Note: Descriptions are shown in the official language in which they were submitted.
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2XXX SERIES ALUMINUM LITHIUM ALLOYS
BACKGROUND
[001] Aluminum alloys are useful in a variety of applications. However,
improving
one property of an aluminum alloy without degrading another property often
proves elusive.
For example, it is difficult to increase the strength of an alloy without
decreasing the
toughness of an alloy. Other properties of interest for aluminum alloys
include corrosion
resistance and fatigue crack growth rate resistance, to name two.
SUMMARY OF THE INVENTION
[002] Broadly, the present patent application relates to wrought 2xxx
aluminum
lithium alloy products having improved properties. Generally, the wrought 2xxx
aluminum
lithium alloy products have 3.0 to 3.8 wt. % Cu, 0.05 to 0.35 wt. % Mg, 0.975
to 1.385 wt.
% Li, where -0.3*Mg-0.15Cu +1.65 < Li < -0.3*Mg-0.15Cu +1.85, 0.05 to 0.50 wt.
% of a
grain structure control element selected from the group consisting of Zr, Sc,
Cr, V. Hf, other
rare earth elements, and combinations thereof, up to 1.0 wt. % Zn, up to 1.0
wt. % Mn, up to
0.15 wt. % Ti, up to 0.12 wt. % Si, up to 0.15 wt. % Fe, up to 0.10 wt. % of
any other
element, with the total of these other elements not exceeding 0.35 wt. %, the
balance being
aluminum. Wrought products incorporating such alloy compositions may achieve
improved
properties.
[003] The wrought products are generally in the form of sheet or thin plate
having a
thickness of from about 0.040 inch to about 0.500 inch. In one embodiment, the
wrought
aluminum alloy product has a thickness of at least 0.050 inch. In another
embodiment, a
thick wrought aluminum alloy product has a thickness of at least 0.060 inch.
The improved
properties described herein may be achieved with thick wrought products having
a thickness
of up to 0.400 inch, or up to 0.300 inch, or up to 0.250 inch. As used in this
paragraph,
thickness refers to the minimum thickness of the product, realizing that some
portions of the
product may realize slightly larger thicknesses than the minimum stated.
[004] Composition limits of several alloys useful in accordance with the
present
teachings are disclosed in Tables la- 1 c, below (values in weight percent).
TABLE la - EXAMPLE COMPOSITION OF ALLOYS
Alloy Cu Mg Li Cu-Mg-Li Relationship
Broad 3.0 - 3.8 0.05 - 0.35 0.975- 1.385 -0.3*Mg-
0.15Cu +1.65
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Alloy Cu Mg Li Cu-Mg-Li Relationship
Pref. (1) 3.1 -3.7 0.10 - 0.30 1.005- 1.355 < Li <
-0.3*Mg-0.15Cu +1.85
Pref. (2) 3.2 - 3.6 0.15 -0.25 1.035 - 1.325
Pref. (3) 3.3 - 3.6 0.15 -0.25 1.035 - 1.310
TABLE lb - EXAMPLE COMPOSITION OF ALLOYS
Grain
Alloy Mn Structure Ti Zn
Control
Broad 0 - 1.0 0.05 - 0.50 0 - 0.15 1.0
Pref (1) 0.10 - 0.80 0.05 - 0.20 Zr 0 - 0.10 l,
0 - 1.0
Pref. (2) 0.20 -0.60 0.07 -0.14 Zr
0.01 - 0.06 0 - 1.0
Pref. (3) 0.20 - 0.40 0.08 - 0.13 Zr
0.01 -0.03 0- 1.0
TABLE le - EXAMPLE COMPOSITION OF ALLOYS
Other Elements
Alloy Fe Si Ag Balance
1 _____________________________________________ Each / Total
=
Include in
Broad < 0.15 5 0.120.10 / 0.35 Al
"Other Elements"
Include in
Pref. (1) 5. 0.12 5_ 0.10 0.05 / 0.15
Al
............................ "Other Elements"
IM .5 0.08 5. 0.06"Other Elements"
Include in
0.05 / 0.15 Al
1 _____
Include in"
Pref. (3) .5 0.05 5. 0.04 0.03 / 0.10
Al
Other Elements"
[005] Copper (Cu) is included in the new alloy, and generally in the range
of from 3.0
wt. % to 3.8 wt. % Cu. In one embodiment, the new alloy includes at least 3.1
wt. % Cu. In
other embodiments, the new alloy may include at least 3.2 wt. % Cu, or at
least 3.3 vvt. %
Cu ,or at least 3.35 wt. % Cuõ or at least 3.4 wt. % Cu. In one embodiment,
the new alloy
includes not greater than 3.75 wt. % Cu. In other embodiments, the new alloy
may include
not greater than 3.7 wt. % Cu, or not greater than 3.65 wt. % Cu, or not
greater than 3.6 wt.
