U.S. patent application number 10/829391 was filed with the patent office on 2005-03-17 for high strength aluminum alloys and process for making the same.
Invention is credited to Brooks, Charles E., Dorward, Ralph C., Matuska, Rob A., Parkinson, Ray D., Shaarbaf, Mory.
Application Number | 20050056353 10/829391 |
Document ID | / |
Family ID | 33563710 |
Filed Date | 2005-03-17 |
United States Patent
Application |
20050056353 |
Kind Code |
A1 |
Brooks, Charles E. ; et
al. |
March 17, 2005 |
High strength aluminum alloys and process for making the same
Abstract
High strength aluminum alloys based on the Al--Zn--Mg--Cu alloy
system preferably include high levels of zinc and copper to provide
increased tensile strength without sacrificing toughness. In
addition, small amounts of scandium are also preferably employed to
prevent recrystalization. Preferred ranges of the elements include
by weight, 8.5-11.0% Zn, 1.8-2.4% Mg, 1.8-2.6% Cu, 0.05-0.30% Sc
and at least one element from the group Zr, V, or Hf not exceeding
about 0.5%, the balance substantially aluminum and incidental
impurities. During formation of the alloys, a homogenization
process is preferably employed after alloy ingot casting in which a
slow rate of temperature increase is employed as the alloy is
heated as near as possible to its melting temperature. For the last
20-30 F below the melting temperature, the rate of increase is
limited to 20 F/hr. or less to minimize the amount of low melting
point eutectic phases and thereby further enhance fracture
toughness of the alloy.
Inventors: |
Brooks, Charles E.;
(Chandler, AZ) ; Dorward, Ralph C.; (Escalon,
CA) ; Parkinson, Ray D.; (Livermore, CA) ;
Matuska, Rob A.; (Heath, OH) ; Shaarbaf, Mory;
(Jackson, TN) |
Correspondence
Address: |
William A. Blake
Jones, Tullar & Cooper, P.C.
Eads Station
P.O. Box 2266
Arlington
VA
22202
US
|
Family ID: |
33563710 |
Appl. No.: |
10/829391 |
Filed: |
April 22, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60464654 |
Apr 23, 2003 |
|
|
|
Current U.S.
Class: |
148/549 ;
420/532 |
Current CPC
Class: |
C22F 1/06 20130101; C22F
3/00 20130101 |
Class at
Publication: |
148/549 ;
420/532 |
International
Class: |
C22C 021/10 |
Claims
What is claimed is:
1. An aluminum alloy product having high strength with good
toughness, containing by weight, 8.5-11.0% Zn, 1.8-2.4% Mg,
1.8-2.6% Cu, 0.05-0.30% Sc and at least one element from the group
Zr, V, or Hf not exceeding about 0.5%, the balance substantially
aluminum and incidental impurities.
2. The alloy product of claim 1, wherein said alloy contains about
0.03-0.25% Zr.
3. The alloy product of claim 1, wherein said alloy includes
8.8-10.2% Zn, 1.8-2.2% Mg and 2.0-2.4% Cu.
4. The alloy product of claim 3, wherein said alloy includes
0.05-0.10% Sc.
5. The alloy product of claim 4, wherein said alloy includes 0.06%
Sc.
6. The alloy product of claim 1, wherein said alloy includes
9.0-10.0% Zn, 1.8-2.2% Mg, 2.0-2.4% Cu and 0.05-0.10% Sc.
7. The alloy product of claim 1, wherein said alloy includes 0.06%
Sc.
8. The alloy product of claim 1, wherein said alloy includes about
0.03-0.10% Si and 0.03-0.12% Fe.
9. The aluminum alloy product of claim 1, wherein said product is
selected from the group including sporting goods such as baseball
and soft ball bats, golf shafts, lacrosse sticks, tennis rackets,
and arrows; aerospace components such as wing plates, bulkheads,
fuselage stringers, and structural extrusions and forgings; and
ordnance parts such as sabots and missile launchers.
10. A process for making an aluminum alloy product containing at
least Al, Zn, Mg and Cu, said method including the steps of:
casting said alloy product to form an alloy ingot; and homogenizing
said alloy ingot to minimize the amount of low melting point
eutectic phases therein by heating said ingot at a heating rate of
no more than 20.degree. F./hr. from a first temperature at least
about 20.degree. F. below the melting temperature of said ingot to
a second temperature of about 5.degree. F. below said melting
temperature.
