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Effects of Thermal Exposure on Properties of Al-Li AlloysAluminum-Lithium (Al-Li) alloys offer significant performance benefits for aerospace structural applications due to their higher specific properties compared with conventional Al alloys. For example, the application of Al-Li alloy 2195 to the space shuffle external cryogenic fuel tank resulted in weight savings of over 7,000 lb, enabling successful deployment of International Space Station components. The composition and heat treatment of 2195 were optimized specifically for strength-toughness considerations for an expendable cryogenic tank. Time-dependent properties related to reliability, such as thermal stability, fatigue, and corrosion, will be of significant interest when materials are evaluated for a reusable cryotank structure. Literature surveys have indicated that there is limited thermal exposure data on Al-Li alloys. The effort reported here was designed to establish the effects of thermal exposure on the mechanical properties and microstructure of Al-Li alloys C458, L277, and 2195 in plate gages. Tensile, fracture toughness, and corrosion resistance were evaluated for both parent metal and friction stir welds (FSW) after exposure to temperatures as high as 300 F for up to 1000 hrs. Microstructural changes were evaluated with thermal exposure in order to correlate with the observed data trends. The ambient temperature parent metal data showed an increase in strength and reduction in elongation after exposure at lower temperatures. Strength reached a peak with intermediate temperature exposure followed by a decrease at highest exposure temperature. Friction stir welds of all alloys showed a drop in elongation with increased length of exposure. Understanding the effect of thermal exposure on the properties and microstructure of Al-Li alloys must be considered in defining service limiting temperatures and exposure times for a reusable cryotank structure.
Document ID
20030001044
Acquisition Source
Marshall Space Flight Center
Document Type
Preprint (Draft being sent to journal)
Authors
Shah, Sandeep
(NASA Marshall Space Flight Center Huntsville, AL United States)
Wells, Douglas
(NASA Marshall Space Flight Center Huntsville, AL United States)
Stanton, William
(NASA Marshall Space Flight Center Huntsville, AL United States)
Lawless, Kirby
(NASA Marshall Space Flight Center Huntsville, AL United States)
Russell, Carolyn
(NASA Marshall Space Flight Center Huntsville, AL United States)
Wagner, John
(NASA Langley Research Center Hampton, VA United States)
Domack, Marcia
(NASA Langley Research Center Hampton, VA United States)
Babel, Henry
(Boeing Co. Huntington Beach, CA United States)
Farahmand, Bahram
(Boeing Co. Huntington Beach, CA United States)
Schwab, David
(Boeing Co. Huntington Beach, CA United States)
Munafo, Paul M.
Date Acquired
August 21, 2013
Publication Date
January 1, 2002
Subject Category
Metals And Metallic Materials
Meeting Information
Meeting: AMPET
Location: Huntsville, AL
Country: United States
Start Date: September 16, 2002
End Date: September 18, 2002
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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