Abstract:In this paper, series experiments were carried under different fatigue load spectrum for different solution annealing treated GH4720Li alloy. The results show that when the solution temperature is between 1080 °C and 1120 °C, the volume fraction of primary γ′ phase in the alloy is high, and the size of the near spherical tertiary γ′ phase gradually grows, and the grain structure is fine and uniform. The dislocation slip mainly cuts and bypasses the spherical γ′ phase and leaves a small slip band, indicating that the γ′ precipitates can effectively hinder the expansion of the slip band, the alloy has good fatigue performance. When the solution temperature is rise to 1140 °C, the primary γ′ phase dissolves unevenly, inducing the obvious mixed grain size distribution, and the morphology of tertiary γ′ phase gradually transforms into square shape. The size of parallel slip bands increases obviously, and the internal deformation of the material has occurred to a large extent, and the fatigue resistance of the material decreases. When the solution treated temperature is over the γ′ phase transformation point, such as at 1180 °C, the γ′ phase completely dissolves, and resulting in the coarse grain structure.The slip bands cross each other and pass through the grain boundary, which seriously reduces the fatigue resistance of the alloy.