Unconstrained growth along a ternary eutectic solidification path in Al–Cu–Ag: Preparation of a MAXUS sounding rocket experiment

Abstract

During casting, unconstrained solidification occurs most frequently. The objectives of the present study were to describe the different stages of a ternary eutectic solidification path, its unconstrained solidification and to assess gravity dependent phenomena as a preparation for a MAXUS sounding rocket microgravity experiment. Two alloys within the Al–Cu–Ag system were selected. They form a different primary phase α(Al) or θ-Al 2Cu that however share the further solidification path. Nucleation of primary non-faceted α(Al) was enhanced by the addition of TiB 2. The same addition did not influence the nucleation of faceted θ-Al 2Cu. Gravity driven flotation of primary α(Al) was observed. Nucleation of the univariant eutectic α(Al) + θ-Al 2Cu is triggered by θ-Al 2Cu, whereas growth occurs with a lamellar, rod-like or irregular morphology. Growth of the invariant eutectic α(Al) + θ-Al 2Cu + ξ-Ag 2Al occurs either with an irregular, semi-regular brick type or regular double-rod type morphology, however, always with a strong association between θ-Al 2Cu and ξ-Ag 2Al.