The microstructure changes of aluminum under implantation with Ni+ ions were investigated. The ion implantation was carried out at 250keV. Needle-like precipitates were formed in the Al matrix after implantation to 0.2×1017Ni+cm−2. This precipitate contained between 8.5 and 13.3at.% Ni. The growth of the precipitates was connected with an amorphous phase under further implantation up to 2×1017Ni+cm−2. The concentration of Ni in the amorphous phase was 10.8–12.8at.%. In order to investigate the phase stability of the precipitate, annealing or electron irradiation experiments were performed in a high voltage electron microscope. The crystalline and the amorphous phases were stable under electron irradiation up to 5dpa. The crystalline phases were also stable during annealing at 673K, whereas the amorphous phase was crystallized during annealing at 593K.