Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
HIGH STRENGTH AND HIGH FRACTURE TOUGHNESS 7XXX
AEROSPACE ALLOY PRODUCTS
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit, under 35 U.S.C. 119(e), of U.S.
Provisional Patent
Application No. 63/112,294 filed November 11, 2020, the contents of which are
incorporated
herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] The present invention relates to high strength 7xxx aluminum alloy
products. The high
strength 7xxx aluminum alloy can be fabricated to produce plate, extrusion or
forging products
suitable for aerospace structural components, especially large commercial
airplane wing structure
applications requiring better strength, fracture toughness, fatigue crack
deviation resistance,
anisotropic ductility, damage tolerance performance, and corrosion resistance
performance.
2. Description of Related Art
[0003] The higher strength 7xxx aluminum alloys are being pursued assertively
by airframe
manufacturers and aluminum material manufacturers in order to aggressively
reduce aircraft
weight for fuel efficiency due to their extensive combination of material
strength, ductility, fracture
toughness, fatigue resistance, and corrosion resistance.
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[0004] The combination of such complicated, comprehensive, and strict material
performance
demands from the aerospace applications necessitates a very finely optimized,
and a very narrow
chemistry range, to meet such requirements for commercial aircraft.
[0005] Obviously the strength, fracture toughness, and corrosion resistance
performances are the
most critical material properties, which are significantly affected by
chemical composition. In
7xxx aluminum alloys, zinc is the major alloying element for achieving high
strength through age
strengthening. Zinc in the most commonly used 7050 and 7075 aerospace aluminum
alloys is in
the range of 5.1 to 6.7 wt.%. Magnesium is normally added along with zinc to
produce MgZn2
and its variant phases, which are the predominant precipitation hardening
phases. Aluminum alloys
having higher Zn and Mg content usually have higher strength. However, higher
Zn and Mg
content also negatively affect stress corrosion cracking (SCC) resistance and
fracture toughness
performance. In 7xxx aluminum alloys, copper is added in order to improve SCC
resistance
performance. Meanwhile, the addition of Cu also improves material strength.
Most of the Cu is
believed to substitute Zn in the metastable MgZn2 phases. In general, Cu has
approximately an
equivalent effect on strength as the same weight percent of Zn addition.
[0006] In order to achieve aging precipitation strengthening, all added
elements have to be in solid
solution before aging. This is generally achieved through the processing steps
of solution heat
treatment (SHT), followed by rapid quenching. With the higher Mg, Zn and Cu
levels, it is
extremely difficult to dissolve all constituent particles, which consume a
significant amount of
added elements, into solid solution. Therefore, it is an extreme challenge to
simultaneously achieve
high strength, high fracture toughness, and desirable corrosion resistance for
7xxx aluminum
alloys.
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[0007] The additional new challenge for increased aircraft component
utilization is the fatigue
crack branching or deviation property. This is a phenomenon in which a crack
suddenly changes
its propagation direction away from the expected fracture plane under Mode I
fatigue loading
condition. Such crack deviation is an increasing concern for aircraft
manufacturers since it is
difficult to take into account during structural design.
[0008] In addition to the fatigue crack deviation performance, the anisotropic
ductility of
aluminum alloy thick plate is another increasingly critical characteristic for
aerospace application,
especially for monolithic part machining technology recently used in airframe
manufacturing. The
anisotropic ductility refers to significant ductility changes when the tensile
testing orientation is
in-between the commonly tested orientations, that are usually either parallel
to or perpendicular to
the material metal flow or microstructural direction, commonly notated as
rolling direction (L).
The ductility is usually significantly lower when tensile direction differs
from the standard
orientations that are determined by metal flow direction.
[0009] Another increasingly challenging aspect for aerospace applications is
the Environmentally
Assisted Cracking (EAC) property. This material property is believed to
evaluate the alloy's
resistance to hydrogen embrittlement, which can result in loss of strength and
ductility due to a
corrosion-like phenomenon. The testing is conducted under abnormally high
humidity and
temperature, in combination with high applied stresses. EAC property is also
believed to be very
sensitive to chemical composition.
[0010] In summary, the combination of the complicated age hardening behavior,
as well as strict
and comprehensive material performance necessitates a very narrow chemistry
range. Aerospace
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µ
applications have a strong need for such high performance alloys to attain
ever increasing fuel
efficiency targets.
BRIEF SUMMARY OF THE INVENTION
[0011] The high strength, fracture toughness, fatigue crack deviation
resistance, and anisotropic
ductility 7xxx aluminum alloy products such as plates, forgings and
extrusions, suitable for use in
making aerospace structural components like large commercial airplane wing
components,
comprises 6.5 to 7.2 wt. % Zn, 1.55 to 1.95 wt. % Cu, 1.75 to 2.15 wt. % Mg,
0.095 to 0.15 wt. %
Zr, up to 0.15 wt. % incidental elements, with the total of these incidental
elements not exceeding
0.35 wt. %, and the balance Al. In one embodiment, the aluminum alloy further
comprises Mg/Cu
and Zn/Mg ratios are in the range of 1.05 to 1.35, and 3.2 to 4.0
respectively.
