EP3080318B2 - Method for manufacturing products made of aluminium-copper-lithium alloy with improved fatigue properties and distributor for this method - Google Patents

Description

Field of the invention

The invention relates to a distributor intended for the semi-continuous casting of aluminum alloy plates and a process for manufacturing wrought aluminum - copper - lithium alloy products, intended in particular for aeronautical and aerospace construction.

State of the art

Rolled aluminum alloy products are developed to produce structural elements intended in particular for the aviation industry and the aerospace industry.

Aluminum - copper - lithium alloys are particularly promising for manufacturing this type of product. The specifications imposed by the aeronautical industry for fatigue life are high. For thick products they are particularly difficult to reach. Indeed, taking into account the possible thicknesses of the cast plates, the reduction in thickness by hot deformation is quite low and consequently the sites linked to the casting on which the fatigue cracks initiate do not see their size reduced during hot deformation.

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

Thick Al-Cu-Li alloy products are notably described in the applications US2005/0006008 And US2009/0159159 .

In the request WO2012/ll0717 , it is proposed to improve the properties, particularly in fatigue, of aluminum alloys containing in particular at least 0.1% Mg and/or 0.1% Li to carry out an ultrasonic treatment during casting. However, this type of treatment remains difficult to carry out for the quantities necessary for the manufacture of thick sheets.

In the request US5383986 , it is proposed to improve the mechanical properties of an Al-Cu-Li alloy to achieve, after solution quenching of the product, a traction of between 1 and 20% followed by tempering.

In the request US2009/0142222 , it is proposed to obtain an excellent compromise of properties, in particular fatigue, to use an extruded alloy consisting essentially of 3.4-4.2 wt% Cu; 0.9-1.4 wt% Li; 0.3-0.7 wt% Ag; 0.1-0.6 wt% Mg; 0.2-0.8 wt% Zn; 0.1-0.6 wt% Mn and 0.01-0.06 wt% of at least one element influencing grain size; the remainder consisting of aluminum and possible impurities.

US5207974 discloses a partitioned dispenser for dispensing molten metal from a nozzle to form an ingot.

There is a need for thick aluminum - copper - lithium alloy products having improved properties compared to those of known products, in particular in terms of fatigue properties while having toughness properties and advantageous static mechanical resistance properties. . Furthermore, there is a need for a simple and economical process for obtaining these products.

Object of the invention

A first object of the invention is a distributor intended for the semi-continuous casting of aluminum alloy plates according to claim 1.

Another object of the invention is a method of manufacturing an aluminum alloy product according to claim 6.

Description of figures

• There Figure 1 is the diagram of the specimens used for the smooth fatigue tests ( Fig 1a ) and in hole fatigue ( Fig 1b ). Dimensions are given in mm.
• There Figure 2 is a general diagram of the solidification device used in one embodiment of the invention.
• There Figure 3 is a general diagram of the distributor used in the method according to the invention.
• There Figure 4 presents representations of the bottom and the lateral and longitudinal parts of the wall of the distributor according to one embodiment of the invention.
• There Figure 5 shows the relationship between 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 the solidification ( Fig. 5b ).
• There Figure 6 shows the Wöhler curves obtained with tests 3, 7 and 8 in the LT direction ( Figure 6a ) and TL ( figure 6b ).

Description of the invention

Unless otherwise stated, all indications regarding the chemical composition of alloys are expressed as a weight percentage 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 done in accordance with the regulations of The Aluminum Association, known to those skilled in the art. Unless otherwise stated, the definitions of metallurgical conditions indicated in European standard EN 515 apply.

The static mechanical characteristics in traction, in other words the breaking strength R _m , the conventional elastic limit 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 direction of the test being defined by standard EN 485-1. The fatigue properties on smooth specimens are measured in ambient air at a maximum stress amplitude of 242 MPa, a frequency of 50 Hz, a stress ratio R = 0.1, on specimens as shown in Figure la, taken at half-width and half-thickness of the sheets in the TL direction. Test conditions comply with ASTM E466. The logarithmic average of the results obtained on at least 4 test pieces is determined.

