EP2836620A1

EP2836620A1 - Aluminium copper lithium alloy with improved impact strength

Info

Publication number: EP2836620A1
Application number: EP13722480.4A
Authority: EP
Inventors: Armelle Danielou; Mathieu MARQUETTE; Jérome PIGNATEL; Gaëlle POUGET; Timothy Warner
Original assignee: Constellium France SAS
Current assignee: Constellium Issoire SAS
Priority date: 2012-04-11
Filing date: 2013-04-10
Publication date: 2015-02-18
Anticipated expiration: 2033-04-10
Also published as: FR2989387A1; CA2869733A1; CN104220616B; US20130269840A1; DE13722480T1; WO2013153292A1; CN104220616A; CA2869733C; US9945010B2; FR2989387B1; EP2836620B1; BR112014025110B1

Abstract

The invention relates to an extruded product made of an aluminium-based alloy comprising 4.2% to 4.8% by weight of Cu, 0.9% to 1.1% by weight of Li, 0.15% to 0.25% by weight of Ag, 0.2% to 0.6% by weight of Mg, 0.07% to 0.15% by weight of Zr, 0.2% to 0.6% by weight of Mn, 0.01% to 0.15% by weight of Ti, an amount of Zn of less than 0.2% by weight, an amount of Fe and of Si of less than or equal to 0.1% by weight each, and inevitable impurities at a content of less than or equal to 0.05% by weight each and 0.15% by weight in total. The sections according to the invention are particularly useful as fuselage stringer or stiffener, fuselage frame, wing stiffener, floor beam or section or seat track, especially due to their improved properties compared to those of known products, in particular in terms of energy absorption during an impact; static mechanical strength and corrosion resistance properties, and their low density.

Description

A copper lithium aluminum bond with improved impact resistance

Field of the invention

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

State of the art

Aluminum alloy spun products are developed to produce high strength parts for the aerospace industry and the aerospace industry in particular.

Aluminum alloy spun products are used in the aerospace industry for many applications, such as stiffeners or fuselage rails, fuselage frames, wing stiffeners, floor profiles or beams, as well as track rails. seat.

The gradual incorporation of more composite materials into aeronautical structures has changed the requirements for spun products incorporated in aircraft, particularly for structural members such as floor beams. It appeared that the absorption of energy during a shock, or more particularly during a crash, is now an important criterion for selecting this product. The other essential properties are the highest possible mechanical characteristics, so as to reduce the weight of the structures, and the resistance to corrosion.

A magnitude such that the specific absorption capacity can be used to characterize the energy absorption during an impact.

The specific energy absorption capacity during an impact can be measured during a crash test in which the force provided is measured as a function of the displacement achieved. during the crash. This is the amount of energy expended to crush a unit mass of material in the stable crush phase. Ductile aluminum alloys have a significant ability to absorb impact energy during impact, in particular because they deform plastically. As a first approximation, the specific energy absorption capacity during a shock of an aluminum alloy profile can be connected to the curve obtained during a tensile test of the material in question, in particular to the area under the curve deformation force. It can thus be evaluated by the product R _m x A% or R _p0 , ₂ x A% in the direction L and in the direction TL.

AlCuLi alloys are known.

U.S. Patent 5,032,359 discloses a broad family of aluminum-copper-lithium alloys in which the addition of magnesium and silver, particularly between 0.3 and 0.5 percent by weight, increases the mechanical strength. .

US Pat. No. 5,455,003 describes a process for manufacturing Al-Cu-Li alloys which have improved mechanical strength and toughness at cryogenic temperature, in particular through appropriate work-hardening and tempering. This patent recommends in particular the composition, in percentage by weight, Cu = 3.0-4.5, Li = 0.7-1.1, Ag = 0-0.6, Mg = 0.3-0.6. and Zn = 0 - 0.75.

