Discovery of confined two-dimensional Laves tiling in a magnesium alloy

Laves phases composed of two-dimensional (2D) Laves tilings are prevalent in condensed matter systems, yet the existence of these 2D tilings as isolated structural motifs has remained unverified. Here, we report the discovery of a metastable, confined 2D Laves tiling precipitate in a compositionally dilute Mg alloy, revealed through aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) in combination with atomic-resolution energy-dispersive X-ray spectroscopy (EDS) mapping. The structure adopts a Laves-type Al₂Ca configuration confined to the (0001) basal plane of the Mg matrix, with a thickness of merely a single tiling layer (~4.62 Å), stabilized by adjacent Mg/Ca interfacial atomic layers. Theoretical calculations reveal that tensile strain in the surrounding matrix suppresses the diffusion of small-sized Al solutes, thereby inhibiting out-of-plane coarsening. Notably, prolonged thermal exposure leads to the formation of multi-configurational layered Laves structures assembled from these fundamental units. These findings elucidate the precipitation behavior in Mg-Al-Ca alloys and uncover a structurally confined Laves tiling motif, advancing our understanding of Laves phase formation and solute clustering in metallic systems.