Quaternary and ternary interdiffusion experiments on AA7000 Al alloys were performed at 725 and 755K. The concentration profiles indicated that the diffusion distance of Cu was shorter than those of Zn or Mg in the solid solutions. The direct interdiffusion coefficients, DZnZnAl and DMgMgAl, were positive and the indirect coefficients, DZnMgAl and DMgZnAl, were negative in the ternary alloys. The effective interdiffusion coefficients in AA7000 alloys were in the order: DZn,C > DMg,C > DCu,C. When the concentration distributions of Zn and Mg were almost constant and the concentration of Cu approached zero in an Al-Zn-Mg/Al-Zn-Mg-Cu couple, it became obvious that DCu,C = DCuCu4 = DCu(Al-Zn-Mg)*. The ratio of the values of the indirect to direct diffusion coefficients suggested that attractive interactions of Zn-Mg and Cu-Mg occurred in Al-Zn-Mg-Cu alloys.

Quaternary Diffusion in 7000 Aluminium Alloys. T.Takahashi, Y.Minamino, T.Yamane: Materials Transactions, 2002, 43[2], 232-8