11. The process of claim 10, wherein said first temperature is
about 30.degree. F. below said melting temperature.
12. The process of claim 10, wherein said first temperature is
selected to be about 870.degree. F. and said second temperature is
selected to be in the range of 885-890.degree. F.
11. The process of claim 10 where the alloy ingot is held at said
first temperature for at least 8 hours.
12. The process of claim 10, further comprising the step of
solution heat treating the alloy ingot at said second
temperature.
13. The process of claim 10, wherein said alloy ingot contains
8.5-11.0% Zn, 1.8-2.4% Mg, 1.8-2.5% Cu, and at least one element
from the group Zr, V, or Hf not exceeding about 0.5%, the balance
substantially aluminum and incidental impurities.
14. The process of claim 13, wherein said alloy contains 0.05-0.30%
Sc.
15. The process of claim 13, wherein said alloy contains about
0.03-0.25% Zr.
16. The process of claim 15, wherein said alloy contains 0.05-0.30%
Sc.
17. The process of claim 13, wherein said alloy ingot contains
8.8-10.2% Zn, 1.8 2.2% Mg and 2.0-2.4% Cu.
18. The process of claim 17, wherein said alloy ingot contains
9.0-10.0% Zn, 1.8-2.2% Mg and 2.0-2.4% Cu.
19. The process of claim 18, wherein said alloy includes 0.05-0.10%
Sc.
20. The process of claim 19, wherein said alloy includes 0.06%
Sc.
21. The process of claim 17, wherein said alloy includes 0.05-0.10%
Sc.
22. The process of claim 21, wherein said alloy includes 0.06%
Sc.
23. An aluminum alloy product having high strength with good
toughness, containing by weight, 9.0-11.0% Zn, 1.8-2.4% Mg,
2.2-2.6% Cu and at least one element from the group Zr, V, or Hf
not exceeding about 0.5%, the balance substantially aluminum and
incidental impurities.
24. The alloy product of claim 23, wherein said alloy contains
about 0.03-0.25% Zr.
25. The alloy product of claim 23, wherein said alloy includes
9.0-10.2% Zn, 1.8-2.2% Mg and 2.2-2.4% Cu.
26. The alloy product of claim 25, wherein said alloy includes
0.05-0.10% Sc.
27. The alloy product of claim 26, wherein said alloy includes
0.06% Sc.
28. The alloy product of claim 23, wherein said alloy includes
9.0-10.0% Zn, 1.8-2.2% Mg, 2.2-2.4% Cu and 0.05-0.10% Sc.
29. The alloy product of claim 23, wherein said alloy includes
0.06% Sc.
30. The alloy product of claim 23, wherein said alloy includes
about 0.03-0.10% Si and 0.03-0.12% Fe.
31. The aluminum alloy product of claim 23, wherein said product is
selected from the group including sporting goods such as baseball
and soft ball bats, golf shafts, lacrosse sticks, tennis rackets,
and arrows; aerospace components such as wing plates, bulkheads,
fuselage stringers, and structural extrusions and forgings; and
ordnance parts such as sabots and missile launchers.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit, under 35 U.S.C. 119(e),
of U.S. Provisional Application No. 60/464,654, which was filed on
Apr. 23, 2003.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates, in general, to a high
strength aluminum alloy based on the Al--Zn--Mg--Cu alloy system
and a process for forming the same. Although not limited thereto,
the alloys are particularly suited for use in sporting goods and
aerospace applications.
[0004] 2. Description of the Background Art
[0005] The highest strength aluminum alloys known at this time are
based on the aluminum-zinc-magnesium-copper system. Commercial
high-strength alloys currently being produced include AA7055
(nominally 8% Zn--2% Mg--2.2% Cu--0.10% Zr), AA7068 (nominally 7.8%
Zn--2.5% Mg--2.0% Cu--0.10% Zr) and a Kaiser Aluminum alloy
designated K749 (nominally 8% Zn--2.2% Mg--1.8% Cu--0.14% Zr).
These alloys are shown graphically on the equilibrium diagram in
FIG. 1, which depicts the published phase relationships at
860.degree. F. for an alloy containing 8% Zn. As may be seen, K749
is near a phase boundary, while the other two alloys are in
multiple phase fields. In the latter case all the alloying elements
are not in solid solution at 860.degree. F., and are not only
unavailable for age hardening, but the undissolved phases remaining
after heat treatment detract from toughness. Although solution heat
treating at a higher temperature than 860.degree. F. will dissolve
more of the solute, care has to be taken to ensure that the alloy
does not undergo eutectic melting, which is a common problem in
commercially cast alloys that have locally enriched regions as a
result of microsegregation that occurred during casting.
