Effects of microstructures obtained by two kinds of thermomechanical treatment, i) solution treatment-cold rolling (67%)-aging and ii) solution treatment-aging-cold rolling (67%), on the fatigue behavior of an Al-1.8wt%Li alloy were investigated by means of optical and transmission electron microscopy. The results obtained are summarized as follows:
Deformation bands perpendicular to the rolling direction were formed inhomogeniously in the cold-rolled specimens, and the dislocation cell structure and microbands were the characteristic features. Fatigue strength in both the thermomechanically-treated specimens was higher than those in the solution-treated specimens, in the solution-treated and cold-rolled specimens and in the aged specimens. The higher fatigue strength is due to the dislocation cell structure with δ'-Al3Li precipitates, because the cell structure alleviates the concentration of dislocation on a slip plane during fatigue test.
Fatigue strength in the specimens with the deformation bands parallel to the axis of fatigue stress was higher than that in the specimens with deformation bands perpendicular to the axis of fatigue stress. The deformation bands perpendicular to the axis of fatigue stress became preferential nucleation sites and propagation path of fatigue cracks. The thermomechanical treatment, i) brought out higher fatigue strength than the treatment, ii).
