CA2281640A1 - Vanadium-free aluminum alloy suitable for sheet and plate aerospace products - Google Patents

Abstract

There is claimed a sheet or plate structural member suitable for aerospace applications and having improved combinations of strength and toughness. The member is made from a substantially vanadium-free aluminum-based alloy consisting essentially of: about 4.85-5.3 wt.% copper, about 0.5-1.0 wt.%
magnesium, about 0.4-0.8 wt.% manganese, about 0.2-0.8 wt.% silver, about 0.05-0.25 wt.% zirconium, up to about 0.1 wt.% silicon, and up to about 0.1 wt.%
iron, the balance aluminum, incidental elements and impurities, the Cu:Mg ratio of said alloy being between about 5 and 9, and more preferably between about 6.0 and 7.5. The invention exhibits a typical tensile yield strength of about 77 ksi or higher at room temperature and can be processed into various lower wing members or into the fuselage skin of high speed aircraft.

Description

WC~ 98/39494 PCT/US97/03638 _ 1 -VANADIUM-FREE ALUMINUM ALLOY S'fJITABLE FOF~
SHEET AND PLATE AERO~pA~''~' pRODUCT~
BACRGROL~D OF THE I~NTIC,~
1. Field of the Invention - This invention relates to the field of age-hardenable aluminum alloys suitable for aerospace and other demanding applications. The invention further relates to new aluminum alloy products having improved combinations of strength and toughness suitable for high speed aircraft applications, especially fuselage skins and wing members. For such applications, resistance to creep and/or stress corrosion cracking may be critical.

2. Technology Review - One important means for enhancing the strength of aluminum alloys is by heat treatment. Three basic steps generally employed for the heat treatment of many aluminum alloys are: (1) solution heat treating; (2) quenching; and (3) aging.
Some cold working may'also be performed between quenching and aging. Solution heat treatment consists of soaking an alloy at a sufficiently high temperature and for a long enough time to achieve a near homogeneous solid solution of precipitate-forming elements within the alloy. The objective is to take into solid solution the most practical amount of soluble-hardening elements. Quenching, or rapid cooling of the solid solution formed during solution heat treatment, produces a supersaturated solid solution at room temperature. Aging then forms strengthening precipitates from this rapidly cooled, supersaturated solid solution. Such precipitates may form naturally at ambient temperatures or artificially using elevated temperature aging techniques. In natural aging, quenched alloy products are held at temperatures ranging from -20° to +50°C., but most .
typically at room temperature, for relatively long periods of time. For some alloy compositions, precipitation hardening from just natural aging produces materials with useful physical and mechanical properties. In artificial aging, a quenched alloy is held at temperatures typically ranging from 100° to 190°C., fox time periods typically ranging from 5 to 48 hours, to cause some precipitation hardening in the final product.
The extent to which an aluminum alloy's strength can be enhanced by heat treatment varies with the type and amount of alloying constituents present.
For example, adding copper to aluminum improves alloy strength and, in some instances, even enhances weldability to some point. The further addition of magnesium to such A1-Cu alloys can improve that alloy's resistance to corrosion, enhance its natural aging response (without prior cold working) and even increase its strength somewhat: At relatively low Mg levels, however, that alloy's weldability may decrease.
One commercially available alloy containing both copper and magnesium is 2024 aluminum (Aluminum Association designation). A representative composition within the range of 2024 is 4.4 wt.~ Cu, 1.5 wt.~ Mg, 0.6 wt.~ Mn and a balance of aluminum, incidental elements and impurities. Alloy 2024 is widely used because of its high strength, good toughness, and good natural-aging response. In some tempers, it suffers from limited corrosion resistance, however.
