An electronic approach to the G.P. zone formation requirement in magnesium and aluminum light metals

The characteristics in electronic states were investigated by DV-Xα method, which could describe the cluster models for both solid solution (cluster model I) and for G.P. zone (cluster model II) of Mg/Al alloys, Mg-M (M; Al, Ag, Zn) alloys and Al-M (M; Mg, Ag, Zn) alloys. The bond order in the cluster model II for G.P. zone increased more than that in the cluster model I for solid solution in the specific alloy systems where the formation of G.P. zone was detected experimentally. Furthermore, the net charge in the cluster model I for solid solution indicated the significant different characteristics from that in the cluster model II for G.P. zone. By changing the bonding length of each cluster model, the local density of the states around the vicinity of Fermi energy varied high sensitively in FCC cluster models (I and II) of Al-Mg alloy, but not so much in HCP cluster models (I and II) of Mg-Al alloy. The energy gap between HOMO and LUMO was recognized from the consideration of the bond contraction of the cluster model II for G.P. zone, which suggesting the increment in electrical resistance because of the formation of G.P. zone.