EP1965936A1

EP1965936A1 - Process for manufacturing semi-finished products comprising two aluminium-based alloys

Info

Publication number: EP1965936A1
Application number: EP06841935A
Authority: EP
Inventors: Philippe Lequeu; Benoît COMMET; Armelle Danielou; David Dumont; Olivier Ribaud
Original assignee: Alcan Rhenalu SAS
Current assignee: Constellium Issoire SAS
Priority date: 2005-12-16
Filing date: 2006-12-14
Publication date: 2008-09-10
Anticipated expiration: 2026-12-14
Also published as: EP1965936B1; CA2632999A1; WO2007080265A1; US20070259200A1; CN101330995B; FR2894857A1; CN101330995A; DE06841935T1; CA2632999C; FR2894857B1; US7938165B2

Abstract

The invention relates to a process for the vertical casting of an intermediate product, comprising step (a) of preparing at least two aluminium-based alloys, especially a first alloy of composition P and a second alloy of composition T; step (b) of casting the first alloy of composition P to a desired height HP; step (c) of casting an additional desired height HT of the second alloy of composition T. The invention makes it possible to manufacture monolithic structural elements having usage properties that vary in at least one direction, and especially bifunctional or multifunctional structural elements for fulfilling at least two functions that are conventionally fulfilled by two different parts.

Description

Process for producing semi-finished products comprising two aluminum-based alloys

Field of the invention

The invention relates to a new manufacturing method for aluminum-based structural elements comprising at least two different alloys, by casting a plate or billet comprising at least two spatially separated alloys, followed by one or more steps. hot processing by rolling, spinning, or forging, and optionally one or more cold processing steps, and intermediate and / or final heat treatments. The invention is particularly useful for the manufacture of structural elements for aircraft construction.

State of the art

Parts with variable mechanical characteristics in space are very attractive for mechanical engineering. Traditionally, they are obtained by assembling two pieces with different properties, but essentially homogeneous inside each room. The assembly can be carried out mechanically (for example by bolting or riveting), by gluing or by a suitable welding technique. It is thus possible to obtain bifunctional or multifunctional parts or structural elements. This bifunctionalization or multifunctionalization can come from the form of assembled parts (which is not the meaning we use here for these two terms) or can be linked to their mechanical properties, especially when two pieces of alloys are assembled. different. By way of example, transition seals are used in shipbuilding (see C. Vargel, Aluminum Corrosion, Paris 1998 (Dunod), page 136), which are structural elements usually assembled by means of explosion welding. from a steel piece and an aluminum piece. The steel side has the function to serve as a base for fixing other steel parts, while the aluminum side serves as a base for fixing other aluminum parts. These transition elements ₁ are therefore bi-functional structural elements that avoid galvanic corrosion that would inevitably settle in a humid environment between two dissimilar metals assembled in a traditional manner.

It is in the field of protection against corrosion and welding that we find other examples for multi-functional parts mainly based on aluminum. Indeed, it has long been used clad plates, having a core protected at least one side by an alloy coating more resistant to corrosion and / or more easily fusible, which serves either to protect the core against corrosion, to allow its easy welding on another part. Plates are obtained by placing on a rolling plate, preferably scalped, an alloy (said alloy core) of a first composition, a second rolling plate or a sheet, preferably scalped, of lower thickness. alloy (called plating alloy) of a second composition. Then, it is hot rolled and obtains a plated strip, the hot rolling providing a strong metallurgical bond between the two alloys. Plated sheets are monolithic pieces, within the meaning of the definition given below. They can be used in aircraft construction, for example as a fuselage coating, see for example US Patent 5,213,639 (Aluminum Company of America) or EP 1 170 118 (Pechiney RJtienalu). The plating process makes it possible to manufacture large pieces, but the variation of the chemical composition is in the thickness and not on the length or width of the piece. Thus, functionalization is quite limited: the desired function for plating is either protection against corrosion or weldability.

In another approach to the manufacture of a monolithic bi-functional part, is applied to each of the two ends of a long product in a single aluminum-based alloy a different income treatment. 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 in a principal direction of the product (length, width, thickness), in which the final income is made in one. structure oven specific 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 industrial difficulties increase with the size of the pieces. Moreover, by limiting itself to a piece in a single alloy, the amplitude of the variation of the mechanical properties over the length of the piece is found to be rather limited. A significant improvement of this process is described in the patent application (FR2868084), but this method also does not make it possible to modify the chemical composition of the alloy.

It is with two different aluminum alloys that one can hope to obtain a significant variation of the mechanical properties.

