The fatigue behavior and dislocation sub-structures of 6063 aluminium alloy were studied under several non-proportional path loadings: circle, ellipse, rectangle and square. After fatigue testing, the microstructure - especially the dislocation sub-structures of the failure materials - was carefully observed using transmission electron microscopy. Under the same 93MPa equivalent stress amplitude loading, the alloy had the shortest life and the most severe cyclic additional hardening with circle-path loading among all the loading paths. This contributed to the complicated dislocation sub-structures and severe stress concentration of the alloy during the cycling process. While under the ellipse-path loading, the alloy had a comparably long life and slight cyclic additional hardening. The deformation of the alloy and the morphology of the dislocation sub-structures determined the fatigue behavior of 6063 alloy under the same equivalent stress amplitude loading. Under the circle-path loading, the fatigue life decreased while the cyclic strain increased as the loading stress amplitude increased from 47 to 163MPa. The dislocation evolution of the alloy during cycling under circle-path loading was examined using transmission electron microscopy. It was found that the dislocation merged with each other and changed from single lines to crossed bands. The mobility of dislocations was reduced and the degree of stress concentration rose during the cycling process.

Fatigue Behavior and Dislocation Substructures for 6063 Aluminum Alloy under Nonproportional Loadings. X.Liu, G.He, X.Ding, D.Mo, W.Zhang: International Journal of Fatigue, 2009, 31[7], 1190-5