U.S. patent application number 17/051672 was filed with the patent office on 2021-06-24 for method for manufacturing an aluminum-copper-lithium alloy having improved compressive strength and improved toughness.
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 | 20210189538 17/051672 |
Document ID | / |
Family ID | 1000005449369 |
Filed Date | 2021-06-24 |
United States Patent
Application |
20210189538 |
Kind Code |
A1 |
MAS; Fanny ; et al. |
June 24, 2021 |
METHOD FOR MANUFACTURING AN ALUMINUM-COPPER-LITHIUM ALLOY HAVING
IMPROVED COMPRESSIVE STRENGTH AND IMPROVED TOUGHNESS
Abstract
The invention relates to a manufacturing method in which an
alloy is prepared that comprises 3.5 to 4.7 wt % of Cu; 0.6 to 1.2
wt % of Li; 0.2 to 0.8 wt % of Mg; 0.1 to 0.2 wt % of Zr; 0.0 to
0.3 wt % of Ag; 0.0 to 0.8 wt % of Zn; 0.0 to 0.5 wt % of Mn; at
most 0.20 wt % of Fe+Si; optionally an element selected from Cr,
Sc, Hf and V, the amount of said element, if selected, being from
0.05 to 0.3 wt % for Cr and for Sc, 0.05 to 0.5 wt % for Hf and for
V; the other elements being at most 0.05 wt % each and 0.15 wt % in
total, a refiner is introduced, the alloy is cast in a crude form,
homogenized, hot-worked, solution heat-treated, quenched,
cold-worked, and tempered, in which the refiner contains particles
of TiC and/or the cold working is between 8 and 16%. The products
obtained by the method according to the invention have an
advantageous compromise between mechanical strength and
toughness.
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 |
|
|
Family ID: |
1000005449369 |
Appl. No.: |
17/051672 |
Filed: |
April 24, 2019 |
PCT Filed: |
April 24, 2019 |
PCT NO: |
PCT/FR2019/050964 |
371 Date: |
October 29, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 21/16 20130101;
C22F 1/057 20130101; C22C 21/18 20130101; B21B 2003/001 20130101;
B21B 3/00 20130101; C22C 21/14 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; B21B 3/00 20060101
B21B003/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 2, 2018 |
FR |
1853799 |
Claims
1. A method for manufacturing a product based on an aluminum alloy
wherein, successively, a) a liquid metal bath based on aluminum is
prepared comprising 3.5 to 4.7 wt % of Cu; 0.6 to 1.2 wt % of Li;
0.2 to 0.8 wt % of Mg; 0.1 to 0.2 wt % of Zr; 0.0 to 0.3 wt % of
Ag; 0.0 to 0.8 wt % of Zn; 0.0 to 0.5 wt % of Mn; at most 0.20 wt %
of Fe+Si; optionally an element selected from Cr, Sc, Hf and V, the
amount of said element, if selected, being from 0.05 to 0.3 wt %
for Cr and for Sc, 0.05 to 0.5 wt % for Hf and for V; other
elements at most 0.05 wt % each and 0.15 wt % in total and the
remainder being aluminum; b) a refiner is introduced into said bath
so that the Ti content is comprised between 0.01 to 0.15 wt %; c) a
crude form is cast from said liquid metal bath; d) 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; e)
said homogenized crude form is hot-worked, optionally by rolling;
f) the hot-worked product is solution heat-treated between
490.degree. C. and 530.degree. C. for 15 min to 8 hours and said
solution heat-treated product is quenched; g) said product is
cold-worked with a cold working of 2 to 16%; h) aging is carried
out wherein said product thus cold-worked reaches a temperature
comprised between 130.degree. C. and 170.degree. C. and optionally
between 140.degree. C. and 160.degree. C. for 5 to 100 hours and
optionally 10 to 70 hours; wherein said refiner contains particles
of the TiC type and/or said cold working is of 8 to 16%.
2. The method according to claim 1, wherein the refiner containing
particles of the TiC type is introduced in a form and an amount
such that an amount of TiC identical to that added with a refiner
AT3C0.15 at a rate of 2 to 5 kg/t of aluminum alloy is added.
