Abstract: The utilization of wire-arc additive manufacturing (WAAM) technology for the preparation of Al-Zn-Mg-Cu aluminum alloy has made some progress in recent years. However, the challenge still remains to achieve ultra-high strength (600 MPa) in WAAM. In this study, the crack-free Al-Zn-Mg-Cu-Sc thin-wall component with ultra-high strength was successfully fabricated by the cold metal transfer (CMT) process using a self-prepared 7B55-Sc filler wire. The microstructures of both as-deposited and T6 heat-treated samples were all composed of fine equiaxed grains with an average size of about 6.0 μm. The primary Al₃(Sc, Zr) particles acted as heterogeneous nuclei to promote the formation of equiaxed grains and refine the microstructures during the solidification process. A large amount of continuous eutectic structures rich in Al, Zn, Mg, and Cu elements formed along the grain boundaries under the as-deposited condition, and the precipitated second phases within the grains mainly included the equilibrium η phase, metastable η′ phase and large-sized T phase. After T6 heat treatment, the majority of the second phases originally distributed within grains and along grain boundaries were dissolved into the Al matrix, and a large amount of fine GP zones, η′ phase and secondary Al₃(Sc,Zr) particles were precipitated within the grains during the aging process. The tensile strength reached a recorded level of 618 MPa in the horizontal direction after T6 heat treatment, which was considered a breakthrough for the manufacturing of 600 MPa grade aluminum alloy by WAAM.

Key words: Wire-arc additive manufacturing, Al-Zn-Mg-Cu alloy, T6 heat treatment, Microstructure, Second phase, Mechanical property