Study on tensile and fatigue failure in the low-hardness zone of AA2519-T62 FSW joint

Abstract

The aim of this research was to investigate the basic performance and failure of AA2519-T62 friction stir welded joint in tensile test and in low cycle fatigue regime. It has been reported that at the retreating side, the layer of overgrowth grains undergoes deformation in the TMAZ and forms a characteristic large-grain band partly surrounding the SZ. The reported UTS is very high and it equals 405 MPa, what corresponds to 86.5% joint efficiency value. The failure occurred in the LHZ at the retreating side with the fracture mechanism characterized by simultaneously cracking in several parallel planes. The LCF behavior of the tested joint indicates three stages of fatigue life: a relatively long period of cyclic hardening (up to 500–1000 cycles), the longest period of cyclic stabilization, followed by cyclic softening until failure. The fatigue crack initiation takes place in the near-surface layer of overgrown grains and then propagates through the low-hardness zone.