Aluminum-base alloys which are provided which possess highly desirable properties, such as relatively low density, high modulus, high strength/ductility combinations, strong natural aging response with and without prior cold work, higher artificially-aged strength than existing Al-Li alloys with and without prior cold work, weldability, good cryogenic properties, and good elevated temperature properties. In one embodiment, aluminum-base alloys are provided having Al-Cu-Li-Mg compositions in the following ranges: 5.0-7.0 Cu, 0.1-2.5 Li, 0.05-4 Mg, 0.01-1.5 grain refiner selected from Zr, Cr, Mn, Ti, Hf, V, Nb, B, TiB.sub.2, and mixtures thereof, and the balance essentially Al. In another embodiment, aluminum-base alloys are provided having Al-Cu-Li-Mg compositions in the following ranges: 3.5-5.0 Cu, 0.8-1.8 Li, 0.25-1.0 Mg, 0.01-1.5 grain refiner selected from Zr, Cr, Mn, Ti, Hf, V, Nb, B, TiB.sub.2, and mixtures thereof, and the balance essentially Al.

FIELD OF THE INVENTION 
The present invention relates to Al-Cu-Li-Mg based alloys that have been 
found to possess extremely desirable properties, such as high 
artificially-aged strength with and without cold work, strong natural 
aging response with and without prior cold work, high strength/ductility 
combinations, low density, and high modulus. In addition, the alloys 
possess good weldability, corrosion resistance, cryogenic properties and 
elevated temperature properties. These alloys are particularly suited for 
aerospace, aircraft, armor, and armored vehicle applications where high 
specific strength (strength divided by density) is important and a good 
natural aging response is useful because of the impracticality in many 
cases of performing a full heat treatment. In addition, the weldability of 
the present alloys allows for their use in structures which are joined by 
welding. 
In accordance with the present invention, highly improved properties are 
achieved in Al-Cu-Li-Mg based alloys by providing amounts of Cu, Li and Mg 
within specified ranges. For Al alloys containing from 5 to 7 weight 
percent Cu, the amount of Li must be held within the range of from 0.1 to 
2.5 weight percent, while the amount of Mg must be limited to from 0.05 to 
4 weight percent. For Al alloys containing from 3.5 to 5 weight percent 
Cu, the Li content must be limited to from 0.8 to 1.8 weight percent, 
while the Mg content must be held within the range of from 0.25 to 1.0 
weight percent. Particular advantage is obtained in accordance with the 
present invention by providing an Al-Cu-Li-Mg alloy having a high Cu to Li 
weight percent ratio. 
BACKGROUND OF THE INVENTION 
The desirable properties of aluminum and its alloys such as low cost, low 
density, corrosion resistance, and ease of fabrication are well known. 
One important means for enhancing the strength of aluminum alloys is heat 
treatment. Conventionally, three basic steps are employed in the heat 
treatment of aluminum alloys: (1) Solution heat treating; (2) Quenching; 
and (3) Aging. Additionally, a cold working step is often added prior to 
aging. Solution heat treating consists of soaking the alloy at a 
temperature sufficiently high and for a long enough time to achieve a 
nearly homogeneous solid solution of precipitate-forming elements in 
aluminum. The objective is to take into solid solution the maximum 
practical amounts of the soluble hardening elements. Quenching involves 
the rapid cooling of the solid solution, formed during the solution heat 
treatment, to produce a supersaturated solid solution at room temperature. 
The aging step involves the formation of strengthening precipitates from 
the rapidly cooled supersaturated solid solution. Precipitates may be 
formed using natural (ambient temperature), or artificial (elevated 
temperature) aging techniques. In natural aging, the quenched alloy is 
held at temperatures in the range of -20.degree. to +50.degree. C., 
typically at room temperature, for relatively long periods of time. For 
certain alloy compositions, the precipitation hardening that results from 
natural aging alone produces useful physical and mechanical properties. In 
artificial aging, the quenched alloy is held at temperatures typically in 
the range of 100.degree. to 200.degree. C. for periods of approximately 5 
to 48 hours, typically, to effect precipitation hardening. 
The extent to which the strength of Al alloys can be increased by heat 
treatment is related to the type and amount of alloying additions used. 
The addition of copper to aluminum alloys, up to a certain point, improves 
strength, and in some instances enhances weldability. The further addition 
of magnesium to Al-Cu alloys can improve resistance to corrosion, enhance 
natural aging response without prior cold work and increase strength. 
However, at relatively low Mg levels, weldability is decreased. 
One commercially available aluminum alloy containing both copper and 
magnesium is alloy 2024, having nominal composition Al - 4.4 Cu - 1.5 Mg - 
0.6 Mn. Alloy 2024 is a widely used alloy with high strength, good 
toughness, good warm temperature properties and a good natural- aging 
response. However, its corrosion resistance is limited in some tempers, it 
does not provide the ultrahigh strength and exceptionally strong 
natural-aging response achievable with the alloys of the present 
invention, and it is only marginally weldable. In fact, 2024 welded joints 
are not considered commercially useful in most situations. 
Another commercial Al-Cu-Mg alloy is alloy 2519 having a nominal 
composition of Al - 5.6 Cu - 0.2 Mg - 0.3 Mn - 0.2 Zr - 0.06 Ti - 0.05 V. 
This alloy was developed by Alcoa as an improvement on 2219, which is 
presently used in various aerospace applications. While the addition of Mg 
to the Al-Cu system can enable a natural-aging response without prior cold 
work, 2519 has only marginally improved strengths over 2219 in the highest 
strength tempers. 
Work reviewed by Mondolfo on conventional Al-Cu-Mg alloys indicates that 
the main hardening agents are CuAl.sub.2 type precipitates in alloys in 
which the Cu to Mg ratio is greater than 8 to 1 (See ALUMINUM ALLOYS: 
STRUCTURE AND PROPERTIES, L.F. Mondolfo, Boston: Butterworths, 1976, p. 
502). 
Polmear, in U.S. Pat. No. 4,772,342, has added silver and magnesium to the 
Al-Cu system in order to increase elevated temperature properties. A 
preferred alloy has the composition Al - 6.0 Cu - 0.5 Mg - 0.4 Ag - 0.5 Mn 
- 0.15 Zr - 0.10 V - 0.05 Si. Polmear associates the observed increase in 
strength with the "omega phase" that arises in the presence of Mg and Ag 
(see "Development of an Experimental Wrought Aluminum Alloy for Use at 
Elevated Temperatures," Polmear, ALUMINUM ALLOYS: THEIR PHYSICAL AND 
MECHANICAL PROPERTIES, E.A. Starke, Jr. and T.H. Sanders, Jr., editors, 
Volume I of Conference Proceedings of International Conference, University 
of Virginia, Charlottesville, Va., Jun. 15-20, 1986, pages 661-674, 
Chameleon Press, London). 
Adding lithium to Al-Mg alloys and to Al-Cu alloys is known to lower the 
density and increase the elastic modulus, producing significant 
improvements in specific stiffness and enhancing the artificial age 
hardening response. However, conventional Al-Li alloys generally possess 
relatively low ductility at given strength levels and toughness is often 
lower than desired, thereby limiting their use. 
Difficulties in melting and casting have limited the acceptance of Al-Li 
alloys. For example, because Li is extremely reactive, Al-Li melts can 
react with the refractory materials in furnace linings. Also, the 
atmosphere above the melt has to be controlled to reduce oxidation 
problems. In addition, lithium lowers the thermal conductivity of 
aluminum, making it more difficult to remove heat from an ingot during 
direct-chill casting, thereby decreasing casting rates. Furthermore, in 
Al-Li melts containing 2.2 to 2.7 percent Lithium, typical of recently 
commercialized Al-Li alloys, there is considerable risk of explosion. To 
date, the property benefits attributable to these new Al-Li alloys have 
not been sufficient to offset the increase in processing costs caused by 
the above-mentioned problems. As a consequence they have not been able to 
replace conventional alloys such as 2024 and 7075. The preferred alloys of 
the present invention do not create these melting and casting problems to 
as great a degree because of their lower Li content. 
Al-Li alloys containing Mg are well known, but they typically suffer from 
low ductility and low toughness. One such system is the low density, 
weldable Soviet alloy 01420 as disclosed in British Patent 1,172,736, to 
Fridlyander et al, of nominal composition Al - 5 Mg - 2 Li. 
Al-Li alloys containing Cu are also well known, such as alloy 2020, which 
was developed in the 1950's, but was withdrawn from production because of 
processing difficulties and low ductility. Alloy 2020 falls within the 
range disclosed in U.S. Pat. No. 2,381,219 to LeBaron, which emphasizes 
that the alloys are "magnesium-free", i.e. the alloys have less than 0.01 
percent Mg, which is present only as an impurity. In addition, the alloys 
disclosed by LeBaron require the presence of at least one element selected 
from Cd, Hg, Ag, Sn, In and Zn. Alloy 2020 has relatively low density, 
good exfoliation corrosion resistance and stress-corrosion cracking 
resistance, and retains a useful fraction of its strength at slightly 
elevated temperatures. However, it suffers from low ductility and low 
fracture toughness properties in high strength tempers, thereby limiting 
its usefulness. 
To achieve the highest strengths in Al-Cu-Li alloys, it is necessary to 
introduce a cold working step prior to aging, typically involving rolling 
and/or stretching of the material at ambient or near ambient temperatures. 
The strain which is introduced as a result of cold working produces 
dislocations within the alloy which serve as nucleation sites for the 
strengthening precipitates. In particular, conventional Al-Cu-Li alloys 
must be cold worked before artificial aging in order to obtain high 
strengths, i.e. greater than 70 ksi ultimate tensile strength (UTS). Cold 
working of these alloys is necessary to promote high volume fractions of 
Al.sub.2 CuLi (T.sub.1) and Al.sub.2 Cu (theta-prime) precipitates which, 
due to their high surface-to-volume ratio, nucleate far more readily on 
dislocations than in the aluminum solid solution matrix. Without the cold 
working step, the formation of the plate-like Al.sub.2 CuLi and Al.sub.2 
Cu precipitates is retarded, resulting in significantly lower strengths. 
Moreover, the precipitates do not easily nucleate homogeneously because of 
the large energy barrier that has to be overcome due to their large 
surface area. Cold working is also useful, for the same reasons, to 
produce the highest strengths in many commercial Al-CU alloys, such as 
2219. 
