U.S. patent application number 17/051659 was filed with the patent office on 2021-10-07 for aluminum-copper-lithium alloy having improved compressive strength and improved toughness.
This patent application is currently assigned to ConsTellium Issoire. The applicant listed for this patent is CONSTELLIUM ISSOIRE. Invention is credited to David BARBIER, Nicolas BAYONA-CARRILLO, Armelle DANIELOU, Samuel JUGE, Fanny MAS, Gaelle POUGET.
Application Number | 20210310108 17/051659 |
Document ID | / |
Family ID | 1000005707990 |
Filed Date | 2021-10-07 |
United States Patent
Application |
20210310108 |
Kind Code |
A1 |
MAS; Fanny ; et al. |
October 7, 2021 |
ALUMINUM-COPPER-LITHIUM ALLOY HAVING IMPROVED COMPRESSIVE STRENGTH
AND IMPROVED TOUGHNESS
Abstract
The invention relates to a product based on an aluminium alloy
comprising, as percentages by weight, 4.0 to 4.6% by weight of Cu,
0.7 to 1.2% by weight of Li, 0.5 to 0.65% by weight of Mg, 0.10 to
0.20% by weight of Zr, 0.15 to 0.30% by weight of Ag, 0.25 to 0.45%
by weight of Zn, 0.05 to 0.35% by weight of Mn, at most 0.20% by
weight of Fe+Si, at least one element selected from Cr, Sc, Hf, V
and Ti, the amount of said element, if selected, being from 0.05 to
0.3% by weight for Cr and for Sc, 0.05 to 0.5% by weight for Hf and
for V and 0.01 to 0.15% by weight for Ti, the other elements being
at most 0.05% by weight each and 0.15% by weight in total, the
remainder being aluminium. The invention also relates to a method
for obtaining such a product and to the use thereof as an aircraft
structural element.
Inventors: |
MAS; Fanny; (Grenoble,
FR) ; BARBIER; David; (Grenoble, FR) ; JUGE;
Samuel; (Saint Simeon De Bressieux, FR) ; DANIELOU;
Armelle; (Les Echelles, FR) ; POUGET; Gaelle;
(Grenoble, FR) ; BAYONA-CARRILLO; Nicolas;
(Coublevie, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CONSTELLIUM ISSOIRE |
Issoire |
|
FR |
|
|
Assignee: |
ConsTellium Issoire
Issoire
FR
|
Family ID: |
1000005707990 |
Appl. No.: |
17/051659 |
Filed: |
April 24, 2019 |
PCT Filed: |
April 24, 2019 |
PCT NO: |
PCT/FR2019/050965 |
371 Date: |
June 22, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 21/16 20130101;
C22C 21/18 20130101; C22C 21/14 20130101; C22F 1/057 20130101 |
International
Class: |
C22F 1/057 20060101
C22F001/057; C22C 21/18 20060101 C22C021/18; C22C 21/16 20060101
C22C021/16; C22C 21/14 20060101 C22C021/14 |
Foreign Application Data
Date |
Code |
Application Number |
May 2, 2018 |
FR |
1853798 |
Claims
1. A product based on an aluminum alloy comprising, in percentage
by weight, 4.0 to 4.6% by weight of Cu, 0.7 to 1.2% by weight of
Li, 0.5 to 0.65% by weight of Mg, 0.10 to 0.20% by weight of Zr,
0.15 to 0.30% by weight of Ag, 0.25 to 0.45% by weight of Zn, 0.05
to 0.35% by weight of Mn, at most 0.20% by weight of Fe+Si, at
least one element selected from Cr, Sc, Hf, V and Ti, the amount of
said element, if selected, being from 0.05 to 0.3% by weight for Cr
and for Sc, 0.05 to 0.5% by weight for Hf and for V and from 0.01
to 0.15% by weight for Ti, other elements at most 0.05% by weight
each and 0.15% by weight in total, the remainder being
aluminum.
2. The product based on an aluminum alloy according to claim 1
wherein the Cu content is comprised between 4.2 and 4.5% by weight,
optionally between 4.2 and 4.4% by weight.
3. The product based on an aluminum alloy according to claim 1
wherein the Li content is comprised between 0.8 and 1.0% by weight,
optionally preferably between 0.85 and 0.95% by weight.
4. The product based on an aluminum alloy according to claim 1
wherein the Zn content is comprised between 0.30 and 0.40% by
weight.
5. The product based on an aluminum alloy according to claim 1
wherein the Mn content comprised between 0.10 and 0.35% by
weight.
6. The product based on an aluminum alloy according to claim 1
wherein the sum of the Zn, Mg and Ag contents comprised between
0.95 and 1.35% by weight, optionally between 1.00 and 1.30% by
weight, optionally between 1.15 and 1.25% by weight.
7. The product based on an aluminum alloy according to claim 1
wherein the Zr content is 0.10 to 0.15% by weight, optionally
between 0.11 and 0.14% by weight.
8. The product based on an aluminum alloy according to claim 1
wherein the Ti content is comprised between 0.01 to 0.15% by weight
for Ti, optionally between 0.01 and 0.08% by weight, optionally
between 0.02 and 0.06% by weight.
9. The product based on an aluminum alloy according to claim 8
wherein the Ti is present in the form of particles of TiC.
