Ternary Interactions and Implications for Third Element Alloying Potency in Al–Ce-Based Alloys

Recently developed Al-Ce-based alloys offer numerous beneficial attributes, including high temperature strength retention, resistance to microstructural coarsening, and excellent castability. Binary alloys around the eutectic composition of ~11 wt% Ce contain a characteristic large volume fraction of eutectic Al₁₁Ce₃ laths. However, further alloying additions to improve properties can stabilize a myriad of ternary Al-Ce-X phases that complicate alloying efficacy in unexpected ways, as relative intermetallic stability often changes between solidification and solutionizing temperatures. Unlike in many Al alloys that can be solution treated to a single phase, Al-Ce and Al-Ce-X intermetallics form during solidification and their morphology is largely retained during heat treatment, similar to composite materials. This morphological stability remains even after stoichiometric changes. Here, empirical relationships for third element alloying potency in Al-Ce-based alloys are derived, using Mg and Cu additions as prototypes for non-interacting and interacting elements, respectively. The relationships pair analytical calculations with empirical phase composition measurements as an aid to alloy design. While not a substitute for CALPHAD-based approaches, the empirical approach based on direct measurement can supplement in Al-Ce-based alloys where the low diffusivity of Ce often results in non-equilibrium phase compositions.