The requirement for cold working to produce the highest strengths in 
Al-Cu-Li alloys is particularly limiting in forgings, where it is often 
difficult to uniformly introduce cold work to the forged part after 
solutionizing and quenching. As a result, forged Al-Cu-Li alloys are 
typically limited to non-cold worked tempers, resulting in generally 
unsatisfactory mechanical properties. 
Recently, Al-Li alloys containing both Cu and Mg have been commercialized. 
These include alloys 8090, 2091, 2090, and CP 276. Alloy 8090, as 
disclosed in U.S. Pat. No. 4,588,553 to Evans et al, contains 1.0-1.5 Cu, 
2.0-2.8,Li, and 0.4-1.0 Mg. The alloy was designed with the following 
properties for aircraft applications: good exfoliation corrosion 
resistance, good damage tolerance, and a mechanical strength greater than 
or equal to 2024 in T3 and T4 conditions. Alloy 8090 does exhibit a 
natural aging response without prior cold work, but not nearly as strong 
as that of the alloys of the present invention. In addition, 8090-T6 
forgings have been found to possess a low transverse elongation of 2.5 
percent. 
Alloy 2091, with 1.5-3.4 Cu, 1.7-2.9 Li, and 1.2-2.7 Mg, was designed as a 
high strength, high ductility alloy. However, at heat treated conditions 
that produce maximum strength, ductility is relatively low in the short 
transverse direction. 
In recent work on alloys 8090 and 2091, Marchive and Charue have reported 
reasonably high longitudinal tensile strengths (see "Processing and 
Properties 4TH INTERNATIONAL ALUMINIUM LITHIUM CONFERENCE, G. Champier, B. 
Dubost, D. Miannay, and L. Sabetay editors, Proceedings of International 
Conference, Jun. 10-12, 1987, Paris, France, pp. 43-49). In the T6 temper, 
8090 possesses a yield strength of 67.3 ksi and an ultimate tensile 
strength of 74 ksi, while 2091 possesses a yield strength of 63.8 ksi and 
an ultimate tensile strength of 75.4 ksi. However, the strengths of both 
8090-T6 and 2091-T6 forgings are still below those obtained in the T8 
temper, e.g. for 8090-T851 extrusions, tensile properties are 77.6 ksi YS 
and 84.1 ksi UTS, while for 2091-T851 extrusions, tensile properties are 
73.3 ksi YS and 84.1 ksi UTS. By contrast, the Al-Cu-Li-Mg alloys of the 
present invention possess highly improved properties compared to 
conventional 8090 and 2091 alloys in both cold worked and non-cold worked 
tempers. 
Alloy 2090, which may contain only minor amounts of Mg, comprises 2.4-3.0 
Cu, 1.9-2.6 Li and 0-0.25 Mg. The alloy was designed as a low-density 
replacement for high strength products such as 2024 and 7075. However, it 
has weldment strengths that are lower than those of conventional weldable 
alloys such as 2219 which possesses weld strengths of 35-40 ksi. As cited 
in the following reference, in the T6 temper alloy 2090 cannot 
consistently meet the strength, toughness, and stress-corrosion cracking 
resistance of 7075-T73 (see "First Generation Products- 2090, " Bretz, 
ALITHALITE ALLOYS: 1987 UPDATE, J. Kar, S.P. Agrawal, W.E. Quist, editors, 
Conference Proceedings of International Aluminum-Lithium Symposium, Los 
Angeles, Calif., Mar. 25-26, 1987, pages 1-40). As a consequence, the 
properties of current Al-Cu-Li alloy 2090 forgings are not sufficiently 
high to justify their use in place of existing 7XXX forging alloys. 
It should be noted that the addition of Mg to the Al-Cu-Li system does not 
in its own right cause an increase in alloy strength in high strength 
tempers. For example alloy 8090 (nominal composition Al - 1.3 Cu - 2.5 Li 
- 0.7 Mg) does not have significantly greater strength compared to 
nominally Mg-free alloy 2090 (nominal composition Al - 2.7 Cu - 2.2 Li - 
0.12 Zr). Furthermore, Mg-free alloy 2020 of nominal composition Al - 4.5 
Cu - 1.1 Li - 0.4 Mn - 0.2 Cd is even slightly stronger than Mg containing 
alloy 8090. 
Several patent documents relating to Al-Cu-Li-Mg alloys exist. European 
Patent No. 158,571 to Dubost, assigned to Cegedur Societe de 
Transformation de l'Aluminum Pechiney, relates to Al alloys comprising 
2.75-3.5 Cu, 1.9-2.7 Li, 0.1-0.8 Mg, balance Al and grain refiners. The 
alloys, which are commercially known as CP 276, are said to possess high 
mechanical strength combined with a decrease in density of 6-9 percent 
compared with conventional 2xxx (Al-Cu) and 7xxx (Al-Zn-Mg) alloys. The 
compositional ranges disclosed by Dubost are outside of the ranges of the 
present invention. Specifically, Dubost's Li content is higher than the Li 
content of the alloys of the present invention containing less than about 
5 percent Cu. Such high levels of Li are required by Dubost in order to 
lower density over that of conventional alloys. In addition, the maximum 
Cu level of 3.5 percent given by Dubost is below the preferred Cu level of 
the present invention. Limiting Cu content to a maximum of 3.5 percent 
also serves to minimize density in the alloys of Dubost. While Dubost 
lists high yield strengths of 498-591 MPa (72-85 ksi) for his alloys in 
the T6 condition, the elongations achieved are relatively low (2.5-5.5 
percent). 
U.S. Pat. No. 4,752,343 to Dubost et al, assigned to Cegedur Sodiete de 
Transformation de l'Aluminum Pechiney, relates to Al alloys comprising 
1.5-3.4 Cu, 1.7-2.9 Li, 1.2-2.7 Mg , balance Al and grain refiners. The 
ratio of Mg to Cu must be between 0.5 and 0.8. The alloys are said to 
possess mechanical strength and ductility characteristics equivalent to 
conventional 2xxx and 7xxx alloys. The compositional ranges disclosed by 
Dubost et al are outside of the ranges of the present invention. For 
example, the maximum Cu content listed by Dubost et al is lower than the 
minimum Cu level of the present invention. Additionally, the minimum Mg 
content of Dubost et al is higher than the maximum Mg level permitted in 
the present alloys containing less than about 5 percent Cu. Further, the 
minimum Mg to Cu ratio of 0.5 permitted by Dubost et al is far above the 
Mg/Cu ratio of the present alloys. While the purpose of Dubost et al is to 
produce alloys having mechanical strengths and ductilities comparable to 
conventional alloys, such as 2024 and 7475, the actual strength/ ductility 
combinations achieved are below those attained by the alloys of the 
present invention. 
U.S. Pat. No. 4,652,314 to Meyer, assigned to Cegedur Societe de 
Transformation de l'Aluminum Pechiney, is directed to a method of heat 
treating Al-Cu-Li-Mg alloys. The process is said to impart a high level of 
ductility and isotropy in the final product. While Meyer teaches that his 
heat treating method is applicable to Al-Cu-Li-Mg alloys, the specific 
compositions disclosed by Meyer are outside of the compositional ranges of 
the present invention. Also, the properties which Meyer achieves are below 
those of the present invention. For example, the highest yield strength 
achieved by Meyer is 504 MPa (73 ksi) for a cold worked, artificially aged 
alloy in the longitudinal direction, which is significantly below the 
yield strengths attained in the alloys of the present invention in the 
cold worked, artificially aged condition. 
U.S. Pat. No. 4,526,630 to Field, assigned to Alcan International Ltd., 
relates to a method of heat treating Al-Li alloys containing Cu and/or Mg. 
The process, which constitutes a modification of conventional 
homogenization techniques, involves heating an ingot to a temperature of 
at least 530.degree. C. and maintaining the temperature until the solid 
intermetallic phases present within the alloy enter into solid solution. 
The ingot is then cooled to form a product which is suitable for further 
thermomechanical treatment, such as rolling, extrusion or forging. The 
process disclosed is said to eliminate undesirable phases from the ingot, 
such as the coarse copper-bearing phase present in prior art Al-Li-Cu-Mg 
alloys. Field teaches that his homogenization treatment is limited to 
Al-Li alloys having compositions within specified ranges. For known 
Al-Li-Cu-Mg based alloys, compositions are limited to 1-3 Li, 0.5-2 Cu, 
and 0.2-2 Mg. For conventional Al-Li-Mg based alloys, compositions are 
limited to 1-3 Li, 2-4 Mg, and below 0.1 Cu. For known Al-Li-Cu based 
alloys, compositions are limited to 1-3 Li, 0.5-4 Cu, and up to 0.2 Mg. 
The alloys of the present invention do not fall within any of these 
compositional ranges disclosed by Field. Furthermore, the present alloys 
possess superior properties, such as increased strength, compared to the 
properties disclosed by Field. 
The following references disclose additional Al, Cu, Li and Mg containing 
alloys having compositional ranges that are outside of the ranges of the 
present invention: U.S. Pat. No. 3,306,717 to Lindstrand et al; U.S. Pat. 
No. 3,346,370 to Jagaciak et al; U.S. Pat. No. 4,584,173 to Gray et al; 
U.S. Pat. No. 4,603,029 to Quist et al; U.S. Pat. No. 4,626,409 to Miller; 
U.S. Pat. No. 4,661,172 to Skinner et al; U.S. Pat. No. 4,758,286 to 
Dubost et al; European Patent Application Publication No. 0188762 to Hunt 
et al; European Patent Application Publication No. 0149193; Japanese Pat. 
No. J6-0238439; Japanese Pat. No. J6-1133358; and Japanese Pat. No. 
J6-1231145. 
There are a limited number of references relating to Al-Cu-Li-Mg alloys 
that disclose amounts of Cu of to 5 percent. None of these references 
disclose the specific alloy compositions of the present invention, nor do 
they disclose the highly desirable properties which the alloys of the 
present invention have been found to possess. In addition, none of these 
references disclose the necessity of the high Cu to Li ratio required in 
the alloys of the present invention. While each of the-following 
references disclose broad ranges of Cu, Li and Mg that may be alloyed with 
Al, none of these references disclose the critical ranges and combinations 
of Cu, Li and Mg of the present invention which produce alloys having 
physical and mechanical properties that heretofore have not been achieved. 
