Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/12—Alloys based on aluminium with copper as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
  • C22F1/057—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys with copper as the next major constituent

Definitions

• the present invention generally relates to aluminum alloy products and, in particular, such products useful in the aerospace industry and suitable for use in fuselage applications.
• compressive and compressive shear strength is an extremely important design guideline, since the heavier fuselage panels suffer this type of constraint.
• it In order for a new material to be able to reduce the weight of these compression-stressed panels, it must have a high modulus of elasticity, a high 0.2% yield strength (to withstand buckling) and a low mass volume.
• the second major guideline is the residual resistance of panels longitudinally (in the axis of the fuselage) cracked.
• Aeronautical certification regulations require the consideration of damage tolerance in design, so it is usual to consider large longitudinal or circumferential cracks in the fuselage panels, to demonstrate that a certain level of stress can be applied. without a catastrophic break.
• a known property of the materials governing the design here is the toughness under plane stress. All known factors of critical stress intensity, however, only give a limited view of toughness.
• the R curve test is a widely recognized means for characterizing toughness properties.
• the curve R represents the evolution of the critical effective stress intensity factor for the crack propagation as a function of the effective crack extension under a monotonic stress. It allows the determination of the critical load for unstable failure for any configuration relevant to cracked aircraft structures.
• the values of the effective stress intensity factor and the crack extension effective are values defined in ASTM E561.
• the length of the curve R - namely the maximum crack extension of the curve - is a parameter in itself important for the fuselage design.
• K app The classical analysis, generally used, of the tests carried out on panels with central crack gives a factor of intensity of stress apparent to the rupture (K app ). This value does not vary significantly with the length of the R curve, especially when the slope of the R curve is close to the slope of the stress intensity factor curve applied to the crack length (applied curve) .
• the applied curve drops due to the bridging effect of the stiffener.
• a lower density is clearly beneficial for the weight of a structural member.
• a third major guideline is thus the density of the material.
• large parts of the fuselage are not so heavily loaded and the weight of the design is limited by a certain limit generally called "minimum thickness".
• the minimum thickness concept is the lowest usable thickness for manufacturing (especially panel handling) and repair (repair riveting). The only way to reduce the weight in this case is to use a lower density material.
• Today, civilian aircraft fuselages are, for the most part, made of alloy sheet 2024, 2056, 2524, 6013, 6156 or 7475, clad on each face with an aluminum alloy f lightly loaded alloying elements , an alloy 1050 or 1070 for example.
• the purpose of the coating alloy is to impart sufficient corrosion resistance. Light, generalized or pitting corrosion is tolerable but should not be penetrating so as not to attack the core alloy. There is a tendency to try to use non-plated materials for fuselage design, so as to reduce the cost. Corrosion resistance, and in particular intergranular corrosion and corrosion under stress, the fuselage panel is thus an important aspect of its properties.
• US Patent 5,032,359 discloses a family of alloys based on aluminum-copper-magnesium-silver alloys to which lithium has been added, in specific ranges and which have a high resistance at room temperature and at high temperatures. temperature, high ductility at room temperature and high temperature, extrusionability, controllability, and good solderability and natural aging response properties. The examples describe extruded products. No information is provided on toughness, fatigue behavior or corrosion resistance.
• the alloy has a composition of 3.0 to 6.5% copper, 0.05 to 2.0% magnesium, 0.05 to 1.2% silver, from 0.2 to 3.1% lithium, from 0.05 to 0.5% of an element chosen from zirconium, chromium, manganese, titanium, boron, hafnium, vanadium, titanium diboride and mixtures thereof.
• US 5 211 910 discloses aluminum-based alloys containing Cu, Li, Zn, Mg and Ag which have favorable properties, such as a relatively low density, a modulus high mechanical strength / ductility combinations, a strong response to natural aging with and without anterior work hardening, and a high modulus after income with or without prior work hardening.
• the alloys have a composition of 1 to 7% Cu, 0.1 to 4% Li, 0.01 to 4% Zn, 0.05 to 3% Mg, 0.01 to 2% of Ag, from 0.01 to 2% of an element selected from Zr, Cr, Mn, Ti, Hf, V, Nb, B and TiB 2 , the remainder being Al together with its unavoidable impurities.
• This invention describes how Zn additions can be used to reduce the Ag content present in the alloys taught in US 5,032,359 in order to reduce the cost.