Another commercial A1-Cu-Mg alloy is sold as 2519 aluminum (Aluminum Association designation). This alloy has a representative composition of 5.8 wt.~ Cu, 0.2 wt~ Mg, 0.3 wt.~s Mn, 0.2 wt.~ Zr, 0.06 wt.~ Ti, 0.05 wt.~s V and a balance of aluminum, incidental elements and impurities. Alloy 2519 developed as an improvement to alloy 2219, is presently used for some . 5 military applications including armor plate.
According to U.S. Patent No. 4,772,342, Polmear added silver to an A1-Cu-Mg-Mn-V system to increase the elevated temperature properties of that alloy. One representative embodiment from that patent has the composition 6.0 wt.$ Cu, 0.5 wt.~ Mg, 0.4 wt.~
Ag, 0.5 wt.~ Mn, 0.15 wt.~ Zr, 0.10 wt.$ V, 0.05 wt.~
Si and a balance of aluminum. According to Polmear, the increase in strength which he observed was due to a plate-like t2 phase on the ~11.1~ planes arising when both Mg and Ag are present. While the typical tensile yield strengths of Polmear's extruded rod sections measured up to 75 ksi, this inventor could not repeat such strength levels for other property forms. When sheet product was made using Polmear's preferred composition range for comparative purposes, such sheet product only exhibited typical tensile yield strengths of about 70 ksi compared to the 77 ksi or higher typical strength levels observed with sheet product equivalents of this invention.
SL.'~ARv OF THE INVEu't'rnrr It is a principal objective of this present invention to provide aerospace alloy products having improved combinations of strength and fracture toughness. It is another objective to provide such alloy products with good long time creep resistance, typically less than 0.1~ creep after 60,000 hours at ' 130°C. and 150 MPa.
It is yet another objective to produce Al-Cu-~ Mg-Ag-Mn alloy products with an overall enhanced fracture toughness performance. It is another objective to provide such alloy products with higher strengths at equal or greater toughness performance levels when compared with non-extruded product forms made according to Polmear's patented, vanadium-containing composition.
Yet another main objective is to provide aerospace alloy products suitable for use as fuselage and/or wing skins on the next generation, supersonic transport planes.
Another objective is to provide 2000 Series aluminum alloy products with little to no 0 20 constituents. Yet another objective is to provide those alloy products with improved stress corrosion cracking resistance. Still another objective is to provide aluminum alloy products with better strength/toughness combinations than 2219 aluminum, and better thermal stability than 2048, 6013 or 8090/8091 aluminum.
These and other advantages of this invention are achieved with an age-formable, aerospace structural part having improved combinations of strength and toughness. The part is made from a substantially vanadium-free, aluminum-based alloy consisting essentially of: about 4.85-5.3 wt.~ copper, about 0.5-1.0 wt.~ magnesium, about 0.4-0.8 wt.~ manganese, about 0.2-0.8 wt.~s silver, about 0.05-0.25 wt.~ zirconium, up to about 0.3. wt.~ silicon, and up to about 0.1 wt.~
iron, the balance aluminum, incidental elements and impurities. Sheet and plate products made with an alloy of that composition exhibit typical tensile yield strength levels of about 77 ksi or higher at room temperature. Such rolled product forms can be further processed into final shapes, including but not limited to supersonic aircraft fuselage skin and lower wing members.
The alloy products of this invention differ from those described in the Polmear patent in several regards, izamely: (a) this invention recognizes that Ag additions enhance the achievable strengths of T6-type -tempers, but that Ag has a much smaller effect on T8-type strengths; (b) for the A1-Cu-Mg-Ag alloys with higher Cu: Mg ratios studied by Polmear, T6- and T8-type strengths are similar. But as this Cu:Mg ratio , 5 decreases, the effects of stretching per T8-type processing becomes beneficial; (c) these alloy products demonstrate that typi~aal strengths even higher than reported by Polmear for extrusions can be achieved in rolled product forms when the Cu:Mg ratio of Polmear is reduced to an intermediate Level and when some stretching prior to artificial aging may be utilized;