U.S. Pat. No. 4,648,913 to Hunt et al, assigned to Alcoa, relates to a 
method of cold working Al-Li alloys wherein solution heat treated and 
quenched alloys are subjected to greater than 3 percent stretch at room 
temperature. The alloy is then artificially aged to produce a final alloy 
product. The cold work imparted by the process of Hunt et al is said to 
increase strength while causing little or no decrease in fracture 
toughness of the alloys. The particular alloys utilized by Hunt et al are 
chosen such that they are responsive to the cold working and aging 
treatment disclosed. That is, the alloys must exhibit improved strength 
with minimal loss in fracture toughness when subjected to the cold working 
treatment recited (greater than 3 percent stretch) in contrast to the 
result obtained with the same alloy if cold worked less than 3 percent. 
Hunt et al broadly recite ranges of alloying elements which, when combined 
with Al, may produce alloys that are responsive to greater than 3 percent 
stretch. The disclosed ranges are 0.5-4.0 Li, 0-5.0 Mg, up to 5.0 Cu, 
0-1.0 Zr, 0-2.0 Mn, 0-7.0 Zn, balance Al. While Hunt et al disclose very 
broad ranges of several alloying elements, there is only a limited range 
of alloy compositions that would actually exhibit the required combination 
of improved strength and retained fracture toughness when subjected to 
greater than 3 percent stretch. Particularly, the alloy compositions of 
the present invention do not exhibit the response to cold working which is 
required by Hunt et al. Rather, the strengths achieved in the alloys of 
the present invention remain substantially constant when subjected to 
varying amounts of stretch. Thus, the alloys of the present invention are 
distinct from, and possess advantages over, the alloys contemplated by 
Hunt et al, because large amounts of cold work are not required to achieve 
improved properties. In addition, the yield strengths which Hunt et al 
achieve in the alloy compositions disclosed are substantially below those 
which are attained in the alloys of the present invention. Further, Hunt 
et al indicate that it is preferred in their process to artificially age 
the alloy after cold working, rather than to naturally age. In contrast, 
the alloys of the present invention exhibit an extremely strong natural 
aging response, providing high elongations and only slightly lower 
strengths than in the artificially aged tempers. 
U.S. Pat. No. 4,795,502 to Cho, assigned to Alcoa, is directed to a method 
of producing unrecrystallized wrought Al-Li sheet products having improved 
levels of strength and fracture toughness. In the process of Cho, a 
homogenized aluminum alloy ingot is hot rolled at least once, cold rolled, 
and subjected to a controlled reheat treatment. The reheated product is 
then solution heat treated, quenched, cold worked to induce the equivalent 
of greater than 3 percent stretch, and artificially aged to provide a 
substantially unrecrystallized sheet product having improved levels of 
strength and fracture toughness. The final product is characterized by a 
highly worked microstructure which lacks well-developed grains. The Cho 
reference appears to be a modification of the Hunt et al reference listed 
above, in that a controlled reheat treatment is added prior to solution 
heat treatment which prevents recrystallization in the final product 
formed. Cho discloses that aluminum base alloys within the following 
compositional ranges are suitable for the recited process: 1.6-2.8 Cu, 
1.5-2.5 Li, 0.7-2.5 Mg, and 0.03-0.2 Zr. These ranges are outside of the 
compositional ranges of the present invention. For example, the maximum Cu 
level of 2.8 percent listed by Cho is well below the minimum Cu level of 
the present invention. However, Cho then goes on to broadly state that the 
alloy of his invention can contain 0.5-4.0 Li, 0-5.0 Mg, up to 5.0 Cu, 
0-1.0 Zr, 0-2.0 Mn, and 0-7.0 Zn. As in the Hunt et al reference, the 
particular alloys utilized by Cho are apparently chosen such that they 
exhibit a combination of improved strength and fracture toughness when 
subjected to greater than 3 percent cold work. The alloys of Cho must 
further be susceptible to the reheat treatment recited. As discussed 
above, the alloys of the present invention attain essentially the same 
ultra-high strength with varying amounts of stretch and do not require 
cold work to obtain their extremely high strengths. While Cho provides a 
process which is said to improve strength in known Al-Li alloys, such as 
2091, the strengths attained are substantially below those achieved in the 
alloys of the present invention. Cho also indicates that artificial aging 
should be used in his process to obtain advantageous properties. In 
contrast, the alloys of the present invention do not require artificial 
aging. Rather, the present alloys exhibit an extremely strong natural 
aging response which permits their use in applications where artificial 
aging is impractical. It can therefore be seen that the alloys of the 
present invention are distinct from the alloys amenable to the process 
taught by Cho. 
European Patent Application No. 227,563, to Meyer et al, assigned to 
Cegedur Societe de Transformation de l'Aluminum Pechiney, relates to a 
method of heat treating conventional Al-Li alloys to improve exfoliation 
corrosion resistance while maintaining high mechanical strength. The 
process involves the steps of homogenization, extrusion, solution heat 
treatment and cold working of an Al-Li alloy, followed by a final 
tempering step which is said to impart greater exfoliation corrosion 
resistance to the alloy, while maintaining high mechanical strength and 
good resistance to damage. Alloys subjected to the treatment have a 
sensitivity to the EXCO exfoliation test of less than or equal to EB 
(corresponding to good behavior in natural atmosphere) and a mechanical 
strength comparable with 2024 alloys. Meyer et al list broad ranges of 
alloying elements which, when combined with Al, can produce alloys that 
may be subjected to the final tempering treatment disclosed. The ranges 
listed include 1-4 Li, 0-5 Cu, and 0-7 Mg. While the reference lists very 
broad ranges of alloying elements, the actual alloys which Meyer et al 
utilize are the conventional alloys 8090, 2091, and CP276. Thus, Meyer et 
al do not teach the formation of new alloy compositions, but merely teach 
a method of processing known Al-Li alloys. The highest yield strength 
achieved in accordance with the process of Meyer et al is 525 MPa (76 ksi) 
for alloy CP276 (2.0 Li, 3.2 Cu, 0.3 Mg, 0.11 Zr, 0.04 Fe, 0.04 Si, 
balance Al) in the cold worked, artificially aged condition. This maximum 
yield strength listed by Meyer et al is below the yield strengths achieved 
in the alloys of the present invention in the cold worked, artificially 
aged condition. In addition, the final tempering method of Meyer et al is 
said to improve exfoliation corrosion resistance in Al-Li alloys, whereby 
sensitivity to the EXCO exfoliation corrosion test is improved to a rating 
of less than or equal to EB. In contrast, the alloys of the present 
invention possess an exfoliation corrosion resistance rating of less than 
or equal to EB without the use of a final tempering step. The present 
alloys are therefore distinct from, and advantageous over, the alloys 
contemplated by Meyer et al, because a final tempering treatment is not 
required in order to achieve favorable exfoliation corrosion properties. 
U.K. Patent Application No. 2,134,925, assigned to Sumitomo Light Metal 
Industries Ltd., is directed to Al-Li alloys having high electrical 
resistivity. The alloys are suitable for use in structural applications, 
such as linear motor vehicles and nuclear fusion reactors, where large 
induced electrical currents are developed. The primary function of Li in 
the alloys of Sumimoto is to increase electrical resistivity. The 
reference lists broad ranges of alloying elements which, when combined 
with Al, may produce structural alloys having increased electrical 
resistivity. The disclosed ranges are 1.0-5.0 Li, one or more grain 
refiners selected from Ti, Cr, Zr, V and W, and the balance Al. The alloy 
may further include 0-5.0 Mn and/or 0.05-5.0 Cu and/or 0.05-8.0 Mg. 
Sumitomo discloses particular Al-Li-Cu and Al-Li-Mg based alloy 
compositions which are said to possess the improved electrical properties. 
In addition, Sumitomo discloses one Al-Li-Cu-Mg alloy of the composition 
2.7 Li, 2.4 Cu, 2.2 Mg, 0.1 Cr, 0.06 Ti, 0.14 Zr, balance aluminum, which 
possesses the desired increase in electrical resistivity. The Li and Cu 
levels given for this alloy are outside of the Li and Cu ranges of the 
present invention. Additionally, the Mg level given is outside of the 
preferred Mg range of the present invention. The strengths disclosed by 
Sumitomo are far below those achieved in the present invention. For 
example, in the Al-Li-Cu based alloys listed, Sumitomo gives tensile 
strengths of about 17-35 kg/mm2 (24-50 ksi). In the Al-Li-Mg based alloys 
listed, Sumitomo discloses tensile strengths of about 43-52 kg/mm2 (61-74 
ksi). It is desired in Sumitomo to produce alloys having the highest 
possible strengths in order to produce alloys for the structural 
applications disclosed. However, since the strengths actually achieved in 
the reference are well below the strengths attained in the alloys of the 
present invention, it is evident that Sumitomo has neither discovered nor 
considered the specific alloys of the present invention. 
It should be noted that prior art Al-Cu-Li-Mg alloys have almost invariably 
limited the amount of Cu to 5 weight percent maximum due to the known 
detrimental effects of higher Cu content, such as increased density. 
According to Mondolfo, amounts of Cu above 5 weight percent do not 
increase strength, tend to decrease fracture toughness, and reduce 
corrosion resistance (Mondolfo, pp. 706-707.) These effects are thought to 
arise because in Al-Cu engineering alloys, the practical solid solubility 
limit of Cu is approximately 5 weight percent, and hence any Cu present 
above about 5 weight percent forms the less desired primary theta-phase. 
Moreover, Mondolfo states that in the quaternary system Al-Cu-Li-Mg the Cu 
solubility is further reduced. He concludes, "The solid solubilities of Cu 
and Mg are reduced by Li, and the solid solubilities of Cu and Li are 
reduced by Mg, thus reducing the age hardening and the UTS obtainable." 
(Mondolfo, p. 641). Thus, the additional Cu should not be taken into solid 
solution during solution heat treatment and cannot enhance precipitation 
strengthening, and the presence of the insoluble theta-phase lowers 
toughness and corrosion resistance. 
One reference that teaches the use of greater than 5 percent Cu is U.S. 
