Components and structures working in the marine environment are exposed to high stresses attributable to the action of wind, waves, and tides. Moreover, they have to face hostile and severe environmental conditions during their lifetime, being placed in the splash zone if not even submerged in saltwater. The application of polymer composites in marine systems has been the focus of intensive studies in the last decades, highlighting potential benefits given by the replacement of several components, such as ship hulls, propeller blades, wind, and tidal turbine blades, to cite but a few. The present paper reports the latest advances in this area, addressing the applications of advanced composites in ships and ship components, offshore oil and gas composites, marine renewable energy and underwater repairing.

The Cold Gas Dynamic Spray technology, generally referred as Cold Spray, is a relatively new additive manufacturing technique able to produce fully dense coatings through the deposition of particles on a substrate. Fine powders are accelerated to high velocity and projected onto a substrate, upon impact with the target surface, conversion of kinetic energy to plastic deformation occurs and the solid particles deform and bond together. During the cold spray deposition process, the particles remain in a solid state during the deposition, resulting in high-quality coatings with low residual stresses and oxide inclusions. The relative lower process temperatures allow the cold spray to manufacture coatings on high temperature-sensitive materials. It could also be a valid method for deposition of a wide variety of materials, from metallic alloys up to ceramics and composites. Depending on the materials employed as substrate and coating, different bonding mechanisms can occur during the deposition. The present review aims to summarise the main bonding theories proposed up to now for the cold spray, focusing on both the particle deformation behaviour during the contact with the surface and the interfacial bonding mechanisms. The available theories for different substrate/coating configurations will be discussed and compared. The effects of deposition parameters, the substrate's surface and microstructure of feedstock powders on the bonding mechanism will also be discussed.

Multi-material lightweight structures are gaining a great deal of attention in several industries, in particular where a trade-off between reduced weight, improved performances, and cost compression is required. Magnesium alloys, such as the zinc-rare earth elements ZE41A alloy, fulfill the first two requirements; however, they are susceptible to corrosion and relatively expensive. Lightweight structures hybridization, for instance combining Magnesium alloys and Aluminium alloys, is currently under consideration as a potential solution to this problem. Nevertheless, dissimilar joining of Magnesium and Aluminium alloys is challenging due to the significant differences in physical properties, as well as to the precipitation of brittle intermetallic compounds, such as Al12Mg17 and Al3Mg2. In this study, the dissimilar joining of Magnesium and Aluminium alloys by friction stir welding process is discussed. In particular, 4 mm thick plates of ZE41A Mg alloy and AA2024-T3 Al alloy were welded in the butt joint configuration. The feasibility of the process was assessed by means of microstructure and mechanical analysis. The formation of brittle intermetallic compounds was investigated as well