Microstructural evolution during annealing of a rapidly solidified Al–12Si alloy

X-ray diffraction, optical-electron metallography, differential scanning calorimetry and microhardness testing were employed to investigate the response to thermal exposure of the rapidly solidified Al–12 wt.% Si alloy ribbons. Al–12 wt.% Si ribbons, melt-spun at a cooling rate of 106 K/s, reveal a very fine and homogeneous cellular structure with nano-size Si particles dispersed in a supersaturated aluminium matrix. These favorable features of the rapidly solidified state survive the annealing treatments performed below 523 K. The hardness of the present alloy, which has more than doubled upon rapid quenching, is thus retained in this temperature range. Si particles grow predominantly via precipitation of the solute Si from the supersaturated solid solution below 573 K while coarsening is the predominant mechanism at higher temperatures, producing a much coarser structure and a substantial decrease in hardness.