[0012] It has been discovered that an aluminum alloy having an optimized
chemistry range,
associated with precise Zn, Mg and Cu content as well as Mg/Cu and Zn/Mg
ratios is capable of
producing plate products with high strength, desirable fracture toughness,
fatigue crack deviation
resistance, higher anisotropic ductility, damage tolerance, and corrosion
resistance properties, in a
combination that has never been achieved before.
[0013] A high strength 7xxx thick plate aluminum alloy product offers a
promising opportunity
for significant fuel efficiency and cost reduction advantage for commercial
airplanes. An example
of such an application for the present invention is the integral design wing
box, which requires
thick cross section 7xxx aluminum alloy products. Material strength is a key
design factor for
weight reduction. Also important are ductility, damage tolerance, stress
corrosion resistance, and
fatigue crack growth resistance.
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BRIEF DESCRIPTION OF DRAWINGS
[0014] The features and advantages of the present invention will become
apparent from the
following detailed description of a preferred embodiment thereof, taken in
conjunction with the
accompanying drawings, in which:
[0015] FIG. 1 is a graph showing the Cu and Mg chemical compositions of the
invention alloy
used to make the present 7xxx aluminum alloy products;
[0016] FIG. 2 is a graph showing the Mg and Zn chemical compositions of the
invention alloy
used to make the present 7xxx aluminum alloy products;
[0017] FIG. 3 is a graph showing the Cu and Mg chemical composition of
invention alloy used
to make the present 7xxx aluminum alloy products compared to non-invention
alloys;
[0018] FIG. 4 is a graph showing the Mg and Zn chemical composition of
invention alloys used
to make the present 7xxx aluminum alloy products compared to non-invention
alloys;
[0019] FIG. 5 is a graph showing the strength of the present 7xxx aluminum
alloy products using
the invention alloy compared to non-invention alloy plates;
[0020] FIG. 6 is a graph showing a combination of strength and fracture
toughness of the present
7xxx aluminum alloy products using the invention alloy compared to non-
invention alloys for 3
inch thick plates;
[0021] FIG. 7 shows the fracture toughness sample orientations relative to the
plate geometry;
[0022] FIG. 8 shows the overall coupon configuration; B=6.35mm; W=76.2mm;
H=46mm;
W1=95mm;
[0023] FIG. 9 is a graph showing the Kmax-dev vs. strength of the present 7xxx
aluminum alloy
products using the invention alloy compared to non-invention alloy for 4 inch
thick plates; and
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[0024] FIG. 10 is a graph showing a combination of orthotropic strength and
ductility of the
present 7xxx aluminum alloy products using the invention alloy compared to non-
invention
alloys.
DETAILED DESCRIPTION OF THE INVENTION
[0025] A high strength 7xxx aluminum alloy product is produced using a precise
chemistry range.
The high strength, fracture toughness, better fatigue crack deviation and
anisotropic ductility 7xxx
aluminum alloy product comprises, consists of, or consists essentially of, 6.5
to 7.2 wt. % Zn, 1.55
to 1.95 wt. % Cu, 1.75 to 2.15 wt. % Mg, 0.095 to 0.15 wt. % Zr, up to 0.15
wt. % incidental
elements, with the total of these incidental elements not exceeding 0.35 wt.
%, and the balance Al.
In one embodiment, the aluminum alloy further comprises Mg/Cu and Zn/Mg ratios
in the range
of 1.05 to 1.35, and 3.2 to 4.0 respectively. The 7xxx aluminum alloy product
provides high
strength, high damage tolerance performance, better corrosion resistance as
well as desirable
fatigue crack deviation resistance, and better anisotropic ductility suitable
for aerospace
applications. FIG.1 and FIG. 2 show graphs of the chemical composition range
for the key Cu, Mg
and Zn elements used to make the 7xxx aluminum alloy product according to the
present invention.
[0026] The present invention includes alternate embodiments wherein the upper
or lower limit
for the amount of Zn in the aluminum alloy product may be selected from 6.5,
6.6, 6.7, 6.8, 6.9,
7.0, 7.1, and 7.2 wt.%. In addition to the alternate upper and lower limits
listed above for Zn, the
present invention includes alternate embodiments wherein the upper or lower
limit for the
amount of Cu may be selected from 1.55, 1.60, 1.65, 1.70, 1.75, 1.80, 1.85,
1.90, and 1.95 wt.%.
