Determination of the Effective Vacancy Concentrations and the Vacancy Losses after the Quench of Al–Zn–Mg Alloys

On the basis of

• 1 the experimental observation of dislocation loops by means of TEM,
• 2 the conclusion from this that the concentration of vacancies in the dislocation loops exists at the cost of the vacancy concentration primarily present at T_q, and
• 3 the inversion of the decomposition kinetics of Al–Zn–Mg alloys found out by means of resistivity and microhardness measurements, the effective vacancy concentration c_v.eff being at disposal for the GP-zone formation was found out by means of the relation t_R,max (t_R,max being the time required to reach the maximum of resistivity) and the Arrhenius plot In t_R,max = f(1/T_q) of the isothermal resistivity measurements. From the comparison of c_v.eff with the theoretical V concentration at T_q it is possible to derive statements about the loss of vacancies during and after the quench through loop formation, building-in of vacancies in GP-zones and annealing of vacancies at lattice defects. From this comparison follows:
  • The ideal ZnV concentration at T_q (calculated by means of the Lomer equation) is sufficiently great to account for the effective vacancy concentration.
  • The part of c_MgV in the loss concentration is rising with increasing c_Mg.
  Both these statements support the hypothesis that the initial process of the decomposition in Al–Zn–Mg alloys is caused by the ZnV diffusion.