Effects of aging temperature on microstructure and high cycle fatigue performance of 7075 aluminum alloy

The hardness, the tensile and the high-cycle fatigue (HCF) performances of 7075 aluminum alloy were investigated under temper T651, solution treated at 380 °C for 0.5 h and aged at different temperatures (150, 170, 190 °C) for 10 hours. The optimal microstructures and the fatigue fracture surfaces were observed. The results show that the hardness and the tensile performances are at their optimum at T651, but the fatigue life is the shortest. The hardness and the elongation are the lowest after solution treatment. With the aging temperature increasing (150-190 °C), the HCF is improved. The crack is initiated from the impurity particles on the subsurface. Treated at 170 °C,the area of the quasi-cleavage plane and the width of parallel serrated sections of the crack propagation are the largest. With increasing aging temperature, the dimple size of finally fracture surfaces becomes larger and the depth deeper.