US Pat. No. 7,438,772 describes alloys comprising, in percentage by weight, Cu: 3-5, Mg: 0.5-2, Li: 0.01-0.9 and discourages the use of higher lithium contents due to degradation of the compromise between toughness and mechanical strength.

US Pat. No. 7,229,509 describes an alloy comprising (% by weight): (2.5-5.5) Cu, (0.1-2.5) Li, (0.2-1.0) Mg, (0, 2-0.8) Ag, (0.2-0.8) Mn, 0.4 max Zr or other grain refining agents such as Cr, Ti, Hf, Se, V.

US patent application 2009/142222 A1 discloses alloys comprising (in% by weight), 3.4 to 4.2% Cu, 0.9 to 1.4% Li, 0.3 to 0.7% of Ag, 0, 1 to 0.6% Mg, 0.2 to 0.8% of Zn, 0.1 to 0.6% Mn and 0.01 to 0.6% of at least one element for controlling the granular structure. This application also describes a process for manufacturing spun products.

Patent application WO 2009/036953 discloses an alloy for structural elements comprising (in% by weight) 3.4 to 6.0% Cu, 0.9 to 1.7% Li, about 0.2 to 0 , 8% Mg, about 0.1 to 0.8% Ag, about 0.1 to 0.8% Mn, up to 1.5% Zn, and one or more members selected from the group consisting of Zr, Cr, Ti, Se and Hf, with Fe <0.15 and Si <0.15.

AA2195 alloy comprising (in% by weight) 3.7 to 4.3% Cu, 0.8 to 1.2% Li, 0.25 to 0.8% Mg, O, is also known. 25 to 0.6% Ag, less than 0.25% Mn, less than 0.25% Zn 0.08 to 0.16% Zr, less than 0.10% Ti, less than 0, 15% Fe and less than 0.12% Si. 2195 alloy sections are described, for example, in the document "Friction on Welding Dissimilar Alloys for Tailoring Properties of Aerospace Parts", I. Eberl, C. Hantrais, J. C. Ehrstrom and C. Nardin, Science and Technology of Welding and Joining, 2010 Vol 15 No. 8 pp 699 - 705.

There is a need for aluminum-copper-lithium alloy spun products having improved properties over those of the known products, particularly in terms of energy absorption during impact, static mechanical strength properties and resistance to corrosion, while having a low density. At the same time, it is necessary to maintain a satisfactory tenacity for these products.

Object of the invention

A first object of the invention is an aluminum alloy spun product comprising

4.2 to 4.8% by weight of Cu,

0.9 to 1.1% by weight of Li,

0.15 to 0.25% by weight of Ag,

0j2 to 0.6% by weight of Mg,

0.07 to 0.15% by weight of Zr, 0.2 to 0.6% by weight of Mn,

0.01 to 0.15% by weight of Ti, a quantity of Zn of less than 0.2% by weight, an amount of Fe and Si of less than or equal to 0.1% by weight each, and unavoidable impurities at a rate of content less than or equal to 0.05% by weight each and 0.15% by weight in total.

Another subject of the invention is a method for manufacturing a spun product according to the invention in which:

(a) casting a raw form of alloy according to the invention,

(b) homogenizing said crude form at a temperature of 490 ° C to 520 ° C for 8 to 48 hours,

(c) hot-spinning said raw form with an initial hot deformation temperature of 420 ° C to 480 ° C to obtain a spun product,

(d) dissolving said spun product at a temperature of 500 ° C to 520 ° C for 1 minute to 8 hours,

(e) quenching,

(f) controlling said spun product in a controlled manner with a permanent deformation of 2 to 4%,

(g) optionally, a dressing is carried out of said spun product,

(h) yielding said spun product by heating at a temperature of 100 ° C to 170 ° C for 5 to 100 hours.

Yet another object of the invention is the use of a product according to the invention for the aeronautical construction as a stiffener or smooth fuselage, fuselage frame, wing stiffener, profile or beam floor or seat rail.

Description of figures

Figure 1: Sectional view of the spun product of Example 1.

