Abstract
Composites based on two aluminium alloys (A536 and 6061) reinforced with 10% or 20% volume fraction of SiC particles were
produced by gravity casting and a novel two-step mixing method was applied successfully to improve the wettability and distribution of
the particles. The SiC particles were observed to be located predominantly in the interdendritic regions, and a thermal lag model is
proposed to explain the concentration of particles. It was found that the SiC particles acted as substrates for heterogeneous nucleation
of Si crystals in one of the cast composites. This observation can also be explained by the thermal lag model proposed.
Keywords: casting, metal matrix composites, wettability, particle distribution, and thermal lag.