Thermodynamics of the Effect of Alloying of Phase Formation during Crystallization of Aluminum Matrix Composites with Exogenous Reinforcement

A thermodynamic assessment of the influence of alloying elements (Si, Mg, Cu, Ti) on the processes of phase formation during the production and liquid-phase processing of cast aluminum matrix composite materials with exogenous reinforcement (Al–SiC, Al–B4C) has been carried out. It is shown that without suppression of the formation of Al–Si–C and Al4C3 carbides in the range of carbon concentrations from 0 to 4.5 wt %, the equilibrium phase composition of composites of the Al–SiC system in the solid state at temperatures from 423 to 575ºC lies in the three-phase region (Al) + Si + Al4SiC4, and below a temperature of 423ºC, the Al4SiC4 ternary carbide is replaced by the Al8SiC7 compound. In the Al–SiC–Mg system, the crystallization of composites containing more than 0.58 wt % magnesium ends in the four-phase region (Al) + Al3Mg2 + SiC + Mg2Si. In the Al–SiC–Ti system, the end of crystallization is fixed in the three-phase region (Al) + Al3Ti + SiC. In the Al–B4C system, after suppression of the formation of the Al4C3 phase, with a deviation from the concentrations of elements that provide 10 vol % B4C, aluminum borides are formed in the direction of increasing boron, and free carbon is formed in the direction of decreasing boron. Under equilibrium conditions, with a silicon content of up to 0.67 wt %, the crystallization of the Al–B4C–Si system ends in the four-phase region (Al) + B4C + AlB12 + Al8SiC7, and at a higher silicon content, it ends in the region (Al) + Si + AlB12 + Al8SiC7. In the Al–B4C–Ti system, with a Ti content of less than 0.42 wt %, crystallization ends in the three-phase (Al) + TiB2 + B4C region.