| Aluminum foams are finding an increasing application in many fields such asautomobile and architecture industry due to their special structure and performances.However, the high preparation cost of aluminum foams becomes a barrier for theirmass applications in every walk of life. So, researching the low-cost preparationtechnology of aluminum foams is significant. After systemically investigating thetraditional aluminum foam preparation technology using TiH2 as foaming agent andanalyzing the limitations existing in traditional technology, a novel low-cost foamingagent substituting for TiH2 was originally developed, and the preparation processusing the novel foaming agent was also researched in this paper. In addition, aquantificational method for expressing the uniformity of aluminum foam wasoriginally put forward. Main research conclusions in this paper are as follows:(1) After systemically researching the traditional aluminum foam technologyusing TiH2 as foaming agent, the following results can be obtained: the increase ofTiH2 can lead to the rise of porosity rises of aluminum foam; foaming efficiency anduniformity decrease obviously with the increase of foaming temperature; whileprolonging the soaked time, porosity increases, but foaming efficiency and uniformitydecrease. Aluminum foam samples with porosity of 75％～85％, foaming efficiencyof above 80％, uniformity of above 80 and average diameter of 1～4mm can beproduced when the foaming agent addition of 1.1％～1.3％, foaming temperature of620～640℃, stirring time of 2.5～5.0min, stirring rate of 1500～2500rpm andholding time of 3.0～5.0min.(2) A novel cheap foaming material is synthesized, which can substitute for theexpensive foaming agents such as TiH2 and ZrH2. The testing results by DSC-DTAmethod indicate that the novel foaming material has a wide decompositiontemperature scope (608.31～755.86℃) and mild decomposition speed. The completedecomposition time of the foaming material at 680℃,700℃,720℃and 740℃is30min, 18min, 11min and 8min respectively. Decomposition reaction process offoaming material accord with the shrinking unreacted core model, its decompositionreaction is controlled by chemical reaction, and the reaction activation energies is182.596 KJ.mol-1.(3) After systemically researching the new aluminum foam technology using thenovel foaming material, the following results can be obtained: (a) the porosity firstly increases and then decreases with foaming temperature rising; the free-bubble zone inmaterial decreases with foaming agent increasing, and the flee-bubble zonedisappears while foaming agent addition is more than 1.4％; (b) the effects of stirringtime and stirring rate have a little effect on the porosity and density of aluminum.Generally, stirring rate should be more than 800rpm and stirring time should becontrolled in the range of 2.0 min to 4.0 min. (c) With the soaked time prolonging, theporosity of aluminum foam gradually rises, but the foaming efficiency decreasesmeanwhile: the cells in aluminum foam becomes non-uniformity and the free-bubblezone appears if the soaked time prolongs excessively. A soaked time of 1-6min shouldbe the optimum in this study.(4) Aluminum foam product with uniform cell distribution, no free-bubble zone,pore sizes of 2～5mm and porosity of 60～80％can be obtained from the technologyusing the novel foaming material, while the foaming temperature of 740℃, foamingagent addition of 1.40～2.20％, stirring time of 2.0～4.0 min stirring rate more than800rpm and holding time of 5min. The compression experiment indicates that: withporosity increasing, the compressive strength of aluminum foam gradually reducedand the intensity between 5％strain and 48％strain also reduced gradually; while theporosity of pure aluminum loam of 70％, its stress plateau is above 10MPa.(5) This novel foaming agent has the ability of enhancing viscosity of aluminummelt itself may be due to the fact that some fine particles are formed at the gas-liquidinterface. Therefore, the extra addition such as Ca metal was unnecessary while usingthis foaming agent; this set a foundation for the low cost production of aluminumfoam.(6) The experimental results show that the wettability between novel foamingmaterial and aluminum melt is not good, but the wettability improves while thefoaming material is mixed with TiB2 powder and A1Si alloy powder.(7) A method used to calculate the uniformity of aluminum foam was originallyproposed. This method can be employed to quantificationally characterize theuniformity of cell distribution but also calculate the porosity of aluminum foam. Theresults demonstrate that the error of porosity between calculated and measured isapproximately 4％, meanwhile the calculated uniformity is coincident with theobservational result.
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