EP3080318A2 - Method for manufacturing products made of aluminium-copper-lithium alloy with improved fatigue properties and distributor for this method - Google Patents

Abstract

The invention relates to a method for manufacturing an aluminium alloy product including the steps of: creating a bath of liquid metal in an aluminium - copper - lithium alloy, casting said alloy by vertical semi-continuous casting so as to obtain a plate with thickness T and width W such that, during solidification, the hydrogen content of said liquid metal bath (1) is lower than 0.4 ml/100 g, the oxygen content above the liquid surface (14, 15) is less than 0.5 % by volume, the tundish used (7) for casting is made of a fabric including essentially carbon, including a lower surface (76), an upper surface defining the opening through which the liquid metal is inserted (71) and a wall with a substantially rectangular section, the wall containing two longitudinal portions parallel to the width W (720, 721) and two transverse portions parallel to the thickness T (730, 731) said transverse and longitudinal portions being formed by at least two fabrics, a first substantially sealing and semi-rigid fabric (77) ensuring that the tundish keeps its shape during casting, and a second non-sealing fabric (78) allowing the passage and filtration of the liquid, said first and second fabrics being connected to one another with no overlap and no gaps separating same, said first fabric continuously covering at least 30 % of the surface of said wall portions (720, 721, 730, 731) and being positioned such that the liquid surface is in contact with same over the entire section.

Description

 Process for producing aluminum alloy - copper - lithium products with improved fatigue properties

Field of the invention

The invention relates to wrought products aluminum alloys - copper - lithium, more particularly, such products, their manufacturing processes and use, intended in particular for aeronautical and aerospace construction.

State of the art

Aluminum alloy rolled products are developed to produce structural elements for the aerospace industry and the aerospace industry in particular.

Aluminum - copper - lithium alloys are particularly promising for this type of product. The specifications imposed by the aeronautical industry for fatigue performance are high. For thick products they are particularly difficult to reach. Indeed, given the possible thicknesses of the cast slabs, the thickness reduction by hot deformation is quite low and therefore the sites related to the casting on which the fatigue cracks are initiated do not see their reduced size during hot deformation.

 Since lithium is particularly oxidizable, the casting of aluminum-copper-lithium alloys generally generates more fatigue crack initiation sites than for 2XXX lithium-free or 7XXX-type alloys. Thus the solutions usually found for obtaining thick rolled products of 2XXX type alloys without lithium or 7XXX do not make it possible to obtain sufficient fatigue properties for aluminum-copper-lithium alloys.

Thick products of Al-Cu-Li alloy are described in particular in applications US2005 / 0006008 and US2009 / 0159159. In the application WO2012 / 110717, it is proposed to improve the properties, especially in fatigue, aluminum alloys containing in particular at least 0.1% Mg and / or 0.1% Li to achieve during casting an ultrasound treatment. However, this type of treatment remains difficult to perform for the quantities necessary for the manufacture of thick plates.

There is a need for thick aluminum-copper-lithium alloy products having improved properties over those of the known products, particularly in terms of fatigue properties while having advantageous toughness properties and static strength properties. . Moreover, there is a need for a simple and economical method of obtaining these products.

Object of the inveution

 A first object of the invention is a method of manufacturing an aluminum alloy product comprising the steps in which

 (a) forming an alloy molten metal bath comprising, in% by weight, Cu: 2.0 - 6.0; Li: 0.5 - 2.0; Mg: 0-1.0; Ag: 0 - 0.7; Zn 0 - 1.0; and at least one member selected from Zr, Mn, Cr, Se, Hf and Ti, the amount of said element, if selected, being from 0.05 to 0.20% by weight for Zr, 0.05 to 0 , 8% by weight for Mn, 0.05 to 0.3% by weight for Cr and for Se, 0.05 to 0.5% by weight for Hf and from 0.01 to 0.15% by weight for Ti , Si <0, 1; Fe <0, 1; others <0.05 each and <0.15 in total,

 (b) pouring said alloy by vertical semi-continuous casting to obtain a plate of thickness T and width W such that, during solidification,

 the hydrogen content of said liquid metal bath (1) is less than 0.4 ml / 100 g, the oxygen content measured above the liquid surface (14, 15) is less than 0.5% by volume ,

the distributor used (7) for the casting is made of fabric comprising essentially carbon, that it comprises a lower face (76), an upper face defining the orifice through which the liquid metal is introduced (71) and a wall; of substantially rectangular section, the wall comprising two longitudinal parts parallel to the width W (720, 721) and two transverse parts parallel to the thickness T (730, 731) said portions transverse and longitudinal being formed of at least two tissues, a first substantially obturating and semi-rigid tissue (77) ensuring the maintenance of the dispenser shape during casting and a second non-sealing fabric (78) allowing the passage and filtration liquid, said first and second webs being bonded to each other without overlapping or overlapping and without gap between them, said first fabric continuously covering at least 30% of the area of said wall portions (720,721, 730 731) and being positioned so that the liquid surface is in contact with it over the entire section.

