X-ray tomography of failure behaviors of arc welded AA2219 joints under tensile and cyclic loading

Abstract

As one of the main structural materials widely used for the new generation of launch vehicles, the tensile properties and microstructural characterization of tungsten inert gas (TIG) welded 2219 aluminium alloy has been studied extensively. However, there are significant differences between fatigue fracture and tensile fracture modes. In this paper, the tensile and fatigue damage behaviors of arc-welded AA2219 joints were investigated in depth. Combined with the microstructure observation and fracture analysis done by using X-ray computed tomography, the main factors that affect the fatigue damage behavior are discussed. The results show that there are a large number of porosity defects in the weld zone, showing an aggregation distribution at the weld toe and weld pool line. The fine-grain zone around the fusion line is the softening zone of the welded joint. For tensile conditions, the cracks were initiated at the softening zone and extended along the fusion line to the final fracture. Under fatigue loading conditions, the weld reinforcement leads to the stress concentration at the weld toe, and at the same time, a lot of pore defects at the weld toe, which causes crack initiation at the pores in the weld toe. Due to the small plastic zone at the fatigue crack tip, the crack propagates almost perpendicular to the loading direction in the heat-affected zone, driven by a mode I crack. A large number of gas pores in the weld zone have no substantial effect on fatigue crack propagation.