Research on the High-cycle Fatigue and Crack Initiation Behavior of AA7449 Alloy

This study mainly focused on the high-cycle fatigue and crack initiation behavior of AA7449-T7951 alloy. The fatigue-life tests were carried out over a range of stress amplitudes with the stress ratio (R) of 0.5 and -1.0 at room temperature for both smooth and notch specimens,. Further evaluations were performed with the help of optical microscopy, scanning electron microscopy and transmission electron microscopy, in order to reveal the relationships between microstructure and fatigue crack initiation behavior of this alloy. The results showed that AA7449-T791 alloy had excellent fatigue properties. The fatigue limit (sigma(N)) of smooth specimens was 349 MPa for R=0.5 and 134 MPa for R= -1.0. while it was 138 MPa for R=0.5 and 70 MPa for R=-1.0 in notched specimens with the notch factor (Kt) of 3.0. The crack initiation behavior of this alloy can be related to the joint influence of inclusions, precipitates, grain structure and their interactions with dislocations or persistent slip bands.