où σ_max est la contrainte maximale appliquée à un échantillon donné, N est le nombre de cycles jusqu'à la rupture, No est égale à 100 000 et n = -4,5. On rapporte l'IQF correspondant à la médiane, soit 50% rupture pour 100 000 cycles.The fatigue properties on hole specimens are measured in ambient air for variable stress levels, at a frequency of 50 Hz, a stress ratio R = 0.1, on specimens as shown in the figure. Figure 1b , Kt = 2.3, taken from the center and mid-thickness of the sheets in the LT and TL direction. The Walker equation was used to determine a maximum stress value representative of 50% non-failure at 100,000 cycles. To do this, a fatigue quality index (IQF) is calculated for each point of the Wöhler curve with the formula $$\mathit{IQF}={\sigma }_{\max }{\left(\frac{{\mathrm{NOT}}_0}{\mathrm{NOT}}\right)}^{1/\mathrm{not}}$$

where σ _max is the maximum stress applied to a given sample, N is the number of cycles until failure, No is equal to 100,000 and n = -4.5. We report the IQF corresponding to the median, i.e. 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 stated, the definitions in EN 12258 apply. In particular, a sheet metal is according to the invention a rolled product of rectangular cross section whose uniform thickness is at least 6 mm and does not exceed 1/10th of the width.

Here we call "structural element" or "structural element" of a mechanical construction 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 carried out. 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 in particular the elements which make up the fuselage (such as the fuselage skin), the fuselage stiffeners or stringers (stringers), the bulkheads (bulkheads), the fuselage frames. 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 floor beams, seat tracks and doors.

Here we call “assembly of the casting installation” all of the devices making it possible to transform a metal in any form into a semi-finished product in raw form by passing through the liquid phase. A casting installation may include numerous devices such as one or more furnaces necessary for melting the metal (“melting furnace”) and/or maintaining it (“maintaining furnace”) in temperature and/or for processing operations. preparation of the liquid metal and adjustment of the composition (“preparation furnace”), one or more tanks (or “pockets”) intended to carry out a treatment to eliminate impurities dissolved and/or suspended in the liquid metal , this treatment may consist of filtering the liquid metal on a filter media in a “filtration bag” or introducing into the bath a so-called “treatment” gas which can be inert or reactive in a “degassing bag”, a degassing device. solidification liquid metal (or “casting craft”), by vertical semi-continuous casting by direct cooling in a casting well, which may include devices such as a mold (or “ingot mold”), a device for supplying liquid metal ( or “busette”) 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 be transported.

The present inventors have found that, surprisingly, it is possible to obtain thick wrought products made of aluminum copper lithium alloy having improved fatigue performance by preparing these sheets using the following process.

In a first step, a bath of liquid alloy metal is produced 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 element chosen from Zr, Mn, Cr, Sc, Hf and Ti, the quantity of said element, if chosen, being 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 Sc, 0.05 to 0.5% by weight for Hf and 0.01 to 0.15% by weight for Ti , If ≤ 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 chosen from Zr, Mn and Ti, the quantity of said element, if chosen, being 0.06 to 0.15% by weight for Zr, 0, 05 to 0.8% by weight for Mn and 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 if 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 alloy AA2050.

This liquid metal bath is prepared in a furnace of the casting installation. It is known, for example, to US 5,415,220 to use lithium-containing molten salts such as KCl/LiCl mixtures in the melting furnace to passivate the alloy as it is transferred to the casting facility. The present inventors have, however, obtained excellent fatigue properties for thick sheets without using molten salt containing lithium in the melting furnace, but by maintaining in this furnace an atmosphere poor in oxygen and believe that the presence of salt in the melting furnace could in certain cases have 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, an oxygen content of less than 0.5% by volume and preferably less than 0.3% by volume is maintained in the furnace(s) of the casting installation. However, an oxygen content of at least 0.05% by volume and even at least 0.1% by volume can be tolerated in the furnace(s) of the casting installation, which is advantageous in particular for the aspects economics of the process. Advantageously, the furnace(s) of the casting installation are induction furnaces. The present inventors have found that this type of oven is advantageous despite the mixing generated by induction heating.

This liquid metal bath is then treated with a degassing bag and 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 commercial equipment such as the device marketed under the brand 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 bath of liquid metal in the melting furnace during the degassing and filtration stages 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 0.3% by volume for the entire installation of casting. However, an oxygen content of at least 0.05% by volume and even at least 0.1% by volume can be tolerated for the entire casting installation, which is advantageous in particular for the economic aspects of the process.

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

In this example of a suitable device, the liquid metal coming from a chute (63) is introduced into a nozzle (4) controlled by a stopper (8) which can move up and down (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 (11, 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) to ensure sealing with the casting table (32). The liquid metal in the chute (63) can advantageously be protected by a cover (64). An inert gas (9) is introduced into the chamber (65) defined between the cover and the casting 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 inert gas flow can be adjusted to achieve the desired oxygen content. However, it is advantageous to maintain sufficient suction in the casting well (10) using a pump (101). In fact, the present inventors have noted that there is generally not a sufficient seal between the ingot mold (31) and the solidified metal (5), which leads to diffusion of the atmosphere from the casting well (10) towards 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 be preferably obtained by imposing a speed of the atmosphere through the open surfaces of the casting well 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 enclosure (10) is lower than atmospheric pressure, typically 0.95 times atmospheric pressure. As part of the process according to the invention, an oxygen content of less than 0.5% by volume and preferably less than 0.3% by volume is maintained in the chamber (65), thanks to the devices described.