Pat. No. 2,915,391 to Criner, assigned to Alcoa. The reference discloses 
Al-Cu-Mn base alloys containing Li, Mg, and Cd with up to 9 weight percent 
Cu. Criner teaches that Mn is essential for developing high strength at 
elevated temperatures and that Cd, in combination with Mg and Li, is 
essential for strengthening the Al-Cu-Mn system. Criner does not achieve 
properties comparable to those of the present invention, i.e. ultra high 
strength, strong natural aging response, high ductility at several 
technologically useful strength levels, weldability, resistance to stress 
corrosion cracking, etc. 
Copending U.S. Pat. application Ser. No. 07/83,333, of Pickens et al, filed 
Aug. 10, 1987, discloses an Al-Cu-Mg-Li-Ag alloy with compositions in the 
following broad range: 0-9.79 Cu, 0.05-4.1 Li, 0.01-9.8 Mg, 0.01-2.0 Ag, 
0.05-1.0 grain refiner, and the balance Al. Specific alloys within these 
ranges possess extremely high strengths, which appear to be due in part to 
the presence of silver-containing precipitates. 
Copending U.S. Pat. application Ser. No. 07/233,705 of Pickens et al, filed 
Aug. 18, 1988, of which this application is a continuation-in-part, 
discloses Al-Cu-Mg-Li alloys with compositions in the following broad 
range: 5.0-7.0 Cu, 0.1-2.5 Li, 0.05-4 Mg, 0.01-1.5 grain refiner, and the 
balance Al. The present invention encompasses the ranges disclosed in the 
parent application. In addition, the present invention encompasses an 
embodiment to alloys comprising lower amounts of Cu, i.e. 3.5-5.0 percent, 
in which the levels of Li and Mg are held within narrow limits. The lower 
Cu embodiment of the present invention represents a group of alloys which 
have been found to possess highly improved properties over prior art 
Al-Cu-Li-Mg alloys. Thus, the present invention encompasses a family of 
alloys which exhibit improved properties compared to conventional alloys. 
For example, the present alloys possess improved strengths in both cold 
worked and non-cold worked tempers. In addition, the present alloys 
exhibit an extremely strong natural aging response. Further, the alloys 
have high strength/ductility combinations, low density, high modulus, good 
weldability, good corrosion resistance, improved cryogenic properties and 
improved elevated temperature properties. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a novel aluminum-base 
alloy composition. 
A further object of the present invention is to provide an Al-Li alloy with 
outstanding naturally aged properties both with (T3) and without (T4) cold 
work, including high ductility, weldability, excellent cryogenic 
properties, and good elevated temperature properties. 
A further object of the present invention is to provide an Al-Li alloy with 
outstanding T8 properties, such as ultrahigh strength in combination with 
high ductility, weldability, excellent cryogenic properties, good high 
temperature properties, and good resistance to stress-corrosion cracking. 
A further object of the present invention is to provide an Al-Li alloy with 
substantially improved properties in the non-cold worked, artificially 
aged T6 temper, such as ultra high strength in combination with high 
ductility, weldability, excellent cryogenic properties, and good high 
temperature properties. 
It is a further object of the present invention to provide an Al-Cu-Li-Mg 
alloy having a composition within the following ranges: 3.5-5 Cu, 0.8-1.8 
Li, 0.25-1.0 Mg, 0.01-1.5 grain refiner selected from Zr, Cr, Mn, Ti, Hf, 
V, Nb, B, TiB.sub.2 and combinations thereof, and the balance aluminum. 
A further object of the present invention is to provide an Al-Cu-Li-Mg 
alloy having a composition within the following ranges: 5-7 Cu, 0.1-2.5 
Li, 0.05-4 Mg, 0.01-1.5 grain refiner selected from Zr, Cr, Mn, Ti, Hf, V, 
Nb, B, TiB.sub.2 and combinations thereof, and the balance aluminum. 
It is a further object of the present invention to provide an Al-Cu-Li-Mg 
alloy having a composition within the following ranges: 3.5-7 Cu, 0.8-1.8 
Li, 0.25-1.0 Mg, 0.01-1.5 grain refiner selected from Zr, Cr, Mn, Ti, Hf, 
V, Nb, B, TiB.sub.2 and combinations thereof, and the balance aluminum. 
It is a further object of the present invention to provide an Al-Cu-Li-Mg 
alloy in which the weight percent ratio of Cu to Li is greater than 2.5 
and preferably greater than 3.0. 
Unless stated otherwise, all compositions are in weight percent.

DETAILED DESCRIPTION OF THE INVENTION 
The alloys of the present invention contain the elements Al, Cu, Li, Mg and 
a grain refiner or combination of grain refiners selected from the group 
consisting of Zr, Ti, Cr, Mn, B, Nb, V, Hf and TiB.sub.2. 
In one embodiment of the invention, an Al-Cu-Li-Mg alloy has a composition 
within the following ranges: 5.0-7.0 Cu, 0.1-2.5 Li, 0.05-4 Mg, 0.01-1.5 
grain refiner(s), with the balance being essentially Al. Preferred ranges 
are: 5.0-6.5 Cu, 0.5-2.0 Li, 0.2-1.5 Mg, 0.05-0.5 grain refiner(s), and 
the balance essentially Al. More preferred ranges are: 5.2-6.5 Cu, 0.8-1.8 
Li, 0.25-1.0 Mg, 0.05-0.5 grain refiner(s). The most preferred ranges are: 
5.4-6.3 Cu, 1.0-1.4 Li, 0.3-0.5 Mg, 0.08-0.2 grain refiner(s) and the 
balance essentially Al (see Table I). 
In another embodiment of the invention, an Al-Cu-Li-Mg alloy has a 
composition within the following ranges: 3.5-5.0 Cu, 0.8-1.8 Li, 0.25-1.0 
Mg, 0.01-1.5 grain refiner(s), with the balance being essentially Al. 
Preferred ranges are: 3.5-5.0 Cu, 1.0-1.4 Li, 0.3-0.5 Mg, 0.05-0.5 grain 
refiner(s), and the balance essentially Al. The more preferred ranges are: 
4.0-5.0 Cu, 1.0-1.4 Li, 0.3-0.5 Mg, 0.08-0.2 grain refiner(s), with the 
balance essentially Al. The most preferred ranges are: 4.5-5.0 Cu, 1.0-1.4 
Li, 0.3-0.5 Mg, 0.08-0.2 grain refiner(s) and the balance essentially Al 
(see Table Ia). As stated above, all percentages herein are by weight 
percent based on the total weight of the alloy., unless otherwise 
indicated. 
Incidental impurities associated with aluminum such as Si and Fe may be 
present, especially when the alloy has been cast, rolled, forged, 
extruded, pressed or otherwise worked and then heat treated. Ancillary 
elements such as Ge, Sn, Cd, In, Be, Sr, Ca and Zn may be added, singly or 
in combination, in amounts of from about 0.01 to about 1.5 weight percent, 
to aid, for example, in nucleation and refinement of the precipitates. 
TABLE 1 
______________________________________ 
COMPOSITIONS 
(HIGH COPPER RANGE) 
Cu Li Mg Grain 
Weight Weight Weight Refiner* 
Percent Percent Percent Weight Percent 
Al 
______________________________________ 
Broad 5.0-7.0 0.1-2.5 0.05-4 0.01-1.5 Bal. 
Preferred 
5.0-6.5 0.5-2.0 0.2-1.5 
0.05-0.5 Bal. 
More 5.2-6.5 0.8-1.8 0.25-1.0 
0.05-0.5 Bal. 
Preferred 
Most 5.4-6.3 1.0-1.4 0.3-0.5 
0.08-0.2 Bal. 
Preferred 
______________________________________ 
*To be selected from 1 or more of the following alone or in combination: 
Zr, Ti, Cr, Hf, Nb, B, TiB.sub.2, V, and Mn. 
______________________________________ 
Cu Li Mg Grain 
Weight Weight Weight Refiner* 
Percent Percent Percent Weight Percent 
Al 
______________________________________ 
Broad 3.5-5.0 0.8-1.8 0.25-1.0 
0.01-1.5 Bal. 
Preferred 
3.5-5.0 1.0-1.4 0.3-0.5 
0.05-0.5 Bal. 
More 4.0-5.0 1.0-1.4 0.3-0.5 
0.08-0.2 Bal. 
Preferred 
Most 4.5-5.0 1.0-1.4 0.3-0.5 
0.08-0.2 Bal. 
Preferred 
______________________________________ 
*To be selected from 1 or more of the following alone or in combination: 
Zr, Ti, Cr, Hf, Nb, B, TiB.sub.2, V, and Mn. 
In accordance with the parameters of the present invention, several alloys 
were prepared having the following compositions, as set forth in Table II. 
TABLE II 
______________________________________ 
Nominal Compositions of Experimental Alloys (wt %) 
Comp. Cu Li Mg Zr Al 
______________________________________ 
I 6.3 1.3 0.4 0.14 balance 
II 6.3 1.3 0.2 0.14 balance 
III 6.3 1.3 0.6 0.14 balance 
IV 5.4 1.3 0.2 0.14 balance 
V 5.4 1.3 0.6 0.14 balance 
VI 5.4 1.3 0.4 0.14 balance 
VII 5.4 1.7 0.4 0.14 balance 
VIII 5.4 1.3 0.8 0.14 balance 
IX 5.4 1.3 1.5 0.14 balance 
X 5.4 1.3 2.0 0.14 balance 
XI 5.0 1.3 0.4 0.14 balance 
XII 5.2 1.3 0.4 0.14 balance 
______________________________________ 
All alloys extruded extremely well with no cracking or surface tearing at a 
ram speed of 2.5 mm/second at approximately 370.degree. C. (700.degree. 
F.). 
In addition to the alloys listed in Table II, alloys containing Ti 
additions along with various ancillary element additions were prepared. 
These alloys are listed in Table IIa. 
TABLE IIa 
______________________________________ 
Nominal Compositions of Experimental Alloys (wt %) 
Comp. Cu Li Mg Zr Ti Addition 
Al 
______________________________________ 
XIII 5.4 1.3 0.4 0.14 0.03 0.25 Zn balance 
XIV 5.4 1.3 0.4 0.14 0.03 0.5 Zn balance 
XV 5.4 1.3 0.4 0.14 0.03 0.2 Ge balance 
XVI 5.4 1.3 0.4 0.14 0.03 0.1 In balance 
XVII 5.4 1.3 0.4 0.14 0.03 0.4 Mn balance 
XVIII 5.4 1.3 0.4 0.14 0.03 0.2 V balance 
______________________________________ 
Several alloys were prepared having lower Cu concentrations than listed 
above. These alloys are given in Table IIb. 
