Experimental investigation of fatigue crack growth in the welding nugget of FSW joints of a 6060 Aluminum Alloy

The work investigates the fatigue behavior of friction stir welded butt joints by means of fracture mechanics techniques. FSW joints of artificially aged AA6060 T6 aluminum alloy were studied. The welding was performed on 8 mm thick butt joined sheets by means of a CNC machine tool. Welding speed in the range between 117 and 683 mm/min and tool rotational speed between 838 and 1262 rpm were considered. Fatigue crack growth tests were performed according to ASTM E647 standard on CT specimens, under constant load amplitude conditions, at 0.1 minimum to maximum load ratio, with the notch placed in the dynamic recrystallization zone of weld nugget, oriented along the welding direction. The comparison of results demonstrates the crack growth rate is always equal or lower than the base material at low values of stress intensity range. At ΔK values above 12 MPa√m, crack growth rate was found to be higher than base material for high feed, low speed and high feed/speed ratio.