 Another object of the invention is a dispenser for the semi-continuous casting of fabric aluminum alloy plates comprising essentially carbon, comprising a lower face (76), an upper face defining the orifice through which the metal liquid is introduced (71) and a wall of substantially rectangular section, the wall comprising two longitudinal portions parallel to the width W (720, 721) and two transverse portions parallel to the thickness T (730, 731) said transverse and longitudinal portions being formed of at least two fabrics, a first substantially obturating and semi-rigid fabric (77) ensuring the maintenance of the shape of the dispenser during casting and a second non-sealing fabric (78) permitting the passage and filtration of the liquid, said first and second webs being bonded to one another without overlapping or overlapping and without interstices separating them, said first web covering continuously at least 30% of the area of said wall portions (720, 721, 730, 731) being positioned so that the liquid surface is in contact therewith throughout the section.

Description of figures

Figure 1 is the diagram of the test pieces used for the tests in smooth fatigue (Fig la) and in fatigue with hole (Fig lb). Dimensions are given in mm.

 Figure 2 is a general diagram of the solidification device used in one embodiment of the invention.

Figure 3 is a general diagram of the dispenser used in the process according to the invention. Figure 4 shows representations of the bottom and the lateral and longitudinal parts of the distributor wall according to one embodiment of the invention.

 Figure 5 shows the relationship between the smooth fatigue performance and the hydrogen content of the liquid metal bath during solidification (Fig. 5a) or the oxygen content measured above the liquid surface during solidification (Fig. 5b).

 Figure 6 shows the Wohler curves obtained with tests 3, 7 and 8 in the direction L-T (Figure 6a) and T-L (Figure 6b).

Description of the invention

Unless stated otherwise, all the information concerning the chemical composition of the alloys is expressed as a percentage by weight based on the total weight of the alloy. The expression 1.4 Cu means that the copper content expressed in% by weight is multiplied by 1.4. The designation of alloys is in accordance with the regulations of The Aluminum Association, known to those skilled in the art. Unless otherwise stated, the definitions of the metallurgical states given in the European standard EN 515 apply.

The static mechanical characteristics in tension, in other words the tensile strength R _m , the conventional yield stress at 0.2% elongation R _p0.2 , and the elongation at break A% are determined by a tensile test according to standard NF EN ISO 6892-1, the sampling and the direction of the test being defined by the EN 485-1 standard. The fatigue properties on smooth specimens are measured in ambient air at a maximum amplitude stress of 242 MPa, a frequency of 50 Hz, a stress ratio R = 0.1, on specimens as shown in FIG. la, taken at mid-width and at mid-thickness of the sheets in the direction TL. The test conditions follow the ASTM E466 standard. The logarithmic average of the results obtained on at least 4 test pieces is determined.

The fatigue properties on hole specimens are measured in the ambient air for variable stress levels, at a frequency of 50 Hz, a stress ratio R = 0.1, on specimens as shown in FIG. K _t = 2,3, taken at the center and at mid-thickness of the sheets in the direction LT and TL. Walker's equation was used to determine a maximum stress value representative of 50% of non-rupture at 100,000 cycles. To do this a fatigue quality index (IQF) is calculated for each point of the Wôhler curve with the formula

where a _max is the maximum stress applied to a given sample, N is the number of cycles to failure, N ₀ is equal to 100,000 and n = -4.5. The IQF corresponding to the median is reported, ie 50% rupture per 100,000 cycles.

In the context of the invention, a thick wrought product is a product whose thickness is at least 6 mm. Preferably the thickness of the products according to the invention is at least 80 mm and preferably at least 100 mm. In one embodiment of the invention the thickness of the wrought products is at least 120 mm or preferably 140 mm. The thickness of the thick products according to the invention is typically at most 240 mm, generally at most 220 mm and preferably at most 180 mm.