An example of a dispenser (7) of the method according to the invention is presented on the figures 3 And 4 . The distributor according to the invention is made of fabric essentially comprising carbon, it comprises a lower face (76), a typically empty upper face defining the orifice through which the liquid metal is introduced (71) and a wall of substantially rectangular 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 parts and longitudinal being formed of at least two fabrics, a first substantially sealing and semi-rigid fabric (77) ensuring the maintenance of the shape of the distributor during casting and a second non-closing fabric (78) allowing the passage and filtration of the liquid, said first and second fabrics being linked to each other without overlap or with overlap and without gap separating them, said first fabric continuously covering at least 30% of the surface of said wall parts (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 to one another without overlap or with overlap and without gap separating them, that is to say in contact, the liquid metal cannot 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 Figures 2 to 5 . Thanks to the support provided by the first fabric, the distributor is semi-rigid and does not deform significantly 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 designates the total height of the distributor wall.

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

There Figure 4 represents the bottom and the longitudinal wall parts. The bottom (76) is covered by the first and second fabrics. Advantageously the first fabric is at least located in the central part of the bottom (76) over 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.

The surface portion covered by the first fabric is between 50 and 80% for the longitudinal parts (720) and (721), and between 40 and 60% for the lateral parts (730, 731) and between 50 and 80% for the bottom (76).

It is advantageous for the length L1 of first fabric located in the bottom (76) to be greater than the length L2 of first fabric located in the part of the longitudinal walls (720) and (721) in contact with the bottom.

The present inventors believe that the geometry of the distributor 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 thread essentially comprising carbon. Weaving graphite wire is particularly advantageous. The fabrics are typically sewn together. It is also possible, instead of a first and second fabric, to use a single diffuser fabric having at least two weaving zones, more or less dense. It is advantageous for the ease of weaving that the thread comprising carbon is coated with a layer facilitating sliding. This layer may for example comprise a fluoropolymer such as Teflon or a polyamide such as xylon. The first fabric is noticeably obturating. Typically this is a fabric having mesh sizes of less than 0.5 mm, preferably less than 0.2 mm. The second fabric is non-obstructive and allows the passage of 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 fabric locally covers the second fabric, while being in intimate contact so as not to leave a gap between the two fabrics.

Advantageously, the plate thus obtained is then transformed to obtain a wrought product. The plate thus obtained is then homogenized before or after optionally being machined to obtain a shape that can be deformed under heat. In one embodiment, the plate is machined in the form of a rolling plate so as to then be hot deformed by rolling. In another embodiment, the plate is machined in the form of a forging blank so as to then be hot deformed by forging. In yet another embodiment the plate is machined in the form of billets so as to then be deformed hot 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.

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

The wrought product thus obtained is then put into solution and quenched. The solution 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, said wrought product thus put into solution is relieved by plastic deformation with a deformation of at least 1%. In the case of rolled products it is advantageous to relieve tension by controlled traction of said wrought product thus put into solution with a permanent elongation of at least 1% and preferably between 2 and 5%.

Finally, the product thus placed in solution and optionally released is subjected to an income. The tempering is carried out in one or more stages at a temperature advantageously between 130 and 160°C for a period of 5 to 60 hours. Preferably, at the end of the tempering, a metallurgical state T8 is obtained, 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 average fatigue of wrought products whose thickness is at least 80 mm, obtained by the process according to the invention, measured at mid-thickness in the direction

TL on smooth specimens 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 whose thickness is at least 100 mm or preferably at least 120 mm or even at least 140 mm.

The wrought products according to the invention with a thickness of at least 80 mm also have advantageous fatigue properties for hole specimens, thus the fatigue quality index IQF obtained on hole specimens Kt = 2.3 according to the Figure 1b at a frequency of 50 Hz to ambient air with a value R = 0.1 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 including in % by weight, Cu: 3.0 - 3.9; Li: 0.7 - 1.3; Mg: 0.1 - 1.0, at least one element chosen from Zr, Mn and Ti, the quantity of said element, if chosen, being 0.06 to 0.15% by weight for Zr, 0, 05 to 0.8% by weight for Mn and 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, the yield strength measured at quarter thickness in 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 as well as for any other use for which the properties of the products according to the invention are advantageous .

