Fatigue behavior of friction stir weld joints of Al–Zn–Mg alloy AA7039 developed using base metal in different temper condition

• Pre weld base metal temper condition influenced fatigue behavior of FSW joints.
• Fatigue tests were performed using tensile stress ratio to develop S–N curves.
• FSW joints of AA7039 exhibited fatigue strength better than base metal.
• Wider crack propagation stage, homogeneous microstructure improves fatigue behavior.
• Fracture of FSW joints took place from low hardness region of WNZ, HAZ and BM.

This paper presents the influence of base metal temper conditions (O, W and T6) on fatigue behavior of friction stir weld joints of Al–Zn–Mg alloy AA7039. Fatigue tests were performed at stress ratio of 0.1 and tensile to tensile stress in the range of 85–215 MPa to develop S–N curves. Fractured surfaces were investigated by SEM to determine the mode of fracture. On the basis of this study, friction stir welding of Al–Zn–Mg alloy AA7039 is recommended to be performed in W temper condition because of better tensile properties and superior fatigue strength.