Patent Application
20070246137
Aspects of the invention relate to worked products and structural components made of aluminium alloy, particularly for aeronautical construction. The worked products may be rolled products (such as thin structural plates, medium thickness plates, thick plates), extruded products (such as bars, sections, tubes or wires) and forged products.
Unless mentioned otherwise, the chemical composition of the alloys is expressed as a percent by mass. Consequently, in a mathematical expression, “0.4 Zn” means 0.4 times the content of zinc expressed in percent by mass; this is applicable mutatis mutandis to other chemical elements. Alloys are designated in accordance with the rules of The Aluminum Association known to those skilled in the art. Metallurgical tempers and heat treatments are defined in European standard EN 515. The chemical composition of normalized aluminium alloys is defined, for example, in standard EN 573-3. Unless mentioned otherwise, the static mechanical characteristics, in other words the ultimate strength Rm, the yield stress Rp0.2 and the elongation at failure A, are determined by a tensile test according to standard EN 10002-1, the location and direction at which test pieces are taken being defined in standard EN 485-1. The toughness KIC is measured according to standard ASTM E 399.
Unless mentioned otherwise, the definitions in European standard EN 12258-1 are applicable, and in particular an alloy with no heat treatment is an alloy that cannot be substantially hardened by a heat treatment and an alloy with a heat treatment is an alloy that can be hardened by an appropriate heat treatment.
The term “plate” is used in this description for all thicknesses of rolled products.
Cold plastic deformation in this description means a plastic deformation in which the metal is not deliberately heated either before being deformed or during deformation. There are several types of cold plastic deformations, particularly cold rolling, controlled stretching (flattening), wire drawing, drawing, die forging, die stamping, bending, compression and cold forging. By hot working step it is meant a working step wherein the initial metal temperature is at least 200° C.
The work-hardening ratio for rolling from a thickness e0 to a thickness e is defined by τ(%)=(e0−e)/e, and for stretching from a length L0 to a length L is defined by τ(%)=(L−L0)/L0.
Generalized plastic deformation is known to those skilled in the art, and is defined for example in the manual “Mise en forme des métaux—Calculs sur la plasticité” (Forming of metals—Plasticity calculations) pages 24-25 by P. Baque, E. Felder, J. Hyafil and Y. D'Escatha published by Editions Dunod, Paris (1973) or in the book “Mise en forme des métaux et alliages” (forming of metals and alloys) pages 40-41 containing texts compiled by B. Baudelet, published by Editions du CNRS, 1976, Paris. Conventionally, the generalized deformation is a measurement of the deformation amplitude, and the deformation value
where dε1, dε2 and dε3 are the principal elementary deformations.
In the case of a plastic deformation, the volume variation is zero and therefore dε1+dε2+dε3=0. The generalized plastic deformation is additive for successive different steps of plastic deformation.
When rolling from a thickness e0 to a thickness e in which the deformation is plane (dε3=0, dε2=−dε1), the generalized plastic deformation is equal to ε(%)=(2/√3)ln(e0/e).
In the case of stretching from a length l0 to a length l, the generalized plastic deformation is equal to ε(%)=ln(l/l0).
For compression from a length l0 to a length l, the generalized plastic deformation is equal to ε(%)=ln(l0/l).
The average generalized plastic deformation refers to the average of the generalized plastic deformation within a given volume.
The term “machining” includes any process for removal of material such as turning, milling, drilling, reaming, tapping, spark machining, grinding, polishing, chemical machining.
The term “extruded product” also includes products that have been drawn after extrusion, for example by cold extrusion through a die. It also includes hard drawn products.
The term “worked product” refers to a semi-finished product ready to be transformed, in particular by sawing, machining and/or forming into a structural element. In some cases, the worked product may be used directly as a structural element. Worked products may be rolled products (such as thin structural plates, medium thickness plates, thick plates), extruded products (such as bars, sections, tubes or wires) and forged products. When the fabrication process of the worked product comprises a stress relieving step by controlled stretching, the ends of the piece which were under the jaws of the tension bench are cut in order to make the piece suitable for mechanical construction.
