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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Superplastic formability of Al-Cu-Li alloy Weldalite (TM) 049

Extensive research during the past decade shows that several aluminum lithium alloys can be processed to attain a microstructure that enables superplasticity. The high tensile stress of Al-Cu-Li alloy Weldalite (TM) 049 in the T4 and T6 tempers offers tremendous potential for attaining exceptional post-SPF (superplastic formability) properties. The used SPF material is Weldalite, which was shown to induce SPF behavior in other Al-Cu-Li alloys. The superplastic behavior and resulting post-SPF mechanical properties of this alloy, which was designed to be the next major structural alloy for space applications, were evaluated. The results indicate that Weldalite alloy does indeed exhibit excellent superplasticity over a wide range of temperatures and strain rates and excellent post-SPF tensile strength at various potential service temperatures.

Ma, Bao-Tong↗
NASA NTRS1997

Microstructure Characterization and Stress Corrosion Evaluation of Autogenous and Hybrid Friction Stir Welded Al-Cu-Li 2195 Alloy

Friction stir welding process is being evaluated for application on the Al-Cu-Li 2195 Super-Light Weight External Tank of the Space Transportation System. In the present investigation Al-Cu-Li 2195 plates were joined by autogenous friction stir welding (FSW) and hybrid FSW (friction stir welding over existing variable polarity plasma arc weld). Optical microscopy and transmission electron microscopy (TEM) were utilized to characterize microstructures of the weldments processed by both welding methods. TEM observations of autogenous FSW coupons in the center section of the dynamically-recrystallized zone showed an equiaxed recrystallized microstructure with an average grain size of approx. 3.8 microns. No T(sub 1), precipitates were present in the above-mentioned zone. Instead, T(sub B) and alpha precipitates were found in this zone with a lower population. Alternate immersion, anodic polarization, constant load, and slow strain tests were carried out to evaluate the general corrosion and stress-corrosion properties of autogenous and hybrid FSW prepared coupons. The experimental results will be discussed.

Li, Zhixian↗
NASA NTRS1991

Identification of strengthening phases in Al-Cu-Li alloy Weldalite (tm) 049

Microstructure property relationships were determined for a family of ultrahigh strength weldable Al-Cu-Li based alloys referred to as Weldalite (tm) alloys. The highest strength variant of this family, Weldalite 049, has a high Cu/Li wt pct. ratio with a nominal composition of Al-6.3Cu-1.3Li-0.4Ag-0.4Mg-0.14Zr. Increasing the alloy's lithium content above 1.3 wt pct. resulted in a decrease in both yield and ultimate tensile strength. Strength was shown to be strongly dependent on lithium content, with a maximum in strength occurring in the range of about 1.1 to 1.4 wt pct. lithium. The strengthening phases present in Weldalite 049 (1.3Li) and an Al-6.3Cu-1.9Li-0.4Mg-0.14Zr alloy were identified using transmission electron microscopy (TEM).

Source record↗
NASA NTRS1998

Catalogue of X-Ray Texture Data for Al-Cu-Li Alloy 1460, 2090, 2096 and 2195 Near-Net-Shape Extrusions, Sheet and Plate

The effect of crystallographic texture on the mechanical properties of near-net-shape extrusions is of major interest ff these products are to find application in launch vehicle or aircraft structures. The objective of this research was to produce a catalogue containing quantitative texture information for extruded product, sheet and plate. The material characterized was extracted from wide, integrally stiffened panels fabricated from the Al-Cu-Li alloys 1460, 2090, 2096 and 2195. The textural characteristics of sheet and plate products of the same alloys were determined for comparison purposes. The approach involved using X-ray diffraction to generate pole figures in combination with orientation distribution function analysis. The data were compiled as a function of location in the extruded cross-sections and the variation in the major deformation- and recrystallization-related texture components was identified.

Hales, Stephen J.↗
NASA NTRS1998

Characterization of Al-Cu-Li Alloy 2090 Near Net Shape Extrusion

Aluminum-lithium (Al-Li) alloys near net shape extrusions are being evaluated for potential application in launch vehicle structures. The objective of this study was to determine tensile and fracture properties, corrosion resistance, and weldability of integrally stiffened panels of Al-Cu-Li alloy 2090 in the T8 temper. The microstructure was pre-dominantly unrecrystallized. Texture analyses revealed the presence of fiber components in the stiffeners and a combination of fiber and rolling components in the skin. Variations in grain morphology and texture through the extruded cross section were correlated with the tensile, fracture, and corrosion behavior. Tensile strengths at room and cryogenic temperatures of the 2090 extrusions were similar to other 2090 product forms and were higher than 2219-T87, the primary structural material in the Space Shuttle external tank; however, ductilities were lower. The fracture resistance of the 2090 extrusion was lower than 2219-T87 plate at room temperature. At cryogenic temperatures, tensile ductility and fracture behavior of the 2090 extrusion were similar to other 2090 product forms but were lower than 2219-T87 plate. The exfoliation and stress corrosion resistance of the 2090 extrusion compared favorably with the characteristics of other 2090 product forms. The weldability and weldment properties of the extrusions were similar to 2090 and 2219 plates.