(d) this invention identifies the preferred (i.e.

intermediate) Cu: Mg ratios required to achieve such very high typical strength levels; (e) it further recognizes the importance of Mn additions for texture strengthening; (f) the invention identifies Zn as a potential partial substitute for more costly Ag additions in alternate embodiments of this invention;

and (g) it does not rely on vanadium for performance enhancements.

B1z?E~' DESCRIPTION OF THE DRAWINGS

Further features, objectives and advantages of the present invention shall become clearer from the following detailed description made with reference to the drawings in which:

Figure 1 is a graph comparing the Rockwell B

hardness values as a function of aging time for invention alloy samples C and D from Table I, specimens of both alloy samples having been stretched by 8~, or naturally aged for 10 days prior to artificial aging at 325F.;

Figure 2a is a graph comparing the Rockwell B

hardness value for three silver bearing A1-Cu-Mg-Mn ' alloy samples R, L and M from Table I, all of which were stretched 8~ prior to artificial aging at 325F.;

Figure 2b is a graph comparing the Rockwell B

hardness values for alloy samples R, L and M after specimens of each were naturally aged for ZO days prior to artificial aging at 325°F.;
Figure 3 is a graph comparing the typical , tensile yield strengths of alloy samples K, L and M
after each were aged to a T8- and T6-type temper , respectively;
Figure 4 is a graph comparing typical tensile yield strengths of alloy samples H, D, J, and F from Table I, all of which were aged to a T8-type temper, then subjected to exposure conditions for simulating Mach 2.0 service;
Figure 5 a.s a graph comparing the plane stress fracture toughness (or Rc) values versus typical tensile yield strengths for alloy sheet samples N, P, Q, R, S, T, U and V from Table II, after each had been artificially aged to a T8-type temper;
Figure 6 a.s a graph comparing Rr crack extension resistance values at Daeff=0.4 inch versus typical tensile yield strengths for alloy samples W, X
and Y from Table III when stretched by either 0.5~, 2~
or 8~ prior to artificial aging at 325°F.;
Figure 7a is a graph comparing typical tensile yield strengths of zirconium-bearing alloy samples Z and AA from Table III when stretched by various percentages prior to artificial aging at 325°F.
to show the affect of vanadium thereon; and Figure 7b a.s a.graph comparing typical tensile yield strengths of zirconium-free alloy samples CC and DD from Table III when stretched by various percentages prior to artificial aging at 325°F. to show the affect of vanadium thereon.
DETAILED DES RTn~rTnN OF PREFERRFn F~nr~T~,lEt'rT~~ ' Definitions: For the description of preferred alloy compositions that follows, all references to percentages are by weight percent (wt.~) unless otherwise indicated.
When referring to any numerical range of - 7 _ values herein, such ranges are understood to include each and every number and/or fraction between the stated range minimum and maximum. A range of about 4.85-5.3~ copper, for example, would expressly include all intermediate values of about 4.86, 4.87, x.88 and 4.95 all the way up to and including 5.1, 5.25 and 5.29 Cu. The same applies to all other elemental ranges set forth below such as the intermediate Cu: Mg ratio level of between about 5 and 9, and more preferably between about 6.0 and 7.5.
Then referring to minimum versus typical strength values herein, it is to be understood that minimum levels are those at which a material's property value can be guaranteed or those at which a user can rely for design purposes subject to a safety factor.
In some cases, "minimum" yield strengths have a statistical basis such that 99~ of that product either conforms or is expected to conform to that minimum guaranteed with 95~ confidence. Fox purposes of this invention, typical strength levels have been compared to Polmear's typical levels as neither material has been produced (a) on place scale; and (b) in sufficient quantities as to measure a statistical minimum therefor. And while typical strengths may tend to run a little higher than the minimum guaranteed levels associated with plant production, they at least serve to illustrate an invention's improvement in strength properties when compared to other typical values in the prior art.
As used herein, the term "substantially-free"
means having no significant amount of that component ' purposefully added to the composition to import a certain characteristic to that alloy, it being ' understood that trace amounts of incidental elements and/or impurities may sometimes find their way into a desired end product. For example, a substantially vanadium-free alloy should contain less than about 0.1~

WO 98!39494 PCT/US97/03638 V, or more preferably less than about 0.03 V, due to contamination from incidental additives or through contact with certain processing and/or holding .
equipment. All preferred first embodiments of this invention are substantially vanadium-free. On a , preferred basis, these same alloy products are also substantially free of cadmium and titanium.
BACKGROUND OF THE INtTENTIO~
Recently, there has been increased interest in the design and development of a new supersonic transport plane to eventually replace the Anglo/French Concorde. The high speed civil transport (HSCT) plane of the future presents a need for two new materials: a damage tolerant material for the lower wing and fuselage; and a high specific stiffness material for the plane's upper wing. An additional set of requirements will be associated with performance both at and after elevated temperature exposures.
Of conventional ingot metallurgy alloys, 2229 and 2618 aluminum are the two currently registered alloys generally considered for elevated temperature use. Both were registered with the Aluminum Association in the mid 1950°s. A nominal composition for alloy 2219 is 6.3 wt.~ Cu, 0.3 wt.~ Ma, 0.1 wt.~ V, 0.15 wt.~ Zr, and a balance of aluminum, incidental elements and impurities. For alloy 2618, a nominal composition contains 2.3 wt.~ Cu, 1.5 wt.$ Mg, 1.1 wt.~
Fe, 1.1 wt.$ Ni and a balance of aluminum, incidental elements and impurities. Both belong to the 2000 Series Al-Cu-Mg systems, but because of different Cu: Mg ratios, these two alloys are believed to be strengthened by different means: 2219 generally by p' precipitates, and 2618 generally by S' precipitates.
Proposed End Use Sheet and Plat Producer While the next generation of high speed civil transport (HSCT) aircraft may riot be faster than today's Concorde, they will be expected to be larger, _ g travel longer distances, and carry more passengers so as to operate at more competitive costs with subsonic aircraft. For such next generation aircraft, a more damage tolerant material will be desired for both the lower wing and fuselage members.
Although different airframers may have different conceptual designs, each emphasizes speeds of Mach 2.0 to 2.4 with operating stresses of I5 to 20 ksi. Future damage tolerant materials will be expected to meet certain requirements associated with thermal exposures at the high temperatures representative of such supersonic service, namely: (a) a minimal loss in ambient temperature properties should occur during the lifetime of the aircraft; (b) properties at supersonic cruise temperatures should be sufficient; and (c) minimal amounts of allowable creep during the plane's la.fetime. For many of the test described below, it should be noted that exposures at 300°F. for 100 hours were intended to simulate Mach 2.0 service.
Promising strength levels were obtained for several alloy samples produced as small 2 lb ingots and compared for this invention. Another set of sample alloy compositions were run on direct chill cast, large (i.e., greater than 500 lb.) laboratory ingots. Sets of 20 lb. alloy ingots were also prepared to study the effect of combining both Ag and Zn in the invention alloy. Sample alloy compositions, which cover Cu: Mg ratios ranging from 2.9 to 20, various Mn levels and alternating levels of Ag and/or Zn, are summarized in Tables I, II and III.

