A First Principle Study On The Properties Of Clusters And Phases In Aluminum Alloy

Aluminum alloy has been widely used in industry because of its high specific strength,low density and excellent conductivity.According to chemical composition,aluminum alloy can be divided into Al-Si alloy,Al-Cu alloy,Al-Mg alloy,Al-Zr alloy,Al-Ni and Al-Re alloy etc..The 7000 series aluminum alloy is super high strength aluminum alloy.It can be strengthened by heat treatment.It is the aluminum alloy with the highest strength at room temperature and widely used in aerospace,transportation,automobile manufacturing and other fields.Clusters are relatively stable microscopic or sub-microscopic aggregates which composed of several thousands of atoms,molecules or ions by a combination of physical or chemical forces.Their physical and chemical properties vary with the number of atoms.It is possible to understand the stability,electrical,thermodynamic and mechanical properties of the multi-component system by analyzing the physical and chemical properties of the clusters.In this study,the structures,stability,growth mechanism,thermodynamic properties,electrical properties and mechanical properties of clusters and phases in aluminum alloys were studied by first principles based on density functional theory.The calculated results of Al-Cu alloy show that the Cu atom tends to convergence aluminum clusters to close-packed structures.The average binding energies of Al_nCu are slightly higher than that of Al_N clusters.Local peaks of the HOMO-LUMO gaps are found at n=1,4,6,and 9.Al_nCu clusters are easier to react with Al clusters.Cu atom prior reacts with Al atom.The calculated results of Al-Zr alloy show that the Al_nZr clusters are more likely to form the dense accumulation structures than the Al_N（N=1-10）clusters.The average binding energies of Al_nZr are higher than those of Al_N clusters.The Al_n Zr（n=3,5,and 7）clusters are more stable than others.The electron’s adsorption ability of Zr is slightly lower than that of Al except for AlZr cluster.Local peaks of the HOMO-LUMO gap curve are found at n=3,5,and 7.Zr atom preferential reacts with Al₂ cluster.Local peaks of the magnetic dipole moments are found at n=2,5,and8.The calculated results of Al-Ni alloy show that AlNi is the most anisotropic of all phase,Al₃Ni₂ is the most isotropic of all phase.In addition to Al₃Ni and Al₃Ni₂ are brittle materials,other intermetallics are tougher materials.Among which,AlNi has the best toughness,Al₃Ni₂has the best brittleness.The study of Debye temperature suggests that Al₃Ni has the highest Debye temperature,AlNi has the lowest Debye temperature.The calculated results of Mg-Zn clusters show that the Zn atoms tend to replace the Mg atoms which are far from the cluster center.The doped Zn atoms decrease the stability of Mg clusters.Mg₃Zn and Mg₃Zn₂ are more stable than their neighbors by the second derivative of the binding energies.NBO analysis reveals that there are orbital hybridization in the Mg-Zn clusters.The calculated results of Ni doped into Al₂Cu show that the stable structures can be formed are Al₇Cu₄Ni and Al₈Cu₃Ni.The toughness of Al₂Cu will be reduced and the brittleness will be increased.The results of anisotropy show that Al₂Cu has the the largest anisotropy,the anisotropy of Al₂Cu will be reduced after doping Ni.The Al₈Cu₃Ni has the highest Debye temperature,the Al₇Cu₄Ni has the lowest Debye temperature.