10. A method for manufacturing a product based on an aluminum alloy
wherein, successively, a) a liquid metal bath based on aluminum is
prepared comprising 4.0 to 4.6% by weight of Cu; 0.7 to 1.2% by
weight of Li; 0.5 to 0.65% by weight of Mg; 0.10 to 0.20% by weight
of Zr; 0.15 to 0.30% by weight of Ag; 0.25 to 0.45% by weight of
Zn; 0.05 to 0.35% by weight of Mn; at most 0.20% by weight of
Fe+Si; at least one element selected from Cr, Sc, Hf, V and Ti, the
amount of said element, if selected, being from 0.05 to 0.3% by
weight for Cr and for Sc, 0.05 to 0.5% by weight for Hf and for V
and from 0.01 to 0.15% by weight for Ti; other elements at most
0.05% by weight each and 0.15% by weight in total and the remainder
being aluminum; b) a crude form is cast from said liquid metal
bath; c) said crude form is homogenized at a temperature comprised
between 450.degree. C. and 550.degree. C. and optionally between
480.degree. C. and 530.degree. C. for a period comprised between 5
and 60 hours; d) said homogenized crude form is hot-worked,
optionally by rolling; e) the hot-worked product is solution
heat-treated between 490 and 530.degree. C. for 15 min to 8 h and
said solution heat-treated product is quenched; f) said product is
cold-worked with a working of 2 to 16%; g) aging is carried out
wherein said product reaches a temperature comprised between 130
and 170.degree. C. and optionally between 140 and 160.degree. C.
for 5 to 100 hours and optionally 10 to 70 hours.
11. The product according to claim 1, with a thickness comprised
between 8 and 50 mm having, at mid-thickness: i) a compressive
yield strength Rc.sub.p0.2(L).gtoreq.590 MPa, optionally
Rc.sub.p0.2(L) 595 MPa; ii) a toughness K.sub.app (L-T).gtoreq.60
MPa m, optionally K.sub.app (L-T).gtoreq.75 MPa m, with K.sub.app
(L-T) the value of the apparent stress intensity factor at rupture
defined according to standard ASTM E561 (2015) measured on CCT test
specimens of width W=406 mm and thickness B=6.35 mm; iii) a
difference between the tensile yield strength R.sub.p0.2(L) and the
compressive yield strength Rc.sub.p0.2(L),
R.sub.p0.2(L)-Rc.sub.p0.2(L), less than or equal to 10 MPa,
optionally .ltoreq.5 MPa.
12. An aircraft structure element, optionally an aircraft upper
wing skin element, comprising a product according to claim 1.
Description
FIELD OF THE INVENTION
[0001] The invention relates to products made of
aluminum-copper-lithium alloys, more particularly, such products
intended for aeronautical and aerospace construction.
PRIOR ART
[0002] Aluminum alloy products are developed to produce high
strength parts intended in particular for the aircraft industry and
the aerospace industry.
[0003] Aluminum alloys containing lithium are of great interest in
this regard, as lithium can reduce the density of aluminum by 3%
and increase the modulus of elasticity by 6% for each weight
percent lithium added. For these alloys to be selected in
aircrafts, their performance in relation to other properties of use
must reach that of commonly used alloys, in particular in terms of
compromise between the properties of static mechanical strength
(tensile and compressive yield strength, ultimate tensile strength)
and damage tolerance properties (toughness, resistance to the
fatigue crack propagation), these properties being generally
mutually exclusive. For some parts such as the upper wing skin, the
compressive yield strength is an essential property. These
mechanical properties should moreover preferably be stable over
time and have good thermal stability, that is to say not be
significantly modified by aging at operating temperature.
[0004] These alloys must also have sufficient corrosion resistance,
be able to be shaped according to the usual methods and have low
residual stresses so that they can be fully machined. Finally, they
must be able to be obtained by robust manufacturing methods, in
particular, the properties must be able to be obtained on
industrial tools for which it is difficult to guarantee temperature
homogeneity within a few degrees for large parts.
[0005] U.S. Pat. No. 5,032,359 describes a large family of
aluminum-copper-lithium alloys wherein the addition of magnesium
and silver, in particular between 0.3 and 0.5 percent by weight,
allows to increase the mechanical strength.
[0006] U.S. Pat. No. 5,455,003 describes a method for manufacturing
Al--Cu--Li alloys which have improved mechanical strength and
improved toughness at cryogenic temperature, in particular thanks
to suitable work hardening and ageing. 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.
[0007] U.S. Pat. No. 7,438,772 describes alloys comprising, in
weight percentage, Cu: 3-5, Mg: 0.5-2, Li: 0.01-0.9 and discourages
the use of higher lithium content due to degradation of the
compromise between toughness and mechanical strength.
[0008] U.S. 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 refiner agents such as Cr,
Ti, Hf, Sc, V.
[0009] Patent application US 2009/142222 A1 describes alloys
comprising (in % by weight), 3.4 to 4.2% of Cu, 0.9 to 1.4% of Li,
0.3 to 0.7% of Ag, 0.1 to 0.6% of Mg, 0.2 to 0.8% of Zn, 0.1 to
0.6% of Mn and 0.01 to 0.6% of at least one element for controlling
the granular structure. This application also describes a method
for manufacturing extruded products.
