Local fatigue crack propagation behavior of a two-pass friction stir welded aluminum alloy

Abstract

Fatigue behavior of a two-pass, double-sided, friction stir welded joint was studied to get a basic understanding on the local fatigue crack propagation (FCP) behaviors of the different zones within the weld. The fatigue crack propagation tests were carried out on center notched specimens with initial notch positions in the different weld regions and longitudinal to the weld direction. The experimental results demonstrated that the microstructure, as dictated by the thermomechanical history, may play an important role in the fatigue crack propagation within the two-pass friction stir welded joint. The FCP rates were found to be higher in the weld affected zones than in the base metal. Within the weld zones, the heat affected zone and the fine-grained double stirred zone (DSZ) had the highest propagation rates. The effect of the second pass was found to be minimal on the fatigue behavior of the areas outside the stirred zones; however, in the DSZ where the two weld passes overlap, the FCP rates were higher than in the single stirred zones. Furthermore, within the heat affected zones the FCP rates were higher on the retreating side than on the advancing sides of both welds indicating sensitive of the FCP to the tool rotation direction.