The effect of solidification conditions on the structure and properties of the Al-6wt% Li-15wt%Cu eutectic alloy containing T2 phase

Abstract

The morphology of T2 and of αAI-T2 eutectic dendrites has been studied in two ingot samples of nominally eutectic composition (Al-6wt% Li–15wt% Cu) and the effect of growth velocity in Bridgman solidification on eutectic interlamellar spacing and hardness has been determined for one of the ingot compositions. The results show that the αAI-T2 eutectic dendrites forming in these samples are characterized by the main stem and secondary arms growing along the five-fold rotational axes of the T2 phase of the eutectic and that this growth mode is an example of the complex regular morphology exhibited by eutectics with entropy of solution exceeding 23 kJ mor−1 and approximately equal volume fractions of the constituent phases. The eutectic spacing, λ, in Bridgman samples depends on the growth velocity, V, in the range 0.1 to 1 mm sec−1 according to the relationship λV1/2 = 19.6 ± 0.5 µm3/2 sec−1/2 while hardness, H, depends on λ according to a modified Hall-Petch relationship H= H0 + Kλ−1 with H0 = 137 ± 6 kg mm−2 and K = 0.048 ± 0.003 kg mm−1.