U.S. patent application number 14/727341 was filed with the patent office on 2016-12-01 for high strength 7xxx series aluminum alloy products and methods of making such products.
This patent application is currently assigned to KAISER ALUMINUM FABRICATED PRODUCTS, LLC. The applicant listed for this patent is KAISER ALUMINUM FABRICATED PRODUCTS, LLC. Invention is credited to Florence Andrea Baldwin, Jane Elizabeth Buehler, Philippe Gomiero, Philippe Lassince, Zhengdong Long, Robert A. Matuska, Roy Austin Nash, Jason Nicholas Scheuring, Junsheng Wang.
Application Number | 20160348224 14/727341 |
Document ID | / |
Family ID | 56097021 |
Filed Date | 2016-12-01 |
United States Patent
Application |
20160348224 |
Kind Code |
A1 |
Long; Zhengdong ; et
al. |
December 1, 2016 |
High Strength 7xxx Series Aluminum Alloy Products and Methods of
Making Such Products
Abstract
The present invention is directed to a thick plate high strength
7xxx aluminum alloy product comprising 8.0 to 8.4 wt. % Zn, 1.5 to
2.0 wt. % Mg, 1.1 to 1.5 wt. % Cu, and 0.05 to 0.15 wt. % Zr, 4.0
to 5.3 of Zn/Mg weight percentage ratio, 0.14 to 0.19 of Cu/Zn
weight percentage ratio, and 10.7 to 11.6 wt. % of Cu+Mg+Zn. This
alloy can be fabricated to produce 3-10 inch thick plate, extrusion
or forging products, and is especially suitable for aerospace
structural components, especially large commercial airplane wing
structure applications. The product provides high strength, high
damage tolerance performance as well as better corrosion resistance
performance suitable for aerospace application.
Inventors: |
Long; Zhengdong; (Spokane,
WA) ; Buehler; Jane Elizabeth; (Spokane, WA) ;
Baldwin; Florence Andrea; (Mead, WA) ; Wang;
Junsheng; (Liberty Lake, WA) ; Scheuring; Jason
Nicholas; (Spokane, WA) ; Lassince; Philippe;
(Vodable, FR) ; Matuska; Robert A.; (Heath,
OH) ; Nash; Roy Austin; (Spokane, WA) ;
Gomiero; Philippe; (Liberty Lake, WA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KAISER ALUMINUM FABRICATED PRODUCTS, LLC |
Foothill Ranch |
CA |
US |
|
|
Assignee: |
KAISER ALUMINUM FABRICATED
PRODUCTS, LLC
Foothill Ranch
CA
|
Family ID: |
56097021 |
Appl. No.: |
14/727341 |
Filed: |
June 1, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 21/10 20130101;
C22F 1/053 20130101; C22F 1/002 20130101 |
International
Class: |
C22F 1/053 20060101
C22F001/053; C22F 1/00 20060101 C22F001/00; C22C 21/10 20060101
C22C021/10 |
Claims
1. A thick plate high strength 7xxx aluminum alloy product
comprising 8.0 to 8.4 wt. % Zn, 1.5 to 2.0 wt. % Mg, 1.1 to 1.5 wt.
% Cu, and one or more elements selected from the group consisting
of up to 0.2 wt. % Zr, up to 0.2% wt. Sc, and up to 0.2 wt. % Hf,
with the balance Al, and impurities wherein said alloy product has
a Zn/Mg weight percentage ratio between 4.0 to 5.3, a Cu/Zn weight
percentage ratio between 0.14 to 0.19, and an amount of Cu+Mg+Zn
between 10.7 to 11.6 wt. %.
2. The aluminum alloy product of claim 1 comprising .ltoreq.0.12
wt. % Si.
3. The aluminum alloy product of claim 2 comprising .ltoreq.0.05
wt. % Si.
4. The aluminum alloy product of claim 1 comprising .ltoreq.0.15
wt. % Fe.
5. The aluminum alloy product of claim 4 comprising .ltoreq.0.08
wt. % Fe.
6. The aluminum alloy product of claim 1 comprising .ltoreq.0.20
wt. % Mn.
7. The aluminum alloy product of claim 1 comprising .ltoreq.0.04
wt. % Cr.
8. The aluminum alloy product of claim 1 comprising .ltoreq.0.06
wt. % Ti.
9. The aluminum alloy product of claim 1 consisting essentially of
8.0 to 8.4 wt. % Zn, 1.5 to 2.0 wt. % Mg, 1.1 to 1.5 wt. % Cu, one
or more elements selected from the group consisting of up to 0.2
wt. % Zr, up to 0.2 wt. % Sc, and up to 0.2 wt. % Hf, .ltoreq.0.12
wt. % Si, .ltoreq.0.15 wt. % Fe, .ltoreq.0.20 wt. % Mn,
.ltoreq.0.04 wt. % Cr, and .ltoreq.0.06 wt. % Ti with the balance
Al, and impurities wherein said alloy product has a Zn/Mg weight
percentage ratio between 4.0 to 5.3, a Cu/Zn weight percentage
ratio between 0.14 to 0.19, and an amount of Cu+Mg+Zn between 10.7
to 11.6 wt. %.
