Foaming Agents for Powder Metallurgy Production of Aluminum Foam

Abstract

Metallic foams are commonly produced using hydride foaming agents. Carbonates are safer to handle than hydrides; however, their use in the powder metallurgy (PM) route to obtaining a fine and homogenous cell structure has not been evaluated. In this study, carbonates and hydroxides were investigated as foaming agents for the production of Al-Si-Cu alloy foams by the PM route. The thermal decomposition behavior of the foaming agents was evaluated in conjunction with the cell structure of the aluminum foams produced. From the results, it was clarified that a foaming agent that began decomposing after the matrix melted is required to obtain a fine and homogenous cell structure. The TiH 2 foam formed under similar conditions was obviously different and had a coarse and rounded cell structure. MgCO 3 and CaMg(CO 3 ) 2 were selected as suitable foaming agents for the Al-Si-Cu alloy. Once expanded, the CaMg(CO 3 ) 2 foam had a specific gravity of 1.19 and a homogeneous, fine and spherical cell structure.

A Study of Manufacturing and Mechanical Properties of Mg-foam Using Dolomite as the Blowing Agent: A Review

“…However it is found that melt foaming process is best for fabrication of Mg-foam because it can be easily controlled and is cheaper than others [1]. Different foaming agents were found for production of Al foam [15]. However, in conclusion it is found that CaCO 3 and Dolomite are the best suitable agents due to their cost and stability [15].…”

“…Out of which there are two methods of fabricating the cellular Mg-foams i.e. melt foaming method also known as Alporas Method and powder metallurgy method (Fraunhofer method) [15]. However it is found that melt foaming process is best for fabrication of Mg-foam because it can be easily controlled and is cheaper than others [1].…”

“…Different foaming agents were found for production of Al foam [15]. However, in conclusion it is found that CaCO 3 and Dolomite are the best suitable agents due to their cost and stability [15]. So much research has been done using CaCO 3 [1,4,5] and TiH 2 [12] as blowing agents in fabrication of metallic foam.…”

Method of Preventing Shrinkage of Aluminum Foam Using Carbonates

“…The mass reduction rates of dolomite, magnesium carbonate, and calcium carbonate obtained by thermogravimetric analysis-differential thermal analysis (TG-DTA) are shown in Figure 5 [9]. Dolomite started to decompose at 773 K and rapidly decomposed above 1013 K. In contrast, magnesium carbonate decomposed from 793 to 993 K and calcium carbonate from 993 to 1113 K. Calcium carbonate is ineffective for multiple additions, because it does not decompose at 968 K, at which foam produced using dolomite shrinks.…”

“…The foams produced using dolomite and magnesium carbonate have a fine and homogenous cell structure [9][10][11]. The foam produced using TiH 2 shows the coalescence of cells, before rupture by gravity [12,13].…”