From slip resistance control to on-demand tuning of strength and ductility through solute engineering in Mg-Mn-X solid solutions

The understanding of synergistic solid-solution strengthening and ductilizing (SSSD) effects in Mg-Mn-based alloys remains limited, hindering the on-demand tuning of strength and ductility. In this study, first-principles calculations combined with the Peierls-Nabarro (P-N) model were employed to systematically investigate the role of non-rare-earth solutes (Zn, Sn, Ca, and Li) in regulating dislocation slip behavior in Mg-Mn-X alloys. The results demonstrate that all selected solutes promote pyramidal slip by reducing the slip resistance gap relative to basal slip, while Ca and Li activate prismatic slip, and Zn and Sn strengthen the alloys by increasing basal slip resistance. Further analyses indicated that the reduction in stacking fault energy (SFE) in Mg-Mn-Ca is dominated by lattice distortion, whereas SFE in Mg-Mn-Zn is primarily governed by charge redistribution effects. Experimental validation on representative Ca- and Zn-containing alloys was consistent with the theoretical predictions, showing a 110% increase in ductility with Ca addition and a 20% increase in strength with Zn addition. Slip trace analysis and double-beam TEM observations further confirmed the corresponding activation of the slip systems. These findings provide guidelines for designing high performance Mg-Mn based materials through optimized solute selection, enabling the on-demand tuning of strength and ductility.