Decomposition of the supersaturated solid solution in a rapidly solidified hypereutectic AlCu alloy

Abstract

Laser rapid solidification experiments have been performed on Al-40wt.%Cu alloys at the maximum growth velocity (about 2.0 ms −1) that can be obtained with the experimental arrangement. The resulting solidification growth microstructures have been studied by transmission electron microscopy, using thin foils taken from the surface of the laser traces. At about 2.0 m s −1, plane front growth with a columnar-grained morphology is observed, the grains consisting of a supersaturated solid solution of Cu in Al. This is highly unstable and decomposes very readily during natural aging. However, the microdomains produced in this extended solid solution differ markedly from those observed in dilute age-hardened alloys; most obviously the characteristic σ″ thin plate morphology is completely absent. Further aging to produce σ′ also results in a precipitate that differs from the dilute alloy from.