Stress ratio effect on crack growth behavior of dissimilar friction stir welded butt joint between AA6061 and AA7075 alloys

Many engineering components are subjected to random nature of loading during their life period. In this work, the fatigue crack growth in friction stir welded dissimilar AA6061 and AA7075 was investigated under different stress ratio. AA6061 was kept on the advancing side due to having a higher solidus temperature and softer than AA7075 for smooth material flow. The microstructure characterization, tensile and crack growth behavior was studied. It was observed that the joint material exhibited lower strength and ductility as compared to the base material. About 41%, 34%, and 66% reduction in tensile strength, yield strength, and percentage of elongation as compared to AA6061 (base material) were observed. About 27% higher hardness in the HAZ of retreating side than the advancing side was noticed. The crack deflection and tortuosity features were observed in the fatigue fractured specimens. In this paper, a comparative study using different crack growth models has been studied and a simple crack growth rate equation has been proposed considering the crack closure effect.