1991 Volume 40 Issue 451 Pages 444-450
Tensile properties and fatigue behaviour under rotating bending were investigated on both underaged and overaged specimens of two aluminum-lithium alloys, 2090 and 8090. The results were compared with those of the peakaged specimens of the same materials and conventional aluminum alloys, 2024 and 7075, obtained in a previous report.
The metastable δ'-phase precipitated and grew during aging, and the diameters of the particles were approximately 10nm, 20nm and 30nm for the underaged, peakaged and overaged conditions, respectively. The elongation of the underaged and overaged specimens slightly increased compared with that of the peakaged specimens, while the proof stress and tensile strength decreased. The fatigue strength was decreased by the underaging and overaging process. This was due to the decrease in both crack initiation and growth resistances. The crack initiation and growth were discussed based on the observation of precipitation of δ'-phase during aging.