In the field of molding, the manufacture of monolithic parts comprising several alloys has been described. The international application WO 2005/063422 thus discloses a manufacturing method in which a casting mass formed by laminating alloys having a sufficiently different solidification range to prevent their mixing is introduced in the semi-solid state into a shell so as to fill it up and get a solidified molded product.

But the present inventors are not aware of wrought monolithic parts having two spatially separated alloys that are industrially manufactured by a process other than hot rolling plating. The idea of starting from raw shapes (i.e. castings, for example spinning billets, rolling plates) comprising two spatially separated alloys is not new. There are several approaches.

A first approach uses one or more fixed or mobile partitions. U.S. Patent 3,353,934 (Reynolds) discloses vertical casting of rolling plates or a billet with a fixed partition disposed vertically (i.e., along the length of the plate). This fixed partition is made of marinite, stainless steel or graphite. The patent describes the casting of the following pairs of alloys: 7075/6063, 7075/5052, 7075/5083. JP 485 411 70 (Sumitomo) discloses another method of vertical partitioning applied to a casting of plates. Another embodiment of a casting with vertical partition is described in patent application DE 44 20 697 (Institut fur Verformungskunde und Heuttenmaschinen). No. 6,705,384 (Alcoa, Inc.) proposes to use one or more partitions in the form of a thin or thick aluminum sheet which remains incorporated in the cast billet or billet. Pouring with partition has also been adapted to continuous casting between strips. Patents GB 1,174,764 and FR 1,505,826 (Glacier) describe the use of a moving partition applied to an interband casting for casting pairs of Al + 6% Sn / AS5G alloys.

A second approach uses the concept of the inner mold: a first alloy is solidified by an inner mold, and the solid shell thus formed serves as a mold for the second alloy. This concept is described in DE 844 806 (Wieland Werke). It is also possible to simply use a metal tube or a hollow billet as an outer shell, into which a liquid alloy is cast, as described in patent FR 1 516 456 (Kennecott Cooper Corporation). This principle has been adapted to the continuous vertical casting of plated plates in US Pat. No. 4,567,936 (Kaiser). The patent application WO 2004/112992 (Alcan) describes several methods for forming rolling plates comprising two vertical semi-continuous casting alloys using vertical separators. This process is particularly suitable for making plated rolling plates.

All these processes according to the state of the art lead to long cast products which comprise two different alloys separated by partitions or interfaces parallel to the direction of casting.

The problem that the present invention seeks to solve is to propose a new approach to the production of wrought monolithic structural elements having variable properties of use in at least one direction other than that of the thickness, and in particular of elements dual-functional or multifunctional structure wrought to perform at least two functions that are traditionally provided by two different parts. Object of the invention

The subject of the invention is a process for vertically casting an intermediate product of final height in the casting direction H _F , comprising the steps of

(a) preparing at least two alloys based on aluminum, in particular a first alloy of composition P and a second alloy of composition T,

(b) casting said first alloy of composition P to a desired height Hp,

(c) casting a desired additional height HT of said second alloy so as to achieve a cast height Hp + HT which is less than or equal to HF.

The alloy preparations in step (a) are not necessarily concomitant. The steps of preparation (a) and casting (b and c) are not necessarily successive, in particular the preparation of the second alloy or any additional alloy of step (a) may be concomitant with one or the other stages of casting. In an advantageous embodiment of the invention, steps (b) and (c) are performed without interruption of the flow of liquid metal. In this process, the preparation of the alloys can be carried out in different ways. For example, (i) the preparation of aluminum-based alloys can be carried out independently, or (ii) the preparation of alloys of different composition of P can be carried out from the first alloy during casting by adding to said first alloying the necessary quantities of elements to achieve the composition of the alloys of composition different from P ₅ or else (iii) the preparation of the at least two alloys based on aluminum can be carried out during casting from a aluminum alloy of composition B, adding to said alloy of composition B the necessary amounts of elements to achieve the composition of said at least two alloys based on aluminum P and T.

The invention also relates to a first solid intermediate product intended to be rolled, spun or forged, obtainable by the vertical casting method defined above. This product shows for at least one alloying element at least one concentration gradient in the direction of casting which is most often the direction of its height (ie of its greater dimension) This intermediate product may be for example a plate or a billet.

Another object of the invention is a method of producing a sheet, a profile or a forged part from a plate or a billet made according to the vertical casting process defined above. .

Yet another object of the invention is a second solid intermediate product such as a sheet, a profile or a forging piece that can be produced by the manufacturing method described above.

Yet another object of the present invention is a structural element capable of being manufactured from a second intermediate product as defined above. This structural element can be bi-functional or multifunctional.