[0006] There is a need in many applications, such as sporting goods
and aerospace applications, for even stronger alloys based on the
aluminum-zinc-magnesium-copper system that do not sacrifice
toughness. However, this requirement presents a problem because, in
general, as the tensile strength of an aluminum alloy is increased,
its toughness decreases.
SUMMARY OF THE INVENTION
[0007] The present invention addresses the foregoing need in a
number of ways. More particularly, there are three distinct avenues
for increasing an alloy's strength while maintaining its toughness:
rich alloy chemistries; processing to maximize alloying
effectiveness; and preventing recrystallization. Rich alloys
provide more solute, which is potentially available for age
hardening to higher strength levels; effective processing ensures
that the solute is available for strengthening and not out of
solution as second phases, which detract from fracture toughness;
and maintaining an unrecrystallized microstructure optimizes both
strength and toughness.
[0008] To provide increased tensile strength without sacrificing
toughness through the use of rich chemistries, the present
invention comprises aluminum alloys based on the Al--Zn--Mg--Cu
alloy system that preferably include high levels of zinc and
copper. In addition, small amounts of scandium are also preferably
employed to prevent recrystallization. Each of the alloys
preferably includes at least 8.5% Zn and 1.8% Cu by weight. Higher
levels of each of these elements up to about 11.0% Zn and 2.6% Cu
can be used. The preferred ranges of all elements in the alloys
include by weight, 8.5-11.0% Zn, 1.8-2.4% Mg, 1.8-2.6% Cu, and at
least one element from the group Zr, V, or Hf not exceeding about
0.5%, the balance substantially aluminum and incidental impurities.
In the preferred embodiments, 0.05-0.30% Sc is also included in the
alloys to prevent recrystallization.
[0009] To maximize alloying effectiveness during formation of the
alloys, a homogenization process is preferably employed after alloy
ingot casting in which a slow rate of temperature increase is
employed as the alloy is heated as near as possible to its melting
temperature. In particular, for the last 20-30.degree. F. below the
melting temperature, the rate of increase is limited to 20.degree.
F./hr. or less to minimize the amount of low melting point eutectic
phases and thereby further enhance fracture toughness of the
alloy.
[0010] The foregoing alloys and processing operations enhance the
properties of the Al--Zn--Mg--Cu alloy system, such that they can
be more effectively employed in numerous applications. Specific
products or items in which the subject alloys can be employed
include, among others, sporting goods including baseball and soft
ball bats, golf shafts, lacrosse sticks, tennis rackets, and
arrows; and aerospace application including aerospace components
such as wing plates, bulkheads, fuselage stringers, and structural
extrusions and forgings; and ordnance parts such as sabots and
missile launchers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The features and advantages of the present invention will
become apparent form the following detailed description of a
preferred embodiment thereof, taken in conjunction with the
accompanying drawings, in which:
[0012] FIG. 1 is an equilibrium diagram which depicts the published
phase relationships at 860.degree. F. as a function of percentages
of Cu and Mg for three known alloys each containing about 8%
Zn;
[0013] FIG. 2 is an equilibrium diagram which depicts the phase
relationships at 860.degree. F. as a function of percentages of Cu
and Mg for two alloys formed in accordance with the preferred
embodiments and compared with a third known alloy containing about
8% Zn;
[0014] FIG. 3 is a graph depicting fracture toughness as a function
of the average (of longitudinal and transverse) yield strength for
a number of sample alloys;
[0015] FIG. 4 is a graph illustrating the effect on yield strength
of adding scandium to an alloy that has been extruded in a first
case and formed into a sheet in a second case;
[0016] FIG. 5 is a graph depicting second phase volume percent as a
function of heating rate in a formation process for Alloy
AA7068;
[0017] FIG. 6 is an equilibrium diagram which depicts the phase
relationships at 860.degree. F. as a function of percentages of Cu
and Mg for two alloys formed in accordance with the preferred
embodiments; one with 9% Zn and the other with 10% Zn;
[0018] FIG. 7 is a graph illustrating the effect of magnesium and
copper on strength of Al--Zn--Mg--Cu alloys; and
[0019] FIG. 8 is a graph illustrating the effect of zinc on
strength of Al--Zn--Mg--Cu alloys.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] The following examples illustrate how alloy modifications
and efficient processing operations can be used to enhance the
properties of the Al--Zn--Mg--Cu alloy system in accordance with
the preferred embodiments of the present invention, such that they
can be more effectively utilized in sporting goods and aerospace
applications.
