MICROSTRUCTURE OF RAPIDLY SOLIDIFIED ALUMINUM-BASED IMMISCIBLE ALLOYS

The microstructures of melt spun hypomonotectic Al-4.5wt.%Cd, Al-7wt.%In and hypoeutectic Al-5wt.%Sn and Al-10wt.%Sn have been studied by transmission electron microscopy. The alloy microstructures are formed by monotectic reaction with decreasing solidification rate through the melt spun ribbon thickness. Near the chilled ribbon surface, columnar aluminium grains contain a homogeneous distribution of fine scale cadmium, indium or tin particles; in the ribbon mid-section, cellular aluminium grains contain fine scale cadmium, indium or tin particles within the cells and coarse particles at the cell boundaries; and near the unchilled ribbon surface, cellular aluminium grains contain only coarse particles at the cell boundaries. The cadmium, indium and tin particles exhibit orientation relationships with the surrounding aluminium matrix, and faceted shapes bounded by {111}A1 and {100}A1. Particle-free zones of 0.2-0.5-mu-m thickness are often found adjacent to the aluminium grain boundaries, sometimes on one side and sometimes on both sides of the grain boundary.