Study of the Fatigue Property for 6082 - T6/7075 - T6 Dissimilar Aluminum Alloys Joints by Friction Stir Welding

Abstract

With the purpose of improving the service reliability of dissimilar high strength aluminum alloy welded joints under complex alternating loads, the influencing factors of fatigue property and fatigue fracture for 6082 - T6 / 7075 - T6 dissimilar aluminum alloy joints by friction stir welding with thickness of 6 mm were studied by fatigue limit measurement, fatigue fracture morphology analysis, metallographic analysis and microhardness testing etc. Result showed that the fatigue limit of welded joint was 107.5 MPa under the conditions of 1 200 r/min and 80 mm/min. In 110 MPa fatigue loading, fatigue cracks originated from the vicinity of the sharp corners edge at the junction of weld nugget zone of forward side (6082 - T6) and thermo - mechanical affected zone (TMAZ). These resulted from the combination effects of the welding thermal cycle caused the β″ phase to transform into β′ phase and coarsened to form a softened zone, a brittle second phase on the surface of the sample, the stress concentration caused by the uneven mixing of the two materials at the junction of the weld nugget zone and the thermo - mechanical affected zone, as well as the stress concentration caused by the sharp corners of the sample edge.