QUATERNARY DIFFUSION IN THE ALPHA-SOLID-SOLUTIONS OF AL-ZN-MG-CU SYSTEM

Quaternary interdiffusion experiments of Al-rich alpha Al-Zn-Mg-Cu all oys have been performed in the temperature range from 755 to 833 K. Th e concentration profiles indicate that the diffusion distance of Cu is shorter than those of Zn and Mg in the solid solutions. The direct in terdiffusion coefficients (D) over tilde(ZnZn)(4), (D) over tilde(MgMg )(4) and (D) over tilde(CuCu)(4) are positive, and indirect coefficien ts are negative. The impurity diffusion coefficients of Zn (or Cu) in Al-Cu (or Zn)-Mg alloys can be expressed by the follwing equations. DZ n(Al-Cu-Mg) = 3.9 x 10(-5) exp (-124 kJ mol(-1)/RT-1) m(2)/s, DCu(Al- Zn-Mg) = 5.7 x 10(-5) exp (-132 kJ mol(-1)/RT-1) m(2)/s. From the rat io values of indirect coefficient to direct one, it is expected that a ttractive interactions of Zn-Mg, Zn-Cu and Cu-Mg atoms exist in the Al -Zn-Mg-Cu alloys.