U.S. patent application number 15/780273 was filed with the patent office on 2018-12-20 for aluminum copper lithium alloy with improved mechanical strength and toughness.
The applicant listed for this patent is CONSTELLIUM ISSOIRE. Invention is credited to Alireza ARBAB, Bernard BES, Christophe SIGLI, Ricky WHELCHEL.
Application Number | 20180363114 15/780273 |
Document ID | / |
Family ID | 55862869 |
Filed Date | 2018-12-20 |
United States Patent
Application |
20180363114 |
Kind Code |
A1 |
WHELCHEL; Ricky ; et
al. |
December 20, 2018 |
ALUMINUM COPPER LITHIUM ALLOY WITH IMPROVED MECHANICAL STRENGTH AND
TOUGHNESS
Abstract
The invention is a rolled and/or forged product, made of an
aluminium-based alloy comprising, in % by weight, Cu: 3.2-4.0; Li:
0.80-0.95; Zn: 0.45-0.70; Mg: 0.15-0.7; Zr: 0.07-0.15; Mn: 0.1-0.6;
Ag:<0.15; Fe+Si.ltoreq.0.20; at least one element from Ti:
0.01-0.15; Se: 0.02-0.1; Cr: 0.02-0.1; Hf: 0.02-0.5; V: 0.02-0.1;
other elements .ltoreq.0.05 each and .ltoreq.0.15 in total,
remainder aluminium. In the process for manufacturing the products
according to the invention a bath of liquid metal based on
aluminium as alloy according to the invention is melted, an
unwrought product is cast from said bath of liquid metal; said
unwrought product is homogenized at a temperature between
450.degree. C. and 550.degree. C.; said unwrought product is hot
worked and optionally cold worked preferably to a thickness of at
least 15 mm: said product is solution treated between 490.degree.
C. and 530.degree. C. for 15 min to 8 h and quenched; said product
is drawn in a controlled manner with a permanent deformation of 1%
to 7% and a tempering of said product is carried out. The product
is advantageous for the manufacture of an aircraft structural
component.
Inventors: |
WHELCHEL; Ricky; (Grenoble,
FR) ; ARBAB; Alireza; (Rives-sur-fure, FR) ;
BES; Bernard; (Seyssins, FR) ; SIGLI; Christophe;
(Grenoble, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CONSTELLIUM ISSOIRE |
Issoire |
|
FR |
|
|
Family ID: |
55862869 |
Appl. No.: |
15/780273 |
Filed: |
December 1, 2016 |
PCT Filed: |
December 1, 2016 |
PCT NO: |
PCT/FR2016/053175 |
371 Date: |
May 31, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 21/14 20130101;
C22C 21/16 20130101; C22F 1/002 20130101; C22C 21/18 20130101; C22F
1/057 20130101 |
International
Class: |
C22F 1/057 20060101
C22F001/057; C22F 1/00 20060101 C22F001/00; C22C 21/14 20060101
C22C021/14; C22C 21/16 20060101 C22C021/16; C22C 21/18 20060101
C22C021/18 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 4, 2015 |
FR |
1561852 |
Claims
1. Rolled and/or forged aluminum-based alloy product comprising the
following % by weight, Cu: 3.2-4.0; Li: 0.80-0.95; Zn: 0.45-0.70;
Mg: 0.15-0.7; Zr: 0.07-0.15; Mn: 0.1-0.6; Ag: <0.15;
Fe+Si.ltoreq.0.20; at least one element from among Ti: 0.01-0.15;
Sc: 0.02-0.15, optionally 0.02-0.1; Cr: 0.02-0.3, optionally
0.02-0.1; Hf: 0.02-0.5; V: 0.02-0.3, optionally 0.02-0.1; other
elements<0.05 each and<0.15 total, remainder aluminum.
2. Product according to claim 1, in which the magnesium content is
at most (0.55-5*Ag).
3. Product according to claim 1, in which the copper content is
between 3.3 and 3.8%; and optionally between 3.4 and 3.7% by
weight.
4. Product according to claim 1, in which the zinc content is
between 0.50 and 0.60% by weight.
5. Product according to claim 1, in which the manganese content is
between 0.2 and 0.4% by weight.
6. Product according to claim 1, in which the lithium content is
between 0.84% and 0.93% by weight, and optionally the lithium
content is at least 0.86% by weight.
7. Product according to claim 1 for which the thickness is equal to
at least 12 mm and optionally at least 40 mm.
8. Product according to claim 1 in a rolled and/or forged, solution
heat treated, quenched, stress relieved optionally by stretching,
and aged temper with at least one of the following pairs of
characteristics for thicknesses of between 40 and 75 mm: (i) at
quarter thickness, yield stress R.sub.p0.2(LT).ltoreq.480 MPa and
optionally R.sub.p0.2(LT).ltoreq.490 MPa and toughness K.sub.1C
(T-L).ltoreq.31 MPa m and advantageously such that K.sub.1C
(T-L).ltoreq.-0.175 R.sub.p0.2(LT)+119.2, optionally K.sub.1C
(T-L).ltoreq.-0.175 R.sub.p0.2(LT)+120.5 and optionally K.sub.1C
(T-L).ltoreq.-0.175 R.sub.p0.2(LT)+121.5, (ii) at mid thickness,
yield stress R.sub.p0.2(ST).ltoreq.450 MPa and optionally
R.sub.p0.2(ST).ltoreq.455 MPa and toughness K.sub.1C
(S-L).ltoreq.24 MPa m and advantageously such that K.sub.1C
(S-L).ltoreq.-0.34 R.sub.p0.2(ST)+185.6, optionally K.sub.1C
(S-L).ltoreq.-0.34 R.sub.p0.2(ST)+187.2 and optionally K.sub.1C
(S-L).ltoreq.-0.34 R.sub.p0.2(ST)+188.7,
9. Product according to claim 1 having, in a rolled and/or forged,
solution heat treated, quenched, stress relieved optionally by
stretching, and aged temper, at least one of the following pairs of
characteristics for thicknesses of between 40 and 150 mm, the
toughness in plane stress K.sub.app being measured on test pieces
type CCT406 (2ao=101.6 mm) (i) for thicknesses of between 40 and 75
mm K.sub.app, in the L-T direction of at least 105 MPa m and
optionally at least 110 MPa m and a yield stress R.sub.p0.2 (L)
equal to at least 500 MPa and optionally at least 510 MPa, (ii) for
thicknesses of between 40 and 75 mm K.sub.app, in the T-L direction
of at least 60 MPa m and optionally at least 70 MPa m and a yield
stress R.sub.p0.2(LT) equal to at least 480 MPa and optionally at
least 490 MPa. (iii) for thicknesses of between 76 and 120 mm
K.sub.app, in the L-T direction of at least 80 MPa m and optionally
at least 90 MPa m and a yield stress R.sub.p0.2(L) equal to at
least 475 MPa and optionally at least 485 MPa, (iv) for thicknesses
of between 76 and 120 mm K.sub.app, in the T-L direction of at
least 40 MPa m and optionally at least 50 MPa m and a yield stress
R.sub.p0.2(LT) equal to at least 455 MPa and optionally at least
465 MPa. (v) for thicknesses of between 121 and 150 mm K.sub.app,
in the L-T direction of at least 75 MPa m and optionally at least
80 MPa m and a yield stress R.sub.p0.2(L) equal to at least 470 MPa
and optionally at least 480 MPa, (vi) for thicknesses of between
121 and 150 mm K.sub.app, in the T-L direction of at least 40 MPa m
and optionally at least 45 MPa m and a yield stress R.sub.p0.2(LT)
equal to at least 445 MPa and optionally at least 455 MPa.
