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.

在本研究中，研究了搅拌摩擦焊铝 2024 合金在不同平均应力下的高周疲劳行为。焊接区显微组织的复杂性和拉伸残余应力对焊接接头的疲劳行为有显着影响。由于拉伸残余应力导致平均应力的明显增加，降低了焊接接头的疲劳寿命。R 比从 -1 增加到 0.1 导致疲劳寿命和耐力极限显着降低，而当进一步增加到 0.5 时，它是微不足道的，因此表明有害平均应力效应可能饱和。观察到裂纹成核位置随着施加载荷幅度的变化而变化。焊接接头热处理后，焊缝截面重新出现硬化析出物，阻碍位错运动，稳定晶界，从而提高疲劳寿命。所有这些观察都归因于平均应力、残余应力和微观结构障碍的综合影响，并进行了讨论。