Birt, M. J.↗
NASA NTRS1999

Time Temperature-Precipitation Behavior in An Al-Cu-Li Alloy 2195

Al-Cu-Li alloy 2195, with its combination of good cryogenic properties, low density, and high modulus, has been selected by NASA to be the main structural alloy of the Super Light Weight Tank (SLWT) for the Space Shuttle. Alloy 2195 is strengthened by an aging treatment that precipitates a particular precipitate, labeled as T1(Al2CuLi). Other phases, such as GP zone, (theta)', (theta)", theta, (delta)', S' are also present in this alloy when artificially aged. Cryogenic strength and fracture toughness are critical to the -SLWT application, since the SLWT will house liquid oxygen and hydrogen. Motivation for the Time-Temperature-Precipitation (TTP) study at lower temperature (lower than 350 F) comes in part from a recent study by Chen, The study found that the cryogenic fracture toughness of alloy 2195 is greatly influenced by the phases present in the matrix and subgrain boundaries. Therefore, the understanding of TTP behavior can help develop a guideline to select appropriate heat treatment conditions for the desirable applications. The study of TTP behavior at higher temperature (400 to 1000 F) was prompted by the fact that the SLWT requires a welded construction. Heat conduction from the weld pool affects the microstructure in the heat-affected zone (HAZ), which leads to changes in the mechanical properties. Furthermore, the SLWT may need repair welding for more than one time and any additional thermal cycles will increase precipitate instability and promote phase transformation. As a result considerable changes in HAZ microstructure and mechanical properties are expected during the construction of the SLWT. Therefore, the TTP diagrams can serve to understand the thermal history of the alloy by analyzing the welded microstructure. In the case welding, the effects of thermal cycles on the microstructure and mechanical properties can be predicted with the aid of the TTP diagrams. The 2195 alloy (nominally Al + 4 pct Cu + 1 pct Li + 0.3 pct Ag + 0.3 pct Mg + 0.1 pct Zr) used in this study was received in the form of 1.7 inch thick rolled plates. In brief goal of this study is to develop TTR diagram for the solutiontreated and stretched alloy 2195 from which the precipitation sequence at any service or aging conditions can be preducted.A subgrain boundary TTR diagram is also presented since precipitations at subgrain boundary can control and/or modify a wide veriety of material properties, such as cryogenic fracture toughness.

Chen, P. S.↗
NASA NTRS1991

The influence of Ag+Mg additions on the nucleation of strengthening precipitates in a non-cold-worked Al-Cu-Li alloy

Aluminum-copper-lithium alloys generally require cold work to attain their highest strengths in artificially aged tempers. These alloys are usually strengthened by a combination of the metastable delta prime (Al3Li) and theta prime (Al2Cu) phases and the equilibrium T sub 1 (Al2CuLi) phase, and where the T sub 1 phase is a more potent strengthener than the delta prime. Various investigators have shown that the high strengths obtained after artificial aging associated with cold work result from the heterogeneous precipitation of T sub 1 on matrix dislocations. The objective here is to elucidate the mechanism by which the Ag+Mg additions stimulate the precipitation of T sub 1 type precipitates without cold work. To accomplish this, the microstructure of an Al-6.3Cu-1.3Li-0.14Zr model alloy was evaluated in a T6 type temper with and without the Ag+Mg addition.

Source record↗
NASA NTRS1991

The effect of TiB2 reinforcement on the mechanical properties of an Al-Cu-Li alloy-based metal-matrix composite

The addition of ceramic particles to aluminum based alloys can substantially improve mechanical properties, especially Young's modulus and room and elevated temperature strengths. However, these improvements typically occur at the expense of tensile ductility. The mechanical properties are evaluated to a metal matrix composite (MMC) consisting of an ultrahigh strength aluminum lithium alloy, Weldalite (tm) 049, reinforced with TiB2 particles produced by an in situ precipitation technique called the XD (tm) process. The results are compared to the behavior of a nonreinforced Weldalite 049 variant. It is shown that both 049 and 049-TiB2 show very attractive warm temperature properties e.g., 625 MPa yield strength at 150 C after 100 h at temperature. Weldalite 049 reinforced with a nominal 4 v pct. TiB2 shows an approx. 8 pct. increase in modulus and a good combination of strength (529 MPa UTS) and ductility (6.5 pct.) in the T3 temper. And the high ductility of Weldalite 049 in the naturally aged and underaged tempers makes the alloy a good, high strength matrix for ceramic reinforcement.

