Evaluation of 7XXX-series aluminum alloys for the W87 aft support ring
The study showed that the tensile properties of both 7075-T6 and 7050-T73651 decreased significantly after holding the alloys for any length of time at temperatures greater than 500/sup 0/F. After a 2-min hold at 575/sup 0/F, the yield strengths of 7075-T6 and 7050-T73651 were 217 MPa (31.5 ksi) and 245 MPa (35.6 ksi), respectively. There did not appear to be a significant difference in the mechanical properties between 7075-T6 and 7050-T6. Time at temperature appeared to be a critical parameter. Cycling the microstructure to 575/sup 0/F or above with no hold at temperature caused considerably less degradation in mechanical properties than a 2-min hold at temperature in all cases. Above 650/sup 0/F, both the ultimate tensile strength and the yield strength of the alloys reached a minimum of around 310 MPa (45 ksi) and 138 MPa (20 ksi), respectively. Evidence of a continuous grain boundary film of eta phase precipitates was found in the 7075-T6 alloy after a typical 575/sup 0/F thermal cycle. The presence of this grain boundary precipitate indicated a potential sensitivity of this alloy to stress corrosion cracking. Although the general environment for the aft support ring is controlled, the ring is expected to be under tension after assembly and exposure to small amounts of water vapor will probably occur. The conditions of stress, moisture, and susceptible microstructure increase the likelihood of stress corrosion cracking.
- Research Organization:
- Lawrence Livermore National Lab., CA (USA)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 5771768
- Report Number(s):
- UCID-20329; ON: DE85009987
- Country of Publication:
- United States
- Language:
- English
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