The term “structural element” refers to an element used in a mechanical construction for which the static and/or dynamic mechanical characteristics are particularly important for performance and integrity of the structure, and for which a structural calculation is usually required or performed. It is typically a mechanical part, which if it fails will endanger the safety of the said construction, its users, passengers or others. For an aircraft, these structural elements include particularly elements making up the fuselage, such as the fuselage skin, stiffeners or stringers, bulkheads, circumferential frames, wings (such as the wing skin), stiffeners, ribs and spars, and the tail fin composed particularly of horizontal or vertical stabilisers, and floor beams, seat tracks and doors.
The term “monolithic structural element” refers to a structural element obtained from a single rolled, extruded, forged or cast partly finished product with no assembly such as riveting, welding, bonding with another part.
The term “multi-functional structural element” refers principally to the functions conferred by the metallurgical properties of the product and not by its geometric shape.
Aspects of the invention are directed to a process for fabricating a worked product or a structural element that comprises at least one cold plastic deformation step subsequent to the hot deformation step, wherein at least two zones of the worked product of the structural element are subjected to average generalized plastic deformations that differ by at least 2%, at least 3%, at least 4% or 5%. The zones considered have a significant volume compared with the total volume of the structural element. Advantageously, the volume of the zones considered represents at least 5%, at least 10% or at least 15% of the total volume of the worked product or of the structural element. Advantageously, every zone of the worked product or of the structural element undergo a minimal generalized plastic deformation of at least 1% or at least 1.5%
Advantageously, the process according to aspects of the invention comprises at least two working steps by cold plastic deformation subsequent to the hot working step.
The process leads to the production of worked products and of structural elements with a principal dimension or final length Lf in the principal direction or length direction L and a final section equal to Sf in the plane perpendicular to the principal direction. For example, the section Sf is substantially constant at all points on the worked product. If the worked product is a plate with a final length Lf, final width if and final thickness ef, advantageously the thickness ef is substantially constant at all points. If it is an extruded product with length L and with a complex shape, advantageously the shape is identical at all points along the length.
Machining may be a final step in the process according to the invention to obtain a substantially constant final section and/or final thickness at all points of the worked product.
The process according to the invention can be used to produce worked products, and particularly plates or sections, and structural elements made of any wrought aluminium alloy. In particular, the invention may be used with alloys with no heat treatment such as the 1XXX, 3XXX, 5XXX alloys and some alloys in the 8XXX series, and particularly advantageously with 5XXX alloys containing scandium, particularly having a scandium content of 0.001 to 5% by weight or 0.01 to 0.3% by weight. The differences in the mechanical properties resulting from the differences in work-hardening obtained by the process according to the invention confer a multifunctional nature on structural elements made from worked products of an alloy with no heat treatment.
In an aspect of the invention, a heat treated aluminium alloy is used, and a solution heat treatment step and a quenching step are carried out between the hot working and the first working by cold plastic deformation, with an optional artificial ageing step subsequent to the working steps by cold plastic deformation. In particular, worked products and structural elements made of aluminium alloy in the 2XXX, 4XXX, 6XXX and 7XXX series, and a structurally hardened alloy in the 8XXX series containing lithium can be produced. By alloy containing lithium it is meant an alloy with a lithium content of at least 0.1 wt %. For alloys in the 2XXX series, artificial ageing can be used, for example, to obtain a T8X temper, or on the contrary, natural ageing to a T3X temper can be used. This aspect of invention is particularly advantageous for making worked products or structural elements made of 2XXX alloy in the T3X temper.
