ENGULFMENT OF AL2O3 PARTICLES DURING SOLIDIFICATION OF ALUMINUM-MATRIX COMPOSITES

Through the analysis of forces acting on the particles at the solid/li quid interface based on the interfacial energies, we propose a new the oretical particle transfer model. This model can predict the behavior of the particles at the interface. The main concept of this model is p roved by the mutual wetting behavior among the solid, liquid and parti cle phases. If the contact angle at a solid/liquid interface and a par ticle is < 90 degrees, the particle can be engulfed into the solid, an d if the contact angle is > 90 degrees, the particle would be pushed. This contact angle is measured by unidirectional solidification (UDS) experiments. But if solidification experiments were carried out for pa rticle dispersed composites in a conventional UDS, the particles compl etely descended before freezing, therefore, a zone-UDS was used in the experiment. In Al-Sr, Al-Ca and AI-Ce matrix composites, Al2O3 partic les are pushed by the solid because the contact angles are > 90 degree s. On the other hand, in Al-12.6wt.%Si-Sr-Al2O3 composites alloyed wit h Ca, the Al2O3 particles are engulfed into the solid because the cont act angle is < 90 degrees. (C) 1998 Elsevier Science S.A. All rights r eserved.