In addition to the alternate upper and lower limits listed above for Zn and
Cu, the present
invention includes alternate embodiments wherein the upper or lower limit for
the amount of Mg
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may be selected from 1.75, 1.80, 1.85, 1.90, 1.95, 2.00, 2.05, 2.10, and 2.15
wt.%. In addition to
the alternate upper and lower limits listed above for Zn, Cu, and Mg the
present invention
includes alternate embodiments wherein the upper or lower limit for the amount
of Zr may be
selected from 0.095, 0.10, 0.11, 0.12, 0.13, 0.14, and 0.15 wt.%. In addition
to the alternate
upper and lower limits listed above for Zn, Cu, Mg, and Zr, the present
invention includes
alternate embodiments wherein the upper or lower limit for the ratio of Mg/Cu
may be selected
from 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, and 1.35. In addition to the
alternate upper and lower
limits listed above for Zn, Cu, Mg, Zr and Mg/Cu ratio, the present invention
includes alternate
embodiments wherein the upper or lower limit for the ratio of Zn/Mg may be
selected from 3.2,
3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, and 4Ø In addition to the alternate upper
and lower limits listed
above, the present invention includes alternate embodiments wherein the upper
limit for the
incidental elements is 0.15, 0.12, 0.10, 0.08, 0.05, 0.02, and 0.10 wt.%. In
addition to the
alternate upper and lower limits listed above, the present invention includes
alternate
embodiments wherein the upper limit for the total incidental elements is 0.35,
0.30, 0.25, 0.20,
0.15, 0.12, 0.10, 0.08, 0.05, 0.02, and 0.10 wt.%.
[0027] In one embodiment, the aluminum alloy product is a thick plate
including <0.12 wt.% Si,
preferably <0.05 wt.% Si. In one embodiment, the aluminum alloy product is a
thick plate
including <0.15 wt.% Fe, preferably <0.10 wt.% Fe. In one embodiment, the
aluminum alloy
product is a thick plate including Zr in the range from 0.095 to 0.15 wt%. In
one embodiment, the
aluminum alloy product is a thick plate including <0.04 wt.% Cr, preferably no
Cr is added to the
alloy other than that provided as an impurity. In one embodiment, the aluminum
alloy product is
a thick plate including 0.005 - 0.10 wt.% Ti.
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[0028] The aluminum alloy product of the present invention may also include
low levels of
"incidental elements" that are not included intentionally. The "incidental
elements" means any
other elements except those described above (Al, Zn, Cu, Mg, Zr, Si, Fe, Cr,
and Ti).
[0029] In a preferred embodiment, the aluminum alloy product of the present
invention is a thick
plate have a thickness of 1-10 inches. Alternatively, such thick plate
products may have
thicknesses of 1-3 inches, or 1-5 inches, or 3-5 inches, or 5-10 inches, or 5-
8 inches, or 8-10 inches.
[0030] The ingots of the high strength aluminum alloy product may be cast,
homogenized, hot
rolled, solution heat treated, cold water quenched, optionally stretched, and
aged to desired temper.
A thick plate high strength aluminum alloy is a plate product provided in a
T7651 or T7451 temper
and in the thickness range of 1 inch to 10 inch. The ingots may be homogenized
at temperatures
from 454 to 491 C (849 to 916 F). The hot rolling start temperature may be
from 385 to 450 C
(725 to 842 F). The exit temperature may be in a similar range as the start
temperature. The plates
may be solution heat treated at a temperature range of 454 to 491 C (849 to
916 F). The plates are
cold water quenched to room temperature and may be stretched by about 1.5 to
3%. The quenched
plate may be subjecting to any aging practices known by those of skill in the
art including, but not
limited to, two-step aging practices that produce a final T7651 or T7451
temper. When using a
T7651 or T7451 temper, the first stage temperature may be in the range of 100
to 140 C (212 to
284 F) for 4 to 24 hours and the second stage temperature may be in the range
of 135 to 200 C
(275 to 392 F) for 5 to 20 hours.
[0031] High strength 7xxx aluminum alloy plate products preferably have a
yield tensile strength
(YTS) in the LT direction? 67 ksi, or? 68 ksi, or? 70 ksi, or? 71 ksi. These
7xxx aluminum
alloy products may also have T-L K1 c values? 28 ksi-in1/2, or? 29 ksi-in1/2,
or? 30 ksi-in1/2.
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These 7xxx aluminum alloy products may also have Kmax-dev values? 33 MPa-m"2,
or? 34 MPa-
m1"2, or? 35 MPa-m1/2, or? 36 MPa-m1/2, or? 37 MPa-m1/2, or? 38 MPa-m"2. These
7xxx
aluminum alloy products may also have EAC values? 100 days, or? 110 days, or?
120 days, or
> 130 days, or? 140 days, or? 150 days. These 7xxx aluminum alloy plate
products may also
have any combination of or all the aforementioned YTS in the LT direction, T-L
K1 c, Kmax-dev, ,
and EAC values. In one embodiment of the present invention, these YTS and Kl c
values are found
in thick plates having a thickness? 3 inches, or? 4 inches, and have the above-
mentioned Km._
dev, and EAC values. The tensile testing was conducted based on ASTM B557
specification, the
contents of which are expressly incorporated herein by reference. The plane
strain fracture
toughness (KO was measured under ASTM E399, the contents of which are
expressly
incorporated herein by reference, using CT specimens. As described below, and
incorporated
herein, Environmentally Assisted Cracking (EAC) resistance is evaluated under
the test conditions
of Temperature=70 C, relative humidity=85% with a loading stress at 85% of
Rp0.2 at ST
direction centered at T/2 (middle of the thickness). The determination of
external crack deviation
(Kmax-dev ) are based on "anything that would normally invalidate the E647 FCG
test". The contents
of the E647 FCG test is expressly incorporated herein by reference.