Example

In this example, heavy plates made of AA2050 alloy were prepared. AA2050 alloy plates were cast by direct-cooled 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 less than 0.3% by volume for the entire casting installation. The casting installation included a hood placed above the casting well to limit the oxygen content. For tests 8 and 9, a suction (101) was also used such that the pressure in the enclosure (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. The oxygen content was measured using an oximeter during casting. Furthermore, the hydrogen content in the liquid aluminum was measured using an Alscan ^™ type probe under nitrogen sweeping. Two types of liquid metal dispensers were used. A first distributor of the “Combo Bag” type as described for example in the Figures 2 to 6 international demand WO 99/44719 , which does not call into question the invention, but made of fabric essentially comprising carbon, referenced below "distributor A" and a second distributor as described Figure 3 referenced below “distributor B” is made of graphite wire fabric.
The casting conditions of the different tests carried out are given in table 1. Table 1 - Casting conditions for the different tests Essay H2 [ml/100g] O2 measured above the casting well (% by volume) Distributer 1 0.41 0.3 HAS 2 0.43 0.1 HAS 3 0.37 0.1 HAS 4 0.33 0.1 HAS 5 0.35 0.4 HAS 6 0.38 0.3 HAS 7 0.47 0.7 B 8 0.34 0.1 B 9 0.29 0.1 B

The plates were homogenized for 12 hours at 505°C, machined to a thickness of approximately 365 mm, hot rolled to sheets with a final thickness of between 154 and 158 mm, put into solution at 504°C , quenched and relieved by controlled traction with a permanent elongation of 3.5%. The sheets thus obtained were tempered for 18 hours at 155°C.

Static and toughness mechanical properties were characterized at quarter thickness. Static mechanical characteristics and toughness are given in Table 2. Table 2 Mechanical characteristics Essay Thickness [mm] Rm (L) MPa Rp0.2 (L) MPa A % (L) 1 158 528 495 6.5 2 155 538 507 7.0 3 155 525 493 8.3 4 158 528 four hundred ninety seven 7.0 5 158 529 495 6.0 6 158 527 496 6.8 7 154 514 486 8.3 8 158 533 502 6.3 9 158 542 512 5.8

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

For smooth fatigue characterizations, four specimens, the diagram of which is given in

Figure la, were tested at half-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 the hole fatigue characterizations, the specimen reproduced on the Figure 1b , whose K _t value is 2.3. The specimens were tested at a frequency of 50 Hz in ambient air with a value R = 0.1. The corresponding Wöhler curves are presented on the Figures 6a and 6b . The fatigue quality index IQF was calculated. Table 3 - Fatigue test results Essay Smooth fatigue results (number of cycles) IQF hole fatigue results (MPa), 50% failure for 100,000 cycles Test tube 1 Test tube 2 Test tube 3 Test tube 4 Lo garithmic average L.T. TL 1 101423 101761 116820 118212 109263 2 102570 140030 152120 178860 140600 3 112453 163422 152620 167113 147138 175 152 4 101900 110300 139400 144100 122580 5 93400 105000 112600 129900 109439 6 114000 116500 188100 195000 148564 7 192300 >200000 189600 >200000 >195400 183 168 8 >300000 >300000 >300000 >300000 >300000 186 196 9 >300000 >300000 >300000 >300000 >300000

The combination of a hydrogen content of less than 0.4 ml/100g, an oxygen content measured above the liquid surface of less than 0.3% by volume and distributor B makes it possible to achieve an excellent level of fatigue performance. These results are presented on the Figure 5 . Table 3 - Fatigue test results Essay Smooth fatigue results (number of cycles) IQF hole fatigue results (MPa), 50% failure for 100,000 cycles Test tube 1 Test tube 2 Test tube 3 Test tube 4 Logarithmic average L.T. TL 1 101423 101761 116820 118212 109263 2 102570 140030 152120 178860 140600 3 112453 163422 152620 167113 147138 175 152 4 101900 110300 139400 144100 122580 5 93400 105000 112600 129900 109439 6 114000 116500 188100 195000 148564 7 192300 >200000 189600 >200000 >195400 183 168 8 >300000 >300000 >300000 >300000 >300000 186 196 9 >300000 >300000 >300000 >300000 >300000

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

Claims (12)

