Achieving isotropic ultra-high strength and fatigue properties in a wire arc directed energy deposited Al-Zn-Mg-Cu-Sc alloy via interlayer friction stir processing

Pore defects are the most critical issue in the wire arc directed energy deposition (WA-DED) of aluminum alloys, hindering their application in the aerospace and transportation field. The interlayer friction stir processing (FSP), as an innovative composite technique applied in WA-DED, not only effectively addresses pore defects but also improves the material's microstructure, significantly enhancing its tensile and fatigue properties. However, interlayer FSP-treated aluminum alloys are prone to abnormal grain growth (AGG) during subsequent heat treatment processes, leading to a significant reduction in mechanical performance. This study utilized a custom Al-Zn-Mg-Cu-Sc filler wire and employed a combination of WA-DED and interlayer FSP processes to manufacture an alloy that not only eliminates all pore defects but also shows no AGG phenomenon after T6 heat treatment. The manufactured alloy achieves isotropy in mechanical properties, with a tensile strength and elongation of 645 +/- 8 MPa and 12.6 +/- 0.5 %, respectively. The fatigue performance is significantly improved to 250 MPa, marking the highest values in the field of WA-DED aluminum alloys to date. This method provides a feasible approach for eliminating defects and achieving isotropy in aluminum alloys during the additive manufacturing process.