The Solid Solutions And Precipitations In Several Mg-based Binary Alloys:First-Principles Determination

Magnesium alloy,which is the lightest commonly used structural metal,has promising applications in many fields including aircraft,aerospace and automotive industries.However,the poor mechanical properties seriously restrict the applications and development of magnesium alloy.Alloying can significantly improve the limited mechanical properties of magnesium alloy.Therefore,a study on the solid solution and precipitation strengthen of alloy elements of Mg-based alloys has an significantly practical meaning.Devoted to the design of high strength and toughness light-weight magnesium alloy,we systematically investigated the the compositions,structures,and mechanical properties of the solid solutions and stable/metastable precipitations in several Mg-based binary alloys.First-principles calculations have been carried out to study the stability,elastic properties and ideal shear strength of Mg52RE2(RE = Sc,Y,Gd-Tm)solid solutions;and the compositions,structures,and elastic properties of the precipitations in Mg-X(X = Sn,Sc,Y,Ag)binary systems.From electronic and atomic level,we put forward some suggestions on the design of compositions,structures,and mechanical properties for novel magnesium alloys.The main conclusions are as follows:(1)Within the solid solubility,the stability,elastic properties and ideal shear strength of Mg52RE2(RE = Sc,Y,Gd-Tm)are studied.It was found that Mg52RE2(RE = Sc,Y,Gd-Tm)are thermodynamically and mechanically stable alloy systems.The bulk modulus and hardness of Mg52RE2 strongly depend on the degree of localization of valence electron orbitals of solute atoms.Based on the study of ideal shear stress-strain relations,we propose that the addition of RE elements into Mg lattice increases the shear strength and anisotropy of mechanical property,but reduces the strain of deformation-to-failure.Mg52Sc2 alloy has the highest hardness and strength,while Mg52Gd2 alloy has the best ductility.(2)Using ab-initio evolutionary algorithm,the compositions,corresponding structures and elastic properties of stable or metastable precipitations in the binary Mg-X(X = Sn,Y,Sc,Ag)alloys are predicted.Our predictions are well consistent with the existing phase diagrams but further yield potential phases and their crystallographic informations.Toward designing high strength and toughness light-weight Mg alloys,Mg-Ag alloy exhibits the larger bulk modulus and ductility when Ag composition increases,and the Mg-Sc alloy should be a promising candidate to meet the comprehensive strength,weight,economy,and efficiency requirements.Taking both solid solution strengthen and precipitation strengthen into consideration,Sc is a promising alloy element for the strengthen of Mg-based alloy.