9,494 PCT/US97/03638 Table I
Chemical Analyses for Al-Cu-Mg-Mn-(Ag) Alloy samples Produced as 11/~~ x 23i~~ ,r ~ n n...,.,".. .~_, ~ r ~ .~~
Sample Cu Mg Mn V Zr Fe ~ Ag ' ~
a Si A 4.4 1.5 0.6 0.01 0.00 0.00 0.00 --B 4.5 1.5 0.6 0.00 0.00 0.01 0.00 0.5 C 5.1 0.8 0.6 0.01 0.00 0.00 0.00 --D 5.1 0.8 0.6 0.00 0.00 0.00 0.00 0.5 E 5.8 0.3 0.6 0.01 0.00 0.00 0.00 --F 6.0 0.3 0.6 0.01 0.00 0.01 0.00 0.5 G 5.2 0.7 0.06 0.00 0.00 0.00 0.00 H 5.3 0.8 0.06 0.00 0.00 0.00 0.00 0.6 I 5.9 0.3 0.06 0.00 0.00 0.00 0.00 --J 6.0 0.3 0.05 0.00 0.00 0.00 0.00 0.5 I5 R 4.4 1.6 0.6 0.00 0.00 0.01 0.00 0.5 L 5.0 0.8 0.6 0.00 0.00 0.00 0.00 0.5 M 6.0 0.3 0.6 0.01 0.00 0.00 0.00 0.5 Table II
Chemical Analyses for A1-Cu-Mg-Mn (Ag) Alloy samples Produced as DC caQt ~,n v , ~n .. tnn T___~_ W ~v Sample Cu Mg Mn V Zr Fe VO Ag Si N 5.71 O.I8 0.29 0.09 0.15 0.05 0.06 --P 5.83 0.52 0.30 0.10 0.14 0.05 0.05 --Q 5.75 0.52 0.30 0.09 0.16 0.06 0.05 0.49 R 5.18 0.82 0.00 0.00 0.16 0.05 0.05 0.50 S 5.12 0.82 0.60 0.13 0.15 0.06 0.05 0.49 T 5.23 0.82 0.59 0.10 0.14 0.07 0.05 --U 6.25 0.52 0.60 0.3.0 0.15 0.05 0.05 0.51 V 6.62 0.51 1.01 0.10 0.15 0.06 0.05 0.51 ' WO 98/39494 PCTlUS97/03638 Table III
Chemical Analyses for Al-Cu-Mg-Mn (Ag, Zn) Alloy samples Produced as 2 ~~ x 10 ~~ x ~ ~ ~r Rnnlr Mr.'1 r1 T".~..-.~
Sample Cu Mg Mn V Zr Fe Si Ag Zn W 4.63 0.80 0.61 -- 0.17 0.06 0.04 0.51 0.00 ' X 4.66 0.81 0.62 -- 0.17 0.06 0.04 0.00 0.36 Y 4.62 0.80 0.62 -- 0.16 0.06 0.04 0.25 0.16 Z 4.88 0.81 0.60 0.01 0.13 0.07 0.05 0.50 0.00 AA 5.02 0.84 0.61 0.10 0.13 0.06 0.05 0.53 0.01 ~B 4.75 0.83 0.62 0.02 0.00 0.05 0.05 0.00 0.00 CC 4.97 0.84 0.61 0.02 0.00 0.06 0.05 0.53 0.00 DD 4.97 0.84 0.62 0.11 0.00 0.07 0.05 0.53 0.00 Table IV shows the effect of Ag additions on Rockwell B hardness values arid tensile strengths of A1-Cu-Mg-Mn-(Ag) alloy samples aged according to T6- and T8-type tempers. Alloy samples with and without silver have been grouped with comparative samples having similar Cu: Mg ratios.

O O O O, O O O O ~
O

.-~ r.;
W O ~ ~' ~ .-~ .-.~~ .M-~~ ~ O~

~ _N

i ~".~, ~ d- 00 V7 Ov O O V: t~ 00 n - ' P~ ~ _ 00 0~ d ri ~ ~ ~ n ~
d ...'''-'~~(~ l~ i~ ~
N ~ ~
~

-r a) ~ ~"~ C/~ C
p ry' ' +-~

~ H
.~ ~n O v0 V t~ ~

: t cn d wn N

do U
~

.

O ~, ~ ~ O 00 M O~ O O1 l~ ~h o0 M rt N d' Sri Op pp U

'~ cd ~
i=.~

V y.r ~ ~ O O O O ~ O O O
N ' ~
~

O D ~.,~.,V7 .--.~~ O 0 0 ~ ~

H~' w~~

~

H

H ~

_ tt3 :--~ O tr1 l~
' Lj ~p..~-i _ M M O ~t M
N -f", d' ~O
~ .- 01 ' ~ .~, ..-n N .~4' d M

"CJ
H

H

H
~ ~~ ' by ~ n ~r ~ O M V~ O~ ~n M v~ N
N

"S , ~ d' t~ 01 M O 00 O d-~t-w o ~ ~ n ~
on 00 0 ~ oy r o U N i _ ~ O l~ p O p i~ OO T".e~",00 00 ~' H ..

