Abstract
The fatigue behavior of the Al-4%Cu alloy having various aged structures was studied at room temperature. Different aged structures result in different shapes of S-N curves: the alloy containing G. P. zones (or θ") is superior in the fatigue strength in the region of lower fatigue life to that containing θ'. This relation tends to be inverse in the region of higher fatigue life. This is attributed to the difference in the mode of crack initiation and propagation between those alloys. A cyclic softening in stress response curves is found only in the alloy containing G. P. zones (or θ"). Hardening in Hv-N curves is accompanied in this case. Neither re-solution nor overaging is found in deformation bands formed in the alloys.
