Abstract: The complex non-equilibrium solidification effects of the laser powder bed fusion (LPBF) combined with the high solubility of rare-earth (RE) elements, provide a new advanced powder metallurgy process for Mg RE alloys with outstanding mechanical performances. However, its creep mechanism has not been revealed yet. The present study systematically investigates and evaluates the high-temperature creep mechanism of LPBFed WE43 alloy under varying temperatures and applied stress conditions. In addition, it thoroughly elucidates the interactions and evolution mechanisms between precipitates and dislocations during the creep process. Subject to residual stresses and thermal cycling, the β phase is formed in the form of “precipitation chains” (PCs) within the grains. The metastable phases β″, β′, and β₁ in-situ precipitate between the PCs. The creep resistance of the (LPBFed) WE43 alloy is governed by the evolution of precipitates and their interactions with dislocations during the creep. Under creep conditions at 200 °C, a large number of 〈c + a〉 and 〈a〉 dislocations undergo climb and cross-slip behaviors within the grains. During the climb and cross-slip of dislocations, the Orowan strengthening effect of β″, the cutting mechanisms of β′ and β₁ phases relative to dislocations, and the dislocation barriers formed by the β phase arrays collectively impart excellent creep resistance to the WE43 alloy. As creep time progresses, dislocations accumulate within the grains, and the β and β₁ phases promote the formation of subgrain boundaries, further triggering discontinuous dynamic recrystallization behaviors during the creep process. Furthermore, influenced by the directional diffusion of elements, precipitates dynamically form around the grain boundaries of recrystallized grains, thereby enhancing the resistance to grain boundary sliding. When the creep temperature increases to 250 °C or 300 °C, a large number of 〈c + a〉 dislocations, accompanied by the dissolution of metastable phases and elemental re-diffusion, transform during the creep process into stacking faults (SFs). SFs not only exhibit high thermal stability but also act as effective dislocation barriers at high temperatures through lattice mismatch mechanisms. However, under high-temperature conditions, thermal activation leads to the dissolution of unstable metastable phases, promoting rapid coarsening and transformation of precipitates into various morphologies of β phases, thereby causing a catastrophic decline in creep performance. At the same time, high temperatures further exacerbate elemental diffusion, resulting in precipitate-free zones near grain boundaries, thereby inducing crack initiation. Therefore, the creep resistance of as-deposited alloys decreases significantly at higher temperatures. Building on this, the future development trends of LPBFed WE43 alloys are envisioned, where homogenizing heterostructures or introducing high aspect ratio precipitates and high-density SFs prior to creep can be regarded as a promising approach for enhancing creep resistance in LPBFed WE43 alloys.

Key words: Laser powder bed fusion, WE43, Creep, Heterogeneous microstructure, Dislocations, Stacking faults