[0032] Although the following examples demonstrate various embodiments of the
present
invention, one skilled in the art should understand how additional high
strength aluminum alloy
products can be fabricated in accordance with the present invention. The
examples should not be
construed to limit the scope of protection provided for the present invention.
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Examples (Plant Trial)
[0033] Fifty (50) industrial scale plates were produced by commercial DC
(Direct Chill) casting
followed by homogenization, hot rolling, solution heat treatment, quenching,
stretching and aging
processes to different thickness plates. Table 1 gives the chemical
compositions of 50 commercial
size plates.
[0034] Alloys 1 to 18 are invention alloys. Alloy 19 to 39 are 7050 type non-
invention alloys since
they have too high Cu, too low Zn, too low Mg/Cu ratio, and too low Zn/Mg
ratio. Alloy 40 to 50
are 7075 type non-invention alloys since they have too high Mg, too low Zn,
too high Mg/Cu ratio,
and too low Zn/Mg ratio.
[0035] FIG. 3 and FIG. 4 are graphs showing the chemical composition
difference between the
present 7xxx aluminum alloy products made from the invention alloys compared
to non-invention
alloys.
CA 3135591 2021-10-26
Inyension
Plate ID Gauge, in Cu, wt. % Mg, wt. % Zn, wt. % Mg/Cu Zn/Mg Cr, wt. % Zr, wt.
% Ti, wt. % Si, wt. % Fe, wt. %
Alloy?
1 1 1.72 1.98 6.85 1.15 3.46 0.00 0.12
0.015 0.03 0.07
2 1 1.72 1.98 6.85 1.15 3.46 0.00 0.12
0.015 0.03 0.07
3 2 1.74 1.96 6.87 1.13 3.50 0.00 0.12
0.025 0.04 0.08
4 2 1.74 1.96 6.87 1.13 3.50 0.00 0.12
0.025 0.04 0.08
2 1.72 1.98 6.85 1.15 3.46 0.00 0.12 0.015 0.03
0.07
6 2 1.72 1.98 6.85 1.15 3.46 0.00 0.12
0.015 0.03 0.07
>= 7 3 1.72 1.98 6.85 1.15 3.46 0.00 0.12
0.015 0.03 0.07
o
71 8 3 1.72 1.98 6.85 1.15 3.46 0.00 0.12
0.015 0.03 0.07
c 9 4 1.74 1.96 6.87 1.13 3.50 0.00 0.12
0.025 0.04 0.08
o
=,r.. 10 4 1.72 1.98 6.85 1.15 3.46 0.00
0.12 0.015 0.03 0.07
c
a)
> 11 4 1.72 1.98 6.85 ., 1.15 3.46
0.00 0.12 0.015 0.03 0.07 ,
c
- 12 4 1.72 1.98 6.85 1.15 3.46 0.00 0.12
0.015 0.03 0.07
13 4 1.72 1.98 6.85 1.15 3.46 0.00 0.12
0.015 0.03 0.07
14 4 1.74 1.96 6.87 1.13 3.50 0.00 0.12
0.025 0.04 0.08
6 1.74 1.96 6.87 1.13 3.50 0.00 0.12 0.025 0.04
0.08
16 6 1.74 1.92 6.84 1.11 3.56 0.00 0.12
0.028 0.04 0.09
17 8 1.74 1.92 6.84 1.11 3.56 0.00 0.12
0.028 0.04 0.09
18 8 1.74 1.96 6.87 1.13 3.50 0.00 0.12
0.025 0.04 0.08
19 1 2.15 2.26 6.22 1.05 2.75 0.01 0.09
0.034 0.05 0.09
1 2.17 2.16 6.14 1.00 2.84 0.01 0.09 0.032 0.04
0.08
21 2 2.19 2.19 6.15 1.00 2.81 0,01 0.09
0.027 0.04 0.09
22 2 2.15 2.19 6.17 1.02 2.82 0.00 0.09
0.030 0.04 0.08
23 3 2.16 2.17 6.14 1.01 2.83 0.01 0.09
0.031 0.05 0.09
24 3 2.15 2.16 6.06 1.00 2.81 0.00 0.09
0.033 0.04 0.09
4 2.16 2.05 6.20 0.95 3.02 0.00 0.11 0.024 0.04
0.08
>.
o 3 26 4 2.10 1.93 6.23 0.92 3.23 0.00
0.09 0.025 0.04 0.07
R 2 27 4 2.19 2.07 6.27 0.95 3.03 0.00 0.12
0.033 0.04 0.08
c :Tr
o w 28 4 2.19 2.22 6.29 1.02 2.83 0.01
0.09 0.031 0.04 0.09
IP 0.
