Microstructure tuning enables synergistic improvements in strength and ductility of wire-arc additive manufactured commercial Al-Zn-Mg-Cu alloys

Abstract

It remains challenging to achieve attractive mechanical strength and ductility in commercial 7xxx alloys fabricated by wire-arc additive manufacturing (WAAM). Here, we combine WAAM processing with solution and artificial aging treatments to functionalise their inherent age-hardening capabilities via microstructure controlling. The as-deposit WAAM 7055 alloy shows a heterogeneous microstructure with a bimodal grain size distribution, and the primary metallurgical defects are spherical gas pores with an inter-layer distribution. Upon the optimised T6 temper (470°C/2 h for solution treatment and 120°C/65 h for artificial aging), nano-sized platelike η’ precipitates are generated, and the tensile strength boosts from ∼226 MPa to ∼562 MPa. Evident yielding with a uniform plastic deformation is also mediated by the T6 temper, with the yield strength > 500 MPa and the fracture strain > 5%, which is comparable to conventional wrought 7xxx alloys. This work provides insight into the microstructure tuning for commercial 7xxx alloys via WAAM for achieving excellent mechanical properties.