3. The method according to claim 1 wherein the cold working of g
comprises: g1) said product is cold rolled with a thickness
reduction rate comprised between 8 to 12%; g2) said product is
tensioned in a controlled manner with a permanent set comprised
between 0.5 and 4%.
4. The method according to claim 1, wherein the aging is carried
out at a temperature comprised between 140 and 155.degree. C.,
optionally between 145 and 150.degree. C., optionally for 18 to 22
hours.
5. The method according to claim 1, wherein the copper content is
comprised between 4.0 and 4.6 wt % and optionally between 4.1 and
4.5 wt %.
6. The method according to claim 1, wherein the manganese content
is comprised between 0.05 and 0.4 wt %.
7. The method according to claim 1 wherein the Ag content is of 0.1
to 0.27 wt % and/or the Zn content is of 0.2 to 0.40 wt %.
8. A product based on an aluminum alloy that can be obtained by the
method according to claim 1.
9. The product according to claim 8 comprising a rolled product
with a thickness comprised between 8 and 50 mm and having, at
mid-thickness, K.sub.app(L-T).gtoreq.-0.5Rc.sub.p0.2(L)+375,
optionally K.sub.app(L-T).gtoreq.-0.5Rc.sub.p0.2(L)+386 with Kapp
(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).
10. The product according to claim 8 comprising a rolled product
with a thickness comprised between 8 and 50 mm and having, at
mid-thickness, K.sub.app(L-T).gtoreq.-0.5Rc.sub.p0.2(L)+386,
optionally K.sub.app(L-T).gtoreq.-0.5Rc.sub.p0.2(L)+391, and
R.sub.p0.2(L)>600 MPa, optionally 615 MPa, with Kapp (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), and R.sub.p0.2 (L) the conventional yield strength
at 0.2% elongation measured in the longitudinal direction of the
product, determined by a tensile test according to standard NF EN
ISO 6892-1 (2016).
11. An aircraft structure element, optionally an aircraft upper
wing skin element, comprising a product according to claim 9.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a method for manufacturing products
made of aluminum-copper-lithium alloys, in particular, 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 as well as the toughness in plane stress
are essential properties. 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.
[0005] 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.
[0006] 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.
[0007] 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 working 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.
[0008] 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.
[0009] U.S. Pat. No. 7,229,509 describes an alloy comprising (wt
%): (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.
[0010] Patent application US 2009/142222 A1 describes alloys
comprising (in wt %), 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.
[0011] 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.
[0012] 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 wt % of Cu, 0.8 to 1.30 wt % of Li, 0.3 to
0.8 wt % of Mg, 0.05 to 0.18 wt % of Zr, 0.05 to 0.4 wt % of Ag,
0.0 to 0.5 wt % of Mn, at most 0.20 wt % of Fe+Si, less than 0.20
wt % 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 wt % for
Cr and for Se, 0.05 to 0.5 wt % for Hf and from 0.01 to 0.15 wt %
for Ti, the other elements at most 0.05 wt % each and 0.15 wt % 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.
[0013] 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 wt % of Cu, from 0.05 to 0.35 wt % of Mg, from 0.975 to
1.385 wt % of Li, wherein -0.3 Mg-0.15Cu+1.65.ltoreq.Li.ltoreq.-0.3
Mg-0.15Cu+1.85, from 0.05 to 0.50 wt % 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 wt %
of Zn, up to 1.0 wt % of Mn, up to 0.12 wt % of Si, up to 0.15 wt %
of Fe, up to 0.15 wt % of Ti, up to 0.10 wt % of other elements
with a total not exceeding 0.35 wt %.
[0014] 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.
[0015] There is a need for aluminum-copper-lithium alloy products
having ever more 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.
[0016] In addition, there is a need for a method for manufacturing
these products that is robust, reliable and economical.
