Abstract
Aluminum foams are manufactured using various viscosity increasing methods at present. Although it is well known that calcium addition is one of the most successful thickening processes for fabricating fine foams, the intimate mechanism is still lacking. The aim of this paper is the investigation of the detailed thickening mechanism and the influence of increase viscosity conditions on fabricating aluminum foams. Thickened samples were prepared using pure aluminum admixed various contents of calcium or aluminum powder as viscosity increasing agents. Microstructure analysis of thickened samples was carried out. As quantitative evaluations, the measurements of stirring torques and oxygen contents were also performed. The effect of aluminum powder addition on the melt viscosity and microstructure of thickened sample cannot be confirmed. In the case of calcium addition, the stirring torques increase with the calcium content and the agitating time till the values achieve the stationary stage. More the oxide grains formed by folded oxide film are observed in the thickened sample which contains more the calcium amount. In addition, the oxygen content increases with the stirring time and the quantity of calcium addition. Thus, it is found that the oxide grain causes to increase the melt viscosity. Further, those content can be controlled by adjusting the calcium addition and the stirring time.