Figure 2: Compromise between the yield strength and the EA parameter for the spun products of Example 1. 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. The density depends on the composition and is determined by calculation rather than a weight measurement method. The values are calculated in accordance with the procedure of The Aluminum Association, which is described on pages 2-12 and 2-13 of "Aluminum Standards and Data". The definitions of the metallurgical states are given in the European standard EN 515.

The static mechanical characteristics in tension, in other words the tensile strength R _m , 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 standard NF EN ISO 6892-1, the sampling and the direction of the test being defined by the EN 485-1 standard.

The stress intensity factor (KQ) is determined according to ASTM E399. ASTM E399 gives the criteria for determining whether KQ is a valid Kic value. For a given test piece geometry, the KQ values obtained for different materials are comparable to one another as long as the yield strengths of the materials are the same. are of the same order of magnitude.

Unless otherwise specified, the definitions of EN 12258 apply.

The thickness of the spun products is defined according to EN 2066: 2001: the cross section is divided into elementary rectangles of dimensions A and B; A being always the largest dimension of the elementary rectangle and B can be considered as the thickness of the elementary rectangle. The sole is the elementary rectangle with the largest dimension A.

According to the present invention, a selected class of aluminum-copper-lithium alloys makes it possible to manufacture spun products having improved properties with respect to those of known products, in particular in terms of energy absorption during impact, static mechanical strength properties, corrosion resistance and low density.

The simultaneous addition of manganese, titanium, zirconium, magnesium and silver allows for the selected copper and lithium contents, to obtain a compromise between a representative parameter of the energy absorption during a shock and the yield point particularly advantageous.

The copper content is at least 4.2% by weight, preferably at least 4.3%, and most preferably at least 4.35% by weight. In one embodiment of the invention, the copper content is at least 4.50% by weight. The copper content is at most 4.8 wt.%, Preferably at most 4.7 wt.% And most preferably 4.55 wt.%. The selected copper content improves in particular the static mechanical properties. A high copper content is, however, unfavorable especially for the density of the alloy.

The lithium content is at least 0.9% by weight and preferably at least 0.95% by weight. The lithium content is at most 1.1% by weight and preferably at most 1.05% by weight. In one embodiment of the invention, the lithium content is at most 1.04% by weight. The selected lithium content improves in particular the energy absorbed during an impact. An excessively low lithium content is however unfavorable, especially for the density of the alloy.

The addition of manganese is an important aspect of the present invention. The manganese content is at least 0.2% by weight and preferably at least 0.3% by weight. The manganese content is at most 0.6% by weight and preferably at most 0.5% by weight. In one embodiment of the invention, the manganese content is at most 0.40% by weight. The addition of manganese in these amounts improves in particular the compromise between the desired properties.

The magnesium content is at least 0.2% by weight and preferably at least 0.30% by weight. The magnesium content is at most 0.6% by weight and preferably at most 0.50% by weight. In one embodiment of the invention, the magnesium content is at most 0.40% by weight. The silver content is at least 0.15% by weight. Content silver is at most 0.25% by weight. The present inventors have found that surprisingly silver addition of more than 0.25% by weight could have an adverse effect on the energy absorption during an impact. It is important to combine the silver content from 0.15% to 0.25% by weight to a controlled pull after dissolution and quenching with a permanent deformation of 2 to 4%, in particular because a controlled pull of less than 2% does not then allow to obtain the desired mechanical strength. The addition of magnesium and silver is necessary to achieve the favorable compromise between static mechanical strength, absorbed energy, density and toughness.

The zirconium content is at least 0.07% by weight and preferably at least 0.10% by weight. The zirconium content is at most 0.15% by weight and preferably at most 0.13% by weight. The addition of zirconium is in particular necessary to maintain the essentially non-recrystallized structure desired for the spun products according to the invention.

The titanium content is between 0.01 and 0.15% by weight and preferably between 0.02 and 0.05% by weight. The addition of titanium makes it possible in particular to obtain a controlled granular structure of the raw form obtained after casting.

