MICROSTRUCTURES AND AGE HARDENABILITY OF AL-5-PERCENT-SI-0.2-PERCENT-MG BASED COMPOSITES REINFORCED WITH PARTICULATE SIC

Composites of an Al-0.5%Si-0.2%Mg alloy reinforced with particulate Si C have been produced by the compocasting route. The silicon carbide wa s oxidized at 900 degrees C for 2 h and mixed into the semi-liquid all oy by means of a special stirrer. The slurry was held at 750 degrees C for 5 min and cast into a permanent die preheated to different temper atures and composite ingots containing 9, 13, 17, 22, and 26 vol.% SiC were obtained. The distribution of SiC particles, the porosity conten t and the dendrite arm spacing of the composites were determined. The phases other than the matrix and the reinforcement were identified to be Mg2Si, MgAl2O4 and FeSi3Al9. It was found that the oxidation of SiC and the presence of magnesium in the matrix alloy rendered easy incor poration without causing any significant magnesium depletion in the ma trix. It was found that the composites produced were age hardenable. A fter prolonged exposure to temperatures above 500 degrees C in the sol id state, no formation of additional phases was found to take place in the microstructures. (C) 1997 Elsevier Science Limited.