The initiation and growth kinetics of discontinuous precipitation in an Al-14.6at% Zn alloy were investigated at temperature range from 70℃ to 220℃ by measuring cell growth rate, interlamellar spacing and degree of segregation of a cell using resistometric technique, light microscopy, and X-ray diffraction. Particular emphasis was placed on the influence of teh continuous precipitation on the initiation and growth kinetics of discontinuous precipitation.
Resistivity decrement of specimen during aging was directly proportional to the degree of decomposition. Using resistometric technique, TTT curve of continuous precipitation could be extracted from the total transformation kinetics, and the degree of segregation of α cell was calculated successfully.
Increasing solution treatment temperature in the range of 350℃ to 450℃, decrease the degree of decomposition of specimen at the beginning of aging. The initiation and growth kinetics of the discontinuous precipitation are faster in the case of lower solution treatment temperature.
At high aging temperature, considerable volume diffusion occurs in depleted α cell, which affects significantly the degree of segregation.
Consideration of the effects of continuous precipitation and volume diffusion in depleted α cell results in a more accurate estimation of grain boundary diffusivity.
The critical temperature for the growth of cellular structure was interpreted in terms of competition between the discontinuous and continuous precipitation.