10. The aluminum alloy product of claim 1 wherein said aluminum
alloy product is a 3-10 inches thick plate, extrusion, or forging
product.
11. The aluminum alloy product of claim 9 wherein said aluminum
alloy product is a 3-10 inches thick plate, extrusion, or forging
product.
12. The aluminum alloy product of claim 1 wherein said aluminum
alloy product is a 4-10 inches thick plate, extrusion, or forging
product.
13. The aluminum alloy product of claim 1 wherein said aluminum
alloy product is a 4-8 inches thick plate, extrusion, or forging
product.
14. The aluminum alloy product of claim 1 wherein the aluminum
alloy product has a minimum Long-Transverse (LT) yield strength at
quarter-thickness (th/4) of (74-0.56*plate thickness in inch) ksi
and a minimum LT ultimate strength at th/4 of (78-0.36*plate
thickness in inch) ksi.
15. A method of manufacturing a thick plate high strength 7xxx
aluminum alloy product comprising the steps of: a. casting stock of
an ingot of a 7xxx aluminum alloy comprising the aluminum alloy
product of claim 1 b. homogenizing the cast stock; c. hot working
the stock by one or more methods selected from the group consisting
of rolling, extrusion, and forging; d. solution heat treating (SHT)
of the hot worked stock; e. cold water quenching said SHT stock; f.
optionally stretching the SHT stock; and h. ageing of the SHT, cold
water quenched and optionally stretched stock to a desired
temper.
16. The method of claim 15, wherein said step of homogenizing
includes homogenizing at temperatures from 454 to 491.degree. C.
(849 to 916.degree. F.).
17. The method of claim 15, wherein said step of hot working
includes hot rolling at a temperature of 385 to 450.degree. C. (725
to 842.degree. F.).
18. The method of claim 15, wherein said step of solution heat
treating includes solution heat treated at temperature range from
454 to 491.degree. C. (849 to 916.degree. F.).
19. The method of claim 15, wherein said step of optionally
stretching includes stretching at about 1.5 to 3%.
20. The method of claim 15, wherein said step of ageing includes a
two-step T7651 ageing process wherein a first stage temperature
ranges from 100 to 140.degree. C. (212 to 284.degree. F.) for 4 to
24 hours and a second stage temperature ranges from 135 to
200.degree. C. (275 to 392.degree. F.) for 5 to 20 hours.
21. The method of claim 15, wherein b. said step of homogenizing
includes homogenizing at temperatures from 454 to 491.degree. C.
(849 to 916.degree. F.); c. said step of hot working includes hot
rolling at a temperature of 385 to 450.degree. C. (725 to
842.degree. F.); d. said step of solution heat treating includes
solution heat treated at temperature range from 454 to 491.degree.
C. (849 to 916.degree. F.); e. said step of cold water quenching
includes cold water quenching to room temperature; f. said step of
optionally stretching includes stretching at about 1.5 to 3%; g.
said step of ageing includes a two-step T7651 ageing process
wherein a first stage temperature ranges from 100 to 140.degree. C.
(212 to 284.degree. F.) for 4 to 24 hours and a second stage
temperature ranges from 135 to 200.degree. C. (275 to 392.degree.
F.) for 5 to 20 hours.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This present invention generally relates to high strength
7xxx aluminum alloy products and methods for making such
products.
[0003] 2. Background
[0004] High strength 7xxx (Al--Zn) aluminum alloy products are
extensively used in aerospace structure application, in which the
material strength, fracture toughness, fatigue resistance, and
corrosion resistance are required simultaneously. In order to
aggressively reduce aircraft weight for fuel efficiency, thick
plate, high strength 7xxx aluminum alloys are being pursued
assertively by airframe manufacturers and aluminum material
manufacturers. This is especially critical for large size
commercial aircraft in which a significant amount of large parts
are fabricated through monolithic fabrication processing for cost
reduction. A thick plate is required for such large monolithic
components. However, the combination of high strength and high
thickness imposes an extreme metallurgical challenge to produce
such thick plate, high strength, aluminum products for the aluminum
manufacturing industry. Due to such extreme metallurgical
challenges, only very limited commercial products are currently
available for this key aerospace application based on the most
recent "Aluminum Association: 2011 Yellow/Tan Sheets" and "Addendum
to 2011 Edition of Yellow/Tan Sheets" for aluminum and aluminum
alloy products registered in Aluminum Association.
