Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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IMPROVED THICK WROUGHT 7XXX ALUMINUM ALLOYS, AND METHODS
FOR MAKING THE SAME
FIELD OF THE INVENTION
[001] The present patent application relates to improved thick wrought 7xxx
aluminum
alloy products and methods for producing the same.
BACKGROUND
[002] Aluminum alloys are useful in a variety of applications. However,
improving one
property of an aluminum alloy without degrading another property is elusive.
For example, it
is difficult to increase the strength of a wrought aluminum alloy without
affecting other
properties such as fracture toughness or corrosion resistance. 7xxx (Al-Zn-Mg
based) are
prone to corrosion. See, e.g., Bonn, W. Grubl, "The stress corrosion behaviour
of high strength
AlZnMg alloys," Paper held at the International Meeting of Associazione
Italiana di
Metallurgie, "Aluminum Alloys in Aircraft Industries," Turin, October 1976.
[003] Patent Owner has described some 7xxx aluminum alloy products in,
inter alia,U U.S.
Patent Nos. 6,972,110, and 8,673,209, and International Patent Application
Publication Nos.
W02016/183030 and W02018/237196.
SUMMARY OF THE DISCLOSURE
[004] Broadly, the present patent application relates to improved thick
wrought 7xxx
aluminum alloy products, and methods for producing the same. The new thick
wrought 7xxx
aluminum alloy products ("the new 7xxx aluminum alloy products") may realize
an improved
combination of environmentally assisted crack (EAC) resistance and at least
one of strength,
elongation, and fracture toughness, among other properties.
[005] The new 7xxx aluminum alloy products generally include (and in some
instances
consist of, or consist essentially of) 5.5-6.5 wt. % Zn, 1.7-2.3 wt. % Cu, and
1.3-1.7 wt. % Mg.
The new wrought 7xxx aluminum alloy products are generally at least 2.5 inches
thick, and
may be up to 12 inches thick, and realize resistance to environmentally
assisted cracking in the
short transverse (ST) direction, which resistance is important for aerospace
and other
applications, especially those with structural loading in the short transverse
(ST) direction.
Such thick, wrought 7xxx aluminum alloy product generally also realize good
strength,
elongation, fracture toughness and/or crack-deviation resistance properties.
Thus, the new
wrought 7xxx aluminum alloy products may realize an improved combination of
environmentally assisted cracking resistance and at least one of strength,
elongation, fracture
toughness and crack-deviation resistance. In addition to zinc, magnesium and
copper, the new
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7xxx aluminum alloy products may include normal grain structure control
materials, grain
refiners, and impurities. For instance, the new 7xxx aluminum alloy products
may include one
or more of Zr, Cr, Sc, and Hf as grain structure control materials (e.g., from
0.05-0.25 wt. %
each of one or more of Zr, Cr, Sc, and Hf), limiting the total amounts of
these elements such
that large primary particles do not form in the alloy. As another example, new
7xxx aluminum
alloy products may include less than 0.15 wt. % Mn. As yet another example,
the new 7xxx
aluminum alloy products may include up to 0.15 wt. % Ti as a grain refiner,
optionally with
some of the titanium in the form of TiB2 and/or TiC. The new 7xxx aluminum
alloy products
may include up to 0.20 wt. % Fe and up to 0.15 wt. % Si as impurities. Lower
amounts of iron
and silicon may be used. The balance of the new 7xxx aluminum alloy products
is generally
aluminum and other unavoidable impurities (other than iron and silicon).
[006] As noted above, the new 7xxx aluminum alloy products generally
include tailored
amounts of zinc, magnesium and copper to facilitate realization of EAC
resistance in
combination with good strength and/or fracture toughness properties, among
others. In this
regard, the new 7xxx aluminum alloy products generally include from 5.5 to 6.5
wt. % Zn. In
one embodiment, a new alloy includes not greater than 6.4 wt. % Zn. In another
embodiment,
a new alloy includes not greater than 6.3 wt. % Zn. In yet another embodiment,
a new alloy
includes not greater than 6.2 wt. % Zn. In one embodiment, a new alloy
includes at least 5.6
wt. % Zn. In another embodiment, a new alloy includes at least 5.7 wt. % Zn.
In yet another
embodiment, a new alloy includes at least 5.8 wt. % Zn. In another embodiment,
a new alloy
includes at least 5.9 wt. % Zn.
[007] As noted above, the new 7xxx aluminum alloy products generally
include from 1.7
to 2.3 wt. % Cu. In one embodiment, a new alloy includes not greater than 2.25
wt. % Cu. In
another embodiment, a new alloy includes not greater than 2.20 wt. % Cu. In
one embodiment,
a new alloy includes at least 1.75 wt. % Cu. In another embodiment, a new
alloy includes at
least 1.80 wt. % Cu. In yet another embodiment, a new alloy includes at least
1.85 wt. % Cu.
In another embodiment, a new alloy includes at least 1.90 wt. % Cu. In yet
another
embodiment, a new alloy includes at least 1.95 wt. % Cu. In another
embodiment, a new alloy
includes at least 2.00 wt. % Cu.
[008] As noted above, the new 7xxx aluminum alloy products generally
include from 1.3
to 1.7 wt. % Mg. In one embodiment, a new alloy includes at least 1.35 wt. %
Mg. In another
embodiment, a new alloy includes at least 1.40 wt. % Mg. In one embodiment, a
new alloy
includes not greater than 1.65 wt. % Mg. In another embodiment, a new alloy
includes not
greater than 1.60 wt. % Mg. In yet another embodiment, a new alloy includes
not greater than
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1.55 wt. % Mg. In another embodiment, a new alloy includes not greater than
1.50 wt. % Mg.
In another embodiment, a new alloy includes not greater than 1.45 wt. % Mg.
[009] In one embodiment, the amounts of zinc, magnesium and copper within
the 7xxx
aluminum alloy product satisfy the relationship: 2.569 < Mg+0.500*Cu+0.067*Zn
< 3.269. In
another embodiment, the amounts of zinc, magnesium and copper within the 7xxx
aluminum
alloy product satisfy the relationship: 2.709 <Mg+0.500*Cu+0.067*Zn <3.119. In
yet another
embodiment, the amounts of zinc, magnesium and copper within the 7xxx aluminum
alloy
product satisfy the relationship: 2.869 < Mg+0.500*Cu+0.067*Zn < 3.269. In
another
embodiment, the amounts of zinc, magnesium and copper within the 7xxx aluminum
alloy
product satisfy the relationship: 2.869 < Mg+0.500*Cu+0.067*Zn < 3.119. Any of
the zinc,
magnesium, and copper amounts described in the preceding paragraphs may be
used in
combination with the above-shown empirical relationships.
[0010] In one approach, the amounts of zinc and magnesium within the 7xxx
aluminum
alloy product are such that the weight ratio of zinc-to-magnesium is not
greater than 4.75:1
(i.e., (wt. % Zn / wt. % Mg) < 4.75:1). In one embodiment, a weight ratio of
zinc-to-magnesium
is not greater than 4.60:1 (i.e., (wt. % Zn / wt. % Mg) < 4.60:1). In another
embodiment, a
weight ratio of zinc-to-magnesium is not greater than 4.50:1 (i.e., (wt. % Zn
/ wt. % Mg) <
4.50:1). In yet another embodiment, a weight ratio of zinc-to-magnesium is not
greater than
4.40:1 (i.e., (wt. % Zn / wt. % Mg) < 4.40:1). In another embodiment, a weight
ratio of zinc-
to-magnesium is not greater than 4.35:1 (i.e., (wt. % Zn / wt. % Mg) <
4.35:1). In yet another
embodiment, a weight ratio of zinc-to-magnesium is not greater than 4.30:1
(i.e., (wt. % Zn /
wt. % Mg) < 4.30:1). In another embodiment, a weight ratio of zinc-to-
magnesium is not
greater than 4.25:1 (i.e., (wt. % Zn / wt. % Mg) < 4.25:1). In yet another
embodiment, a weight
ratio of zinc-to-magnesium is not greater than 4.20:1 (i.e., (wt. % Zn / wt. %
Mg) < 4.20:1). In
another embodiment, a weight ratio of zinc-to-magnesium is not greater than
4.15:1 (i.e., (wt.
