Additive Manufactured High Strength Al-Mg Alloy Through Well-Controlled Hierarchical Precipitation at Sub-Micro to Nano-Scale

In this study, the intrinsic heterogeneous structure derived from the special temperature gradient in each molten pool and the repetitive remelting process were utilized for constructing a high-strength AlMg alloy. The alternative distribution of the coarse-grained (CG) layer in the middle of the pool and ultrafine-grained (UFG) layer at the boundary between the adjacent two pools were produced by using laser powder bed fusion (L-PBF) technology. High contents of Sc and Zr elements were deliberately introduced into the Al−Mg alloy, which contributed to the stabilization of UFG boundaries in the form of sub-micro primary Al3(Sc, Zr) particles and resulted in the formation of supersaturated Sc and Zr solid solutions in CG. The afterward well-controlled hot isostatic pressing induced uniform precipitation of the high-density nano-scale coherent Al3(Sc, Zr) phase in CG. It exhibits a tensile strength of 560 MPa with a uniform elongation of 12%. This high strength was mainly attributed to the hierarchical precipitation of the Sc-rich phase, exerting a “dragging effect” on intergranular boundary migration as well as a “pinning effect” on intragranular dislocation sliding. The findings in the work provide an avenue for the design of high-performance alloys by taking advantage of additive manufactured intrinsic heterogeneity