Description of figures

Figure 1 schematically shows a spar according to the invention.

Figure 2 shows schematically a sheet, according to the invention, from which the spar according to the invention can be developed.

Figure 3 shows schematically a rolling plate according to the invention, from which the strong plate according to the invention can be developed.

Figure 4 shows a rolling pass in the direction perpendicular to the length of the plate.

Figure 5 shows schematically a fuselage panel according to the invention obtained by rolling perpendicular to the direction of casting.

Figure 6 shows the evolution in the direction of the height of the Zn content during casting according to the invention.

FIG. 7 shows conductivity measurements at mid-thickness and at different positions in the width direction for a sheet according to the invention laminated perpendicularly to the direction of casting. Description of the invention

a) Definitions

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 those skilled in the art. 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, that is the breaking strength R _m , the yield point R _p o, ₂ , and the elongation at break A, are determined by a tensile test according to the EN 10002-1 standard, the location and direction of sample collection being defined in EN 485-1 (rolled products) or EN 755-1 (extruded products). Kic toughness is measured according to ASTM E 399.

Unless otherwise stated, the definitions of the 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.

The term "casting plant" is used here to refer to all the devices making it possible to convert metals in any form into semifinished product by passing through the liquid phase. A casting installation may comprise one or more furnaces necessary for the melting of the metals or their maintenance in temperature, one or more furnaces intended to carry out operations of preparation of the liquid metal and adjustment of the composition, one or more tanks ( or "pouches") intended to carry out a treatment for removing dissolved or suspended impurities in the liquid metal, this treatment possibly consisting of filtering the liquid metal on a filter medium and / or introducing into the bath a gas known as treatment which can be inert or reactive, a device for solidification δ of the liquid metal (or "casting machine") comprising at least the following devices: a mold (or "mold"), at least one device for supplying the liquid metal (or "nozzle"), these different devices being connected between them by channels called "chutes" in which the liquid metal can be transported and a cooling system

Here, a "structural element" or "structural element" of a mechanical construction is called a mechanical part, the failure of which is likely to endanger the safety of the 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" or "monolithic part" refers here to a structural element or a part which has been obtained, most often by machining, from a single piece of rolled semi-finished product, Forged or molded, without assembly, such as riveting, welding, gluing, with another piece.

The term "bi-functional or multi-functional structural element" here refers primarily to the functions conferred by the metallurgical and / or mechanical characteristics of the product and not by its geometric form.

b) Detailed description of the invention

According to the invention, the problem is solved by rolling, spinning or forging a rolling plate or a billet whose composition is variable in the casting direction and advantageously whose foot has a composition different from that of the head. The terms "foot" and "head" refer respectively to the casting first and last, that is to say to the part which is respectively, during a vertical casting, at the bottom and at the top. The method of vertically casting a piece of final height H _F according to the invention comprises the preparation and pouring of an aluminum-based alloy of first composition P up to a desired height Hp, the casting of an additional height HT desired of the second alloy so as to achieve a cast height Hp + HT less than or equal to H _F , and optionally the casting of other alloys based on aluminum or alloy P to the final height hp. In a preferred embodiment, the flow of liquid metal is not interrupted when passing from the casting of the alloy of first composition P to that of the alloy of second composition T, and advantageously when one passes from the casting of the alloy of composition T to that of other alloys.

This vertical casting process generates solid intermediate products to be rolled, spun or forged, having at least two spatially separated alloys in the casting direction. The solid intermediate products according to the invention have, for at least one alloying element, a concentration gradient in the casting direction.

This vertical casting process usually generates between two successively cast alloys a "transition zone" Z of intermediate composition. The control of this transition zone between the alloys is important. In a preferred variant, a transition zone is made as short as possible, that is to say a transition as abrupt as possible. But for some applications, one can also consider a wider area, controlling concentration gradients so as to ensure repeatability from one casting to another. In order to obtain an abrupt transition between alloys, it is preferable to carry out the transition so that the mixing between the successive alloys takes place in a part of the casting installation having a small volume and close to the casting machine. . Typically this transition can be performed in a chute using a dam. In order to obtain an abrupt transition, the metal of composition T can also be produced from the metal of composition P by adding the necessary elements into a liquid metal processing bag. If the transition is carried out in a part of the plant having a high volume, such as a liquid metal treatment ladle for degassing or filtration, or upstream of such a part of the installation, the transition obtained will be wider because the two successive alloys can mix in larger proportions. In a preferred embodiment of the invention to obtain a short transition zone, the transition between alloys is performed in a trough or POcIIe ₁ low volume treatment

