Friction Stir Welding (FSW) is a solid-state joining process; i.e., no melting occurs. The welding process is promoted by the rotation and translation of an axis-symmetric non-consumable tool along the weld centerline. Thus, the FSW process is performed at much lower temperatures than conventional fusion welding, nevertheless it has some disadvantages. Laser Assisted Friction Stir Welding (LAFSW) is a combination in which the FSW is the dominant welding process and the laser pre-heats the weld. In this work FSW and LAFSW tests were conducted on 6 mm thick 5754H111 aluminum alloy plates in butt joint configuration. LAFSW is studied firstly to demonstrate the weldability of aluminum alloy using that technique. Secondly, process parameters, such as laser power and temperature gradient are investigated in order to evaluate changes in microstructure, micro-hardness, residual stress, and tensile properties. Once the possibility to achieve sound weld using LAFSW is demonstrated, it will be possible to explore the benefits for tool wear, higher welding speeds, and lower clamping force.

Surface treatment techniques such as laser shock peening (LSP) represent a consolidated strategy to induce the presence of compressive residual stresses beneath the surface of various metallic alloys. However, surface roughening caused by the process must be monitored, since it may negatively affect fatigue life, resulting in earlier crack initiation. For this reason, the interplay between the key factors affecting both the surface roughness and the development of residual stresses was experimentally examined. The surface roughness was assessed through the determination of roughness average and roughness total height values, whereas residual stresses were assessed using the x-ray diffraction technique and hole drilling method to obtain information about the stress status of the components. Higher values of laser power density resulted in higher values of maximum compressive stress both along scanning and stepping direction and residual stresses remained approximately constant up to a depth of about 0.7-0.8 mm beneath the treated surface. No substantial difference was observed between the residual stress components in the two main LSP directions. Moreover, it was found that the approach to use lower values of nominal power density together with a higher number of layers allows obtaining the same stress condition determined by the use of the highest value of nominal power density but a significantly lower impact on the surface roughness.