EXAMPLE 1
[0021] The alloy compositions listed in Table 1 were cast as 9"
billet, most of which contained a relatively high nominal zinc
content of 9%.
1 TABLE 1 % by wt. (Spectrographic analysis) Alloy No. Si Fe Cu Mg
Zn Zr Sc 45 0.02 0.04 1.41 2.57 7.96 0.12 0.053 36 0.03 0.06 1.91
2.17 9.02 0.15 0.054 39 0.04 0.05 1.28 2.74 9.02 0.13 0.059 43 0.03
0.03 1.44 2.55 9.04 0.13 0.053 47 0.04 0.06 1.59 2.34 8.95 0.14
0.055
[0022] These alloys are depicted on the 860.degree. F. (F=degrees
Fahrenheit) phase diagram in FIG. 2 together with a K749 "control"
containing nominally 8% Zn. Note that all of these alloys contain
about 0.05% scandium, an element which in combination with
zirconium is effective in preventing recrystallization.
[0023] The billets were homogenized at 880.degree. F. and extruded
to seamless tubes 4" in diameter with a 0.305" wall thickness.
After sections of the extrusions were cut and flattened to pieces
about 12" square, they were solution heat treated at 880.degree. F.
and quenched in cold water. They were then tested for tensile
properties and fracture toughness in a peak-aged condition, the
results of which are provided in Table 2.
2 TABLE 2 Yield Strength (ksi) Kpmax Alloy No. Cu Mg Zn Long.
Trans. (ksi rt.in.) K749 1.98 2.18 8.02 91.5 92.4 28.6 36 1.91 2.17
9.02 94.9 94.6 24.5 39 1.28 2.74 9.02 92.7 94.6 20.2 45 1.41 2.57
7.96 91.1 89.9 26.1 43 1.44 2.55 9.04 93.9 94.9 21.3 47 1.59 2.34
8.95 93.9 95.2 22.7
[0024] The effect of raising the zinc from 8% to 9% can be seen by
comparing alloys K749 with #36 (at nominally 2.2% Mg--2% Cu) and
alloy #45 with #43 (at nominally 2.6% Mg--1.4% Cu). The average
increase in yield strength is about 3.5 ksi. The observed decrease
in toughness is what would be expected in accordance with the
strength increment, i.e., approximately 1 ksi rt.in. per ksi in
yield strength; however, the high Mg--low Cu alloys have a poorer
combination of strength and toughness than the more balanced
K749-type composition. This is shown graphically in FIG. 3, where
fracture toughness is plotted against the average (of longitudinal
and transverse) yield strength.
EXAMPLE 2
[0025] Another alloy similar to #36, except for a 0.11% Sc content
(9.22% Zn--2.14% Mg--1.88% Cu) was prepared and likewise extruded
to a 4" diameter tube with a 0.305" wall thickness. Tubes of this
alloy together with K749 and #36 (both with 0.05% Sc) were
subsequently cold drawn to a diameter of 2.25" and a 0.10" wall
thickness. After solution heat treating and aging, longitudinal
yield strengths were measured with the results in Table 3.
3 TABLE 3 Yield Strength Alloy Cu Mg Zn Sc (ksi) K749 1.98 2.18
8.02 0.050 99.3 36 1.91 2.17 9.02 0.054 103.3 37 1.88 2.14 9.22
0.107 104.0
[0026] Note that the experimental alloys with the higher zinc
concentrations again were significantly stronger than the K749
alloy with 8% Zn. Also, noteworthy is the fact that both alloys
containing 0.05% Sc maintained much higher strength levels after
the cold drawing operation than was evident in the as-extruded
condition (compare with previous table). In other words, as little
as 0.05% Sc was sufficient to prevent recrystallization during the
solution heat treating operation. As will be discussed in the next
example, this is important from an economic viewpoint, because
scandium is extremely rare and very expensive.
