Wire-arc directed energy deposition 7075-Sc aluminum alloy: Heat input adjustment forming quality, microstructure and mechanical properties

In this study, high-strength thick-walled Al-Zn-Mg-Cu-Sc alloy components were successfully fabricated using inhouse developed 7075-Sc welding wires via wire-arc directed energy deposition (DED) technique. To elucidate the influence of heat input during deposition process on the microstructure and mechanical properties, alloy components with varying heat inputs were deposited using the cold metal transfer (CMT) process. The results indicate that the CMT process exhibits effective control over porosity defects. As the heat input decreases, the porosity is reduced from 0.51 % to 0.37 %, with the maximum pore diameter approximately 38.72 mu m. Under varying heat inputs, all samples consist of fine equiaxed grains with an average size of approximately 24.17 +/- 8.57 mu m. The addition of Sc elements results in the formation of high-melting-point Al3Sc particles during solidification, which not only promote heterogeneous nucleation and grain refinement but also create physical barriers that restrict dendritic growth. The thermal cycling during the deposition process facilitates the precipitation of secondary phases, further enhancing the alloy's strength. The as-deposited alloy exhibits yield strength of 324.5 MPa, ultimate tensile strength of 402.8 MPa, and an elongation of 3.7 %. Among them, the contribution of 6GB and 6Orowan to yield strength can be calculated as approximately 51.14 MPa and 271.36 MPa respectively. The tensile strength of samples with different heat inputs remains comparable, while the elongation decreases significantly from 3.7 % to 2.4 %, indicating a marked difference. Higher heat input increases porosity defects, thereby reducing the plasticity of samples.