Phase Transformations in Rapidly Solidified Al-Cu-Li-Mg-SC-Zr Alloy During Model Homogenization Studied by In-Situ STEM

Rapid solidification by melt‑spinning produces aluminum alloys with extremely refined microstructures but also introduces strong structural gradients across the ribbon thickness. In this work, the microstructural evolution of a rapidly solidified Al‑Cu‑Li‑Mg‑Sc‑Zr alloy was investigated during model homogenization using in‑situ STEM heating experiments and correlated with bulk electrical‑resistivity measurements. The as‑cast ribbons exhibit two distinct solidification zones: a near‑contact region consisting of columnar cells containing fine Cu‑rich spherical precipitates, and a central region composed of larger eutectic cells enriched in Al₂Cu and Al₇Cu₂Fe phases. Stepwise in‑situ annealing between 200 °C and 550 °C reveals a sequence of transformations, including matrix depletion due to precipitation of strengthening phases, coarsening and dissolution of primary phases, and the formation of Al₃(Sc,Zr) dispersoids. Above 500 °C, rapid dissolution of primary phases followed by their coagulation into a limited number of stable grain‑boundary particles eliminates the original two‑zone structure and results in a fully homogenized ribbon. Ex‑situ annealing confirms that the resulting microstructure is uniform across the ribbon thickness and enables consistent precipitation strengthening during artificial aging. Microhardness measurements from both ribbon surfaces reveal identical peak‑aged hardness, validating the effectiveness of the short‑time homogenization strategy for rapidly solidified Al‑Cu‑Li‑Mg-based alloys.