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

Abstract

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.