Selective laser melting (SLM) is one of the most interesting technologies used in rapid prototyping processes because of the possibility of building complex three-dimensional metal parts of nearly full density and with mechanical properties similar to those obtained with conventional manufacturing processes. This goal can be achieved using high-power lasers and low values of scan velocity. These conditions, together with an appropriate scanning strategy, allow full melting of the powders used in the process to be obtained. The aim of this paper is to investigate the residual stresses in SLM specimens manufactured from AISI Marage 300 steel. First, the strain gauge hole drilling method is utilized to determine residual stress profiles in a set of test samples of different thicknesses, placed in different positions on the building platform. Statistical analyses are performed in order to study the relationships between sample position on the platform, the distance from the specimen surface, and maximum/minimum principal residual stresses. The experimental results show that the melting/solidification mechanism generates highly variable thermal residual stresses in the SLM parts used in this study.

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.

The need to use components with improved surface characteristics in relation to severe operating conditions, together with the aim of cost reduction associated with the replacement of damaged components, has led to an increasing use of coatings and repairing processes. The most common deposition processes are generally characterized by high equipment costs and, sometimes, by long deposition time. Furthermore, some repair technologies, especially those characterized by high heat input, are not suitable for alloys used in aerospace applications due to the degradation of their mechanical characteristics. In the last decades, a novel eco-friendly method capable of overcoming the limits set out above emerged: the electrospark deposition (ESD) technology. Thanks to its efficiency, simplicity, cost-effectiveness, and low heat input, this technology has proved to be suitable both for improving surface properties, such as thermo and wear resistance, higher hardness and corrosion resistance, and for the repair of high-value components. The aim of this review is to describe in detail some aspects of the ESD technique to understand the ESD processing preparation of alloys normally considered difficult to weld by traditional processes and to give some important clues to the readers to contribute to the defect-free repair of damaged areas and coatings deposition.