Effect of Mass Fraction of Dolomite on the Foaming Behavior of AlSiCu Alloy Foam by Powder Metallurgy Route

Metallic foams are commonly produced using hydride foaming agents. Carbonates are safer to handle than hydrides; furthermore, a fine and homogenous cell structure can be obtained by carbonates in the powder metallurgy route. In this study, the principle of foaming by dolomite, which is a carbonate, for AlSiCu alloy was investigated by observing foaming with a high-temperature transmission X-ray system and identifying the foaming gas with a gas chromatography–mass spectrometry technique. During foaming by dolomite, two stages of expansion were observed. The first stage of expansion was induced by the water vapor absorbed onto the AlSiCu powder surface, and the second stage of expansion was induced by the decomposition of dolomite. The coarse cells of the first stage of expansion were filled with H₂, and the fine cells of the second stage of expansion were filled with CO. A fine and homogenous cell structure was achieved by controlling the mass fraction of dolomite with the fraction of adsorbed water, which induced cell coarsening.