INFLUENCE OF AGING ON DISCONTINUOUS DISSOLUTION IN AL-22AT-PERCENT-ZNALLOY

The influence of prior aging and volume diffusion on the kinetic param eters of discontinuous dissolution were studied in Al-21.55at.%Zn allo y. The following kinetic parameters were considered: the critical temp erature of discontinous dissolution T(cr), the rate of discontinuous d issolution V(d)1, the diffusivity KD(b,m)lambda at the boundary of rec eding cells, and the activation energy of discontinuous dissolution. A new method of calculation of KD(b,m)lambda is proposed. It is conclud ed that T(cr), V(d)1, and KD(b,m)lambda are strongly affected by the c onditions of prior aging. The estimated diffusivities for discontinuou s dissolution are more than two orders of magnitude smaller than those for diffusion at stationary grain boundaries. This result is caused b y volume diffusion ahead of the precipitation front and within alpha-p hase lamellae. However, the discontinuous dissolution is still control led by diffusion at the boundary of receding cells. The influence of a ging temperature and volume diffusion on KD(b,m)lambda values was foun d to be connected with the change in pre-exponential factor in the Arr henius equation.