Fatigue Property and Microstructure of FSW Joint of 7A09-T6 Aluminum Alloy

The 7A09-T6 aluminum alloy was welded by the FSW. The fatigue property of joints prepared by different processes was tested by high frequency fatigue testing machine and the S-N curves were obtained. In addition, the fatigue fracture of welding joints were studied by OM and SEM. The results show that fatigue life was shorter with the increase of the stress amplitude, and the fatigue life of welded joints was the longest when welding speed was 37.5 mm·min-1. The fracture of the joints was located in the juncture of the heat affected zone and the nugget, the obvious plastic deformation was not found in this area. Moreover, the joints fatigue fracture existed at the bottom of the welding sample and the fatigue striations were found in expansion area, the instantaneous break area showed a dimple morphology. All of the above were the typical tear characteristics of static load.