An investigation of the cyclic fatigue and fracture behavior of aluminum alloy 7055

In this research paper, the cyclic stress- and strain-amplitude-control fatigue response of aluminum alloy 7055 is presented and discussed. Specimens of the alloy in the T7751 temper were cyclically deformed over a range of stress amplitudes at both ambient and elevated temperatures. An increase in test temperature was found to have a detrimental influence on cyclic fatigue life of the transverse-oriented specimens and little influence on the longitudinally oriented counterparts. Under total strain-amplitude control, the alloy showed evidence of softening to failure at the two test temperatures. The degree of cyclic softening increased with increasing temperature. For both stress- and strain-amplitude control fatigue, the macroscopic fracture mode was essentially identical, regardless of the orientation of the test specimen with respect to the wrought rolled plate. Cyclic fatigue fracture on a microscopic scale revealed features reminiscent of locally ductile and brittle mechanisms. The plausible mechanisms governing damage and failure of the alloy are discussed in terms of the competing influences of intrinsic microstructural effects, matrix deformation characteristics arising from a combination of mechanical and microstructural interactions, the magnitude of cyclic stress and cyclic strain amplitudes and the test temperature.