% Zn / wt. % Mg) < 4.15:1). In yet another embodiment, a weight ratio of zinc-
to-magnesium
is not greater than 4.10:1 (i.e., (wt. % Zn / wt. % Mg) < 4.10:1). In another
embodiment, a
weight ratio of zinc-to-magnesium is not greater than 4.00:1 (i.e., (wt. % Zn
/ wt. % Mg) <
4.00:1). In yet another embodiment, a weight ratio of zinc-to-magnesium is not
greater than
3.95:1 (i.e., (wt. % Zn / wt. % Mg) < 3.95:1). In another embodiment, a weight
ratio of zinc-
to-magnesium is not greater than 3.90:1 (i.e., (wt. % Zn / wt. % Mg) <
3.90:1).
[0011] In one approach, the amounts of zinc and magnesium within the 7xxx
aluminum
alloy product are such that the weight ratio of zinc-to-magnesium is at least
3.25:1 (i.e., (wt. %
Zn / wt. % Mg) > 3.25:1). In one embodiment, the amounts of zinc and magnesium
within the
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7xxx aluminum alloy product are such that the weight ratio of zinc-to-
magnesium is at least
3.33:1 (i.e., (wt. % Zn / wt. % Mg) > 3.33:1). In another embodiment, the
amounts of zinc and
magnesium within the 7xxx aluminum alloy product are such that the weight
ratio of zinc-to-
magnesium is at least 3.45:1 (i.e., (wt. % Zn / wt. % Mg) > 3.45:1). In
another embodiment,
the amounts of zinc and magnesium within the 7xxx aluminum alloy product are
such that the
weight ratio of zinc-to-magnesium is at least 3.55:1 (i.e., (wt. % Zn / wt. %
Mg) > 3.55:1). In
yet another embodiment, the amounts of zinc and magnesium within the 7xxx
aluminum alloy
product are such that the weight ratio of zinc-to-magnesium is at least 3.60:1
(i.e., (wt. % Zn /
wt. % Mg) > 3.60:1).
[0012] As noted above, the new 7xxx aluminum alloy product may include one
or more of
Zr, Cr, Sc, and Hf as grain structure control materials (e.g., from 0.05-0.25
wt. % each of one
or more of Zr, Cr, Sc, and Hf), limiting the total amounts of these elements
such that large
primary particles do not form in the alloy. Grain structure control materials
may, for instance,
facilitate an appropriate grain structure (e.g., an unrecrystallized grain
structure). When
employed, a new 7xxx aluminum alloy product generally includes at least 0.05
wt. % of the
grain structure control materials. In one embodiment, a new 7xxx aluminum
alloy product
includes at least 0.07 wt. % of the grain structure control materials. In
another embodiment, a
new 7xxx aluminum alloy product includes at least 0.09 wt. % of the grain
structure control
materials. When employed, a new 7xxx aluminum alloy product generally includes
not greater
than 1.0 wt. % of the grain structure control materials. In one embodiment, a
new 7xxx
aluminum alloy product includes not greater than 0.75 wt. % of the grain
structure control
materials. In yet another embodiment, a new 7xxx aluminum alloy product
includes not greater
than 0.50 wt. % of the grain structure control materials. In one embodiment,
the grain structure
control materials are selected from the group consisting of Zr, Cr, Sc, and
Hf. In another
embodiment, the grain structure control materials are selected from the group
consisting of Zr
and Cr. In another embodiment, the grain structure control material is Zr. In
another
embodiment, the grain structure control material is Cr.
[0013] In one embodiment, the grain structure control materials comprise
both Zr and Cr,
and a new 7xxx aluminum alloy product includes at least 0.07 wt. % Zr and at
least 0.07 wt. %
Cr, wherein the wt. % Zr plus the wt. % Cr is not greater than 0.40 wt. %
(i.e., wt. % Zr + wt.
% Cr < 0.40 wt. %). In another embodiment, the grain structure control
materials comprise
both Zr and Cr, and a new 7xxx aluminum alloy product includes at least 0.07
wt. % Zr and at
least 0.07 wt. % Cr, wherein the wt. % Zr plus the wt. % Cr is not greater
than 0.35 wt. % (i.e.,
wt. % Zr + wt. % Cr < 0.35 wt. %). In another embodiment, the grain structure
control materials
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comprise both Zr and Cr, and a new 7xxx aluminum alloy product includes at
least 0.07 wt. %
Zr and at least 0.07 wt. % Cr, wherein the wt. % Zr plus the wt. % Cr is not
greater than 0.30
wt. % (i.e., wt. % Zr + wt. % Cr < 0.30 wt. %). In another embodiment, the
grain structure
control materials comprise both Zr and Cr, and a new 7xxx aluminum alloy
product includes
at least 0.07 wt. % Zr and at least 0.07 wt. % Cr, wherein the wt. % Zr plus
the wt. % Cr is not
greater than 0.25 wt. % (i.e., wt. % Zr + wt. % Cr < 0.25 wt. %). In another
embodiment, the
grain structure control materials comprise both Zr and Cr, and a new 7xxx
aluminum alloy
product includes at least 0.07 wt. % Zr and at least 0.07 wt. % Cr, wherein
the wt. % Zr plus
the wt. % Cr is not greater than 0.20 wt. % (i.e., wt. % Zr + wt. % Cr < 0.20
wt. %). In any of
these embodiment, a new 7xxx aluminum alloy product may include at least 0.09
wt. % of at
least one of Zr and Cr. In any of these embodiments, a new 7xxx aluminum alloy
product may
include at least 0.09 wt. % of both Zr and Cr.
[0014] In one embodiment, the grain structure control material is Zr, and a
new 7xxx
aluminum alloy product includes from 0.07 to 0.18 wt. % Zr. In another
embodiment, the grain
structure control material is Zr, and a new 7xxx aluminum alloy product
includes from 0.07 to
0.16 wt. % Zr. In yet another embodiment, the grain structure control material
is Zr, and a new
7xxx aluminum alloy product includes from 0.08 to 0.15 wt. % Zr. In another
embodiment,
the grain structure control material is Zr, and a new 7xxx aluminum alloy
product includes
from 0.09 to 0.14 wt. % Zr. In embodiments where the grain structure control
material is Zr, a
new 7xxx aluminum alloy product generally contains low amounts of the Cr, Sc,
and Hf (e.g.,
<0.04 wt. % each of Cr, Sc, and Hf.). In one embodiment, a new 7xxx aluminum
alloy product
contains not greater than 0.03 wt. % each of Cr, Sc, and Hf. In another
embodiment, a new
7xxx aluminum alloy product contains not greater than 0.02 wt. % each of Cr,
Sc, and Hf. In
another embodiment, a new 7xxx aluminum alloy product contains not greater
than 0.01 wt. %
each of Cr, Sc, and Hf. In another embodiment, a new 7xxx aluminum alloy
product contains
not greater than 0.005 wt. % each of Cr, Sc, and Hf.
