Coarsening of grain-refined semi-solid Al–Ge32 alloy: X-ray microtomography and in situ radiography

The Lifshitz, Slyozov and Wagner theory (LSW) describes the coarsening of low volume fraction dispersed particles in a supersaturated solution as governed by a t1/3 power law, while stating that ripening occurs in a self-similar manner. Only a few experiments have reported three-dimensional (3D) coarsening in binary semi-solid alloys, which differs from the LSW theory. We report here on in situ coarsening of Al–Ge32 (wt.%), which is used as a model system for a large variety of technical alloys. Numerical analysis of 2D and 3D images of the microstructure measured by X-ray radiography and microtomography reveals the evolution of the solid particles during annealing. Ripening of a grain-refined particle network is found to be quite well described by LSW theory, although somewhat smaller exponents (t1/4–t1/5) are found. Changes in coarsening behavior are observed in samples which are thinner than 0.5 mm, as well as in non-equiaxed alloy microstructures, characterized by anisotropic dendrites.