10. Product according to claim 1, in which the magnesium content is
at least 0.34% by weight, and the silver content is less than 0.05%
by weight.
11. Product according to claim 10 in a rolled and/or forged,
solution heat treated, quenched, stress relieved optionally by
stretching, and aged temper, with at least one of the following
pairs of characteristics for thicknesses of between 76 and 150 mm:
(i) for thicknesses of 76 to 120 mm, at quarter thickness, yield
stress R.sub.p0.2(LT).ltoreq.460 MPa and optionally
R.sub.p0.2(LT).ltoreq.470 MPa and a toughness K.sub.1C
(T-L).ltoreq.27 MPa m and advantageously such that K.sub.1C
(T-L).ltoreq.-0.1 R.sub.p0.2(LT)+77, optionally K.sub.1C
(T-L).ltoreq.-0.1 R.sub.p0.2(LT)+78 and optionally K.sub.1C
(T-L).ltoreq.-0.1 R.sub.p0.2(LT)+79, (ii) for thicknesses of 76 to
120 mm, at mid thickness, yield stress R.sub.p0.2(ST).ltoreq.435
MPa and optionally R.sub.p0.2(ST).ltoreq.445 MPa and toughness
K.sub.1C (S-L).ltoreq.23 MPa m and advantageously such that
K.sub.1C (S-L).ltoreq.-0.25 R.sub.p0.2 (ST)+139.25, optionally
K.sub.1C (S-L).ltoreq.-0.25 R.sub.p0.2(ST)+140.85 and optionally
K.sub.1C (S-L).ltoreq.-0.25 R.sub.p0.2(ST)+142.45, (iii) for
thicknesses of 121 to 150 mm, at mid thickness, yield stress
R.sub.p0.2(ST).ltoreq.420 MPa and optionally
R.sub.p0.2(ST).ltoreq.425 MPa and toughness K.sub.1C
(S-L).ltoreq.20 MPa m and advantageously such that K.sub.1C
(S-L).ltoreq.-0.25 R.sub.p0.2(ST)+133, optionally K.sub.1C
(S-L).ltoreq.-0.25 R.sub.p0.2(ST)+133 and optionally K.sub.1C
(S-L).ltoreq.-0.25 R.sub.p0.2(ST)+134,
12. Product according to claim 1 in a rolled and/or forged,
solution heat treated, quenched, stress relieved optionally by
stretching, and aged temper, for which the number of days before
failure tested according to ASTM standards G47 and G49 at
mid-thickness for a stress in the ST direction equal to 350 MPa is
at least 30 days and optionally, for plates between 40 and 75 mm
thick, the number of days before failure for a stress of 450 MPa in
the ST direction is at least 30 days.
13. Method of manufacturing a rolled and/or forged product based on
an aluminum alloy, in which a) a bath of liquid metal is created
based on an aluminum alloy according to claim 1; b) an unwrought
product is cast from said liquid metal bath; c) said unwrought
product is homogenized at a temperature of between 450.degree. C.
and 550.degree., and optionally between 480.degree. C. and
530.degree. C. for a duration of between 5 and 60 hours; d) said
unwrought product is hot and optionally cold worked optionally to a
thickness of at least 12 mm, optionally at least 15 mm, and
optionally at least 40 mm into a rolled and/or forged product; e)
said product is solution heat treated at between 490 and
530.degree. C. for 15 minutes to 8 h and is quenched; f) said
product is stress relieved, optionally by stretching, in a
controlled manner, with a permanent set of 1 to 7% and optionally
at least 4%; g) said product is aged including heating to a
temperature of between 130 and 170.degree. C., optionally between
140 and 160.degree. C., and optionally between 140 and 150.degree.
C., for 5 to 100 hours and optionally 10 to 50 h.
14. Method according to claim 13, in which the controlled
stretching is applied with a permanent set of between 5 and 7% and
the ageing time is between 10 and 30 hours.
15. Structural element of an aircraft, optionally the lower wing
skin or upper wing skin element in which the skin and the
stiffeners are made from the same initial product, a spar or a rib,
comprising a product according to claim 1.
Description
DOMAIN OF THE INVENTION
[0001] The invention relates to aluminum-copper-lithium alloy
products, and more particularly such products and methods of
manufacturing and use, intended particular for aeronautical and
aerospatial construction.
STATE OF PRIOR ART
[0002] Products, and particularly thick rolled and/or forged
products made of aluminum alloy, are developed to produce high
strength parts intended particularly for the aeronautical industry,
the aerospatial industry or mechanical construction, by cutting,
surfacing or machining from one block.
[0003] Aluminum alloys containing lithium are very attractive in
this respect because lithium can reduce the density of aluminum by
3% and increase the modulus of elasticity by 6% for each percent by
weight of lithium added. If these alloys are to be selected for use
in aircraft, their performance in service must be as good as that
of currently used alloys, particularly in terms of a balance
between static mechanical strength properties (yield stress,
ultimate strength) and damage tolerance properties (toughness,
resistance to propagation of fatigue cracks), these properties
generally being antinomic. For thick products, these products must
be obtained particularly at quarter-thickness and at mid-thickness
and therefore the products must have low sensitivity to quenching.
It is said that a product is sensitive to quenching if its static
mechanical properties such as its yield stress decrease as the
quenching rate decreases. The quenching rate is the average cooling
rate of the product during quenching.
[0004] These alloys must also have sufficient resistance to
corrosion, it must be possible to shape them using normal methods,
and they must have low residual stresses so that they can be
integrally machined.
[0005] Several Al--Cu--Li alloys are known in which silver is
added.
[0006] U.S. Pat. No. 5,032,359 describes a large family of
aluminum-copper-lithium alloys in which the addition of magnesium
and silver, particularly between 0.3 and 0.5 percent by weight, can
increase the mechanical strength.