Unless otherwise specified, the definitions of EN 12258 apply. In particular, a sheet is according to the invention a laminated product of rectangular cross section whose uniform thickness is at least 6 mm and does not exceed 1 / 10th of the width.

Here, a "structural element" or "structural element" of a mechanical construction is called a mechanical part for which the static and / or dynamic mechanical properties are particularly important for the performance of the structure, and for which a structural calculation is usually prescribed or realized. These are typically elements 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), the wings (such as the wing skin), the stiffeners (stringers or stiffeners), the ribs (ribs) and spars) and the empennage composed in particular of stabilizers Horizontal and vertical (horizontal or vertical stabilizers), as well as floor beams, seat rails and doors.

 The term "set of the casting plant" is here referred to as the set of devices making it possible to transform a metal in any form into a semi-product of raw form via the liquid phase. A casting plant may include a number of devices such as one or more ovens required for melting the metal ("melting furnace") and / or maintaining it ("holding furnace") in temperature and / or preparation of the liquid metal and adjustment of the composition ("preparation furnace"), one or more tanks (or "pockets") intended to carry out a treatment for the removal of impurities dissolved and / or suspended in the liquid metal this treatment may consist of filtering the liquid metal on a filter medium in a "filtration bag" or introducing into the bath a so-called "treatment" gas that can be inert or reactive in a "degassing bag", a device for solidification of the liquid metal (or "casting loom") by vertical semi-continuous casting by direct cooling in a casting well, which may comprise devices such as a mold (or "mold") a liquid metal supply device (or "nozzle") and a cooling system, these different furnaces, tanks and solidification devices being interconnected by transfer devices or channels called "chutes" in which the liquid metal can to be transported.

The present inventors have found that, surprisingly, thick wrought products of copper lithium aluminum alloy with improved fatigue performance can be obtained by preparing these sheets by the following method.

 In a first step, an alloy liquid metal bath comprising, in% by weight Cu: 2.0 - 6.0; Li: 0.5 - 2.0; Mg: 0-1.0; Ag: 0 - 0.7; Zn 0 - 1.0; and at least one member selected from Zr, Mn, Cr, Se, Hf and Ti, the amount of said element, if selected, being from 0.05 to 0.20% by weight for Zr, 0.05 to 0 , 8% by weight for Mn, 0.05 to 0.3% by weight for Cr and for Se, 0.05 to 0.5% by weight for Hf and from 0.01 to 0.15% by weight for Ti , Si <0,1; Fe <0.1; others <0.05 each and <0.15 in total, remains aluminum.

An advantageous alloy for the process according to the invention comprises, in% by weight, Cu: 3.0 - 3.9; Li: 0.7 - 1.3; Mg: 0.1 - 1.0, at least one element selected from Zr, Mn and Ti, the amount of said element, if selected, being from 0.06 to 0.15% by weight for Zr, 0.05 to 0.8% by weight for Mn and from 0.01 to 0.15% by weight for Ti; Ag: 0 - 0.7; Zn <0.25; If <0.08; Fe <0.10; others <0.05 each and <0.15 in total, remains aluminum.

Advantageously, the copper content is at least 3.2% by weight. The lithium content is preferably between 0.85 and 1.15% by weight and preferably between 0.90 and 1.10% by weight. The magnesium content is preferably between 0.20 and 0.6% by weight. The simultaneous addition of manganese and zirconium is generally advantageous. Preferably, the manganese content is between 0.20 and 0.50% by weight and the zirconium content is between 0.06 and 0.14% by weight. Advantageously, the silver content is between 0.20 and 0.7% by weight. It is advantageous that the silver content is at least 0.1% by weight. In one embodiment of the invention the silver content is at least 0.20% by weight. Preferably, the silver content is at most 0.5% by weight. In one embodiment of the invention, the silver content is limited to 0.3% by weight. Preferably, the silicon content is at most 0.05% by weight and the iron content is at most 0.06% by weight. Advantageously, the titanium content is between 0.01 and 0.08% by weight. In one embodiment of the invention, the zinc content is at most 0.15% by weight.

A preferred aluminum-copper-lithium alloy is AA2050 alloy.

