Cell Structure Evolution of Aluminum Foams Under Reduced Pressure Foaming

Ti-H particles are used to increase the gas content in aluminum melts for reduced pressure foaming. This paper reports on the RPF process of AlCa alloy by adding TiH₂, but in smaller amounts compared to traditional process. TiH₂ is completely decomposed by stirring the melt, following which reduced pressure is applied. TiH₂ is not added as the blowing agent; instead, it is added for increasing the H₂ concentration in the liquid AlCa melt. It is shown that pressure change induces further release of hydrogen from Ti phase. It is also found that foam collapse is caused by the fast bubble coalescing during pressure reducing procedure, and the instability of liquid film is related to the significant increase in critical thickness of film rupture. A combination of lower amounts of TiH₂, coupled with reduced pressure, is another way of increasing hydrogen content in the liquid aluminum. A key benefit of this process is that it provides time to transfer the molten metal to a mold and then apply the reduced pressure to produce net shape foam parts.