c >,, 29 4.0 2.17 2.06 6.13 0.95 2.97 0.00 0.11
0.033 0.05 0.09
tu i_
> 30 , 4 2.20 2.07 6.32 0.94 3.05
0.01 0.12 0.023 0.05 0.10
c 0
- Ln
c o 31 5 2.20 2.04 6.14 0.93 3.01 0.00 0.12
0.025 0.05 0.09
or**-
Z 32 5 2.29 2.09 6.15 0.91 2.94 0.00 0.11
0.022 0.04 0.09
33 6 2.19 2.02 6.27 0.92 3.11 0.01 0.11
0.018 0.04 0.07
34 6 2.05 1.94 6.11 0.94 3.16 0.00 0.11
0.017 0.04 0.06
6 2.16 1.97 6.14 0.92 3.11 0.00 0.11 0.021 0.03
0.06
36 7 2.10 1.99 6.16 0.95 3.10 0.00 0.11
0.019 0.04 0.06
37 7 2.14 1.96 6.10 0.92 3.11 0.00 0.11
0.016 0.03 0.07
38 8 2.09 1.95 6.20 0.93 3.17 0.00 0.11
0.021 0.04 0.07
39 8 2.05 1.94 6.11 0.94 3.16 0.00 0.11
0.017 0.04 0.06
1 1.50 2.37 5.63 1.58 2.38 0.20 0.02 0.032 0.08
0.17
41 2 1.50 2.53 5.71 1.69 2.26 0.20 0.01
0.023 0.09 0.18
>.
o 3 42 2 1.56 2.72 5.83 1.75 2.14 0.20
0.01 0.022 0.07 0.13
zr o 43 3 1.50 2.49 5.68 1.66 2.28 0.20 0.02
0.030 0.11 0.22
c R
o
7.: 44 3 1.44 2.51 5.84 1.74 2.33 0.21 0.02
0.026 0.10 0.20
. a
4 1.65 2.49 5.66 1.51 2.27 0.21 0.01 0.027 0.06
0.13
WI-
46 i_
> 46 4 1.41 2.47 5.74 1.76 2.32 0.20
0.02 0.024 , 0.06 0.14
c Ln
- N
c o 47 5 1.47 2.58 5.83 1.75 2.26 0.20 0.00
0.031 0.05 0.11
O N
Z 48 6 1.54 2.46 5.94 1.60 2.42 0.19 0.01
0.014 0.05 0.19
49 7 1.60 2.67 5.95 1.67 2.23 0.20 0.01
0.030 0.08 0.15
8 1.57 2.45 5.84 1.56 2.38 0.20 0.03 0.032 0.07
0.16
Table 1: Chemical compositions of industrial scale ingots
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[0036] Ingots were homogenized, hot rolled, solution heat treated, quenched,
stretched and aged
to final temper plates in the thickness range from 1 inch to 8 inch. The
ingots were homogenized
at a temperature from 465 to 485 'V (869 to 905 F). The hot rolling start
temperature is from 400
to 440 C (752 to 824 F).
[0037] The plates were solution heat treated at temperature range from 470 to
485 C (878 to
905 F), cold water quenched to room temperature and stretched at about 1.5 to
3%. A two-step
aging practice was used to produce final T7651 and T7451 tempers. The first
stage temperature is
in the range of 110 to 130 C (230 to 266 F) for 4 to 12 hours and the second
stage temperature is
in the range of 145 to 160 C (293 to 320 F) for 8 to 20 hours.
[0038] The final production plates were characterized for strength, fracture
toughness, corrosion
resistance, fatigue crack deviation resistance, and anisotropic ductility that
are critical for
aerospace applications.
[0039] The tensile testing was conducted based on ASTM B557 specification, the
contents of
which are expressly incorporated herein by reference. The plane strain
fracture toughness (KO
was measured under ASTM E399, the contents of which are expressly incorporated
herein by
reference, using CT specimens. Table 2 gives the tensile properties and
fracture toughness for
aluminum alloy products using invention and non-invention alloy samples. The
common
terminologies familiar to those skilled in the art were used in this table for
strength and fracture
toughness.
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[0040] Table 2 shows significantly better strength for aluminum alloy products
using invention
alloys (Sample 1-18) than non-invention alloys. The fracture toughness for
aluminum alloy
products is also better for invention alloy compared with 7050 type non-
invention alloys.
[0041] Fig. 5 demonstrates the higher strength of aluminum alloy products
using the invention
alloys compared with non-invention alloys.
[0042] The strength and fracture properties have to be considered together for
aerospace
applications. The combination of strength and fracture toughness for aluminum
alloy products
made from invention alloys is much better than non-invention alloys based on
Table 2. For
instance, FIG. 6 demonstrates that 3" thick aluminum alloy plates made from
the invention alloy
have a better combination of strength and fracture toughness compared with non-
invention alloys.