This liquid metal bath is prepared in a furnace of the casting plant. It is known, for example from US Pat. No. 5,415,220, to use lithium-containing molten salts such as KCl / LiCl mixtures in the melting furnace to passivate the alloy during its transfer to the casting plant. The present inventors, however, have obtained excellent fatigue properties for thick plates without using molten salt containing lithium in the melting furnace, but maintaining in this furnace a low oxygen atmosphere and believe that the presence of salt in the furnace Melting furnace could have in some cases a detrimental effect on the fatigue properties of thick wrought products. Advantageously, molten salt containing lithium is not used throughout the casting installation. In an advantageous embodiment, no molten salt is used throughout the casting installation. Preferably, in the furnace or furnaces of the casting installation, an oxygen content of less than 0.5% by volume and preferably less than 0.3% by volume is maintained. However one can tolerate an oxygen content at least 0.05% by volume and even at least 0.1% by volume in the furnace (s) of the casting plant, which is advantageous especially for the economic aspects of the process. Advantageously, the furnace or furnaces of the casting installation are induction furnaces. The present inventors have found that this type of oven is advantageous despite the stirring generated by the induction heating.

 This bath of liquid metal is then treated with a degassing bag and in a filtration bag so that its hydrogen content is less than 0.4 ml / 100g and preferably less than 0.35 ml / 100g . The hydrogen content of the liquid metal is measured using a commercial apparatus such as the apparatus marketed under the tradename ALSCAN ™, known to those skilled in the art, the probe being maintained under a nitrogen sweep. Advantageously, the oxygen content of the atmosphere in contact with the liquid metal bath in the melting furnace during the degassing steps, filtration is less than 0.5% by volume and preferably less than 0.3% by volume. Preferably, the oxygen content of the atmosphere in contact with the liquid metal bath is less than 0.5% by volume and preferably less than 0% by volume for the entire casting plant. However, it is possible to tolerate an oxygen content of at least 0.05% by volume and even at least 0.1% by volume for the entire casting plant, which is advantageous especially for the economic aspects of the casting. process.

The liquid metal bath is then solidified in the form of a plate. A plate is an aluminum block of substantially parallelepipedic shape, length L, width W and thickness T. The atmosphere is controlled above the liquid surface during solidification. An example of a device for controlling the atmosphere above the liquid surface during solidification is shown in Figure 2.

In this example of a suitable device, the liquid metal coming from a trough (63) is introduced into a nozzle (4) controlled by a stopper rod (8) which can move upwards and downwards (81), in an ingot mold (31) placed on a false bottom (21). The aluminum alloy is solidified by direct cooling (5). The aluminum alloy (1) has at least one solid surface (1 1, 12, 13) and at least one liquid surface (14, 15). An elevator (2) makes it possible to maintain the level of the liquid surface (14, 15) substantially constant. A distributor (7) allows the distribution of the liquid metal. A cover (62) covers the liquid surface. The cover may include seals (61) for sealing with the casting table (32). The liquid metal in the trough (63) can be advantageously protected by a cover (64). An inert gas (9) is introduced into the chamber (65) defined between the cover and the pouring table. The inert gas is advantageously chosen from rare gases, nitrogen and carbon dioxide or mixtures of these gases. A preferred inert gas is argon. The oxygen content is measured in the chamber (65) above the liquid surface. The flow of inert gas can be adjusted to achieve the desired oxygen content. However, it is advantageous to maintain sufficient suction in the casting well (10) by means of a pump (101). Indeed the present inventors have found that there is generally no sufficient seal between the mold (31) and the solidified metal (5) which leads to a diffusion of the atmosphere of the casting well (10) to the room (65). Advantageously, the suction of the pump (101) is such that the pressure in the enclosure (10) is lower than the pressure in the chamber (65), which can preferably be obtained by imposing a speed of the atmosphere through the open surfaces of the casting well of at least 2 m / s and preferably at least 2.5 m / s. Typically the pressure in the chamber (65) is close to atmospheric pressure and the pressure in the chamber (10) is lower than atmospheric pressure, typically 0.95 times the atmospheric pressure. In the context of the process according to the invention, the chamber (65) is maintained, thanks to the devices described, with an oxygen content of less than 0.5% by volume and preferably less than 0.3% by volume.