The amount of Fe and Si is less than or equal to 0.1% by weight each. Preferably, the content of Fe and Si is less than 0.08% by weight each.

The Zn content is less than 0.2% by weight, preferably less than 0.15% by weight and preferably less than 0.1% by weight. The presence of Zn can have an adverse effect on the compromise between static mechanical resistance, absorbed energy, density and toughness, especially since this element adversely affects the density of the alloy without having a favorable effect on the static mechanical resistance, absorbed energy and toughness. The unavoidable impurities are maintained at a content of less than or equal to 0.05% by weight each and 0.15% by weight in total.

The spun products according to the invention are prepared by means of a process in which firstly a raw form of an alloy according to the invention is cast. Preferably, the raw form is a spinning billet. The crude form is then homogenized at 490 ° C to 520 ° C for 8 to 48 hours. The homogenization can be carried out in one or more stages. The raw form can be cooled to room temperature after homogenization or directly brought to the temperature of hot deformation. The homogenized raw form is hot deformed by spinning with an initial hot deformation temperature of 420 ° C to 480 ° C to obtain a spun product. The spinning temperature used in particular makes it possible to obtain the desired essentially non-recrystallized structure.

The products spun according to the invention are preferably profiles whose thickness of at least one of the elementary rectangles is between 1 mm and 30 mm, preferably between 2 to 20 mm and preferably between 5 and 16 mm. Spun products used in aeronautical construction generally comprise several segments or elementary rectangles of different thicknesses. A difficulty encountered with these products is to achieve satisfactory properties in the different segments. The alloy according to the invention makes it possible in particular to obtain a favorable compromise between static mechanical strength, absorbed energy, density and toughness for elementary rectangles of different thicknesses.

The spun product thus obtained is then dissolved at a temperature of 500 ° C to 520 ° C for 15 minutes to 8 hours and then quenched with water at room temperature. Quenching is preferably carried out with water, by spraying or immersion.

The spun product thus dissolved and quenched is then tractionned with a permanent deformation of 2 to 4%. A permanent deformation by too weak a traction, such as a deformation by traction of 1.5%, does not make it possible to reach the compromise between desired properties. A permanent deformation by traction that is too high, such as a deformation of 6%, makes it impossible in particular to guarantee the dimensional characteristics of the spun product, typically as regards the angles between the various elementary rectangles. It may be necessary to perform a dressing operation of the spun product to obtain the desired properties from a dimensional point of view.

The spun product was finally heated back to a temperature of 100 ° C to 170 ° C for 5 to 100 hours. The income can be made in one or more levels. Preferably, the income is carried out in a stage at a temperature between 130 ° C and 170 ° C and preferably between 150 and 160 ° C for a period of 20 to 40 hours.

The spun products thus obtained preferably have a substantially non-recrystallized granular structure. In the context of the present invention, the term granular structure essentially non-recrystallized a granular structure such that the recrystallization rate between ¼ and ½ thickness of an elementary rectangle is less than 30% and preferably less than 10%.

The spun products according to the invention have particularly advantageous mechanical properties.

Thus, preferably, the spun products according to the invention have as properties at half thickness:

for a thickness between 5 and 16 mm

an average yield strength R _p0,2 in the L direction of at least 630 MPa and preferably at least 635 MPa and

a mean yield strength R _p0.2 in the TL direction of at least 625 MPa and preferably at least 630 MPa and

an EA factor

EA = (Rm (L) + RpO, 2 (L)) 12 * A% (L) + (Rm (TL) + Rp0.2 (TL)) 12 * A% (TL) of at least 14,000 and of preferably at least 14500

and or

for a thickness of between 17 and 30 mm

a mean yield strength R _p0,2 in the L direction of at least 655 MPa and preferably at least 660 MPa and

an average yield strength R _p o, 2 in the TL direction of at least 600 MPa and preferably at least 605 MPa and

an EA factor

EA = (Rm (L) + RpO, 2 (L)) 12 * A% (L) + (Rm (TL) + Rp0.2 (TL)) 12 * A% (TL) at least equal to 9500 and of preferably at least 9800.

