Fabrication of Metal/Ceramic In situ Composites by Directed Oxidation of Aluminum Melt

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Directed melt oxidation is an attractive process for fabrication of dense, near net shaped metal/ceramic composite materials. An experimental and theoretical study was conducted to study the growth mechanism of the Al_2O_3/Al alloy composites. The oxidation of Al-Mg-Si alloys was carried out at temperatures ranging from 900 to 1700K under dry air gar atmosphere. The optimum processing variables were obtained experimentally and microstructure of the obtained composite was compared with the processing condition. The typical composite structure was three-dimensionally interconnected Al_2O_3 phase (70 vol%) and residual aluminum alloy phase (30 vol%). The growth process was divided into three characteristic stages. Stage I corresponded to formation of porous spinel layr above the liquid aluminum alloy. After stage I, bulk Al_2O_3/Al alloy composite formed and the growth rate showed the maximum value. During stage III, the oxidation rate constantly decreased. The decreased oxidation rates were due to increased melt viscosity, higher diffusion distances from aluminum and depletion of aluminum alloy reservoir. The modeling and analysis have been done on the growth process and the result reasonably agrees with the experimental result. The application of this process to Al_2O_3/Al alloy matrix reinforced with SiC fiber or SiC particle was also carried out.