The casting method according to the invention can be implemented according to several different embodiments, which are distinguished by the manner in which the alloys are prepared and by the manner of carrying out the transition (s) between alloys. Figure 3 shows an example of cast plate according to the invention. The casting direction defines the direction of the height H of the plate. The plate has a total height HF- It is usual to saw ("crop") the ends of the plate after casting on a height HEP at the bottom and H _E T at the head so as to eliminate the parts corresponding to the beginning and the end of the cast form that do not have the required quality to be transformed. The useful length Hu of the cast form, typically a plate or billet, is therefore equal to Hp - (HEP + H _E T). In the most advantageous embodiments, the height Hp is greater than the height of the plate or billet. trimmed billet in HEP foot. The height Hp depends on the intended application, however, in the context of the invention, the height Hp is generally greater than HEP + Hu / 4 and sometimes higher H _E P + Hu / 2. The transition zone has a height Hz. In the example of FIG. 3, two alloys have been cast and the relation Hp = Hp + HT is therefore.

In a first embodiment, at least two alloys (here referred to as "foot alloy" or "P alloy" and "head alloy" or "T alloy") are produced independently, for example in at least two separate furnaces. The foot alloy is cast first, by pouring the liquid metal from the first furnace into the chute. When the desired metal height Hp in the casting loom is reached, the flow of metal from the first furnace is interrupted and replaced by a flow from the second furnace. This switching from one oven to another is preferably done without interrupting the flow of liquid metal in the chute which empties into the casting machine. Thus, an additional height HT of the alloy of composition T is cast so as to reach a cast height Hp + H _T less than or equal to Hp. In an advantageous embodiment of the invention, the sum Hp + HT is equal to H _F. Optionally casting other aluminum-based alloys T ', T "from a third or a fourth furnace or alloy P from the first furnace to the final height HF makes it possible to achieve more plates or billets complexed with for example composition sequences such as P / T / P, P / T / T 'or P / T / T7T "This embodiment is suitable for all combinations of alloys, the alloys belong to the same family, for example alloys of the 7XXX family, or to different families such as for example a 2XXX alloy and a 7XXX alloy.

In a second embodiment, the foot alloy is poured to the desired height Hp, and the alloy element or elements whose content in the alloy T is greater than that of the alloy are added at the desired moment. P-alloy in wire form or any other suitable form. Thus, an additional height HT of the alloy of composition T is cast so as to reach a cast height Hp + Hx less than or equal to HF. By way of example, if the alloy P is an Al-Zn 5.0-Cu 1.5 -Mg 1.5 alloy and the alloy T is an Al-Zn 5.0-Cu 1 alloy. 5 - Mg 2.5, a liquid alloy is produced whose composition corresponds to that of alloy P, and at the desired moment during casting, magnesium wire is added to the liquid metal in an appropriate part of the metal. casting plant such as the casting furnace, chute or treatment pocket.

In a third embodiment, casting a base alloy of composition B to which is added, typically in the form of son, the alloying elements in an amount necessary to obtain the composition P then the composition T, then any other compositions. The amount of alloying elements added per unit mass of cast metal is changed when the desired height Hp is reached, and the casting is stopped when the desired final RF height is reached. For example, zinc wire, magnesium wire and copper wire can be used and added to a pure aluminum or aluminum which contains, if necessary, other elements whose concentration The target is approximately the same for alloy P, alloy T and any other alloys. It is also possible to use parent alloy wire, for example based on aluminum. This wire is typically supplied in the form of coils, and introduced into the liquid metal via a stripper in an appropriate part of the plant. In an advantageous embodiment of the invention, this yarn is supplied in a chute, downstream of the treatment pockets, so as to obtain a sudden transition between alloys when the quantity of yarn supplied per unit of time is changed. In another example of this third embodiment, the alloy of composition P is obtained by adding the necessary alloying elements to the alloy of composition B in a treatment bag and the alloy of composition T has the same composition as the alloy of composition B.

The first embodiment has the disadvantage of requiring at least two casting furnaces. In order to facilitate an abrupt transition between the alloys, it may be advantageous to have at least two independent liquid metal treatment lines (filtration and degassing pockets).

Embodiments based on the addition of wire have the disadvantage of requiring a very strict process control. A critical parameter is the temperature control, since the melting of a wire consumes energy, which causes the cooling of the liquid metal. It is found, for example, that the addition of unheated zinc wire to a liquid aluminum bath at a temperature of 720 ^° C. leads to a liquid metal temperature drop of about 15 ° C. for a mass flow rate of about 2.8 kg / s. According to the findings of the inventors, this drop in temperature can nevertheless be compensated by a rapid increase in the temperature of the holding furnace when the liquidus temperature of the alloy T is lower than that of the alloy P.