i ~ 1 ~ I ~ ~

1 f ~J O O O

U U ~~ ~~ U U ~ ~ ~~ ~

x ~

U ~U ,~ .~ ~U ~U
~o 0 0 . .~ ~n bn bn ~

m v r~ w w a , a H

SUBSTITUTE SHEET (RULE 26) U
O
"

N

TJ
U
N

Cd o +S ~
s o 'C~ U
NN~~O

Cp O ~O ~n o aW n O CV ~ in ~
~
a n .s'~ _4 c b~

W O TJ +..O
U N

U U 'Tf b ,-~ ~ U ~,' ~ U

a~ H~ ~ Q,~ ~ ~ N
O

.. ~Y .--~N N O p .""'. ~ '~ ~ v"
bA O' '~ ~ p ~

.. O O ~D N ., ~ ~ ~ ~ ,~ ~ ~ 'C 'z3 ~ ..~, ~ y ' 'r ~~ ~ ~ l~ 00 t~ 00 ~ ~ ~ U ~ G~
N , +..
S~ ~, U ~ .~..~ ~
v.-n .._, E-~N

- n b bD. \O M ~ M ~; .-~ ~ r-' ~, ~
~ N ~'' U
' H~~ ~o ~.~ ~,b.~ ..fl ' U O ~c , U
N~~

O~~
_ ~
<~ ~ U s;

c~ v v' V ~ ' N

~H ~ fs.
o ~

c~~ ~~'' ~~ ~ ~o ~

M M O .~
~ .-~ ..-~--~ ~ ~ L~ U '~U"
y .~
Q.,o w U a o . o d _ _ ~o U .'~ ~n w .~
~
'~ ~

n .i'", ttS
~M
U ~ U

_ M ~

~ ...0 'n N ~1 f~~ci ~ :~ ~d "

N t bD ~ ' >C~ I~.GUO~~ ~ U
~N
M
CT' O dp .-r D ct ~O 01 ~
D N N ~ ~ l~ M t~ " ~ crt O N v ~ w' N ~ ~ N ~"
~' i >
' 'C

- . \
, ~ ~ ~ ~ , N s..
U ~ ~ ~ ~!~ ~ ~ U

as t3, tCSrn~~Up o.a;
-'--n ~ U ~
-r +~ N ~ ~'.., p _ r O

V~
~"~~NwOpN

m N M v1 O O ~ ~j ~ ~ ~ O ~ ~
Cr" ~ i iZ, .'~w _ ~' ~
y ' ~
U ~
W

~..y. O t~ ~O t~ N
.a .~ O, N
~ C!~ v~ ~

..0~'WT3~~O~00N

... p .t".r ~O f3-~
..L~

~

~
~
~

~,' f..'~i T~' " U O L."
bU
~ DG
~ b0 ~ 3 ~

~
.~ ~s a"

~
vi ~, o ~ ~~~ ~,~_a~~

by ~ ~ ~ ~ ~ U 7G C/~ .~ ~

O ~ y0 4w a O

~
" ~
d U
~ c ~
~
~

~
H ~

O U ~'.,~~U"C O .f.
~ ' '~

., ~ ~ ~ ~ ~ ~v~ ~ cs., s on an ~n nn ~ ~_~ w ~
~

uU'~D"'O
Dvr00 ~

.

~U ~U ~U ~U

a 3 ~ ~ v SUBSTITUTE SHEET (RULE 26) Effect of ~,a Silver additions dramatically improve the typical T6-type strengths and Rockwell hardness values of Al-Cu-Mg-Mn alloy samples. For example, a typical tensile yield strength as high as 74.2 ksi was achieved in alloy sample S as compared to the 60.5 ksi value measured for a companion silver-free, unstretched alloy such as alloy sample T from Table IV.
Tni'hen Ag is present, and a small amount of cold work (e. g. <1~ stretching) has been introduced prior to artificial aging to flatten sheet product for typical T6-type aging conditions, these T6-type tensile yield strengths were observed to be generally similar to those for typical T8-type tensile yield strengths where a greater amount of cold work has ben introduced.
For example, a typical tensile yield strength of 70.4 ksi for the T8-type temper is roughly equivalent to a typical 68.3 ksi tensile yield strength for the T6-type temper of the same material (e. g. alloy sample Q from Table IV).
Figure 1 demonstrates this effect for the hardnesses of two alloy samples having intermediate Cu:Mg ratios, alloy samples C and D from Table I. The Ag-bearing example in this comparison, alloy sample D, achieves nearly the same level of hardness regardless of whether a.t is 8~ stretched or naturally aged for 10 days prior to artificial aging. The Ag-free alloy sample C, however, achieves a much higher hardness when stretched by 8~ rather than just naturally aged for 10 days.
Cog Ratios In Figures 2a and 2b, Rockwell B hardness values are plotted as a function of aging time at 325°F. for Ag-bearing alloy samples K, L and M from Table I, i.e. those representative of low, intermediate and high Cu: Mg ratios, respectively. The highest hardness values were observed in T8-type tempers of the alloy samples with low to intermediate Cu: Mg ratio (samples R and L) and, in the T6-type temper, of only one alloy sample having an intermediate Cu: Mg ratio (alloy sample L).
The benefit of this invention's intermediate Cu:Mg ratios is further demonstrated in Figure 3 and following Table V. Both presentations show that alloy samples with an intermediate Cu: Mg ratio (e. g. alloy sample L) develop the highest tensile yield strengths of three samples compared in T6- and T8-type tempers.
Table V
Typical Tensile Data and Rockwell B Hardness Values for Al-Cu-Mg-Mn-Ag Sheet Aged Using T6-type and T8-type Practices, l5 Illustrative thA F!ffo..+- ,.,f n" .M.. n..~; __ Sample Cu: Temper HRB Tensile Ultimate Elonga-(a) Mg Yield Tensile tion Ratio Strength Strength (1~) (ksi) (ksi) R 2.75 T6 81.4 57.7 73.1 16.0 T8 86.6 72.6 77.8 14.0 L 6.25 T6 86.4 7I.0 76.5 13.0 T8 ~ 87.5 77.4 80.0 13.0 M 20.0 T6 84.2 66.8 76.5 13.0 T8 84.9 70.7 76.8 13.0 ~ a ~ ~ ..,e~-o~." a n ~ +.

