Investigating the influence of stress ratio variation on the crack growth rate in friction stir welded dissimilar aluminum alloys

•Investigation of crack growth in dissimilar aluminum alloys (AA7075, AA2024) under optimized FSW parameters.•Comprehensive analysis of mechanical properties across weld zones and base metals.•Established a direct correlation between stress ratios and fatigue life in FSW joints.•Revealed the influence of stress ratio variation on structural integrity in dissimilar aluminum alloy joints. This research focuses on the friction stir welding (FSW) of dissimilar aluminum alloys AA2024 and AA7075 and investigates the effect of different stress ratios on crack growth within dissimilar welded joints. The FSW process was performed at 760 rpm rotational speed and a feed rate of 50 mm/min. Subsequent crack growth tests were conducted on Compact Tension (CT) specimens extracted from the dissimilar FSW joint, applying varying stress ratios (R: −0.5, 0.0, 0.1, 0.5, 0.8) at a maximum load (Pmax) of 5 kN and a frequency of 6 Hz. The study meticulously analyzed and compared the tensile properties of weld joints and base metals. The hardness profile was plotted across the various weld zones. Experimental data were utilized to construct fundamental curves such as the a-N curve, crack growth rate curve, and stress–strain curve, enabling the determination of Paris constants. Notably, the research unveiled a clear relationship between stress ratio and fatigue life, indicating a decrease in fatigue life as the stress ratio increased. Specifically, the highest fatigue life of 45,000 cycles was observed at R=−0.5, while the lowest of 26,000 cycles was noted at R=0.8. Furthermore, electron microscopy was employed to scrutinize the fracture surface, providing valuable insights into its behavior.