Achieving high strength-ductility of Al-Zn-Mg-Cu alloys via hot-wire arc additive manufacturing enabled by strengthening precipitates

Abstract

The Al-Zn-Mg-Cu alloys fabricated by wire arc additive manufacturing (WAAM) have inferior performance due to poor microstructures and inevitable defects, which restrict their development. This study explored the hot-wire arc additive manufacturing (HWAAM) of the 7055 alloy, and proposed a three-stage solution and aging heat treatment method to further improve its mechanical properties. Both as-deposited and heat treated samples were mainly composed of equiaxed grains. Within grains of the as-deposited sample, the Mg(Zn,Cu) 2 were precipitated. After heat treatment, apart from the small and abundant Mg(Zn,Cu) 2 precipitates, the Al 3 Zr were also precipitated. Crack-free 7055 alloy parts were obtained, and the low porosity of as-deposited and heat treated samples were 0.18 % and 0.26 %, respectively. In addition, the alternating clustered-pore zones and discrete-pore zones were observed in both samples. After heat treatment, UTS and elongation were 563 ± 7 MPa and 10.0 ± 1.2 %, respectively, and negligible mechanical anisotropy of Al-Zn-Mg-Cu alloys was obtained. The good properties, which reached the wrought level, were attributed to the equiaxed grains and low porosity, as well as abundant strengthening phases. This work demonstrated the potential of additive manufacturing to fabricate alloys with unique microstructures and high performance for structural applications. • HWAAM method was used to deposit Al-Zn-Mg-Cu alloys, followed by a novel heat treatment to improve the properties. • The as-deposited parts with fine and equiaxed grains, as well as crack-free and low porosity were obtained. • The Mg(Zn,Cu) 2 phases and Al 3 Zr phases were precipitated after heat treatment. • The Al-Zn-Mg-Cu alloys with high strength-ductility and negligible anisotropy were manufactured.