Rheology of foaming aluminum melts

Aluminum foam with a closed cellular structure was prepared by a direct foaming method. In the foaming process, the aluminum melt was mechanically agitated, and when a suitable viscosity was achieved, a granular blowing agent was injected. Foam expansion ensued rapidly, and control of the melt viscosity was critical to achieve stable foam without slumping. The rheology of molten aluminum foam was studied as a function of position within the mold cavity and correlated with changes in cell geometry. The deformation pattern of the cell shapes during foam expansion was considered macroscopically and microscopically. Simple mechanical models were introduced to describe the expansion process.