[0010] Patent application WO2009/036953 relates to an aluminum
alloy product for structural elements having a chemical composition
comprising, by weight Cu from 3.4 to 5.0, Li from 0.9 to 1.7, Mg
from 0.2 to 0.8, Ag from about 0.1 to 0.8, Mn from 0.1 to 0.9, Zn
up to 1.5, and one or more elements selected from the group
consisting of: (Zr about 0.05 to 0.3, Cr 0.05 to 0.3, Ti about 0.03
to 0.3, Sc about 0.05 to 0.4, Hf about 0.05 to 0.4), Fe<0.15,
Si<0.5, normal and unavoidable impurities.
[0011] Patent application WO 2012/085359 A2 relates to a method for
manufacturing rolled products made of an aluminum-based alloy
comprising 4.2 to 4.6% by weight of Cu, 0.8 to 1.30% by weight of
Li, 0.3 to 0.8% by weight of Mg, 0.05 to 0.18% by weight of Zr,
0.05 to 0.4% by weight of Ag, 0.0 to 0.5% by weight of Mn, at most
0.20% by weight of Fe+Si, less than 0.20% by weight of Zn, at least
one element selected from Cr, Se, Hf and Ti, the amount of said
element, if selected, being 0.05 to 0.3% by weight for Cr and for
Se, 0.05 to 0.5% by weight for Hf and from 0.01 to 0.15% by weight
for Ti, the other elements at most 0.05% by weight each and 0.15%
by weight in total, the remainder being aluminum, comprising the
steps of preparation, casting, homogenization, rolling with a
temperature greater than 400.degree. C., solution heat-treating,
quenching, tensioning between 2 and 3.5% and ageing.
[0012] Patent application US2012/0225271 A1 relates to wrought
products with a thickness of at least 12.7 mm containing from 3.00
to 3.80% by weight of Cu, from 0.05 to 0.35% by weight of Mg, from
0.975 to 1.385% by weight of Li, wherein -0.3
Mg-0.15Cu+1.65.ltoreq.Li.ltoreq.-0.3Mg-0.15Cu+1.85, from 0.05 to
0.50% by weight of at least one grain structure control element,
wherein the grain structure control element is selected from the
group consisting of Zr, Sc, Cr, V, Hf, other rare earth elements,
and combinations thereof, up to 1.0% by weight of Zn, up to 1.0% by
weight of Mn, up to 0.12% by weight of Si, up to 0.15% by weight of
Fe, up to 0.15% by weight of Ti, up to 0.10% by weight of other
elements with a total not exceeding 0.35% by weight.
[0013] Application WO 2013/169901 describes alloys comprising, in
percentage by weight, 3.5 to 4.4% of Cu, 0.65 to 1.15% of Li, 0.1
to 1.0% of Ag, 0.45 to 0.75% of Mg, 0.45 to 0.75% of Zn and 0.05 to
0.50% of at least one element for the control of granular
structure. The alloys advantageously have a Zn to Mg ratio
comprised between 0.60 and 1.67.
[0014] There is a need for aluminum-copper-lithium alloy products
having improved properties compared to those of known products, in
particular in terms of compromise between the properties of static
mechanical strength, in particular the tensile and compressive
yield strength and the properties of damage tolerance, in
particular toughness, thermal stability, corrosion resistance and
machinability, while having a low density.
[0015] In addition, there is a need for a method for manufacturing
these products that is robust, reliable and economical.
OBJECT OF THE INVENTION
[0016] A first object of the invention is a product based on an
aluminum alloy comprising, in percentage by weight, 4.0 to 4.6% by
weight of Cu, 0.7 to 1.2% by weight of Li, 0.5 to 0.65% by weight
of Mg, 0.10 to 0.20% by weight of Zr, 0.15 to 0.30% by weight of
Ag, 0.25 to 0.45% by weight of Zn, 0.05 to 0.35% by weight of Mn,
at most 0.20% by weight of Fe+Si, at least one element selected
from Cr, Sc, Hf, V and Ti, the amount of said element, if selected,
being 0.05 to 0.3% by weight for Cr and for Sc, 0.05 to 0.5% by
weight for Hf and for V and from 0.01 to 0.15% by weight for Ti,
other elements at most 0.05% by weight each and 0.15% by weight in
total and the remainder being aluminum.
[0017] A second object of the invention is a method for
manufacturing a product based on an aluminum alloy wherein,
successively, [0018] a) a liquid metal bath based on aluminum is
prepared comprising 4.0 to 4.6% by weight of Cu; 0.7 to 1.2% by
weight of Li; 0.5 to 0.65% by weight of Mg; 0.10 to 0.20% by weight
of Zr; 0.15 to 0.30% by weight of Ag; 0.25 to 0.45% by weight of
Zn; 0.05 to 0.35% by weight of Mn; at most 0.20% by weight of
Fe+Si; at least one element selected from Cr, Sc, Hf, V and Ti, the
amount of said element, if selected, being from 0.05 to 0.3% by
weight for Cr and for Sc, 0.05 to 0.5% by weight for Hf and for V
and from 0.01 to 0.15% by weight for Ti; other elements at most
0.05% by weight each and 0.15% by weight in total and the remainder
being aluminum; [0019] b) a crude form is cast from said liquid
metal bath; [0020] c) said crude form is homogenized at a
temperature comprised between 450.degree. C. and 550.degree. C. and
preferably between 480.degree. C. and 530.degree. C. for a period
comprised between 5 and 60 hours; [0021] d) said homogenized crude
form is hot-worked, preferably by rolling; [0022] e) the hot-worked
product is solution heat-treated between 490 and 530.degree. C. for
15 min 125 to 8 h and said solution heat-treated product is
quenched; [0023] f) said product is cold-worked with a working of 2
to 16%; [0024] g) an ageing is carried out wherein said cold-worked
product reaches a temperature comprised between 130 and 170.degree.
