Fabrication of Al/Al2O3 composites by in-situ powder metallurgy (IPM)

Al6061/Al2O3 composites containing 15–40 vol.% of different-sized (37–276 μm) alumina particles were produced by in-situ powder metallurgy (IPM). In this method, the stir casting and powder metallurgy (PM) synthesizing processes are combined into an integrated net shape forming process. For the preparation of each powder mixture, alumina particles were added to the molten aluminum alloy, and the resulting slurry was stirred at a specified temperature for a predetermined time. During the stirring process, alumina particles disintegrated into the molten alloy, and subsequent quenching resulted in a mixture of alumina and aluminum alloy powder particles. These powder mixtures were cold pressed and then sintered. The effects of stirring time and temperature, along with the alumina content and particle size on the size distribution, microstructure and morphology of the aluminum particles produced were investigated. It was found that the finer aluminum powder particles were produced by increasing the alumina content and by decreasing both the stirring temperature (from 780 to 710 °C) and alumina particle size (within the range of 37–150 μm). A comparison of optical and SEM micrographs of aluminum particles produced by IPM, solid assisted melt disintegration (SAMD) and gas atomization revealed that pore-free and more spherical particles were produced by the IPM and SAMD methods. Moreover, a microstructural investigation of the final products proved that consolidated composites with high contents of well-distributed reinforcing particles could be fabricated by the IPM method.

A mixture of specified amounts of ceramic particles and aluminum alloy melt is stirred via an impeller. The kinetic energy of the impeller is transferred to the melt via non-wetting ceramic particles and results in melt disintegration and hence the formation of liquid droplets. These liquid droplets can then solidify to produce an Al/ceramic powder mixture.Figure optionsDownload as PowerPoint slideHighlights
► Al/Al2O3 composites were produced by the simple and cost-effective IPM method.
► The effects of stirring time and temperature and alumina content were studied.
► Pore-free powders were produced by the IPM method.
► Composites with high contents of well-distributed reinforcing particles produced.