Fatigue crack growth behavior in weld nugget zone of FSWed similar and dissimilar aluminum alloys joint

Abstract

Fatigue crack growth behavior in weld nugget zone (WNZ) of friction stir welded (FSWed) dissimilar aluminum alloys joints were investigated comparing to that of the FSWed similar aluminum alloy joints and the base materials. Materials combination for FSWed dissimilar materials joint were 6N01-A5052 and 6N01-7N01 aluminum alloys. FSW was carried out by using a bobbin type tool. Fatigue crack was introduced at the weld center line in WNZ of the joint to propagate along the welding direction. Crack closure behavior was evaluated during fatigue crack growth test by unloading elastic compliance method with strain measurement at back face of the specimen. In case of FSWed 5052 and 6N01 similar aluminum alloy joints, fatigue crack growth resistance in WNZ was lower than that in the base materials and no crack closure was observed in WNZ. In contrast, crack closure was found in WNZ of FSWed 7N01 similar aluminum alloy joint and the fatigue crack growth resistance was higher than that of the base material. In case of FSWed 6N01-5052 dissimilar aluminum alloys joint, no crack closure was observed in WNZ and fatigue crack growth resistance in WNZ was almost the same as that in WNZ of the FSWed 5052 and 6N01 similar aluminum alloy joints. Fatigue crack growth resistance in WNZ of FSWed 6N01-7N01 dissimilar aluminum alloys joint was higher than that observed in WNZ of FSWed 6N01 similar aluminum alloy joint but was lower than that observed in WNZ of FSWed 7N01 similar aluminum alloy joint. Crack closure behavior was observed in WNZ of FSWed 6N01-7N01 dissimilar aluminum alloys joint. Fatigue crack growth behavior of FSWed dissimilar aluminum alloys joint includes effect of the both alloys.