• US 5 455 003 discloses a process for producing aluminum-copper-lithium alloys which have improved strength and toughness at cryogenic temperatures.
• the improved cryogenic properties are achieved by adjusting the composition of the alloy, together with the processing parameters such as the amount of work hardening and the income.
• the product is used for cryogenic tanks in space launch vehicles.
• US 5,389,165 discloses an aluminum alloy useful in aircraft and aerospace structures which has low density, high mechanical strength and high toughness and has the formula: Cu a LibMg c ⁇ gdZr AlbaI e wherein a, b, c, d, e and bal indicate the amount in% by weight of alloying components, and wherein 2.8 ⁇ a ⁇ 3.8,
• the copper and lithium components are adjusted so that the combined copper and lithium content is kept below the solubility limit in order to avoid a loss of toughness during high temperature exposure.
• the relationship between copper and lithium grades must also satisfy the following relationship:
• the present inventors have come to the present invention concerning an aluminum-copper-lithium-magnesium-silver alloy, which exhibits high mechanical strength, high toughness and specifically high crack extension prior to unstable rupture of pre-cracked wide panels, and a high resistance to corrosion.
• An object of the present invention is a method of manufacturing an aluminum alloy sheet having a high toughness and mechanical strength, wherein: a) a liquid metal bath comprising 2.7 to 3 is produced; , 4% by weight of Cu, 0.8 to 1.4% by weight of Li, 0.1 to 0.8% by weight of Ag, 0.2 to 0.6% by weight of Mg and at least an element selected from Zr, Mn, Cr, Sc, Hf and Ti, the amount of said element, if selected, being from 0.05 to 0.13% 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 0.05 to 0.15% by weight for Ti, the remainder being aluminum and unavoidable impurities, with the additional requirement that the amount of Cu and Li be such that
• Another subject of the invention is a laminated, extruded and / or forged aluminum alloy product comprising 2.7 to 3.4% by weight of Cu, 0.8 to 1.4% by weight of Li, 0 , 1 to 0.8% by weight of Ag, 0.2 to 0.6% by weight of Mg and at least one element selected from Zr, Mn, Cr, Sc, Hf and Ti, the amount of said element, it is selected from 0.05 to 0.13% 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 0.5 to 0.5 wt% for Hf and 0.05 to 0.15 wt% for Ti, the remainder being aluminum and unavoidable impurities, with the additional requirement that the amount of Cu and Li or such that Cu (% by weight) + 5/3 Li (% by weight) ⁇ 5.2.
• Still other objects of the invention are elements of structures, stiffeners and fuselage panels obtained from said rolled, extruded and / or forged products. Description of figures
• FIG. 1 Curve R in the direction T-L (specimen CCT760).
• Figure 2 Curve R in the L-T direction (CCT760 specimen).
• Figure 3 evolution of the cracking speed in the T-L direction when the amplitude of the stress intensity factor varies.
• Figure 4 evolution of the cracking speed in the L-T direction when the amplitude of the stress intensity factor varies.
• Figure 5 Curve R in the direction T-L (specimen CCT760) samples according to the invention having been obtained with different levels of strain by traction.
• the static mechanical characteristics in other words the ultimate tensile strength Rm, the conventional yield stress at 0.2% elongation R p o, 2 and the elongation at break A, are determined by a tensile test according to the EN 10002-1, the sampling and the sense of the test being defined by EN-485-1.
• the cracking rate (da / dN) is determined according to the ASTM E 647 standard.
• the critical stress intensity factor K c in other words the intensity factor that makes the crack unstable, is calculated from the curve R.
• the stress intensity factor K C o is also calculated in attributing the initial crack length to the critical load at the beginning of the monotonic load. These two values are calculated for a specimen of the required form.
• K app represents the K C o factor corresponding to the specimen that was used to perform the R curve test.
• K ⁇ ff represents the K 0 factor corresponding to the specimen that was used to perform the R curve test.
• ⁇ a e ff ⁇ max represents the crack extension of the last valid point of the R curve.
• the crack size at the end of the fatigue pre-cracking stage is W / 3 for specimens of the type M (T), wherein W is the width of the specimen as defined in ASTM E561.
• W is the width of the specimen as defined in ASTM E561.
• the width of the specimen used in an R curve test can have a substantial influence on the stress intensity measured in the test.
• the fuselage sheets being large panels, the results of curve R obtained on sufficiently large samples, such as samples having a width greater than or equal to 400 mm, are judged the most significant for the evaluation of toughness. For this reason, CCT760 test specimens, which had a width of 760 mm, were used preferentially for the evaluation of toughness.