Aspect of the invention can be used to make worked products or structural elements made of a 2XXX alloy in the T3X temper containing at least two zones Z1 and Z2 with mechanical properties (measured at mid-thickness) selected from the group formed from
Worked products or structural elements made of a 2XXX alloy in the T3X temper can also be obtained containing at least two zones Z1 and Z2 with physical and mechanical properties (measured at mid-thickness) in which:
Aspect of the invention can also be used to obtain worked products or structural elements made of a 2XXX alloy containing lithium in the T8X temper containing at least two zones Z1 and Z2 with mechanical properties selected from the group formed from:
In the case of artificially aged alloys and in particular of alloys in the 7XXX series and of some alloys in the 2XXX series, cold plastic deformation done after the solution heat treatment and quenching steps can modify the artificial ageing rate. Thus, zones in which average generalized plastic deformations will reach different metallurgical tempers during artificial ageing giving the structural element its multi-functional nature. In one aspect of the invention applicable to all heat treated alloys subjected to artificial ageing, artificial ageing is done in a furnace with a temperature gradient so as to amplify property differences between the ends of the structural element.
In a first variant of the invention, the at least two zones of the worked product or of the structural element that are subjected to average generalized plastic deformations that are different by at least 2% are located in a different position along the principal or length direction L. In this case, the zones advantageously have a section SZ in the plane perpendicular to the direction L equal to the section of the worked product in this plane. In particular, when the section Sf of the worked product is substantially constant, the section SZ is advantageously equal to substantially Sf. In this first variant, the length of the said zones along the L direction is for example equal to at least 1 m or to at least 5 m.
Advantageously, a first variant of the process according to the invention includes at least one cold plastic deformation step by controlled stretching. Controlled stretching is normally used to flatten or straighten and to reduce residual stresses. In one aspect of the invention, a controlled stretching step is performed in which one of the ends of the intermediate product on which the controlled stretching is carried out projects significantly beyond the jaws of the tension bench, and can also be used to generate average generalized plastic deformations that are different in two zones of the structural element.
The process using successive stretching steps described in
In another aspect of the invention generally applicable to manufacturing of plates, at least one cold plastic deformation step is made by compression. This aspect is illustrated in
In yet another aspect of the first variant of the invention applicable only to manufacturing of plates, the process according to the invention includes a cold rolling step in which the plate thickness is variable at the entry to the rolling mill and is substantially constant at the exit from the rolling mill.
The plate with variable thickness along the L direction necessary in the aspect described in
In yet another aspect of the first variant of the invention that is only applicable to manufacturing of plates, the process according to the invention includes a cold rolling step in which the plate thickness is substantially constant at the entry to the rolling mill and is variable in the direction L at the exit from the rolling mill and a subsequent machining step to obtain an substantially constant thickness at all points.
In a second variant of the invention suitable for manufacturing of plates with a principal direction or length along the L direction, a transverse dimension or width in the direction l and a thickness dimension in the direction e, the zones in the structural element subjected to average generalized plastic deformations different by at least 2% are located at a different position along the transverse direction l. In this case, the zones advantageously have a thickness ez in the direction of the thickness e equal to the thickness of the worked product. In particular, when the thickness ef of the worked product is substantially constant, the thickness ez is advantageously equal to substantially ef.
In this second variant, the width of the said zones is for example equal to at least 0.2 m or at least 0.4 m.
In one aspect of this second variant, the process according to invention includes a cold rolling step in which the plate thickness is variable along the transverse direction l at the entry to the rolling mill and is substantially constant at the exit from the rolling mill. The variation in the thickness of the plate may be obtained particularly by hot rolling, machining after hot rolling or forging. This aspect is illustrated on
In yet another aspect of the second variant of the invention that is only applicable to manufacturing of plates, the process according to the invention includes a cold rolling step in which the thickness of the plate is substantially constant at the entry to the rolling mill and is variable in the direction l at the exit from the rolling mill, and a subsequent machining step to obtain an substantially constant thickness at all points.
A 25 mm thick plate with variable properties within the plate is made of an AA2023 alloy.
A 30 meter long, 2.5 meter wide and 28.2 mm thick plate is made by hot rolling of a rolling ingot.
The composition of the alloy used is given in Table 1 below.
The rolling ingot is homogenized at 500° C. for 12 hours. The hot rolling entry temperature is 460° C.
After hot rolling, the plate is machined as shown on
zone Z31: 28.1 m
zone Z32: 26.3 m
zone Z33: 25.5 m
The plate is then solution heat treated at 500° C. and quenched.
