Atomic bonding of precipitate and phase transformation of Al–Cu–Mg alloy

Atomic bonding of the GPB zone and S″ phase of Al–Cu–Mg alloys in early aging stage are calculated using the empirical electron theory (EET) in solid. The results show that not only the covalence bond-network is very strong in GPB zone, but the whole covalence bond energy of S″ phase is also very large, and all the primary bond-net framework of these precipitates can consolidate the matrix of alloy. Phase transformation from GPB zone to S″ phase is explained reasonably based on atomic bonding and total binding capacity of Al and Cu atoms in these precipitates.