Solidification of Al–50 at.%Si alloy in a drop tube

Solidification of 0.1–1.0 mm diameter droplets of Al–50 at.%Si hypereutectic alloy was achieved in a 3 m drop tube. Phase morphologies of deeply etched sections of the solidified samples with different diameters are examined. With decreasing of the diameter of the droplets, refinement of the primary silicon phase is observed. A tendency for the primary silicon crystals to form granular morphology is found in the smaller samples. Stratified deposits of aluminum in the primary silicon along the silicon plate are evident in bigger samples, but less evident with decreasing of the sample size. Morphologies of Al–Si eutectics change from needle-like to short, blunt and worm-like forms with decreasing of the sample size. Through calculation of the nucleation rates at different sizes of the solidified sample and analyses of the crystal morphologies, grain refinement of the primary silicon can find its origins of copious nucleation during rapid cooling and solute-restriction to crystal growth.