Object of the Invention
[0017] A first 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 3.5 to 4.7 wt % of Cu; 0.6 to 1.2 wt % of Li;
0.2 to 0.8 wt % of Mg; 0.1 to 0.2 wt % of Zr; 0.0 to 0.3 wt % of
Ag; 0.0 to 0.8 wt % of Zn; 0.0 to 0.5 wt % of Mn; at most 0.20 wt %
of Fe+Si; optionally an element selected from Cr, Sc, Hf and V, the
amount of said element, if selected, being from 0.05 to 0.3 wt %
for Cr and for Sc, 0.05 to 0.5 wt % for Hf and for V; other
elements at most 0.05 wt % each and 0.15 wt % in total and the
remainder being aluminum; [0019] b) a refiner is introduced into
said bath so that the Ti content is comprised between 0.01 to 0.15
wt %; [0020] c) a crude form is cast from said liquid metal bath;
[0021] d) 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; [0022] e) said homogenized crude form is hot-worked,
preferably by rolling; [0023] f) the hot-worked product is solution
heat-treated between 490.degree. C. and 530.degree. C. for 15 min
to 8 hours and said solution heat-treated product is quenched;
[0024] g) said product is cold-worked with a cold working of 2 to
16%; [0025] h) a ageing is carried out wherein said product thus
cold-worked reaches a temperature comprised between 130.degree. C.
and 170.degree. C. and preferably between 140.degree. C. and
160.degree. C. for 5 to 100 hours and preferably 10 to 70 hours;
wherein said refiner contains particles of the TiC type and/or said
cold working is of 8 to 16%.
[0026] Another object of the invention is a product that can be
obtained by the method according to the invention and such that it
is a rolled product with a thickness comprised between 8 and 50 mm
and having, at mid-thickness,
K.sub.app(L-T).gtoreq.-0.5Rc.sub.p0.2(L)+375,
preferably K.sub.app(L-T).gtoreq.-0.5Rc.sub.p0.2(L)+386 [0027] with
Kapp (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 [0028] Rc.sub.p0.2(L), expressed in MPa,
the compressive yield strength measured at 0.2% compression
according to standard ASTM E9 (2018).
[0029] Yet another object is an aircraft structure member,
preferably an aircraft upper wing skin element, comprising a
product according to the invention.
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: Graph showing the difference between the value of
K.sub.app (L-T) measured according to the alloys of example 1 and
the value calculated according to the formula -0.5
R.sub.cp0.2(L)+386 as a function of the conventional yield strength
R.sub.p0.2 measured in the longitudinal direction of the
product.
[0032] FIG. 3: Compromise between the toughness Kapp L-T and the
compressive yield strength Rc.sub.p0.2 L of the alloys of Example
2.
[0033] FIG. 4: Graph showing the difference between the value of
K.sub.app (LT) measured according to the alloys of example 2 and
the value calculated according to the formula -0.5 R.sub.cp0.2
(L)+375 as a function of the conventional yield strength R.sub.p0.2
measured in the longitudinal direction of the product.
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 wt % 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.1C) 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, its
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, and zirconium allows to
prepare, under certain processing conditions, products, in
particular rolled products, having an improved compromise between
toughness, tensile and compressive yield strength. The present
inventors have observed that, surprisingly, it is possible to
improve, for the products produced from these alloys, the
properties of use, in particular those making the products suitable
for the production of structure elements in the aeronautical and
aerospace fields. In particular, the products according to the
invention are particularly well adapted to the production of
aircraft upper wing skin elements since they have a particularly
improved compromise compressive yield strength Rc.sub.p0.2
(L)-toughness Kapp (L-T).
[0044] The invention relates in particular to a method wherein an
alloy is prepared comprising 3.5 to 4.7 wt % of Cu; 0.6 to 1.2 wt %
of Li; 0.2 to 0.8 wt % of Mg; 0.1 to 0.2 wt % of Zr; 0.0 to 0.3 wt
% of Ag; 0.0 to 0.8 wt % of Zn; 0.0 to 0.5 wt % of Mn; at most 0.20
wt % of Fe+Si; optionally an element selected from Cr, Sc, Hf and
V; the amount of said element, if selected, being 0.05 to 0.3 wt %
for Cr and for Sc, 0.05 to 0.5 wt % for Hf and for V; other
elements at most 0.05 wt % each and 0.15 wt % in total, a refiner
is introduced, the alloy is cast in a crude form, homogenized,
hot-worked, solution heat-treated, quenched, cold-worked and
tempered, wherein the refiner contains particles of TiC and/or the
cold working is comprised between 8 to 16%.
