Superstrengthening effect of beyond-solid-solution laser powder bed fused WE43 magnesium alloy triggered by direct aging treatment

Abstract

Laser powder bed fusion (LPBF) technology exhibits the potential to develop magnesium alloys as lightweight, load-bearing components in critical industries such as aerospace and automotive. This study investigated the effects of various direct aging treatments on the microstructural evolution and mechanical properties of the beyond-solid-solution WE43 magnesium alloy fabricated via LPBF. The results show that the limited kinetic conditions provided by aging at 175°C lead to the decomposition of the beyond-solid-solution to form the β' metastable phase. The original β1 phase transformed to β' and β'' along the direction of least resistance. These nanoscale coherent phases increased the stored deformation energy, acting as nucleation sites for dynamic recrystallization and stimulating the formation of low-angle grain boundaries. This contributed to segmenting grains into multiple zones and subcrystals. Therefore, after aging at 175°C for 64 h, the grain size decreased from 3.39 to 1.96 μm. Meanwhile, the ultimate tensile strength (UTS) increased from 313 to 353 MPa, yield strength (YS) from 236 to 297 MPa, and elongation (EL) from 7.6 % to 12.4 %. Additionally, the aging treatment at 175°C for 128 h shifted the dominant strengthening mechanism from grain boundary strengthening to Orowan strengthening. As a result, the strengths of the alloy aged at 175°C/128 h exceeded the as-built alloy by 53 and 80 MPa for UTS and YS, respectively.