[0007] U.S. Pat. No. 7,229,509 describes an alloy containing (% by
weight): (2.5-5.5) of Cu, (0.1-2.5) of Li, (0.2-1.0) of Mg,
(0.2-0.8) of Ag, (0.2-0.8) of Mn, 0.4 max of Zr or other grain
refining agents such as Cr, Ti, Hf, Sc, V, particularly with
toughness K.sub.1C(L)>37.4 MPa m for yield stress
R.sub.p0.2(L)>448.2 MPa (products thicker than 76.2 mm) and
particularly toughness K.sub.1C(L)>38.5 MPa m for yield stress
R.sub.p0.2(L)>489.5 MPa (products thinner than 76.2 mm).
[0008] The AA2050 alloy comprises (% by weight): (3.2-3.9) of Cu,
(0.7-1.3) of Li, (0.20-0.6) of Mg, (0.20-0.7) of Ag, 0.25max. of
Zn, (0.20-0.50) of Mn, (0.06-0.14) of Zr and the AA2095 alloy
comprises (3.7-4.3) of Cu, (0.7-1.5) of Li, (0.25-0.8) of Mg,
(0.25-0.6) of Ag, 0.25 max. of Zn, 0.25 max. of Mn, (0.04-0.18) of
Zr. AA2050 alloy products are known for their quality in terms of
static mechanical strength and toughness, particularly for thick
rolled products and are selected for some aircraft.
[0009] Patent application WO2009036953 describes an alloy with
composition as a % by weight equal to Cu 3.4 to 5.0, Li 0.9 to 1.7,
Mg 0.2 to 0.8, Ag 0.1 to 0.8, Mn 0.1 to 0.9, Zn up to 1.5, and one
or several elements chosen from the group composed of: (Zr about
0.05 to 0.3, Cr about 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 inevitable impurities, the remainder being aluminum.
[0010] Patent application US 2009/142222 A1 describes alloys
comprising (% 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.
[0011] Patent application WO2011130180 describes strain hardened
aluminum alloy products containing (in % by weight) from 2.75 to
5.0% of Cu, from 0.2 to 0.8% of Mg, in which the copper to
magnesium (Cu/Mg) ratio in the aluminum alloy is within the range
from about 6.1 to environ 17, from 0.1 to 1.10% of Li, from 0.3 to
2.0% of Ag, from 0.5 to 1.5% of zinc, up to 1.0% of Mn, the
remainder being `aluminum, optional accessory elements and
impurities.
[0012] Patent application WO2013169901 describes aluminum alloys
containing (in % by weight) from 3.5 to 4.4% of Cu, 0.45 to 0.75%
of Mg, from 0.45 to 0.75% of Zn, 0.65-1.15% of Li, 0.1 to 1.0% of
Ag, 0.05 to 0.50% of at least one grain structure control element,
up to 1.0% de Mn, up to 0.15% of Ti, up to 0.12% of Si, up to 0.15%
Fe, up to 0.10% of any other element, with the total of these
elements not exceeding 0.35%, the remainder being aluminum.
[0013] Al--Cu--Li alloys are also known in which the addition of
silver is optional or is not mentioned.
[0014] U.S. Pat. No. 5,455,003 describes a method of manufacturing
Al--Cu--Li alloys that have improved mechanical strength and
toughness at cryogenic temperatures, particularly due to
appropriate strain hardening and ageing. In particular, this patent
recommends the following composition as a 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.
[0015] U.S. Pat. No. 5,211,910 describes alloys that may comprise
(as a % by weight) from 1 to 7% of Cu, from 0.1 to 4% of Li, from
0.01 to 4% of Zn, from 0.05 to 3% of Mg, from 0.01 to 2% of Ag,
from 0.01 to 2% of a grain refiner chosen from among Zr, Cr, Mn,
Ti, Hf, V, Nb, B and TiB2, the remainder being Al with accidental
impurities.
[0016] U.S. Pat. No. 5,234,662 describes alloys with composition (%
by weight) equal to Cu=2.60-3.30, Mg=0.0-0.50, Li=1.30-1.65, Mg:
0.0-1.8, elements controlling the granular structure chosen from
among Zr and Cr=0.0-1.5.
[0017] One embodiment of U.S. Pat. No. 5,259,897 describes a method
of making aluminum-based alloys with compositions as a % by weight
within the following ranges: from 3.5 to 5.0 of Cu, from 0.8 to 1.8
of Li, from 0.25 to 1.0 of Mg, from 0.01 to 1.5 of a grain refiner
chosen from among Zr, Cr, Mn, Ti, Hf, V, Nb, B, TiB2 and mixtures
thereof, the remainder being essentially Al.
[0018] U.S. Pat. No. 7,438,772 describes alloys containing the
following (percent by weight), Cu=3-5, Mg=0.5-2, Li=0.01-0.9, and
discourages the use of higher lithium contents due to a degradation
in the balance between toughness and mechanical strength.
[0019] Patent application WO2009103899 describes a rolled
essentially unrecrystallized product containing the following % by
weight: 2.2 to 3.9% by weight of Cu, 0.7 to 2.1% by weight of Li;
0.2 to 0.8% by weight of Mg; 0.2 to 0.5% by weight of Mn; 0.04 to
0.18% by weight of Zr; less than 0.05% by weight of Zn, and
optionally 0.1 to 0.5% by weight of Ag, the remainder being
aluminum and inevitable impurities, with low propensity to crack
bifurcation during a fatigue test in the LS direction.
[0020] Patent application WO2010149873 relates to a strain hardened
product such as an extruded, rolled and/or forged product made of
an aluminum based alloy containing the following % by weight;
Cu=3.0-3.9; Li=0.8-1.3; Mg=0.6 to 1.0: Zr=0.05-0.18; Ag=0.0 to 0.5;
Mn=0.0 to 0.5; Fe+Si.gtoreq.0.20; Zn.gtoreq.0.15; at least one
element among Ti (from 0.01 to) 0.15; Sc (from 0.05 to 0.3); Cr
(from 0.05 to 0.3); Hf (from 0.05-0.5), other elements <0.05
each and <0.15 total, the remainder being aluminum,
[0021] Patent application WO2012112942 describes products at least
12.7 mm thick made of aluminum alloy containing (% by weight) from
3.00 to 3.80% of Cu, from 0.05 to 0.35% of Mg, from 0.975 to 1.385%
of Li, in which the Li content is between -0.3 Mg-0.15Cu+1.65 and
-0.3 Mg-0.15Cu+1.55, from 0.05 to 0.50% of at least one element to
control the granular structure chosen from the group composed of
Zr, Sc, Cr, V, Hf, other rare earth elements and combinations of
them up to 1.0% of Zn, up to 1.0% of Mn, up to 0.12% of Si, up to
0.15% of Fe, up to 0.15% of Ti, up to 0.10% of other elements, with
the total of these other elements not exceeding 0.35%, the
remainder being aluminum.
