Al-Mg-Si Alloy Structure Characteirzation And Its Thermodynamic Properties Calculation

Al-Mg-Si (6xxx series) aluminum alloy has small density, high strength, goodplasticity, good adornment and good formability. As a kind of high plasticity and a typeof heat treatment strengthen available aluminum alloy, it has been widely used in aviationindustry, construction industry, automobile industry and everyday life. It occupies mostof the world’s aluminum alloy market proportion. Therefore, the thesis Al-Mg-Si alloystructure characterization and its thermodynamic properties calculation" is of importanttheoretical significance and value.In this article, the Al-Mg-Si alloy was prepared first and material proportion wasselected as Al-0.8%Mg-0.6%Si. In the characterization of the sample, there are threemain means to observe and analyze the sample, namely transmission electron microscope(TEM), high-resolution transmission electron microscopy (HRTEM) and selected areaelectron diffraction picture (SADP) respectively. On this basis, phase change law in theaging process of Al-Mg-Si alloy is studied and alloy ageing precipitation sequence isobtained. Based on density functional theory and the first principles calculation, the heatof formation and binding energy of several typical mesophase in Al-Mg-Si alloy are insimulated calculation. Through the analysis of calculation results, it shows that among thethree typical phase Mg2Si, Mg5Si6and Mg17Al12in Al-Mg-Si alloy, Mg2Si phase ispreference to other phase precipitation in alloy solidification process, and its structure isstable, it is the main strengthening phase. in order to control the performance of the Al-Mg-Si alloy from nano scale and atomic scale, the thermodynamic properties of Mg2Siphase is calculated further in this paper, and get the equilibrium lattice constant elasticitycoefficient, the phonon spectrum and density of states and related thermodynamicparameters of Mg2Si phase. Through the calculating we know that Mg2Si crystal hasgood rigidity, strong brittleness. There are nine dispersion relation curve in Mg2Si crystal,3of them are acoustic waves,6of them are optical waves, and vibration of the latticewave is stronger around8.51THz. With the increase of temperature, entropy andenthalpy of Mg2Si crystal are increasing while free energy reducing; When the temperature is under200K, the heat capacity significantly increased with the increase oftemperature, After the temperature reaching to400K, the heat capacity was closed to beconstant. The calculation result is consistent with the laws of physics.In this paper, the conclusion of experiment and calculation provides the beneficialreference for the related theory research and application.