Characteristic of cellular microstructure evolution for Al-0.85wt%Cu alloy during directional solidification

Directional solidification experiments were carried out on Al-0.85%Cu alloy under different withdrawal rates. It is showed that there is no dendrite appears in the whole range of withdrawal rate. Cellular microstructure changes from classical hexagon and banded cellular to banded cellular as withdrawal rate increases from 50μm/s to 100μm/s. When the withdrawal rate increases to 300μm/s, the transition from banded microstructure to square cellular is occurred again. There is no obvious cellular microstructure transition as the withdrawal rate increases from 300μm/s to 1000μm/s. The tendency of cellular primary spacing is first increase and then decrease as the withdrawal rate increasing. The cellular ripening mechanism is used to analyze the transition from hexagonal cellular to banded cellular, it is indicated that the change of cellular orientation which is that the surface energy generate the cellular microstructure transition, the primary spacing is increased as the withdrawal rate increasing during the transition. The refinement of square cellular in high withdrawal rate is also researched, it is obtained that the cellular groove became relatively deeper and wider with the increasing withdrawal rate, which is the reason that cellular shape became round gradually.