Quaternary interdiffusion experiments were performed on Al-rich alloys at 755 to 833K. 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, DZnZn4, DMgMg4 and DCuCu4, were all positive and the indirect coefficients were all negative (table 4). The impurity diffusion of Zn in Al-1.15Cu-2.01Mg could be described by:

D (m2/s) = 3.9 x 10-5 exp[-124(kJ/mol)/RT]

and the impurity diffusion of Cu in Al-3.37Zn-2.75Mg could be described by:

D (m2/s) = 5.7 x 10-5 exp[-132(kJ/mol)/RT]

The ratios of indirect to direct diffusion coefficients suggested that attractive interactions between Zn-Mg, Zn-Cu and Cu-Mg atoms occurred in the quaternary alloys.

Quaternary Diffusion in the α Solid Solutions of Al-Zn-Mg-Cu Alloys. T.Takahashi, Y.Minamino, K.Hirao, T.Yamane: Materials Transactions, 1999, 40[9], 997-1004

Table 4

Interdiffusion Coefficients in Al-Zn-Mg-Cu Alloys