Abstract:The phase diagram of the Al-Ca-Fe system in the aluminum corner, including the liquidus projection and solidification reactions, was studied by using thermodynamic calculations and experimental techniques. The results show that instead of the Al₃Fe phase, a ternary compound whose composition corresponds to the formula Al₁₀CaFe₂ should be in equilibrium with the aluminum solid solution (Al). Thе transition from the binary to the ternary compound occurs via the peritectic transformation L + Al₃Fe → (Al) + Al₁₀CaFe₂ (at 638 °C, 3.3 at.% Ca and 0.5 at.% Fe). Primary and eutectic crystals of the ternary compound have a compact morphology, in contrast to needle-shaped inclusions of the Al₃Fe phase. First principles calculations and X-ray diffraction analysis were used to determine the crystal lattice structure of Al₁₀CaFe₂ ternary compound. In addition, the near eutectic alloy Al-6wt.%Ca-1wt.%Fe after annealing at 500-600 °C has a fine structure with a total fraction of excess phases of about 25 vol.%. Thus, the Al-Ca-Fe system can be used to create new aluminum-matrix composite alloys.

Key words: Al-Ca alloys; intermetallic; phase diagram; phase transition; microstructure; aluminum-matrix composites