Another disadvantage of embodiments based on the introduction of wire is that the amplitude of variation of the chemical composition between the alloy P, the alloy T and the possible other alloys is limited by the speed of dissolution of the wire in the liquid metal. This problem can be solved at least partially by preheating the wire before it is introduced into the liquid metal. This preheating can be performed using an inert heated tube immersed in the liquid metal which ensures both unwinding of the wire and its dispersion in the liquid metal. Such a device has been described in patent application EP 819 772 A1 (Alusuisse). The present inventors have found that this device can be used so that the wire enters the liquid metal substantially in the liquid state. Another disadvantage of the wire introduction embodiments is when the base alloy composition is distanced from that of the P, T or other composition alloys: a large length of wire has to be unrolled with a wire. quite a lot of unwinding speed or installing several thread unwinding devices which is not always easy. An advantage of the embodiments based on the introduction of wire is to allow a great flexibility as to the transition between the two alloys: it is possible to obtain an abrupt transition, but above all it is possible to spread this transition more easily over the length of the plate. or billet to obtain a gradual transition. This supposes that it is possible to vary the speed of movement of the thread (or threads, if several are used, of the same composition or of different compositions) and / or the number of threads introduced.

In all these three embodiments, it is advantageous to use a liquid metal treatment pouch (for example with an Ar-Cl ₂ mixture) of known type and / or a filtration bag such as a gravel filter, slab filter or any other suitable filtration mode, in order to minimize the hydrogen content of the liquid metal and to obtain a satisfactory inclusion quality. Advantageously, in the case where an abrupt transition is sought, the transition between alloys is carried out downstream of the treatment pockets.

In a fourth embodiment, a large liquid metal processing bag is used, which acts as a P alloy tank to form the alloy T. This embodiment has the advantage of not requiring an additional furnace. compared to the usual casting modes. On the other hand, the amount of metal available for the casting of the alloy T is limited to the pocket volume.

These four embodiments, which can be easily combined with one another, make it possible to produce a first solid intermediate product intended to be rolled, spun or forged, and in particular a plate or a billet having a variable composition in the direction of casting. This first solid intermediate product preferably has a constant section over at least 95% of its length.

Then, the first intermediate product, for example the plate or billet, thus obtained is converted by heat treatment, typically hot, in one or more steps, possibly followed by one or more processing steps by cold working to obtain a second product. intermediate, such as a sheet, a profile, a bar spun or a forging.

The billets can be used to spin profiles or bars having a variable length composition, or forging blanks. The plaques can be used as forging blanks or as rolling plates. The problem of making rolled products which exhibit spatially variable mechanical characteristics can be solved by using a rolling plate according to the invention and laminating it to obtain a sheet. The rolling in the length direction (ie in the casting direction H) leads to lengthen the transition zone Z which may be advantageous for certain applications. In one embodiment of the invention, the plate is subjected to at least one rolling pass in the direction of casting. Generally, however, lamination in the width direction (ie perpendicular to the casting direction H) is preferred, since this makes it possible not to lengthen the transition zone. This induces constraints in choosing the size of the plates to achieve the desired sheet size. Figure 4 illustrates the rolling of a plate according to the invention in the width direction. The rolling direction L is perpendicular to the casting direction H.

It is thus possible to develop thick plates that can be used for the manufacture of spars of variable composition, one side of which is compatible with the function of an extrados, oriented towards the upper part of the wing and particularly dimensioned in compression, while the other side is compatible with the intrados function, oriented towards the lower part of the wing and particularly dimensioned in toughness. For this application, it is preferable to have a transition as short as possible between the two alloys in the cast rolling plate.

Such a product is likely to be used as structural element in aeronautical construction. More particularly, it can be used as a spar, rib or wing skin.

It may also be advantageous to use the invention to produce fuselage sheets of variable properties, adapted to the constraints of the upper part and the lower part of the fuselage. For this application it is advantageous to choose to roll partly or totally perpendicularly to the direction of casting ie in the direction of the width of the initial plate (Figure 5).

The invention can be applied to all aluminum alloys and advantageously structural hardening alloys from the 2XXX, 6XXX, 7XXX or 8XXX families are used. In a preferred embodiment, the alloys used are all from the 7XXX family. In another mode of advantageously, the alloys used are all from the 2XXX family and / or are all alloys of aluminum-lithium type (ie alloys containing at least 0.1% by weight of lithium and preferably at least less than 0.5% by weight of lithium). By way of example, the pairs of alloys P and T (or conversely) are 7040 and 7449 or 2024A and 2027 or 2050 and 2195. In the case of a composition sequence P / T / T ', it is advantageous to use alloy 7475 for P, alloy 7040 for T and alloy 7449 for T '.

