Influence of mean stress and overaging on fatigue life of aluminum alloy EN AW-2618A

Fatigue tests were performed on the forged aluminum alloy EN AW-2618A in the T61 state. Different stress ratios (R =-1, R = 0.1) were selected to study the influence of mean stress on fatigue life. Two overaged states (10 h/ 230 degrees C, 1000 h/230 degrees C) were also tested to investigate the influence of overaging on fatigue life. Transmission electron microscopy (TEM) was used to characterize the precipitates (S-phase), which are mainly responsible for the strength of the alloy. A fractographic analysis was also performed to determine the failure mode. Overaging reduces the fatigue life compared to the T61 state. The longer the aging time, the lower the fatigue resistance. The reason is the decrease in (yield) strength, which correlates with the radius of the S-phase: the precipitate radius increases by a factor of approximately two for the overaged states compared to the initial state. The analysis of the fracture surfaces showed crack initiation occurs predominantly on the outer surface and is associated with the primary phases.

Automated summary

The fatigue properties of forged aluminum alloy were studied under different stress ratios and aging states. The results showed that overaging significantly reduced the fatigue life of the alloy, which was mainly attributed to the decrease in yield strength and the increase in precipitate radius.