The effects of process parameters on the cell morphology of the aluminum foam

Abstract

Aluminum foams have gained a considerable amount of attention in recent years with their very low specific weight, relatively high compression strength among cellular materials combined with good energy absorption. In the present study, powder metallurgy method, which offers flexibility in materials selection and possibilities like near net shaping, was utilized to produce aluminum foams by using pre-alloyed AlMg1SiCu (AA6061) powders as base material and titanium hydride (TiH2) as blowing agent. First, effects of compaction temperature, pressure and time on precursor quality were investigated. Then optimum foaming parameters were found by foaming trials with various parameters. Heat treatment of TiH2 powders was conducted and modification of decomposition properties was analyzed by thermogravimetric analysis (TGA). Enhancements of foam morphology by tailoring the decomposition properties of TiH2 and addition of Al2O3 particles were analyzed by scanning electron microscopy (SEM). Aluminum foams were subjected to heat treatments in order to investigate the effects on compression strength. Quasi-static compression tests of heat treated foams were performed and precipitated phases were analyzed by EDAX (Energy Dispersive X-Ray) analyses. As a conclusion, it was found that compaction of the powder mixture by primarily cold pressing and subsequently hot pressing under 270 MPa at 450 oC for 30 minutes resulted in sufficient densification which was very close to theoretical density. Optimum foaming temperature for AA6061 was found to be between 750 and 775 oC. Heat treating the TiH2 powders was found to shift the decomposition temperature up to 75 oC. It was observed that addition of Al2O3 particles prevented drainage and cell coalescence by mechanically supporting the cell structure. Strength increase about 25 % was achieved by solution heat treatment and subsequently ageing of the aluminum foams.