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.

Aluminium alloys processed by wire arc additive manufacturing (WAAM) exhibit a relatively coarse microstructure with a columnar morphology. A powerful measure to refine the microstructure and to enhance mechanical properties is to promote grain refinement during solidification. Addition of ceramic nanoparticles has shown great potential as grain refiner and strengthening phase in aluminium alloys. Thus, an Al-Mg alloy mixed with TiC nanoparticles was manufactured by the novel metal screw extrusion method to a wire and subsequently deposited by WAAM. Measures to restrict oxidation of magnesium during metal screw extrusion were examined. Purging of CO₂ gas into the extrusion chamber resulted in a remarkable reduction in formation of MgO and Mg(OH)₂. TiC decomposed to Al₃Ti during WAAM deposition, leading to a significant grain refinement of 93% compared to a commercial benchmark. The presence of remaining TiC nanoparticles accounted for an increased hardness of the WAAM material through thermal expansion mismatch strengthening and Orowan strengthening. Exposure of TiC to moisture in air during metal screw extrusion increased the internal hydrogen content significantly, and a highly porous structure was seen after WAAM deposition.

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.

A fine-grained fusion zone characterises a tough aluminium weld. To improve the solidification characteristics and refine the grains in aluminium welding, different inoculation particle combinations were introduced to the filler wire by solid state metal screw extrusion. Filler wires were I-joint welded with two different welding methods to reveal the potency for grain refinement. Grain size, microstructure, porosity content, and hardness across the weld was revealed. Gas metal arc welding with a Ti-TiC inoculated filler wire exhibited a remarkable grain refinement of 91% compared to a base reference of commercial pure aluminium. The Al $$_3$$3 Ti intermetallic phase was found as nucleation point. Gas tungsten arc welding showed lower grain refinement potency, and no Al $$_3$$3 Ti phase was found in any weld. Thus, the effect of welding method must be taken into consideration upon development of inoculant containing filler wires.