On the thermodynamic stability of intermetallic phases in the AA6111 aluminum alloy

An experimental investigation of both as-cast and heat-treated AA6111 alloys pointed to the quaternary phase Al16(Fe,Mn)4Si3 as the dominant intermetallic phase. Weight fractions of this phase were determined by extracting it from the alloys via a selective dissolution of the FCC matrix in boiling phenol. The fractions found were significantly greater than those predicted by thermodynamic modeling. In an attempt to resolve the contradiction, it was assumed that the thermodynamic stability of the quaternary phase reported in literature had been underestimated. In order to refine its thermodynamic characteristics, conditions of phase equilibria in which Al16(Fe,Mn)4Si3 participated were handled within the framework of the CALPHAD method.