TABLE IIb 
______________________________________ 
Nominal Compositions of Experimental Alloys (wt %) 
Comp. Cu Li Mg Zr Ti Al 
______________________________________ 
XIX 4.5 1.3 0.4 0.14 0.03 balance 
XX 4.0 1.3 0.4 0.14 0.03 balance 
XXI 3.5 1.3 0.4 0.14 0.03 balance 
XXII 3.0 1.3 0.4 0.14 0.03 balance 
XXIII 2.5 1.3 0.4 0.14 0.03 balance 
______________________________________ 
Of the alloys listed in Table IIb, compositions XIX, XX and XXI containing 
4.5, 4.0 and 3.5 percent Cu are considered to be within the scope of the 
present invention, while compositions XXII and XXIII containing 3.0 and 
2.5 percent Cu are considered to fall outside of the compositional ranges 
of the present invention. It has been found that Cu concentrations below 
about 3.5 percent do not yield the significantly improved properties, such 
as ultrahigh strength, which are achieved in alloys that contain greater 
amounts of Cu. 
Thus, in accordance with the present invention, the use of Cu in relatively 
high concentrations, i.e. 3.5-7.0 percent, results in increased tensile 
and yield strengths over conventional Al-Li alloys. Additionally, the use 
of greater than about 3.5 Cu is necessary to promote weldability of the 
alloys, with weldability being extremely good above about 4.5 percent Cu. 
Concentrations above about 3.5 percent Cu are necessary to provide 
sufficient Cu to form high volume fractions of T.sub.1 (Al.sub.2 CuLi) 
strengthening precipitates in the artificially aged tempers. -These 
precipitates act to increase strength in the alloys of the present 
invention substantially above the strengths achieved in conventional Al-Li 
alloys. While Cu concentrations of up to 7 percent are given in the broad 
compositional range in one embodiment of the present invention, it is 
possible to exceed this amount, although additional copper above 7 percent 
may result in decreased corrosion resistance and fracture toughness, while 
increasing density. 
The use of Li in the alloys of the present invention permits a significant 
decrease in density over conventional Al alloys. Also, Li increases 
strength and improves elastic modulus. It has been found that the 
properties of the present alloys vary to a substantial degree depending 
upon Li content. In the high Cu embodiments (5.0-7.0 percent) of the 
present invention, substantially improved physical and mechanical 
properties are achieved with Li concentrations between 0.1 and 2.5 
percent, with a peak at about 1.2 percent. Below 0.1 percent, significant 
reductions in density are not realized, while above 2.5 percent, strength 
decreases to an undesirable degree. In the low Cu embodiments (3.5-5.0 
percent) of the present invention, substantially improved physical and 
mechanical properties are achieved with Li concentrations between about 
0.8 and 1.8 percent, with a peak at about 1.2 percent. Outside of this 
range, properties such as strength tend to decrease to an undesirable 
level. 
The high Cu to Li weight percent ratio in the alloys of the present 
invention, which is at least 2.5 and preferably greater than 3.0, is 
necessary to provide a high volume fraction of T.sub.1 strengthening 
precipitates in the alloys produced. Cu to Li ratios below about 2.5 have 
been found to yield substantially decreased properties, such as decreased 
strength. 
The use of Mg in the alloys of the present invention increases strength and 
permits a slight decrease in density over conventional Al alloys. Also, Mg 
improves resistance to corrosion and enhances natural aging response 
without prior cold work. It has been found that the strength of the 
present alloys varies to a substantial degree depending upon Mg content. 
In the high Cu embodiments (5.0-7.0 percent) of the present invention, 
substantially improved physical and mechanical properties are achieved 
with Mg concentrations between 0.05 and 4 percent, with a peak at about 
0.4 percent. In the low Cu embodiments (3.5-5.0 percent) of the present 
invention, substantially improved physical and mechanical properties are 
achieved with Mg concentrations between about 0.25 and 1.0 percent, with a 
peak at about 0.4 percent. Outside of the above ranges, significant 
improvements in properties, such as tensile strength, are not achieved. 
Particularly advantageous properties have been observed when Li contents 
are in the range 1.0-1.4 percent and Mg contents are in the range 0.3-0.5 
percent, showing that the type and extent of strengthening precipitates is 
critically dependent on the amounts of these two elements. 
For ease of reference, the temper designations for the various combinations 
of aging treatment and presence or absence of cold work have been 
collected in Table III. 
TABLE III 
______________________________________ 
TEMPER DESIGNATIONS 
Temper* Description 
______________________________________ 
T3 solution heat treated 
cold worked** 
naturally aged to substantially stable condition 
T4 solution heat treated 
naturally aged to substantially stable condition 
T6 solution heat treated 
artificially aged 
T8 solution heat treated 
cold worked 
artificially aged 
______________________________________ 
*Where additional numbers appear after the standard temper designation, 
such as T81, this simply indicates a specific type of T8 temper, for 
example, at a certain aging temperature or for a certain amount of time. 
**While a T4 or T6 temper may have cold work to effect geometric 
integrity, this cold work does not significantly influence the respective 
aged properties. 
A Composition I alloy was cast and extruded using the following techniques. 
The elements were induction melted under an inert argon atmosphere and 
cast into 160 mm (61/4 in.) diameter, 23 kg (50 lb) billets. The billets 
were homogenized in order to affect compositional uniformity of the ingot 
using a two-stage homogenization treatment. In the first stage, the billet 
was heated for 16 hours at 454.degree. C. (850.degree. F.) to bring low 
melting temperature phases into solid solution, and in the second stage it 
was heated for 8 hours at 504.degree. C. (940.degree. F.). Stage I was 
carried out below the melting point of any nonequilibrium low-melting 
temperature phases that form in the as-cast structure, because melting of 
such phases can produce ingot porosity and/or poor workability. Stage II 
was carried out at the highest practical temperature without melting, to 
ensure rapid diffusion to homogenize the composition. The billets were 
scalped and then extruded at a ram speed of 25 mm/s at approximately 
370.degree. C. (700.degree. F.) to form rectangular bars having 10 m by 
102 mm (3/8 inch by 4 inch) cross sections. 
It was determined by hot torsion testing that this alloy is readily 
workable using conventional aluminum working equipment in practical 
deformation temperature and strain rate regimes. For example, hot working 
parameters for more demanding operations such as rolling were determined. 
Test specimens having a diameter of 6.1 mm (0.24 inch) and a gauge length 
of 50 mm (2 inches) were machined from extruded stock and rehomogenized. 
Hot torsion testing was performed at an equivalent tensile strain rate of 
0.06 S.sup.-1 at temperatures ranging from 370.degree. to 510.degree. C. 
(700.degree. to 950.degree. F.). The equivalent tensile flow stress and 
equivalent tensile strain-to-failure were evaluated over this temperature 
range as illustrated in FIG. 1. The strain-to-failure is maximized over a 
broad range of hot working temperatures from below 427.degree. C. 
(800.degree. F.) to just over 482.degree. C. (900.degree. F.) allowing 
sufficient flexibility in choosing temperatures for rolling and forging 
operations. Liquation occurs at 508.degree. C. .degree.(946.degree. F.) as 
determined using differential scanning calorimetry (DSC) and cooling curve 
analysis, and this accounts for the sharp drop in hot ductility at 
510.degree. C. (950.degree. F.). The flow stresses over the optimum hot 
working temperature range are low enough such that processing can be 
readily performed on presses or mills having capacities consistent with 
conventional aluminum alloy manufacturing. From a commercial point of 
view, it is interesting to note that similar studies using as-cast and 
homogenized material of Composition I show the same trends. 
The rectangular bar extrusions that were not used in the hot torsion 
testing were subsequently solution heat treated at 503.degree. C. 
(938.degree. F.) for 1 hour and water quenched. Some segments of each 
extrusion were stretch straightened approximately 3 percent within 3 hours 
of quenching. This stretch straightening process straightens the extrusion 
and also introduces cold work. Some of the segments, both with and without 
cold work, were naturally aged at approximately 20.degree. C (68.degree. 
F.). Other segments were artificially aged, at 160.degree. C. (320.degree. 
F.) if cold worked, or at 180.degree. C. (356.degree. F.) if not cold 
worked. 
The superior properties of Composition I compared to conventional alloys 
2219 and 2024 are shown in Table IV. In particular, it should be noted 
that the naturally aged (T3 and T4) conditions for Composition I are being 
compared to the optimum high strength T8 tempers for the conventional 
alloys. 
TABLE IV 
______________________________________ 
TENSILE PROPERTIES 
YS UTS El. 
Alloy Temper (ksi) (ksi) 
(%) 
______________________________________ 
Comp. I T4 61.9 85.0 16.5 
T3 60.3 76.6 15.0 
2219 T81 minima 44.0 61.0 6.0 
T81 typicals 51.0 66.0 10.0 
2024 T42 minima 38.0 57.0 12.0 
T81 minima 58.0 66.0 5.0 
______________________________________ 
Table V shows naturally aged tensile properties for various alloys of the 
present invention. 
TABLE V 
______________________________________ 
NATURALLY AGED TENSILE PROPERTIES 
Aging 
Alloy Time YS UTS El. 
