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Environmentally Assisted Cracking Properties of AA7249 Extrusions for Aerospace Applications

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Trident Scholar Project rept. no. 304

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The Development of new military aerospace platforms is costly and time-consuming. Therefore, it is important that current platforms maximize their service lifetime. Exposure to environmental elements, particularly seawater, is especially troublesome to the Navy because it shortens required aircraft lifetime. The P-3C is an example of a versatile aircraft whose lifetime has been extended to the point that environmental attacks is now becoming a significant concern. Structural components in the P-3C are currently composed of aluminum alloy AA7075-T6, which has high strength but limited corrosion resistance. In particular, AA7075-T6 is susceptible to environmentally assisted cracking EAC, which can cause catastrophic fracture of a stressed part. In 1999, Lockheed Martin Aeronautical Systems was granted funding to complete the Service Life Assessment Program SLAP for the P-3. One objective of this program was to identify a possible replacement for corrosion-prone AA7075-T6 extruded components that would help reach the goal service life of 2015. AA7249 is currently under development as a possible replacement material. The objective of this Trident project is to extend the ongoing evaluation of AA7249 extrusions to include corrosion testing, mechanical testing, and evaluations of the effects of processing on wide panel extrusions. The results of this study will contribute to the ongoing evaluation of these alloys for replacement of AA7075-T6 in aerospace structures and contribute to a better basic understanding of the structureproperty relationship obtained for these component parts as well as the effect of processing on EAC behavior and material performance.

Subject Categories:

  • Patrol and Reconnaissance Aircraft
  • Manufacturing and Industrial Engineering and Control of Production Systems
  • Mechanics

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