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!mansion LT UTS IT YTS IT ELG L UTS L YTS L ELG ST UTS
ST YTS ST ELG L-T KIC, T-L KIC, S-L KIC,
Alloy? Plate ID Gauge, in Temper (ksi) (ksi) (%) (ksi)
(ksi) (%) (ksi) (ksl) (%) ksi*In1/2 ksi*in1/2 ksi*in1/2
1 1 17451 78.9 72.1 14.6 80.7 73.9 15.0 no no
na 38.5 31.3 no
2 1 17651 79.9 73.3 14.3 81.4 74.9 15.2 no no
no 35.1 29.3 no
3 2 T7451 77.9 70.3 12.5 76.9 70.7 16.2 no no
no 38.4 28.5 no
4 2 17651 78.2 70.8 12.8 77.7 71.4 15.6 no no
no 38.4 29.5 no
2 17451 77.9 70.8 12.7 76.6 70.2 15.7 76.4 66.7
7.7 38.9 30.2 31.7
6 2 17651 79.2 72.7 12.9 77.6 71.9 15.7 75.8
68.4 6.0 37.3 29.1 31.2
). 7 3 T7451 77.3 70.4 11.7 76.5 70.1 14.6
75.4 65.0 7.6 40.1 30.7 30.1
o
8 3 17651 78.1 71.4 11.4 77.3 71.6 14.3 76.5
66.4 7.7 37.4 30.1 28.6
ZC
c 9 4 17451 77.1 69.6 10.2 74.4 69.6 15.3
74.8 64.9 7.5 39.6 29.8 27.6
0
..g 10 4 T7451 76.8 69.4 10.9 75.2 69.6 15.6
74.8 64.6 7.4 39.5 30.5 30.1
tu 11 4 17451 77.4 69.9 10.6 75.3 69.9 15.2
75.0 65.0 7.6 39.1 30.6 28.7
>
c
- 12 4 17651 78.5 71.0 10.6 76.9 71.6 14.6
76.3 66.7 6.9 36.6 29.1 28.0
13 4 17651 78.5 72.0 10.5 76.0 71.4 15.3 76.5
66.5 6.8 38.2 30.1 29.2
14 4 17651 78.3 71.4 10.6 75.6 70.9 14.3 75.9
66.0 8.3 35.2 29.4 27.1
6 17651 76.8 69.1 6.0 76.8 71.7 10.2 74.3 65.5
5.0 32.5 26.0 24.4
16 6 17651 77.3 70.3 6.6 75.9 71.1 11.0 74.2
65.8 5.8 32.4 25.5 24.4
17 8 17651 75.0 67.7 4.3 75.4 69.9 8.7 71.6
63.1 3.9 32.2 25.1 24.6
18 8 17651 76.0 69.0 4.4 75.9 71.1 7.1 73.1
65.0 4.3 30.4 23.7 25.0
19 1 17451 74.3 65.6 13.4 74.3 65.7 14.7 no no
no 32.5 27.3 no
1 17451 75.0 66.6 13.0 75.2 66.8 14.4 no no no 32.8 27.7 no
21 2 17451 75.5 65.9 12.0 74.9 66.5 13.8 no no
no 34.2 28.2 no
22 2 17451 76.7 68.0 12.9 74.3 66.6 15.5 no no no 34.7 29.5 no
23 3 17451 74.0 65.2 10.7 74.0 65.3 12.7 71.0
59.7 6.6 33.0 26.5 24.2
24 3 17451 73.8 64.6 11.2 74.7 66.0 12.9 72.0
61.6 6.3 34.3 27.5 24.9
4 17451 75.8 64.3 10.1 73.9 67.0 14.9 73.2 62.8
6.1 36.7 27.6 26.6
).
26 4 17651 69.5 61.7 7.7 71.4 64.2 12.0 73.5
63.3 6.2 31.7 26.1 25.8
Ti = 2 27 4 17651 72.7 63.9 9.8 75.9 67.6 12.7
71.1 63.1 3.3 28.9 22.3 20.4
c Tz
o u 28 4 17651 73.5 65.4 10.2 75.3 68.0 11.3
65.2 59.9 1.7 26.4 20.5 20.0
. 0_
c - 29 4.0 17651 75.7 66.7 10.3 73.6 66.5 14.8
73 62.2 6 36.1 26.1 23.3
CU g.
0 30 4 17451 74.4 65.1 10.3 73.0 64.9 14.1
72.4 61.9 6.6 35.9 27.3 24.7
- Ln
c o 31 5 17451 73.1 63.7 7.2 73.5 65.5 12.5
71.2 60.7 5.2 30.4 22.1 23.8
o t.
z 32 5 17451 73.1 63.5 8.3 72.9 64.8 13.0
71.0 60.8 4.9 30.2 24.8 23.6
33 6 17451 74.3 62.2 8.8 74.1 66.1 12.2 72.1
60.3 6.4 31.8 24.8 25.7
34 6 17451 74.7 65.0 7.6 74.4 66.7 11.5 72.3
61.0 6.0 32.0 26.3 24.5
6 17451 73.8 64.3 6.9 74.3 66.2 11.2 71.5 60.9
6.0 34.1 28.2 25.8
36 7 17451 72.2 61.3 7.1 72.4 63.9 10.6 70.0
59.0 6.5 33.0 25.6 27.9
37 7 17451 72.2 60.3 7.2 72.5 63.6 11.2 70.6
60.2 5.7 32.0 26.4 27.5
38 8 17451 70.2 59.6 5.9 71.1 62.5 10.1 68.9
57.8 5.3 32.9 24.9 26.1
39 8 17451 70.6 60.6 5.3 72.3 63.5 9.7 68.9
58.7 5.0 32.2 24.9 26.9
1 17351 70.6 60.0 12.6 no no no no no no no no no
41 2 17351 68.1 55.9 12.4 no no no no no no no no no
>.