to sheet. __ .~ __ _.. __ _ ___~....~ ,."....
Effect of Ma It is believed that sufficient amounts of silver promote the formation of a plate-like iZ phase on the ~111~ planes of this invention. At the lower Cu: Mg ratios of about 2.9 (4.4 wt.~: 1.5 wt.~), this LZ phase is dominant thereby replacing the GPB zones and S' particulates that would otherwise be expected for such an alloy. At higher Cu:Mg ratios of about 20 (or 6 wt.~s: 0.3 wt.~), these t2 phases replace the ~100~ GP
zones and,~100~ o' precipitates. At the preferred intermediate Cu:Mg ratios of this invention, the C2 phase is still dominant.
Effects ofd Table VI shows the effect of Mn additions on typical tensile properties of the A1-Cu-Mg-Mn-(Ag) alloy samples aged to T8-type tempers. Alloys with two or more Mn levels have been grouped together with companion alloy samples having roughly the same Ag levels and Cu: Mg ratios.
Table VI
Typical Tensile Data for A1-Cu-Mg-Mn-(Ag) Sheet Aged Using TS-type Practices, Illustrating the Effect of Mn T 8-type (b) Sample Description Mn Tensile Ultimate Elonga-(a) (wt~) Yield Tensile Lion Strength Yield ($) (ksi) Strength (ksi) H intermed. 0.06 71.8 74.5 8.0 Cu: Mg w/Ag D intermed. 0.60 75.4 77.5 11.0 Cu: Mg w/Ag G intermed. 0.06 65.1 69.8 10.0 Cu:Mg no Ag C intermed. 0.60 72.6 74.8 Cu:Mg no Ag I high Cu: Mg 0.06 65.4 71.5 13.0 no Ag E high Cu: Mg 0.60 67.7 72.9 11.0 no Ag J high Cu: Mg 0.05 64.6 70.5 13.0 w/Ag F high Cu: Mg 0.60 68.7 74.0 12.0 w/Ag intermed. 0.00 73.4 76.2 10.0 Cu:Mg w/Ag S intermed. 0.60 76.2 78.8 9.5 Cu: Mg w/Ag Q high Cu: Mg 0.30 70.4 74.4 11.0 w/Ag WO 98/39494 PCT/f1S97/03638 T8-type (b) Sample Description Mn Tensile Ultimate Elonga-_ (a) (wt~) Yield Tensile tion Strength Yield (~) (ksi) Strength (ksi) U high Cu:Mg 0.60 73.5 77.2 9.5 w/Ag V high Cu:Mg 1.01 74.4 77.7 9.5 w/Ag (a) Samples H, D, G, C, I, E, J and F were cast as 11/" x 2%" x 6" ingots and rolled to sheet. Samples R, S, Q, U, and V were direct chill cast as 6" x 16'° x 60" ingots.
(b) Typical T8-type properties were obtained from sheet which had been heat treated, quenched, stretched 8~ and artificially aged at temperatures between 325°F. and 350°F.
Manganese additions of around 0.6 wt.~
typically provide about 3 ksi or more of added strength to these alloy samples. For example, the Ag-bearing, Mn-free alloy with an intermediate Cu: Mg ratio, alloy I5 sample R, developed a typical T8-type tensile yield strength of 73.4 ksi while its Mn-bearing equivalent (alloy sample S) developed a typical T8-type tensile yield strength of 76.2 ksi. Figure 4 shows that the strength advantage attributable to Mn is not lost in these alloy samples as a result of extended exposures to either 600 hours at 300°F. or 3000 hours at 275°F.
Effects of Zn Substitution of Zn for at least some of the Ag a.n this invention does not appear to have a significant deleterious effect on the strength levels and other main properties of these alloy products.
Instead, zinc substitutions for silver serve a positive purpose of cost reduction in these alternate embodiments. Table VII compares the typical sheet - i$ -strengths of a silver-only sample (alloy sample W), zinc-only sample (alloy sample X) and a silver-and-zinc comparative (alloy sample Y) after each were -artificially aged following stretching to various levels of ~.5~, 2~ and $$, , I

on ~ o 0 0 y O \ N O

W

'~ ~4~ ~~ ~ N

~ y 3C O ~D o0 00 i~ l~

_L ~

O

.~.~ M l0 01 N ~

F

N

>..

