Fatigue behavior of friction stir butt-welded joints inclined to applied stress

In recent years, some fatigue tests have been performed to investigate the fatigue behavior of friction stir butt-welded joints in aluminum alloy. However, the fatigue behavior of the joints with thick plate of around 10 mm rarely has been investigated. In addition, the influence of the inclined angle of friction stir welding (FSW) line to applied stress has not yet been clarified in the previous studies. In this research, fatigue tests were carried out on four types of model specimens. The specimens have FSW of inclined angles of 0°, 30°, 60° and 90° to perpendicular direction of the applied stress. The observations of fatigue failure condition and fracture surfaces indicate that fatigue crack mainly initiates and propagates at the heat affected zone (HAZ) when the inclined angle is 0°. For the angle of 30°, 60° and 90°, the cracks tend to initiate at the stirred zone (SZ) and then the cracks propagate through the thickness of the specimen in the direction of perpendicular to the applied stress. The tests results shows that the change in the fatigue strength is small, despite of the different FSW line angles.