Processing of aluminum alloys by wire arc additive manufacturing (WAAM) gained significant attention from industry and academia in the last decade. With the possibility to create large and relatively complex parts at low investment and operational expenses, WAAM is well-suited for implementation in a range of industries. The process nature involves fusion melting of a feedstock wire by an electric arc where metal droplets are strategically deposited in a layer-by-layer fashion to create the final shape. The inherent fusion and solidification characteristics in WAAM are governing several aspects of the final material, herein process-related defects such as porosity and cracking, microstructure, properties, and performance. Coupled to all mentioned aspects is the alloy composition, which at present is highly restricted for WAAM of aluminum but received considerable attention in later years. This review article describes common quality issues related to WAAM of aluminum, i.e., porosity, residual stresses, and cracking. Measures to combat these challenges are further outlined, with special attention to the alloy composition. The state-of-the-art of aluminum alloy selection and measures to further enhance the performance of aluminum WAAM materials are presented. Strategies for further development of new alloys are discussed, with attention on the importance of reducing crack susceptibility and grain refinement.

Wire and arc additive manufacturing (WAAM) of metallic materials is expected to become part of the new industrial revolution. The possibilities for complex designs and superior mechanical properties can in many cases replace traditional manufacturing processes such as casting. In order to benchmark the properties of aluminium WAAM components, a comparative study was performed with two different casting techniques: permanent casting with steel mould and sand mould casting. Aluminium-silicon alloys with near eutectic composition were used for the comparison. Porosity levels, secondary dendrite arm spacing, grain size distribution, tensile strength and microhardness were considered for the comparison. The WAAM material exhibited superior mechanical properties originating from a finer dendritic and eutectic microstructure compared with the castings. A slight anisotropy in tensile ductility was observed in the WAAM material, probably due to a coarse microstructural zone between individual beads. All investigated materials had low levels of porosity, <1% by area fraction. The comparative study has shown that WAAM of aluminium-silicon alloys is well suited for high-integrity applications.

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The development of customised aluminium alloys for welding and additive manufacturing (AM) is proposed to solve several quality issues and to enhance the mechanical integrity of components. The introduction of ceramic grain refining agents shows great potential as alloy addition as to limit cracking susceptibility and increase the strength. Thus, a versatile solid-state manufacturing route for nanoparticle reinforced aluminium wires has been developed based on the metal screw extrusion principle. In fact, the Al-Si alloy AA4043 mixed with 1 wt.% TiC nanoparticles has been manufactured as a wire. The accumulated strain on the material during metal screw extrusion has been estimated, classifying the process as a severe plastic deformation (SPD) method. A chemical reaction between silicon and TiC particles after metal screw extrusion was found, possibly limiting the grain refining effect. Electric arc bead-on-plate deposition was performed with metal screw extruded and commercial material. The addition of TiC induced a grain morphology transition from columnar to equiaxed after electric arc deposition, and increased the hardness. A high amount of porosity was found in the AA4043-TiC material, probably arising from hydrogen contamination on TiC surfaces prior to metal screw extrusion. The results are encouraging as a new direction for aluminium alloy development for additive manufacturing.