o 57; 42 2 17351 71.1 59.1 10.7 no no no
no no no no no no
Tt 2 43 3 17351 64.5 52.0 11.1 no no no no
no no no no no
c ZE
o w 44 3 17351 68.1 55.9 10.7 no no no no
no no no no no
7. p.
c >. 45 4 17351 62.1 47.3 11.4 no , no no no
no no no no no
c Ln 46 4 17351 63.3 50.0 11.2 no no no no
no no no no no
- N
c r9. 47 5 17351 58.3 42.8 12.5 no no no no
no no no no no
2 - 48 6 17351 54.2 38.7 11.5 no no no no
no no no no no
49 7 1651 59.2 39.6 12.0 no no no no no no
no no no
8 1651 56.3 37.3 11.5 no no no no no no no
no no
Table 2: Tensile and fracture toughness of aluminum alloy plate products made
from the invention
alloy and non-invention alloy
14
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,
[0043] The fatigue crack growth deviation was evaluated based on ASTM E647,
the contents of
which are expressly incorporated herein by reference. The coupon orientation
is L-S, which has
the highest chance to have crack deviation during crack propagation. FIG. 7
shows the orientation
of this sample relative to the plate geometry. FIG. 8 illustrates the coupon
configuration used
herein. The standard Compact Tension, i.e. C(T), coupon was used for this
test. The dimension B
is 6.35mm and W is 76.2mm for all testing coupons. The FCGR testing procedure
was according
to ASTM E647 in general with the following specific requirements: (1) R = 0.1
and f=25 Hz; (2)
Pre-cracking was conducted under constant load amplitude, and the starting AK
reaches the AKi
= 10 MPa*mil2 values at the end of pre-cracking. After pre-cracking, the
testing is conducted under
constant load amplitude at the same load as pre-cracking. The test was
conducted at room
temperature. The relative humidity (RH) is under normal lab environment.
[0044] The determination of external crack deviation was based on "anything
that would
normally invalidate the E647 FCG test" (e.g. crack growth out of plane by more
than 20' or
crack deviation after the remaining ligament criterion is exceeded). After the
deviation branching
point was determined, the crack length was calculated by three point weighted
average method
based on measurements taken on fracture sample. The equation for weighted
average length is a
= (front + back + 2* center) /4.
[0045] The fatigue cycles, crack length and Kmax-dev at the crack deviation
point are given in
Table 4 for invention and non-invention alloy lots. FIG. 9 is a graph showing
the comparison of
the combination of strength and Km.-dev for f
aluminum
alloy products made from the invention
alloy compared to the non-invention alloys plates in the thickness range of 4
to 5 inches.
CA 3135591 2021-10-26
External Kmax at External
Plate Ga, LT-YTS
Alloy Plate ID Temper Orientation Loc Branching
Branching,
in ksi
Cycles .. MPa*mliz
9 17451 4 L-S 1/2 91496 37.8
69.6
9 17451 4 L-S 1/2 87922 38.2
69.6
Invention Alloy
14 T7651 4 L-S T/2 91997 38.5
71.4
14 17651 4 L-S T/2 88088 33.8
71.4
26 T7451 4 L-S 1/2 66630 40.8
63.7
26 T7451 4 L-S T/2 116766 29.6
63.7
Non Invention Alloy 27 T7451 4 L-S 1/2 97437 32.9
66.8
(7050-type) 27 17451 4 L-S 1/2 96752 31.0
66.8
28 17451 4 L-S 1/2 132635 33.2
66.8
28 17451 4 L-S T/2 137664 27.3
66.8
Table 4: The fatigue cycles, crack length and Kmax-dev at the crack deviation
points of 4 inch thick
plates
[0046] The tensile properties, especially tensile ductility, can be
significantly different for
different testing directions. Such anisotropic material behavior is very
important for high strength
thick plate aerospace applications.
[0047] The orthotropic tensile coupons were extracted such that the gauge
length was centered at
T/2 location. The tensile direction is 45 degrees off thickness (ST) direction
(ST-45). The testing
results are given in Table 5. As demonstrated in FIG. 10, the aluminum alloy
products made from
the invention alloy has unexpectedly better combination of orthotropic
strength and ductility.
16
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Alloy Plate
ID Gage, in Location Orientation YTS (ksi) UTS (ksi) Elongation
9 4 T/2 45 64.5 69.5 2.91
9 4 T/2 45 64.7 70.1 3.2
9 4 1/2 45 64.8 69.8 2.963
Invention Alloy
14 4 T/2 45 66.2 70.8 2.75
14 4 T/2 45 66.1 70.8 2.8
14 4 1/2 45 66 70.2 2.26
Non Invention Alloy 29 4.1 1/2 45 62.9 66.8 1.90
(7050-type) 29 4.1 1/2 45 62.8 66.2 1.71
Table 5: Anisotropic tensile properties for alloy lots for 4-4.25 inch thick
plates.
[0048] Stress corrosion resistance is critical for aerospace application. The
standard stress
corrosion cracking testing was performed in accordance with the requirements
of ASTM G47, the
contents of which are expressly incorporated herein by reference, which is
alternate immersion in
a 3.5% NaCl solution under constant deflection. Three specimens were tested
per sample.
