Laser powder bed fusion of an age-hardenable Mg-10Gd-0.2Zr alloy with excellent strength-ductility synergy

Abstract

Generally, Mg-Gd alloys need to be firstly solution treated at relatively high temperatures and then artificially aged at low temperatures to achieve adequate strength, which costs dozens of hours. Herein a Mg-10Gd-0.2Zr (wt%) alloy was reported to achieve excellent strength-ductility synergy with the product of ultimate tensile strength and elongation of 2791.3 MPa × % just by laser powder bed fusion (LPBF). The excellent strength-ductility synergy is attributed to the novel multi-scale hierarchical microstructure containing heterogeneous grain structure, intragranular lamellae substructure and nano-sized precipitates. Abnormal precipitation of a large number of intragranular β 1 phases with blocky shape is first found in the as-built Mg-10Gd-0.2Zr alloy. The findings demonstrate that the unique heat and strain history during LPBF can be exploited to deliberately regulate the type, area number density, morphology and distribution of precipitates, thus controlling mechanical properties. • Mg-10Gd-0.2Zr (wt%) alloy prepared by LPBF achieves excellent strength-ductility synergy. • The multi-scale hierarchical microstructure leads to excellent strength-ductility synergy. • Abnormal precipitation of β 1 phases with blocky shape and unique distribution is found for the first time.