A tablet formed by prealloys iron-aluminum produced from atomized powders to be used as additive element in aluminum alloys, is manufactured by the method having the steps of obtaining a metallic alloy by fusion of iron and aluminum with the iron and aluminum added in an electric arc or induction furnace, atomizing the melted alloy by transporting the melted alloy to an intermediary container with an opening as a metal flux controlled by a valve located in the opening for controlling and proportionating a continuous flux and supplying a jet of water under pressure when the liquid metal drains to provide atomization and to produce small droplets that cool in water, solidify and are deposited as a powder; reducing humidity of the powder; classifying the thusly produced material, and compacting a thin fraction of the material for obtaining tablets; a tablet.