[0045] The copper content of the products according to the
invention is comprised between 3.5 and 4.7 wt %, preferably between
4.0 and 4.6 wt %. In a particularly advantageous embodiment, the
copper content is comprised between 4.1 and 4.5 wt %, preferably
between 4.2 and 4.4 wt %. The increase in the copper content
contributes to an improvement in the tensile and compressive yield
strength. However, copper, in an excessively high quantity, induces
a decrease in the toughness in plane stress Kapp.
[0046] The lithium content of the products according to the
invention is comprised between 0.7 to 1.2 wt %. Advantageously, the
lithium content is comprised between 0.8 and 1.0 wt %; preferably
between 0.85 and 0.95 wt %. 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
selected lithium content allows an improvement in the compromise
between mechanical strength, in particular the tensile and
compressive yield strength, and toughness. A very high lithium
content can lead to a degradation of the toughness.
[0047] The magnesium content of the products according to the
invention is comprised between 0.2% and 0.8 wt %. Preferably, the
magnesium content is at least 0.3% or even 0.4% or 0.5 wt %, which
simultaneously improves static mechanical strength and toughness.
Preferably, the magnesium content is less than 0.7 wt % or even
0.65 wt %. Indeed, a high magnesium content can induce a
degradation of the toughness.
[0048] The alloy may contain zinc up to 0.8 wt %. In an
advantageous embodiment, the Zn content is comprised between 0.05
and 0.6 wt %, preferably 0.2 and 0.5 wt % and, more preferably
still, between 0.30 and 0.40 wt %. In another embodiment, the alloy
contains less than 0.05 wt % of Zn, preferably less than 0.02 wt
%.
[0049] The alloy may also contain up to 0.3 wt % of silver. In one
embodiment, the alloy comprises more than 0.05 wt %, preferably
more than 0.1% and more preferably still from 0.2 to 0.3 wt % of
Ag. In one embodiment the maximum Ag content is 0.27 wt %.
[0050] The presence of zinc and/or silver allows to obtain a
compressive yield strength having a value close to that of the
tensile yield strength. In one embodiment, the Ag content is of 0.1
to 0.27 wt % and/or the Zn content is of 0.2 to 0.40 wt %. The
alloy may also contain up to 0.5 wt % of manganese. Advantageously,
the manganese content is comprised between 0.05 and 0.4 wt %. In
one embodiment the manganese content is comprised between 0.2 and
0.37 wt % and preferably between 0.25 and 0.35 wt %. In another
embodiment the manganese content is comprised between 0.1 and 0.2
wt % and preferably between 0.10 and 0.20 wt %. In particular, the
addition of Mn allows to obtain high toughness. However, if the Mn
content is too high, the fatigue life can be significantly
reduced.
[0051] The Zr content of the alloy is comprised between 0.1 and 0.2
wt %. In an advantageous embodiment, the Zr content is comprised
between 0.10 and 0.15 wt %, preferably between 0.11 and 0.14 wt
%.
[0052] The alloy also contains titanium, the Ti content is
comprised between 0.01 and 0.15 wt %, preferably between 0.02 and
0.08 wt %. In one embodiment, the refiner introduced into the
aluminum alloy bath contains particles of the TiC type.
Advantageously the refiner has the formula AlTi.sub.xC.sub.y which
is also written ATxCy where x and y are the contents of Ti and C in
wt % for 1 wt % of Al, and x/y>4. Against all expectations, the
present inventors have observed that, in the particular case of the
present alloy, the presence in the refiner and therefore in the
alloy of particles of TiC at the origin of a particular refining of
the alloy during casting (AlTiC refining), allows to obtain a
product having an optimized compromise of properties. In
particular, the presence of particles of TiC in the grain refining
rod and in the alloy of an embodiment of the method of the present
invention allows an improvement in the compromise between the
toughness K.sub.app L-T and the compressive yield strength
R.sub.cp0.2 L.
