UNUSUAL FATIGUE BEHAVIOR OF DISSIMILAR AL/TI FRICTION-STIR LAP WELDS

Abstract

This work was undertaken in order to evaluate the fatigue performance of dissimilar AA6013/Ti-6Al-4V friction-stir lap welds. It was shown that the avoidance of direct contact between thewelding tool and titanium part results in a narrow (~0.5 μm) intermetallic layer at a dissimilarinterface. Consequently, the fatigue failure of dissimilar welds occurred solely within the aluminiumpart. In other words, the intermetallic layer was not a critical issue in the fatigue behaviour of thewelded joints. It was also found that the fatigue endurance of dissimilar welds was approximately anorder of magnitude lower than that of a monolithic aluminium alloy. This effect was attributed to aspecific geometry of the lap-welded joints. Specifically, the end section of the welded joint virtuallyserved as a precursor of a fatigue crack. Thus, the fatigue behaviour of the welded joints was solelygoverned by a crack propagation.