[0022] It is observed that products according to prior art made of
alloy essentially contain no silver making it impossible to obtain
properties as beneficial as those obtained with alloys containing
silver such as the AA2050 alloy. In particular, the advantageous
balance between the mechanical strength and toughness is not
reached for thick products, particularly for thicknesses of at
least 12 mm or at least 40 mm, while maintaining satisfactory
resistance to corrosion. The addition of silver, that is an element
infrequently used in aluminum alloys, could contaminate other
alloys during recycling and affect their properties because there
is an effect at low contents. Furthermore, the limitation of the
quantity of silver is economically very positive. Products with a
low sensitivity to quenching would also be particularly
advantageous.
[0023] There is a need for products made of an
aluminum-copper-lithium alloy, particularly thick products, with
better properties than known products that contain essentially no
silver, particularly in terms of the balance between static
mechanical strength properties, damage tolerance properties,
thermal stability, resistance to corrosion and machinability, while
having a low density.
PURPOSE OF THE INVENTION
[0024] A first purpose of the invention is a rolled and/or forged
aluminum-based alloy comprising the following % by weight,
[0025] Cu: 3.2-4.0;
[0026] Li: 0.80-0.95;
[0027] Zn: 0.45-0.70;
[0028] Mg: 0.15-0.70;
[0029] Zr: 0.07-0.15;
[0030] Mn: 0.1-0.6;
[0031] Ag %<0.15;
[0032] Fe+Si.gtoreq.0.20;
[0033] at least one element from among
[0034] Ti: 0.01-b 0.15;
[0035] Sc: 0.02-0.15, preferably 0.02-0.1;
[0036] Cr: 0.02-0.3, preferably 0.02-0.1;
[0037] Hf: 0.02-0.5;
[0038] V: 0.02-0.3, preferably 0.02-0.1;
[0039] other elements <0.05 each and <0.15 total, remainder
aluminum,
[0040] A second purpose of the invention is a method of
manufacturing a product according to the invention in which [0041]
a) a bath of liquid metal is created based on an aluminum alloy
according to the invention; [0042] b) an unwrought product is cast
from said liquid metal bath; [0043] c) said unwrought product is
homogenized at a temperature of between 450.degree. C. and
550.degree., and preferably between 480.degree. C. and 530.degree.
C. for a duration of between 5 and 60 hours; [0044] d) said
unwrought product is hot and optionally cold worked preferably to a
thickness of at least 12 mm, preferably at least 15 mm, and even
more preferably at least 40 mm into a rolled and/or forged product;
[0045] e) said product is solution heat treated at between 490 and
530.degree. C. for 15 minutes to 8 h and is quenched; [0046] f)
said product is stress relieved, preferably by stretching, in a
controlled manner, with a permanent set of 1 to 7% and preferably
at least 4%; [0047] g) said product is aged including heating to a
temperature of between 130 and 170.degree. C., preferably between
140 and 160.degree. C., and more preferably between 140 and
150.degree. C., for 5 to 100 hours and preferably 10 to 50 h.
[0048] Another purpose of the invention is a structural element of
an aircraft comprising a product according to the invention.
DESCRIPTION OF THE FIGURES
[0049] FIG. 1 represents the balance between the yield stress
R.sub.p0.2 in the LT direction and the toughness K.sub.1C in the
T-L direction for a thickness of 50 mm.
[0050] FIG. 2 represents the balance between the yield stress
R.sub.p0.2 in the ST direction and the toughness K.sub.1C in the
S-L direction for a thickness of 50 mm.
[0051] FIG. 3 represents the balance between the yield stress
R.sub.p0.2 in the LT direction and the toughness K.sub.1C in the
T-L direction for a thickness of 102 mm.
[0052] FIG. 4 represents the balance between the yield stress
R.sub.p0.2 in the ST direction and the toughness K.sub.1C in the
S-L direction for a thickness of 102 mm.
[0053] FIG. 5 represents the balance between the yield stress
R.sub.p0.2 in the ST direction and the toughness K.sub.1C in the
S-L direction for a thickness of 130 mm.
[0054] FIG. 6 represents the difference in toughness for quenching
conditions as a function of the difference in yield stress for
these two quenching conditions for the tests in example 2.
DESCRIPTION OF THE INVENTION
[0055] Unless mentioned otherwise, all indications about the
chemical composition of alloys are expressed as a percent by weight
based on the total weight of the alloy. The expression 1.4 Cu means
that the copper content expressed as a % by weight is multiplied by
1.4. Alloys are designated in accordance with the rules of the
Aluminum Association, known to an expert in the subject. The
definitions of metallurgical tempers are indicated in European
standard EN 515 (EN515: 1993).
[0056] Unless mentioned otherwise, static mechanical properties, in
other words the ultimate strength R.sub.m, the conventional yield
stress at 0.2% elongation R.sub.p0.2, and elongation at rupture A
%, are determined by a tensile test according to standard EN ISO
6892-1: 2009 (formerly EN 10002-1:2001), sampling and the direction
of the test being defined by standard EN 485-1 (EN
485-1:2008+A1:2009).
[0057] The stress intensity factor (K.sub.Q) is determined
according to standard ASTM E 399 (ASTM E 399-12e3). Standard ASTM E
399 (ASTM E 399-12e3) gives criteria to determine if K.sub.Q is a
valid value of K.sub.1C. For a given test piece geometry, the
values of K.sub.Q obtained for different materials are comparable
with each other provided that the yield stresses of the materials
are the same order of magnitude.
[0058] A curve giving the effective stress intensity factor as a
function of the effective crack extension, known as the R curve, is
determined according to ASTM standard E 561 (ASTM E 561-10e2). The
critical stress intensity factor K.sub.C, in other words the
intensity factor that makes the crack unstable, is calculated from
the R curve. The stress intensity factor K.sub.CO is also
calculated by assigning the initial crack length at the beginning
of the monotonous load, to the critical load. These two values are
calculated for a test piece with the required shape. K.sub.app
represents the factor K.sub.CO corresponding to the test piece that
was used to make the R curve test. K.sub.eff represents the factor
K.sub.C corresponding to the test piece that was used to make the R
curve test.
[0059] Stress corrosion studies were carried out according to
standards ASTM G47 and G49 (ASTM G47-98(2011) and G49-85(2011))
along the ST and LT directions for samples taken at
mid-thickness.
[0060] According to this invention, a selected class of aluminum
alloys containing specific and critical quantities of copper,
lithium, magnesium, zinc, manganese and zirconium but essentially
containing no silver can be used to prepare strain hardened
products with an improved balance between toughness and mechanical
strength, and good resistance to corrosion.