o ~ cw tip ~ bD ~ O O O
qp o O_ ~ M

o W

~ ~ o ~ \

I
U

~ w ,,\.~~ ~ N ~C
W

~ o ~ ~ ~ :~ t~ c o E~ s ~p.~

., . ~ i: r A a . ~
~

ew ~ n c~
a o n Q ~ H r ~ N

U N ' M d-~ ~ ~

' a> ~ C _ a_~

~Y

i by Li O O O
o ~r (~ .
H

I.1 '/

O

O

'~ ~ t!7M
~...~., x N ~n O

~ n ~ n bD

C by i ~ o d N ~ -N

U ~f ~ M ~s to N ~

O
o a 3 x SUBSTITUTE SHEET (RULE 26) WO 98/39.494 PCT/LTS97/03638 Fract-_ttre TOL~1'~rtp~Q
The strength/toughness combinations of various Al-Cu-Mg-Mn-(Ag-Zn) alloy samples are compared in accompanying Figures 5 and 6. The data from Figure 5 is summarized in Table VIII below.
Table VIII
Typical Tensile and Fracture Toughness Data fcfr ~l -P4,_1~.._~r_, irw ...,_ Sample Temper Tensile Yield Rc Fracture Toughness Strength (ksi) (ksiv/in) N T8 62.8 105.2 P T8 70.3 94.5 S2 T8 70.4 110.4 T8 73.4 102.4 S T8 76.2 107.7 S T8 77.4 129.4 T T8 74.5 92.7 T8 73.5 95.4 V T8 74.4 72.2 From this data, an Ag-bearing alloy with an intermediate Cu:Mg ratio (alloy sample S in Figure 5 and alloy sample W in Figure 6) developed the best overall combination of strength and toughness. The alloy for which a partial substitution of Zn for Ag was made (alloy sample Y) developed nearly as high a combination of strength and toughness properties.
One of the alloys investigated above, alloy sample Q, very closely resembles the composition of several examples in the Polmear patent. Table IX
compares the typical tensile yield strengths noted by Polmear, and those of alloy sample Q to those observed for this invention. Note that Polmear obtained typical , tensile yield strengths of up to 75 ksi for his extruded rod examples. But sheets of a similar composition, produced on this inventor's behalf for WO 98/39.494 PCT/US9'7/03638 comparison purposes. attained only typical tensile yield strengths of 68 to 70 ksi. One preferred embodiment of this invention in sheet form, alloy sample S, developed typical tensile yield strengths as high as 77 ksi in the T8-type temper, or 10~ higher typical yield strengths than those achieved by a Polmear-like composition in a comparative sheet product form.
Table IX
Comparison of Typical Tensile Yield Strengths obtained on Polmear Patent Extrusions to Those Obtained in the Current Study with the Invention Alloy and Other n 1 't .,.. a ~,."~ i e..
Alloy composition Product yTemperT.Y.S. Reference (wt.~) Form (ksi) Al-6cu-O.Mg-0.4Ag extruded T6 75.1 from the -0.5Mn-0.15Zr- rod Polmear O.1V-0.04 Si patent Al-5.3Cu-0.6Mg-0.3Ag extruded T6 71.0 from the -0.5Mn-0.25Zr rod Polmear 0.15V-0.08Si patent A1-6.7Cu-0.4Mg-0.8Ag extruded T6 73.9 from the -0.8Mn-0.15Zr rod Polmear 0.05V-0.06Si _ patent Al-6Cu-0.5Mg-0.4Ag extruded T6 75.4 from the -0.5Mn-0.15Zr rod Polmear 0.1V-0.04Si patent A1-5.75Cu-0.5Mg-0.5Ag sheet T8 70.4 made for -0.3Mn-0.16Zr comparison 05Si _ __________ Purposes _ _ -_____________ _________________-___ (Alloy sample Q) sheet T6 68.3 made for comparison purposes A1-5.12Cu-0.82Mg-0.5Agsheet T8 76.2 invention -0.6Mn-0.15Zr 77.9 alloy 0.13V-0.0653 sample Al-4.8Cu-0.8Mg-0.5Ag sheet T8 7?.3 invention -0.6Mn-0.15Zr alloy ' (Alloy sample W) sample Al-4.8Cu-0.8Mg-0.25Ag sheet T8 75.9 invention -0.6Mn-0.15Zr alloy (Alloy sample V) sample Additional tensile specimens were artificially aged by T6-type and T8-type practices, then exposed to elevated temperature conditions .
intended to simulate Mach 2.0 service. Such exposures included heat treatments at 300°F. for 600 hours and at .
275°F. for 3000 hours. After 300°F. exposures for 600 hours, typical T8-type tensile yield strengths of the invention dropped only from about 8 to 12 ksi.
Somewhat smaller 3osses of only 5 to 10 ksi were observed following 275°F. exposures for 3000 hours.
Such typical strength levels, nevertheless, represent a considerable high temperature improvement over the minimum levels observed for 2618 aluminum and other existing alloys.
From the data set forth in Figure 7a, for both zirconium-bearing alloys, it was observed that roughly equivalent typical strength levels (less than 1 ksi difference) were measured for alloy samples Z and AA, regardless of the amount of stretch imparted to these two comparative compositions differing primarily in vanadium content. While in their zirconium-free equivalents, alloy samples CC and DD a.n Figure 7b, the presence of vanadium actually had a deleterious effect on observed typical strength values.
Based on the foregoing, most preferred embodiments of this invention are believed to contain about 5.0 wt.~ Cu, an overall Mg level of about 0.8 wt.~, an Ag content of about 0.5 wt.~, an overall Mn content of about 0.6 wt.~s and a Zr level of about 0.15 wt.~.
Having described the presently preferred embodiments, it is to be understood that the invention may be otherwise embodied within the scope of the appended claims. '

