Abstract
ABSTRACT In the current study, the effect of different tool pin profiles on fatigue crack growth rate, tensile strength, microstructural behaviour, and microhardness of friction stir welded joints of AA7075-T651 was studied. The friction stir welding joints known as J1 and J2 were formed using two different tool pin profiles: square pin tool profiles and left-hand threaded cylindrical tool pin tool profiles. All pin profile has scrolled shoulder. The results showed that the fatigue crack growth rate for the J2 joint was lesser than that of J1 joint, whereas the average grain size of J2 joint was lower than the J1 joint which led to the higher tensile strength of the J2 joint when compared to the J1 joint. Both joints were found to have residual stresses that were compressive in the longitudinal direction. The grain size of the weld nugget zone, internal residual stresses and strengthening precipitates impede the fatigue crack growth rate. The crack closure and non-homogenous microstructure play an important role in the variation of the fatigue crack growth rate.
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