[0061] The inventors have observed that, surprisingly, for thick
products it is possible to obtain an at least equivalent balance
between static mechanical strength properties and damage tolerance
properties as that obtained with an aluminum-copper-lithium allow
containing silver, particularly such as the AA2050 alloy, by making
a narrow selection of quantities of lithium, copper, magnesium,
manganese, zinc and zirconium.
[0062] The copper content of products according to the invention is
between 3.2 and 4.0% by weight. In one advantageous embodiment of
the invention, the copper content is at least 3.3 or preferably at
least 3.4% by weight and/or at most 3.8 and preferably at most 3.7%
by weight.
[0063] The lithium content of products according to the invention
is between 0.80 and 0.95% by weight. The lithium content is
advantageously between 0.84 and 0.93% by weight. Preferably, the
lithium content is at least 0.86% by weight.
[0064] The silver content is less than 0.15% by weight, preferably
less than 0.10% by weight and more preferably less than 0.05% by
weight. The inventors have observed that the advantageous balance
between the mechanical strength and the damage tolerance known for
alloys typically containing 0.3 to 0.4% by weight of silver can be
obtained for alloys containing essentially no silver with the
selected composition.
[0065] The magnesium content of products according to the invention
is between 0.15 and 0.7%; and preferably between 0.2 and 0.6% by
weight. Advantageously, the magnesium content is at least 0.30% by
weight and preferably at least 0.34%, and more preferably at least
0.38% by weight. The inventors have observed that when the
magnesium content is less than 0.30% by weight, the advantageous
balance between mechanical strength and damage tolerance is not
obtained for the highest thicknesses, particularly for thicknesses
of more than 76 mm.
[0066] The inventors have observed that for the lowest contents of
magnesium, typically contents of less than 0.5% by weight,
preferably less than 0.45% by weight, the presence of a small
quantity of silver can be advantageous, preferably the magnesium
content is equal to at least (0.3-1.5*Ag). In one embodiment of the
invention, the magnesium content is at most (0.55-1.5*Ag).
[0067] In one embodiment of the invention, the magnesium content is
at most 0.45% by weight and preferably at most 0.43% by weight. In
one advantageous embodiment, the magnesium content is at most 0.45%
by weight and preferably at most 0.43% by weight and the Ag content
is less than 0.15% by weight, and preferably less than 0.10% by
weight.
[0068] The zinc content is between 0.45 and 0.70% by weight.
Advantageously, the zinc content is between 0.50 and 0.60% by
weight that can contribute to achieving the required balance
between toughness and mechanical strength.
[0069] The zirconium content is between 0.07 and 0.15%; and
preferably between 0.09 and 0.12% by weight.
[0070] The manganese content is between 0.1 and 0.6% by weight.
Advantageously, the manganese content is between 0.2 and 0.4% by
weight and can improve the toughness without comprising the
mechanical strength. If there is no added manganese, the required
balance is not achieved.
[0071] The sum of the iron content and the silicon content is not
more than 0.20% by weight. Preferably, the iron and silicon
contents are not more than 0.08% each by weight. In one
advantageous embodiment of the invention, the iron and silicon
contents are not more than 0.06% and 0.04% by weight
respectively.
[0072] The alloy also contains at least one element that can
contribute to controlling the grain size, chosen from among V, Cr,
Sc, Hf and Ti, the quantity of the element, if it is chosen, being
from 0.02 to 0.3% by weight, preferably from 0.02 to 0.1 by weight
for V, Cr; from 0.02 to 0.15% by weight, preferably from 0.02 to
0.1% by weight for Sc; from 0.02 to 0.5% by weight for Hf and from
0.01 to 0.15% by weight for Ti. Preferably, between 0.02 and 0.10%
by weight of titanium will be chosen.
[0073] The alloy according to the invention is intended
particularly for the manufacture of thick rolled and/or forged
products, and more particularly thick rolled products. For the
purposes of this invention, thick products means products that are
at least 12 mm and preferably at least 40 mm thick. In one
advantageous embodiment, the rolled and/or forged products
according to the invention are at least 76 mm thick or even at
least 121 mm thick.
[0074] The thick products according to the invention provide a
particularly advantageous balance between mechanical strength and
toughness.
[0075] When in a rolled and/or forged, solution heat treated,
quenched, stretched and aged temper, products according to the
invention have at least one of the following pairs of
characteristics for thicknesses of between 40 and 75 mm: [0076] (i)
at quarter thickness, yield stress R.sub.p0.2(LT).ltoreq.480 MPa
and preferably R.sub.p0.2(LT).ltoreq.490 MPa and toughness K.sub.1C
(T-L).ltoreq.31 MPa m and advantageously such that K.sub.1C
(T-L).ltoreq.-0.175 R.sub.p0.2(LT)+119.2, preferably K.sub.1C
(T-L).ltoreq.-0.175 R.sub.p0.2(LT)+120.5 and preferably K.sub.1C
(T-L).ltoreq.-0.175 R.sub.p0.2(LT)+121.5, [0077] (ii) at mid
thickness, yield stress R.sub.p0.2(ST).ltoreq.450 MPa and
preferably R.sub.p0.2(ST).ltoreq.455 MPa and toughness K.sub.1C
(S-L).ltoreq.24 MPa m and advantageously such that K.sub.1C
(S-L).ltoreq.-0.34 R.sub.p0.2(ST)+185.6, preferably K.sub.1C
(S-L).ltoreq.-0.34 R.sub.p0.2(ST)+187.2 and preferably K.sub.1C
(S-L).ltoreq.-0.34 R.sub.p0.2(ST)+188.7,
[0078] Products according to the invention in which the magnesium
content is at least 0.34% by weight and preferably at least 0.38%
by weight and the silver content is less than 0.10% by weight, and
preferably less than 0.05% by weight, are advantageous and when in
a rolled and/or forged, solution heat treated, quenched, stress
relieved preferably by stretching, and aged temper, have at least
one of the following pairs of characteristics for thicknesses of
between 76 and 150 mm: [0079] (i) for thicknesses of 76 to 120 mm,
at quarter thickness, yield stress R.sub.p0.2(LT).ltoreq.460 MPa
and preferably R.sub.p0.2(LT).ltoreq.470 MPa and advantageously a
toughness K.sub.1C (T-L).ltoreq.27 MPa m and such that K.sub.1C
(T-L).ltoreq.-0.1 R.sub.p0.2(LT)+77, preferably K.sub.1C
(T-L).ltoreq.-0.1 R.sub.p0.2(LT)+78 and preferably K.sub.1C
(T-L).ltoreq.-0.1 R.sub.p0.2(LT)+79, [0080] (ii) for thicknesses of
76 to 120 mm, at mid thickness, yield stress
R.sub.p0.2(ST).ltoreq.435 MPa and preferably
R.sub.p0.2(ST).ltoreq.445 MPa and toughness K.sub.1C
