Mechanisms governing cyclic deformation and failure during elevated temperature fatigue of aluminum alloy 7055

Abstract

The cyclic stress response, deformation and damage characteristics of aluminum alloy 7055 was studied at ambient and elevated temperatures. Specimens of the alloy were cyclically deformed using tension-compression loading under total strain-amplitude control. The alloy showed evidence of softening to failure at the ambient and elevated test temperatures. The degree of cyclic softening increased with an increase in test temperature. The presence of deformable matrix strengthening precipitates and particles in the T7751 microstructure resulted in a local decrease in resistance to the motion of “mobile” dislocations, causing a progressive loss of strengthening contributions to hardening. At the elevated temperatures, the occurrence of localized oxidation and embrittlement at the grain boundaries are promoted by the applied cyclic stress and play an important role in accelerating crack initiation and exacerbating stable crack propagation. The damage response of the alloy is discussed in terms of competing influences of intrinsic microstructural effects, matrix deformation characteristics arising from a combination of mechanical and microstructural interactions, cyclic plastic strain amplitude and concomitant response stress, and test temperature.