Isotropic high strength Mg-Gd-Y-Zn-Zr alloy fabricated by wire arc additive manufacturing based on cold metal transfer

Abstract

The Mg-Gd-Y-Zn-Zr (GWZ) alloy containing a long-period ordered stacking (LPSO) phase fabricated by Wire arc additive manufacturing (WAAM) shows substantial potential in the aerospace and automotive industries. In this work, Mg-9Gd-4Y-1Zn-0.4Zr (wt%) single-layer and multilayer components with high-forming-quality were fabricated using WAAM based on cold metal transfer (WAAM-CMT). The deposition parameters were optimized, achieving better deposition morphology and surface quality. The layer-by-layer cyclic microstructure includes remelting zone (RMZ) and non-remelting zone (NRZ), which consisted of α-Mg matrix, blocky LPSO phase, and eutectic phase. The average grain size were 26.8 µm in RMZ and 39.3 µm in NRZ, and the volume fraction of secondary phases was around 8%, remaining consistent across different layers. The coarse-fine-grain alternating structure generated hetero deformation induced (HDI) strengthening, while at the same time caused the fracture occurring between the NRZ and RMZ due to the weak interlayer bonding. The thermally stabilized blocky LPSO phase played an effective role on inhibiting grain growth during the solid-solution treatment. The specimen achieved highest isotropic mechanical properties after optimized heat treatment with yield strength, ultimate tensile strength, and elongation higher than 220 MPa, 370 MPa, and 8.0%, respectively. The GWZ alloys fabricated by WAAM with great isotropic strength-ductility-synergy are promising candidates to replace the conventionally cast counterparts.