Friction extrusion experiments were performed to study the process characteristics and microstructural evolution of aluminium alloys. Two fundamentally distinct extrusion types have been identified, one leading to a fully homogenous recrystallized fine-grained wire material. A novel material flow model has been proposed for this case, illustrating a layer-by-layer pattern in terms of material flow. To investigate the precipitation kinetics in-depth, the first friction extrusion set-up for in-situ synchrotron measurements has been developed. Furthermore, the effect of different feedstock materials was investigated, identifying the characteristics and different requirements for performing the friction extrusion process efficiently. Friction consolidation has shown the potential to enhance the properties of the extruded wires and could be demonstrated as a single-step process to mechanically alloy blended Al-Cu-Li powder.
In terms of solid-state AM, the friction surfacing process was studied, gaining an in-depth understanding for single and multi-layer structures. Next to analyses of the temperature evolution and process efficiency, the effect of pre- and post-processing techniques in terms of consolidating volumetric defects was successfully investigated, allowing the fabrication of large-scale structures. Based on in-depth microstructure analyses of the deposited material, a periodic variation in the average grain size along the build direction could be proven. This is attributed to the complex material flow, resulting in varying strain and temperature conditions along the height of each individual layer during deposition, representing a characteristic feature of the process independent of the specific alloy.
In terms of modelling, a primary thermodynamic assessment of the unary systems of the considered aluminium alloys was performed via the CALPHAD method. A phase-field formalism for describing precipitation and the grain size evolution has been implemented. In terms of process simulation, a thermo-mechanical process simulation of friction extrusion has been validated against experimental data. A heat transfer model for friction surfacing has been developed, which has been employed to build a data-enhanced hybrid surrogate model, based on limited available experimental data. Shapley Additive Explanation values were used to evaluate the built machine learning model and most particular findings were confirmed by existing knowledge in literature, thereby allowing for an extension of this knowledge. Furthermore, a 3D GPU-accelerated smoothed-particle hydrodynamics model has been developed for the solid-state AM process friction surfacing, allowing detailed insight into the deposition process.
