Fatigue behavior of friction stir spot welding and riveted joints in an Al alloy

摘要

The main aim of this study was to compare the fatigue resistance of welded joints produced by FSSW process and riveted joints of AA2024 alloy. The specimens welded with the best preliminary parameters determined by previous tensile shear tests were tested in fatigue under load control, R=0.1, at room temperature. Two welding parameter sets were used, and P-N curves (load versus cycles) were plotted, using 2x10~6 cycles as the fatigue life limit. A similar curve was obtained for riveted specimens. The FSSW welding procedures were carried out in a CNC milling machining and the riveted specimens were produced in accordance with aircraft industry parameters. Although the welded specimens presented almost the same results in the tensile shear tests, the results were fairly lower than those observed for riveted joints in fatigue. The main failure mode observed in the welded joints was shearing, besides some cases of crack propagation in the perpendicular load direction, while for riveted specimens occurred mainly fretting nucleation followed by crack propagation in the perpendicular load direction. The evidences of shearing and lower fatigue lives for welded specimens indicate that the joint geometry highly affects the joint properties, due probably to stress concentrators presented locally.