C. and preferably between 140 and 160.degree. C. for 5 to 100 hours
and preferably 10 to 70 hours.
[0025] Another object of the invention is an alloy product
according to the invention or that can be obtained according to the
method of the invention, with a thickness comprised between 8 and
50 mm having, at mid-thickness: [0026] i) a compressive yield
strength Rc.sub.p0.2(L).gtoreq.590 MPa, preferably
Rc.sub.p0.2(L).gtoreq.595 MPa; [0027] ii) a toughness K.sub.app
(L-T).gtoreq.60 MPa m, preferably K.sub.app (L-T).gtoreq.75 MPa m,
with Kapp (L-T) the value of the apparent stress intensity factor
at rupture defined according to standard ASTM E561 (2015) measured
on CCT test specimens of width W=406 mm and thickness B=6.35 mm;
[0028] iii) a difference between the tensile yield strength
Rp.sub.0.2(L) and the compressive yield strength Rc.sub.p0.2(L),
Rp.sub.0.2(L)-Rc.sub.p0.2(L), less or equal to 10 MPa, preferably
.ltoreq.5 MPa.
[0029] Yet another object is an aircraft structure member,
preferably an aircraft upper wing skin element.
DESCRIPTION OF THE FIGURES
[0030] FIG. 1: Compromise between the toughness K.sub.app L-T and
the compressive yield strength Rc.sub.p0.2 L of the alloys of
Example 1.
[0031] FIG. 2: Compromise between the toughness K.sub.q L-T and the
compressive yield strength Rc.sub.p0.2 L of the alloys of Example
2.
[0032] FIG. 3: Compromise between the compressive yield strength
Rc.sub.p0.2 L and the tensile yield strength R.sub.p0.2 L for the
alloys of Example 2.
[0033] FIG. 4: Compromise between the toughness K.sub.app L-T and
the compressive yield strength Rc.sub.p0.2 L of the alloys of
Example 3.
DESCRIPTION OF THE INVENTION
[0034] Unless otherwise indicated, all indications relating to the
chemical composition of the alloys are 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 the alloys is made in
accordance with the regulations of The Aluminum Association, known
to the person skilled in the art. When the concentration is
expressed in ppm (parts per million), this indication also refers
to a mass concentration.
[0035] Unless otherwise indicated, the definitions of metallurgical
states given in European standard EN 515 (1993) apply.
[0036] The tensile static mechanical features, in other words the
ultimate tensile strength R.sub.m, the conventional yield strength
at 0.2% elongation R.sub.p0.2, and the elongation at rupture A %,
are determined by a tensile test according to standard NF EN ISO
6892-1 (2016), the sampling and direction of the test being defined
by standard EN 485 (2016). R.sub.p0.2 (L) means R.sub.p0.2 measured
in the longitudinal direction.
[0037] The compressive yield strength Rc.sub.p0.2 was measured at
0.2% compression according to standard ASTM E9-09 (2018).
Rc.sub.p0.2 (L) means Rc.sub.p0.2 measured in the longitudinal
direction. The stress intensity factor (K.sub.IC) is determined
according to standard ASTM E 399 (2012). The stress intensity
factor (K.sub.Q) is determined according to standard ASTM E 399
(2012). The standard ASTM E 399 (2012) gives the criteria that
allow determining whether K.sub.Q is a valid value of K.sub.1C. For
a given test specimen geometry, the values of K.sub.Q obtained for
different materials are comparable with each other provided that
the yield strengths of the materials are of the same order of
magnitude.
[0038] Unless otherwise indicated, the definitions of standard EN
12258 (2012) apply.
[0039] The values of the apparent stress intensity factor at
rupture (K.sub.app) and the stress intensity factor at rupture
(K.sub.c) are as defined in standard ASTM E561.
[0040] A curve giving the effective stress intensity factor as a
function of the effective crack extension, known as the curve R, is
determined according to standard ASTM E 561 (ASTM E 561-10-2).
[0041] The critical stress intensity factor K.sub.C, in other words
the intensity factor which makes the crack unstable, is calculated
from the curve R. The stress intensity factor K.sub.CO is also
calculated by assigning the length of the initial crack at the
beginning of the monotonic load, to the critical load. These two
values are calculated for a test specimen of the required shape.
K.sub.app represents the factor K.sub.CO corresponding to the test
specimen which was used to perform the test of curve R. K.sub.eff
represents the factor K.sub.C corresponding to the test specimen
which was used to perform the test of curve R.