An example of a dispenser (7) of the process according to the invention is shown in FIGS. 3 and 4. The dispenser according to the invention is made of a fabric essentially comprising carbon, it comprises a lower face (76), an upper face typically vacuum defining the orifice through which the liquid metal is introduced (71) and wall of substantially rectangular cross section typically substantially constant and of height h typically substantially constant, the wall comprising two longitudinal parts parallel to the width W of the plate (720, 721 ) and two transverse parts parallel to the thickness T of the plate (730, 731), said transverse and longitudinal portions being formed of at least two tissues, a first substantially obturating and semi-rigid tissue (77) ensuring the maintenance of the shape of the dispenser during the casting and a second non sealing device (78) for passage and filtration of the liquid, said first and second webs being bonded to one another without overlapping or overlapping and without interstices separating them, said first fabric continuously covering at least 30% of the surface of said wall portions (720, 721, 730, 731) and being positioned so that the liquid surface is in contact with it over the entire section of the dispenser. The first and second fabrics being sewn together without overlapping or overlapping and without interstices separating them, i.e., in contact, the liquid metal can not pass through the first fabric and be deflected by the second fabric as is the case for example in a combo-bag as described in the application WO 99/44719 Fig 2 to 5. Thanks to the maintenance provided by the first fabric, the dispenser is semi-rigid and does not deform substantially during casting. In an advantageous embodiment, the first fabric has a height, hl, measured from the upper face on the circumference of the wall (720, 721, 730, 731) such that h1> 0.3 h and preferably h1> 0, 5 h, where h denotes the total height of the distributor wall.

The liquid surface being in contact with said first liquid-sealing fabric passes through the dispenser only under the liquid surface in certain directions of each part of the wall. Preferably the height immersed in the liquid wall metal (720, 721, 730, 731) of the distributor (7) covered by the first fabric is at least 20%, preferably 40% and preferably 60% of the height. total submerged wall.

 Figure 4 shows the bottom and the longitudinal wall portions. The bottom (76) is typically covered by the first and / or second fabric. Advantageously, the first fabric is at least located in the central part of the bottom (76) along a length L1 and / or in the central part of the longitudinal parts (720) and (721) over the entire height h and over a length L2.

Advantageously, the surface portion covered by the first fabric is between 30 and 90% and preferably between 50 and 80% for the longitudinal portions (720) and (721), and / or between 30 and 70% and preferably between 40 and 60% for the side parts (730, 731) and / or between 30 and 100% and preferably between 50 and 80% for the bottom (76). It is advantageous if the length L1 of the first tissue located in the bottom (76) is greater than the length L2 of the first tissue situated in the part of the longitudinal walls (720) and (721) in contact with the bottom.

 The present inventors believe that the geometry of the dispenser makes it possible in particular to improve the quality of the flow of the liquid metal, to reduce turbulence and to improve the temperature distribution.

 The first fabric and the second fabric are advantageously obtained by weaving a yarn essentially comprising carbon. The weaving of graphite yarn is particularly advantageous. The tissues are typically sewn to each other. It is also possible instead of first and second fabrics to use a single diffuser fabric having at least two weaving areas, more or less dense.

 It is advantageous for the ease of weaving that the wire comprising carbon is coated with a layer facilitating sliding. This layer may for example comprise a fluorinated polymer such as Teflon or a polyamide such as xylon.

The first fabric is substantially obturant. Typically it is a fabric having mesh size of less than 0.5 mm, preferably less than 0.2 mm. The second fabric is non-sealing and allows the passage of the molten metal. Typically, it is a fabric having mesh sizes of between 1 and 5 mm, preferably 2 to 4 mm. In one embodiment of the invention the first tissue locally covers the second tissue, while being in intimate contact so as not to leave a gap between the two tissues.

Advantageously, the plate thus obtained is then transformed to obtain a wrought product.

The plate thus obtained is then homogenized before or after having been optionally machined to obtain a shape that can be deformed while hot. In one embodiment, the plate is machined as a rolling plate so as to be hot deformed by rolling. In another embodiment, the plate is machined as a forging blank so as to be hot deformed by forging. In yet another embodiment, the plate is machined in the form of billets so as to then be hot deformed by extrusion. Preferably the homogenization is carried out at a temperature between 470 and 540 ° C for a period of between 2 and 30 hours.

The shape thus homogenized is deformed hot and optionally cold so as to obtain a wrought product. The heat-forming temperature is advantageously at least 350 ° C and preferably at least 400 ° C. The rate of deformation hot and optionally cold, that is to say the ratio between the difference between the initial thickness, before deformation but after the possible machining, and the final thickness and on the other hand, the initial thickness is less than 85% and preferably less than 80%. In one embodiment, the deformation rate during the deformation is less than 75% and preferably less than 70%.

