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.
Here, we show the strategies to strengthen Mg alloys through modifying the matrix by planar faults and optimizing the local lattice strain by solute atoms. The anomalous shifts of the local phonon density of state of stacking faults (SFs) and long periodic stacking-ordered structures (LPSOs) toward the high-frequency mode are revealed by HCP-FCC transformation, resulting in the increase of vibrational entropy and the decrease of free energy to stabilize the SFs and LPSOs. Through integrating bonding charge density and electronic density of states, electronic redistributions are applied to reveal the electronic basis for the 'strengthening' of Mg alloys. IMPACT STATEMENT Through integrating the bonding charge density, the phonon and electronic density of states, this work provides an atomic and electronic insight into the strengthening mechanism of Mg alloys.
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