| The influence of solidification condition on solute redistribution (that is, microsegregation) in dendritic growth was investigated with unidirectionally solidified Al-8% Mg alloy. The aim of the present investigation is to interpret the mechanism of the solute redistibution determined as a function of the fraction of solid which is given by two dimensional solidification model, and moreover to provide the quantitative data of the microsegregation and the microstructure in alloys of engineering interest in order to explain the homogenization process. For this purpose XMA analysis for a dendrite element at each distance from the water cooled copper chill face was made. The results obtained are as follows; 1) The segregation index (S) decrease by increasing the solidification rate (R), and the S between primary dendrite arms is more remarkable than that between secondary dendrite arms. 2) Minimum Mg solute concentration is demonstrated at the center of primary dendrite stalk, and increase by increasing solidification rate R(that is, decreasing distance from the chill face) 3) The degree of microsegregation (included β-phase) in Al-8% Mg alloy was determined by the change of the effective partition coefficient Ke. 4) The influence of diffusion layer on the solute movement ahead of the solid-liquid interface near the dendrite tip which was not obtained by means of the prior linear analysis was clearly demonstrated by determining the fraction of solid from two dimensional solidification model, and it was found that the diffusion layer has a remarkable effect upon the solute redistribution. The degree of microsegregation was dependent upon the change of the effective partition coefficient with the change in the rate of solidification, and could be interpreted quantitatively by the partially mixed liquid model. |
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