1. Dispenser used for semi-continuous casting of aluminium alloy slabs made of fabric comprising essentially carbon, having a lower face (76), an upper face defining the opening through which the molten metal is introduced (71) and a wall of substantially rectangular section, the wall comprising two longitudinal portions parallel with width W (720, 721) and two transverse portions parallel with thickness T (730, 731), said transverse and longitudinal portions being formed from at least two fabrics, a first fabric having mesh sizes of less than 0.5 mm and semi-rigid (77) ensuring that the dispenser keeps its shape during casting, and a second non-sealing fabric (78) allowing the passage and filtration of liquid, said first and second fabrics being bonded to each other without overlap or with overlap and no gap 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 therewith over the entire section, and characterized in that the surface area covered by the first fabric is between 50 and 80% for the longitudinal portions (720) and (721), and between 40 and 60% for the lateral portions (730, 731) and between 50 and 80% for the base (76).
2. Dispenser according to claim 1 characterized in that the first fabric has a height h1 as 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 is the total height of the wall of the dispenser.
3. Dispenser according to claim 1 or claim 2 characterized in that the section of the wall changes linearly as a function of height h, typically so that the surface of the lower face (76) of the dispenser is higher or lower by at most 10% than the surface of the upper face (71) of the dispenser .
4. Dispenser according to any of claims 1 to 3 characterized in that length L1 of the first fabric located in the base (76) is greater than length L2 of the first fabric in the portion of the longitudinal walls (720) and (721) in contact with the base.
5. Dispenser according to any of claims 1 to 4 characterized in that the first fabric has a mesh size of less than 0.2 mm and/or the second fabric is non-sealing and allows molten metal to pass through, typically having a mesh size of between 1 and 5 mm, preferably 2 to 4 mm.
6. Method of manufacturing an aluminium alloy wrought product comprising steps in which

   (a) a bath of molten alloy metal is prepared comprising, as a percentage 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 element selected from Zr, Mn, Cr, Sc, Hf and Ti, the amount of said element, if selected, being 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 Sc, 0.05 to 0.5 by weight Hf and 0.01 to 0.15% by weight for Ti, Si ≤ 0.1; Fe ≤ 0.1; others ≤ 0.05 each and ≤ 0.15 in total, the rest aluminium,

   (b) said alloy is cast by semi-continuous vertical casting to obtain a slab of thickness T and width W so that upon solidification,

   - the hydrogen content of said molten metal bath (1) is less than 0.4 ml/100g,

   - the oxygen content measured above the liquid surface (14,15) is less than 0.5% by volume,

   - the dispenser used (7) for casting is a dispenser according to any one of claims 1 to 5.

   (c) said slab is homogenized before or after optionally machining it to get a shape that can be hot-worked

   (d) said shape, homogenized in this way, is hot worked and optionally cold worked to obtain a wrought product,

   (e) said wrought product undergoes solution heat treatment and quenching,

   (f) optionally said wrought product that has undergone solution heat treatment is stress-relieved by plastic deformation with a deformation of at least 1 %.

   (g) said solution heat-treated and optionally stress-relieved product is subjected to ageing.
7. Method according to claim 6 wherein the oxygen content of the atmosphere in contact with the liquid metal bath in the melting furnace during the degassing step, filtration is less than 0.5% by volume and preferably 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 facility.
8. Method according to either of claims 6 or 7 wherein a lid (62) covers the liquid surface during solidification (14,15), said lid preferably comprising seals (61) to ensure pressure tightness with the casting table (32) and wherein an inert gas (9) is introduced into the chamber (65) defined between the lid and the casting table and wherein suction is maintained in the casting pit (10) by means of a pump (101), preferably so that the pressure within the containment (10) is less than the pressure in the chamber (65).
9. Method according to any of claims 6 to 8 in which a molten salt containing lithium is not used throughout the entire casting facility.
10. Method according to any of claims 6 to 9 in which said hot and/or cold working is performed by extrusion, rolling and/or forging.
11. Method according to any of claims 6 to 10 in which the deformation ratio during step (d) is lower than 85% and preferably lower than 80%.
12. Method according to any of claims 6 to 7 in which the alloy comprises, as a percentage by weight, Cu: 3.0 - 3.9; Li: 0.7 - 1.3, Mg: 0.1 to 1.0, at least one element selected from Zr, Mn and Ti, the amount of said element, if selected, is from 0.06 to 0.15 by weight for Zr, 0.05 to 0.8 by weight for Mn and 0.01 to 0.15% by weight for Ti; Ag: 0 - 0.7; Zn ≤ 0.25; Si ≤ 0.08; Fe ≤ 0.10; others ≤ 0.05 each and ≤ 0.15 in total.

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