Al-Zn, Al-Ag and Al-Cu base ternary alloys were studied by measurement of electrical resistivity. An approximate methods to estimate the binding energy between an atom of a third element and a vacancy was derived. The binding energy between a vacancy and an atom of Cu, Ag, Au, Be, Ca, Cd, In, Si, Ti, Ge, Zr, Sn, Pb or Mn was estimated to be 0.35, 0.28, 0.27, 0.32, 0.39, 0.28, 0.30, 0.33, 0.33, 0.43, >0.38 or <0.23 (±0.05) eV, respectively. The results may be summarized as follows: (I) The ratio of the time required to reach the maximum electrical resistivity in isothermal aging curves of the Al-Zn-X or Al-Ag-X ternary alloy to that in the Al-Zn or Al-Ag binary alloy may be inversely proportional to the ratio of the concentration of vacancies bound to Zn or Ag atoms immediately after quenching in the ternary alloy to that in the binary alloy. And also the ratio of initial rate of clustering for AI-Cu-X ternary alloy to that in the binary alloy may be inversely proportional to the ratio of the concentration of vacancies bound to Cu atoms immediately after quenching in the ternary alloy to that in the binary alloy. It is possible to deduce the binding energy
between an atom of X element and a vacancy using this relations. (2) The effect of the valence of the solute element on the binding energy between an atom of a third element and a vacancy was remarkable. (3) The effect of the radius of an atom of the solute element on the binding energy is also observed, but this effect is smaller than that of the valence