In addition, the products according to the invention have an advantageous tenacity.

Thus, the products according to the invention preferably have a Kic (LT) toughness of at least 24 MPa Vm and preferably at least 25 MPaVm for a thickness of between 5 and 16 mm and for a thickness of between 17 and 15 μm. 30 mm Kic toughness (LT), at least 21 MPa m and preferably at least 22 MPa m.

Finally, the products according to the invention have an excellent resistance to corrosion. Thus the spun products according to the invention have a resistance of at least 30 days when a stress corrosion test according to ASTM G44 and ASTM G49 standards on specimens taken in the TL direction for a voltage of 450 MPa.

The spun products according to the invention are particularly advantageous for aircraft construction. Thus, the products according to the invention are used for aeronautical construction as a stiffener or smooth fuselage, fuselage frame, wing stiffener, profile or beam floor or seat rail. In a preferred embodiment, the products according to the invention are used as a floor beam, in particular as a beam of the lower floor of the aircraft, or cargo floor, this floor being particularly important during the impact.

Examples Example 1.

In this example, five alloys whose composition is given in Table 1 were prepared and cast in a raw form.

Table 1. Composition in% by weight of alloys

inv: invention - ref: reference

The raw forms were homogenized at a temperature of 490 ° C to 520 ° C adapted according to their composition, spun as spun product described in Figure 1, the thickness of the elementary rectangles is between 17 and 22 mm, with an initial hot deformation temperature of about 460 ° C. The spun products obtained were dissolved at a temperature suitable for the alloy of between 500 ° C. and 520 ° C., quenched, triturated for about 3% and recovered for 30 hours at 155 ° C. The mechanical properties obtained for cylindrical samples of diameter 10 mm taken at mid-thickness and quarter-width in the 18 mm thick sole of the spun products are presented in Table 2. In order to evaluate the energy absorption during of a shock we calculated the parameter

EA = (R _ra (L) + R _p0.2 (L)) 12 * A (L) + (R _m (TL) + R _p0.2 (TL)) 12 * A% (TL)

The structure of the spun products obtained was essentially non-recrystallized. The degree of recrystallized granular structure between ¼ and ½ thickness was less than 10.

Table 2. Mechanical properties obtained for different alloys.

Figure 2 shows the tradeoff between the yield strength and the EA parameter. The alloy according to the invention makes it possible to reach a particularly advantageous compromise.

The alloy spun product A according to the invention underwent a stress corrosion test according to ASTM G44 and ASTM G49 standards for a tension of 450 MPa on specimens taken in the TL direction. No rupture was observed after 30 days of testing.

Example 2

he In this example, the alloys A and B presented in Example 1 were spun as a spun product of a different shape and having lower elementary rectangles thicknesses between 5 and 12 mm. The crude forms were homogenized 15h at 500 ° C and then 20-25 h at 510 ° C, spun as I-spun product with an initial hot deformation temperature of about 460 ° C. The spun products obtained were dissolved at a temperature of approximately 510 ° C., quenched, triturated approximately 3.5% and returned for 30 hours at 155 ° C.

The mechanical properties in the longitudinal direction were measured on "full thickness" specimens taken from the various elementary rectangles of the spun product (thicknesses 5, 7 and 12 mm) and averaged for the different sections obtained. The "full thickness" measurement underestimates the real value measured at mid-thickness on machined specimens, because of the effect of the different microstructure close to the surface. A correction factor was introduced to account for this bias, however, the factor was chosen such that the actual machined test specimen value would likely be greater than the indicated corrected value. The mechanical properties in the transverse direction were measured on machined specimens taken from the zone of smaller thickness, the only possible zone for this type of measurement because of the length of the specimens necessary for this measurement. The toughness properties were measured on specimens taken from the thickest zone.

