Doping and adsorption mechanism of modifying the eutectic Mg_2Si phase in magnesium alloys with rare earth elements: A first-principles study

摘要

Modification mechanism of the rare earth elements (RE = La, Ce, Nd and Sm) on the eutectic Mg2Si phases investigated by experiments and theoretical calculations in this work. Experimental results indicate that La has the best modification effect on eutectic Mg2Si. The properties of RE atoms doping and adsorption on Mg2Si(1 0 0) and (1 1 1) surfaces were calculated by first-principles calculation method. Results show that Nd atom exhibit the greatest doping effect on Mg2Si(1 0 0), whereas La atom is most likely to dope on (1 1 1) surface rather than (1 0 0) surface. RE atoms are prefer to be adsorbed at vacancy site on (1 0 0) surface and H2 site on (1 1 1) surface. And the adsorption energies of both vacancy and H2 sites are in the order of La < Ce < Nd < Sm. Both theoretical and experimental results suggest that adsorption should be the primary reason of modifying the eutectic Mg2Si phase in magnesium alloy with addition of RE elements La, Ce Nd and Sm. And the best modification effect on eutectic Mg2Si phase can be achieved with the addition of La element.