[0053] The sum of the iron content and the silicon content is at
most 0.20 wt %. Preferably, the iron and silicon contents are each
at most 0.08 wt %. In an advantageous embodiment of the invention
the iron and silicon contents are at most 0.06% and 0.04 wt %,
respectively. A controlled and limited iron and silicon content
helps improve the compromise between mechanical strength and damage
tolerance.
[0054] The alloy may also contain at least one element which can
contribute to the control of the grain size selected from Cr, Sc,
Hf and V, the amount of said element, if selected, being from 0.05
to 0.3 wt % for Cr and for Sc and 0.05 to 0.5 wt % for Hf and for
V.
[0055] 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.
[0056] The content of the other elements is at most 0.05 wt % each
and 0.15 wt % in total. The other elements are typically
unavoidable impurities.
[0057] The method for manufacturing products according to the
invention comprises the steps of preparation, casting, introducing
a refiner, homogenization, hot working, solution heat-treating and
quenching, cold working and ageing.
[0058] In a first step, a liquid metal bath is prepared so as to
obtain an aluminum alloy of a composition according to the
invention. A refiner is then introduced into said bath so that the
Ti content is comprised between 0.01% to 0.15 wt %, optionally the
refiner contains particles of the TiC type. Advantageously, the Ti
content is comprised between 0.02 and 0.08 wt %, preferably between
0.03 and 0.06 wt %. In one embodiment the refiner contains
particles of the TiC type. Advantageously, the refiner containing
particles of the TiC type is introduced in a form and an amount
such that an amount of TiC identical to that added with a refiner
AT3C0.15 at a rate of 2 to 5 kg/t of aluminum alloy is added.
Preferably, the refiner containing particles of the TiC type is
introduced in the form of AT3C0.15 at a rate of 2 to 5 kg/t of
aluminum alloy.
[0059] The liquid metal bath is then cast in the form of crude
form, preferably in the shape of an ingot for rolling.
[0060] 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.
[0061] 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.
[0062] 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.
[0063] The product then undergoes cold working with a cold working
of 2 to 16%. In one embodiment the cold working is a controlled
tensioning with a permanent set of 2 to 6%, preferably from 2.0% to
4.0%. In one embodiment said product is cold-worked with a cold
working rate comprised between 8 to 16%. In one 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
and 12%, preferably 9 and 11%, then subsequently tensioned in a
controlled manner with a permanent set comprised between 0.5 and
4%, preferably between 0.5 and 2%.
[0064] 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. In a particularly advantageous
embodiment, the ageing is carried out at a temperature comprised
between 140 and 155.degree. C., preferably between 145 and
150.degree. C., preferably for 18 to 22 hours.
[0065] The present inventors have observed that, surprisingly, the
method according to the invention allows to obtain an advantageous
product. Thus the specific and critical contents of the alloy of
the present invention associated with a particular manufacturing
method allow to achieve excellent properties. In particular, the
product according to the invention is advantageously a rolled
product with a thickness comprised between 8 and 50 mm and having,
at mid-thickness,
K.sub.app(L-T).gtoreq.-0.5Rc.sub.p0.2(L)+375,
preferably K.sub.app(L-T).gtoreq.-0.5Rc.sub.p0.2(L)+386 [0066] even
more preferably K.sub.app(L-T).gtoreq.-0.5 Rc.sub.p0.2(L)+391,
[0067] 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 [0068] Rc.sub.p0.2(L)
expressed in MPa, the compressive yield strength measured at 0.2%
compression according to standard ASTM E9 (2018).
[0069] Advantageously, the product according to the invention is a
rolled product with a thickness comprised between 8 and 50 mm and
having, at mid-thickness,
K.sub.app(L-T).gtoreq.-0.5R.sub.cp0.2(L)+375
and a yield strength value R.sub.p0.2(L) of at least 580 MPa,
preferably 600 MPa, even more preferably 615 MPa, [0070] with Kapp
(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 [0071] Rc.sub.p0.2(L) expressed in MPa,
the compressive yield strength measured at 0.2% compression
according to standard ASTM E9 (2018), [0072] and R.sub.p0.2(L) the
conventional yield strength at 0.2% elongation measured in the
longitudinal direction of the product, determined by a tensile test
according to standard NF EN ISO 6892-1 (2016).
