Effect of Si alloying content on the microstructure and thermophysical properties of SiC honeycomb/Al–Mg–Si composites prepared by spontaneous infiltration

Directional SiC honeycomb/Al–Mg–Si composites with different Si alloying contents (2–12 wt%) were prepared by spontaneous infiltration. The effect of Si alloying content on the phase composition, microstructure and thermophysical properties of the composites were investigated. The results showed that the equilibrium contact angles between the SiC ceramic and different Al alloys were in the range of 60.5–72° at 1273 K, benefitting the infiltration process. Meanwhile, the Si alloying content not only changed the phase composition of the composites, but also influenced the microstructure of the infiltrated Al alloys, especially changing the microstructure of Mg₂Si phase from small flake-like eutectic phase (Mg₂Si_E) to large polygon-like primary phase (Mg₂Si_P). Due to the anisotropic feature of SiC honeycomb and the tunable phase composition and microstructure of the infiltrated Al alloys, the composites exhibited anisotropic and tailored thermophysical characteristics. The composites with the Si alloying content of 7 wt% possessed the optimum properties, with the highest TC of 140.95 W m⁻¹ K⁻¹ in axial direction and relatively low CTE of 11.1 × 10⁻⁶/K in radial direction. Additionally, the reduction of anisotropy of composites’ CTEs in two principal directions with the increase of Si alloying content was also discussed.