[0015] In one embodiment, the grain structure control material is Cr, and a
new 7xxx
aluminum alloy product includes from 0.07 to 0.25 wt. % Cr. In another
embodiment, the grain
structure control material is Cr, and a new 7xxx aluminum alloy product
includes from 0.07 to
0.20 wt. % Cr. In yet another embodiment, the grain structure control material
is Cr, and a new
7xxx aluminum alloy product includes from 0.08 to 0.15 wt. % Cr. In another
embodiment,
the grain structure control material is Cr, and a new 7xxx aluminum alloy
product includes
from 0.10 to 0.15 wt. % Cr. In other embodiments, a new 7xxx aluminum alloy
product
contains low amounts of Cr (e.g., < 0.04 wt. % Cr.) In one embodiment, a new
7xxx aluminum
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alloy product contains not greater than 0.03 wt. % Cr. In another embodiment,
a new 7xxx
aluminum alloy product contains not greater than 0.02 wt. % Cr. In yet another
embodiment,
a new 7xxx aluminum alloy product contains not greater than 0.01 wt. % Cr. In
another
embodiment, a new 7xxx aluminum alloy product contains not greater than 0.005
wt. % Cr.
[0016] In some embodiments, a new 7xxx aluminum alloy includes low amounts
of
zirconium (e.g., < 0.04 wt. % Zr). In one embodiment, a new 7xxx aluminum
alloy product
contains not greater than 0.03 wt. % Zr. In another embodiment, a new 7xxx
aluminum alloy
product contains not greater than 0.02 wt. % Zr. In yet another embodiment, a
new 7xxx
aluminum alloy product contains not greater than 0.01 wt. % Zr. In another
embodiment, a
new 7xxx aluminum alloy product contains not greater than 0.005 wt. % Zr.
[0017] As noted above, the new 7xxx aluminum alloy product generally
includes less than
0.15 wt. % Mn. In one embodiment, a new 7xxx aluminum alloy product includes
not greater
than 0.12 wt. % Mn. In another embodiment, a new 7xxx aluminum alloy product
includes not
greater than 0.10 wt. % Mn. In yet another embodiment, a new 7xxx aluminum
alloy product
includes not greater than 0.08 wt. % Mn. In another embodiment, a new 7xxx
aluminum alloy
product includes not greater than 0.05 wt. % Mn. In yet another embodiment, a
new 7xxx
aluminum alloy product includes not greater than 0.04 wt. % Mn. In another
embodiment, a
new 7xxx aluminum alloy product includes not greater than 0.03 wt. % Mn. In
yet another
embodiment, a new 7xxx aluminum alloy product includes not greater than 0.02
wt. % Mn. In
another embodiment, a new 7xxx aluminum alloy product includes not greater
than 0.01 wt. %
Mn.
[0018] As noted above, the new 7xxx aluminum alloy product may include up
to 0.15 wt.
% Ti. Titanium may be used to facilitate grain refining during casting, such
as by using TiB2
or TiC. Elemental titanium may also or alternatively be used. In one
embodiment, the new
7xxx aluminum alloy product includes from 0.005 to 0.025 wt. % Ti.
[0019] As noted above, the new 7xxx aluminum alloy product may include up
to 0.15 wt.
% Si and up to 0.20 wt. % Fe as impurities. The amount of silicon and iron may
be limited so
as to avoid detrimentally impacting the combination of strength, fracture
toughness and crack
deviation resistance. In one embodiment, the new 7xxx aluminum alloy product
may include
up to 0.12 wt. % Si and up to 0.15 wt. % Fe as impurities. In another
embodiment, the new
7xxx aluminum alloy product may include up to 0.10 wt. % Si and up to 0.12 wt.
% Fe as
impurities. In another embodiment, the new 7xxx aluminum alloy product may
include up to
0.08 wt. % Si and up to 0.10 wt. % Fe as impurities. In yet another
embodiment, the new 7xxx
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aluminum alloy product may include up to 0.06 wt. % Si and up to 0.08 wt. % Fe
as impurities.
In yet another embodiment, the new 7xxx aluminum alloy product may include up
to 0.04 wt.
% Si and up to 0.06 wt. % Fe as impurities. In another embodiment, the new
7xxx aluminum
alloy product may include up to 0.03 wt. % Si and up to 0.05 wt. % Fe as
impurities.
[0020] As noted above, the new 7xxx aluminum alloy product has a thickness
of from 2.5
to 12.0 inches. Thickness refers to the cross sectional thickness of the
product at its thickest
point. In one embodiment, a new 7xxx aluminum alloy product has a thickness of
at least 3.0
inches. In another embodiment, a new 7xxx aluminum alloy product has a
thickness of at least
3.5 inches. In yet another embodiment, a new 7xxx aluminum alloy product has a
thickness of
at least 4.0 inches. In another embodiment, a new 7xxx aluminum alloy product
has a thickness
of at least 4.5 inches. In yet another embodiment, a new 7xxx aluminum alloy
product has a
thickness of at least 5.0 inches. In one embodiment, a new 7xxx aluminum alloy
product has
a thickness of not greater than 10.0 inches. In another embodiment, a new 7xxx
aluminum
alloy product has a thickness of not greater than 9.0 inches. In yet another
embodiment, a new
7xxx aluminum alloy product has a thickness of not greater than 8.0 inches.
[0021] In one embodiment, a new 7xxx aluminum alloy product is a rolled
product (e.g., a
plate product). In another embodiment, a new 7xxx aluminum alloy product is an
extruded
product. In yet another embodiment, a new 7xxx aluminum alloy product is a
forged product
(e.g., a hand forged product, a die forged product).
[0022] As mentioned above, the new 7xxx aluminum alloy products may realize
an
improved combination of properties. In one embodiment, a new 7xxx aluminum
alloy product
realizes a typical tensile yield strength (L) of at least 63 ksi as per ASTM
E8 and B557. In
another embodiment, a new 7xxx aluminum alloy product realizes a typical
tensile yield
strength (L) of at least 64 ksi. In yet another embodiment, a new 7xxx
aluminum alloy product
realizes a typical tensile yield strength (L) of at least 65 ksi. In another
embodiment, a 7xxx
aluminum alloy product may realize a typical tensile yield strength (L) of at
least 66 ksi. In
yet another embodiment, a 7xxx aluminum alloy product may realize a typical
tensile yield
strength (L) of at least 67 ksi. In another embodiment, a 7xxx aluminum alloy
product may
realize a typical tensile yield strength (L) of at least 68 ksi. In yet
another embodiment, a 7xxx
aluminum alloy product may realize a typical tensile yield strength (L) of at
least 69 ksi. In
another embodiment, a 7xxx aluminum alloy product may realize a typical
tensile yield
strength (L) of at least 70 ksi. In yet another embodiment, a 7xxx aluminum
alloy product may
realize a typical tensile yield strength (L) of at least 71 ksi. In another
embodiment, a 7xxx
aluminum alloy product may realize a typical tensile yield strength (L) of at
least 72 ksi. In
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yet another embodiment, a 7xxx aluminum alloy product may realize a typical
tensile yield
strength (L) of at least 73 ksi.
[0023] In one embodiment, a new 7xxx aluminum alloy product realizes a
typical tensile
yield strength (ST) of at least 57 ksi as per ASTM E8 and B557. In another
embodiment, a
7xxx aluminum alloy product may realize a typical tensile yield strength (ST)
of at least 58 ksi.
In yet another embodiment, a 7xxx aluminum alloy product may realize a typical
tensile yield
strength (ST) of at least 59 ksi. In another embodiment, a 7xxx aluminum alloy
product may
realize a typical tensile yield strength (ST) of at least 60 ksi. In yet
another embodiment, a
7xxx aluminum alloy product may realize a typical tensile yield strength (ST)
of at least 61 ksi.
In another embodiment, a 7xxx aluminum alloy product may realize a typical
tensile yield
strength (ST) of at least 62 ksi. In yet another embodiment, a 7xxx aluminum
alloy product
may realize a typical tensile yield strength (ST) of at least 63 ksi. In
another embodiment, a
7xxx aluminum alloy product may realize a typical tensile yield strength (ST)
of at least 64 ksi.
