Tetsuyuki Ikeda1 and Seiki Nishi2
1Graduate School, Nagoya University, Nagoya
The precipitation-decomposition process of a supersaturated Al-3%Mn solid solution, obtained by solidifying rapidly from the liquid state, is complicated but is of great interest as discussed in the previous report. In this paper, the changes of lattice parameter were analyzed by applying a simple nucleation-growth model for the precipitation of the supersaturated solid solution consisting of the network structure of cylindrical cells and assuming the manganese concentration profile in the matrix. Furthermore, the precipitation process and the decomposition process in the supersaturated solid solution were investigated. The results obtained were as follows:
(1) The precipitation processes of compounds containing manganese on isothermal heating were classified by the exponent m value in the Johnson-Mehl equation, and those values were m=5/2 for the early stage of the precipitation-decomposition process, m=1 for the middle stage and m=1/2∼1/3 for the last stage.
(2) The decomposition process of the supersaturated solid solution progressed in diffusion zones around precipitate zones at the early stage, and at the middle stage, in the inner part of cells. At the last stage, the manganese concentration in the matrix became almost homogeneous and the decomposition progressed at all parts of the matrix.
(3) At aging temperatures above 550°C the activation energy for precipitation of Al6Mn+G' was 40.7 kcal/mol, and below 550°C that of G+G'+G'' was 21.4 kcal/mol.
Please do not copy without permission.