[0073] The inventors have in particular observed that,
surprisingly, the combination of the introduction into the liquid
metal bath of a refiner containing particles of the TiC type so
that the Ti content is comprised between 0.01 to 0.15 wt % and a
cold working after solution heat-treating with a cold working rate
comprised between 8 to 16% is advantageous. In particular, this
combination allows to obtain a rolled product with a thickness
comprised between 8 and 50 mm, at mid-thickness
K.sub.app(L-T).gtoreq.-0.5Rc.sub.p0.2(L)+386,
preferably K.sub.app(L-T).gtoreq.-0.5Rc.sub.p0.2(L)+391 [0074] with
Kapp (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 [0075] Rc.sub.p0.2(L) expressed in MPa,
the compressive yield strength measured at 0.2% compression
according to ASTM E9 (2018).
[0076] Advantageously, the combination comprising the introduction
into the liquid metal bath of a refiner containing particles of TiC
type so that the Ti content is comprised between 0.01 to 0.15 wt %
and a cold working after solution heat-treating with a cold working
rate comprised between 8 to 16% allows to obtain, for a rolled
product with a thickness comprised between 8 and 50 mm, at
mid-thickness,
K.sub.app(L-T).gtoreq.-0.5Rc.sub.p0.2(L)+386,
preferably K.sub.app(L-T).gtoreq.-0.5Rc.sub.p0.2(L)+391
and a yield strength value R.sub.p0.2(L) of at least 600 MPa, even
more preferably of at least 615 MPa, [0077] with Kapp (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 [0078] Rc.sub.p0.2 (L) expressed in MPa, the
compressive yield strength measured at 0.2% compression according
to ASTM E9 (2018), and [0079] R.sub.p0.2 (L) the conventional yield
strength at 0.2% elongation measured in the longitudinal direction
of the product, determined by a tensile test according to standard
NF EN ISO 6892-1 (2016).
[0080] 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.
[0081] These and other aspects of the invention are explained in
more detail using the following illustrative and non-limiting
examples.
EXAMPLES
Example 1
[0082] In this example, two plates with a thickness of 406 mm for
each of the alloys, the composition of which is given in Table 1,
were cast. Alloy 1 was refined using 2.7 kg/t AT3B. Alloy 2 was
refined using 4 kg/t AT3C0.15.
TABLE-US-00001 TABLE 1 Composition in wt % of alloys 1 and 2 Alloy
Si Fe Cu Mn Mg Zn Ti Zr Li Ag 1 0.02 0.03 4.3 0.31 0.60 0.35 0.03
0.12 0.91 0.24 2 0.02 0.04 4.3 0.14 0.61 0.36 0.05 0.13 0.88
0.25
[0083] The plates were homogenized at about 510.degree. C. The
homogenized plates were hot rolled at an input temperature of about
450.degree. C. and an output temperature of about 390.degree. C. to
obtain for each alloy sheets of thickness 28 mm The sheets were
solution heat-treated at about 510.degree. C. for 3 h, quenched
with water at 20.degree. C. One sheet of each alloy 1 and 2 was
then cold rolled with a thickness reduction rate of 10% ("LAF 10%"
condition) followed by tensioning with a permanent elongation of
about 1%. For each alloy another sheet was also tensioned with a
permanent set of 3% without prior cold rolling.
[0084] 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 as well as the
toughness K.sub.Q. The test specimens used for the toughness
measurement had a width W=40 mm and a thickness B=20 mm. The
measurements taken were valid according to the ASTM E399 standard.
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. The results are shown in Table 2 and FIG. 1.
[0085] FIG. 2 shows the difference between the measured value of
Kapp (L-T) and the value calculated according to the formula "-0.5
R.sub.cp0.2(L)+386" as a function of the conventional yield
strength R.sub.p0.2(L) measured in the longitudinal direction L of
the product.
