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 TiH(2)) 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 AI-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 degrees C). The foaming treatment was carried out in a furnace preheated to 750 degrees C using several heating times. The density changed from 2.03 to 2.10g/cm(3) after cold isostatic pressing to 2.64-2.69 g/cm(3) 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/cm(3) 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/m(3) of energy absorption were obtained on AA6061 foams with a density between 0.53 and 0.56 g/cm(3). (c) 2008 Elsevier B.V. All rights reserved.