% Cu.
[006] Magnesium (Mg) is included in the new alloy, and generally in the
range of from
0.05 wt. % to 0.35 wt. % Mg. In one embodiment, the new alloy includes at
least 0.10 wt.
% Mg. In other embodiments, the new alloy may include at least 0.15 wt. % Mg.
In one
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embodiment, the new alloy includes not greater than 0.35 wt. % Mg. In other
embodiments,
the new alloy may include not greater than 0.30 wt. % Mg, or not greater than
0.25 wt. %
Mg.
[007] Lithium (Li) is included in the new alloy, and generally in the range
of from
0.975 wt. % to 1.385. In one embodiment, the new alloy includes at least 1.005
wt. % Li.
In other embodiments, the new alloy may include at least 1.035 wt. % Li, or at
least 1.050
wt. % Li, or at least, or at least 1.065 wt. % Li, or at least 1.080 wt. % Li,
or at least 1.100
wt. % Li, or at least 1.125 wt. % Li, or at least 1.150 wt. %. In one
embodiment, the new
alloy includes not greater than 1.355 wt. % Li. In other embodiments, the new
alloy
includes not greater than 1.325 wt. % Li, or not greater than 1.310 wt. %, or
not greater than
1.290 wt. % Li, or not greater than 1.270 wt. % Li, or not greater than 1.250
wt. % Li.
1_008] The combined amounts of Cu, Mg, and Li may be related to realization
of
improved properties. In one embodiment, the aluminum alloy includes Cu, Mg,
and Li per
the above requirements, and in accordance with the following expression:
(1) -0.3*Mg-0.15Cu +1.65 < Li < -0.3*Mg-0.15Cu +1.85
In other words:
(2) Limin = 1.65-0.3(Mg)-0.15(Cu); and
(3) Li, = 1.85-0.3(Mg)-0.15(Cu)
Aluminum alloy products having an amount of Cu, Mg, and Li falling within the
scope of
these expressions may realize an improved combination of properties (e.g., an
improved
strength-toughness relationship).
[009] Zinc (Zn) may optionally be included in the new alloy and up to 1.0
wt. % Zn.
In one embodiment, the new alloy includes at least 0.20 wt. % Zn. In one
embodiment, the
new alloy includes at least 0.30 wt. % Zn. In one embodiment, the new alloy
includes not
greater than 0.50 wt. % Zn. In another embodiment, the new alloy includes not
greater than
0.40 wt. % Zn.
[0010] Manganese (Mn) may optionally be included in the new alloy, and in
an amount
up to 1.0 wt. %. In one embodiment, the new alloy includes at least 0.05 wt. %
Mn. In
other embodiments, the new alloy includes at least 0.10 wt. % Mn, or at least
0.15 wt. %
Mn. or at least 0.2 wt. % Mn. In one embodiment, the new alloy includes not
greater than
0.8 wt. % Mn. In other embodiments, the new alloy includes not greater than
0.7 wt. % Mn,
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or not greater than 0.6 wt. % Mn, or not greater than 0.5 wt. % Mn, or not
greater than 0.4
wt. % Mn. In the alloying industry, manganese may be considered both an
alloying
ingredient and a grain structure control element -- the manganese retained in
solid solution
may enhance a mechanical property of the alloy (e.g., strength), while the
manganese in
particulate form (e.g., as A16Mn, A112Mn3Si2 -- sometimes referred to as
dispersoids) may
assist with grain structure control. However, since Mn is separately defined
with its own
composition limits in the present patent application, it is not within the
definition of "grain
structure control element" (described below) for the purposes of the present
patent
application.
