Abstract
This work was undertaken in an attempt to ascertain the generic characteristics of fatigue behavior of friction-stir welded aluminum alloys. To this end, different alloy grades belonging to both the heat-treatable and non-heat-treatable types in both the cast and wrought conditions were studied. The analysis was based on the premise that the fatigue endurance of sound welds (in which internal flaws and surface quality are not the major issues) is governed by residual stress and microstructure. Considering the relatively low magnitude of the residual stresses but drastic grain refinement attributable to friction-stir welding, the fatigue performance at relatively low cyclic stress was deduced to be dictated by the microstructural factor. Accordingly, the fatigue crack typically nucleated in relatively coarse-grained base material zone; thus, the fatigue strength of the welded joints was comparable to that of the parent metal. At relatively high fatigue stress, the summary (i.e., the cyclic-plus residual-) stress may exceed the material yield strength; thus, the fatigue cracking should result from the preceding macro-scale plastic deformation. Accordingly, the fatigue failure should occur in the softest microstructural region; thus; the fatigue strength of the welded joint may be inferior to that of the original material.
Highlights
Due to the high stress concentrations and intrinsic defects, welded structures usually exhibit poor fatigue performance
Despite a vast volume of experimental data on fatigue behavior of friction-stir welded (FSWed) aluminum alloys existing in the literature, the generic characteristics of this phenomenon are still unclear
Defects, and (iii) the were obtained in various alloythe grades and initial (ii) the fatigue specimens were data analysis was based on the the presumption of the dominant rolethe of “kissing the friction-stir welding (FSW)-induced residual stress carefully machined to remove characteristic tool marks and bond” defects, and (iii) and microstructure in fatigue cracking
Summary
Due to the high stress concentrations and intrinsic defects, welded structures usually exhibit poor fatigue performance This is the case for aluminum welds, whose exceptionally low characteristics are widely known and even necessitate using a riveting approach for manufacturing of joint assemblies. Given significant potential of FSW for transportation industry, considerable research effects have been undertaken to explore fatigue behavior of aluminum friction-stir joints [3,4,5,6,7,8,9,10,11,12,13,14,15,16] As expected, their fatigue properties are typically found to be superior to that of comparable fusion welds [3,4]
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