Anisotropy in fatigue crack propagation behavior of Al-Cu-Li alloy thick plate

Anisotropy in fatigue crack propagation (FCP) behavior of Al-Cu-Li-T87 alloy thick plate is investigated by means of optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron back scattering diffraction (EBSD) in the present work. Results show that FCP rates of the three orientations show distinct difference. Grain size and boundary, coarse inclusion particles, precipitates and grain orientations are capable of affecting the fatigue performance, but coarse inclusion particles and T1 precipitates are found to be the main factors in determining the fatigue performance. Grain boundaries of pan-caked grain structure fail to impede the fatigue crack growth effectively because of the coarse inclusion particles and precipitates along grain boundaries. Fatigue cracks easily propagate along the grain boundaries, therefore result in a low FCP resistance. In addition, Brass grains can induce crack deflection due to the relative large twist angle of grain boundaries between Brass grain and neighboring grain when considerable T1 precipitates are observed in Al-Cu-Li alloy.