[0011] The alloy may include 0.05 to 0.50 wt. % of at least one grain
structure control
element selected from the group consisting of zirconium (Zr), scandium (Sc),
chromium
(Cr), vanadium (V) and/or hafnium (Hf), and/or other rare earth elements, and
such that the
utilized grain structure control element(s) is/are maintained below maximum
solubility. As
used herein, "grain structure control element" means elements or compounds
that are
deliberate alloying additions with the goal of forming second phase particles,
usually in the
solid state, to control solid state grain structure changes during thermal
processes, such as
recovery and recrystallization. For purposes of the present patent
application, grain
structure control elements include Zr, Sc, Cr, V, Hf, and other rare earth
elements, to name
a few, but excludes Mn.
[0012] The amount of grain structure control material utilized in an alloy
is generally
dependent on the type of material utilized for grain structure control and/or
the alloy
production process. In one embodiment, the grain structure control element is
Zr, and the
alloy includes from 0.05 wt. % to 0.20 wt. % Zr. In another embodiment, the
alloy includes
from 0.05 wt. % to 0.15 wt. % Zr. In another embodiment, the alloy includes
0.07 to 0.14
wt. % Zr. In another embodiment, the alloy includes 0.08 - 0.13 wt. % Zr. In
one
embodiment, the aluminum alloy includes at least 0.07 wt. % Zr. In another
embodiment,
the aluminum alloy includes at least 0.08 wt. % Zr. In one embodiment, the
aluminum alloy
includes not greater than 0.18 wt. % Zr. In another embodiment, the aluminum
alloy
includes not greater than 0.15 wt. % Zr. In another embodiment, the aluminum
alloy
includes not greater than 0.14 wt. % Zr. In another embodiment, the aluminum
alloy
includes not greater than 0.13 wt. % Zr.
[0013] The alloy may include up to 0.15 wt. % Ti cumulatively for grain
refining and/or
other purposes. Grain refiners are inoculants or nuclei to seed new grains
during
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solidification of the alloy. An example of a grain refiner is a 9.525 mm rod
comprising 96%
aluminum, 3% titanium (Ti) and 1% boron (B), where virtually all boron is
present as finely
dispersed TiB2 particles. During casting, the grain refining rod is fed in-
line into the molten
alloy flowing into the casting pit at a controlled rate. The amount of grain
refiner included
in the alloy is generally dependent on the type of material utilized for grain
refining and the
alloy production process. Examples of grain refiners include Ti combined with
B (e.g.,
TiB2) or carbon (TiC), although other grain refiners, such as Al-Ti master
alloys may be
utilized. Generally, grain refiners are added in an amount ranging from 0.0003
wt. % to
0.005 wt. % to the alloy, depending on the desired as-cast grain size. In
addition, Ti may be
separately added to the alloy in an amount up to 0.15 wt. %, depending on
product form, to
increase the effectiveness of grain refiner, and typically in the range of
0.01 to 0.03 wt. %
Ti. When Ti is included in the alloy, it is generally present in an amount of
from 0.01 to
0.10 wt. %. In one embodiment, the aluminum alloy includes a grain refiner,
and the grain
refiner is at least one of TiB2 and TiC, where the wt. % of Ti in the alloy is
from 0.01 to
0.06 wt. %, or from 0.01 to 0.03 wt. %.
