Study on the semi-solid rheocasting of magnesium alloy by mechanical stirring

In this work, the effect of the pouring temperature of magnesium melt, the preheating temperature of the barrel of the screw mixer and the shear rate, on the solidified microstructures of semi-solid slurry was investigated by the mechanical stirring method. The appropriate processing parameters of slurry preparation were obtained. The mold filling for a thin-walled casting was examined. The results indicated that the solid volume fraction of non-dendritic structure increased with decrease in the pouring temperature of the magnesium melt and in the barrel preheating temperature of the screw mixer. Also, the grain size of the primary alpha-phase was reduced. Furthermore, the solid volume fraction of semi-solid non-dendritic structure decreased with increase in the shear rate. At the same time, the grain size of the primary alpha-phase changed slightly. A fine round granular solidified structure of 30-50 mum of prepared AZ91D magnesium semi-solid slurry was obtained. Finally, it was possible to successfully fabricate a 1.0 mm extremely thin-walled casting with a clear contour and good soundness. (C) 2002 Elsevier Science B.V. All rights reserved.