Towards thick layer formation and mcrostructural evolution in multi-Layer friction surfacing of AA2011 alloy

Multi-layer Friction Surfacing is emerging as a new solid-state Additive Manufacturing process able to build and repair materials that cannot be processed by fusion-based AM techniques. In this work, a dual approach was employed to investigate the effect of the main process parameters on the mechanical and microstructural properties of the builds. First, the influence of process parameters on the geometry of AA2011 aluminum alloy single layers was investigated through an experimental optimization campaign to assess the possibility of a thick layer formation. Second, the microstructure and mechanical properties of both the deposited material and the consumable tool after multi-layer friction surfacing were analyzed. The use of optimized parameters for the multi-layer deposition allows a thick-layer stacking, while the material behavior changes due to the substrate effect, resulting in a potential increase in the number of defects with the growth of the sample. Microstructural observations showed that the fraction of low-angle grain boundaries increases from the retreating side toward the advancing side, and from the bottom toward the top of the layer. The intensity of the pole figures and orientation distribution functions demonstrates a strain gradient throughout the layer. Although the average hardness and ultimate tensile strength of the as-built material were lower than those of the starting consumable rod, post-process heat treatment improved the hardness distribution and tensile strength up to 97 % of the AA2011-T6.