[0014] The aluminum alloy may include iron (Fe) and silicon (Si), typically
as
impurities. The iron content of the new alloy should generally not exceed 0.15
wt. %. In
one embodiment, the iron content of the alloy is not greater than 0.12 wt. %.
In other
embodiments, the aluminum alloy includes not greater than 0.10 wt. % Fe, or
not greater
than 0.08 wt. % Fe, or not greater than 0.05 wt. % Fe, or not greater than
0.04 wt. % Fe.
Similarly, the silicon content of the new alloy should generally not exceed
0.12 wt. %. In
one embodiment, the silicon content of the alloy is not greater than 0.10 wt.
% Si, or not
greater than 0.08 wt. % Si, or not greater than 0.06 wt. % Si, or not greater
than 0.04 wt. %
Si, or not greater than 0.03 wt. % Si.
[0015] In some embodiments of the present patent application, silver (Ag)
is considered
an impurity, and, in these embodiments, is included in the definition of
"other elements",
defined below, i.e., is at an impurity level of 0.10 wt. % or less, depending
on which "other
element" limits are applied to the alloy. In other embodiments, silver is
purposefully
included in the alloy (e.g., for strength) and in an amount of from 0.11 wt. %
to 0.50 wt. %.
[0016] The new 2xxx aluminum lithium alloys generally contain low amounts
of "other
elements" (e.g., casting aids and impurities, other than the iron and
silicon). As used herein,
"other elements" means any other element of the periodic table except for
aluminum and the
above-described copper, magnesium, lithium, zinc, manganese, grain structure
control
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elements (i.e., Zr, Sc, Cr, V Hf, and other rare earth elements), iron and/or
silicon, as
applicable, described above. In one embodiment, the new 2xxx aluminum lithium
alloys
contain not more than 0.10 wt. % each of any other element, with the total
combined
amount of these other elements not exceeding 0.35 wt. %. In another
embodiment, each one
of these other elements, individually, does not exceed 0.05 wt. % in the 2xxx
aluminum
lithium alloy, and the total combined amount of these other elements does not
exceed 0.15
wt. % in the 2xxx aluminum lithium alloy. In another embodiment, each one of
these other
elements, individually, does not exceed 0.03 wt. % in the 2xxx aluminum
lithium alloy, and
the total combined amount of these other elements does not exceed 0.10 wt. %
in the 2xxx
aluminum lithium alloy.
[0017] The new
alloys may be used in all wrought product forms, including plate,
forgings and extrusions.
[0018] The new
alloy can be prepared into wrought form, and in the appropriate temper,
by more or less conventional practices, including direct chill (DC) casting
the aluminum
alloy into ingot form. After conventional scalping, lathing or peeling (if
needed) and
homogenization, which homogenization may be completed before or after
scalping, these
ingots may be further processed by hot working the product. The product may
then be
optionally cold worked, optionally annealed, solution heat treated, quenched,
and final cold
worked. After the final cold working step, the product may be artificially
aged. Thus, the
products may be produced in a T3 or T8 temper.
[0019] Unless
otherwise indicated, the following definitions apply to the present
application: =
[0020] "Wrought
aluminum alloy product" means an aluminum alloy product that is hot
worked after casting, and includes rolled products (sheet and thin plate),
forged products,
and extruded products.
[0021] "Forged
aluminum alloy product" means a wrought aluminum alloy product that
is either die forged or hand forged.
[0022] "Solution
heat treating" means exposure of an aluminum alloy to elevated
temperature for the purpose of placing solute(s) into solid solution.
[0023] "Hot
working" means working the aluminum alloy product at elevated
temperature, generally at least 250 F.
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[0024] "Cold working" means working the aluminum alloy product at
temperatures that
are not considered hot working temperatures, generally below about 250 F.
[0025] "Artificially aging" means exposure of an aluminum alloy to elevated
temperature for the purpose of precipitating solute(s). Artificial aging may
occur in one or a
plurality of steps, which can include varying temperatures and/or exposure
times.
