Simulation of Processes during Formation of Foamed Aluminum

The model of growing gas bubbles in an aluminum Al–Ca melt is used to obtain numerical estimates of the dynamics of forming foamed metal. The sizes of spherical pores are determined together with the time of forming, the changes in the concentration of hydrogen and the diffusion flow on the surfaces of the bubbles depending on the amount of dissolved gas in the melt. It is established that the most significant changes in pressure in bubbles occur with a rapid increase in the size within the time interval from 10–6 to 10–4 s starting with the moment of nucleation. As soon as the gas pressure in the growing bubbles decreases to 3.55 × 105 N/m2, the subsequent increase depends on the diffusion of hydrogen from the surrounding melt and it does not depend on the initial saturation of the melt with gas. The dimensions of the cells containing uniformly distributed bubbles and half the thickness of the bridge between the cells is found in published reports. The calculated porosity of the foamed metal ranges from 72 to 83% depending on the amount of hydrogen dissolved in the melt, which is fairly consistent with the experimental data. Using a model of solidifying foamed aluminum, it is determined that the final formation of gas bubbles takes ~10 ms and the initial temperature of the melt cooling in the crucible during this time remains practically the same. Simulation was carried out to estimate the solidification time of a porous aluminum melt in a graphite crucible as a function of the concentration of the foaming agent (TiH2).