Comp. Temper (h) (ksi) (ksi) 
(%) 
______________________________________ 
II T3 1300 51.1 67.0 14.6 
T4 1400 50.9 75.0 17.8 
III T3 1300 58.2 75.9 17.4 
T4 1400 58.0 80.9 18.1 
IV T3 1300 51.0 69.0 17.6 
T4 1400 54.5 78.0 20.1 
V T3 1300 58.2 75.4 16.5 
T4 1400 58.0 82.5 19.2 
VI T3 1300 58.2 75.3 16.9 
T4 1400 59.9 83.4 18.2 
VII T3 1300 57.3 71.6 14.4 
T4 1400 60.6 81.2 14.1 
VIII T3 1300 58.4 75.0 16.7 
T4 1400 60.7 82.8 16.5 
IX T3 1100 55.8 68.2 14.3 
T4 1100 53.5 71.1 15.1 
X T3 1100 53.7 64.4 12.1 
T4 1100 49.4 67.2 15.1 
XI T3 1000 58.8 75.0 15.5 
T4 1000 64.5 84.6 14.1 
T4 1400 57.9 81.8 16.9 
XII T3 1000 60.2 76.6 17.2 
T4 1000 59.0 81.1 14.8 
XIII T3 2300 58.3 76.5 15.1 
T4 1000 56.3 80.3 15.5 
XIV T3 2300 58.4 77.2 18.2 
T4 1000 62.5 85.3 16.4 
XV T4 1000 52.0 75.2 18.7 
XVI T4 1000 53.9 77.7 18.1 
XVII T4 1000 54.8 79.3 18.0 
XVIII T4 1000 58.0 78.1 14.1 
XIX T3 1000 54.6 72.2 16.1 
T4 1000 60.4 83.8 17.0 
XX T3 1000 49.9 64.5 13.8 
T4 1000 58.9 80.8 18.6 
XXI T3 1000 51.7 66.7 18.1 
T4 1000 45.6 67.5 15.4 
XXII T3 1000 49.3 63.1 14.5 
T4 1000 49.6 71.7 18.4 
XXIII T3 1000 43.5 57.1 13.9 
T4 1000 41.1 62.3 15.8 
______________________________________ 
Composition I exhibits a phenomenal natural aging response. The tensile 
properties of Composition I in the naturally aged condition without prior 
cold work, T4 temper, are even superior to those of alloy 2219 in the 
artificially aged condition with prior cold work, i.e. in the fully heat 
treated condition or T81 temper. Composition I in the T4 temper has 61.9 
ksi YS, 85.0 ksi UTS and 16.5 percent elongation. By contrast, the 
handbook property minima for extrusions of 2219-T81, the current standard 
space alloy, are 44.0 ksi YS, 61.0 ksi UTS and 6 percent elongation (See 
Table IV). The T81 temper is the highest strength standard temper for 2219 
extrusions of similar geometry to the Composition I alloy. Composition I 
in the naturally aged tempers also has superior properties to alloy 2024 
in the high strength T81 temper, one of the leading aircraft alloys, which 
has 58 ksi YS, 66 ksi UTS and 5 percent elongation handbook minima. Alloy 
2024 also exhibits a natural aging response, i.e. T42, but it is far less 
than that of Composition I (see Table IV). 
To determine the appropriate temperatures for artificial aging, aging 
studies were performed and indicated that near-peak strengths could be 
obtained in technologically practical periods of time as follows: 
160.degree. C. for stretched material, or 180.degree. C. for unstretched 
material. The lower temperature was selected for the stretched material 
because the dislocations introduced by the cold work accelerate the aging 
kinetics. 
In the artificially-aged condition, Composition I attains ultrahigh 
strength. Of particular significance is the fact that peak tensile 
strengths (UTS) close to 100 ksi and elongations of a percent may be 
obtained in both the T8 and T6 tempers. This indicates that cold work is 
not necessary to achieve ultrahigh strengths in the alloys of the present 
invention, as it typically is in conventional 2XXX alloys. This is 
illustrated graphically in FIG. 2, which shows that Rockwell B hardness (a 
measure of alloy hardness that corresponds approximately one-to-one with 
UTS for these alloys) reaches the same ultimate value irrespective of the 
amount of cold work (stretch) after sufficient aging time. This should 
provide considerable freedom in the manufacturing processes associated 
with aircraft and aerospace hardware. Additionally, elongations of up to 
25 percent were achieved in grossly underaged, i.e. reverted, tempers (see 
Table VI for properties of compositions I, VI, XI, and XII, and Table VI a 
for additional properties of alloys prepared in accordance with the 
present invention). High ductility tempers such as this can be extremely 
useful in fabricating aerospace structural components because of the 
extensive cold-forming limits. The curves in FIGS. 3 and 4 show how the 
strength/ductility combination varies with artificial aging times for 
non-cold worked and cold worked alloys. 
TABLE VI 
______________________________________ 
ARTIFICIALLY AGED TENSILE PROPERTIES 
Ag- 
Temper ing Aging 
Alloy Tem- Descrip- Time Temp. YS UTS El. 
Comp. per tion (h) (.degree.C.) 
(ksi) (ksi) (%) 
______________________________________ 
I T8 near peak 24 160 95.7 99.4 4.5 
T8 near peak 24 160 94.5 98.0 5.0 
T8 near peak 15.5 160 94.8 99.0 6.5 
T8 under aged 
2 160 58.6 77.7 20.0 
T6 reversion 0.5 180 40.1 72.6 25.0 
T6 near peak 22 180 87.4 94.1 4.0 
T6 over aged 38.5 180 89.5 96.6 4.0 
VI T8 under aged 
6 160 80.5 89.1 11.8 
T8 near peak 20 160 93.0 96.8 8.3 
T8 near peak 24 160 92.0 95.5 6.4 
T6 near peak 22 180 82.7 90.1 7.0 
T6 under aged 
16 180 78.3 87.0 7.8 
XI T8 reversion 0.25 160 53.8 74.0 16.3 
T8 under aged 
6 160 81.2 88.6 12.9 
T8 under aged 
16 160 93.8 97.1 7.5 
T8 under age 20 160 92.4 96.2 8.9 
T8 near peak 24 160 95.1 98.4 8.4 
T8 near peak 24 160 96.7 100.3 6.7 
T6 reversion 0.25 180 39.1 68.9 23.9 
T6 under aged 
6 180 83.4 91.3 7.9 
T6 under aged 
16 180 81.6 90.7 7.3 
T6 near peak 22 180 84.6 92.4 5.5 
T6 near peak 22.5 180 88.8 94.2 7.4 
XII T8 under aged 
16 180 91.8 96.3 7.2 
T8 under aged 
20 160 92.3 96.3 7.4 
*T8 20 160 102.4 104.5 6.1 
T6 near peak 22 180 85.3 92.3 5.5 
*T6 16 180 84.4 92.9 7.1 
______________________________________ 
*measurements made on 0.375 inch extruded rod 
TABLE VI a 
______________________________________ 
ARTIFICIALLY AGED TENSILE PROPERTIES 
Ag- 
ing Aging 
Alloy Tem- Temper Time Temp. YS UTS El. 
Comp. per Description 
(h) (.degree.C.) 
(ksi) (ksi) (%) 
______________________________________ 
II T8 under aged 
6 160 74.1 84.0 11.2 
T8 under aged 
20 160 89.4 93.8 7.3 
T8 near peak 24 160 90.1 94.3 5.8 
T6 under aged 
16 180 63.4 77.7 6.4 
T6 near peak 22.5 180 68.2 81.0 4.9 
III T8 under aged 
6 160 76.1 85.1 10.9 
T8 under aged 
20 160 91.7 95.3 6.9 
T8 near peak 24 160 92.2 95.8 7.4 
T6 under aged 
16 180 78.8 88.0 8.1 
T6 near peak 22.5 180 82.1 89.4 4.3 
IV T8 under aged 
6 160 71.5 83.3 14.6 
T8 under aged 
20 160 87.0 92.3 8.2 
T8 near peak 24 160 89.6 94.9 7.4 
T6 under aged 
16 180 58.1 77.5 11.7 
T6 near peak 22.5 180 65.7 80.8 8.2 
V T8 under aged 
6 160 78.0 87.0 11.7 
T8 under aged 
20 160 87.7 92.6 7.8 
T8 near peak 24 160 89.1 94.1 8.3 
T6 under aged 
16 180 75.4 85.6 9.1 
VII T8 under aged 
6 160 73.2 81.3 8.9 
T8 under aged 
20 160 85.3 89.1 5.9 
T8 near peak 24 160 85.7 89.7 6.5 
T6 under aged 
16 180 70.5 81.5 9.5 
T6 near peak 22.5 180 80.4 86.3 6.4 
VIII T8 under aged 
6 160 75.7 83.9 11.0 
T8 under aged 
20 160 90.1 93.5 7.2 
T8 near peak 24 160 89.8 93.5 6.4 
T6 under aged 
16 180 76.0 86.0 8.0 
T6 near peak 22.5 180 81.0 87.6 7.0 
IX T8 under aged 
24 160 662.2 72.1 11.0 
T8 under aged 
24 180 75.4 76.6 4.5 
X T8 under aged 
24 160 55.2 68.2 12.7 
T8 under aged 
24 180 70.0 72.8 7.6 
XIII T8 under aged 
20 160 93.4 97.5 7.1 
T8 near peak 24 160 98.5 101.9 6.3 
T6 near peak 22 180 89.2 94.8 3.9 
XIV T8 under aged 
20 160 99.4 102.6 7.6 
T8 under aged 
22 160 93.3 97.1 8.4 
T8 near peak 24 160 95.9 99.1 6.0 
T6 near peak 21 180 89.3 94.9 4.9 
XV T8 under aged 
20 160 89.5 94.7 7.8 
T8 near peak 24 160 91.8 95.4 7.7 
T6 near peak 22 180 80.4 89.9 5.9 
XVI T8 under aged 
20 160 92.7 97.0 8.1 
T8 near peak 24 160 92.3 96.1 7.7 
T6 near peak 22 180 80.8 89.0 6.2 
XVII T8 under aged 
20 160 91.4 94.6 8.2 
T8 near peak 24 160 94.1 97.5 6.9 
XVIII T8 under aged 
20 160 96.0 99.0 4.6 
T8 near peck 24 160 93.0 95.4 3.6 
XIX T8 reversion .25 160 48.9 72.0 20.5 
T8 under aged 
6 160 73.8 82.3 11.5 
T8 under aged 
16 160 95.7 98.7 9.0 
T8 underaged 16 180 87.0 91.8 8.0 
T8 under aged 
20 160 89.3 93.7 9.6 
T8 near peak 24 160 92.7 96.1 8.4 
T6 reversion .25 180 36.5 65.4 25.5 
T6 under aged 
6 180 66.3 80.1 12.4 
T6 near peak 22 180 82.2 88.4 7.3 
XX T8 under aged 
16 180 80.1 85.3 10.9 
T8 under aged 
24 160 88.6 92.0 11.5 
T6 near peak 22 180 66.8 75.7 12.0 
XXI T8 under aged 
16 180 78.3 83.7 10.2 
T8 under aged 
24 160 77.8 82.8 12.4 
T6 near peak 22 180 65.3 75.3 10.9 
XXII T8 under aged 
16 180 68.8 74.1 10.1 
T8 under aged 
24 160 67.3 73.2 11.8 
T6 near peak 22 180 54.8 67.6 11.4 
XXIII T8 under aged 
16 180 59.0 66.0 8.8 
T8 under aged 
24 160 57.7 63.8 10.2 
______________________________________ 
It is noted that while certain processing steps are disclosed for the 
production of the alloy products of the present invention, these steps may 
be modified in order to achieve various desired results. Thus, the steps 
including casting, homogenization, working, heat treating, aging, etc. may 
be altered, or additional steps may be added, to affect, for example, the 
physical and mechanical properties of the final products formed. 
