Fatigue Property of Al-5Zn-2Mg Aluminum Alloy Welding Joints Used in High-speed Trains

The fatigue property of Al-5Zn-2Mg aluminum alloy Metal-Inert Gas (MIG) welding joints used in high-speed trains was studied by a fatigue machine. Scanning electron microscopy (SEM) was used to observe the fatigue fracture and the surface damage. The results show that uniaxial ratcheting behavior occurs in the welding zone (WZ) when the stress is higher than 0.5ωb; there are obvious plastic deformations in the WZ and a lot of slip bands on the surface, which reduce the fatigue life of the sample. The uniaxial ratcheting behavior mainly appears in the first cycle and the final failure stage of the fatigue process. When the stress is lower than 0.5ωb, the fatigue samples crack in the heat affected zone (HAZ). The fatigue fracture of the WZ and the fusion zone (FZ) is typical ductile fracture pattern while that of the HAZ and the base metal (BM) is quasi-cleavage fracture. The fatigue life of the BM is much longer than that of the HAZ