In yet another embodiment, a 7xxx aluminum alloy product may realize a typical
tensile yield
strength (ST) of at least 65 ksi. In another embodiment, a 7xxx aluminum alloy
product may
realize a typical tensile yield strength (ST) of at least 66 ksi.
[0024] In one embodiment, a new 7xxx aluminum alloy product realizes a
typical Kw
plane-strain fracture toughness (L-T) of at least 25 ksi-sqrt-inch as per ASTM
E8 and E399-
12. In yet another embodiment, a new 7xxx aluminum alloy product realizes a
typical Kw
plane-stain fracture toughness (L-T) of at least 27 ksi-sqrt-inch. In another
embodiment, a new
7xxx aluminum alloy product realizes a typical Kw plane-stain fracture
toughness (L-T) of at
least 28 ksi-sqrt-inch. In yet another embodiment, a new 7xxx aluminum alloy
product realizes
a typical Kw plane-stain fracture toughness (L-T) of at least 29 ksi-sqrt-
inch. In another
embodiment, a new 7xxx aluminum alloy product realizes a typical Kw plane-
stain fracture
toughness (L-T) of at least 30 ksi-sqrt-inch. In yet another embodiment, a new
7xxx aluminum
alloy product realizes a typical Kw plane-stain fracture toughness (L-T) of at
least 31 ksi-sqrt-
inch. In another embodiment, a new 7xxx aluminum alloy product realizes a
typical Kw plane-
stain fracture toughness (L-T) of at least 32 ksi-sqrt-inch. In yet another
embodiment, a new
7xxx aluminum alloy product realizes a typical Kw plane-stain fracture
toughness (L-T) of at
least 33 ksi-sqrt-inch. In another embodiment, a new 7xxx aluminum alloy
product realizes a
typical Kw plane-stain fracture toughness (L-T) of at least 34 ksi-sqrt-inch.
In yet another
embodiment, a new 7xxx aluminum alloy product realizes a typical Kw plane-
stain fracture
toughness (L-T) of at least 35 ksi-sqrt-inch. In another embodiment, a new
7xxx aluminum
alloy product realizes a typical Kw plane-stain fracture toughness (L-T) of at
least 36 ksi-sqrt-
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inch. In yet another embodiment, a new 7xxx aluminum alloy product realizes a
typical Kw
plane-stain fracture toughness (L-T) of at least 37 ksi-sqrt-inch. In another
embodiment, a new
7xxx aluminum alloy product realizes a typical Kw plane-stain fracture
toughness (L-T) of at
least 38 ksi-sqrt-inch. In yet another embodiment, a new 7xxx aluminum alloy
product realizes
a typical Kw plane-stain fracture toughness (L-T) of at least 39 ksi-sqrt-
inch. In another
embodiment, a new 7xxx aluminum alloy product realizes a typical Kw plane-
stain fracture
toughness (L-T) of at least 40 ksi-sqrt-inch. In yet another embodiment, a new
7xxx aluminum
alloy product realizes a typical Kw plane-stain fracture toughness (L-T) of at
least 41 ksi-sqrt-
inch. In another embodiment, a new 7xxx aluminum alloy product realizes a
typical Kw plane-
stain fracture toughness (L-T) of at least 42 ksi-sqrt-inch. In yet another
embodiment, a new
7xxx aluminum alloy product realizes a typical Kw plane-stain fracture
toughness (L-T) of at
least 43 ksi-sqrt-inch. In another embodiment, a new 7xxx aluminum alloy
product realizes a
typical Kw plane-stain fracture toughness (L-T) of at least 44 ksi-sqrt-inch.
In yet another
embodiment, a new 7xxx aluminum alloy product realizes a typical Kw plane-
stain fracture
toughness (L-T) of at least 45 ksi-sqrt-inch.
[0025] In one embodiment, a new 7xxx aluminum alloy product realizes a
typical Kw
plane-strain fracture toughness (S-L) of at least 20 ksi-sqrt-inch as per ASTM
E8 and E399-
12. In another embodiment, a new 7xxx aluminum alloy product realizes a
typical Kw plane-
strain fracture toughness (S-L) of at least 22 ksi-sqrt-inch. In another
embodiment, a new 7xxx
aluminum alloy product realizes a typical Kw plane-strain fracture toughness
(S-L) of at least
24 ksi-sqrt-inch. In another embodiment, a new 7xxx aluminum alloy product
realizes a typical
Kw plane-strain fracture toughness (S-L) of at least 26 ksi-sqrt-inch. In
another embodiment,
a new 7xxx aluminum alloy product realizes a typical Kw plane-strain fracture
toughness (S-
L) of at least 28 ksi-sqrt-inch. In another embodiment, a new 7xxx aluminum
alloy product
realizes a typical Kw plane-strain fracture toughness (S-L) of at least 30 ksi-
sqrt-inch. In
another embodiment, a new 7xxx aluminum alloy product realizes a typical Kw
plane-strain
fracture toughness (S-L) of at least 32 ksi-sqrt-inch. In another embodiment,
a new 7xxx
aluminum alloy product realizes a typical Kw plane-strain fracture toughness
(S-L) of at least
34 ksi-sqrt-inch. In another embodiment, a new 7xxx aluminum alloy product
realizes a typical
Kw plane-strain fracture toughness (S-L) of at least 36 ksi-sqrt-inch. In
another embodiment, a
new 7xxx aluminum alloy product realizes a typical Kw plane-strain fracture
toughness (S-L)
of at least 38 ksi-sqrt-inch. In another embodiment, a new 7xxx aluminum alloy
product
realizes a typical Kw plane-strain fracture toughness (S-L) of at least 40 ksi-
sqrt-inch.
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[0026] In one embodiment, a new 7xxx aluminum alloy product realizes a
typical
elongation (L) of at least 6% as per ASTM E8 and B557. In another embodiment,
a new 7xxx
aluminum alloy product realizes a typical elongation (L) of at least 7%. In
yet another
embodiment, a new 7xxx aluminum alloy product realizes a typical elongation
(L) of at least
8%. In another embodiment, a new 7xxx aluminum alloy product realizes a
typical elongation
(L) of at least 9%. In yet another embodiment, a new 7xxx aluminum alloy
product realizes a
typical elongation (L) of at least 10%. In another embodiment, a new 7xxx
aluminum alloy
product realizes a typical elongation (L) of at least 11%. In yet another
embodiment, a new
7xxx aluminum alloy product realizes a typical elongation (L) of at least 12%.
In another
embodiment, a new 7xxx aluminum alloy product realizes a typical elongation
(L) of at least
13%. In yet another embodiment, a new 7xxx aluminum alloy product realizes a
typical
elongation (L) of at least 14%. In another embodiment, a new 7xxx aluminum
alloy product
realizes a typical elongation (L) of at least 15%. In yet another embodiment,
a new 7xxx
aluminum alloy product realizes a typical elongation (L) of at least 16%.
[0027] In one embodiment, a new 7xxx aluminum alloy product realizes a
typical
elongation (ST) of at least 3% as per ASTM E8 and B557. In another embodiment,
a new 7xxx
aluminum alloy product realizes a typical elongation (ST) of at least 4%. In
yet another
embodiment, a new 7xxx aluminum alloy product realizes a typical elongation
(ST) of at least
5%. In another embodiment, a new 7xxx aluminum alloy product realizes a
typical elongation
(ST) of at least 6%. In yet another embodiment, a new 7xxx aluminum alloy
product realizes
a typical elongation (ST) of at least 7%. In another embodiment, a new 7xxx
aluminum alloy
product realizes a typical elongation (ST) of at least 8%. In yet another
embodiment, a new
7xxx aluminum alloy product realizes a typical elongation (ST) of at least 9%.