Characteristics such as the type, size and distribution of strengthening 
precipitates may thus be controlled to some degree depending upon 
processing techniques. Also, grain size and crystallinity of the final 
product may be controlled to some extent. Therefore, in addition to the 
processing techniques taught in the present disclosure, other conventional 
methods may be used in the production of the alloys of the present 
invention. 
While the formation of ingots or billets of the present alloys by casting 
techniques is preferred, the alloys may also be provided in billet form 
consolidated from fine particulate. The powder or particulate material can 
be produced by such processes as atomization, mechanical alloying and melt 
spinning. 
An investigation was made on the effect of Mg content on the tensile 
properties of alloys prepared according to the present invention. FIG. 5A 
shows that alloys of the composition Al - 6.3 Cu - 1.3 Li - 0.14 Zr, with 
various amounts of Mg, have a peak in naturally aged strength at 0.4 
weight percent Mg in the T3 temper and FIG. 6A shows a similar peak in the 
T4 temper. In addition, the highest strength in the artificially aged T6 
and T8 tempers is also attained at 0.4 weight percent Mg, as shown in 
FIGS. 7A and 8A. It is known in conventional 2XXX alloys that increasing 
Mg content produces increasing strength, e.g. 2024, 2124, and 2618 alloys 
generally contain 1.5 weight percent Mg. It is thus surprising that a peak 
should be obtained in the present alloys at such a low Mg level and that 
increased Mg content above about 0.4 weight percent does not increase 
strength. 
The situation is similar in Al - 5.4 Cu - 1.3 Li - 0.14 Zr alloys with 
varying Mg content. For example, naturally aged strength is highest around 
0.4 weight percent Mg with a gradual decrease in strength at 1.5 and 2.0 
weight percent Mg in both the T3 and T4 tempers, as shown in FIGS. 9A and 
10A. In the T6 temper (both near peak and under aged conditions) the 
strength is again highest around 0.4 weight percent Mg. See FIG. 11A (near 
peak aged) and FIG. 12A (under aged). In the T8 temper (FIG. 13A), 
strength is also highest at 0.4 weight percent Mg, although the peak is 
less dramatic than in the T3, T4 and T6 tempers. 
The tensile properties of the alloys of the present invention are highly 
dependent upon Li content. Peak strengths are attained with Li 
concentrations of about 1.1 to 1.3 percent, with significant decreases 
above about 1.4 percent and below about 1.0 percent. For example, a 
comparison between tensile properties of alloy Composition VI of the 
present invention (Al - 5.4 Cu - 1.3 Li - 0.4 Mg - 0.14 Zr) and alloy 
Composition VII (Al - 5.4 Cu - 1.7 Li - 0.4 Mg - 0.14 Zr) reveals a 
decrease of over 8 ksi in both yield strength and ultimate tensile 
strength (see Tables VI and VIa). 
In general, it has been found that the most advantageous properties, such 
as strength and elongation, have been achieved in alloys having a 
combination of relatively narrow Mg and Li ranges. For a particular 
temper, alloys of the present invention in the range 4.5-7.0 Cu, 1.0-1.4 
Li, 0.3-0.5 Mg, 0.05-0.5 grain refiner, and the balance Al, possess 
extremely useful longitudinal strengths and elongations. For example, in 
the T3 temper, alloys within the above mentioned compositional ranges 
display a YS range of from about 55 to about 65 ksi, a UTS range of from 
about 70 to about 80 ksi, and an elongation range of from about 12 to 
about 20 percent. In the T4 temper, alloys within this compositional range 
display a YS range of from about 56 to about 68 ksi, a UTS range of from 
about 80 to about 90 ksi, and an elongation range of from about 12 to 
about 20 percent. Additionally, in the T 6 temper, these alloys display a 
YS range of from about 80 to about 100 ksi, a UTS range of from about 85 
to about 105 ksi, and an elongation range of from about 2 to about 10 
percent. Further, in the T8 temper, alloys within the above-noted 
compositional range display a YS range of from about 87 to about 100 ksi, 
a UTS range of from about 88 to about 105 ksi, and an elongation range of 
from about 2 to about 11 percent. 
An investigation was made on the effect of Cu content on the hardness and 
tensile properties of alloys prepared according to the present invention. 
Alloys comprising Al - 1.3 Li - 0.4 Mg - 0.14 Zr and 0.05 Ti, with varying 
concentrations of Cu ranging from 2.5 to 5.4 percent, were cast, 
homogenized, scalped, extruded, solution heat-treated, quenched, stretched 
by either 0 percent or 3 percent, and heat treated in a manner similar to 
that discussed for Composition I above. FIG. 14 shows hardness vs. aging 
time curves for alloys with varying Cu content which have been subjected 
to 3 percent stretch and aged at 160.degree. C. As can be seen from FIG. 
14, hardness increases with increasing Cu content for alloys in the cold 
worked, artificially aged condition. FIG. 15 shows hardness vs. aging time 
curves for alloys with varying Cu content which have been subjected to 
zero stretch and aged at 180.degree. C. As can be seen from FIG. 15, 
hardness increases with increasing Cu content for alloys in the non-cold 
worked, artificially aged condition. 
FIG. 16A shows that alloys of the composition Al - 1.3 Li - 0.4 Mg - 0.14 
Zr - 0.05 Ti, with various amounts of Cu, have the highest naturally aged 
strengths between about 5 and 6 percent Cu in the T3 temper. Below about 5 
percent Cu, strengths decrease gradually. FIG. 17A shows a similar 
tendency in the T4 temper. Similarly, the highest strengths in both the 
artificially aged T6 and T8 tempers are attained between about 5 and 6 
percent Cu, as shown in FIGS. 18A and 19A. As in the T3 and T4 tempers, 
strengths decrease below about 5 percent Cu, however, the decrease is more 
pronounced in the T6 and T8 tempers. 
Table VII lists tensile properties of alloys of the present invention 
comprising Al - 1.3 Li - 0.4 Mg - 0.14 Zr - 0.05 Ti, with various amounts 
of Cu. The weight percentages of Cu given are measured values. 
TABLE VII 
__________________________________________________________________________ 
Tensile Properties of Alloys with Increasing Copper Content 
Cu Level 
Aging Temp 
(Time) YS UTS EL 
Comp (wt %) 
(.degree.C.) 
(h) Temper 
(ksi) 
(ksi) 
(%) 
__________________________________________________________________________ 
XXIV 2.62 -- -- T3 43.5 
57.1 
13.9 
-- -- T4 41.1 
62.3 
15.8 
180 (16) 
T8 59.0 
60.0 
8.8 
160 (24) 
T8 57.7 
63.8 
10.2 
180 (22) 
T6 49.9 
61.2 
13.5 
XXV 3.06 -- -- T3 49.3 
61.2 
13.5 
-- -- T4 49.6 
71.7 
18.4 
180 (16) 
T8 68.8 
74.1 
10.1 
160 (24) 
T8 67.3 
73.2 
11.8 
180 (22) 
T6 54.8 
67.6 
11.4 
XXVI 3.55 -- -- T3 51.7 
66.7 
18.1 
-- -- T4 45.6 
67.5 
15.4 
180 (16) 
T8 78.3 
83.7 
10.2 
160 (24) 
T8 77.8 
82.8 
12.4 
180 (22) 
T6 65.3 
75.3 
10.9 
XXVII 
4.07 -- -- T3 49.9 
64.5 
13.8 
-- -- T4 58.9 
80.8 
18.6 
(16) 
T8 80.1 
85.3 
10.9 
160 (24) 
T8 88.6 
92.0 
11.5 
180 (22) 
T6 66.8 
75.7 
12.0 
XXVIII 
4.42 -- -- T3 54.6 
72.2 
16.1 
-- -- T4 60.4 
83.8 
17.0 
180 (16) 
T8 87.0 
91.8 
8.0 
160 (16) 
T8 95.7 
98.7 
9.0 
160 (20) 
T8 89.3 
93.7 
9.6 
180 (22) 
T6 82.2 
88.4 
7.3 
XXIX 4.98 -- -- T3 58.8 
75.0 
15.5 
-- -- T4 64.5 
84.6 
14.1 
180 (16) 
T8 92.0 
96.8 
6.1 
160 (20) 
T8 93.3 
96.7 
7.8 
180 (22) 
T6 84.6 
92.4 
5.5 
XXX 5.16 -- -- T3 60.2 
76.7 
17.2 
-- -- T4 59.0 
81.8 
14.8 
180 (16) 
T8 91.8 
96.3 
7.2 
160 (20) 
T8 92.3 
96.3 
7.4 
180 (22) 
T6 85.3 
92.3 
5.5 
XXXI 5.30 -- -- T3 61.8 
77.3 
14.3 
-- -- T4 60.7 
83.1 
17.2 
180 (16) 
T8 90.3 
95.8 
7.1 
160 (20) 
T8 93.0 
96.8 
8.3 
180 (22) 
T6 81.3 
89.5 
5.4 
__________________________________________________________________________ 
It is noted that the above mentioned outstanding age hardening responses 
and high strengths achievable with the alloys of the present invention 
would typically be expected for alloys with very high solid solubility of 
precipitate forming elements. The results are thus quite unexpected in 
comparison to prior art Al-Cu-Li-Mg alloys, where as previously indicated, 
Mondolfo (p. 641) concludes that the addition of Li to Al-Cu-Mg alloys 
lowers the solid solubility of Cu and Mg, and the addition of Mg to 
Al-Cu-Li alloys lowers the solid solubility of copper and lithium and thus 
reduces the age hardening response and UTS values achievable. In contrast, 
it has been found that highly improved age hardening response and higher 
strengths than previously obtainable can be achieved in the alloys of the 
present invention. 