• the initial crack length 2ao 253 mm.
• the toughness was also evaluated in the TL directions using the global energy at break E 9 according to the Kahn test.
• the stress Kahn R e (in MPa) is equal to the ratio of the maximum load F max that the specimen can withstand on the section of the specimen (product of the thickness B by the width W). R e does not evaluate the relative toughness of samples whose static mechanical properties are different.
• the overall energy at break E 9 is determined as the area under the Force-Displacement curve until the test piece breaks, E g is directly related to toughness.
• the test is described in the article "Kahn-Type Tear Test and Crack Toughness of Aluminum Alloy Sheet", published in the journal Materials Research & Standards, April 1964, p. 151-155.
• the test specimen used for the Kahn toughness test is described, for example, in the Metals Handbook, 8th Edition, Vol. 1, American Society for Metals, pp. 241-242.
• sheet is meant here a rolled product not exceeding 12 min thick.
• structural element refers to an element used in mechanical engineering for which the static and / or dynamic mechanical characteristics are of particular importance for the performance and integrity of the structure, and for which a calculation of the structure is usually prescribed or performed. It is typically a mechanical part whose failure is likely to endanger the safety of said construction, its users, its users or others.
• these structural elements include the elements that make up the fuselage (such as the skin of
• fuselage fuselage skin
• stiffeners or stringers bulkheads
• circumferential frames wings (such as wing skin)
• stiffeners stringers or stiffeners
• ribs ribs
• longitudinal members spars
• Preferred 3 0 to 3, 4 0.8 to 1, 2 o, o, 5 o, 2 to o, 6
• the relationship between copper and lithium is preferably:
• At least one element such as Zr, Mn, Cr, Sc, Hf, Ti or a combination thereof is included to refine the grain.
• the additions depend on the element: from 0.05 to 0.13% by weight (preferably from 0.09 to 0.13% by weight) for Zr, from 0.05 to 0.8% by weight for Mn from 0.05 to 0.3% by weight for Cr and Sc, from 0.05 to 0.5% by weight for Hf and from 0.05 to 0.15% by weight for Ti.
• the sum can be limited by the appearance of primary phases.
• grain refining is achieved by the addition of 0.05 to 0.13% by weight of Zr, from 0.02 to 0.3% by weight of Sc and optionally from 0.05 to 0.8% in Mn weight, 0.05 to 0.3% by weight of Cr, 0.05 to 0.5% by weight of Hf and 0.05 to 0.15% by weight of Ti.
• Mn content it may be advantageous to limit the Mn content to 0.05% by weight and preferably to 0.03% by weight. The inventors have observed that for such thicknesses the presence of Mn makes it more difficult to control the granular structure and may affect both the mechanical properties and the toughness.
• Fe and Si generally affect toughness properties.
• the amount of Fe should preferably be limited to 0.1% by weight and the amount of Si should preferably be limited to 0.1% by weight (preferably to 0.05% by weight). All other elements should also preferably be limited to 0.1% by weight (preferably to 0.05% by weight).
• the inventors have found that if the copper content is greater than 3.4% by weight, the toughness properties can in some cases fall rapidly. For certain embodiments of the invention, it is recommended not to exceed a copper content of 3.3% by weight. Preferably, the copper content is greater than 3.0% or even 3.1% by weight.
• the present inventors have found that Zr contents greater than 0.13% by weight can, in some cases, lead to a lower toughness performance. Whatever the reason for this drop in toughness, the inventors found that the higher Zr content led to a formation of Al 3 Zr primary phases. In this case, a temperature of High casting may be used to avoid formation of the primary phases, but this may lead to lower liquid metal quality, in terms of inclusion and gas content. This is why the present inventors consider that the Zr should advantageously not exceed 0.13% by weight.
• the inventors have found that if the Li content is less than 0.8% by weight or even 0.9% by weight, the improvement in mechanical strength is too low. In some cases, it may be advantageous if the Li content is> 0.9% by weight. Also, with these low Li content, the decrease in the density of the alloy is too low. For a Li content greater than 1.4% or more than 1.2% by weight or even greater than 1.1% by weight, the toughness is significantly reduced. Also, these high Li levels have several disadvantages related in particular to the thermal stability, flowability and cost of raw materials.
• the addition of Ag is an essential feature of the invention. The strength and toughness performances observed by the inventors are not usually achieved for alloys containing no silver.