 The wrought product thus obtained is then dissolved and quenched. The dissolution temperature is advantageously between 470 and 540 ° C and preferably between 490 and 530 ° C and the duration is adapted to the thickness of the product.

Optionally, the wrought product thus solubilized is de-tensioned by plastic deformation with a deformation of at least 1%. In the case of rolled products, it is advantageous to detension by controlled traction said wrought product thus put into solution with a permanent elongation of at least 1% and preferably between 2 and 5%.

Finally, we make an income to the product thus put in solution and optionally relieved. The income is made in one or more steps at a temperature advantageously between 130 and 160 ° C for a period of 5 to 60 hours. Preferably one obtains at the end of the income a metallurgical state T8, such as in particular T851, T83, T84, or T85.

The wrought products obtained by the process according to the invention have advantageous properties.

The logarithmic fatigue mean of the wrought products whose thickness is at least 80 mm, obtained by the method according to the invention, measured at mid-thickness in the direction TL on smooth test pieces according to Figure la at a maximum amplitude stress of 242 MPa, a frequency of 50 Hz, a stress ratio R = 0.1 is at least 250,000 cycles, advantageously the fatigue property is obtained for the wrought products obtained by the process according to the invention, the thickness of which is at least 100 mm or preferably at least 120 mm or even at least 140 mm.

 The wrought products according to the invention having a thickness of at least 80 mm also have advantageous fatigue properties for hole specimens, thus the fatigue quality index IQF obtained on specimens with a hole Kt = 2.3 according to FIG. at a frequency of 50 Hz to ambient air with an R-0.1 value is at least 180 MPa and preferably is at least 190 MPa in the TL direction.

 In addition, the products obtained by the process according to the invention have advantageous static mechanical characteristics. Thus for wrought products whose thickness is at least 80 mm comprising in% by weight, Cu: 3.0 - 3.9; Li: 0.7 - 1.3; Mg: 0.1 - 1.0, at least one element selected from Zr, Mn and Ti, the amount of said element, if selected, being from 0.06 to 0.15% by weight for Zr, O, From 0.5 to 0.8% by weight for Mn and from 0.01 to 0.15% by weight for Ti; Ag: 0 - 0.7; Zn <0.25; If <0.08; Fe <0.10; other <0.05 each and <0.15 in total, remains aluminum, the yield strength measured at quarter-thickness in the direction L is at least 450 MPa and preferably at least 470 MPa and / or the breaking strength measured is at least 480 MPa and preferably at least 500 MPa and / or the elongation is at least 5% and preferably at least 6%.

 The wrought products obtained by the process according to the invention can advantageously be used to produce structural elements, preferably aircraft structural elements. Preferred aircraft structural elements are spars, ribs or frames. The invention is particularly advantageous for parts of complex shape obtained by integral machining, used in particular for the manufacture of aircraft wings and for any other use for which the properties of the products according to the invention are advantageous. .

Example

In this example, AA2050 alloy plates were prepared. AA2050 alloy plates were cast by direct cooling vertical semi-continuous casting. The alloy was prepared in a melting furnace. For Examples 1 to 7, a KCL / LiCl mixture was used on the surface of the liquid metal in the melting furnace. For Examples 8 to 9 no salt was used in the melting furnace. For Examples 8 to 9 the atmosphere in contact with the liquid metal with an oxygen content of less than 0.3% by volume for the entire casting installation. The casting installation included a hood disposed above the pouring well to limit the oxygen content. For tests 8 and 9, an aspiration (101) was also used such that the pressure in the chamber (10) was lower than the pressure in the chamber (65) and such that the speed of the atmosphere through the open surfaces of the casting well was at least 2 m / s. Oxygen content was measured with an oximeter during casting. Furthermore, the hydrogen content in the liquid aluminum was measured using an Alscan ™ type probe under nitrogen flushing. Two types of liquid metal dispensers were used. A first "Combo Bag" type dispenser as described for example in Figures 2 to 6 of the international application WO99 / 44719 but made of fabric comprising essentially carbon, referenced below "distributor A" and a second distributor such as described in Figure 3 referenced below "distributor B" is made of graphite wire cloth.

 The casting conditions of the various tests carried out are given in Table 1.

