[en] Transmission electron microscopy (TEM) was used to perform a systematic study of the microstructural evolution in Al as a function of the fluence received during 65 keV Kr⁺ ion implantation at room temperature. At the lower fluences (2 x 10¹⁶ to 2 x 10¹⁹ Kr⁺m^-2), isolated dislocation loops and the evolution of a dislocation network was observed by TEM. Above fluences of 10¹⁹ Kr⁺m^-2, the microstructure is dominated by a high density of Kr bubbles whose average size increases with dose. The appearance of additional electron diffraction reflections indicates that the majority of the bubbles contain solid fcc Kr that is epitaxially aligned with the fcc Al matrix. Above fluences of 2 x 10²⁰ Kr⁺m^-2 an increasing fraction of the Kr is in a liquid or gas-like phase. The thermal stability of the microstructure, characteristic of the different fluence regimes, was investigated up to 640⁰C by in situ TEM annealing experiments