Study On Fatigue Properties Of Friction Stir Welded AA7050-T7451Aluminum Alloy

The fatigue properties of AA7050-T7451aluminum alloy joint with thickness of6mm byfriction stir welding(FSW) at room temperature were studied. The S-N curves ofAA7050-T7451and friction stir welded joints were given by fatigue testing, and fatiguefracture surfaces were examined by SEM. The results show that the FSW joints have goodwelding performance when the rotating speed is800r/min and the welding speed is100mm/min. The fatigue limit of AA7050-T7451is144MPa, while95MPa for FSW joints whichis66%of that of AA7050-T7451. The fracture occurs the region between thermo-mechanically affected zone(TMAZ) and the weld nugget(WN) in the advancing side. Thefatigue cracks initiate at the top of the surface. The fatigue straits and holes caused by thesecond-phase particles debonding are found in the crack propagation regions at low stresslevel. The grains crystallographic orientation and misorientation angle distribution in thewelded nugget and thermo-mechanically affected zone of7050-T7451aluminum alloy areanalyzed by Electron back scattering diffraction (EBSD) technique. The results show that thewelded nugget zone consists of equiaxial fine recrystallized grains, high-angle grainboundaries are up to91.5%, and the grains orientation distribution is irregular. Lots oflow-angle grain boundaries exist in thermo-mechanically affected zone.