Table 1 - Casting conditions for different tests

The plates were homogenized for 12 hours at 505 ° C., machined to a thickness of about 365 mm, hot-rolled to sheets with a final thickness of between 154 and 158 mm, dissolved at 504 ° C. , quenched and relieved by controlled traction with a permanent elongation of 3.5%. The sheets thus obtained have an 18 hour income at 155 ° C.

Static mechanical properties and toughness were characterized at quarter-thickness. Static mechanical characteristics and toughness are given in Table 2.

Table 2 Mechanical characteristics

The fatigue properties were characterized on smooth test specimens and hole test specimens for some samples taken at mid-thickness.

For the smooth fatigue characterizations, four test pieces, whose diagram is given in Figure la, were tested at mid-thickness and half-width in the TL direction, the test conditions being σ = 242 MPa, R = 0.1 . Some tests were stopped after 200,000 cycles and other tests were stopped after 300,000 cycles.

For hole fatigue characterizations, the specimen reproduced in Figure 1b, whose K _t value is 2.3, was used. The test pieces were tested at a frequency of 50 Hz in ambient air with a value R = 0.1. The corresponding Wohler curves are shown in Figures 6a and 6b. The IQF fatigue quality index was calculated. Table 3 - Fatigue Test Results

The combination of a hydrogen content of less than 0.4 ml / 100g of an oxygen content measured above the liquid surface of less than 0.3% by volume and of the distributor B makes it possible to achieve an excellent level of fatigue performance. These results are shown in Figure 5.