In another
embodiment, a new 7xxx aluminum alloy product realizes a typical elongation
(ST) of at least
10%.
[0028] In one embodiment, a new 7xxx aluminum alloy product realizes a
typical L-S crack
deviation resistance (Kmax-dev) of at least 25 ksi-sqrt-in. In another
embodiment, a new 7xxx
aluminum alloy product realizes a typical L-S crack deviation resistance (Kmax-
dev) of at least
27 ksi-sqrt-in. In yet another embodiment, a new 7xxx aluminum alloy product
realizes a
typical L-S crack deviation resistance (Kmax-dev) of at least 29 ksi-sqrt-in.
In another
embodiment, a new 7xxx aluminum alloy product realizes a typical L-S crack
deviation
resistance (Kmax-dev) of at least 31 ksi-sqrt-in. In yet another embodiment, a
new 7xxx
aluminum alloy product realizes a typical L-S crack deviation resistance (Kmax-
dev) of at least
33 ksi-sqrt-in. In another embodiment, a new 7xxx aluminum alloy product
realizes a typical
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L-S crack deviation resistance (Kmax-dev) of at least 35 ksi-sqrt-in. In yet
another embodiment,
a new 7xxx aluminum alloy product realizes a typical L-S crack deviation
resistance (Kmax-dev)
of at least 37 ksi-sqrt-in. In another embodiment, a new 7xxx aluminum alloy
product realizes
a typical L-S crack deviation resistance (Kmax-dev) of at least 39 ksi-sqrt-
in. In yet another
embodiment, a new 7xxx aluminum alloy product realizes a typical L-S crack
deviation
resistance (Kmax-dev) of at least 41 ksi-sqrt-in. In another embodiment, a new
7xxx aluminum
alloy product realizes a typical L-S crack deviation resistance (Kmax-dev) of
at least 43 ksi-sqrt-
in. In yet another embodiment, a new 7xxx aluminum alloy product realizes a
typical L-S crack
deviation resistance (Kmax-dev) of at least 45 ksi-sqrt-in. In another
embodiment, a new 7xxx
aluminum alloy product realizes a typical L-S crack deviation resistance (Kmax-
dev) of at least
47 ksi-sqrt-in. In yet another embodiment, a new 7xxx aluminum alloy product
realizes a
typical L-S crack deviation resistance (Kmax-dev) of at least 49 ksi-sqrt-in.
In another
embodiment, a new 7xxx aluminum alloy product realizes a typical L-S crack
deviation
resistance (Kmax-dev) of at least 50 ksi-sqrt-in.
[0029] As noted above, the new 7xxx aluminum alloys may be EAC resistant,
which EAC
resistance may be determined by Hot and Humid SCC testing. In one embodiment,
a new 7xxx
aluminum alloy product has a thickness of at least 63.5 mm and passes Hot and
Humid SCC
(stress corrosion cracking) testing using standard stress-corrosion tension
test specimens
conforming to ASTM G49, as defined below ("HHSCC-G49"). To create the HHSCC-
G49
test specimens, at least three short transverse (ST) samples are taken from
mid-thickness of the
final product and between W/4 and 3W/4 of the final product. The extracted
specimens are
then machined into tensile specimens with a diameter as defined in ASTM G47-20
and
dimensions proportional to the standard specimen as defined in ASTM E8/8M-
16ael. If the
final product thickness is at least 2.25 inches (57.15 mm), then the length of
the tensile
specimen is 2.00 inches (50.8 mm), as shown in FIG. 2. If the final product
thickness is from
1.50 inches (38.1 mm) to less than 2.25 inches (< 50.8 mm), the length of the
specimen must
be at least 1.25 inches (31.75 mm) and should be as close to 2.00 inches (50.8
mm) as possible.
Prior to testing the tensile specimens are to be cleaned / degreased by
washing in acetone. The
tensile specimens are then strained in the short-transverse direction at 85%
of their ST tensile
yield strength at T/2. The alloy's ST tensile yield strength is measured at
room temperature
and in accordance with ASTM E8 and B557 prior to the HHSCC-G49 testing. The
stressing
frame used is a constant strain type per ASTM G49, section 7.2.2 (see, e.g.,
FIG. 4a of ASTM
G49). The strained specimens are then placed into a controlled cabinet having
air at 85%
relative humidity (without additions to the air, such as chlorides) and a
temperature of 70 C or
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90 C. At least three specimens must be tested. For purposes of this patent
application, an alloy
passes HEISCC-G49 testing at 70 C when all specimens survive at least 100
days. For
purposes of this patent application, an alloy passes HEISCC-G49 testing at 90
C when all
specimens survive at least 10 days. A failure is when the specimen breaks into
two halves,
either along the gauge length or at one of the specimen shoulders adjoining
the gauge length.
Shoulder failures are statistically equivalent to gauge length failures.
Thread failures are only
included when they are statistically equivalent to the gauge length failures
when determining
whether an alloy passes HEISCC-G49. A thread failure is when a crack occurs in
a threaded
end of a specimen as opposed to in the gauge length. In some instance, thread
failures may not
be detectable until the specimen is removed from the stressing frame.
[0030] In one approach, the HEISCC-G49 testing is conducted at 70 C and a
new 7xxx
aluminum alloy product passes 120 days of HEISCC-G49 testing at 70 C, wherein
all samples
survive 120 days of the HEISCC-G49 test defined above. In one embodiment, a
new 7xxx
aluminum alloy product passes 140 days of HEISCC-G49 testing at 70 C, wherein
all samples
survive 140 days of the HEISCC-G49 test defined above. In yet another
embodiment, a new
7xxx aluminum alloy product passes 150 days of HEISCC-G49 testing at 70 C,
wherein all
samples survive 150 days of the HEISCC-G49 test defined above. In another
embodiment, a
new 7xxx aluminum alloy product passes 160 days of HEISCC-G49 testing at 70 C,
wherein
all samples survive 160 days of the HEISCC-G49 test defined above. In yet
another
embodiment, a new 7xxx aluminum alloy product passes 180 days of HEISCC-G49
testing at
70 C, wherein all samples survive 180 days of the HEISCC-G49 test defined
above. In another
embodiment, a new 7xxx aluminum alloy product passes 200 days of HEISCC-G49
testing at
70 C, wherein all samples survive 200 days of the HEISCC-G49 test defined
above. In yet
another embodiment, a new 7xxx aluminum alloy product passes 220 days of
HEISCC-G49
testing at 70 C, wherein all samples survive 220 days of the HEISCC-G49 test
defined above.
In another embodiment, a new 7xxx aluminum alloy product passes 240 days of
HEISCC-G49
testing at 70 C, wherein all samples survive 240 days of the HEISCC-G49 test
defined above.
In yet another embodiment, a new 7xxx aluminum alloy product passes 260 days
of 1-11-1SCC-
G49 testing at 70 C, wherein all samples survive 260 days of the HEISCC-G49
test defined
above. In another embodiment, a new 7xxx aluminum alloy product passes 280
days of
HEISCC-G49 testing at 70 C, wherein all samples survive 280 days of the HEISCC-
G49 test
defined above. In yet another embodiment, a new 7xxx aluminum alloy product
passes 300
days of HEISCC-G49 testing at 70 C, wherein all samples survive 300 days of
the 1-11-1SCC-
G49 test defined above. The above stress corrosion cracking resistance
properties may be
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realized in products having a thickness of at least 80 mm, or at least 100 mm,
at least 120 mm,
or at least 140 mm, or higher.