Source record↗
NASA NTRS1989

Identification of strengthening phases in Al-Cu-Li alloy Weldalite 049

The tensile properties in the peak-strength T8 temper for Weldalite 049, a family of ultrahigh-strength weldable Al-Cu-Li-based alloys with a Li content ranging from 0 to 1.9 wt percent, are investigated, and strengthening precipitates at selected Li levels are identified. Relatively small amounts of Ag and Mg were found to be extremely effective in stimulating precipitation in Weldalite 049, resulting in a homogeneous distribution of fine, platelike precipitates with a 111-type habit plane in the peak-aged, T8 temper. The yield and tensile strengths are strongly dependent on Li content, with a peak in the range of 1.1 to 1.4 wt percent Li. At above 1.4 wt percent Li, strength decreases rapidly, which is associated with delta-prime precipitation. For high-resolution TEM, the structure of T(1)-type precipitates in Weldalite 049 is similar to that of T(1) platelets in 2090.

Langan, T. J.↗
NASA NTRS1991

The effect of TiB2 reinforcement on the mechanical properties of an Al-Cu-Li alloy-based metal-matrix composite

Weldalite 049, an Al-base Cu-Li-Mg-Ag-Zr alloy, achieves 700 MPa tensile strengths in the near-peak-aged temper in virtue of the nucleation of a T(1)-type platelike strengthening precipitate. Attention is presently given to the possibility that the alloy's modulus could be further increased through the addition of high-modulus TiB2 particles, using the 'XD' process, due to TiB2's good wettability with liquid Al. An 8-percent modulus increase is obtained with 4 vol pct TiB2.

Langan, T. J.↗
NASA NTRS1998

Friction Stir Weld Tooling Development for Application on the 2195 Al-Cu-Li Space Transportation System External Tank

Friction Stir Welding (FSW) is a new and innovative solid-state joining process which can be applied to difficult-to- weld aluminum alloys. However, the large forces involved with the process have posed a production tooling challenge. Lockheed Martin Michoud Space Systems has overcome many of these challenges on the Super Lightweight External Tank (ET) program. Utilizing Aluminum-Copper-Lithium alloy 2195 in the form of plate and extrusions, investigations of FSW process parameters have been completed. Major loading mechanisms are discussed in conjunction with deflection measurements. Since the ET program is a cryogenic application, a brief comparison of cryogenic material properties with room temperature material properties is offered for both FSW and fusion welds. Finally, a new approach to controlling the FSW process from a load perspective is introduced. Emphasis will be put on tooling development, as well as the impact of tooling design and philosophy on Friction Stir Weld success probability.

Loftus, Zachary↗
NASA NTRS1998

Friction Plug Welding of 2195 Al-Cu-Li for Manned Space Launch Vehicles

Friction Plug Welding (FPW) is currently being studied for use on the Space Transportation System's Super Light weight External Tank. This process has demonstrated the potential to solve on of Al-Li 2195's most challenging aspects repair welding. The current weld repair process is successful, but is labor intensive and inconsistent. Technology advances in FPW and tooling designs will be presented. The results of plug welding optimization, production implementation, considerations and cost benefit analysis are discussed. Among the tests to be discussed are tensile, surface crack tension, simulated service, liquid oxygen compatibility results and methods of repairing plug repairs. Tool design, computerized process control equipment and database record retention and analyses may also be addressed.

Takeshita, Riki P.↗
NASA NTRS1991

Microstructural evolution during aging of an Al-Cu-Li-Ag-Mg-Zr alloy

Alloys in the Al-Cu-Li Ag-Mg subsystem were developed that exhibit desirable combinations of strength and ductility. These Weldalite (trademark) alloys, are unique for Al-Cu-Li alloys in that with or without a prior cold stretching operation, they obtain excellent strength-ductility combinations upon natural and artificial aging. This is significant because it enables complex, near-net shape products such as forgings and super plastically formed parts to be heat treated to ultra-high strengths. On the other hand, commercial extrusions, rolled plates and sheets of other Al-Cu-Li alloys are typically subjected to a cold stretching operation before artificial aging to the highest strength tempers to introduce dislocations that provide low-energy nucleation sites for strengthening precipitates such as the T(sub 1) phase. The variation in yield strength (YS) with Li content in the near-peak aged condition for these Weldalite (trademark) alloys and the associated microstructures were examined, and the results are discussed.