[0005] The chemical composition of an aluminum alloy product has a
phenomenal influence on the final production properties. In 7xxx
series aluminum alloys, the high levels of Zn, Mg and Cu are
usually added in order to achieve high strength and corrosion
resistance. However, compositions with too high Zn and Mg content
generally negatively affect stress corrosion cracking (SCC)
resistance and fracture toughness performance. Additionally,
concentrations of Cu that are too high also significantly increase
the risk of high level of undesirable coarse Al.sub.2MgCu particles
and macro-segregation from plate surface to center. During casting,
large Al.sub.2CuMg particles can form during solidification. Such
large particles normally can be dissolved during subsequent
homogenization and solution heat treatment. If the Cu content is
too high, however, this could promote extreme high levels of
Al.sub.2CuMg particles, which cannot be dissolved during subsequent
thermal treatments. Those undissolved Al.sub.2CuMg particles
significantly reduce the strength and damage tolerance
performance.
[0006] In order to achieve aging precipitation hardening, Cu, Mg
and Zn alloying element have to be in solid solution before aging.
This is generally achieved through the processing steps of Solution
Heat Treatment, followed by cold water quench. With the higher Mg,
Zn and Cu levels, it is extremely difficult to dissolve all
constituent particles, which consume a significant amount of added
alloying elements, into solid solution. More importantly, the
higher levels of alloying element increase the potential coarse
particles precipitation during quenching. This is especially
critical for thick plate with slow cooling rate during quench. It
is easier to achieve better strength and other properties for a
thin cross section product than for a thick cross section product
of high strength 7xxx aluminum alloy. As cross section increases
the quench related cooling rate in the plate significantly
decreases, resulting in not only lowering overall strength but also
the fracture toughness. This phenomenon is also referred to as high
strength 7xxx thick plate quench sensitivity, which is of great
concern in high strength 7xxx aluminum alloy.
[0007] In summary, the combination of the complicated age hardening
behavior, specific quenching condition for thick plate, strict
damage tolerance and corrosion requirements necessitates a very
fine, optimized, and probably very narrow chemistry range that
needs to be discovered. There is a strong need of such new alloys
in aerospace application, especially for large size commercial
aircraft.
BRIEF SUMMARY OF THE INVENTION
[0008] Thick plate high strength 7xxx aluminum alloy products
comprise Zn from 8.0 to 8.4 wt. %, Mg from 1.5 to 2.0 wt. % and Cu
from 1.1 to 1.5 wt. %, 4.0 to 5.3 of Zn/Mg weight percentage ratio,
0.14 to 0.19 of Cu/Zn weight percentage ratio, and 10.7 to 11.6 wt.
% of Cu+Mg+Zn, one or more elements selected from the group
consisting of up to 0.2% Zr, up to 0.2% Sc, up to 0.2% Hf, and the
balance Al, and impurities.
[0009] In one embodiment of the present invention, the thick plate
high strength 7xxx aluminum alloy product is produced using
precisely controlled thermal mechanical processes.
[0010] Preferably, the alloy can be fabricated to a thickness of
3-10 inch, more preferably 4-10 inch, even more preferably 4-8
inches thickness plates, extrusions, and forging products. In one
embodiment, the aluminum alloy product also provides necessary
short-transverse ductility, damage tolerance performance as well as
corrosion resistance performance required for aerospace
applications. Such plates, forgings and extrusions are suitable for
use in making aerospace structural components like large commercial
airplane wing components,
[0011] It has been surprisingly discovered that an aluminum alloy
having a high Zn chemistry, associated with precise Mg and Cu
content, Zn/Mg and Cu/Zn weight percentage ratios along with
deliberately controlled thermal mechanical processing, is capable
of producing 3 to 10'' gauge thick products with high strength,
better damage tolerance, and corrosion properties never achieved
before.
[0012] In one embodiment, the high strength 7xxx thick plate
aluminum product offers a promising opportunity for significant
fuel efficiency and cost reduction advantage for commercial
airplanes, especially large size commercial aircraft. An example of
such application of 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 Short Transfer (ST) tensile
ductility, damage tolerance, corrosion resistance performance, such
as exfoliation and stress corrosion resistance, and fatigue crack
growth resistance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] 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:
[0014] FIG. 1 is a graph showing a comparison of the Cu and Zn
levels between 32 chemistries in U.S. Pat. No. 6,972,110 and
present invention range;
[0015] FIG. 2 is a graph showing the strength and fracture
toughness of 4'' invention and non-invention alloy plates;
[0016] FIG. 3 is a graph showing the strength and fracture
toughness of 6'' invention and non-invention alloy plates;
[0017] FIG. 4 is a graph showing the strength and fracture
toughness of 7.5'' invention and non-invention alloy plates;
[0018] FIG. 5 is a graph showing the effect of Cu+Mg+Zn on fracture
toughness of 7.5'' thick plate showing that too low or too high
Cu+Mg+Zn gives worse fracture toughness;
[0019] FIG. 6 is a graph showing the effect of Cu/Zn ratio on
fracture toughness of 7.5'' thick plate; and
[0020] FIG. 7 is a graph showing the effect of Zn/Mg ratio on
fracture toughness of 6'' thick plate.