[0031] In another approach, the HHSCC-G49 testing is conducted at 90 C and
a new 7xxx
aluminum alloy product passes 15 days of HHSCC-G49 testing at 90 C, wherein
all samples
survive 15 days of the HHSCC-G49 test defined above. In one embodiment, a new
7xxx
aluminum alloy product passes 20 days of HHSCC-G49 testing at 90 C, wherein
all samples
survive 20 days of the HHSCC-G49 test defined above. In another embodiment, a
new 7xxx
aluminum alloy product passes 25 days of HHSCC-G49 testing at 90 C, wherein
all samples
survive 25 days of the HHSCC-G49 test defined above. The above stress
corrosion cracking
resistance properties may be realized in products having a thickness of at
least 80 mm, or at
least 100 mm, at least 120 mm, or at least 140 mm, or higher.
[0032] In one embodiment, a new 7xxx aluminum alloy product has a thickness
of at least
63.5 mm and passes stress corrosion cracking, per ASTM G47 using standard
stress-corrosion
tension test specimens conforming to ASTM G49 under alternate immersion
exposure
conditions per ASTM G44 ("SCC alternate immersion testing"). For purposes of
this patent
application, a new 7xxx aluminum alloy passes SCC alternate immersion testing
when all
samples survive 20 days of the SCC alternate immersion testing at a net stress
of 172 MPa in
the ST direction, where the test environment is 3.5% NaCl, and with a minimum
of five (5)
samples required to be tested. In one embodiment, a new 7xxx aluminum alloy
passes 30 days
of SCC alternate immersion testing, as defined above. In another embodiment, a
new 7xxx
aluminum alloy passes 20 days of SCC alternate immersion testing, as defined
above, but at a
net stress of 241 MPa. In yet another embodiment, a new 7xxx aluminum alloy
passes 30 days
of SCC alternate immersion testing, as defined above, but at a net stress of
241 MPa. The
above stress corrosion cracking resistance properties may be realized in
products having a
thickness of at least 80 mm, or at least 100 mm, at least 120 mm, or at least
140 mm, or higher.
[0033] In one embodiment, a new 7xxx aluminum alloy product has a thickness
of at least
63.5 mm and passes Hot and Humid SCC (stress corrosion cracking) testing under
ASTM
G168, as defined below ("HHSCC-G168"). For purpose of this patent application,
a new 7xxx
aluminum alloy passes HHSCC-G168 testing when (a) the stress intensity factor
gives a crack
growth rate of not greater than 10-7 mm/s, and (b) the realized K value is at
least 13 MPa-sqrt-
m (MPaAim). The HHSCC-G168 testing is to be conducted at 70 C and 85% relative
humidity,
at T/2 and with S-L specimens. In one embodiment, the realized K value is at
least 14 MPa-
sqrt-m at a crack growth rate of not greater than 10-7 mm/s. In another
embodiment, the realized
K value is at least 15 MPa-sqrt-m at a crack growth rate of not greater than
10-7 mm/s. In yet
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another embodiment, the realized K value is at least 16 MPa-sqrt-m at a crack
growth rate of
not greater than 10' mm/s. In another embodiment, the realized K value is at
least 17 MPa-
sqrt-m at a crack growth rate of not greater than 10' mm/s. In yet another
embodiment, the
realized K value is at least 18 MPa-sqrt-m, or higher, at a crack growth rate
of not greater than
10' mm/s. The above stress corrosion cracking resistance properties may be
realized in
products having a thickness of at least 80 mm, or at least 100 mm, at least
120 mm, or at least
140 mm, or higher.
[0034] In one embodiment, a new 7xxx aluminum alloy product passes at least
two of the
above-defined SCC tests (i.e., at least two of: (a) the HHSCC-G49 test, as
defined above, (b)
the SCC alternate immersion test, as defined above, and (c) the HHSCC-G168
test, as defined
above). In another embodiment, a new 7xxx aluminum alloy passes all of the
above-defined
SCC tests.
[0035] While the above L and ST properties generally relate to thick plate
products, similar
properties may also be realized in thick forged product and thick extruded
products. Further,
many of the above properties may be realized in combination, as shown by the
below examples.
[0036] As noted above, the new thick 7xxx aluminum alloy products may be
suitable for
parts in various aerospace applications. In one embodiment, the alloy product
is an aerospace
structural component. The aircraft structural component may be any of an upper
wing panel
(skin), an upper wing stringer, an upper wing cover with integral stringers, a
spar, a spar cap,
a spar web, a rib, rib feet or a rib web, stiffening elements, frames, a
landing gear component
(e.g., a cylinders, beams), drag braces, bulkheads, flap track assemblies,
fuselage and
windshield frames, gear ribs, side stays, fittings, a fuselage component
(e.g., a fuselage skin),
and space components (e.g., for rockets and other vehicles that may exit the
earth). In one
embodiment, the alloy product is an armor component (e.g., of a motorized
vehicle). In one
embodiment, the alloy product is used in the oil and gas industry (e.g., as
pipes, structural
components). In one embodiment, the alloy product is a thick mold block / mold
plate product
(e.g., for injection molding). In one embodiment, the alloy product is an
automotive product.
[0037] The new thick 7xxx aluminum alloy products may be made into wrought
products
by casting an aluminum alloy having any of the aforementioned compositions
into an ingot or
billet, followed by homogenizing of the ingot or billet. The homogenized ingot
or billet may
be worked by rolling, extruding, or forging to final gauge, generally by hot
working, optionally
with some cold working. The final gauge product may be solution heat treated,
and then
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quenched, and then stress relieved (e.g., by stretching or compression) and
then artificially
aged.
[0038] Aside from traditional wrought products, the new 7xxx aluminum
alloys may be
made into shape castings or by additive manufacturing into additively
manufactured products.
The additively manufactured products may be used as-is, or may be subsequently
processed,
e.g., processed via mechanical, thermal, or thermomechanical treatment.
Definitions
[0039] As used herein, "typical longitudinal (L) tensile yield strength" or
TYS(L) is
determined in accordance with ASTM B557-10 and by measuring the tensile yield
strength
(TYS) in the longitudinal direction (L) at the T/4 location from at least
three different lots of
material, and with at least duplicate specimens being tested for each lot, for
a total of at least 6
different measured specimen values, with the typical TYS(L) being the average
of the at least
6 different measured specimen values. Typical elongation (L) is measured
during longitudinal
tensile testing.
[0040] As used herein, "typical longitudinal (ST) tensile yield strength"
or TYS(ST) is
determined in accordance with ASTM B557-10 and by measuring the tensile yield
strength
(TYS) in the short transverse direction (ST) from at least three different
lots of material, and
with at least duplicate specimens being tested for each lot, for a total of at
least 6 different
measured specimen values, with the typical TYS(ST) being the average of the at
least 6
different measured specimen values. Short transverse tensile specimens are
taken so that the
midpoint of the gage section coincides with the plate mid-thickness plane.
Typical elongation
(ST) is measured during short transverse tensile testing.
[0041] As used herein, "typical plane strain fracture toughness (Kw) (L-T)"
is determined
in accordance with ASTM E399-12, by measuring the plane strain fracture
toughness in the L-
T direction at the T/4 location from at least three different lots of material
using a C(T)
specimen, where "W" is 4.0 inches, and where "B" is 2.0 inches for products
having a thickness
of at least 2.0 inches and where "B" is 1.5 inches for products having a
thickness less than 2.0
inches, with at least duplicate specimens being tested for each lot, for a
total of at least 6
different measured specimen values, and with the typical plane strain fracture
toughness (Kw)
(L-T) being the average of the at least 6 different valid Kw measured specimen
values.
[0042] As used herein, "typical plane strain fracture toughness (Kw) (S-L)"
is determined
in accordance with ASTM E399-12, by measuring the plane strain fracture
toughness in the S-
L direction at the T/2 location from at least three different lots of material
using a C(T)
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specimen, where "W" and "B" are per the below table, with at least duplicate
specimens being
tested for each lot, for a total of at least 6 different measured specimen
values, and with the
typical plane strain fracture toughness (Kw) (S-L) being the average of the at
least 6 different
valid Kw measured specimen values.