• the advantageous effect of Ag is observed for a content of this element greater than 0.1% by weight and preferably greater than 0.2% by weight. In order to limit the cost associated with the addition of Ag, it may be advantageous not to exceed 0.5% by weight or even 0.4% by weight.
• the addition of Mg improves the mechanical strength and decreases the density. An excessive addition of Mg, however, would have a detrimental effect on toughness. In an advantageous embodiment of the invention, the Mg content is limited to 0.4% by weight. The inventors believe that the addition of Mg could also have a role during the formation of copper-containing phases.
• the bath of liquid metal having a composition according to the invention is then cast.
• the present invention makes it possible to obtain a laminated, extruded and / or forged product whose thickness is, advantageously, between 0.8 and 12 mm and preferably between 2 and 12 mm.
• an alloy having adjusted amounts of alloying elements is cast as a plate.
• the plate is then homogenized at 490 to 530 ° C. for 5 to 60 hours.
• the inventors have observed that homogenization temperatures above 530 ° C. can tend to reduce the tenacity performance in certain cases.
• the plates are heated at 490 to 530 ° C. for 5 to 30 hours. Hot rolling is carried out to obtain a thickness of between 4 and 12 mm. For a thickness of approximately 4 mm or less, a cold rolling step may be added, if necessary.
• the sheet obtained at a thickness preferably between 0.8 and 12 mm, and the invention is more advantageous for sheets of 2 to 12 mm thick and even 2 to 9 mm and even more advantageous for sheets of 3 to 7 mm thick.
• the sheets are then put in solution, for example by heat treatment between 490 and 530 ° C for 15 min to 2 h, then quenched with water at room temperature or preferably cold water.
• the product then undergoes a controlled pull of 1 to 5% and preferably 2.5 to 4%.
• Such cold hardening levels can also be achieved by cold rolling, planing, forging or a combination of these methods and controlled pulling.
• the total cold working after quenching is between 2.5 and 4%.
• the controlled tensile deformation may be between 1.7 and 3.5. %.
• the inventors have observed that the tenacity tends to decrease when the controlled tensile deformation is greater than 5%.
• the results of Kahn test, in particular E g tends to decrease for permanent deformations greater than 5%. It is therefore recommended not to exceed a permanent deformation of 5%.
• the traction is greater than 5%, there may be industrial difficulties such as high implementation as well as that formatting difficulties, which would increase the cost of the product.
• An income is produced at a temperature of between 140 and 170 ° C. for 5 to 30 hours, which makes it possible to obtain a T8 state.
• the income is more preferably carried out between 140 and 155 ° C. for 10 to 30 hours.
• Low tempering temperatures generally favor high toughness.
• the revenue step is divided into two steps: a pre-revenue step prior to a welding operation, and a final heat treatment of a welded structure member.
• friction stir welding is a preferred welding technique.
• the sheets according to the invention have advantageous properties for recrystallized, non-recrystallized or mixed microstructures (that is to say comprising recrystallized zones and non-recrystallized zones).
• the inventors have observed that it could be advantageous to avoid mixed microstructures: for sheets whose thickness is between 4 and 12 mm, it may be advantageous for the microstructure to be completely uncrystallized.
• the conventional yield strength R p o, 2 in the direction L is preferably at least 440 MPa, preferably at least 450 MPa or even at least 460 MPa.
• the resistance to breaking Rm in the direction L is preferably at least 470 MPa, preferably at least 480 MPa or even at least 490 MPa.
• K app in the direction TL is preferably at least 110 MPa Vm and preferably at least 130 MPaVm or even at least 140 MPaVm;
• K app in the LT direction is at least
• K ⁇ ff in the TL direction is at least
• K eff in the LT direction is at least 170
• the crack extension of the last valid point of the curve R in the TL direction is preferably at least 30 mm and preferably at least 40 mm;
• the crack extension of the last valid point of the curve R in the LT direction is preferably at least 50 mm.
• the forming of the sheet of the invention may advantageously be carried out by deep drawing, stretching, spinning, rolling or folding, these techniques being known to those skilled in the art.
• a structural element formed of at least one product according to the invention, in particular a sheet according to the invention and stiffeners or frames, these stiffeners or frames being preferably made of extruded profiles, can be used in particular for the manufacture of aircraft fuselage panels as well as any other use where the present properties could be advantageous.
