MODELING OF GRAIN-BOUNDARY SEGREGATION, PRECIPITATION AND PRECIPITATE-FREE ZONES OF HIGH-STRENGTH ALUMINUM-ALLOYS .1. THE MODEL

The earlier combined model [Faulkner and Jiang, Mater. Sci. Technol. 9 , 665 (1993)] is improved by means of modifying the kinetics of segreg ation and taking into account the nucleation of grain boundary precipi tates, the precipitate growth and coarsening. The newly developed mode l predicts the influence of the heat treatment on the widths of precip itate-free zones, the growth rate and the dispersion of the precipitat es on the grain boundaries during the growth of precipitates. It also predicts the critical time when coarsening begins, the size and disper sion of precipitates on the grain boundaries during coarsening. The ap plication of the model in predicting the size and inter-particle spaci ng of MgZn2 grain boundary precipitate and the widths of precipitate-f ree zones in 7150 aluminium alloy as a function of heat treatment is d iscussed in Part I of this paper, and the comparison of the predicted and experimental results will be addressed in Part II.