Evolution of the hardening precipitates with an enclosed structure in pre-deformed Mg-Sm-Nd-Zn-Zr alloy

Precipitation evolution of pre-deformed Mg-5Sm-1.4Nd-0.4Zn-0.5Zr alloy during aging at 200 degrees C was investigated by using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). A long lamellae beta(B)' phase was found in the pre-deformed alloy. The beta(B)' phase has a disordered hexagonal structure, and the closely packed planes in beta(B)' have the ABCA stacking sequence with Sm, Nd and Zn atoms in B and C planes. The beta(B)' precipitating on basal plane and beta'/beta(1) precipitating on prismatic plane form an enclosed structure. This special structure has a stronger impeding effect on dislocations slip. The precipitation sequence of the pre-deformed Mg-5Sm-1.4Nd-0.4Zn-0.5Zr alloy is: supersaturated solid solution -> Guinier Preston (G.P.) zones -> beta(B)'/beta' -> beta(1) -> beta. The age-hardening response of the Mg-Sm-Nd-Zn-Zr alloy is enhanced significantly by pre-deformation. (C) 2019 Elsevier B.V. All rights reserved.