• structural members, stiffeners, and / or fuselage panels can be made from the rolled, extruded, and / or forged products obtained.
• the inventors have found that the sheet of the invention has mechanical properties Particularly favorable statics and high tenacity.
• the high-tenacity sheets generally have low yield strengths and breaking strength.
• the high mechanical properties favor an industrial application for aircraft structural parts, the elastic limit and the breaking strength of said sheet being characteristics which are directly taken into account for the calculation. structural dimensioning.
• Calculations of structural elements and in particular of fuselage panels comprising sheets and / or stiffeners according to the invention have shown a possibility of weight reduction with respect to structural elements of comparable properties comprising only metal sheets. prior art alloy 2024, 2056, 2098, 7475 or 6156. Such weight reductions are generally from 1 to 10% and in some cases even greater weight reductions can be achieved.
• the simple substitution of the alloy 2024 with an alloy according to the invention may allow a weight reduction of the order of 3 to 3.5%.
• the high mechanical properties of the alloys according to the invention make it possible to develop products of a lighter size and shape, which makes it possible to reach or even exceed a weight reduction of 10%.
• the sheet of the invention does not generally induce any particular problem during subsequent surface treatment operations conventionally used in aircraft construction.
• the resistance to intergranular corrosion of the sheet of the invention is generally high; for example, only pits are generally detected when the metal is subjected to a corrosion test.
• the sheet of the invention can be used without plating.
• the static mechanical properties of the samples according to the invention are very high compared to the conventional alloy of the 2XXX range which is tolerant to damage, and of the same order of magnitude as the sample 7475 T76 referenced C.
• the mechanical strength of the samples according to the invention considers that the lower copper content and the lower zirconium content of the samples according to the invention have a slight influence on their mechanical strength.
• the curves R of certain samples according to the invention and reference samples E are given in FIGS. 1 and 2, for directions T-L and LT, respectively.
• FIG. 1 clearly shows that the crack extension of the last valid point of the curve R ( ⁇ a e ff (max)) is much greater for the samples of the invention than for the sample E # 1, E # 3 , E # 31 and E # 4.
• the results from the curve R are grouped together in Table 8.
• the crack extension of the last valid point of the curve R is greater for the samples of the invention than for the reference samples.
• all the samples according to the invention reach a crack extension of at least 30 mm and even at least 40 mm while the maximum crack extension is less than 40 mm for the samples of the invention. reference.
• the inventors consider that several reasons can be proposed to explain this performance, such as the lowest Cu content, and / or the lowest Zr content.
• Figures 3 and 4 show the evolution of the cracking rate da / dN (in mm / cycle) in the TL and LT orientation, respectively, for different levels of stress intensity factor ( ⁇ K).
• the cracking rate of the sample F is in the same range as that typically obtained for alloy 2056 (Sample B) and lower than that obtained for alloy 6156 (Sample D).
• the intergranular corrosion resistance was tested according to ASTM GI10. For all the samples according to the invention, no intergranular corrosion was detected. No intergranular corrosion was either detected on the 2098 alloy reference samples (E # 1 to E # 4). For Sample B (for which plating had been removed), intergranular corrosion with an average depth of 120 ⁇ m was observed and for Sample D (for which plating had been removed) intergranular corrosion was observed. with an average depth of 180 ⁇ m. The resistance to intergranular corrosion was thus very high for the samples according to the invention.
• the income was made either before or after assembly by friction stir welding.
• the results are given in Table 13.
• the performance of the welded joints obtained with the sheets according to the invention was particularly satisfactory for two aspects.
• the joint efficiency coefficient which is the ratio between the breaking strength of the welded joint and that of the non-welded sheet, is greater than 70% and even greater than 75% for the sheets of the invention. This coefficient reaches 80% in some cases. This result is better than that obtained with sheets from casting E.
• the results are little influenced by the position of the stage of income (before or after welding), which allows a flexible process. On the contrary, for the sheets obtained from the casting D (6156), a significant influence of the position of the income stage is observed.
• Samples L and M reach the mechanical characteristics according to the invention in the T8 state. Furthermore, the static strength and toughness performances are lower for the sample L, which contains Mn and a low Zr content, than for the other examples according to the invention. The inventors believe that the lower performance of the sample L is related to a less favorable microstructure characterized in particular by the presence of recrystallized zones and non-recrystallized zones (mixed microstructure).

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• 2006
  • 2006-06-02 EP EP08018130A patent/EP2017361A1/de not_active Withdrawn
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