Thermodynamics of the effect of alloying on phase formation during crystallization of aluminum matrix composites with exogenous reinforcement

Abstract

A thermodynamic assessment of the effect of alloying elements (Si, Mg, Cu, Ti) on phase formation processes during the production and liquid-phase processing of cast aluminum matrix composite materials with exogenous reinforcement (Al–SiC, Al–B4C) was carried out. It was shown that without suppressing Al–Si–C and Al4C3 carbide formation in the range of carbon concentrations from 0 to 4.5 wt.%, the equilibrium phase composition of Al–SiC composites in the solid state at 423 to 575 °C lies in the (Al) + Si + Al4SiC4 three-phase region, and the Al4SiC4 ternary carbide is replaced by the Al8SiC7 compound at a temperature below 423 °C. SiC and B4C phases in Al–SiC–Cu and Al–B4C–Cu systems are stable in the entire crystallization range and do not interact with aluminum or copper. In the Al–SiC–Mg system, the crystallization of composites containing more than 0.58 wt.% magnesium ends in the (Al) + Al3Mg2 + SiC + Mg2Si four-phase region. In the Al–SiC–Ti system, the end of crystallization is observed in the (Al) + Al3Ti + SiC three-phase region. In the Al–B4C system, once Al4C3 phase formation is suppressed, aluminum borides are formed with a deviation from the concentrations of elements providing 10 vol.% B4C towards boron increase and free carbon is formed with a deviation towards boron decrease. Under equilibrium conditions, Al–B4C–Si system crystallization ends in the (Al) + B4C + AlB12 + Al8SiC7 four-phase region (at a silicon content of up to 0.67 wt.%, and in the (Al) + Si + AlB12 + Al8SiC7 region at a higher silicon content. In the Al–B4C–Ti system, crystallization ends in the (Al) + TiB2 + B4C three-phase region at a titanium content of less than 0.42 wt.%.