Surface Pulverization Cause of High Volume Fraction SiCp/Al Composites

Reaction bonded silicon carbide (RBSiC) green body was separately immersed in aluminum melt and Al-Si alloy melt with silicon mass fraction of 5%, 12.5% and 20% respectively at 850 ℃, and then a series of high volume fraction SiCp/Al composites with various silicon contents were prepared. The surface pulverization of the composite after standing in air for a long period was observed, and the microstructures, morphology and composition of the composite and its powders were studied by scanning electron microscopy, X-ray diffraction and energy dispersive spectroscopy. The reason for pulverization was also analyzed. The results show that after standing in air for two months, plenty of powders formed at the surface of the SiCp/Al composites with a relatively low silicon content (silicon mass fraction of 0 and 5% in raw materials), but the pulverization at the surface of the composites with a relatively high silicon content was prevented. The powders mainly consisted of long rod-like and tabular-like Al(OH)3. Aluminum carbide was generated during the preparation of the composite due to insufficient silicon content and then hydrolyzed in the air, resulting in the pulverization.