Mechanical Propertiles Of Mg Binary Alloy In Solid Solution State By First Principles

With the rapid development of computer technology and numerical algorithm, the algorithmic method of first-principles based on the density functional theory has become an important mean for studying material properties, which is universally acknowledged in studying lattice defect, phase stability and effectivity of mechanical property of materials. In this paper, the method of first-principles is adopted for mechanical property and energy calculation of magnesium (Mg) solid solution binary alloy which is tested difficultly in practical situation. The study mainly includes calculation and analysis of elastic constant, determination of rigidity and ductility, analysis and forecast of the electron structure, and other aspects of the alloy. The above calculation provides theoretical basis and foundation for Mg alloying.Chapter 1 briefly introduces the basic framework of the computational materials science and the development situation of the first-principles based on the density functional theory, as well as the basic information of magnesium and magnesium alloy. Besides, the CASTEP software applied in the calculation is introduced at the end of the paper.Chapter 2 mainly introduces the preparation work before the calculation. Firstly, it is ensured that the alloy is substitution solid solution, and a computational model is ensured through calculating vacancy formation energy; secondly, the calculation accuracy is ensured through calculating singleton energy of fives elements, namely, Al, Ca, Li, Sc and Y; and finally, the calculated value of elasticity modulus of pure magnesium is compared with the experimental value so as to prove that the result is more or less the same with the experimental value and is true and believable.In cheaper 3, the mechanical property of the five binary alloys is concluded through two aspects of electron structure analysis and elastic constant analysis. Firstly, the electron structure of the alloy is analyzed through the DOS, the difference electron density plot and the population value, so that it can be predicted that Y has the best performance in the improvement of the mechanical property of Mg and can improves the hardness of Mg while maintaining the extensibility of the alloy; Al hardly changes the alloy, so that the alloy keeps good metallicity; and the three elements of Sc, Ca and Li will greatly improve the hardness of the alloy, but the extensibility of the alloy is reduced after the alloy is mixed. Afterwards, the influence to the mechanical property of Mg alloy is obtained through judging five elastic constants of the solid solution alloy and four extensibilities, and the conclusion is identical with the prediction. Finally, the stress-strain curve of the five solid solution alloys is simulated by a computer, so that the theoretical elastic modulus of the alloy is obtained, and the result is the same with the calculated value.In cheaper 4, the influence of elements of different contents to the mechanical property of the alloy is analyzed through the VCA method. The solid solution alloy containing the five elements Al, Ca, Li, Sc and Y with different contents is mixed in the Mg basal body, and the influence to the mechanical property of the alloy is calculated as the contents change. Through the calculation, within the range of solid solubility limit, the extensibility of Mg-Al alloy is good, and the hardness is increased by a small margin; the mixing of Ca is kept below 0.3 at.%; the Mg-Li alloy formsβphase and has good extensibility in case of above 16.7 at.% and forms a phase and shows brittleness in case of below 16.7 at.%; the hardness of the alloy can be improved by mixing a little Sc; and when the Mg alloy is mixed in the element Y with the mixing below 3 at.%, the hardness of the alloy can be improved, and the extensibility of the alloy can be well maintained.