Comparison of fatigue crack propagation behavior of friction stir welded and metal inert-gas welded A6N01 joints

Fatigue crack propagation (FCP) behavior at different locations of friction stir welded (FSW) and metal inert-gas welded (MIG) A6N01 joints were studied. The fatigue fractures and microstructures of the joints were analyzed. For FSW and MIG joints, the fatigue crack propagation rate (FCPR) in nugget (weld) zone was the highest, while the FCPR in heat-affected zone (HAZ) was lower than that in the nugget (weld) zone. The base metal had the highest fatigue crack propagation resistance. The FCPR had no significant difference when crack propagated in the same regions of FSW and MIG joints. However, the fatigue crack growth threshold (ΔK_th) of crack propagating in the nugget zone of FSW joint was higher than that of MIG joint, in other words, the resistance to fatigue crack propagation in the nugget zone of FSW joint was superior to that of MIG joint. The fracture surface of fatigue crack propagating in the nugget (weld) zone of FSW and MIG joints revealed brittle fracture, while that in heat-affected zone was mainly plastic fatigue striation.