A 7XXX alloy comprising 4.1 to 5.1% Zn, 1.5 to 2.5% by weight of Cu and 1.2 to 1.8% by weight of Mg has proved particularly advantageous in the context of the invention. This alloy makes it possible to achieve very high toughness by minimizing the loss of static mechanical characteristics with respect to an alloy such as 7040. In an advantageous embodiment of the invention, the alloy P is thus an alloy comprising 4.1 to 5 , 1% of Zn, 1.5 to 2.5% by weight of Cu and 1.2 to 1.8% by weight of Mg and the alloy T is an alloy comprising 7 to 10% of Zn, 1.0 to 3.0% by weight of Cu and 1.0 to 3.0% by weight of Mg. The combination of 7040 and 7449 alloys is particularly favorable for spar type applications while the combination of 7475 and 7449 alloys is particularly favorable for wing skin type applications.

The methods according to the present invention allow the manufacture of bi-functional or multi-functional monolithic structural elements.

The methods according to the present invention make it possible in particular to develop structural elements suitable for use in aeronautical construction comprising wing spars or wing ribs of large capacity aircraft. Figure 1 schematically shows a bi-functional spar according to the invention. Its height HL can reach 1000 mm or more, its length L can reach ten meters or more, its thickness E is typically of the order of 100 mm, but can be greater. The spars are manufactured by machining from heavy plates. They may comprise a lower sole (4), an upper sole (1), a core (2) and stiffeners machined in the mass (3). The transition zone Z can be positioned equidistant from the flanges or closer to one or the other, depending on the design requirements. Figure 2 shows schematically the heavy plate in which these rails have been machined. In an advantageous embodiment of the invention, the strong plate has been obtained by rolling in the direction of the width of the plate according to the invention so that the height HL is slightly less than Hu- The rolling in the cross direction is illustrated in Figure 4.

The methods according to the present invention also make it possible to develop structural elements suitable for use in aeronautical construction comprising fuselage elements. Figure 5 schematically illustrates the use of a sheet according to the invention to produce a fuselage panel (6), reinforced by riveted stiffeners, glued or welded (5). In each of the figures, the two alloys used are schematically indicated. Other structural elements suitable for use in aeronautical construction, obtainable from intermediate products according to the invention, comprising for example a wing stiffener or a wing panel, which are suitable for use in an aircraft, can also be produced. use in aircraft construction.

The range of transformation carried out which may comprise, in the case of a plate, the steps of homogenization, hot rolling, cold rolling, solution setting, quenching, cold deformation (for example traction) and tempering must be compatible with the alloys contained in the plate according to the invention. This condition can be limiting as to the choice of alloys because the optimum temperatures are sometimes very different between the alloys and a temperature compromise may lead to not obtaining the desired properties. The person skilled in the art tries to adapt the processing range to the alloys at best. Similar problems arise for the person skilled in the art mutatis mutandis in the case of the spinning billet transformation process, or a forging draft.

In another embodiment of the present invention, the rolling plate is rolled mainly or exclusively along its length, i.e., in the casting direction. Thus, sheets of great length are obtained, one of the geometric ends of which is made of alloy of composition P, and the other geometric end is of alloy of composition T. These sheets show a gradient in their mechanical properties in the direction of their length. . This embodiment is particularly applicable to the production of wing plates. Other embodiments of the present invention are described in the dependent claims.

In the examples which follow, advantageous embodiments of the invention are illustrated by way of illustration. These examples are not limiting in nature.

Examples

Example 1

In this example, a rolling plate (mark A) was cast whose foot (reference P) was in alloy Al-Zn 5% - Cu 1.8% - Mg 1.5% and the head (mark T) in Al-Zn alloy 8% - Cu 1.8% - Mg 1.9%. Both alloys were made in two separate furnaces. Table 1 shows the composition of the two alloys measured on pions obtained by solidification of liquid metal taken from each of the two furnaces.

Table 1. Measured compositions (% by weight)

The two liquid alloys were treated for 90 minutes with an Ar - Cl ₂ mixture in an IRMA ® type treatment bag. The transition between alloys was carried out in a chute. Liquid metal was taken in the trough for the manufacture of spectrometric pins before, during and after the composition transition, approximately every 50 mm of descent. It has thus been found that the transition of the composition takes place over a descent height of about 200 mm. The height Hp was 2100 mm, the height HT was about 1600 mm and the total height of the HF plate was about 3700 mm. A 750mm HEP foot length and a 300mm HET head length were drilled to give a usable length Hu of about 2600mm. Example 2

A plate was cast as shown in Example 1. The compositions of the alloys are shown in Table 2.