EXAMPLE 3
[0027] It has been recognized for a number of years that scandium
in combination with zirconium is an effective recrystallization
inhibitor. A Russian review article noted that it is desirable to
add scandium to aluminum alloys in a quantity from 0.1 to 0.3%
together with zirconium (0.05-0.15%). However, the greatest effect
is observed for alloys not containing alloy elements combining with
scandium in insoluble phases; with a limited copper content
[scandium combines with copper] alloying with scandium together
with zirconium of Al--Zn--Mg--Cu and Al--Cu--Li alloys is possible.
As such, commercial alloys based on Al--Zn--Mg--Sc--Zr have been
developed.
[0028] Two potential drawbacks to scandium additions to 7XXX alloys
containing about 2% copper are evident:
[0029] 1) the copper level is high enough to combine with scandium,
thereby rendering it ineffective, and
[0030] 2) the high price of scandium; at the 0.2% level it would
add about $10 a pound to the cost of the aluminum alloy.
[0031] It would therefore be economically and technically
attractive if scandium levels could be effectively used below those
recommended in the Russian literature.
[0032] Alloys of the compositions listed in the following table
were prepared as 5" diameter billets, which were processed as
described below in Table 4.
4 TABLE 4 % by wt. Alloy No. Si Fe Cu Mg Zn Zr Sc A 0.03 0.04 1.95
2.20 8.07 0.11 0.00 B 0.03 0.05 1.86 2.17 8.05 0.00 0.22 C 0.03
0.05 1.89 2.18 8.09 0.11 0.06 D 0.03 0.04 1.84 2.12 8.11 0.12 0.11
E 0.03 0.05 1.95 2.18 8.08 0.11 0.22
[0033] The ingots were homogenized at 875.degree. F. using a
50.degree. F./hr heating rate and air cool, and then reheated to
800.degree. F. and extruded to a 0.25" by 3" flat bar. Sections of
each extrusion were annealed at 775.degree. F. for 3 hr, cooled
50.degree. F./hr to 450.degree. F., held 4 hr and cooled 50.degree.
F./hr to room temperature. The sections were then cold rolled to
0.040" sheet using five pass reductions (84% total reduction). The
sheets were solution heat treated at 885.degree. F. for 30 min,
quenched in cold water, and then aged to the peak strength
condition (10 hrs. at 305.degree. F.). The as-extruded bars were
also heat treated similarly and both products were tested for
transverse tensile properties, as listed in Table 5. The specific
effects of scandium on strength are also shown in FIG. 4.
5 TABLE 5 Yield Strength UTS (ksi) (ksi) Alloy No. % Zr % Sc
Extrusion Sheet Extrusion Sheet A 0.11 0 94.7 90.7 91.4 87.8 B 0
0.22 88.2 92.0 86.1 88.4 C 0.11 0.06 95.7 97.1 92.2 93.3 D 0.12
0.11 95.2 96.6 92.2 93.3 E 0.11 0.22 94.5 96.5 91.1 92.5
[0034] A number of points are evident from these results:
[0035] 1) The strongest alloy in both extrusion and sheet form
contains 0.06% Sc (with 0.11% Zr).
[0036] 2) At the 0.1% Zr level, 0.06% Sc is effective in raising
the strength of the sheet product by about 6 ksi.
[0037] 3) 0.22% Sc in the absence of zirconium raises the strength
of the sheet product by only 1 ksi, and lowers the extrusion
strength by about 6 ksi. The effectiveness of only 0.06% Sc in
preventing recrystallization was confirmed by comparing the
microstructures of the sheet products containing (a) 0.11% Zr, (b)
0.11% Zr+0.06% Sc, and (c) 0.22% Sc (no Zr) .
[0038] In view of the foregoing, the preferred range in the alloys
for Sc is 0.05-0.30%, with a more preferred range of 0.05-0.10% and
a most preferred value of 0.06%.
EXAMPLE 4
[0039] As noted earlier it is important that undissolved second
phases not remain after processing so that fracture toughness can
be maximized. To illustrate how homogenizing practice can affect
the amount of such undissolved phase(s), samples of as-cast AA7068
alloy billet were heated from 850.degree. F. at various rates in a
differential scanning calorimeter (DSC), and the energy associated
with eutectic melting, which started at about 885.degree. F. was
measured. This energy measurement is directly proportional to the
amount of undissolved second phase remaining at the incipient
melting point, and the relationship between these factors has been
determined by quantitative microscopy. As was shown in FIG. 1, the
relatively rich 7068 alloy is well within a multiple phase field at
860.degree. F., and would be expected to have a significant amount
of undissolved second phase unless processed very effectively. FIG.
