Synergistically Improving the Strength and Anisotropy of Wire Arc Additively Manufactured Al-Mg-Sc-Zr alloy by Regulating Heat Input

Wire arc additive manufacturing (WAAM) is one of the most promising approaches to manufacturing large and complex metal components owing to its low cost and high efficiency. However, pores and coarse columnar grains caused by thermal accumulation in WAAM significantly decrease the strength and increase the anisotropy, preventing the achievement of both high strength and isotropy. In this study, the strength and anisotropy of Al-Mg-Sc-Zr alloys were improved by regulating heat input. The results indicated that as the heat input increased from 60 to 99 J/mm, all the components had lower porosity (lower than 0.04 %), the size of the Al 3 (Sc 1- x , Zr x ) phases decreased, and the number density increased. The average grain size gradually decreased, and the grain morphologies transformed from coarse equiaxed grain (CEG) + fine equiaxed grain (FEG) to FEG owing to the increase in Al 3 (Sc 1- x , Zr x ) phases with increasing heat input. After heat treatment at 325 °C for 6 h, high-density dispersed Al 3 Sc phases (<10 nm) precipitated. The alloy possessed the highest strength at 79 J/mm, ultimate tensile strength (UTS) of approximately 423 ± 3 MPa, and in-plane anisotropy of approximately 4.3 %. At a heat input of 99 J/mm, the in-plane anisotropy decreased to 1.2 % and UTS reached 414 ± 5 MPa. The reduction in the CEG prolonged the crack propagation path, which improved the UTS in the vertical direction and reduced the anisotropy. Theoretical calculations indicated that the main strengthening mechanisms were solid solution and precipitation strengthening. This study lays the theoretical foundations for WAAM-processed high-strength and isotropic Al alloy components.