On the excellent strength-ductility synergy of wire-arc directed energy deposited Mg-Gd-Y-Zn-Zr alloy via manipulating precipitates

As a high-efficiency and low-cost additive manufacturing technology, wire-arc directed energy deposition (DED) has been progressively used to fabricate large components of AZ-series and magnesium rare-earth (Mg-RE) alloys. However, it is generally known that AZ-series Mg-alloys exhibit inferior strength and Mg-RE alloys suffer from poor ductility. Herein, we describe a novel Mg-4.4Gd-2.2Y-1.0Zn-0.5Zr (wt%) alloy possessing excellent strength-ductility synergy (yield strength of 157 ± 1.15 MPa, ultimate tensile strength of 288 ± 2.52 MPa and elongation of 17.1 ± 0.32%), achieved through manipulating precipitates enabled by heat treatment. Besides, the mechanisms of gradient microstructure caused by the unique thermal history of wire-arc DED and precipitates evolution induced by heat treatment are systematically revealed. The enhanced strength can be attributed to the dense lamellar long period stacking ordered (LPSO) structures developed by the solution treatment and the abundant nano-β′ precipitates formed by the aging treatment. Increased strain hardening rate and the fracture suppression impact of LPSO-structures worked together to provide the noticeable ductility. The combined impacts of both the kinking deformable LPSO-structures and special nanoscale closed volume configuration, which effectively relieve stress concentration and suppress crack propagation, are the major mechanisms of such an excellent strength-ductility synergy. This study thus sheds new light on the alloy design and precipitates regulation of large-sized Mg-alloy components with high-performance fabricated by wire-arc DED.