AA8090 Al-Li Alloy FSW parameters to minimize defects and increase fatigue life

Increasing payload and fuel efficiency of aircrafts have become the major issues for the aerospace industry, which has increased the development of more advanced materials with highly specific properties. Low density aluminium lithium alloys are attractive to the aerospace industry since the structural weight reduction that they allow leads to an improvement of aircraft performance. Significant interest has been shown in the use of advanced welding techniques like Friction Stir Welding, particularly due to the design and manufacturing benefits that they afford over established mechanical joining methods. A significant benefit of FSW is the fact that it implies only a few process parameters to control: tool rotational speed, travel speed and applied normal load are easily controlled. This work presents an approach to optimise FSW process parameters which govern the tensile strength and the fatigue life of AA8090 Al-Li alloy through their effects on plastic flow in the nugget and in the thermo-mechanically affected zone (TMAZ), and through the thermal alteration in the heat affected zone (HAZ) of the weld. Therefore a close relationship exists between microstructure and fatigue performance, the typical plastic flow of a FSW joint and the occurrence of defect types, specific to FS process, can influence the fatigue behaviour of the joints.