Manufacturing of Al–Mg–Si alloy foam using calcium carbonate as foaming agent

Aluminium foams can be manufactured by two main methods: casting and powder metallurgy. When the latter route is used, a foaming agent (usually TiH2) is mixed with the aluminium or aluminium alloy powders, followed by powder mixture consolidation (usually hot extrusion) into a precursor and finally its foaming treatment. In this research, two calcium carbonate powders were used as foaming agents on an Al–Mg–Si (AA6061) alloy. Their different characteristics (particle size and chemical composition) modified the manufacturing process to achieve the final foam. AA6061 powders were then mixed with 10% calcium carbonate and, after cold isostatic pressing into green cylinders, hot extruded at different temperatures (475–545 °C). The foaming treatment was carried out in a furnace preheated to 750 °C using several heating times. The density changed from 2.03 to 2.10 g/cm3 after cold isostatic pressing to 2.64–2.69 g/cm3 in precursor materials obtained by hot extrusion. Foaming behaviour depends on the carbonate powder as well as the extrusion temperature. Thus, natural carbonate powder (white marble) produces a foam density close to 0.65 g/cm3 after a shorter time than when chemical carbonate is used. The foam structure showed a low degree of aluminium draining, no wall cell cracks and a good fine cell size distribution. Compressive strength of 6.11 MPa and 1.8 kJ/m3 of energy absorption were obtained on AA6061 foams with a density between 0.53 and 0.56 g/cm3.