DETAILED DESCRIPTION OF THE INVENTION
[0021] The thick plate high strength 7xxx aluminum alloy product
comprises 8.0 to 8.4 wt. % Zn, 1.5 to 2.0 wt. % Mg, 1.1 to 1.5 wt.
% Cu, 4.0 to 5.3 of Zn/Mg weight percentage ratio, 0.14 to 0.19 of
Cu/Zn weight percentage ratio, and 10.7 to 11.6 wt. % of Cu+Mg+Zn,
one or more elements selected from the group consisting of up to
0.2 wt. % Zr, up to 0.2 wt. % Sc, and up to 0.2 wt. % Hf, and the
balance Al, and impurities.
[0022] The upper or lower limits for the ranges provided above are
understood to include all of the numbers provided within the range.
It is understood that within the range of 8.0 to 8.4 wt. % Zn, the
upper or lower limit for the amount of Zn may be selected from 8.0,
8.1, 8.2, 8.3 and 8.4 wt. % Zn. It is understood that within the
range of 1.5 to 2.0 wt. % Mg, the upper or lower limit for the
amount of Mg may be selected from 1.5, 1.6, 1.7, 1.8, 1.9 and 2.0
wt. % Mg. It is understood that within the range of 1.1 to 1.5 wt.
% Cu, the upper or lower limit for the amount of Cu may be selected
from 1.1, 1.2, 1.3, 1.4 and 1.5 wt. % Cu. It is understood that
within the range of 4.0 to 5.3 Zn/Mg weight percentage ratio, the
upper or lower limit for the Zn/Mg weight percentage ratio may be
selected from 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9,
5.0, 5.1, 5.2 and 5.3 Zn/Mg weight percentage ratio. It is
understood that within the range of 0.14 and 0.19 Cu/Zn weight
percentage ratio, the upper or lower limit for the Cu/Zn weight
percentage ratio may be selected from 0.14, 0.15, 0.16, 0.17, 0.18
and 0.19 Cu/Zn weight percentage ratio. It is understood that
within the range of 10.7 to 11.6 wt. % Cu+Mg+Zn, the upper or lower
limit for the amount of Cu+Mg+Zn may be selected from 10.7, 10.8,
10.9, 11.0, 11.1, 11.2, 11.3, 11.4, 11.5 and 11.6 wt. %
Cu+Mg+Zn.
[0023] The unique chemistry range along with the ratios of Zn/Mg
and Cu/Zn in accordance with the present invention gives the
distinctive thermodynamic and kinetic behaviors of precipitations
during quenching and aging heat treatment.
[0024] Zn and Mg are generally added to produce metastable and/or
stable MgZn.sub.2 (.eta.' and/or .eta. Phase) and its variant
phases, which are the predominant precipitation hardening phases.
However, the actual chemical compositions of age hardening phases
are far more complicated than 1:2 atomic ratio of Mg/Zn. The Zn/Mg
weight percentage ratio in the range of 4.0 to 5.3 surprisingly
gives the optimized physical metallurgy suitable for thick plate
high strength and fracture toughness properties.
[0025] Copper is generally added in order to improve SCC resistance
performance. Cu can significantly increase the breakdown
potentials, resulting in better corrosion resistance performance.
During quenching and aging process, Cu can substitute with Zn in
MgZn.sub.2 type phase to form Mg(ZnCuAl).sub.2 phases in grain
boundary and/or matrix. Therefore, the level of Cu should be
carefully considered for different Zn and Mg levels as well as the
plate thickness which affects the precipitation during quenching.
The Cu/Zn ratio in the range of 0.14 to 0.19 surprisingly gives the
optimized physical metallurgy suitable for thick plate high
strength and fracture toughness properties.
[0026] In one embodiment, the thick plate high strength 7xxx
aluminum alloy product includes .ltoreq.0.12 wt. % Si, preferably
.ltoreq.0.05 wt. % Si. In one embodiment, the thick plate high
strength 7xxx aluminum alloy product includes .ltoreq.0.15 wt. %
Fe, preferably .ltoreq.0.08 wt. % Fe. In one embodiment, the thick
plate high strength 7xxx aluminum alloy product includes
.ltoreq.0.2 wt. % Mn. In one embodiment, the thick plate high
strength 7xxx aluminum alloy product includes .ltoreq.0.04 wt. %
Cr, preferably no Cr is added to the alloy other than that provided
as an impurity. In one embodiment, the thick plate high strength
7xxx aluminum alloy product includes .ltoreq.0.06 wt. % Ti.
[0027] The thick plate high strength 7xxx aluminum alloy product of
the present invention may also include low level of "impurities"
that are not included intentionally. The "impurities" means any
other elements except above described Al, Zn, Mg, Cu, Zr, Sc, Hf,
Si, Fe, Mn, Cr and Ti.
