2198 Al-Li plates joined by Friction Stir Welding: Mechanical and microstructural behavior

Al-Li alloys are characterized by strong anisotropy. 2198 Al-Li sheets were joined via Friction Stir Welding (FSW) in parallel and orthogonal direction with respect to the rolling one. The material microstructure and the different phases were individuated by means of TEM observations in different sections of the produced joints; in addition, the mechanical properties were evaluated by means of tensile and fatigue tests at room temperature; the fatigue tests were conducted in axial control mode with R = sigma(min)/sigma(max) = 0.33 for different welding conditions. The crack initiation and propagation in the welded zone was also studied by applying thermoelastic stress analysis (TSA) during cyclic fatigue tests, employing single edge notched specimens. Thermoelastic data were used to measure the principal stresses and principal strains on the specimens surface around the crack tip, according to growth rate; all the results were validated by employing finite element analysis (FEM) to model the crack evolution. (C) 2009 Elsevier Ltd. All rights reserved.