Claims (25)

1. A rolled structural member having improved combinations of strength and toughness, said structural member made from a substantially vanadium-free, aluminum-based alloy consisting essentially of: about 4.85-5.3 wt.% copper, about 0.5-1.0 wt.% magnesium, about 0.4-0.8 wt.% manganese, about 0.2-0.8 wt.%
silver, up to about 0.25 wt.% zirconium, up to about 0.1 wt.% silicon, and up to about 0.1 wt.% iron, the balance aluminum, incidental elements and impurities.

2. The structural member of claim 1, which has a typical tensile yield strength level of about 77 ksi or higher at room temperature.

3. The structural member of claim 1, which is a sheet product.

4. The structural member of claim 3, which is suitable for use as aircraft wing or fuselage skin material.

5. The structural member of claim 1, which is a plate product.

6. The structural member of claim 1, wherein said alloy has a Cu:Mg ratio between about 5 and 9.

7. The structural member of claim 6, wherein said Cu:Mg ratio of said alloy is between about 6.0 and 7.5.

8. The structural member of claim 1, wherein said alloy includes about 5.0 wt.% or more copper.

9. The structural member of claim 1, wherein said alloy further includes up to about 0.5 wt.% zinc.

10. A sheet-derived, aerospace structural member having improved combinations of strength and toughness, said structural member being made from a substantially vanadium-free aluminum-based alloy consisting essentially of: about -4.85-5.3 wt.% copper, about 0.5-1.0 wt.% magnesium, about 0.4-0.8 wt.% manganese, about 0.2-0.8 wt.% silver, about 0.05-0.25 wt.% zirconium, up to about 0.1 wt.% silicon, and up to about 0.1 wt.%

iron, the balance aluminum, incidental elements and impurities.

11. The structural member of claim 10, which has been stretched by 1% or mare to improve its flatness and increase its strength.

12. The structural member of claim 10, which has a typical tensile yield strength of about 77 ksi or higher at room temperature.

13. The structural member of claim 10, which is suitable for use as aircraft wing or fuselage skin material.

14. The structural member of claim 10, wherein said alloy has a Cu:Mg ratio between about 5 and 9.

15. The structural member of claim 10, wherein said Cu:Mg ratio of said alloy is between about 6.0 and 7.5.

16. The structural member of claim 10, wherein said alloy includes about 5.0 wt.% or more copper.

17. The structural member of claim 10, wherein said alloy further includes up to about 0.5 wt.% zinc.

18. A substantially unstretched sheet or plate product having improved combinations of strength and toughness in more than one direction, said sheet or plate product made from a substantially vanadium-free, aluminum-based alloy consisting essentially of: about 4.85-5.3 wt.% copper, about 0.5-1.0 wt.% magnesium, about 0.4-0.8 wt.% manganese, about 0.2-0.8 wt.%
silver, up to about 0.25 wt.% zirconium, up to about 0.1 wt.% silicon, and up to about 0.1 wt.% iron, the balance aluminum, incidental elements and impurities, said alloy having a Cu:Mg ratio between about 5 and 9.

19. The sheet or plate product of claim 18, which has been solution heat treated at one or more temperatures between about 955-980°F. (513-527°C.).

20. The sheet or plate product of claim 18, which is an aircraft wing member.

21. The sheet or plate product of claim 18, which is suitable for use as aircraft wing or fuselage skin material.

22. The sheet or plate product of claim 18, which has a typical tensile yield strength of about 77 ksi or higher at room temperature.

23. The sheet or plate product of claim 18, wherein the Cu: Mg ratio of said alloy is between about 6.0 and 7.5.

24. The sheet or plate product of claim 18, wherein said alloy includes about 5.0 wt.% or more copper.

25. The sheet or plate product of claim 18, wherein said alloy further includes up to about 0.5 wt.% zinc.