Evolution of globular microstructures during processing of aluminium slurries

Slurry processing experiments were performed with AlSi7Mg0.6 to identify the globularization mechanisms. The melt sample water quenched slightly above the liquidus point is predominantly dendritic while that cooled into the semi-solid temperature range internally via stirring the melt with a rotating cylindrical block of the alloy itself becomes fully globular. The globules are much smaller when internal cooling and stirring are employed longer to achieve higher solid fractions before casting. Coarse dendrite fragments of various sizes are revealed, in the case of stirring after an initial fraction of solid is first formed without the benefit of additional internal cooling.