5 shows how heating rate affects the amount of this phase as
determined from the DSC data.
[0040] Note that a slow heating rate of about 10.degree. F./hr
reduces the amount of second phase (probably "S" and "M") to a
level below 1 vol. %. One would expect that a .about.5.degree.
F./hr heating rate would reduce the "soluble" portion to near zero.
We note that for heating rates of 10-20.degree. F./hr, the volume
fraction of undissolved eutectic is no greater than the amount of
insoluble Fe-containing constituent (independent of heating rate or
homogenization temperature) at a nominal 0. 12% Fe level (approx. 1
vol. %).
EXAMPLE 5
[0041] A series of alloys containing either nominally 9% or 10%
zinc (see Table 6) were cast as 6" diameter billets. Copper and
magnesium concentrations ranged from 2.0% to 2.5% and 2.0 to 2.4%,
respectively, such that a nominal Mg/Cu ratio of 1.0 was
maintained. These compositions are shown diagrammatically in FIG. 6
relative to the 860.degree. F. equilibrium diagram for 8% zinc.
6 TABLE 6 % by wt. Alloy No. Si Fe Cu Mg Zn Zr 84 0.03 0.07 1.88
1.96 9.84 0.10 88 0.04 0.07 2.12 2.08 8.52 0.10 86 0.06 0.08 2.34
2.42 8.58 0.10 94 0.07 0.09 2.00 2.14 10.04 0.10 95 0.07 0.08 2.30
2.36 10.18 0.11 99 0.08 0.08 2.46 2.50 10.00 0.10
[0042] The billets were homogenized for 8 hr at 870.degree. F. plus
12 hr at 885-890.degree. F. using a 10.degree. F./hr heating rate
from 870.degree. F. This heating rate was chosen based on FIG. 5,
which showed that a slow heating rate of 5-20.degree. F./hr is
desired to minimize the amount of undissolved second phase in the
alloy that would detract from good mechanical properties,
particularly fracture toughness. This slow heating rate should
preferably be employed from 20-30 degrees below the alloy melting
temperature, up to the homogenization temperature, which is chosen
to be as close to the melting temperature, e.g., within about
5.degree. F., as possible. The homogenized billets were then
extruded to a 0.75" by 2.5" bar section, which was heat-treated at
885.degree. F. The resultant T6 tensile properties obtained by
artificial aging for 24 hours are listed in Table 7 and are shown
graphically in FIG. 7, where yield is plotted against magnesium
plus copper content.
7 TABLE 7 Alloy UTS No. (ksi) YS (ksi) % Elgn 84 100.7 97.1 16.3 88
103.0 99.0 15.5 86 105.0 100.6 15.0 94 103.5 100.6 15.5 95 106.9
103.9 13.5 99 106.9 103.7 11.8
[0043] This graph shows that strength increases up to a
concentration of about 4.7% total magnesium plus copper. Since it
is known that magnesium levels above about 2.2% result in decreased
toughness in Al--Zn--Mg--Cu alloys, it is desirable to maintain the
copper at a level of about 2.2% or more to obtain the maximum
strength benefit.
[0044] Additional experiments were conducted to evaluate the effect
that different levels of zinc have on yield strength in
Al--Zn--Mg--Cu alloys. Four different allows were evaluated as
listed in Table 8. The results are graphically depicted in FIG. 8
which show that strength of the Al--Zn--Mg--Cu alloys increases
almost linearly in the range of 8.6% and 10.1% Zn.
8TABLE 8 Alloy # Si % Fe % Cu % Mg % Zn % Ti % Zr % Sc % 0189 0.04
0.08 2.14 1.89 8.60 0.012 0.12 0.05 0190 0.03 0.09 2.31 1.86 9.21
0.016 0.13 0.05 0191 0.03 0.11 2.35 1.81 9.63 0.019 0.13 0.05 0192
0.04 0.10 2.33 1.87 10.13 0.015 0.12 0.05
[0045] Although the present invention has been described in terms
of a number of preferred embodiments and variations thereon, it
will be understood that numerous additional variations and
modifications may be made without departing from the scope of the
invention. Thus, it is to be understood that within the scope of
the appended claims, the invention may be practiced otherwise than
as specifically described above.
* * * * *