Abstract: The seaweed-like microstructure in quasi-two-dimensional (2D) and three-dimensional (3D) samples is studied by controlling the orientation-dependent interface energy anisotropy during directional solidification of an Al-3 wt.% Mg alloy. Here, we produce asymmetrically shaped seaweed and degenerate seaweed patterns in 2D samples for the (0$\bar{1}$1)[111] and ($\bar{2}$11)[111] orientations. During solidification in the 3D sample, a hyperbranched seaweed formation prevails for the [111] orientation. The comparison of these growth patterns shows that the morphologic features are qualitatively similar. In addition, the spacing (λ) and frequency (ƒ) of tip splitting in seaweed patterns follow a power law with respect to growth velocity. The 3D sample exhibits a lower tip spacing and higher frequency than the 2D sample. These quantitative relationships between growth dynamics and the role of sample size deserve attention. Our results clearly show that the seaweed pattern could survive and grow stably in 3D metallic alloys, and the exploration of this complex morphology for application is feasible in the future.

Key words: Directional solidification, Seaweed, Interface energy anisotropy, Microstructure