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Published in:
01-12-2009 | Case History---Peer-Reviewed
Cracking of Al–Zn–Mg Aluminum Alloy Nozzle Weld of Propellant Storage Tank: A Metallurgical Investigation
Published in: Journal of Failure Analysis and Prevention | Issue 6/2009
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Abstract
Afnor 7020 (Al–4.5Zn–1.5Mg) is an aluminum alloy used in the fabrication of propellant tanks for satellite launch vehicles. The cylindrical portion of the tank (6 m length and 2.1 m diameter) is fabricated by TIG welding of 4.5 mm-thick sheets, while end domes at both the ends are fabricated by welding petals. Shrink fit nozzles; machined from forgings in T652 condition, provide nozzle openings for liquid conduit. One such tank developed crack at nozzle weld region during storage, 5 years after construction. The in-depth metallurgical analysis revealed that the crack developed due to stress corrosion cracking which was promoted by the formation of a liquated region during the welding operations.