Quaternary interdiffusion experiments were performed on Al-rich a-phase alloys at temperatures ranging from 755 to 833K. The concentration profiles indicated that the diffusion distance of Cu was shorter than that of Zn or Mg in the solid solutions. The direct interdiffusion coefficients, DZnZn4, DMgMg4 and DZnZn4, were positive and the indirect coefficients were negative (table 3). The impurity diffusion coefficients could be described by:

DZn(Al-Cu-Mg) (m2/s) = 3.9 x 10-5 exp[-124(kJ/mol)/RT]

DCu(Al-Zn-Mg) (m2/s) = 5.7 x 10-5 exp[-132(kJ/mol)/RT]

It was deduced, from the ratios of the indirect coefficients to the direct ones, that attractive interactions existed between Zn-Mg, Zn-Cu and Cu-Mg atoms.

Quaternary Diffusion in the a Solid Solutions of the Al-Zn-Mg-Cu System. T.Takahashi, K.Miura, Y.Minamino, K.Hirao, T.Yamane: Journal of the Japan Institute of Metals, 1998, 62[10], 905-11

Table 3

Interdiffusion Coefficients of Quaternary Al-Zn-Mg-Cu Alloys