PRODUCTION OF AL-(12-25) WT-PERCENT SI ALLOYS BY RAPID SOLIDIFICATION - MELT SPINNING VERSUS CENTRIFUGAL ATOMIZATION

Al-Si-x(x = Cu, Mg, Ni, Co or Sr) alloys with Si content in the range 12-25 wt% were quenched from the liquid state using two methods: melt spinning and centrifugal atomization. The powders obtained were degassed followed by hot extrusion. Effects of chemical composition, quenching conditions, hot extrusion and heat treatment on the variation in the microstructure were examined. The present results show the necessary conditions for supersaturated solid solution, and those required for mechanism of solute trapping by moving the solid/liquid interface. Also, the mechanical properties of the products obtained were evaluated. It is observed that melt spun ribbons with Si concentrations of more than 12% possess high yield strength with low ductility. These materials undergo softening on ageing at temperatures above 150-degrees-C. The properties of extruded alloy powders are markedly improved as compared to those made by ingot metallurgy. This effect is mainly due to the silicon particle refinement brought about by rapid solidification with cooling rates higher than 10(5) Ks-1.