Ductility improvement of Mg alloys by solid solution: Ab initio modeling, synthesis and mechanical properties

The I1 intrinsic stacking fault energy (I1 SFE) serves as an alloy design parameter for ductilizing Mg alloys. In view of this effect we have conducted quantum–mechanical calculations for Mg15X solid-solution crystals (X = Dy, Er, Gd, Ho, Lu, Sc, Tb, Tm, Nd, Pr, Be, Ti, Zr, Zn, Tc, Re, Co, Ru, Os, Tl). We find that Y, Sc and all studied lanthanides reduce the I1 SFE and render hexagonal closed-packed (hcp) and double hcp phases thermodynamically, structurally and elastically similar. Synthesis, experimental testing and characterization of some of the predicted key alloys (Mg–3Ho, Mg–3Er, Mg–3Tb, Mg–3Dy) indeed confirm reduced I1 SFEs and significantly improved room-temperature ductility by up to 4–5 times relative to pure Mg, a finding that is attributed to the higher activity of non-basal dislocation slip.