[0028] Preferably, the thick plate high strength 7xxx aluminum
alloy products, such as plates, forgings and extrusions, are
suitable for use in making aerospace structural components like
large commercial airplane wing components. Preferably, the alloy
has a thickness of 3-10 inch, preferably 4-10 inch, more preferably
4-8 inch for producing plates, extrusion, and forging products. In
one embodiment, the aluminum alloy product also provides necessary
damage tolerance performance as well as corrosion resistance
performance required for aerospace application.
[0029] The present invention has various advantageous mechanical
and physical properties. In one embodiment of the present invention
the term "high strength" means the minimum Long-Transverse (LT)
yield strength at quarter-thickness (th/4) is (74-0.56*plate
thickness in inch) ksi, and the minimum LT ultimate strength at
th/4 is (78-0.36*plate thickness in inch) ksi. In one embodiment of
the present invention, the thick plate high strength 7xxx aluminum
alloy product has fracture toughness values of a minimum 27
ksi-in.sup.1/2 at th/4. In one embodiment of the present invention,
the ST tensile ductility is at least (7-0.5*plate thickness in
inch) %. In one embodiment of the present invention improved
exfoliation, such as better than or equal to EA EXCO rating per
ASTM G34 at th/10 and th/2, may be observed. In one embodiment of
the present invention, improved stress corrosion resistance, such
as at least 20 days at 25 ksi and preferably at least 20 days at 30
ksi per ASTM G47 in a T7651 temper, may be observed.
[0030] In one embodiment of the present invention, the thick plate
high strength 7xxx aluminum alloy product is produced using a
precise chemistry range along with precisely controlled thermal
mechanical processes. In one embodiment, this thick plate high
strength 7xxx aluminum alloy product is used in aerospace
applications.
[0031] As indicated, the thick plate high strength 7xxx aluminum
alloy product may be used to produce plates, extrusions, and
forging products. In one embodiment, the thick plate high strength
7xxx aluminum alloy product is used to produce a wrought product
that is a rolled thick plate including any of the chemistries
provided in the above-mentioned embodiments. The rolled thick plate
may be manufactured using known process conditions such as
homogenization, hot-rolling, solution heat treatments and ageing
treatments.
[0032] In one embodiment, ingots of the thick plate high strength
7xxx aluminum alloy product may be cast, homogenized, hot rolled,
solution heat treated, cold water quenched, optionally stretched,
and aged to desired temper. In one embodiment, the thick plate high
strength 7xxx aluminum alloy is a plate subjected to a final T7651
and T7451 tempers in the thickness range from 3 inch to 10 inch.
The ingots may be homogenized at temperatures from 454 to
491.degree. C. (849 to 916.degree. F.). The hot rolling start
temperature may be from 385 to 450.degree. C. (725 to 842.degree.
F.). The exit temperature may be in a similar range as the start
temperature. The plates may be solution heat treated at temperature
range from 454 to 491.degree. C. (849 to 916.degree. F.). The
plates are cold water quenched to room temperature and may be
stretched at about 1.5 to 3%. The quenched plate may be subjecting
to any known 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 temper,
the first stage temperature may be in the range of 100 to
140.degree. C. (212 to 284.degree. F.) for 4 to 24 hours and the
second stage temperature may be in the range of 135 to 200.degree.
C. (275 to 392.degree. F.) for 5 to 20 hours.
[0033] Table 1 compares the present invention alloy chemistry with
other aluminum alloy products currently available based on the most
recent "Aluminum Association: 2014 Yellow/Tan Sheets" and "Aluminum
Standard and Data 2013" for more than 4'' thick plates with T7651
temper. It should be mentioned that although there are more
commercial alloys available for lower than 4'' thickness plates and
T7451 temper, only very few alloys are available for thicker than
4'' plates with high strength T7651 temper.
[0034] As shown in Table 1, the invention alloy has distinguished
chemistry with other alloys. AA7140 and AA7081 have much lower Zn
than present invention alloy, and AA7085 has lower Zn than
invention alloy. The Zn is very critical for high strength
property. In addition, the Cu/Zn weight percentage ratios of AA7065
and AA7140 alloy are much higher than that of current invention
alloy. The high Cu/Zn weight percentage ratio can significantly
reduce the strength potential since the Cu may consume more Mg
during solidification to form undesirable Al.sub.2CuMg
particles.
TABLE-US-00001 TABLE 1 Cu, Cu, Mg, Mg, Zn, Zn, Zn/Mg, Zn/Mg, Cu/Zn,
Cu/Zn, Mg + Cu + Zn, Mg + Cu + Zn, Alloy Gage Range Min. Max. Min.