(S-L).ltoreq.23 MPa m and advantageously such that K.sub.1C
(S-L).ltoreq.-0.25 R.sub.p0.2(ST)+139.25, preferably K.sub.1C
(S-L).ltoreq.-0.25 R.sub.p0.2(ST)+140.85 and preferably K.sub.1C
(S-L).ltoreq.-0.25 R.sub.p0.2(ST)+142.45, [0081] (iii) for
thicknesses of 121 to 150 mm, at mid thickness, yield stress
R.sub.p0.2(ST).ltoreq.420 MPa and preferably
R.sub.p0.2(ST).ltoreq.425 MPa and toughness K.sub.1C
(S-L).ltoreq.20 MPa m and advantageously such that K.sub.1C
(S-L).ltoreq.-0.25 R.sub.p0.2(ST)+133, preferably K.sub.1C
(S-L).ltoreq.-0.25 R.sub.p0.2(ST)+133.5 and preferably K.sub.1C
(S-L).ltoreq.-0.25 R.sub.p0.2(ST)+134,
[0082] Products according to the invention also have advantageous
properties in terms of toughness as measured according to standard
ASTM E561 (ASTM E 561-10e2). Thus, when in a rolled and/or forged,
solution heat treated, quenched, stress relieved preferably by
stretching, and aged temper, products according to the invention
have at least one of the following pairs of characteristics for
thicknesses of between 40 and 150 mm, the toughness in plane stress
K.sub.app being measured on test pieces type CCT406 (2ao=101.6 mm)
[0083] (i) for thicknesses of between 40 and 75 mm K.sub.app, in
the L-T direction of at least 105 MPa m and preferably at least 110
MPa m and a yield stress R.sub.p0.2(L) equal to at least 500 MPa
and preferably at least 510 MPa, [0084] (ii) for thicknesses of
between 40 and 75 mm K.sub.app, in the T-L direction of at least 60
MPa m and preferably at least 70 MPa m and a yield stress
R.sub.p0.2(LT) equal to at least 480 MPa and preferably at least
490 MPa, [0085] (iii) for thicknesses of between 76 and 120 mm
K.sub.app, in the L-T direction at least 80 MPa m and preferably at
least 90 MPa m and a yield stress R.sub.p0.2(L) equal to at least
475 MPa and preferably at least 485 MPa, [0086] (iv) for
thicknesses of between 76 and 120 mm K.sub.app, in the T-L
direction of at least 40 MPa m and preferably at least 50 MPa m and
a yield stress R.sub.p0.2(LT) equal to at least 455 MPa and
preferably at least 465 MPa, [0087] (v) for thicknesses of between
121 and 150 mm K.sub.app, in the L-T direction of at least 75 MPa m
and preferably at least 80 MPa m and a yield stress R.sub.p0.2(L)
equal to at least 470 MPa and preferably at least 480 MPa, [0088]
(vi) for thicknesses of between 121 and 150 mm K.sub.app, in the
T-L direction of at least 40 MPa m and preferably at least 45 MPa m
and a yield stress R.sub.p0.2(LT) equal to at least 445 MPa and
preferably at least 455 MPa.
[0089] The resistance of products according to the invention to
stress corrosion is generally high; advantageously, the number of
days before failure tested according to ASTM standards G47 and G49
(ASTM G47-98(2011) and G49-85(2011)) at mid-thickness for a stress
in the ST direction equal to 350 MPa is at least 30 days and
preferably, particularly for plates between 40 and 75 mm thick, the
number of days before failure for a stress of 450 MPa in the ST
direction is at least 30 days.
[0090] The method of manufacturing products according to the
invention includes steps for production, casting, rolling and/or
forging, solution heat treatment, quenching, stress relieving and
ageing.
[0091] In a first step, a liquid metal bath is produced so as to
obtain an aluminum alloy with a composition according to the
invention.
[0092] The liquid metal bath is then poured as an unwrought
product, typically a rolling slab or as forging stock.
[0093] The unwrought product is then homogenized at a temperature
of between about 450.degree. C. and 550.degree., and preferably
between about 480.degree. C. and 530.degree. C. for a duration of
between 5 and 60 hours;
[0094] After homogenization, the unwrought product is generally
cooled to ambient temperature before being preheated to be hot
worked. The purpose of preheating is to reach a temperature
preferably between 400 and 550.degree. C. and preferably of the
order of 500.degree. C. so that the unwrought product can be
worked.
[0095] Hot working is achieved by rolling and/or forging so as to
obtain a rolled and/or forged product preferably with a thickness
of at least 12 mm and preferably at least 40 mm. The product is
then solution heat treated at between 490 and 550.degree. C. for 15
minutes to 8 hours, then quenched typically in water at ambient
temperature. The product is then subjected to controlled stress
relieving, preferably by tension and/or by compression, with a
permanent set of 1 to 7% and preferably at least 2%. The rolled
products are preferably subjected to controlled stretching with a
permanent set equal to at least 4%. In one advantageous embodiment
of the invention that in particular can improve the balance between
static mechanical strength and toughness, the controlled stretching
is done with a permanent set of between 5 and 7%. The preferred
metallurgical tempers are the T84 and T86 tempers, and preferably
T86. Steps such as rolling, planing, straightening, shaping can be
done optionally after solution heat treatment and before or after
controlled stretching. In one embodiment of the invention, a cold
rolling step is done to at least 7% and preferably at least 9%
before applying controlled stretching with a permanent set of from
1 to 3%.
[0096] Said product is aged including heating to a temperature of
between 130 and 170.degree. C., preferably between 140 and
160.degree. C., and more preferably between 140 and 150.degree. C.,
for 5 to 100 hours and preferably 10 to 50h. The inventors have
observed that the balance between mechanical strength and toughness
can be improved by ageing within the preferred range. In one
advantageous embodiment, controlled stretching is applied with a
permanent set of between 5 and 7% and ageing is done at a
temperature of between 140 and 160.degree. C., preferably between
140 and 150.degree. C., for a duration of 10 to 30 h.
[0097] Products according to the invention can advantageously be
used in structural elements, and particularly in aircraft. For the
purposes of this description, a "structure element" or "structural
element" in mechanical construction means a mechanical part for
which the static and/or dynamic properties are particularly
important for performance of the structure, and for which a
structural calculation is normally specified or is performed. These
are typically elements that, if they fail, could jeopardize the
safety of said construction, its users or others. For the purposes
of this invention, these aircraft structural elements include
particularly bulkheads, wings (such as the wing skin), ribs and
spars and the tail plane composed particularly of horizontal or
vertical stabilizer, and doors.
