Wires of aluminium and aluminium-silicon alloys containing 5.2 and 12.1 wt% Si were exploded in air by electric discharge, and the properties of the powders obtained were examined. The powders consisted of large particles of several micrometres and very fine spherical ones, which were formed from the metallic droplets and vapours, respectively, and were mostly oxidized. The large particles decreased with an increase in the charged energy. Although the particle-size distribution was broad, the average particle sizes were small and were increased from 0.7 mu m to 1.3 mu m with an increase in the charged energy. These powders were identified as gamma-alumina, amorphous alumina-silica compound and a small amount of the metal. The amorphous phase crystallized to mullite in the temperature range 1153-1243 K, and the crystallization temperature fell with increase in the charged energy because the amount of fine particles formed from the vapours increased.