[0026] These and other aspects, advantages, and novel features of this new
technology
are set forth in part in the description that follows and will become apparent
to those skilled
in the art upon examination of the following description and figures, or may
be learned by
practicing one or more embodiments of the technology provided for by the
present
disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIGS. 1-3 are graphs illustrating the performance of Alloy A of
Example 1.
DETAILED DESCRIPTION
[0028] An example alloy (Alloy A) was cast as ingot and homogenized. The
composition of Alloy A is shown in Table 1, below.
TABLE 1- COMPOSITION OF ALLOY A
=Alloy Si Fe Cu
Mg Mn Zn Ti Zr Ag Li I
A
, 0.018 0.027 3.50 0.21 1 0.30 0.35 0.019 0.130 - 1.18
[0029] Alloy A was then hot rolled to a gauge of 2.5 inch, after which it
was solution
heat treated and quenched, and then stretched, and then artificially aged to a
T8 temper. A
portion of this plate (17 inches by 14.5 inches) was then heated to about 900
F, and then
processed to a final thickness of 0.125 inch using the following process:
= The material was first hot rolled and the first two hot rolling passes
were in the
transverse direction to broaden the sheet to 19 in. wide and the material was
hot
rolled in 10 rolling passes to a thickness of approximately 0.25 in. Following
hot
rolling the material was anneal at 800 F for 4 hours, then cooled 50 F/hr to
room
temperature. After annealing the material was cold rolled to a final thickness
of
0.125 in.
[0030] Following rolling, the material was solution heat treated and
quenched, and then
stretched about 3% (L direction). The material was then artificially aged for
two times
(about 24 hours and about 48 hours) at 290 F. Mechanical properties were then
measured,
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the results of which are shown in Table 2, below (values average of duplicate
specimens).
Strength testing was conducted in accordance with ASTM E8 and B557. The
fracture
toughness was measured in accordance with ASTM E561 and ASTM B646 using middle
cracked tension M(T) specimens. Specimens were in the T-L and L-T orientations
and have
a nominal 2a/W =0.25. A 16 in. wide specimen was used for the L-T test and a
6.3 in. wide
specimen was used for the T-L test. The tests were run at full thickness and
at room
temperature lab air (18 to 28 C). Anti-budding guides are required.
TABLE 2 MECHANICAL PROPERTIES OF ALLOY A
Age Time
Test Yield Tensile
Elongation
at 290FStrength Strength
Direction (0/
(hrs.) (ksi) ..... (ksi) 0)
24 L 56.7 63.7 MEM
24 Li 56.25 66.05 10
........... 48 L 64.3 69.3 10
........... 48 LT 62.7 69.7 1 8
[0031] Fatigue crack growth (FCG) was measured The fatigue crack growth
tests were
run in accordance with ASTM E 647 using W = 102 mm wide T-L orientation,
middle-
cracked tension M(T) specimen with a starting notch length of 2an = 5.08 mm.
Tests were
run using a constant load amplitude covering a range of AK from about 10 to 45
MPa=qm
with a stress ratio of R = 0.1, and a testing frequency between 2 and 25 Hz.
Tests are run in
room temperature lab air (18 to 28 C) with relative humidity greater than 20%
and a
maximum relative humidity of 55%.
[0032] The test data for Alloy A was compared to the incumbent fuselage
skin alloy,
Alclad 2524-T3, the result of which are illustrated in FIGS. 1-3, below.. For
the FCG
testing, the test data shown are from M(T) specimens of the same geometry as
the C77W
specimen. The test was run in accordance with ASTM E 647 using a constant K
gradient.
The R-curve data shown for Alclad 2524 were run on M(T) specimens, W=16 in.
and
2a/W=0.25.
[0033] While various embodiments of the present disclosure have been
described in
detail, it is apparent that modifications and adaptations of those embodiments
will occur to
those skilled in the art. However, it is to be expressly understood that such
modifications
and adaptations are within the spirit and scope of the present disclosure.
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