Control of macro-/microstructure and mechanical properties of a wire-arc additive manufactured aluminum alloy

Wire-arc additive manufacturing (WAAM) has received considerable attention in the past years due to advantages in terms of deposition rate, design freedom, and buy-to-fly ratio. Particularly, cold metal transfer welding has been used extensively allowing for precise process control during manufacturing. Processing parameters have to be adjusted to advance this novel fabrication technique to meet the alloys' requirements with the aim of meeting property goals and increasing microstructural homogeneity. In the present contribution, the alteration of the building strategy during WAAM of an aluminum alloy via variation of the polarity sequence is suggested. These parameters allow adjusting the heat input and, thus, the component's temperature and cooling rate. Firstly, the quality of the surface is improved using adjusted deposition parameters. Secondly, a deposition strategy with a lower thermal exposure of the alloy provides a more homogeneous microstructure in terms of grain size, grain morphology, and distribution of second phases. Thirdly, the burn-off of volatile elements is reduced with decreasing heat input. The observed microstructural changes also result in more homogeneous local mechanical properties. It is demonstrated that the adjustment of the polarity sequence is a strong tool to influence the microstructure during WAAM enabling increased exploitation of this innovative technology.