Nano-steps in long-period stacking ordered structures for ductility asymmetry of a strong-textured Mg-Gd-Zn alloy

Ductility asymmetry in extruded Mg alloys containing dense thin long-period stacking ordered (LPSO) plates was always ignored although with yield symmetry. Here, an extruded Mg97.3Gd2.1Zn0.6 alloy of <1%-vol% recrystallization exhibits strong ductility asymmetry at room temperature. Atomic-resolution aberration-corrected scanning transmission electron microscopy (STEM) observations reveal plenty of deformation steps in LPSO plates engulfed by {101¯2} twins which reflect great contribution to the compressive ductility. One/two/three/four-basal-layer high steps with different associated dislocations were observed although the two-basal-layer high step is the most frequently observed. Their formation mechanisms were modeled based on atomic-resolution STEM observations and are the results of the interaction of interfacial partial dislocations with basal partial dislocations in LPSO blocks. The results expand fundamental insights into the deformation modes and mechanisms of thin LPSO plates and, also, provide well understanding the ductility asymmetry of extruded Mg alloys containing LPSO plates.