Addition of Sc in wire-based directed energy deposition of Al–Mg–Zn–Cu alloy: Microalloying to refine grains and improve mechanical properties

A high-strength Al–Mg–Zn–Cu–Sc alloy was fabricated using a directed energy deposition method. A gas tungsten arc (GTA) was used as the heat source, and Al–Zn–Mg–Cu wire and Al–Mg–Sc wire were fed synchronously as the feedstocks. The microstructure and mechanical properties of the deposited alloys were investigated. The results show that, with the addition of Sc, the original columnar grains transformed to equiaxed grains and the anisotropy of the mechanical properties was weakened. A post-heat treatment that involved “aging (300 °C/2h) + solution (470 °C/3 h) + aging (120 °C/21 h)” was proposed to further improve the microstructure and mechanical properties. After the post-heat treatment, the Al₃Sc and η’ phases precipitated and dispersedly distributed. The mechanical properties were further improved owing to the high-density distribution of the dual-nanoprecipitated phases. Under the combined action of fine-grain strengthening and precipitation strengthening, the yield strength, tensile strength, and elongation reached 400 MPa, 449 MPa, and 6%, respectively.