Cracking of Al–Zn–Mg Aluminum Alloy Nozzle Weld of Propellant Storage Tank: A Metallurgical Investigation
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.
KeywordsFailure analysis of propellant tank Al–Zn–Mg aluminum alloy Liquated film in aluminum alloy Stress corrosion cracking
The authors are indebted to Dr. K. Radakrishnanan, Director, VSSC for permission to publish this work.
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