Max. Min. Max. min. max. min. max. min. max. 7140 4'' to 10'' 1.30
2.30 1.50 2.40 6.20 7.00 2.58 4.67 0.19 0.37 9.0 11.7 7081 1'' to
6'' 1.20 1.80 1.80 2.20 6.90 7.50 3.14 4.17 0.16 0.26 9.9 11.5 7085
4'' to 7'' 1.30 2.00 1.20 1.80 7.00 8.00 3.89 6.67 0.16 0.29 9.5
11.8 7065 1'' to 6'' 1.90 2.30 1.50 1.80 7.10 8.30 3.94 5.53 0.23
0.32 10.5 12.4 Inven- 3'' to 10'' 1.1 1.5 1.5 2.0 8.0 8.4 4.00 5.30
0.14 0.19 10.7 11.6 tion
[0035] As shown in the Table 1, the closest product is
AA7085-T7651, in which Zn is lower than the present invention.
AA7085 was registered by Alcoa and described in U.S. Pat. No.
6,972,110. In this patent, 28 different chemistries were studied in
lab scale samples and 4 commercial scale products. FIG. 1 shows a
graph comparing the Cu and Zn levels between those 32 chemistries
and present invention range. It clearly demonstrates the uniqueness
of the current invention alloy. Although a very broad chemistry
range was explored in U.S. Pat. No. 6,972,110, the chemistry range
of the present invention alloy was not studied in U.S. Pat. No.
6,972,110.
[0036] 7xxx high strength aluminum alloys with high Zn were also
explored in U.S. Pat. No. 6,790,407. It should be noticed that the
alloys described in U.S. Pat. No. 6,790,407 intentionally require
the addition of Cr, Ni, and hydrogen in certain levels for better
grain structures, precipitations, and uniform non-metallic
inclusions. In contrast, the present invention alloy requires none
of these elements due to the potential negative impacts on fracture
toughness. In U.S. Pat. No. 6,790,407, seven (7) alloys were
specifically disclosed. All alloys except Alloy 2 in U.S. Pat. No.
6,790,407 have higher than 1.5 wt. % Cu. For Alloy 2 in U.S. Pat.
No. 6,790,407, the Mg and Zn are much higher than those presently
provided in the invention alloy which includes ranges of Cu and Mg
are 1.1 to 1.5 wt. % and 1.5 to 2.0 wt. % respectively.
[0037] Although the following examples demonstrate various
embodiments of the present invention, one of skill in the art
should understand how additional thick plate high strength 7xxx
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.
Examples
Plant Trial
[0038] Sixteen (16) industrial scale ingots were cast by commercial
DC (Direct Chill) casting process and processed to different
thickness plates. Table 2 gives the typical chemical compositions
of selected plates with different gauges.
TABLE-US-00002 TABLE 2 Chemical compositions of industrial scale
ingots Patent Plate Sample ID Alloy Si Fe Cu Mg Zn Mn Zr Zn/Mg
Cu/Zn Cu + Mg + Zn Thickness in Alloy A Yes 0.022 0.038 1.3 1.8 8.0
0.001 0.11 4.5 0.16 11.1 4 Alloy B Yes 0.039 0.078 1.2 1.7 8.1
0.004 0.09 4.7 0.15 11.0 4 Alloy C No 0.04 0.063 1.2 2.1 8.1 0.005
0.10 3.9 0.15 11.4 4 Alloy D Yes 0.04 0.065 1.4 1.6 8.2 0.003 0.10
5.2 0.17 11.2 6 Alloy E yes 0.039 0.054 1.5 1.6 8.2 0.133 0.04 5.0
0.18 11.3 6 Alloy F Yes 0.032 0.055 1.2 1.7 8.2 0.001 0.10 4.9 0.15
11.1 6 Alloy G No 0.04 0.059 1.6 1.9 6.8 0.003 0.10 3.6 0.24 10.3 6
Alloy H No 0.04 0.06 1.3 2.1 8.1 0.005 0.10 3.9 0.16 11.5 6 Alloy I
Yes 0.035 0.06 1.4 1.6 8.2 0.003 0.11 5.1 0.18 11.2 7.5 Alloy J Yes
0.039 0.062 1.5 1.6 8.2 0.003 0.11 5.1 0.18 11.2 7.5 Alloy K Yes
0.033 0.054 1.3 1.9 8.0 0.002 0.11 4.1 0.16 11.2 7.5 Alloy L Yes
0.039 0.056 1.4 1.7 8.1 0.129 0.04 4.8 0.17 11.2 7.5 Alloy M No
0.04 0.059 1.6 2.0 6.8 0.002 0.10 3.5 0.23 10.4 7.5 Alloy N No 0.03
0.051 1.3 1.6 8.6 0.002 0.11 5.3 0.14 11.5 7.5 Alloy O No 0.04
0.059 1.8 1.7 8.5 0.002 0.11 4.9 0.22 12.0 7.5 Alloy P No 0.04
0.059 1.5 1.6 9.0 0.002 0.11 5.5 0.17 12.1 7.5
[0039] Alloy A, B, D to F, and I to L are invention alloys. Alloy C
is not an invention alloy since the Mg is too high and Zn/Mg weight
percentage ratio is too low compared with the invention alloy.
