Solid Solution Softening Mechanisms in Mg-Ca Alloy

Abstract

In the present work, electronic structures of pure Mg, Mg-Ca and Mg-Al alloys were investigated by first-principle calculations. The charge density between the solute and solvent atoms in the Mg-Ca alloy was lower than that in the Mg-Al alloy. The local charge density of states (LDOS) of Mg atom in the Mg-Ca alloy was almost the same as the LDOS of the Mg atom in the pure Mg, suggesting that the solute Ca atoms had little effect on the Mg-Mg bonding in the Mg-Ca alloy. On the other hand, there is more and deeper valley in the LDOS of the Mg atom in the Mg-Al alloy, compared with that in the Mg-Ca alloy, suggesting that the solute Al atom may increase the covalency of the Mg-Mg bonds. A series of the calculations indicates that Ca atoms enhance the formation of double kinks rather than hinder the movement of dislocations, resulting in solid solution softening of Mg-Ca alloy.

Modified embedded-atom method interatomic potentials for Mg–X (X=Y, Sn, Ca) binary systems

“…higher-level calculation is available for the (0001)[10-10] GSFE of Mg-Ca alloys. However, first-principles calculation shows that the addition of Ca decreases the I 2 SFE and USFE [21][22][23], and also the GSFE along the [ À 2110] direction [71] on the basal plane, which is qualitatively in accordance with the present calculation. The biggest discrepancy comes from the Mg-Sn alloys.…”

Mechanical, thermal, and physical properties of Mg–Ca compounds in the framework of the modified embedded-atom method

“…5 and compared to the data reported by Chino et al (2011). In the case of pure Mg, the magnitude of the unstable stacking predicted using the MEAM potential is overestimated by 25% compared to the DFT prediction of Chino et al (2011). As a consequence, the lattice friction on the basal plane one could evaluate in the MEAM framework is expected to be overestimated compared to experimental data.…”

“…The evolution of the energy per area as a function of the normalized shear, u/b, where b is the magnitude of the burgers vector, is plotted in Fig. 5 and compared to the data reported by Chino et al (2011). In the case of pure Mg, the magnitude of the unstable stacking predicted using the MEAM potential is overestimated by 25% compared to the DFT prediction of Chino et al (2011).…”

“…To gain insight into the fundamental understanding of solid solution softening in magnesium alloys, Chino et al (2011) calculated the (0002) generalized stacking fault energy curves along the <-2110> direction for pure Mg and Mg-Ca alloys. For pure magnesium, their calculations were performed using a model made of 40 atoms distributed over 10 layers along the <0001> direction, whereas a Ca atom substituted one Mg atom adjacent to the slip plane in pure magnesium for calculating the generalized stacking fault in MgCa.…”

“…As first-principle calculations provide the most reliable information on atomic-scale materials properties, a large number of theoretical studies based on density functional theory (DFT) were carried out to: (i) Identify the effect of Ca on the microscopic properties of dilute Mg-Ca alloys (Chino et al, 2011;Zhang et al 2014;Shang et al, 2014;Moitra et al, 2014); and (ii) Determine new possible ordered Mg-Ca alloys with different concentrations of Ca (Yu et al, 2009;Zhou and Gong, 2012;Zhang et al 2012;Mao et al, 2014). However, due to the limited number of atoms that can be considered in DFT calculations, large-scale simulations are required to predict/model the inelastic behavior of the alloys (either ordered or dilute solution), and to identify mechanisms occurring during mechanical deformation.…”