A detailed transmission electron microscopy (TEM) study including selected 
area diffraction (SAD) measurements has shown that the ultrahigh strength 
of the alloys of the present invention in the T8 temper may be associated 
with the fine homogeneous distribution of T.sub.1 (Al.sub.2 CuLi) 
precipitates rather than-the other strengthening precipitates, such as 
delta-prime (Al.sub.3 Li) and theta-prime (Al.sub.2 Cu), commonly found in 
Al-Li and Al-Cu-Li alloys. 
In a recent study of the alloy 2090 by Huang and Ardell (see "Crystal 
Structure and Stability of T.sub.1 (Al.sub.2 CuLi) Precipitates in Aged 
Al-Li-Cu Alloys", Mat. Sci. and Technology, March, Vol. 3, pp. 176-188, 
1987), it was found that alloy 2090 in the T8 temper contains both the 
T.sub.1 and delta-prime phases, with the T.sub.1 phase being a more potent 
strengthener than the delta-prime phase. In contrast, a selected area 
diffraction pattern (SADP) study of alloys of the present invention 
(Composition I, T8 temper) shows that T.sub.1 is the major strengthening 
phase present and no delta-prime is observed. This conclusion is reached 
by comparing selected area diffraction patterns for the [110], [112], 
[114], and (013] zone axes (ZA) from an alloy of Composition I in the T8 
temper with the predicted patterns from Huang and Ardell. The SADP study 
also shows that the T.sub.1 platelet volume fraction of the Composition I 
alloy in the T8 temper appears to be greater and more uniformly 
distributed than in alloy 2090 (by observation of a centered dark field 
(CDF) photograph taken from the (1010) T.sub.1 spot with ZA - [114]). 
Additionally, alloy 2090 requires cold work for extensive T.sub.1 
precipitation to occur, while in the alloys of the present invention, high 
volume fractions of T.sub.1 are observed in artificially aged tempers 
irrespective of the presence of cold work. 
The alloys of the present invention resemble more closely the Al-Cu-Li 
system studied by Silcock (see J.M. Silcock, "The Structural Aging 
Characteristics of Aluminum-Copper-Lithium Alloys," J. Inst. Metals, 88, 
pp. 357-364, 1959-1960.) At similar copper and lithium levels, Silcock 
showed that the phases present in the artificially aged condition are 
T.sub.1, theta-prime, and aluminum solid solution. Unexpectedly, in the 
present invention the precipitation of theta-prime is suppressed, 
apparently by the extensive nucleation of the T.sub.1 phase, but this 
effect is not fully understood. 
In addition to the superior room temperature properties, tests show that 
the alloys of the present invention possess excellent cryogenic 
properties. Not only are the tensile and yield strengths retained, but 
there is actually an improvement at low temperatures. The properties are 
far superior to those of alloy 2219 as shown in Table VIII. For example, 
Composition I in a T8 temper at -196.degree. C. (-320.degree. F.) displays 
tensile properties as high as 109 ksi YS, and 114 ksi UTS (see FIG. 20A). 
This has important implications for space applications where cryogenic 
alloys are often necessary for fuel and oxidizer tankage. 
TABLE VIII 
______________________________________ 
Cryogenic Properties 
Temperature YS UTS El 
(.degree.F.) 
Temper (ksi) (ksi) (%) 
______________________________________ 
Composition I 
-80 T3 63.5 78.4 14.3 
-320 T3 reversion 64.7 85.5 19.5 
-320 T3 76.7 93.9 14.0 
-80 T4 65.1 87.9 13.0 
-320 T4 75.8 99.0 12.5 
-80 T6 reversion 39.8 65.7 22.0 
-80 T6 under aged 
79.8 89.6 7.2 
-80 T6 96.5 102.8 2.0 
-320 T6 reversion 47.8 79.0 25.9 
-320 T6 under aged 
85.5 99.6 6.0 
-320 T6 101.8 107.8 2.0 
-80 T8 reversion 51.8 69.3 16.1 
-80 T8 underaged 87.8 94.0 7.0 
-80 T8 99.0 102.3 3.0 
-320 T8 reversion 64.7 85.5 19.6 
-320 T8 underaged 100.6 107.8 4.0 
-320 T8 109.0 114.2 2.0 
Composition XI 
-80 T3 60.8 78.1 14.6 
-320 T3 76.9 97.2 13.5 
-80 T4 64.5 85.7 11.3 
-320 T4 80.5 106.2 12.4 
-80 T6 reversion 40.6 64.9 22.3 
-80 T6 under aged 
79.0 89.0 8.6 
-80 T6 95.0 99.0 4.2 
-320 T6 reversion 44.8 77.9 28.2 
-320 T6 under aged 
92.9 105.6 8.3 
-320 T6 103.0 109.9 3.7 
-80 T8 reversion 49.7 69.7 17.6 
-80 T8 under aged 
88.4 95.3 9.3 
-80 T8 98.6 101.6 5.0 
-320 T8 reversion 58.3 82.7 19.8 
-320 T8 under aged 
98.5 110.0 9.6 
-320 T8 110.9 118.7 5.8 
2219 
-80 T62 43.0 62.0 13.0 
-320 T62 51.0 74.0 14.0 
-80 T87 52.0 71.0 9.5 
-320 T87 64.0 84.0 12.0 
______________________________________ 
The Composition I alloy also exhibits excellent elevated temperature 
properties. For example, in the T6 temper, with peak aging of 16 hours, it 
retains a large portion of its strength and a useful amount of elongation 
at 149.degree. C. (300.degree. F.), i.e. 74.4 ksi YS, 77.0 ksi UTS and 7.5 
percent elongation. In the near peak aged T8 temper, Composition I at 
149.degree. C. (300.degree. F.) has 84.7 ksi YS, 85.1 ksi UTS and 5.5 
percent elongation (see Table IX and FIG. 21A). 
TABLE IX 
______________________________________ 
Elevated Temperature Properties 
Temperature YS UTS El 
(.degree.F.) 
Temper (ksi) (ksi) 
(%) 
______________________________________ 
Composition I 
300 T6 74.4 77.0 7.5 
300 T8 84.7 85.1 5.5 
500 T8 44.5 45.2 5.5 
______________________________________ 
Welding studies of the alloys of the present invention indicate that they 
are readily weldable, possessing excellent resistance to hot cracking that 
can occur during welding. Tungsten Inert Gas (TIG) butt welds of 
Composition I were made from the 10 mm.times.102 mm (3/8.times.4 inch) 
extruded bar using filler alloy 2319 (Al - 6.3 Cu - 0.3 Mn - 0.15 Ti - 0.1 
V - 0.18 Zr). The plates were highly constrained, yet no hot cracking was 
observed. The welding was performed using direct current straight 
polarity. The punch pass parameters were 240 volts, 13.6 amps at 4.2 
mm/second (10 inch/minute) travel speed. The 2319 filler (1.6 mm 
(1/16-inch) diameter rod) was fed into the weld at 7.6 mm/second (18 
inches/minute) with 178 volts and 19 amps. A quantitative assessment of 
weldability is difficult to attain, but the weldability appears to be very 
close to that of 2219, which has a rating of " A" in MIL. HANDBOOK V, 
indicating that the alloy is generally weldable by all commercial 
procedures and methods. 
Mechanical properties were measured on weldments of Composition VI with 
Composition VI filler and with 2319 filler, as well as Composition XI with 
Composition XI filler and with 2319 filler. The weld strengths from these 
alloys in the naturally aged condition are in several cases higher than 
those of 2219-T81 and 2519-T87, alloys that are generally considered to be 
weldable (see Table X). 
TABLE X 
______________________________________ 
Properties of Experimental Alloys in As Welded, Bead-off, 
Naturally Aged Condition 
Parent Temper 
Metal Before Filler YS UTS El 
Comp. Welding Comp. Proc. (ksi) 
(ksi) (%) 
______________________________________ 
VI T3 VI GTAW 34.8 41.0 1.5 
37.4 41.6 1.3 
36.0 40.6 1.5 
34.6 42.4 2.1 
VI T8 VI GTAW 35.1 41.8 1.9 
VI T8 2319 GTAW 32.2 37.1 1.2 
33.8 40.7 2.3 
31.2 37.1 1.5 
XI T3 XI GTAW 36.8 47.9 3.7 
38.9 50.5 4.4 
35.6 49.9 6.3 
XI T8 XI GTAW 36.2 44.0 2.2 
36.9 47.0 3.1 
36.4 49.9 5.0 
XI T8 2319 GTAW 31.0 43.4 3.9 
33.0 45.0 3.9 
31.8 40.3 2.6 
(Parent metal taken from 9.5 mm bar.) 
2519 T87 2319 GMAW 30.3 43.7 4.4 
2519 T87 2319 GMAW 27.3 43.4 3.6 
(Parent Metal taken from 19 mm plate.) 
2219 T81 2319 GMAW 26.0 38.0 3.0 
2219 T81 2319 GMAW 34.0 41.0 2.0 
(Parent metal taken from 9.5 mm plate.) 
______________________________________ 
High strength aluminum alloys typically have low resistance to various 
types of corrosion, particularly stress-corrosion cracking (SCC), which 
has limited the usefulness of many high-tech alloys. In contrast, the 
alloys of the present invention show promising results from SCC tests. For 
Composition I, a stress vs. time-to-failure test, (ASTM standard G49, with 
test duration ASTM standard G64) shows that 4 LT (long transverse) 
specimens loaded at each of the following stress levels, 50 ksi, 37 ksi 
and 20 ksi, all survived the standard 40-day alternate immersion test. 
This is significant because it demonstrates excellent SCC resistance at 
stress levels approximately equal to the yield strengths of existing 
aerospace alloys such as 2024 and 2014. Additionally, Composition I in a 
T8 temper possesses SCC resistance comparable to artificially peak-aged 
8090, but at a strength level 25-30 ksi higher. 
The EXCO test (ASTM standard G34), a test for exfoliation susceptibility 
for 2XXX Al alloys, reveals that alloy Composition I has a rating of EA. 
This indicates only minimal susceptibility to exfoliation corrosion. 
It is to be understood that the above description of the present invention 
is susceptible to various modifications, changes, and adaptations by those 
skilled in the art, and that the same are to be considered to be within 
the spirit and scope of the invention as set forth by the claims which 
follow.