The plate is first cold rolled to obtain a substantially constant thickness of 25.5 mm over the entire plate, and then subjected to controlled stretching with a permanent elongation of about 2%, after which the ends of the piece which were under the jaws of the tension bench are cut off.
The rolling step changes the length of zone Z31 to about 11 meters.
Deformations in the different zones are summarized in Table 2 below:
Samples are taken from zones Z31, Z32 and Z33. The results of the mechanical tests are given in table 3 below:
The process according to the invention results in compromises of different properties in zones Z31, Z32 and Z33. Thus, zone Z31 is characterized by high strength at the detriment of a limited elongation while zone Z33 is distinguished by high elongation with lower static mechanical strength.
A 15 mm thick plate with variable properties is made of an AA2024A alloy.
A 30 meter long, 2.5 meter wide and 16.8 mm thick plate is made by hot rolling of a rolling ingot.
The composition of the alloy used is given in Table 4 below.
The rolling ingot is homogenized and then hot rolled.
After hot rolling, the plate is machined as described in
Zone Z31: 16.7 mm
Zone Z32: 15.9 mm
Zone Z33: 15.3 mm
The plate is then solution heat treated at 500° C. and quenched.
The plate is first cold rolled to obtain a substantially constant thickness of 15.3 mm over the entire plate, and then subjected to controlled stretching with a permanent elongation of about 2% after which the ends of the piece which were under the jaws of the tension bench are cut off.
The length of zone Z31 after the rolling step is equal to substantially 10.9 meters.
Deformations in the different zones are summarized in Table 5 below:
Samples are taken from zones Z31, Z32 and Z33. The results of the mechanical tests are given in Table 6 below:
The process according to the invention results in compromises of different properties in zones Z31, Z32 and Z33. Thus, zone Z31 is characterized by high strength at the detriment of a limited elongation while zone Z33 is distinguished by high elongation with lower static strength.
A section with variable properties with a 170×45 mm cross-section is made of a AA2027 alloy.
A 15 meter long section is made with a 170×45 mm cross-section, by hot extrusion of an extrusion billet.
The composition of the alloy is given in Table 7 below:
The extrusion billet is homogenized at 490° C. and hot extruded.
After extrusion, the section is solution heat treated at 500° C. and quenched.
A first controlled stretching step is then carried out on it with the permanent elongation of 2.8%. One of the jaws of the tension bench is then displaced as shown on
The deformations in the zones are summarized in Table 8 below:
Samples are taken in zones Z11, Z12 and Z13. The results of the mechanical tests are given in Table 9 below:
The process according to the invention results in compromises with different properties in zones Z11, Z12 and Z13. Thus, zone Z11 is characterized by high mechanical strength to the detriment of limited elongation and limited toughness, while zone Z13 is distinguished by a high elongation and high toughness but for a relatively low static mechanical strength.
A 30 mm thick plate with variable properties is made of an AA2195 alloy.
A 30 meter long, 2.5 meter wide and 33 mm thick plate is made by hot rolling of a rolling ingot.
The composition of the alloy is given in Table 10 below:
The rolling ingot is homogenized and then hot rolled. The plate is then solution heat treated at 510° C. and quenched.
Half of the plate (zone G) is then cold rolled to a thickness of 30 mm while the other half is subjected to controlled stretching of 2.5% (zone H).
The plate is first machined to obtain a substantially constant thickness of 30 mm over the entire plate, and then subjected to controlled stretching with a permanent elongation of about 1.5% after which the ends of the piece which were under the jaws of the tension bench are cut off.
The deformations in the different zones are summarized in Table 11 below:
Samples are taken from zones G and H. The results of the mechanical test are given in table 12 below:
The process according to the invention results in compromises of different properties in zones G and H. Thus, zone G is characterized by high strength at the detriment of limited elongation and limited toughness while zone H is distinguished by higher elongation and toughness with lower static strength.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0603567 | Apr 2006 | FR | national |
| Number | Date | Country | |
|---|---|---|---|
| 60803553 | May 2006 | US |