The two liquid alloys were treated with an Ar - Cl ₂ mixture in an ALPUR ® type treatment bag. In order to obtain a steep transition, the metal of composition T was prepared from the composition metal P in the ALPUR ® pocket, then the bag was fed with the liquid metal from the second furnace. Liquid metal was taken in the trough for the manufacture of spectrometric pins before, during and after the composition transition, approximately every 50 mm of descent. Figure 6 illustrates the results obtained. The transition of the composition takes place on a descent height of less than 100 mm. The height Hp was 2100 mm. The final height Hp of the plate was about 3850 mm. A 800 mm HE _P foot length and a 300 mm HET head length were drilled to give a usable length Hu of about 2750 mm.

Example 3

In this example, a strong plate is manufactured which can be used for the manufacture of an aircraft wing spar.

The plate obtained from Example 2 is used. This plate has a height Hu of about 2750 mm, which is sufficient for a spar with a height of about 2000 mm. The plate is homogenized for 48 hours at 470 ^° C. It is hot-rolled in the cross direction (ie perpendicular to the casting direction H of the plate) to a final thickness of 80 mm. The hot rolling temperature is between 400 ° C. and 46O ⁰ C. The sheet thus obtained is dissolved at 473 ^° C. for 12 hours. After quenching, the sheet is subjected to a controlled pull with a permanent deformation of about 2%. A characterization of the sheet obtained by conductivity measurement is then performed.

FIG. 7 illustrates the conductivity profile obtained at mid-thickness in the casting direction H. The transition zone between alloys extends over a height of approximately 400 mm. This height is greater than the transition height of 100 mm measured by sampling pions during casting because it integrates the shape of the interface between solid and liquid ("the marsh") which is not a plane perpendicular to the casting direction but a surface whose shape depends on the cooling conditions during solidification. Then, the sheet is subjected to a treatment of income in two stages: 6 hours at 120 ⁰ C followed by 20 hours at 155 ° C. Table 3 below illustrates the static mechanical characteristics, toughness and corrosion resistance obtained for samples taken at mid-thickness and at quarter-thickness.

Table 3

This gives a sheet having at the end T a value of R _p o. ₂ above 510 MPa and a Kic value greater than 32 MPaVm ₅ and at the P end a value of Rpo. ₂ greater than 410 MPa and a Kic value greater than 54 MPaVm. In this sheet metal, it is possible to machine a bi-functional structural element for aeronautical construction, namely a spar, so as to have the extrados side of alloy composition T, and the lower side of alloy of composition P. This spar, is schematically shown in Figure 1.

Example 4

In this example, an aluminum alloy rolling plate is cast whose head composition T (alloy type AA 7449) comprises 8% zinc, 1.9% magnesium and 1.8% copper, and whose foot composition P (alloy type

AA7040) comprises 5% zinc, 1.5% magnesium and 1.8% copper. The zirconium content is 0.11%. To cast this plate, an alloy of composition P is prepared, the metal is treated with a gas (Ar + Cl ₂ ) in a treatment bag, and the composition alloy P is cast with the desired height Hp. , which is the final mid-height Hp of the target plate, and then the casting is continued to the final height Hp by adding to the casting alloy, after the treatment bag, the necessary amount of solid metal rich in zinc and magnesium to bring the alloy of composition P to the composition T. This solid metal supply is made by unwinding, via a rewinder, two son with appropriate zinc and magnesium contents, which are supplied in coils.

Example 5

In this example, an aluminum-based alloy rolling plate is poured whose foot composition P comprises 1.8% magnesium, 7.8% zinc and 1.8% copper and whose top composition T comprises 1.3% magnesium, 7.8% zinc and 1.8% copper. The zirconium content is 0.10%. To cast this plate, an alloy of the composition T is prepared, the amount of Mg necessary to reach the target composition P is then added to a treatment bag and then poured. The transition between the two compositions is progressive, the composition T being reached for a cast height of 800 mm. The plate is then converted by homogenization, hot rolling to a thickness of 100 mm, dissolution, quenching and tempering.

The results obtained at the foot and at the top are presented in Table 4 for 4 different income conditions.

