Fatigue Behavior of a Dissimilar Aluminum Alloy Welding Joint With and Without Natural Defect

In order to investigate the influence of natural defect on the fatigue behavior of 5A06/7A05 dissimilar aluminum alloys welding joint, fatigue tests of two types of specimens with and without defects were carried out systematically under stress amplitude control conditions (stress ratio R=0.1) at normal temperature in laboratory air condition. Furthermore, a new parameter, i e, fatigue defect effect factor (FDEF) was introduced to assess the effect of defect on fatigue strength. The fatigue failure analysis was conducted as well to compare the fatigue and fracture behavior of the two types of specimens. The results show that: (1) natural defects have a strong effect on the fatigue lives of welding joint, and the differences between the specimens with and without defects can reach 80 times under a same theoretical net sectional stress; (2) the FDEF parameter introduced is effective to deal with the defect effect, and the FDEF decreases along with the increase of fatigue life. The mean relative error between the experimental data and predicted fatigue strength based on the FDEF is 10.2%; (3) the macro fracture of both types of specimens have three typical zones, i e, fatigue source zone, crack propagation zone and final fracture zone, while there are more than one fatigue sources for specimens with natural defects. The overall pattern of crack propagation zone and fracture zone are quite similar, but the morphologies are different in details.