not monolithic but assembled from at least two parts or semi-finished products laminated, spun or forged (preferably made of hardened aluminum alloy 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 which is not an aluminum alloy.

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

The invention will be better understood using the following example, which however is not limiting.

Example:

A sheet metal with a length of 36 meters, a width of 2.5 meters and a thickness of 30 mm was produced by hot rolling of 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 elements <0.01 each.

The rolling plate was homogenized for 14 hours at 475 ° C. The inlet temperature to the hot rolling mill was 428 ° C, the outlet temperature from the hot rolled sheet was 401 ° C. The sheet was dissolved, quenched and fractionated under the following conditions: maintenance for 6 hours at 471 ° C, quenching in water at a temperature between about 15 and 16 ° C, then controlled traction with permanent elongation about 2.5% The sheet was trimmed to give a sheet 34 meters in length. It was positioned lengthwise 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 tempering treatment consisted of a first homogeneous treatment stage at 120 ° C for 6 hours ("first stage"), immediately followed by a second stage during which a geometric end of 18 meters (called Zi, corresponding to 15 oven zones) was treated for 15 hours at 155 ° C ("second stage", preceded by an adjustment period of approximately 1 hour), while the other geometric end of 10.8 meters (called Z ₂ , corresponding to 9 oven zones) was maintained for 16 hours at 120 ° C. The transition zone between these two ends corresponded to 7.2 meters (called Zι, ₂ , corresponding to 6 furnace zones). After this second step, the electrical conductivity of the sheet was measured at different locations: Pi segment: between 18.2 and 19.5 MS / m. P ₂ segment: between 22.5 and 23.5 MS / m P _{1> 2} segment: between 18.2 and 23.6 MS / m

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

The sheet was 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 distributed over the width of the sheet. No significant variation in properties was found in the width of the sheet. Note that for R _p o.2 in the L and TL directions, the values were also measured by a compression test; they are indicated in table 1 in brackets.

Table 1

The Kic toughness and K _{app results} (the latter obtained with a CT127 type test piece and with a CCT406 type test piece) are shown in Table 2.

Table 2

Such a sheet with a length of 34 meters can be used as a sail panel for cargo or passenger aircraft of very large capacity. For this use, the geometric end X of the sheet (corresponds to high KJC 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, the toughness Kic being lower) corresponds to the geometrical end of the wing.

The setpoint, sheet and air temperatures in the furnace zones for the second tempering step are shown in Table 3. The temperature profile during the tempering step at 120 ° C and 15 is shown. -5 ° C in 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

Claims

1. A method of manufacturing a part of a-luminium alloy with structural hardening, comprising: a) dissolving a rolled, spun or forged semi-finished product, followed by quenching, b) optionally controlled traction with a permanent elongation of at least 0.5%, c) the tempering treatment, characterized in that at least one step of said tempering treatment is carried out in an oven with controlled thermal profile comprising at least two zones or groups of zones Zi, Z ₂ with initial temperatures Ti, T ₂ , in which the variation of the temperature around the set temperature at which each of the temperatures Ti and T ₂ does not exceed ± 5 ° C over the length of the said zones or groups of zones, the difference between the set temperatures of the initial temperatures Ti and T ₂ being greater than or equal to 5 ° C., and said zones or groups of zones which can be separated by a zone or a group of zones Z _lι2 said to be transition to the inside which or from which the initial temperature varies from Ti to T ₂ , and characterized in that the length parallel to the axis of the linear furnace of each of said at least two zones or groups of zones Z \ and Z ₂ is at least minus one meter.

2. Method according to claim 1, in which the "variation of the temperature around the set temperature of each of the temperatures Ti and T ₂ does not exceed ± 4 ° C, and preferably ± 3 ° C over the length of said at least two zones or groups of zones Zi and Z ₂ .

3. Method according to claim 1 or 2, wherein the difference between the set temperatures Ti and T ₂ is between 10 ° C and 80 ° C, and preferably between 10 ° C and 50 ° C, and even more preferably between 20 ° C and 40 ° C.

4. Method according to any one of claims 1 to 3, wherein in at least one of the zones or one of the groups of zones Zi or Z ₂ , the temperature varies as a function of time according to at least two temperature levels, or according to a ramp temperature without bearing.

5. Method according to any one of claims 1 to 4, in which said tempering treatment in an oven with controlled thermal profile is followed by at least one shaping or machining operation and by a tempering treatment step. in a homogeneous oven.

6. Method according to any one of claims 1 to 5, wherein said tempering treatment in an oven with controlled thermal profile is preceded by a tempering treatment step in a homogeneous oven.

7. Method according to any one of claims 1 to 6, in which the length of the part is at least 5 meters, preferably at least 7 meters, more preferably at least 15 meters, and even more preferably greater than 25 meters.

8. Method according to any one of claims 1 to 7, wherein said piece of aluminum alloy with structural hardening is monolithic.

9. Method according to any one of claims 1 to 7, in which said part in structural curing aluminum alloy is assembled from at least two parts in structural curing aluminum alloy.

10. The method of claim 9, wherein the assembly is carried out by riveting, bonding, welding, laser welding, friction welding or electron beam welding.

