Rapid solidification of metallic particulates

The property improvements of aluminum alloys through rapid solidification techniques are reviewed, i.e., quenching from the melt through splat cooling of flakes, roller quenching of foils and ultrasonic gas atomization of powders. By rapid quenching from the melt, a high degree of microstructural refinement, extended solubilities of alloying elements, and elimination of complex constituent phases can be obtained. The refinement of the structure is directly related to the cooling rate from the melt. In the case of atomized powders, this is related to the particle size and particle velocity; but with other techniques, such as the solid substrate cooling of fine droplets, high cooling rates are based on substrate conductivity and flake thickness. The effect of higher average oxide content and the possibility of utilizing its strengthening effect are also considered.