S-L specimen parameters
Product Thickness "W" "B"
> 5.0 inches 4.0 inches 2.0 inches
<5.0 inches to > 3.8 inches 3.0 inches 1.5 inches
<3.8 inches to > 3.2 inches 2.5 inches 1.25 inches
<3.2 inches to > 2.6 inches 2.0 inches 1.0 inches
<2.6 inches to > 2.0 inches 1.5 inches 0.75 inches
<2.0 inches to > 1.5 inches 1.0 inches 0.5 inches
[0043] The typical L-S crack deviation resistance properties (Kinax_dev)
are to be determined
per the procedure described in commonly-owned U.S. Patent Application
Publication No.
2017/0088920, paragraph 0058, which procedure is incorporated herein by
reference, except:
(a) the "W" dimension of the specimen shall be 2.0 inches (5.08 cm), (b) the
specimen shall be
centered at T/2 (as opposed to the notch tip), and (c) the test specimens may
be tested in lab air
as opposed to high humidity air.
[0044] The term "square root" may be abbreviated herein as "sqrt."
[0045] Throughout the specification and claims, the following terms take
the meanings
explicitly associated herein, unless the context clearly dictates otherwise.
The phrases "in one
embodiment" and "in some embodiments" as used herein do not necessarily refer
to the same
embodiment(s), though they may. Furthermore, the phrases "in another
embodiment" and "in
some other embodiments" as used herein do not necessarily refer to a different
embodiment,
although they may. Thus, as described below, various embodiments of the
invention may be
readily combined, without departing from the scope or spirit of the invention.
[0046] In addition, as used herein, the term "or" is an inclusive "or"
operator, and is
equivalent to the term "and/or," unless the context clearly dictates
otherwise. The term "based
on" is not exclusive and allows for being based on additional factors not
described, unless the
context clearly dictates otherwise. In addition, throughout the specification,
the meaning of
"a," "an," and "the" include plural references, unless the context clearly
dictates
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otherwise. The meaning of "in" includes "in" and "on", unless the context
clearly dictates
otherwise.
BRIEF DESCRIPTION OF THE DRAWINGS
[0047] FIG. 1 is a graph illustrating the strength versus Kw fracture
toughness properties
for the Example 1 alloys.
[0048] FIG. 2 is a graph illustrating the strength versus EAC resistance
for the Example 1
alloys.
DETAILED DESCRIPTION
[0049] Example 1
[0050] Two aluminum alloys were cast as 6 x 18-inch (D x W) ingots, the
compositions of
which are provided in Table 1, below.
Table 1 ¨ Composition of Example 1 Alloys (wt. %)
Alloy Si Fe Zn Mg Cu Zr Mn Cr Ti
1 0.05 0.05 5.88 1.60 2.17 0.10 0.02 0.02 0.02
2 0.02 0.06 5.98 1.50 2.12 0.10 -- -- 0.02
The ingots were then conventionally prepared for homogenization (e.g. by
sawing and
scalping). The first ingot was then processed to its final temper as per
Japanese Patent No.
H03-41540 (1991), Example 1, Alloy 4.1 The second ingot was processed
according to the
inventive processes disclosed herein.
[0051] Specifically, Alloy 1 was homogenized at 842 F (450 C) as per JPH03-
41540. The
alloy was then hot rolled to a final gauge of 1.75 inches (44.45 mm). Alloy 1
was then solution
heat treated at 842 F (450 C) for 1 hour as per JPH03-41540, then quenched in
190 F water
(87.8 C), and then stretched 1.5%. After stretching, Alloy 1 was artificially
aged by first aging
at 248 F (120 C) for 24 hours, heating to 302 F and then aging at 302 F (150
C) for 24 hours
as per JPH034-41540.
[0052] Alloy 2 was homogenized at 895 F (479 C) and then hot rolled to a
final gauge of
1.75 inches (44.45 mm). Alloy 2 was then solution heat treated at 895 F (479
C) for 2 hours,
quenched in 190 F water (87.8 C), and then stretched 2.25%. After stretching,
some Alloy 2
was subjected to two different artificially aging practices:
'Also published as JP01-290737 (1989).
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= Practice 1: First aging at 250 F (121 C) for 6 hours, then heating to 320
F (160 C) and
holding for 5.6 hours, air cooling to ambient, and then reheating to 250 C
(121 C) and
holding for 24 hours.
= Practice 2: First aging at 250 F (121 C) for 6 hours, then heating to 320
F (160 C) and
holding for 9.75 hours, air cooling to ambient, and then reheating to 250 C
(121 C) and
holding for 24 hours.
The 190 F quench temperature simulates the quench rate of the middle of a
thick ingot (e.g.,
an eight-inch (203.2 mm) thick ingot).
[0053] Alloys 1-2 were metallographically examined and were found to be
unrecrystallized, i.e., contained not greater than 45% recrystallized grains
as determined using
standard metallographic analysis procedures. In one embodiment, a new wrought
7xxx
aluminum alloy product contains not greater than 35% recrystallized grains. In
another
embodiment, a new wrought 7xxx aluminum alloy product contains not greater
than 25%
recrystallized grains. In another embodiment, a new wrought 7xxx aluminum
alloy product
contains not greater than 15% recrystallized grains. In another embodiment, a
new wrought
7xxx aluminum alloy product contains not greater than 5% recrystallized
grains.
[0054] The alloys were then subjected to mechanical testing, the results of
which are shown
in Table 2, below. Test results relating to similarly produced conventional
7050 alloys are also
provided, which results are from commonly-owned International Patent
Application
Publication No. W02020/102441. Measurements are relative to the T/2 location
for all alloys.
Fracture toughness is relative to the S-L orientation.
Table 2 - Mechanical Properties of Example 1 Alloys*
Strength
UTS TYS Elong. Kic (ksi-
Alloy Testing
(ksi
Orientation ) (ksi) (%) sqrt-in.)
1 L 76.8 70.2 12.1
1 ST 73.4 63.5 5.6 18.1
2 (AP1) L 78.0 72.1 12.6
2 (AP1) ST 75.5 65.8 9.4 20.7
2 (AP2) L 76.7 69.9 13.7
2 (AP2) ST 73.2 62.5 9.5 23.3
7050 L 72.3 61.6 11.7 30.7 (KQ)
7050 L 72.2 61.2 12.5 28.2 (KQ)
7050 ST 70.4 56.3 9.4 18.5
7050 ST 70.3 56.2 10.2 18.4
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*API = aging practice 1; AP2 = aging practice 2; sqrt = square root
[0055] The alloys were also subjected to EAC (environmentally assisted
crack) resistance
testing as per the HEISCC-G49 procedure provided above. Plant produced 7050-
T7651 (3.9
inches thick) having a strength level similar to that of Alloys 1-2 was also
tested. The HEISCC-
G49 results are provided in Table 3, below.
Table 3¨ HHSCC-G49 Test Results
90 C / 85 % RH
Stress Applied
Alloy (% TYS- stress Days Days to failure
ST) (ksi) rep 1 rep 2 rep 3 rep 4 rep 5
test
1 85 54 18 11 11 14 18 18
2 (API) 85 55.9 21 11 11 11 21 18
2 (AP2) 85 53.1 46 28 32 28 46 35
7050 85 53.0 55 28 55 55 19 41
[0056] As shown above and in FIGS. 1-2, Alloy 2 realizes an improved
combination of
properties over Alloy 1. As shown in FIG. 1, Alloy 2 realizes a much higher
combination of
strength and toughness over Alloy 1 and the conventional 7050 alloy. As shown
in FIG. 2,
Alloy 2 also realizes a much better combination of strength and EAC resistance
over Alloy 1.
Further, as shown in Table 2, the ST ductility of Alloy 2 is significantly
higher than that of
Alloy 1.
