Abstract Scope |
Scandium is well known to produce grain refinement in Al-based alloys, and its potency is generally attributed to intermetallic Al3Sc formation within liquid phase. However, the influence of Sc atoms and Al3Sc on the local structure of the surrounding melt, and subsequent nucleation remains unclear. Towards that end, we have probed structural changes in three bulk compositions, i.e., Al-xSc (x = 0, 0.4, 1.0 at.%), and near liquid-Al/Al3Sc interfacial regions using ab initio molecular dynamics. In-liquid ordering was determined using unsupervised learning techniques, i.e., structural fingerprinting, dimensionality reduction, and cluster analysis. Sc atoms ordered the surrounding liquid Al atoms by forming Sc-centered polyhedrons, while liquid-Al/Al3Sc interface manifested planar ordering that resembled {100}fcc−Al. Through this effort, we postulate two transformation pathways during Al-Sc solidification: (i) Sc−centered polyhedrons → Al3Sc → liquid−Al/Al3Sc inter f acial ordering → f cc−Al; and (ii) Sc−centered polyhedrons → hcp−Al → bcc−Al → f cc−Al. |