Enhanced age-hardening and formation of plate precipitates in Mg-Gd-Ag-Al alloy fabricated by wire-arc additive manufacturing

Abstract

In this work, the microstructure of the WAAM-fabricated Mg-12.1Gd-1.6Ag-0.7Al (wt.%) alloy featured a distinct lamellar structure with alternating dendrites and equiaxed grains. The second phase contained MgAg, GdH_2, (Mg, Ag)₅Gd and Al₂Gd. After the solid solution treatment at 500°C for 2 h, coarse (Mg, Ag)₅Gd phase dissolved, followed by the formation of lamellar Al₂Gd phase. With additional aging treatment at 200°C for 24 h, dense γ″ and β′ nano-precipitates formed in the α-Mg matrix, resulting in remarkable precipitation strengthening, namely the improved UTS of 312 ± 7.9 MPa, YS of 224 ± 5.3 MPa and EL of 4.3 ± 0.5%. This work contributes to the development of high-performance, advanced magnesium alloy workpieces.