The thermodynamic analysis of the SiC/Al-Si-Mg system has been performed in order to find the conditions to produce SiC/Al-Si-Mg composite materials with the stable SiC/alloy interface (for both alpha-SiC and beta-SiC) and with the solidification of primary alpha-Al solid solution. The conditions to avoid the formation of Al4C3 are expressed as function of temperature, and the silicon and magnesium content of the liquid aluminium alloy. It has been shown that to ensure stabilization of (the more stable) alpha-SiC, lower Si-content is needed and higher working temperature is allowed, compared to the requirements to stabilize (the less stable) alpha-SiC.