[0049] Table 6 gives the SCC testing results for both T7451 and T7651 tempers.
It shows that the
lots designated as T7451 temper pass the 35ksi stress threshold. In addition,
a vast majority of
samples at a higher 40ksi stress level also pass SCC to 30 days. The lots
designated as T7651
temper pass the 25ksi threshold. In addition, they also pass SCC testing at a
higher 30ksi stress
level, to 30 day duration.
SCC Results
Plate Stress,
Alloy Gauge Temper Repl Rep2 Rep3
ID ksi
1 1 T7451 35 > 30 day > 30 day > 30
day
2 T7451 35 > 30 day > 30 day > 30 day
Invention Alloy _______________________________________________________
7 3 17451 35 > 30 day > 30 day > 30
day
4 17451 35 > 30 day > 30 day > 30 day
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11 1 4 1 T7451 1 35
1 > 30 day 1 > 30 day 1 > 30 day 1
SCC Results
Plate Stress,
Alloy Gauge Temper Repl Rep2 Rep3
ID ksi
2 1 17651 25 > 30 day > 30 day > 30 day
6 2 T7651 25 > 30 day > 30 day > 30 day
Invention Alloy 8 3 T7651 25 >30 day >30 day > 30 day
12 4 17651 25 > 30 day > 30 day > 30 day
13 4 17651 25 > 30 day > 30 day > 30 day
SCC Results
Plate Stress,
Alloy Gauge Temper Repl Rep2 Rep3
ID ksi
I 1 17451 40 > 30 day > 30 day > 30 day
2 T7451 40 17 > 30 day > 30 day
Invention Alloy 7 3 T7451 40 > 30 day > 30 day > 30 day
4 T7451 40 > 30 day > 30 day > 30 day
11 4 T7451 40 10 >30 day >30 day
SCC Results
Plate Stress,
Alloy Gauge Temper Repl Rep2 Rep3
ID ksi
_______________________________________________________________________ _
2 1 17651 30 > 30 day > 30 day > 30 day
Invention Alloy _______________________________________________________
6 2 17651 30 > 30 day > 30 day > 30 day
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8 3 T7651 30 > 30 day > 30 day >
30 day
12 4 T7651 30 > 30 day > 30 day >
30 day
13 4 T7651 30 > 30 day > 30 day >
30 day
Table 6: SCC testing performance of invention alloy.
[0050] In recent years there have been other alloys that have provided
superior higher yield
strength properties than incumbent alloys such as 7050 and 7075, especially
for thicker plate
applications. These alloys, however, have proven to be susceptible to a
different failure mechanism
referred to as Environmentally Assisted Cracking (EAC).
[0051] Table 7 gives the chemical composition of such new high strength 7xxx
alloys developed
in recent years. The plates were commercial scale plates. The non-invention
chemistries, especially
Zn content, are significantly different compared with the present invention
alloy.
Alloy Plate ID Mg Zn Mg/Cu In/Mg Cr Zr Ti Si
Fe
Invention Alloy 18 1.96 6.87 1.13 3.50 0.00 0.12 0.02
0.04 0.08
N7085 1.53 7.32 0.93 4.80 0.00 0.12 0.02
0.03 0.03
N7449 2.10 7.82 1.10 3.73 0.01 0.10 0.02
0.04 0.07
Non Invention Alloy N7056 1.70 8.65 1.00 5.09 0.00 0.07
0.03 0.04 0.07
N197 1.85 8.19 1.36 4.44 0.00 0.11 0.02
0.03 0.07
N199 2.05 7.73 1.18 3.77 0.00 0.09 0.04
0.03 0.05
Table 7: The chemical compositions of non-invention new high strength alloy
plates for EAC
testing
[0052] Environmentally Assisted Cracking (EAC) resistance was evaluated under
the test
conditions of Temperature=70 C, relative humidity=85%. The loading stress is
at 85% of Rp0.2
at ST direction. The sample is taken at ST direction centered at T/2 (middle
of the thickness).
19
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[0053] Three testing coupons (Rep1, Rep2, Rep3) were tested for invention
alloy plate #18 along
with some new non-invention high strength alloy plates. Table 8 gives the EAC
testing results.
The results indicate that the aluminum alloy products made from the invention
alloy have much
better EAC resistance performance than other non-invention high strength
alloys. For invention
alloy plate ID 18, the three coupons failed at 116, 150 and 159 days. In
contrast, all non-invention
alloy coupons failed EAC testing in the range from 3 to 21 days.
EAC Days of Failures
Alloy Plate ID
Repl Rep2 Rep3
Invention Alloy 18 159 150
116
N7085 15 20 14
N7449 12 12 12
Non Invention Alloy N7056 3 1 1
N T97 3 3 3
N T99 17 18 21
Table 8: EAC testing performance of alloys, at 70 C and 85% RH.
[0054] Although the present invention has been disclosed in terms of a
preferred embodiment, it
will be understood that numerous additional modifications and variations could
be made thereto
without departing from the scope of the invention as defined by the following
claims:
CA 3135591 2021-10-26