[0042] 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 required or performed is here called
"structure element" or "structural element" of a mechanical
construction. These are typically elements the failure of which is
likely to endanger the safety of said construction, its users,
customers or others. For an airplane, these structure elements
comprise in particular the elements that compose the fuselage (such
as the fuselage skin), the stiffeners or stringers of the fuselage,
the watertight bulkheads, the circumferential frames of the
fuselage, the wings (such as the upper or lower wing skin), the
stiffeners (or stringers), the ribs and spars and the empennage in
particular composed of horizontal and vertical stabilizers, as well
as floor beams, seat tracks and doors.
[0043] According to the present invention, a selected class of
aluminum alloys containing in particular specific and critical
amounts of lithium, copper, magnesium, silver, manganese and zinc
allows to prepare structure elements, in particular upper wing skin
sheets, having a high compressive yield strength Rcp.sub.0.2(L), a
small difference between compressive yield strength Rcp.sub.0.2(L)
and tensile yield strength Rp.sub.0.2(L) and a particularly
improved apparent stress intensity factor at rupture K.sub.app. The
selected alloy composition of the invention further allows to
obtain all or part of the aforementioned advantages for a wide
range of ageing times (in particular a range of at least 5 hours at
a given ageing temperature). Such a composition thus allows to
guarantee the robustness of the manufacturing method and therefore
to guarantee the final properties of the product during industrial
manufacture.
[0044] The product based on an aluminum alloy according to the
invention comprises, in percentage by weight, 4.0 to 4.6% by weight
of Cu; 0.7 to 1.2% by weight of Li; 0.5 to 0.65% by weight of Mg;
0.10 to 0.20% by weight of Zr; 0.15 to 0.30% by weight of Ag; 0.25
to 0.45% by weight of Zn; 0.05 to 0.35% by weight of Mn; at most
0.20% by weight of Fe+Si; at least one element selected from Cr,
Sc, Hf, V and Ti; other elements at most 0.05% by weight each and
0.15% by weight in total and the remainder being aluminum.
[0045] The copper content of the products according to the
invention is comprised between 4.0 and 4.6% by weight, preferably
between 4.2 and 4.5% by weight and more preferably between 4.2 and
4.4% by weight. In an advantageous embodiment, the minimum copper
content is 4.25% by weight.
[0046] The lithium content of the products according to the
invention is comprised between 0.7 to 1.2% by weight.
Advantageously, the lithium content is comprised between 0.8 and
1.0% by weight; preferably between 0.85 and 0.95% by weight.
[0047] The increase in the copper content and to a lesser extent
the lithium content contributes to improving the static mechanical
strength, however, copper having a detrimental effect in particular
on the density, it is preferable to limit the copper content to the
preferred maximum value of 4.4% by weight. The increase in the
lithium content has a favorable effect on the density, however the
present inventors have observed that for the alloys according to
the invention, the preferred lithium content comprised between
0.85% and 0.95% by weight allows an improvement in the compromise
between mechanical strength (tensile and compressive yield
strength) and toughness. A high lithium content, in particular
above the preferred maximum value of 0.95% by weight, can lead to a
degradation of the toughness.
[0048] The magnesium content of the products according to the
invention is comprised between 0.5% and 0.65% by weight.
Preferably, the magnesium content is at least 0.50% or even at
least 0.55% by weight, which simultaneously improves static
mechanical strength and toughness. In particular, for the selected
compositions of the present invention, a magnesium content greater
than 0.65% by weight can induce a degradation of the toughness.
[0049] The zinc and silver contents are respectively comprised
between 0.25 and 0.45% by weight and 0.15 and 0.30% by weight. Such
zinc and silver contents are necessary to guarantee a compressive
yield strength having a value close to that of the tensile yield
strength. In an advantageous embodiment, the products according to
the invention have a difference between the tensile yield strength
Rp.sub.0.2(L) and the compressive yield strength Rcp.sub.0.2(L)
less than or equal to 10 MPa, preferably less than or equal to 5
MPa.
[0050] The presence of silver and zinc allows to obtain a good
compromise between the various desired properties. In particular,
the presence of silver allows to obtain a product in a reliable and
robust manner, that is to say that the desired compromise in
properties is achieved for a wide range of ageing times, in
particular a time range greater than 5 hours, which is compatible
with the variability inherent in an industrial manufacturing
method. A minimum content of 0.20% by weight of silver is
advantageous. A maximum content of 0.27% by weight of silver is
advantageous.
[0051] A minimum content of 0.30% by weight of zinc is
advantageous. A maximum content of 0.40% by weight of zinc is
advantageous. Preferably, the Zn content is comprised between 0.30
and 0.40% by weight.
[0052] Advantageously, the sum of the Zn, Mg and Ag contents
comprised between 0.95 and 1.35% by weight, preferably between 1.00
and 1.30% by weight, more preferably still between 1.15 and 1.25%
by weight. The present inventors have observed that the desired
optimum compromise in properties, in particular for elements of the
upper wing skin, was only achieved for specific and critical values
of the sum of Zn, Mg and Ag.
