Structural Characterization of Aluminum Foams Obtained by Powder Metallurgy

Abstract

The porous structure of aluminum foams was quantitatively monitored in terms of pore density, pore area, and shape and size distribution using image analysis; then, related to density and expansion profiles by interrupted experiments. This practice offers important information in the control and reproducibility of foams. The aluminum foams were produced by the powder compact melting method at 800°C. The foamable precursors consisted in uniaxial cold pressed Al-TiH₂ mixtures compacted at 387 MPa; the pressure applied and particle size distribution of the mixture originated preforms with 95.9% densification. This procedure eliminated the traditional hot-compaction step; besides, the amount of foaming agent was kept to a minimum of 0.5 wt.% TiH₂. A volume expansion of 215 to 236% and densities from 0.7730 to 0.8206 g/cm³were obtained in a time window of 420 to 570 s. The calculated shape factors and Feret diameters defined how the roundness of pores varies with size all along the foaming process.