TABLE-US-00002 TABLE 2 Ageing conditions and mechanical properties
obtained for the different sheets. Kq L-T, R.sub.p0.2 R.sub.cp0.2
Kapp mean Cold (L) (L) L-T value, Alloy Refiner Ref working Ageing
(MPa) (MPa) (MPa m) (MPa m) 1 AT3B 1-A Tension 3 15 h 155.degree.
C. 598 593 76 30.63 20 h 155.degree. C. 599 599 69 29.93 25 h
155.degree. C. 604 613 63 27.61 1 AT3B 1-B LAF 10% + 15 h
147.degree. C. 610 602 78 Tension 1% 20 h 147.degree. C. 629 620 75
25.85 25 h 147.degree. C. 632 622 69 25.96 2 AT3C0.15 2-C Tension 3
20 h 155.degree. C. 598 599 84 28.71 25 h 155.degree. C. 603 603 80
26.81 30 h 155.degree. C. 613 606 78 26.87 2 AT3C0.15 2-D LAF 10 +
16.5 h 147.degree. C. 620 605 90 Tension 1% 18 h 147.degree. C. 611
88 29.79 20 h 147.degree. C. 628 615 93.5 26.99 22 h 147.degree. C.
619 86 26.25
Example 2
[0086] Plates with a section of 406.times.1520 mm, the composition
of which is given in Table 3, were cast. The refiner used was
AT3B.
TABLE-US-00003 TABLE 3 Composition in wt % of alloys 3, 4 and 5
Alloy Si Fe Cu Mn Mg Zn Ti Zr Li Ag 3 0.05 0.05 4.5 0.37 0.35 0.02
0.03 0.11 1.02 0.21 4 0.03 0.05 4.5 0.34 0.71 0.04 0.04 0.11 1.02
0.21 5 0.03 0.04 4.6 0.35 0.23 0.04 0.02 0.14 1.05 0.22
The plates were homogenized at about 510.degree. C. After
homogenization, the plates were hot rolled to obtain sheets having
a thickness of 25 mm. The sheets were solution heat-treated for 5
hours at about 510.degree. C., quenched in cold water. One plate of
each alloy was cold rolled with a thickness reduction rate of 10%
("LAF 10%" condition), followed by tensioning with a permanent
elongation of about 1.2%. Another plate of each alloy was tensioned
with a permanent elongation without prior cold rolling. The values
of the permanent elongations are shown in Table 4.
[0087] The sheets then underwent an ageing comprised between 10
hours and 25 hours at 155.degree. C. as indicated in Table 2.
Samples were taken at mid-thickness to measure the tensile,
compressive static mechanical features as well as the toughness in
plane stress K.sub.app (L-T). The test specimens used for the
toughness measurement are CCTs with a width W=406 mm and a
thickness B=6.35 mm. The results obtained are presented in Table 4
and FIG. 3. FIG. 4 shows the difference between the measured value
of Kapp (L-T) and the value calculated according to the formula
-0.5 Rcp0.2(L)+375 as a function of the conventional yield strength
Rp0.2 measured in the longitudinal direction L of the product.
TABLE-US-00004 TABLE 4 Ageing conditions and mechanical properties
obtained for sheets made of alloy 3, 4 and 5. Final R.sub.p0.2
R.sub.cp0.2 Kapp thickness Cold (L) (L) L-T Alloy Refiner Ref. (mm)
working Ageing (MPa) (MPa) (MPa m) 3 AT3B 3-A 25 4% tension 22 h
631 630 56 155.degree. C. 3-B 22.5 10% LAF + 10 h 617 633 61 1.2%
tension 155.degree. C. 4 AT3B 4-A 25 3.1% tension 25 h 637 643 48
155.degree. C. 4-B 22.5 10% LAF + 10 h 668 642 57 1.2% tension
155.degree. C. 5 AT3B 5-A 25 3.1% tension 25 h 638 651 41
155.degree. C. 5-B 22.5 10% LAF + 10 h 657 648 52 1.2% tension
155.degree. C.
* * * * *