Sintering of pure aluminum and nano-alumina powders by ECAP and hot extrusion

Metal matrix nano-composites (MMNCs) are a new class of materials which exhibit high mechanical performance combined with good tribological and damping properties. They are constituted by a ductile metal matrix reinforced by hard nano-particles. In order to overcome the poor wettability of the small ceramic compound in the molten metal and to achieve a good dispersion of the reinforcements into the matrix, several unconventional fabrication processes were proposed in recent studies. This research is aimed at investigating two powder metallurgy synthesis routes for the production of MMNCs. A preliminary study on pure aluminum powder was performed to analyze the performance of the two processing for the production of full compacted billets. Aluminum micro-powder was attritioned by high energy ball milling and sintered by Equal channel angular pressing (ECAP) at 200 degrees C and hot extrusion at 300 degrees C. SEM analysis was carried out in order to monitor the microstructure of the material at different stages of the whole process. Density measurements and Vickers hardness tests were also carried out on final products. ECAP revealed a very efficient method for powder compaction and it was adopted for the preparation of Al composites reinforced by 2% and 5% of 20nm -alumina. The reinforcements resulted partially aggregated in micro-clusters and partially distributed as single nano-particles within the metal matrix. Nonetheless, the composites exhibit higher Vickers hardness if compared with the pure aluminum compacted sample.