11. Method according to any one of claims 1 to 10, wherein said tempering treatment comprises a first homogeneous step at a temperature between 115 ° C and 125 ° C for a period between 2 and 12 hours, a second step during which one end is treated at a temperature between 1 15 ° C and 125 ° C, while the other end is treated at a temperature between 150 ° C and 160 ° C, both for a period between 8 and 24 hours .

12. monolithic structural element of aluminum alloy with slxuctural hardening having a length L greater than the width B and the thickness E, in particular for aircraft construction, said monolithic structural element being characterized in that at least two segments Pi and P ₂ located on a different length of said structural element have physical and mechanical properties (measured at mid-thickness) selected from the group formed by: a) Pi: K _{1C (L} -τ)> 38 MPaVm and P ₂ : R _m (L)> 580 MPa (and preferably> 590 MPa, and even more preferably> 600 MPa). b) Pi: K _{IC (L} -τ)> 40 MPaVm and P ₂ : R _m (L)> 580 MPa (and preferably> 590 MPa). c) Pi: K _1C ( _L -τ)> 41 MPaVm and P ₂ : R _m (L)> 580 MPa (and preferably> 590 MPa). d) Pi: K _{IC (L} -τ)> 42 MPaVm and P ₂ : R _m (L)> 590 MPa. e) Pi: KIC ₍ -T)> 39 MPaVm and P ₂ : R _m (L)> 580 MPa and P ₂ : R _m (TL)> 550 MPa. f) Pi: KIC (LT)> 39 MPaVm and P ₂ : R _m (L)> 580 MPa and P2: R _p0 , ₂ (L)> 550 MPa, i) Pi: IC (LT)> 39 MPaVm and PI : R _m (L)> 530 MPa, and P ₂ : R _m (L)> 580 MPa. j) Pi: KIC (LT)> 40 MPaVm and Pi: R _m (L)> 540 MPa, and P ₂ : R _m (L)> 590 MPa. k) PI: K _{app (L} -τ) (ccτ406)> 125 MPaVm and P2: R _m (L)> 590 MPa.

13. Structural element according to claim 12, in which A ( _L )> 9% (and preferably> 10%) in the segments)? and P .

14. Structural element according to claim 13, characterized in that A (L)> 9% outside the segments? \ And P ₂ .

15. A structural element according to claim 12, in which the length F _P ι and F _P2 (expressed as a percentage of the length L) of said segments? Ι and P ₂ is such that F _PI > 25% and F _P2 > 25% and preferably F _P1 > 30% and F _P2 > 30%.

16. Structural element according to claim 15, in which F _P1 > 35% and F _P2 > 30%.

17. Structural element according to claim 16, in which F _P1 > 40% and F _P2 > 30%.

18. Structural element according to one of claims 12 to 17, wherein said alloy comprises between 6 and 15% of zinc, between 1 and 3% of copper and between 1.5 and 3 ₃ 5% of magnesium.

19. A structural element according to claim 18, in which the zinc content is greater than 7%.

20. Structural element according to claim 18, in which the zinc content is between 8 and 13%, and preferably between 8.5 and 11%.

21. A structural element according to claim 20, in which the copper content is between 1.3 and 2.1%.

22. Structural element according to claim 21, wherein the magnesium content is between 1.8% and 2.7%.

23. Structural element according to any one of claims 12 to 22, characterized in that its length L is at least 7 meters, preferably at least 15 meters, and even more preferably at least 25 meters.

24. Monolithic structural element of aluminum alloy with structural hardening having a length L greater than the width B and the thickness E, in particular for aircraft construction, said monolithic structural element being characterized in that it consists of '' an Al-Cu type alloy and in that it has at least two segments PI and P2 situated on a different length of said structural element, one of which is in a T8 state and the other in a sub state -returned.

25. Structural hardening aluminum alloy monolithic structural element having a length L greater than the width B and the thickness E, in particular for aircraft construction, said monolithic structural element being characterized in that they have two segments Pi and P ₂ in which a) R _p0 . , measured in the L direction or in the LT direction, has a difference R _{p0.2 (} p ₂₎ - R _P o.2 (Pi) of at least 50 MPa and preferably at least> 75 MPa, and / or b ) R _p0 . ₂ , measured in the TC direction, has a deviation R _p o.2 (P ₂ ) - Rpo.2 (Pi) of at least 30 MPa and preferably at least 50 MPa, and / or c) KJC, measured in the direction LT, presents a deviation Kiqpi) - Kιc ( _P 2) of at least 5 MPaVm and preferably of at least 7 MPaVm, and / or d) Ka _PP , measured in the direction of LT, presents a deviation K _{app (} pi ₎ - K _{app (} p ₂ ) of at least 10 MPaVm and preferably of at least 15 MPaVm.

26. Use of a structural element according to any one of claims 12 to 25 for the manufacture of an airplane wing panel, wing stiffeners, wing spars, fuselage beams, fuselage panels or junction panels.

27. Airplane comprising at least one wing made from a structural element according to any one of claims 12 to 25, characterized in that the segment Vι is located close to the fuselage, and the segment P ₂ close to the geometric end of the wing.