[0098] The use of a structure element incorporating at least one
product according to the invention or fabricated from such a
product is advantageous, particularly for aeronautical
construction. Products according to the invention are particularly
advantageous for manufacturing products machined from one block,
particularly for lower wing skin or upper wing skin elements for
which the skin and stiffeners originate from the same initial
product, spars and ribs, and also for any other use for which these
properties could be advantageous.
[0099] These and other aspects of the invention are explained in
more detail by means of the following illustrative and
non-limitative examples.
EXAMPLES
Example 1
[0100] In this example, several 400 mm thick slabs with the
composition given in table 1 were cast.
TABLE-US-00001 TABLE 1 Composition as a % by weight of Al--Cu--Li
alloys cast in the form of a slab. Cu Mn Mg Zn Li Ag Zr Fe Si Ti 54
3.61 0.34 0.17 0.56 0.93 0.13 0.10 0.023 0.015 0.022 55 3.60 0.52
0.17 0.54 0.94 0.13 0.10 0.023 0.015 0.021 56 3.60 0.34 0.43 0.57
0.93 0.00 0.10 0.021 0.015 0.022 57 3.62 0.55 0.34 0.56 0.95 0.00
0.10 0.017 0.015 0.023 71 3.62 0.36 0.43 0.56 0.90 0.01 0.10 0.040
0.024 0.031 72 3.55 0.00 0.51 0.56 0.90 0.00 0.10 0.035 0.023
0.029
[0101] The slabs were homogenized at about 500.degree. C. for about
12 hours and then scalped. The slabs were then hot rolled to obtain
50 mm, 102 mm or 130 mm thick slabs. The plates were solution heat
treated at 527.degree. C. and quenched with cold water. The plates
were then stretched to give a permanent elongation of 4% or 6%.
[0102] The plates were aged at 145.degree. C. or at 150.degree. C.
Samples were taken at 1/4-thickness to measure the static
mechanical properties in tension and in toughness in the L, LT, L-T
and T-L directions at 1/2-thickness to measure the static
mechanical properties in tension and in toughness in the ST and S-L
directions. The test pieces used for measuring the toughness were
test pieces with CT geometry and their dimensions were as defined
below:
TABLE-US-00002 Thick- ness L-T T-L S-L 50 mm Thickness B =
Thickness B = Thickness B = 20 mm 20 mm 15 mm Width W = 40 mm Width
W = 40 mm Width W = 30 mm 102 mm Thickness B = Thickness B =
Thickness B = 40 mm 40 mm 30 mm Width W = 80 mm Width W = 80 mm
Width W = 60 mm 130 mm Thickness B = Thickness B = Thickness B = 40
mm 40 mm 30 mm Width W = 80 mm Width W = 80 mm Width W = 60 mm
[0103] The results are given in table 2 and table 3.
TABLE-US-00003 TABLE 2 Static mechanical properties obtained for
different plates. Permanent set Final (controlled RmL Rp02L RmLT
Rp02LT a RmST Rp02ST Alloy thickness stretching) Aged (MPa) (MPa) A
% L (MPa) (MPa) % LT (MPa) (MPa) A % L 54 50 mm 4% 145.degree. C.
53 h 542 495 9.3 540 464 6.7 54 50 mm 4% 150.degree. C. 40 h 548
516 11.1 545 499 9.6 543 473 5.8 54 102 mm 4% 150.degree. C. 40 h
535 500 9.5 541 489 4.9 510 460 1.2 55 50 mm 4% 150.degree. C. 40 h
546 512 10.2 536 490 9.0 528 464 5.5 55 102 mm 4% 145.degree. C. 53
h 517 467 7.3 503 439 4.2 56 50 mm 4% 145.degree. C. 53 h 540 491
10.0 540 463 5.3 56 50 mm 6% 150.degree. C. 22 h 527 481 11.6 533
453 7.0 56 50 mm 6% 150.degree. C. 30 h 538 493 10.2 536 461 5.2 56
50 mm 6% 150.degree. C. 40 h 542 499 9.6 544 467 6.2 56 50 mm 4%
150.degree. C. 40 h 551 522 10.3 543 494 9.1 549 468 6.2 56 102 mm
4% 145.degree. C. 53 h 523 469 7.4 520 442 4.8 56 102 mm 4%
150.degree. C. 40 h 532 500 9.7 534 477 5.9 524 452 3.6 57 102 mm
4% 145.degree. C. 53 h 518 466 7.7 509 440 4.2 57 102 mm 6%
150.degree. C. 30 h 521 473 8.1 509 449 3.8 57 102 mm 6%
150.degree. C. 40 h 527 479 6.7 516 453 3.8 71 130 mm 6%
150.degree. C. 20 h 509 454 7.7 495 427 4.3 71 130 mm 6%
150.degree. C. 30 h 519 465 6.4 506 437 3.9 71 130 mm 6%
150.degree. C. 40 h 527 476 5.4 515 447 3.6 71 130 mm 6%
150.degree. C. 50 h 527 478 5.5 516 451 3.1 72 102 mm 6%
150.degree. C. 30 h 526 475 3.7 501 449 1.7
TABLE-US-00004 TABLE 3 Toughness properties K1C obtained for the
different plates. Permanent K1C (*:Kq) set L-T K1C (*:Kq) Final
(controlled (MPa K1C T-L S-L Alloy thickness stretching) Aged m)
(MPa m) (MPa m) 54 50 mm 4% 145.degree. C. 53 h 33.0 31.1 54 50 mm
4% 150.degree. C. 40 h 36.2* 32.8 31.0 54 102 mm 4% 150.degree. C.
40 h 30.3* 25.9 24.9* 55 50 mm 4% 150.degree. C. 40 h 39.9 33.6
28.8 55 102 mm 4% 145.degree. C. 53 h 30.7 30.3 56 50 mm 4%
145.degree. C. 53 h 34.6 29.6* 56 50 mm 6% 150.degree. C. 22 h 38.0
33.2* 56 50 mm 6% 150.degree. C. 30 h 35.7 32.6* 56 50 mm 6%
150.degree. C. 40 h 33.8 30.6 56 50 mm 4% 150.degree. C. 40 h 39.6
34.4 29.0 56 102 mm 4% 145.degree. C. 53 h 31.6 30.2 56 102 mm 4%
150.degree. C. 40 h 34.0* 29.8 27.3 57 102 mm 4% 145.degree. C. 53
h 31.5 30.3 57 102 mm 6% 150.degree. C. 30 h 31.8 31.7 57 102 mm 6%
150.degree. C. 40 h 30.7 29.5 71 130 mm 6% 150.degree. C. 20 h 29.4
27.7 71 130 mm 6% 150.degree. C. 30 h 26.3 25.1 71 130 mm 6%
150.degree. C. 40 h 24.5 21.4* 71 130 mm 6% 150.degree. C. 50 h
23.9 22.1 72 102 mm 6% 150.degree. C. 30 h 24.2 21.7
[0104] The results are illustrated in FIGS. 1 to 2 (thickness 50
mm) and 3 and 4 (thickness 102 mm) and 5 (thickness 130 mm).
