Cracking of AFNOR 7020 Aluminum Alloy Weld Joint of Water Tank for Satellite Launch Vehicle: A Metallurgical Investigation
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Aluminum alloys are frequently used as the preferred material for aerospace applications owing to their high-specific strength and ease of fabrication. In one such application, a torroidal-shaped water tank made of AFNOR 7020 (Al–4.5Zn–1.5Mg) alloy sheet and rings, stores water to provide for the initial run of a turbo pump and for the cooling of engine components. During the stage leak test, one of the water tanks leaked near the interconnecting ring welded to the shell. Detailed metallurgical investigations found that leakage was due to stress-assisted cracking, which was caused due to locked-in stresses introduced in the material during welding and to an inferior microstructure of the ring parent material. This article brings out the details of the investigations and recommends actions to avoid future failures.
KeywordsAFNOR 7020 aluminum alloy Liquated film Stress-assisted cracking
The authors are indebted to Shri P.S. Veeraraghavan, Director, VSSC for permission to publish this work.
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