Influence of rotation speed on interfacial bonding mechanism and mechanical performance of aluminum 6061 fabricated by multilayer friction-based additive manufacturing

Friction-based additive manufacturing processes that allow the free design of the deposition path are expected to be used for the rapid production of large-scale high-performance aluminum alloy components. This study successfully fabricated multilayer deposits for 6061 aluminum alloy by friction extrusion additive manufacturing (FEAM) at a high deposition rate. The interfacial bonding properties and material utilization of the final deposits prepared at different rotational speeds were thoroughly investigated and evaluated based on the microstructural observations and mechanical test results. The multilayer deposition process was more stable and reliable at 400 rpm, and each layer was constant in width and thickness, approximately 32 mm wide and 4 mm thick. Planar interfaces were produced regardless of rotation speed, except that metal flow was more intense near the interface at 400 r/min in the driving friction zone, resulting in better interface formation and material utilization of 62.5%. The recrystallization fraction in the extrusion zone (EZ) of the fresh deposit at 400 r/min is 8.9% higher, and the deformation and recrystallization textures predominated in this region. After multiple thermal cycles and plastic deformation, dynamic recovery and subsequent static recovery occurred in the EZ, accompanied by subgrain coarsening and grain growth. Tensile properties in the build direction at 400 r/min are superior to those at 600 r/min, with tensile strength, 0.2% proof stress, and elongation after fracture being 47.4%, 32.0%, and 103% of the extruded 6061-T651 aluminum alloy, respectively.