Cyclic behaviour of model Al–Li alloys: effect of the precipitate state

The effect of the precipitate state on the cyclic behaviour of model Al–Li alloys was investigated. The study has shown that the precipitate state has a significant effect on the low-cycle fatigue behaviour of the Al–Li alloys — on both the stress–response curve and dislocation structures. Al–Li alloys containing δ′ precipitates alone appear to undergo cyclic hardening, whereas an alloy with both δ′ and T1 precipitates shows a saturation state. ission electron microscopy on deformed samples shows that plastic deformation in Al–Li alloys is inhomogeneous. Microbands are present in the alloys that contain δ′ precipitates alone. An increase of the δ′ precipitate size leads to more pronounced strain localization. This has a detrimental effect on the fatigue life. The presence of T1 precipitates causes the plastic deformation to be more homogenous and improves the fatigue properties of the material. In this case, transmission electron microscopy examination reveals numerous dislocation loops formed during the fatigue test.