Abstract:The fracture mechanisms of Al-Cu-Li-Zr-Ce alloys aged for different time were studied by means of semi-quantity method. The effects of aging time and stress state of the crack tip on the fracture mechanisms were discussed. The results show that in the initial cracking area, with longer aging time the delamination percentage increases, the dimple percentage decreases, and even quasi-cleavage character appears. In the stable crack growth area, the delamination is the main fracture mechanism. However, in the near unstable crack growth area, the delamination percentage decreases and the quasi-cleavage become the main fracture mechanism gradually. The delamination thickness decreases with aging time prolonging and crack growing. The formation and propagation of the delamination cracks are significantly dependent on the main crack growth and the aging time of alloys. The higher delamination percentage leads to higher values both of toughness and strength.