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 alloy s - on both the stress-response curve and dislocation structures. Al-Li all oys containing delta' precipitates alone appear to undergo cyclic hardening , whereas an alloy with both delta' and T-1 precipitates shows a saturation state. Transmission electron microscopy on deformed samples shows that pla stic deformation in Al-Li alloys is inhomogeneous. Microbands are present i n the alloys that contain delta' precipitates alone. An increase of the del ta' precipitate size leads to more pronounced strain localization. This has a detrimental effect on the fatigue life. The presence of T-1 precipitates causes the plastic deformation to be more homogenous and improves the fati gue properties of the material. In this case, transmission electron microsc opy examination reveals numerous dislocation loops formed during the fatigu e test. (C) 2000 Elsevier Science Inc. All rights reserved.