Asymmetric tilt boundaries on conventional twin boundaries (TBs) are significant for understanding the role of twins on coordinating plastic deformation in many metallic alloys. However, the formation modes of many asymmetric tilt boundaries are hard to be accounted for based on traditional theoretical models, and the corresponding solute segregation is complex. Herein, atomic structures of a specific asymmetric boundary on {1012} TBs were reveled using aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), molecular dynamics (MD) and density functional theory (DFT) simulations. Reaction between <a₆₀>_M dislocations and the {1012} TB can generate a ~61°/25° asymmetric tilt boundary. The segregation of Gd and Zn atoms is closely related to the aggregated <a> dislocations and the interfacial interstices of the asymmetric tilt boundary, which is energetically favorable in reducing the total system energy.

This work reports an exceptional reversed yield strength asymmetry at room temperature for a rare-earth free magnesium alloy containing a mass of fine dispersed quasicrystal (I-phase) precipitates. Although exhibiting traditional basal texture, it owns an exceptional CYS/TYS as high as ~1.17. Electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM) examinations indicate pyramidal < c + a > and prismatic < c > dislocations plus tensile twinning being activated after immediate yielding in compression while basal and non-basal < a > dislocations in tension. I-phase particles transferred the concentrated stress by self-twinning to provide the driving force for tensile twin initiating in neighboring grains, thereby significantly increasing the critical resolved shear stress of tensile twinning to possibly the level of pyramidal < c + a > slip, finally leading to the dominance of pyramidal < c + a > slip plus tensile twinning in texture grains. This results in a higher contribution on yield strength by ~55 MPa in compression than in tension, which reasonably agrees with the experimental yield strength difference (~38 MPa). It can be concluded that I-phase particles influence deformation modes in tension and in compression, finally result in reversed yield strength asymmetry.

Instantaneous reactions of Al, Mn, Zn, Zr and Y with Ni by mixing the prepared Mg-8Al-0.4Mn, Mg-6Zn-2Y-0.5Zr and Mg-0.6Ni melts were investigated in this work to reveal the underlying mechanisms of their effects on the removal of Ni impurity. The results indicate three Ni-containing intermetallics, namely Al₄NiY, Al₄Ni(Y,Zr) and Al₃₁Ni₂Mn₆. The former two phases present lath-like and have a relatively larger size (> 20 µm in length) than the latest one which is granular with the diameter of ~120 nm. This illustrates that Al and Y(/Zr) can efficiently remove Ni by forming Al₄NiY or Al₄Ni(Y,Zr) which would precipitate to the bottom of the melt. Furthermore, adding Y into Mg-Al based alloys can simultaneously remove Fe and Ni, which contributes their excellent corrosion resistance. Finally, this paper proposes two methods helped to efficiently remove Ni for both Mg-Al based alloys and Al-free Mg alloys, and both of them are also benefit to improve alloys’ strength.