The effects of viscosity and cooling conditions on the foamability of aluminum alloy

The effect of viscosity and cooling conditions on the foamability of the molten Al–Si–Mg alloy was investigated using the unidirectional solidification method. The mechanism of pore formation in the Al–Si–Mg alloy has been observed and analyzed theoretically. The results obtained are given as follows: 1. The optimum torque of the melt for foaming is approximately 0.29 N m and is about 1.7 times that of the original melt. 2. The existence of alumina particles in the melt is necessary for nucleation of the bubbles and the increase in viscosity. 3. With the increase in the solidification time, the time for bubble growth increases during the unidirectional solidification. 4. The pore size and the total volume of the porosity increase with the diffusion of hydrogen and is controlled by the local solidification time during cooling of the hydrogen saturated melt. 5. Properly controlled viscosity and solidification of the melt are good for promoting uniformity of the pore structure of the aluminum foams.