Kumar, K. S.↗
NASA NTRS1991

Effect of a prior stretch on the aging response of an Al-Cu-Li-Ag-Mg-Zr alloy

Recently, a family of Al-Cu-Li alloys containing minor amounts of Ag, Mg, and Zr and having desirable combinations of strength and toughness were developed. The Weldalite (trademark) alloys exhibit a unique characteristic in that with or without a prior stretch, they obtain significant strength-ductility combinations upon natural and artificial aging. The ultra-high strength (approximately 690 MPa yield strength) in the peak-aged tempers (T6 and T8) were primarily attributed to the extremely fine T(sub 1) (Al2CuLi) or T(sub 1)-type precipitates that occur in these alloys during artificial aging, whereas the significant natural aging response observed is attributed to strengthening from delta prime (Al3Li) and GP zones. In recent work, the aging behavior of an Al-Cu-Li-Ag-Mg alloy without a prior stretch was followed microstructurally from the T4 to the T6 condition. Commercial extrusions, rolled plates, and sheets of Al-Cu-Li alloys are typically subjected to a stretching operation before artificial aging to straighten the extrusions and, more importantly, introduce dislocations to simulate precipitation of strengthening phases such as T(sub 1) by providing relatively low-energy nucleation sites. The goals of this study are to examine the microstructure that evolves during aging of an alloy that was stretch after solution treatment and to compare the observations with those for the unstretched alloy.

Kumar, K. S.↗
NASA NTRS1991

High resolution electron microscopy study of a high Cu variant of Weldalite (tm) 049 and a high strength Al-Cu-Ag-Mg-Zr alloy

Weldalite (trademark) 049 is an Al-Cu-Li-Ag-Mg alloy that is strengthened in artificially aged tempers primarily by very thin plate-like precipitates lying on the set of (111) matrix planes. This precipitate might be expected to be the T(sub 1) phase, Al2CuLi, which has been observed in Al-Cu-Li alloys. However, in several ways this precipitate is similar to the omega phase which also appears as the set of (111) planes plates and is found in Al-Cu-Ag-Mg alloys. The study was undertaken to identify the set of (111) planes precipitate or precipitates in Weldalite (trademark) 049 in the T8 (stretched and artificially aged) temper, and to determine whether T(sub 1), omega, or some other phase is primarily responsible for the high strength (i.e., 700 MPa tensile strength) in this Al-Cu-Li-Ag-Mg alloy.

Herring, R. A.↗
NASA NTRS1991

Temperature effects on the deformation and fracture of Al-Li-Cu-In alloys

The crack initiation and growth fracture resistance of Al-Cu-Li and Al-Cu-Li-In alloys were characterized and optimized for cryogenic tank applications. Presently, the effects of stress state and temperature is being determined on the fracture toughness and fracture mechanisms of commercially available Vintage 3 2090-T81 and experimental 2090+In-T6. Precracked J-integral specimens of both alloys were tested at ambient and cryogenic temperatures in the plane stress and plane strain conditions. Considering ambient temperature, results showed that 2090-T81 exhibited the highest toughness in both plane strain and plane stress conditions. For the plane strain condition, reasonable crack initiation and growth toughness of 1090-T81 are associated with a significant amount of delamination and transgranular fracture. Plane stress toughnesses were higher and fracture was characterized by shear cracking with minimal delaminations. In comparisons, the fracture behavior of 2090+In-T6 is significantly degraded by subgrain boundary precipitation. Toughness is low and characterized by intersubgranular fracture with no delamination in the plane stress or plane strain conditions. Intersubgranular cracking is a low energy event which presumably occurs prior to the onset of slip band cracking. Copious grain boundary precipitation is atypical of commercially available 2090. At cryogenic temperatures, both alloys exhibit increased yield strength, toughness, and amount of delamination and shear cracking. The change in fracture mode of 2090+In-T6 from intersubgranular cracking at ambient temperature to a combination of intersubgranular cracking, shear cracking, and delamination at cryogenic temperature is the subject of further investigation.

Wagner, John A.↗
NASA NTRS1989

Intermediate temperature thermomechanical processing of Al 2090 for superplasticity

The Al-Cu-Li phase diagram indicates that during thermomechanical processing of Al 2090 at 300 C both T(1) and T(2) phases will precipitate. Following work on Al-Mg-X alloys, it is possible that TMP at such temperatures might promote intragranular formation of these phases and promote microstructural refinement during recrystallization. Microstructural analyses reveal that the T(2) phase in Al 2090 may play a similar role to the beta-phase in Al-Mg-X alloys during microstructural evolution. Mechanical property data indicate that Al 2090 can be moderately (215-245 percent) superplastic at 370 C following processing at 300 C.

Hales, S. J.↗