[0053] The manganese content is comprised between 0.05 and 0.35% by
weight. Advantageously, the Mn content comprised between 0.10 and
0.35% by weight. In one embodiment, the manganese content is
comprised between 0.2 and 0.35% by weight and preferably between
0.25 and 0.35% by weight. In another embodiment, the manganese
content is comprised between 0.1 and 0.2% by weight and preferably
between 0.10 and 0.20% by weight. In particular, the addition of Mn
allows to obtain high toughness. However, if the Mn content is
greater than 0.35% by weight, the fatigue life can be significantly
reduced.
[0054] The Zr content of the alloy is comprised between 0.10 and
0.20% by weight. In an advantageous embodiment, the Zr content is
comprised between 0.10 and 0.15% by weight, preferably between 0.11
and 0.14% by weight.
[0055] The sum of the iron content and the silicon content is at
most 0.20% by weight. Preferably, the iron and silicon contents are
each at most 0.08% by weight. In an advantageous embodiment of the
invention the iron and silicon contents are at most 0.06% and 0.04%
by weight, respectively. A controlled and limited iron and silicon
content helps improve the compromise between mechanical strength
and damage tolerance.
[0056] The alloy also contains at least one element which can
contribute to the control of the grain size selected from Cr, Sc,
Hf, V and Ti, the amount of said element, if selected, being from
0.05 to 0.3% by weight for Cr and for Sc, 0.05 to 0.5% by weight
for Hf and for V and from 0.01 to 0.15% by weight for Ti. In an
advantageous embodiment, it is selected to add between 0.01 and
0.15% by weight of titanium. In a preferred embodiment, the Ti
content is comprised between 0.01 and 0.08% by weight, preferably
between 0.02 and 0.06% by weight. Advantageously in the embodiments
wherein it is selected to add titanium, the content of Cr, Sc, V
and Hf is limited to a maximum content of 0.05% by weight, these
elements possibly having an unfavorable effect, in particular on
the density and being added only to further promote the production
of an essentially non-recrystallized structure if necessary. In a
particularly advantageous manner, the Ti is present in particular
in the form of particles of TiC. Against all expectations, the
present inventors have observed that, in the particular case of the
present alloy, the presence of particles of TiC in the grain
refining rod during casting (AlTiC refining), allows to obtain a
product having an optimized compromise in properties.
Advantageously the refiner has the formula AlTi.sub.xC.sub.y which
is also written AT.sub.xC.sub.y where x and y are the contents of
Ti and C in % by weight for 1% by weight of Al, and x/y>4. In
particular, the AlTiC refinement in the alloy of the present
invention allows an improvement of the compromise between the
toughness K.sub.app L-T and the compressive yield strength
R.sub.cp0.2 L.
[0057] The content of the alloy elements can be selected to
minimize the density. Preferably, the additive elements
contributing to increase the density such as Cu, Zn, Mn and Ag are
minimized and the elements contributing to decrease the density
such as Li and Mg are maximized so as to achieve a density less
than or equal to 2.73 g/cm.sup.3 and preferably less than or equal
to 2.72 g/cm.sup.3.
[0058] The content of the other elements is at most 0.05% by weight
each and 0.15% by weight in total. The other elements are typically
unavoidable impurities.
[0059] The method for manufacturing products according to the
invention comprises the steps of preparation, casting,
homogenization, hot working, solution heat-treating and quenching,
tensioning between 2 and 16% and ageing.
[0060] In a first step, a liquid metal bath is prepared so as to
obtain an aluminum alloy of a composition according to the
invention.
[0061] The liquid metal bath is then cast in the form of crude
form, preferably in the shape of a ingot for rolling or an
extrusion billet.
[0062] The crude form is then homogenized so as to reach a
temperature comprised between 450.degree. C. and 550.degree. and
preferably between 480.degree. C. and 530.degree. C. for a period
comprised between 5 and 60 hours. The homogenization treatment can
be carried out in one or more stages.
[0063] After homogenization, the crude form is generally cooled to
room temperature before being preheated in order to be hot-worked.
The hot working can in particular be an extrusion or a hot rolling.
Preferably, this is a hot rolling step. The hot rolling is carried
out to a thickness preferably comprised between 8 and 50 mm and in
a preferred manner between 15 and 40 mm.
[0064] The product thus obtained is then solution heat-treated to
reach a temperature comprised between 490 and 530.degree. C. for 15
min to 8 h, then quenched typically with water at room
temperature.
[0065] The product then undergoes cold working with a working of 2
to 16%. It can be a controlled tensioning with a permanent set of 2
to 5%, preferably from 2.0% to 4.0%. In an alternative advantageous
embodiment, the cold working is carried out in two steps: the
product is first of all cold rolled with a thickness reduction rate
comprised between 8 to 12% then subsequently tensioned in a
controlled manner with a permanent set comprised between 0.5 and
4%.
[0066] The product is then subjected to an ageing step carried out
by heating at a temperature comprised between 130 and 170.degree.
C. and preferably between 140 and 160.degree. C. for 5 to 100 hours
and preferably 10 to 70 hours.
[0067] The present inventors have observed that, surprisingly, the
specific and critical contents of the alloy of the present
invention allow to achieve excellent properties, in particular a
compromise between the compressive yield strength Rc.sub.p0.2(L)
and toughness in plane stresses K.sub.app particularly improved.
Advantageously, these properties can be obtained, for the alloys of
the invention, regardless of the ageing time between 15 h and 25 h
at 155.degree. C., which guarantees the robustness of the
manufacturing method.
