Fatigue lifetime and tearing resistance of AA2198 Al–Cu–Li alloy friction stir welds: Effect of defects

•The fatigue lives of sound and flaw bearing FSW of a Al–Cu–Li alloyare investigated.•The fatigue crack initiation mechanisms are identified with respect to the defects.•The crack behavior is interpreted in terms of fracture mechanics.•For GAP welds intergranular cracking is identified as initiation...

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Bibliographic Details
Published in:International journal of fatigue 2015-01, Vol.70, p.463-472
Main Authors: Le Jolu, T., Morgeneyer, T.F., Denquin, A., Gourgues-Lorenzon, A.F.
Format: Article
Language:English
Subjects:
2198 Al–Cu–Li alloy
ALUMINUM ALLOYS (50 TO 99 AL)
Aluminum base alloys
Bearing
COPPER ALUMINUM ALLOYS
DEFECTS
Fatigue
Fatigue (materials)
Fatigue strength
Fracture mechanics
Friction stir welding
FRICTION WELDING
JOINTS
Reduction
Sound
S–N curves
Welded joints
WELDING
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Summary:•The fatigue lives of sound and flaw bearing FSW of a Al–Cu–Li alloyare investigated.•The fatigue crack initiation mechanisms are identified with respect to the defects.•The crack behavior is interpreted in terms of fracture mechanics.•For GAP welds intergranular cracking is identified as initiation mechanism.•Tearing resistance for different welds is assessed affecting cycles to final failure. The fatigue strength and failure mechanisms of defect-free (“sound”) and flaw bearing friction stir butt-welds of 3.1mm-thick AA2198-T8 Al–Li–Cu alloy have been investigated via S–N curves at R=0.1 using cross weld specimens. The fatigue strength of sound welds is only reduced by 10–15% at the aimed lifetime of 105 cycles compared to the base material. Joint Line Remnant (JLR) bearing welds have a similar fatigue strength as sound welds and the JLR is not the crack initiation site. Kissing Bond (KB) bearing welds that have undergone a weld root polishing show a reduction in fatigue strength by 17% compared to sound welds. For specimens loaded at or above yield strength of the weld nugget the crack systematically initiates from the KB during the first cycle, which is interpreted further using fracture mechanics. The strongest reduction, about 28% in fatigue strength, is found for welds with an initial gap between the parent sheets (GAP welds) along with initiation at intergranular surface microcracks. Kahn tear tests show a reduction in tearing resistance for the flaw bearing welds with a similar ranking as for the fatigue strength.
ISSN:0142-1123
1879-3452
DOI:10.1016/j.ijfatigue.2014.07.001