Abstract: Fracture processes of 6061 aluminum alloy specimens under different stress states are investigated with in-situ tensile experiments. The results indicate that a lot of slip bands are produced in all specimens’ surfaces under different stress states, but the fracture mechanism is different. With stress triaxiality decreasing, the fracture modes vary from dimple-coalescence mixing shear fracture to pure shear fracture and the fracture surfaces also vary from dimple fracture mode to shear fracture mode. The grain boundaries of 6061 aluminum alloy are the weakest area and microcracks initiate at the grain boundaries. With loading increasing, the microcracks extend and coalesce. The specimens fracture due to coalescence or shearing between the microcracks. The less the stress triaxiality is, the more obvious the orientation of the dimple on the two surfaces of fracture surface tends to be, and the smoother the fracture surfaces will be.

Key words: 6061 aluminum alloy, Fracture mechanism, In-situ SEM tensile