The structure of the spun products obtained was essentially non-recrystallized. The degree of recrystallized granular structure between ¼ and ½ thickness was less than 10%.

The mechanical properties thus obtained are presented in Table 3.

Table 3. Mechanical properties obtained for different alloys.

EA I 14540 I 13840 |

* correction factor 1.033 applied to the result obtained on a full thickness test specimen

Again, the spun product according to the invention achieves a more favorable compromise than the spun product of reference between the mechanical strength and the EA parameter.

Claims

claims

1. Spun aluminum alloy product comprising

4.2 to 4.8% by weight of Cu,

0.9 to 1, 1% by weight of Li,

0.15 to 0.25% by weight of Ag,

0.2 to 0.6% by weight of Mg,

0.07 to 0, 15% by weight of Zr,

0.2 to 0.6% by weight of Mn,

0.01 to 0.15% by weight of Ti,

an amount of Zn of less than 0.2% by weight, an amount of Fe and Si of less than or equal to 0.1% by weight each, and unavoidable impurities at a content of less than or equal to 0.05% by weight each and 0.15% by weight in total.

2. Spun product according to claim 1, comprising 4.3% to 4.7% by weight of Cu and preferably 4.35% to 4.55% by weight of Cu.

The spun product of claim 1 or claim 2 comprising 0.95 to 1.05% by weight of Li.

4. Spun product according to any one of claims 1 to 3 comprising 0.30 to 0.50% by weight of Mg and / or 0.10 to 0.13% by weight of Zr.

5. Spun product according to any one of claims 1 to 4 comprising 0.3 to 0.5% by weight of Mn.

6. Spun product according to any one of claims 1 to 5 comprising less than 0, 15% of Zn and preferably less than 0, 1% of Zn.

7. Spun product according to any one of claims 1 to 6 characterized in that it is a profile whose thickness of at least one elementary rectangle is between 1 mm and 30 mm, preferably between 2 and 20 mm and preferably between 5 and 16 mm.

8. Product according to any one of claims 1 to 7, the recrystallization rate between ¼ and ½ thickness of an elementary rectangle is less than 30% and preferably less than 10%.

9. Spun product according to any one of claims 1 to 8 having mid-thickness

for a thickness between 5 and 16 mm

a mean yield strength R _p0 , ₂ in the TL direction of at least 625 MPa and preferably at least 630 MPa and

an EA factor

EA = (Rm (L) + RpO, 2 (L)) 12 * A% (L) + (Rm (TL) + RpO, 2 (TL)) 12 * A% (TL) of at least 14,000 and of preferably at least 14500

and or

for a thickness of between 17 and 30 mm

an average yield strength R _p o, ₂ in the direction L of at least 655 MPa and preferably at least 660 MPa and

an average yield strength R _p o _{, 2} in the TL direction of at least 600 MPa and preferably at least 605 MPa and

an EA factor

EA = (Rm (L) + RpO, 2 (L)) 12 * A% (L) + (Rm (TL) + RpO, 2 (TL)) 12 * A% (TL) at least equal to 9500 and of preferably at least 9800.

The product of claim 9 having

for a thickness between 5 and 16 mm Kic toughness (L-T), of at least 24

MPa Vm and preferably at least 25 MPa Vm and

for a thickness between 17 and 30 mm Kic toughness (L-T), of at least 21

MPa Vm and preferably at least 22 MPa m.

11. A method of manufacturing a spun product according to any one of claims 1 to 10 wherein:

(a) pouring a raw form of alloy according to one of claims 1 to 6,

(d) dissolving said spun product at a temperature of 500 ° C to 520 ° C for 15 minutes to 8 hours,

(e) quenching,

(g) optionally, a dressing is carried out of said spun product,

Use of a product according to any one of claims 1 to 10 for aeronautical construction such as stiffener or fuselage beam, fuselage frame, wing stiffener, profile or beam of floor or seat rail.