Claims

claims A method of manufacturing an aluminum alloy product comprising the steps in which an alloy liquid metal bath comprising, in% by weight, Cu: 2.0 - 6.0; Li: 0.5 - 2.0; Mg: 0-1.0; Ag: 0 - 0.7; Zn 0 - 1.0; and at least one member selected from Zr, Mn, Cr, Se, Hf and Ti, the amount of said element, if selected, being from 0.05 to 0.20% by weight for Zr, 0.05 to 0 , 8% by weight for Mn, 0.05 to 0.3% by weight for Cr and for Se, 0.05 to 0.5% by weight for Hf and from 0.01 to 0.15% by weight for Ti , Si <0,1; Fe <0.1; other <0.05 each and <0.15 in total, pouring said alloy by vertical semi-continuous casting to obtain a plate of thickness T and width W such that, during solidification,  the hydrogen content of said bath of liquid metal (1) is less than 0.4 ml / 100 g,  the oxygen content measured above the liquid surface (14, 15) is less than 0.5% by volume, the distributor used (7) for the casting is made of fabric comprising essentially carbon, that it comprises a lower face (76), an upper face defining the orifice through which the liquid metal is introduced (71) and a wall; of substantially rectangular section, the wall comprising two longitudinal parts parallel to the width W (720, 721) and two transverse parts parallel to the thickness T (730, 731), said transverse and longitudinal portions being formed of at least two tissues, a first substantially occluding and semi-rigid fabric (77) ensuring the maintenance of the shape of the dispenser during casting and a second non-sealing fabric (78) allowing passage and filtration of the liquid, said first and second fabric being bonded to the to one another without overlapping or overlapping and without gap between them, said first fabric continuously covering at least 30% of the area of said parts by oi (720,721, 730, 731) and being positioned so that the liquid surface is in contact with it over the entire section. 2. The method of claim 1 wherein the oxygen content of the atmosphere in contact with the liquid metal bath in the melting furnace during degassing steps, filtration is less than 0.5% by volume and preferably in wherein the oxygen content of the atmosphere in contact with the liquid metal bath is less than 0.5% by volume for the entire casting plant. 3. Method according to any one of claims 1 to 2 wherein a cover (62) covers the liquid surface during solidification (14,15), said cover preferably comprising seals (61) for sealing with the casting table (32) and wherein an inert gas (9) is introduced into the chamber (65) defined between the cover and the casting table and wherein suction is maintained in the casting well (10) by means of a pump (101). ), preferably so that the pressure in the chamber (10) is less than the pressure in the chamber (65). 4. Method according to any one of claims 1 to 3 wherein no molten salt containing lithium throughout the casting plant. A method according to any one of claims 1 to 4 wherein said dispenser (7) is such that the first fabric has a height, hl, measured from the top face on the circumference of the wall (720, 721, 730, 731) such that hl> 0.3 h and preferably hl> 0.5 h, where h denotes the total height of the distributor wall. 6. Method according to any one of claims 1 to 5 wherein the height  immersed in the liquid metal wall (720, 721, 730, 731) of the distributor (7) covered by the first fabric is at least 20%, preferably 40% and preferably 60% of the total immersed wall height . 7. A process according to any one of claims 1 to 6 wherein the surface portion covered by the first fabric is between 30 and 90% and preferably between 50 and 80% for the longitudinal portions (720) and (721), and / or between 30 and 70% and preferably between 40 and 60% for the lateral parts (730, 731) and / or between 30 and 100% and preferably between 50 and 80% for the bottom (76). 8. Method according to any one of claims 1 to 7 wherein after the steps (a) and (b), the steps are carried out  (c) homogenizing before or after optionally machining said plate to obtain a heat-deformable shape  (d) said shape thus homogenized is deformed hot and optionally cold so as to obtain a wrought product,  (e) the solution is soaked and soaked,  (f) optionally, said wrought product thus dissolved is deformed by plastic deformation with a deformation of at least 1%,  (g) an income is made to the said product thus dissolved and optionally relieved. The method of any one of claims 1 to 8 wherein said  Hot and / or cold deformation is performed by spinning, rolling and / or forging. The method of any one of claims 1 to 9 wherein said wrought product has a thickness of at least 80 mm. The method of any one of claims 1 to 10 wherein the rate of  deformation in step (d) is less than 85% and preferably less than 80%. The method of any one of claims 1 to 11 wherein the alloy comprises, in% by weight, Cu: 3.0 - 3.9; Li: 0.7 - 1.3; Mg: 0.1 - 1.0, at least one element selected from Zr, Mn and Ti, the amount of said element, if selected, being from 0.06 to 0.15% by weight for Zr, 0, 0.5 to 0.8% by weight for Mn and from 0.01 to 0.15 % by weight for Ti; Ag: 0 - 0.7; Zn <0.25; If <0.08; Fe <0.10; others <0.05 each and <0.15 in total. 13. A dispenser for semi-continuous casting of fabric aluminum alloy plates comprising substantially carbon, comprising a lower face (76), an upper face defining the orifice through which the liquid metal is introduced (71) and a wall of substantially rectangular section, the wall comprising two longitudinal parts parallel to the width W (720, 721) and two transverse parts parallel to the thickness T (730, 731), said transverse and longitudinal portions being formed of at least two fabrics, a first substantially obturating and semi-rigid fabric (77) ensuring the maintenance of the shape of the dispenser during casting and a second non-sealing fabric (78) allowing passage and filtration of the liquid, said first and second fabric being bonded together; to one another without overlap or overlap and without gap between them, said first fabric continuously covering at least 30% of the surface area said wall portions (720, 721, 730, 731) and being positioned so that the liquid surface is in contact with it over the entire section. 14. Dispenser according to claim 13 characterized in that the first fabric has a height, hl, measured from the upper face on the circumference of the wall (720, 721, 730, 731) such that hl> 0.3 h and preferably hl> 0.5 h, where h denotes the total height of the distributor wall. 15. Dispenser according to claim 13 or claim 14 characterized in that the section of its wall changes linearly depending on the height h, typically so that the surface of the lower face (76) of the distributor is higher or lower not more than 10% on the surface of the upper face (71) of the dispenser. 16. Dispenser according to any one of claims 13 to 15 characterized in that the surface portion covered by the first fabric is between 30 and 90% and preferably between 50 and 80% for the longitudinal portions (720) and (721), and / or between 30 and 70% and preferably between 40 and 60% for the lateral parts (730, 731) and / or between 30 and 100% and preferably between 50 and 80% for the bottom (76). 17. Dispenser according to any one of claims 13 to 16 characterized in that the length L1 of the first tissue located in the bottom (76) is greater than the length L2 of the first tissue located in the portion of the longitudinal walls (720) and (721 ) in contact with the bottom. 18. Dispenser according to any one of claims 13 to 16 characterized in that the first fabric and the second fabric are obtained by weaving a graphite wire. 19. Dispenser according to claim 18 characterized in that the wire is coated with a layer facilitating sliding. 20. Dispenser according to any one of claims 13 to 19 characterized in that the first fabric is substantially obturating, typically having mesh size of less than 0.5 mm, preferably less than 0.2 mm and / or the second fabric is non-sealing and allows the passage of molten metal, typically having mesh size of between 1 and 5 mm, preferably 2 to 4 mm.