Investigation of stress corrosion cracking of friction stir welded 2060 Al-Li alloy

Aluminum–lithium 2060 alloy is an ideal structural material for aeronautical components. Friction stir welding (FSW) of 2-mm-thick 2060 Al-Li alloy plates having a welding speed of 600 mm/min and rotation speed of 400 rpm exhibits better joining properties, compared to other conventional welding processes. In the FSW process, three zones are formed due to the stirring of tool and axial force that are the stir zone (SZ), thermo-mechanical affected zone (TMAZ), and heat-affected zone (HAZ), along with base metal (BM). BM showed a lamellar structure of lath-shaped α-Al phase arranged along the rolling direction. The microstructure of SZ appeared as fine and equiaxed grains, which is a distinctive feature of severe plastic deformation at high temperatures. The TMAZ, a transition zone surrounding the weld nugget, experiences a combined action of friction heating and high bending. The equipment was designed and fabricated to investigate the stress corrosion cracking behavior in a simulated environment. The electrochemical properties of FSW welded Al-Li 2060 alloy were determined in 3.5 wt.% NaCl solution by conducting open circuit potential, electrochemical impedance spectroscopy, and cyclic potentiodynamic polarization in both unloaded and loaded (with applied stress of 4 and 8 MPa) conditions in specific time intervals (1, 24, and 48 h). Results showed that corrosion resistance decreases in loaded condition and with the increase in the immersion time. The corrosion rate was 25.21 mm/year for unloaded conditions, which increased up to 91.18 mm/year at 8 MPa applied stress.