Alloy G is not an invention alloy since the Cu is too high, Zn is
too low, Zn/Mg weight percentage ratio is too low, Cu/Zn weight
percentage ratio is too high, and Cu+Mg+Zn is too low. Alloy H is
not an invention alloy since the Mg is too high and Zn/Mg weight
percentage ratio is too low. Alloy M is not an invention alloy
since the Cu is too high, Zn is too low, Zn/Mg weight percentage
ratio is too low, Cu/Zn weight percentage ratio is too high, and
Cu+Mg+Zn is too low. Alloy N is not an invention alloy since the Zn
is too high. Alloy O is not an invention alloy since the Cu is too
high, Zn is too high, and Cu+Zn+Mg is too high. Alloy P is not an
invention alloy since the Zn is too high, Zn/Mg weight percentage
ratio is too high, and Cu+Mg+Zn is too high.
[0040] Ingots were homogenized, hot rolled, solution heat treated,
quenched, stretched and aged to final T7651 temper plates in the
thickness range from 4 inch to 7.5 inch. The ingots were
homogenized at a temperature from 465 to 485.degree. C. (869 to
905.degree. F.). The hot rolling start temperature is from 400 to
440.degree. C. (752 to 824.degree. F.). The exit rolling
temperature is in the similar range as start temperature. The
rolling reduction of each pass was deliberately controlled to
achieve target temperature during hot rolling process.
[0041] The plates were solution heat treated at temperature range
from 470 to 485.degree. C. (878 to 905.degree. 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 temper. The
first stage temperature is in the range of 110 to 130.degree. C.
(230 to 266.degree. F.) for 4 to 12 hours and the second stage
temperature is in the range of 145 to 160.degree. C. (293 to
320.degree. F.) for 8 to 20 hours.
[0042] Tables 3 give tensile and fracture toughness properties. The
0.2% offset yield strength (TYS) along transverse direction (LT)
was measured at quarter thickness (T/4) under ASTM B557
specification. The plane strain fracture toughness (K.sub.1c) in
T-L orientations at quarter thickness (T/4) was measured under ASTM
E399 using CT specimens.
TABLE-US-00003 TABLE 3 Tensile and fracture toughness properties of
final T7651 temper plates Patent Plate LT TYS @T/4 LT UTS @T/4 LT
Elongation K1c T-L @T/4 Sample ID Alloy Thickness in ksi ksi @T/4 %
ksi-in.sup.1/2 Alloy A Yes 4 72.2 77.8 10.4 28.65 Alloy B Yes 4
73.2 77.6 11.0 27.2 Alloy C No 4 70.7 78.0 11.0 27.1 Alloy D Yes 6
73.0 78.0 6.9 27.9 Alloy E yes 6 71.5 77.1 7.1 30.4 Alloy F Yes 6
71.0 76.3 7.5 28.7 Alloy G No 6 69.1 76.2 8.3 26.1 Alloy H No 6
69.9 77.7 7.9 24.8 Alloy I Yes 7.5 69.8 75.4 5.8 31.8 Alloy J Yes
7.5 70.5 76.1 5.8 30.5 Alloy K Yes 7.5 72.2 78.0 4.1 28.9 Alloy L
Yes 7.5 70.6 76.4 5.0 28.9 Alloy M No 7.5 70.1 77.1 5.0 26.7 Alloy
N No 7.5 68.2 74.3 5.2 30.1 Alloy O No 7.5 72.3 77.9 4.6 24.9 Alloy
P No 7.5 68.3 75.2 6.4 27.9
[0043] FIG. 2 is a graph showing a comparison of the strength and
fracture toughness of invention alloys (Alloy A and B) and
non-invention alloy (Alloy C) 4'' thickness plates. With same
industrial processing route and final plate thickness, the
invention Alloy A and Alloy B have much better performance of
strength and fracture toughness than Alloy C, which has too high Mg
and too low Zn/Mg ratio than invention alloys. The results
demonstrate that the invention alloys has surprisingly much better
performance than non-invention alloy. It also demonstrates that the
small chemistry deviation from invention alloy can severely
decreases final production properties.
[0044] FIG. 3 is a graph showing the strength and fracture
toughness of invention alloys (D, E, and F) and non-invention
alloys (G and H) 6'' thickness plates. Both Alloy G and H have
lower fracture toughness with similar or lower strength than Alloy
D to F invention alloys. Alloy G is not an invention alloy since
the Cu is too high, Zn is too low, and Zn/Mg weight percentage
ratio is too low, Cu/Zn weight percentage ratio is too high, and
Cu+Mg+Zn is too low. Alloy H is not an invention alloy since the Mg
is too high and Zn/Mg weight percentage ratio is too low. The
results demonstrate that the invention alloys surprisingly have
much better performance than non-invention alloy. It also confirms
that even small chemistry deviation from invention alloy can
severely decreases final production properties.
