Interconnected network of AlN/Al composites are produced by in situ liquid metal-gas reactions. In this study, various Al-Si-Mg alloys are nitrided in N₂-4 %H₂ atmosphere to understand the composite growth mechanism. Both fibre and particulate SiC reinforcements are infiltrated with AlN/Al reaction product to form near dense composites and mechanical properties are compared with those of AlN particulate reinforced AlN/Al composite. The composite microstructure is found to be sensitive to the processing temperature, alloy composition and filler material size and chemistry. The variation in mechanical property is also dependent on the residual porosity. Formation of moisture sensitive Al₄C₃ in SiC reinforced composites causes deterioration of mechanical properties. Various alternatives to prevent Al₄C₃ formation are discussed in the text.