Fundamental Study on Additive Manufacturing of Aluminum Alloys by Friction Surfacing Layer Deposition

Friction Surfacing Layer Deposition (FSLD) is a friction-based process capable of depositing similar or dissimilar materials on a substrate surface. The process is based on the plastic deformation of a rotating metallic consumable rod, which is pressed against the substrate material under an applied axial load. Frictional heat is then generated at the interface between the rod and the substrate due to their relative motion, resulting in a layer of plasticized material that forms a continuous deposit by the translation of the stud along the substrate. On top of this deposit more layers can be realized to build up a multi-layered wall in a solid-state fashion. In this study, the Al alloy 5083 was deposited on an AA2024 substrate. The resulting microstructure including the layer interfaces were investigated by metallographic methods as well as SEM-based techniques including EBSD. Hardness mapping was used for examining local mechanical properties. According to the process monitoring, the quality of the layers is very reproducible. EBSD maps show a sound bonding around the interface between the first layer and the substrate with its upper part showing recrystallized grains where the lower part consists of partially recrystallized grains due to the thermal and mechanical impact, while the heat-affected changes little. All layers exhibit fine, equiaxed recrystallized grains with a typical grain size of 4-5 microns. The variation in size and shape over the height of the structure are limited. Consequently, the multilayered deposit exhibits very homogenous local mechanical properties, i.e., microhardness. In summary, FSLD has shown the feasibility and required flexibility for multi-layer depositing. The process may be an effective alternative to melting-based additive manufacturing methods for specific applications.