[0045] FIG. 4 is a graph showing the strength and fracture
toughness of invention alloys (I to L) and non-invention alloys (M
to P) 7.5'' thickness plates. All non-invention alloys have lower
combination of strength and fracture toughness compared with
invention alloys. As shown in Table 2, Alloy M is not an invention
alloy since the Cu is too high, Zn is too low, Zn/Mg weight
percentage ratio is too low, Cu/Zn weight percentage ratio is too
high, and Cu+Mg+Zn is too low. Alloy N is not an invention alloy
since the Zn is too high. Alloy O is not an invention alloy since
the Cu is too high, Zn is too high, and Cu+Zn+Mg is too high. Alloy
P is not an invention alloy since the Zn is too high, Zn/Mg weight
percentage ratio is too high, and Cu+Mg+Zn is too high. The results
confirm that the invention alloys surprisingly has much better
performance than non-invention alloys. It once again demonstrates
that even small chemistry deviation from invention alloy can
severely decreases final production properties.
[0046] FIG. 5 is a graph showing the fracture toughness as function
of total Cu+Mg+Zn amount. It can been seen that the invention alloy
range of 10.7 to 11.6% of total Cu+Mg+Zn gives the best
performance. It is very critical to control total Cu+Mg+Zn in an
optimized range in order to achieve both higher strength and better
fracture toughness especially for thick plate product.
[0047] FIG. 6 is a graph showing the fracture toughness as function
of total Cu/Zn weight percentage ratio. It can be seen that the
range provided by the invention alloy Cu/Zn weight percentage ratio
range of 0.14 to 0.19 gives better performance than other range.
The beneficial impact of Cu on corrosion resistance performance is
also strongly affected by Zn level. In addition, Cu contents that
are too high also significantly increase the risk of undesirable
coarse Al.sub.2MgCu particles and macro-segregation from plate
surface to center. Therefore, the ratio of Cu/Zn is very critical
for high strength, high damage tolerance, and corrosion resistance
performance required by aerospace application.
[0048] FIG. 7 gives the fracture toughness as function of Zn/Mg
weight percentage ratio. It can be seen that the invention alloy
Zn/Mg weight percentage ratio range of 4.0 to 5.3 gives the better
performance than other range. The Zn/Mg ratio strongly affects the
metastable and/or stable MgZn.sub.2 (.eta.' and/or .eta. Phase) and
its variant phases at different aging stages.
[0049] The more comprehensive strength and fracture toughness at
different through layers and orientations were evaluated for
invention alloys A, E, and K with 4'', 6'' and 7.5'' plate
thickness respectively. Table 4 gives the comprehensive strength
and fracture toughness testing results. T/2 represents half
thickness of plate, L, LT and ST indicates rolling direction, long
transverse direction, and short transverse direction
respectively.
TABLE-US-00004 TABLE 4 The comprehensive strength and fracture
toughness testing results Alloy A Invention Alloy E Alloy K Alloy
Invention Alloy Invention Alloy Plate Thickness (in.) 4.0 6.0 7.5
LT TYS @T/4 (ksi) 72.2 71.5 72.2 LT UTS @T/4 (ksi) 77.8 77.1 78.0
LT El. @ T/4 (%) 10.4 7.1 4.1 LT TYS @T/2 (ksi) 69.4 68.9 LT UTS
@T/2 (ksi) 75.0 75.4 LT El. @T/2 (%) 6.0 5.9 L TYS @ T/4 (ksi) 73.4
72.5 73.3 L UTS @ T/4 (ksi) 77.1 75.7 76.7 L El. @ T/4 (%) 15.3 9.5
10.6 L TYS @ T/2 (ksi) 73.7 74.6 L UTS @ T/2 (ksi) 78.1 79.6 L El.
@ T/2 (%) 9.2 8.8 ST TYS @ T/2 (ksi) 65.5 68.4 68.5 ST UTS @ T/2
(ksi) 75.4 75.4 75.7 ST El. @ T/2 (%) 8.3 5.2 3.7 K1c L-T @ T/4
(ksi-in.sup.1/2) 36.6 34.0 34.1 K1c T-L @ T/4 (ksi-in.sup.1/2) 28.7
30.4 28.9 K1c S-L @ T/2 (ksi-in.sup.1/2) 32.1 27.4 26.1
[0050] Stress corrosion resistance is critical for aerospace
application. The standard stress corrosion cracking resistance
testing was performed in accordance with the requirements of ASTM
G47 which is alternate immersion in a 3.5% NaCl solution under
constant deflection. Three specimens were tested per sample. All
specimens survived 30 days testing without failing under 30 ksi
stress level in ST direction. Meanwhile, the exfoliation corrosion
resistance was tested according to ASTM G34. The specimen size was
51 mm (2'') in the LT direction and 102 mm (4'') in the L
direction. Testing was performed at thickness positions of surface
(T/10) and plate center (T/2). All samples were rated as pitting
based on ASTM G34.
[0051] 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:
* * * * *