Engulfment of Al2O3 particles during solidification of aluminum matrix composites

Through the analysis of forces acting on the particles at the solid/liquid interface based on the interfacial energies, we propose a new theoretical particle transfer model. This model can predict the behavior of the particles at the interface. The main concept of this model is proved by the mutual wetting behavior among the solid, liquid and particle phases. If the contact angle at a solid/liquid interface and a particle is <90°, the particle can be engulfed into the solid, and if the contact angle is >90°, the particle would be pushed. This contact angle is measured by unidirectional solidification (UDS) experiments. But if solidification experiments were carried out for particle dispersed composites in a conventional UDS, the particles completely descended before freezing, therefore, a zone-UDS was used in the experiment. In Al–Sr, Al–Ca and Al–Ce matrix composites, Al2O3 particles are pushed by the solid because the contact angles are >90°. On the other hand, in Al–12.6wt.%Si–Sr–Al2O3 composites alloyed with Ca, the Al2O3 particles are engulfed into the solid because the contact angle is <90°.