This study focuses on characterizing the microstructural evolution of the aluminum alloy 7075 in the friction extrusion process under different extrusion forces and die angles. Depending on these conditions, two fundamentally different extrusion types are found, showing significant differences in the process characteristics and microstructural evolution. One of the two extrusion types is associated with high extrusion force and low die angle, leading to fully recrystallized wires with average grain size around 1.2 $$\upmu$$
μ
m. The microstructural analysis indicates that the microstructure present in the wires is generated in the charge material by the combination of tool geometry, load induced material flow and friction conditions in the initial stages of the friction extrusion process. The identified processing conditions and influencing factors introduce an alternative route for friction extrusion at low extrusion ratios, capable of producing completely refined wires.
Friction surfacing (FS) is a solid-state layer deposition process for metallic materials at temperatures below their melting point. While the bonding of the deposited layers to the substrate is proven suitable for coating applications, so far the mechanical properties of additively manufactured stacks have not been systematically investigated. In particular, the effect of successive deposited FS layers, i.e., repetitive thermo-mechanical loading, on the interface properties as well as anisotropy and strength of the deposited stack is unknown. For this purpose, the mechanical properties of FS deposited multi-layer stacks from dissimilar aluminum alloys have been investigated, characterizing layer-to-layer as well as layer-to-substrate bonding interfaces via micro-flat tensile testing. Furthermore, directional dependencies in the stack and failure mechanisms are analyzed. The results show a homogeneous, fine-grained microstructure with average grain sizes between 4.2 and 4.6 μ m within the deposited material. The resulting tensile properties with no significant directional dependency present an ultimate tensile strength between 320 and 326 MPa exceeding the strength of the AA5083 H112 consumable base material. No difference was obtained in terms of layer-to-layer or layer-to-substrate interface strength. Furthermore, homogeneous hardness was observed within the deposited structure, which is in the range of AA5083 base material’s hardness of 91 HV. The results indicate that the FS process in conjunction with the material used is suitable for additively generated structures and highlight the potential of this solid-state layer deposition technology.
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