Table 4

Claims

A method of vertically casting an intermediate product of final height HF in the casting direction, comprising the steps of

(b) casting said first alloy of composition P to a desired height Hp,

(c) casting a desired additional height Hx of said second alloy so as to achieve a cast height Hp + H _T which is less than or equal to H _F , and wherein

(i) the preparation of said aluminum-based alloys is carried out independently, or in which

(ii) the preparation of the aluminum alloys of composition different from P is carried out from said first alloy during casting by adding to said first alloy the necessary quantities of elements to reach the composition of said alloys of composition different from P, or in which

(iii) the preparation of said at least two aluminum-based alloys is carried out during casting from an aluminum-based alloy of composition B, adding to said alloy of composition B the necessary quantities of elements to achieve the composition of said at least two alloys based on aluminum P and T.

2. The method of claim 1 wherein the transition between the alloys P and T is performed without interrupting the flow of liquid metal.

3. Method according to claim 1 or 2 wherein the sum Hp + Hx is equal to H _F

4. Method according to claim 1 or 2 wherein the sum Hp + Hx is less than HF and wherein the following additional step is carried out

(d) casting of the alloy P from the height Hp + Hx to the height HF-

5. The method of claim 1 or 2 wherein the sum Hp + H _T is less than Hp ₅ wherein step (a) comprises preparing an alloy T 'and wherein is performed the additional step of ( d) casting of the alloy T 'from the height Hp + HT to the height Hp.

6. Method according to any one of claims 1 to 5 wherein the height Hp is greater than or equal to the cropped length H _E P.

7. The method of claim 6 wherein the height Hp is greater than or equal to HEP + Hu / 4 where Hu is the useful length of the cast form.

The method of any one of claims 1 to 7 wherein said aluminum alloys are structural hardening alloys comprised in the group consisting of 2XXX, 6XXX ₅ 7XXX and 8XXX alloys.

The method of any one of claims 1 to 7 wherein said aluminum alloys are 7XXX aluminum alloy.

The method of any one of claims 1 to 7 wherein said aluminum alloys are 2XXX aluminum alloy.

11. A method according to any one of claims 1 to 7 wherein said aluminum alloys are aluminum-lithium alloy type.

The method of claim 3 or 4 wherein the P alloy is 7040 and the T alloy is 7449.

13. The method of claim 3 or 4 wherein the alloy P is an alloy comprising 4.1 to 5.1% by weight of Zn, 1.5 to 2.5% by weight of Cu and 1.2 to 1 , 8% by weight of Mg and the alloy T is an alloy comprising 7 to 10% by weight of Zn, 1.0 to 3.0% by weight of Cu and 1.0 to 3.0% by weight of Mg

14. The method of claim 5 wherein the alloy P is 7475, the alloy

T is 7040 and the alloy T 'is 7449.

15. Solid intermediate product intended to be rolled, spun or forged obtainable by the method according to any one of claims 1 to 14.

16. Intermediate product according to claim 15 characterized in that it comprises between two alloys successively cast at least one "transition zone" Z of intermediate composition.

17. Intermediate product according to claim 15 or claim 16, characterized in that said intermediate product is a plate or billet of constant section over at least 95% of its length.

A method of producing a sheet from a plate according to claim 17, wherein

(a) supplying a plate according to claim 16,

(b) laminating said plate to obtain a second intermediate product.

19. A method of producing a sheet according to claim 18 wherein said rolling is carried out in the direction perpendicular to the direction of casting.

20. Process for producing a sheet according to claim 18, wherein said plate is subjected to at least one rolling pass in the direction of casting.

21. Sheet metal capable of being produced by the method according to any one of claims 18 to 20.

22. A method of producing a profile or bar from a billet according to claim 17 wherein

(a) supplying a billet according to claim 17 (b) spinning said billet to obtain a second intermediate product

23. Profile or bar that can be produced by the method according to claim 22.

24. A method of producing a forged part from a plate or a billet according to claim 17 wherein

(a) supplying a plate or a billet according to claim 17,

(b) forging said billet or said plate to obtain a second intermediate product.

Forging piece that can be produced by the method according to claim 24.

26. Bi-functional or multi-functional monolithic structure element manufactured from an intermediate product according to any one of claims 21, 23 or 25.

The structural member of claim 26, wherein said structural member comprises a spar suitable for use in aircraft construction.

The structural member of claim 26, wherein said structural member comprises a rib suitable for use in aircraft construction.

The structural member of claim 26, wherein said structural member comprises a fuselage panel suitable for use in aircraft construction.

The structural member of claim 26, wherein said structural member comprises a wing stiffener suitable for use in aircraft construction.

31. The structural member of claim 26, wherein said structural member comprises a wing panel suitable for use in aircraft construction.