Influence of microstructure on fatigue crack propagation behaviors of an aluminum alloy: Role of sheet thickness

Fatigue crack propagation behaviors of Al-Cu-Mg alloy sheets with the thickness of 30 mm and 55 mm were investigated by means of optical microscope, scanning electron microscope, transmission electron microscope and electron back scatter diffraction (EBSD) analysis technique. The results show that, the crack propagation rate of 30 mm sheet appears more sensitive to the variation of stress intensity factor dispersion at the crack tip in the stable crack propagation stage, and the crack propagation rate is slower. The precipitation strengthening phase, coarse particles, grain boundaries, sub structure, grain micro orientation and other microstructure have a very significant influence on fatigue crack propagation behaviors. The precipitation strengthening phase, grain boundaries and sub structure have a positive significance to delay the fatigue crack propagation rate. The coarse particles will locally accelerate the fatigue crack propagation and grain micro orientation affects the path selection of fatigue crack propagation in grains and grain boundaries.