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Specimens of 1100, 5454, and 6061 aluminum alloys were examined after failure in creep rupture tests of up to 20 000 h duration. No microstructural changes occurred in 1100-O and 5454-O alloys during testing other than slight grain growth at the highest test temperatures. Such growth had only a small effect on creep-rupture properties. Cold-worked alloys 1100-H14 and 5454-H34 were unstable during creep, passing through stages of recovery, recrystallization, and grain growth. These changes invalidate extrapolation of short-time data. The precipitation-hardened 6061 alloy underwent drastic changes in microstructure during testing, from thin needle-shaped precipitates to larger β′ rods to coarse β-Mg2Si plates. These changes produced several different slopes in the log stress-log rupture time plots and long-time rupture stresses considerably below those predicted by extrapolation.
Rockwell International, Los Angeles, Calif.
Federal Mogul Corp., Ann Arbor, Mich.
Air Force Weapons Laboratory, Kirtland Air Force Base, Albuquerque, N. Mex.
University of Michigan, Ann Arbor, Mich.
Stock #: JTE11633J