[0068] Advantageously, the granular structure of the products
obtained is predominantly non-recrystallized. The rate of
non-recrystallized granular mid-thickness structure is preferably
at least 70% and preferably at least 80%.
[0069] The products obtained by the method according to the
invention, in particular the rolled products having a thickness
comprised between 8 and 50 mm, at mid-thickness, have the following
features: [0070] i) a compressive yield strength
Rc.sub.p0.2(L).gtoreq.590 MPa, preferably Rc.sub.p0.2(L).gtoreq.595
MPa, with Rc.sub.p0.2(L) the compressive yield strength measured at
0.2% compression according to the standard ASTM E9 (2018) in the
longitudinal direction; [0071] ii) a toughness K.sub.app
(L-T).gtoreq.60 MPa m, preferably K.sub.app(L-T).gtoreq.75 MPa m,
with K.sub.app (L-T) the value of the apparent stress intensity
factor at rupture defined according to standard ASTM E561 (2015)
measured on CCT test specimens of width W=406 mm and thickness
B=6.35 mm; [0072] iii) a difference between the tensile yield
strength R.sub.p0.2(L) and the compressive yield strength
Rc.sub.p0.2(L), R.sub.p0.2(L)-Rc.sub.p0.2(L), less than or equal to
10 MPa, preferably .ltoreq.5 MPa.
[0073] Advantageously, the features i) and ii) are obtained for a
wide range of ageing time, in particular a range of at least 5
hours at a given ageing temperature. Such a composition thus allows
to guarantee the robustness of the manufacturing method and
therefore to guarantee the final properties of the product during
industrial manufacture.
[0074] In an advantageous embodiment, the toughness is such that
K.sub.app (L-T).gtoreq.-0.48 Rc.sub.p0.2(L)+355.2, with K.sub.app
(L-T) expressed in MPa m, the value of the apparent stress
intensity factor at rupture defined according to standard ASTM E561
(2015) measured on CCT test specimens of width W=406 mm and
thickness B=6.35 mm, and Rc.sub.p0.2 (L) expressed in MPa, the
compressive yield strength measured at 0.2% compression according
to standard ASTM E9 (2018).
[0075] The alloy products according to the invention allow in
particular the manufacture of structure elements, in particular
aircraft structure elements. In an advantageous embodiment, the
preferred aircraft structure element is an aircraft upper wing skin
element.
[0076] These and other aspects of the invention are explained in
more detail using the following illustrative and non-limiting
examples.
EXAMPLES
Example 1
[0077] In this example, plates with a section of 406.times.1520 mm
made of an alloy, the composition of which is given in Table 1,
were cast.
TABLE-US-00001 TABLE 1 Composition in % by weight of alloys
N.degree.1 to 8 Alloy Si Fe Cu Mn Mg Zn Ti Zr Li Ag 1 0.02 0.03 4.6
0.32 0.62 0.62 0.03 0.13 0.91 0.01 2 0.02 0.03 4.3 0.31 0.60 0.35
0.03 0.12 0.91 0.24 3 0.03 0.05 4.5 0.34 0.71 0.04 0.04 0.11 1.03
0.21 4 0.03 0.04 4.3 -- 0.33 0.03 0.02 0.15 1.13 0.21 5 0.03 0.04
4.2 0.33 0.54 -- 0.03 0.13 0.88 0.19 6 0.02 0.04 4.4 0.02 0.21 0.04
0.02 0.14 1.05 0.21 7 0.03 0.04 3.9 -- 0.36 -- 0.03 0.11 1.31 0.36
8 0.04 0.06 4.1 0.42 0.42 0.02 0.02 0.15 1.18 0.29
[0078] For each composition, the plate was homogenized with a 1st
stage of 15 h at 500.degree. C., followed by a second stage of 20 h
at 510.degree. C. The plate was hot rolled at a temperature above
440.degree. C. to obtain sheets of a thickness of 25 mm for alloys
2 to 8 and 28 mm for alloy 1. The sheets were solution heat-treated
at about 510.degree. C. for 3 h, water quenched at 20.degree. C.
The sheets were then tensioned with a permanent elongation
comprised between 2% and 6%.
[0079] The sheets underwent a single-stage ageing as indicated in
Table 2. Samples were taken at mid-thickness to measure the static
mechanical features in tension and in compression in the
longitudinal direction. The toughness in plane stress was also
measured at mid-thickness during tests of curve R with CCT test
specimens 406 mm wide and 6.35 mm thick in the L-T direction. The
results are shown in Table 2 and FIG. 1.
[0080] The structure of the obtained sheets was mostly
non-recrystallized. The rate of non-recrystallized granular
mid-thickness structure was 90%.
TABLE-US-00002 TABLE 2 Controlled tensile and ageing conditions and
mechanical properties obtained for the various mid-thickness
sheets. Permanent Rc.sub.p0.2 elongation Rp.sub.0.2 (L) during (L)
Com- Kapp controlled Tension pression (L-T) Alloy Ageing tensioning
(Mpa) (Mpa) (MPa m) 1 15 h 155.degree. C. 3.0 593 585 71 20 h
155.degree. C. 3.0 604 610 59 2 15 h 155.degree. C. 3.0 591 593 76
20 h 155.degree. C. 3.0 601 599 69 25 h 155.degree. C. 3.0 613 63 3
15 h 155.degree. C. 3.3 612 607 60 4 15 h 155.degree. C. 3.1 619
614 59 20 h 155.degree. C. 3.1 636 637 55 5 20 h 155.degree. C. 3.2
574 570 105 25 h 155.degree. C. 3.2 585 580 79 6 20 h 155.degree.
