Achieving high strength and fatigue performance of wire-arc additive manufactured 6061 aluminum alloy via interlayer friction stir processing and heat treatment

•Superior tensile properties of WAAM 6061 Al achieved via IFSP and T6 treatment.•High fatigue performance due to elimination of defects by WAAM + IFSP hybrid technique.•Systematic investigation of microstructure evolution after T6 treatment. Interlayer friction stir processing (IFSP) has been proved to be an effective method for addressing metallurgical defects and modifying the microstructure of 6061 aluminum alloy produced by wire-arc additive manufacturing (WAAM). In this study, the effect of T6 post-heat-treatment on the microstructure, tensile properties and fatigue behavior were systematically investigated. The results show that the WAAM + IFSP-T6 component has excellent mechanical properties matching wrought counterparts, despite the abnormal grain growth in the stir zone, but there are no defects and a large number of nanometer β'' phases precipitate within the grains in the component. The mechanical properties of WAAM + IFSP-T6 component are isotropic, and the average yield strength, ultimate tensile strength, elongation and fatigue strength are 314 MPa, 336 MPa, 13% and 127 MPa, respectively.