Grain-Boundary Segregation and Corrosion Mechanism of Al-Zn-Mg-Cu Ultra High Strength Aluminum Alloys

The atomic cluster models of alpha-Al, eta phase and large angle grain boundary of a-Al with eta phase in Al-Zn-Mg-Cu alloys have been founded by a computer program. The environment-sensitive embedding energy, and the atom action energy of Zn, Mg, Cu and the atom binding energy, the fermi energy of alpha-Al and/or eta phase have been calculated by a recursion method. The corrosion character of Al-Zn-Mg-Cu alloys has been studied according to the calculated electronic parameter. The results show that Mg and Zn elements are easy to segregate on grain boundaries, and to form eta phase. The eta phase on grain boundary are large then that in grain due to the segregation of Mg in the grain boundary. The calculated results indicate that the fermi energy of 17 phase is the highest, will be decomposed firstly in the corrosion as an anode. The alloy element Zn has the function to increase the electrode potential difference between grain boundary and grains, to deteriorate the corrosion character of alloys. The alloy element Cu can reduce the difference of Fermi energy and the potential difference between grain and grain boundary, so as to slow down the corrosion process.