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

Abstract Precipitation evolution of pre-deformed Mg-5Sm-1.4Nd-0.4Zn-0.5Zr alloy during aging at 200 °C was investigated by using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). A long lamellae β B ′ phase was found in the pre-deformed alloy. The β B ′ phase has a disordered hexagonal structure, and the closely packed planes in β B ′ have the ABCA stacking sequence with Sm, Nd and Zn atoms in B and C planes. The β B ′ precipitating on basal plane and β′/β 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 → β B ′/β′ → β 1  → β. The age-hardening response of the Mg-Sm-Nd-Zn-Zr alloy is enhanced significantly by pre-deformation.