ANALYTICAL APPROACH TO PARTICLE DISSOLUTION IN A FINITE MEDIUM

An important part in the total production process of extrudable alumin ium alloys is the homogenisation treatment of the as cast billets befo re hot extrusion. During this homogenisation treatment several microst ructural changes take place. The most important changes are the dissol ution of the precipitates formed during solidification and the homogen eous redistribution of alloying elements. Modelling of the particle di ssolution in simple binary systems has recently been achieved by Tunda l and Ryum using a numerical model. In their model a moving interface between the particle and the aluminium rich matrix was taken into acco unt as well as the finite size of the cell in which the particles diss olve. Furthermore, conditions of local equilibrium at the particle/mat rix interface were assumed at all stages of the dissolution process. T his was a significant improvement to earlier analytical models in whic h the interface was assumed to be stationary. The present work describ es the development of a semianalytical model for the dissolution of sp herical particles in finite media also assuming a moving boundary. The results of the present semianalytical model are compared to those of the numerical model. A fairly good agreement was obtained for most con ditions. At long dissolution times the predictions of the two models d eviate due to a simplifying assumption used in the analytical model.