Analysis on Fatigue Crack Propagation and Fractography of A7075 Aluminum Alloy

The fatigue fractography and surface of A7075 aluminum alloy was investigated by means of optical microscope, scanning electron microscope and technology of metallurgic replica. The results show that the fatigue crack generally initiated in the surface or near the surface of the sample area, such as hole and inclusion. The crack propagation regions under high stress amplitude was characterized by furrow and hollow, and obviously presented fine ripple vein. While lots of fatigue striations and sidesteps with the holes and secondary cracks generated in the crack propagation regions of low stress amplitude. Fatigue transient breaking area is a mixed fracture of brittle and ductile fracture. In the fatigue crack propagation stage, with the increasing of cycle times, secondary cracks gradually merged into primary crack on the path of crack propagation. The dislocation of crack tip,grain boundaries and different grain orientations have great influence on the path of crack growth, which can make cracks bending.