The electronic theory of the mechanism of the role of Sc in Al-Zn-Mg-Cu ultra high strength aluminium alloys

Abstract

The atomic cluster models of α-Al, Al3Sc,η phase in Al-Zn-Mg-Cu ultra high strength aluminum alloys have been constructed by cell translation and the atomic cluster models of the interfaces α-Al /liquid Al and α-Al /Al3Sc have been set up by self-programmed software. The electronic structure parameters such as the density of states, the bonding energy of atom, the Fermi energy of the microscopic structure in alloys, the interaction energy between Sc and vacancy, have been calculated by recursion method. The physical nature of grain refinement and corrosion behavior of Al-Zn-Mg-Cu alloys has been explained according to the calculated electronic structure parameter. The results show that the energy given off by Al3Sc precipitating from liquid Al is less than that by α-Al and Al3Sc can precipitate from liquid Al prior to α-Al. Because of the lower interface energy of α-Al /Al3Sc compared with α-Al /liquid Al, the Al3Sc phase may offer the condition for the nucleation and growth of α-Al, which increases the nucleation rate of α-Al and refines the grain. The calculated results also indicate that Sc can attract the vacancy, decreasing the diffusion ability of vacancy and solute atoms, which makes the precipitate free zone along grain boundaries become narrower, and decreases the potential difference between grain and grain boundary, leading to the improvement of the corrosion resistance.