SYNTHESIS OF IN-SITU REINFORCED AL COMPOSITES FROM AL-SI-MG-O PRECURSORS

Al matrix composites reinforced with micro-composite Al2O3/Al particle s were synthesized by reactive infiltration of molten Al into preforms of particulate SiO2 or Mg + SiO2 mixtures at 1075 degrees C. Displace ment reactions between silica and magnesium containing oxides lead to in-situ formation of the reinforcements and also aid the infiltration of the melt. In the presence of Mg, it was found that the consistency of infiltration was better and that the transformation of silica to al umina involved intermediate displacement reactions unlike the single s tep reaction without Mg in the preform. It was observed that the morph ology and size scale of the micro-composite Al2O3/Al particles were af fected by the presence of Mg. Without Mg a finer scale Al2O3/Al micros tructure with a tendency to be elongated in the growth direction forme d, while a coarser morphology with interconnectivity in both phases de veloped from Mg + SiO2 preforms. Potential for such microstructural va riations of the reinforcements permits control of the overall mechanic al properties of the composite. (C) 1997 Acta Metallurgica Inc.