Combined effect of residual and mean stresses on fatigue behavior of welded aluminum 2024 alloy

In this study, high cycle fatigue behavior of friction stir welded aluminum 2024 alloy was investigated at different mean stresses. Complexity in the microstructure and tensile residual stress in the weld zone had a significant impact on the fatigue behavior of the welded joints. Apparent increase in mean stresses due to tensile residual stresses, decreased the fatigue lives of the welded joints. Increase in R-ratio from-1 to 0.1 resulted in significant depreciation of fatigue lives and endurance limit, while it was marginal when increased further to 0.5, thus suggesting the probable saturation of the detrimental mean stress effect. A shift in crack nucleation sites with a change in applied load amplitudes was observed. Hardening precipitates re-appeared across the weld section after heat-treatment of the welded joints thus hindering the movement of dislocations and stabilizes the grain boundary, thereby resulting in improvement of the fatigue lives. All these observations were attributed to the combined effect of mean stresses, residual stresses and the microstructural barriers, and are discussed.

Automated summary

The study found that the complexity in microstructure and tensile residual stress in the weld zone significantly influenced the fatigue behavior of the welded joints. Increase in tensile residual stresses led to an apparent increase in mean stresses, reducing fatigue lives. Re-appearance of hardening precipitates after heat-treatment improved fatigue lives in the welded joints.