Phase changes in sintering of Al/Mg/NaCl compacts for manufacturing Al foams by the sintering and dissolution process

Addition of small amount of Mg in the Al/NaCl compacts has previously found to be an effective method for improving the sintering in manufacturing Al foams by SDP. However, the mechanism of the improvement is not fully understood. This paper investigates the phase changes in the Al/Mg/NaCl compacts during heating up and sintering by thermogravimetric analysis and electron microscopy. The results showed that the alumina hydrates formed on the surface of the Al particles gradually dissociate into hydrous alumina during heating up. Mg consumes the oxygen trapped in the compact and reduces some of the Al oxide to form MgAl2O4. Consequently, more fresh metal contacts between the Al particles and less further oxidation during sintering lead to the improved sintering response.