[0105] The stress corrosion results obtained are presented in Table
4 below.
TABLE-US-00005 TABLE 4 Results of stress corrosion tests Number of
Permanent set days (controlled Ageing Ageing Stress level without
Thickness stretching) temperature duration (MPa) Direction failure
54 50 mm 4% 150.degree. C. 40 450 ST and LT 30 54 102 mm 4%
150.degree. C. 40 350 ST 30 55 50 mm 4% 150.degree. C. 40 450 ST
and LT 30 55 102 mm 4% 150.degree. C. 40 350 ST 30 56 50 mm 4%
150.degree. C. 40 450 ST and LT 30 56 102 mm 4% 150.degree. C. 40
350 ST 30 57 102 mm 4% 150.degree. C. 40 350 ST 30
Example 2
[0106] In this example, several 120 mm thick slabs with the
composition given in table 5 were cast.
TABLE-US-00006 TABLE 5 Composition as a % by weight of Al--Cu--Li
cast in the form of a slab. Alloy Cu Mn Mg Zn Li Ag Zr Fe Si Ti 58
3.68 0.33 0.30 0.68 0.81 0.00 0.10 0.021 0.015 0.025 59 3.64 0.35
0.32 0.00 0.85 0.12 0.10 0.023 0.015 0.025 61 3.64 0.34 0.51 0.66
0.84 0.00 0.10 0.020 0.015 0.025 62 3.67 0.35 0.33 0.70 0.86 0.14
0.10 0.020 0.015 0.025
[0107] The slabs were machined to a thickness of 100 mm. The slabs
were homogenized at about 500.degree. C. for about 12 hours and
then scalped. After homogenization, the slabs were hot rolled to
obtain 27 mm thick slabs. The plates were solution heat treated and
quenched in cold water or in hot water at 90.degree. C. so as to
vary the quenching rate and stretched with a permanent set of
3.5%.
[0108] The plates were aged at between 15 h and 50 h at 155
.degree. C. Samples were taken at mid-thickness to measure static
mechanical properties in tension and the toughness K.sub.Q. The
width W of the test pieces used to measure the toughness in the T-L
direction was 50 mm and their width B was 25 mm. The validity
criteria of K.sub.1C were satisfied for all samples. For the S-L
direction, the measurements were made on test pieces with width
W=36 mm and thickness B=25.4 mm. The results obtained are given in
tables 6 and 7.
TABLE-US-00007 TABLE 6 Mechanical properties obtained for the
different plates after quenching in water at 90.degree. C. Ageing
RmLT Rp02LT K1C T-L Kq S-L duration (MPa) (MPa) A % L (MPa m) (MPa
m) 58 15 495 441 10.3 28.4 30.3 18 506 455 9.6 26.3 26.2 24 514 466
8.8 24.7 26.6 50 521 476 8.5 23.5 23.7 59 15 485 427 11.1 28.5 28.5
18 496 443 7.6 26.2 26.0 24 505 453 10.3 25.2 25.3 50 510 463 9.2
23.6 24.1 61 15 496 435 8.5 30.9 37.0 18 512 453 7.1 29.8 27.5 24
521 466 7.6 27.7 25.6 50 530 480 5.9 23.4 24.7 62 15 517 462 10.1
25.4 26.3 18 524 470 9.1 24.3 23.6 24 528 475 8.4 23.6 23.7 50 532
483 6.4 21.4 23.0
TABLE-US-00008 TABLE 7 Mechanical properties obtained for the
different plates after quenching in water at 25.degree. C. Ageing
RmLT Rp02LT K1C T-L Kq S-L duration (MPa) (MPa) A % L (MPa m) (MPa
m) 58 15 503 455 10.7 48.0 60.9 18 512 465 10.7 46.9 62.1 24 520
474 10.7 43.8 55.2 50 530 488 8.9 38.9 51.1 59 15 507 458 11.7 45.4
53.1 18 516 471 11.5 42.1 52.0 24 522 478 11.4 41.4 49.1 50 531 491
10.0 38.1 44.9 61 15 505 450 10.2 46.1 59.2 18 522 474 7.3 40.9
54.2 24 535 487 8.0 40.6 52.2 50 546 501 7.1 34.7 44.5 62 15 530
481 12.4 45.7 53.4 18 539 493 11.0 41.3 51.9 24 545 499 10.0 39.6
50.4 50 551 508 9.9 35.7 47.5
[0109] FIG. 6 shows the reduction in properties (mechanical
strength, toughness) for quenching in water at 90.degree. C. as a
percentage relative to the value with quenching in water at
25.degree. C. Composition 61 is the least sensitive to quenching
for toughness, and composition 58 is the least sensitive to
quenching for the yield stress.
Example 3
[0110] In this example, we studied the effect of controlled
stretching and ageing on toughness results K.sub.app and K.sub.eff
measured by an R curve.
[0111] 50 mm and 102 mm thick plates were obtained with alloys 56
and 71 in table 1. The plates were solution heat treated at
527.degree. C. and were quenched in cold water. Plates made of
alloy 56 were then stretched to a permanent elongation of 4% and
plates made of alloy 71 were stretched to a permanent elongation of
6%.
[0112] Plates made of alloy 56 were then aged for 40 hours at
150.degree. C. and plates made of alloy 71 were aged for 20 hours
at 150.degree. C.
[0113] Samples were taken at 1/2 thickness for 50 mm thick plates
and at 1/4-thickness for 102 mm and 130 mm thick plates, to measure
mechanical static tension and toughness characteristics in plain
stress K.sub.app and K.sub.eff in the L, LT, L-T and T-L
directions. For toughness, the R curve was measured on CCT test
pieces with width W=406 mm and thickness B=6.35 mm.
[0114] The results are summarized in Table 8 below:
TABLE-US-00009 TABLE 8 measured mechanical properties Rp0.2
Thickness Aged Rp0.2 LT Kapp L-T Keff L-T Kapp T-L Keff T-L (mm)
tension Alloy L MPa MPa [MPa m] [MPa m] [MPa m] [MPa m] 50 4% 40 h
56 522 494 110 138 61 69 50 6% 20 h 71 510 487 114 146 74 81 102 4%
40 h 56 500 477 83 95 46 52 102 6% 20 h 71 490 467 99 121 51 61 130
6% 20 h 71 483 460 86 100 47 53
[0115] The combination of controlled stretching with a permanent
set of 6% and 20 hours at 150.degree. C. is particularly
advantageous.
* * * * *