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Effect of Rare Earth Y and Ce on Properties of Ma-Al Based Alloy Via First-principles Calculation

Author: FuLi
Tutor: ZhaoYuHong
School: University of North
Course: Materials Science
Keywords: Mg-Al alloy Y Ce alloy effect First-principles
CLC: TG146.22
Type: Master's thesis
Year: 2014
Downloads: 15
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Abstract


As the lightest structural metallic materials, magnesium alloys have high specificstrength, high specific stiffness, and magnesium alloys have been extensively applied inautomotive, communication and aircraft industries. The current commercial use ofmagnesium alloys is mainly focused on the Mg-Al-based alloys, especially on the AM andAZ series, because these alloys combine good room temperature strength and ductility andexcellent castability. However, its lower strength and creep resistance at elevatedtemperature cause the poor heat resistance of magnesium alloy, which is the main factor oflimiting its application field. Rare earth as a kind of effective alloying elements, cansignificantly improve the comprehensive mechanical properties of magnesium alloys,expand the use area of Magnesium Alloy. It has been found that the addition of alloyingrare earth （RE） elements Ce and Y is one of the effective methods to optimize themicrostructure and improve mechanical properties of Mg-Al based alloys. For the sake ofcomprehending Mg-Al-Ce and Mg-Al-Y alloy, intermetallic compounds in these alloy hasbeen calculated by First-principles.Using first-principles method, obtain four better stability phase by analysis of differentatomic site in Mg-Al-Y-Ce alloy. The calculated cohesive energy indicate that the structurestability decrease in the sequence of AlY>MgY>AlCe>MgCe. In addition, The calculatedenthalpies of formation （ΔH） demonstrate that Al has better alloying ability than Mg withCe and Y elements in Mg-Al-Y-Ce alloy. the isotropic bulk modulus B, shear modulus G,Young modulus E and Poisson’ ratio υ of these phases are also calculated, lower the Cauchypressure and Poisson’ ratio υ is, better the brittleness is. the structural, electronic and mechanical properties under high hydrostatic pressure andthermodynamic properties of the hexagonal C14-Mg2Y （MgZn2） and face centered cubicC15-Al2Y （MgCu2） Laves phases have been analyzed by means of the first-principlesmethod based on the density functional theory. The obtained enthalpies of formation andcohesive energy at0Gpa show that Al2Y and Mg2Y have better alloying ability andstructural stability than that of Mg17Al12. The single-crystal elastic constants of Al2Y andMg2Y phases as a function of pressure are also predicted, including bulk modulus, shearmodulus, Young’s modulus, Poisson’s ratio, and universal elastic anisotropy index,implying that high hydrostatic pressure can be improved the mechanical properties withincertain ranges.the effect of pressure on the structural, electronic properties and mechanical propertiesof tetragonal Al4Ce phase have been analyzed by means of the first-principles method basedon the density functional theory within generalized gradient approximation（GGA）. Thecalculated equilibrium lattice parameters under zero pressure are in good agreement withthe previous experimental and other theoretical data. The obtained total density ofstate（TDOS） and partial density of states（PDOS） of Al4Ce at varying pressure indicate thatthis compound exhibits favorable metallic behavior. In addition, the isotropic bulk modulusB, shear modulus G, Young modulus E and Poisson’ ratio υ of Al4Ce at different pressurewere investigated by using the Voigt-Reuss-Hill averaging scheme. The results demonstratethat the Al4Ce phase is ductile according to the analysis of BH/GHand has good mechanicalstability. Finally, the Debye temperatures（ΘD） is also obtained from the elastic constantsincrease with increasing pressure.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metallic materials > Non - ferrous metals and their alloys > Light non-ferrous metals and their alloys > Magnesium
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