Developing a novel high-strength Mg-Gd-Y-Zn-Mn alloy for laser powder bed fusion additive manufacturing process

Abstract

Laser powder bed fusion (LPBF) of Mg alloys mainly focuses on the traditional commercial casting Mg alloys such as AZ91D, ZK60 and WE43, which usually display relatively low tensile strengths. Herein we developed a novel high-strength Mg-12Gd-2Y-1Zn-0.5Mn (wt.%, GWZ1221M) alloy for the LPBF additive manufacturing process, and the evolution of microstructure and mechanical properties from the as-built state to LPBF-T4 and LPBF-T6 states was systematically investigated. The as-built GWZ1221M alloy exhibited fine equiaxed grains with an average grain size of only 4.3 ± 2.2 µm, while the as-cast alloy displayed typical coarse dendrite grains (178.2 ± 73.6 µm). Thus, the as-built alloy showed significantly higher tensile strengths than the as-cast counterpart, and its yield strength (YS), ultimate tensile strength (UTS) and elongation (EL) were 315 ± 8 MPa, 340 ± 7 MPa and 2.7 ± 0.5% respectively. Solution treatment transformed hard and brittle β-(Mg,Zn)₃(Gd,Y) phase into basal X phase and lamellar long period stacking ordered (LPSO) with better plastic deformability, leading to the improvement of EL. Then peak-aging heat treatment introduced numerous nano-sized prismatic β′ precipitates inside grains, resulting in the enhancement of YS. Finally, the LPBF-T6 alloy achieved appreciably high strength with YS, UTS and EL of 320 ± 3 MPa, 395 ± 4 MPa and 2.1 ± 0.4% respectively. Both as-built and LPBF-T6 GWZ1221M alloys showed remarkably higher tensile strengths than the as-cast counterparts and as-built commercial Mg alloys, highlighting the great potential of high-strength as-built Mg-Gd based alloys for structural applications.