C. 3.1 628 628 51 7 24 h 150.degree. C. 4.5 606 590 64 8 24 h
150.degree. C. 4.0 594 587 72
Example 2
[0081] In this example, in addition to the alloy plate 2 of example
1, a plate with a section of 406.times.1520 mm, the composition of
which is given in Table 3, was cast.
TABLE-US-00003 TABLE 3 Composition in % by weight of alloys 2 and
10, Alloy Si Fe Cu Mn Mg Zn Ti Zr Li Ag 2 0.02 0.03 4.3 0.31 0.60
0.35 0.03 0.12 0.91 0.24 10 0.04 0.02 4.3 0.31 0.64 0.33 0.03 0.14
0.90 0.35
[0082] The plates were homogenized at about 510.degree. C. then
scalped. After homogenization, the plates were hot rolled to obtain
sheets having a thickness of 25 mm. The sheets were solution
heat-treated for 3 hours at about 510.degree. C., quenched in cold
water and tensioned with a permanent elongation of 3%.
[0083] The structure of the sheets obtained was predominantly
non-recrystallized. The rate of non-recrystallized mid-thickness
granular structure was 90%.
[0084] The sheets were tempered between 15 h and 50 h at
155.degree. C. Samples were taken at mid-thickness to measure the
static mechanical features in tension, in compression in the
longitudinal direction as well as the toughness K.sub.Q in the L-T
direction. The test specimens used for the toughness measurement
had a width W=40 mm and a thickness B=20 mm. The results obtained
are presented in Table 4 and FIGS. 2 and 3.
TABLE-US-00004 TABLE 4 Ageing conditions and mechanical properties
obtained for the sheets 2 and 10. Difference between Rp.sub.0.2
(MPa) Com- Tough- in tension Tension properties pression ness and
RP.sub.0.2 Ageing Rp.sub.0.2 Rm properties K.sub.Q (MPa) in time at
(L) (L) A Rc.sub.p0.2 (MPa m) com- Alloy 155.degree. C. (MPa) (MPa)
(%) (L) (MPa) L-T pression N.degree.2 10 h 560 598 10 565 -5 15 h
591 617 8.3 593 30.6 -2 20 h 601 625 8.5 599 29.9 2 25 h 613 27.6
30 h 609 632 7.9 615 -6 N.degree.10 10 h 587 620 10 559 28 15 h 604
632 8.5 588 30.7 16 20 h 620 644 8.2 607 25.1 13 25 h 609 24.8 30 h
621 645 7.5 609 12
Example 3
[0085] In this example, in addition to the plate of alloy 2 of
example 1, a plate with a section 406.times.1700 mm, the
composition of which is given in Table 3 was cast using an AlTiC
refining (grain refining rod containing nuclei of the TiC
type).
TABLE-US-00005 TABLE 5 Composition in % by weight of alloys 2 and
9. Alloy Si Fe Cu Mn Mg Zn Ti Zr Li Ag 2 0.02 0.03 4.3 0.31 0.60
0.35 0.03 0.12 0.91 0.24 9 0.02 0.04 4.3 0.14 0.61 0.36 0.05 0.13
0.88 0.25
[0086] The plates were homogenized at about 510.degree. C. then
scalped. After homogenization, the plates were hot rolled to obtain
sheets having a thickness of 25 mm. The sheets were solution
heat-treated for 3 h at around 510.degree. C., quenched in cold
water and tensioned with a permanent elongation of 3%.
[0087] The sheets were tempered between 15 h and 25 h at
155.degree. C. Samples were taken at mid-thickness to measure the
static mechanical features in tension, in compression in the
longitudinal direction as well as the toughness K.sub.Q in the L-T
direction. The test specimens used for the toughness measurement
had a width W=40 mm and a thickness B=20 mm. The validity criteria
of K.sub.1C were met for some samples. Measurements of toughness in
plane stress were also obtained on CCT samples 406 mm wide and 6.35
mm thick. The results obtained are presented in Table 6 and in FIG.
4.
TABLE-US-00006 TABLE 6 Ageing conditions and mechanical properties
obtained for sheets 2 and 9 at mid-thickness Tension properties
Rp.sub.0.2 (L) Compression Toughness Ageing in properties K.sub.Q
K.sub.app time at Rm (L) tension A Rc.sub.p0.2 (L) L-T L-T Alloy
155.degree. C. (MPa) (MPa) (%) (MPa) (MPa m.sup.1/2) (MPa
m.sup.1/2) N.degree.2 15 h 591 617 8.3 593 30.6 76 20 h 601 625 8.5
599 29.9 69 25 h 613 27.6 63 N.degree.9 15 h 597 622 9.1 599 28.7
84 20 h 603 26.8 80 25 h 602 626 8.5 607 26.9 78
* * * * *