Solid-Solution Hardening in Mg-Gd-TM (TM = Ag, Zn, and Zr) Alloys: An Integrated Density Functional Theory and Electron Work Function Study

The current work aims to reveal the effects of solute atoms (TM = Ag, Zn, and Zr) on the age hardening of Mg-Gd-based alloys via the density functional theory and electron work function (EWF) approaches. The 10H LPSO phases of Mg-Gd-TM alloys are selected as the model case due to the improved strength and ductility such long periodic stacking ordered precipitates (LPSOs) offer. The CALPHAD-modeling method is applied to predict the EWF in the ternary Mg-Gd-TM alloys. The obtained EWFs of these Mg alloys are shown to match well with previous experimental and theoretical results. Moreover, the variation of EWF in the ternary Mg-Gd-TM alloys is attributed to the structure contribution [i.e., the formation of face-centered cubic (fcc)-type fault layers] and the chemical effect of solute atoms (i.e., electron redistributions). With the knowledge of bonding charge density between the solute and solvent atoms, the present work provides insight into the correlations between the EWF and hardness of Mg-Gd-TM alloys.