[0057] An analysis of the homogenization temperature for this alloy system
was
completed. It was determined that, for these particular alloys having 5.5-6.5
wt. % Zn, 1.3-1.7
wt. % Mg, and 1.7-2.3 wt. % Cu, the homogenization temperature should be at
least as high as
T(homog.), wherein T(homog.) is calculated in degrees Fahrenheit from the
following formula:
= T(homog.) = 614.4+55.2*Cu+83.1*Mg-1.8*Zn
For the above formula, the Cu, the Mg, and the Zn are the weight percent
amounts of copper,
magnesium and zinc, respectively, in the wrought 7xxx aluminum alloy. The
below table
shows the calculation for Alloys 1 and 2.
Table 4 ¨ T(homog.) of Alloys 1-2
T(homog.)
Alloy Zn Mg Cu
( F)
1 5.88 1.60 2.17 856.5
2 5.98 1.50 2.12 845.3
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As shown, the minimum homogenization temperature of Alloy 1 is 856.5 F and the
minimum
homogenization temperature of Alloy 2 is 845.3 F.
[0058] Preferably, the homogenization temperature is higher than T(homog.)
In one
embodiment, the homogenization temperature is at least 5 F higher than
T(homog.), i.e., is >
F+T(homog.). In another embodiment, the homogenization temperature is at least
10 F
higher than T(homog.), i.e., is > 10 F+T(homog.). In yet another embodiment,
the
homogenization temperature is at least 15 F higher than T(homog.), i.e., is >
15 F+T(homog.).
In another embodiment, the homogenization temperature is at least 20 F higher
than
T(homog.), i.e., is > 20 F+T(homog.). In yet another embodiment, the
homogenization
temperature is at least 25 F higher than T(homog.), i.e., is > 25 F+T(homog.).
In another
embodiment, the homogenization temperature is at least 30 F higher than
T(homog.), i.e., is >
30 F+T(homog.). In yet another embodiment, the homogenization temperature is
at least 35 F
higher than T(homog.), i.e., is > 35 F+T(homog.). In another embodiment, the
homogenization
temperature is at least 40 F higher than T(homog.), i.e., is > 40 F+T(homog.).
In yet another
embodiment, the homogenization temperature is at least 45 F higher than
T(homog.), i.e., is >
45 F+T(homog.). In another embodiment, the homogenization temperature is at
least 50 F
higher than T(homog.), i.e., is > 50 F+T(homog.). However, the homogenization
temperature
should be below the incipient melting temperature of the aluminum alloy.
Preferably, the
homogenization temperature is at least 10 F below the incipient melting
temperature of the
aluminum alloy.
[0059] As it relates to solution heat treatment, all of the above teachings
regarding
homogenization apply equally to the solution heat treatment temperature. That
is, the solution
heat treatment temperature may be the same as T(homog.) and preferably is from
10-50 F
higher than T(homog.), as per above, but below the incipient melting
temperature of the
aluminum alloy, and preferably at least 10 F below the incipient melting
temperature of the
aluminum alloy. Following solution heat treatment the alloy should be quenched
in an
appropriate medium, such as water or air. Preferably, the water is room
temperature.
[0060] Based on the above data, an aging analysis was also completed. It
was found that
the alloys should be aged to a total equivalent aging time, t(eq.), of from 7
to 20 hours, the total
equivalent artificial aging time being:
f exp(-12800 / T) dt
t(eq.) =
exp(-12800/Tref)
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In the above formula, T is the instantaneous temperature in Kelvin (K) during
the artificial
aging, and Tref is a reference temperature selected at 160 C (433.15K). The
t(eq.) for Alloys
1-2 are shown in the below table.
Table 5 ¨ t(eq.) of Alloys 1-2
Alloy t(eq.)
(hours)
1 14.58
2-AP1 10.57
2-AP2 14.57
[0061] As shown, both Alloy 1 and Alloy 2-AP2 were aged to generally the
same total
equivalent aging time. However, the aging practice of Alloy 2 is superior, at
least partially
contributing to its significantly improved properties. Accordingly, in one
embodiment, t(eq.)
is from 7 to 19 hours. In another embodiment, t(eq.) is from 7 to 18 hours. In
yet another
embodiment, t(eq.) is from 7 to 17 hours. In another embodiment, t(eq.) is
from 7 to 16 hours.
In yet another embodiment, t(eq.) is from 7 to 15 hours. In another
embodiment, t(eq.) is from
7 to 14 hours. In yet another embodiment, t(eq.) is from 7 to 13.5 hours. In
another
embodiment, t(eq.) is from 7 to 13 hours. In yet another embodiment, t(eq.) is
from 7 to 12.5
hours. In another embodiment, t(eq.) is from 7 to 12 hours. In yet another
embodiment, t(eq.)
is from 7 to 11.5 hours. In another embodiment, t(eq.) is from 7 to 11 hours.
[0062] It is believed that both a two-step and a three-step aging practice
may be used with
the presently disclosed wrought 7xxx aluminum alloys provided the proper
homogenization
and solution heat treatment practices are followed. Thus, in one embodiment,
the artificial
aging comprises first aging at a first aging temperature of from 200-300 F
followed by second
aging at a second aging temperature of from 250-350 F, wherein the second
aging temperature
is at least 10 F higher than the first aging temperature. In one embodiment,
the second aging
temperature is at least 20 F higher than the first aging temperature. In
another embodiment,
the second aging temperature is at least 30 F higher than the first aging
temperature. In yet
another embodiment, the second aging temperature is at least 40 F higher than
the first aging
temperature. In another embodiment, the second aging temperature is at least
50 F higher than
the first aging temperature. In yet another embodiment, the second aging
temperature is at
least 60 F higher than the first aging temperature. In another embodiment, the
second aging
temperature is at least 70 F higher than the first aging temperature.
[0063] In one embodiment, the first aging temperature is not greater than
280 F. In another
embodiment, the first aging temperature is not greater than 270 F. In yet
another embodiment,
the first aging temperature is not greater than 260 F. In another embodiment,
the first aging
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temperature is not greater than 250 F. Multiple aging temperatures may be used
within the
first aging temperature range provided t(eq) is achieved.
[0064] In one embodiment, the second aging temperature is at least 305 F.
In another
embodiment, the second aging temperature is at least 310 F. In yet another
embodiment, the
second aging temperature is at least 315 F. In another embodiment, the second
aging
temperature is at least 320 F. Multiple aging temperatures may be used within
the second
aging temperature range provided t(eq) is achieved. After the second aging
step, the product
may be cooled to room temperature.
[0065] When a third aging step is used, it follows the second aging step.
In one approach,
the third aging step is similar or the same as the first aging step, such as
by using an aging
temperature of from 200-300 F. Multiple aging temperatures may be used within
the third
aging temperature range provided t(eq) is achieved. In one embodiment, the
third aging
temperature is at least 10 F lower than second aging temperature. In another
embodiment, the
third aging temperature is at least 20 F lower than second aging temperature.
In yet another
embodiment, the third aging temperature is at least 30 F lower than second
aging temperature.
In another embodiment, the third aging temperature is at least 40 F lower than
second aging
temperature. In yet another embodiment, the third aging temperature is at
least 50 F lower
than second aging temperature. In another embodiment, the third aging
temperature is at least
60 F lower than second aging temperature. In yet another embodiment, the third
aging
temperature is at least 70 F lower than second aging temperature.
[0066] In one embodiment, the third aging temperature is not greater than
280 F. In
another embodiment, the third aging temperature is not greater than 270 F. In
yet another
embodiment, the third aging temperature is not greater than 260 F. In another
embodiment,
the third aging temperature is not greater than 250 F. Multiple aging
temperatures may be used
within the third aging temperature range provided t(eq) is achieved.
[0067] 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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